Laminating shaping system for powdery starting materials and method for manufacturing parts

Abstract

The present invention relates to an additive manufacturing system for powder-like starting materials, which includes an electron beam gun 6 as an irradiation unit. The system is configured with improved shielding against ionizing radiation, in particular X-rays. By using the additive manufacturing system according to the invention, a compact and lightweight shielding of the construction area is achieved.

Description

Technical Field

[0001] The present invention relates to a laminating shaping system for powder starting materials that includes an electron beam gun as an irradiation unit. The system is configured to improve shielding from ionizing radiation, particularly X-rays.

Background Art

[0002] Devices and methods for the laminated shaping of workpieces are also known under the term additive manufacturing (AM) and are known from the prior art. The terms "generative manufacturing method" or "3D printing" are also used. The raw material may be in powder form or liquid form. Powder processes include, for example, Selective Laser Melting (SLM), Selective Laser Sintering (SLS), or Electron Beam Melting (EBM). The raw material consists of plastic or metal.

[0003]

[0004] A system operating by an Electron Beam Melting (EBM) process uses one or more electron beam guns as radiation sources, unlike a laser process. In these uses, when an electron beam collides with the powder surface, X-rays are generated in addition to desirable heat, so these systems need to shield ionizing radiation. Currently, in order to shield ionizing radiation, especially X-rays, a coating made mainly of lead or steel is laboriously attached to the walls of the system. In order to reliably absorb ionizing radiation, a minimum thickness of these coatings is required. As a result, the system becomes very heavy and maintenance becomes difficult. Furthermore, thick coatings also cause high costs. Additionally, lead has physiological problems.

Summary of the Invention

[0005] Objective In view of such problems, it is an object of the present invention to provide a additive manufacturing system including an electron beam gun that overcomes the drawbacks of prior art devices. In particular, an object of the present invention is to provide a device capable of implementing a shield with smaller and lighter dimensions without impairing the construction process, and a method for manufacturing parts using the same.

[0006] This object is achieved by the additive manufacturing system according to claim 1 and the method for manufacturing parts according to claim 11. Variations of the preferred forms are the subject matter of the dependent claims.

[0007] The additive manufacturing system of the present invention for a powdery starting material includes a vacuum chamber, wherein the vacuum chamber has at least one construction area with a construction platform, and at least one powder reservoir arranged on the side of the construction area, At least one powder application element that is horizontally movable between at least one of the powder reservoirs and at least one of the construction platforms for supplying a powdery starting material from at least one of the powder reservoirs to at least one of the construction platforms, the at least one powder application element traversing the construction area at least once per powder distribution process, and, At least one electron beam gun attached to at least one of the construction areas is configured to include, At least one of the construction areas is surrounded by a shield against ionizing radiation, the shield being composed of four walls, two of which can be formed by the walls of the vacuum chamber, The walls of the shield on at least two sides in the moving direction of at least one of the powder application elements consist of an upper part and a lower part, The upper part is firmly connected to the vacuum chamber and is formed by 2 to 11 horizontally spaced metal sheets, having a height above the construction platform such that the powder application element can move horizontally through the construction area, The lower part is connected to a vertically movable frame and is arranged to mesh with the metal sheets of the upper part, and is formed by 2 to 11 horizontally spaced refractory metal sheets that are radiation-impermeable and attached to the movable frame, and, The lower part is movable relative to the upper part in the vertical direction between a closed position and an open position, and the refractory metal sheets of the lower part are, In the closed position, their lower edges are arranged to mesh with a groove structure on the surface of the construction area while forming a labyrinth structure, and their upper edges are arranged to mesh with the metal sheets of the upper part while forming a labyrinth structure, In the open position, it is characterized by being stationary between the upper metal sheets to such an extent that at least horizontal movement through the construction area of the powder application element is possible.

[0008] The additive manufacturing system according to the invention can comprise a plurality of electron beam guns covering individual regions of a larger construction platform, or can also comprise a plurality of construction platforms each with one or more electron beam guns attached. In the latter setup, in this case, there is the advantage that only a single vacuum chamber needs to be evacuated.

[0009] In the context of the present application, the construction area is understood to mean the area within the vacuum chamber of the additive manufacturing system in which the construction platform is located, onto which the powdered starting material is impinged by an electron beam and thus components are manufactured.

[0010] The powder application element can be, for example, a doctor blade or an application roller. The powder supplied from the powder reservoir for the next layer of the component is evenly distributed by the powder application element over the surface of the construction platform or the layer already arranged thereon. For this purpose, the powder application element traverses the entire construction area once. Its movement is made at least to the end of the construction platform and generally, since a collection container for excess powder or another powder reservoir is usually attached there, to the end position of the wall on the completely opposite side. As a result, no equipment can be attached above the movement area of the powder application element, especially above the construction platform. However, this is the location where X-ray radiation is generated when the electron beam impinges on the powder surface.

[0011] In the additive manufacturing system according to the invention, this problem is solved in that a shield against ionizing radiation that can be raised in synchronization with the movement of the powder application element is used directly around the construction area. Thus, it is not necessary to provide a shield over the entire outer wall of the system, and since it is arranged closer to the source point of the radiation, a much smaller shielding surface is sufficient. In this way, a significant weight saving can be achieved simply by reducing the surface area.

[0012] However, in this case, if the shielding surface of the outer wall is simply reduced and designed in the same way, there remains the problem that a significant mass has to be moved. In addition to the mechanical stresses and a stable mechanism commensurate with them, the movement of the heavy mass cannot be as fast as that of a normal powder application element, so the construction process is also slowed down.

[0013] To solve this problem, the shield against ionizing radiation according to the invention is not made of a solid plate that has to be moved completely and requires a vacuum-tight passage to be provided in the ceiling of the vacuum chamber. Instead, the shield is split into an upper part fixed to the ceiling of the vacuum chamber and a movable lower part. As a result, only the part located within the movement range of the powder application element needs to be moved. Furthermore, by replacing the solid sheet with a number of thin sheets arranged at intervals, the upper and lower sheets can be moved so as to engage with each other. This engagement arrangement forms a labyrinth structure, ensuring the absence of a direct beam path, and the radiation is reflected several times by the meshing metal sheets and thus decelerated.

[0014] Furthermore, the sheet of the movable lower part is made of a refractory metal. When the term "refractory metal sheet" is mentioned in the present application, this is understood to be a sheet made of a mixture or alloy containing 50% by weight or more, for example 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, particularly 99% by weight or more of a refractory metal. As a result, in the context of the present application, refractory metals are understood to be high melting point metals such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, etc. In addition to the high melting point, high density and, above all, a high specific absorption coefficient for ionizing radiation are the main characteristics. For this reason, shielding performance equivalent to that of the thick lead or steel layers of conventional outer walls can be achieved with a thinner sheet. Here, the advantage of the particularly high heat resistance of refractory metals, especially compared to lead, is very important, as the shield can be moved closer to the radiation source, so that less area is required. Furthermore, since lead has insufficient mechanical stability, it cannot be attached to the movable frame in sheet form for mechanical reasons alone without a temperature increase. In this case, the steel one has high stability but a low absorption coefficient, so it has to be thickened and becomes heavy.

[0015] The lower refractory metal sheet preferably consists of tungsten, molybdenum, rhenium, tantalum and / or a mixture or alloy thereof. Tungsten, molybdenum, tantalum and / or a mixture or alloy thereof are particularly preferred. The alloy and mixture can preferably contain copper.

[0016] The upper part of the shield does not need to be moved and does not necessarily have to be made of a refractory metal, but it is also possible to be composed of other metals from a cost perspective. However, when the vacuum chamber has to be kept very low or a very high temperature has to be generated to process the metal powder, it may still be desirable to manufacture the upper sheet from a refractory metal. In this case, the same refractory metal as the lower part can be used. In design variations, the upper metal sheet consists of stainless steel, copper, refractory metal and / or a mixture or alloy thereof.

[0017] It has been found advantageous to design the individual upper sheets to decrease in length from the outside to the inside. In this case, the lower edges are evenly arranged and the upper edges are stepped offset. This facilitates the attachment of the metal sheet to the ceiling of the vacuum chamber.

[0018] The number of upper and lower sheets is determined by the output of the electron beam gun and the resulting ionizing radiation, and by the metal used. Depending on the absorption capacity of the selected metal, it has been found that 2 to 11 sheets are optimal. For safety reasons, it is preferred that the number of sheets be selected such that one more sheet is always installed than the number required for shielding.

[0019] For cost reasons, the shield is preferably manufactured from individual refractory metal sheet parts commercially available in standard dimensions. Each layer of the refractory metal sheet is preferably provided with at least two Joints (Stoesse) are provided. In the upper and / or lower Joints (Stoessen) to avoid tilting caused by distortion due to thermal expansion, the sheets are made not to overlap. The individual sheets can have a gap of up to 50 mm, up to 40 mm, up to 30 mm or up to 20 mm in Joints (Stoessen) . The gap is preferably 5 mm to 25 mm, most preferably 10 mm to 20 mm. The Joints (Stoesse) between two consecutive layers of the refractory metal sheet in the upper and / or lower are not arranged in alignment with each other, respectively, to avoid a free beam path.

[0020] The lower refractory metal sheets preferably each have a thickness of 0.1 to 20 mm. The thickness of the sheets can be 0.1 to 20 mm, 0.5 to 15 mm, 1 to 10 mm, 2 to 8 mm, or 3 to 6 mm. In particular, the thickness can be at most 20 mm, at most 15 mm, at most 10 mm, at most 8 mm, or at most 6 mm. In particular, it can be at least 0.1 mm, at least 0.5 mm, at least 1 mm, at least 2 mm, or at least 3 mm.

[0021] In addition to the refractory metal sheets, the lower part can also be composed of one or two stainless steel layers as the innermost layer for additional heat protection. These can be arranged as a double layer at a smaller distance from each other than the refractory metal plates. The stainless steel sheets mainly function as a heat countermeasure, but also have a slight effect on radiation countermeasures. This protects the more expensive refractory metal sheets from heat and aims to extend their lifespan. On the other hand, the cheaper stainless steel sheets need to be replaced more frequently.

[0022] The upper metal sheets preferably each have a thickness of 1 to 100 mm. The thickness of the metal sheets can be 1 to 100 mm, 2 to 75 mm, 3 to 50 mm, 4 to 25 mm, or 5 to 15 mm. In particular, the thickness can be at most 100 mm, at most 75 mm, at most 50 mm, at most 25 mm, or at most 15 mm. In particular, it can be at least 1 mm, at least 2 mm, at least 3 mm, at least 4 mm, or at least 5 mm. The thickness of the upper metal sheets is preferably designed to match that of the lower refractory metal sheets so that the upper and lower parts absorb approximately the same amount of radiation. The upper metal sheets do not necessarily have to be of uniform thickness. For example, it is also possible to make the outer side of the stacked sheets thicker than the inner side.

[0023] Most preferably, the lower refractory metal sheet and the upper metal sheet have a distance of 1 mm to 50 mm from each other when meshed. Therefore, the distance between the refractory metal sheets is, for example, 1 mm + the thickness of the upper metal sheet + 1 mm. In any case, in order to reliably realize the radiation trap, it is preferable that the distance between the sheets is much smaller than the height of the sheets. In particular, the distance between the sheets is preferably at most about half of the distance at which the upper and lower parts mesh in the closed state. By doing so, multiple reflections can be maximized in the generated optical ray labyrinth.

[0024] A corresponding groove is formed on the upper surface of the construction area, and in the state where the shield is closed, the lower edge of the sheet at the lower part of the shield engages with the upper edge of the sheet at the upper part in the same way as the lower edge of the upper sheet. Therefore, a labyrinth is also formed on the lower side of the lower part of the shield, and it is possible to prevent radiation from escaping in advance.

[0025] In one embodiment, the lower refractory metal sheet has a density of 10 g / cm (at 20 °C) 3 or more.

[0026] Shielding against ionizing radiation can be constructed in two different ways. In either case, it is composed of four walls and is constructed to surround the construction area for shielding. Two of these walls can be formed by the outer walls of the vacuum chamber, and thus the shielding material is arranged in the normal way. This material may be a normal material such as lead or steel, but preferably lead is not used and refractory metal or steel is used. In this case, these two walls become the walls of the shield that do not lie across the moving direction of the powder application element. And the wall that lies across the moving direction of the powder application element is designed in two parts, the upper and the lower, so that the shield can be raised to allow the powder application element to pass through.

[0027] However, it is more desirable to use four separate walls for shielding. This results in the shortest distance to the radiation source on all sides and uses the smallest surface area and mass of the shield.

[0028] Most preferably, all four walls of the shield consist of an upper part and a lower part. This is particularly advantageous because with two fixed walls, all kinds of powder application elements or their drives are not possible. For example, in the case of a doctor blade, if these are guided and / or driven laterally, all four walls have to be raised so that the doctor blade can pass above the construction area. Therefore, the degree of freedom in the design of the powder application element is increased.

[0029] In a design variation, the radiation-impermeable attachment of the lower refractory metal sheet to the movable frame consists of spacer bolt fasteners with two different diameters. The first diameter is dimensioned to match the holes in the refractory metal sheet. The second diameter that the spacer bolt has outside the holes is larger so that radiation passing through the holes is shielded by the spacer bolt as well as by the refractory metal sheet in the non-open area of the holes.

[0030] In a preferred design variation, the powder application element is a doctor blade or a roller.

[0031] The method for manufacturing a component using the additive manufacturing system of the present invention includes the following steps. a) Prepare an additive manufacturing system according to the present invention, b) Supply a powdery starting material into at least one powder reservoir, evacuate the vacuum chamber, c) Move the lower part of the shield to an open position, d) By horizontally moving the powder application element between at least one powder reservoir and at least one construction platform while completely traversing the construction area at least once, supplying a powdery starting material onto at least one construction platform, e) Moving the lower part of the shield to the closed position, f) Generating a layer of the component by irradiating the powdery starting material with at least one electron beam gun, g) Repeating steps c) to f) until the component is completed.

[0032] Due to the design of the powder application element and the coating process, the powder layer can be applied either in a simple single movement or in a reciprocating movement. In the latter case, after the second movement, the shield remains open until the powder coating element returns to its starting position. Then, the shielding plate descends and the irradiation is started.

[0033] The radiation is only carried out while the shield is closed. While the shield is open, the electron gun is deactivated.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0035] Description of the Drawings The figures merely show variants of preferred embodiments as an example of the present invention. Therefore, they should not be understood as limiting.

[0036] FIG. 1 is a cross-sectional perspective view showing a laminated manufacturing system according to the present invention. Inside a vacuum chamber (1), a construction area (2) is arranged, and inside that, a single construction platform (3) is arranged. This is shown at the upper starting position at the start of construction. On the left and right sides of the construction area (2), there are respective powder reservoirs (4) having adjacent slots for receiving excess powder. A powder application element (5), in this example a doctor blade suspended from a movable traverse, conveys from the powder reservoir (4) an amount of powder slightly more than the required amount for one layer of the part onto the construction platform (3) in the construction area (2), so as to ensure that the entire surface of the construction platform (3) is uniformly coated. The excess powder is conveyed through the slot over to the opposite powder reservoir (4) and from there to a collection container. In FIG. 1, the powder application element (5) is in the starting position on the left.

[0037] The electron beam gun (6) is embedded in the ceiling of the vacuum chamber (1) above the construction area (2). The entire construction area (2) is surrounded on all four sides by a shield (7) consisting of an upper part (8) and a lower part (9). Since the powder application element (5) is still in the starting position, the shield (7) is in a closed state. Figure 2 shows, again, an enlarged view of the construction area (2) surrounded by the shield (7). In the example shown here, the upper part (8) is made of stainless steel with a thickness of 30 mm on the outside and 20 mm on the inside, and consists of four metal sheets (10) arranged at an interval of 13 mm. The lower part (9) is made of pure tungsten with a thickness of 3 mm and consists of three refractory metal sheets (11) arranged at an interval of 30 mm. The density of the refractory metal sheet (11) is 19.25 g / cm 3 ³. The refractory metal sheets (11) of the lower part (9) are arranged so as to mesh with the metal sheets (10) of the upper part (8) and overlap by 45 mm.

[0038] The metal sheets (10) of the upper part (8) are each dimensioned slightly shorter from the outside towards the construction area (2). This allows them to be more easily attached by bolts to the stepped attachment provided on the ceiling of the vacuum chamber (1). The refractory metal sheets (11) are attached to a movable frame (12) and can be raised above it. In the closed position shown here, their lower edges engage with a groove structure (13) that forms the edge region of the construction area (2). The groove structure (13) has the same dimensions as the upper structure. That is, in this example, on the surface of the vacuum chamber (1), grooves with a width of 13 mm are machined at an interval of 20 mm around the construction platform (3). The grooves correspond to the distance between the sheets, and the webs remaining in between correspond to the thickness of the sheets.

[0039] To manufacture a component, the powder reservoir (4) is filled with a powdery starting material, for example titanium powder, the system is moved to the starting position shown in FIG. 1, and the vacuum chamber (1) is evacuated. To manufacture the first layer of the component, the titanium powder is conveyed from the powder reservoir (4) towards the construction area (2) by using the powder application element (5). Immediately before the powder application element (5) moves or when it has almost reached the closed shield (7), the lower part (9) is lifted by the movable frame (12) and pushed into the upper part (8) to enable the movement range of the powder application element (5). During this time, the electron beam gun (6) is deactivated. This state is shown in FIG. 3. Since the shield (7) is open there, the groove structure (13) can now also be clearly seen.

[0040] FIG. 4 shows the powder application element (5) crossing the construction area (2) and supplying titanium powder onto the construction platform (3). FIG. 5 shows immediately after the powder application element (5) has crossed the construction area (2). As soon as the powder application element (5) leaves the construction area (2) again, the lower part (9) is lowered back into the closed position. The lower edge of the refractory metal sheet (11) engages again with the groove structure (13). Then, the powder application element (5) moves to the position of the rear end behind the right powder reservoir (4), and thus discharges the excess titanium powder into the collection slot. At the same time as the shield (7) is closed again, the electron gun (6) can be activated to start writing the layer data of the first layer.

[0041] After the first layer has been written, the process starts again from the other direction. In a system where only one powder reservoir (4) is installed, the powder application element (5) remains in a position beyond the construction area (2) until the layer is written and the lower part (9) of the shield (7) is lifted again and then returns to the starting position for the first time to pick up new powder, or returns to the starting position in a reciprocating motion either immediately after crossing the construction area (2) before the shield (7) is closed.

Explanation of Signs

[0042] 1 Vacuum chamber 2 Construction area 3 Construction platform 4 Powder reservoir 5 Powder application element 6 Electron beam gun 7 Shield 8 Upper part 9 Lower part 10 Metal sheet 11 Refractory metal sheet 12 Frame 13 Groove structure

Claims

1. A laminating system for a powdery starting material, comprising a vacuum chamber (1), wherein the vacuum chamber (1) has at least one construction area (2) provided with a construction platform (3), at least one powder reservoir (4) arranged on the side of the construction area (2), at least one powder application element (5) horizontally movably arranged between at least one of the powder reservoirs (4) and at least one of the construction platforms (3) for supplying a powdery starting material from at least one of the powder reservoirs (4) to at least one of the construction platforms (3), the at least one powder application element (5) traversing the construction area (2) at least once per powder distribution process, and at least one electron beam gun (6) attached to at least one of the construction areas (2) in the laminating system configured to include at least one of the construction areas (2) is surrounded by a shield (7) against ionizing radiation, the shield being composed of four walls, two of which can be formed by the walls of the vacuum chamber (1), and the walls of the shield (7) on at least two sides in the moving direction of at least one of the powder application elements (5) consist of an upper part (8) and a lower part (9), the upper part (8) is firmly connected to the vacuum chamber (1) and is formed by 2 to 11 horizontally spaced metal sheets (10), having a height above the construction platform (3) such that the powder application element (5) can move horizontally through the construction area (2), the lower part (9) is connected to a vertically movable frame (12), is arranged to engage with the metal sheet (10) of the upper part (8), and is formed by 2 to 11 horizontally spaced refractory metal sheets (11) attached to the movable frame (12) in a radiation-impermeable manner, and the lower part (9) is relatively movable with respect to the upper part (8) in the vertical direction between a closed position and an open position, and the refractory metal sheet (11) of the lower part (9) is In the closed position, their lower edges are arranged to engage with the groove structure (13) on the surface of the construction area (2) while forming a labyrinth structure, and their upper edges are arranged to engage with the metal sheet (10) of the upper part (8) while forming a labyrinth structure. In the open position, the powder application system is characterized in that it is stationary between the metal sheets (10) of the upper part to such an extent that at least horizontal movement through the construction area (2) of the powder application element (5) is possible. **Claim 2** The refractory metal sheet (11) of the lower part (9) has a density of 10 g / cm at 20 °C ３ The additive manufacturing system according to claim 1, characterized in that it has a density of 10 g / cm or more. **Claim 3** The refractory metal sheet (11) of the lower part (9) is made of tungsten, molybdenum, rhenium, tantalum and / or a mixture or alloy thereof, according to the powder application system of claim 1 or 2. **Claim 4** The metal sheet (10) of the upper part (8) is made of stainless steel, copper, refractory metal and / or a mixture or alloy thereof, according to the powder application system of any one of claims 1 to 3. **Claim 5** All four walls of the shield (7) consist of an upper part (8) and a lower part (9), according to the powder application system of any one of claims 1 to 4. **Claim 6** The radiation-impermeable attachment of the refractory metal sheet (11) of the lower part (9) to the movable frame (12) is configured to include spacer bolt fasteners having two different diameters. The first diameter is sized to match the bore of the refractory metal sheet (11), and the second diameter that the spacer bolt has outside the bore is large enough so that radiation passing through the bore is shielded by the spacer bolt in the same way as the refractory metal sheet (11) in the area where there are no holes. This is according to the powder application system of any one of claims 1 to 5. **Claim 7** The refractory metal sheets (11) of the lower part (9) each have a thickness of 0.1 to 20 mm, according to the powder application system of any one of claims 1 to 6. **Claim 8** The metal sheets (10) of the upper part (8) each have a thickness of 1 to 100 mm, according to the powder application system of any one of claims 1 to 7. **Claim 9** The refractory metal sheet (11) of the lower part (9) and the metal sheet (10) of the upper part (8) each have a spacing of 1 to 50 mm from each other in the meshing engagement, and the laminated manufacturing system according to any one of claims 1 to 8 is characterized thereby.

10. The laminated manufacturing system according to any one of claims 1 to 9 is characterized in that at least two joints (Stoesse) are provided in each layer of the metal sheet (10) of the upper part (8) and / or the refractory metal sheet (11) of the lower part (9) at intervals of at most 50 mm.

11. The laminated manufacturing system according to claim 10 is characterized in that the joints (Stoesse) of two consecutive layers of the metal sheet (10) in the upper part (8) and / or the refractory metal sheet (11) in the lower part (9) are not arranged in alignment in order to avoid free beam paths respectively.

12. The laminated manufacturing system according to any one of claims 1 to 11 is characterized in that the powder application element (5) is a doctor blade or a roller.

13. A method for manufacturing a component using a laminated manufacturing system, including the following steps. a) Prepare a laminated manufacturing system according to any one of claims 1 to 12. b) Supply a powdery starting material into at least one of the powder reservoirs (4), and evacuate the vacuum chamber (1). c) Move the lower part (9) of the shield (7) to an open position. d) Supply the powdery starting material onto at least one of the construction platforms (3) by horizontally moving the powder application element (5) between at least one of the powder reservoirs (4) and at least one of the construction platforms (3) while at least once completely traversing the construction area (2). e) Move the lower part (9) of the shield (7) to a closed position. f) Generate a layer of the component by irradiating the powdery starting material with at least one of the electron beam guns (6). g) Repeat steps c) to f) until the component is completed.

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