Technique for powder extraction during a multi-material powder bed fusion process

Abstract

A method for powder extraction during a multi-material powder bed fusion process for generating a three-dimensional workpiece from a powder bed is provided. The method comprises applying a first raw material powder to a substrate in order to produce a raw material powder layer consisting of the first raw material powder, selectively irradiating the raw material powder layer consisting of the first raw material powder with electromagnetic radiation or particle radiation in order to produce a solidified first workpiece layer portion from the first raw material powder, removing non-solidified first raw material powder from the substrate with a powder extraction device, applying a second raw material powder to the substrate in order to produce a raw material powder layer portion consisting of the second raw material powder adjacent to the first workpiece layer portion, selectively irradiating the raw material powder layer portion with electromagnetic radiation or particle radiation in order to produce a solidified second workpiece layer portion from the second raw material powder adjacent to the first workpiece layer portion, and during or before the step of removing, inducing a vibration into the powder bed with a vibration device. Further, a corresponding multi-material powder bed fusion apparatus for generating a three- dimensional workpiece from a powder bed is provided.

Description

[0001] Technique for powder extraction during a multi-material powder bed fusion process

[0002] The present invention generally relates to a technique for powder extraction during a multi-material powder bed fusion process for generating a three-dimensional workpiece from a powder bed. The multi-material powder bed fusion process may be, without limitation, selective laser sintering, selective laser melting, or electron beam melting.

[0003] Powder bed fusion is an additive layering process by which pulverulent, in particular metallic and / or ceramic raw materials can be processed to three-dimensional workpieces of complex shapes. To that end, a raw material powder layer is applied onto a carrier and subjected to radiation (e.g., laser or particle radiation) in a site-selective manner in dependence on the desired geometry of the workpiece that is to be produced. The radiation penetrating into the powder layer causes heating and consequently melting or sintering of the raw material powder particles. Further raw material powder layers are then applied successively to the layer on the carrier that has already been subjected to radiation treatment, until the workpiece has the desired shape and size. Powder bed fusion may be employed for the production of prototypes, tools, replacement parts, high value components, or medical prostheses, such as, for example, dental or orthopedic prostheses, on the basis of CAD data. Examples for powder bed fusion techniques include selective laser melting, selective laser sintering, and electron beam melting.

[0004] Apparatuses are known for producing one or more workpieces (also referred to as "objects") according to the above technique. For example, EP 2 961 549 Al and EP 2 878 402 Al, respectively, describe an apparatus for producing a three-dimensional workpiece according to the technique of selective laser melting. The general principles described above and / or in these documents may also apply to the technique of the present disclosure.

[0005] Further, a multi-material powder bed fusion process is generally known, wherein at least two different types of raw material powder (i.e., a first raw material powder and a second raw material powder) are used to built up a three-dimensional workpiece. In this way, a workpiece consisting of parts of at least two different martial types can be built up. In general, a known process of multi-material powder bed fusion may comprise at least the following steps:

[0006] (i) applying a first raw material powder to a substrate in order to produce a raw material powder layer consisting of the first raw material powder,

[0007] (ii) selectively irradiating the raw material powder layer consisting of the first raw material powder with electromagnetic radiation or particle radiation in order to produce a solidified first workpiece layer portion from the first raw material powder,

[0008] (iii) removing non-solidified first raw material powder from the substrate with a powder extraction device,

[0009] (iv) applying a second raw material powder to the substrate in order to produce a raw material powder layer portion consisting of the second raw material powder adjacent to the first workpiece layer portion, and

[0010] (v) selectively irradiating the raw material powder layer portion with electromagnetic radiation or particle radiation in order to produce a solidified second workpiece layer portion from the second raw material powder adjacent to the first workpiece layer portion.

[0011] As used herein, the term "adjacent" refers to sections next to each other within the same layer, i.e., having the same z-coordinates (in case the z-direction is defined perpendicular to the substrate). Thus, "adjacent", in particular, does not refer to sections on top of each other (i.e., having different z-coordinates). The raw material powder layer portion consisting of the second raw material powder is irradiated and solidified with the irradiation device or with a further irradiation device.

[0012] The above steps (i) to (v) can be repeated in order to produce the three-dimensional workpiece. Further, between the steps (v) and (i) of subsequent workpiece layers, a further step of removing may be carried out. In this further step of removing, nonsolidified second raw material powder is removed with the powder extraction device or with a further powder extraction device.

[0013] In this way, the three-dimensional workpiece consisting of at least two types of raw material powder can be built up.

[0014] One problem that may occur in the context of multi-material powder bed fusion is cross-contamination. In other words, it may be difficult to separate the first raw material powder and the second raw material powder from each other, such that the two types of powder are mixed, e.g., during the removal of the first and / or second powder and / or during the application of a new powder layer. Eventually, such crosscontamination may reduce the build quality of the generated workpiece since regions of the first material and the second material are not clearly separated from each other. Further, cross-contamination may make it difficult or even impossible to reuse the removed powder in case, e.g., the removed first raw material powder is contaminated with second raw material powder or vice versa.

[0015] The invention is therefore directed at the object of solving one of the above problems or a related problem. In particular, the invention is directed at the object of specifying a method and an apparatus that facilitate the production of high-quality multi-material workpieces.

[0016] This object is achieved by a method with the features of claim 1 and an apparatus with the features of claim 9.

[0017] According to a first aspect, a method for powder extraction during a multi-material powder bed fusion process for generating a three-dimensional workpiece from a powder bed is provided. According to the method, a first raw material powder is applied to a substrate in order to produce a raw material powder layer consisting of the first raw material powder. The raw material powder layer consisting of the first raw material powder is selectively, in particular site-selectively, irradiated with electromagnetic radiation or particle radiation to produce a solidified first workpiece layer portion from the first raw material powder. Located on the substrate is then the solidified first workpiece layer portion, which is surrounded by non-solidified, loose first raw material powder. If desired or necessary, in the selective irradiation of the raw material powder layer consisting of the first raw material powder, several first workpiece layer portions formed separately from one another can be produced that can be arranged distributed arbitrarily on the substrate and can be embedded into the surrounding layer of non-solidified first raw material powder.

[0018] The substrate may comprise a platform. The substrate may comprise at least one plate, in particular, at least one metal plate. The substrate may comprise a so-called plate package consisting of a plurality of plates. The substrate may comprise an upper surface onto which the raw material powder is applied and on which the workpiece is built. The upper surface may extend within a horizontal plane (e.g., x-y- plane). The substrate may be configured to be moved in a vertical direction (e.g., z- direction), in particular by using a substrate vertical movement device. Non-solidified first raw material powder is then removed from the substrate. In particular, the non-solidified first raw material powder is removed from an area of the substrate that is not covered by the first workpiece layer portion. For example, the non-solidified first raw material powder can be extracted by suction or otherwise removed from the substrate and if applicable also from a process chamber accommodating the substrate. In one or more embodiments, only the first workpiece layer portion is then still located on the substrate.

[0019] In the next step, a second raw material powder is now applied to the substrate in order to produce a raw material powder layer portion consisting of the second raw material powder adjacent to the first workpiece layer portion. The second raw material powder may be applied at least to the area of the substrate that is not covered by the first workpiece layer portion, so that following the application of the second raw material powder, the raw material powder layer portion consisting of the second raw material powder surrounds the first workpiece layer portion. It is accordingly understood here by the term "adjacent" that the raw material powder layer portion consisting of the second raw material powder and the first workpiece layer portion are arranged next to one another with regard to the substrate and not above one another on the substrate. Following application of the raw material powder layer portion to the substrate, a surface of the raw material powder layer portion facing away from the substrate and a surface of the first workpiece layer portion facing away from the substrate may be arranged substantially coplanar with one another.

[0020] The second raw material powder preferably consists of a material that differs from the material of the first raw material powder(s). For example, the first and the second raw material powder can be a metal powder and a metal alloy powder, respectively. Alternatively, however, it is also conceivable for the first and / or second raw material powder to consist of a ceramic material or a plastic material. Generally speaking, the first raw material powder may be a first type of raw material and the second raw material powder may be a second, different type of raw material. The first and second type may differ, e.g., in one or more of grain size, material, quality (e.g., number of impurities), etc.

[0021] The raw material powder layer portion consisting of the second raw material powder is now, like the raw material powder layer consisting of the first raw material powder previously, selectively, in particular site-selectively, irradiated with electromagnetic radiation or particle radiation, in order to produce a solidified second workpiece layer portion from the second raw material powder adjacent to the first workpiece layer portion. It is understood once again here by the term "adjacent" that the first workpiece layer portion and the second workpiece layer portion are arranged next to one another with regard to the substrate and not above one another on the substrate.

[0022] An irradiation unit that is used to irradiate the raw material powder layers applied to the substrate can comprise at least one optical element. The optical element can be a scan unit, a focusing unit and / or an F-theta lens, for example. Furthermore, the irradiation unit can comprise a radiation source, for example an electron beam source or a laser. The radiation emitted by the irradiation unit can also be supplied to the irradiation unit by a beam source, however, which is located outside the irradiation unit. Mirrors, optical fibres and / or other light conductors can be used for this, for example.

[0023] Following the selective irradiation of the raw material powder layer portion consisting of the second raw material powder, the solidified first workpiece layer portion and the solidified second workpiece layer portion are located on the substrate, the first and the second solidified workpiece layer portion being surrounded by non-solidified, loose second raw material powder. If desired or necessary, in the selective irradiation of the raw material powder layer portion consisting of the second raw material powder, several second workpiece layer portions formed separately from one another can also be produced, which can be arranged distributed arbitrarily adjacent to the at least one first workpiece layer portion on the substrate and can be embedded into the surrounding layer of non-solidified second raw material powder.

[0024] In the method described above, it is important to note that the step of applying the first raw material powder is not necessarily carried out such that the raw material powder layer is applied directly onto the substrate. The step of applying the first raw material powder may be a step during the course of building up the multi-material workpiece after one or more powder layers have already been applied and / or irradiated. In other words, the first raw material powder may be applied on top of an already solidified workpiece layer and / or on top of an underlying layer of non-solidified raw material powder.

[0025] Further, in the step of removing non-solidified first raw material powder, not only one powder layer may be removed but a plurality of raw material powder layers, e.g. 2, 3, 10, at least 10, at least 20, or at least 30. In particular, in methods of the prior art, it was necessary to remove approximately 30 powder layers of non-solidified raw material powder in order to avoid cross-contamination. A removal step had to be carried out at each powder change, i.e., each time the method changes from applying and solidifying the first material powder to applying and solidifying the second material powder and each time the method changes from applying and solidifying the second material powder to applying and solidifying the first material powder. This number of removed non-solidified raw material powder layers may be reduced according to the technique presented herein.

[0026] It should further be noted that a material change may but does not have to occur after every applied and solidified raw material powder layer. In other words, one or more layers of the first raw material powder may be applied and subsequently irradiated. After that, a removal step may be carried out, in which one or more (see above) layers of non-solidified first raw material powder are removed. Subsequently, one ore more layers of second raw material powder may be applied and solidified. This process may be carried out in the case that one or more workpiece layers of the workpiece are no multi-material layers in the sense that at least two raw material powders are solidified in one and the same layer. In other words, a powder change only has to be carried out when necessary and not when multiple layers of the same raw material powder shall be built up on top of each other.

[0027] In view of the above, the steps of applying and selectively irradiating (the first raw material powder) may be carried a plurality of times in a row. These steps may be carried out until a section of the workpiece consisting of the first raw material powder is finished. After that, the removing step is carried out. Subsequently, the steps of applying and selectively irradiating (the second raw material powder) may be carried out a plurality of times in a row. These steps may be carried out until a section of the workpiece consisting of the second raw material powder is finished. After that, a removing step, i.e., a step of removing non-solidified second raw material powder from the substrate with the powder extraction device or with a further powder extraction device, may be carried out.

[0028] Thus, after applying and solidifying one or more layers of the second raw material, the method may continue with applying and solidifying one or more layers of the first raw material powder. The method may therefore be carried out multiple times before the workpiece is finished. When the method changes from the second raw material powder to the first raw material powder, a step of removing non-solidified second raw material powder may be carried out, similar to the step of removing non-solidi- fied first raw material powder.

[0029] The method further comprises a step of, during or before the step of removing, inducing a vibration into the powder bed with a vibration device. The vibration may be induced at least into the powder bed, i.e., the one or more layers of non-solidified raw material powder that has been applied onto the substrate. The vibration may be induced over the air (e.g., via sound waves) or via direct contact, e.g., from the substrate or from a build cylinder wall. These options will be explained in more detail below.

[0030] In particular, the step of inducing the vibration into the powder bed with a vibration device may be carried out during the step of removing non-solidified first raw material powder from the substrate with the powder extraction device. In other words, the vibration device and the powder extraction device may operate at the same time, at least for a certain period of time. Thus, at least a section of an operation time of the vibration device may overlap with an operation time of the powder extraction device. The operation time of the vibration device may fully overlap with the operation time of the powder extraction device, such that the vibration device is not operated at times the powder extraction device is not operated. Additionally or alternatively, the operation time of the powder extraction device may fully overlap with the operation time of the vibration device, such that the powder extraction device is not operated at times the vibration device is not operated. In this way, an efficient loosening of powder and an improved extraction of powder may be achieved. When the vibration device is operated during the step of extraction, it can be ensured that the powder is not compacted again after being loosened by the vibration.

[0031] The above-described method may have the advantage that cross-contamination of the first raw material powder and the second raw material powder can be reduced. As a consequence, it may be sufficient to remove less powder layers of non-solidified powder in the step of removing as compared to prior art methods. The step of inducing the vibration may cause powder, which has been compacted (e.g., in previous steps of powder application and / or powder removal) to loosen, such that it can be removed easier by the powder extraction device. Further, the step of inducing the vibration may have the positive consequence that a surface of the powder bed (i.e., a surface of the non-solidified raw material powder) is levelled, such that it is plane and parallel to the substrate. The step of removing may comprise suction via a powder suction nozzle of the powder extraction device and / or magnetic removal via a magnet of the powder extraction device. The magnet may be an electric magnet. The powder suction nozzle may be connected to a powder storage container for storing the removed powder. Similarly, the magnet may be configured to transfer the removed powder to a powder storage container for storing the removed powder. From the powder storage container, the powder may be transferred to a powder preparation system, where the powder is cleaned and / or sieved in order to remove impurities. After that, the cleaned / sieved powder may be recycled into the process chamber, such that it can be applied again to the substrate.

[0032] The method may further comprise moving at least a powder extraction section of the powder extraction device in a horizontal direction parallel to the substrate. The powder extraction section may be a section of the powder extraction device, comprising the magnet or comprising the powder suction nozzle. In other words, the powder extraction section may be a section of the powder extraction device, which is configured to be moved to the raw material powder in order to remove it. Thus, the powder extraction section may be the section of the powder extraction device, which comes closest to the raw material powder to be removed, during removal. Further, not only the powder extraction section but the entire powder extraction device may be moved in the horizontal direction. For example, in the case of a powder suction nozzle, it may be possible that the nozzle forms a first end of a powder suction hose. In this case, the first end of the hose (which is configured to suck in the raw material powder) can be moved horizontally while a second end of the hose stays attached to a stationary section of the powder extraction device.

[0033] The method may further comprise, during the horizontal movement of the powder extraction section, pushing raw material powder along the horizontal direction with a brush, a rubber lip, or a scraper.

[0034] For example, the pushed raw material may be pushed along a horizontal upper surface of an already solidified section of the workpiece. The raw material powder may be removed by the powder extraction device while it is pushed.

[0035] The method may further comprise moving at least a powder extraction section of the powder extraction device in a vertical direction perpendicular to the substrate. In particular, the powder extraction section may be moved downwards, i.e., towards the substrate during the removal step. Thus, deeper layers of raw material powder (i.e., layers applied earlier) may be removed from the powder bed. For example, the powder removal may begin with a first layer or a plurality of layers including the first layer and move further downwards during the powder removal in order to remove deeper layers.

[0036] The vibration may be induced into the powder bed by means of a vibration unit coupled to the substrate. Additionally or alternatively, the vibration may be induced into the powder bed by means of a vibration unit coupled to a build cylinder wall.

[0037] The vibration device comprises the vibration unit and, optionally, one or more additional vibration units. Thus, the vibration device may comprise one or more vibration units. The vibration device may consist of one or more vibration units. The vibration units may be distributed such that, e.g., one vibration unit is arranged in or below the substrate and another vibration unit is arranged in or behind the build cylinder wall.

[0038] The build cylinder wall may be a side wall of the build cylinder into which the carrier is lowered during a build process. The build cylinder and, thus, the substrate, may have a substantially rectangular footprint.

[0039] Each one of the vibration devices may be configured to induce a vibration into the powder bed. The vibration units may comprise an electric motor rotating a mass, a linear motor moving a mass back and forth, a piezo actuator, a loudspeaker including a coil and a magnet, or any other suitable device for generating a vibration.

[0040] The vibration may be induced by emitting sound from a vibration unit in the form of a sound emitting device. The sound may comprise ultrasound or infrasound.

[0041] The vibration unit may therefore comprise a loudspeaker including a coil or a piezo speaker. The vibration unit may comprise a sound emitting device configured to generate sound waves that can be used for inducing a vibration into the powder bed. The sound may be emitted through the air towards a surface of the powder bed.

[0042] The sound emitting device may be attached to the powder extraction device, to a process chamber wall, or to a process chamber ceiling. Further, more than one vibration units comprising a sound emitting device may be provided. The sound emitting devices may be distributed to one or more of the aforementioned locations. The sound emitting device may be directed to a surface of the powder bed. The vibration may be induced into the powder bed by means of a gas blowing nozzle.

[0043] The gas blowing nozzle may be configured to blow a plurality of gas blasts towards the powder bed. The plurality of gas blasts may have a predefined constant duration and a predefined constant pitch, thereby inducing a vibration having a predefined constant frequency. A duration, a pitch, and / or an intensity of the gas blasts may be controllable. The gas emitted by the gas blowing device may be an inert gas, in particular argon or nitrogen.

[0044] The gas blowing nozzle may be integrated into a movable device comprising the gas blowing nozzle and a powder suction nozzle of the powder extraction device. The gas blowing nozzle and the powder suction nozzle may therefore form part of a so-called suction blowing nozzle, i.e., an integrated device being able to suck and blow, in particular, suck and blow simultaneously. The suction blowing nozzle may be provided movable with regard to the powder bed, in particular along a direction parallel to the powder bed.

[0045] The powder suction nozzle may be surrounding the gas blowing nozzle. Thus, in a top view (i.e., a view along a z-direction perpendicular to the powder bed), in a cross-sectional view, the gas blowing nozzle may be fully surrounded by the powder suction nozzle. In other words, the gas blowing nozzle may be provided within the powder suction nozzle.

[0046] The gas blowing nozzle may be subdivided into a plurality of gas blowing sections, wherein each of the gas blowing sections can be selectively activated and deactivated. For example, each of the gas blowing sections may be provided with a corresponding valve or shutter, which can be activated and deactivated by a control unit of the apparatus. Thus, the control unit can decide, which one or more of the gas blowing sections are active / not active at a given time. For example, the gas blowing sections may be controlled such that only gas blowing sections in a certain maximum distance to a build part are active and the remaining gas blowing sections are deactivated.

[0047] The first raw material powder and the second raw material powder may be applied by a powder application device, wherein a first powder suction nozzle is arranged in front of the powder application device and a second powder suction nozzle is arranged behind the powder application device with regard to a first movement direction of the powder application device parallel to the substrate.

[0048] The first movement direction may be a positive x-direction. The powder application device may be configured to carry out a movement along a second movement direction (negative x-direction) opposite to the first movement direction. The powder application device may be configured such that for at least two movement directions, there is always provided a powder suction nozzle in front and a powder suction nozzle behind the powder application device.

[0049] At least one of the first powder suction nozzle and the second powder suction nozzle may be integrated into a movable device comprising a gas blowing nozzle and the respective powder suction nozzle of the powder extraction device. Thus, at least one of the first powder suction nozzle and the second powder suction nozzle may be part of a suction blowing nozzle.

[0050] In the example described with regard to the first and second powder suction nozzle, a vibration may be applied to the powder bed according to any of the methods described herein. In particular, the vibration may be applied in the form of gas bursts coming from a gas blowing nozzle.

[0051] During movement in the first movement direction of the powder application device, second raw material powder may be applied by the powder application device simultaneously to first raw material powder being removed by the first powder suction nozzle. Thus, powder can be efficiently removed and deposited at the same time and an amount of runs of the powder application device and / or the powder removal device may be reduced.

[0052] The first powder suction nozzle and the second powder suction nozzle may be operated simultaneously during movement into the first movement direction while the powder application device is not operated. By operating both powder suction nozzles, powder can be reliably and thoroughly removed.

[0053] In a subsequent movement of the powder application device along a second movement direction opposite to the first movement direction, the powder application device may be operated while the first powder suction nozzle and the second powder suction nozzle are not operated. The subsequent movement is subsequent to the movement into the first movement direction mentioned above.

[0054] According to a second aspect, a multi-material powder bed fusion apparatus for generating a three-dimensional workpiece from a powder bed is provided. The apparatus comprises a substrate for accommodating the workpiece and a powder bed comprising a plurality of raw material powder layers, a powder application device for applying raw material powder the substrate, an irradiation device for selectively irradiating and solidifying portions of an uppermost raw material powder layer of the powder bed, a first powder storage configured to store a first raw material powder, a second powder storage configured to store a second raw material powder, first powder transfer means configured to transfer the first raw material powder to the powder application device, second powder transfer means configured to transfer the second raw material powder to the powder application device or to a further powder application device of the apparatus, a powder extraction device for removing non-solidified raw material powder from the substrate, beginning with the uppermost raw material powder layer of the powder bed, and a vibration device configured to induce a vibration into at least the powder bed.

[0055] The apparatus may be configured to carry out a multi-material powder bed fusion, i.e., a process, wherein a three-dimensional workpiece is generated, consisting of at least two raw material powders, in particular consisting of at least two types of raw material powder.

[0056] The apparatus of the second aspect may be configured to carry out the method of the first aspect. The apparatus may further be configured to carry out any of the method steps described in the present disclosure and, in particular, described above. Thus, the above-described details and features of the method of the first aspect may apply accordingly to the apparatus of the second aspect.

[0057] The powder extraction device may comprise a powder suction nozzle for powder suction and / or a magnet for magnetic removal of the non-solidified raw material powder.

[0058] The apparatus may further comprise a horizontal movement device configured to move at least a powder extraction section of the powder extraction device in a horizontal direction parallel to the substrate. The powder extraction device may comprise a brush, a rubber lip, or a scraper configured to push raw material powder along the horizontal direction. The brush, the lip, or the scraper may be arranged in front of the powder suction nozzle and / or the magnet of the powder extraction device with regard to the horizontal direction.

[0059] The apparatus may further comprise a vertical movement device configured to move at least a powder extraction section of the powder extraction device in a vertical direction perpendicular to the substrate.

[0060] The vibration device may comprise a vibration unit coupled to the substrate. In particular, according to a preferred embodiment, a vibration unit is coupled to the substrate in order to induce a vibration in the powder bed by causing a vibration of the substrate. To this end, the vibration unit may be integrated into the substrate or may be provided at a lower surface of the substrate, directly contacting the lower surface of the substrate. The vibration unit may be coupled to the lower surface of the substrate, e.g., by means of one or more of screws, bolts, clamps, glue, etc.

[0061] The vibration device may comprise a vibration unit coupled to a build cylinder wall of a build cylinder of the apparatus. The vibration device may comprise a vibration unit in the form of a sound emitting device. The sound emitting device may be attached to the powder extraction device, to a process chamber wall of a process chamber of the apparatus, or to a process chamber ceiling of the process chamber of the apparatus.

[0062] The vibration device may comprise a gas blowing nozzle.

[0063] The gas blowing nozzle may be integrated into a movable device comprising the gas blowing nozzle and a powder suction nozzle of the powder extraction device.

[0064] The powder suction nozzle may be surrounding the gas blowing nozzle.

[0065] The gas blowing nozzle may be subdivided into a plurality of gas blowing sections, wherein each of the gas blowing sections can be selectively activated and deactivated.

[0066] A movable device as described above and / or an operation of such a movable device (also referred to herein as suction blowing nozzle) may be claimed independently, i.e., without at least some of the features of the apparatus of the second aspect. The details described with regard to the suction blowing nozzle described herein may apply to an independently claimed suction blowing nozzle and / or to a suction blowing nozzle described in the context of the first or second aspect, in particular in the context of a vibration induced into the powder bed. The same applies to the corresponding method(s).

[0067] Thus, an apparatus may be claimed as follows: A multi-material powder bed fusion apparatus for generating a three-dimensional workpiece from a powder bed, the apparatus comprising: a substrate for accommodating the workpiece and a powder bed comprising a plurality of raw material powder layers; a powder application device for applying raw material powder the substrate; an irradiation device for selectively irradiating and solidifying portions of an uppermost raw material powder layer of the powder bed; a first powder storage configured to store a first raw material powder; a second powder storage configured to store a second raw material powder; first powder transfer means configured to transfer the first raw material powder to the powder application device; second powder transfer means configured to transfer the second raw material powder to the powder application device or to a further powder application device of the apparatus; a powder extraction device for removing non-so- lidified raw material powder from the substrate, beginning with the uppermost raw material powder layer of the powder bed, wherein the powder extraction device comprises a movable device comprising a gas blowing nozzle and a powder suction nozzle.

[0068] The powder application device may be configured to apply the first raw material powder and the second raw material powder, wherein a first powder suction nozzle is arranged in front of the powder application device and a second powder suction nozzle is arranged behind the powder application device with regard to a first movement direction of the powder application device parallel to the substrate.

[0069] At least one of the first powder suction nozzle and the second powder suction nozzle may be integrated into a movable device comprising a gas blowing nozzle and the respective powder suction nozzle of the powder extraction device.

[0070] The apparatus may further comprise a control unit, the control unit being configured such that during movement in the first movement direction of the powder application device, second raw material powder is applied by the powder application device simultaneously to first raw material powder being removed by the first powder suction nozzle. The control unit may be configured such that the first powder suction nozzle and the second powder suction nozzle are operated simultaneously during movement into the first movement direction while the powder application device is not operated.

[0071] The control unit may be configured such that, in a subsequent movement of the powder application device along a second movement direction opposite to the first movement direction, the powder application device is operated while the first powder suction nozzle and the second powder suction nozzle are not operated.

[0072] An apparatus comprising a first and second powder suction nozzle as described above may be claimed independently, i.e., without at least some of the features of the apparatus of the second aspect. The details described with regard to the first and second powder suction nozzles described herein may apply to an independently claimed apparatus and / or method described in the context of the second or first aspect, in particular in the context of a vibration induced into the powder bed. The same applies to the corresponding method(s).

[0073] Thus, an apparatus may be claimed as follows: A multi-material powder bed fusion apparatus for generating a three-dimensional workpiece from a powder bed, the apparatus comprising: a substrate for accommodating the workpiece and a powder bed comprising a plurality of raw material powder layers; a powder application device for applying raw material powder the substrate; an irradiation device for selectively irradiating and solidifying portions of an uppermost raw material powder layer of the powder bed; a first powder storage configured to store a first raw material powder; a second powder storage configured to store a second raw material powder; first powder transfer means configured to transfer the first raw material powder to the powder application device; second powder transfer means configured to transfer the second raw material powder to the powder application device or to a further powder application device of the apparatus; a powder extraction device for removing non-so- lidified raw material powder from the substrate, beginning with the uppermost raw material powder layer of the powder bed, wherein the powder extraction device comprises a first powder suction nozzle in front of the powder application device and a second powder suction nozzle behind the powder application device with regard to a first movement direction of the powder application device parallel to the substrate. The apparatus may further comprise a control unit configured to control the apparatus to carry out the method of the first aspect and / or any of the methods described above.

[0074] In particular, the control unit may be configured to control the apparatus to operate the vibration device and the powder extraction device at the same time, at least for a certain period of time.

[0075] Preferred embodiments of the invention are described in greater detail with reference to the appended schematic drawings, wherein

[0076] Fig. 1 shows a step of generating a multi-material workpiece with a multi-mate- rial powder bed fusion apparatus according to an embodiment of the present disclosure;

[0077] Fig. 2 shows another step of generating the multi-material workpiece with the multi-material powder bed fusion apparatus according to the embodiment of Fig. 1;

[0078] Fig. 3 shows a detail of a step of generating a multi-material workpiece according to a technique of the prior art;

[0079] Fig. 4 shows a detail of a multi-material powder bed fusion apparatus according to an embodiment of the present disclosure;

[0080] Fig. 5 shows a detail of a multi-material powder bed fusion apparatus according to an embodiment of the present disclosure;

[0081] Fig. 6 shows a detail of a multi-material powder bed fusion apparatus according to an embodiment of the present disclosure;

[0082] Fig. 7 shows a process of powder removal via a suction blowing nozzle;

[0083] Fig. 8 shows the suction blowing nozzle of Fig. 7 in a perspective view;

[0084] Fig. 9 shows how a blowing nozzle of the suction blowing nozzle can be subdivided into a plurality of sections, wherein each section can be selectively activated and deactivated; Figs. 10-15 show a schematic side view of an apparatus having a first powder suction nozzle and a second powder suction nozzle, wherein a process of simultaneous powder removal and powder application is shown; and

[0085] Figs. 16-24 show a schematic side view of an apparatus having a first powder suction nozzle and a second powder suction nozzle, wherein both the first and second powder suction nozzle are operated simultaneously.

[0086] In Figures 1 and 2, a multi-material powder bed fusion apparatus 10 for generating a three-dimensional workpiece 12 from a powder bed 62 is shown. The apparatus 10 comprises a process chamber 14 and an irradiation apparatus 16 arranged above the process chamber 14. The process chamber 14 is sealed against the ambient atmosphere so that an inert or reactive gas atmosphere or a pressure that is reduced compared with atmospheric pressure can be set if required in the process chamber 14. Arranged in the process chamber 14 is a substrate 18, which serves to hold raw material powder and the workpiece 12 produced from the raw material powder by an additive layering method. The substrate 18 can be displaced downwards in a vertical direction (z-direction) relative to the process chamber 14 into a build cylinder 20.

[0087] The irradiation apparatus 16 of the apparatus 10 comprises a beam source, preferably a laser source, which emits light at a wavelength of approximately 1064 nm, for example. Alternatively to this, the beam source (for example, a laser) can also be located outside of the irradiation apparatus 16 and a beam to be guided over the raw material powder can be supplied to the irradiation apparatus 16 by means of an optical fibre, for example. The irradiation apparatus 16 also has optical elements, such as a scan unit, a focusing unit and an F-theta lens, for example. The scan unit is adapted to scan the beam over the topmost raw material powder layer within a horizontal plane (in x-direction and y-direction). The focusing unit is adapted to change or adjust a focus position of the beam (in z-direction) so that a focal plane of the irradiation apparatus 16 is located in the area of the topmost raw material powder layer, which is irradiated by the irradiation apparatus 16. If desired the irradiation apparatus 16 can also comprise several scan units and if applicable also several radiation sources.

[0088] The apparatus 10 further comprises a powder application device 22, which is used to apply the raw material powder provided for production of the workpiece 12 in layers to the surface of the substrate 18. The powder application device 22 is adapted to apply different raw material powders to the substrate 18. In an alternative embodiment, separate powder application devices are provided for the different raw material powders, e.g., a first powder application device for a first raw material powder and a second powder application device for a second raw material powder.

[0089] In one embodiment, the powder application device 22 comprises a slider, which moves during operation of the powder application device 22 in a horizontal direction over the surface of the substrate 18 and has several powder reservoirs to hold the raw material powder to be applied to the substrate 18. The raw material powders can then be applied as required either all over or site-selectively to the substrate 18 by suitable control of the powder discharge from the powder reservoirs. In an alternative embodiment, the powder application device 22 comprises fixed powder reservoirs, which are arranged adjacent to the substrate 18, for example, and from which the slider of the powder application device 22 removes powder and distributes it over the surface of the substrate 18. The slider then comprises a nozzle, for example, which is movable across the substrate 18 in order to apply the raw material powder site-selectively if required to the substrate.

[0090] The apparatus 10 is further equipped with a powder extraction device 24, which makes it possible to remove raw material powder from the substrate 18. In the exemplary embodiment illustrated in the figures, the powder extraction device 24 comprises a flexible hose 26, which can be moved either manually, for example by means of intervention gloves, or automatically inside the process chamber 14.

[0091] The powder suction hose 26 has a first end and a second end. At the first end, a powder suction nozzle 60 is provided, wherein the second end is attached to a side wall of the process chamber 14. Thus, the first end of the hose 26 defines a powder extraction section of the powder extraction device 24. The first end of the hose 26 comprising the nozzle 60 can be moved over a surface of the powder bed while the second end stays fixedly attached to the wall of the process chamber 14. The first end can be moved horizontally via a horizontal movement device (not shown). In addition, according to an embodiment, the first end can be moved vertically via a vertical movement device (not shown).

[0092] The powder extraction device 24 further comprises a powder conveying apparatus 28, formed here by way of example as a suction pump and connected to the flexible hose 26. In operation of the powder extraction device 24, the first end of the hose 26 (powder extraction section) can be moved over the substrate 18. At the same time, the powder conveying apparatus 28 is operated so that raw material powder can be sucked from the substrate 28.

[0093] The powder conveying apparatus 28 is connected to a powder circuit 30, via which powder removed by means of the power extraction device 24 from the substrate 18 and from the process chamber 14 can be returned to the process chamber 14, i.e., a suitable powder reservoir of the powder application device 22. Provided in the powder circuit 30 is a powder preparation system 32, which is used to prepare powder removed from the substrate 18 by means of the powder extraction device 24 prior to its return to the process chamber 14. The power preparation system 32 can comprise a screening system, for example, by means of which the raw material powder can be cleaned and sized. The powder circuit 30 is also connected to a storage container 34. Raw material powder that has been removed from the substrate 18 by means of the powder extraction device 24 but is not to be returned directly to the process chamber 14 can be taken up in the storage container 34. The supply of raw material powder from the powder circuit 30 to the process chamber 14 or the storage container 34 is controlled by means of suitable control valves 36, 38.

[0094] The apparatus 10 further comprises a first powder storage 70 configured to store a first raw material powder and a second powder storage 72 configured to store a second raw material powder. The first and second raw material powders may be different types of raw material powder and, in particular, may differ with regard to at least one of material, grain size, quality, etc. First powder transfer means 74 are provided to transfer the first raw material powder from the first powder storage 70 to the powder application device 22. Second powder transfer means 76 are provided to transfer the second raw material powder from the second powder storage 72 to the powder application device 22. Each of the powder transfer means may comprise a powder transfer line comprising a tube and a powder conveying apparatus (not shown) similar to the powder conveying apparatus 28 described above. Further, one common powder conveying apparatus 28 may be provided and the respective powder transfer means 74 and / or 76 may be activated and deactivated via respective valves. It should further be noted that it is possible to provide one common powder application device 22 for both powders or two separate powder application devices, one for the first raw material powder and one for the second raw material powder.

[0095] Further, it should be noted that the storage container 34 may be connected to or may be the same as one of the powder storages 72 or 74. It should further be noted that the above-described components in the context of the powder extraction device 24 and the powder circuit 30 may be provided twice: a first set of components for removing the first raw material powder and a second set of components for removing the second raw material powder. This holds, in particular, for one or more of the components 60, 26, 24, 28, 30, 36, 34, 38, and 32. Hence, a first powder circuit 30 comprising a first powder extraction device 24 may be provided for removing the first raw material powder and a second powder circuit comprising a second powder extraction device may be provided for removing the second raw material powder.

[0096] The apparatus 10 further comprises a vibration device comprising one or more vibration units 44a-d. In the following, the vibration units 44a-d will be commonly referenced as vibration unit(s) 44. In Figures 1 and 2, four exemplary vibration units 44 are shown, wherein the disclosure is not limited to these four vibration units 44. In fact, one or more vibration units 44 may be provided, e.g., at one or more of the positions shown in Figures 1 and 2 and / or at one or more of the positions shown in Figures 4 to 6.

[0097] Vibration unit 44a is integrated into the substrate 18 and is configured to induce a vibration into the powder bed 62 via the substrate 18 on which the powder bed 62 is applied. In this disclosure, the powder bed 62 is defined as the total amount of nonsolidified raw material powder applied onto the substrate 18, irrespective whether it is first raw material powder or second raw material powder. Additionally or alternatively, a vibration unit could be arranged below the substrate 18 and coupled to the substrate. Vibration unit 44b is coupled to a build cylinder wall of the build cylinder 20. The build cylinder wall is a side wall of the build cylinder 20. The vibration unit 44b is configured to induce a vibration into the powder bed via the build cylinder wall, which directly contacts the powder bed 62. Vibration unit 44c is a sound emitting device attached to a process chamber wall of the process chamber 14. The process chamber wall is a side wall of the process chamber 14. The sound emitting device of vibration unit 44c is directed towards an upper surface of the powder bed 62. The vibration unit 44c is configured to generate sound waves that propagate towards the powder bed 62 and which induce a vibration within the powder bed 62. Vibration unit 44d is a sound emitting device attached to a process chamber ceiling of the process chamber 14. The sound emitting device of vibration unit 44d is directed towards an upper surface of the powder bed 62. The vibration unit 44d is configured to generate sound waves that propagate towards the powder bed 62 and which induce a vibration within the powder bed 62. Additional or alternative vibration units may be provided. For example, as explained below, a vibration unit may be attached to the powder extraction device 24, in particular, to the powder extraction section of the powder extraction device 24. The vibration unit attached to the powder extraction section of the powder extraction device 24 may be a sound emitting device directed towards an upper surface of the powder bed 62 and configured to generate sound waves that propagate towards the powder bed 62 and which induce a vibration within the powder bed 62.

[0098] To summarize the above, a vibration device comprising one or more vibration units 44 is provided, for inducing a vibration into the powder bed 62. The one or more vibration units 44 may be provided at any of the aforementioned positions (in particular, the positions of vibration units 44a-d) or at a different position of the apparatus 10.

[0099] A control unit 46 designed here in the form of an electronic control unit is used to control the operation of the apparatus 10. In particular, the control unit 46 is adapted to control the operation of the powder application device 22, the operation of the irradiation apparatus 16, and the operation of the vibration device automatically. If the powder extraction device 24 is suitable for automatic operation, the operation of the powder extraction device 24 is also controlled by the control unit 46.

[0100] A method for producing the three-dimensional workpiece 12 by means of the apparatus 10 illustrated in Figures 1 to 2 is explained below. In the method described here, a first raw material powder 50 is applied to the substrate 18 initially by means of the powder application device 22 under the control of the control unit 46, so that a raw material powder layer consisting of the first raw material powder 50 is produced on the substrate 18. This raw material powder layer is acted upon by means of the irradiation apparatus 16, again under the control of the control unit 46, site- selectively with laser radiation. The energy input of the laser radiation ensures local melting and / or sintering of the first raw material powder 50 and consequently a site- selective solidification of the raw material powder layer consisting of the first raw material powder 50. A solidified first workpiece layer portion 52 is produced here from the first raw material powder 50, see Figure 1.

[0101] On completion of the irradiation of the raw material powder layer consisting of the first raw material powder 50, the first workpiece layer portion 52 is consequently arranged on the substrate 18. Only one first workpiece layer portion 52 is illustrated in the figures. Depending on the geometry of the three-dimensional workpiece 12 to be produced, several first workpiece layer portions 52 can also be produced from the raw material powder layer consisting of the first raw material powder 50, however, which are then arranged adjacent to one another on the substrate 18. Furthermore, as yet non-solidified first raw material powder 50 is also located on the substrate 18 in the areas of the raw material powder layer consisting of the first raw material powder 50 that were not acted upon by laser radiation.

[0102] Further, the first workpiece layer portion 52 may be produced to have a thickness along the z-direction of more than one workpiece layer, in particular, in the case that no second workpiece layer portion(s) shall be bonded to the lower layers of the first workpiece layer portion 52. In other words, the first workpiece layer portion 52 may be produced for several workpiece layers like a normal one-material workpiece by applying and selectively irradiating sections of the first raw material.

[0103] The non-solidified first raw material powder 50 is then removed from the substrate 18 by means of the powder extraction device 24. To this end the powder extraction section of the powder extraction device 24 (i.e., the first end of the hose 26 comprising the nozzle 60) is guided manually or automatically across the substrate 18. The powder conveying apparatus 28 is operated at the same time, so that the non-solidified first raw material powder 50 is sucked from the substrate 18. The first raw material powder 50 extracted by means of the removal apparatus 24 from the process chamber 14 is prepared in the powder preparation system 32 and then either conducted into the storage container 34 or returned via the powder circuit 30 to the process chamber 14 by suitable control of the control valves 36, 38. If the first raw material powder 50 is conducted into the storage container 34, it can be used at a later time to produce another three-dimensional workpiece. In contrast thereto, first raw material powder 50 returned to the process chamber 14 is reused directly in the current build process to produce the three-dimensional workpiece.

[0104] The processing of only one first raw material powder 50 is illustrated in the figures. If desired, however, the steps described above of producing a first workpiece layer portion 52 by application of a first raw material powder 50 to the substrate 18 and subsequent selective irradiation with electromagnetic radiation or particle radiation and the subsequent removal of the non-solidified first raw material powder 50 from the substrate 18 can be carried out repeatedly, i.e., for two or more times. In this case different first raw material powders 50 can also be used. Several first workpiece layer portions 52, which can consist of the same material or of different materials, can be produced on the substrate 18 in this way. These first workpiece layer portions 52 are then arranged adjacent to one another on the substrate 18.

[0105] Following the removal of the non-solidified first raw material powder 50 from the substrate 18, a second raw material powder 54 is applied to the substrate 18 under the control of the control unit 46 by means of the powder application device 22. Here the application of the second raw material powder 54 to the substrate 18 takes place site-selectively, i.e. the second raw material powder 54 is applied only to the areas of the substrate 18 that are not covered by the first workpiece layer portion(s) 52. A raw material powder layer portion consisting of the second raw material powder 54 is accordingly produced on the substrate 18 adjacent to the first workpiece layer portion^) 52.

[0106] This raw material powder layer portion consisting of the second raw material powder 54 is acted upon by means of the irradiation apparatus 16, again under the control of the control unit 46, site-selectively with laser radiation. The energy input of the laser radiation ensures, as in the irradiation of the first raw material powder 50, local melting and / or sintering of the second raw material powder 54 and consequently site-selective solidification of the raw material powder layer portion consisting of the second raw material powder 54. A solidified second workpiece layer portion 56 is produced here from the second raw material powder 54, which portion is arranged adjacent to the first workpiece layer portion 52 on the substrate 18, see Figure 2.

[0107] In the exemplary embodiment shown in the figures, the first layer of the workpiece 12 comprises only one annular second workpiece layer portion 56. Depending on the geometry of the three-dimensional workpiece 12 to be produced, several second workpiece layer portions 56 can be produced from the raw material powder layer portion consisting of the second raw material powder 54, however, which are then arranged adjacent to one another and adjacent to the first workpiece layer portion(s) 52 on the substrate 18. As yet non-solidified second raw material powder 54 is also located on the substrate 18 in the areas of the raw material powder layer portion consisting of the second raw material powder 54 that were not acted upon by laser radiation.

[0108] The method for producing the three-dimensional workpiece 12 may continue by removing non-solidified second raw material powder 54 from the substrate 18 with the powder extraction device 24. It should be noted that a separate powder extraction device (not shown) may be provided for the second raw material powder 54. Further, a separate powder circuit with the corresponding elements of such a powder circuit (see the powder circuit 30 and its corresponding elements) may be provided for the second raw material powder 54.

[0109] Subsequently, the substrate 18 is lowered in the z-direction for one layer thickness and the method starts again with applying the first raw material powder to the substrate 18. For lowering the substrate 18, a substrate vertical movement device (not shown) is used. The method is continued until a last workpiece layer of the workpiece 12 has been finished. In this way, a multi-material workpiece 12 can be built up from at least the two raw material powders, i.e., the first raw material powder and the second raw material powder. Sections of the first raw material powder and the second raw material powder in the workpiece 12 can be arbitrarily generated since, for each workpiece layer, in fact two powder layers are generated (namely one powder layer of the first raw material powder and one powder layer of the second raw material powder).

[0110] It should further be noted that, during the step of removing the non-solidified first raw material powder (as well as during the step of removing the non-solidified second raw material powder), more than one powder layers may be removed. In the prior art, this was necessary in order to remove enough powder such that cross-contamination of the first powder and the second powder can be reliably prevented.

[0111] However, according to the technique of the present disclosure, a step of inducing a vibration into the powder bed is carried out. This may loosen and / or flatten the powder bed. Consequently, the amount of powder layers that have to be removed at the powder change may be reduced and cross-contamination of the first and second raw material powder may be reduced or prevented.

[0112] The step of inducing a vibration and the corresponding vibration device are described below in further detail. It should be noted that the vibration may be induced before and / or during the step of removing via the powder extraction device. For example, the vibration may be induced for a time span that is at least as long as the step of removing via the powder extraction device 24.

[0113] Figure 3 is a schematic representation of a section of an apparatus 10 as shown, e.g., in Figures 1 and 2. Figure 3 shows a situation that may occur during a multimaterial additive manufacturing process of the prior art. In Figure 3, a part of a multi-material workpiece 12 has already been built up on the substrate 18. Figure 3 is a schematic representation and the sections of workpiece 12 that have been generated from different powders are not individually indicated in the figure.

[0114] Further, the powder extraction section (i.e., the first end of hose 26) of the powder extraction device 24 is shown in Figure 3. The powder extraction section comprises the suction nozzle 60, through which raw material powder can be sucked in as described with regard to Figures 1 and 2 above. Further, as indicated by two doublesided arrows, the powder extraction section of the powder extraction device 24 can be moved at least along an x-direction (i.e., a horizontal direction parallel to an upper surface of the substrate 18) and along a z-direction (i.e., a vertical direction perpendicular to the upper surface of the substrate 18). The capability of moving along the vertical direction, however, is optional. In order to move the powder extraction section along the horizontal direction, a horizontal movement device (not shown) is provided, which comprises, for example, a linear motor configured to move the powder extraction section along the x-direction. In order to move the powder extraction section along the vertical direction, a vertical movement device (not shown) is provided, which comprises, for example, a linear motor configured to move the powder extraction section along the z-direction. The horizontal movement device and the vertical movement device may be integrated into one common movement device. Further, it may be possible to move the powder extraction section along the y-direc- tion (i.e., perpendicular to the x- and z-direction).

[0115] A powder pushing device 66 is coupled to the powder extraction section, wherein the powder pushing device 66 may comprise at least one of a brush, a rubber lip, and a scraper. The powder pushing device 66 is configured to push non-solidified raw material powder along the horizontal direction during the horizontal movement of the powder extraction section. Pushing of the powder may be carried out during powder extraction via the suction nozzle 60.

[0116] Further, the powder bed 62 is shown in Figure 3, wherein the two different powders are indicated in different brightness.

[0117] As shown in Figure 3, in apparatuses of the prior art, it could be the case that the use of the powder pushing device 66 leads to compacted powder 64 accumulating, in particular, at a wall region of the workpiece 12. It may be difficult or impossible to completely remove this compacted powder 64 via the powder extraction device 24. Hence, at least a part of the compacted powder 64 remains in the powder bed 62 even after a step of powder extraction (i.e., removing powder). Some of the compacted powder 64 may then be pushed into the following layer which is made of a different powder (in particular, a different material), mixing both powders together and causing cross-contamination. In the prior art, in order to prevent the aforementioned situation, many powder layers had to be removed by the powder extraction device 24.

[0118] Figure 4 shows an embodiment of a solution of the aforementioned problem and / or other problems of the prior art. The representation of Figure 4 is similar to Figure 3 and, therefore, only the different aspects of both techniques are described in the following. Aspects not mentioned in the following are the same as those discussed with regard to Figure 3. Further, the section shown in Figure 4 may be part of an apparatus 10 as shown in Figures 1 and 2.

[0119] According to Figure 4, a vibration device is provided, which is configured to induce a vibration into the powder bed 62. In the example shown in Figure 4, the vibration device comprises a vibration unit 44e coupled to the substrate 18. As shown, the vibration unit 44e may directly contact a lower surface of the substrate 18.

[0120] A vibration caused by the vibration unit 44e propagates via the substrate 18 into the powder bed 62. Thus, the embodiment of Figure 4 is similar to that shown in Figure 1, where the vibration unit 44a is located within the substrate 18. The vibration unit 44e may be a shaker or an ultrasound generator.

[0121] The vibration unit 44e is activated at least during the step of removing powder from the powder bed 62. In particular, each time the powder extraction device 24 is operated, the vibration unit 44e may be active. This may be the case for each vibration unit 44 described herein. Thus, during the powder removal, the powder may be loosened which may make it easier to remove the powder from the powder bed 62, in particular, since compacted powder 64 may be avoided. Further, the removal of the powder may be easier since a surface of the powder bed 62 may be flattened due to the vibration induced into the powder bed 62.

[0122] Figure 5 shows a further embodiment of another solution. The solution of Figure 5 may be combined with that shown in Figure 4. The representation of Figure 5 is similar to Figure 3 and, therefore, only the different aspects of both techniques are described in the following. Aspects not mentioned in the following are the same as those discussed with regard to Figure 3. Further, the section shown in Figure 5 may be part of an apparatus 10 as shown in Figures 1 and 2.

[0123] According to Figure 5, the vibration device comprises a vibration unit 44f. The vibration unit 44f is a sound generation device and is configured to emit a sound wave towards a surface of the powder bed 62 in order to induce a vibration into the powder bed 62. The vibration unit 44f may comprise a piezo speaker or a loudspeaker having a coil and a magnet. The vibration unit 44f is coupled to the powder extraction section of the powder extraction device 24. In particular, the vibration unit 44f is moved together with a movement (in particular, a horizontal movement) of the powder extraction section of the powder extraction device 24. The vibration unit 44f may be active and may remain active during a powder extraction via the powder extraction device 24.

[0124] In this regard, the description made above with regard to Figure 4 also applies to Figure 5.

[0125] Figure 6 shows a further embodiment of another solution. The solution of Figure 6 may be combined with that shown in Figure 4 and / or Figure 5. The representation of Figure 6 is similar to Figure 3 and, therefore, only the different aspects of both techniques are described in the following. Aspects not mentioned in the following are the same as those discussed with regard to Figure 3. Further, the section shown in Figure 6 may be part of an apparatus 10 as shown in Figures 1 and 2.

[0126] According to Figure 6, the vibration device comprises two vibration units 44g and 44h. Both vibration units 44g and 44h are sound generation devices and each of the units 44g and 44h is configured to emit a sound wave towards a surface of the powder bed 62 in order to induce a vibration into the powder bed 62. The vibration units 44g and 44h may comprise a piezo speaker or a loudspeaker having a coil and a magnet.

[0127] Each of the vibration units 44g and 44h may be coupled to a process chamber wall (a side wall of the process chamber 14) or a process chamber ceiling. Hence, the vibration units 44g and 44h may correspond to vibration units 44d and 44c shown in Figures 1 and 2. The vibration units 44g and 44h may be active and may remain active during a powder extraction via the powder extraction device 24. In this regard, the description made above with regard to Figure 4 also applies to Figure 6.

[0128] Fig. 7 shows another way of inducing a vibration into the powder bed 62. According to the embodiment shown in Fig. 7, a suction blowing nozzle 80 is provided. The suction blowing nozzle 80 is part of a powder extraction device. The suction blowing nozzle 80 comprises a gas blowing nozzle 82 and a powder suction nozzle 60. The powder suction nozzle 60 may be arranged in the form of a suction bell. As shown in the cross-sectional view of Fig. 7, the gas blowing nozzle 82 is arranged within the powder suction nozzle 60 (or suction bell). In particular, in a top view, the powder suction nozzle 60 may have a circular cross section, wherein the gas blowing nozzle 82 is arranged in the center of said circular cross section. However, the powder suction nozzle 60 may also have a rectangular cross section as shown, e.g. in Fig. 8.

[0129] The gas blowing nozzle 82 is attached to a gas blowing device of the powder extraction device. The gas suction nozzle 60 is attached to a gas suction device of the powder extraction device. The gas suction device and the gas blowing device may be the same device, e.g., a motor, a fan, or a blower. The gas sucked in by the gas suction device may be cleaned and, in particular, sucked in powder may be removed from the sucked in gas, e.g., by means of a cyclone separator, a filter, and / or a sieve. After that, the gas may be recirculated to the gas blowing nozzle. The gas blown through the gas blowing nozzle 82 is an inert gas, such as nitrogen or argon. The used gas may be the same that is used for establishing an inert gas atmosphere within the process chamber 14.

[0130] The gas blowing nozzle 82 is configured to blow a plurality of gas bursts towards the powder bed 62, thereby loosening the powder. This may enable sucking in the unsolidified powder with the gas suction nozzle 60 at a much lower absolute pressure than it would be required in case of no gas blowing nozzle 82. Further, the gas blowing nozzle 82 may already lift up powder particles towards the gas suction nozzle 60, which facilitates sucking these particles in by the powder suction nozzle 60.

[0131] The gas bursts emitted by the gas blowing nozzle 82 represent or cause a vibration induced in the powder bed 62. In particular, the gas bursts may have a constant preset duration and a constant preset pitch. Thus, a vibration with a constant frequency (corresponding to the pitch) may be induced in the powder bed 62. The suction blowing nozzle 80 represents a movable device. The suction blowing nozzle 80 may be movable, in particular, in a horizontal direction (e.g., x-direction) parallel to the substrate 18.

[0132] With the suction blowing nozzle 80, it is possible to prevent the situation shown in Fig. 3, where powder accumulates at the edge of the workpiece 12 (i.e., in a slipstream of the workpiece 12). By applying gas bursts with the gas blowing nozzle 82, this powder may be loosened and sucked in with the gas suction nozzle 60.

[0133] Fig. 8 shows a perspective view of the suction blowing nozzle 80. In the embodiment of Fig. 8, the gas suction nozzle 60 has a rectangular cross section and the gas suction nozzle 82 is arranged within the gas suction nozzle 60 and also has a rectangular but smaller cross section.

[0134] Fig. 9 shows a top view of the powder bed 62, wherein the gas blowing nozzle 82 of the suction blowing nozzle 80 is subdivided into a plurality of gas blowing sections 84, indicated by the small squares in Fig. 9. Each of the gas blowing sections 84 can be activated and deactivated individually and independently from each other. For example, only the gas blowing sections 84 in the vicinity of a build part of the workpiece 12 may be activated as shown in Fig. 9. More precisely, the gas blowing sections 84 having a distance to the build part smaller than a predefined maximum distance are activated, the remaining gas blowing sections 84 are deactivated. In this way, an efficient removal of the powder may be achieved.

[0135] The suction blowing nozzle 80 of at least one of the above-described Figs. 7 to 9 may also be used for removing powder in a multi-material powder bed fusion process, without the step of inducing a vibration. In other words, a constant gas stream may be emitted from the gas blowing nozzle 82, for example.

[0136] The suction blowing nozzle 80 described above may also be described as follows.

[0137] The background of the use of a suction blowing nozzle is the suction process in the powder bed that is necessary for a multi-material process. In a multi-material process, it is necessary to extract the powder from the construction cylinder before the next, different powder material is applied. The key factor here is to avoid mixing the two different powders to be processed. To ensure this, a suction depth of the powder in the construction cylinder of up to 3 mm may be necessary. When the powder is extracted, an air slip effect may occur at the edges of the workpiece, whereby the powder is not sufficiently removed at these edges. These areas result in contamination by foreign powder in the manufactured workpiece. Furthermore, a large pressure difference is necessary for the developing flow to be strong enough to suck the powder out of the powder bed.

[0138] Physical limits must be observed when accelerating the process and limit the suction power due to a maximum possible vacuum difference of approximately 1 bar. In addition, the large vacuum makes the prior art system susceptible to gas leakage, which can increase the oxygen content in the process. In addition, in a prior art system, high power is required to realize this pressure difference.

[0139] The idea involves a suction bell in which a relatively low suction flow is generated. The flow is so low that almost no powder is released from the powder bed. In this suction bell there is also a blowing nozzle that blows into the powder bed and thus swirls up the powder. The powder that has been swirled up is now transported away in the suction bell via the background flow (suction flow).

[0140] This injection of process gas makes it possible to achieve a significantly deeper effect in the powder bed. Powder removal at the component edges is significantly improved by injecting the powder bed from above. The overpressure in the blowing nozzle also makes it possible to achieve significantly higher powder removal rates, since larger pressure differences can be generated than with pure vacuum extraction. These advantages may reduce the construction time and at the same time may increase the component quality.

[0141] In addition, the vacuum pump power is significantly reduced, as is the potential oxygen input. It can be expected that the suction-blowing combination will reduce the height of the suction-blowing nozzle.

[0142] The gas for the blowing nozzle may be generated by a small additional compressor that takes the gas from the return line of the main pump. Alternatively, this function can be realized with an additional gas supply.

[0143] Optionally, selective powder removal could also be realized with a suction-blowing combination. In this case, the blowing nozzle would be divided into individual sections. The individual sections would then be switched on and off independently of each other. The suction cup and the suctioning process are identical. Selective powder removal would greatly reduce the total powder throughput, which in turn reduces the load on the powder conveyor and powder separator and can also reduce process times.

[0144] It should be noted that the embodiments of Figures 4 to 9 may be arbitrarily combined with each other. More precisely, one or more vibration units may be provided at any of the positions shown in Figures 4 to 9 or at a different position.

[0145] Figs. 10 to 15 show a schematic side view of an apparatus having a first powder suction nozzle and a second powder suction nozzle, wherein a process of simultaneous powder removal and powder application is shown.

[0146] In Figs. 10 to 24, reference signs are provided for Fig. 10, wherein in the following Figures 11 to 24, it should be understood that the same elements have the same reference signs although not explicitly indicated. For example, in each of Figures 10 to 24, areas 92 filled with small dots indicate unsolidified raw material powder of a first material, areas 94 filled with large dots indicate a solidified workpiece section of the first material, areas 96 filled with thin stripes indicate unsolidified raw material powder of a second material, and areas 98 filled with thick stripes indicate a solidified workpiece section of the second material.

[0147] In the following, it is referred to Figures 10 to 15. A movable powder application device 22 is provided, wherein the powder application device is movable, in particular in a first movement direction (positive x-direction) and a second movement direction (negative x-direction) opposite to the first movement direction. With regard to the first movement direction, a first powder suction nozzle 60a is arranged in front of the powder application device 22 and a second powder suction nozzle 60b is arranged behind the powder application device. The first and second powder suction nozzles 60a, 60b are attached to the movable powder application device 22, such that they are moved together with the powder application device 22.

[0148] Each of the powder suction nozzles 60a, 60b may be configured in the form of a blowing suction nozzle 80 as described above. However, the powder suction nozzles 60a, 60b may also be configured in the form of a pure suction nozzle. One or more vibration devices are provided as described in the above description. In particular, a vibration may be provided by a gas blowing nozzle integrated in one or both of the powder suction nozzles 60a, 60b.

[0149] Overflow containers 90a and 90b are provided at both sides of the substrate 18. The overflow containers 90a and 90b are configured to receive excess raw material powder.

[0150] In Figs. 10 to 15, an embodiment is shown, wherein the apparatus is controlled by a control unit such that the powder application device 22 and the powder suction nozzle 60a or 60b is operated simultaneously. Depending on a direction of movement (i.e., first or second movement direction) either the first powder suction nozzle 60a or the second powder suction nozzle 60b is operated simultaneously with the powder application device 22. With regard to a direction of movement, always the powder suction nozzle is operated, which is in front of the powder application device 22. Hence, when the powder application device 22 moves along the fist movement direction (positive x-direction), the first powder suction nozzle 60a is operated. When the powder application device 22 moves along the second movement direction (negative x-direction), the second powder suction nozzle 60b is operated.

[0151] In this way, powder can be removed and new powder can be applied simultaneously, i.e., in one run of the powder application device 22.

[0152] After application of raw material powder of the first or second material, said raw material powder is solidified by a radiation beam (in particular, a laser beam), as shown in Figs. 12 and 15.

[0153] Figures 16 to 24 show another embodiment, wherein no overflow containers 90a, 90b are needed. Only small cavities 100a, 100b are needed for temporarily collecting powder at each side of the substrate 18. Raw material powder that has been removed from the substrate 18 by means of the powder extraction device 24 during the movement of the powder application device over the substrate or powder material that has been removed out of the small cavities 100a, 100b and is not to be returned directly to the process chamber 14 can be taken up in the storage container 34. Therefore, the powder circuit 30 is also connected to a storage container 34 (shown in Fig. 1). In this way, there is no need for overflow containers 90a, 90b which reduces the needed amount of space and components. In the embodiment of Figures 16 to 24, the structural description of Figures 10 to 15 applies and is therefore not repeated. However, during movement of the powder application device 22 in a first run along the first movement direction (Figs. 16 to 19), both powder suction nozzles 60a, 60b are operated simultaneously. After that, a layer of new raw material powder is applied by the powder application device 22.

[0154] Then, during movement of the powder application device 22 in a second run along the second movement direction (Figs. 20 to 23), both powder suction nozzles 60a, 60b are operated simultaneously.

[0155] The apparatuses shown in Figs. 10 to 24 and the corresponding operations may also be implemented without a vibration device, i.e., without inducing a vibration into the powder bed 62.

[0156] The apparatuses shown in Figs. 10 to 24 and the corresponding operations of Figs. 10 to 15 and Figs. 16 to 24 may also be described as follows.

[0157] Challenges lie in a multi-material process with long process times due to successive suction and coating of the powder layers, the cross-contamination of the powder during powder layer application. Furthermore, the amount of powder from the different locations (powder bed and the two overflows) is an effort for the powder handling in the preparation for reuse of the powder.

[0158] A core idea is the simultaneous application and extraction of powder. To do this, the coater is equipped with a suction nozzle at the rear (rear suction) and a suction nozzle at the front (front suction). This makes it possible to extract the powder previously required from the powder bed and at the same time apply the next powder required in a single coating process. With the implementation of rear and front suction, all powder can be removed from the process chamber floor. This means that a great deal of progress can be made in terms of the purity of the powder in the powder bed. With this approach, it is possible to dispense with the overflows. The powder can be collected in a flat recess in the process chamber floor and removed by the two suction nozzles. The tanks at the overflows and, in the case of a reloop system, the collection (powder conveying) of these are no longer necessary.

Claims

Claims1. A method for powder extraction during a multi-material powder bed fusion process for generating a three-dimensional workpiece (12) from a powder bed (62), the method comprising:(i) applying a first raw material powder (50) to a substrate (18) in order to produce a raw material powder layer consisting of the first raw material powder (50),(ii) selectively irradiating the raw material powder layer consisting of the first raw material powder (50) with electromagnetic radiation or particle radiation in order to produce a solidified first workpiece layer portion (52) from the first raw material powder (50),(iii) removing non-solidified first raw material powder (50) from the substrate (18) with a powder extraction device (24),(iv) applying a second raw material powder (54) to the substrate (18) in order to produce a raw material powder layer portion consisting of the second raw material powder (54) adjacent to the first workpiece layer portion (52),(v) selectively irradiating the raw material powder layer portion with electromagnetic radiation or particle radiation in order to produce a solidified second workpiece layer portion (56) from the second raw material powder (54) adjacent to the first workpiece layer portion (52), and(vi) during or before the step of removing, inducing a vibration into the powder bed (62) with a vibration device.

2. The method of claim 1, wherein the step of removing comprises suction via a powder suction nozzle (60) of the powder extraction device (24) and / or magnetic removal via a magnet of the powder extraction device (24).

3. The method of claim 1 or 2, further comprising moving at least a powder extraction section of the powder extraction device (24) in a horizontal direction parallel to the substrate (18).

4. The method of claim 3, further comprising, during the horizontal movement of the powder extraction section, pushing raw material powder along the horizontal direction with a brush, a rubber lip, or a scraper.

5. The method of any of claims 1 to 4, further comprising moving at least a powder extraction section of the powder extraction device (24) in a vertical direction perpendicular to the substrate (18).

6. The method of any of claims 1 to 5, wherein the vibration is induced into the powder bed (62) by means of a vibration unit (44) coupled to the substrate (18) and / or wherein the vibration is induced into the powder bed (62) by means of a vibration unit (44) coupled to a build cylinder wall.

7. The method of any of claims 1 to 6, wherein the vibration is induced by emitting sound from a vibration unit (44) in the form of a sound emitting device.

8. The method of claim 7, wherein the sound emitting device is attached to the powder extraction device (24), to a process chamber wall, or to a process chamber ceiling.

9. The method of any of claims 1 to 5, wherein the vibration is induced into the powder bed (62) by means of a gas blowing nozzle.

10. The method of claim 9, wherein the gas blowing nozzle is integrated into a movable device comprising the gas blowing nozzle and a powder suction nozzle (60) of the powder extraction device (24).

11. The method of claim 10, wherein the powder suction nozzle (60) is surrounding the gas blowing nozzle.

12. The method of any of claims 1 to 11, wherein the gas blowing nozzle is subdivided into a plurality of gas blowing sections, wherein each of the gas blowing sections can be selectively activated and deactivated.

13. The method of any of claims 1 to 12, wherein the first raw material powder (50) and the second raw material powder (54) are applied by a powder application device, wherein a first powder suction nozzle is arranged in front of the powder application device and a second powder suction nozzle is arranged behind the powder application device with regard to a first movement direction of the powder application device parallel to the substrate.

14. The method of claim 13, wherein at least one of the first powder suction nozzle and the second powder suction nozzle is integrated into a movable device comprising a gas blowing nozzle and the respective powder suction nozzle of the powder extraction device (24).

15. The method of claim 13 or 14, wherein, during movement in the first movement direction of the powder application device, second raw material powder is applied by the powder application device simultaneously to first raw material powder being removed by the first powder suction nozzle.

16. The method of any of claims 13 to 15, wherein the first powder suction nozzle and the second powder suction nozzle are operated simultaneously during movement into the first movement direction while the powder application device is not operated.

17. The method of claim 16, wherein, in a subsequent movement of the powder application device along a second movement direction opposite to the first movement direction, the powder application device is operated while the first powder suction nozzle and the second powder suction nozzle are not operated.

18. A multi-material powder bed fusion apparatus (10) for generating a three-dimensional workpiece (12) from a powder bed (62), the apparatus (10) comprising: a substrate (18) for accommodating the workpiece (12) and a powder bed (62) comprising a plurality of raw material powder layers; a powder application device (22) for applying raw material powder (50) the substrate (18); an irradiation device (16) for selectively irradiating and solidifying portions of an uppermost raw material powder layer of the powder bed (62); a first powder storage (70) configured to store a first raw material powder (50); a second powder storage (72) configured to store a second raw material powder (54); first powder transfer means (74) configured to transfer the first raw material powder (50) to the powder application device (22); second powder transfer means (76) configured to transfer the second raw material powder (54) to the powder application device (22) or to a further powder application device of the apparatus (10);a powder extraction device (24) for removing non-solidified raw material powder (50) from the substrate (18), beginning with the uppermost raw material powder layer of the powder bed (62); and a vibration device configured to induce a vibration into at least the powder bed (62).

19. The apparatus (10) of claim 18, wherein the powder extraction device (24) comprises a powder suction nozzle (60) for powder suction and / or a magnet for magnetic removal of the non-solidified raw material powder.

20. The apparatus (10) of claim 19, further comprising a horizontal movement device configured to move at least a powder extraction section of the powder extraction device (24) in a horizontal direction parallel to the substrate (18).

21. The apparatus (10) of claim 20, wherein the powder extraction device (24) comprises a brush, a rubber lip, or a scraper configured to push raw material powder along the horizontal direction, wherein, in particular, the brush, the lip, or the scraper is arranged in front of the powder suction nozzle (60) and / or the magnet of the powder extraction device (24) with regard to the horizontal direction.

22. The apparatus (10) of any of claims 18 to 21, further comprising a vertical movement device configured to move at least a powder extraction section of the powder extraction device (24) in a vertical direction perpendicular to the substrate (18).

23. The apparatus of any of claims 18 to 22, wherein the vibration device comprises a vibration unit (44) coupled to the substrate (18) and / or wherein the vibration device comprises a vibration unit (44) coupled to a build cylinder wall of a build cylinder (20) of the apparatus (10) and / or wherein the vibration device comprises a vibration unit (44) in the form of a sound emitting device, the sound emitting device being preferably attached to the powder extraction device (24), to a process chamber wall of a process chamber (14) of the apparatus (10), or to a process chamber ceiling of the process chamber (14) of the apparatus (10).

24. The apparatus of any of claims 18 to 22, wherein the vibration device comprises a gas blowing nozzle.

25. The apparatus of claim 24, wherein the gas blowing nozzle is integrated into a movable device comprising the gas blowing nozzle and a powder suction nozzle (60) of the powder extraction device (24).

26. The apparatus of claim 25, wherein the powder suction nozzle (60) is surrounding the gas blowing nozzle.

27. The apparatus of any of claims 24 to 26, wherein the gas blowing nozzle is subdivided into a plurality of gas blowing sections, wherein each of the gas blowing sections can be selectively activated and deactivated.

28. The apparatus of any of claims 1 to 27, wherein the powder application device is configured to apply the first raw material powder (50) and the second raw material powder (54), wherein a first powder suction nozzle is arranged in front of the powder application device and a second powder suction nozzle is arranged behind the powder application device with regard to a first movement direction of the powder application device parallel to the substrate.

29. The apparatus of claim 28, wherein at least one of the first powder suction nozzle and the second powder suction nozzle is integrated into a movable device comprising a gas blowing nozzle and the respective powder suction nozzle of the powder extraction device (24).

30. The apparatus of claim 28 or 29, further comprising a control unit, the control unit being configured such that during movement in the first movement direction of the powder application device, second raw material powder is applied by the powder application device simultaneously to first raw material powder being removed by the first powder suction nozzle.

31. The apparatus of any of claim 30, wherein the control unit is configured such that the first powder suction nozzle and the second powder suction nozzle are operated simultaneously during movement into the first movement direction while the powder application device is not operated.

32. The apparatus of claim 31, wherein the control unit is configured such that, in a subsequent movement of the powder application device along a second movement direction opposite to the first movement direction, the powder application device isoperated while the first powder suction nozzle and the second powder suction nozzle are not operated.

33. The apparatus (10) of any of claims 18 to 32, further comprising a control unit (46) configured to control the apparatus (10) to carry out the method of any of claims 1 to 17.

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