A method for constructing a porous metal transpiration flat plate and its selective laser melting forming

Abstract

The present invention belongs to the field of advanced manufacturing technology, and specifically discloses a method for constructing a porous metal transpiration flat plate and its selective laser melting forming method. First, a porous region skeleton unit cell is constructed using the minimal surface equation, and a Boolean subtraction is performed between it and a cube with a corresponding characteristic length to form a transpiration flat plate unit cell containing internal flow channels. By arraying the transpiration flat plate unit cells along three perpendicular directions, a digital model for printing the porous transpiration flat plate can be obtained. The method provided by the present invention enables the micropores contained in the porous transpiration flat plate to have periodic repeatability and intercommunication, and at the same time, the surface of the transpiration flat plate is flat. By using the selective laser melting forming technology, the preparation of a metal porous transpiration flat plate with high mechanical properties and precise geometric shape can be realized, solving the problems of poor mechanical properties of the existing transpiration flat plate and uneven cooling of the transpiration flat plate.

Description

Technical Field

[0001] The present invention relates to a method for constructing a porous metal transpiration flat plate and its selective laser melting forming method, belonging to the field of advanced manufacturing technology. Background Art

[0002] With the development of modern aerospace technology, the temperature and heat flux density of key hot-end components in reusable liquid rocket engines are increasing, and thermal protection has become a key technical problem that urgently needs to be solved in the development of aerospace engines. Among many cooling technologies, transpiration cooling is considered to be one of the most effective active cooling methods for reducing the surface temperature of high heat flux.

[0003] However, traditional porous materials still have problems such as insufficient strength and poor designability. In particular, the common sintered metal porous transpiration materials have insufficient strength, which is the main reason restricting the large-scale application of transpiration cooling. The most common preparation method of porous metal is sintered porous materials. This preparation process of metal porous media is simple and the internal heat transfer specific surface area is large. However, the mechanical properties of sintered particle porous materials need to be further improved. At the same time, the pores generated in the sintering process are randomly generated, so the pore structure cannot be accurately designed, resulting in ineffective transpiration cooling. The advantages of sintered wire mesh porous materials are high porosity and high mechanical properties. However, due to the lack of design flexibility and shape controllability, and the complex weaving process, long manufacturing cycle and high cost, its application potential in aerospace is limited.

[0004] In summary, it is of great significance to develop a porous material with high mechanical properties and precise geometric shape based on selective laser melting forming for the development of transpiration cooling. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a method for constructing a porous metal transpiration flat plate and its selective laser melting forming method, which can obtain a metal transpiration flat plate with high mechanical properties and precise geometric shape, and solve the problems of insufficient mechanical properties and poor shape controllability of traditional transpiration materials.

[0006] The technical solution of the present invention is:

[0007] The present invention discloses a method for constructing a porous metal transpiration flat plate and its selective laser melting forming method, including:

[0008] Constructing a porous skeleton unit cell according to the minimal surface equation;

[0009] Performing a Boolean subtraction operation on the porous skeleton unit cell and a cube with a corresponding characteristic length to form a porous transpiration flat plate unit cell;

[0010] Based on the porous transpiration flat single cell, a cuboid region is obtained;

[0011] Construct a porous transpiration flat volume domain, and based on the cuboid region, obtain a porous transpiration flat printing digital model;

[0012] Based on the porous transpiration flat printing digital model, adjust the position of the model to be printed and perform printing to form a porous transpiration flat;

[0013] Prepare a selective laser melting equipment, and use the selective laser melting equipment to perform selective laser melting forming on the porous transpiration flat to obtain a formed part;

[0014] Perform subsequent cleaning and machining on the formed part to obtain the required product.

[0015] Further, in the above forming method, perform a Boolean subtraction operation on the porous skeleton single cell and a cube with a corresponding characteristic length to form a porous transpiration flat single cell. Specifically: adjust the center coordinates of the porous skeleton single cell and the corresponding cube to be the same, make the boundaries of the porous skeleton single cell and the cube coincide, and then perform a Boolean subtraction operation to subtract the porous skeleton single cell from the cube to obtain a porous transpiration flat single cell with internal flow channels.

[0016] Further, in the above forming method, the construction of the porous transpiration flat volume domain and obtaining the porous transpiration flat printing digital model based on the cuboid region are specifically as follows:

[0017] Arrange the porous transpiration flat single cells in an array in the x, y, and z directions to obtain a cuboid region with periodic pore characteristics;

[0018] Construct a porous transpiration flat volume domain according to the required shape of the porous transpiration flat;

[0019] Perform a Boolean intersection operation on the cuboid region and the porous transpiration flat volume domain, and control the morphology of the porous transpiration flat printing digital model by adjusting the relative positions of the two. The intersection part obtained is the porous transpiration flat printing digital model.

[0020] Further, in the above forming method, the position adjustment and printing of the model to be printed are specifically as follows:

[0021] Adjust the model to be printed perpendicular to the building plane substrate, flatten the solid support along the outer contour of the porous transpiration flat printing digital model to the substrate, and add R2 - R3 round corners at the contact with the substrate.

[0022] Further, in the above forming method, the minimal surface equation is specifically as follows:

[0023]

[0024]

[0025] wherein, X = 2πx / L, Y = 2πy / L, Z = 2πz / L, x, y, and z are the spatial coordinates of the surface, L is the characteristic length of the unit cell of the porous skeleton, and c is a constant.

[0026] Furthermore, in the above-mentioned forming method, the preparation of the selective laser melting equipment specifically includes:

[0027] Prepare a selective laser melting forming equipment;

[0028] Install a scraper and a substrate;

[0029] After the installation preparation is completed, start purging the gas. After the oxygen content in the forming chamber of the selective laser melting forming equipment drops to a preset level, turn on the heating plate for preheating to make the forming chamber reach the preset temperature.

[0030] Furthermore, in the above-mentioned forming method, the oxygen content at the preset level in the forming chamber is less than 400 ppm.

[0031] Furthermore, in the above-mentioned forming method, the preset temperature of the forming chamber is 80 - 100 °C.

[0032] Furthermore, in the above-mentioned forming method, the parameters of the selective laser melting forming equipment are: laser power 280 - 350 W, scanning pitch 0.9 - 0.12 mm, scanning speed 950 - 1100 m / s, and layer thickness 30 - 40 μm.

[0033] Furthermore, in the above-mentioned forming method, the subsequent cleaning and machining treatment of the formed part specifically includes: powder cleaning, annealing, substrate cutting, and support removal operations on the formed part.

[0034] The beneficial effects of the present invention compared with the prior art are as follows:

[0035] (1) The outer surface of the unit cell of the porous transpiration flat plate obtained by the Boolean subtraction of the porous skeleton unit cell and the cube unit corresponding to the characteristic length in the present invention is all a plane. After arraying them, the outer surface of the porous transpiration flat plate still remains a plane. Compared with directly arraying the skeleton unit cells, this method enables the surface gas film generated by transpiration cooling to cover the flat plate surface more uniformly, improving the uniformity of transpiration cooling;

[0036] (2) The implementation process of the method for constructing the porous transpiration flat plate in the present invention is simple, and the porosity and flow channel size of the porous transpiration material can be changed by adjusting the relative density and characteristic size of the representative volume unit;

[0037] (3) After the printing process of the metal transpiration flat plate based on selective laser melting forming of the present invention is completed, it needs to be cut off from the substrate. During the wire cutting process, debris is extremely likely to be generated, causing blockage in the porous area. Therefore, the transpiration flat plates in this article are all perpendicular to the xy plane, that is, perpendicular to the building plane. And through the design of the support structure, the blockage of the pores of the porous transpiration flat plate by wire cutting debris can be effectively reduced. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the porous metal transpiration flat plate adopted by the present invention: (a) is a schematic diagram of the porous single cell obtained by Boolean operation; (b) is a schematic diagram of the minimal surface skeleton representative volume unit array; (c) is a schematic diagram of the porous transpiration flat plate single cell array;

[0039] Figure 2 It is the constituent structural unit of the porous metal transpiration flat plate of the present invention; (a) is the minimal surface skeleton representative volume unit; (b) is the cube composed of characteristic dimensions; (c) is a schematic diagram of the porous single cell;

[0040] Figure 3 It is a schematic diagram of the cylindrical porous flat plate of the present invention: (a) is the cuboid area; (b) is the volume domain of the transpiration flat plate; (c) is the digital model for printing the porous transpiration flat plate;

[0041] Figure 4 It is a schematic diagram of the solid support of the porous flat plate of the present invention. Detailed Embodiment

[0042] The following further describes the present invention patent in detail in conjunction with the drawings and specific embodiments.

[0043] The present invention discloses a method for constructing a porous metal transpiration flat plate and its selective laser melting forming, including:

[0044] Step S1, constructing a porous skeleton single cell according to the minimal surface equation;

[0045] Step S2, performing a Boolean subtraction operation on the porous skeleton single cell and the cube with the corresponding characteristic length to form a porous transpiration flat plate single cell;

[0046] Step S3, obtaining a cuboid area according to the porous transpiration flat plate single cell;

[0047] Step S4, constructing the volume domain of the porous transpiration flat plate, and obtaining the digital model for printing the porous transpiration flat plate according to the cuboid area;

[0048] Step S5, adjusting the position of the model to be printed and printing according to the digital model for printing the porous transpiration flat plate to form a porous transpiration flat plate;

[0049] Step S6: Prepare a selective laser melting equipment and perform selective laser melting forming on the porous transpiration flat plate with the selective laser melting equipment to obtain a formed part.

[0050] Step S7: Perform subsequent cleaning and machining on the formed part to obtain the required product.

[0051] In step S2, perform a Boolean subtraction operation on the porous skeleton unit cell and a cube with the corresponding characteristic length to form a porous transpiration flat plate unit cell. Specifically, adjust the central coordinates of the porous skeleton unit cell and the corresponding cube to be the same, make the boundaries of the porous skeleton unit cell and the cube coincide, and then perform a Boolean subtraction operation to subtract the porous skeleton unit cell from the cube to obtain a porous transpiration flat plate unit cell with internal flow channels.

[0052] In step S4, construct a porous transpiration flat plate volume domain and obtain a porous transpiration flat plate printing digital model according to the cuboid region. Specifically:

[0053] Step S41: Arrange the porous transpiration flat plate unit cells in the x, y, and z directions to obtain a cuboid region with periodic pore characteristics.

[0054] Step S42: Construct a porous transpiration flat plate volume domain according to the required shape of the porous transpiration flat plate.

[0055] Step S43: Perform a Boolean intersection operation on the cuboid region and the porous transpiration flat plate volume domain, and control the morphology of the porous transpiration flat plate printing digital model by adjusting the relative positions of the two. The intersection part obtained is the porous transpiration flat plate printing digital model.

[0056] In step S5, perform position adjustment and printing on the model to be printed. Specifically:

[0057] Adjust the model to be printed perpendicular to the building plane substrate, flatten the solid support along the outer contour of the porous transpiration flat plate printing digital model to the substrate, and add R2 - R3 fillets at the contact with the substrate.

[0058] In step S1, the minimal surface equation is specifically:

[0059] cosX + cosY + cosZ = c

[0060] 2(cosXcosY + cosYcosZ + cosXcosZ) - (cos2X + cos2Y + cos2Z) = c

[0061] In the formula, X = 2πx / L, Y = 2πy / L, Z = 2πz / L, x, y, and z are the surface space coordinates, L is the characteristic length of the porous skeleton unit cell, and c is a constant.

[0062] In step S6, prepare a selective laser melting equipment, specifically:

[0063] Step S61: Prepare a selective laser melting forming equipment;

[0064] Step S62: Install a scraper and a substrate;

[0065] Step S63: After the installation preparation is completed, start purging the gas. After the oxygen content in the forming chamber of the selective laser melting forming equipment drops to a preset level, turn on the heating plate for preheating to make the forming chamber reach a preset temperature. The oxygen content at the preset level in the forming chamber is lower than 400 ppm. The preset temperature of the forming chamber is 80 - 100 °C. The parameters of the selective laser melting forming equipment are: laser power 280 - 350 W, scanning spacing 0.9 - 0.12 mm, scanning rate 950 - 1100 m / s, and layer thickness 30 - 40 μm.

[0066] In step S7, perform subsequent cleaning and machining operations on the formed part, specifically: perform powder cleaning, annealing, substrate cutting, and support removal operations on the formed part.

[0067] Embodiment

[0068] As Figure 1 shown, the porous metal transpiration flat plate adopted in the present invention is composed of a minimal surface skeleton representative volume element 1, a cube 2 composed of characteristic dimensions, a porous unit cell 3 obtained by the Boolean operation of 1 and 2, and a transpiration flat plate volume domain 4.

[0069] This embodiment provides a method for constructing a porous metal transpiration flat plate and its selective laser melting forming method, which includes the following steps:

[0070] Step (1): Construct a porous structure skeleton unit cell and a cube unit corresponding to its characteristic length, and construct a pore - skeleton interface of the porous structure through a selected surface equation. There are two types of surface equations, namely P - type and IWP - type, as shown in formulas (1) and (2):

[0071] As a type of triply periodic minimal surface, Schwarz Primitive TPMS, that is, P - TPMS, can be described by the following equation (1), and the Schoen - IWP structure can be described by equation (2):

[0072] φ P (X, Y, Z) = cosX + cosY + cosZ = c (1)

[0073] Schoen - IWP:

[0074]

[0075] Wherein, X = 2πx / L, Y = 2πy / L, Z = 2πz / L, and L is the characteristic length of the unit cell. When the level set equation is at c = 0, the surface divides the space into sub-domains of equal volume. These sub-domains can be controlled by the isovalue constant, so that the volume can be enlarged or reduced by offsetting from the zero value in the normal or opposite direction. In this embodiment, an IWP-TPMS minimal surface skeleton representative volume element 1 is constructed, with a characteristic length of 2 mm and a porosity of 80%. Then, a cubic unit with a length of 2 mm is established, the central coordinates of the two units are adjusted to be the same, and a Boolean subtraction operation is performed to subtract the IWP-TPMS unit from the cubic unit. Through the above steps, a square unit with hole features, that is, a porous unit cell 3, is obtained;

[0076] Step (2): As Figure 2 shown, the central coordinates of the triply periodic minimal surface skeleton unit cell obtained by modeling in formula (1) are adjusted to be the same as those of its corresponding cube, so that the boundaries of the two coincide, and then a Boolean subtraction operation is performed to subtract the porous skeleton unit cell from the cube. Thus, the porous transpiration flat plate unit cell is obtained. In this embodiment, the porous unit cell 3 is arrayed 7 times in the x and y directions respectively, and 2 layers in the z direction, and a porous flat plate with a size of 14 mm * 14 mm * 4 mm can be obtained.

[0077] Step (3): The unit cell of the porous transpiration flat plate obtained in formula (2) is arrayed in the x, y, and z directions, and a cuboid region containing periodically distributed internal flow channels can be obtained. As Figure 3 shown, the cuboid porous region and the volume domain of the required transpiration flat plate are subjected to Boolean summation, and the boundary shape of the transpiration flat plate is controlled by adjusting their relative positions. The result of the Boolean summation is the final digital model for printing the porous transpiration flat plate.

[0078] In this embodiment, a cylindrical volume domain with a size of Φ14 * 4 mm is constructed, its coordinate center is coincident with the coordinate center of the constructed flat plate, and the two are subjected to Boolean summation, and a cylindrical porous metal transpiration flat plate can be obtained.

[0079] Step (4): As Figure 4 shown, the transpiration flat plate is adjusted to a direction perpendicular to the construction plane, and the support is flattened along the outer contour of the three-dimensional model to the substrate, and R2 - R3 rounded corners are added at the contact with the substrate. In this embodiment, the direction of the cylindrical porous metal transpiration flat plate in step (3) is adjusted to be perpendicular to the construction plane and then the support is added. The downward-facing surface of the cylindrical region is projected and stretched to form a solid support on the substrate, and R2 - R3 rounded corners are added at the contact with the substrate.

[0080] Step (5): In this embodiment, a selective laser melting device is prepared.

[0081] Specifically, the following steps are included: preparing a selective laser melting forming device; installing a scraper and a substrate; starting gas washing after the installation preparation is completed. After the oxygen content in the forming chamber of the selective laser melting forming device drops to a preset level, turn on the heating plate for preheating to make the forming chamber reach a preset temperature. Preferably, the oxygen content at the preset level in the forming chamber is lower than 400 ppm. The preset temperature of the forming chamber is 80 - 100 °C.

[0082] Step (6), in this embodiment, selective laser melting forming is performed on the part to be formed.

[0083] Adjust the position of the three-dimensional model including supports, select printing parameters, divide the model, output the slice file to the selective laser melting forming device, and then perform selective laser melting forming according to the set process parameters until a complete part is formed.

[0084] The product structure process parameters adopt specific energy input to ensure good porosity formability and high mechanical properties inside the product. Specifically, they include: laser power 280 - 350 W, scanning spacing 0.9 - 0.12 mm, scanning rate 950 - 1100 m / s, and layer thickness 30 - 40 μm;

[0085] Step (7), in this embodiment, subsequent cleaning and machining processes are performed on the formed part. After the forming is completed, wait for the device to cool down, take out the product, and then perform operations such as powder cleaning, annealing, substrate cutting, and support removal to obtain the required product.

[0086] The above combines specific embodiments to more detailedly illustrate the specific implementation manners of the present invention, so as to better understand the solution of the present invention and its advantages. However, the specific implementation manners and embodiments described above are only for the purpose of illustration, rather than a limitation to the present invention.

[0087] Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation to the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

[0088] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A method for constructing a porous metal transpiration flat plate and its selective laser melting forming method, characterized in that: Including: Construct a porous skeleton unit cell according to the minimal surface equation; Perform a Boolean subtraction operation on the porous skeleton unit cell and a cube with a corresponding characteristic length to form a porous transpiration flat plate unit cell; Obtain a cuboid region according to the porous transpiration flat plate unit cell; Construct a porous transpiration flat plate volume domain, and obtain a porous transpiration flat plate printing digital model according to the cuboid region; According to the porous transpiration flat plate printing digital model, adjust the position of the model to be printed and perform printing to form a porous transpiration flat plate; Prepare a selective laser melting equipment, and use the selective laser melting equipment to perform selective laser melting forming on the porous transpiration flat plate to obtain a formed part; Perform subsequent cleaning and machining on the formed part to obtain the required product; Performing a Boolean subtraction operation on the porous skeleton unit cell and a cube with a corresponding characteristic length to form a porous transpiration flat plate unit cell, specifically: adjusting the central coordinates of the porous skeleton unit cell and the corresponding cube to be consistent, making the boundaries of the porous skeleton unit cell and the cube coincide, and then performing a Boolean subtraction operation to subtract the porous skeleton unit cell from the cube to obtain a porous transpiration flat plate unit cell with internal flow channels; The construction of the porous transpiration flat plate volume domain, and obtaining a porous transpiration flat plate printing digital model according to the cuboid region, specifically: Arrange the porous transpiration flat plate unit cells in an array in the x, y, and z axes to obtain a cuboid region with periodic pore characteristics; Construct a porous transpiration flat plate volume domain according to the required shape of the porous transpiration flat plate; Perform a Boolean intersection operation on the cuboid region and the porous transpiration flat plate volume domain, and control the morphology of the porous transpiration flat plate printing digital model by adjusting their relative positions. The intersection part obtained is the porous transpiration flat plate printing digital model; The adjustment of the position and printing of the model to be printed, specifically: Adjust the model to be printed perpendicular to the building plane substrate, flatten the solid support along the outer contour of the porous transpiration flat plate printing digital model to the substrate, and add R2-R3 fillets at the contact with the substrate.

2. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 1, characterized in that: The minimal surface equation, specifically: cosX + cosY + cosZ = c (1) In the formula, X = 2πx / L, Y = 2πy / L, Z = 2πz / L, x, y, and z are the spatial coordinates of the surface, L is the characteristic length of the porous skeleton unit cell, and c is a constant.

3. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 1, characterized in that: The preparation of the selective laser melting equipment, specifically: Prepare a selective laser melting forming equipment; Install a scraper and a substrate; After the installation preparation is completed, start purging the gas. After the oxygen content in the forming chamber of the selective laser melting forming equipment drops to a preset level, turn on the heating plate for preheating to make the forming chamber reach a preset temperature.

4. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 3, characterized in that: The oxygen content in the forming chamber at the preset level is less than 400 ppm.

5. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 3, characterized in that: The preset temperature of the forming chamber is 80 - 100 °C.

6. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 3, characterized in that: The parameters of the selective laser melting forming equipment are: laser power 280 - 350 W, scanning spacing 0.9 - 0.12 mm, scanning speed 950 - 1100 m / s, and layer thickness 30 - 40 μm.

7. The method for constructing a porous metal transpiration flat plate and its selective laser melting forming method according to claim 1, characterized in that: The subsequent cleaning and machining of the formed part, specifically: perform powder cleaning, annealing, substrate cutting, and support removal operations on the formed part.

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