GB2550339A

GB2550339A - Additive manufacturing systems

Info

Publication number: GB2550339A
Application number: GB1608360.2A
Authority: GB
Inventors: Alejandre Ignacio; Ramirez Muela David; Manuel De Pena Alejandro
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2016-05-12
Filing date: 2016-05-12
Publication date: 2017-11-22
Also published as: GB201608360D0

Abstract

An additive manufacturing device 100 comprises a bed 106 to contain a volume of build material such as a powder; at least one heater 210 to selectively fuse portions of the build material to form a portion of an object 218; an air mover, or fan system 104, to invoke a gas flow across a surface of the build material to provide predetermined convection conditions across the surface of the build material in the bed and control a temperature condition across the surface of the build material. The air mover may be a fan which is adjustable to change the gas flow based on a temperature of the build material which may be detected by a thermal sensor. A printhead is preferably provided to increase the absorption rate of portions of the build material. A first heater 208 may be used to maintain a base temperature and a second heater 210 may be used to apply thermal energy to the build material to selectively fuse portions with increased absorption rate. A method for controlling an additive manufacturing device comprises invoking a gas flow across a surface of build material in a bed to remove heat, or cool, the surface during selective fusing; detecting with a thermal sensor, a temperature of the surface and adjusting the gas flow across the surface based on the temperature.

Description

ADDITIVE MANUFACTURING SYSTEMS

BACKGROUND

[0001] Additive manufacturing machines produce three-dimensional 3D objects by building up layers of material. Some additive manufacturing machines are referred to as "3D printing devices" because they use inkjet or other printing technology to apply some of the manufacturing materials. 3D printing devices and other additive manufacturing devices make it possible to convert a computer aided design CAD model or other digital representation of an object directly into the physical object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are given merely for illustration, and do not limit the scope of the claims.

[0003] Fig. 1 is a block diagram of an additive manufacturing device with a fan system, according to an example of the principles described herein.

[0004] Fig. 2 is a cross-sectional diagram of an additive manufacturing device with a fan system, according to an example of the principles described herein.

[0005] Fig. 3 is a block diagram of an additive manufacturing system with a fan system, according to an example of the principles described herein.

[0006] Fig. 4 is a flowchart of a method for controlling an additive manufacturing device temperature condition, according to an example of the principles described herein.

[0007] Fig. 5 is an isometric view of an additive manufacturing system with a fan system, according to an example of the principles described herein.

[0008] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.

DETAILED DESCRIPTION

[0009] Additive manufacturing devices make a 3D object through the solidification of layers of a build material on a bed within the device. Additive manufacturing devices make objects based on data in a 3D model of an object generated, for example, with a CAD computer program product. The model data is processed into slices, each slice defining a layer of build material that is to be solidified. In some examples, an agent is dispensed onto a layer of build material such as a fusible material in the desired pattern. The agent disposed in the desired pattern increases the absorption of the underlying layer of build material on which the agent is disposed. The build material is then exposed to electromagnetic radiation. The electromagnetic radiation may include infrared light, laser light, or other suitable electromagnetic radiation. Due to the increased heat absorption properties imparted by the agent, those portions of the build material that have the agent disposed thereon heat to a temperature greater than the fusing temperature for the build material. Accordingly, these portions of the build material fuse together to form a solid layer that makes up a portion of the object to be printed. Those portions of the build material that receive the agent and thus have increased heat absorption properties may be referred to as fused portions. By comparison, the applied heat is not so great so as to increase the heat of the portions of the build material that are free of the agent to this fusing temperature. Those portions of the build material that do not receive the agent and thus do not have increased heat absorption properties may be referred to as unfused portions. Accordingly, a predetermined amount of heat is applied to an entire bed of build material, the portions of the build material that receive the agent, due to the increased heat absorption properties imparted by the agent, fuse and form the object while the unfused portions of the build material are unaffected, i.e., not fused, in the presence of such application of thermal energy.

[0010] Heating of the build material may occur in two processes. In a first process, the build material is heated to and maintained at a temperature just below the build material’s fusing temperature. In a second process, an agent is "printed" or otherwise dispensed onto the build material in the desired pattern and exposed to another, relatively, higher intensity electromagnetic radiation source. This relatively higher intensity light is absorbed into the patterned agent causing the underlying build material to fuse. Halogen lamps emitting light over a broad spectrum may be used in both these processes.

[0011] With these additive manufacturing devices, a higher quality of the printed 3D object can be achieved when the temperature of the building material is more effectively controlled. For example, if too much heat is applied to the portions of the unfused build material, the unfused portions may clump together, or “cake.” Such caking increases the object cost as well as increases the difficulty in manufacturing such objects. For example, during formation, unfused build material can be recycled and re-used in later 3D printing operations. However, when the unfused build material cakes, it is no longer recyclable. Accordingly, the lack of accurate temperature control may result in wasted build material, thus increasing the cost of manufacture of 3D printed objects.

[0012] Still further, in some examples, the heat energy absorbed by fused portions of the build material, may transfer by conduction to immediately adjacent unfused portions of the build material. This is sometimes referred to as thermal bleed and can also increase the cost and difficult in manufacturing 3D printed objects. For example, after a 3D printed object is formed, unused build material is removed from around the object. Due to the thermal bleed described above, immediately adjacent unfused build material may become temporarily, or semi-permanently, affixed to the object. Removal of this material can be difficult, time-consuming, and in some cases may even damage the 3D printed object.

[0013] Accordingly, the present specification describes a device and system for more accurately controlling the temperature conditions and selectivity within the additive manufacturing device so as to alleviate these undesirable byproducts of ineffective heat control. More specifically, the additive manufacturing device includes an air mover, such as a fan system, to invoke a gas flow across the surface of the build material. Such a gas flow more quickly removes heat from the surface of the bed, thus reducing the likelihood of caking and thermal bleed, and also increasing the strength of the resultant 3D printed object. In other words, the greater the control over the temperature within the printing device, the stronger the corresponding 3D printed objects will be.

[0014] For example, in general the higher the temperature reached by the fused build material, the better the mechanical properties of the corresponding 3D printed object. If there is no gas flow, the temperature of the fused portions is reduced so as to prevent the caking of unfused portions that may be raised to too high a temperature. An introduced gas flow can keep the unfused portions at a lower temperature, thus allowing for a higher thermal energy to be applied to the fused portions. This higher temperature in the fused portions increases the molecular mixing and linking during the fusing and solidification processes, which results in an increased part strength. Accordingly, it is desirable that high temperatures are reached in the fused build material and lower temperatures in the unfused portions. This concept is referred to as selectivity.

[0015] In some examples, a thermal sensor measures the temperature of the build material within the bed or the rate of decrease in temperature of the build material within the bed. If the temperature of the unfused portions is too great or the rate of temperature decrease too slow, a processor increases the output of the fan system to increase gas flow to lower the temperature of the build material or increase the rate of temperature decrease. By comparison, if the temperature of the unfused portions is too low or the rate of temperature decrease is too high, the processor can slow down the fan system so as to decrease the gas flow or decrease the rate of temperature decrease and bring the temperature of the build material up, closer to the fusing temperature of the build material.

[0016] Specifically, the present specification describes an additive manufacturing device. The additive manufacturing device includes a bed to contain a volume of build material. At least one heater of the additive manufacturing device selectively fuses portions of the build material to form a portion of an object via the application of heat to the build material in the bed. The additive manufacturing device also includes an air mover, such as a fan system, to invoke a gas flow across a surface of the build material in the bed during the application of heat to the build material. The gas flow provides predetermined convection conditions across the surface of the build material in the bed and controls a temperature condition across the surface of the build material in the bed.

[0017] The present specification also describes an additive manufacturing system that includes an additive manufacturing device. The additive manufacturing device includes a bed to hold a volume of build material. The additive manufacturing device also includes at least one heater to, in a layer-wise fashion, selectively fuse portions of the build material to form an object via the application of heat to the build material in the bed. At least one fan of the additive manufacturing device invokes a gas flow across a surface of the build material in the bed during the application of heat to the build material. The additive manufacturing system further includes a thermal sensor to detect the temperature condition of various portions of the surface of the build material and a processor to adjust the operation of the at least one fan based on readings from the thermal sensor.

[0018] Still further, the present specification describes a method for controlling an additive manufacturing device temperature condition. In the method, a gas flow is invoked across a surface of build material in a bed to remove heat from the surface of the build material in the bed during a selective fusing of portions of the build material. A thermal sensor detects a temperature condition of the surface of the build material in the bed and the gas flow across the surface of the build material in the bed is adjusted based on the temperature condition of the surface of the build material in the bed.

[0019] Using such an additive manufacturing device 1 provides greater control over the temperature conditions within the additive manufacturing device; 2 increases the robustness, specifically the tensile strength, of 3D printed objects; 3 enhances the recyclability of unfused build material by reducing caking of unfused build material; 4 simplifies the post-printing operations, for example cleaning a 3D printed object, by reducing the effects of thermal transfer between fused and unfused regions of the build surface; 5 reduces cost of production as build material recyclability is increased and a time to clean parts is reduced; and 6 increases the repeatability and predictability of the additive manufacturing processes. However, it is contemplated that the devices disclosed herein may provide useful in addressing other matters and deficiencies in a number of technical areas. Therefore the systems and methods disclosed herein should not be construed as addressing any of the particular matters.

[0020] As used in the present specification and in the appended claims, the term “temperature condition” refers broadly to a temperature condition of the build material. One example of a temperature condition is a temperature of the surface of the build material. Another example of a temperature condition is the rate at which the temperature of the build material drops, also referred to as the temperature decrease rate.

[0021] Further, as used in the present specification and in the appended claims, the term “a number of or similar language is meant to be understood broadly as any positive number comprising 1 to infinity.

[0022] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to “an example” or similar language means that a particular feature, structure, or characteristic described in connection with that example is included as described, but may not be included in other examples.

[0023] Turning now to the figures, Fig. 1 is a block diagram of an additive manufacturing device 100 with a fan system 104, according to an example of the principles described herein. The additive manufacturing device 100 includes a bed 106. The bed 106 may be any type of bed onto which a build material, such as a fusible material, may be layered. The build material is deposited in the bed 106 in layers. Each layer of the build material that is fused in the bed 106 forms a slice of the 3D printed object such that multiple layers of fused build material form the entire 3D printed object. The bed 106 may accommodate any number of layers of build material. For example, the bed 106 may accommodate up to 4,000 layers or more. In an example, a number of build material supply receptacles may be positioned alongside the bed 106.

Such build material supply receptacles source the build material that is placed on the bed 106 in a layer-wise fashion.

[0024] Various types of build material may be held within the bed 106. In one example, the build material is a fusible material. With a fusible material, particulate matter fuses together when the particulate matter reaches a fusing temperature. One example of a fusible material is polyamide 12, which has a fusing temperature of 185 degrees Celsius. In this example, portions of the polyamide 12 that are heated above 185 degrees Celsius fuse together to form a solid object. While specific mention is made to polyamide 12 as a fusible build material, other build materials may be used, including, but not limited to polyamide 11 or other fusible materials.

[0025] The build material is deposited into the bed 106 via a build material deposition device. Specifically, the build material deposition device may acquire build material from the build material supply receptacles, and deposit such acquired material as a layer in the bed 106, which layer may be deposited on top of other layers of build material already processed that reside in the bed 106.

[0026] The additive manufacturing device 100 also includes at least one heater 102 to selectively fuse portions of the build material to form an object via the application of heat to the build material. A heater 102 may be any component that applies thermal energy. Examples of heaters 102 include infrared lamps, visible halogen lamps, resistive heaters, light emitting diodes LEDs, and lasers. As described above, build material may include a fusible build material that fuses together once a fusing temperature is reached. Accordingly, the heater 102 may apply thermal energy to the build material so as to heat portions of the build material past this fusing temperature. Those portions that are heated past the fusing temperature have an agent disposed thereon and are formed in the pattern of the 3D object to be printed. The agent increases the absorption rate of that portion of the build material. Thus, a heater 102 may apply an amount of energy such that those portions with an increased absorption rate reach a temperature greater than the fusing temperature while those portions that do not have the increased absorption rate to not reach a temperature greater than the fusing temperature. In the present specification, those portions that have an increased absorption rate are identified as fused portions and those portions that do not have an increased absorption rate are identified as unfused portions.

[0027] As the temperature of the build material is relevant to the forming of a 3D printed object, an accurate temperature control of the printing environment increases the efficacy and strength of corresponding 3D printed objects. For example, if the temperature at the surface of the build material in the bed 106 is too low, the fused portions may not properly fuse. By comparison, if the temperature at the surface of the build material in the bed 106 is too high, parts of the unfused portions may fuse in an operation referred to as caking, or at the boundary of fused and unfused portions, heat energy may be transferred by conduction from higher temperature fused portions to lower temperature unfused portions, which may temporarily, or semi-permanently adhere unfused portions to adjacent fused portions. The removal of these adjacent unfused portions can be difficult, time-intensive, and may even damage the 3D printed object.

[0028] Accordingly, the additive manufacturing device 100 includes a fan system 104 to invoke a gas flow across a surface of the build material in the bed 106 and to facilitate an appropriate output path for the gas flow. In some examples, the gas may be air. Other gasses may be used as well such as argon and nitrogen.

[0029] The fan system 104 may include a mechanical fan, or mechanical fans, that include rotating vanes or blades that act on the gas. For example, the vanes or blades may rotate in a radial fashion around a hub. The fan blades may be disposed within a housing or a case. The fan system 104 may be coupled to an electric motor that causes the fan blades or vanes to rotate. The fans included in the fan system 104 may be forced air cooling fans. In some examples, the fans may be turbo cooler fans. The gas flow generated by the fan system 104 may be perpendicular to the surface of the build material in the bed 106.

[0030] The fan system 104 may rely on different mechanisms for invoking the cooling gas flow across the surface of the build material. For example, the fan may draw cool gas into the device 100 or it may expel warm gas from inside the device 100. In some examples, there may be multiple fans in the fan system, for example an intake fan to draw cool gas into the device 100 and an exhaust fan to expel warm gas from inside the device 100. Specific types of fans that could be used include axial-flow fans, centrifugal flow fans, and crossflow fans. In some examples a series of fans can be used to increase the gas flow through the system.

[0031] In some examples, the fan system 104 includes a container with single or multiple gas inputs. The input gas enters the fan system 104 via the suction action of fans disposed within the fan system. In some examples, between the input and the fan, a filtering media permits the retention of particulate matter. Examples of such particulate matter include powder present in the printing chamber. In some examples, depending upon the degree of filtration desired, different types and different numbers of filters can be used.

The fan system 104 also may include protective grills on either side of the fan and filter so as to avoid involuntary contact of users with the moving fan.

[0032] In this example, the fan system 104 increases the pressure of the gas and impels the gas it to an output side of the fan system 104, which output side may be interior to the device 100. Variables of the fan system can be controlled by a control device. For example, the revolutions per minute, voltage supplied, and current used can be varied. This control device can react to variations in air density resultant from height above sea level to maintain a desired gas flow and/or pressure. For example, if inside the print chamber, a desired pressure with respect to the environment can be maintained.

[0033] This fan system 104 may operate during the selective fusing of the fused portions of the build material. The fan system 104 provides predetermined convection conditions across the surface of the build material in the bed 106 and controls a temperature condition across the surface of the build material in the bed 106. For example, while the heater 102 can apply an amount of heat energy to the build material, if the heat does not dissipate from the surface of the build material quickly enough, the unfused portions may cake together. Further, exposure of the fused portions of the build material to the increased energy of a fusing lamp for too long may result in thermal transfer from those fused portions onto the unfused portions. The gas flow invoked by the fan system 104 increases the dissipation of heat such that the layer of build material returns to a sub-fusing temperature more quickly after the selective fusing by the at least one heater 102.

[0034] Accordingly, the introduction of a fan system 104 to remove heat from the surface of the build material in the bed 106 results in increased control over the thermal conditions of the printing environment, specifically increased control over the temperature of the build material, both unfused and fused portions, so as to prevent caking and thermal transfer, all while increasing the tensile strength of any resultant 3D printed object.

[0035] Fig. 2 is a cross-sectional diagram of an additive manufacturing device 100 with a temperature control fan system 104 according to an example of the principles described herein. Specifically, Fig. 2 depicts a first heater 208, a second heater 210, a fan system 104, and the bed 106. A detailed description of each component and others follows.

[0036] As described above, the bed 106 is a receptacle that holds a volume of build material 212, which build material 212 may be a fusible material such as polyamide 12. The build material 212 is used to form 3D printed objects 218. In such an operation, a build material deposition device passes over the bed 106 and deposits layers of build material 212 in the bed 106. A printhead then passes over the bed 106 to selectively deposit an agent on selected portions of the build material that are to form the 3D printed objects 212. For example, the printhead may deposit an agent that tints certain portions of the build material 212 a darker color, such as black. The darkened portions, also referred to as the fused portions of the build material 212, absorb more heat energy. Specifically, the increased absorption exhibited by the fused portions of the build material 212 absorb sufficient heat form the second heater 210 such that these fused portions surpass the fusing temperature of the build material 212 while the unfused portions to not absorb sufficient heat from the second heater 210 to surpass the fusing temperature of the build material 212. As the fused portions have surpassed the fusing temperature, the fused portions of the build material 212 fuses together to form a solid 3D printed object.

[0037] The additive manufacturing device 100 also includes a first heater 208 to maintain the build material 212 at a base temperature. In one example, the first heater 208 may include a number of heat lamps 216-1, 216-2, 216-3, and 216-4 which emit electromagnetic radiation to heat the build material 212. The operation of these lamps 216 may be controlled by a processor.

Specifically, the processor may direct the heat lamps 216 to turn on, turn off, increase emitted electromagnetic radiation output, and/or decrease emitted electromagnetic radiation output.

[0038] As described above, the first heater 208 maintains the build material 212 at a base temperature. The base temperature is less than a fusing temperature of the build material 212. For example, if the build material 212 is polyamide 12, which has a fusing temperature of 185 degrees Celsius, the first heater 212 may emit sufficient thermal energy to maintain a temperature of the surface of the build material 212 at 165 degrees Celsius. While specific mention is made to particular temperatures and particular build materials different build materials may be used, and the particular base temperature dependent upon that build material. Maintaining the surface of the build material 212 near, but below the fusing temperature decreases the amount of energy used to raise the temperature of the build material past its fusing temperature, as explained below in regards to the second heater 210. In other words, if the base temperature were far below the fusing temperature, the second heater 210 would have to emit greater amounts of electromagnetic radiation, or the build material 212 would have to be exposed to the second heater 210 for longer periods of time in order to increase the temperature of the surface of the build material 212 to the fusing temperature. In other words, maintaining the build material 212 at a base temperature above room temperature, but below the fusing temperature increases the efficiency of the additive manufacturing device 100 as a lower energy second heater 210 may be used for a shorter amount of time as compared to keeping the build material 212 at room temperature.

[0039] Moreover, the first heater 208 maintains the entire surface of the build material 212 at a constant temperature. If the build material 212 were not maintained at a constant temperature, imperfections resulting from an uneven temperature distribution may result.

[0040] The second heater 210 applies thermal energy to the build material 212 such that the temperature of fused portions of the build material 212 is greater than a fusing temperature for the build material 212. Specifically such that just those fused portions of the build material 212 have a temperature greater than the fusing temperature of the build material. The thermal energy emitted by the second heater 210 however is not so great so as to raise the temperature of unfused portions of the build material 212 past the fusing temperature for the build material 212.

[0041] An example illustration of the formation of a 3D printed object 218 is now presented. In this example, a build material deposition device, deposits a layer of build material 212 in the bed 106. A printhead then applies an agent onto portions of the build material 212 that are to form a slice of the 3D printed object. This agent increases the thermal absorption of these fused portions of the build material 212. In some examples, both the build material deposition device and the printhead are disposed on the carriage 214 that passes over the top of the bed 106 to deposit the build material 212 and the agent that is disposed on the build material 212. In another example, the build material deposition device is not disposed on the carriage 214, but may be positioned on another carriage, or otherwise disposed so as to layer build material 212 across the bed 106.

[0042] All this time, the first heater 208 is applying thermal energy to the surface of the build material 212 so as to keep the temperature of the surface of the build material 212 1 at a temperature below, for example, just below, the fusing temperature for the build material 212 and 2 constant across the surface of the build material 212 in the bed 106.

[0043] The second heater 210, which may be a heat lamp that emits an increased intensity of electromagnetic radiation as compared to the heat lamps 216 of the first heater 208, then applies additional thermal energy to the build material 212. Specifically, the second heater 210 may be disposed on the carriage 214. The carriage 214 moves across the bed 106 and the electromagnetic radiation emitted by the second heater 210 is absorbed by the build material 212 in the bed 106. The thermal energy supplied by the second heater 210 raises the temperature of the build material 212 in the bed 106. However, due to the different absorption rates of the fused portions and unfused portions, the temperature increase of each portion is different. Specifically, the fused portions, having an increased absorption rate, rise to a temperature greater than the fusing temperature of the build material 212. By comparison, the unfused portions, having a lesser absorption rate, do not rise to a temperature greater than the fusing temperature of the build material 212. Accordingly, the thermal energy emitted by the second heater 210 may be selected so as to increase the temperature effused portions above a fusing temperature, while maintaining unfused portions below the fusing temperature.

[0044] Following the above described operation, the processes of 1 depositing a successive layer of build material 212, 2 depositing an absorption agent via the printhead, and 3 applying thermal energy to the build material 212 to fuse the fused portions of the build material are alternately carried out in a layer-wise fashion. As can be seen in Fig. 2, some of the objects 218-1,218-3, 218-4, and 218-5 have been completely formed, while another object 218-2 is still being processed in a layer-wise fashion as described above.

[0045] However, as mentioned above, during such a layer-wise forming, it is difficult to maintain a specific temperature on the different portions of the build material 212 so as to prevent caking and thermal transfer. For example, after the second heater 216 has passed over and fused a layer of fused portion of build material 212, if the heat is not removed from the unfused portions quickly enough, the unfused portions may cake together. Moreover, if the heat is not removed from the fused portions quickly enough, the fused portions may transfer thermal energy into immediately adjacent unfused portions, thus temporarily or semi-permanently adhering the immediately adjacent unfused portions to the fused portions. As described above such thermal transfer and caking increase the complexity of manufacturing 3D printed objects.

[0046] Accordingly, the additive manufacturing device 100 includes a fan system 104 to invoke a gas flow across a surface of the build material 212 in the bed 106. In other words, the fan system 104 removes heat from the surface of the build material 212 in the bed 106 to reduce the temperature of the build material 212. Specifically, the fan system 104 reduces the temperature of the build material 212, both the fused portions and the unfused portions, to below a fusing temperature. The fan system 104 adds another modality of heat transfer. Specifically, the heaters 208, 210 effectuate radiative heat transfer and the fan system 104 effectuates a convective heat transfer.

[0047] The fan system 104 may be adjustable to invoke different gas flows across the surface of the build material 212 based on a temperature condition reading of the build material 212. For example, a thermal sensor such as a camera may measure the temperature of an entire surface of the build material 212 in the bed 106. Such measurements may indicate that the temperature of the build material 212 is above the fusing temperature, or too close to the fusing temperature. Accordingly, the fan system 104 may be adjusted to invoke a greater gas flow to reduce the temperature or to increase the temperature decrease rate. By comparison, the thermal camera may measure the temperature of the build material 212 as too far below the fusing temperature. Accordingly, the fan system 104 may be adjusted to invoke a lesser gas flow to increase the temperature or to decrease the temperature decrease rate.

[0048] In some examples, during the entire process of depositing layers, depositing an absorption agent onto the build material 212, and fusing fused portions of the build material 212, the fan system 104 may be continuously running. That is, the second heater 210 and the fan system 104 simultaneously selectively fuse fused portions of the build material 212 and remove heat energy from the build material 212, respectively. So doing allows for increased control over the temperature conditions within the additive manufacturing device 100 so as to reduce the temperature of the build material 212 to prevent caking and to prevent thermal transfer from fused portions of the build material 212 to unfused portions of the build material 212.

[0049] As described, the additive manufacturing device 100 as described herein provides greater selectivity, i.e., a greater control over the temperature conditions within the additive manufacturing device 100. Specifically, depending on such conditions as gas flow speed, gas flow temperature, radiation from top lamps, etc. a different rate of heat exchanged by fused portions and unfused portions is obtained. Such increased control allows for a reduction in caking and thermal transfer as well as an increase in 3D printed object strength.

[0050] Fig. 3 is a block diagram of an additive manufacturing system 320 with a fan system 104, according to an example of the principles described herein. The additive manufacturing system 320 includes an additive manufacturing device 100, which additive manufacturing device 100 includes a bed 106 to hold a volume of build material, at least one heater 102 to, in a layer-wise fashion, selectively fuse build material Fig. 2, 212 to form a 3D object via the application of heat to the build material Fig. 2, 212 in the bed 106. The additive manufacturing device 100 also includes a fan system 104 including at least one fan to invoke a gas flow across a surface of the build material Fig. 2, 212 in the bed 106 during the application of heat to the build material Fig. 2, 212.

[0051] The additive manufacturing system 320 also includes a thermal sensor 324 to detect a temperature condition of various portions of the surface of the build material Fig. 2, 212. Specifically, the thermal sensor 324 could detect the temperature of various portions of the surface of the build material Fig. 2, 212. Another example of a temperature condition detected by the thermal sensor 324 is the temperature decrease rate, or the rate at which the temperature drops. The thermal sensor 324 may be any type of sensor that can detect electromagnetic radiation such as infrared radiation emitting from a layer of build material Fig. 2, 212 on the surface of the bed 106. For example, the thermal sensor 324 may include any number of thermal cameras. Any number of thermal cameras may be used to detect the temperature condition of the whole bed 106 or a portion of the bed 106. For example, the thermal sensor 324 may measure a matrix of points that cover the whole bed 106 surface. Based on the purpose of the measurement, particular attention may be made to some points or zones. For example, sometimes data relating to fused portions is analyzed and sometimes data relating to unfused portions is analyzed. In some cases, average values of several areas on the surface of the bed 106 are calculated.

[0052] In an example, the thermal sensor 324 detects electromagnetic radiation emitted from the bed 106 having wavelengths up to 14,000 nm. In this example, the thermal sensor 324 continuously detects this emitted infrared radiation along the entirety of the bed 106. In an example, an array of pyrometers may be used instead of a thermal camera with each pyrometer detecting the emissivity of a single point on the surface of the bed 106. In this example, the number of pixels of temperature data may depend on the number of pyrometers in the array.

[0053] The additive manufacturing system 320 may include a processor 322 to adjust the operation of the fan system 104 based on readings from the thermal sensor 324. Additionally, during operation, the processor 322 may serve to provide instructions to a number of other devices associated with the additive manufacturing system 320 and the additive manufacturing device 100 to accomplish the functionality of the additive manufacturing system 320.

Specifically, the processor 322 may direct a number of heat lamps Fig. 2, 216 to turn on, turn off, increase emitted electromagnetic radiation output, and/or decrease emitted electromagnetic radiation output. Additionally, the processor 322 may direct the build material deposition device to add a layer or an additional layer of build material Fig. 2, 212 onto the bed 106. Further, the processor 322 may send instructions to direct the printhead to selectively deposit the agent onto the surface of a layer of the build material Fig. 2, 212. The processor 322 may also direct the printhead to eject the agent at specific locations along the bed 106.

[0054] The processor 322 may include the hardware architecture to retrieve executable code from a data storage device and execute the executable code. The executable code may, when executed by the processor 322, because the processor 322 to implement at least the functionality of invoking a gas flow, detecting a temperature of the build material Fig. 2, 212, and adjusting the gas flow based on the detected temperature.

[0055] Fig. 4 is a flowchart of a method 400 for controlling an additive manufacturing device Fig. 1, 100 temperature condition, according to an example of the principles described herein. According to the method 400, a gas flow is invoked block 401 across a surface of build material Fig. 2, 212 in a bed Fig. 1, 106. Specifically, the gas flow is invoked block 401 simultaneously as a 3D printed object is being formed in a layer-wise fashion. That is, at the same time that a first heater Fig. 2, 208, a second heater Fig. 2, 210, a printhead, and a build layer deposition device are operating, the fan system Fig. 1, 104 is continually running to prevent both the unfused portions and fused portions of the build material from getting too hot, i.e., having temperatures too far above the fusing temperature, or too far above other desired temperatures. For example, prior to application of thermal energy via the second heater Fig. 2, 210, the gas flow may aid in maintaining both the unfused portions of the build material Fig. 2, 212 and the fused portions of the build material Fig. 2, 212 below the fusing temperature. During selective fusing by the second heater Fig. 2, 210, the gas flow may also aid in maintaining the unfused portions of the build material Fig. 2, 212 below the fusing temperature while allowing the fused portions to heat past the fusing temperature. Still further, after selective fusing of a layer, the gas flow may aid in returning the fused portions to a sub-fusing temperature, while reducing the temperature of the unfused portions even further so as to prevent caking.

[0056] Not only does the gas flow help to reduce the temperature of the surface of build material Fig. 2, 212, it does so more quickly than in the absence of such a fan system Fig. 1, 104. That is, after the second heater Fig. 2, 210 has applied thermal energy to the surface of the build material Fig. 2, 212 in the bed Fig. 1, 106, the gas flow more quickly removes heat energy from the surface, thus reducing any prolonged heat exposure, or residual heat exposure from the heaters Fig. 2, 208, 210. In other words, the gas flow increases the rate of heat conductions such that the unfused and fused portions of the build material Fig. 2, 212 cool down faster. This faster cooling down reduces the effects of prolonged heat exposure, i.e., caking and thermal transfer.

[0057] A thermal sensor Fig. 3, 324 then detects block 402 a temperature condition of the surface of the build material Fig. 2, 212 in the bed Fig. 1, and 106. Specifically, as mentioned above, the thermal sensor Fig. 3, 324 may detect at least one of a temperature of the surface of the build material Fig. 2, 212 and a rate of temperature decrease of the surface of the build material Fig. 2, 212 and may take such measurements over the whole of the surface or a portion of the surface. The thermal sensor Fig. 3, 324 may indicate the temperature values of different portions of the bed Fig. 1, 106. A processor Fig. 3, 322 then adjusts block 403 the gas flow across the surface based on the detected temperature condition of the surface.

[0058] A numeric example is given as follows. In this example, the first heater Fig. 2, 208 may maintain the surface of the build material Fig. 2, 212 in the bed Fig. 1, and 106 at a temperature below the fusing temperature. Given a polyamide 12 build material Fig. 2, 212, which has a fusing temperature of 185 degrees Celsius, the first heater Fig. 2, 208 may apply thermal energy to the surface of the build material Fig. 2, 212 to maintain the surface at a temperature of 165 degrees Celsius. As the second heater Fig. 2, 210 passes over the build material Fig. 2, 212 in the bed Fig. 1, 106, and fuses the fused portions of the build material Fig. 2, 212, the thermal sensor Fig. 3, 324 may detect that the surface of the unfused portions of the build material Fig. 2, 212 have a temperature of 172 degrees Celsius, which may be too close to the fusing temperature and may result in caking. Accordingly, the processor Fig. 3, 322 may increase the gas flow across the surface so as to increase the convective removal of heat and thus reduce the temperature of the surface of the build material Fig. 2, 212.

[0059] As another example, the thermal sensor Fig. 3, 324 may indicate that after a pass by the second heater Fig. 2, 210, the fused portions of the build material Fig. 2, 212 remain at too hot a temperature for too long a period, thus resulting in thermal transfer. Accordingly, the processor Fig. 3, 322 may increase the gas flow to more quickly reduce the temperature of the fused portions thus reducing the effects of thermal transfer.

[0060] Accordingly, by adjusting gas flow based on detected temperature conditions of the build material Fig. 2, 212, a closed-loop temperature control operation is performed for maintaining a desired temperature condition of the build material Fig. 2, 212 in the bed Fig. 1, 106, thus resulting in higher recyclability of unfused powder, a more simple cleaning process, and increased 3D printed object strength.

[0061] Fig. 5 is an isometric view of an additive manufacturing system 320 with a fan system Fig. 1, 104, according to an example of the principles described herein. As described above, the additive manufacturing system 320 includes a bed 106 to hold a volume of build material 212.

[0062] As described above, the additive manufacturing system 320 includes a build material deposition device 526. The build material deposition device 526 translates over the top of the surface of the build material 212 in the bed 106. The build material deposition device 526 passes across the surface of the bed 106 and deposits a layer of build material 212 into the bed 106. While Fig. 5 depicts the build material deposition device 526 as orthogonal to the carriage 214, the build material deposition device, in some examples, is coupled to the carriage 214.

[0063] Next, the carriage 214 passes over the bed 106 to allow a printhead within the carriage 214 to deposit an absorption agent on selected portions of the build material 212 that are to define a pattern of a slice of the 3D object. More specifically, the agent may tint portions of the build material 212 to a color that is more absorptive in relation to the heaters Fig. 208, 210 electromagnetic radiation, so as to enhance those portions ability to absorb thermal energy. All this time, a first heater Fig. 2, 208, which may be disposed behind a glass platen 530 maintains the temperature of the surface of the build material 212 at a predefined temperature, which temperature may be just below the fusing temperature of the build material 212. Maintaining the build material 212 at a temperature below the fusing temperature, but above room temperature reduces the amount of thermal energy applied by the second heater Fig. 2, 210 to raise the build material 212 temperature above the fusing temperature.

[0064] Coupled to the carriage 214 are at least one, and in some cases multiple, fusing lamps 528-1, 528-2. The fusing lamps 528 are examples of the second heater Fig. 2, 210 described above which may be heating lamps that emit an increased intensity of electromagnetic radiation as compared to the heating lamps Fig. 2, 216 of the first heater Fig. 2, 208. This higher intensity electromagnetic radiation fuses the fused portions while maintaining the unfused portions in a particulate form. That is, the increased absorption of the fused portions absorbs more heat energy from the fusing lamps 528-1, 528-2 so as to fuse together while, the unfused portions do not have sufficient absorption to absolve sufficient energy to surpass the fusing temperature. Accordingly, portions of the build material 212 are fused to form a slice of the 3D printed object, while other portions, i.e., negative space, is retained in powder form.

[0065] All the while, a fan system Fig. 1, 104 is invoking a gas flow across the build material 212 in the bed 106 so as to provide an additional heat transfer mechanism, i.e., convection, to remove heat from the surface of the build material 212. Such removal of heat allows for more quickly reducing the temperature of the unfused portions and the fused portions of the build material 212 so as to prevent the ill-effects of build material that is fused to heat for too long, i.e., caking and thermal transfer.

[0066] In some examples the fan system 104 includes a number of fans 532-1,532-2 that invoke a gas flow across the surface of the build material 212 in the bed 106. Different fans 532-1,532-2 may be disposed on either side of the bed 106 so as to provide gas flow in different directions. In some examples, gas flow may be invoked in one direction, for example from a first fan 532-1 towards a second fan 532-2. In another example, gas flow may be invoked in another direction, for example from the second fan 532-2 towards the first fan 532-1. In still further examples both fans 532-1, 532-2 may be initiated so as to invoke gas flow in both directions, i.e., the first fan 532-1 moves gas towards the second fan 532-2 and the second fan 532-2 moves gas towards the first fan 532-1.

[0067] In some examples, the fan system Fig. 1, 104 may move a coolant, for example, a coolant added to the gas flow, through the interior of the additive manufacturing system 320. Moving a coolant through the additive manufacturing system 320 further increases the convective heat transfer inside the additive manufacturing system 320.

[0068] Using such an additive manufacturing device 1 provides greater control over the temperature conditions within the additive manufacturing device; 2 increases the robustness, specifically the tensile strength, of 3D printed objects; 3 enhances the recyclability of unfused build material by reducing caking of unfused build material; 4 simplifies the post-printing operations, for example cleaning a 3D printed object, by reducing the effects of thermal transfer; 5 reduces cost of production as build material recyclability is increased and a time to clean parts is reduced; and 6 increases the repeatability and predictability of the additive manufacturing processes.

However, it is contemplated that the devices disclosed herein may provide useful in addressing other matters and deficiencies in a number of technical areas. Therefore the systems and methods disclosed herein should not be construed as addressing any of the particular matters.

[0069] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. An additive manufacturing device comprising: a bed to contain a volume of a build material; at least one heater to selectively fuse portions of the build material to form a portion of an object via the application of heat to the build material; and an air mover to invoke a gas flow across a surface of the build material in the bed during the selective fusing of the portions of the build material, the air mover to: provide predetermined convection conditions across the surface of the build material in the bed; and control a temperature condition across the surface of the build material in the bed.

2. The device of claim 1, wherein the air mover is adjustable to invoke different gas flows across the surface of the build material based on a temperature condition reading of the build material.

3. The device of claim 1, further comprising a thermal sensor to detect a temperature condition of the surface of the build material.

4. The device of claim 1, wherein the at least one heater and the air mover simultaneously selectively fuse build material and remove heat energy from the surface of the build material, respectively.

5. The device of claim 1, further comprising a printhead to increase an absorption rate of the portions of the build material, which portions of the build material are to form the portion of the object.

6. The device of claim 5, wherein the at least one heater comprises: a first heater to maintain the surface of the build material at a base temperature; and a second heater to apply thermal energy to the build material such that a temperature of the portions of the build material that are to form portions of the object, which portions of the build material have an increased absorption rate, is greater than a fusing temperature for the build material.

7. The device of claim 6, wherein the second heater applies thermal energy such that just a temperature of the portions of the build material with an increased absorption rate is greater than a fusing temperature for the build material.

8. The device of claim 6, wherein a printhead and the second heater alternate increasing the absorption rate of portions of the build material and applying heat to the build material such that the temperature of the portions of the build material with an increased absorption rate is greater than a fusing temperature in a layer-wise fashion.

9. The device of claim 6, wherein the base temperature is less than a fusing temperature for the build material.

10. An additive manufacturing system comprising: an additive manufacturing device comprising: a bed to hold a volume of build material; at least one heater to, in a layer-wise fashion, selectively fuse portions of the build material to form an object via the application of heat to the build material in the bed; and at least one air mover to invoke a gas flow across a surface of the build material in the bed during the application of heat to the build material; a thermal sensor to detect a temperature condition of various portions of the surface of the build material; and a processor to adjust the operation of the at least one fan based on a reading from the thermal sensor.

11. The system of claim 10, wherein: the at least one air mover comprises multiple fans; and each fan directs gas in opposite directions.

12. The system of claim 10, wherein the at least one fan directs a coolant over the surface of the build material.

13. A method for controlling an additive manufacturing device temperature condition, comprising: invoking a gas flow across a surface of build material in a bed to remove heat from the surface of the bed of build material during a selective fusing of portions of the build material; detecting, with a thermal sensor, a temperature condition of the surface of the build material in the bed; and adjusting the gas flow across the surface of the build material in the bed based on the temperature condition of the surface of the build material in the bed.

14. The method of claim 13, wherein the gas flow is continually invoked across the surface of the build material during a layer-wise selective fusing of the build material which layer-wise selective fusing generates a three-dimensional object.

15. The method of claim 13, wherein the gas flow returns the build material to a sub- fusing temperature.