An additive manufacturing process that improves the efficiency of titanium alloy selective laser melting technology

Abstract

The present invention discloses an additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology, which belongs to the field of metal additive technology. The process of the present invention first performs an initial screening of the selected process parameters by simulation means to determine the rationality of the selected process parameters. Subsequently, a suitable combination of process parameters is determined by depositing a single-channel sample, and on this basis, the optimal process parameters after fixing the powder thickness are determined through physical preparation, thereby obtaining complete laser power, scanning speed, scanning spacing and powder thickness process parameters for preparing finished product samples. Finally, performance testing can determine whether the selected parameters are better process parameters, and finally obtain process samples with good strength and density; the powder thickness of the present invention is 80-160μm. Compared with the commonly used powder thickness of 20μm-30μm, the present invention adopts a large powder thickness of more than 80μm to directly improve the additive efficiency, but it is necessary to ensure that the sample forming quality meets the requirements after the powder thickness is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and in particular relates to an additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology. Background Art

[0002] Titanium alloys are widely used in aerospace, automotive, and biomedical fields due to their excellent mechanical properties, corrosion resistance, and biocompatibility. Ti-6Al-4V, with its unique properties, is well-suited to additive manufacturing, making it a popular choice. Selective laser melting, an additive manufacturing technology that directly forms metal by melting metal powder layer by layer, plays a crucial role in various fields.

[0003] However, for the current selective laser melting method for preparing titanium alloys, a low layer thickness of 20μm-30μm is usually used as the printing layer thickness, so as to ensure the production of titanium alloy specimens with good density and porosity. Although the use of a lower powder thickness has certain benefits for the quality of the molded specimens to a certain extent, the thinner powder layer also significantly limits the preparation efficiency. In addition, it is worth noting that the powder thickness cannot be increased indefinitely. Increasing the powder thickness requires increasing the laser power and reducing the scanning speed, and there will be a certain loss in surface quality, which will bring defects and reduce performance. In the case of a higher powder thickness, although the preparation efficiency can be improved, it is difficult to produce qualified finished products by the selective laser melting process. Therefore, there is an urgent need to explore a preparation process that improves the quality of the finished product while having high efficiency. Summary of the Invention

[0004] In view of the above shortcomings of the prior art, the present invention provides an additive manufacturing process that improves the efficiency of titanium alloy selective laser melting technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] An additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology includes the following steps:

[0007] S1: The process parameters were simulated and analyzed through Ansys-Workbench simulation. The model was established as a single-channel model consisting of a 4×0.8×0.5mm substrate and 10 0.02×0.3×0.08mm blocks. The grid type was set using the edge size, and the laser heat source was assigned using a Gaussian body heat source, as shown in formula (1). The resulting temperature cloud map was then analyzed, and the molten pool depth was measured using ImageJ software. The average value was obtained after multiple measurements, and the process parameters corresponding to the model with a molten pool depth greater than the set powder thickness were selected and recorded as the initial screening process parameters. The process parameters included laser power, scanning speed, and powder thickness, and the powder thickness was 80μm-160μm.

[0008]

[0009] Where: A is the material's absorption rate for laser light, %; P is the laser power, W; R is the laser light source spot radius, μm; S is the laser penetration depth in the material, equivalent to the powder coating thickness, μm; xyz corresponds to the Cartesian coordinate system, the x direction is the same as the laser movement direction; z is parallel to the powder coating thickness direction, v is the laser movement speed, mm / s, t is the time, and Q is the Gaussian body heat source.

[0010] S2: The process parameters initially screened out in S1 were tested in a single-pass preparation experiment. Using 316L as the substrate and Ti6Al4V aerosolized spherical powder as the raw material, the powder particles were spherical or nearly spherical to increase fluidity during the preparation process. The substrate was preheated, and based on the initial screening process parameters in S1, the laser power, scanning speed, and powder thickness were set. A single-pass deposition experiment was then conducted. A single-pass experimental parameter combination was selected in which there was no powder particle adhesion on the top and side surfaces, and no fracture in the melt path, indicating continuous deposition. The single-pass deposition experimental parameter combination included laser power, scanning speed, and powder thickness.

[0011] S3: Draw the required sample structure on the computer, set the process parameters of the solid forming parameter combination according to the single-channel deposition experimental parameter combination screened out by the single channel to prepare the required sample, use the scanning strategy of 90° rotation between layers, use ImageJ software to measure the width of the single-channel molten pool, and set 60%, 70%, and 80% of the molten pool width as the scanning interval, and screen out the scanning interval with smooth overlap between the molten channels and the least powder particles attached to the surface.

[0012] S4: After the printer has prepared all the samples, the substrate and the sample are removed, and the sample is separated by wire cutting equipment to complete additive manufacturing and perform performance testing and metallographic structure observation. The parameter combination of the sample with relative density ≥99%, hardness ≥350HV, surface roughness Ra≤12.5μm, and metallographic structure of acicular martensite is obtained. Based on the obtained parameter combination, the selective laser melting technology is used to additively manufacture titanium alloy. The obtained parameter combination includes laser power, scanning speed, powder thickness and scanning spacing.

[0013] The performance test includes: testing of relative density, hardness, defects, surface roughness and observation of metallographic structure.

[0014] As a preferred embodiment of the present invention, the Ti6Al4V powder is an aerosolized powder with a particle size of 20 μm to 50 μm. Its elemental weight percentage composition is as follows: Al 5.9%, V 3.92%, Fe 0.022%, O 0.14%, N 0.004%, and Ti as the balance.

[0015] As a preferred embodiment of the present invention, in said S2, the length of a single melt channel in the single channel deposition experiment is 10 mm.

[0016] As a preferred embodiment of the present invention, the additive manufacturing of S2-S3 is performed in a protective gas atmosphere. The additive manufacturing equipment is an EOS M290; the preparation space is a closed space, and argon is used as the protective gas to ensure that the oxygen content is less than 0.02%.

[0017] As a preferred embodiment of the present invention, the sample size prepared in S3 is 10×10×10 mm. 3 .

[0018] As a preferred embodiment of the present invention, the metallographic sample in S4 is first ground with 100#, 200#, 600#, and 1200# sandpaper, then polished, etched with Kroll solvent, and observed with an optical microscope.

[0019] As a preferred embodiment of the present invention, the relative density of the sample in S4 was measured using the Archimedean displacement method, with the average value obtained from multiple measurements. The sample in S4 was measured on both the side and top surfaces using a digital Vickers hardness tester. The defects and metallographic structure of the sample in S4 were observed using a scanning electron microscope and an optical microscope, and the defect size was measured using ImageJ. The roughness of the sample in S4 was measured using a white light interferometer.

[0020] As a preferred embodiment of the present invention, in step S1, the powder spreading thickness is 80 μm-100 μm.

[0021] More preferably, in step S1, the powder spreading thickness is 80 μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology described in the present invention is first preliminarily screened by simulation software, and then the appropriate combination of laser power and scanning speed is determined by depositing a single channel. On this basis, process parameters with less spheroidization, less serious powder adhesion and continuous and smooth melt channels are selected as benchmarks, thereby obtaining complete laser power, scanning speed, scanning spacing and powder thickness process parameters for preparing finished samples. Finally, density, hardness testing and defect characterization are performed to determine whether the selected parameters are optimal process parameters, thereby obtaining a process window for preparing samples with large layer thickness.

[0024] (2) Compared with the commonly used powder coating thickness of 20μm-30μm, the present invention adopts a large powder coating thickness of 80μm or more, which can directly increase the additive efficiency by several times. First, the simulation software is used for preliminary screening, and then the single-pass deposition method is used for screening, which can significantly reduce the time spent and reduce the waste of powder. The method is reliable, economical and practical. The titanium alloy specimens obtained by this method can meet the needs of titanium alloys in various fields and industries of selective laser melting technology, and the present invention can also be applied to the search for process windows of other metal materials in selective laser melting technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the additive manufacturing process for improving the efficiency of the titanium alloy selective laser melting technology described in Example 1.

[0026] Figure 2 The surface and cross-sectional micromorphology images of the single track prepared in Example 1 are as follows: G1 is the surface and cross-sectional micromorphology image of the single track of group 1, G2 is the surface and cross-sectional micromorphology image of the single track of group 2, G4 is the surface and cross-sectional micromorphology image of the single track of group 4, G5 is the surface and cross-sectional micromorphology image of the single track of group 5, G7 is the surface and cross-sectional micromorphology image of the single track of group 7, and G8 is the surface and cross-sectional micromorphology image of the single track of group 8.

[0027] Figure 3 This is a relative density diagram of the multi-channel and multi-layer (solid) sample prepared in Example 1.

[0028] Figure 4 The Vickers hardness comparison diagram of the multi-layer (solid) sample prepared in Example 1, (a) is the Vickers hardness comparison diagram of the top surface of the sample, and (b) is the Vickers hardness comparison diagram of the side surface of the sample.

[0029] Figure 5The metallographic structure diagram of the multi-layer (solid) sample prepared in Example 1; (a) the metallographic structure diagram of the top surface of the sample; (b) the metallographic structure diagram of the side surface of the sample.

[0030] Figure 6 Schematic diagram of defects of the multi-channel and multi-layer (solid) samples prepared in Example 1: Schematic diagram of defects of the prepared samples at different scanning speeds: (a) Group 1; (b) Schematic diagram of unmelted powder phenomenon of Group 5; (c) Schematic diagram of cracks in Group 5.

[0031] Figure 7 Schematic diagram of the roughness of the multi-layer (solid) Group 3 and Group 4 samples prepared in Example 1: G3 is Group 3, and G4 is Group 4. DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology described in this embodiment includes the following steps:

[0035] S1: Through Ansys-Workbench simulation, the process parameters were simulated and analyzed, and the single-channel model was used to analyze the molten pool morphology to determine whether the selected process parameters met the process requirements: the model was established as a single channel and substrate, and the heat source was assigned to a Gaussian moving body heat source. The simulation results were analyzed, and the temperature cloud map was screened out. The melting depth can penetrate the preset 80μm-160μm powder thickness, confirming that the theoretically determined process parameters are effective and can be used for comparative analysis in physical preparation; the feasible experimental data obtained are shown in Table 1.

[0036] S2: Using 316L as substrate and Ti6Al4V atomized powder with a particle size of 20μm-50μm as raw material; preheat the substrate, set the laser power, scanning speed and powder thickness according to Table 1, and then perform single-track deposition to obtain a single-track sample. The surface and cross-section of the prepared single-track sample were then microscopically observed (partial results are shown in Figure 2). Figure 2 When the groups are 1-5 (the results are shown in Figure 2 As shown in Figure 2, the surface morphology of the sample showed a continuous and smooth forming phenomenon, with no powder particles attached to the top and side surfaces, and no fracture in the melt path. Due to the low powder thickness in Groups 9-13, the laser energy can completely melt the powder particles and form similar surface morphologies. Subsequently, in Groups 6-8, it was found that the melt path gradually twisted, and obvious powder spheroidization and adhesion were observed. In addition, when the cross-sectional morphology of the melt pool was observed in Group 8, a large number of unmelted particles appeared in the powder ( Figure 2On the other hand, samples in groups 14-16, due to lower laser energy, exhibited severe powder adhesion during the preparation process, even leading to melt path depression and fracture at high speeds. Samples in groups 17-19, due to higher laser power, experienced significant powder splashing during preparation, resulting in distortion. Samples in groups 20-24 exhibited similar shortcomings to those in groups 14-16, resulting in poor single-pass forming and failing to meet requirements.

[0037] S3: The prepared sample was drawn on the computer, and the single-channel melt width obtained in S2 was measured using ImageJ software. Square samples were prepared based on the scanning intervals of 60%, 70%, and 80% of the melt pool width. There was no obvious difference in the overlap of the melt channels of the formed samples under the three scanning intervals. The melt channels were well bonded with each other, and no distortion, cracks, or pore defects occurred. The sample prepared with a scanning interval of 70% of the melt pool width showed the least spheroidization preparation defects, and the scanning strategy used a 90° interlayer rotation method.

[0038] S4: Based on the above parameters, the finished samples were prepared on the EOS M290 equipment, and the samples were separated from the substrate using a wire cutting device for relative density testing. All relative density test samples were measured multiple times to reduce errors, such as Figure 3 As shown. And the relative density measurement of multiple samples prepared under the same parameters has a deviation of only 0.02%, which proves that the product qualification rate is close to 100% under this process parameter. Figure 3 As shown, the groups that meet the requirements are 2, 3, 4, 5, 9, 10, 11, 12, and 13. Then, groups 2-5 are mainly analyzed to compare the 80μm powder thickness specimens with the normal 30μm prepared specimens.

[0039] S5: The hardness of the sample surface and side are analyzed by digital Vickers hardness tester, and compared with the casting titanium alloy 315HV ~ 350HV, the microhardness of groups 1-5 is as follows: Figure 4 As shown. Among them, the side surface of the sample in group 3 is lower than the hardness of the cast titanium alloy, which does not meet the preparation requirements. The samples with a powder thickness of 30μm (groups 9-13) are superior to groups 1-5 in microhardness due to their relative density of up to 99% and fine needle-shaped α′ martensite, but the performance improvement is small and the efficiency is significantly reduced by nearly 1.7-7 times. On the other hand, groups 14-24 have poor interlayer bonding performance due to common preparation defects in the preparation process, and the relative density is relatively low and there are many pore defects. This series of factors leads to poor microhardness of the samples.

[0040] S6: The metallographic structure of the sample after grinding, polishing and corrosion was observed using an optical microscope. The top surface of the sample showed typical needle-shaped α′ martensite (such as Figure 5(a) shows that the side surface shows the boundary of epitaxially grown β columnar grains, and the interior is needle-shaped α′ martensite (as shown in Figure 5 (b) shows that the metallographic structure of the titanium alloy prepared at 30 μm is similar. The only difference is the size, which does not cause any structural changes and meets the requirements of the preparation process.

[0041] S7: Defect analysis was conducted on the samples prepared in accordance with the S4-S6 process. The samples should not have large pores, cracks, or unmelted powder. Through electron microscopy, Group 1 and Group 2 showed widely distributed pores (such as Figure 6 Group 5 showed cracks and unmelted powder (as shown in a); Figure 6 In contrast, groups 4, 9, 10, 11, 12, and 13 only have a small amount of pores, which is why these groups have a relatively high density.

[0042] S8: Roughness analysis of samples prepared according to S4-S7 revealed that the surface roughness of Groups 3 and 4 was more severe than that of the 30μm powder layer thickness, but both met the established requirements. The parameter combination that ultimately achieved an 80μm powder layer thickness was a laser power of 300W, a scan speed of 800mm / s (Group 4), and a scan spacing of 70% of the melt pool width.

[0043] The additive manufacturing of S2-S4 is carried out in a protective gas; the additive manufacturing equipment is EOS M290; the preparation space is a closed space, argon is used as the protective gas, and the oxygen content is ensured to be less than 0.02%.

[0044] The density sample is a 10*10*10mm square sample. The density is tested by the drainage method, and the average value is calculated by multiple measurements. The hardness is tested by a Vickers hardness tester, and six points on the top and side surfaces are measured to ensure that the fluctuation of each point does not exceed 30HV, thereby reducing experimental errors.

[0045] The metallographic analysis of the sample was first performed by grinding with 100#, 200#, 600#, and 1200# sandpaper, and then polishing, and then etching with Kroll solvent and observing with an optical microscope.

[0046] According to the principle of preparation efficiency = speed * layer thickness * spacing, compared with the commonly used powder thickness of 20μm-30μm, the additive manufacturing efficiency of the additive manufacturing process based on the selective laser melting technology of 80μm large powder thickness is increased from 1.125-3mm. 3 / s increased to 8.96mm 3 / s, an efficiency improvement of nearly 1.7-7 times, as shown in Table 2. It is also worth noting that the titanium alloy prepared under the present invention at 800 mm / s (or in the process window of 700 mm / s < v < 850 mm / s) meets the requirements for various properties, has no obvious defects, and obtains high hardness, relative density and good surface roughness.

[0047] Table 1 Process parameter values ​​used in preparing samples

[0048]

[0049] Table 2 Comparison of the efficiency of titanium alloy prepared by traditional selective laser melting and the additive manufacturing process of the present invention

[0050]

[0051]

[0052] As shown in Table 2, the additive manufacturing process of the present invention is more efficient than the traditional selective laser melting method for preparing titanium alloys (Group 4), and obtains samples with a relative density ≥99%, a hardness ≥350HV, a surface roughness Ra≤12.5μm, and a metallographic structure of acicular martensite, and the forming efficiency is higher under this process parameter.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology, characterized in that: The steps include: S1: Through Ansys-Workbench simulation, the process parameters are modeled and analyzed: the model is a single-channel model consisting of a 4×0.8×0.5mm substrate and 10 0.02×0.3×0.08mm blocks; the grid type uses the edge size setting, and the laser heat source uses the Gaussian body heat source, as shown in formula (1); then the obtained temperature cloud map is analyzed, and the molten pool depth is measured using ImageJ software. The average value is obtained by measuring more than 3 times, and the process parameters corresponding to the model with a molten pool depth greater than the set powder thickness are selected and recorded as the initial screening process parameters; the process parameters include laser power, scanning speed and powder thickness, and the powder thickness is 80μm-160μm; （1） in: A is the absorption rate of the material for laser, %; P is the laser power, W; R is the laser light source spot radius, μm; S is the penetration depth of the laser in the material, equivalent to the powder coating thickness, µm; xyz Corresponding to the Cartesian coordinate system, x The direction is the same as the laser movement direction; z Parallel to the thickness direction of the powder, v is the scanning speed, mm / s, t is the time, Q is the Gaussian heat source; S2: Single-channel preparation is performed based on the initial screening process parameters of S1: 316L is used as the substrate, and Ti6Al4V aerosolized spherical powder is used as the raw material, with the powder particles being spherical or nearly spherical; the substrate is preheated, and based on the initial screening process parameters obtained in S1, the laser power, scanning speed, and powder thickness are set, and then a single-channel deposition experiment is performed, wherein the melt channel length of the single-channel deposition is 10 mm; among the prepared single channels, a single-channel experimental parameter combination is selected in which there is no powder particle adhesion on the top and side surfaces, and the melt channel does not break, indicating continuous deposition; the single-channel deposition experimental parameter combination includes laser power, scanning speed, and powder thickness; S3: Draw the required sample structure on the computer, set the sample forming parameter combination according to the selected single-channel deposition experimental parameter combination to prepare the required sample, use the scanning strategy of rotating the layers 90°, use ImageJ software to measure the single-channel molten pool width, and set the scanning interval at 60%, 70%, and 80% of the molten pool width to screen out the scanning interval that achieves smooth overlap between the molten channels and the least amount of powder particles attached to the surface; S4: After the printer has prepared all the samples, the substrate and samples are removed, and the samples are separated using a wire cutting device to complete additive manufacturing and perform relative density, hardness, surface roughness and metallographic structure tests. The parameter combination of the sample with relative density ≥99%, hardness ≥350HV, surface roughness Ra ≤12.5μm and metallographic structure of acicular martensite is obtained. The parameter combination of the sample includes laser power, scanning speed, powder thickness and scanning spacing.

2. The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology according to claim 1, characterized in that: The Ti6Al4V powder is an aerosolized powder with a particle size of 20-50 μm, and its element weight percentage composition is: Al element 5.9%, V element 3.92%, Fe element 0.022%, O element 0.14%, N element 0.004%, and Ti element as the balance.

3. The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology according to claim 1, characterized in that: The additive manufacturing equipment for S2-S3 is EOS M290; the preparation space is a closed space, argon is used as the protective gas, and the oxygen content is less than 0.02%.

4. The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology according to claim 1, characterized in that: The size of the sample prepared in S3 is 10×10×10 mm 3 .

5. The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology as claimed in claim 1, characterized in that: In the step S1, the thickness of the powder is 80 μm-100 μm.

6. The additive manufacturing process for improving the efficiency of titanium alloy selective laser melting technology according to claim 1, characterized in that: In the step S1, the thickness of the powder is 80 μm.

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