Additive manufacturing system for powder-like 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 an additive manufacturing system for powder starting materials comprising an electron beam gun as an irradiation unit, said system being configured with improved shielding from ionizing radiation, in particular X-rays. [Background technology]

[0002] Apparatuses and methods for the additive manufacturing of workpieces are also known in the prior art under the term additive manufacturing (AM). They are also referred to as "generative manufacturing methods" or "3D printing". The raw material can be in powder or liquid form. Powder processes include, for example, selective laser melting (SLM), selective laser sintering (SLS) or electron beam melting (EBM). The raw material can consist of plastic or metal.

[0003] In processes using powdered raw materials, the raw material is applied in a layer onto a lowerable work surface where it is partially melted or sintered. The work surface is then lowered one layer's thickness. Another layer is applied on top of that layer, and the same process as the first layer is repeated. Portions are selected to be melted or sintered, and a three-dimensional workpiece is built up layer by layer.

[0004] Systems operating by the electron beam melting (EBM) process, unlike laser processes, use one or more electron beam guns as the radiation source. In these applications, when an electron beam strikes the powder surface, it generates X-rays in addition to the desired heat, so these systems must be shielded from ionizing radiation. To shield against ionizing radiation, especially X-rays, the walls of these systems are currently painstakingly fitted with coatings, primarily made of lead or steel. A minimum thickness of these coatings is required to ensure the absorption of ionizing radiation. This makes the systems very heavy and difficult to maintain. Furthermore, thick coatings also result in significant costs. Furthermore, lead is physiologically problematic. Summary of the Invention

[0005] the purpose In view of these problems, it is an object of the present invention to provide an additive manufacturing system including an electron beam gun that overcomes the drawbacks of prior art devices, and in particular to provide a device and a method for manufacturing parts using the same that can implement shielding with smaller and lighter dimensions without compromising the construction process.

[0006] This object is achieved by an additive manufacturing system according to claim 1 and a method for manufacturing a part according to claim 11. Preferred variations are the subject of the dependent claims.

[0007] The additive manufacturing system for powdery starting materials of the present invention comprises: a vacuum chamber, The vacuum chamber is at least one construction area with a construction platform; at least one powder reservoir disposed on a side of the construction area; at least one powder application element arranged horizontally movably between the at least one powder reservoir and the at least one construction platform to supply powdered starting material from the at least one powder reservoir to the at least one construction platform, the at least one powder application element traversing the construction area at least once per powder dispensing process; and at least one electron beam gun associated with at least one of said construction areas; It is composed of At least one of the construction regions is surrounded by a shield against ionizing radiation, the shield having four walls, two of which may be formed by the walls of the vacuum chamber; the walls of the shield on at least two sides in the direction of movement of the at least one powder application element comprise an upper portion and a lower portion; the upper portion is rigidly connected to the vacuum chamber and is formed of 2 to 11 horizontally spaced metal sheets and has a height above the construction platform such that the powder application elements can move horizontally through the construction area; the lower portion is connected to a vertically movable frame and is formed of 2 to 11 horizontally spaced refractory metal sheets arranged to interlock with the metal sheets of the upper portion and radiopaquely attached to the movable frame; and the lower portion is movable relative to the upper portion in a vertical direction between a closed position and an open position, and the refractory metal sheet of the lower portion is In the closed position, their lower edges are arranged to interlock with a groove structure on the surface of the construction area while forming a labyrinth structure, and their upper edges are arranged to interlock with the upper metal sheet while forming a labyrinth structure; In the open position, the powder application element rests between the upper metal sheets at least to an extent that allows horizontal movement through the construction area.

[0008] An AM system according to the invention can comprise multiple electron beam guns covering individual areas of a larger construction platform, or it can comprise multiple construction platforms each with one or more electron beam guns attached, the latter setup having the advantage that in this case only a single vacuum chamber needs to be evacuated.

[0009] In the context of the present application, construction area is understood to mean the area within the vacuum chamber of the additive manufacturing system in which the construction platform is located, on which the powdered starting material is bombarded with the electron beam and thus the part is manufactured.

[0010] The powder application element can be, for example, a doctor blade or a coating roller. The powder supplied from the powder reservoir for the next layer of the part is evenly distributed by the powder application element onto the surface of the construction platform or onto the layer already placed thereon. For this purpose, the powder application element traverses the entire construction area once. Its movement extends at least to the end of the construction platform, and generally all the way to the end of the opposite wall, since a collection container for excess powder or a separate powder reservoir is usually attached there. As a result, no equipment can be installed in the movement area of ​​the powder application element, especially above the construction platform. However, this is where X-ray radiation is generated when the electron beam strikes the powder surface.

[0011] In the additive manufacturing system according to the invention, this problem is solved in that a shield against ionizing radiation is used directly around the construction area, which can be raised in synchronization with the movement of the powder application elements. Therefore, it is not necessary to provide shielding on the entire outer wall of the system, but rather a much smaller shielding surface is sufficient, since it is located closer to the source of the radiation. In this way, considerable weight can be saved simply by reducing the surface area.

[0012] However, if the shielding surface of the exterior wall were simply scaled down and designed in the same way, the problem would remain: a significant amount of mass would have to be moved. In addition to the mechanical stresses and the need for a stable mechanism, the construction process would also be slower, as the movement of a heavy mass would not be as fast as the movement time of a typical powder coating element.

[0013] To solve this problem, the ionizing radiation shield of the present invention is not made of a solid plate, which must be completely movable and provide a vacuum-tight passage to the ceiling of the vacuum chamber. Instead, the shield is divided into two parts: 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 range of movement 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 in an interlocking manner. This interlocking arrangement forms a labyrinth structure, ensuring the absence of a direct beam path; radiation is reflected several times by the interlocking metal sheets, thereby slowing it down.

[0014] Furthermore, the movable lower sheet is made of refractory metal. When the term "refractory metal sheet" is used herein, it is understood to mean a sheet made of a mixture or alloy containing 50% or more by weight of refractory metal, for example, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, 95% or more by weight, and in particular, 99% or more by weight. Consequently, in the context of this application, refractory metals are understood to mean high-melting-point metals such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten. In addition to a high melting point, their main characteristics are high density and, above all, a high specific absorption coefficient for ionizing radiation. This allows for the same shielding performance as the thick lead or steel layers of conventional exterior walls to be achieved with a thinner sheet. Here, the high heat resistance of refractory metals, especially compared to lead, is particularly important, as the shielding can be moved closer to the radiation point, thereby requiring less surface area. Furthermore, lead has insufficient mechanical stability and therefore cannot be attached in sheet form to a moving frame for mechanical reasons alone without causing a temperature rise, whereas steel is more stable in this case, but its lower absorption coefficient means it must be thicker and heavier.

[0015] The lower refractory metal sheet is preferably made of tungsten, molybdenum, rhenium, tantalum, and / or mixtures or alloys thereof. Tungsten, molybdenum, tantalum, and / or mixtures or alloys thereof are particularly preferred. The alloys and mixtures may preferably include copper.

[0016] The upper part of the shield does not need to move and does not necessarily have to be made of refractory metal, although other metals can be used for cost reasons. However, if the vacuum chamber must be kept very cold or very high temperatures must be generated to process the metal powder, it may be desirable to also make the upper sheet of refractory metal. In this case, the same refractory metal as the lower part may be used. In design variations, the upper metal sheet can be made of stainless steel, copper, refractory metals, and / or mixtures or alloys thereof.

[0017] It has proven advantageous to design the individual upper sheets so that their length decreases from the outside to the inside, with the lower edges evenly spaced and the upper edges offset in stages, which makes it easier to attach the metal sheets to the ceiling of the vacuum chamber.

[0018] The number of sheets at the top and bottom is determined by the power of the electron beam gun and the ionizing radiation it generates, as well as the metal used. Two to eleven sheets have been found to be optimal, depending on the absorption capacity of the selected metal. For safety reasons, it is preferable to select the number of sheets so that there is always one more sheet installed than is required for shielding.

[0019] For cost reasons, the shield is preferably manufactured from individual refractory metal sheet components, which are commercially available in standard dimensions. Each layer of refractory metal sheet is advantageously provided with at least two joints. At the joints within the upper and / or lower sections, the sheets do not overlap to avoid tilting caused by distortion due to thermal expansion. 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 at the joints. The gap is preferably 5 mm to 25 mm, most preferably 10 mm to 20 mm. The joints between two consecutive layers of refractory metal sheet within the upper and / or lower sections, respectively, are not aligned to avoid free beam paths.

[0020] The lower refractory metal sheets preferably each have a thickness of 0.1 to 20 mm. The sheet thickness may 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 may be at most 20 mm, at most 15 mm, at most 10 mm, at most 8 mm, or at most 6 mm. In particular, the thickness may 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 sheet, the bottom section can also be constructed with one or two stainless steel layers as the innermost layer for additional thermal protection. These can be arranged as a double layer, closer together than the refractory metal sheets. The stainless steel sheet primarily functions as a thermal protection, but also provides some radiation protection. This protects the more expensive refractory metal sheet from heat, extending its lifespan. On the other hand, the cheaper stainless steel sheet will 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 up to 100 mm, up to 75 mm, up to 50 mm, up to 25 mm, or up to 15 mm. In particular, the thickness 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 sheet is preferably designed to match the thickness of the lower refractory metal sheet so that the upper and lower sheets absorb approximately the same amount of radiation. The upper metal sheet does not necessarily have to be of uniform thickness. For example, the outer side of the stacked sheets can be thicker than the inner side.

[0023] Most preferably, the lower refractory metal sheet and the upper metal sheet are spaced apart by 1 mm to 50 mm when interlocked. 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, to ensure a radiation trap, it is preferable that the distance between the sheets is much smaller than the height of the sheets. In particular, it is preferable that the distance between the sheets is at most half the distance between the upper and lower sheets when they are closed. This maximizes multiple reflections in the generated light labyrinth.

[0024] A corresponding groove is formed on the upper surface of the construction region, and when the shielding is closed, the lower edge of the lower sheet of the shielding engages with this groove in the same manner as the upper edge of the lower edge of the upper sheet, thus forming a labyrinth under the lower part of the shielding, which can prevent radiation from escaping in advance.

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

[0026] Shielding against ionizing radiation can be implemented in two different ways. In either case, it consists of four walls surrounding and shielding the construction area. Two of these walls can be formed as the outer walls of the vacuum chamber, where shielding material is arranged in the usual way. This material can be a conventional 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 are the walls of the shield that do not lie in the direction of movement of the powder application element. The wall that lies in the direction of movement of the powder application element is designed in two parts, upper and 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 the shield, which provides the shortest distance to the radiation point 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 and a lower part. This is particularly advantageous, since two fixed walls would not allow for any kind of powder application element or its drive. For example, if these are guided and / or driven laterally, as in the case of a doctor blade, all four walls would have to be raised to allow the doctor blade to pass above the construction area. This allows for greater freedom in the design of the powder application element.

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

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

[0031] A method of manufacturing a part using an additive manufacturing system of the present invention includes the following steps. a) providing an additive manufacturing system according to the present invention; b) providing a powdered starting material in at least one powder reservoir and evacuating the vacuum chamber; c) moving the bottom of the shield to the open position; d) dispensing powdered starting material onto the at least one construction platform by horizontally moving a powder application element between the at least one powder reservoir and the at least one construction platform while traversing the construction area at least once completely; e) moving the bottom of the shield to the closed position; f) generating layers of the component by irradiating a powdered starting material with at least one electron beam gun; g) Repeat steps c) through f) until the part is complete.

[0032] Depending on the design of the powder application element and the application process, the powder layer can be applied in a single simple motion or in a reciprocating motion. In the latter case, after the second motion, the shield remains open until the powder coating element returns to its starting position. The shield is then lowered and irradiation begins.

[0033] Emission occurs only with the shield closed. When the shield is open, the electron gun is deactivated. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a cutaway perspective view of an additive manufacturing system according to the present invention in a closed starting position. [Figure 2] FIG. 2 is a cutaway perspective view of a construction area surrounded by a shield. [Figure 3] FIG. 3 is a cutaway perspective view of the system of FIG. 1 in an open position with the powder application element prior to entering the construction area. [Figure 4] FIG. 4 is a cutaway perspective view of the system of FIG. 1 in an open state with a powder application element in the construction area. [Figure 5] FIG. 5 is a cutaway perspective view of the system of FIG. 1 in a closed state after the powder application elements have re-exited the construction area. DETAILED DESCRIPTION OF THE INVENTION

[0035] Text description of the illustration image022.gif. The figures depict variations of preferred embodiments only as examples of the present invention, and therefore should not be construed as limiting.

[0036] FIG. 1 is a cross-sectional perspective view of an additive manufacturing system according to the present invention. Located within a vacuum chamber (1) is a construction area (2), within which a single construction platform (3) is positioned. This is shown in an upper, starting position at the beginning of construction. The left and right sides of the construction area (2) each have a powder reservoir (4) with adjacent slots for receiving excess powder. A powder application element (5), in this example a doctor blade suspended on a movable traverse, transfers powder from the powder reservoir (4) onto the construction platform (3) in the construction area (2) in an amount slightly greater than that required for one layer of the part, ensuring that the entire surface of the construction platform (3) is evenly coated. Excess powder is transferred beyond the powder reservoir (4) on the opposite side and into the slot, from which it reaches a collection container. In FIG. 1, the powder application element (5) is in its left, starting position.

[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 (8) and lower (9) section. The shield (7) is closed because the powder application element (5) is still in its starting position. Figure 2 again shows a close-up of the construction area (2) surrounded by the shield (7). In this example, the upper section (8) consists of four metal sheets (10) spaced 13 mm apart, each made of stainless steel, 30 mm thick on the outside and 20 mm thick on the inside. The lower section (9) consists of three refractory metal sheets (11) spaced 30 mm apart, each made of pure tungsten, 3 mm thick. The density of the refractory metal sheets (11) is 19.25 g / cm 3 The lower (9) refractory metal sheet (11) is arranged to fit over the upper (8) metal sheet (10), overlapping by 45 mm.

[0038] The metal sheets (10) of the upper part (8) are each slightly shorter from the outside toward the construction area (2). This allows them to be more easily attached to the stepped mounting points on the ceiling of the vacuum chamber (1) with bolts. The fireproof 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 area of ​​the construction area (2). The groove structure (13) has the same dimensions as the upper structure. That is, in this example, 13 mm wide grooves are machined on the surface of the vacuum chamber (1) around the construction platform (3) at 20 mm intervals, with the grooves corresponding to the distance between the sheets and the remaining web corresponding to the thickness of the sheets.

[0039] To produce a part, the powder reservoir (4) is filled with powdered starting material, such as titanium powder, and the system is moved to the start position shown in FIG. 1, where the vacuum chamber (1) is evacuated. To produce the first layer of the part, titanium powder is transported from the powder reservoir (4) toward the construction area (2) using the powder application element (5). Either just before the powder application element (5) begins to move or when it nearly reaches the closed shield (7), the lower part (9) is lifted by the movable frame (12) and pushed into the upper part (8), enabling the range of movement of the powder application element (5). During this time, the electron beam gun (6) is at rest. This state is shown in FIG. 3, where the shield (7) is in the open position, and the groove structure (13) is now clearly visible.

[0040] Figure 4 shows the powder application element (5) crossing the construction area (2) and dispensing titanium powder onto the construction platform (3). Figure 5 shows the powder application element (5) immediately after it 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 to its closed position again. The lower edge of the refractory metal sheet (11) again engages with the groove structure (13). The powder application element (5) then moves to a position at the rear end of the right powder reservoir (4), thus expelling excess titanium powder into the collection slot. As soon as the shield (7) is closed again, the electron gun (6) is activated and can begin writing the layer data for the first layer.

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

[0042] 1. Vacuum chamber 2 Construction Area 3 Construction Platform 4 Powder Reservoir 5 Powder application elements 6 Electron Beam Gun 7 Shield 8. Top 9 Lower 10 Metal Sheet 11 Refractory metal sheet 12 frames 13 Groove structure

Claims

1. An additive manufacturing system for powder-like starting materials, comprising a vacuum chamber (1), The vacuum chamber (1), At least one construction area (2) 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) arranged horizontally movably between said at least one powder reservoir (4) and said at least one construction platform (3) for supplying powdered starting material from said at least one powder reservoir (4) to said at least one construction platform (3), said at least one powder application element (5) crossing said construction area (2) at least once per powder distribution process; and At least one electron beam gun (6) associated with at least one of said construction areas (2); In the additive manufacturing system, At least one of the construction areas (2) is surrounded by a shield (7) against ionizing radiation, the shield being made up of four walls, two of which may be formed by the walls of the vacuum chamber (1); and The walls of the shield (7) on at least two sides in the direction of movement of the at least one powder application element (5) consist of an upper part (8) and a lower part (9), said upper part (8) is rigidly connected to said vacuum chamber (1) and is formed of 2 to 11 horizontally spaced metal sheets (10) and has a height above said construction platform (3) such that said powder application elements (5) can move horizontally through said construction area (2); the lower part (9) being connected to a vertically movable frame (12) and being arranged to interlock with the metal sheets (10) of the upper part (8) and being formed of 2 to 11 horizontally spaced refractory metal sheets (11) radiopaquely attached to the movable frame (12); The lower part (9) is movable relative to the upper part (8) in a 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 interlock with a groove structure (13) on the surface of the construction area (2) while forming a labyrinth structure, and their upper edges are arranged to interlock with the metal sheet (10) of the upper part (8) while forming a labyrinth structure; in said open position, said powder application element (5) is stationary between said upper metal sheets (10) at least to an extent that allows horizontal movement through said construction area (2).

2. The refractory metal sheet (11) of the lower part (9) has a thermal resistance of 10 g / cm at 20° C. ３ The additive manufacturing system of claim 1 having a density of at least 100 MPa.

3. 3. The additive manufacturing system according to claim 1 or 2, characterized in that the refractory metal sheet (11) of the lower part (9) consists of tungsten, molybdenum, rhenium, tantalum and / or mixtures or alloys thereof.

4. The additive manufacturing system according to any one of claims 1 to 3, characterized in that the metal sheet (10) of the upper part (8) consists of stainless steel, copper, a refractory metal and / or mixtures or alloys thereof.

5. The additive manufacturing system according to any one of claims 1 to 4, characterized in that all four walls of the shielding body (7) consist of an upper part (8) and a lower part (9).

6. 6. The additive manufacturing system according to claim 1, characterized in that the radiopaque attachment of the refractory metal sheet (11) of the lower part (9) to the movable frame (12) comprises spacer bolt fasteners with two different diameters, a first diameter dimensioned to match the bore in the refractory metal sheet (11) and a second diameter that the spacer bolt has outside the bore, which is larger such that radiation on its way through the bore is shielded by the spacer bolt as well as the refractory metal sheet (11) in the non-perforated areas.

7. The additive manufacturing system according to any one of claims 1 to 6, characterized in that the refractory metal sheets (11) of the lower part (9) each have a thickness of 0.1 to 20 mm.

8. The additive manufacturing system according to any one of the preceding claims, characterized in that the metal sheets (10) of the upper part (8) each have a thickness of 1 to 100 mm.

9. The additive manufacturing system according to any one of claims 1 to 8, characterized in that the refractory metal sheets (11) of the lower part (9) and the metal sheets (10) of the upper part (8) respectively have a spacing of 1 to 50 mm from each other in meshing engagement.

10. 10. The additive manufacturing system according to claim 1, characterized in that at least two seams 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), with a maximum distance of 50 mm between them.

11. 11. The additive manufacturing system according to claim 10, characterized in that the seams of two successive layers of the metal sheet (10) in the upper part (8) and / or the refractory metal sheet (11) in the lower part (9), respectively, are not aligned in order to avoid a free beam path.

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

13. 1. A method for manufacturing a part using an additive manufacturing system, comprising the steps of: a) providing an additive manufacturing system according to any one of claims 1 to 12, b) providing a powdered starting material in at least one of said powder reservoirs (4) and applying a vacuum to said vacuum chamber (1); c) moving the lower portion (9) of the shield (7) to an open position; d) distributing said starting material in powder form on at least one of said construction platforms (3) by horizontally moving said powder application element (5) between at least one of said powder reservoirs (4) and at least one of said construction platforms (3) while traversing said construction area (2) completely at least once; e) moving the lower part (9) of the shield (7) to a closed position; f) generating layers of said component by irradiating said starting material in powder form with at least one said electron beam gun (6); g) Repeating steps c) through f) until the part is complete.

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