Preparation method of micron-sized gradient porous structure based on selective laser melting

Abstract

The invention belongs to the technical field of aerodynamic thermal protection of hypersonic aircrafts, and discloses a preparation method of a micron-sized gradient porous structure based on selective laser melting. The preparation method comprises the following steps: selecting spherical powder with a required particle size; preparing a micron-sized gradient porous structure by adopting a selective laser melting technology; and adjusting technological parameters of selective laser melting, and repeatedly preparing the required micron-sized gradient porous structure. According to the preparation method of the micron-sized gradient porous structure based on selective laser melting, the adopted selective laser melting technology has the advantages of being high in precision, high in efficiency and low in cost, the preparation method is suitable for manufacturing parts in complex shapes, and high-quality and high-precision parts can be produced; according to the selective laser melting technology, a subjective three-dimensional model can be established, optimized technological parameters are used for directly forming parts in complex shapes, secondary machining is not needed in the subsequent process, and the selective laser melting technology has wide application prospects in the fields of sweating cooling, energy storage, heat management and the like of hypersonic aircrafts.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerodynamic thermal protection of hypersonic aircraft, and in particular relates to a method for preparing a micron-level gradient porous structure based on selective laser melting. Background Art

[0002] Hypersonic vehicles have been a hot topic of research in recent years and are also one of the future development directions of aerospace vehicles. When a hypersonic vehicle flies at high speed, the gas at the front end of the hypersonic vehicle is heated by shock waves, causing the outer surface to be wrapped in a high temperature of thousands of degrees Celsius, causing the hypersonic vehicle to be severely affected by aerodynamic heat. In order to prevent the internal structure of the hypersonic vehicle from being damaged by aerodynamic heat, a thermal protection system must be used to prevent heat from directly entering the fuselage, so that the temperature and stress of the internal structure of the hypersonic vehicle are controlled within an acceptable range, and the fuselage and internal structure of the hypersonic vehicle are protected.

[0003] Active cooling technology has great application prospects for aerodynamic heating of hypersonic vehicles. Active cooling technology mainly uses cooling fluid (solid, liquid, gas) to block or take away most of the heat to achieve cooling effect. Currently, commonly used active cooling technologies include divergent cooling, film cooling, and convection cooling. Among them, divergent cooling refers to transporting the cooling fluid to the heated wall through porous media in a form similar to human "sweating". Therefore, divergent cooling is also called sweating cooling. There are two main cooling forms of divergent active cooling technology: one is that the cooling medium flows through the internal structure during the transportation to the outer surface of the structure, taking away some heat; the other is that the cooling medium diverges outward from the pores of the porous medium to form a layer of low-temperature air film covering the surface of the high-temperature structure, blocking the transfer of aerodynamic heat to the inside of the structure. The key is that the pore size of the porous medium material used in the divergent active cooling technology needs to be small enough. When the structural size is the same, the contact area through which the fluid flows is increased, the flow uniformity is better, and the cooling effect is significantly improved. Although the divergent active cooling technology has a good cooling effect, the minimum pore size of the porous structure prepared by the 3D printing process can only reach 0.4mm~0.5mm, which greatly limits the application of the divergent cooling technology. Therefore, how to prepare a highly reliable micron-level porous structure through 3D printing is the key to solving the application of the sweat cooling technology in the aerospace field.

[0004] Currently, there is an urgent need to develop a preparation method for micron-scale gradient porous structures based on selective laser melting. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method of a micron-level gradient porous structure based on selective laser melting, which is used to overcome the defects of the existing active cooling technology for thermal protection of the surface of hypersonic aircraft.

[0006] The preparation method of the micron-scale gradient porous structure based on selective laser melting of the present invention comprises the following steps: S10. Select a spherical powder having a desired particle size; According to the pore size requirements of the micron-scale gradient porous structure, spherical powders with the required particle size are selected, and gaps are formed between the powders by stacking the powders; S20. Fabrication of micron-scale gradient porous structure using selective laser melting technology; By adjusting the process parameters of the selective laser melting, the incomplete melting of the spherical powder is achieved; after the incomplete melting of the spherical powder, the required pore size is formed between the spherical powder, and then 3D printing is performed to obtain the required micron-level gradient porous structure; S30. adjusting the selective laser melting process parameters to repeatedly prepare the desired micron-level gradient porous structure; According to the requirements of porous medium materials for different parts of hypersonic aircraft, the selective laser melting process parameters are adjusted, and the 3D printing is repeated in combination with the model digital design plan to obtain the required composite micron-level gradient porous structure.

[0007] Furthermore, the selective laser melting process parameters include laser diameter, laser power, scanning speed, path distance and powder layer thickness.

[0008] Furthermore, the pore size ranges from 10 μm to 200 μm.

[0009] Furthermore, the micron-scale gradient porous structure has a connecting support structure inside, which is used to enhance the overall structural strength and enhance the interface connection between different gradient porous structures. The micron-scale gradient porous structure with a support structure is obtained by filling incompletely melted spherical powder in the space of the connecting support structure.

[0010] Furthermore, the connection support structure is a face-centered cubic structure, a body-centered cubic structure, a close-packed hexagonal structure or a topological structure, or a combination of two or more thereof.

[0011] The preparation method of the micron-level gradient porous structure based on selective laser melting of the present invention prepares the porous structure by combining the method of regulating the process parameters of the selective laser melting technology and establishing a simple supporting structure. The preparation method is simple and does not require the construction of a complex model.

[0012] The preparation method of the micron-scale gradient porous structure based on selective laser melting of the present invention can prepare a porous structure with a pore size of 10μm to 200μm, the micropores are randomly distributed inside the material, and a supporting structure is added, so that the porous structure has excellent mechanical properties.

[0013] The selective laser melting technology used in the preparation method of the micron-level gradient porous structure based on selective laser melting of the present invention has the advantages of high precision, high efficiency and low cost, is suitable for the manufacture of parts with complex shapes, and can produce high-quality and high-precision parts; the selective laser melting technology can directly form the preparation of parts with complex shapes by establishing a subjective three-dimensional model and using optimized process parameters, without the need for subsequent secondary processing, and can be used for large-scale engineering applications.

[0014] The large and small pores in the micron-sized porous structure prepared by the preparation method of the micron-sized gradient porous structure based on selective laser melting of the present invention are randomly distributed inside the material, wherein the large pores provide channels for the flow and transmission of cooling medium and steam, and the strong capillary force of the small pores is used to enhance the flow efficiency of the fluid.

[0015] The micron-sized porous structure prepared by the preparation method of the micron-sized gradient porous structure based on selective laser melting of the present invention uses large and small pore sizes in combination, which can enhance the circulation of the cooling medium and has the advantages of high porosity, high specific surface area, and good mechanical properties. It has broad application prospects in the fields of hypersonic aircraft sweat cooling, energy storage, thermal management, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a micron-sized porous support structure obtained by the method for preparing a micron-sized gradient porous structure based on selective laser melting of the present invention; Figure 2 The micron-sized porous metallographic photograph is obtained by the preparation method of the micron-sized gradient porous structure based on the selective laser melting of the present invention.

[0017] 1. Internal support frame; 2. Internal filling material; 3. Holes; 4. Matrix. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention rather than all the embodiments. Based on the embodiments of the present invention, all embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0019] Example: This example is used to prepare a 316L stainless steel micron-scale gradient porous structure. The specific steps are as follows: a. To ensure that the 316L stainless steel metal powder has excellent fluidity, this embodiment uses spherical powder of 200-300 meshes. The commercially purchased metal powder is sieved on a vibrating sieve machine using 200-mesh and 300-mesh sieves. The sieved powder is collected and placed in a vacuum drying oven at 50°C for 24 hours for subsequent use; b. Use modeling software to model the porous structure to obtain Figure 1 The micron-scale porous support structure shown is used to determine the shape, size and other parameters of the internal support frame 1, and to determine the filling position of the internal filler 2; the model established in this embodiment is a 10mm×10mm×10mm cube; c. Import the established model into Magics software, where the printing parameters of the internal support frame 1 are laser diameter 0.1mm, laser power 190W, scanning speed 960mm / s, and path distance 0.1mm; the printing parameters of the internal filler 2 are laser diameter 0.05mm, laser power 290W, scanning speed 2600mm / s, and path distance 0.1mm; d.3D printing is completed and the following is obtained: Figure 2 The micron-scale porous structure shown has a complex structure with a matrix 4 and holes 3, a high porosity, and a certain strength.

[0020] It should be noted that the style and size of the support structure of this embodiment can be adjusted according to actual application conditions.

Claims

1. A method for preparing a micron-scale gradient porous structure based on selective laser melting, characterized in that: The following steps are involved: S10. Select a spherical powder having a desired particle size; According to the pore size requirements of the micron-scale gradient porous structure, spherical powders with the required particle size are selected, and gaps are formed between the powders by stacking the powders; S20. Fabrication of micron-scale gradient porous structure using selective laser melting technology; By adjusting the process parameters of the selective laser melting, the incomplete melting of the spherical powder is achieved; after the incomplete melting of the spherical powder, the required pore size is formed between the spherical powder, and then 3D printing is performed to obtain the required micron-level gradient porous structure; S30. adjusting the selective laser melting process parameters to repeatedly prepare the desired micron-level gradient porous structure; According to the requirements of porous medium materials required for different parts of hypersonic aircraft, the selective laser melting process parameters are adjusted, and the 3D printing is repeated in conjunction with the model digital design plan to obtain the required composite micron-level gradient porous structure.

2. The method for preparing a micron-scale gradient porous structure based on selective laser melting according to claim 1, characterized in that: The selective laser melting process parameters include laser diameter, laser power, scanning speed, path distance and powder layer thickness.

3. The method for preparing a micron-scale gradient porous structure based on selective laser melting according to claim 1, characterized in that: The pore size range is 10 μm to 200 μm.

4. The method for preparing a micron-scale gradient porous structure based on selective laser melting according to claim 1, characterized in that: The micron-scale gradient porous structure has a connecting support structure inside, which is used to enhance the overall structural strength and enhance the interface connection between different gradient porous structures. The micron-scale gradient porous structure with a support structure is obtained by filling incompletely melted spherical powder in the space of the connecting support structure.

5. The method for preparing a micron-scale gradient porous structure based on selective laser melting according to claim 4, characterized in that: The connection support structure is a face-centered cubic structure, a body-centered cubic structure, a close-packed hexagonal structure or a topological structure, or a combination of two or more thereof.

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