Process optimization method for preparing high-density formed part through selective laser melting

Abstract

The invention discloses a process optimization method for preparing a high-density formed part through selective laser melting, and belongs to the field of additive manufacturing. According to the method, three main influence factors of laser power P, scanning speed V and scanning interval S in selective laser melting forming are selected or designated for an experiment, relative density serves as an evaluation index, and the extreme value of the relative density in the experiment is the optimal parameter combination of selective laser melting forming of the material. According to the method, the accuracy of selecting the optimal parameters for material forming of the process can be remarkably improved, the material development period is shortened, the development cost is saved, and the selective laser melting forming part with high density and excellent performance can be prepared easily.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing, and more particularly to a process optimization method for preparing high-density formed parts by selective laser melting. Background Art

[0002] With the continuous development of the manufacturing industry, traditional processing methods are difficult to achieve integrated forming of complex geometric shapes and high-precision structures due to their high production costs, long processing periods, and low material utilization rates, which greatly limit the application scope of this material. The advent of additive manufacturing (AM) technology has brought new impetus to the manufacturing industry. Compared with traditional processes, additive manufacturing slices parts using 3D software and then stacks them layer by layer to finally manufacture three-dimensional solid parts. It does not require molds, has high material utilization rates, short production and processing cycles, and can achieve customized production of complex parts. Among them, selective laser melting (SLM) is the most representative metal additive manufacturing technology and has currently been successfully applied in fields such as aerospace, automotive manufacturing, and medical and health.

[0003] Currently, the common method for optimizing the process parameters of selective laser melting forming in this field is to conduct cross-experiments on various factors, evaluate the advantages and disadvantages of the forming parameter combinations by testing the density and observing the metallographic structure of the final formed parts, and select the optimal parameters. However, this method has a large experimental workload, a long cycle, high costs, and low accuracy, and it is impossible to accurately predict whether the obtained parameter combination is the best forming parameter for this material. Selective laser melting forming is a three-dimensional component construction process from point to line (single melt track) - from line to surface (multi-track single layer) - from surface to body. Among them, if the tiny defects that occur during the single melt track and multi-track single layer forming processes are not controlled, they will gradually accumulate and amplify during the subsequent solid forming process, directly affecting the density and mechanical properties of the final component.

[0004] Therefore, providing a method to provide theoretical guidance for developing and selecting the best process parameter combination for selective laser melting forming materials, reducing the experimental workload, shortening the development cycle, and preparing formed parts with high density and excellent properties is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] In view of this, the present invention provides a process parameter optimization method for preparing high-density formed parts by selective laser melting, which has the advantages of a simple process, a short experimental cycle, high efficiency, accurate parameter selection, and high density of the obtained formed parts.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A process optimization method for preparing high-density formed parts by selective laser melting, comprising the following steps:

[0008] (1) Measure the particle size distribution of the formed alloy powder using a laser particle size analyzer. Taking the average particle size D50 as the reference value, round up to determine the powder layer thickness h for selective laser melting forming of the component of this material.

[0009] (2) Select the "S"-shaped scanning strategy.

[0010] (3) Select the laser power and scanning speed as influencing factors to conduct single-pass forming experiments. According to the single-pass morphology, determine the optimal parameter combination scheme for the laser power and scanning speed.

[0011] (4) Adopt the optimal parameter combination scheme of the laser power and scanning speed obtained in step (3), introduce the scanning spacing as an influencing factor, conduct single-layer multi-pass overlapping experiments, and obtain the optimized parameter combination scheme of the laser power, scanning speed, and scanning spacing.

[0012] (5) Based on the optimized parameter combination scheme of the laser power, scanning speed, and scanning spacing obtained in step (4), adjust the parameter value range to design a three-factor and five-level block orthogonal experiment for the laser power, scanning speed, and scanning spacing, conduct block forming, and take the relative density as the evaluation index. Select the optimal value of the relative density in the experiment as the best process parameter combination for selective laser melting forming of this material.

[0013] Furthermore, in step (1), the average particle size D50 is 15 - 53 μm, and the powder layer thickness h is taken as 20 - 60 μm. The particle size distribution of the alloy powder and D50 can be detected by a laser particle size analyzer.

[0014] Moreover, the formed alloy powder is a powder material of stainless steel, titanium alloy, aluminum alloy, superalloy, or other newly developed materials suitable for selective laser melting forming.

[0015] Further, in step (2), the interlayer rotation angle of the "S"-shaped scanning strategy is 67°, so as to improve the residual stress distribution state, prevent warping deformation, and improve the mechanical properties of the formed component.

[0016] Further, step (3) is to print a single pass on a 316L stainless steel secondary substrate of 10×10×3 mm, and the length of the single pass is 30 mm. For subsequent observation and measurement. Select a group with the best surface morphology, regular pass, and uniform width in the experimental results as the optimized parameter combination of the two factors for the single-pass experiment.

[0017] Further, in step (4), the diameter d of the laser melting equipment is used as a reference value, and the same levels above and below it are selected as the parameter range of the scanning spacing. The "S" - shaped strategy is adopted to perform single - layer printing on a 10×10×3 mm secondary substrate of 316L stainless steel. The printing specification is 10×10 mm. The surface roughness of the formed surface is measured by the confocal mode of the laser confocal microscope, and the optimized parameter combination scheme of the laser power, scanning speed, and scanning spacing is obtained.

[0018] Further, in step (5), the block orthogonal experiment is designed with reference to the optimized parameter combination determined by the single - melt - channel and single - layer multi - channel lap joint. Five level values are taken respectively above and below the optimal parameters of each single factor, and an orthogonal experiment with three factors and five levels is designed. Among them, the block printing specification is 10×10×10 mm, and the forming substrate is a 316L stainless steel substrate.

[0019] Furthermore, the relative density of the formed parts in the orthogonal experiment is measured by the Archimedes drainage method. The relative density of the formed parts can be obtained from the following formula:

[0020]

[0021] In the formula: ρ a is the theoretical density of distilled water at an atmospheric pressure of 1×10 5 Pa and 25 °C, and the value is taken as 1 g / cm 3 ; ρ b is the theoretical density of the forming material, ma is the mass of the formed part in air, and Mb is the mass of the formed part in water.

[0022] Further, during the experimental forming process, the protective atmosphere is N2, and printing is carried out when the oxygen content in the forming chamber is lower than 500 ppm.

[0023] Further, before printing, the powder needs to be dried at 120 °C for 2 h in a vacuum drying oven.

[0024] The beneficial effects of the present invention are as follows: By designing single - melt - channel, single - layer multi - channel lap joint, and block orthogonal forming experiments, with the laser power, scanning speed, and scanning spacing as influencing factors, the optimal forming process parameter combination of the selective laser melting of the forming material is gradually selected, effectively shortening the experimental range, reducing the experimental workload, reducing the development cost, and shortening the development cycle of the material.

[0025] The present invention provides a set of scientific and effective material development ideas for practitioners in the field of selective laser melting, which can not only be used for the development of new forming materials, but also for the verification and optimization of the forming processes of existing forming materials.

[0026] The process parameter optimization method for preparing high-density formed parts by selective laser melting provided by the present invention can ensure the formation of formed parts with high density and excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the SEM diagram of the 316L stainless steel powder produced by gas atomization in Example 1;

[0028] Figure 2 It is the schematic diagram of the printing strategy of rotating 67° between layers in an "S" shape in Example 1;

[0029] Figure 3 It is the surface scan result diagram of the roughness of the multi-pass lap joint in Example 1;

[0030] Figure 4 It is the cross-sectional morphology diagram of the formed part under the optimal forming parameters in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] Example 1

[0033] A process parameter optimization method for preparing high-density formed parts by selective laser melting:

[0034] (1) The forming powder selects the 316L stainless steel powder produced by gas atomization, dries it at 120°C for 2 hours, and the SEM morphology of this powder is for reference Figure 1 . Using a Mastersizer 2000 laser particle size analyzer to measure the particle size distribution of the powder, the average particle size D50 is 35μm, so rounding up to determine the powder layer thickness h is 40μm. Select the laser melting equipment as the BLT-S210 equipment, the spot diameter is 100μm, the substrate material is a 316L stainless steel substrate, and the substrate is polished, degreased and derusted before installation.

[0035] (2) The scanning strategy selects the printing strategy of rotating 67° between layers in an "S" shape to improve the residual stress distribution state, prevent warping deformation, and improve the mechanical properties of the formed part. The schematic diagram is for reference Figure 2 .

[0036] (3) Select the laser power and scanning speed as the influencing factors and select the interval range for single-pass forming experiments. According to the single-pass morphology, determine the optimized parameter combination of the laser power and scanning speed.

[0037] In this embodiment, a single-pass forming experiment is carried out with laser power and scanning speed as influencing factors. The forming range of laser power is 50 - 300 W, with an interval of 50 W; the scanning speed range is 500 - 2500 mm / s, with an interval of 400 mm / s. A comprehensive experiment is carried out within this parameter range. Printing is carried out on a 316L secondary substrate of 10×10×3 mm, with a melt channel length of 30 mm, and a total of 36 groups of results are obtained. By comparing the single-pass morphology and the melt channel width, it is found that when the laser power is 200 W and the scanning speed is 900 mm / s, the obtained single-pass is continuous and regular, with an appropriate width and an obvious fish-scale structure, which is suitable for selective laser melting forming. Therefore, the optimized parameters for the single-pass experiment are selected as a laser power of 200 W and a scanning speed of 900 mm / s, and a multi-pass overlapping experiment is designed according to these parameters.

[0038] (4) On the basis of the optimized parameters of the single-pass forming experiment (laser power 200 W, scanning speed 900 mm / s), the scanning spacing S is introduced as an influencing factor. The interval range of the scanning spacing is selected as 0.06 - 0.14 mm with reference to the spot diameter of the equipment, and a single-layer multi-pass overlapping experiment is carried out to obtain 6 groups of experimental results. The confocal mode of a Zeiss LSM800 laser confocal microscope is used to perform a roughness surface scan on the multi-pass overlapping surface, and 3 regions are selected for each sample for measurement and the average value is taken. The obtained results are referred to Figure 3 , and it is found that when the scanning spacing is 0.08 mm, the surface roughness of the overlap is the smallest, which is 3.72 μm. Therefore, the optimized parameter of the scanning spacing is selected as 0.08 mm. Through the single-pass and single-layer multi-pass overlapping experiments, the optimized parameter combination of the three factors is determined as laser power 200 W, scanning speed 900 mm / s, and scanning spacing 0.08 mm.

[0039] (5) Based on the optimized parameter combination selected in the above steps, an orthogonal experiment with three factors and five levels of laser power, scanning speed, and scanning spacing is designed. Among them, the laser power range is selected as 160 - 240 W, with an interval of 20 W; the scanning speed range is 700 - 1100 mm / s, with an interval of 100 mm / s; the scanning spacing range is 0.06 - 0.10 mm, with an interval of 0.01 mm. Design the experiment referring to the three-factor and five-level orthogonal experiment table to perform bulk forming. After printing is completed, cut the bulk specimen from the substrate, perform surface sandblasting treatment, and then use the Archimedes drainage method to measure the relative density corresponding to the formed part. The orthogonal experiment and the relative density results are shown in Table 1 below. Taking the relative density as the evaluation index, through comparing the results, it is found that the density of the formed part reaches the highest at the 13th group of parameters (laser power 200 W, scanning speed 900 mm / s, scanning spacing 0.08 mm), which is 99.58%, almost completely dense. Therefore, the laser power of 200 W, the scanning speed of 900 mm / s, and the scanning spacing of 0.08 mm are selected as the best parameter combination for selective laser melting forming of this material. The cross-sectional morphology of the formed part under the best forming parameters is referred to Figure 4 .

[0040] Table 1 Results of orthogonal experiment design and relative density of formed parts in Example 1

[0041]

[0042]

[0043] In this example, for the material to be formed, by designing single-pass experiments, single-layer multi-pass lap experiments, and bulk orthogonal experiments, the best forming parameters corresponding to this material can be determined only through 3 groups of stage experiments. The designed experimental procedures are simple and can greatly shorten the development cycle. It only takes at least several working days to complete the optimization of the parameter combination. In addition, the accuracy of the technical solution of the present invention is relatively high. The density of the formed part prepared by the best parameters determined through the examples can reach 99.58%, almost completely dense. At the same time, it is observed that the cross-sectional porosity is extremely low and the pore diameter is also extremely small, indicating that the formed part has excellent performance.

[0044] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A process optimization method for preparing high-density formed parts by selective laser melting, characterized in that, It includes the following steps: (1) Measure the particle size distribution of the formed alloy powder using a laser particle size analyzer. Taking the average particle size D50 as a reference value, round up to determine the powder spreading layer thickness h of the selective laser melting formed part of this material; (2) Select the "S"-shaped scanning strategy. (3) Select the laser power and scanning speed as influencing factors to conduct a single melt channel forming experiment. According to the single melt channel morphology, determine the optimal parameter combination scheme of the laser power and scanning speed; (4) Adopt the optimal parameter combination scheme of the laser power and scanning speed obtained in step (3), introduce the scanning spacing as an influencing factor, conduct a single-layer multi-channel overlapping experiment, and obtain the optimized parameter combination scheme of the laser power, scanning speed and scanning spacing; (5) Based on the optimized parameter combination scheme of the laser power, scanning speed and scanning spacing obtained in step (4), adjust the parameter value range to design a three-factor five-level block orthogonal experiment of the laser power, scanning speed and scanning spacing, conduct block forming, and take the relative density as the evaluation index. Select the optimal value of the relative density in the experiment as the best process parameter combination for the selective laser melting of this material.

2. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 1, wherein In step (1), the average particle size D50 is 15 - 53 μm, and the powder spreading layer thickness h is taken as 20 - 60 μm.

3. According to the process optimization method for preparing a high-density formed part by selective laser melting described in claim 2, the formed alloy powder is a powder material of stainless steel, titanium alloy, aluminum alloy, superalloy or other newly developed materials suitable for selective laser melting forming.

4. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 1, wherein In step (2), the interlayer rotation angle of the "S"-shaped scanning strategy is 67°.

5. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 1, wherein Step (3) is to print a single melt channel on a 316L stainless steel secondary substrate of 10×10×3 mm, and the length of the single melt channel is 30 mm.

6. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 5, characterized in that, In step (4), taking the diameter d of the laser melting equipment as a reference value, and selecting the same levels above and below it as the parameter range of the scanning spacing, use the "S"-shaped strategy to conduct single-layer printing on a 316L stainless steel secondary substrate of 10×10×3 mm, and measure the surface roughness of the formed surface using the confocal mode of a laser confocal microscope to obtain the optimized parameter combination scheme of the laser power, scanning speed and scanning spacing.

7. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 1, characterized in that, In step (5), the block orthogonal experiment takes the optimized parameter combination determined by the single melt channel and single-layer multi-channel overlapping as a reference, and takes five level values above and below the optimal parameters of each single factor to design a three-factor five-level orthogonal experiment; among them, the block printing specification is 10×10×10 mm, and the forming substrate is a 316L stainless steel substrate.

8. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 7, wherein, The relative density of the formed part in the orthogonal experiment is measured by the Archimedes drainage method; the relative density of the formed part can be obtained by the following formula: where: ρ a is the theoretical density of distilled water at an atmospheric pressure of 1×10 5 Pa and 25°C, with a value of 1 g / cm 3 ; ρ b ρ is the theoretical density of the forming material, ma is the mass of the formed part in air, and Mb is the mass of the formed part in water.

9. The process optimization method for preparing a high-density formed part by selective laser melting according to claim 1, wherein During the experimental forming process, the protective atmosphere is N2, and printing is carried out in the forming chamber with an oxygen content lower than 500 ppm.

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