A modeling method for gradient wall thickness TPMS porous structure based on additive manufacturing

Abstract

A modeling method for a gradient wall thickness TPMS porous structure based on additive manufacturing belongs to the field of porous structures. A surface is generated according to the spatial function of the TPMS structure, and the surface is divided into a grid. The nodes on the grid are first biased to generate a grid of uniform thickness; the normal of the surface where each node in the uniform grid structure is located is selected as the direction of the secondary offset, the coordinates are read, and the coordinate origin is taken as the reference point. According to the distance between each node and the reference point, all nodes are sorted from near to far. The result of the sorting corresponds to the offset of each node. The offset and the offset direction are combined to form a new vector; all nodes generate a new grid after the secondary offset with the new vector; the closer to the center of the structure, the greater the offset of the node, and the greater the thickness value of the structure, forming a TPMS porous structure with continuous gradient wall thickness. The present invention can design porous structures with different gradient wall thicknesses by modifying parameters, and is suitable for complex mechanical environments.

Description

Technical Field

[0001] The present invention belongs to the field of porous structures, and more specifically, relates to a modeling method for a three-periodic minimal surface gradient wall thickness porous structure. Background Art

[0002] Porous structure design is a design method based on mimicking natural structures. Triple-periodic minimal surfaces (TPMS) are curved structures defined by implicit level set functions. They offer high specific strength, axisymmetric stiffness, and excellent energy absorption properties. They are ideal porous structures and are currently widely used in fields such as medicine, architecture, and automotive.

[0003] Currently studied porous metal structures are mostly uniform lattice structures, with relatively simple mechanical properties, making them difficult to adapt to complex mechanical environments. A gradient structure is one in which the composition or structure changes along a certain direction within the material. The material properties change in a gradient manner, which can meet the structural requirements of different working environments.

[0004] With the rapid development of additive manufacturing technology, powder-based laser selective melting technology, which uses the basic method of discrete / accumulated molding, can produce complex structures that cannot be formed by traditional manufacturing technologies, providing a rapid manufacturing method for porous structures. However, how to quickly and efficiently design and manufacture the required gradient porous structure model is a key technology in the process of preparing gradient porous structures through additive manufacturing methods. Current gradient porous structure design methods mostly control the continuous change of structural pores, while there are fewer design and processing methods for gradient porous structures with continuously changing wall thickness.

[0005] In this context, developing a method for fabricating porous structures with continuously varying wall thickness is of great significance. This method can produce three-periodic minimal surface structures with continuously varying wall thickness and few surface defects. Because the structure's wall thickness varies continuously, its performance also varies continuously, allowing it to meet the structural requirements of diverse operating environments. Such structures could find widespread application in industries such as aerospace and mechanical engineering. Summary of the Invention

[0006] In response to the need for improvement in the existing technology, in order to prepare a structure with continuously changing wall thickness and fewer surface defects, the present invention provides a modeling method for a gradient wall thickness TPMS porous structure based on additive manufacturing. First, a surface is generated according to the spatial function of the TPMS structure, and the surface is meshed. After the nodes on the mesh are offset for the first time, a mesh of uniform thickness is generated. Secondly, the normal of the surface where each node in the uniform mesh structure is located is selected as the direction of the secondary offset, and its coordinates are read. Then, the coordinate origin is taken as the reference point, and all nodes are sorted from near to far according to the distance between each node and the reference point. The result of the sorting corresponds to the offset of each node, and the offset and the offset direction are combined to form a new vector; all nodes generate a new mesh after the secondary offset with the new vector; the closer to the center of the structure, the greater the offset of the node, and the greater the thickness value of the structure, forming a TPMS porous structure with continuous gradient wall thickness.

[0007] To achieve the above objectives, the present invention proposes a modeling method for a gradient wall thickness TPMS porous structure based on additive manufacturing, which includes the following steps:

[0008] Step 1: Perform mathematical modeling based on the spatial function of the TPMS structure to generate the initial surface of the structure. The initial surface has no thickness.

[0009] Step 2: Mesh the initial surface generated in step 1;

[0010] Step 3: Perform the first mesh offset to generate a TPMS structure with uniform wall thickness;

[0011] Furthermore, using the initial surface generated in step 1 as the middle surface, the mesh nodes on the middle surface are offset by a fixed distance to both sides of the middle surface along the normal direction of the middle surface, completing the first mesh offset. The lines connecting all the nodes on the two surfaces generated after the offset form a new mesh, which is closed into an overall model to generate a TPMS structure with uniform wall thickness.

[0012] Step 4: To generate a gradient grid structure with continuously varying thickness, the nodes in the uniform grid structure need to be offset a second time. Before offsetting, the normal direction of the surface where each node in the uniform grid structure is located is selected as the direction of the second offset.

[0013] Step 5: Determine the offset of each node in the uniform grid structure based on the distance between each node and the reference point;

[0014] Furthermore, in order to generate a grid structure with gradient thickness, during secondary offset, the closer the node is to the center of the structure, the larger the offset; all nodes in the structure need to be sorted, and the sorting result corresponds to the offset of each node.

[0015] Furthermore, the center of the porous structure, the coordinate origin (0, 0, 0), is selected as the reference point. All nodes in the structure are sorted from closest to farthest, using the distance between each node and the reference point as a metric. The closer the distance, the higher the node is ranked, and the corresponding offset is larger. The farther the distance, the lower the node is ranked, and the corresponding offset is smaller. This determines the offset of each node in the uniform grid structure.

[0016] Step 6: Perform a second mesh offset to generate a TPMS structure with a gradient wall thickness.

[0017] Furthermore, the offset value for each node determined in step 5 is combined with the offset direction determined in step 4 to form a new vector. Starting with the second mesh offset, all nodes in the uniform mesh are offset to new positions along the new vector. The lines connecting all nodes form a new mesh, closing the mesh into a complete model, thus forming a TPMS structure with a gradient wall thickness.

[0018] Furthermore, in step 6, the method of changing the uniform porous structure includes modifying the coordinate parameters of the grid nodes in the uniform porous structure so that the uniform porous structure presents a continuous gradient change in thickness, the total number of nodes remains unchanged, and the number and distribution of pores in the uniform porous structure remain unchanged.

[0019] Furthermore, in step 6, the model mesh is modified so that all nodes at the same distance from the reference point throughout the structure have the same offset. As the distance from the reference point decreases, the offset of the node gradually increases, and the model thickness gradually increases, achieving a continuous gradient change in thickness.

[0020] Step 7: After the second mesh offset is completed, soften and repair the mesh structure to optimize the mesh quality.

[0021] In general, the above technical solutions conceived by the present invention have the following advantages and beneficial effects compared with the prior art:

[0022] 1. The three-periodic minimal surface structure constructed by the present invention has a wide range of surfaces to choose from. By modifying the thickness of the model, three-periodic minimal surface models with different thickness gradients can be generated, thereby generating porous structures with various different structural characteristics. This has greater design freedom, a simple and efficient process, and good model quality.

[0023] 2. The thickness gradient porous structure obtained by the present invention is conducive to solving the disadvantage of the single mechanical properties of the traditional uniform thickness porous structure. The wall thickness of the structure can show a continuous gradient change. Gradient porous structures with different structural characteristics can be designed according to different application environments. It is suitable for engineering problems that require personalized design and has a wider range of uses. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0025] Figure 1 3 is a schematic structural diagram of the initial surface in step 1 of an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of the structure after the initial surface is meshed in step 2 of an embodiment of the present invention.

[0027] Figure 3 This is a schematic structural diagram of generating a uniform thickness grid after the nodes on the initial surface are offset in step 3 of an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of a uniform structure and its cross-sectional view generated after the uniform thickness grid is closed in step 3 of the embodiment of the present invention.

[0029] Figure 5 This is an example flow chart of determining the secondary offset of each node in step 5 of an embodiment of the present invention.

[0030] Figure 6 This is a schematic diagram of a gradient wall thickness structure and its cross-sectional view generated after the nodes in the grid structure are offset twice in step 6 of an embodiment of the present invention.

[0031] Figure 7 This is a diagram of a primitive structure model with gradient wall thickness in step 7 of an embodiment of the present invention.

[0032] Figure 8 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION

[0033] To further clarify the objectives, technical solutions, and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and examples. The software used in this example is Rhino7 and Magics. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention. Furthermore, the technical features involved in the various embodiments of the present invention described below may be combined as long as they do not conflict with each other.

[0034] The embodiment of the present invention specifically includes the following steps:

[0035] Step 1: This embodiment uses the primitive structure among the three-periodic minimal surface structures as an example to prepare a structure with continuously varying wall thickness. The surface equation of the primitive structure is shown in formula (1-1):

[0036] cos(x)+cos(y)+cos(z)=t (1-1)

[0037] In the spatial coordinate system, the surface is defined and established by the surface equation. Input the spatial function formula (1-1) of the primitive structure into the function editing terminal and assign the logical modeling instructions. Set the size of the structure to 10mm×10mm×10mm, the number of arrays to 1, and generate the initial surface of the structure. The initial surface has no thickness, such as Figure 1 shown.

[0038] Step 2: Divide the mesh of the initial surface generated in step 1, such as Figure 2 As shown, the node on the top edge of the initial surface is recorded as A0.

[0039] Step 3: Using the initial surface generated in step 1 as the middle surface, offset the mesh nodes on the middle surface along the normal direction of the middle surface to the inside and outside of the middle surface by a fixed distance. The offset direction of node A0 is as follows: Figure 2 As shown by the arrow in the middle. Set the offset of all nodes to 0.5mm to complete the first mesh offset. The mesh structure generated after the offset is as follows Figure 3 As shown. The uniform structure formed by the closed grid structure is as follows Figure 4 As shown, Figure 2 The node A0 in the figure is offset to both sides of the middle surface to generate two new nodes A1 and A2. The distance between the two nodes A1 and A2 is 1mm. Figure 4 Take two nodes, A3 and A4, with a distance of 1 mm between them. The lines connecting all the nodes generated by the first mesh offset form a primitive mesh structure with a uniform wall thickness of 1 mm.

[0040] Step 4: In order to generate a gradient grid structure with continuously changing thickness, the nodes in the uniform grid structure generated in step 3 need to be offset for the second time. Before offsetting, the normal direction of the surface where each node in the uniform grid structure is located is selected as the direction of the second offset. Each node has only one fixed direction during offset. Figure 4 As shown in the figure, the offset directions of the two nodes A3 and A4 are both the normal directions of the surfaces where the nodes are located.

[0041] Step 5: Determine the offset of each node in the uniform grid structure based on the distance between each node and the reference point.

[0042] In this embodiment, the center of the porous structure, that is, the coordinate origin (0, 0, 0) is selected as the reference point, denoted as point O. Figure 4 In order to generate a grid structure with gradient thickness, during the secondary offset, the closer the node is to the coordinate origin (0, 0, 0), the larger the offset required.

[0043] The example diagram of the process of determining the secondary offset of each node is as follows: Figure 5 As shown. The coordinates of all nodes in the uniform grid structure are read in and stored in the corresponding array. All nodes in the structure are sorted from near to far using the distance between each node and the reference point as a criterion. Each node in the structure corresponds to an offset according to its sorting. The node farthest from the reference point, that is, the node with the largest coordinate difference, has the smallest corresponding offset, which is set to 0% of the existing thickness, i.e., no thickening. The node closest to the reference point, that is, the node O(0, 0, 0) with the smallest coordinate difference, has the largest corresponding offset, which is set to 50% of the existing thickness. The existing thickness of all nodes before the offset is the uniform thickness of 1mm generated in step 3. In this embodiment, an offset of 50% of the existing thickness is an offset of 0.5mm.

[0044] Nodes closer to the reference point are ranked higher, resulting in larger offsets and thickening. Nodes farther from the reference point are ranked lower, resulting in smaller offsets and thinning. As the distance between each node and the origin decreases, the node offsets gradually increase, and the thickness of the structure gradually increases, creating a gradient overall.

[0045] Step 6: Perform a second mesh offset to generate a primitive structure with a gradient wall thickness.

[0046] In this embodiment, the offset corresponding to the sorting result of each node determined in step 5 and the offset direction determined in step 4 are combined to form a new vector. When the second grid offset begins, all nodes in the grid are offset to new positions along the new vector. Figure 6 As shown, Figure 4 The nodes A3 and A4 on the uniform structure are offset: A3 is offset to B3, and A4 is offset to B4. The line between B3 and B4 replaces the line between A3 and A4, becoming the new mesh line. Similarly, after the second offset, the lines connecting all the new nodes form a mesh, closing the entire model and forming a primitive structure with gradient wall thickness. The thickness at the reference point is the maximum structure thickness of 1.5 mm. The thickness of the node farthest from the reference point remains the thickness from the initial offset, which is the minimum thickness of the entire model of 1 mm.

[0047] Step 7: After the second mesh offset is completed, a primitive structure with gradient wall thickness is generated. The mesh structure is softened and repaired to optimize the mesh quality.

[0048] During the modeling process, the mesh nodes of the model were offset twice, and the mesh shape changed, so there would be some problems with the quality of the model. After the modeling is completed, the mesh structure is first softened in the Rhino software, which can preliminarily improve the quality of the model and reduce defects such as holes. After the initial repair, the model is exported to the STL format commonly used for additive manufacturing and imported into the 3D model design software. The 3D model design software used in this embodiment is Magics. In Magics software, model errors can be eliminated and model quality can be improved by repairing bad edges and removing interfering shells. Finally, because the nodes are offset to the outside, the size of the model will be slightly larger than the initial value of 10mm. At this time, the redundant boundaries of the model need to be cut to make the size more accurate. After repair, a gradient wall thickness Primitive structure with a size of 10mm×10mm×10mm can be obtained. The overall model is as follows Figure 7 shown.

[0049] The specific embodiments described above further illustrate the objectives and technical solutions of the present invention. It should be understood that the above description is merely a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A modeling method for a gradient wall thickness TPMS porous structure based on additive manufacturing, characterized in that: The specific steps include: Step 1: Perform mathematical modeling based on the spatial function of the TPMS structure to generate the initial surface of the structure. The initial surface has no thickness. Step 2: Mesh the initial surface generated in step 1; Step 3: Perform the first mesh offset to generate a TPMS structure with uniform wall thickness; Using the initial surface generated in step 1 as the middle surface, the mesh nodes on the middle surface are offset a fixed distance to both sides of the middle surface along the normal direction of the middle surface to complete the first mesh offset. The lines connecting all the nodes on the two surfaces generated after the offset form a new mesh, which is closed into an overall model to generate a TPMS structure with uniform wall thickness. Step 4: To generate a gradient grid structure with continuously varying thickness, the nodes in the uniform grid structure need to be offset a second time. Before offsetting, the normal direction of the surface where each node in the uniform grid structure is located is selected as the direction of the second offset. Step 5: Determine the offset of each node in the uniform grid structure based on the distance between each node and the reference point; In order to generate a grid structure with gradient thickness, during secondary offset, the closer the node is to the center of the structure, the larger the offset. It is necessary to sort all the nodes in the structure and correspond the sorting results to the offset of each node. Step 6: Perform a second mesh offset to generate a TPMS structure with a gradient wall thickness. Combine the offset of each node determined in step 5 with the offset direction determined in step 4 to form a new vector. The second mesh offset begins, and all nodes in the uniform mesh are offset to new positions along the new vector. The lines connecting all nodes form a new mesh, closing the mesh into a complete model, thus forming a TPMS structure with a gradient wall thickness. Step 7: After the second mesh offset is completed, soften and repair the mesh structure to optimize the mesh quality.

2. A modeling method for a gradient wall thickness TPMS porous structure based on additive manufacturing according to claim 1, characterized in that: Step 5: Select the center of the porous structure, that is, the coordinate origin (0, 0, 0) as the reference point, and use the distance between each node and the reference point as the measurement standard to sort all the nodes in the structure from near to far; the closer the distance, the higher the node is sorted, and the corresponding offset is larger; the farther the distance, the lower the node is sorted, and the corresponding offset is smaller; thereby determining the offset of each node in the uniform grid structure.

3. The modeling method of a gradient wall thickness TPMS porous structure based on additive manufacturing according to claim 1, characterized in that: In step 6, the method of changing the TPMS structure with uniform wall thickness includes modifying the coordinate parameters of the grid nodes in the TPMS structure with uniform wall thickness, so that the TPMS structure with uniform wall thickness presents a continuous gradient change in thickness, the total number of nodes remains unchanged, and the number and distribution of holes in the TPMS structure with uniform wall thickness remain unchanged.

4. The modeling method of a gradient wall thickness TPMS porous structure based on additive manufacturing according to claim 1, characterized in that: In step 6, the model mesh is modified so that all nodes at the same distance from the reference point in the entire structure have the same offset; as the distance from the reference point decreases, the offset of the node gradually increases, and the model thickness gradually increases, achieving a continuous gradient change in thickness.

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