WO2022025903A1

WO2022025903A1 - Thermal regulation of a build of a 3d printing system

Info

Publication number: WO2022025903A1
Application number: PCT/US2020/044329
Authority: WO
Inventors: Arnau CODINA SABORIT; Gerard GARCIA TORRENTS
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2022-02-03

Abstract

A thermal regulation unit of a 3D printing system is described. The thermal regulation unit comprises a thermal chamber to receive a printed build from a build unit of the 3D printing system. A fluid channel is provided on a wall of the thermal chamber, and an inlet port and an outlet port are connectable to a fluid delivery system to carry a heat exchange fluid to and from the fluid channel. Also described is a fluid delivery system comprising a supply conduit and a return conduit connectable to a unit of the 3D printing system. The fluid delivery system further comprises a pump to circulate a heat exchange fluid through a fluid circuit that includes the supply conduit and the return conduit, a thermal device to heat or cool the heat exchange fluid, and a controller to control at least one of the pump and the thermal device. A thermal regulation system comprising the thermal regulation unit and the fluid delivery system is also described.

Description

THERMAL REGULATION OF A BUILD OF A 3D PRINTING SYSTEM

BACKGROUND

[0001] In some 3D printing systems, parts may be formed on a layer-by-layer basis through the selective solidification of a build material. The resulting build may be hot which may delay further processing of the build until it has cooled to a suitable temperature.

BRIEF DESCRIPTION OF THE DRAWINGS [0002] Figure 1 shows an example printing system;

[0003] Figure 2 shows an example thermal regulation system;

[0004] Figures 3(a) and 3(b) show examples of a fluid channel provided on a wall of a thermal regulation unit;

[0005] Figure 4 shows an alternative example in which multiple fluid channels are provided on a wall of the thermal regulation unit;

[0006] Figure 5 shows an example of different cooling rates that may be employed by the thermal regulation system; and

[0007] Figure 6 illustrates an example of post-processing of a printed build.

DETAILED DESCRIPTION

[0008] Parts formed by some 3D printing systems may be hot during their generation which may delay further processing of the build until it has cooled to a suitable temperature. For example, in 3D printing systems that employ powder bed fusion, successive layers of build material may be selectively solidified by applying thermal energy to cause portions of the powder bed to melt and fuse together. In selective laser sintering systems, a focused laser may be used to apply thermal energy to specific portions of the layer of build material to cause melting and fusing. In agent-based jetting systems, a fusing agent may be printed onto specific portions of the layer of build material and a non-focused heat source may apply thermal energy to the build material layer. Those portions of the build material on which the fusing agent is printed absorb sufficient energy to cause those portions to melt and fuse.

[0009] Figure 1 shows an example printing system 10 that comprises a printer 20, a build unit 30, a processing station 40, and a thermal regulation system 50. [0010] The build unit 30 comprises a build platform upon which a build is formed. In addition, the build unit 30 may store build material for use in forming the build. In one example, the build unit 30 may be maneuvered into the processing station 40 prior to printing, and the build unit 30 may be loaded with build material from the processing station 40. The build unit 30 may then be maneuvered into the printer 20 for printing.

[0011] In this particular example, the printer 30 employs agent-based jetting to form the build. During printing, a layer of build material is deposited on the build platform. A printhead of the printer 30 selectively applies a fusing agent to areas of the build material. The printhead may also apply a detailing agent to selected areas in order to reduce or prevent coalescence of build material that is not intended to be fused. A heat lamp, or other heat source, within the printer 20 applies thermal energy to the build material, causing those areas of the build material with the fusing agent to fuse. The build platform of the build unit 30 is then lowered, a new layer of powder is deposited, and the process is repeated. [0012] After the build is complete, the build unit 30 may be removed from the printer 20 and maneuvered to the processing station 40 for post-processing. Post-processing may involve cooling the build, after which the printed parts may be removed from the build and the non-fused build material may be recovered. [0013] Cooling may comprise leaving the printed build within the build unit 30 and allowing the build to cool naturally. Alternatively, as will now be described, the printed build may be transferred to the thermal regulation system 50.

[0014] Figure 2 shows an example thermal regulation system 50 that comprises a thermal regulation unit 60 and a fluid delivery system 70.

[0015] The thermal regulation unit 60 comprises a thermal chamber 61 into which a printed build 90 may be received. The thermal chamber is enclosed by four side walls 62, a bottom wall 63 and a top wall 64. The walls 62, 63, 64 may be formed of a metal or some other material having a relatively high thermal conductivity.

[0016] A fluid channel 65 is provided on each of the side walls 62. The fluid channel 65 may be serpentine in shape and may extend over a significant portion of the side wall 62. In one example, illustrated in Figure 3(a), the fluid channel 65 may be provided as a pipe or other conduit in thermal contact with the side wall 62. In another example, the fluid channel 65 may be embedded within the side wall 62 or may be formed in a surface of the side wall 62. In the example illustrated in Figure 3(b) the fluid channel 65 is formed in a surface of the side wall 62, which is then covered with a cover plate 66, perhaps with a seal or gasket (not shown) located between the two.

[0017] In the examples of Figures 3(a) and 3(b), a single fluid channel 65 is provided on each of the side walls 62. Additional fluid channels may, however, be provided. By way of example, Figure 4 illustrates an example in which three fluid channels 65, 65’, 65” are provided on each wall 62. The provision of additional fluid channels 65 may help achieve a more even temperature distribution across the wall 62.

[0018] The thermal regulation unit 60 further comprises an inlet port 68 and an outlet port 69 fluidly coupled to each of the fluid channels 65. In one example, the thermal regulation unit 60 may comprise an inlet manifold and an outlet manifold (not shown). The inlet manifold may comprise a single inlet coupled to the inlet port 68 and four outlets, each coupled to an inlet of a fluid channel 65. The output manifold may comprise four inlets, each coupled to an outlet of a fluid channel 65, and a single outlet coupled to the outlet port 69.

[0019] The thermal regulation unit 60 may be removably connected to the fluid delivery system 70. In particular, the inlet port 68 and the outlet port 69 may each be removably connectable to the fluid delivery system 70. Alternatively, the thermal regulation unit 60 may be connected to the fluid delivery system 70 in a manner that is not intended for removal.

[0020] The fluid delivery 70 system comprises a supply conduit 71, a return conduit 72, a pump 73, a thermal device 74, a temperature sensor 75 and a controller 80.

[0021] The supply conduit 71 is removably connectable to the inlet port 68 of the thermal regulation unit 60, and the return conduit 72 is removably connectable to the outlet port 69 of the regulation unit 60. When the two conduits 71, 72 are connected to the thermal regulation unit 60, a fluid circuit 76 is formed around which a heat exchange fluid may circulate. The fluid circuit 76 comprises each of the fluid channels 65 of the thermal regulation unit 60.

[0022] Although not shown, the fluid delivery system 70 may comprise a filling loop for admitting a heat exchange fluid into the fluid circuit 76. Additionally, the fluid delivery system 70 may comprise an expansion vessel to accommodate thermal expansion of the heat exchange fluid, and/or valves for controlling the flow of the heat exchange fluid within the fluid circuit 76.

[0023] The heat exchange fluid may comprise a liquid having a relatively high thermal heat capacity, such as water, coolant or oil.

[0024] The pump 73 circulates the heat exchange fluid around the fluid circuit 76. The pump 73 may operate at a single speed or flow rate. Alternatively, the speed and/or the flow rate of the pump 73 may be controllable.

[0025] The thermal device 74 heats and/or cools the heat exchange fluid within the fluid circuit 76. In one example, the thermal device 74 may comprise a reversible heat pump capable of both heating and cooling the heat exchange fluid. In another example, the thermal device 74 may comprise a heat exchanger to cool the heat exchange fluid or an electrical heating element to heat the heat exchange fluid. In a further example, the fluid delivery system 70 may comprise a thermal device 74 to cool the heat exchange fluid and a further thermal device (not shown) to heat the heat exchange fluid.

[0026] The temperature sensor 75 measures the temperature of the heat exchange fluid within the fluid circuit 76.

[0027] The controller 80 comprises a processor 81, a storage medium 82, an input/output interface 83, and a user interface 84. The processor 81 is responsible for controlling the operation of the thermal regulation system 50 and executes an instruction set 85 stored in the storage medium 82. Each of the pump 73, the thermal device 74 and temperature sensor 75 are connected to the controller 80 via the input/output interface 83.

[0028] The controller 80 monitors the temperature of the heat exchange fluid via the temperature sensor 75 and, in response, controls the pump 73 and/or the thermal device 74. For example, the controller 80 may control the speed of the pump 73 in order to vary the flow rate of the heat exchange fluid around the fluid circuit 76. Additionally or alternatively, the controller 80 may control the thermal energy output by the thermal device 74.

[0029] The controller 80 may control the pump 73 and/or the thermal device 74 so as to control the rate of cooling within the thermal chamber 61 of the thermal regulation unit 60. In particular, the controller 80 may control the pump 73 and/or thermal device 74 such that the temperature of the heat exchange fluid, and thus the temperature within the thermal chamber 61, over time has a particular profile.

[0030] Control over the rate of cooling may be achieved in a number of ways. In one example, the controller 80 may store a look-up table (e.g. in the storage medium 82) of different settings for the pump 73 and/or the thermal device 74 for different temperatures. The controller 80 then selects a setting(s) from the lookup table according to the measured temperature and uses the selected setting(s) to control the pump 73 and/or thermal device 74. The settings within the lookup table may then be defined such that a particular rate of cooling is achieved. In a further example, the controller 80 may employ a form of proportional-integration-derivative (PID) control, such as PI control. In this instance, the controller 80 may control the pump 73 and/or the thermal device 74 so as to minimize an error between the measured temperature and a setpoint. The controller 80 may then vary the setpoint with time such that a particular rate of cooling is achieved. These are just two examples of how the controller 80 might control the pump 73 and/or the thermal device 74 in order to control the rate of cooling. Other forms of feedback or closed-loop control might be equally be employed by the controller 80.

[0031] The controller 80 may control the pump 73 and/or the thermal device 74 according to a property of the printed build 90. For example, the controller 80 may control the pump 73 and/or thermal device 74 such that the rate of cooling depends on a property of the printed build 90. The property of the printed build 90 may include the size of the build 90 (and in particular the height of the build 90), the type of build material, the packing density of printed parts 91 within the build 90, and/or the starting temperature of the build 90. [0032] The property of the printed build 90 may be selected or input by a user using the user interface 84. Alternatively, the property of the printed build 90 may be determined without user involvement. For example, data relating to the build, such as build size, build material, packing density, starting temperature etc., may be stored on a storage device forming part of the thermal regulation unit 60 and may be transmitted to or read by the controller 80. In one example, the thermal regulation unit 60 may comprise an RFID tag that stores data relating to the printed build 90. The data may be written to the RFID tag by the processing station 40 when transferring the printed build 90 from the build unit 30 to the thermal regulation unit 60. The fluid delivery system 70 may then comprise an RFID reader, which reads the RFID tag and transmits the data relating to the printed build 90 to the controller 80.

[0033] In one example, the controller 80 may control the rate of cooling according to the type of build material of the printed build 90. The rate at which printed parts are cooled may influence part quality and dimensional accuracy. For example, for some build materials at least, excessively high cooling rates may induce undesirable internal stresses within the printed parts. Such stresses may cause the printed parts to deform, such as warp or curl. Excessively slow cooling rates, on the other hand, may degrade some of the mechanical properties of the printed parts and increase turnaround times.

[0034] By controlling the rate of cooling according to the type of build material, cooling may be optimized for different build materials. As a result, shorter turnaround times may be achieved without adversely affecting part quality, dimensional accuracy and/or mechanical properties.

[0035] A user may use the user interface 74 to select or input control parameters that are then used to define the rate of cooling. For example, a user may set the cooling period to 30 hours, and the controller 80 may control the rate of cooling such that, after 30 hours, the build 90 is at a temperature (e.g. 50°C) suitable for unpacking. In this way, a user is able to control the rate of cooling in order to schedule unpacking of the build 90.

[0036] Figure 5 illustrates an example of three cooling rates that may be employed by the thermal regulation system 50 when cooling a printed build 90 formed of a particular type of build material, such as polyamide PA12. The build 90 may be cooled to a temperature of 50°C (i.e. suitable for unpacking) over a period of 30 hours, 40 hours or 50 hours. As already noted, the rate at which the build 90 is cooled may influence part quality and dimensional accuracy. In this particular example, part quality and dimensional accuracy may be highest when the build 90 is cooled over 50 hours, and lowest when the build 90 is cooled over 30 hours. A user may be provided with the option of selecting one of the cooling rates. As a result, a user is able to select a rate of cooling according to need, i.e. dimensional accuracy vs turnaround time. In this particular example, the different rates of cooling may be presented to the user (e.g. on the user interface) as ‘Best (50 hours)’, ‘Normal (40 hours)’ and ‘Fast (30 hours)’.

[0037] By providing a thermal regulation system 50 as described above, the rate of cooling of a printed build 90 may be controlled so as to improve part quality and dimensional accuracy, improve the mechanical properties of the printed parts 91 , and/or decrease turnaround times. Different cooling rates may be employed according to a property of the build 90, such as build size, build material, packing density, starting temperature etc. As a result, shorter turnaround times may be achieved without adversely affecting part quality, dimensional accuracy and/or mechanical properties. Furthermore, a user may select or define the rate of cooling in order to balance part quality with turnaround time, or to schedule unpacking of the build.

[0038] For some types of build material, the build material surrounding the printed parts may begin to stick to the parts 91 when the temperature of the build 90 drops below a threshold. The thermal regulation system 50 may therefore initially cool and then maintain the temperature of the build 90 above this threshold. As a result, a user may have greater flexibility when scheduling the unpack of the build 90. This in turn may lead to greater flexibility when scheduling printing.

[0039] In examples described above, the controller 80 monitors the temperature of the heat exchange fluid and, in response, controls the pump 73 and/or the thermal device 74, e.g. in order to achieve a certain rate of cooling. As a result, the temperature within the thermal chamber 61 may be regulated using a relatively simple thermal regulation unit 60. In particular, the thermal regulation unit 60 may be devoid of any electronics. In an alternative example, the thermal regulation unit 60 may comprise a temperature sensor to measure a temperature within the thermal regulation unit 60. For example, the temperature sensor may measure a temperature within the thermal chamber 61. The temperature sensor of the thermal regulation unit 60 may be provided in addition to or as a substitute for the temperature sensor of the fluid delivery system 70. The temperature sensor may be provided as an RFID tag and the fluid delivery system may comprise an RFID reader, which reads the RFID tag and transmits the measured temperature to the controller 80.

[0040] Conceivably, the temperature sensor(s) may be omitted and the controller 80 may employ an open-loop scheme in order to control the pump 73 and/or the thermal device 74. For example, the controller 80 may store a look up table (e.g. in the storage medium 82) of different settings for the pump 73 and/or thermal device 74 for different time intervals. The controller 80 then selects a setting(s) from the lookup table according to the time elapsed and uses the selected setting(s) to control the pump 73 and/or the thermal device 74.

[0041] A fluid channel 65 is provided on each of the side walls 62 of the thermal chamber 61. As a result, a relatively uniform temperature distribution may be achieved within the thermal chamber 61. Conceivably, fluid channels may be employed on fewer or additional walls of the thermal chamber 61. For example, a fluid channel may be provided on the bottom wall 63 and/or the top wall 64 of the chamber 61. Flowever, by omitting fluid channels from these walls, the bottom and top walls 63, 64 may be more easily moved and/or removed during transfer and unpacking of the printed build 90.

[0042] With the thermal regulation system 50 described above, the printed build 90 may be transferred from the build unit 30 for cooling. As a result, the build unit 30 is available for reuse and printing may continue uninterrupted. Conceivably, the build unit 30, like that of the thermal regulation unit 60, may comprise fluid channels provided on walls of the build chamber, and inlet and outlet ports for connection to the fluid delivery system 70. The printed build 90 may then be cooled within the build unit 30 in the same or similar manner as that described above for the thermal regulation unit 60. Whilst this then ties up the build unit 30 during cooling, it may provide a more cost effective option for achieving controlled cooling.

[0043] Figure 6 illustrates an example of post-processing of a printed build. The thermal regulation unit 60 may be mountable to the build unit 30, and a wall of the thermal chamber 61 may be moveable to provide an opening through which the printed build 90 may be transferred from the build unit 30 to the thermal regulation unit 60. For example, after printing, the build unit 30 may be maneuvered to the processing station 40. The thermal regulation unit 60 may then be mounted on top of the build unit 30, and the bottom wall 63 of the thermal regulation unit 60 may be removed, e.g. by sliding the bottom wall 63 out from the thermal regulation unit 60. The build platform 31 of the build unit 30 may be then raised, so as to raise the printed build 90 into the thermal chamber 61 of the thermal regulation unit 60, as illustrated in Figure 6(a). Once the printed build 90 is received within the thermal chamber 61 , the bottom wall 63 of the thermal regulation unit 60 may be returned, e.g. by sliding the wall 63 between the printed build 90 and the build platform 31. Finally, the build platform 31 may be lowered and the thermal regulation unit 60 may be removed from the processing station 40 and connected to the fluid delivery system 70 for cooling, as illustrated in Figure 6(b).

[0044] When the printed build 90 is transferred from the build unit 30 to the thermal regulation unit 60, the outer surfaces of the build 90 may experience a sudden and sizeable drop in temperature. This may influence the part quality of printed parts located at or near the outer surfaces of the build 90. The thermal regulation unit 60 may therefore be preheated prior to transferring the printed build 90 in order to reduce this temperature difference.

[0045] After cooling the printed build 90, the thermal regulation unit 60 may be disconnected from the fluid delivery system 70 and the thermal regulation unit 60 may be returned to the processing station 40 for unpacking. Unpacking may comprise opening or removing the top wall 64 of the thermal regulation unit 60 to reveal the printed build 90. The printed parts 91 may then be removed from the build 90. A nozzle 41 attached to a vacuum source of the processing station 40 may be used to remove and recover unfused build material 92 from the build 90, as illustrated in Figure 6(c). Alternatively, unpacking may comprise removing the bottom wall 63 of the thermal regulation unit 60 and allowing the printed build 90 to fall onto a worksurface of the processing station 40. The printed parts 91 may then be separated from the unfused build material 92. Again, a nozzle 41 attached to a vacuum source of the processing station 40 may be used to remove and recover unfused build material 92 from the printed parts 91. Once removed from the build 90, the printed parts 91 may undergo further post-processing (e.g. bead and/or air blasting) in order to remove any remaining build material.

[0046] 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. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with any features of any other of the examples, or any combination of any other of the examples.

Claims

CLAIMS What is claimed is:

1. A thermal regulation unit of a 3D printing system, the thermal regulation unit comprising: a thermal chamber to receive a printed build from a build unit of the 3D printing system; a fluid channel provided on a wall of the thermal chamber; and an inlet port and an outlet port connectable to a fluid delivery system to carry a heat exchange fluid to and from the fluid channel.

2. A thermal regulation unit as claimed in claim 1, wherein the thermal regulation unit is mountable to the build unit, and a wall of the thermal chamber is moveable to provide an opening through which the printed build is received.

3. A thermal regulation unit as claimed in claim 2, wherein the thermal regulation unit is mountable to a top of the build unit, and a bottom wall of the thermal chamber is moveable to provide the opening.

4. A thermal regulation unit as claimed in claim 1, wherein the fluid channel is provided on a side wall of the thermal chamber.

5. A thermal regulation unit as claimed in claim 1, wherein the fluid channel is serpentine in shape.

6. A thermal regulation system of a 3D printing system, the thermal regulation system comprising: a thermal chamber to receive a printed build from a build unit of the 3D printing system; a fluid circuit comprising a fluid channel provided on a wall of the thermal chamber; a pump to circulate a heat exchange fluid around the fluid circuit; a thermal device to heat or cool the heat exchange fluid; and a controller to control at least one of the pump and the thermal device.

7. A thermal regulation system as claimed in claim 6, wherein the controller controls at least one of the pump and the thermal device according to a property of the printed build.

8. A thermal regulation system as claimed in claim 7, wherein the property comprises one of a size of the printed build, a type of build material of the printed build, a packing density of the printed build, and a starting temperature of the printed build.

9. A thermal regulation system as claimed in claim 7, wherein the controller controls at least one of the pump and the thermal device to control a rate of cooling within the thermal chamber.

10. A thermal regulation system as claimed in claim 9, wherein the controller controls at least one of the thermal device and the pump such that the rate of cooling depends on a property of the printed build.

11. A thermal regulation system as claimed in claim 6, wherein the thermal regulation system comprises a temperature sensor to measure a temperature of the heat exchange fluid or a temperature within the thermal regulation unit, and the controller controls at least one of the thermal device and the pump in response to the measured temperature.

12. A thermal regulation system as claimed in claim 6, wherein the controller controls at least one of the pump and the thermal device in response to a user input.

13. A thermal regulation system as claimed in claim 12, wherein the user input is a selection of one of a plurality of cooling rates.

14. A fluid delivery system of a 3D printing system, the fluid delivery system comprising: a supply conduit and a return conduit connectable to a unit of the 3D printing system; a pump to circulate a heat exchange fluid through a fluid circuit comprising the supply conduit and the return conduit; a thermal device to heat or cool the heat exchange fluid; and a controller, wherein the unit contains a printed build and the controller controls at least one of the pump and the thermal device according to a property of the printed build.

15. A fluid delivery system as claimed in claim 14, wherein the property comprises one of a size of the printed build, a type of build material of the printed build, a packing density of the printed build, and a starting temperature of the printed build.