Methods and arrangements for a build tank

Abstract

The present invention relates to additive manufacturing arrangements for additive manufacturing by selective fusion of layers of a three-dimensional product from a powder bed (240) comprising successively formed powder layers. An energy beam emitter (210) is configured to deliver an energy beam (220) towards a top surface (242) of the powder bed (240). A build chamber (280) is arranged to maintain vacuum and high temperature conditions, wherein a build temperature in a top surface (242) of the powder bed (240) is at least 500oC. A movable part (285) is arranged in a build compartment (270) and is arranged to be lowered between build compartment walls (287) of the build compartment (270) to allow successively formed powder layers. A sealing member (286) is arranged to provide a sealing between said movable part (285) and the build compartment walls (287) to prevent leakage of powder particles from said powder bed (240) and the sealing member (286) is arranged in a sealing region (288), wherein the functionality of the sealing member (286) is adapted to the locally lower temperature and to seal against leakage of a minimum size of the powder particles.

Description

[0001] METHODS AND ARRANGEMENTS FOR A BUILD TANK TECHNICAL FIELD

[0002] The present disclosure relates generally to arrangements and methods for additive manufacturing for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion.

[0003] BACKGROUND

[0004] Presently available powder bed additive manufacturing machines normally have a movable table for lowering the consecutively built three-dimensional object inside a build compartment during the manufacturing process. To prevent leakage of powder, a compressible sealing material, such as an elastomer, a textile felt or braided rope, is usually applied between the movable table and the build compartment surrounding the powder and three-dimensional object. However, a common problem is powder leakage due to a defective seal or that the seal is not suitable in design or material to sufficiently prevent leakage of powder. This could for example be due to a challenging environment in the machine such as friction, heat, vacuum, radiation, etc. causing the seal material to degrade and lose its sealing properties. The ability for the seal to avoid powder leakage is also dependant of the powder size, material composition and morphology. For instance, a powder consisting of smaller powder particles is typically more challenging to seal than coarser powder, because smaller particles can pass through smaller gaps. Also, spherical powder is usually more susceptible to powder leakage than non-spherical powder due to the higher intrinsic flowability of spherical powder. An additional problem is that the powder and three-dimensional object could be contaminated by debris released from the degraded seal. Such contamination could degrade the material properties of the three-dimensional object, and it could also make it impossible to reuse excess powder from the build compartment.

[0005] Hence, the above-mentioned problems are even more pronounced and difficult to handle in Electron Beam Powder Bed Fusion (E-PBF) build tanks with a movable bottom which is sealed to prevent leakage of powder. In E-PBF machines on the market today, where the build tank is enclosed inside a vacuum chamber and well insulated by vacuum, the build tank is allowed to become very hot. In case of a tungsten E-PBF process, for example, the tungsten parts being built may have a temperature above 1200 °C throughout the process. The powder bed surrounding the part continuously conducts heat to the build tank, which may reach temperatures as high as 700 °C.

[0006] Due to these very high temperatures, it is not possible to use the established elastomer or polymer sealing materials that are commonly used for various purposes in high vacuum systems, for example fluorocarbon rubber (also known as FKM, FPM and Viton®).

[0007] Fluorocarbon rubber is known for its good vacuum compatibility, but its maximum service temperature is about 200 °C only. It should also be pointed out that the maximum service temperature of an elastomer usually refers to a static condition. The seal in an E-PBF build tank is also subjected to friction as the seal is sliding against the inner walls of the build tank. This friction may damage the elastomer even at temperatures below the maximum service temperature.

[0008] For these reasons, elastomer seals are normally not used in E-PBF build tanks. Instead, the standard seal material for the build tank in E-PBF is a heat-resistant rope seal, braided seal or band seal made of fibrous material, such as glass fibre, ceramic fibre or metallic fibre. There are fibrous materials that can withstand temperatures as high as 1200 °C under static conditions. Common vacuum-compatible elastomers and polymers which can be used for sealing solutions at low temperature, such as Nitrile®, Viton®, Kalrez®, Teflon®, silicone, etc., cannot withstand the high temperature of the E-PBF build tank in existing E-PBF machine designs.

[0009] A drawback of fibrous materials such as the rope seal is that they easily release dust or fibres that contaminate the metal powder. Fibrous materials can also outgas volatile contaminants into the vacuum, because they are composed of thin fibres with a large specific surface area absorbing moisture and contaminants. The rate of outgassing is dependent on the temperature of the fibrous material and for high temperatures the outgassing can sometimes be so high that a low enough vacuum pressure to facilitate the E-PBF process cannot be sustained. Fibrous materials can also degrade and start leaking powder at the extreme temperatures used particularly in a tungsten E-PBF process or when processing other high temperature materials such as other refractories than tungsten, nickel-based superalloys, Intermetallics, or other high temperature alloys. Fibrous materials are not elastic and can start leaking as the sealing gap grows bigger due to thermal expansion at very high temperatures. A seal made of fibrous material must usually be clamped quite hard, creating a high friction against the build tank walls. This friction also contributes to the degradation of the fibrous material and the release of unwanted debris into the metal powder. Sealing by fibrous materials in E-PBF is not an ideal solution, but it has still been used for E-PBF for many years. In demanding cases, the seal needs to be replaced frequently because of wear and degradation.

[0010] Hence, there is still a need in the art for improved solutions for sealing build tanks to maintain a long lifetime of the seal, to prevent leakage of powder from the build tank, to prevent outgassing from the sealing material, and to prevent debris being released into the powder feedstock.

[0011] SUMMARY

[0012] The above-described problems are addressed by the claimed additive manufacturing arrangement for successively forming layers of a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion.

[0013] Initially, it should be noted that the words “seal” and “sealing” in the context of the present invention refer to an arrangement positioned in a gap between two solid bodies, preventing powder particles from passing through. Thus, a seal does not necessarily need to be hermetic.

[0014] The present invention is based on providing a functionality of a sealing member that is adapted to a locally lower temperature and to seal against leakage of a minimum size of the powder particles by improved self-sealing. This can be achieved by providing a locally significantly lower temperature in a sealing region compared to the build temperature, in embodiments 100 - 800°C lower, which enables the use of previously unthinkable sealing materials such as elastomer or polymer sealing materials that are robust and have a functionality that can be correlated to the minimum size of the powder particles providing a self-sealing effect. The sealing region is the region where a sealing member is arranged to seal between the build compartment walls and the movable part with a table where the product is built. Thus, the functionality of the sealing member is correlated to the minimum size of the powder particles to be used. It is understood that a seal that works properly for coarse powder particles may cause leakage for finer powder particles. By designing or arranging the build compartment with a local temperature in a sealing region between the movable part and the build compartment walls lower than the build temperature at the top surface of the powder bed, a sealing material with a lower maximum service temperature can be used. Further, by locally lowering the temperature, the sealing member can be made more robust. This in combination with the predetermined minimum size of the powder particles - in embodiments of the present invention the sealing member is arranged to seal against leakage of powder particle sizes down to 10 pm, or down to 5 pm - achieves efficient leakage prevention between the sealing member and build compartment walls since the coarser particles will fill the micro-gaps between the sealing member and build compartment walls and thereby providing an improved self-sealing effect. Hence, it is possible to use coarser and more durable polymer sealing members without increasing the risk for leakage. This also reduces the risk for abrasion particles caused by abrasion of the sealing member which is common when using conventional sealing members where fibrous materials such as rope seals easily release dust or fibres that contaminate the metal powder. Fibrous materials can also outgas volatile contaminants into the vacuum, because they are composed of thin fibres with a large specific surface area absorbing moisture and contaminants. Conventional sealing members also needs to be replaced frequently because of wear and degradation. Consequently, the present invention reduces or removes the risk for contamination of the powder caused by abrasion and wear and tear of the sealing member, which in turn entails a higher quality of the manufactured product. Furthermore, the need for maintenance and service is reduced since the seal member according to the present invention can be made more robust and durable.

[0015] Accordingly, there is provided an additive manufacturing apparatus for additive manufacturing by selective fusion of layers of a three-dimensional product from a powder bed comprising successively formed powder layers. The apparatus comprises a build chamber arranged to maintain vacuum and high temperature conditions. A build compartment is arranged in communication with the build chamber, sharing the same vacuum environment. The build compartment comprises a movable part and build compartment walls. The movable part is arranged to be lowered between the build compartment walls to allow successively formed powder layers. A build temperature at a top surface of the powder bed is at least 500°C. An energy beam emitter is configured to deliver an energy beam towards the top surface of the powder bed, wherein the energy beam is used in the selective fusion of the three-dimensional product. A sealing member is arranged to provide a sealing between the movable part and the build compartment walls to prevent leakage of powder particles from the powder bed. The sealing member is arranged with functionality correlated to the minimum size of the powder particles and adapted to to seal against leakage of minimum size of powder particle sizes, wherein the minimum size of powder particles is down to 5 pm, or down to 10 pm. In embodiments, the movable part and / or the build compartment walls are arranged to provide a local temperature in a sealing region that is lower than the build temperature at the top of the powder bed. The present invention is based on the insight of the inventor that it is possible to design or arrange the build compartment with a local temperature in a sealing region between the movable part and the build compartment walls that is lower than the build temperature at the top surface of the powder bed to enable use a sealing material with a functionality adapted to coarse powder particles, a lower maximum service temperature and higher robustness. Hence, the lower maximum service temperature and higher robustness in combination with the predetermined minimum size of the powder particles - according to embodiments of the present invention the sealing member is arranged to seal against leakage of powder particle sizes down to 10 pm, or down to 5 pm - achieves efficient leakage prevention between the sealing member and build compartment walls since the coarser particles will fill the microgaps between the sealing member and build compartment walls and thereby providing an improved self-sealing effect. Accordingly, the functionality of the sealing member is adapted to the locally lower temperature and to seal against leakage of a minimum size of the powder particles.

[0016] Hence, the local temperature in a sealing region can be significantly lower than the build temperature of at least 500°C. In embodiments, sealing materials having a maximum service temperature of up to 350 °C or up to 300 °C, or up to 250 °C, or up to 200 °C, or up to 150 °C, or up to 100 °C, are used. There are multiple benefits arising from this invention such as improved sealing against powder leakage, a longer lifetime of the sealing member, reduced and lower risk of contamination caused by fibre loss or debris from the sealing, lower risk of outgassing, lower friction when the build tank is moved up or down, lower cost, easier to fabricate as closed-loops (O-rings, X-rings and other closed-loop seals), in contrast to fibrous materials such as rope seal that is usually cut in a long piece from a spool and wound around the sealing region with some overlap. The present invention opens up for low-temperature sealing materials due to the locally reduced or lowered temperature in an area of the sealing member.

[0017] Accordingly, by locally reducing the temperature in an area at the sealing member, it is possible to use a large variety of vacuum-compatible sealing materials that cannot withstand the build temperature of at least 500 °C. This locally reduced temperature in the sealing region can be achieved by, for example, active cooling systems or passive cooling, for example, in the build compartment walls and / or the movable part.

[0018] According to embodiments of the present invention, there is provided an additive manufacturing arrangement where the sealing member is made of at least one material from the group comprising sealing materials suitable for vacuum applications, known under different denominations, acronyms and brands and classified as elastomers or polymers, such as butyl rubber, chloroprene rubber, ethylene propylene rubber, nitrile rubber, nitrile butadiene rubber, polyurethane rubber, fluoro rubber, fluorocarbon rubber, silicone rubber, fluorosilicone rubber, neoprene, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyetheretherketone, CR, NBR, FKM, FPM, MQ, PMQ, VMQ, PVMQ, FVMQ, PTFE, FFKM, FFPM, SCVBR, EPDM, PCTFE, PTFCE, PEEK, Buna-N, Viton, Fluorel, Teflon, Kalrez, Chemraz, Perlast, Kel-F, Neoflon, Markez, Kapton, Vespel, Torlon, and Delrin.

[0019] In embodiments of the present invention, the sealing member comprises one part, which may be made from any one of the above-mentioned materials.

[0020] According to embodiments of the present invention, there is provided an additive manufacturing arrangement where the locally lower temperature in the sealing region is up to 350 °C or up to 300 °C, or up to 250 °C, or up to 200 °C, or up to 150 °C, or up to 100 °C.

[0021] In embodiments of the present invention, the sealing member comprises at least two parts with different materials. The at least two parts can be either separate parts or parts physically joined together, for example, an outer part can be arranged contacting the movable part and the build compartment walls and enclosing an inner core of a different material, or an inner part arranged to contact with and seal against the movable part and an outer part arranged to contact with and seal against the build compartment walls. By using an outer part contacting the build compartment walls and an inner part contacting the movable part, it is possible to design the sealing member with an outer part having a different maximum service temperature and an inner part with higher resilient or spring-like properties. Moreover, it is further possible to design a sealing member with for example three parts: an inner part arranged to contact with and seal against the movable part and an outer part arranged to contact with and seal against the build compartment walls, and a middle part in-between the outer and inner parts to provide an improved adhesion between the inner and outer part. It is also possible to design the sealing member with an outer part with a low friction coefficient to enable improved gliding or sliding conditions against the build compartment walls, a middle part having a higher maximum service temperature and an inner part with higher resilient or spring-like properties.

[0022] According to embodiments of the present invention, the outer part is made of a first material capable of withstanding a temperature up to 250 - 300 °C and the inner part is made of a second material capable of withstanding a temperature up to 150 - 200 °C In embodiments, the inner part is made of the elastomer FKM / Viton® and the outer part is made of the polymer PTFE / Teflon® .

[0023] In embodiments of the present invention, the sealing member comprises a part with a core made of one material and a surface coating made of another material. For example, the core can be Viton® to provide the elastic properties and the coating can be Teflon® to provide a low-friction surface of the sealing member.

[0024] According to embodiments of the present invention, the movable part and / or build compartment walls is / are arranged with passive and / or active cooling. For example, the movable part and / or build compartment walls is made of a material with high thermal conductivity, in embodiments at least 150 W / mK, or 250 W / mK. A suitable material that provides high thermal conductivity is for example copper. A heat exchanging device may be arranged in contact with the movable part and / or the build compartment walls and wherein heat is conducted by the movable part and / or build compartment walls to the heat exchanging device.

[0025] In further embodiments of the present invention, a cooling system is arranged in the movable part and / or build compartment walls, wherein the cooling arrangement comprises fluid channels for circulating cooling fluids in the build compartment walls. Further, the cooling system may include heat exchange geometries, a heat sink, or a cooling fin structure provided on the outer wall surface capable of cooling by means of an air flow over the heat exchange geometries.

[0026] According to embodiments of the present invention, an inner surface of the build compartment walls is provided with a coating with a low friction coefficient made of, for example, PTFE / Teflon®.

[0027] The scope of the invention is defined by the claims which are incorporated into this section by reference. A more complete understanding of embodiments of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by consideration of the following detailed description of one or more embodiments.

[0028] Reference will be made to the appended sheets of drawings that will first be described briefly. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Fig. 1 schematically shows an arrangement for electron beam powder bed fusion in which the present invention can be implemented.

[0030] Fig. 2 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments.

[0031] Fig. 3 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments.

[0032] Fig. 4 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments.

[0033] Fig. 5 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments.

[0034] Fig. 6 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments.

[0035] Fig. 7 schematically illustrates parts of an additive manufacturing arrangement for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion in a cross-sectional view, in accordance with one or more embodiments. Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

[0036] DETAILED DESCRIPTION

[0037] Additive manufacturing and 3D-printing refer to the process of manufacturing objects from 3D model data by joining feedstock material, for example such as a powder, layer upon layer. Powder bed fusion means additive manufacturing or 3D-printing where objects are built up in a powder bed. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. The powder bed is preferably lowered one nominal layer thickness (e.g. 0,02-0,1 mm) before distribution of the next powder layer. The energy source can be, for example, a laser or an electron gun. Upon finishing a powder bed fusion process, the built object will be embedded in powder. The powder is removed after completion of the build.

[0038] The present disclosure relates generally to arrangements and methods for additive manufacturing for successively forming a three-dimensional product from a powder bed comprising at least one powder layer by means of powder bed fusion. Embodiments of the disclosed solution are presented in more detail in connection with the figures. It should be appreciated that like reference numerals are used to identify like elements illustrated in the figures and thereby will not be described again.

[0039] To facilitate the understanding of this invention, the term “build temperature” will be defined below. "Build temperature” refers in this context to the average temperature at the top surface area of the part or parts being built, during the ongoing build process. Additive manufacturing with E-PBF takes place in vacuum using a high beam power electron gun sequentially melting selected areas of powder layers, repeatedly layer by layer, to form solid parts. Being a vacuum process which inherently provides good thermal insulation, and considering the high beam power available in E-PBF, there is also a secondary heating effect being that the power delivered by the electron beam maintains the entire build at an elevated temperature. The resulting elevated build temperature is often advantageous since it often improves the material properties of the produced parts; it can for example eliminate residual stresses without costly thermal post-processing and prevent crack formation in materials that are prone to cracking when processed by other additive manufacturing technologies. Optimal values for elevated build temperatures vary depending on which material is being processed.

[0040] Typically, the optimal build temperatures are above 500 °C for most materials processed with E-PBF, sometimes even well above 1000 °C. The temperature in a build is often not a fully uniform temperature in the entire part produced throughout the entire build. Hence, a reasonable definition of the build temperature throughout the build is the temperature of the top surface area of the part being built although every section of the build under these condition experiences an elevated temperature far above the room temperature. This top surface build temperature would typically have to be measured by a non-contact temperature sensitive measurement device such as for instance a thermal camera or a pyrometer. However, even if we here follow the above definition, alternative definitions would be possible. The temperature in a build is often not a fully uniform temperature in the entire section of the part produced throughout the entire build. A relevant alternative definition of the build temperature could therefore be the temperature in the lowest layer of the build as this is a section of the build which exist from the first layer being selectively melted while all other layers are added one after each other. Often the first layer of a build is firmly attached to a start plate which is pre-heated before the first layer is formed by the electron beam melting process. If a start plate is used for the build, then the temperature of the start plate could also be valid to define as the build temperature measure for instance by a temperature sensor kept in contact with the start plate.

[0041] Turning now to Figure 1, an additive manufacturing arrangement 100 for successively forming layers of a three-dimensional product in which the present invention can be implemented is schematically illustrated. The arrangement 100 comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product from a powder bed comprising at least one powder bed 240 by means of powder bed fusion, in accordance with one or more embodiments described herein.

[0042] Electron beam powder bed fusion normally takes place in vacuum, and the electron beam may operate in several process steps: it may preheat the powder layers to a semi-sintered state, fuse the powder by melting to solidify the powder in a selected portions of the powder layers, and add additional heat to the powder bed to maintain a predetermined temperature of the powder bed throughout the build. These process steps are preferably carried out under computer control to achieve predetermined quality requirements of the manufactured objects. In an E-PBF process, the powder bed is normally also preheated for semi-sintering or agglomeration of the powder to reduce the risk for later levitation of charged powder and to increase the electrical conduction in the powder bed for increased transportation of electrons from the powder bed to avoid such levitation of powder.

[0043] The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a vacuum chamber or a build chamber 280. The build chamber 280 can be a vacuum chamber, typical of E-PBF. Further, a build compartment 270 is mounted in communication with the build chamber 280. In the illustrated embodiment, the build compartment 270 is arranged below the build chamber 280. In other embodiments, the build compartment 270 may be arranged fully inside the build chamber 280. A movable part or floor 285 is arranged within the build compartment 270 to be gradually lowered during the fusion process between build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283.

[0044] The top surface of the powder bed 242 is allowed to become very hot; in case of a tungsten E-PBF process it can reach an average temperature above 1200 °C. This heat is conducted down to the build tank which may become as hot as 700 °C if not cooled by any means. As discussed above, due to these high temperatures; it is not possible to use conventional vacuum sealing materials such as elastomers or polymers for the powder seal. Therefore, the standard seal material for the build tank in E-PBF is a heat-resistant rope seal, braided seal or band seal made of fibrous material, such as glass fibre, ceramic fibre or metallic fibre. Common elastomers and polymers which have good sealing properties for vacuum applications at low temperature, such as Nitrile®, Viton®, Kalrez®, Teflon®, silicone, etc., cannot withstand the high temperature. However, the inventor has found that it is possible to design or arrange the build compartment 270 with a locally significantly lower temperature in a sealing region 288 (see fig. 2 - 6). This locally lower temperature is lower than 350 °C, or lower than 300 °C, or lower than 250 °C, or lower than 200 °C or lower than 150 °C or lower than 100 °C. As will be explained below, this locally reduced temperature can be achieved, for example, by active cooling systems or passive cooling. In Fig. 1, an active cooling system 295 including cooling channels for circulating of cooling fluids. This particular embodiment will be discussed in more detail with reference to Fig. 3. However, as described, there are other conceivable means for achieve the local cooling of the sealing region 288 which will be evident in following description.

[0045] The powder bed 240 may e.g. be formed by metal powder being distributed from a powder container 230 using a recoater mechanism 290. The powder bed 240 may comprise powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, intermetallics, metal matrix composite, ceramic powder, a mix of metal powder and ceramic powder, glass, graphite, diamond, composites, polymers, nanomaterials, and / or ionic compounds or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder. The powder in the powder bed 240 is exposed to an energy beam, e.g. an electron beam, 220 from the beam source 210. During the exposure to the electron beam 220, the metal powder is melted to form a melt pool.

[0046] In order to prevent leakage of powder, a compressible sealing member 286, see figure 2, is arranged in a recess 284 of the movable part 285. The powder bed 240 is preferably lowered one nominal layer thickness (e.g. 0,02-0,1 mm) before distribution of the next powder layer. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. The sealing member 286 is hence arranged to provide a sufficiently tight seal between the movable part 285 and the build compartment walls 287 to prevent leakage of powder particles from the powder bed 240, and the sealing member 286 is arranged in a sealing region 288 with locally lower temperature than the build temperature of at least 500 °C. Thereby, it is possible to use materials in the sealing member 286 that has lower temperature tolerance than 500 °C. This can be achieved by means of, for example, passive cooling or active cooling systems as illustrated in fig. 1, 3, 5 and 7 and discussed with reference to these figures, f

[0047] In embodiments of the present invention, the sealing member 286 is selected from the group comprising sealing materials suitable for vacuum applications, known under different denominations, acronyms and brands and classified as elastomers or polymers, such as butyl rubber, chloroprene rubber, ethylene propylene rubber, nitrile rubber, nitrile butadiene rubber, polyurethane rubber, fluoro rubber, fluorocarbon rubber, silicone rubber, fluorosilicone rubber, neoprene, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyetheretherketone, CR, NBR, FKM, FPM, MQ, PMQ, VMQ, PVMQ, FVMQ, PTFE, FFKM, FFPM, SCVBR, EPDM, PCTFE, PTFCE, PEEK, Buna-N, Viton, Fluorel, Teflon, Kalrez, Chemraz, Perlast, Kel-F, Neoflon, Markez, Kapton, Vespel, Torlon, and Delrin. In embodiments of the present invention, the sealing member is arranged to seal against leakage of powder particle sizes down to 5pm.

[0048] The electron beam source 210 may comprise a laser adapted to generate a laser beam to heat the back side of a charged particle emitter mounted in a cathode holder system in the vacuum chamber 280. The charged particle emitter, when radiated with the laser beam, emits an electron beam into a charged particle channel of an anode. When the electron beam source is used for electron beam powder bed fusion, the electron beam 220 is directed onto a powder bed 240. The electron beam source 210 is adapted to direct an electron beam 220 generated by a back heated charged particle emitter of a cathode onto the powder bed 240 via an anode, and thereby fuse a three-dimensional product by selectively fusing layer by layer of the powder in the powder bed 240 using the electron beam 220. In embodiments, the laser is a CO2 laser. In operation, a high voltage on the level of for example -60 kV is applied to the cathode and the anode kept at ground potential in a per se known manner.

[0049] The powder bed 240 has a top surface or top powder layer 242. The top powder layer 242 is preferably formed by powder distributed from the powder container 230 using the recoater mechanism 290. The recoater mechanism may e.g. be in the form of a powder layer distributing member or recoater 290, which may e.g. be a linear actuator for distributing powder at the powder bed 240.

[0050] Turning now to Fig. 3, another embodiment of the present invention is illustrated. The powder bed 240 is provided on a movable part or floor 285 arranged to be gradually lowered during the fusion process between the build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283. In order to prevent leakage of powder, a compressible sealing member 286 is arranged in a recess 284 in the movable part 285. The powder bed is preferably lowered one nominal layer thickness (e.g.

[0051] 0,02-0,1 mm) before distribution of the next powder layer. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. According to this embodiment, a locally lower temperature in the sealing region 288 is achieved by means of cooling system 310 arranged inside or directly onto the outside of the build compartment walls 287. The cooling system 310 may comprise fluid channels for circulating cooling fluids in the build compartment walls 287. The fluid channels may be connected to a heat exchanger 315 and a temperature controller 320 for controlling the temperature of the circulating fluid and in the sealing region 288.

[0052] With reference now to Fig. 4, a further embodiment of the present invention will be discussed. The powder bed 240 is provided on a movable part or floor 285 arranged to be gradually lowered during the fusion process between the build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283. The powder bed is preferably lowered one nominal layer thickness (e.g. 0,02-0,1 mm) before distribution of the next powder layer. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. In order to prevent leakage of powder, a compressible sealing member is arranged at the sealing are 288. In this embodiment, the sealing member is comprised of two parts: an inner part 415 arranged to contact with and seal against the movable part 285 and an outer part 410 arranged to contact with and slide along the build compartment walls 287 thereby sealing against the build compartment walls 287. According to an embodiment of the present invention, the outer part 410 is made of a material with a low friction coefficient, such as the polymer PTFE / Teflon®. The inner part 415 is made of an elastomer, having resilient or elastic properties and a maximum service temperature of about 150 - 200 °C such as the elastomer FKM / Viton®.

[0053] Turning now to Fig. 5, another embodiment of the present invention is illustrated. The powder bed 240 is provided on a movable part or floor 285 arranged to be gradually lowered during the fusion process between the build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283. In order to prevent leakage of powder, a compressible sealing member 286 is arranged in a recess 284 in the movable part 285. The powder bed is preferably lowered one nominal layer thickness (e.g.

[0054] 0,02 - 0,1 mm) before distribution of the next powder layer. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. According to this embodiment, a locally lower temperature in the sealing region 288 is achieved by means of passive cooling. A high-conductivity material like e.g. copper or tungsten is used for the build compartment walls 287 that conducts the heat by thermal conduction through the build compartment walls themselves to, for example, an external heat exchanger 515 that may be connected to a temperature controller 520 for controlling a temperature in the heat exchanger 515 and the build compartment walls 287.

[0055] Turning now to Fig. 6, yet another embodiment of the present invention is illustrated. The powder bed 240 is provided on a movable part or floor 285 arranged to be gradually lowered during the fusion process between the build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283. In order to prevent leakage of powder, a compressible sealing member 286 is arranged in a recess 284 in the movable part 285. In this embodiment, an inner surface 610 of the build compartment walls 287 is covered or coated with a coating. The coating may be of a material with a low friction coefficient to enable a smooth movement of the movable part 285 within the build compartment walls 287 with very low friction. Thereby, for example, the wear of the sealing member 286 can be reduced and the life-length of the sealing member 286 can be increased. Turning now to Fig. 7, another embodiment of the present invention is illustrated. The powder bed 240 is provided on a movable part or floor 285 arranged to be gradually lowered during the fusion process between the build compartment walls 287. For example, the movable part 285 may be in form of a table arranged on a piston 283. In order to prevent leakage of powder, a compressible sealing member 286 is arranged in a recess 284 in the movable part 285. The powder bed is preferably lowered one nominal layer thickness (e.g.

[0056] 0,02-0,1 mm) before distribution of the next powder layer. Thin layers of powder are repeatedly spread by a powder distributing member over a powder bed and fused by a beam from an energy source to a predetermined geometry for each layer. According to this embodiment, a locally lower temperature in the sealing region 288 is achieved by means of cooling system 710 arranged outside or in connection to the build compartment walls 287. The cooling system 710 may comprise a cooling fin structure or a heat sink and a air cooling device 715 may be arranged to provide a flow a cooling air directed to the cooling fins of heat sink 710. A temperature controller 720 may be arranged for controlling the temperature of the flow of cooling air, the temperature of the cooling flange or heat sink and / or in the sealing region 288.

[0057] The foregoing disclosure is not intended to limit the present invention to the precise forms or particular fields of use disclosed. It is contemplated that various alternate embodiments and / or modifications to the present invention, whether explicitly described or implied herein, are possible in light of the disclosure. Accordingly, the scope of the invention is defined only by the claims.

Claims

CLAIMS1. Additive manufacturing arrangement (100) comprising an additive manufacturing apparatus (200) for additive manufacturing by selective fusion of layers of a three- dimensional product from a powder bed (240) comprising successively formed powder layers, the apparatus (200) comprising:a build chamber (280) arranged to maintain vacuum and high temperature conditions,a build compartment (270) arranged in communication with said build chamber (280), wherein a movable part (285) is arranged in the build compartment (270), said movable part (285) being arranged to be lowered between build compartment walls (287) of said build compartment (270) to allow successively formed powder layers;wherein a build temperature at a top surface (242) of the powder bed (240) is at least 500 °C during the selective fusion process;an energy beam emitter (210) configured to deliver an energy beam (220) towards the top surface (242) of the powder bed (240), wherein the energy beam (220) is used in the selective fusion of the three-dimensional object;wherein said movable part (285) and / or said build compartment walls (287) are arranged to provide a locally lower temperature in a sealing region (288) that is lower than said build temperature; anda sealing member (286) arranged in the sealing region to provide a sealing between said movable part (285) and the build compartment walls (287), wherein the functionality of the sealing member (286) is adapted to the locally lower temperature and to seal against leakage of powder particle sizes down to 10 pm or down to 5 pm.

2. Additive manufacturing arrangement (100) according to claim 1, wherein said locally lower temperature in the sealing region is at least 150 °C lower than the build temperature.

3. Additive manufacturing arrangement (100) according to claim 1 or 2, wherein said locally lower temperature in the sealing region is at least 350 °C lower than the build temperature.

4. Additive manufacturing arrangement (100) according to claim 1, wherein said sealingmember (286) is made of at least one material from the group comprising sealing materials suitable for vacuum applications, known under different denominations, acronyms and brands and classified as elastomers or polymers, such as butyl rubber, chloroprene rubber, ethylene propylene rubber, nitrile rubber, nitrile butadiene rubber, polyurethane rubber, fluoro rubber, fluorocarbon rubber, silicone rubber, fluorosilicone rubber, neoprene, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyetheretherketone, CR, NBR, FKM, FPM, MQ, PMQ, VMQ, PVMQ, FVMQ, PTFE, FFKM, FFPM, SCVBR, EPDM, PCTFE, PTFCE, PEEK, Buna-N, Viton, Fluorel, Teflon, Kalrez, Chemraz, Perlast, Kel-F, Neoflon, Markez, Kapton, Vespel, Torlon, or Delrin.

5. Additive manufacturing arrangement (100) according to any one of preceding claims, wherein said movable part and / or build compartment walls is / are arranged with passive and / or active cooling system to maintain said local temperature at least 150°C, or 200°C, 250°C, or 300°C, or 350°C, or 400°C, or 450°C, or 500°C, or 550°C, or 600°C, or, 650°C, or 700°C, or 750°C, or 800°C lower than the build temperature at the powder bed (240).

6. Additive manufacturing arrangement (100) according to any one of preceding claims, wherein said build compartment is fully or partially assembled with material with a thermal conductivity of at least 150 Wm / K at room temperature.

7. Additive manufacturing arrangement (100) according to claim 5, wherein said active cooling system comprises a heat exchanging device arranged in connection with said movable part and / or build compartment walls, and wherein heat is conducted by the movable part and / or build compartment walls to heat exchanging device.

8. Additive manufacturing arrangement (100) according any one of preceding claims, wherein an inner surface (610) of build compartment walls (287) is arranged with a coating with a low friction coefficient under vacuum conditions.

9. Additive manufacturing arrangement (100) according to claim 5, wherein the active cooling system is arranged inside or in connection to said movable part and / or build compartment walls.

10. Additive manufacturing arrangement (100) according to claim 5, wherein said active cooling system comprises fluid channels for circulating cooling fluids in said build compartment walls.

11. Additive manufacturing arrangement (100) according to claim 5, wherein said active cooling system comprises a heat sink arrangement or a cooling fin arrangement arranged in connection with or at said build compartment walls (287), and a cooling device arranged to provide a gaseous cooling stream to cool said heat sink arrangement or a cooling fin arrangement.18

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