Magnesium alloy selective laser melting manufacturing method for manually separating part from printing platform

Abstract

The invention discloses a magnesium alloy selective laser melting manufacturing method for manually separating a part from a printing platform, which comprises the following steps: carrying out pre-oxidation treatment on unoxidized magnesium alloy powder by using a drying box to obtain pre-oxidized magnesium alloy powder; the pre-oxidized magnesium alloy powder and the unoxidized magnesium alloy powder are mixed to serve as supporting printing powder; unoxidized magnesium alloy powder is firstly laid in a powder cylinder of the printing equipment, a scraper is used for scraping after laying is completed, then the powder cylinder descends to a certain height, supporting printing powder is laid, and feeding is completed after scraping is completed; printing the supporting body and the part on the base plate in sequence by the printing equipment, and directly and manually taking down the part from the base plate to obtain a semi-finished part product with the supporting body; and performing post-treatment on the semi-finished part product, removing the support body and eliminating surface defects to obtain a finished product. The support body and the substrate can be manually separated, the preparation complexity is reduced, and the preparation quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal 3D printing, and in particular to a magnesium alloy laser selective melting manufacturing method in which a part is manually separated from a printing platform. Background Art

[0002] As a lightweight and high-strength material, magnesium alloy has shown broad application prospects in aerospace, automobile manufacturing, electronic communications, biomedicine and other fields due to its excellent physical and chemical properties. Its lightweight characteristics significantly reduce the weight of products and improve energy efficiency. At the same time, its good corrosion resistance and recyclability also meet the requirements of modern industry for environmental protection and sustainable development.

[0003] With the rapid development of additive manufacturing technology, additive manufacturing of magnesium alloys has become a research hotspot. Additive manufacturing technology, especially selective laser melting (SLM) technology, provides a new solution for the manufacture of complex structures of magnesium alloys with its advantages of high precision, high flexibility and high material utilization. SLM technology can directly manufacture parts with complex geometric shapes by melting metal powder layer by layer, which greatly broadens the application range of magnesium alloys.

[0004] However, additive manufacturing of magnesium alloys still faces many challenges in practical applications. First, magnesium alloys have relatively poor ductility and insufficient product consistency during the SLM process, which is mainly due to the defects such as easy oxidation and evaporation of magnesium alloys at high temperatures, as well as deformation and cracking caused by thermal stress. Secondly, due to the rapid melting-cooling process during the SLM process, a huge temperature gradient is formed, which leads to significant thermal stress inside the part, which may cause warping and deformation. Therefore, the part needs to form a good metallurgical bond with the printed substrate to ensure the molding quality. However, this strong metallurgical bond brings about separation difficulties in subsequent processing. Traditional machining methods such as saw blade cutting may not only damage parts and substrates, but also have low precision. Although wire cutting technology can achieve separation, it will cause corrosion to parts and substrates, seriously affecting the performance of the part.

[0005] Therefore, developing a new SLM preparation method for magnesium alloys, which aims to ensure the molding quality while achieving manual separation of parts and substrates and avoiding damage and corrosion to parts and substrates caused by traditional machining methods, has become an important direction of current research. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a magnesium alloy laser selective melting manufacturing method in which parts are manually separated from a printing platform, which can manually separate a support body and a substrate, reduce preparation complexity, and improve preparation quality.

[0007] In order to solve the above technical problems, the present invention provides a magnesium alloy laser selective melting manufacturing method in which a part is manually separated from a printing platform, comprising the following steps:

[0008] S1: pre-oxidizing the unoxidized magnesium alloy powder using a drying oven to obtain pre-oxidized magnesium alloy powder;

[0009] S2: mixing the pre-oxidized magnesium alloy powder with the unoxidized magnesium alloy powder as support printing powder;

[0010] S3: First, unoxidized magnesium alloy powder is laid in the powder cylinder of the printing device as the main part of the printed part. After the laying is completed, it is leveled with a scraper, and then the powder cylinder is lowered to a certain height h, and then the supporting printing powder is laid, and the loading is completed after the leveling;

[0011] S4: The printing device prints the support body on the substrate and prints the part on the support body according to a preset program. After completion, the part is manually removed directly from the substrate to obtain a semi-finished part with a support body;

[0012] S5: Post-process the semi-finished parts to remove the support and eliminate surface defects to obtain finished products. Further, in S1, the pre-oxidation temperature of the drying oven is 40-70°C, and the oxidation time is not less than 1 week.

[0013] Furthermore, the support printing powder is mixed with the unoxidized magnesium alloy powder in a weight ratio ranging from 30:70 to 70:30.

[0014] Furthermore, before mixing, the support printing powder and the unoxidized magnesium alloy powder were sieved using a 300-mesh screen.

[0015] Furthermore, in S3, the particle size of the unoxidized magnesium alloy powder is 200-360 mesh.

[0016] Furthermore, in S3, the height h is calculated by the following formula: h=h0×n, where h0 is the distance between the part and the substrate, and n is the feeding coefficient.

[0017] Furthermore, in S4, the distance between the part and the substrate is 1-5 mm, the diameter of the support body is between 0.05 mm and 0.5 mm, and the inclination angle is 30-60°.

[0018] Furthermore, in S5, the support body is removed using a tool.

[0019] Beneficial effects of the present invention:

[0020] The present invention uses a lattice structure as support between the printed part and the substrate, and uses a fusion of partially oxidized powder and unoxidized powder as a support structure for printing. On the one hand, this solution ensures the stability and integrity of the part structure during the printing process, effectively preventing common defects such as warping; on the other hand, this unique bottom layer design significantly reduces the bonding strength between the part and the substrate, so that after printing, the part can be directly peeled off by manual means simply and safely, completely abandoning the reliance on traditional machining or wire EDM and other complex and potentially damaging separation methods.

[0021] In addition, magnesium alloys are prone to oxidation during actual use, and oxidation usually causes the powder bonding effect to deteriorate, ultimately leading to a decrease in the quality of printed parts. Therefore, most studies are trying to avoid the oxidation of magnesium alloys. However, the present invention proposes to use partially oxidized powder as the printing base material, so that the printing of the bottom support is controlled within a suitable range, so that the parts can be manually separated from the substrate while ensuring good bonding between the parts and the quality of the printed parts. The present invention solves the problem that magnesium alloy SLM parts are difficult to separate from the substrate, and opens up a new path for additive manufacturing of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0023] Figure 2 is a diagram of a support body printing structure according to Embodiment 1 of the present invention;

[0024] Figure 3 is a parts printing structure diagram of embodiment 1 of the present invention;

[0025] Figure 4 It is a structural diagram of the parts that were not successfully removed in Comparative Example 1 of the present invention;

[0026] Figure 5 is a schematic structural diagram of the support body in Example 1 of the present invention under a microscope;

[0027] Figure 6 It is a schematic diagram of the structure of the parts in Example 1 of the present invention under a microscope. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0029] Example 1

[0030] Reference Figure 1As shown, an embodiment of the magnesium alloy laser selective melting manufacturing method of the present invention in which the parts and the printing platform are manually separated includes the following steps:

[0031] Firstly, ZK61 magnesium alloy powder, which is unoxidized magnesium alloy powder, is selected as the raw material. The unoxidized magnesium alloy powder is pre-oxidized in a drying oven. The temperature of the drying oven is set at 60° C. The oxidation time is one week to obtain pre-oxidized magnesium alloy powder.

[0032] The unoxidized magnesium alloy powder (raw material) is then mixed with the pre-oxidized magnesium alloy powder in a weight ratio of 6:4. Manual mixing or equipment-assisted mixing can be used, and the powder is sieved with a 300-mesh sieve to obtain support printing powder.

[0033] Before printing, first lay unoxidized magnesium alloy powder, namely ZK61 spherical powder (particle size ~300 mesh, vacuum dried, and sieved with a 300 mesh screen) inside the bottom of the powder cylinder. After laying, use a scraper to level it. Then adjust the height of the powder cylinder. Considering that the support thickness used this time is 0.5mm, the feed coefficient when printing the support structure is 2.38. Through the formula h=h0×n, it can be calculated that the powder cylinder drop height h is set to 1.19mm. And the support body adopts an FCC lattice structure with a lattice size of 6mm, a support rod radius of 1.2mm, and an inclination angle of 45 degrees.

[0034] Based on this, the powder cylinder is lowered by 1.19mm, and then the support printing powder is added. After the paving is completed, the scraper is used to scrape it flat. Then upload the print file in the printer and print it. First print the support body, such as Figure 2 As shown in FIG. 1 , after the support body is printed, the support printing powder in the sub-cylinder can be used up, and then the part can be printed. Figure 3 As shown, after printing is completed, the part is manually removed directly from the substrate to obtain a semi-finished part with a support body, and the support body is removed and surface defects are eliminated to obtain a finished product.

[0035] Embodiment 2:

[0036] Firstly, ZK61 magnesium alloy powder, which is unoxidized magnesium alloy powder, is selected as the raw material. The unoxidized magnesium alloy powder is pre-oxidized in a drying oven. The temperature of the drying oven is set at 60° C. The oxidation time is one week to obtain pre-oxidized magnesium alloy powder.

[0037] The unoxidized magnesium alloy powder (raw material) is then mixed with the pre-oxidized magnesium alloy powder in a weight ratio of 4:6. Manual mixing or equipment-assisted mixing can be used, and the powder is sieved with a 300-mesh sieve to obtain support printing powder.

[0038] Before printing, first lay unoxidized magnesium alloy powder, namely ZK61 spherical powder (particle size ~250 mesh, vacuum dried, and sieved with a 250 mesh screen) inside the bottom of the powder cylinder. After laying, use a scraper to level it. Then adjust the height of the powder cylinder. Considering that the support thickness used this time is 0.3mm, the feed coefficient is 2.38 when the support structure is printed. According to the formula h=h0×n, it can be calculated that the powder cylinder drop height h is set to 0.714mm. The support body adopts an FCC lattice structure with a lattice size of 5mm, a support rod radius of 1mm, and an inclination angle of 60 degrees.

[0039] Based on this, the powder cylinder is operated to drop 0.714mm, and then support printing powder is added. After the laying is completed, a scraper is used to scrape it flat. Then the print file is uploaded to the printer for printing. The support body is printed first. After the support body is printed, the support printing powder in the sub-cylinder is used up, and then the parts are printed. After the printing is completed, the parts are manually removed directly from the substrate to obtain a semi-finished part with a support body. The support body is removed and surface defects are eliminated to obtain a finished product.

[0040] The thickness of the support body needs to be effectively controlled. If the support body is too thick, it is easy to cause thermal stress accumulation and bending. However, if the number of supports is too small, it will not be able to resist the thermal stress, causing large deformation of the parts and ultimately failure. The diameter of the support body also needs to be controlled. If the diameter of the support rod is too large, for example, greater than 1 cm, failure will occur.

[0041] Embodiment 3:

[0042] Firstly, ZK61 magnesium alloy powder, which is unoxidized magnesium alloy powder, is selected as the raw material. The unoxidized magnesium alloy powder is pre-oxidized in a drying oven. The temperature of the drying oven is set at 60° C. The oxidation time is one week to obtain pre-oxidized magnesium alloy powder.

[0043] The unoxidized magnesium alloy powder (raw material) is then mixed with the pre-oxidized magnesium alloy powder in a weight ratio of 7:3. Manual mixing or equipment-assisted mixing can be used, and the powder is sieved with a 300-mesh sieve to obtain support printing powder.

[0044] Before printing, first lay unoxidized magnesium alloy powder, namely ZK61 spherical powder (particle size ~300 mesh, vacuum dried, and sieved with a 300 mesh screen) inside the bottom of the powder cylinder. After laying, use a scraper to level it. Then adjust the height of the powder cylinder. Considering that the support thickness used this time is 0.1mm, the feed coefficient is 2.38 when the support structure is printed. According to the formula h=h0×n, it can be calculated that the powder cylinder drop height h is set to 0.238mm. And the support body adopts an FCC lattice structure with a lattice size of 4mm, a support rod radius of 0.8mm, and an inclination angle of 30 degrees.

[0045] Based on this, the powder cylinder is operated to drop 0.238mm, and then support printing powder is added. After the laying is completed, a scraper is used to scrape it flat. Then the print file is uploaded to the printer for printing. The support body is printed first. After the support body is printed, the support printing powder in the sub-cylinder is used up, and then the parts are printed. After the printing is completed, the parts are manually removed directly from the substrate to obtain a semi-finished part with a support body. The support body is removed and surface defects are eliminated to obtain a finished product.

[0046] Comparative Example 1:

[0047] Unoxidized ZK61 magnesium alloy powder was selected as the raw material diameter for printing, and the corresponding support body in Example 1 was also printed. The structural parameters of the support body were the same as those in Example 1. Then, a tensile testing machine was used to press the part down from the side to try to separate the printed part from the substrate, but the separation was unsuccessful. Figure 4 The figure shows a broken part. This proves that this technology can separate the part from the substrate while ensuring the integrity of the part.

[0048] In order to further illustrate the principle of the present invention and to prove that the solution of the present invention will not lead to the printing quality of the main parts, Figure 5 and Figure 6 The following are micrographs of the support and parts printed in Example 1 at 20 μm. It can be seen from the figure that the support printed by mixing oxidized powder and unoxidized powder has more unmelted parts and holes, while the parts printed by unoxidized powder have fewer holes and good printing quality. At the same time, the Archimedean drainage method was used to measure the density of the support and the main part. The density of the support structure is 72.8%, while the density of the printed main part reaches 94.3%.

[0049] Specifically, refer to Figure 5 and Figure 6 As shown in the micrograph, it can be observed that the addition of oxide particles causes the support structure to show multiple unfused parts, which reduces the structural strength, but at the same time can still ensure the bonding between layers. The micrograph of the printed part shows that its internal bonding is good. Therefore, the part can be removed from the substrate manually without the help of tools. Of course, it is easier to remove with the help of tools.

[0050] Specifically, too much oxidized powder will prevent the part from being formed directly, while too little will not effectively provide support. The main reason is that the support structure needs to be able to resist the deformation caused by thermal stress on the one hand, and on the other hand, it needs to have a low bonding force with the parts so that they can be effectively separated. The principle is that the oxidized powder cannot achieve metallurgical bonding with the unoxidized powder, but is evenly dispersed among the unoxidized powder. In the end, the unoxidized powder also forms a mesh skeleton, which is effectively bonded to the substrate and parts, but its strength is not very high, so it is easy to remove.

[0051] Moreover, in the method of the present application, the powder material used is not doped with other substances, and the preparation method is simpler; compared with the support structure printed with a combination of multiple substances, there are uncertain factors in the influence of the support structure with different material combinations on the connection position of the part between the support structure and the printed part, such as deformation problems caused by the inconsistency between the thermal conductivity of the support structure and the part, and after disassembly, a relatively thick structural layer needs to be ground off to effectively ensure the quality of the part, so sufficient thickness needs to be reserved at the connection position, which greatly increases the use of materials; and the same substance has less effect on the bottom surface of the part, and the processing of the bottom surface of the part is convenient, and only simple polishing is required, so the use of printing materials can be effectively reduced, and the printed parts have higher stability.

[0052] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A magnesium alloy selective laser melting manufacturing method in which parts and a printing platform are manually separated, characterized in that: The following steps are involved: S1: pre-oxidizing the unoxidized magnesium alloy powder using a drying oven to obtain pre-oxidized magnesium alloy powder; S2: mixing the pre-oxidized magnesium alloy powder with the unoxidized magnesium alloy powder as support printing powder; S3: First, unoxidized magnesium alloy powder is laid in the powder cylinder of the printing device as the main part of the printed part. After the laying is completed, it is leveled with a scraper, and then the powder cylinder is lowered to a certain height h, and then the supporting printing powder is laid, and the loading is completed after the leveling; S4: The printing device prints the support body on the substrate and prints the part on the support body according to a preset program. After completion, the part is manually removed directly from the substrate to obtain a semi-finished part with a support body; S5: Post-process the semi-finished parts to remove the support and eliminate surface defects to obtain the finished product.

2. The magnesium alloy laser selective melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1 is characterized in that: In S1, the pre-oxidation temperature of the drying oven is 40-70°C, and the oxidation time is not less than 1 week.

3. The magnesium alloy laser selective melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1 is characterized in that: The support printing powder is mixed with the unoxidized magnesium alloy powder in a weight ratio ranging from 30:70 to 70:

30.

4. The magnesium alloy selective laser melting manufacturing method with manual separation of parts and printing platform as claimed in claim 3 is characterized in that: Before mixing, the support printing powder and the unoxidized magnesium alloy powder were sieved using a 300-mesh screen.

5. The magnesium alloy selective laser melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1, characterized in that: In S3, the particle size of the unoxidized magnesium alloy powder is 200-360 mesh.

6. The magnesium alloy laser selective melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1, characterized in that: In S3, the height h is calculated by the following formula: h = h0 × n, where h0 is the distance between the part and the substrate, and n is the feeding coefficient.

7. The magnesium alloy selective laser melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1, characterized in that: In S4, the distance between the part and the substrate is 1-5 mm, the diameter of the support body is between 0.05 mm and 0.5 mm, and the inclination angle is 30-60°.

8. The magnesium alloy laser selective melting manufacturing method with manual separation of parts and printing platform as claimed in claim 1, characterized in that: In S5, the support body is removed using a tool.

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