Method for producing a thin-walled structure

Abstract

Method for producing a thin-walled structure from a starting material (1) by additive manufacturing in which a continuous, uninterrupted contour of the thin-walled structure to be manufactured is defined in a control unit (5), wherein The contour to be produced is divided into different geometry classes, and for each of the different geometry classes, the exposure strategies to be used and their parameterization are then determined manually or automatically using an algorithm. In a manufacturing process step, a radiation source (3) is controlled by the control unit (5) such that the defined contour is traced by an energy beam (4) emitted by the radiation source (3), at least one layer of the starting material (1) is irradiated along the contour and is thereby locally melted or sintered with the energy beam (4), so that the thin-walled structure is formed by an energy input, wherein the uninterrupted continuous contour is divided into at least two sub-sections, each of which is at least partially traversed by a single-line exposure, and wherein spatially directly adjacent subsections are irradiated with the energy beam (4) in such a way that an endpoint of one subsection irradiated by single-line exposure is not used as the starting point of the other subsection to be irradiated by single-line exposure in immediate succession.

Description

[0001] The present invention relates to a method for producing a thin-walled structure.

[0002] In the additive manufacturing of thin-walled component sections using typically powder bed-based manufacturing processes, warpage-related manufacturing defects pose a significant problem. Particularly in straight, thin-walled component sections, introduced residual stresses cause longitudinal contraction of the weld seams forming the component, resulting in bulging (also known as "warping") or cracking of the component. Such component defects increase with the length of the straight, thin-walled section.

[0003] The orientation of the weld seams has a significant influence on the severity of distortion-related component defects. For a given component, the determination of the individual weld paths is usually automated by an algorithm. This algorithm applies predefined rules, the scan strategy, for the position and orientation of the individual scan vectors to the geometric characteristics of a specific component. Currently, the selection of which scan strategy should be used for a particular component is typically made by a human.

[0004] The severity of distortion problems is highly dependent on the material used. Therefore, up to now, either the achievable minimum wall thickness of straight wall sections has been limited, additional support elements have been added, or such geometries are considered unmanufacturable. Currently, regardless of the component geometry to be manufactured, the contour hatch (CH) exposure strategy is almost exclusively used as the standard exposure strategy. In this strategy, the contours of the component within the manufacturing plane (possibly with an offset) are traced by a laser beam, and the areas to be melted are traced by the laser beam along meanders or according to a hatching pattern ("hatches"). Adjustments to the hatch parameterization are usually machine-specific and material-specific, but not geometry-specific.For example, publication GB 2 378 150 A discloses a process in which a powder is scanned using computer optimization to achieve an optimal scan time and is irradiated in the process.

[0005] In DE 10 2021 200 994 A1, a method is described in which a first pulsed energy input is applied to the material layer along an irradiation vector, the first energy input causing a plurality of separate melt pools in the material layer. A second pulsed energy input is then applied to the material layer along the same irradiation vector, the second energy input causing the irradiation of material regions between the separate melt pools created by the first pulsed energy input. In this process, the layer material is continuously irradiated along the irradiation vector with both the first and second pulsed energy inputs.

[0006] Additionally, US 2018 / 0 290 241 A1 discloses a scanning strategy in which the laser beam is guided point by point or section by section along a scan path. The irradiated areas are spaced apart to allow local cooling before the next melting process. The scan path can be traversed multiple times, irradiating different areas each time. Furthermore, the scan angle can be changed between successive layers.

[0007] The CH exposure strategy typically exhibits comparatively low distortion, but is limited in terms of the minimum achievable wall thickness and has low productivity. For thin-walled component areas, single-line exposure represents another approach. In this method, the cross-section of the wall to be manufactured is scanned by the laser along a single scan path. While it offers very high productivity, it is also very susceptible to distortion, particularly warping.

[0008] The present invention therefore aims to propose a method that avoids the aforementioned disadvantages, thus enabling the rapid and reliable production of mechanically stable thin-walled structures.

[0009] This problem is solved according to the invention by a method according to claim 1 and a device according to the dependent claim. Advantageous embodiments and further developments are described in the dependent claims.

[0010] In a process for manufacturing a thin-walled structure from a starting material using additive manufacturing, an uninterrupted, continuous contour of the thin-walled structure to be produced is defined in a control unit, and a manufacturing process step is subsequently carried out. Here, the contour to be produced is divided into different geometry classes, and for each of the different geometry classes, the exposure strategies to be used and their parameterization are then defined manually or automatically using an algorithm.In this manufacturing process step, a radiation source is controlled by the control unit in such a way that the defined contour is traced by an energy beam emitted by the radiation source, at least one layer of the starting material is irradiated along the contour, and is thereby locally melted or sintered by the energy beam, so that the thin-walled structure is formed by an energy input.The uninterrupted continuous contour (which does not necessarily have to be closed, but can of course be) is divided into at least two, preferably at least three, particularly preferably at least four subsections, each of which is at least partially traversed by single-line exposure, wherein spatially immediately adjacent subsections are irradiated with the energy beam in such a way that an endpoint of one subsection irradiated by single-line exposure is not used as the starting point of the other subsection to be irradiated by single-line exposure in immediate temporal succession.

[0011] The energy input from the energy beam enables reliable melting or sintering of the starting material, which, after solidification, exists as a thin-walled structure. By dividing the structure to be manufactured into several sub-sections, which are produced sequentially within a single layer, relatively short sub-sections can be manufactured, minimizing or eliminating the aforementioned problems of warping and other component distortions. Furthermore, this form of single-line exposure ensures rapid production. Because only parts of sub-sections are irradiated in immediate succession (thus transforming the respective contour sections from the starting material into sections of the thin-walled structure), and these sections are not in direct spatial contact with each other, the scan path length is reduced, and component distortion is minimized.A thin-walled structure is understood here to be, in particular, a structure whose height is at least as great as its width. Typically, however, the height is at least twice as great as the width. By using an additive manufacturing process, a corresponding component can be manufactured quickly and efficiently from a powder, i.e., in particular from a powdered starting material, by irradiation or exposure, with powder bed-based manufacturing being particularly preferred. Alternatively or additionally, in addition to the fact that an endpoint of one subsection irradiated by single-line exposure is not used as the starting point of another subsection to be irradiated by single-line exposure in immediate succession, it can also be provided that spatially immediately adjacent subsections are not irradiated with the energy beam in immediate succession.The described process can also be used for wire cladding welding.

[0012] It can be designed that the energy beam forms a thin-walled structure with a wall thickness that is at most three to four times the focal point diameter of the energy beam at the surface of the starting material. This allows for single-line production, enabling correspondingly fast manufacturing, while keeping the thickness or width of the thin-walled structure small, thus allowing for the production of a narrow, thin-walled structure. The focal point diameter is typically defined for a round focal point, but an elliptical shape is also possible, where the diameter is the length of the major or minor axis. The shape of the focal point can also be torus-shaped or a flat-head design.The energy beam can also be used to form a thin-walled structure with a wall thickness that exactly corresponds to the diameter of the weld bead formed on the surface of the base material by the energy input from the energy beam. The wall thickness can therefore be exactly the diameter of the forming weld bead, twice this diameter, three times this diameter, or up to a maximum of four times the stated diameter.

[0013] A section of the energy beam, partially irradiated by single-line exposure, which is deflected or deflectable in two dimensions, can be irradiated with the two-dimensionally deflected energy beam in the section that has not yet been irradiated, after at least partially scanning another section, in order to achieve coverage and thus a planar processing of the starting material.

[0014] Typically, each section is traversed and irradiated in the same or identical direction to ensure time-efficient processing.

[0015] The subsections preferably have a maximum length of one hundred times the diameter of the melt pool, preferably 5 mm, particularly preferably 10 mm. Typically, the thickness of a layer produced by a single pass and irradiation is 25 µm to 100 µm.

[0016] It can be planned that the manufacturing process step is repeated after each layer of the starting material has been produced or applied (possibly with offset or distortion, i.e., not necessarily geometrically identical) until the thin-walled structure is completed as a three-dimensional element. This allows the thin-walled structure to grow vertically while simultaneously reducing or preventing component distortions that occur in conventional manufacturing processes, without requiring any changes to the underlying geometry.

[0017] Furthermore, various sections can be offset or rotated relative to each other and irradiated in this geometric orientation to create any desired geometric structures.

[0018] A device for carrying out the described method comprises a control unit and a radiation source, wherein the control unit is configured to control the radiation source in such a way that a predefined continuous contour of the thin-walled structure to be produced is traced by an energy beam emitted from the radiation source and deflectable or deflected in two dimensions, and the starting material is irradiated along the contour, so that the thin-walled structure is formed by an energy input in which the starting material is locally melted or sintered, wherein the continuous contour is divided into at least two, preferably at least three, particularly preferably at least four subsections, each of which is at least partially traced by a single-line exposure.and in which spatially adjacent sections of a layer of the starting material are not irradiated with the energy beam in immediate succession. The contour to be produced is divided into different geometry classes, and for each of these classes, the exposure strategies to be used and their parameterization are defined manually or automatically using algorithms.

[0019] It can be provided that the energy beam has a focal point diameter, focus diameter or focal spot diameter of a maximum of 100 µm, preferably a maximum of 200 µm, particularly preferably a maximum of 300 µm, in order to be able to produce a sufficiently thin-walled structure.

[0020] It is also possible for the radiation source to be a laser radiation source and the energy beam to be a laser beam. However, the radiation source can also be an electron radiation source. If a laser beam is used, it can be continuously emitted or pulsed.

[0021] A computer program product contains a sequence of instructions that performs the described procedure and / or controls the described device when the sequence of instructions is executed in the control unit of the device.

[0022] Exemplary embodiments of the invention are shown in the drawings and are described below with reference to the Fig. 1 and Fig. 2 explained.

[0023] They show: Fig. 1 a schematic representation of a device for producing a thin-walled structure and Fig. 2. A top view of several implementation variants of the exposure strategy.

[0024] Fig. Figure 1 shows a schematic side view of a device for producing a thin-walled structure. A powdered starting material 1, for example, a metal powder (e.g., aluminum alloys: AlSi10Mg, titanium alloys: NiTi, Ti6Al4V, nickel-based alloys, iron-based alloys: 316L, copper-based alloys), a plastic powder (e.g., a thermoplastic), a ceramic powder, or a glass powder, is held in a container 2. The container 2 is open at the top, and a laser radiation source 3 is arranged above the container 2, emitting a laser beam 4 as an energy beam. The container 2 itself can be designed as a fixed build plate that is successively lowered layer by layer. The powdered starting material 1 is typically applied by a recoater either from a portable or a stationary powder supply.The laser beam 4, optionally after passing through an optical arrangement located between the laser radiation source 3 and the powdered starting material 1, which focuses the laser beam 4, for example as a lens arrangement, is focused onto a surface of the powdered starting material 1 contained as a powder bed in the container 2 and can melt or sinter the powdered starting material 1 by means of energy input. The laser radiation source 3 is in . Fig. 1 is shown schematically for the sake of simplicity and is often located next to the container 2, with the laser beam 4 being transmitted via optical conductors, e.g., optical fibers, to the in Fig. The laser radiation source 3 is coupled in at the point shown in section 1. It may also include a deflection unit and / or the aforementioned optical arrangement as a focusing unit.

[0025] The laser radiation source 3 is controlled by a control unit 5, for example a computer, and can thus be deflected two-dimensionally and trace different patterns. To produce a thin-walled structure from the powdered starting material 1, an uninterrupted continuous contour is first defined in the control unit. This can be done either by manual input from a user or by an algorithm that calculates the contour based on predefined boundary conditions.

[0026] In a subsequent manufacturing step, the laser radiation source 3 is controlled by the control unit 5 such that the defined contour is traced by the laser beam 4 and a layer of the powdered starting material 1 is irradiated or exposed along the traced contour. The resulting melting or sintering of the powdered starting material 1 forms the thin-walled structure and ultimately produces an entire component.

[0027] Here, the predefined contour is divided into at least two sub-sections, each of which is traversed and illuminated by a single-line exposure, i.e., by traversing a single line and illuminating or exposing it. Sub-sections that are spatially directly adjacent to one another, i.e., sub-sections that are in direct contact with each other, are not illuminated immediately sequentially or in such a way that the endpoint of one sub-section illuminated by single-line exposure is not immediately used as the starting point of the other sub-section to be illuminated by single-line exposure.

[0028] The laser beam 4 points in the Fig. In the embodiment shown in Figure 1, a focus diameter of a maximum of 100 µm is formed on the surface of the powdered starting material 1. Accordingly, the resulting thin-walled structure can have a wall thickness or width that exactly corresponds to the focus diameter or focal point diameter, but the wall thickness can also be up to a maximum of four times the focus diameter. Furthermore, after a layer has been completed, the manufacturing process step can be repeated as often as necessary until the thin-walled structure has been completed as a three-dimensional element.

[0029] In each embodiment of the invention, the geometric areas to be produced, i.e., the contour to be produced, are first divided into different geometry classes. This is done either manually or automatically using geometry-analyzing algorithms. A geometry class always comprises geometric areas whose geometry exhibits a common optimum for the scan strategy and process parameterization used. For each of the different geometry classes, the exposure strategies to be used and their parameterization are then determined manually or automatically using an algorithm.

[0030] The process is based on the single-line exposure strategy, but it differs in that the entire length of a wall, as a thin-walled structure to be produced, is not exposed with a single continuous scan path. Instead, this continuous path is replaced by segments. These segments are not exposed according to their spatial arrangement; rather, the exposure sequence is chosen so that adjacent segments are not exposed in direct succession, and that the endpoint of one segment does not correspond to the starting point of the immediately adjacent segment. Effectively, this shortens the scan path length at the time of exposure compared to a single line, and component distortion is significantly reduced. Simply segmenting the scan path is not the only way to shorten the exposed sections.Additionally, the sections can be offset or rotated relative to each other to relieve the introduced residual stresses. Further variations that divide a continuous wall into successively exposed sections are conceivable. A computer program therefore runs in control unit 5, which carries out the described process or controls the laser radiation source 3 to perform this process.

[0031] Fig. Figure 2 schematically shows a top view of the surface of the starting material 1, illustrating different scanning strategies or different thin-walled structures. Fig. 2a) A section of the two-dimensionally deflected laser beam 4 that has already been partially irradiated is moved again over the first exposed section after at least a partial traversal of another section, but is now slightly offset by the distance Vers_a and serves generally to clarify the procedure. Fig. Figure 2b) shows an embodiment in which a continuous, straight wall is divided into a total of four sections, of which the two sections shown in dark are irradiated first, starting with the middle section from left to right, followed by the left-hand section being irradiated from left to right, then the two remaining sections being irradiated, starting with the right-hand section (from right to left or from left to right) and subsequently processing the remaining middle section (from right to left or from left to right), which is also referred to as piecemeal processing.

[0032] Fig. Figure 2c) shows an embodiment in which the structuring is carried out such that immediately adjacent subsections are arranged at an angle to each other. The individual steps are designated Stru_I1 and Stru_I2, i.e., in a further embodiment, in a first step the right black subsection can be processed from left to right, and then the section to its right is processed from right to left, so that the endpoints of both subsections are aligned. A combination of the methods described in the Fig. 2a) and Fig. 2b) The exposure and scanning strategies shown are in Fig. 2d) is shown, in which the dark-drawn sections are illuminated in a first pass, followed by the light-drawn sections. Finally, the following can also be shown: Fig. 2e) the scan strategy provided for will be applied. This corresponds to the one in one layer. Fig.2b) In the procedure described (a+1), in the layer below (a), the first irradiated subsection is shortened and the positions of the subsequent subsections are adjusted accordingly, such that the start and end points of the subsections are offset from each other in successive layers. These differences between two successive layers, which occur at the same location but at different times during the process, are shown spatially offset in the figure for clarity.

[0033] In the described scanning strategies, each section is scanned in the same direction during the manufacturing process step. However, it is also possible to scan and irradiate at least two of the sections in opposite directions. In the illustrated embodiment, the individual sections have a length of three times the focus diameter of the laser beam 4, but in other embodiments, they can be longer.

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