METHOD FOR GENERATING A STRUCTURE MESH, USE OF A STRUCTURE MESH, COMPUTER PROGRAM, AND COMPUTER-READABLE MEDIUM

Abstract

A method for generating a structure mesh of a structure that is to be built-up in a three-dimensional build-up volume in an additive manufacturing build-up process. The structure includes at least one specimen and at least one support for supporting the at least one specimen on a boundary of the build-up volume. The structure mesh may be used in simulating the additive manufacturing build-up process of the structure 2. A use of a structure mesh 9, a computer program, and a computer-readable medium are also provided.

Claims

1. A computer-implemented method for generating a structure mesh of a structure that is to be built up in a three-dimensional build-up volume in an additive manufacturing build-up process, the structure comprising at least one specimen and at least one support for supporting the at least one specimen on a boundary of the build-up volume, wherein the structure mesh is usable in simulating the additive manufacturing build-up process of the structure, the method comprising: providing a build-up volume surface mesh that represents the boundary of the three-dimensional build-up volume; providing at least one specimen mesh including a specimen surface mesh representing at least an outer surface of a corresponding specimen within an interior space surrounded by the build-up volume surface mesh; creating a three-dimensional background mesh in a cavity between the build-up volume surface mesh and the at least one specimen surface mesh using the at least one specimen surface mesh as a seed mesh, wherein the three-dimensional background mesh is composed of elements consisting of background mesh nodes and background mesh edges extending between the background mesh nodes; and identifying at least one support mesh and at least one environment mesh that is defined by the background mesh except for regions of the at least one support mesh using the background mesh and surface data that describe a facetted surface of the at least one support, wherein the at least one support mesh and the at least one specimen mesh together define the structure mesh that is generated such that the at least one support mesh, the at least one specimen mesh, and the at least one environment mesh are connected with each other so that two neighboring meshes share same nodes at interfaces in a transition area.

2. The computer-implemented method of claim 1, wherein: providing the at least one specimen mesh comprises providing at least one three-dimensional specimen mesh that represents a discretization not only of the surface of the at least one specimen but of the entire volume of the at least one specimen, and creating the three-dimensional background mesh comprises discretizing the cavity with background mesh elements having a same size, shape, or size and shape as three-dimensional specimen mesh elements of the at least one three-dimensional specimen mesh; creating the three-dimensional background mesh comprises creating a three-dimensional background mesh having background mesh elements that are tetrahedron-shaped, pyramid-shaped, hexahedron-shaped, cuboid-shaped, or any combination thereof; or a combination thereof.

3. The computer-implemented method claim 1, wherein creating the three-dimensional background mesh comprises creating a background mesh having smaller elements in a region of the three-dimensional build-up volume where the at least one support is expected to be located, and larger elements outside the region.

4. The computer-implemented method of claim 1, wherein identifying the at least one support mesh comprises identifying surfaces of the at least one support within the background mesh, the identifying of the surfaces comprising identifying points of intersection of the surfaces of the at least one support with background mesh edges, creating new nodes at the points of intersection, thus splitting the respective background mesh edges, and interconnecting at least some of the new nodes to create at least one support surface mesh.

5. The computer-implemented method of claim 4, wherein the identified surfaces of the at least one support are surfaces of a sub-volume of the three-dimensional build-up volume that represent the at least one support as simulated in contrast to the at least one support as actually built-up in the additive manufacturing build-up process.

6. The computer-implemented method of claim 5, wherein the sub-volume of the three-dimensional build-up volume that represents the at least one support as simulated is defined as the set of points within the three-dimensional build-up volume that are located at a distance inferior to a threshold to a closest facet of the facetted surface of the at least one support described by the surface data, wherein the threshold is selectable as a minimal distance such that any point located in an interior of the at least one support is at most at a distance to the closest facet of the at least one support, and wherein a value of the distance corresponds to a value of the threshold.

7. The computer-implemented method of claim 1, wherein: identifying the at least one support mesh and the at least one environment mesh comprises identifying an environment mesh that is an environment bubble mesh enclosed in a support mesh, the environment bubble mesh being eliminated by making the environment bubble mesh part of the support mesh in which the environment bubble mesh is enclosed; identifying the at least one support mesh and the at least one environment mesh comprises identifying a support mesh that is a support bubble mesh not connected to the at least one specimen nor a build-up volume boundary, wherein the support bubble mesh is eliminated by making the support bubble mesh part of the at least one environment mesh; or a combination thereof.

8. The computer-implemented method of claim 7, wherein after eliminating bubble meshes, at least one resulting mesh is improved to meet a predefined element quality and element size.

9. The computer-implemented method of claim 8, wherein the background mesh elements are adapted by a mesh adaptation method.

10. The method of claim 8, further comprising remeshing at least one surface mesh, the remeshing of the at least one surface mesh comprising replacing the at least one surface mesh with a new surface mesh of at least substantially uniform edge length, wherein the at least one new surface mesh resulting from the remeshing is used as seed mesh in generating new three-dimensional meshes.

11. The method of claim 1, wherein an interior of the at least one specimen defined by the at least one specimen surface mesh is meshed.

12. The method of claim 4, wherein a support surface mesh defines a closed volume that is meshed by a volume meshing technique.

13. A method comprising: using a structure mesh of a structure for simulating an additive manufacturing build-up process of the structure, the structure comprising at least one specimen and at least one support for supporting the at least one specimen on a boundary of a build-up volume, generation of the structure comprising provision of a build-up volume surface mesh that represents the boundary of the build-up volume, provision of at least one specimen mesh including a specimen surface mesh representing at least an outer surface of a corresponding specimen within an interior space surrounded by the build-up volume surface mesh, creation of a three-dimensional background mesh in a cavity between the build-up volume surface mesh and the at least one specimen surface mesh using the at least one specimen surface mesh as a seed mesh, wherein the three-dimensional background mesh is composed of elements consisting of background mesh nodes and background mesh edges extending between the background mesh nodes, and identification of at least one support mesh and at least one environment mesh that is defined by the background mesh except for regions of the at least one support mesh using the background mesh and surface data that describe a facetted surface of the at least one support, wherein the at least one support mesh and the at least one specimen mesh together define the structure mesh that is generated such that the at least one support mesh, the at least one specimen mesh, and the at least one environment mesh are connected with each other so that two neighboring meshes share same nodes at interfaces in a transition area.

14. (canceled)

15. In a non-transitory computer-readable storage medium that stores instructions executable by at least one computer to generate a structure mesh of a structure that is to be built up in a three-dimensional build-up volume in an additive manufacturing build-up process, the structure comprising at least one specimen and at least one support for supporting the at least one specimen on a boundary of the build-up volume, wherein the structure mesh is usable in simulating the additive manufacturing build-up process of the structure, the instructions comprising: providing a build-up volume surface mesh that represents the boundary of the three-dimensional build-up volume; providing at least one specimen mesh including a specimen surface mesh representing at least an outer surface of a corresponding specimen within an interior space surrounded by the build-up volume surface mesh; creating a three-dimensional background mesh in a cavity between the build-up volume surface mesh and the at least one specimen surface mesh using the at least one specimen surface mesh as a seed mesh, wherein the three-dimensional background mesh is composed of elements consisting of background mesh nodes and background mesh edges extending between the background mesh nodes; and identifying at least one support mesh and at least one environment mesh that is defined by the background mesh except for regions of the at least one support mesh using the background mesh and surface data that describe a facetted surface of the at least one support, wherein the at least one support mesh and the at least one specimen mesh together define the structure mesh that is generated such that the at least one support mesh, the at least one specimen mesh, and the at least one environment mesh are connected with each other so that two neighboring meshes share same nodes at interfaces in a transition area.

16. The computer-implemented method of claim 1, wherein the at least one support is for supporting the at least one specimen on a build-up platform that defines a lower part of the boundary of the build-up volume.

17. The computer-implemented method of claim 3, wherein the region is a region defined by a geometrical bounding box that encloses the at least one support and comprises all elements thereof.

18. The computer-implemented method of claim 7, wherein the environment mesh is a powder mesh.

19. The computer-implemented method of claim 9, wherein the mesh adaptation method is a local mesh adaptation method.

20. The computer-implemented method of claim 10, wherein the at least one surface mesh comprises surface meshes made of boundaries of specimen, support, and environment regions within the three-dimensional build-up volume.

21. The method of claim 11, wherein the interior of the at least one specimen defined by the at least one specimen surface mesh is meshed in accordance with a discretization that is extracted from existing CAD data of the at least one specimen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIGS. 1-5 are purely schematic illustrations illustrating acts of a method for generating a structure mesh according to a first embodiment;

[0042] FIG. 6 is a purely schematic illustration illustrating the act of identifying support meshes of a method for generating a structure mesh according to a second embodiment;

[0043] FIG. 7 is a spatial representation of a part of another kind of support arrangement by facetted surfaces;

[0044] FIG. 8 is a section view along section line VIII-VIII in FIG. 7 showing the support arrangement as built-up as well as simulated;

[0045] FIG. 9 is a spatial representation of yet another kind of support arrangement by facetted surfaces;

[0046] FIG. 10 a section view along section line X-X in FIG. 9 showing the support arrangement as build-up as well as simulated;

[0047] FIG. 11 is a spatial representation of yet another kind of support arrangement by facetted surfaces; and

[0048] FIG. 12 is a section view along section line XII-XII in FIG. 11 showing the support arrangement as build-up as well as simulated.

DETAILED DESCRIPTION

[0049] FIGS. 1-5 show a purely schematic illustration illustrating acts of a method according to a first embodiment. FIG. 1 shows an X-Z sectional view of a three-dimensional build-up volume 1 with a structure 2 in the three-dimensional build-up volume 1. The structure 2 has been built-up or is to be built-up by a powder bed based additive manufacturing build-up process that may be a selective laser melting (SLM) process. In the SLM process, a metal powder 3 to be processed is applied in a thin layer to a build-up platform 4 defining a lower part of a boundary 5 of the build-up volume 1 and then completely melted locally using a laser radiation so that a solid material layer is formed after solidification. The boundary 5 of the build-up volume 1 is partly shown in FIGS. 1 and 5, for example. For reasons of illustration, only four of the total of six boundary surfaces of the build-up volume 1 is shown in these figures. The above-mentioned procedure is repeated layer by layer until the desired structure 2 is completed. The structure 2 consists of two cuboid specimens 6a,b and a complex support arrangement 7 that includes two nearly columnar supports 8 and supports the specimen 6b shown in FIG. 1 on the right on the build-up platform 4. The supports 8 thus each extend at a distance from each other between the build-up platform 4 and the specimen 6b and connect the build-up platform 4 with the specimen 6b. The other specimen 6a shown in FIG. 1 on the left is directly placed on the build-up platform 4 without using any supports 8.

[0050] The method according to the first embodiment is used to generate a structure mesh 9 of the structure 2. The structure mesh 9 consists of two specimen meshes 9a and at least one support mesh 9b. First, a build-up volume surface mesh 10 that represents the boundary 5 of the three-dimensional build-up volume 1 is provided. Then, two specimen surface meshes 11a,b each representing the outer surface of a corresponding specimen 6a,b are provided within an interior space surrounded by the build-up volume surface mesh 10. The specimen surface meshes 11a,b are based on available CAD data of the specimens 6a,b. In a next act, a three-dimensional background mesh 12 is created in the cavity between the build-up volume surface mesh 10 and the two specimen surface meshes 11a,b using both specimen surface meshes 11a,b as two-dimensional seed meshes, as shown in FIG. 2. The resulting background mesh 12 is composed of tetrahedron-shaped elements 13 consisting of background mesh nodes 14 and background mesh edges 15 extending between the background mesh nodes 14. For the sake of simplicity, in the X-Z sectional views of FIGS. 1-5, the meshes are merely indicated by lines or squared areas. The squared areas are thus only intended to indicate that the respective area represents a mesh. The squares of the squared areas do not allow any conclusions to be drawn about the actual type or size of mesh elements and connections between meshes. Different sizes of squares only serve to distinguish different meshes and do not necessarily provide that the respective meshes have different mesh sizes. However, background mesh elements 13 are shown in connection with the second embodiment in FIG. 6. Using both specimen surface meshes 11a,b as seed meshes results in nodes and edges of the specimen surface meshes 11a,b to match background mesh nodes 14 and background mesh edges 15 at the outer boundary of the background mesh 12.

[0051] For both supports 8, only surface data (e.g., STL data), instead of CAD construction data, is available. This surface data describes facetted surfaces 16 of the two supports 8 and is to be converted into data of at least one solid geometry (e.g., volume data) that may be meshed. To achieve this, two support meshes 9b and one environment mesh 17 (e.g., a powder mesh) that is defined by the background mesh 12 except for regions of the two support meshes 9b are identified using the background mesh 12 and the surface data of the supports 8. More precisely, surfaces 18 of the two supports 8 are identified within the background mesh 12 by identifying points of intersection 19 of the surfaces 18 of the two supports 8 with background mesh edges 15. At the points of intersection 19, new nodes are created, and thus, the respective background mesh edges 15 are split. Then, at least some of the created new nodes are interconnected to create support meshes 9b and environment meshes 17. The surfaces 18 that intersect the background mesh edges 15 are surfaces 18 of a sub-volume 20 of the build-up volume 1 that represents the two supports 8 as simulated later in contrast to the facetted surfaces 16 of the two supports 8 and/or in contrast to the supports 8 as actually built-up in the additive manufacturing build-up process. The sub-volume 20 is defined as the set of points within the build-up volume 1 that are located at a distance inferior to a threshold D to the closest facet of the facetted surfaces 16 of the two supports 8. In the present example, the threshold D is chosen as the minimal distance such that any point located in the interior of the supports 8 is at most at a distance d to the closest facet of the facetted surfaces 16 of the two supports 8, where the value of d corresponds to the value of D. The sub-volume 20 and the threshold D are shown in FIGS. 6, 8, 10 and 12.

[0052] In the present example, four support meshes 9b and four environment meshes 17 are created, where two of the four support meshes 9b are support bubble meshes and three of the four environment meshes 17 are environment bubble meshes, as shown in FIG. 3. The support bubble meshes 9b are fully enclosed in the environment mesh 17, which is not an environment bubble mesh. Hence, the support bubble meshes 9b are neither connected to specimen 6b, nor to boundary 5, nor to another support mesh 9b. The environment bubble meshes 17 are each enclosed in one of the two support meshes 9b that are not support bubble meshes.

[0053] In the next act, the two support bubble meshes 9b are eliminated by making the two support bubble meshes 9b part of the only environment mesh 17 that is not an environment bubble mesh. Likewise, the three environment bubble meshes 17 are eliminated by making the three environment bubble meshes 17 part of the respective support mesh 9b in which the three environment bubble meshes 17 are enclosed. The result of this bubble elimination procedure is that only two support meshes 9b and one environment mesh 17 remain, which is shown in FIG. 4.

[0054] Thereafter, at least some of the resulting meshes are improved to meet a predefined element quality and element size. More precisely, surface meshes made of boundaries of specimen, support, and environment regions within the build-up volume 1 are remeshed. This is done by replacing a respective surface mesh (e.g., a surface mesh between the support 8a and/or support 8b and the powder environment) with a new surface mesh of at least substantially uniform edge length. The new surface mesh resulting from the remeshing may than be used as a seed mesh in generating a corresponding new three-dimensional mesh. Additionally or alternatively, the background mesh elements 13 may be adapted by a common mesh adaptation method.

[0055] Finally, the interior of the two specimens 6a,b defined by the specimen surface meshes 11a,b is meshed in accordance with a discretization that is extracted and/or taken over from the existing CAD data of the specimens 6a,b. Additionally or alternatively, if a support surface mesh of the support meshes 9a,b defines a closed volume, this closed volume may be meshed by a common volume meshing technique.

[0056] The structure mesh 9 is thus generated such that the two support meshes 9b, the two specimen meshes 9a, and the environment mesh 17 are connected with each other so that two neighboring meshes share the same nodes at their interfaces in their transition area. The generated structure mesh 9 may be used for simulating (e.g., thermal, mechanical, and/or thermos-mechanical simulating) the powder bed fusion based additive manufacturing build-up process of the structure 2. The embodiments of the method of the present embodiments described herein may also be used in conjunction with any other additive manufacturing build-up processes.

[0057] FIG. 6 shows a purely schematic illustration illustrating the act of identifying support meshes 9b of a method for generating a structure mesh 9 according to a second embodiment. Thereby, FIG. 6 represents an X-Z sectional view of a three-dimensional build-up volume 1. The method according to the second embodiment differs from the method according to the first embodiment only in that a different kind of support arrangement 7 is meshed (e.g., different support meshes 9b are identified). More precisely, the support arrangement 7 in the second embodiment consists of a block support 8 shown on the left side in FIG. 6 and a line support 8 shown on the right side in FIG. 6.

[0058] Another kind of support arrangement 7 shown in FIG. 7 includes a plurality of pipe-like supports 8 that may be seen as a grid-like structure in the section view of FIG. 8. In this example, the distance i between two adjacent grid lines 21 is equal to twice the threshold D (e.g., i=2D). Since the support arrangement 7 has a closed boundary, the value for D is chosen relatively small as compared to the support arrangements 7 shown in FIGS. 10 and 12.

[0059] Yet another kind of support arrangement 7 shown in FIG. 9 includes four parallel wall-like supports 8 that may be seen as four parallel lines 22 in the section view of FIG. 10. In this example, the distance i between two adjacent lines 22 is equal to twice the threshold D (e.g., i=2D).

[0060] Yet another kind of support arrangement 7 shown in FIG. 11 includes five supports 8 in the form of parallel cylindrical columns that are shown as five dots 23 in the section view of FIG. 12. In this example, the distance i between two adjacent dots 23 is equal to the threshold D multiplied by cos(30°).

[0061] As shown, for example, in FIGS. 10 and 12, the support arrangement 7 consisting of the supports 8 represented by facetted surfaces 16 is converted into a volume that is a sub-volume 20 of the build-up volume 1 and represents the support arrangement 7 as a solid body.

[0062] Although the present invention has been described in detail with reference to the exemplary embodiments, it is to be understood that the present invention is not limited by the disclosed examples. Numerous additional modifications and variations may be made thereto by a person skilled in the art without departing from the scope of the invention.

[0063] The elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent. Such new combinations are to be understood as forming a part of the present specification.

[0064] While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.