Oxygen removal in powder-based additive manufacturing processes

Abstract

In accordance with one or more embodiments herein, an arrangement (100) for oxygen removal from metallic materials used in additive manufacturing is provided The arrangement (100) comprises an additive manufacturing apparatus (200) for additive manufacturing by selective fusion of a three-dimensional product from a powder bed (240) containing a metal powder which is exposed to an energy beam (220), and a hydrogen plasma generator (150), wherein the metal powder is exposed to hydrogen plasma generated by the hydrogen plasma generator (150) only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer.

Description

[0001] OXYGEN REMOVAL IN POWDER-BASED ADDITIVE

[0002] MANUFACTURING PROCESSES

[0003] TECHNICAL FIELD

[0004] The present disclosure relates generally to arrangements and methods for oxygen removal or oxide reduction in powders used in additive manufacturing such as metallic materials including metal powders.

[0005] BACKGROUND

[0006] When an energy beam interacts with a metal powder bed during an additive manufacturing process such as e.g. Electron Beam Powder Bed Fusion (E-PBF), oxygen bound to the powder may be disadvantageous for the additive manufacturing process in several ways. Oxygen can bind either to the surface of the powder particles, for example in the form of surface oxides, or oxygen can be incorporated inside the powder particles, for example as dissolved oxygen or bulk oxides. Surface oxides can affect the sintering and melting behavior of the powder, they can lead to a need for a high process temperature, and they can affect the material properties of the built material. Oxides can also affect the recyclability of the powder. Oxygen in the bulk of the powder can also affect the material properties of the built material as well as the recyclability of the powder.

[0007] It is known from US20100310404 that a reactive gas can be fed into an apparatus for producing a three- dimensional object from a metal powder, in order to remove oxygen from the powder and / or to add carbon and / or nitrogen to the powder.

[0008] PROBLEMS WITH THE PRIOR ART

[0009] Oxygen is often considered as an undesired contamination in powder-based additive manufacturing technologies. Oxygen can affect the behavior of the powder in the additive manufacturing machine before the powder is consolidated into solid parts, such as recoating behavior or pre-sintering behavior. Oxygen can also affect the behavior of the powder during the consolidation by the energy beam, for example spattering behavior. Oxygen can also affect the material properties of the built parts, for example brittleness, cracking propensity, thermal conductivity or electrical conductivity. Oxygen can also affect the lifetime of the powder, that is how many times the powder can be reused before it must be scrapped.

[0010] If oxygen could be removed in a more efficient way, it could lead to several benefits. In the case of E-PBF, for example, a method for oxygen removal could give benefits such as lower build temperature, reduced heat load on the E-PBF machine, increased build area, increased build speed, better material properties in built material, and better recyclability of powder. A method for oxygen removal could enable successful E-PBF processing of powder materials that have been considered difficult or impossible in the past.

[0011] Regarding the applicability of US20100310404, hydrogen gas may be highly explosive, and high gas pressure and / or high temperature may be needed to make hydrogen gas reactive enough to remove oxygen from a metal powder. Some metals and alloys may bind oxygen too hard, making hydrogen gas exposure ineffective for oxygen removal, regardless of temperature and gas pressure.

[0012] There is thus a need for improved arrangements and methods for oxygen removal or oxide reduction, especially surface oxide reduction, in powder-based additive manufacturing processes.

[0013] SUMMARY

[0014] The above-described problem is addressed by arrangements for oxide reduction or oxygen removal in a powder used in additive manufacturing. The arrangement preferably comprises an additive manufacturing apparatus for additive manufacturing by selective fusion of a three-dimensional product from a powder bed containing a powder which is exposed to an energy beam such as a laser beam or an electron beam, and a plasma generator, wherein the powder is exposed to plasma generated by the plasma generator only after being exposed to the energy beam and before a new powder layer has been supplied, and the hydrogen plasma thereby removes oxygen from the powder and / or the fused material after the fusion process.

[0015] In accordance with an aspect of the present invention, an arrangement for oxygen removal from a powder of an electrically conductive material used in additive manufacturing, the arrangement comprising an additive manufacturing apparatus for additive manufacturing by selective fusion of a three-dimensional product build up by consecutively laid powder layers on a powder bed containing the powder which is exposed to an energy beam, wherein the arrangement comprises at least one plasma generator, wherein the at least one plasma generator is controlled to deliver and expose the powder bed to plasma only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer.

[0016] In embodiments of the present invention, the powder of an electrically conductive material is a metal power comprising pure tungsten or a tungsten alloy, or pure copper or a copper alloy. However, the metal powder may also be based on for example iron, nickel, cobalt, molybdenum, niobium, titanium or noble metals or alloys containing any of these. Other conceivable materials include intermetallic compounds such as titanium aluminide, as well as other electrically conductive materials such as silicon, graphite, tungsten carbide, or titanium nitride. According to a further aspect of the present invention, there is provided a method for oxygen removal from a powder of an electrically conductive material used in an additive manufacturing apparatus for additive manufacturing by selective fusion of a three-dimensional product build up by consecutively laid powder layers by directing an energy beam to a powder bed with the powder, the method comprising controlling at least one plasma generator to deliver plasma and expose the powder bed to plasma only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer.

[0017] The plasma generator is in preferred embodiments a hydrogen plasma generator but may also be a plasma generator using mixtures of hydrogen and argon or any other inert gas.

[0018] Hence, according to embodiments of the present invention, the powder bed is not exposed to the plasma during the powder distribution phase, the preheating phase and the melting phase, but only after melting the powder layer has finished, and before a new powder layer is distributed over the powder bed. During this late part of the E-PBF layer cycle, it is common to have a postheating or a postcooling process to maintain thermal balance of the build. It is also common to use process monitoring tools such as optical photography or backscatter electron imaging during this late part of the layer cycle. An advantage of plasma exposure after melting only is that the plasma generator can be better protected against harmful metal vapor, powder particles, spatter particles, spatter droplets, electromagnetic radiation and electron radiation that can be emitted from the powder bed during preheating and melting. By using a shielding device, for example a mechanical shutter, a sliding door arrangement, or similar device, in front of the plasma generator, the plasma generator can be shielded from the powder bed during powder distribution, preheating and melting. After melting, the shielding device opens, and the plasma generator exposes the powder bed to plasma. At this point, the freshly melted areas on the powder bed are not covered by powder and thus they are easily accessible for the plasma to remove oxygen. Furthermore, plasma can also remove oxygen from the preheated areas of the powder bed that were not melted. When a new powder layer is distributed, the shielding device closes again to protect the plasma generator during powder distribution, preheating and melting. Another alternative is to move the plasma generator to an exposure position after melting, and back into a shielded position when a new powder layer is distributed.

[0019] According to embodiments of the present invention, the step of controlling comprises delivering plasma for exposure to the top powder layer synchronized with melting and distribution of a new powder layer; and exposing the top powder layer including the freshly melted and resolidified powder to plasma generated by the at least one plasma generator only after the melting and before distribution of a new powder layer.

[0020] In embodiments of the present invention, the step of controlling further comprises shielding the at least one plasma generator from the powder bed during powder distribution, preheating and melting. According to embodiments, the controlling comprises generating the plasma by at least one plasma generator synchronized with melting and distribution of a new powder layer.

[0021] In embodiments of the present invention, the controlling comprises the step of generating the plasma by at least one plasma generator continuously.

[0022] According to embodiments, the step of controlling further comprises opening a shielding mechanism for the at least one plasma generator synchronized with the selective melting and resolidification of a top powder layer and before distribution of a new powder layer and closing the shielding mechanism after delivery of plasma.

[0023] In embodiments, the controlling further comprises moving the at least one plasma generator to an exposure position during generation and delivery of plasma and to a shielded position after delivery of plasma.

[0024] According to embodiments, the controlling comprises controlling a shutter mechanism to open during delivery of plasma and to close after delivery of plasma.

[0025] In embodiments, the powder is shuffled sequentially in synchronism with delivery or exposure to plasma such that powder is distributed after the delivery of plasma to obtain a layer-by-layer exposure of the powder to plasma.

[0026] According to embodiments, the powder bed is formed by distributing the powder from a powder container using a recoater mechanism, wherein the recoater mechanism is operated synchronized with the controlling of the at least one plasma generator.

[0027] In embodiments, the powder is exposed to the plasma in synchronism with distribution of the powder from the powder container to the powder bed by the recoater mechanism such that the powder is exposed to the plasma before distribution of a new powder layer.

[0028] The term "hydrogen plasma” is to be understood as hydrogen gas which has been excited to the level of splitting the hydrogen molecules, H2, into hydrogen free radicals with unpaired electrons, H, which are much more reactive than hydrogen molecules. Plasma is generally recognized as the fourth state of matter and is fundamentally different from the three well-known states: solids, liquids and gases.

[0029] The terms "hydrogen plasma” and "plasma” are also to be understood as plasma being made from hydrogen gas only, or plasma being made from hydrogen gas mixed with at least one inert gas, such as argon or helium. Such a gas mixture may be easier to use in an additive manufacturing machine from a safety perspective, and while excited as a plasma, it still contains hydrogen free radicals capable of removing oxygen from metals.

[0030] The term "oxide” is to be understood as any oxygen-containing chemical species, not only metal oxide, but also for example hydroxide, or oxygen atoms dissolved into metal.

[0031] 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 a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figs. 1a-e schematically illustrate arrangements for oxygen removal from a metal powder used in additive manufacturing, in accordance with one or more embodiments described herein.

[0034] Fig. 2 schematically illustrates a method for oxygen removal from a metal powder used in an additive manufacturing apparatus for additive manufacturing by selective fusion of a three-dimensional product by exposing a powder bed to an energy beam, in accordance with one or more embodiments described herein.

[0035] Fig. 3 schematically illustrates arrangements for oxygen removal from a metal powder used in additive manufacturing, in accordance with one or more embodiments described herein.

[0036] Fig. 4 schematically illustrates arrangements for oxygen removal from a metal powder used in additive manufacturing, in accordance with one or more embodiments described herein.

[0037] Fig. 5 schematically illustrates a method for oxygen removal from a metal powder used in an additive manufacturing apparatus for additive manufacturing by selective fusion of a three-dimensional product by exposing a powder bed to an energy beam, in accordance with one or more embodiments described herein.

[0038] 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. DETAILED DESCRIPTION

[0039] When an energy beam interacts with a metal powder bed during an additive manufacturing process such as e.g. Electron Beam Powder Bed Fusion (E-PBF) or Laser Powder Bed Fusion (L-PBF), oxygen bound to the powder may constitute a problem. Oxygen can be present in the powder particles in different chemical forms, for example as metal oxides on the particle surfaces, or as oxygen-rich inclusions inside the particles, or as atomic oxygen dissolved into the bulk of the particles. Such bound oxygen, regardless of its chemical form and location in the powder particles, may create process stability issues as well as problems with material properties in the built parts.

[0040] Surface oxides on the powder, for example, may reduce the electrical conductivity between powder particles which increases the risk of so-called "smoke events” and eventually a build failure of the E-PBF process. Surface oxides can affect the interparticle friction in the recoating process, leading to poor packing density and / or layer thickness variation. Surface oxides on the powder can also contribute to increased spatter formation in the melting process, both for L-PBF and E-PBF. Spatter is undesired since it means that material is removed from the melt pool. Surface oxides can also affect the melting behavior of a powder and reduce the wettability of the melt pool, leading to so-called "balling effects”.

[0041] Too high oxygen content in the built parts is also a potential problem, both for E-PBF and L-PBF. Unalloyed copper, for example, must maintain a very low oxygen content to preserve its high electrical conductivity necessary for many industrial applications. Refractory metals such as tungsten and molybdenum are other examples. Oxygen contamination is known to embrittle tungsten and molybdenum and increase the risk of cracking.

[0042] When metal powder is repeatedly reused in a powder bed fusion process, there is a risk of a gradual oxygen buildup in the metal powder due to traces of oxygen or moisture that are always present in the build environment. After a certain number of build cycles, the recycled powder may reach the maximum allowed limit of oxygen, prohibiting further use of the recycled powder.

[0043] Oxide reduction, especially surface oxide reduction, in a metal powder may improve the electrical conductivity and / or the sinterability of the metal powder. This may enable a lower process temperature in E- PBF, which would lower the heat load on the additive manufacturing apparatus, and allow for a faster build process. This opens the possibility to build over a larger powder bed for a given beam power. There may also be less spatter from the melt pool, as well as a better cracking resistance in built material, thanks to a lower amount of oxygen in the builds. In conclusion, there are numerous cases where oxygen content is considered detrimental for additive manufacturing processes. There is thus a great need for arrangements and methods for oxygen removal, both from metal powder used in additive manufacturing and from material built in the additive manufacturing process. The present disclosure relates generally to arrangements and methods for oxygen removal in powder-based additive manufacturing processes. Embodiments of the disclosed solution are presented in more detail in connection with the figures.

[0044] Figs. 1a-e schematically illustrate arrangements 100 for oxygen removal in powder-based additive manufacturing processes. The schematically illustrated arrangement 100 comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product. The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a powder bed 240, arranged in a build chamber 280. The build chamber can be a vacuum chamber, typical of E-PBF, or a chamber containing inert gas, typical of L-PBF. 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 metal-based powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, intermetallics, metal matrix composite, or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder, The metal powder may e.g. comprise tungsten or copper. The metal powder in the powder bed 240 is exposed to a energy beam 220 from the beam source 210. During the exposure to the energy beam 220, the metal powder is melted to form a melt pool.

[0045] In embodiments, the build chamber 280 and the powder container 230 are separated with a partitioning wall 235. The partitioning wall 235 is provided with a shutter mechanism 238 arranged to swiftly open and close , for example, when the recoater mechanism 290 moves back and forth to deliver metal powder into the built chamber 280. Thereby, an efficient delivery mechanism of metal powder is enabled at the same time as the vacuum conditions in the build chamber 280 can be preserved and maintained.

[0046] The schematically illustrated arrangement 100 further comprises at least one hydrogen plasma generator 150. The metal powder is exposed to hydrogen plasma generated by the hydrogen plasma generator 150 before being exposed to the energy beam 220, and / or during the exposure to the energy beam 220 (see Fig. 1d or 1 e), which allows the hydrogen plasma to remove oxygen from the metal powder (or melt pool) before (or during) the selective fusion process. In the embodiment shown in Fig. 1a, the hydrogen plasma generator 150 is arranged to generate and deliver hydrogen plasma into the powder container 230. In other embodiments, as will be discussed below, and shown in Figs. 1d and 1e, the hydrogen plasma generator may be arranged to generate and deliver hydrogen plasma into build chamber 280. A further embodiment shown in Fig. 1d comprises one hydrogen plasma generator 150 arranged to generate and deliver hydrogen plasma into the powder container 230 and one hydrogen plasma generator 150 arranged to generate and deliver hydrogen plasma into the build chamber 280.

[0047] Since the hydrogen free radicals (H) are very reactive, they will easily recombine or react upon collision with surfaces or gaseous species. Hydrogen free radicals are therefore short lived, and energy must be continuously added to the hydrogen plasma generator 150 to maintain an active hydrogen plasma. The hydrogen plasma generator 150 is therefore preferably arranged close to the metal powder, to make sure that the hydrogen plasma does not lose its reactivity before reaching the metal powder. In the embodiment schematically illustrated in Fig. 1a, the exposing of the metal powder to hydrogen plasma takes place while the metal powder is contained in a container, which may be a separate container or the powder container 230.

[0048] In the embodiment shown in Fig. 1a, a pump 260 is arranged for pumping or removing any gases in the powder container 260 and / or the build chamber 280, respectively. The pump 260 is however only used in case an E-PBF equipment is used. In other embodiments, a L-PBF equipment may be used and in which case the pump can be omitted and a gas outflow can be used instead.

[0049] In the embodiment schematically illustrated in Fig. 1a, the exposing of the metal powder to hydrogen plasma takes place while the metal powder is contained in the powder container 230. The oxide reduction may e.g. take place on the top layer of metal powder in the powder container 230, just before the distribution of the metal powder to the powder bed 240 by the recoater mechanism 290. The exposing of the metal powder to the hydrogen plasma may e.g. involve directing low-pressure hydrogen plasma towards the metal powder on top of the powder container 230. The hydrogen plasma generator 150 is preferably arranged in a position from where hydrogen free radicals can reach the powder container 230 with few or no intermediate collisions with other surfaces. The oxide removal may be speeded up by the use of a heating device, e.g. an IR heater 270, arranged inside the additive manufacturing apparatus 200.

[0050] In embodiments, the exposure of the metal powder to the hydrogen plasma takes place before connecting the powder container 230a to the additive manufacturing apparatus 200 as shown in Fig. 1b. In this way, oxides may be reduced in the whole powder batch before the additive manufacturing process is started. The hydrogen plasma generator 150 is preferably connected to the tank containing the metal powder, so that the container may be filled with hydrogen plasma. In this embodiment it is possible to use a higher pressure, e.g. up to near atmospheric pressure. Heating and / or stirring of the powder is preferably used to speed up the oxide reduction, because hydrogen plasma is not likely to penetrate into a stationary and densely packed powder volume. For example, heating can be made using an IR heating device 270 and stirring can be achieved using a mixing device or an agitator 275. After the oxide reduction of the metal powder, it is preferred that the metal powder is not exposed to air before being transferred to the additive manufacturing apparatus 200, to prevent re-oxidation of the metal powder. In embodiments where the metal powder is exposed to the hydrogen plasma in the powder container 230, this may e.g. be achieved by transferring the powder container 230 to the additive manufacturing apparatus 200 through a load-lock.

[0051] In a further embodiment, as shown in Fig. 1c, the metal powder is arranged to be fed into the powder container 230 by means of a metal powder feeder 285 to fall through the container under the influence of gravity under exposure to hydrogen plasma. In this embodiment, the metal powder feeder is arranged at the top of the powder container 230, but may be arranged for example at a side wall of the powder container 230. In this way, oxides may be reduced in the whole powder batch before the additive manufacturing process is started. The hydrogen plasma generator 150 is preferably connected to the tank containing the metal powder, so that the container may be filled with hydrogen plasma. In this embodiment it is possible to use a higher pressure, e.g. up to near atmospheric pressure. Heating of the powder is preferably used to speed up the oxide reduction. For example, heating can be made using an IR heating device 270. After the oxide reduction of the metal powder, it is preferred that the metal powder is not exposed to air before being transferred to the additive manufacturing apparatus 200, to prevent re-oxidation of the metal powder. In embodiments where the metal powder is exposed to the hydrogen plasma in the powder container 230, this may e.g. be achieved by transferring the powder container 230 to the additive manufacturing apparatus 200 through a load-lock. The principle used in the embodiment described with reference to Fig. 1c, that is the metal powder being arranged to be fed into the powder container 230 by means of a metal powder feeder 285 to fall through the container under the influence of gravity under exposure to hydrogen plasma from plasma generator 150 and, optionally, also under IR heating by the IR heating device 270, can be combined with other embodiments such as the embodiment described with reference to Fig. 1a and 1d.

[0052] In another embodiment, as schematically illustrated in Fig. 1 d, the arrangement 103 for oxygen removal in powder-based additive manufacturing processes comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product comprising a first hydrogen plasma generator 150a and a second hydrogen plasma generator 150b. The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a powder bed 240, arranged in a build chamber 280. The build chamber can be a vacuum chamber, typical of E-PBF, or a chamber containing inert gas, typical of L-PBF. 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 metal-based powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, i ntermetallics, metal matrix composite, or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder, The metal powder may e.g. comprise tungsten or copper. The metal powder in the powder bed 240 is exposed to an energy beam 220 from the beam source 210. During the exposure to the energy beam 220, the metal powder is melted to form a melt pool. In embodiments, if the vacuum chamber is a L-PBF, an IR heating device 270 may be arranged to heating of the powder to speed up the oxide reduction.

[0053] The metal powder is exposed to hydrogen plasma generated by a first hydrogen plasma generator 150a before being exposed to the energy beam 220, and during the exposure to the energy beam 220 using a second hydrogen plasma generator 150b, which allows the hydrogen plasma to remove oxygen from the metal powder (or melt pool) before and during the selective fusion process. In the embodiment shown in Fig. 1 d, the first hydrogen plasma generator 150a is arranged to generate and deliver hydrogen plasma into the powder tank container 230 and the second hydrogen plasma generator 150b is arranged to generate and deliver hydrogen plasma into build chamber 280.

[0054] Since the hydrogen free radicals (H) are very reactive, they will easily recombine or react upon collision with surfaces or gaseous species. Hydrogen free radicals are therefore short lived, and energy must be continuously added to the hydrogen plasma generator 150 to maintain an active hydrogen plasma. The first and second hydrogen plasma generator 150a and 150b are therefore preferably arranged close to the metal powder, to make sure that the hydrogen plasma does not lose its reactivity before reaching the metal powder. In the embodiment shown in Fig. 1a, a pump 260 is arranged for pumping or removing any gases in the powder container 260 and / or the build chamber 280, respectively. However, in case the build chamber 280 is a L-PBF vacuum chamber the pump 260 can be omitted, and only a gas outflow can be arranged to ensure gas outflow. In the embodiment schematically illustrated in Fig. 1 d, the exposing of the metal powder to hydrogen plasma takes place both in build chamber 280 and while the metal powder is contained in the powder container 230. The oxide reduction may e.g. take place on the top layer of metal powder in the powder container 230, just before the distribution of the metal powder to the powder bed 240 by the recoater mechanism 290. The exposing of the metal powder to the hydrogen plasma may e.g. involve directing low- pressure hydrogen plasma towards the metal powder on top of the powder container 230. The second hydrogen plasma generator 150b is preferably connected to the build chamber 280, e.g. by being attached to the wall or roof of the build chamber 280, preferably in a position from where hydrogen free radicals can reach the metal powder with few or no intermediate collisions with other surfaces. In the case of E-PBF, the pressure of the hydrogen plasma may e.g. be in the range of 102mbar, or lower, so as not to interfere with the vacuum needed for operating an electron beam. The oxide removal may be speeded up by the use of a heating device, e.g. an IR heater 270, arranged inside the additive manufacturing apparatus 200.

[0055] In yet another embodiment, as schematically illustrated in Fig. 1 e, the arrangement 104 for oxygen removal in powder-based additive manufacturing processes comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product comprising a hydrogen plasma generator 150 arranged in the build chamber 280. In the embodiment schematically illustrated in Fig. 1 e, the exposing of the metal powder to hydrogen plasma takes place in the powder bed 240. The exposing of the metal powder to hydrogen plasma may e.g. involve directing a low-pressure hydrogen plasma towards the metal powder on top of the powder bed 240. The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a powder bed 240, arranged in a build chamber 280. The build chamber can be a vacuum chamber, typical of E-PBF, or a chamber containing inert gas, typical of L- PBF. 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 metal-based powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, I ntermetall ics, metal matrix composite, or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder, The metal powder may e.g. comprise tungsten or copper. The metal powder in the powder bed 240 is exposed to an energy beam 220 from the beam source 210. During the exposure to the energy beam 220, the metal powder is melted to form a melt pool.

[0056] The metal powder is exposed to hydrogen plasma generated by a hydrogen plasma generator 150 during the exposure to the energy beam 220, which allows the hydrogen plasma to remove oxygen from the metal powder (or melt pool) during the selective fusion process. In the embodiment shown in Fig. 1 e, the hydrogen plasma generator 150 is arranged to generate and deliver hydrogen plasma into build chamber 280. Since the hydrogen free radicals (H) are very reactive, they will easily recombine or react upon collision with surfaces or gaseous species. Hydrogen free radicals are therefore short lived, and energy must be continuously added to the hydrogen plasma generator 150 to maintain an active hydrogen plasma. The hydrogen plasma generator 150 is therefore preferably arranged close to the metal powder, to make sure that the hydrogen plasma does not lose its reactivity before reaching the metal powder. In the embodiment shown in Fig. 1 e, pump 260 is arranged for pumping or removing any gases in the powder container 260 and / or the build chamber 280, respectively. However, in case the build chamber 280 is a L-PBF vacuum chamber the pump can be omitted, and a gas outflow can be arranged to remove gases.

[0057] In the embodiment schematically illustrated in Fig. 1 e, the exposing of the metal powder to hydrogen plasma takes place in build chamber 280. The hydrogen plasma generator 150 is preferably connected to the build chamber 280, e.g. by being attached to the wall or roof of the build chamber 280, preferably in a position from where hydrogen free radicals can reach the metal powder with few or no intermediate collisions with other surfaces. In the case of E-PBF, the pressure of the hydrogen plasma may e.g. be in the range of 102mbar, or lower, so as not to interfere with the vacuum needed for operating an electron beam.

[0058] The hydrogen plasma generator 150 is preferably connected to the build chamber 280, e.g. by being attached to the wall or roof of the build chamber 280, preferably in a position from where hydrogen free radicals can reach the powder bed 240 with few or no intermediate collisions with other surfaces. In the case of E-PBF, there is normally no need for any additional heating, since there is typically already a high temperature in the powder bed 240. In the case of E-PBF, the pressure of the hydrogen plasma may e.g. be 102mbar, or lower, so as not to interfere with the vacuum inside build chamber 280. In the case of L-PBF, additional heating, for example by means of an IR heating device 270, may be beneficial since L-PBF normally operates at a much lower powder bed temperature than E-PBF.

[0059] Fig. 2 schematically illustrates a method 300 for oxygen removal from a metal powder, or from the melt pool, or from the fused material. The method is preferable used in an additive manufacturing apparatus 200 for additive manufacturing by selective fusion of a three-dimensional from a powder bed containing a metal powder which is exposed to an energy beam such as a laser beam or an electron beam, and a hydrogen plasma generator, wherein the metal powder is exposed to hydrogen plasma generated by the hydrogen plasma generator before being exposed to the energy beam, and / or during the exposure to the energy beam, and the hydrogen plasma thereby removes oxygen from the metal powder or melt pool before or during the selective fusion process.

[0060] The method 300 preferably comprises, before exposing the metal powder in the powder bed 240 to the energy beam 220, and / or during the exposure of the metal powder to the energy beam 220: Step 320: generating hydrogen plasma by at least one hydrogen plasma generator 150.

[0061] Step 330: delivering hydrogen plasma for exposure to the metal powder.

[0062] Step 340: optionally handling the metal power in the powder container such that the metal powder is exposed to the hydrogen plasma in a batch fashion, so that essentially all powder particles in the powder container become exposed to the hydrogen plasma. In a sub-step 340a the metal powder may be stirred in the powder container, wherein the stirring occurs in synchronism with delivery or exposure to hydrogen plasma, continuously and / or in intervals during delivery or exposure to hydrogen plasma. In an alternative sub-step 340b, the metal powder may be shuffled sequentially in synchronism with delivery or exposure to hydrogen plasma, continuously and / or in intervals during delivery or exposure to hydrogen plasma to obtain a layer-by-layer exposure of the metal powder to hydrogen plasma.

[0063] Step 350: exposing the metal powder to hydrogen plasma generated by the at least one hydrogen plasma generator 150 before exposing the metal powder to the energy beam 220, and / or during the exposure of the metal powder to the energy beam 220.

[0064] Step 360: removing oxygen from the metal powder, using the hydrogen plasma.

[0065] This enables a removal of oxygen from a metal powder used in additive manufacturing, before the selective fusion process begins in the metal powder, and / or in the melt pool during the selective fusion process. This may improve the electrical conductivity and / or the sinterability of the metal powder.

[0066] In embodiments, the exposing 320 takes place while the metal powder is contained in a powder container 230. In embodiments, the exposing 320 comprises exposing the metal powder to hydrogen plasma in the powder bed 240.

[0067] The method 300 may further comprise one or more of:

[0068] Step 310: forming the powder bed 240 by distributing the metal powder from the powder container 230 using a recoater mechanism 290.

[0069] Step 345: connecting the powder container 230 to the additive manufacturing apparatus 200 after exposing the metal powder in the powder container 230 to hydrogen plasma.

[0070] The above listed steps may be performed in any order.

[0071] In embodiments, the exposing 320 comprises exposing the metal powder to hydrogen plasma just after the distribution of the metal powder from the powder container 230 to the powder bed 240 by a recoater mechanism 290.

[0072] In embodiments, the exposing 320 comprises exposing the metal powder to hydrogen plasma during the exposure of the metal powder to the energy beam 220, when the metal powder is melted to form a melt pool.

[0073] With reference now to Fig. 3, another embodiment schematically illustrated, will be described. The arrangement 104 for oxygen removal in powder-based additive manufacturing processes comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product comprising a hydrogen plasma generator 150 arranged in the build chamber 280. In the embodiment schematically illustrated in Fig. 3, the exposing of the metal powder to hydrogen plasma takes place in the powder bed 240. The exposing of the metal powder to hydrogen plasma may e.g. involve directing a low- pressure hydrogen plasma towards the metal powder on top of the powder bed 240. The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a powder bed 240, arranged in a build chamber 280. The build chamber can be a vacuum chamber, typical of E-PBF, or a chamber containing inert gas, typical of L-PBF. 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 metal-based powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, intermetallics, metal matrix composite, or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder, The metal powder may e.g. comprise tungsten or copper. The metal powder in the powder bed 240 is exposed to an energy beam 220 from the beam source 210. During the exposure to the energy beam 220, the metal powder is melted to form a melt pool.

[0074] The metal powder is exposed to hydrogen plasma generated by a hydrogen plasma generator 150 during the exposure to the energy beam 220, which allows the hydrogen plasma to remove oxygen from the metal powder (or melt pool) during the selective fusion process. In the embodiment shown in Fig. 3, the hydrogen plasma generator 150 is arranged to generate and deliver hydrogen plasma into build chamber 280. Since the hydrogen free radicals (H) are very reactive, they will easily recombine or react upon collision with surfaces or gaseous species. Hydrogen free radicals are therefore short lived, and energy must be continuously added to the hydrogen plasma generator 150 to maintain an active hydrogen plasma. The hydrogen plasma generator 150 is therefore preferably arranged close to the metal powder, to make sure that the hydrogen plasma does not lose its reactivity before reaching the metal powder. In the embodiment shown in Fig. 3, pump 260 is arranged for pumping or removing any gases in the powder container 260 and / or the build chamber 280, respectively. However, in case the build chamber 280 is a L-PBF vacuum chamber the pump can be omitted, and a gas outflow can be arranged to remove gases.

[0075] In the embodiment schematically illustrated in Fig. 3, the plasma generator is controlled to generate and deliver plasma such that the exposing of the metal powder to hydrogen plasma takes place in build chamber 280 only after melting and before a new powder layer has been distributed to the powder bed 240. The hydrogen plasma generator 150 is preferably connected to the build chamber 280, e.g. by being attached to the wall or roof of the build chamber 280, preferably in a position from where hydrogen free radicals can reach the metal powder with few or no intermediate collisions with other surfaces. In the case of E-PBF, the pressure of the hydrogen plasma may e.g. be in the range of 102mbar, or lower, so as not to interfere with the vacuum needed for operating an electron beam.

[0076] With reference now to Fig. 4, another embodiment schematically illustrated, will be described. The arrangement 104 for oxygen removal in powder-based additive manufacturing processes comprises an additive manufacturing apparatus 200, for additive manufacturing by selective fusion of a three-dimensional product comprising a hydrogen plasma generator 150 arranged in the build chamber 280. In the embodiment schematically illustrated in Fig. 4, the exposing of the metal powder to hydrogen plasma takes place in the powder bed 240. The exposing of the metal powder to hydrogen plasma may e.g. involve directing a low- pressure hydrogen plasma towards the metal powder on top of the powder bed 240. The schematically illustrated additive manufacturing apparatus 200 comprises an energy beam source 210 and a powder bed 240, arranged in a build chamber 280. The build chamber can be a vacuum chamber, typical of E-PBF, or a chamber containing inert gas, typical of L-PBF. 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 metal-based powder of any kind, such as e.g. metal powder composed of pure metal, metal alloys, intermetallics, metal matrix composite, or any powder mixture thereof. The powder can also be a mixture of metal-based powder and insulating or semiconducting powder, The metal powder may e.g. comprise tungsten or copper. The metal powder in the powder bed 240 is exposed to an energy beam 220 from the beam source 210. During the exposure to the energy beam 220, the metal powder is melted to form a melt pool.

[0077] The metal powder is exposed to hydrogen plasma generated by a hydrogen plasma generator 150 during the exposure to the energy beam 220, which allows the hydrogen plasma to remove oxygen from the metal powder (or melt pool) during the selective fusion process. In the embodiment shown in Fig. 4, the hydrogen plasma generator 150 is arranged to generate and deliver hydrogen plasma into build chamber 280. Since the hydrogen free radicals (H) are very reactive, they will easily recombine or react upon collision with surfaces or gaseous species. Hydrogen free radicals are therefore short lived, and energy must be continuously added to the hydrogen plasma generator 150 to maintain an active hydrogen plasma. The hydrogen plasma generator 150 is therefore preferably arranged close to the metal powder, to make sure that the hydrogen plasma does not lose its reactivity before reaching the metal powder. In the embodiment shown in Fig. 3, pump 260 is arranged for pumping or removing any gases in the powder container 260 and / or the build chamber 280, respectively. However, in case the build chamber 280 is a L-PBF vacuum chamber the pump can be omitted, and a gas outflow can be arranged to remove gases.

[0078] In the embodiment schematically illustrated in Fig. 4, the plasma generator 150 is controlled to generate and deliver plasma such that the exposing of the metal powder to hydrogen plasma takes place in build chamber 280 only after melting and before a new powder layer has been distributed to the powder bed 240. The hydrogen plasma generator 150 is preferably connected to the build chamber 280, e.g. by being attached to the wall or roof of the build chamber 280, preferably in a position from where hydrogen free radicals can reach the metal powder with few or no intermediate collisions with other surfaces. In the case of E-PBF, the pressure of the hydrogen plasma may e.g. be in the range of 102mbar, or lower, so as not to interfere with the vacuum needed for operating an electron beam.

[0079] A shielding device 295, for example a mechanical shutter, a sliding door arrangement, or similar device, is arranged in front of the plasma generator. Thereby, the plasma generator 150 can be shielded from the powder bed during powder distribution, preheating and melting. After melting, the shielding device 295 opens, and the plasma generator 150 exposes the powder bed to plasma. At this point, the freshly melted areas on the powder bed 240 are not covered by powder and thus they are easily accessible for the plasma to remove oxygen. Furthermore, plasma can also remove oxygen from the preheated areas of the powder bed 240 that were not melted. At the moment when a new powder layer is distributed, the shielding device 295 closes again to protect the plasma generator during powder distribution, preheating and melting. Another alternative is to move the plasma generator to an exposure position after melting, and back into a shielded position when a new powder layer is distributed. Fig. 5 schematically illustrates a method 500 for oxygen removal from a metal powder, or from the melt pool, or from the fused material. The method is preferable used in an additive manufacturing apparatus 200 for additive manufacturing by selective fusion of a three-dimensional from a powder bed containing a metal powder which is exposed to an energy beam such as a laser beam or an electron beam, and a hydrogen plasma generator, wherein the metal powder is exposed to hydrogen plasma generated by the hydrogen plasma generator before being exposed to the energy beam, and / or during the exposure to the energy beam, and the hydrogen plasma thereby removes oxygen from the metal powder or melt pool before or during the selective fusion process.

[0080] The method 500 for oxygen removal from a powder of an electrically conductive material used in an additive manufacturing apparatus 200 for additive manufacturing by selective fusion of a three-dimensional product build up by consecutively laid powder layers by directing an energy beam 220 to a powder bed 240 with the powder preferably comprises the step of controlling 510, 530, 540, 550, and 560 at least one plasma generator 150 to deliver plasma and expose the powder bed to plasma only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer. More specifically, the method may comprise:

[0081] Step 510: forming a new powder layer on the powder bed.

[0082] Step 530: melting or fusing the powder layer.

[0083] Step 540: delivering hydrogen plasma for exposure to the top powder layer.

[0084] Step 550: exposing the top powder layer including the freshly melted and resolidified powder to plasma generated by the at least one plasma generator 150 only after the melting and before distribution of a new powder layer.

[0085] Step 560: if the process is not finished, the procedure returns to step 510, otherwise, the procedure is stopped or interrupted.

[0086] The controlling may further comprise shielding the at least one plasma generator from the powder bed during powder distribution, preheating and melting. According to embodiments, the controlling comprises generating the plasma by at least one plasma generator synchronized with melting and distribution of a new powder layer. In embodiments of the present invention, the controlling comprises the step of generating the plasma by at least one plasma generator continuously. According to embodiments, the step of controlling further comprises opening a shielding mechanism for the at least one plasma generator synchronized with the selective melting and resolidification of a top powder layer and before distribution of a new powder layer and closing the shielding mechanism after delivery of plasma. In embodiments, the controlling further comprises moving the at least one plasma generator to an exposure position during generation and delivery of plasma and to a shielded position after delivery of plasma. According to embodiments, the controlling comprises controlling a shutter mechanism to open during delivery of plasma and to close after delivery of plasma. In embodiments, the powder is shuffled sequentially in synchronism with delivery or exposure to plasma such that powder is distributed after the delivery of plasma to obtain a layer-by-layer exposure of the powder to plasma. According to embodiments, the powder bed is formed by distributing the powder from a powder container using a recoater mechanism, wherein the recoater mechanism is operated synchronized with the controlling of the at least one plasma generator.

[0087] In embodiments, the powder is exposed to the plasma in synchronism with distribution of the powder from the powder container to the powder bed by the recoater mechanism such that the powder is exposed to the plasma before distribution of a new powder layer.

[0088] 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 . Method (500) for oxygen removal from a powder of an electrically conductive material used in an additive manufacturing apparatus (200) for additive manufacturing by selective fusion of a three-dimensional product build up by consecutively laid powder layers by directing an energy beam (220) to a powder bed (240) with said powder, the method (300) comprising: controlling at least one plasma generator (150) to deliver plasma and expose the powder bed to plasma only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer.

2. Method (500) according to claim 1 , wherein said step of controlling comprises the step of: delivering (540) plasma for exposure to the top powder layer synchronized with melting and distribution of a new powder layer; and exposing (550) the top powder layer including the freshly melted and resolidified powder to plasma generated by the at least one plasma generator (150) only after the melting and before distribution of a new powder layer.

3. Method (500) according to claim 1 , wherein said step of controlling further comprises the step of: shielding the at least one plasma generator (150) from the powder bed during powder distribution, preheating and melting.

4. Method (500) according to claim 1 - 3, wherein the step of controlling comprises the step of: generating the plasma by at least one plasma generator (150) synchronized with melting and distribution of a new powder layer.

5. Method (500) according to claim 1 - 3, wherein the step of controlling comprises the step of: generating the plasma by at least one plasma generator (150) continuously.

6. Method (500) according to claim 1 - 5, wherein said step of controlling further comprises the step of: opening a shielding mechanism for the at least one plasma generator (150) synchronized with the selective melting and resolidification of a top powder layer and before distribution of a new powder layer, and closing the shielding mechanism after delivery of plasma.

7. Method (500) according to claim 1 , wherein said step of controlling further comprises moving the at least one plasma generator to an exposure position during generation and delivery of plasma and to a shielded position after delivery of plasma.

8. Method (500) according to claim 1 - 7, wherein said step of controlling comprises controlling a shutter mechanism to open during delivery (540) of plasma and to close after delivery of plasma.

9. Method (500) according to claim 1, further comprising shuffling (340b) the powder sequentially in synchronism with delivery or exposure to plasma such that powder is distributed after the delivery of plasma to obtain a layer-by-layer exposure of the powder to plasma.

10. Method (500) according to claim 1, further comprising forming (510) the powder bed (240) by distributing the powder from a powder container (230) using a recoater mechanism (290), wherein said recoater mechanism is operated synchronized with said controlling of the at least one plasma generator (150).11 . Method (500) according to claim 1 , further comprising exposing (540) the powder to the plasma in synchronism with distribution of the powder from the powder container (230) to the powder bed (240) by the recoater mechanism (290) such that the powder is exposed to the plasma before distribution of a new powder layer.

12. Arrangement (100) for oxygen removal from a powder of an electrically conductive material used in additive manufacturing, the arrangement (100) comprising an additive manufacturing apparatus (200) for additive manufacturing by selective fusion of a three-dimensional product build up by consecutively laid powder layers on a powder bed (240) containing the powder which is exposed to an energy beam (220), wherein said arrangement (100) comprises at least one plasma generator (150), wherein said at least one plasma generator (150) is controlled to deliver and expose the powder bed to plasma only after selective melting and resolidification of a top powder layer and before distribution of a new powder layer.

13. Arrangement (100) according to claim 12, further comprising a shielding device (295) arranged to shield the at least one plasma generator (150) from the powder bed during powder distribution, preheating and melting.

14. Arrangement (100) according to claim 12 or 13, wherein said shielding device (295) is arranged to open and close synchronized with generation (320) and delivery of plasma.

15. Arrangement (100) according to claim 12 or 13, wherein said at least one plasma generator (150) is arranged to generate the plasma continuously.

16. Arrangement (100) according to claim 12 - 15, wherein said at least one plasma generator (150) is arranged to be moved to an exposure position during generation and delivery of plasma and to a shielded position shielded by the shielding device (295) when said delivery of plasma has been stopped.

17. Arrangement (100) according to claim 12 - 15, wherein said shielding mechanism (295) comprises a shutter mechanism arranged to open during delivery (330) of plasma and to close after delivery of plasma.

18. Arrangement (100) according to any one of claim 12- 17, further comprising forming (310) the powder bed (240) by distributing the powder from a powder container (230) using a recoater mechanism (290).

19. Arrangement (100) according to claim 18, wherein the recoater mechanism (290) is arranged to shuffle the powder sequentially in synchronism with delivery or exposure to plasma, such that powder is distributed after delivery of plasma to obtain a layer-by-layer exposure of the powder to plasma.

20. Arrangement (100) according to any one of claim 12 - 19, wherein said at least one plasma generator (150) is arranged to deliver plasma to a region where the powder is exposed to the energy beam (220), and wherein the exposing (320) of the powder to plasma occurs after the exposure of the powder to the energy beam (220), when the powder has been re-solidified.

21. Arrangement (100) according to claim 15, wherein the recoater mechanism (290) is arranged to shuffle the powder sequentially in synchronism with delivery or exposure to plasma, continuously and / or in intervals during delivery or exposure to plasma to obtain a layer-by-layer exposure of the powder to plasma.

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