Methods and devices for constructing compression chambers in powder-based additive manufacturing to relieve a built-up part from powder loading

Abstract

Method for producing an object (240) comprising: (a) providing a build platform (214) having at least one passage (220) each connected by a line (222) to a valve (224) which in turn is connected to a vacuum source (228) by a vacuum line (226); (b) closing each valve (224) prior to commencing a build operation, and filling the at least one passage (220) with powder (212) up to a top surface of the build platform (214); (c) irradiating a layer of powder (212) in a build region above the build platform (214) to form a fused region; (d) providing a subsequent layer of the powder over the build-up area; (e) repeating steps (c) and (d) until at least a portion of the object (240), at least one chamber (234) in a region enclosed by a wall (242, 244) of the object (240) and a conduit (232) in the build region are formed, wherein the chamber (234) encloses a region of unfused powder (212) and the conduit (232) extends from the passage (220) within the build platform (214) to the chamber (234); and (f) opening the respective valve (224) and removing unfused powder from within the chamber (234) by means of the vacuum generated by the vacuum source (228) via the line (232) and the passage (220), so that the chamber (234) can be compressed by the pressure of unfused powder outside the chamber (234) and within the area enclosed by the wall (242, 244) of the object (240).

Description

INTRODUCTION

[0001] The present disclosure relates generally to additive manufacturing (AM) methods that fuse powders in a process to build objects, as well as novel compression chambers to be used within this AM process. BACKGROUND

[0002] AM processes generally involve the buildup of one or more materials to create a net-shape or near-net-shape (NNS) object, as opposed to subtractive manufacturing processes. Although "additive manufacturing" is an industry-standard term (ASTM F2792), AM encompasses diverse manufacturing and prototyping techniques known by a variety of names, including freeform manufacturing, 3D printing, rapid prototyping / rapid tooling, etc. AM techniques are capable of producing complex components from a wide variety of materials. Generally, a freestanding object can be manufactured from a computer-aided design (CAD) model. One specific type of AM process uses an energy beam, e.g.an electron beam or electromagnetic radiation, such as a laser beam, to sinter or melt a powder material, creating a solid three-dimensional object in which particles of the powder material are bonded together. Different material systems, such as engineering plastics, thermoplastic elastomers, metals, and ceramics, are in use. Laser sintering or laser melting is a notable AM ​​process for the rapid production of functional prototypes and tools. Applications include the direct fabrication of complex workpieces, patterns for precision casting, metal molds for injection molding and die casting, and molds and cores for sand casting. The production of prototype objects to improve communication and testing of concepts during the design cycle are other common uses of AM processes.

[0003] Selective laser sintering, direct laser sintering, selective laser melting, and direct laser melting are common industry terms used to refer to the creation of three-dimensional (3D) objects by using a laser beam to sinter or melt a fine powder. For example, U.S. Patent No. 4,863,538 and U.S. Patent No. 5,460,758 describe conventional laser sintering techniques. More specifically, sintering involves the fusing (agglomeration) of powder particles at a temperature below the melting point of the powder material, whereas melting involves the complete melting of the powder particles to form a solid, homogeneous mass. The physical processes associated with laser sintering or laser melting include the transfer of heat to a powder material and then either the sintering or melting of the powder material.Although laser sintering and laser melting processes are applicable to a wide range of powder materials, the scientific and technical aspects of production progress, such as the sintering or melting rate and the effects of process parameters on microstructural developments during the layer fabrication process, are not well understood. This fabrication process involves multiple modes of heat, mass, and momentum transfer, as well as chemical reactions, making the process highly complex.

[0004] Fig. 1 is a schematic diagram showing a cross-sectional view of an exemplary conventional direct metal laser sintering (DMLS) or direct metal laser melting (DMLM) system 100. The apparatus 100 builds objects, e.g., part 122, in a layer-by-layer manner by sintering or melting a powder material (not shown) using an energy beam 136 generated by a source such as a laser 120. The powder to be melted by the energy beam is supplied by a supply 126 and evenly distributed across a build plate 114 using a scraper arm 116 to maintain the powder at a level 118 and remove excess powder material that extends above the powder level 118 to the waste container 128. The energy beam 136 sinters or melts a cross-sectional layer of the object to be built under the control of the galvano scanner 132.The build plate 114 is lowered, and another layer of powder is spread over the build plate and the object to be built, followed by the subsequent melting / sintering of the powder by the laser 120. This process is repeated until the part 122 is completely built from the melted / sintered powder material. The laser 120 can be controlled by a computer system having a processor and a memory. The computer system can determine a scan pattern for each layer and control the laser 120 to irradiate the powder material according to the scan pattern. After the fabrication of the part 122 is complete, various post-processing operations can be applied to the part 122. Post-processing operations include the removal of unfused powder, e.g., by blowing or suction. Other post-processing operations include a stress relief process.In addition, mechanical, thermal and chemical post-processing operations can be used to finish Part 122.

[0005] WO 2014 / 206573 A2 describes a method and a device for producing an object by selective laser melting. In addition to the object, a process control device is also produced, by means of which already finished areas of the object can be thermally and / or chemically influenced, so that the object can be heated or cooled in the produced area, for example. A pipe and / or a conduit, for example, can be produced as a process control device. A fluid can flow through the pipe for temperature control, or the object can be inductively heated via the conduit.

[0006] The method for producing an object according to US 2001 / 0045678 A1 involves moving the finished object to a station where any remaining, unbound powder is removed. For this purpose, the object is blown onto a fan and simultaneously moved in an oscillating motion on a support.

[0007] CN 102029389 A proposes producing an object layer by layer and activating a vacuum pump after each layer has been created. This creates a vacuum in a chamber located beneath a base plate to remove any powder residue present on the base plate.

[0008] EP 1 521 657 discloses a metallic workpiece consisting of a prefabricated lower part and an upper part arranged thereon using a metal powder sintering process. Both the prefabricated lower part and the upper part contain cooling passages that can be used to cool the workpiece during an injection molding process.

[0009] The present inventors have recognized that additive manufacturing techniques can be used to create objects, support structures, or combinations thereof that form enclosed spaces. The enclosed spaces can retain powder. As these objects cool, thermal contraction can cause the object to compress the stored powder. One possible effect is that the stored powder does not compress, and the cooling object may crack or develop structural weaknesses. Another possible effect is that the stored powder may become confined, making it more difficult to remove during post-processing operations.

[0010] In view of the above, it can be understood that there are problems, shortcomings, and disadvantages associated with AM techniques and that it would be desirable if improved methods and apparatus were available for managing thermal contraction during additive manufacturing. SUMMARY

[0011] The following presents a simplified summary of one or more aspects of the invention in order to provide a basic understanding of such aspects. The summary is not a comprehensive overview of all contemplated aspects and is not intended to identify key or critical elements of all aspects, nor to limit the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form, as an introduction to the more detailed description presented below.

[0012] In one aspect, the disclosure provides a method for manufacturing an object. The method includes the steps: (a) providing a build platform having at least one passage, each passage being connected by a line to a valve, which in turn is connected to a vacuum source by a vacuum line; (b) closing each valve prior to commencing a build operation, and filling the at least one passage with powder up to an upper surface of the build platform; (c) irradiating a layer of powder in a build region above the build platform to form a fused region; (d) providing a subsequent layer of the powder over the build-up area; (e) repeating steps (c) and (d) until at least a portion of the object, at least one chamber in a region enclosed by a wall of the object, and a conduit in the build region are formed, the chamber enclosing a region of unfused powder and the conduit extending from the passage within the build platform to the chamber; and (f) Opening the respective valve and removing unfused powder from within the chamber by means of the vacuum created by the vacuum source via the conduit and passageway so that the chamber can be compressed by the pressure of unfused powder outside the chamber and within the area enclosed by the wall of the object.

[0013] In any embodiment of the method, it may be advantageous that the method further comprises repeating steps (c) and (d) after step (f).

[0014] In any embodiment of the method, it may be advantageous for the chamber to be compressible.

[0015] In any embodiment of the method, it may be advantageous for step (f) to comprise opening a valve that retains the unfused powder within the passage.

[0016] In any embodiment of the method, it may be advantageous for step (f) to comprise sucking unfused powder from the passage.

[0017] In any embodiment of the method, it may be advantageous that by repeating steps (c) and (d) a rod having at least one conduit is formed, the rod extending from a nozzle within the passage, wherein step (f) comprises removing the rod extending within the conduit.

[0018] In any embodiment of the method, it may be advantageous for the object to have a wall enclosing a region of unfused powder within the object, and for the chamber to be located within the region of unfused powder.

[0019] In any embodiment of the method, it may be advantageous for step (f) to be carried out after the wall encloses the region of unfused powder within the object.

[0020] In any embodiment of the method, it may be advantageous for the object to have a horizontal ceiling connected to the wall and at least partially enclosing the region of unfused powder.

[0021] In any embodiment of the method, it may be advantageous for the at least one chamber to have a plurality of chambers formed at different heights.

[0022] In any embodiment of the method, it may be advantageous that step (f) comprises removing unfused powder from each chamber after a level of unfused powder exceeds the respective height of the chamber.

[0023] In any embodiment of the method, it may be advantageous that step (f) comprises removing unfused powder from each chamber after forming a horizontal wall above the chamber.

[0024] In any embodiment of the method, it may be advantageous for a first conduit connected to a first chamber of the plurality of chambers to be internal to a second conduit connected to a second chamber.

[0025] In any embodiment of the method, it may be advantageous for the first conduit to pass through the second chamber.

[0026] A device for producing an object from metal powder. The device includes a mounting unit having a power supply unit, a scraper arm, and an energy beam steering device. The device includes a base plate with a passage therethrough. The device includes a valve connected to the passage and configured to selectively open and close the passage.

[0027] In any embodiment of the device, it may be advantageous for the passage to be connected to unfused powder.

[0028] In any embodiment of the device, it may be advantageous for the device to further comprise a vacuum source connected to the passage.

[0029] In any embodiment of the device, it may be advantageous for the device to further comprise a rod extending through the passage to an upper surface of the mounting plate, the rod being retractable within the passage.

[0030] In any embodiment of the method, it may be advantageous for the build unit to be configured to selectively irradiate powder over the base plate to form a conduit in communication with the passageway and a chamber enclosing a region of unfused powder and in communication with the conduit.

[0031] In any embodiment of the apparatus, it may be advantageous for the valve to be arranged to open during operation of the build-up unit to allow the unfused powder to exit the chamber via the conduit and passage.

[0032] These and other aspects of the invention will be more fully understood after reviewing the detailed description that follows. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing an example of a conventional additive manufacturing apparatus. Fig. 2 is a schematic diagram showing an example of an apparatus having passages connected to compression chambers in accordance with aspects of the present invention. Fig. Figure 3 illustrates a plan view of the device of Fig. 2. Fig. 4 illustrates a first exemplary cross-sectional shape of a chamber. Fig. 5 illustrates a second exemplary cross-sectional shape of a chamber. Fig. 6 illustrates a third exemplary cross-sectional shape of a chamber. Fig. Figure 7 illustrates a fourth exemplary cross-sectional shape of a chamber. Fig. Figure 8 illustrates an example of compression chambers utilizing nested conduits in accordance with aspects of the present invention. Fig. Figure 9 illustrates an example of an apparatus including a rod for relieving pressure on constrained powder in accordance with aspects of the present invention. Fig. 10 illustrates the device of Fig. 9 with the rod retracted in accordance with aspects of the present invention. DETAILED DESCRIPTION

[0033] The detailed description set forth below, in conjunction with the accompanying drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. It will be apparent, however, to those skilled in the art that these concepts may be practiced without these specific details. In some examples, well-known components are shown in block diagram form to avoid obscuring such concepts.

[0034] Turning now to the figures, illustrate Fig. 2 and Fig. 3 shows an example of a device 200 having passages 220 connected to compression chambers 234. Fig. Figure 2 illustrates a vertical cross-section of the device 200. Fig. Figure 3 illustrates a horizontal cross-section of apparatus 200. Apparatus 200 is an additive manufacturing apparatus for forming an object from a metal powder. Apparatus 200 may be similar to conventional apparatus 100 in that apparatus 200 includes an energy beam emitter 204, a powder dispensing unit 218, a scraper arm 216, and an energy beam directing device 206. Energy beam emitter 204 may be, for example, a laser or an electron beam generator (e-beam generator). Energy beam directing device 206 may be a galvo scanner.

[0035] As illustrated, the apparatus 200 includes walls 202 that contain powder 212 above a base plate 214. In one aspect, the walls 202 may form a fixed powder container, and the base plate 214 may move within the powder container in a manner similar to the build platform 114. The powder dispensing unit 218 may be similar to the reservoir 126, and the scraper arm 216 may distribute the powder similar to the scraper arm 116. In another aspect, the walls 202 may be a dynamically constructed build envelope into which powder is dispensed by the powder dispensing unit 218 (e.g., a hopper) to bring the powder 212 to the level of the walls 202. The base plate 214 may be stationary and a build-up unit comprising the energy beam emitter 204, the powder dispensing unit, the scraper arm 216 and the energy beam steering device 206 may be moved upwardly when the object 240 is built.

[0036] The base plate 214 includes passages 220 for removing unfused powder during a build operation. The passages 220 are connected to respective valves 224, e.g., via lines 222. The valves 224 are also connected to a vacuum source 228, e.g., via vacuum lines 226. Before a build operation begins, the valves 224 are closed, and the passages 220 are filled with powder up to an upper surface of the base plate 214. Therefore, powder can be dispensed over a flat surface at the start of the build operation.

[0037] The object 240 is formed by selectively melting or sintering the powder 212 in a layer-by-layer manner. The object 240 includes a main portion having a wall 242 forming a substantially cylindrical shape with a varying diameter. The wall 242 encloses a portion of the powder at least in a horizontal plane. As the object 240 having the wall 242 cools, the wall 242 may contract, thereby compressing the enclosed portion of the powder radially inward. In some cases where the enclosed portion of the powder is incompressible, the stress on the wall 242 may cause cracking or other structural weaknesses in the object 240. The object 240 also includes an outer portion 248 formed between the wall 242, a wall 244, and a horizontal ceiling 246, which encloses a portion of the powder.As wall 242, wall 244, and ceiling 246 cool, the enclosed portion of the powder may be compressed both horizontally and vertically. Again, compressing incompressible powder may result in ripening or other structural weaknesses of outer portion 248.

[0038] Compression chambers 234 are formed by the apparatus in a similar manner to the object 240. Generally, the compression chambers 234 are thin-walled structures that enclose unfused powder. For example, the thin walls may have a minimum thickness possible by the apparatus 200 based on the beam width and / or support requirements. For example, the walls of the compression chambers 234 may be approximately 10-20 mm thick. Each compression chamber 234 is connected to a conduit 232, which in turn is connected to a passageway 220. The conduits 232 are formed by selectively fusing a cross-section (e.g., a circle) of powder around the passageway 220 into each layer above the base plate 214, down to the bottom of the compression chamber 234. The compression chamber 234 may expand outward from the conduit 232 to enclose a larger volume of powder.The powder enclosed by a compression chamber 234 is removed by opening the respective valve 224. Vacuum may also be applied by vacuum source 228. As the powder is removed, the compression chamber 234 may be compressed by the pressure of unfused powder outside the compression chamber 234 (which may be compressed by a thermally contracting wall 242, 244, or ceiling 246). Accordingly, the compression chambers 234 may be selectively emptied to reduce the pressure within the object 240.

[0039] As illustrated, the apparatus 200 includes four passageways 220 connected to respective compression chambers 234. The compression chambers 234 can be strategically arranged to release pressure at desired locations at desired times during a build operation. For example, three compression chambers 234 are arranged within the wall 242 at varying heights. The valves 224 connected to the compression chambers can be opened sequentially when the level of the powder 212 exceeds the height of the respective compression chamber and / or after the compression chamber 234 is complete. In another aspect, the opening of the valves 224 can be delayed until a horizontal ceiling is formed over the compression chamber 234 so that removal of the powder does not affect the top layer of the powder.

[0040] Fig. 4 illustrates a first exemplary cross-sectional shape 400 of a chamber 234. The shape 400 may be an oval. The oval shape may allow the chamber 234 to compress in a desired direction (e.g., the short axis of the oval) while maintaining another dimension (e.g., the long axis of the oval). Accordingly, the shape 400 may allow pressure to be released in a desired direction.

[0041] Fig. 5 illustrates a second exemplary cross-sectional shape 500 of a chamber 234. The shape 500 has three internal corners 510. As the internal powder is removed from the mold 500, external pressure can cause the mold 500 to fold at the internal corners 510, enabling a significant reduction in volume in multiple directions.

[0042] Fig. 6 illustrates a third exemplary cross-sectional shape 600 of a chamber 234. The shape 600 has four internal corners 610. As the internal powder is removed from the shape 600, external pressure can cause the shape 600 to fold at the internal corners 610, thereby enabling a significant reduction in volume in several directions.

[0043] Fig. 7 illustrates a fourth exemplary cross-sectional shape 700 of a chamber 234. The shape 700 includes a semicircular portion 710 and an angled portion 720. The shape 700 may be relatively resistant to compression. Accordingly, the shape 700 may provide gradual compression to maintain a total pressure below a threshold without creating a sudden pressure drop.

[0044] Fig. 8 illustrates an exemplary build environment 800 including an object 810 being built using the apparatus 200. For simplicity, the components of the apparatus 200 above the base plate 214 are not shown. The object 810 includes a lower portion 811 and an upper portion 820. The lower portion 811 has a wall 812 and a horizontal ceiling 814 forming an enclosed area 816. A compression chamber 832 is formed within the enclosed area 816 and is connected to the passageway 220 by a conduit 834. The upper portion 820 also has a wall 822 and a horizontal ceiling 824 forming an enclosed area 826. The horizontal ceiling 814 includes a passageway 828 connecting the enclosed area 816 and the enclosed area 826. A compression chamber 836 is formed within the enclosed area 826.A conduit 838 extends from the compression chamber 836 through the passage 828, the compression chamber 832, and the conduit 834 to the passage 220. That is, the conduit 838 is embedded within the conduit 834 to form two lumens that communicate with the compression chamber 832 and the compression chamber 836. The passage 220 includes an inner conduit 840. The inner conduit 840 extends through the passage 220 at a Y-connector 842. The inner conduit 840 and the passage 220 are connected to respective valves 224, which in turn are connected to the vacuum source 228 via the vacuum conduits 226.

[0045] In operation, when the object 820 is constructed vertically, the compression chamber 832 is complete first. After the horizontal ceiling 824 is formed and begins to cool, thermal contraction can increase the pressure in the enclosed region 816. The compression chamber 832 can be compressed by opening the appropriate valve 224 and evacuating the powder retained in the compression chamber 832. Because the horizontal ceiling 814 vertically closes off the region 816, the powder in the region 826 can be supported by the horizontal ceiling 814, even if removing the powder causes the powder in the region 816 to have a smaller volume than in the region 816. Because the line 838 is connected to a separate valve 224, the powder in the region 826 should not be affected. The compression chamber 836 can be emptied once the horizontal wall 824 is formed.

[0046] Fig. 9 illustrates an example of an apparatus 900 including a rod 910 for depressurizing compressed powder within a compression chamber 234. Because the compression chamber 234 is formed from molten or sintered metal powder, the compression chamber 234 may also be subject to thermal contraction. Although the compression chamber 234 is generally flexible due to its thin walls, thermal contraction may cause the retained powder to be compressed. Vacuum alone may be insufficient to remove the compressed powder from the compression chamber 234.

[0047] The device 900 may include a rod extending through the passageway 220. Initially, the rod may extend to the top surface of the base plate 214. The rod 910 may pass through the conduit 222 at a bend. During the build operation, the rod 910 may be extended by forming an extension 912 on top of the rod 910 and within the conduit 232. For example, in one layer, a solid circular cross-section of the extension 912 may be fused within an annular cross-section of the conduit 232. Similarly, the extension 912 may be formed to extend into the chamber 234.

[0048] To remove the unfused powder from the chamber 234, the rod 910 can be retracted as shown in Fig.10. The extension 912 is fused to the rod 910 and is also retracted. The compressed powder is released by retracting the extension 912. The valve 224 is then opened to remove the unfused powder within the compression chamber 234. The compression chamber 234 can then be compressed by the pressure of the external powder.

[0049] The written description uses examples to disclose the invention, including the preferred embodiment, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that will be apparent to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not depart from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.Aspects of the various described embodiments, as well as other known equivalents for each of these aspects, may be mixed and matched by one skilled in the art to construct additional embodiments and techniques consistent with the principles of this application.

Claims

[1] A method for producing an object (240) comprising: (a) providing a build platform (214) having at least one passage (220) each connected by a line (222) to a valve (224) which in turn is connected to a vacuum source (228) by a vacuum line (226); (b) closing each valve (224) prior to commencing a build operation, and filling the at least one passage (220) with powder (212) up to a top surface of the build platform (214); (c) irradiating a layer of powder (212) in a build region above the build platform (214) to form a fused region; (d) providing a subsequent layer of the powder over the build-up area; (e) repeating steps (c) and (d) until at least a portion of the object (240), at least one chamber (234) in a region enclosed by a wall (242, 244) of the object (240) and a conduit (232) in the build region are formed, wherein the chamber (234) encloses a region of unfused powder (212) and the conduit (232) extends from the passage (220) within the build platform (214) to the chamber (234); and (f) opening the respective valve (224) and removing unfused powder from within the chamber (234) by means of the vacuum generated by the vacuum source (228) via the line (232) and the passage (220), so that the chamber (234) can be compressed by the pressure of unfused powder outside the chamber (234) and within the area enclosed by the wall (242, 244) of the object (240). [2] The method of claim 1, further comprising repeating steps (c) and (d) after step (f) [3] A method according to claim 1 or 2, wherein the chamber is compressible. [4] A method according to any one of the preceding claims, wherein step (f) comprises opening a valve (224) that retains unfused powder within the passageway. [5] A method according to any one of the preceding claims, wherein step (f) comprises sucking unfused powder from the passage. [6] A method according to any one of the preceding claims, wherein repeating steps (c) and (d) forms a rod (912) within at least the conduit, the rod extending from a nozzle (910) within the passageway, wherein step (f) comprises removing the rod extending within the conduit. [7] A method according to any one of the preceding claims, wherein the object has a wall (242, 244) enclosing a region of unfused powder within the object and wherein the chamber is disposed within the region of unfused powder and / or wherein the object has a horizontal ceiling 814 connected to a wall at least partially enclosing the region of unfused powder. [8] A method according to claim 7, wherein step (f) is carried out after the wall encloses the region of unfused powder within the object and / or wherein step (f) comprises removing unfused powder from each of the chambers after a horizontal ceiling has been formed over the chamber. [9] A method according to any one of the preceding claims, wherein a first conduit connected to a first chamber is within a second conduit connected to a second chamber. [10] Device for producing an object from metal powder, comprising: a construction unit (200) comprising a powder dispensing unit (218), a scraper arm (216) and an energy beam steering device (206); a build-up platform (214) with at least one passage (220), each of which is connected by means of a line (222) to a valve (224), which in turn is connected to a vacuum source (228) by means of a vacuum line (226), wherein the device is adapted to carry out a method according to one of the preceding claims.

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