System for rapid post-build powder removal for additive manufacturing using the powder bed fusion process

Abstract

A post-build powder evacuation system for a powder bed melting system (100) comprising the following: a construction platform (102) including: a work bed (112); a platform wall (302, 402) that interacts with the work bed (112) to define a powder chamber (116), wherein the platform wall (302, 402) has an inner surface (306, 406), an outer surface (308, 408) opposite the inner surface (306, 406), and at least one opening surface (309) extending from the inner surface (306, 406) to the outer surface (308, 408) to define at least one powder evacuation opening (310, 410) in fluid communication with the powder chamber (116); and a sealing system for the powder evacuation opening (310, 410) which can be actuated to selectively close and open the powder evacuation opening (310, 410); the sealing system for the powder evacuation opening (310, 410) includes: an outer sleeve (304, 404) which is slidably mounted on the platform wall (302, 402) such that either the platform wall (302, 402) or the outer sleeve (304, 404) is slidably displaceable in a first direction to close the at least one powder evacuation opening (310, 410) and is slidably displaceable in an opposite second direction to open the at least one powder evacuation opening (310, 410); wherein the outer sleeve (304, 404) comprises: an inner surface (312, 412), an outer surface (314, 414) opposite the inner surface (312, 412) and at least one opening surface (315, 415) defining at least one opening (316, 416) extending from the inner surface (312, 412) to the outer surface (314, 414) of the outer sleeve (304, 404), wherein the inner surface (312, 412) of the outer sleeve (304, 404) is in sliding contact with the outer surface (308, 408) of the platform wall (302, 402), and wherein the outer sleeve (304, 404) is displaceable in the first direction to seal the at least one powder evacuation opening (310, 410), thereby closing the at least one powder evacuation opening (310, 410), and in the second direction to align the at least one opening (316, 416) of the sleeve (304, 404) with the at least one powder evacuation opening (310, 410) of the platform wall (302, 402), thereby opening the at least one powder evacuation opening (310, 410).

Description

Technical area

[0001] The present disclosure relates to powder bed fusion additive manufacturing, and more particularly to a post-build powder removal system for powder bed fusion additive manufacturing. introduction

[0002] Additive manufacturing can create complex manufactured objects from a wide variety of materials. Similar to 3D printing, additive manufacturing typically adds material layer by layer to create a manufactured object, such as a prototype or a commercial automotive part. Such a manufactured object is also referred to as a 3-dimensional (3D) part or simply a part. Powder bed fusion is an additive manufacturing process used to create parts from metal, ceramic, polymer, and composite powder materials. Powder bed fusion is a process that induces the fusion of powder material particles by exposing selected powder material particles to one or more focused thermal energies, such as lasers, electron beams, and infrared energy.

[0003] The powder bed fusion process begins with the application of a layer of powder material to a surface of a moving build platform; the application of focused heat energy to the top layer of powder material in a two-dimensional pattern that defines a layer of the part (part layer), fusing the powder material into a solidified part layer; the application of another layer of powder material onto the solidified part layer; and the application of focused heat energy to the additional layer of powder material in a pattern that defines another part layer. The process repeats until the layer-by-layer build of the 3D part is complete. Each newly formed part layer is fused with the previously formed part layer during the process to form a solid layered structure. The fusing process can be accomplished by solid-state sintering and / or by melting and solidifying the powder material.

[0004] Typically, the build platform comprises a work bed with a work surface onto which the powder material layer is applied, and a platform wall that surrounds the work bed, defining a powder chamber for containing the powder material within the build platform. When part build is complete, a quantity of loose, unfused powder material remains on the finished 3D part and in the powder chamber. The remaining unfused powder material is typically removed by manually sweeping, vacuuming, and / or inverting the build platform. While manual sweeping and vacuuming serves the intended purpose, it is labor-intensive and time-consuming, especially for delicate 3D parts where care must be taken to avoid damaging the newly formed 3D part.

[0005] US 2002 / 0 090 410 A1 describes a removal device for removing unbound powder material remaining around a three-dimensional model which is a bound structure of the powder material.

[0006] US 2019 / 0 240 913 A1 describes a depowdering basket. The depowdering basket comprises a housing having at least one side wall and a bottom wall. The housing is configured such that the outer surfaces of the at least one side wall substantially adjoin the inner walls of the kit when the housing is arranged in a kit. The housing further comprises one or more openings arranged in the at least one side wall, each of the openings comprising a cavity extending through the at least one side wall from an inner surface of the side wall to an outer surface of the side wall. The housing can be configured to receive a build plate located within the housing. The outer edges of the build plate can cooperate with the inner surfaces of the side walls of the housing to prevent loose powder from becoming trapped between the outer edges of the build plate and the side walls.

[0007] WO 2020 / 081098 A1 describes a method for 3D printing that includes identifying a feature of an object in a model and automatically selecting a depowdering process for an object printed using the model based on the identified feature.

[0008] US 2017 / 0 120 536 A1 describes a three-dimensional printing apparatus equipped with one or more chutes for collecting excess separated particles. These chutes can be positioned to collect the excess separated particles into a particle receiving chamber of the chute. At the bottom of each chute is an evacuation chamber. A partition separates the evacuation chamber from the receiving chamber of the chute. The partition is selectively perforated to allow a desired amount of particles to flow from the receiving chamber into the evacuation chamber.The evacuation chamber is connected to a vacuum source to periodically or continuously draw ambient gas from a gas inlet into the evacuation chamber and / or from the receiving chamber through the perforations of the partition wall and then through the evacuation chamber to the vacuum source to entrain a quantity of the particles and to carry the entrained particles out of the evacuation chamber.

[0009] Therefore, it is an object of the invention to provide a system for removing unfused powder from the build platform after construction that is less labor- and time-intensive while minimizing potential damage to the newly built 3D part and potential hazards associated with loose powder material. Description of the invention

[0010] The invention is defined by the claims.

[0011] According to the invention, a post-production powder evacuation system for a powder bed melting system is disclosed. The post-production powder evacuation system includes a work bed, a platform wall having at least one powder evacuation port, and a removal port sealing system for selectively closing and opening the powder evacuation port. The platform wall cooperates with the work bed to define a powder chamber. The platform wall includes an inner surface, an outer surface opposite the inner surface, and at least one mating surface extending from the inner surface to the outer surface to define the at least one powder evacuation port in fluid communication with the powder chamber.The powder evacuation port sealing system includes an external sleeve slidably mounted on the outer surface of the platform wall such that the external sleeve is slidably displaceable in a first direction and closes the at least one powder evacuation port. The outer sleeve is also displaceable in an opposite second direction to open the at least one powder evacuation port. The outer sleeve includes an inner surface, an outer surface opposite the inner surface, and at least one opening surface defining an opening extending from the inner surface to the outer surface of the outer sleeve. The inner surface of the outer sleeve is in sliding contact with the outer surface of the platform wall.The outer sleeve is displaceable in the first direction such that a portion of the outer sleeve seals the at least one removal opening and thus closes the at least one removal opening, and in the second direction such that the at least one opening of the sleeve is aligned with the at least one powder evacuation opening of the platform wall and thus opens the at least one removal opening.

[0012] According to one embodiment, the platform wall and the outer sleeve extend along an axis. The outer sleeve is axially displaceable in the first direction along the axis and axially displaceable in an opposite second direction along the axis.

[0013] According to a further embodiment, the platform wall and the outer sleeve extend along an axis. The outer sleeve is rotatably displaceable about the axis in the first direction and rotatably displaceable about the axis in an opposite second direction.

[0014] In another aspect of the present disclosure, the post-build powder evacuation system includes at least one movable brush and a pressurized air source configured to selectively remove loose powder material from a part after build.

[0015] Further areas of applicability will become apparent from the description provided herein. It is to be understood that the description and specific examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. Brief description of the drawings

[0016] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. 1 is a diagram showing a cutaway side view of a powder bed melting system with a post-production powder removal system according to an exemplary embodiment; Fig. 2 is a block diagram illustrating a process for operating a powder bed fusion system of Fig. 1 according to an exemplary embodiment; Fig. 3 is an illustration of a mesh screen for the powder bed melting system of Fig. 1; Fig. Figure 4 is a perspective view of a portion of a platform wall with iris valves for the powder bed melting system of Fig. 1, according to an exemplary embodiment; Fig. 5 is a perspective view of a ball valve assembly for the powder bed melting system of Fig. 1, according to an exemplary embodiment; Fig. 6 is a perspective view of a powder evacuation valve for the powder bed melting system of Fig. 1, according to an exemplary embodiment; Fig. 7 is a perspective view of an alternative embodiment of a platform wall assembly with selectively closable powder extraction openings, according to an exemplary embodiment; Fig. 8A and Fig. 8B are perspective views of another embodiment of a platform wall assembly with selectively closable powder extraction openings according to an exemplary embodiment; and Fig. 9A and Fig. 9B are perspective views of another embodiment of a platform wall assembly with selectively closable powder extraction openings, according to an exemplary embodiment. Detailed description

[0017] The following description is merely exemplary and is not intended to limit the present disclosure, application, or uses. The illustrated embodiments are disclosed with reference to the drawings, wherein like numerals designate corresponding parts in the several drawings. The drawings are not necessarily to scale, and some features may be exaggerated or reduced to show details of particular features. The specific structural and functional details disclosed are not to be interpreted as limiting, but rather as a representative basis for showing one skilled in the art how to practice the disclosed concepts.

[0018] Fig. 1 shows a schematic representation of a powder bed melting system 100 including a build platform 102, a powder material dispenser 104 configured to dispense layers of powder material 106 into the build platform 102, and an energy source 108 configured to direct and guide focused thermal energy 110 through predetermined 2D patterns onto a topmost layer 111 of powder material 106 in the build platform 102. The powder material dispenser 104 is capable of adjusting the thicknesses of the various layers of powder material 106, as well as sorting and removing the powder material 106. Powder materials may include, but are not limited to, metal, ceramic, glass, polymer powder, other fusible materials capable of undergoing a thermally induced phase change from solid to liquid and back again, or combinations thereof.The energy source 108 may include, among others, lasers, electron beams, infrared energy, and microwave energy capable of melting, fusing, sintering, amalgamating, and / or otherwise chemically or physically modifying the dispensed powder material 106 to form a solid structural member 120.

[0019] The build platform 102 includes a workbed 112 and a platform wall 114 surrounding the workbed 112 to define a powder chamber 116, generally indicated by the reference numeral 116, for receiving the powder material 106 dispensed from the powder material dispenser 104. The build platform 102 further includes an actuator 118 engaged with the worktable 112 to selectively move the worktable 112 away from the focused energy source 108 at incremental intervals corresponding to the thickness of a layer of powder dispensed from the powder material dispenser 104, while the platform wall 114 remains in a fixed position.

[0020] The powder material dispenser 104 is selectively movable across the powder chamber 116 to dispense successive layers 111 of the powder material 106 into the powder chamber 116 and includes a recoating blade (not shown). For each layer of dispensed powder material 106, the recoating blade sweeps excess powder into an overflow opening (not shown), thereby forming a thin layer 111 of the powder material 106 of uniform thickness that is substantially flush with the top surface of the platform wall 114.

[0021] The powder bed melting system 100 also includes an inert gas source 122 configured to supply an inert gas atmosphere 124 to the working chamber 116 to reduce undesirable chemical interactions and mitigate the risk of fire or explosion, particularly with reactive metal powders. The inert gas is supplied to the working chamber 116 before and while the powder material 106 is dispensed into the powder chamber 116 by the powder material dispenser 104. The inert gas source 122 is further configured to supply an inert gas stream 128 to assist in evacuating the loose powder material 106 from the powder chamber 116 and to remove loose powder material 106 from the replicated part, which will be disclosed in more detail below.

[0022] The powder bed melting system 100 includes a system for removing unfused powder material 106, also referred to as loose powder material 106, from the powder chamber 116 after completion of part build. The post-build powder removal system includes a directional pressurized gas source 126, a movable brush 128, a plurality of powder evacuation ports 130 defined by the platform wall 114, a plurality of perforated screens 132 covering an inlet side of the powder evacuation ports 130, a plurality of powder evacuation fittings 134 engaging an opposite side of the powder evacuation ports 130, and valves 135 or other evacuation port sealing systems or devices for selectively closing and opening the powder evacuation ports 130. The powder evacuation ports 130 are in fluid communication with the powder chamber 116.The powder evacuation ports 130 are closed, also referred to as sealed, during part manufacture and are opened, also referred to as unsealed, after part manufacture to remove unfused powder materials.

[0023] The pressurized gas source 126 is configured to selectively direct short bursts or pulses of pressurized gas onto and around a newly built 3D part, also referred to as a post-build part, by blowing away small amounts of loose powder material 106 trapped in crevices of the post-build part. The pressurized gas source 126 can also function as an inert gas source 122 instead of having a separate inert gas source 122. The movable brush 128 is connected to a gantry system (not shown) to guide the movable brush 128 and remove loose powder material 106 from the post-build 3D part.

[0024] Fig. 2 is a flowchart 200 illustrating the process of Fig. 1. In step 202, the powder evacuation ports 130 are moved to the closed (sealed) position, an inert gas blanket is introduced into the powder chamber 116, and a layer of the powder material 106 is dispersed on the work bed 112 in the powder chamber 116 of the build platform 102. In step 204, the energy source 108 directs focused thermal energy 110 onto the topmost layer of the powder material 106 and guides the focused thermal energy 110 through a predetermined 2-dimensional (2-D) pattern. The focused thermal energy 110 fuses a portion of the powder material 106 defined by the 2-D pattern into a layer of a solid, three-dimensional (3-D) part being built.

[0025] In step 206, the work bed 112 is moved away from the heat source by a predetermined distance substantially equal to the thickness of the next layer of the 3D part to be created.

[0026] Another layer of powder material 106 is dispersed in powder chamber 116 on top of the previous layer. In step 208, the focused thermal energy 110 is directed onto the new layer of powder material 106 in another predetermined 2D pattern, forming another layer of the 3D part on top of the previously formed layer. Each newly formed 3D part layer is fused to the previously formed 3D part layer to form a solid 3D layered structure 120. The process of steps 202 through 208 is repeated until the layered buildup of the 3D part 120 is complete.

[0027] In step 210, after the construction of the 3D part is complete, also referred to as post-build, the powder evacuation ports 130 are moved to the open (unsealed) position. The pressurized gas source 126 directs a pressurized gas flow into one portion of the powder chamber 116, while a vacuum is applied to the open powder evacuation ports 130 at another portion of the powder chamber 116 opposite the first portion. Preferably, the pressurized gas flow is directed toward the workbed 112 in the general direction of the powder evacuation ports 130 and is targeted in short bursts at the part to be machined. The pressure difference between the powder chamber 116 and the vacuum, as well as the kinetic energy of the pressurized air flow, force the loose, unfused powder material 106 to evacuate the powder chamber 116 through the powder evacuation ports 130.The extracted unmelted powder can be collected in a suitable downstream filter or cyclone separator (not shown). Once the loose, unmelted powder material 106 is removed from the powder chamber 116 and the 3D part is exposed, the brush 128 moves in a predetermined pattern based on the part's geometry to remove loose powder materials from the surface of the 3D part.

[0028] Fig. 3 shows an exemplary perforated screen 132 disposed within the powder evacuation port 130, preferably upstream of the valves 135. The exemplary perforated screen 132 shown is a mesh-type screen, but it should not be interpreted as being limited to a mesh-type screen. The openings 133 defined by the perforated screen 132 are sufficiently large so that loose, unmelted powder material 106 can pass through the perforated openings 133, but the openings 133 are sufficiently small so that the replicated part and the molten powder material 106 cannot pass through.

[0029] In Fig. 4 is a perspective view of a part of the platform wall 114 from Fig. 1. The platform wall 114 contains a plurality of powder evacuation ports 130. An iris valve 135A, also referred to as an orifice valve 135A, is inserted into each of the powder evacuation ports 130 to selectively open and close the powder evacuation ports 130. The iris valve 135A can be selectively opened and closed by an electric or manual actuator (not shown).

[0030] In Fig. Figure 5 is a perspective view of an array of ball valves 135B for selectively opening and closing the powder evacuation ports 130. The ball valves 135B are aligned and rotatable about an axis A between a closed position and an open position. The ball valves 135B are inserted into a vertical column or horizontal row of corresponding powder evacuation ports 130 in the platform wall 114. A single valve stem 142 extends through the array of ball valves 135B along the axis A. A torque force can be manually or electronically applied to the valve shaft 142 to selectively open and close the ball valves 135B. The array of ball valves 135B can be used in conjunction with the iris valves 135A to finely control the evacuation of loose, unfused powder from the powder chamber 116.

[0031] Fig. Figure 6 shows a perspective view of a powder evacuation fitting 134 for engagement with the powder suction openings 130 of Fig. 1. The powder evacuation fitting 134 includes a first end 144, an opposite second end 146, and a passage 148 extending between the first end 144 and the second end 146. The first end 144 includes a coupling 150 with an elastomer compression seal 152 that can be inserted into the outlet side of the powder evacuation port 130. The second end is configured to be connected to a vacuum pump (not shown). The powder evacuation fitting 134 also includes an annular vibration motor 138 capable of generating vibrations that are transmitted through the powder evacuation opening 130 through the powder evacuation fitting 134 and the platform wall 114 to reduce the amount of unmelted powder material 106 that settles in the powder evacuation openings 130 and powder evacuation fittings 134.The vibrations facilitate the loosening of layers of powder material 106 that may have formed a packed powder cake during the build process, thereby reducing the time required to evacuate the powder material 106 from the powder chamber 116.

[0032] Fig. 7 is a perspective view of an exemplary embodiment of a platform wall assembly 250 configured to selectively open and close powder evacuation ports 274 without the need for valves. For clarity, the work bed 112 and other features of the powder bed melting system 100 are not shown. The platform wall assembly 250 includes a platform wall 252 and a seal plate 254 removable from one side of the platform wall 252. The platform wall 252 includes an inner surface 268, an opposing outer surface 270, and a plurality of opening surfaces 272 defining a plurality of removal ports 274 extending between the inner surface 268 and the outer surface 270.

[0033] The sealing plate 254 includes an inner plate surface 262 having a plurality of protruding sealing plugs 276 complementary in shape and size to the powder evacuation openings 274, such that the plurality of sealing plugs 276 can be inserted into the powder evacuation openings 274, thereby closing the powder evacuation openings 274 when the inner plate surface 262 of the sealing plate 254 is engaged with the outer surface 270 of the platform wall 252. Elastomeric seals 278 are provided on the sealing plugs 276 to ensure a seal between the sealing plugs 276 and the powder evacuation openings 274.While the sealing plugs 276 and the powder evacuation openings 274 are illustrated as circular, it should be understood that they are not intended to be so limited and may include any shapes that are complementary to each other to provide a sealed powder evacuation opening 274 when the sealing plate 254 is engaged with the platform wall 252.

[0034] Fig. 8A and Fig. 8B are perspective views of another exemplary embodiment of a platform wall assembly 300 configured to selectively open and close powder evacuation ports 310 without the need for valves. Platform wall assembly 300 includes a platform wall 302 and an outer sleeve 304, also referred to as an outer shell 304, which is slidable against platform wall 302 along axis B. As shown in Fig. 8B, the platform wall 302 includes an inner surface 306, an opposing outer surface 308, and a plurality of opening surfaces 309 defining a plurality of powder evacuation openings 310 extending between the inner surface 306 and the outer surface 308. The outer sleeve 304 includes an inner surface 312, an opposing outer surface 314, and a plurality of opening surfaces 315, also referred to as aperture surfaces 315, defining a plurality of openings 316, also referred to as apertures 316, extending between the inner surface 312 and the outer surface 314 of the outer sleeve 304.

[0035] Both in Fig. 8A as well as Fig. 8B, the outer sleeve 304 is slidably mounted on the platform wall 302 such that the inner surface 312 of the outer sleeve 304 is in direct sliding contact with the outer surface 308 of the platform wall 302. The openings 316 of the outer sleeve 304 correspond in position, shape, and size to those of the powder evacuation openings 310 of the platform wall. Referring to Fig. 8A, the outer sleeve 304, in a closed position, also referred to as the first position, blocks the powder evacuation openings 310 of the platform wall 302 when either the platform wall 302 or the outer sleeve 304 is displaced along the axis B in a first direction. One of the platform wall 302 and the outer sleeve 304 means either the platform wall 302 or the outer sleeve 304. Referring to Fig. 8B, in the open position, also referred to as the second position, the openings 316 of the outer sleeve 304 are in alignment with the powder evacuation openings 310 of the platform wall 302 when either the platform wall 302 or the sleeve 304 is translated along the axis-B in a second direction opposite to the first direction.

[0036] For example, the powder evacuation ports 310 are in a closed, sealed position when the outer sleeve 304 is pushed in an axial direction, as shown in Fig. 8A, and are in an open, unsealed position when the sleeve 304 is slid along the platform wall 302 in an opposite axial direction, as shown in Fig. 8B. It should be understood that while powder evacuation ports 310 and ports 316 are depicted as having round profiles, this is not to be construed as limiting. Powder evacuation ports 310 and ports 316 are sized to facilitate the evacuation of loose powder material 106 from powder chamber 116.

[0037] Fig. 9A and Fig. 9B are perspective views of another exemplary embodiment of a platform wall assembly 400 configured to selectively open and close powder evacuation ports 410 without the need for valves. The platform wall assembly 400 includes a cylindrical platform wall 402 and an outer cylindrical sleeve 404, or shell 404, rotatably slidable against the cylindrical platform wall 402 about axis C. The cylindrical platform wall 402 includes an inner surface 406, an opposing outer surface 408, and defines a plurality of axially elongated powder evacuation ports 410 extending between the inner surface 406 and the outer surface 408.The outer cylindrical sleeve 404 includes an inner surface 412, an opposite outer surface 414, and a plurality of slotted surfaces 415 defining a plurality of slotted openings 416 extending between the inner surface 412 and the outer surface 414.

[0038] Both in Fig. 9A as well as Fig. 9B, the outer sleeve 404 is slidably mounted on the platform wall 402 such that the inner surface 412 of the outer sleeve 404 is in direct sliding contact with the outer surface 408 of the platform wall 402 along the axis C. The elongated openings 416 of the sleeve 404 correspond in location, shape, and size to those of the powder evacuation openings 410 of the platform wall. Referring to Fig. 9A, the sleeve 404 in the closed position blocks the powder evacuation opening 410 of the platform wall 402 when either the platform wall 402 or the outer sleeve 404 is rotated about the axis-C in one direction.

[0039] The platform wall 402 or the outer sleeve 404 means either the platform wall 402 or the outer sleeve 404. Referring to Fig. 9B, the slotted openings 416 of the sleeve 404 are aligned with the powder evacuation opening 410 of the platform wall 402 in the open position when either the platform wall 402 or the outer sleeve 404 is rotated about the axis-C in the opposite direction.

[0040] For example, the powder evacuation ports 410 are closed when the outer sleeve 404 is rotated in an axial direction, as shown in Fig. 9A, and they are opened when the outer sleeve 404 is rotated in an opposite axial direction, as shown in Fig.9B. It should be understood that while the powder evacuation ports 410 and ports 416 are depicted with an elongated slot profile, this is not intended to be limiting. The powder evacuation ports 410 and ports 416 are sized to facilitate the evacuation of unmelted powder material 106 from the powder chamber 116.

[0041] The post-build loose powder removal system described above quickly removes excess loose powder material 106 once construction is complete. The platform wall has powder evacuation ports to allow excess loose powder to freely drain from the powder chamber 116. The powder evacuation ports are closed during the build process to seal the powder chamber 116 area and are opened after the build process to remove excess loose powder.

Claims

[1] A post-build powder evacuation system for a powder bed melting system (100), comprising: a building platform (102) including: a work bed (112); a platform wall (302, 402) cooperating with the work bed (112) to define a powder chamber (116), the platform wall (302, 402) having an inner surface (306, 406), an outer surface (308, 408) opposite the inner surface (306, 406), and at least one opening surface (309) extending from the inner surface (306, 406) to the outer surface (308, 408) to define at least one powder evacuation opening (310, 410) in fluid communication with the powder chamber (116); and a powder evacuation port sealing system (310, 410) operable to selectively close and open the powder evacuation port (310, 410); wherein the sealing system for the powder evacuation opening (310, 410) comprises: an outer sleeve (304, 404) slidably mounted on the platform wall (302, 402) such that either the platform wall (302, 402) or the outer sleeve (304, 404) is slidably displaceable in a first direction to close the at least one powder evacuation opening (310, 410) and is slidably displaceable in an opposite second direction to open the at least one powder evacuation opening (310, 410); wherein the outer sleeve (304, 404) comprises: an inner surface (312, 412), an outer surface (314, 414) opposite the inner surface (312, 412) and at least one opening surface (315, 415) defining at least one opening (316, 416) extending from the inner surface (312, 412) to the outer surface (314, 414) of the outer sleeve (304, 404), wherein the inner surface (312, 412) of the outer sleeve (304, 404) is in sliding contact with the outer surface (308, 408) of the platform wall (302, 402), and wherein the outer sleeve (304, 404) is displaceable in the first direction to seal the at least one powder evacuation opening (310, 410), thereby closing the at least one powder evacuation opening (310, 410), and in the second direction to align the at least one opening (316, 416) of the sleeve (304, 404) with the at least one powder evacuation opening (310, 410) of the platform wall (302, 402), thereby opening the at least one powder evacuation opening (310, 410). [2] A post-build powder evacuation system according to claim 1, wherein: the platform wall (302) and the outer sleeve (304) extend along an axis (B); and the outer sleeve (304) is axially displaceable in the first direction along the axis (B) and is axially displaceable in the second direction opposite to the first direction along the axis (B). [3] A post-build powder evacuation system according to claim 1, wherein: the platform wall (402) and the outer sleeve (404) extend along an axis (C); and the outer sleeve (404) is rotatably displaceable about the axis (C) in the first direction and is rotatably displaceable about the axis (C) in the second direction opposite to the first direction. [4] A post-build powder evacuation system according to any preceding claim, further comprising at least one movable brush (128) and a pressurized gas source (126) for selectively removing unfused powder material (106) from a post-build part.

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