Selective laser melting forming preparation method based on topological optimization supporting structure

Abstract

The invention discloses a selective laser melting forming preparation method based on a topological optimization supporting structure. The method belongs to the technical field of metal additive manufacturing and comprises the operation steps that a topological optimization supporting structure is selected for pretreatment and slicing treatment; metal powder is selected for printing; simulation analysis is conducted on the 3D printing process of the supporting structure, and technological parameters are determined; the processed data are imported into laser melting forming equipment, and workpiece printing is started; the printed sample is cut from the printing substrate, and the density of the sample is observed; and grinding the cut support structure sample by using abrasive paper, carrying out mechanical polishing treatment by using suspension liquid matched with polishing cloth, observing the density of the topological optimization support structure printing sample, and researching the tensile property of the topological optimization support structure printing sample. Compared with a blocky supporting structure, the powder consumption is reduced by 62%; the waste of metal powder is reduced by adding the topological optimization supporting structure, and the influence on the quality of a formed product is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and relates to a selective laser melting forming preparation method based on a topology-optimized support structure. Background Art

[0002] As one of the core technologies in the field of metal additive manufacturing, selective laser melting technology is a precision additive manufacturing process based on a high-energy laser beam. This technology realizes the integrated and precise manufacturing from a three-dimensional digital model to a solid metal part through the layer-by-layer slicing process of a CAD model assisted by computer-aided design, and uses a laser energy source to selectively melt and stack the metal powder bed layer by layer. With its technical advantages such as high forming accuracy, high material utilization rate, ability to form complex geometric structures, high density of formed parts, and excellent mechanical properties, SLM technology has been widely used in many high-end manufacturing fields.

[0003] However, when forming precision parts with overhanging structures by selective laser melting, since there is no underlying solid structure connecting the overhanging structure to the substrate, and the heat conduction rate of the powder is only 1 / 100 of that of the solid structure, heat accumulation occurs in the overhanging area, resulting in the accumulation of residual stress in the overhanging structure area, and thus obvious warping deformation appears in the overhanging structure. Therefore, it is necessary to add a support structure as a connecting member between the overhanging structure and the forming substrate to achieve mechanical restraint. And since this support structure is not a forming part, it will be treated as waste after the preparation of the forming part is completed, which increases the waste of metal powder. Therefore, how to balance the heat conduction performance and anchoring effect of the support structure while reducing the volume of the support structure and thus reducing the powder usage is still a hot topic and a difficult point in current research. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a selective laser melting forming preparation method that takes into account the heat conduction performance and anchoring effect of the topology-optimized support structure, reduces the volume of the support structure, and reduces the powder usage.

[0005] Technical Solution: A selective laser melting forming preparation method based on a topology-optimized support structure according to the present invention comprises the following operating steps:

[0006] (1) Select a suitable topology-optimized support structure and perform pre-processing and slicing processing using slicing software;

[0007] (2) Select metal powder for printing and dry the metal powder before printing;

[0008] (3) Use additive manufacturing simulation software to simulate and analyze the 3D printing process of the support structure and preliminarily determine the printing process parameters;

[0009] (4) Import the sliced data in step (1) into the laser melting forming equipment and start printing the workpiece;

[0010] (5) Cut the printed sample from the printing substrate and observe its density;

[0011] (6) For the cut support structure sample, embed the sample with epoxy resin and polish it successively with 80-mesh, 240-mesh, 400-mesh, 800-mesh, 1200-mesh, and 1500-mesh sandpapers. Then, use a 50nm SiO2 suspension in combination with a polishing cloth to perform mechanical polishing treatment through a metallographic embedding machine and a polishing machine. Use optical microscopy for microstructure observation and image acquisition to observe the density of the topologically optimized support structure printed sample;

[0012] (7) Use a selective laser melting forming equipment to form a tensile sample bar with a support structure and study its tensile properties.

[0013] Further, the design steps of the topologically optimized support structure in step (1) are as follows:

[0014] (11) Select the basic support unit shape and design a support structure unit that meets the mechanical properties;

[0015] (12) Use 3D modeling software to reconstruct the model of the structure after topological optimization;

[0016] (13) Perform equal-proportion scaling on the reconstructed model using 3D software to construct topologically optimized support structures of different size specifications to meet overhanging surfaces of different sizes.

[0017] Further, when reconstructing the model in step (12), its inclined plane ≥ 45° to meet the forming requirements of the selective laser melting technology.

[0018] Further, the topologically optimized support structure constructed in step (13) is a hollow structure with holes. Its vertical plane is provided with a hole structure, and chamfering and hole digging are set at the top.

[0019] Further, in step (1), use slicing software to perform slicing processing on the topologically optimized support structure to form sliced data.

[0020] Further, in step (2), the titanium alloy metal powder is TC4 metal powder; its particle size distribution is 15 - 53μm.

[0021] Further, step (3) is to use selective laser melting forming process simulation software to simulate the process parameters during the selective laser melting forming process and optimize the process.

[0022] Further, in step (4), selective laser melting forming technology is used for 3D printing.

[0023] Further, in step (5), the printing process parameters are as follows: the laser power is 160 - 280 W, the laser scanning speed is 800 - 1200 mm / s, and the laser scanning spacing is 0.10 - 0.12 mm.

[0024] Further, in step (7), a universal tensile testing machine is used to conduct a tensile test on the specimen at room temperature. The displacement speed of the tensile testing machine is set to 1 mm / min. Three tensile tests need to be carried out for each group of parameters, and the average value of the three results is taken as the final result.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant features: (1) The powder usage of the reformed structure is reduced by 62% compared with the block support structure; by adding a topology-optimized support structure, the waste of metal powder is greatly reduced. At the same time, it can meet the problem of deformation caused by thermal stress during the part forming process, effectively reduce the impact on the quality of the formed product, and greatly improve the product qualification rate; (2) At the same time, the process parameters are optimized through forming experiments; (3) The topology-optimized support structure has good thermal conductivity and mechanical properties, providing a new support structure design and preparation scheme for the laser selective melting forming of overhanging structures. Description of the Drawings

[0026] Figure 1 is a schematic diagram of the topology optimization process of an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the three-dimensional model reconstruction of the unit cell support structure of an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of the structure combining multi-layer array support and printing layer of an embodiment of the present invention;

[0029] Figure 4 is a printing sample diagram and density diagram of the topology-optimized support structure of an embodiment of the present invention;

[0030] Figure 5 is a comparison diagram of the stress-displacement curves of the topology-optimized support structure and other lattice structures of an embodiment of the present invention. Detailed Embodiments

[0031] The following further describes the content of the present invention with specific embodiments.

[0032] As shown in the figure, a selective laser melting forming preparation method based on a topology-optimized support structure disclosed by the present invention has the following operating steps:

[0033] (1) Select a suitable topology optimization support structure and perform pre - processing and slicing using slicing software;

[0034] (2) Select TC4 metal powder for printing. The metal powder needs to be dried before printing;

[0035] (3) Use additive manufacturing simulation software to simulate and analyze the 3D printing process of the support structure, thereby preliminarily determining the printing process parameters;

[0036] (4) Import the data processed by slicing in step (1) into a laser melting forming device and start printing the workpiece;

[0037] (5) Cut the printed sample from the printing substrate and observe its density;

[0038] (6) After the support structure sample cut in step (5), embed the sample with epoxy resin and polish it successively with 80 - mesh, 240 - mesh, 400 - mesh, 800 - mesh, 1200 - mesh and 1500 - mesh sandpapers, then perform mechanical polishing treatment with 50nm SiO2 suspension and polishing cloth, and observe and collect images of the microstructure using optical microscopy to observe the density of the topology - optimized support structure printed sample;

[0039] (7) Use a selective laser melting forming device to form a tensile test bar with a support structure and study its tensile properties.

[0040] The topology - optimized support structure in step (1) is used to connect the substrate and the formed part during the process of preparing parts by selective laser melting. Its design steps are as follows:

[0041] (11) Select the basic shape of the support unit and design a support structure unit that meets the mechanical properties;

[0042] Use topology optimization software based on the grid support structure to perform topology optimization on the grid support structure;

[0043] The design of the topological support structure first applies a certain load on the grid support structure, as Figure 1 shown, and then performs a static analysis on the reticulated support structure. After 15 cycles of iteration, the state of the topology - optimized support structure can be obtained. The topology optimization software uses the variable density analysis method. For the grid cells in the structure that have a poor effect on deformation under external forces, the value is assigned 0, and the remaining grid cells are assigned 1. When performing topology optimization, the elements assigned 0 are removed to obtain the topology - optimized support structure. The present invention aims to maximize the stiffness of the support structure, constrains the material volume fraction, and uses the variable density method to generate the optimal material distribution;

[0044] (12) Reconstruct the 3D model of the structure after topological optimization of the output model obtained in the previous step using 3D modeling software. As Figure 2 shown, during the process of model reconstruction, the requirement that the forming slope degree in the model should not be less than 45° should be met, so that the reconstructed model can meet the conditions of selective laser melting forming;

[0045] (13) Perform equal-proportion scaling on the reconstructed model using 3D software to construct support structures of different size specifications to meet overhanging surfaces of different sizes.

[0046] Four vertical surfaces on the outer side of the topological optimization support structure in step (1) are provided with hole structures, which can meet the requirement of timely clearing the metal powder inside the support structure after printing and can complete the recycling and reuse of the metal powder, thus reducing the waste of metal powder;

[0047] Chamfering and hole-drilling are set at its top, which is convenient for the support structure to be separated from the formed overhanging structure, reducing the difficulty and operation time of post-processing;

[0048] The topological optimization support structure can be scaled proportionally to meet overhanging structures of different specifications. As Figure 3 shown, it can realize the combined reuse of multiple support structure units and be arrayed in three directions of up and down, front and back, and left and right in 3D space.

[0049] The topological optimization support structure is prepared by selective laser melting forming technology, and 3D printing of the topological optimization support structure is carried out through parameters such as corresponding laser power, scanning speed, and scanning spacing.

[0050] The topological optimization support structure is a hollow structure with holes to facilitate powder recovery.

[0051] The wall thickness of the topological optimization support structure is 0.5 mm - 2 mm.

[0052] The topological optimization support structure can be used as a unit cell support structure, and the support structure can be arrayed to meet the support requirements of overhanging structures of different specifications.

[0053] A concave notch is set at the top of the topological optimization support structure to facilitate the removal of the support structure during post-processing.

[0054] The height of the topological optimization support structure is 5 mm.

[0055] The topological optimization support structure can be set in one layer or multiple layers according to the needs of the part to enhance the adaptability of the support structure to different parts and at the same time enhance the support strength for the part.

[0056] The topological optimization support structure is sliced using slicing software to form slice data.

[0057] In step (2), the particle size distribution of the titanium alloy metal powder is 15 - 53 μm; TC4 metal powder is selected as the printing material, and the topological optimization support structure is prepared from TC4 alloy powder by selective laser melting forming technology;

[0058] The TC4 metal powder is placed in the printing powder bin of the selective laser melting equipment, and then printing preparation is carried out. Before printing the sample, the forming chamber of the equipment needs to be purged with high-purity inert gas two to three times to ensure that the oxygen content is below 1000 ppm during the building process, preventing oxidation and contamination, thereby ensuring the forming quality;

[0059] The support structure of this design helps to improve product performance, reduce the powder usage for manufacturing the support structure, and the production is effectively controlled;

[0060] The light metal alloy powder in the current slice area is selectively melted by a laser beam. After the molten pool solidifies, single-layer forming is completed; then the working cylinder is driven to descend by a preset slice thickness, and the next layer of powder is evenly laid by a powder spreading device. The above laser melting and powder spreading processes are repeated, and layer-by-layer cumulative forming is carried out; during this process, it is necessary to ensure that the process parameters are set well, and finally the forming with a topological optimization support structure is realized.

[0061] Step (3) is to optimize the process by using the process parameters during the selective laser melting forming process simulation software to simulate the selective laser melting forming process.

[0062] Step (4) uses selective laser melting forming technology for 3D printing.

[0063] In step (5), the printing process parameters for laser selective melting are a laser power of 160 - 280 W, a laser scanning speed of 800 - 1200 mm / s, a laser scanning spacing of 0.10 - 0.12 mm, a laser spot diameter of 0.05 - 0.1 mm, a powder spreading layer thickness of 35 - 45 μm, and a substrate preheating temperature of 100 - 120 °C.

[0064] In step (6), a metallographic embedding machine and a polishing machine are used to process the sample, and an optical microscope is used to observe the density of the sample;

[0065] The printed sample of the topological optimization support structure is as Figure 4As shown, after the selective laser melting formed sample is selected, the target area sample is first obtained by wire cutting technology, and then metallographic sample preparation is carried out; after the sample is embedded in epoxy resin, it is polished successively with sandpapers for different purposes, and then mechanically polished with a suspension and a polishing cloth until it becomes a flat and flawless mirror surface. Immediately after that, it is rinsed with pure water, wiped with cotton dipped in alcohol and dried with a hair dryer. Optical microscopy is used for microstructure observation and image acquisition to obtain a support structure with good density;

[0066] In the step (7), a universal tensile testing machine is used to conduct a tensile test on the sample at room temperature. The displacement speed of the tensile testing machine is set to 1 mm / min. Three tensile tests need to be carried out for each set of parameters, and the average value of the three results is taken as the final result.

[0067] The oxygen content in the printing cavity of the equipment during the selective laser melting forming process is lower than 1000 ppm, and the printing cavity is filled with an inert gas; the inert gas is argon, the pressure in the printing chamber of the equipment is 0 - 25 mbar, and the dust removal component is 18 - 20 m 3 / h.

[0068] The stress-displacement curves of the topological optimization support structure and other support structures are as Figure 5 shown. The black curve in the figure is the topological optimization support structure, and the red curve is other support structures. It can be seen from the figure that the fracture displacement and reaction force of the topological optimization support structure are greater than those of other support structures, which indicates that the topological optimization support structure has relatively better mechanical properties and can better limit the warping deformation of the overhanging structure during the selective laser melting forming process.

Claims

1. A preparation method for selective laser melting forming based on a topology-optimized support structure, characterized in that The operation steps are as follows: (1) Select a suitable topological optimization support structure and perform pre-processing and slicing using slicing software; (2) Select metal powder for printing and dry the metal powder before printing; (3) Use additive manufacturing simulation software to simulate and analyze the 3D printing process of the support structure, and preliminarily determine the printing process parameters; (4) Import the sliced data in step (1) into a laser melting forming device to start printing the workpiece; (5) Cut the printed sample from the printing substrate and observe its density; (6) Inlay the cut support structure sample with epoxy resin, and polish it successively with sandpapers of 80 mesh, 240 mesh, 400 mesh, 800 mesh, 1200 mesh and 1500 mesh, then use 50nm SiO2 suspension and polishing cloth to perform mechanical polishing treatment through a metallographic inlaying machine and a polishing machine, and use optical microscopy to observe the microstructure and collect images to observe the density of the printed sample of the topological optimization support structure; (7) Use a selective laser melting forming device to form a tensile sample bar with a support structure and confirm its tensile properties.

2. The preparation method of selective laser melting forming based on a topology optimization support structure according to claim 1, wherein The design steps of the topological optimization support structure in step (1) are as follows: (11) Select the basic shape of the support unit and design a support structure unit that meets the mechanical properties; (12) Use 3D modeling software to reconstruct the model of the structure after topological optimization; (13) Perform equal-proportion scaling on the reconstructed model using 3D software to construct topological optimization support structures of different size specifications to meet overhanging surfaces of different sizes.

3. The preparation method of selective laser melting forming based on a topological optimization support structure according to claim 2, characterized in that In step (12) during model reconstruction, its inclined surface ≥ 45° to meet the forming requirements of the selective laser melting technology.

4. A method for preparing a selective laser melting forming based on a topologically optimized support structure according to claim 2, wherein The topological optimization support structure constructed in step (13) is a hollow structure with holes, and its vertical surface is provided with a hole structure, and chamfering and hole digging are set at the top.

5. A selective laser melting forming preparation method based on a topologically optimized support structure according to claim 1, characterized in that In step (1), use slicing software to slice the topological optimization support structure to form sliced data.

6. The preparation method of selective laser melting forming based on a topological optimization support structure according to claim 1, characterized in that, In step (2), the titanium alloy metal powder is TC4 metal powder; its particle size distribution is 15 - 53μm.

7. A selective laser melting forming preparation method based on a topology-optimized support structure according to claim 1, characterized in that Step (3) is to use selective laser melting forming process simulation software to simulate the process parameters during the selective laser melting forming process and optimize the process.

8. A method for preparing a selective laser melting formed body based on a topologically optimized support structure according to claim 1, wherein Step (4) uses selective laser melting forming technology for 3D printing.

9. A method for preparing a selective laser melting forming based on a topologically optimized support structure according to claim 1, wherein, In step (5), the printing process parameters are that the laser power is 160 - 280W, the laser scanning speed is 800 - 1200mm / s, and the laser scanning spacing is 0.10 - 0.12mm.

10. A method for preparing a selective laser melting formed body based on a topologically optimized support structure according to claim 1, characterized in that, In step (7), use a universal tensile testing machine to perform tensile tests on the specimens at room temperature. The displacement speed of the tensile testing machine is set to 1mm / min. Three tensile tests need to be performed for each group of parameters, and the average value of the three results is taken as the final result.

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