HK40001095A - Magnetohydrodynamic deposition of metal in manufacturing - Google Patents

Description

Magnetohydrodynamic deposition of metals in manufacture

Cross Reference to Related Applications

The benefit of U.S. provisional patent application No.62/303,341, filed 2016, 3, is hereby incorporated by reference herein in its entirety, according to 35 § 119 (e).

Technical Field

The devices, systems, and methods described herein relate to manufacturing Magnetohydrodynamic (MHD) systems, and more particularly to magnetohydrodynamic systems for manufacturing from metallic materials.

Background

The current may be combined with a magnetic field to impart MHD forces on the liquid metal. Such force may push the liquid metal to form the metal object. While MHD forces can be used to form metal objects, issues related to speed, accuracy, control and material properties present challenges for object formation in large quantities using MHD forces. Thus, there is a need for a commercially viable technique for metal fabrication using MHD forces.

Disclosure of Invention

Devices, systems, and methods relate to applying magnetohydrodynamic forces to liquid metal to eject the liquid metal in a controlled pattern, such as a controlled three-dimensional pattern, as part of additive manufacturing of an object. Magnetohydrodynamic forces may be applied in a pulsed manner to eject droplets of liquid metal to provide control over the accuracy of the fabricated object. The pulsation can be applied in a fluid chamber with a high resonant frequency, such that droplet ejection can be effectively controlled over a wide range of frequencies, including high frequencies suitable for liquid metal ejection at rates suitable for commercially viable three-dimensional fabrication. In one aspect, a nozzle for spraying liquid metal includes a housing defining at least a portion of a fluid chamber having an entry region and an exit region; one or more magnets disposed relative to the housing, a magnetic field of the magnets being directed through the housing; and an electrode defining at least a portion of the launching chamber in the fluid chamber between the entry region and the exit region, wherein at least at a point substantially near the exit orifice of the exit region, an electrical current is conducted from the electrode to the launching chamber, and at a point substantially near the exit orifice, the electrical current intersects the magnetic field in the launching chamber to eject liquid metal from the exit orifice.

The volume of the fluid chamber between the firing chamber and the discharge orifice may be less than about ten percent of the total volume of the fluid chamber. The volume of the launching chamber may be greater than about 50 percent of the total volume of the fluid chamber. The fluid chamber may have an axial length greater than about 2mm and less than about 2 cm. At least one of the electrodes may be integrally formed with a portion of the housing defining at least a portion of the fluid chamber such that the at least one electrode and the portion of the housing defining at least one of the fluid chambers are formed from the same material. At least one of the electrodes may be integrally formed with a portion of the housing defining at least the exhaust region of the fluid chamber such that the at least one electrode and the portion of the housing defining the exhaust region are formed from the same material. The housing may be a rod of electrically conductive material and the electrical current may be conducted between the electrodes along an axis parallel to the axial dimension of the rod. The firing chamber may include a generally rectangular cross-section in a plane perpendicular to a direction of travel of the liquid metal from the entry region toward the exit region, and electrical current from the electrode may be conducted into the liquid metal along the generally rectangular cross-section.

The nozzle may include a filter disposed along the fluid chamber and spaced apart from the discharge region. At least one of the electrodes may be formed of tantalum, niobium, or a combination thereof.

In another aspect, an additive manufacturing system disclosed herein comprises: a nozzle comprising one or more magnets and an electrode, the nozzle defining a fluid chamber having an entry region and an exit region, the one or more magnets directing a magnetic field through the housing, and the electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein current is conducted from the electrode such that the current intersects the magnetic field in the emission chamber at a point substantially near an exit orifice of the exit region; a robotic system mechanically coupled to the nozzle; a power source in electrical communication with the electrode; and a controller in electrical communication with the robotic system and the power source, the controller configured to move the robotic system to position the discharge area of the nozzle in the controlled three-dimensional pattern, and actuate the power source to deliver a pulsed current to the electrode to cause the liquid metal to be ejected from the discharge area to form the three-dimensional object based on a position of the discharge area along the controlled three-dimensional pattern.

The frequency of the pulsed current may be less than about 5kHz at the maximum speed of motion of the discharge area. The pulsed current may have a frequency based on the nozzle velocity. The pulsed current may have a frequency based on one or more characteristics of the three-dimensional pattern.

In another aspect, an additive manufacturing method disclosed herein comprises: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; directing a magnetic field through the nozzle; moving the discharge area along a controlled three-dimensional pattern; and conducting a pulsed current to the liquid metal in the launch chamber in the fluid chamber between the entry region and the exit region based on the location of the exit region along the controlled three-dimensional pattern, wherein the frequency of the pulsed current is less than the resonant frequency of the liquid metal in the fluid chamber and the pulsed current is in a direction that intersects the magnetic field in the launch chamber such that the current pulses eject the liquid metal from the exit region to form the three-dimensional object.

The pulsed electrical current may be conducted to the liquid metal in the launching chamber substantially near the discharge region. The resonant frequency of the liquid metal in the fluid chamber may be greater than about 10 kHz. The volume of the launching chamber may be greater than about 50 percent of the volume of the fluid chamber. The resistivity of the liquid metal may be substantially similar to the resistivity of the material defining the firing chamber.

In one aspect, a nozzle for spraying liquid metal disclosed herein comprises: a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region; one or more magnets supported on the housing, the magnetic field of the magnets being directed through the housing; and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein an electrical current is conducted from the electrode to the emission chamber in a direction transverse to a magnetic field in the emission chamber, and a portion of the housing defining the exit region of the fluid chamber is formed from a ceramic material.

The ceramic material may comprise one or more of alumina, sapphire, ruby, aluminum nitride, aluminum carbide, silicon nitride, sialon, and boron carbide. A portion of the housing defining at least a portion of the fluid chamber remote from the discharge region may be formed of metal. A portion of the housing defining at least a portion of the fluid chamber remote from the discharge region may be formed from a ceramic material. The electrode defining at least a portion of the firing chamber may be formed from a metal. At least one of the electrodes may be integrally formed with a portion of the housing defining at least a portion of the fluid chamber remote from the exhaust aperture such that the at least one electrode and the portion of the housing defining at least a portion of the fluid chamber remote from the exhaust aperture are formed from the same material. The launching chamber may be substantially adjacent the discharge orifice discharge region. The launching chamber may be greater than about 50 percent of the total volume of the fluid chamber.

The electrode may include a liner disposed along at least a portion of the fluid chamber between the intake region and the exhaust region. The liner may be plated onto the material of the housing defining the fluid chamber. The shell material on which the liner is provided may comprise one or more of titanium nitride, titanium aluminium nitride, titanium carbide, alumina, titanium and titanium carbonitride. The nozzle may include at least one heater in thermal communication with the firing chamber. The heater may comprise an induction coil disposed around at least a portion of the firing chamber. The electrode may be formed of a first material and the housing may be formed of a second material. The second material has a higher melting temperature than the first material. The electrodes may be formed from tantalum, niobium, or a combination thereof.

In another aspect, an additive manufacturing method disclosed herein includes providing a liquid metal in a fluid chamber having an intake region and an exhaust region, the fluid chamber defined at least in part by a housing, the fluid chamber; directing a magnetic field through the housing; moving the discharge area in a controlled pattern; and conducting an electrical current through an electrode defining at least a portion of a launch chamber in the fluid chamber between the entry region and the exit region based on a position of the exit region along the controlled pattern, wherein the electrode defining at least a portion of the launch chamber has a resistivity substantially equal to a resistivity of the liquid metal moving through the launch chamber, and a portion of the housing defining the exit region may have a resistivity substantially greater than a resistivity of the liquid metal moving through the exit region, and the electrical current conducted through the electrode is conducted into the liquid metal in a direction transverse to a magnetic field in the launch chamber to eject at least a portion of the liquid metal from the exit region.

In one aspect, a nozzle for spraying liquid metal disclosed herein comprises: a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region, and the exhaust region having a throat adjacent the exhaust aperture; one or more magnets disposed relative to the housing, a magnetic field of the magnets being directed through the housing; and the electrode defining at least a portion of an emission chamber in the fluid chamber between the intake region and the exhaust region, wherein an outer surface of the housing in the vicinity of the exhaust orifice includes a membrane that may be substantially non-wetting with respect to a liquid metal that may be stably supported in at least a portion of the emission chamber defined by the electrode.

The devices, systems, and methods involve applying magnetohydrodynamic forces to liquid metal to eject the liquid metal in a controlled pattern, such as a controlled three-dimensional pattern, as part of additive manufacturing of an object. The housing material defining the throat may be wettable with respect to liquid metal that may be stably supported in the firing chamber. The liquid metal in the emission chamber may be stably supported with a greater contact angle with the membrane than the housing material defining the throat. The throat may be substantially cylindrical, and a diameter of the throat may be substantially equal to a diameter of the discharge hole. The membrane may be integrally formed with the portion of the housing adjacent the discharge orifice. The membrane may comprise an oxide of the material forming the portion of the housing defining the throat. The film may include one or more of tantalum oxide and chromium oxide. The film may be non-wetting with respect to one or more of aluminum, aluminum alloys, and solder.

At least one of the electrodes may be integrally formed with a portion of the housing in the vicinity of the at least one of the electrodes such that the at least one of the electrodes and the portion of the housing are formed of the same material. The one or more magnets may be arranged such that a magnetic field is directed through the firing chamber, and the electrodes may be arranged such that a current conducted from the electrodes into the firing chamber intersects the magnetic field in the firing chamber.

In another aspect, an additive manufacturing method contemplated herein comprises: providing a liquid metal in a fluid chamber, the fluid chamber having an inlet orifice and an outlet orifice, and the fluid chamber having a throat adjacent the outlet orifice, wherein the fluid chamber is at least partially defined by the housing; directing a magnetic field through the housing; and pulsing an electrical current into the liquid metal in the launching chamber in the fluid chamber, the pulsed electrical current intersecting the magnetic field in the launching chamber to cause the liquid metal to be ejected from the discharge orifice, wherein during the flow of the electrical current pulse into the liquid metal, the throat is wetted by the liquid metal and an outer surface of the housing defining the discharge orifice is substantially unwetted by the liquid metal.

The outer surface of the housing defining the exhaust aperture may include a film that is an oxide film of the housing material defining the throat. The film may include one or more of tantalum oxide and chromium oxide. The contact angle between the liquid metal and the outer surface of the housing defining the discharge orifice may be greater than the contact angle between the liquid metal and the material of the housing defining the throat. The contact angle between the liquid metal and the outer surface of the housing defining the drain hole may be greater than about 90 degrees. The liquid metal may include one or more of aluminum, aluminum alloys, and flux. The pulsed current may have a maximum frequency of less than about 10 kHz.

The method may include moving the shell in a controlled three-dimensional pattern relative to the build surface to form the three-dimensional object.

In another aspect, the methods disclosed herein comprise: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; directing a magnetic field through the housing; delivering a first current to the liquid metal in the launching chamber in the fluid chamber between the entry region and the exit region, the first current comprising a fluctuating current crossing the magnetic field in the liquid metal to exert a fluctuating force on the meniscus attached to the exit region, the fluctuating force on the liquid metal attached to the exit region bouncing the meniscus attached to the exit region.

The drain region may include a drain hole and a throat, and the meniscus may be attached to one or more of the throat and the drain hole. The pulsating force exerted on the meniscus can have a magnitude sufficient to cause a metal oxide layer formed on the meniscus to break, the metal oxide layer comprising a metal oxide of the liquid metal. The method may include ejecting liquid metal through the drain region based at least in part on a duration of delivering the first current to the liquid metal in the housing. The liquid metal may be sprayed from the discharge hole over a predetermined period of time. The method may include delivering a second current to the liquid metal in the firing chamber, wherein the second current intersects the magnetic field in the liquid metal to eject the liquid metal through the ejection region to form the object. The second current may include a pulse current different from the pulse current of the first current. The method may include moving the discharge region along a controlled pattern corresponding to the manufacture of the object, wherein delivering the second current into the liquid is based on a position of the discharge region along the controlled pattern. The controlled pattern may include a three-dimensional pattern. Delivering the second current to the liquid metal in the launching chamber may include switching between a pulsed current and a straight current based at least in part on a position of the discharge orifice along the controlled pattern.

In another aspect, disclosed herein is a manufacturing system comprising: a nozzle comprising a housing at least partially defining a fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the fluid chamber, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that a current from the electrode intersects the magnetic field in the emission chamber; a robotic system mechanically coupled to the nozzle, the robotic system movable to position the discharge area; a power source in electrical communication with the electrode of the nozzle; and a controller in electrical communication with the robotic system and the power source, the controller configured to move the robotic system to position the ejection region along a controlled pattern corresponding to the fabrication of the object, deliver a first current to the liquid metal in the launch chamber through the electrode, the first current comprising a pulsed current that intersects the magnetic field in the liquid metal in the launch chamber to generate a pulsating force on a meniscus of the liquid metal attached to the ejection region, and move along the controlled pattern of the ejection region to deliver a second current to the liquid metal in the launch chamber through the electrode, the second current intersecting the magnetic field in the liquid metal to eject the liquid metal through the ejection region to form the object.

The controller may be further configured to deliver a third current to the liquid metal in the firing chamber through the electrode, the third current intersecting the magnetic field in the liquid metal to eject the liquid metal through the ejection region at a location remote from the controlled pattern of ejection orifices. The controller may be configured to deliver the third current to the liquid metal in the launching chamber based at least in part on a duration of delivery of the first current to the liquid metal. The controller may be configured to deliver the third current between switching from delivering the first current to delivering the second current. The controller may be configured to deliver the third current for a predetermined period of time. The controlled pattern may include a three-dimensional pattern.

In another aspect, an additive manufacturing method disclosed herein comprises: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; directing a magnetic field through the housing; moving the discharge area along a controlled three-dimensional pattern; and delivering an electrical current between electrodes at least partially defining an emission chamber in the fluid chamber between the entry region and the exit region, the electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit region; and controlling the porosity of one or more predetermined portions of the sprayed liquid metal aggregation on the build plate or on a previous metal deposition layer based on the position of the drainage area along the controlled three-dimensional pattern.

Controlling the porosity of one or more predetermined portions of the ejected liquid metal aggregation can include forming an interface between a three-dimensional object in the aggregation and a support structure, the support structure and the three-dimensional object having a lower porosity than the interface. The interface, the support structure, and the three-dimensional object may be formed from the same material. The interface may be fragile with respect to the three-dimensional object. The method may include separating the three-dimensional object from the support structure by applying one or more of a compressive force and a shear force to the interface. Controlling the porosity of one or more predetermined portions of the aggregation of ejected liquid metal can include varying the velocity of the liquid metal ejected from the ejection region. Varying the velocity of the liquid metal ejected from the ejection region may include varying the magnitude of the current delivered to the liquid metal in the launching chamber. Delivering the electrical current to the liquid metal in the launching chamber may comprise delivering the electrical current in a pulsed manner. Varying the velocity of the liquid metal ejected from the ejection region may include varying at least one of an amplitude and a duration of the current pulse. Controlling the porosity of one or more predetermined portions of the aggregation of ejected liquid metal can include varying the temperature of the liquid metal ejected from the ejection zone. Varying the temperature of the liquid metal ejected from the drainage zone can include decreasing the temperature of the ejected liquid metal to increase the porosity of a predetermined portion of the ejected liquid metal aggregation on the build plate or on a previously deposited metal layer.

In another aspect, a computer program product disclosed herein comprises: non-transitory computer executable code embodied in a non-transitory computer readable medium that, when executed on one or more processors, performs the steps of: moving the discharge area of the housing in a controlled three-dimensional pattern; delivering an electrical current to the liquid metal in an emission chamber defined at least in part by the electrodes, the delivered electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from a discharge region in fluid communication with the emission chamber; and controlling the porosity of one or more predetermined portions of the sprayed liquid metal aggregation on the substrate or on a previous metal deposition layer based on the location of the drainage area along the controlled three-dimensional pattern.

Controlling the porosity of one or more predetermined portions of the aggregation of ejected liquid metal can include varying the velocity of the liquid metal ejected from the ejection region. Varying the velocity of the liquid metal ejected from the ejection region may include varying the current amplitude. Delivering the electrical current to the liquid metal in the launching chamber may comprise delivering the electrical current in a pulsed manner. Varying the velocity of the liquid metal ejected from the ejection region may include varying at least one of an amplitude and a duration of the current pulse. Controlling the porosity of one or more predetermined portions of the aggregation of ejected liquid metal can include varying the temperature of the liquid metal ejected from the ejection zone. Varying the temperature of the liquid metal ejected from the ejection zone can include decreasing the temperature of the ejected liquid metal to increase the porosity of a predetermined portion of the ejected liquid metal aggregation on the substrate or on a previously deposited metal layer.

In one aspect, a nozzle for spraying liquid metal disclosed herein comprises: a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region; one or more magnets disposed relative to the housing, a magnetic field of the magnets extending through the housing; and electrodes defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein an electrical current conducted between the electrodes intersects a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit orifice; and a thermal insulation layer disposed between at least one of the one or more magnets and the housing, the thermal insulation layer having a thermal conductivity less than a thermal conductivity of a portion of the housing to which the insulation layer is mounted.

The housing may be thinner along the direction in which the magnetic field extends through the housing than along the direction in which current is conducted between the electrodes. The one or more magnets may be less than about 2mm from the firing chamber. The thermal insulation layer may be about 0.8mm to about 1.2mm thick. The thermal insulation layer may comprise one or more of a quartz ceramic and an aluminum silicon ceramic. The thermal insulation layer may be held in place by the magnetic force exerted on the housing by the magnet. The thermally insulating layer may have a thermal conductivity greater than about 0.015W/m-K and less than about 0.1W/m-K. The one or more magnets may be in thermal communication with a heat sink that is spaced apart from the housing. The heat sink may include a cooling fluid nozzle movable through the heat sink to carry heat away from the one or more magnets may include a fan facing the heat sink to carry heat away from the one or more magnets. The one or more magnets may include one or more of a fixed magnet and an electromagnet.

In another aspect, an additive manufacturing method disclosed herein comprises: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; heating the liquid metal to a temperature greater than a temperature associated with a loss of magnetic field strength of at least one magnet coupled to the housing through the thermally insulating layer; delivering an electric current to the heated liquid metal between electrodes defining an emitting chamber in the fluid chamber between an entrance region and an exit region; and directing a magnetic field from the at least one magnet to the heated liquid metal in the launching chamber, the magnetic field intersecting the current in the launching chamber to eject the liquid metal from the discharge region.

The at least one magnet may be less than about 2mm from the firing chamber. The thermal insulation layer may be held in place by magnetic forces between the at least one magnet and the housing. The method may comprise allowing the at least one magnet to cool. Cooling the at least one magnet may include removing heat from the at least one magnet by a heat sink in thermal communication with the at least one magnet and spaced apart from the housing. Removing heat from the at least one magnet may include moving a cooling fluid through the heat sink. Removing heat from the at least one magnet may include forcing air flow over the heat sink for forced convection cooling. The at least one magnet may comprise one or more of a fixed magnet and an electromagnet. The housing may be thinner in a direction parallel to the magnetic field axis than in the direction of the current flow.

In another aspect, an additive manufacturing method disclosed herein comprises: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; directing a magnetic field through the housing; moving the discharge area in a controlled pattern; and delivering an electrical current between electrodes defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit region; and controlling the current between the pulsed current and the direct current based on the position of the discharge area along the controlled pattern to form the object.

The controlled pattern may be a three-dimensional pattern and the object may be a three-dimensional object. The current may be controlled as a pulsed current along the boundary of the object being formed. The current may be controlled to be direct current as the discharge region moves along an offset (extension) in the boundary of the object being formed. The frequency of the pulsed current may be less than the resonant frequency of the liquid metal in the fluid chamber. The frequency of the pulsed current may be based on the speed of movement of the discharge area. The frequency of the pulsed current may be based on the distance from the edge of the controlled pattern. The frequency of the pulsed current may be less than about 5kHz at the maximum speed of motion of the discharge area. Switching from pulsed current to direct current can increase the mass flow rate of liquid metal ejected from the discharge region.

In another aspect, a computer program product disclosed herein comprises: non-transitory computer executable code embodied in a non-transitory computer readable medium that, when executed on one or more processors, performs the steps of: moving the discharge area of the nozzle in a controlled pattern; delivering an electric current between electrodes defining at least a portion of the launch chamber in fluid communication with the exit region, the electric current crossing the magnetic field in the liquid metal in the launch chamber to eject the liquid metal from the exit region; and controlling the current delivered to the liquid metal in the launching chamber based on the position of the discharge region along the controlled pattern, wherein the current is controlled between a pulsed current and a direct current to form the object.

The current may be controlled as a pulsed current along the boundary of the object being formed. The current may be controlled to be direct as the discharge area moves along deviations in the boundary of the object being formed. The frequency of the pulsed current may be based on the speed of movement of the discharge area. The frequency of the pulsed current may be based on the distance from the edge of the controlled pattern. The frequency of the pulsed current may be less than about 5kHz at the maximum speed of motion of the discharge area.

In another aspect, an additive manufacturing system disclosed herein comprises: a nozzle comprising a housing defining at least a portion of a fluid chamber, the fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the housing, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that an electrical current conveyed between the electrodes intersects the magnetic field in the emission chamber; a robotic system mechanically coupled to the nozzle and movable to position the discharge area; a power source in electrical communication with the electrode of the nozzle; and a controller in electrical communication with the power source, the controller configured to move the robotic system to position the discharge region in a controlled pattern, deliver current from the electrode to the liquid metal in the launching chamber, control the current delivered to the liquid metal in the launching chamber based on the position of the discharge region along the controlled pattern, wherein the current can be controlled between a pulsed current and a direct current to form the object.

The current may be controlled as a pulsed current along the boundary of the object being formed. The current may be controlled to be direct as the discharge area moves along deviations in the boundary of the object being formed. The frequency of the pulsed current may be based on the speed of movement of the discharge area. The frequency of the pulsed current may be based on the distance from the edge of the controlled pattern.

In another aspect, a manufacturing system disclosed herein comprises: a nozzle comprising a housing defining a fluid chamber, the fluid chamber having an entry region and an exit region, one or more magnets disposed relative to the housing, a magnet magnetic field directed through the housing, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, the electrode being arranged relative to the magnets such that a current flowing between the electrodes crosses the magnetic field in the emission chamber to eject liquid metal from the exit region; and a robotic system coupled to the nozzle and movable to position the discharge area along a controlled pattern; and a feed system engageable with the wire, the feed system being actuatable to direct the wire to the fluid chamber through the entry region as the liquid metal is ejected from the exit region in a controlled pattern to form the object.

The feeding system may include a plurality of rollers engageable with the wire, the plurality of rollers being rotatable to feed the wire into the fluid chamber. The system may include a heater in thermal communication with the fluid chamber. The heater may comprise an induction heater. The feed system may be actuated to direct the wire into the entry region at a variable rate based at least in part on the rate at which the liquid metal is ejected from the exit region. The system may include a sensor directed toward the entry area, the sensor configured to detect an interface between the wire and the liquid metal along a predetermined axial distance on each side of the entry area, and the sensor in electrical communication with the feed system to vary a rate of movement of the wire into the entry area based on signals received from the sensor. The sensor may be configured to detect a discontinuity between the metal wire and the liquid metal along a predetermined axial distance on each side of the entry region. The predetermined axial distance on each side of the entry region may be substantially equal to half the maximum dimension of the entry region. The sensor may include one or more of a machine vision and optical break beam sensor. The system may include a wiper that is movable relative to the access area to remove debris in or near the access area. The system may include a source of pressurized gas actuatable to distribute the pressurized gas relative to the intake area to remove debris in or near the intake area. The source of pressurised gas may be arranged to direct pressurised gas through the entry region in a direction towards the exit region.

In another aspect, an additive manufacturing method disclosed herein comprises: directing the wire toward a fluid chamber defined at least in part by the housing, the fluid chamber having an entry region and an exit region; melting a portion of the metal wire to liquid metal, wherein an interface between the metal wire and the liquid metal is near the entry region; transferring liquid metal from the fluid chamber to an emission chamber defined at least in part by the electrodes, the emission chamber being in the fluid chamber between the entry region and the exit region; and applying magnetohydrodynamic forces to the liquid metal in the firing chamber, wherein the wire is directed into the fluid chamber at a rate sufficient to maintain continuous contact between the wire and the liquid metal at the interface as the liquid metal is ejected from the discharge region by the magnetohydrodynamic forces.

The interface may be external to the housing. The interface may be within a predetermined axial distance on each side of the access region. The predetermined axial distance may be about half of the maximum axial dimension of the access region. The method may include mechanically removing debris in and near the entry region. Mechanically removing the debris may include moving the wiper relative to the access area. The method may include pneumatically removing debris in and near the entry region. Pneumatically removing the debris may include directing pressurized gas through the intake region in a direction toward the exhaust region. The method may include electrically removing debris in and near the entry region, wherein electrically removing debris includes directing a pulse of electrical current between the electrodes in a direction relative to the magnetic field to create magnetohydrodynamic forces in the liquid metal in a direction from the launch chamber toward the entry region.

In another aspect, a method of manufacture disclosed herein comprises: providing liquid metal in an emission chamber defined at least in part by an electrode, the emission chamber being in fluid communication with a drain region defined by a housing supporting the electrode; directing a magnetic field to the liquid metal in the launching chamber; and supplying a current from the electrodes to the liquid metal in the firing chamber in a direction crossing the magnetic field in the firing chamber to eject the liquid metal from the ejection area to form the object, wherein the electrodes and the liquid metal are formed of the same material at respective interfaces between each of the electrodes and the liquid metal.

The method may include moving a discharge region in a controlled three-dimensional pattern, the discharge region in fluid communication with the firing chamber, wherein the current is delivered from the electrode to the liquid metal in the firing chamber based on a position of the discharge region along the controlled three-dimensional pattern. The method may include cooling each electrode away from a respective interface of each electrode and the liquid metal, the cooling creating a respective temperature gradient in each electrode. The temperature gradient in each electrode may maintain a respective interface between the electrode and the liquid metal in a respective recess defined by the housing, each interface remaining in the respective recess as the liquid metal is ejected from the discharge region. Each recess may extend in a direction radial to the direction of travel of the liquid metal towards the discharge region. Cooling each electrode may include forced convective cooling of each electrode along a portion of each electrode away from the respective interface with the liquid metal. The forced convection cooling of each electrode may include adjusting a velocity of the cooling fluid based at least in part on a velocity of the liquid metal being ejected from the discharge region. Providing the liquid metal in the launching chamber may include directing the liquid metal to the launching chamber from an entry region defined by the housing, the direction of travel of the liquid metal from the entry region to the launching chamber being transverse to the current and magnetic field in the launching chamber. The axial length of the launching chamber may be greater than half the axial length from the entry region to the exit region. The axial length from the intake region to the discharge region may be greater than about 2mm and less than about 2 cm.

In another aspect, a system for spraying liquid metal disclosed herein comprises: electrodes defining at least a portion of the firing chamber, an electrical current being conductable to the liquid metal in the firing chamber between the electrodes; one or more magnets disposed relative to the electrodes, a magnetic field of the magnets extending through the firing chamber and crossing the current in the firing chamber; and a housing defining at least a portion of a fluid chamber having an entrance region, an exit region, and a recess, wherein the electrode is disposed in the recess such that the firing chamber is located in the fluid chamber between the entrance region and the exit region, and a maximum radial dimension of the firing chamber is greater than a maximum radial dimension of a portion of the fluid chamber adjacent the firing chamber.

The system may include a metal feed that is movable into the fluid chamber, the metal feed and the electrode being formed of the same material. The system may include a heat source in thermal communication with the metal feed in or near the fluid chamber to form liquid metal movable into the launching chamber. The shell may have a higher melting temperature than the electrode material. At least a portion of each electrode may extend beyond the housing in a direction away from the firing chamber. The system may include a heat sink coupled to at least a portion of each electrode remote from the emission chamber. The heat sink may comprise a fluid movable away from the at least a portion of each electrode to effect cooling at the at least a portion of each electrode. The launching chamber may have an axial length greater than 50 percent of the axial length of the fluid chamber. The axial length of the fluid chamber may be greater than about 2mm and less than about 2 cm.

The method disclosed herein comprises: providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region; directing a magnetic field through the housing; delivering a first current to the liquid metal in the housing at rest, the first current crossing the magnetic field in the liquid metal to exert a pull back force on the liquid metal, the pull back force being sufficient to draw the liquid metal at rest in a direction from the exit region toward the entry region; and selectively delivering a second current to the liquid metal, the second current crossing the magnetic field in the liquid metal to exert an emissive force on the liquid metal to eject the liquid metal from the ejection region.

The pull back force may be sufficient to maintain a meniscus of liquid metal in a quiescent state attached to the drain region. The drain region may have a throat near the drain hole, and the pullback force may be sufficient to maintain a meniscus in the throat or attached to the drain hole. The method may include moving the discharge region along a controlled pattern. The controlled pattern may be a controlled three-dimensional pattern. The second current may be selectively delivered to the flow of liquid along less than all of the controlled pattern. The second current may be variable based at least on a position of the discharge region along the controlled pattern. The second current may comprise a pulsed current that ejects liquid metal droplets from the ejection region. Selectively delivering the second current to the liquid metal may include conducting a fire pulse to the liquid metal in the fluid chamber and conducting a pull back pulse to the liquid metal in the fluid chamber, the fire pulse and the pull back pulse having opposite polarities and the pull back pulse having the same polarity as the first current.

The pull-back pulse may precede the fire pulse used to eject the corresponding drop. The pull-back pulse may follow the fire pulse for the corresponding drop ejection. The second current is variable between a pulsed current and a direct current. Selectively delivering the second current to the liquid metal may include directing the second current to the liquid metal between electrodes defining an emission chamber in the fluid chamber between the entry region and the exit region. Delivering the first current to the liquid metal may include directing the first current to the liquid metal between the electrodes.

In another aspect, a manufacturing system disclosed herein may include: a nozzle comprising a housing defining a fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the fluid chamber, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that a current from the electrode intersects the magnetic field in the emission chamber; a power source in electrical communication with the electrode; and a controller in electrical communication with the power source, the controller configured to deliver a first current to the liquid metal in the housing in a quiescent state, the first current intersecting a magnetic field in the liquid metal to exert a pull-back force on the liquid metal, the pull-back force being sufficient to draw the liquid metal in the quiescent state in a direction from the drain region toward the entry region, and to selectively deliver a second current from the electrode to the liquid metal in the firing chamber, the second current intersecting the magnetic field in the liquid metal to exert a firing force on the liquid metal to eject the liquid metal from the drain region, the second current selectively delivering the second current to the liquid metal, the second current intersecting the magnetic field in the liquid metal to exert a firing force on the liquid metal to eject the liquid metal from the drain region.

The system may include a robotic system mechanically coupled to the nozzle and movable to position the discharge region of the nozzle, wherein the controller is further configured to move the robotic system to position the discharge region along the controlled pattern. The second current may be selectively delivered to the flow of liquid along less than all of the controlled pattern. The second current may be variable based at least on a position of the drain hole along the controlled pattern. The controlled pattern may be a three-dimensional pattern. Selectively delivering the second current may include controlling the second current between a pulsed current and a direct current.

Drawings

The systems and methods described herein are set forth in the appended claims. However, for purposes of illustration, some embodiments are presented in the following figures:

FIG. 1 is a block diagram of a three-dimensional printer for MHD deposition for metal fabrication.

Fig. 2A is an isometric view of a feed system and nozzles of the three-dimensional printer of fig. 1.

FIG. 2B is a cross-sectional side view of the feed system and nozzle of FIG. 2A.

Fig. 2C is a top view of the nozzle of fig. 2A.

FIG. 2D is a schematic illustration of the generation of MHD forces in the liquid metal in the nozzle of FIG. 2A.

FIG. 3 is a flow chart of an exemplary method of printing liquid metal by applying MHD force.

FIG. 4 is a flow chart of an exemplary method of controlling current in a pulsed current mode and a direct current mode to control the rate of liquid metal ejection by MHD force.

FIG. 5 is a flow diagram of an exemplary method of using MHD force to form a structure having one or more porous features that facilitate separating a part from a support structure of the part.

FIG. 6 is a flow chart of an exemplary method of using MHD force to pull back a meniscus of stationary liquid metal in a fluid chamber.

Fig. 7A and 7B are a series of comparative schematic views of the meniscus position of the stationary liquid metal of the nozzle when a pullback force is applied to the meniscus.

FIG. 8 is a flow chart of an exemplary method 800 that uses MHD force to bounce a meniscus of stationary liquid metal in a discharge region of a nozzle (bounce).

FIG. 9 is a cross-sectional side view of a nozzle including a filter along an entry region of a fluid chamber.

FIG. 10 is a cross-sectional side view of a nozzle including a channel along an entry region of a fluid chamber.

Fig. 11 is an isometric view of a nozzle including a fan-cooled magnet.

FIG. 12 is an isometric view of a cross-section of a nozzle including an electrode integrally formed with at least a portion of a housing.

FIG. 13 is a cross-sectional side view of a nozzle including an electrode formed as a liner in a housing.

FIG. 14 is a cross-sectional isometric view of a nozzle including a nozzle and a housing formed from a combination of materials.

FIG. 15 is a cross-sectional side view of a nozzle including a non-wetting film on an outer surface of a housing.

FIG. 16 is a cross-sectional isometric view of a nozzle including a neck region.

FIG. 17 is a cross-sectional isometric view of a nozzle including a neck region with a housing cross-section behind the neck region.

FIG. 18 is a cross-sectional isometric view of a nozzle including a neck region, with nozzle portions of different heights.

Detailed Description

Embodiments will now be described with reference to the accompanying drawings. The signed content may, however, be embodied in many different forms and should not be construed as limiting the illustrated embodiments described herein.

All documents mentioned herein are incorporated by reference in their entirety. Items described in the singular should be understood to include plural items and vice versa unless explicitly described otherwise or clear from the context. Grammatical conjunctions are intended to represent any and all separate and conjunctive combinations of the connected phrases, sentences, words, and the like, unless otherwise indicated or clear from the context. Thus, the term "or" should generally be understood to mean "and/or" and the like.

Recitation of ranges of values herein are not intended to be limiting, and denote individual replacement of any and all values within the range, unless otherwise indicated herein, and each separate value within the range is incorporated into the specification as if it were individually recited herein. The terms "about," "approximately," and the like, when used in conjunction with a numerical value, should be understood to represent the deviation in operation required to meet specific objectives by one skilled in the art. Values and/or ranges of values are provided herein by way of example only and constitute limitations on the scope of the described embodiments. The use of any and all examples, or exemplary language ("e.g.," such as ") provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the embodiments. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the embodiments.

In the following description, it is to be understood that such terms as "first," "second," "top," "bottom," "upper," "lower," and the like are words of convenience and are not to be construed as limiting terms.

As used herein, the term "liquid metal" is to be understood as metals and metal alloys in liquid form and additionally or alternatively includes any fluid containing metals and metal alloys in liquid form unless otherwise indicated or known by context.

Referring now to fig. 1-2D, a three-dimensional printer 100 may include a nozzle 102, a feed system 104, and a robotic system 106. Generally, as the feed system 104 moves the solid metal 112 from the metal supply 113 and into the nozzle 102, the robotic system 106 may move the nozzle 102 in a controlled pattern in the process space 108 of the build chamber 110. As described in more detail below, solid metal 112 may be melted in or near nozzle 102 to form liquid metal 112', and a Magnetohydrodynamic (MHD) force may eject liquid metal 112' from nozzle 102 in a direction toward a build plate 114 disposed in build chamber 110 by a combination of a magnetic field and an electric current acting on liquid metal 112' in nozzle 102. By repeatedly jetting the liquid metal 112' as the nozzle 102 moves along a controlled pattern, an object 116 (e.g., a two-dimensional object or a three-dimensional object) may be formed. Alternatively or additionally, the object 116 may be moved under the nozzle 102 (e.g., while the nozzle 102 remains stationary). For example, where the controlled pattern is a three-dimensional pattern, the liquid metal 112' may be ejected from the nozzle 102 in successive layers to form the object 116 by additive manufacturing. Thus, in general, as the nozzle 102 ejects the liquid metal 112', the feed system 104 can provide build material to the nozzle 102 continuously or substantially continuously, which can facilitate use of the three-dimensional printer 100 in various manufacturing applications, including mass production of metal parts. As also described in detail below, the MHD force may be controlled in the nozzle 102 to deliver the liquid metal 112', and in some cases, a substantially continuous stream of liquid metal 112', on demand at a rate in the range of about one drop of liquid metal per hour to several thousand drops of liquid metal per second. Such wide range control of drop flow rate may additionally or alternatively help achieve accuracy and speed goals associated with commercially viable three-dimensional manufacturing.

In general, the liquid metal 112' can be any one or more of a variety of different metals. For example, the liquid metal 112' may include a metal that provides some resistance to oxidation, which may facilitate operation of the nozzle 102 in an incompletely controlled environment in the build chamber 110. Thus, for example, the liquid metal 112' may comprise aluminum or an aluminum alloy. In particular, the liquid metal 112' may comprise an aluminum casting alloy, such as one or more alloys or variations thereof known in the art. Additionally or alternatively, the liquid metal 112' may include one or more alloys that are not typically used for casting, as the grain size of the metal deposited on the object 116 can be controlled by the size of the droplets ejected from the nozzle 102, even if solidification occurs in such alloys. Examples of additional or alternative metals that may form the liquid metal 112' include one or more of carbon steel, tool steel, stainless steel, and tin alloys (e.g., solder).

Referring now to fig. 1 and 2A-2D, the nozzle may include a housing 202, one or more magnets 204, and an electrode 206. The housing 202 may define at least a portion of a fluid chamber 208 having an intake region 210, an exhaust region 212, and a recess 214. One or more magnets 204 may be supported on the housing 202 or otherwise supported in a fixed position relative to the housing 202, with the magnetic field "M" generated by the one or more magnets 204 being directed through the housing 202. In particular, as the liquid metal 112 'moves from the intake region 210 to the discharge region 212, the magnetic field may be directed through the housing 202 in a direction that intersects the liquid metal 112'. Also, or instead, the electrodes 206 may be supported on the housing 202 to define at least a portion of firing chambers 216 in the fluid chamber 208 between the intake region 210 and the exhaust region 212. In use, as described in more detail below, the feed system 104 can engage the solid metal 112, and additionally or alternatively, the feed system 104 can direct the solid metal 112 into the entry region 210 of the fluid chamber 208 as the liquid metal 112' is ejected from the exit region 212 by the MHD force generated using the one or more magnets 204 and the electrodes 206.

In certain embodiments, the power source 118 may be in electrical communication with the electrodes 206 and may be controlled to generate a current "I" flowing between the electrodes 206. In particular, the current "I" may intersect the magnetic field "M" in the liquid metal 112' in the firing chamber 216. It will be appreciated that the result of this crossing is an MHD force (also referred to as a lorentz force) at the liquid metal 112' at the intersection of the magnetic field "M" and the current "I". Because the direction of the MHD force follows the right hand rule, the one or more magnets 204 and electrodes 206 may be oriented relative to each other to exert the MHD force on the liquid metal 112 'in a predictable direction (e.g., a direction that may move the liquid metal 112' toward the drainage area 212). The type of MHD force on the liquid metal 112 'is known as body force, because the body force acts in a distributed manner on the liquid metal 112' wherever the flow of the current "I" and the presence of the magnetic field "M" are located. This build-up of physical forces creates pressure that can result in the ejection of liquid metal 112'. It will be appreciated that by orienting the magnetic field "M" and the current substantially perpendicular to each other and to the direction of travel of the liquid metal 112 'from the intake zone 210 to the exhaust zone 212, the most efficient use of the current "I" can be achieved to eject the liquid metal 112' by using MHD forces.

In use, the power supply 118 can be controlled such that a current "I" is pulsed to flow between the electrodes 206. The pulses may produce corresponding pulses of MHD force applied to the liquid metal 112' in the launching chamber 216. The pulsation of the MHD force on the liquid metal 112' in the launching chamber 208 may eject the respective droplets from the discharge area 212 if the impulse force of the pulsation is sufficient. Thus, by controlling the pulse frequency of the current "I", it is possible to achieve the desired drop of liquid metal 112'. For example, high positional accuracy may be desired when printing the periphery of each layer of a part. In the region of this peripheral, straight or curved line of low curvature, the motion system can pass rapidly and the print head therefore fires (fire) at a high frequency. In some cases, the speed of the motion system is limited by the maximum frequency of possible drop ejection. The maximum frequency will depend on the design of the printhead, the size of the desired drop, and other factors and may vary between 1 and 20 kilohertz. However, as areas of high curvature perimeter are traversed, acceleration requirements (accelerationrequirements) will dictate traversing these areas at lower speeds and thus, the printhead firing at a lower frequency. This is particularly true for sharp corners where the action mechanism would momentarily stop and the printhead would similarly momentarily stop firing.

In certain embodiments, the pulsed current "I" may be driven in a manner that controls the droplet shape of the liquid metal 112' exiting the nozzle 102. In particular, because the current "I" interacts with the magnetic field "M" according to right-hand rules, a change in direction (polarity) of the current "I" through the firing chamber 216 may change the direction of the MHD force on the liquid metal 112' along an axis extending between the entry region 210 and the exit region 212. Thus, for example, by reversing the polarity of the current "I" relative to the polarity associated with the ejection of the liquid metal 112', the current "I" may exert a pull-back force on the liquid metal 112' in the fluid chamber 208.

Each pulse may be shaped by a pre-charge that applies a small pull-back force (opposite to the direction of ejection of liquid metal 112 'from the discharge region 212) before forming an ejection drive signal to push one or more drops of liquid metal 112' from the nozzle 102. In response to this pre-charging, the liquid metal 112' may be pulled slightly upward relative to the drain region 212. Pulling the liquid metal 112 'slightly upward toward the exit orifice in this manner may provide a number of advantages, including providing a path in which the large drops of liquid metal 112' may accelerate to more cleanly separate from the exit orifice as they are ejected therefrom, forming droplets with a better performing (e.g., stable) shape during travel. Similarly, the retracting motion may effectively apply a spring load to the front surface of the liquid metal 112 'by pulling along the discharge region 212 against the surface tension of the liquid metal 112'. As the liquid metal 112' subsequently experiences MHD forces to eject the liquid metal 112', the forces of surface tension may help to accelerate the liquid metal 112' toward ejection from the ejection region 212.

Further, or alternatively, each pulse may be shaped to have a small pull back force after the pulse ends. In this case, a small pull back force after the end of the pulse may help the liquid metal 112' to cleanly separate from the exiting droplets of liquid metal 112' along the exit region 212, because the pull back force is opposite to the direction of travel of the liquid metal 112' jet from the exit region 212. Thus, in some embodiments, the drive signal generated by the power supply 118 may include a wavelet (wavelet) with a pull-back signal to pre-charge the liquid metal 112', a spray signal to discharge a liquid metal droplet, and a pull-back signal to separate an exiting droplet of liquid metal 112' from the liquid metal 112' along the discharge region 212. Additionally or alternatively, the drive signal generated by the power supply 118 may include one or more pauses (dwell) between portions of each pulse.

While pulsing the current "I" at a high frequency may be used to achieve the speed goals associated with feasible three-dimensional printing, it should be understood that the resonant frequency of the liquid metal 112 'in the fluid chamber 208 may limit the upper frequency (upper frequency) associated with pulsing the current "I" to eject drops of the liquid metal 112'. For example, maintaining the pulse rate of the current "I" (and the associated pulsation rate of the MHD force) at a rate less than the rate associated with the resonant frequency of the liquid metal 112' in the fluidic chamber 208 can reduce the likelihood of disadvantageously making the droplet velocity too high or too low, the droplet volume too large or too small, ejecting multiple droplets in place of a single droplet, and with a satellite drop. Thus, in general, the current "I" may be pulsed and conducted to the liquid metal 112 'in the firing chamber 208 along a controlled pattern at a frequency that varies based on the position and/or velocity of the discharge region 212, with an upper limit of the frequency being less than the resonant frequency of the liquid metal 112' in the fluid chamber 208. As described in more detail below, the nozzle 20 may include one or more features for achieving a high resonant frequency of the liquid metal 112' in the fluid chamber 208 to facilitate accurate control of liquid metal droplet delivery at high ejection rates.

Where the resonant frequency of the liquid metal 112' in the fluid chamber 208 is a function of the overall axial length of the fluid chamber 208 (e.g., the axial length from the entry region 210 to the exit region 212), some features of the nozzle 102 may be used to generate MHD forces along a short overall axial length (to support high frequency ejection of the liquid metal 112' in the fluid chamber 208), while remaining low enough to avoid excessive joule heating in the liquid metal 112' during the pulse of current "I". That is, because the overall axial length of the fluid chamber 208 is limited by factors related to the resonant frequency, it is desirable to efficiently utilize the available axial length of the fluid chamber 208 to deliver the current "I" needed for MHD forces corresponding to appropriate drop velocities, sizes, and velocities.

In some embodiments, the overall axial length of the fluid chamber 208 may be greater than about 2mm and less than about 2cm to create a sufficiently high resonant frequency (e.g., about 20kHz) to support a high frequency spray rate (e.g., frequencies up to about 5kHz at the maximum speed of movement of the discharge orifice 218 along a controlled pattern). In some cases, it may be desirable to substantially increase the resonant frequency of the nozzle 102 above (e.g., about 5 times higher, 10 times higher, or more) the maximum spray frequency of the liquid metal 112'. In this case, any excitation of the resonant frequency will allow many oscillations to be buffered. This may be advantageous because the viscosity of the liquid metal 112' is low (e.g., in the range of 1-5 centipoise) and is generally constant. To efficiently use the axial length available to create MHD forces in the liquid metal 112' of the fluid chamber 208, the electrode 206 may be positioned such that the electrical current "I" conducted from the electrode 206 into the firing chamber 216 intersects the magnetic field "M" in the firing chamber 216 at a point substantially adjacent the exit orifice 218 of the exit region 212. As a specific example of introducing current "I" substantially near exhaust orifice 218, the volume of fluid chamber 208 between firing chamber 216 and exhaust orifice 218 may be less than about ten percent of the total volume of fluid chamber 208. Additionally or alternatively, an axial length of the firing chamber 216 at least partially defined by the electrode 206 may be greater than half an axial length of the fluid chamber 208 from the entry region 210 to the exit region 212. In some cases, the sum of the lengths of the intake region 210 and the exhaust region 218 may be less than about 20 percent of the total length of the fluid chamber 208.

A particular difficulty associated with using the electrode 206 to conduct the electrical current "I" to the liquid metal 112 'is selecting an appropriate material that can be used in combination with the liquid metal 112'. In general, it is desirable to select the material of the electrode 206 so that the electrode 206 can operate reliably for long periods of time in the presence of the liquid metal 112', which may require high temperatures to maintain the molten state. Thus, the material of the electrode 206 may have a melting temperature that is equal to or greater than the melting temperature of the liquid metal 112' in contact with the electrode 206, such that the electrode 206 will not be consumed during operation of the nozzle 102 and reduce the likelihood of contamination of the object 116. Additionally or alternatively, the material of the electrode 206 may be substantially non-reactive with the liquid metal 112' (e.g., the material may be inert with respect to the liquid metal 112' or form a passivation layer in the presence of the liquid metal 112'), e.g., to reduce the likelihood of the material degrading over time. Further or alternatively, the material of the electrodes may have a resistivity substantially similar to the resistivity of the liquid metal 112 'to help make the direction of the current "I" and, thus, the direction of the liquid metal 112' ejected from the exit region 212 accurate. Thus, as a specific example, where the liquid metal 112' is aluminum or an aluminum alloy, the electrodes may be formed from one or more of tantalum and niobium.

In some embodiments, the electrodes 206 may be formed of the same material as the liquid metal 112 'at the respective interfaces between each electrode 206 and the liquid metal 112'. It will be appreciated that such embodiments may represent an advantageous solution to material selection issues, particularly those involving one or more materials having a melting temperature, reactivity, and resistivity (resistivity matching is difficult using economically available materials having different compositions). As a specific example, forming the electrode 206 from the same material as the liquid metal 112 'may facilitate the use of steel as the liquid metal 112'.

In embodiments where the electrodes 206 and the liquid metal 112 'are formed of the same material, the respective electrodes 206 melt at the interface 220 between the respective electrodes 206 and the liquid metal 112'. Further, the interface 220 may move in response to temperature fluctuations (among other things) that may occur during normal operation of the nozzle 102. Thus, to facilitate robust operation of the nozzle 102, the position of the interface 220 may be controlled to be in a predetermined area in the fluid chamber 208. For example, the maximum radial dimension of the launching chamber 216 may be wider (e.g., wider than the entry region 210, the exit region 212, or both) than the maximum radial dimension of the fluid chamber 208 proximate to the launching chamber 216. Continuing with this example, each interface 220 may be controlled to follow a portion of the respective recess 214 that is away from the general flow path of liquid metal 112' (which moves from entry region 210 to exit region 212).

In some cases, controlling the position of each interface 220 may include allowing a portion 222 of each electrode 206 to cool away from the corresponding interface 220. In general, it should be appreciated that as the liquid metal 112 'is ejected from the exit region 212, the resulting temperature gradient in the electrode 206 may cause the interface 220 to move in a direction away from the flow path of the liquid metal 112'. Thus, to help control the position of the interface 218, the nozzle 102 may include a heat sink 224, the heat sink 224 being coupled to the portion 222 of each electrode 206. As an example, the heat sink 224 may cool the portion 222 of each electrode 206 by forced convection, which may optionally be controlled (e.g., based at least in part on the ejection rate of the liquid metal 112' from the discharge area 212) to achieve a target temperature. As a more specific example, the heat sink 224 may include a fluid (e.g., water) that may be moved away from the portion 222 of each electrode 206 to cool the electrodes 206. Additionally or alternatively, in embodiments where the portion 222 of each electrode 206 extends beyond the housing 202 in a direction away from the emission chamber 216, the heat sink 224 may include a fan operable to move air over the portion 220 of each electrode 206. Although each of the electrodes 206 is shown thermally coupled to a respective one of the heat sinks 224, it should be understood that the electrodes 206 may alternatively be coupled to a single heat sink.

In general, the direction of travel of the current "I" in the firing chamber can affect the direction of the MHD force exerted on the liquid metal 112', and thus can affect the accuracy of droplet delivery. Although forming the electrode 206 and the liquid metal 112' from the same material or otherwise matching the resistivity of the electrode 206 and the liquid metal 112' can reduce the likelihood of accidental misorientation (misdirection) of the current "I" due to a mismatch in the resistivity of the material of the electrode 206 and the liquid metal 112', some degree of mismatch in resistivity can still exist during use (e.g., due to slight differences in materials). Thus, to reduce the likelihood of accidental misdirection of the current "I" in the launching chamber 208, the launching chamber 208 may be defined as having a generally rectangular cross-section in a plane perpendicular to the direction of travel of the liquid metal 112' from the entry region 210 toward the exit region 212. Because the generally rectangular cross-section does not have a maximum dimension, it is understood that the current "I" is more likely to be uniformly distributed along the generally rectangular cross-section, for example, as compared to a non-rectangular cross-section (e.g., a circular cross-section) having a maximum dimension along which a preferred current path may be formed.

The housing 202 may be formed of a material that thermally, chemically, and electrically supports the electrodes 206 and the liquid metal 112 'for applying an electrical current "I" to the liquid metal 112' to form the MHD force necessary to build the object 116. More specifically, where the current "I" is introduced into the liquid metal 112 'through the interface 220 of the molten material between the electrode 206 and the liquid metal 112', the material of the housing 202 may have a higher melting temperature than the material of the electrode 206 and the liquid metal 112 'to support the interface 218 between the electrode 206 and the liquid metal 112'. For example, the housing 202 may be formed from a material that can support liquid metal having a melting temperature greater than about 550 ℃ and less than about 1500 ℃. As a more specific example, the housing 202 may be formed from a ceramic material that can withstand the high temperatures associated with the molten state of certain metals (e.g., steel). Examples of such ceramic materials include, but are not limited to, one or more of alumina, sapphire, ruby, aluminum nitride, aluminum carbide, silicon nitride, sialon, and boron carbide. Additionally or alternatively, the housing 202 may be formed from more than one material, which may be used to reduce the use of more expensive materials along portions of the housing 202 where the properties of the more expensive materials may be less critical and the less expensive materials may provide sufficient performance.

The heater 226 mayIs supported along the housing 202 and may further or alternatively be in thermal communication with the liquid metal 112 'in the fluid chamber 208 to heat the liquid metal 112' in the fluid chamber 208. Additionally or alternatively, the heater 226 may heat the solid metal 112 as the solid metal 112 moves through the entry region 210 and into the fluid chamber 208. The heater 226 may, for example, comprise a resistive heating circuit comprising resistive wires (e.g., ferritic iron-chromium-aluminum alloys, nichrome, and nickel-chromium alloys available from Sandvik AB of Hallstahammar, swedenOne or more of the above). In embodiments where the housing 202 is formed from a ceramic material, for example, the resistance wire may be wound directly around the housing 202. Additionally or alternatively, a resistive wire may be embedded in at least a portion of the housing 202 to heat the fluid chamber 208. In some cases, the heater 226 may include one or more electrical heating tubes inserted into the housing. Electrical heating tubes include a resistive heating element that is typically enclosed in a tubular container. Further, or alternatively, the heater 226 may include an induction heating circuit comprising an induction coil wound around the housing 202. Other types of heaters may be used in addition or instead to deliver heat to the fluid chamber, including but not limited to radiant heaters, convection heaters, and combinations thereof.

It should be understood that the heating requirements associated with ejecting droplets of liquid metal 112 'may depend on the composition of the liquid metal 112'. In certain embodiments, the metal may be in liquid form at room temperature, such that MHD force may be applied to the liquid metal 112' without the use of the heater 122. In some embodiments, such as in the case of aluminum or aluminum alloys, the housing 202 may be heated to a temperature greater than about 600 ℃ (e.g., about 650 ℃) such that the aluminum or aluminum alloy is in liquid form in the fluid chamber 208. Additionally or alternatively, in certain embodiments, such as in the case of steel, the housing 202 may be heated to greater than about 1550 ℃ such that the steel is in liquid form in the fluid chamber 208.

The one or more magnets 204 may include a fixed magnet. For example, the one or more magnets 204 may include a rare earth magnet or any other magnet or set of magnets capable of generating a sufficient magnetic field across the launching chamber 216. In some embodiments, one or more magnets 204 may also or alternatively comprise an electromagnet. Increasing the magnetic field present in the liquid metal 112' may reduce the need for one or more of the amplitude and duration of the current pulse, and is therefore desirable. In some embodiments, a halbach array of permanent magnets may be used to increase the field strength.

The one or more magnets 204 may be sized and arranged such that the magnetic field "M" generated by the one or more magnets 204 substantially spans the entire fluid chamber 208. Where the electrode (e.g., electrode 206) is formed of the same material as the liquid metal being ejected (e.g., liquid metal 112'), magnetic field "M" may be established along the entire length of the melted portion (e.g., interface 220) to reduce the likelihood of fluid eddy currents. In this manner, the likelihood of fluid eddy currents forming in the liquid metal 112' may be reduced relative to the likelihood of fluid eddy currents forming by a magnetic field across the less-fluid chamber 208.

A challenge associated with generating a sufficient MHD force in the liquid metal 112 'in the launching chamber 208 is thermally managing the one or more magnets 204 in applications where the liquid metal 112' has a melting temperature above a temperature associated with deterioration of the magnetic properties of the one or more magnets 204 (e.g., a temperature greater than about 150 ℃). In particular, the magnetic field strength of many magnets decreases rapidly with distance away from the magnet. Thus, in order to generate a sufficiently strong magnetic field in the firing chamber 208, it may be desirable to place the one or more magnets 204 in relatively close proximity to the fluid chamber 208 (e.g., within about 2mm of the fluid chamber 208). However, in the event that the heater 226 heats the firing chamber 208 above a temperature associated with the deteriorated magnetic field strength of the one or more magnets 204. Such a temperature may correspond, for example, to the curie temperature of the material of the one or more magnets 204. Additionally or alternatively, such temperatures may correspond to temperatures at which the magnetic field strength of the one or more magnets 204 is reduced by more than about 10 percent.

To help balance competing factors of magnetic field strength (competing), through the temperature sensitivity of the one or more magnets 204, the nozzle 102 may include a thermal insulation layer 228. Typically, thermal insulation layer 228 may be thin, having a thickness greater than about 0.5mm and less than about 2mm (e.g., having a thickness greater than about 0.8mm to less than about 1.2 mm) and having a thermal conductivity that is lower than the thermal conductivity of the portion of housing 202 to which thermal insulation layer 228 is mounted. For example, the thermal insulation layer 228 may have a thermal conductivity greater than about 0.015W/m-K and less than about 0.1W/m-K. Exemplary materials suitable for use in thermal insulation layer 228 may include quartz ceramic (silica ceramic), aluminum silicon ceramic (alumina-silica ceramic), and combinations thereof.

Thermal insulation layer 228 may be held in place on housing 202 by the magnetic field created by one or more magnets 204. It should be appreciated that such placement of thermal insulation layer 228 in this manner may reduce or eliminate the need for other forms of fastening of thermal insulation layer 228 to housing 202. Further, or alternatively, because thermal insulation layer 228 need not be altered (e.g., drilled) to be installed in this manner, installation of thermal insulation layer 228 through use of one or more magnets 204 may be used to maintain the thermal performance of thermal insulation layer 228.

Additionally or alternatively, the housing 202 may be thinner in the direction in which the magnetic field of the one or more magnets 204 extends through the housing 202 than in the direction in which current is conducted between the electrodes 206. That is, one or more magnets 204 may be placed along a thinner portion of housing 202 to facilitate the formation of a strong magnetic field in emission chamber 216 through the close proximity of one or more magnets 204. The electrode 206 may be placed along a thicker portion of the housing 202, for example, to facilitate mounting of the electrode 206. Additionally or alternatively, where the electrode 206 and the liquid metal 112' are separated by a molten interface (e.g., interface 220), placement of the electrode along a thicker portion of the housing may provide more significant spacing between the electrodes in the firing chamber 216 to help control the respective interface 220 in the respective recess 214 during operation of the nozzle 10.

In some cases, the nozzle 102 may include a heat sink 230 in thermal communication with the one or more magnets 204 to reduce the likelihood that heat from the housing 202 will adversely affect the magnetic properties of the one or more magnets 204. The heat sink 230 may be spaced from the housing 202, for example, to help carry heat away from the one or more magnets 204, although reducing the likelihood that the heat sink 230 interferes with the control above the temperature of the liquid metal 112' in the hot fluid chamber 208. The heat sink 230 may remove heat from the one or more magnets 204 by forced convection. For example, a cooling fluid (e.g., water) may be moved through the heat sink 230 to provide cooling. Additionally or alternatively, the nozzle 102 may include one or more fans against the heat sink 230, providing forced air convection cooling. In this case, heatsink 230 may be a finned heatsink of the type known in the art.

The use of the nozzle 102 in a high-speed additive manufacturing process to provide a continuous or substantially continuous supply of liquid metal 112' to the fluid chamber 208 may be facilitated by the use of the feed system 104 to move the metal through the system 100. In particular, as described in more detail below, the feed system 104 may move the solid metal 112 toward the entry zone 210 at a rate sufficient to maintain the liquid metal 112' in the hot fluid chamber 208. Additionally or alternatively, as also described in more detail below, the feed system 104 may remove debris formed in or around the entry region 210, which may be used to reduce downtime and/or part defects associated with such debris.

The feed system 104 may include, for example, a plurality of rollers 232 engageable with the solid metal 112. The solid metal 112 may be in the form of a wire or other similar elongated shape such that the solid metal 112 is engaged in respective grooves defined by the plurality of rollers 232. In use, the plurality of rollers 232 may rotate relative to each other to feed the solid metal 112 toward the fluid chamber 208. In certain embodiments, the heat generated by the heater 226 to heat the housing 202 and the fluid chamber 208 may melt the solid metal 112 as the solid metal 112 moves proximate to the entry region 210.

In some embodiments, the feed system 104 may be actuated to thereby direct the solid metal 112 into the entry region 210 at a variable rate. The variable rate may be based on, for example, the rate at which the liquid metal 112' is ejected from the discharge region 212. The spray rate may be a measured rate of the actual amount of liquid metal 112 'sprayed from the discharge area 212 (e.g., as measured by a sensor against the liquid metal 112' sprayed from the discharge area 212). Additionally or alternatively, the spray rate may be a rate estimated based on the amount of liquid metal 112' required to meet the manufacturing requirements of the object 116 for a given point in the manufacturing process of the object 116. More generally, the variable rate may be used to reduce the likelihood that the fluid chamber 208 is starved of liquid metal 112 'before an additional amount of liquid metal 112' is provided to the fluid chamber 208 by the feed system 104.

Generally, the solid metal 112 may be melted to liquid metal 112' above the entry region 210 and at a location outside of the housing 202 or in the entry region 210. However, it will be appreciated that melting the solid metal 112 too far into the entry region 210 may cause interference with the pulses of current "I" in the liquid metal 112' in the hot fluid chamber 208. Also, or instead, melting the solid metal too far out of the entry region 210 may cause a discontinuity between the solid metal 112 and the liquid metal 112'. Such discontinuities are undesirable because they can result in the introduction of air into the fluid chamber 208, which can disrupt the accurate and controlled formation of droplets. Such discontinuities are also undesirable because they can alter jetting by changing the boundary conditions for refluxes at the top of the build chamber.

In view of these competing factors, in certain embodiments, the system 100 may include a sensor 120 facing the entry zone 210 to detect the interface between the solid metal 112 and the liquid metal 112' along a predetermined axial distance on each side of the entry zone 210 (e.g., above and below the entry aperture of the entry zone 210 and defining an entry port into the housing 202). As an example, the predetermined axial distance may be substantially equal to half of the maximum dimension of the access area 210. Thus, where the entry region 210 has a circular cross-section in a plane perpendicular to an axis defined by the entry region 210 and the exit region 212, the predetermined axial distance may be substantially equal to the radius of the entry region 210, such that the sensor 120 may detect the interface between the solid metal 112 and the liquid metal 112' within a predetermined distance of one radius above the entry aperture of the entry region 210 and within a predetermined distance of one radius below the entry aperture of the entry region 210.

In some cases, the sensor 120 may be in electrical communication with the feed system 104 to vary the rate of movement of the solid metal 112 into the entry zone 210 based on signals received from the sensor 120. For example, and without limitation, the feed system 104 may vary the rate of rotation of the rollers 232 based at least in part on the location of the boundary between the solid metal 112 and the liquid metal 112'. Continuing with the example, more specifically, the rate of rotation of the rollers 232 can be increased to move the interface between the solid metal 112 and the liquid metal 112' further into the entry region 210, or can be decreased to move the interface further out of the entry region 210.

In some embodiments, the sensor 120 may detect discontinuities between the solid metal 112 and the liquid metal 112' along a predetermined axial distance on each side of the access region.

The sensor 120 may include any one or more of a variety of sensors known in the art for detecting material continuity. For example, sensor 120 may include machine vision directed toward access area 210. Machine vision, for example, may detect one or more interruptions in the continuity of the solid metal 112 and the liquid metal 112 'and the location of the interface between the solid metal 112 and the liquid metal 112'. Additionally or alternatively, the sensor 120 may include an optical break-beam sensor (optical break-beam sensor) across the liquid metal 112 'at the entry region 210 to detect a break in the continuity of the solid metal 112 and the liquid metal 112'.

In some embodiments, the entry region 210 may include a generally funnel shape to reduce the likelihood of solid metal 112 becoming detached from liquid metal 112' as the solid metal 112 moves toward the entry region 210. The general funnel shape may, for example, be used to accommodate slight variations in the position of the solid metal 112 relative to the entry region 210 due to movement of the feed system 104, the entry region 210, or both.

As the solid metal 112 becomes liquid metal 112' near the entry region 210, debris may form along or near the entry region 210. Over time, this accumulation of debris can increase the likelihood of contamination of the liquid metal 112' and ultimately the object 116 being fabricated. Thus, the feed system 104 may include a wiper 234 that is movable relative to the entry area 210 to remove debris in or near the entry area 210. The wiper 234 may be, for example, a substantially rigid member that is movable through the housing 202 to remove debris from the access area 210. In certain embodiments, the wiper 234 may move relative to the access area 210 during interruptions between the solid metal 112 and the liquid metal 112' (e.g., as part of a routine maintenance protocol, as part of an object manufacturing process, or both). Typically, the wire may be retracted prior to the wiping action, and the wiping action is not performed while the liquid metal 112' is ejected from the nozzle 102.

In certain embodiments, the feed system 104 may include a pressurized gas source 236 that may be actuated to distribute pressurized gas relative to the entry region 210 to remove debris in or near the entry region 210. The pressurized gas may be, for example, a gas in the environment of build chamber 110. Thus, where the gas in the environment of the build chamber 110 is an inert gas (e.g., nitrogen or argon), the pressurized gas may be the same inert gas. In certain embodiments, the pressurized gas source 236 may be arranged to direct pressurized gas through the entry region 210 in a direction toward the exit region 212.

Additionally or alternatively, removing debris in or near the entry area 210 may include using MHD forces to remove debris in and near the entry area. As a specific example, the polarity of the electrical pulse E may be reversed relative to the polarity associated with the ejection of the liquid metal 112' from the discharge region 212. By the polarity of the electrical pulse E driven in this direction, the MHD force exerted on the liquid metal 112' in the hot fluid chamber 208 is in the direction from the exit region 212 towards the entry region 210. Thus, driving an electrical pulse E of sufficient amplitude can generate a force sufficient to cause the liquid metal 112' to be ejected through the entry region 210 to the MHD. It should be appreciated that the jet of liquid metal 112' in this direction may force debris away from the entry region 210 and carry away debris at any location in the fluid chamber 208, including at the throat of the exit region 212.

Referring again to fig. 1, the feed system 104 may supply the solid metal 112 to the nozzle 102 and the nozzle 102 may eject the liquid metal 112' as the robot system 106 moves the nozzle 102 in a controlled pattern relative to the build plate 114 in the process space 108 of the build chamber 110. Movement of nozzle 102 relative to build plate 114 as used herein should be understood to include any combination of relative movement of nozzle 102 and build plate 114, and thus includes movement of nozzle 102 when build plate 114 is stationary, movement of build plate 114 when nozzle 102 is stationary, and movement of nozzle 102 when build plate 114 is also moving.

The robotic system 128 may be any of a variety of different robotic systems known in the art and suitable for moving parts in a controlled pattern (e.g., a controlled two-dimensional pattern, a controlled three-dimensional pattern, or a combination thereof). For example, robotic system 106 may comprise a cartesian or x-y-z robotic system that employs a plurality of linear controllers to independently move along the x-axis, y-axis, and z-axis within build chamber 110. Additionally or alternatively, the robotic system 106 may include a parallel robot (deltarobot), which may provide significant advantages in terms of speed and rigidity in certain embodiments, as well as providing design convenience for stationary motors or drive elements. Other configurations, such as dual parallel robots or triple parallel robots, may additionally or alternatively be used and may increase the range of motion using multiple linkages (linkages). More generally, any robot suitable for controlling the positioning of the nozzle 102 and build plate 114 relative to each other (particularly in a vacuum or similar environment) may form part of the robotic system 106, including any mechanism or combination of mechanisms suitable for actuation, manipulation, action (coordination), etc. in the build chamber 138.

As liquid metal 112 'is ejected from nozzle 102 to form object 116 in build chamber 110, the temperature of object 116 being fabricated may be controlled to help achieve a desired deposition of liquid metal 112' on object 116. For example, the temperature of the object 116 may be controlled by heating the build plate 114, e.g., using closed loop temperature control (as is known in the art). However, where the object 116 is a three-dimensional part, thermal communication between the build plate 114 and the surface of the object 116 being fabricated may decrease as successive layers are built on top of each other. Thus, system 100 may include heater 122 to heat the environment in build chamber 110. For example, heater 122 may heat air or an inert gas in build chamber 110 to a target temperature. Additionally or alternatively, the heater 122 may include a fan to circulate heated air around the object 116 to maintain a target temperature of the object 116 through convective heat transfer.

Given that the droplets have a high thermal conductivity associated with metals, if the object 116 cools, the droplets will quickly solidify when they land on the object 116. This limits the ability to hit droplets for incorporation into the object 116 being fabricated without leaving voids that would otherwise compromise the ability to form fully dense parts. Thus, in general, the temperature of the object 116 in the build chamber 110 may be controlled to facilitate droplet impingement for incorporation into the object 116. For example, object 116 may be maintained at a temperature slightly below the solidus temperature, such that object 116 may be a solid when a new droplet arrives, but object 116 slowly acquires heat from the newly impinging droplet. Additionally or alternatively, the temperature of the part is reduced such that a newly impacted drop has a certain amount of time before it solidifies, but the newly impacted drop solidifies before the next drop appears. Continuing with this example, such temperature control may reduce the likelihood of two droplets merging to form a feature larger than desired, and thus conversely, may help provide resolution (resolution) to the object 116. As a specific example of such temperature control, if droplets are ejected from the nozzle 102 at a frequency of about 1kHz, the temperature of the object 116 can be controlled to solidify in a time ranging from about 0.1 milliseconds to 0.5 milliseconds after impact. In this way, each droplet will solidify before the next droplet reaches, and each droplet will have some time to spread over the object 116, thereby reducing the likelihood of accidental cavitation in the object 116. Additionally, the amount of time required to allow the newly impinged droplets to solidify can be varied by varying the temperature of the sprayed liquid metal 112' and the housing 202. For example, an increase in the temperature of the liquid metal 112' to be ejected will generally increase the amount of time required for the droplets to solidify.

Further, or instead, because of the droplets of liquid metal 112', the object 116 may react in certain environments, so the build chamber 110 is controlled to be a substantially inert environment compatible with the metal used for fabrication. For example, build chamber 110 may include an inert gas such as argon or nitrogen. Additionally or alternatively, the build chamber 116 may be an environmentally sealed chamber that may be evacuated by a vacuum pump 130 or similar device to provide a vacuum environment for fabrication.

Generally, the three-dimensional printer 100 can include a control system 126, the control system 126 can manage the operation of the three-dimensional printer 100 to fabricate the three-dimensional object 116. For example, the control system 126 may be in electrical communication with one or more of the nozzle 102, the feed system 104, the robotic system 106, the build plate 114, the power source 118, the sensor 120, and the heater 122. Thus, for example, the control system 124 may actuate the robotic system 106 to move the nozzle 102 in a controlled three-dimensional pattern, and additionally or alternatively, the control system 124 may actuate the feed system 104 to move the solid metal 112 toward the entry region 210 and the power source 118 to control the ejection of the liquid metal 112' from the nozzle 102 as one or more of the nozzle 102 and build plate 130 are moved in the controlled pattern. The controlled patterns may be based on, for example, models 126 stored in a database 128, used as local memory for a computer of the control system 124, or may be a remote database accessible through a server or other remote resource, or may be stored in memory in any other computer-readable medium that is oriented by the control system 124. In some embodiments, the control system 124 may acquire the model 126 in response to user input and generate machine preparation instructions for execution by the three-dimensional printer 100 to fabricate the object 116. More generally, unless otherwise stated or otherwise known from the context, the control system 126 can be used to control one or more portions of the three-dimensional printer 100 according to any one or more of the various methods described herein.

FIG. 3 is a flow chart of an exemplary method 300 of printing liquid metal by applying MHD force. It should be understood that the exemplary method 300 may be performed, for example, using any one or more of the three-dimensional printers described herein, and thus may be performed using the three-dimensional printer 100 described above with respect to fig. 1-2D. It is further understood that exemplary method 300 may be implemented in addition to or in place of any one or more of the other methods described herein, unless otherwise indicated herein or otherwise known from the context.

As shown in step 310, an exemplary method may include providing a liquid metal in a fluid chamber. The fluid chamber may be any one or more of the various fluid chambers described herein, and thus is at least partially defined by any one or more of the housings described herein, and may have an intake region and an exhaust region.

As shown at step 320, an exemplary method may include directing a magnetic field through a nozzle. For example, the magnet may be positioned sufficiently close to the fluid chamber such that the magnetic field of the magnet passes through a portion of the nozzle containing the liquid metal.

As shown in step 330, an exemplary method may include moving the discharge region of the fluid chamber in a controlled pattern. The discharge region may be moved in a controlled pattern, for example, by actuation of a robotic system (e.g., robotic system 106 as described above for three-dimensional printer 100). In some embodiments, the controlled pattern may be a three-dimensional pattern for forming a three-dimensional object by continuous transport of a layer of liquid metal. Additionally or alternatively, the controlled pattern may be a two-dimensional pattern, such as for forming a pattern or trace (trace) on a substrate or other two-dimensional surface.

As shown at step 340, an exemplary method may include conducting a pulsed current to the liquid metal in the launching chamber in the fluid chamber between the entry region and the exit region. The pulsed current may be crossed by the magnetic field in the firing chamber to exert MHD forces on the liquid metal in the firing chamber, as described above. In particular, the pulses of electrical current may be interleaved with the magnetic field to eject the liquid metal from the ejection region to form an object (e.g., a three-dimensional object). In general, the characteristics of the pulsed current may be based on the location of the discharge region along the controlled pattern. For example, the pulse frequency may be lower when liquid metal is sprayed onto a portion of the part having a high geometric curvature in the build plane (aspect). Similarly, the pulse amplitude, duration, or both may be based on the location of the discharge region along the controlled pattern to control the size of the liquid metal droplet based on the location along the controlled pattern.

Generally, the pulsed electrical current may be conducted into the liquid metal in the launching chamber at a frequency less than the resonant frequency of the liquid metal in the fluid chamber in which the launching chamber is disposed. For example, based on the features of the nozzles described herein, the resonant frequency of the liquid metal in the fluid chamber can be greater than about 20 kHz. Thus, as the discharge region 212 moves along a controlled pattern, the frequency of the pulsed current may vary below 20kHz, in accordance with achieving accuracy and speed targets associated with object manufacturing.

In certain embodiments, the frequency of the pulsed current may be varied based on the speed of travel along the controlled pattern of the discharge region. Thus, for example, the pulsed current may have a lower frequency when the robotic system moves the discharge area at a slower speed, and a higher frequency when the robotic system moves the discharge area at a higher speed. Additionally or alternatively, the frequency of the pulsed current may be based on the location of the bleed holes along the controlled pattern.

FIG. 4 is a flow chart of an exemplary method 400 of controlling current between a pulsed current mode and a direct current mode to control the rate of liquid metal ejection by MHD force. It will be appreciated that, in general, the pulsed current pattern may result in the generation of discrete droplets of liquid metal. By comparison, the direct current mode may result in the generation of a substantially constant flow of liquid metal. Thus, it will be appreciated that switching between pulsed current and direct current can advantageously provide control over both the accuracy and speed of object fabrication using any one or more of the three-dimensional printers described herein. It is further understood that exemplary method 400 may be implemented in addition to or in place of any one or more of the other methods described herein, unless otherwise indicated herein or otherwise known from the context.

As shown in step 410, the exemplary method 400 may include providing a liquid metal in a fluid chamber. The fluid chamber may be any one or more of the fluid chambers described herein, and thus may be defined by the housing, and may have an accessible region and an exhaust region.

As shown at step 420, exemplary method 400 may include directing a magnetic field through a housing. The magnetic field may be directed through the housing by any one or more of the magnets described herein. Thus, for example, even when the liquid metal is heated to an elevated temperature (e.g., greater than about 150 ℃ or higher temperatures associated with significant deterioration of the magnetic properties of the one or more magnets), a magnetic field may be directed through the housing by the one or more magnets supported on the housing and in proximity to the liquid metal in the fluid chamber,

as shown in step 430, exemplary method 400 may include moving the exhaust region of the fluid chamber in a controlled pattern. The controlled pattern may be based on, for example, a model of the object being manufactured. Thus, for example, where the model is manufactured as a three-dimensional object, the controlled style may be based on the three-dimensional style of the three-dimensional model of the object.

The need for liquid metal placement accuracy may vary along the controlled pattern. For example, in some cases, a greater degree of accuracy is required along the boundaries of the object being manufactured. The necessary accuracy along the boundary region can thus be achieved by the ejection of discrete droplets. More specifically, control of parameters such as droplet size, shape, velocity, direction, and cooling can be used to deposit metal on the surface of an object with a greater degree of accuracy. However, this accuracy is usually at the expense of the time required to manufacture the object. As another example, a lesser degree of accuracy may be required away from the boundaries of the object being manufactured (e.g., the portions of the object defined between the boundaries). In these areas, the liquid metal can be advantageously sprayed using less time consuming techniques to reduce the time required to manufacture the object.

As shown at step 440, exemplary method 400 may include delivering an electrical current between electrodes defining at least a portion of an emission chamber in a fluid chamber between an entry region and an exit region. The current may cross the magnetic field in the liquid metal in the launch chamber to generate a MHD force sufficient to eject the liquid metal from the discharge area.

As shown at step 450, exemplary method 400 may include controlling the current between the pulsed current and the direct current to form the object. Generally, controlling the current between a pulsed current and a direct current may be based on the location of the discharge region along the controlled pattern. Thus, for example, the current may be controlled to be a pulsed current along the boundary of the object being formed and the deviation (extension) in the boundary along the object being formed to be a direct current. Such switching between pulsed and direct currents may, for example, facilitate accurate control of liquid metal deposition along the boundaries of the object being fabricated, while also facilitating rapid fabrication of the object away from the boundaries of the object.

In general, the frequency of the pulsed current may be controlled according to any one or more of the various methods of controlling pulsed current described herein. Thus, for example, the frequency of the pulsed current may be less than the resonant frequency of the liquid metal in the fluid chamber. Further, or alternatively, the frequency of the pulsed current may be based on the speed of movement of the discharge region along the controlled pattern. In some embodiments, the frequency of the pulsed current may be less than 20kHz at maximum speed movement along the controlled pattern of discharge regions. In some embodiments, the frequency of the pulsed current may be based on the distance of the discharge area 212 from the edge of the controlled pattern. Thus, for example, as the discharge region 212 decelerates as it approaches the edge of the controlled pattern, the frequency of the pulsed current may thus decrease.

Switching from pulsed current to direct current may increase the mass flow rate of liquid metal from the exit region. Thus, for example, the rate of expulsion of liquid metal under MHD forces generated by the delivery of direct current into the launching chamber may be greater than the maximum rate of expulsion of liquid metal achieved at the maximum frequency of the pulsed current (e.g., a maximum frequency below the resonant frequency of the liquid metal in the fluid chamber). Thus, switching from pulsed current to direct current may help to deposit liquid metal at a faster rate than merely pulsing the current.

FIG. 5 is a flow diagram of an exemplary method 500 of using MHD force to form a part having one or more porous features that facilitate separating the part from a support structure of the part. That is, the object may include a part and a support structure for the part. The example method 500 may be used to form one or more porous features at one or more interfaces between a part and a support structure of the part. In use, the part may be preferentially separated from the support structure along one or more porous features. It should be understood that exemplary method 500 may be implemented in addition to or in place of any one or more of the other methods described herein, unless otherwise indicated herein or otherwise known from the context.

As shown at step 510, exemplary method 500 may include providing a liquid metal in a fluid chamber. The fluid chamber may be any one or more of the fluid chambers described herein, and thus may be defined in part by any one or more of the housings described herein, and may have an accessible region and a vented region.

As shown at step 520, exemplary method 500 may include directing a magnetic field through a housing. The magnetic field may be directed into the housing by one or more of the magnets described herein.

As shown at step 530, exemplary method 500 may include moving the discharge region of the fluid chamber in a controlled pattern. The controlled three-dimensional pattern may correspond to, for example, an object having a part and a support structure. As used herein, the term "support structure" may include any portion of an object used to support a portion of a part during manufacturing, including printing and post-processing (e.g., sintering), and thus the support structure itself may be another part, such that the object includes multiple parts and the introduction of porosity into the object may facilitate separation of the multiple parts.

As shown at step 540, exemplary method 500 may include delivering an electrical current between electrodes that at least partially define an emission chamber in a fluid chamber between an entry region and an exit region. The current may cross the magnetic field in the liquid metal in the firing chamber to eject the liquid metal from the ejection region according to any one or more of the methods described herein. The current may be delivered using one or more pulsed currents or direct currents. For example, the current may be delivered as a direct current away from an interface between the part and the support structure or another part, and the current may be delivered along the interface as a pulsed current.

As shown at step 550, exemplary method 500 may include controlling the porosity of one or more predetermined portions of the object being fabricated. For example, the porosity of one or more predetermined portions of the sprayed liquid metal aggregation on the build plate or on a previously deposited metal layer as the object is fabricated. In general, the porosity may be controlled to form an interface between the support structure and the part, the porosity of the interface having a higher porosity than the porosity of the support structure and the part. For example, the support structure, the interface, and the part may be formed from the same material such that a change in porosity at the interface may define the weakest point in the object, and thereby form a preferential separation location of the support structure from the part. In some cases, the interface may be frangible, for example, such that the support structure and the part may be easily separated from one another by application of one or more of a compressive force and a shear force at the interface. In some cases, sufficient separation force may be provided as a manual force, a force applied by a manual tool (e.g., pliers), or a combination thereof.

Controlling the porosity of the one or more predetermined portions may include, for example, varying the velocity of liquid metal droplets ejected from the ejection region of the fluid chamber. As an example, the interface may be formed by ejecting liquid metal from the drain hole at a lower velocity than a velocity associated with forming one or both of the support structure and the part. Generally, liquid metal ejected at a lower velocity will not penetrate the target material completely as liquid metal ejected at a higher velocity. Such limited penetration may result in increased porosity, which may be advantageous in the case of forming an interface for separating a part from a support structure or another part.

In general, the velocity of liquid metal droplets ejected from a discharge region of a fluid chamber is a function of the amplitude and duration of the pulses used to form the respective droplets. Thus, controlling the porosity may include varying at least one of an amplitude and a duration of the pulse along the interface. For example, the interface may be formed by liquid metal droplets ejected using pulses of smaller amplitude than the amplitude of the pulses used to form objects away from the interface. The velocity of the liquid metal ejected from the ejection zone may be controlled, for example, by varying one or more of the pulse amplitude and duration.

Additionally or alternatively, controlling the porosity of the one or more predetermined portions may include varying a temperature of the liquid metal ejected from the discharge region. For example, liquid metal droplets ejected at lower temperatures may solidify on the target surface more easily than liquid metal droplets ejected at higher temperatures. Thus, liquid metal droplets ejected at lower temperatures tend to spread less on the target surface and thus areas of increased porosity may be formed. Thus, in certain embodiments, controlling the porosity of the one or more predetermined portions may include reducing the temperature of the liquid metal in the fluid chamber.

FIG. 6 is a flow chart of an exemplary method 600 of using MHD force to pull back a meniscus of stationary liquid metal in a fluid chamber. It should be understood that exemplary method 600 may be implemented in addition to or in place of any one or more of the other methods described herein, unless otherwise indicated herein or otherwise known from the context.

As shown in step 610, the example method 600 may include providing a liquid metal in a fluid chamber. The fluid chamber may be, for example, any one or more of the fluid chambers described herein, and may thus be defined by any one or more of the housings described herein, and may have an intake region and an exhaust region.

As shown at step 620, exemplary method 600 may include directing a magnetic field through a housing. The magnetic field may be directed into the housing by any one or more of the magnets described herein.

As shown at step 630, the example method 600 may include delivering a first current into the liquid metal in the housing at rest. A quiescent state of liquid metal in a housing as used herein can include a liquid metal state between liquid metal sprays from a drain portion of the housing, and thus can include a liquid metal state with a meniscus attached to the drain portion of the housing (e.g., attached to the drain portion in a drain portion throat or attached to a drain hole of the drain portion and extending slightly out of the housing).

The first current may be directed in a direction that creates an MHD force (which exerts a pullback force on the liquid metal) and in a direction that crosses the magnetic field in the liquid metal. For example, in an embodiment where the magnetic field is constant, the first current may have a polarity opposite to the polarity that produces the jetting force on the liquid metal. Because the interaction of the current and the magnetic field follows the right hand rule, it will be appreciated that directing the first current in a direction opposite in polarity to that associated with the spray force will produce an MHD force that is substantially opposite to the spray force and therefore can pull the liquid metal back.

The amount of the pull back force exerted on the liquid metal is a function of the magnitude of the first current. Typically, the pullback force is sufficient to overcome a head (pressure head) of the stationary liquid metal in the fluid chamber to move the crescent without significant movement of the liquid metal. Thus, in general, the pull back force is significantly less than the force required to eject the liquid metal. Thus, the magnitude of the first current is generally small relative to the magnitude of the current used to eject the liquid metal from the discharge region. For example, the first current may have a magnitude greater than about 1 amp and less than about 100 amps (e.g., about 2 amps to about 20 amps).

Fig. 7A and 7B are a series of schematic illustrations comparing the position of the meniscus 702 of the stationary liquid metal 704 of the nozzle 706 when a pull-back force P is applied to the meniscus 702. It is understood that the pull-back force P may be, for example, the pull-back force generated by the first current of step 630 in fig. 6.

As shown in fig. 7A, in the absence of a pullback force, the meniscus 702 may be pushed out of the discharge portion 708 of the nozzle 706. The meniscus 702 may extend beyond the drain portion 708 by the pressure created by the weight of the stationary liquid metal 704 above the meniscus. In the absence of an applied pull back force, some of the liquid metal 704 may migrate out of the nozzle 706 and onto the bottom surface 710 of the nozzle 706 under certain circumstances. Such migration may interfere with subsequent ejection of droplets of liquid metal 704 (e.g., by forming droplets of a larger size than intended). Thus, it should be appreciated that reducing the likelihood of the stationary liquid metal 704 migrating onto the bottom surface 710 may advantageously improve the accuracy of droplets that may be delivered from the nozzle 706.

As shown in fig. 7B, the meniscus 702 may be urged in a direction away from the bottom surface 710 by a pullback force P. Thus, the pull-back force P may reduce the likelihood that the meniscus 702 will migrate to the bottom surface 710. In fact, if some liquid metal 704 accumulates on the bottom surface 710 (e.g., from an errant drop), the negative pressure established by the pull-back force P may draw the liquid metal 704 from the bottom surface 710 into the discharge portion 708 of the nozzle 706.

For example, the exhaust portion 708 may include a throat 712 and an exhaust aperture 712. The pull-back force P may be sufficient to keep the meniscus 702 of liquid metal at rest attached to the discharge portion 708 of the nozzle 706. In certain embodiments, the pull-back force P may pull the meniscus 702 into the throat 712 of the exhaust portion 712. Additionally or alternatively, the pull-back force P may keep the meniscus 702 attached to the drain 712.

Referring again to fig. 6, as shown in step 640, the method 600 may include selectively delivering a second current into the liquid metal. The second current may intersect the magnetic field in the liquid metal to exert an emissive force on the liquid metal to eject the liquid metal from the ejection region. Thus, for example, the second current may be selectively delivered to the liquid metal as the discharge region of the nozzle moves along a controlled pattern (e.g., a controlled three-dimensional pattern). For example, the second current may be delivered into the liquid flow along less than all of the controlled pattern such that the second current is periodically interrupted as the discharge region moves along the controlled pattern. More generally, the second electrical current can be directed to the liquid metal according to any one or more of the various methods described herein. Thus, the second current may vary based at least on the location of the drain hole along the controlled pattern. Additionally or alternatively, the second current may comprise a pulsed current, a direct current, or a combination thereof. Where the second electrical current comprises a pulsed electrical current, delivering the second electrical current to the liquid metal along the feed path can include conductively firing pulses to the liquid metal in the feed path and conductively pulling back pulses to the liquid metal in the feed path (e.g., before firing the pulses, after firing the pulses, or both) according to any one or more of the various methods described herein.

The second electrical current may be selectively delivered to the liquid metal between electrodes defining an emission chamber in the fluid chamber between the entry region and the exit region according to any one or more of the various methods described herein. In some cases, a first current may be delivered for the liquid metal between the electrodes. Thereby, more generally, the first and second currents may be conveyed along the same path into the liquid metal.

In certain embodiments, the first current may be continuously applied to the liquid metal and the second current may be superimposed on the first current. Because the second current is greater in magnitude than the first current, the desired ejection of liquid metal occurs. Because the first current is continuously applied, the meniscus will be pulled back between pulses of the second current (e.g., as shown in FIG. 7B). While the first current has been described as being continuously applied to the liquid metal, it is understood that in certain embodiments, the first current may be turned off during the ejection pulse of the second current and turned back on immediately after the ejection pulse of the second current.

FIG. 8 is a flow chart of an exemplary method 800 that uses MHD force to bounce a meniscus of stationary liquid metal in a discharge region of a nozzle (bounce). It should be understood that exemplary method 800 may be implemented in addition to or in place of any one or more of the other methods described herein, unless otherwise indicated herein or otherwise known from the context.

As shown in step 810, the method 800 may include providing a liquid metal in a fluid chamber. The fluid chamber may be any one or more of the fluid chambers described herein, and thus may be at least partially defined by the housing, and may have an accessible region and an exhaust region.

As shown in step 820, the method 800 may include directing a magnetic field through the housing. The magnetic field may be directed through the housing, for example using any one or more of the magnets described herein.

As shown in step 830, the method 800 may include delivering a first current into the emission chamber of the fluid chamber and the liquid metal between the entry region and the exit region. Typically, the first current may comprise a fluctuating current crossing a magnetic field in the liquid metal to exert a pulsating force on a meniscus attached to the drain region. As used herein, fluctuating current is understood to include substantially sinusoidal current, pulsed current, or a combination thereof. In response to pulsating forces on the meniscus, the meniscus can bounce, i.e., alternately cause the meniscus to bend (deflect) and then relax. For example, the drain region may include a drain hole and a throat, and the meniscus may be attached to one or more of the throat and the drain hole, and at that location, the meniscus may experience an alternating bend in response to the first current.

The liquid metal can even build up a metal oxide scale by reacting with trace amounts of oxygen and vapors sometimes present in the atmosphere. These metal oxides are generally strong and, once thick enough, can interfere with jetting as desired (e.g., prevent jetting from occurring). However, these oxide scales are also quite brittle. Thus, the bouncing of the meniscus in response to the first current may help to keep the surface of the liquid metal in a meniscus deflected state (e.g., by causing cracks in the film), and thereby reduce the likelihood that the presence of the film causes the on-demand ejection of droplets to stop.

The first current may be delivered over a wide frequency range (e.g., a frequency range to which the meniscus may respond). In certain embodiments, the oscillation generated by the first current may be kept below the first resonant frequency of the liquid metal in the fluid chamber so that sufficient control of the pulses may be maintained. However, in embodiments where it is desirable to use a small current to excite oscillations in the meniscus, the first current may be delivered as long as it is at or near the resonant frequency of the liquid metal in the fluid chamber. In typical applications, the oscillation amplitude may be greater than about 1 percent and less than about 50 percent (e.g., greater than about 5 percent and less than about 25 percent) of the discharge orifice diameter of the fluid chamber.

In some cases, the method 800 may further include ejecting liquid metal through the drain region to clear the meniscus from the drain region. Such spraying of the liquid metal through the discharge area may be effected, for example, away from the component. In general, it will be appreciated that such spraying of liquid metal through the drain region may be used to refresh the meniscus, particularly if the meniscus has been present in the drain region for a long time. In some cases, the liquid metal may be sprayed from the discharge region over a predetermined period of time.

The method 800 may further include delivering a second current to the liquid metal at the launch, as shown at step 840. The second liquid metal may be crossed by a magnetic field in the liquid metal to eject the liquid metal through the ejection region to form the object. It is understood that the second current may comprise a pulse current that is different (e.g., much larger) than the pulse current of the first current. Because the second electrical current is delivered to eject the liquid metal to form the object, it should be further understood that the second electrical current may be delivered to the liquid metal based on the position of the discharge region along a controlled pattern (e.g., a three-dimensional pattern) according to any one or more of the various methods described herein. Thus, for example and without limitation, delivering the second current to the liquid metal in the launching chamber may include switching between a pulsed current and a straight current based at least in part on a position of the discharge orifice along the controlled pattern.

The first current may be stopped for a short time before the second current is delivered. During the short time, the oscillation induced in the meniscus by the first current may decay before the first droplet is ejected in response to the second current. Thus, more generally, stopping the first current for a short time before delivering the second current during object manufacturing may reduce the likelihood of the first current interfering with a first ejection of liquid metal or interfering with a subsequent ejection of liquid metal. Additionally, or alternatively, the first current may be delivered to the meniscus when a printhead associated with the fluid chamber is not actively printing (e.g., when the printhead is moving between aspects of the object being fabricated or when the printhead is waiting for a new layer to start).

While certain embodiments have been described, other embodiments may be additionally or alternatively implemented.

For example, while devices, systems, and methods have been described in connection with removing certain aspects of debris from an access area, other devices, systems, and methods of debris removal may additionally or alternatively be used. For example, as shown in fig. 9, the nozzle 900 can include a housing 902, the housing 902 defining at least a portion of a fluid chamber 904 having an intake region 906 and an exhaust region 908. The nozzle 900 may include a filter 910 disposed along the fluid chamber 904. Generally, filter 910 may act as a filter as a last resort, reducing the likelihood that debris will reach exhaust region 908 and be ejected during object manufacturing. Thus, the filter 910 may be spaced apart from the drain region 904. By way of example, a filter 910 may be disposed along the access area 906. Generally, filter 910 may include a porous structure formed from a material capable of withstanding the temperature of the molten metal in contact with filter 910. In certain embodiments, filter 910 may advantageously reduce resonant vibration of fluid chamber 904 as compared to the same fluid chamber without the filter, for example, by absorbing energy of an acoustic pulse moving in fluid chamber 904.

Referring now to fig. 10, a nozzle 1000 may include a housing 1002, the housing 1002 defining at least a portion of a fluid chamber 1004 having an intake region 1006 and an exhaust region 1008. Along the access region 1006, the housing 1002 may include a channel (chimney)1010 extending from the housing 1002 in a direction away from the fluid chamber 1004. The channel 1010, for example, may reduce the likelihood that a meniscus of liquid metal along the entry region 1006 will wet the exterior surface of the housing defining the entry region 1006. Thus, for example, by reducing wetting along the housing 1002, the channel 1008 can reduce the likelihood of damage to components (e.g., the heater 1012) carried on the housing 1002.

As another example, although the nozzle has been described as including a liquid-cooled magnet, other embodiments may additionally or alternatively be used. For example, referring now to fig. 11, a nozzle 1100 may include one or more magnets 1102, a heat sink 1104, and a fan 1106. A fan 1106 may be positioned to direct air over the heat sink 1004 to carry heat away from the one or more magnets 1102 by forced air convection.

As another example, while the nozzle has been described as including a metal electrode defining a fluid chamber and carried in a ceramic housing, other embodiments may additionally or alternatively be used. For example, referring now to fig. 12, the nozzle 1200 may include an electrode 1202 integrally formed with a portion of the housing 1204, the electrode 1202 defining at least a portion of the fluid chamber 1206 (e.g., a portion of the fluid chamber distal to the exhaust orifice 1208). Fluid chamber 1206 may have an intake area 1210 and an exhaust area 1212. The housing portion integrally formed with the electrode 1202 should be understood to be a metallic material.

As used herein, "unitary" includes components formed from a single piece of material, such as a solid piece or rod of material, and thus formed from the same type of material. For example, the housing electrode 1202 and the housing 1204 may be integrally formed with the rod (e.g., a rod having a common standard size) such that current may be conducted along the rod in an axial direction and a magnetic field may be conducted radially through the rod. Generally, the fluid chamber 1206 may be formed by removing material (e.g., drilling a through hole) from the integrally formed electrode 1202 and housing 1204. Having the electrode 1202 and the housing 1204 integrally formed, for example, can be advantageously used to manufacture the nozzle 1200 with a low thermal mass, which can be used to accurately control the temperature of the liquid metal in the fluid chamber 1206. Additionally or alternatively, having the electrodes 1202 and the housing 1204 integrally formed may be used to position one or more magnets proximate to the liquid metal in the fluid chamber 1206, such that the magnetic field strength in the feed path is strong enough for the MHD force to be created to eject the liquid metal from the exit orifice 1214. Further, or alternatively, having the electrode 1202 and the housing 1204 integrally formed may reduce the number of interfaces between different materials, which may present difficulties at the high temperatures associated with spraying certain types of liquid metals.

Because the electrode 1202 is integrally formed with a portion of the housing 1204, the emission chamber 1218 formed by the electrode 1202 may be substantially adjacent the venting region 1212, and in particular substantially adjacent the venting orifice 1214. As described above, delivering current into the fluid chamber 1206 at a point substantially near the exhaust region 1212 may facilitate forming a shorter fluid chamber 1206, which in turn may increase the resonant frequency. Thus, having the electrode 1202 integrally formed with a portion of the housing 1204 has certain advantages for ejecting liquid metal droplets at higher frequencies. In general, in embodiments where the housing of the nozzle is formed of metal, having the resistivity match between the liquid metal and the housing is critical to reducing the likelihood of current from the electrodes flowing around the liquid metal in the flow chamber. Thus, in the example of the nozzle 1200, it will be appreciated that the resistivity of the metal of the housing 1204 advantageously substantially matches the resistivity of the liquid metal in the fluid chamber 1206. In embodiments where the electrode 1202 and a portion of the housing 1204 are integrally formed, it is further understood that the material forming the electrode 1202 and the housing 1204 has a melting point greater than the melting point of the liquid metal to be ejected from the fluid chamber 1206. Thus, for example, in embodiments where the liquid metal is aluminum or an aluminum alloy, the material forming the electrode 1202 and the housing 1204 may be tantalum or niobium, each of which has a higher melting point than aluminum or an aluminum alloy, each of which has a resistivity substantially similar to aluminum and its alloys, and each of which has a weak reactivity with molten aluminum.

Where at least a portion of the housing 1204 and the electrode 1202 are integrally formed of metal, including where a ceramic insert is present in the nozzle, the current may flow through the metal sidewalls defining the firing chamber 1218, as well as through the liquid metal flowing in the firing chamber 1218. In this case, the portion of the current flowing through the metal sidewall of the housing 1204 does not contribute to the pressure (for liquid metal jetting) for obtaining MHD. Thus, in certain embodiments, it is advantageous to make the sidewalls of the housing 1204 as thin as possible in a direction parallel to the magnetic field moving through the firing chamber 1206 (e.g., a magnetic field formed according to any one or more of the devices, systems, and methods described herein) to reduce the amount of current that can flow out of the firing chamber 1218.

It is further advantageous to have the liquid metal match as closely as possible the resistivity of the portions of the housing 1204 and the electrode 1202 that define the firing chamber. In an ideal situation, where these resistivities are ideally matched, the current will flow uniformly through the emission chamber 1218 regardless of the shape of the emission chamber 1218. For example, if the fluid chamber 1206 and the firing chamber 1218 are cylindrical (e.g., as may be helpful in the manufacture of the nozzle 1200), the current will flow in a direction perpendicular to the axis of the cylindrical shape. However, if the resistivity of the material of the housing 1204 and the electrode 1202 defining the fluid chamber 1206 and the firing chamber 1218 is higher than the resistivity of the liquid metal, as current flows through the firing chamber 1218, the current will tend to flow towards the center of the firing chamber 1218, which can reduce the effectiveness of the MHD for ejecting the liquid metal by allowing some energy to dissipate as a vortex of fluid due to non-uniform pumping action of the non-uniform current. The eddy currents reduce the likelihood of this reduced MHD effectiveness and the cross-section of the launching chamber 1218 may be rectangular rather than circular. Such a rectangular cross-section may be used to reduce the effect of any mismatch in resistivity between the liquid metal and the metal defining the firing chamber 1218 by at least having no difference in resistance (regardless of the current path between the electrodes 1202 through the firing chamber 1218).

In some cases, the materials forming the electrodes that are compatible with the liquid metal in a given nozzle may be expensive. Additionally or alternatively, the use of a combination of materials in the nozzle may be used, for example, to advantageously utilize a combination of material properties (e.g., electrical resistivity, thermal conductivity, chemical reactivity, etc.). Thus, more generally, it may be useful to combine metals with other types of materials in the nozzle of the present invention.

Returning to the example of the nozzle 1200, a portion of the discharge region 1212 defining the discharge orifice 1214 may be formed with a ceramic insert 1216 supported by the housing 1204 along the discharge region 1212. Ceramic insert 1216 may be formed, for example, from one or more of alumina, sapphire, ruby, aluminum nitride, aluminum carbide, silicon nitride, sialon, and boron carbide. The ceramic insert 1216 may be used to withstand wear as the liquid metal is ejected from the nozzle 1200. That is, in some instances, the material of the ceramic insert 1216 may be better able to withstand wear than the material defining the fluid chamber 1206, thereby providing certain advantages for long-term use of the nozzle 1200. That is, the material of the housing 1204 and/or the electrode 1202 may be formed of a metal that is substantially inert with respect to the liquid metal in the fluid chamber 1206, but may not be sufficiently inert to define the drain hole, as the large amount of liquid metal flowing at high velocity through the drain hole amplifies the incomplete inertness (incompleteness) of the metal. Thus, the discharge holes 1214 may advantageously be defined by the ceramic insert 1216. While the bleed holes 1214 have been described as being defined by the ceramic insert 1216, it should be understood that, in some instances, the ceramic insert 1216 may be omitted and the bleed holes 1214 may be formed through the metallic material of the housing 1204. Referring now to fig. 13, a nozzle 1300 may include a housing 1302 and a liner 1304 defining at least a portion of a fluid chamber 1306. The housing 1302 may be formed of a ceramic material, for example. Examples of ceramic materials used to form the housing 1302 include one or more of titanium nitride, titanium aluminum nitride, titanium carbide, alumina, and titanium carbonitride. The metal material forming the liner 1304 is advantageously a metal compatible with the liquid metal to be ejected from the nozzle 1300, and thus may be, for example, any of the various different electrode materials described herein. It should be appreciated that the liner 1304 may be formed using less of a given material than an electrode integrally formed with the housing. The use of less metal material may be particularly advantageous where the material forming the liner 1304 is expensive. For example, the electrode 1308 may be coupled to the liner 1304 to deliver current to the liner 1304, and in some cases, the electrode 1308 may be formed from a material that is less expensive than the material from which the liner 1304 is formed.

In some embodiments, the electrodes 1304 may be plated onto the material of the housing 1302, for example, the electrodes 1304 may be plated along all or a portion of the housing 1302 (e.g., along all or a portion of the fluid chamber 1306). Further, or alternatively, electrode 1304 may be applied to housing 1302 by any one or more metal deposition techniques known in the art.

Referring now to fig. 14, the nozzle 1400 may include an electrode portion 1402 and a housing portion 1404. In general, the electrode portion 1402 and the housing portion 1404 may be formed from different materials (e.g., different metals). As a specific example, the electrode portion 1402 may be formed from a first material that meets the requirements of relative inertness and thermal stability in contact with the liquid metal to be ejected. Depending on the liquid metal to be sprayed, the choice of the first material to meet these requirements can be relatively expensive. For example, tantalum is suitable for use as the first material in the case where the liquid metal is aluminum or an aluminum alloy. However, tantalum is expensive relative to other types of metals. Thus, more generally, it is desirable to form the electrode portion 1402 as a small piece of the first material suitable for contacting liquid metal, and additionally or alternatively, to form the housing portion 1404 as a larger piece (e.g., for supporting an auxiliary component associated with the nozzle 1400, such as a cartridge heater (cartridge heater) 1406). The second material of the housing portion 1404 may be formed of a material that satisfies thermal stability at the temperature of the liquid metal. However, because the housing portion 1404 does not contact the liquid metal, a material suitable for the second material may be less expensive than a material suitable for the first material. An example where the first material of the return electrode portion 1402 is formed of tantalum, and the second material of the housing portion 1404 is formed of copper, for example. Generally, the electrode portion 1402 and the housing portion 1404 may be joined to each other by welding and brazing as is known in the art.

Referring now to fig. 15, a nozzle 1500 may include a housing 1502, the housing 1502 defining at least a portion of a fluid chamber 1504 extending between an intake region 1506 and an exhaust region 1508. The electrode 1510 defines at least a portion of the firing chamber 1512 in the fluid chamber 1504 between the entry region 1506 and the exit region 1508. In some cases, the nozzle 1500 can be constructed of all metal such that the housing 1502 and the electrode 1510 are formed of metal (e.g., the same metal, such as part of a unitary structure). The drainage region 1508 may have a throat 1514 and a drainage aperture 1516 in fluid communication with the throat 1514 and the fluid chamber 1504 such that, in use, liquid metal moves from the fluid chamber 1504 through the drainage aperture 1516 via the throat 1514. The exit port 1516 may be defined, for example, by an outer surface 1518 of the housing 1502. The throat 1514 may be, for example, substantially cylindrical, and the diameter of the throat 1514 may be substantially equal to the diameter of the exit hole 1516.

In use, the exit port 1516 may be wetted by the liquid metal disposed in the fluid chamber 1504. Such wetting at the drain holes 1516 may improve control over the ejection of liquid metal from the drain holes. However, in some cases, wetting the drain holes 1516 in this manner increases the risk of liquid metal inadvertently extending beyond the drain holes (e.g., along the outer surface 1518 of the housing 1502), which in turn can interfere with the control of liquid metal spraying. For example, liquid metal wetting along the exterior surface 1518 of the housing may adhere to liquid metal droplets being ejected from the exit orifice 1516 and thereby produce larger droplets than desired. Thus, the nozzle 1500 may further or alternatively include a film 1520 along an exterior surface of the housing 1502 (e.g., along a portion of the exterior surface of the housing 1502 defining the exit holes 1516). The membrane 1520 may be used to limit wetting of the liquid metal to a desired surface in the exit region 1516.

The membrane 1520 may be substantially non-wetting (e.g., having a wetting angle greater than about 90 degrees) with respect to the liquid metal being stably supported along the emission chamber 1512 (which is at least partially defined by the electrode 1510). As used herein, liquid metal that may be stably supported in the emission chamber 1512 should be understood to include liquid metal that may be supported along the emission chamber 1512 without modifying the electrode 1510 to a degree that causes significant degradation in the delivery of current to the emission chamber 1512. By way of non-limiting example, where the molten form of aluminum, aluminum alloy, or flux is supported in the fluid chamber 1504 for ejection through the exit holes 1516, the membrane 1520 may be substantially non-wetting with respect to the molten form of aluminum, aluminum alloy, or flux, or the flux and the electrode 1510 may have a melting temperature greater than the melting temperature of the aluminum, aluminum alloy, or flux and remain substantially chemically inert with respect to the aluminum, aluminum alloy, or flux. Thus, more generally, the choice of material for the membrane 1520 may be related to the choice of material for the electrode 1510, at least because each material must have certain properties in the presence of liquid metal for proper operation of the nozzle 1400 for spraying of liquid metal (e.g., for imparting MHD forces in the firing chamber to spray liquid metal through the exit holes 1516 without significantly wetting the exterior surface 1518 of the housing 1502).

In certain embodiments, the throat 1514 is wettable relative to the liquid metal that may be stably supported in the firing chamber. As such, the contact angle of the liquid metal stably supported in the emission chamber 1504 with the film 1520 is greater than the contact angle with the material of the housing 1502 defining the throat 1514. By way of example, the membrane may comprise an oxide of at least one component of a material that forms the portion of the housing 1502 that defines the throat. Thus, for example, where the housing is formed of tantalum, the membrane may comprise tantalum oxide. As another example, where the housing is formed from steel, the film may include chromium oxide or oxides of other components of the steel.

Thus, in use, liquid metal may wet the throat 1514 (e.g., while passing a pulse of current through the emission chamber 1504 according to any one or more of the methods described herein, while the membrane 1520 remains un-wetted. wetting the throat 1514, for example, may be used to accurately eject droplets of liquid metal at high velocity. wetting the throat 1514, for example, may reduce the likelihood that ambient gases (e.g., air, nitrogen, argon, etc.) that may interfere with droplet formation are present in the throat 1514 as the liquid metal is driven through the throat 1514 during liquid metal droplet ejection.

The membrane 1520 may be supported on the outer surface of the housing 1502 by any of a variety of different methods. In some cases, the membrane may be a separate material applied to the outer surface of the housing 1502. Additionally or alternatively, the membrane 1520 may be integrally formed with the outer surface 1518 of the housing 1502. Such integral formation of the membrane 1520 and the housing 1502 may serve to reduce the likelihood of separation between the membrane 1520 and the housing 1502 during operation. Further, or instead, film 1520 may be grown on outer surface 1518 of housing 1502 by oxidizing the material of outer surface 1518 of housing 1502 (e.g., by oxidizing tantalum or steel). Still further or alternatively, the film 1520 may be deposited on the outer surface 1518 of the housing 1502 by Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), and other methods known in the art.

As another example, although the formation of a temperature gradient in the electrode has been described through various different forms of cooling, other embodiments may additionally or alternatively be used. For example, referring to fig. 16, nozzle 1600 may include a housing 1602 and an electrode 1604. The housing 1602 may define at least a portion of a fluid chamber 1606 having an intake region 1608 and an exhaust region 1610. Electrode 1604 may define at least a portion of emission chamber 1612 in fluid chamber 1606. In use, the liquid metal 1614 is disposed in the fluid chamber 1504. In general, the material of the electrode 1604 that is in contact with the liquid metal 1614 may be formed from the same material or substantially the same material, and thus, more specifically, the interface 1616 between the liquid metal 1614 and the electrode 1604 may be a melt formation of the material. In general, operation of the nozzle 1600 may be similar to operation of the nozzle 102 described above with respect to fig. 1 and 2A-D, unless otherwise described or apparent from the context.

The housing 1602 may define a neck region 1618 between respective outer portions 1620 of the electrodes 1604 and the emission chamber 1612. In particular, the neck region 1616 may have a reduced cross-sectional area as compared to the emission chamber 1612 and each outer portion 1620 of the electrode 1604. In some cases, the material of the electrode 1604 may have a much higher thermal conductivity than the material forming the housing 1602 (e.g., where the electrode 1604 is formed of a metal and the housing 1602 is formed of a ceramic material). In this case, reducing the cross-sectional area of the electrodes 1604 along the neck region 1618 of the housing can help establish a significant temperature gradient along each respective electrode 1604. Such a significant temperature gradient may be used, for example, to control the location of the respective interface 1616 between each electrode 1604 and the liquid metal 1614. Additionally or alternatively, the reduced cross-sectional area of electrode 1604 may help reduce the likelihood of fluid vortices forming in emission chamber 1612 due to non-uniform magnetic fields or non-uniform current flow in the region.

Referring now to FIG. 17, the nozzle 1700 may include a housing 1702 and an electrode 1704. The housing 1702 may define at least a portion of a fluid chamber 1706, and the electrodes 1704 may define at least a portion of an emission chamber 1708 in the fluid chamber 1706. Housing 1702 may include a neck region 1710 having a reduced cross-sectional area. The reduced cross-sectional area of the neck region 1710 may extend through the firing chamber 1708. The cross-sectional area of the housing 1702 may follow the cross-section of the electrode 1704, including along the neck region 1710, for example. In comparison to the nozzle 1600 of fig. 16, it will be appreciated that the nozzle 1700 may facilitate formation of a fluid chamber 1706 having a shorter length, which may advantageously increase a resonant frequency associated with the fluid chamber 1706. Thus, more generally, nozzle 1700 may facilitate the formation of shorter fluid chambers and, thus, may facilitate the ejection of liquid metal at higher frequencies without exciting resonant frequencies.

Referring now to fig. 18, the nozzle 1800 may include a housing 1802 and an electrode 1804. The housing 1802 may define at least a portion of a fluid chamber 1806, and the electrodes 1804 may define at least a portion of a firing chamber 1808 in the fluid chamber 1806. The housing 1802 may include a neck portion 1810. The respective maximum heights of the electrode 1804, neck portion 1810, and firing chamber 1808 may each be different from one another.

The above-described systems, devices, methods, processes, etc., may be implemented by hardware, software, or any combination thereof as appropriate for a particular application. The hardware may comprise a general purpose computer and/or a special purpose computing device. This includes implementation in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors or other programmable devices or processing circuits, and internal and/or external memory. This may also or instead include one or more application specific integrated circuits, programmable gate arrays, programmable array logic components, or any other device or devices that may be configured to process electronic signals. It will further be appreciated that an implementation of a process or apparatus as described above may include computer executable code created using a structured programming language such as C, object oriented language such as C + +, or any other high-level or low-level design language (including assembly language, hardware description language, and database design languages and techniques), which may be stored, compiled, or interpreted to run on one of the above-described apparatus, as well as heterogeneous combinations of processors, processor architectures, and combinations of different hardware and software. In another aspect, the method can be implemented in a system that performs the steps and can be distributed across devices in a variety of ways. Also, the processing may be distributed across devices, such as the various systems described above, or all of the functionality may be integrated in a dedicated, stand-alone device or other hardware. In another aspect, the means for performing the steps associated with the processes described above may comprise any of the hardware and/or software described above. All such permutations and combinations are intended to fall within the scope of the present invention.

Embodiments disclosed herein may include a computer program product comprising computer executable code or computer usable code that, when executed on one or more computing devices, performs any and/or all of the steps thereof. The code may be stored in a non-transitory manner in a computer memory, and may be a memory from which a program is executed (e.g., random access memory associated with a processor), or may be a storage device, such as a drive disk, flash memory, or any other optical, electromagnetic, magnetic, infrared, or other device or combination of devices. In another aspect, any of the systems and methods described above may be implemented in computer-executable code carried on and/or any input or output from any suitable transmission or propagation medium.

The method steps of the embodiments described herein are intended to include any suitable method for causing such method steps to be performed, consistent with the patentability of the claims, unless a different meaning is explicitly given or clear from the context. Thus, for example, performing X steps includes any suitable method for causing another party (e.g., a remote user, a remote processing resource (e.g., a server or cloud computer), or a machine to perform X steps similarly, performing steps X, Y and Z may include any method of directing or controlling any combination of such other individuals or resources to perform steps X, Y and Z to obtain the advantages of such steps.

It should be understood that the methods and systems described above are presented by way of example and are not limiting. Many variations, additions, omissions, and other modifications will become apparent to those skilled in the art. Unless explicitly described to the contrary, the disclosed steps may be changed, supplemented, omitted, and/or reordered without departing from the scope of the present invention. Additionally, the order or presentation of method steps in the specification and the drawings is intended to require the order in which the steps are performed, unless a specific order is explicitly required or clear from the context. Thus, while particular embodiments have been shown and described, it will be understood by those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the invention, and it is intended to form a part of the invention as defined in the appended claims, which should be interpreted as broadly as allowed under the law.

Claims (188)

1. A nozzle for spraying liquid metal, the nozzle comprising:

a housing defining at least a portion of a fluid chamber having an intake region and an exhaust region;

one or more magnets disposed relative to the housing, a magnetic field of the magnets being directed through the housing; and

an electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein at least at a point substantially near the exit orifice of the exit region, an electrical current is conducted from the electrode to the emission chamber, and at a point substantially near the exit orifice, the electrical current intersects the magnetic field in the emission chamber to eject liquid metal from the exit orifice.

2. The nozzle of claim 1, wherein the volume of the fluid chamber between the firing chamber and the discharge orifice is less than about ten percent of the total volume of the fluid chamber.

3. The nozzle of claim 1, wherein the volume of the firing chamber is greater than about 50 percent of the total volume of the fluid chamber.

4. The nozzle of claim 1, wherein the fluid chamber has an axial length greater than about 2mm and less than about 2 cm.

5. The nozzle of claim 1, wherein at least one of the electrodes is integrally formed with a portion of the housing defining at least a portion of the fluid chamber such that the at least one electrode and the portion of the housing defining at least one of the fluid chambers are formed from the same material.

6. The nozzle of claim 5, wherein at least one of the electrodes is integrally formed with a portion of the housing defining at least the discharge region of the fluid chamber, such that the at least one electrode and the portion of the housing defining the discharge region are formed from the same material.

7. The nozzle of claim 1, wherein the housing is a rod of electrically conductive material and the electrical current is conducted between the electrodes along an axis parallel to an axial dimension of the rod.

8. The nozzle of claim 1, wherein the firing chamber includes a generally rectangular cross-section in a plane perpendicular to a direction of travel of the liquid metal from the entry region toward the exit region, and current from the electrode is conductable into the liquid metal along the generally rectangular cross-section.

9. The nozzle of claim 1, further comprising a filter disposed along the fluid chamber and spaced apart from the discharge region.

10. The nozzle of claim 1, wherein at least one of the electrodes is formed from tantalum, niobium, or a combination thereof.

11. An additive manufacturing system, the system comprising:

a nozzle comprising a housing, one or more magnets, and an electrode, the nozzle defining a fluid chamber having an entry region and an exit region, the one or more magnets directing a magnetic field through the housing, and the electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein an electrical current is conductable from the electrode such that the electrical current intersects the magnetic field in the emission chamber at a point substantially near the exit orifice of the exit region;

a robotic system mechanically coupled to the nozzle;

a power source in electrical communication with the electrode; and

a controller in electrical communication with the robotic system and the power source, the controller configured to

Moving the robotic system to position the discharge area of the nozzle along a controlled three-dimensional pattern, and

based on the position of the discharge area along the controlled three-dimensional pattern, a power source is actuated to deliver a pulsed current to the electrodes to cause liquid metal to be ejected from the discharge area to form the three-dimensional object.

12. The system of claim 11, wherein the frequency of the pulsed electrical current is less than about 5kHz at a maximum speed of motion of the expulsion area.

13. The system of claim 11, wherein the pulsed current has a frequency based on the nozzle velocity.

14. The system of claim 11, wherein the pulsed electrical current has a frequency based on one or more characteristics of the three-dimensional pattern.

15. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

directing a magnetic field through the housing;

moving the discharge area along a controlled three-dimensional pattern; and

conducting a pulsed current to the liquid metal in the launch chamber in the fluid chamber between the entry region and the exit region based on the location of the exit region along the controlled three-dimensional pattern, wherein the frequency of the pulsed current is less than the resonant frequency of the liquid metal in the fluid chamber and the pulsed current is in a direction that intersects the magnetic field in the launch chamber such that the current pulses eject the liquid metal from the exit region to form the three-dimensional object.

16. The method of claim 15, wherein the pulsed electrical current is conducted to the liquid metal in the launching chamber substantially near the discharge region.

17. The method of claim 15, wherein the resonant frequency of the liquid metal in the fluid chamber is greater than about 10 kHz.

18. The method of claim 15, wherein the volume of the launching chamber is greater than about 50 percent of the volume of the fluid chamber.

19. The method of claim 15, wherein the liquid metal has a resistivity substantially similar to a resistivity of a material defining the firing chamber.

20. A nozzle for spraying liquid metal, the nozzle comprising:

a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region;

one or more magnets supported on the housing, the magnetic field of the magnets being directed through the housing; and

an electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, wherein an electrical current is conducted from the electrode to the emission chamber in a direction transverse to a magnetic field in the emission chamber, and a portion of the housing defining the exit region of the fluid chamber is formed from a ceramic material.

21. The nozzle of claim 20, wherein the ceramic material comprises one or more of alumina, sapphire, ruby, aluminum nitride, aluminum carbide, silicon nitride, sialon, and boron carbide.

22. A nozzle as claimed in claim 20, wherein a portion of the housing defining at least part of the fluid chamber remote from the discharge region is formed from metal.

23. A nozzle as claimed in claim 20, wherein a portion of the housing defining at least part of the fluid chamber remote from the discharge region is formed from a ceramic material.

24. The nozzle of claim 20, wherein the electrode defining at least a portion of the firing chamber is formed from a metal.

25. The nozzle of claim 20, wherein at least one of the electrodes is integrally formed with a portion of the housing defining at least a portion of the fluid chamber remote from the discharge region, such that the at least one electrode and the portion of the housing defining at least a portion of the fluid chamber remote from the discharge region are formed from the same material.

26. The nozzle of claim 20, wherein the firing chamber is substantially adjacent the discharge orifice of the discharge region.

27. The nozzle of claim 20 wherein the firing chamber has a volume greater than about 50 percent of the total volume of the fluid chamber.

28. The nozzle of claim 20, wherein the electrode comprises a liner disposed along at least a portion of the fluid chamber between the intake region and the discharge region.

29. The nozzle of claim 28, wherein the liner is plated onto a material of the housing defining the fluid chamber.

30. The nozzle of claim 28 wherein the liner is provided from a shell material comprising one or more of titanium nitride, titanium aluminum nitride, titanium carbide, alumina, titanium and titanium carbonitride.

31. The nozzle of claim 20, further comprising at least one heater in thermal communication with the firing chamber.

32. The nozzle of claim 31 wherein the heater comprises an induction coil disposed around at least a portion of the firing chamber.

33. The nozzle of claim 20, wherein the electrode is formed from a first material and the housing is formed from a second material, the second material having a higher melting temperature than the first material.

34. The nozzle of claim 20, wherein the electrode is formed from tantalum, niobium, or a combination thereof.

35. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber having an intake region and an exhaust region, the fluid chamber being at least partially defined by a housing, the fluid chamber;

directing a magnetic field through the housing;

moving the discharge area in a controlled pattern; and

conducting an electrical current through an electrode defining at least a portion of a launch chamber in the fluid chamber between the entry region and the exit region based on a position of the exit region along the controlled pattern, wherein the electrode defining at least a portion of the launch chamber has a resistivity substantially equal to a resistivity of the liquid metal moving through the launch chamber and a portion of the housing defining the exit region has a resistivity substantially greater than a resistivity of the liquid metal moving through the exit region, and the electrical current conducted through the electrode is conducted into the liquid metal in a direction transverse to a magnetic field in the launch chamber to eject at least a portion of the liquid metal from the exit region.

36. A nozzle for spraying liquid metal, the nozzle comprising:

a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region, and the exhaust region having a throat adjacent the exhaust aperture;

one or more magnets disposed relative to the housing, a magnetic field of the magnets being directed through the housing; and

the electrode defines at least a portion of an emission chamber in the fluid chamber between the intake region and the exhaust region, wherein an exterior surface of the housing in the vicinity of the exhaust orifice includes a membrane that is substantially non-wetting with respect to a liquid metal that may be stably supported in at least the portion of the emission chamber defined by the electrode.

37. The nozzle of claim 36, wherein a contact angle between the liquid metal stably supportable in the firing chamber and the membrane is greater than about 90 degrees.

38. The nozzle of claim 36 wherein the housing material defining the throat is wettable with respect to liquid metal stably supportable in the firing chamber.

39. The nozzle of claim 38, wherein the liquid metal in the stably supportable firing chamber has a greater contact angle with the membrane than the housing material defining the throat.

40. The nozzle of claim 38, wherein the throat is substantially cylindrical and a diameter of the throat is substantially equal to a diameter of the discharge orifice.

41. A nozzle as claimed in claim 36, wherein the membrane is integrally formed with the portion of the housing adjacent the discharge orifice.

42. The nozzle of claim 36, wherein the membrane comprises an oxide of a material forming the portion of the housing defining the throat.

43. The nozzle of claim 36, wherein the membrane comprises one or more of tantalum oxide and chromium oxide.

44. The nozzle of claim 36, wherein the membrane is non-wetting with respect to one or more of aluminum, aluminum alloys, and solder.

45. The nozzle of claim 36 wherein at least one of the electrodes is integrally formed with a portion of the housing proximate the at least one of the electrodes such that the at least one of the electrodes and the portion of the housing are formed from the same material.

46. A nozzle as claimed in claim 36, wherein the one or more magnets are arranged such that a magnetic field is directed through the firing chamber and the electrodes are arranged such that current conducted from the electrodes into the firing chamber crosses the magnetic field in the firing chamber.

47. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber, the fluid chamber having an inlet orifice and an outlet orifice, and the fluid chamber having a throat adjacent the outlet orifice, wherein the fluid chamber is at least partially defined by the housing;

directing a magnetic field through the housing; and

passing an electrical current in pulses into the liquid metal in the launching chamber in the fluid chamber, the pulsed electrical current intersecting the magnetic field in the launching chamber to cause the liquid metal to be ejected from the discharge orifice, wherein during the flow of the electrical current pulses into the liquid metal, the throat is wetted by the liquid metal and an outer surface of the housing defining the discharge orifice is substantially unwetted by the liquid metal.

48. The method of claim 47, wherein the outer surface of the housing defining the exhaust orifice comprises a film that is an oxide film of the housing material defining the throat.

49. The method of claim 48, wherein the film comprises one or more of tantalum oxide and chromium oxide.

50. The method of claim 47, wherein a contact angle between the liquid metal and an outer surface of the housing defining the discharge orifice is greater than a contact angle between the liquid metal and a material of the housing defining the throat.

51. The method of claim 50, wherein the contact angle between the liquid metal and the outer surface of the housing defining the drain hole is greater than about 90 degrees.

52. The method of claim 47, wherein the liquid metal comprises one or more of aluminum, an aluminum alloy, and a flux.

53. The method of claim 47, wherein the pulsed electrical current has a maximum frequency of less than about 10 kHz.

54. The method of claim 47, further comprising moving the shell in a controlled three-dimensional pattern relative to the build surface to form a three-dimensional object.

55. A method, comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

directing a magnetic field through the housing; and

delivering a first current to the liquid metal in the launching chamber in the fluid chamber between the entry region and the exit region, the first current comprising a fluctuating current crossing the magnetic field in the liquid metal to exert a fluctuating force on the meniscus attached to the exit region, the fluctuating force on the liquid metal attached to the exit region bouncing the meniscus attached to the exit region.

56. The method of claim 55, wherein the exhaust region includes an exhaust aperture and a throat, and the meniscus is attached to one or more of the throat and the exhaust aperture.

57. The method of claim 55, wherein the pulsating force exerted on the meniscus has a magnitude sufficient to cause a metal oxide layer formed on the meniscus to break, the metal oxide layer comprising a metal oxide of the liquid metal.

58. The method of claim 55, further comprising ejecting liquid metal through the drain region based at least in part on a duration of delivering the first current to the liquid metal in the enclosure.

59. The method of claim 58, wherein the liquid metal is sprayed from the discharge region over a predetermined period of time.

60. The method of claim 55, further comprising delivering a second current to the liquid metal in the launch chamber, wherein the second current intersects the magnetic field in the liquid metal to eject the liquid metal through the exit region to form the object.

61. The method of claim 60, wherein the second current comprises a pulse current different from the pulse current of the first current.

62. The method of claim 60, further comprising moving the discharge region along a controlled pattern corresponding to the fabrication of the object, wherein delivering the second current into the liquid is based on a position of the discharge region along the controlled pattern.

63. The method of claim 62, wherein the controlled pattern comprises a three-dimensional pattern.

64. The method of claim 62, wherein delivering the second current to the liquid metal in the launching chamber comprises switching between a pulsed current and a direct current based at least in part on a position of the discharge region along the controlled pattern.

65. A manufacturing system, comprising:

a nozzle comprising a housing at least partially defining a fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the fluid chamber, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that a current from the electrode intersects the magnetic field in the emission chamber;

a robotic system mechanically coupled to the nozzle, the robotic system movable to position the discharge area;

a power source in electrical communication with the electrode of the nozzle; and

a controller in electrical communication with the robotic system and the power source, the controller configured to

Moving the robotic system to position the discharge area along a controlled motion pattern corresponding to the manufacture of the object,

delivering a first current to the liquid metal in the launch chamber through the electrode, the first current comprising a pulsed current that intersects the magnetic field in the liquid metal in the launch chamber to generate a pulsating force on a meniscus of the liquid metal attached to the drain region, and

a second current is delivered to the liquid metal in the firing chamber through the electrode along a controlled motion pattern of the ejection region, the second current intersecting the magnetic field in the liquid metal to eject the liquid metal through the ejection region to form the object.

66. The system of claim 65, wherein the controller is further configured to deliver a third current to the liquid metal in the launching chamber through the electrode, the third current intersecting the magnetic field in the liquid metal to eject the liquid metal through the expulsion area at a location remote from the controlled pattern of expulsion areas.

67. The system of claim 66, wherein the controller is configured to deliver the third current based at least in part on a duration of delivery of the first current to the liquid metal in the launching chamber.

68. The system of claim 66, wherein the controller is configured to deliver the third current between switching from delivering the first current to delivering the second current.

69. The system of claim 66, wherein the controller is configured to deliver the third current for a predetermined period of time.

70. The system of claim 66, wherein the controlled pattern comprises a three-dimensional pattern.

71. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

directing a magnetic field through the housing;

moving the discharge area along a controlled three-dimensional pattern; and

delivering an electrical current between electrodes at least partially defining an emission chamber in the fluid chamber between the entry region and the exit region, the electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit region; and

controlling the porosity of one or more predetermined portions of the sprayed liquid metal aggregation on the build plate or on a previous metal deposition layer based on the location of the drainage area along the controlled three-dimensional pattern.

72. A method as in claim 71, wherein controlling the porosity of the one or more predetermined portions of the ejected liquid metal aggregation comprises forming an interface between a three-dimensional object in the aggregation and a support structure, the support structure and the three-dimensional object having a lower porosity than the interface.

73. The method of claim 72, wherein the interface, the support structure, and the three-dimensional object are formed of the same material.

74. The method of claim 72, wherein the interface is fragile with respect to the three-dimensional object.

75. The method of claim 74, further comprising separating the three-dimensional object from the support structure by applying one or more of a compressive force and a shear force to the interface.

76. A method as claimed in claim 71, wherein controlling the porosity of one or more predetermined portions of the aggregation of ejected liquid metal comprises varying the rate at which liquid metal is ejected from the discharge region.

77. A method as claimed in claim 76 wherein varying the rate at which liquid metal is ejected from the ejection region comprises varying the magnitude of current delivered to the liquid metal in the launching chamber.

78. The method of claim 76, wherein delivering an electrical current to the liquid metal in the launching chamber comprises delivering the electrical current in a pulsed manner.

79. A method as claimed in claim 76, wherein varying the rate at which liquid metal is ejected from the ejection region comprises varying at least one of the amplitude and duration of the current pulse.

80. A method as claimed in claim 71, wherein controlling the porosity of one or more predetermined portions of the sprayed aggregation of liquid metal comprises varying the temperature of the liquid metal sprayed from the discharge zone.

81. The method of claim 80, wherein varying the temperature of the liquid metal ejected from the drainage zone comprises decreasing the temperature of the ejected liquid metal to increase the porosity of a predetermined portion of the ejected liquid metal aggregation on the build plate or on a previous metal deposition layer.

82. A computer program product comprising non-transitory computer executable code embodied in a non-transitory computer readable medium that, when executed on one or more processors, performs the steps of:

moving the discharge area of the housing in a controlled three-dimensional pattern;

delivering an electrical current to the liquid metal in an emission chamber defined at least in part by the electrodes, the delivered electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from a discharge region in fluid communication with the emission chamber; and

controlling the porosity of one or more predetermined portions of the sprayed liquid metal aggregation on the substrate or on a previous metal deposition layer based on the location of the drainage area along the controlled three-dimensional pattern.

83. A computer program product as in claim 82, wherein controlling the porosity of one or more predetermined portions of the ejected liquid metal agglomerates comprises varying a rate of liquid metal ejection from the discharge region.

84. A computer program product as in claim 83, wherein varying the speed of ejecting liquid metal from the discharge region comprises varying a current amplitude.

85. The computer program product of claim 83, wherein delivering electrical current to the liquid metal in the firing chamber comprises delivering electrical current in pulses.

86. A computer program product as in claim 85, wherein varying the speed at which the liquid metal is ejected from the ejection region comprises varying at least one of an amplitude and a duration of the current pulse.

87. A computer program product as in claim 82, wherein controlling the porosity of one or more predetermined portions of the ejected liquid metal agglomerates comprises varying the temperature of the liquid metal ejected from the ejection zone.

88. The computer program product of claim 87, wherein changing the temperature of the liquid metal ejected from the ejection zone comprises decreasing the temperature of the ejected liquid metal to increase the porosity of a predetermined portion of the ejected liquid metal aggregation on the substrate or on a previous metal deposition layer.

89. A nozzle for spraying liquid metal, the nozzle comprising:

a housing defining at least a portion of a fluid chamber, the fluid chamber having an intake region and an exhaust region;

one or more magnets disposed relative to the housing, a magnetic field of the magnets extending through the housing; and

electrodes defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, wherein an electrical current conducted between the electrodes crosses a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit region; and

a thermal insulation layer disposed between at least one of the one or more magnets and the housing, the thermal insulation layer having a thermal conductivity less than a thermal conductivity of a portion of the housing to which the insulation layer is mounted.

90. The nozzle of claim 89, wherein the housing is thinner along a direction along which the magnetic field extends through the housing than along a direction along which current is conducted between the electrodes.

91. The nozzle of claim 89, wherein the one or more magnets are less than about 2mm from the firing chamber.

92. The nozzle of claim 89, wherein the thermal insulation layer is about 0.8mm to about 1.2mm thick.

93. The nozzle of claim 89, wherein the thermally insulating layer comprises one or more of a quartz ceramic and an aluminum silicon ceramic.

94. The nozzle of claim 89, wherein the thermally insulating layer is held in place by magnetic force exerted on the housing by the magnet.

95. The nozzle of claim 89, wherein the thermally insulating layer has a thermal conductivity greater than about 0.015W/m-K and less than about 0.1W/m-K.

96. The nozzle of claim 89, wherein the one or more magnets are in thermal communication with a heat sink that is spaced apart from the housing.

97. A nozzle as defined in claim 96, wherein the heat sink comprises a cooling fluid movable through the heat sink to carry heat away from the one or more magnets.

98. The nozzle of claim 96 further comprising a fan facing the heat sink to carry heat away from the one or more magnets.

99. The nozzle of claim 89, wherein the one or more magnets comprise one or more of a fixed magnet and an electromagnet.

100. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

heating the liquid metal to a temperature greater than a temperature associated with a loss of magnetic field strength of at least one magnet coupled to the housing through the thermally insulating layer;

delivering an electric current to the heated liquid metal between electrodes defining an emitting chamber in the fluid chamber between an entrance region and an exit region; and

directing a magnetic field from the at least one magnet to the heated liquid metal in the launching chamber, the magnetic field intersecting the current in the launching chamber to eject the liquid metal from the discharge region.

101. The method of claim 100, wherein the at least one magnet is less than about 2mm from the firing chamber.

102. The method of claim 100, wherein the thermal insulation layer is held in place by magnetic forces between the at least one magnet and the housing.

103. The method of claim 100, further comprising allowing the at least one magnet to cool.

104. The method of claim 103, wherein cooling the at least one magnet comprises removing heat from the at least one magnet through a heat sink in thermal communication with the at least one magnet and spaced apart from the housing.

105. The method of claim 104, wherein removing heat from the at least one magnet comprises moving a cooling fluid through a heat sink.

106. The method of claim 104, wherein removing heat from the at least one magnet comprises forcing air flow over the heat sink for forced convection cooling.

107. The method of claim 100, wherein the at least one magnet comprises one or more of a fixed magnet and an electromagnet.

108. The method of claim 100, wherein the housing is thinner in a direction parallel to the magnetic field axis than in the direction of the current flow.

109. A method of additive manufacturing, the method comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

directing a magnetic field through the housing;

moving the discharge area in a controlled pattern; and

passing an electrical current between electrodes defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrical current crossing a magnetic field in the liquid metal in the emission chamber to eject the liquid metal from the exit region; and

the current is controlled between the pulsed current and the direct current based on the position of the discharge area along the controlled pattern to form the object.

110. The method of claim 109, wherein the controlled pattern is a three-dimensional pattern and the object is a three-dimensional object.

111. The method of claim 109, wherein the current is controlled as a pulsed current along the boundary of the object being formed.

112. The method of claim 109, wherein the current is controlled to be direct current as the discharge area moves along deviations in the boundary of the object being formed.

113. The method of claim 109, wherein the frequency of the pulsed electrical current is less than a resonant frequency of the liquid metal in the fluid chamber.

114. The method of claim 109, wherein the frequency of the pulsed electrical current is based on the velocity of the movement of the expulsion area.

115. The method of claim 109, wherein the frequency of the pulsed current is based on a distance from an edge of the controlled pattern.

116. The method of claim 109, wherein the frequency of the pulsed electrical current is less than about 5kHz at a maximum speed of motion of the expulsion area.

117. The method of claim 109, wherein switching from pulsed current to direct current increases the mass flow rate of liquid metal ejected from the discharge region.

118. A computer program product comprising non-transitory computer executable code embodied in a non-transitory computer readable medium that, when executed on one or more processors, performs the steps of:

moving the discharge area of the nozzle in a controlled pattern;

delivering an electric current between electrodes defining at least a portion of the launch chamber in fluid communication with the exit region, the electric current crossing the magnetic field in the liquid metal in the launch chamber to eject the liquid metal from the exit region; and

controlling the current delivered to the liquid metal in the launching chamber based on the position of the discharge region along the controlled pattern, wherein the current is controlled between a pulsed current and a direct current to form the object.

119. The computer program product of claim 118, wherein the current is controlled as a pulsed current along the boundary of the object being formed.

120. The computer program product of claim 118, wherein the current is controlled to be direct current as the discharge area moves along deviations in the boundary of the object being formed.

121. The computer program product of claim 118, wherein the frequency of the pulsed electrical current is based on the velocity of the movement of the expulsion area.

122. The computer program product of claim 118, wherein the frequency of the pulsed current is based on a distance from an edge of the controlled pattern.

123. The computer program product of claim 118, wherein the frequency of the pulsed current is less than about 5kHz at the maximum speed of motion of the expulsion area.

124. An additive manufacturing system, the system comprising:

a nozzle comprising a housing defining at least a portion of a fluid chamber, the fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the housing, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that an electrical current conveyed between the electrodes intersects the magnetic field in the emission chamber;

a robotic system mechanically coupled to the nozzle and movable to position the discharge area;

a power source in electrical communication with the electrode of the nozzle; and

a controller in electrical communication with the power source, the controller configured to

Moving the robotic system to position the discharge region along the controlled pattern,

an electric current is delivered from the electrode to the liquid metal in the launching chamber,

controlling the current delivered to the liquid metal in the launching chamber based on the position of the discharge region along the controlled pattern, wherein the current is controlled between a pulsed current and a direct current to form the object.

125. The system of claim 124, wherein the current is controlled as a pulsed current along the boundary of the object being formed.

126. The system of claim 124, wherein the current is controlled to be direct current as the discharge area moves along deviations in the boundary of the object being formed.

127. The system of claim 124, wherein the frequency of the pulsed electrical current is based on the velocity of the movement of the expulsion area.

128. The system of claim 124, wherein the frequency of the pulsed current is based on a distance from an edge of the controlled pattern.

129. A manufacturing system, the system comprising:

a nozzle comprising

A housing defining a fluid chamber having an intake region and an exhaust region,

one or more magnets disposed relative to the housing, a magnetic field of the magnets being directed through the housing; and

an electrode defining at least a portion of an emission chamber in the fluid chamber between the entry region and the exit region, the electrode being arranged relative to the magnet such that a current flowing between the electrodes crosses a magnetic field in the emission chamber to eject liquid metal from the exit region; and

a robotic system coupled to the nozzle and movable to position the discharge area along a controlled pattern; and

a feed system engageable with the wire, the feed system actuatable to direct the wire to the fluid chamber through the entry region as the liquid metal is ejected from the exit region in a controlled pattern to form the object.

130. The system of claim 129, wherein the feed system comprises a plurality of rollers engageable with the wire, the plurality of rollers being rotatable to feed the wire into the fluid chamber.

131. The system of claim 129, further comprising a heater in thermal communication with the fluid chamber.

132. The system of claim 131, wherein the heater comprises an induction heater.

133. The system of claim 129, wherein the feed system is actuatable to direct the wire into the entry region at a variable rate, the variable rate based at least in part on a rate of liquid metal ejection from the exit region.

134. The system of claim 129, further comprising a sensor directed toward the entry zone, the sensor configured to detect an interface between the wire and the liquid metal along a predetermined axial distance on each side of the entry zone, and the sensor in electrical communication with the feed system to vary a rate of movement of the wire into the entry zone based on signals received from the sensor.

135. The system of claim 134, wherein the sensor is configured to detect a discontinuity between the wire and the liquid metal along the predetermined axial distance on each side of the access area.

136. The system of claim 134, wherein the predetermined axial distance on each side of the access region is substantially equal to one-half of a maximum dimension of the access region.

137. The system of claim 134, wherein the sensor includes one or more of a machine vision and optical break beam sensor.

138. The system of claim 129, further comprising a wiper movable relative to the access area to remove debris in or near the access area.

139. The system of claim 129, further comprising a source of pressurized gas actuatable to distribute the pressurized gas relative to the entry region to remove debris in or near the entry region.

140. The system of claim 139, wherein the source of pressurized gas is arranged to direct pressurized gas through the entry region in a direction toward the exit region.

141. A method of manufacturing, the method comprising:

directing the wire toward a fluid chamber, the fluid chamber defined at least in part by the housing, the fluid chamber having an entry region and an exit region;

melting a portion of the metal wire to liquid metal, wherein an interface between the metal wire and the liquid metal is near the entry region;

transferring liquid metal from the fluid chamber to an emission chamber defined at least in part by the electrodes, the emission chamber being in the fluid chamber between the entry region and the exit region; and

applying magnetohydrodynamic forces to the liquid metal in the firing chamber, wherein the wire is directed into the fluid chamber at a rate sufficient to maintain continuous contact between the wire and the liquid metal at the interface as the liquid metal is ejected from the discharge region by the magnetohydrodynamic forces.

142. The method of claim 141, wherein the interface is external to the housing.

143. The method of claim 141, wherein the interface is within a predetermined axial distance on each side of the access region.

144. The method of claim 143, wherein the predetermined axial distance is about half of a maximum axial dimension of the access region.

145. The method of claim 141, further comprising mechanically removing debris in and near the access area.

146. The method of claim 145 wherein mechanically removing debris includes moving a wiper relative to the access area.

147. The method of claim 141, further comprising pneumatically removing debris in and near the entry region.

148. The method of claim 147, wherein pneumatically removing debris comprises directing pressurized gas through the intake region in a direction toward the exhaust region.

149. The method of claim 141, further comprising electrically removing debris in and near the entry region, wherein electrically removing debris comprises directing a pulse of electrical current between the electrodes in a direction relative to the magnetic field to create magnetohydrodynamic forces in the liquid metal in a direction from the launch chamber toward the entry region.

150. A method of manufacturing, the method comprising:

providing liquid metal in an emission chamber defined at least in part by an electrode, the emission chamber being in fluid communication with a drain region defined by a housing supporting the electrode;

directing a magnetic field to the liquid metal in the launching chamber; and

supplying a current from the electrodes to the liquid metal in the firing chamber in a direction crossing the magnetic field in the firing chamber to eject the liquid metal from the ejection area to form the object, wherein the electrodes and the liquid metal are formed of the same material at respective interfaces between each of the electrodes and the liquid metal.

151. The method of claim 150, further comprising moving a discharge region in a controlled three-dimensional pattern, the discharge region in fluid communication with the firing chamber, wherein the current is delivered from the electrode to the liquid metal in the firing chamber based on a position of the discharge region along the controlled three-dimensional pattern.

152. The method of claim 150, further comprising cooling each electrode away from its respective interface with the liquid metal, the cooling creating a respective temperature gradient in each electrode.

153. The method of claim 152, wherein a temperature gradient in each electrode maintains a respective interface between the electrode and the liquid metal in a respective recess defined through the housing, each interface remaining in the respective recess as the liquid metal is ejected from the discharge region.

154. The method of claim 153, wherein each recess extends in a direction radial to the direction of travel of the liquid metal toward the discharge area.

155. The method of claim 153, wherein cooling each electrode comprises forced convection cooling of each electrode away from a portion of each electrode corresponding to an interface with the liquid metal.

156. The method of claim 155, wherein the forced convection cooling of each electrode comprises adjusting a velocity of the cooling fluid based at least in part on a velocity of the liquid metal being ejected from the discharge region.

157. The method of claim 150, wherein providing the liquid metal in the launching chamber comprises directing the liquid metal to the launching chamber from an entry region defined by the housing, a direction of travel of the liquid metal from the entry region to the launching chamber being transverse to the current and magnetic field in the launching chamber.

158. The method of claim 157, wherein an axial length of the launching chamber is greater than half an axial length from the entry region to the exit region.

159. The method of claim 157, wherein an axial length from the entry region to the exit region is greater than about 2mm and less than about 2 cm.

160. A system for spraying liquid metal, the system comprising:

electrodes defining at least a portion of the firing chamber, an electrical current being conductable between the electrodes to the liquid metal in the firing chamber;

one or more magnets disposed relative to the electrodes, a magnetic field of the magnets extending through the firing chamber and crossing the current in the firing chamber; and

a housing defining at least a portion of a fluid chamber having an entrance region, an exit region, and a recess, wherein the electrode is disposed in the recess such that the firing chamber is located in the fluid chamber between the entrance region and the exit region, and a maximum radial dimension of the firing chamber is greater than a maximum radial dimension of a portion of the fluid chamber adjacent the firing chamber.

161. The system of claim 160, further comprising a metal feed and movable into the fluid chamber, the metal feed and the electrode being formed of the same material.

162. The system of claim 161, further comprising a heat source in thermal communication with the metal feed in or near the fluid chamber to form liquid metal movable into the launching chamber.

163. The system of claim 160, wherein the housing has a higher melting temperature than the electrode material.

164. The system of claim 160, wherein at least a portion of each electrode extends beyond the housing in a direction away from the firing chamber.

165. The system of claim 160, further comprising a heat sink coupled to at least a portion of each electrode remote from the emission chamber.

166. The system of claim 165, wherein the heat sink includes a fluid movable away from the at least a portion of each electrode to effect cooling at the at least a portion of each electrode.

167. The system of claim 160, wherein the launching chamber has an axial length that is greater than 50 percent of the axial length of the fluid chamber.

168. The system of claim 160, wherein the axial length of the fluid chamber is greater than about 2mm and less than about 2 cm.

169. A method, comprising:

providing a liquid metal in a fluid chamber defined at least in part by the housing, the fluid chamber having an intake region and an exhaust region;

directing a magnetic field through the housing;

delivering a first current to the liquid metal in the housing at rest, the first current crossing the magnetic field in the liquid metal to exert a pull back force on the liquid metal, the pull back force being sufficient to draw the liquid metal at rest in a direction from the exit region toward the entry region; and

selectively delivering a second current to the liquid metal, the second current crossing the magnetic field in the liquid metal to exert an emissive force on the liquid metal to eject the liquid metal from the ejection region.

170. The method of claim 169, wherein the pullback force is sufficient to maintain a meniscus of liquid metal at rest attached to the drain region.

171. The method of claim 170, wherein the exhaust region has a throat near the exhaust orifice, the pullback force being sufficient to maintain a meniscus in the throat or attached to the exhaust orifice.

172. The method of claim 169, further comprising moving the discharge region along a controlled pattern.

173. The method of claim 172, wherein the controlled pattern is a controlled three-dimensional pattern.

174. The method of claim 172, wherein the second current is selectively delivered to the flow of liquid along less than all of the controlled pattern.

175. The method of claim 172, wherein the second current is variable based on at least a position of the discharge region along the controlled pattern.

176. The method of claim 169, wherein the second current comprises a pulsed current that ejects liquid metal droplets from the ejection region.

177. The method of claim 176, wherein selectively delivering the second current to the liquid metal comprises conducting a firing pulse to the liquid metal in the fluid chamber and conducting a pull-back pulse to the liquid metal in the fluid chamber, the firing pulse and the pull-back pulse having opposite polarities and the pull-back pulse having a same polarity as the first current.

178. The method of claim 177, wherein the pull-back pulse precedes a fire pulse for ejecting a respective droplet.

179. The method of claim 177, wherein a pull-back pulse follows a fire pulse for a respective drop ejection.

180. The method of claim 169, wherein the second current is variable between a pulsed current and a direct current.

181. The method of claim 169, wherein selectively delivering the second electrical current to the liquid metal comprises directing the second electrical current to the liquid metal between electrodes defining an emission chamber in the fluid chamber between the entry region and the exit region.

182. The method of claim 181, wherein delivering the first current to the liquid metal comprises directing the first current to the liquid metal between electrodes.

183. A manufacturing system, comprising:

a nozzle comprising a housing defining a fluid chamber having an entrance region and an exit region, a magnet disposed relative to the housing, a magnetic field of the magnet extending through the fluid chamber, and an electrode defining at least a portion of an emission chamber in the fluid chamber between the entrance region and the exit region, the electrode positioned relative to the magnet such that a current from the electrode intersects the magnetic field in the emission chamber;

a power source in electrical communication with the electrode; and

a controller in electrical communication with the power source, the controller configured to

Delivering a first electrical current to the liquid metal in the housing at rest, the first electrical current crossing the magnetic field in the liquid metal to exert a pull back force on the liquid metal, the pull back force being sufficient to draw the liquid metal at rest in a direction from the exit region toward the entry region, and

selectively delivering a second current from the electrode to the liquid metal in the firing chamber, the second current crossing the magnetic field in the liquid metal to exert a firing force on the liquid metal to eject the liquid metal from the ejection region.

184. The system of claim 183, further comprising a robotic system mechanically coupled to the nozzle and movable to position the discharge region of the nozzle, wherein the controller is further configured to move the robotic system to position the discharge region along the controlled pattern.

185. The system of claim 184, wherein the second current is selectively delivered to the flow of liquid along less than all of the controlled pattern.

186. The system of claim 184, wherein the second current is variable based at least on a position of the exhaust region along the controlled pattern.

187. The system of claim 184, wherein the controlled pattern is a three-dimensional pattern.

188. The system of claim 183, wherein selectively delivering the second current includes controlling the second current between a pulsed current and a direct current.