DE102019007984A1 - 3D printing device with an advantageous sintering unit and process - Google Patents

Abstract

The invention relates to a 3D printing device with advantageous thermal management of the sintering unit.

Description

The invention relates to a 3D printing device with an advantageous sintering unit.

In the European patent specification EP 0 431 924 B1 describes a method for producing three-dimensional objects from computer data. A particle material is applied to a platform in a thin layer by means of a recoater and this is selectively printed with a binder material by means of a print head. The particle area printed with the binder connects and solidifies under the influence of the binder and, if necessary, an additional hardener. The construction platform is then lowered by a layer thickness or the coater / print head unit is raised and a new layer of particulate material is applied, which is also selectively printed as described above. These steps are repeated until the desired height of the object is reached. A three-dimensional object (3D component, molded part) is created from the printed and solidified areas.

This object made of solidified particulate material is embedded in loose particulate material after its completion and is then freed from it. This is done, for example, by means of a suction device. What remains are the desired objects, which are then further cleaned of the residual powder, e.g. by brushing off.

Other powder-based rapid prototyping processes work in a similar way, such as selective laser sintering or electron beam sintering, in which a loose particle material is applied in layers and selectively solidified with the help of a controlled physical radiation source.

In the following, all of these processes are summarized under the term three-dimensional printing process or 3D printing process.

Sintering units with a spectrum converter according to the state of the art are for example in DE102017006860 described. The electromagnetic radiation generated by the radiator is directed downwards by a reflector and hits a primary spectrum converter there. With its help, unwanted wavelength ranges can be filtered out and / or converted so that only the desired wavelength ranges pass.

The inevitably occurring losses in the radiation power due to the conversion of the spectrum lead to an increase in temperature of the transducer surface.

The temperature increase caused by absorption usually takes place in the middle of the transducer surface. The reason for this is that the spectrum converter can only transfer its temperature via heat conduction via the mounting points with which it is connected to the housing of the unit. Even if a secondary spectrum converter is designed to be as transparent as possible for the radiation passing through and does not significantly convert the spectrum, a certain residual part of the radiation remains in it, so that these losses also lead to an increase in temperature. As a result of the temperature increase, the spectrum converter in turn becomes an emitter of the so-called secondary radiation.

The induced secondary radiation mixes with the converted radiation, which is generally not desired. According to the state of the art, a highly transparent, mechanically mostly very fragile and expensive special glass pane is used instead in order to avoid this if a change in the spectrum is not required. It is true that cooling by means of a gas flow in the form of compressed air or by means of a cooling liquid is possible in one embodiment of a radiator unit in FIG EP 1 319 240 mentioned, but there the unit is not made airtight.

However, this is disadvantageous in the context of high speed sintering, since the finest plastic particles can penetrate the unit and damage it. A constant overpressure inside the unit cannot be used either, since the resulting air flow from a non-closed device would negatively affect the sintering process due to temperature fluctuations due to forced convection.

Cooling the spectrum converter with a liquid medium would place high demands on tightness and fluid supply and is not economically desirable. It should be noted here that in a sintering unit like the one used in high-speed sintering, considerable amounts of energy are converted that can easily exceed 10-20 kW. It would then have to be ensured that, for example, the sealants can withstand any waste heat and at the same time reliably fulfill their function. Furthermore, especially with larger versions of the sintering unit, the weight of a liquid medium would not be insignificant, which would entail additional costs due to the need for a more stable mechanical design. In the case of a liquid cooling medium, it must also be ensured that it does not exceed the boiling point.

It is therefore a problem to provide a sintering unit in a high-speed sintering process that has good cooling properties and can be operated maintenance-free. It puts Furthermore, a problem is to provide a controllable cooling in a sintering unit, which enables a differentiated cooling and temperature management in such processes.

It is therefore an object of the present invention to provide a device that can contribute to the temperature management of a sintering unit per se and / and to the temperature management of a high-speed sintering printing device, or at least reduce or completely avoid the disadvantages of the prior art .

It is a further object of the present invention to provide a device that can contribute to the removal of the heat generated in order to bring about a cooling of the sintering unit without the heat dissipation interfering with the particulate material or other components or at least the disadvantages of the prior art reduced or avoided entirely.

Brief summary of the disclosure

In one aspect, the disclosure relates to a sintering unit suitable for a 3D printing device, the sintering unit being characterized by a closed air cooling circuit and a liquid-based cooling circuit.

In a further aspect, the disclosure relates to a 3D printing device that comprises a sintering unit as disclosed herein, the further coolant, preferably an external coolant, being arranged outside the 3D printing device.

In a further aspect, the disclosure relates to a method for producing a molded part by means of particulate material application and selective solidification, a sintering unit according to the disclosure being used in the method, wherein the liquid-based coolant essentially cools the closed air cooling circuit, which in turn essentially cools the spectrum converter (s) cools.

Figure list

• Figure S1 shows a sintering unit with spectrum converter according to the prior art, such as in DE102017006860 described; View in the XZ plane on the left and viewed from below in the XY plane on the right.
• Figure S2 shows an exemplary device according to the disclosure and shows the section through a sintering unit with a closed secondary air circuit.
• FIG. S3 shows an exemplary sintering unit according to the disclosure and is a schematic illustration in the side view (YZ plane) with the air flow drawn in.
• FIG. S4 shows, in a frontal view in section in FIG. S4, frontally in the XZ plane, an exemplary sintering unit according to the disclosure with fans drawn in.

Detailed description of the disclosure

The object on which the application is based is achieved by a sintering unit suitable for a 3D printing device, the sintering unit being characterized by a closed air cooling circuit and a liquid-based cooling circuit as well as a method that uses such a sintering unit.

Some terms are defined in more detail below. Otherwise, the meanings known to the person skilled in the art are to be understood for the terms used.

For the purposes of the disclosure, “layer construction methods” or “3D printing methods” or “3D methods” or “3D printing” are all methods known from the prior art that enable components to be built in three-dimensional shapes and with the here im Further described process components and devices are compatible.

“Binder jetting” in the sense of the disclosure means that powder is applied in layers to a building platform, the cross-sections of the component on this powder layer are printed with one or more liquids, the position of the building platform is changed by one layer thickness from the last position and these steps are repeated until the component is finished. Binder jetting also includes layering processes that require a further process component such as layer-by-layer exposure, e.g. with IR or UV radiation.

In the “high-speed sintering process” in the sense of the disclosure, a thin layer of plastic granulate, such as PA12 or TPU, is applied to a construction platform (construction field), which is preferably heated. An inkjet print head then moves over a large area over the platform and wets the areas of the construction field with ink that absorbs infrared light (IR absorber) on which the prototype is to be created. The construction platform is then irradiated with infrared light. The wetted areas absorb the heat, causing the powder layer underneath to sinter. However, the unprinted powder remains loose. After sintering, the building platform lowers by one layer thickness. This process is repeated until the construction of a component is complete. Then be the sintered parts are cooled in the installation space in a controlled manner before they can be removed and unpacked. It can also be advantageous here if, in addition to a sintered lamp, an overhead lamp or a radiator unit is used that use different wavelength spectra, the wavelength spectrum essentially not overlapping. In a variation, a so-called detailing agent can be printed in addition to the IR absorber, which is used to cool the areas printed with it. A variant of the high-speed sintering process is also known as the fusion jet process, in which the printhead a thermally conductive liquid (often referred to as a “fusing agent”, which corresponds to the absorber) is sprayed onto a layer of the particulate material. A heat source (infrared light) is used immediately after printing. The areas to which the “fusing agent” was applied are heated more than the powder without this liquid. Thus, the required areas are melted together. Another addition is then used, which is also known as the so-called "detailing agent" and is used for isolation. This selective impression takes place around the areas on which the "fusing agent" or absorber "was printed. This addition is intended to promote sharp edge formation. This goal is to be achieved by making the temperature differences between printed and unused powder more significant. A process with these two pressure fluids can also be referred to as a multi-jet fusion process.

“3D molded part”, “molded body” or “component” in the sense of the disclosure are all three-dimensional objects produced by means of the method according to the invention and / or the device according to the invention, which have dimensional stability.

"Construction space" is the geometric location in which the particle material bed grows during the construction process through repeated coating with particle material or through which the bed runs in continuous principles. In general, the construction space is limited by a floor, the construction platform, walls and an open top surface, the construction level. In the case of continuous principles, there is usually a conveyor belt and limiting side walls. The installation space can also be designed by a so-called job box, which represents a unit that can be retracted and extended into the device and allows batch production, whereby a job box is extended after the process is completed and a new job box can be moved into the device immediately, so that the Manufacturing volume and thus the device performance is increased.

As “building material” or “particulate material” or “powder” or “bulk powder” in the sense of the disclosure, all flowable materials known for 3D printing can be used, in particular in powder form, as a slip or as a liquid. These can be, for example, sand, ceramic powder, glass powder, and other powders made of inorganic or organic materials such as metal powder, plastics, wood particles, fiber materials, celluloses and / or lactose powder and other types of organic, powdery materials. The particulate material is preferably a dry, free-flowing powder, but a cohesive, cut-resistant powder can also be used. This cohesiveness can also result from the addition of a binder material or an auxiliary material such as a liquid. The addition of a liquid can result in the particulate material being able to flow freely in the form of a slip. In general, particulate material can also be referred to as fluids in the context of the disclosure.

In the present application, particulate material and powder are used synonymously.

The "particle material application" is the process in which a defined layer of powder is created. This can be done either on the construction platform (construction field) or on an inclined plane relative to a conveyor belt with continuous principles. The application of particle material is also referred to below as “coating” or “recoating”.

“Selective application of liquid” or “selective application of binder” in the sense of the disclosure can take place after each application of particulate material or, depending on the requirements of the molded body and to optimize the production of the molded body, it can also be carried out irregularly, for example several times based on a particle material application. A sectional image is printed through the desired body.

Any known 3D printing device that contains the required components can be used as the “device” for performing a method according to the disclosure. Usual components include coater, construction field, means for moving the construction field or other components in continuous processes, job boxes, dosing devices and heat and irradiation means and other components known to the person skilled in the art, which are therefore not detailed here.

The building material according to the disclosure is always applied in a “defined layer” or “layer thickness”, which is set individually depending on the building material and process conditions. It is, for example, 0.05 to 5 mm, preferably 0.06 to 2 mm or 0.06 to 0.15 mm, particularly preferably 0.06 to 0.09 mm.

A “coater blade” in the sense of the disclosure is an essentially flat metallic component or component made from another suitable material, which is located at the outlet opening of the coater and via which the fluid is released onto the construction platform and is smoothed. A coater can have one or two or more coater blades. A coating blade can be an oscillating blade that oscillates in the sense of a rotary movement when it is excited. Furthermore, this oscillation can be switched on and off by a means for generating oscillations. Depending on the arrangement of the outlet opening, the coating blade is arranged “essentially horizontally” or “essentially vertically” in the sense of the disclosure.

The “storage container” or “preheating container” in the sense of the disclosure is a container that contains particulate material and releases a quantity of it to the coater after each layer or after any number of layers. For this purpose, the storage container can advantageously extend over the entire width of a coater. The storage container has a closure at the lower end that prevents the particulate material from accidentally escaping. The closure can, for example, be designed as a rotary valve, a simple slide or other suitable mechanisms according to the state of the art. A storage container within the meaning of the disclosure can contain particulate material for more than one layer. The storage container preferably even contains particulate material for the application of 20 or more layers. The particulate material either comes from a larger supply in the form of a silo or a big bag via a conveyor or is filled into the container by hand. The filling is preferably carried out through an opening on the upper edge. As a result, the particulate material in the storage container can be conveyed by gravity and no further conveying devices are necessary in the container. The storage container may also have vibrating mechanisms that prevent the particulate material in the container from bridging. The storage container has an area which receives the particulate material, which is usually located between the side walls and the closure. According to the disclosure, it is advantageous if a heating means is arranged in the area that receives the particulate material. The heating means is arranged in such a way that the particulate material flows around the heating means and thus the heating of the particulate material is improved. The storage container can be arranged in a stationary manner, whereby it can then be arranged, for example, above the holding position of the coater or above the construction field. The refilling can then take place, depending on requirements and / or control of the volume, with pre-tempered particulate material by a method of the coater on or below the storage container. The storage container can, however, also be connected to the coater in a detachable or non-detachable manner. It can also be advantageous, for reasons of construction and / or cost, that the coater cannot be heated. The coater can then have passive insulation. However, the coater can also not be heated at all and also not provided with insulation if the preheated particulate material is delivered to the coater in a volume that essentially corresponds to a layer volume or 1.2 to 2 times that, and so it is can be applied to the construction field with practically no dwell time in the coater and thus essentially without heat loss.

“Emitter unit” in the sense of the disclosure is an arrangement of emitter units.

“Radiator unit” in the sense of the disclosure is a unit that emits electromagnetic radiation of a certain spectrum, preferably in the infrared and / or visible range.

"Coolant" in the sense of the disclosure is a means that can cool a radiator unit such as water or another liquid or a blower flow or a heat pipe.

“3D printer” or “printer” in the sense of the disclosure refers to the device in which a 3D printing process can take place. A 3D printer within the meaning of the disclosure has an application means for building material, e.g. a fluid such as a particulate material, and a solidification unit, e.g. a print head or an energy input means such as a laser or a heat lamp. Further machine components known to the person skilled in the art and components known in 3D printing are combined with the above-mentioned machine components depending on the special requirements in the individual case.

“Construction field” is the plane or, in a broader sense, the geometric location on which or in which a particulate matter grows during the construction process through repeated coating with particulate material. The building site is often limited by a floor, the “building platform”, walls and an open top surface, the building level.

The “printing” or “3D printing” process in the sense of the disclosure refers to the summary of the processes of material application, selective solidification or also printing and adjusting the working height and takes place in an open or closed process space.

A “recording level” in the sense of the disclosure is to be understood as the level on which Building material is applied. According to the disclosure, the receiving plane is always freely accessible in one spatial direction by means of a linear movement.

"Construction field tool" or "functional unit" in the sense of the disclosure are all means or device parts that are used for the application of fluid, e.g. particulate material, and the selective solidification in the production of molded parts. All material application means and layer treatment means are also construction site tools or functional units.

“Spreading” or “applying” within the meaning of the disclosure means any manner in which the particulate material is distributed. For example, at the starting position of a coating run, a larger amount of powder can be presented and distributed or spread into the layer volume by a blade or a rotating roller.

“Coater” or “recoater” or “material application means” in the sense of the disclosure is the unit by means of which a fluid is applied to the construction field. This can consist of a fluid storage container and a fluid application unit, wherein, according to the present invention, the fluid application unit comprises a fluid outlet and a “doctor blade device”. This doctor blade device could be a coater blade. However, any other conceivable suitable doctor blade device could also be used. For example, rotating rollers or a nozzle are also conceivable. The material can be fed in freely via storage containers or extruder screws, pressurization or other material conveying devices.

The “print head” or means for selective solidification within the meaning of the disclosure is usually composed of various components. Among other things, these can be print modules. The pressure modules have a large number of nozzles from which the “binder” is ejected in a controlled manner onto the construction site in the form of droplets. The print modules are aligned relative to the print head. The printhead is oriented relative to the machine. This means that the position of a nozzle can be assigned to the machine coordinate system. The plane in which the nozzles are located is usually referred to as the nozzle plate. Another means for selective solidification can also be one or more lasers or other radiation sources or a heat lamp. Arrays of such radiation sources, such as laser diode arrays, can also be considered. For the purposes of the disclosure, it is permissible for the selectivity to be introduced separately from the solidification reaction. A print head or one or more lasers can be used for selective treatment of the layer and solidification can be started with other layer treatment agents. In one embodiment, the particulate material is printed with an IR absorber and then solidified with an infrared source.

“Layer treatment agents” in the sense of the disclosure are all agents that are suitable for achieving a specific effect in the layer. These can be the aforementioned units such as print heads or lasers, but also heat sources in the form of IR emitters or other radiation sources such as UV emitters. Means for de- or ionization of the layer are also conceivable. What all layer treatment agents have in common is that their zone of action is linearly distributed over the layer and that, like the other layer units such as the print head or coater, they have to be guided over the construction field in order to reach the entire layer.

The “coupling” of cooling circuits or of a cooling circuit with a cooling part within the meaning of the disclosure describes the connection of at least two functionally different parts that have a coupling point or connection point and in which heat can be exchanged via it. For example, according to the disclosure, a closed air cooling circuit is coupled with a liquid-based cooling circuit and can thus absorb heat from a radiation converter, for example, from the air cooling circuit, this heat is transferred to the liquid-based cooling circuit and then transported to the environment directly or possibly via another coolant , whereby when using a control loop, the temperature at the radiation converter, for example, can be set or maintained at a target temperature.

A “closed” air cooling circuit in the sense of the disclosure means that the air in this circuit is essentially circulated in this circuit and no supply air is supplied from outside. In a special embodiment, this circuit is sealed in such a way that no contamination, such as particles of the building material, can penetrate into this circuit and so no maintenance of this circuit is necessary.

An "air cooling circuit" in the sense of the disclosure is air circulation in a pipe system of the sintering unit, the air or the gas being circulated e.g. by means of other means such as fans.

A "liquid-based cooling circuit" in the sense of the disclosure is a closed circuit, the coolant of which is a liquid, such as water, oil or other known liquid coolants.

A "radiation converter" in the sense of the disclosure is a component that is produced by a radiator is illuminated and that itself emits radiation in a certain wavelength.

"Surface enlargement" in the sense of the disclosure is any means that enlarges a surface for cooling purposes, such as fins, ribs etc. to increase the cooling capacity.

“Cooling part” in the sense of the disclosure is a heat exchanger.

Detailed description of the disclosure

The various aspects and advantageous configurations of the disclosure are described in more detail below.

The object on which the application is based is achieved by a sintering unit suitable for a 3D printing device, the sintering unit being characterized by a closed air cooling circuit and a liquid-based cooling circuit.

The object on which the application is based is further achieved by a method for producing a molded part by means of particle material application and selective solidification, a sintering unit according to one of claims 1 to 10 being used in the method, wherein the liquid-based coolant essentially cools the closed air cooling circuit, which in turn cools the or the spectrum converter essentially cools.

With the sintering unit according to the disclosure, it is advantageously possible to better dissipate the heat generated by a sintering unit in the 3D process, such as a high-speed sintering process, and to set an advantageous temperature control in the 3D printing system.

It is also advantageous that a sintering unit according to the disclosure is easy to maintain and there is essentially no maintenance effort due to soiling within the sintering unit.

Furthermore, through the targeted cooling of the spectrum converters in the sintering unit, according to the disclosure, the emitted wavelength spectrum can be kept more easily and more constant in the desired spectrum. This also has positive effects on the manufacturing process and quality advantages with regard to the molded parts produced.

A sintering unit according to the disclosure can partially or completely cover the construction field. The shape of the sintering unit results from the considerations for the construction field geometry. In order to keep the loss of time in the X direction when sweeping over the process field by means of the sintering unit and the reversal path included in it, the shape specification is an unit that is as narrow as possible in the X direction. A long and relatively narrow sintering device, however, poses particular challenges for temperature management, which can only be taken into account by means of a special type of design. Due to the large base area of the unit, the amount of heat generated by secondary effects on the radiator unit and the absorbed spectrum of the two spectrum converters can no longer be taken into account by the conventional cooling device with the device cover through which fluid flows. The result is overheating of the spectrum converter, which in turn would cause undesired secondary radiation or would result in a greatly reduced service life of the emitter unit.

This can only be countered by improving the coupling between generated and dissipated heat. The amount of heat cannot simply be transported out of the unit, e.g. by air cooling by means of a built-in fan, as this would result in contamination of the unit space and the fact that the device is in constant motion and runs for several thousand cycles is made more difficult of sweeping over the process field during a single construction process.

This problem can be solved by using a radiator unit which couples all heat-supplying elements with a coolant via a closed air circulation. The air circulation can be generated, for example, by fans and / or by feeding in compressed air and using diffusers.

Preferred configurations according to the disclosure are described in the subclaims.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that the air is circulated in the closed air cooling circuit, preferably by a ventilation means in the air cooling circuit.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that the liquid-based cooling circuit is arranged on the side facing away from the construction field and / or is coupled to a further coolant, preferably an external coolant.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that the closed Air cooling circuit is passed at least partially past a radiation converter, preferably wherein the air cooling circuit is passed at least partially between two radiation converters.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that means for increasing the surface area are arranged in the air cooling circuit, preferably cooling fins, cooling fins, cooling coils or cooling coils, which are coupled to the liquid-based cooling circuit.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that an IR radiator is arranged between a primary and secondary radiation converter and the liquid-based cooling circuit and, if necessary, a reflector is arranged between the IR radiator and a cooling part through which the liquid flows.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that the liquid-based cooling circuit is cooled by means of a cooling part through which liquid flows on the outside of the sintering unit, the cooling part preferably being a supporting cover.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that there are cavities for the closed air cooling circuit between the primary and secondary radiation converters and between the primary radiation converters and the supporting cover, preferably with surface enlargements of the cooling part through which the liquid flows, and each other if necessary, cavities are located in the side walls of the sintering unit, all cavities being connected to one another and thus forming a closed air cooling circuit.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that a reflector is arranged in the cavity between the primary radiation converter and the supporting cover.

In a preferred embodiment, the sintering unit according to the disclosure can be characterized in that the closed air cooling circuit has no connection to the ambient air.

In a further aspect, the disclosure relates to a 3D printing device that comprises a sintering unit according to the disclosure, the further coolant, preferably an external coolant, being arranged outside the 3D printing device.

In a further aspect, the disclosure relates to a method for producing a molded part by means of particle material application and selective solidification, a sintering unit according to one of claims 1 to 10 being used in the method, wherein the liquid-based coolant essentially cools the closed air cooling circuit, which in turn cools the or the spectrum converter essentially cools.

In a preferred embodiment, the method according to the disclosure can be characterized in that the method is a high-speed sintering method or a multi-jet fusion method.

In a preferred embodiment, the method according to the disclosure can be characterized in that the method is a laser sintering method and the sintering unit according to one of claims 1 to 10 is used for temperature control of the particle material on the construction field.

Further exemplary representation of the disclosure

Various aspects of the disclosure are described in the following by way of example, without these should be understood in a restrictive manner. Each aspect from the exemplary figures shown below can also be used in any combination.

In the following, the invention is further explained with the aid of various examples using the figures:

Fig. S1 outlines a sintering unit with a spectrum converter ( S101 ) according to the state of the art, such as In DE102017006860 described in the XZ plane on the left and viewed from below in the XY plane on the right. The through the radiator ( S102 ) generated electromagnetic radiation of essentially Planck's spectrum is reflected by the reflector ( S103 ) directed downwards ( S104 ) and meets there a primary spectrum converter ( S105 ). With its help, unwanted wavelength ranges can be filtered out and / or converted so that only the desired wavelength ranges pass. A secondary spectrum converter ( S106 ) forms the airtight seal on the housing of the sintering unit. It can not only serve as dust and contact protection, but also filter or convert the spectrum of the radiation passing through. The inevitably resulting losses in the radiation power due to the conversion of the spectrum lead to an increase in temperature of the transducer surface, since the following applies: $$\mathrm{A.}+\mathrm{R.}+T=1$$

All radiation is therefore absorbed (A), reflected (R), or transmitted (T) to a certain extent.

The temperature increase caused by absorption usually takes place in the middle of the transducer surface, as shown in the right part of the sketch. The reason for this is that the spectrum converter can only emit its temperature via the mounting points with which it is connected to the housing of the unit. Even if the secondary spectrum converter is designed to be as transparent as possible for the radiation passing through and does not significantly convert the spectrum, a certain residual part of the radiation remains in it, so that these losses also lead to an increase in temperature. As a result of the temperature increase, the spectrum converter in turn becomes an emitter of so-called secondary radiation ( S109 ), which results from Stefan-Boltzmann's law: $$P=\epsilon \left(T\right)\cdot \sigma \cdot \mathrm{A.}\cdot T^{\mathrm{4th}}$$

Here P denotes the power of the emitted electromagnetic radiation, ε (T) the temperature-dependent emissivity, σ the Stefan-Boltzmann constant, A the area ( S108 ) from which the radiation is emitted and T the temperature of the surface.

As can be seen from the sketch, the induced secondary radiation mixes ( S109 ) with the transformed ( S107 ), which is generally not desired. According to the state of the art, ( S106 ) a highly transparent, mechanically mostly very fragile and expensive special glass pane was used to avoid this if a change in the spectrum is not required. It is true that cooling by means of a gas flow in the form of compressed air or by means of a cooling liquid is possible in one embodiment of a radiator unit in FIG EP 1 319 240 mentioned, but there the unit is not made airtight. However, this is absolutely necessary in the additive manufacturing process of high speed sintering, since the finest plastic particles would otherwise penetrate the unit and damage it. A constant overpressure inside the unit cannot be used either, since the resulting air flow from an unclosed device would negatively affect the sintering process due to temperature fluctuations due to forced convection.

Cooling the spectrum converter with a liquid medium would also be conceivable, but this would place high demands on tightness and fluid supply. It should be noted here that in a sintering unit like the one used in high-speed sintering, considerable amounts of energy are converted that can easily exceed 10-20 kW. It would then have to be ensured that, for example, the sealants can withstand any waste heat and at the same time reliably fulfill their function. Furthermore, especially with larger versions of the sintering unit, the weight of a liquid medium would not be insignificant, which would entail additional costs due to the need for a more stable design. In the case of a liquid medium, it must also be ensured that it does not exceed the boiling temperature.

S2 shows the section through a sintering aggregate device with a closed secondary air circuit. On the plate through which a cooling medium flows ( S208 ), here designed as a cover, are coolants with a large surface, in this embodiment cooling fins ( S201 ), assembled. These preferably fill the cavity between the cooling plate and reflector ( S206 ), which is attached to the lid. The emitter ( S207 ) is mounted on the underside of the reflector at a defined distance. The two spectrum converters are located on the underside of the unit ( S203 ) and ( S204 ), which are separated by a cavity. A gas flow ( S205 ), which is able to dissipate the heat generated there. This is then passed past the cooling fins, which are kept at a low temperature with the aid of the cover through which the fluid flows. It is thus possible to transfer the heat dissipated by the air flow to the cooling cover. This acts as a heat exchanger together with the cooling fins. The resulting secondary heat can thus be conducted to the outside from the closed container.

The schematic representation in Fig. S3 shows a sintering unit according to the invention in the side view (YZ plane) with drawn air flow ( S304 ). Another aspect is shown with the recesses in the side wall towards the center of the unit: The gas flow generated inside the unit is preferably passed through the recess ( S307 ) in the side wall between primary ( S305 ) and secondary radiation converter ( S306 ) steered, in order to then return to the cooling fins ( S302 ) to flow past. This ensures that the heat dissipation on the surfaces of the spectrum converters takes place uniformly along the Y-direction shown. The background to this is that the heat flow caused by convection depends on the temperature of the cooling fluid: $$\dot{Q}=\alpha \cdot \left(T_{\mathrm{A.}}-T_{\mathrm{F.}l}\right)\cdot \mathrm{A.}$$

The area on which the convection acts is denoted by A, the heat flow Q̇̇, measured in W / m ² , depends on the temperature difference between the area T _{A and} the fluid T _Fl , as well as on the heat transfer coefficient a. If the gas flow between the spectrum converters is now heated by these, it absorbs less and less heat as the temperature rises, which reduces the cooling capacity. This can only be counteracted by lowering the temperature of the gas flow again by leading it past the cooling fins.

The front view in section in Fig. S4 in the XZ plane shows the sintering unit with drawn fans ( S403 ), with the help of which the gas flow ( S405 ) is set in motion. The gas flow is extracted from the cavity between the spectrum converters ( S408 ) via recesses in the side walls ( S404 ) sucked out the short side and guided past the cooling fins between reflector and cooling cover. Commercially available fans with increased temperature resistance can be used as fans. Since the secondary radiation generated by heating the spectrum converter is temperature-dependent, a sensor can be used that continuously measures the temperature of the gas flow and adjusts the speed of the fans accordingly via a controller so that the temperature of the spectrum converter can be kept constant.

• In einem beispielhaften Ausführungsbeispiel ist das Sinteraggregat S202 mittels einer in sich geschlossenen Luftzirkulation S205 ausgestattet, wie Fig. S2 im Schnitt durch die Vorrichtung in XZ-Ebene schematisch skizziert. Dabei wird die sich im Aggregat befindlich Luft durch den Hohlraum zwischen den Spektrumswandlern S203 und S204 und an Kühlrippen S201, welche mit dem Kühldeckel verbunden sind vorbei geleitet. Dies ermöglicht eine starke Steigerung in der Effizienz der durch den wasserdurchströmten Deckel S208 ermöglichten Wärmeabfuhr. Außerdem wird durch den kontinuierlichen Luftstrom die Wärme gleichmäßiger abgeführt, was der örtlichen Kontinuität des abgegebenen Strahlungsspektrums zu Gute kommt.

Another exemplary embodiment of a sintering unit device:

• In an exemplary embodiment, the sintering unit is S202 by means of a closed air circulation S205 equipped, as sketched schematically in FIG. S2 in section through the device in the XZ plane. The air in the unit is then passed through the cavity between the spectrum converters S203 and S204 and on cooling fins S201 , which are connected to the cooling cover passed over. This enables a strong increase in the efficiency of the cover through which water flows S208 enabled heat dissipation. In addition, the continuous air flow dissipates the heat more evenly, which benefits the local continuity of the emitted radiation spectrum.

The sintering unit in the side view (YZ plane) with the air flow drawn in in FIG. S4 reveals a recess S407 on the side walls through which the cooling air is passed. This ensures that the spectrum converter S407 and S406 should be adequately cooled at their hottest point, which is farthest from the heat-conducting components. The airflow S405 is made by fans S403 generated and sustained. Clearly recognizable is the important aspect that the continuous air flow circulates in a closed housing. Thus, the emitter unit, although equipped with a high output and adapted spectrum, can also be operated in environments where there is a high risk of contamination, e.g. from dust.

List of reference symbols

S101

State-of-the-art sintering unit

S102

IR emitter

S103

reflector

S104

Emitted, essentially Planckian radiation

S105

Primary spectrum converter

S106

Secondary spectrum converter

S107

Emitted converted spectrum

S108

Area of the spectrum converter that experiences a temperature increase due to the conversion

S109

Unwanted secondary radiation emitted by the temperature rise of the spectrum converter

S201

Cooling fins

S202

side walls

S203

Primary spectrum converter

S204

Secondary spectrum converter

S205

Air flow through the cooling fins

S206

reflector

S207

Spotlights

S208

Carrying cover through which cooling fluid flows

S301

Carrying cover through which cooling fluid flows

S302

The cavity above the reflector is fitted with cooling fins

S303

fan

S304

Airflow

S305

Primary radiation converter

S306

Secondary radiation converter

S307

Air flow through the recess in the side wall in the middle of the unit

S401

Carrying cover through which cooling fluid flows

S402

Spotlights

S403

fan

S404

Cavity in short side walls on the short side for air routing

S405

Airflow

S406

Secondary radiation converter

S407

Primary radiation converter

S408

Cavity between the two radiation converters

S409

reflector

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0431924 B1 [0002]
• DE 102017006860 [0006, 0017, 0077]
• EP 1319240 [0009, 0081]

Claims (10)

Sintering unit suitable for a 3D printing device, the sintering unit being characterized by a closed air cooling circuit and a liquid-based cooling circuit. Sintering unit after Claim 1 , wherein the air is circulated in the closed air cooling circuit, preferably by a ventilation means in the air cooling circuit and / or wherein the liquid-based cooling circuit is arranged on the side facing away from the construction site and / or is coupled to a further coolant, preferably an external coolant or / and wherein the closed air cooling circuit is at least partially routed past a radiation converter, preferably wherein the air cooling circuit is at least partially routed past between two radiation converters and / and wherein means for increasing the surface area are arranged in the air cooling circuit, preferably cooling fins, cooling fins, cooling coils or cooling helix, which with are coupled to the liquid-based cooling circuit. Sintering unit according to one of the preceding claims, wherein an IR radiator is arranged between a primary and secondary radiation converter and the liquid-based cooling circuit and, if necessary, a reflector is arranged between the IR radiator and a cooling part through which liquid flows. Sintering aggregate according to one of the preceding claims, wherein the liquid-based cooling circuit is cooled by means of a cooling part through which liquid flows on the outside of the sintering aggregate, wherein the cooling part is preferably a supporting cover. Sintering unit according to one of the preceding claims, wherein there are cavities for the closed air cooling circuit between the primary and secondary radiation converters and between the primary radiation converters and the supporting cover, preferably with surface enlargements of the cooling part through which the liquid flows, and possibly cavities in the side walls of the sintering unit , whereby all cavities are in communication with one another and thus form a closed air cooling circuit. Sintering unit after Claim 5 , wherein a reflector is arranged in the cavity between the primary radiation converter and the supporting cover. Sintering unit according to one of the preceding claims, wherein the closed air cooling circuit has no connection to the ambient air. 3D printing device that uses a sintering unit according to one of the Claims 1 to 7th comprises, wherein the further coolant, preferably an external coolant, is arranged outside of the 3D printing device. A method for producing a molded part by means of particle material application and selective solidification, wherein a sintering unit according to one of the Claims 1 to 7th is used in the method, wherein the liquid-based coolant essentially cools the closed air cooling circuit, which in turn essentially cools the spectrum converter (s), preferably wherein the method is a high-speed sintering method or a multi-jet fusion method. Procedure according to Claim 9 , the process being a laser sintering process or a multi-jet fusion process or a 3D sintering process and the sintering unit according to one of the Claims 1 to 7th is used for particle material temperature control on the construction site.

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