A method for in-situ printing of anti-falling micro-prick cone array metal micro-droplets for fixing heat protection materials

Abstract

This invention provides an in-situ printing method for an anti-detachment micro-spike array of metal microdroplets to fix thermal protection materials, overcoming the shortcomings of current adhesive bonding techniques for connecting thermal protection materials to aircraft shells, which restrict the improvement of aircraft performance and reliable operation. This method achieves in-situ growth of spike structures on the surface of the aircraft shell through metal microdroplet jetting technology, thereby forming a synergistic interface of metallurgical bonding and mechanical interlocking between the thermal protection material and the aircraft shell. This significantly improves the interface bonding strength while achieving controllable structural growth, providing a new and feasible technical approach for the structural design of aircraft thermal protection systems.

Description

Technical Field

[0001] This invention belongs to the field of metal microdroplet 3D printing technology, specifically relating to an in-situ printing method for an anti-detachment micro-spike cone array of metal microdroplets for fixing thermal protective materials. Background Technology

[0002] With the development of aerospace technology, the flight speed of spacecraft is constantly increasing, and the service environment is becoming increasingly harsh. An effective thermal protection system can provide sufficient protection for the spacecraft structure when it faces severe aerodynamic heating. Ablation-type thermal protection materials are a component of ultra-high temperature thermal protection systems. They can provide effective protection when high-speed spacecraft encounter severe aerodynamic heating, significantly extending the safe flight time of the spacecraft and protecting the internal structure. Their structural design has become a key factor in the development of hypersonic spacecraft.

[0003] The literature “Xu Ge, Fang Xiaomin, Liu Haixin, et al. Research on bonding technology of thermal protective layer; Proceedings of the 17th Annual Academic Conference of Fiberglass / Composite Materials, Fiberglass Branch of Chinese Silicate Society. Beijing Fiberglass Research and Design Institute; 2008: 226-229” reports that missile warheads are typically composed of a nose section, nose section body, upper shell, lower shell, and skirt. Except for the nose section, the other components generally adopt an integrated manufacturing method in which ablative thermal protective materials are bonded to the metal shell using adhesives.

[0004] However, with the increasing demands for lightweight design and aerodynamic performance in next-generation aircraft, some missile warhead models have adopted non-rotating metal shells with variable cross-sections. These structures have complex shapes and drastic changes in surface curvature, making it difficult for traditional adhesive bonding techniques to form a uniform and stable bonding interface on the shell surface. Simultaneously, the significant difference in the coefficients of thermal expansion between the thermal protection material and the metal shell material easily leads to thermal stress concentration at high temperatures, resulting in interface delamination or even detachment. These problems severely weaken the structural integrity and service life of the thermal protection layer, becoming a key bottleneck restricting the improvement of aircraft performance and reliable operation.

[0005] Therefore, there is an urgent need to develop a new integrated molding process to achieve a tight connection and collaborative load-bearing between thermal protection materials and the aircraft shell, thereby meeting the comprehensive requirements of aircraft for lightweighting, aerodynamic performance and thermal protection. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of current adhesive bonding techniques for connecting thermal protection materials to aircraft shells, which restrict the improvement of aircraft performance and reliable operation. The invention provides an in-situ printing method for fixing thermal protection materials using a micro-spike cone array of metal microdroplets to prevent detachment.

[0007] To achieve the above objectives, the technical solution provided by this invention is:

[0008] A method for in-situ printing of metal microdroplets in a micro-spiked cone array for fixing thermal protective materials, which is a substrate-spiked integrated additive manufacturing process, achieved by combining mechanical microstructure creation with droplet impaction, is characterized by including the following steps:

[0009] 1) Determine the structural and geometric parameters of the anti-detachment micro-thorn cone array.

[0010] The anti-detachment micro-spiky cone array includes a substrate surface microstructure, a first layer of large droplets, and a spike structure;

[0011] The substrate surface microstructure is an oblique cone array microstructure, which is formed by micro-milling. The geometric parameters include the radial dimension and height of the bottom surface of the oblique cone.

[0012] The first layer of large droplets is a droplet array anchored on the oblique cone array microstructure, and the whole is printed by a piezoelectric jetting device; the geometric parameters include the radius R of the large droplets, which only needs to be able to wrap the oblique cones mentioned above.

[0013] The spiked structure is an array of spiked units corresponding to the droplet array. The spiked unit includes an aluminum cylinder and aluminum branches, and is printed as a whole by a pneumatic jetting device. The geometric parameters include the radius r of the small droplet, the number of spiked units in the array along the X, Y, and Z axes in space, the printing spacing a of the aluminum cylinder (which can also be understood as the distance between two spiked units in the horizontal direction), the height h of the aluminum cylinder, the solidification angle θ of the aluminum branch (i.e., the angle between the aluminum branch and the horizontal plane), the length l of the aluminum branch, and the total height H of the aluminum cylinder in the Z-axis direction.

[0014] 2) Complete trajectory planning

[0015] Before proceeding with trajectory planning, the printing spacing 'a' is first determined based on different design requirements. The formula for the printing spacing in this application is as follows:

[0016] (1)

[0017] In the formula, L is the base length and c is the number of arrays in the X-axis direction;

[0018] The optimal scanning step size is determined based on the droplet radius r and the solidification angle θ. The formula is as follows:

[0019] (2)

[0020] Optimal scan step size It is only related to the droplet radius r and the solidification angle θ. Formula (2) is the optimal scanning step size. Using this scanning step size can obtain better lines.

[0021] The number of droplets required to calculate the side length of the printed mesh That is, the number of droplets required within each spacing, as shown in the following formula:

[0022] (3)

[0023] The coordinates of the large droplet are:

[0024] (4)

[0025] (5)

[0026] In the formula, d is the array index of the printed node on the X-axis, and f is the array index of the printed node on the Y-axis;

[0027] This is so that it can be used to complete subsequent trajectory planning and printing parameters;

[0028] Micro-milling trajectory planning for substrate surface microstructures: Based on the printing node coordinates and the printing spacing of the aluminum cylinders, the three-dimensional model of the oblique cone array microstructure is first completed in 3D modeling software (such as SolidWorks), and the model is exported as a STEP format file. Then, the STEP format file is imported into CAM software (such as Fusion 360), the tool type and cutting parameters are set, and G-code for CNC milling is generated.

[0029] Printing trajectory planning for the first layer of large droplets: Based on the printing spacing of the aluminum cylinders, calculate the deposition position of each large droplet in the droplet array (you can obtain the droplet coordinate position by inputting it into PMAC as needed), and use trajectory planning software (aluminum alloy uniform micro-droplet jet three-dimensional configuration printing trajectory visualization software) to generate the deposition position as the PMAC printing trajectory.

[0030] Printing trajectory planning for spiked cone structures: The 3D lattice model of the designed structure is discretized and transformed into a droplet model suitable for micro-droplet 3D printing; a droplet position function is established, and the spatial coordinates of each droplet are exported as G-code to achieve printing path control;

[0031] The droplet position function is as follows:

[0032] for (int k = 0; k < modelInfo.Parameter1; k++)

[0033] {

[0034] for (int j = 0; j < modelInfo.Parameter2; j++)

[0035] {

[0036] / / Leaning pillar left

[0037] for (int i = 0; i < modelInfo.Parameter4; i++)

[0038] {

[0039] x = (xt + k a) + cosθ i;

[0040] y = yt + j a;

[0041] z = zt + i b+ modelInfo.Parameter3 b;

[0042] }

[0043] / / Leaning support right

[0044] for (int i = 0; i < modelInfo.Parameter4; i++)

[0045] {

[0046] x = (xt + k a) - cosθ i;

[0047] y = yt + j a;

[0048] z = zt + i b + modelInfo.Parameter3 b;

[0049] }

[0050] }

[0051] }

[0052] In the formula: b is the number of arrays along the z-axis, and modelInfo.Parameter1, modelInfo.Parameter2, modelInfo.Parameter3 and modelInfo.Parameter4 are the number of arrays along the x, y, and z axes and the number of aluminum dendrite droplets, respectively;

[0053] 3) Polishing the substrate and preparing microstructures

[0054] 3.1) Grind the substrate to remove the surface oxide layer (e.g., use 800MU, 1200MU, and 1600MU sandpaper to grind the substrate in sequence) to ensure that the surface roughness Ra of the substrate is 0.8-1.6μm, so as to keep the substrate clean and prepare it for subsequent milling;

[0055] 3.2) Run the micro-milling trajectory code of the microstructure on the substrate surface in step 2). The CNC milling machine mills the substrate surface according to the predetermined trajectory to prepare the required oblique cone array microstructure. Then, the substrate is placed in an argon environment glove box with an oxygen content of no more than 20 ppm to prevent the subsequent sprayed aluminum droplets from oxidizing and forming oxide scale, which would result in poor overlapping effect and insufficient stability.

[0056] 4) First-layer large droplet piezoelectric jet printing

[0057] 4.1) Preheating of the piezoelectric injection device

[0058] The piezoelectric injection device is located in an argon-filled glove box with an oxygen content of less than 20 ppm.

[0059] Turn on the induction heating furnace to heat the crucible, so that the aluminum alloy inside the crucible melts and reaches the printing temperature;

[0060] Turn on the flatbed heater and heat the printing substrate temperature in step 3) to 190°C. Compared with the current operation of printing aluminum microdroplets, which requires heating the substrate to above 400°C, at this temperature, not only can the substrate structure be avoided and the mechanical properties affected, but the strength and hardness of the aluminum alloy can also be improved.

[0061] 4.2) The printing trajectory code of the first layer of large droplets in step 2) is executed. The piezoelectric jetting device sprays large droplets according to the predetermined printing trajectory, so that the large droplets are deposited on the oblique cone array microstructure and fused with it; the printing of the first layer of large droplets is completed. When the large droplets are deposited on the surface of the microstructure, fluid encapsulation and remelting effects are generated at the same time, so that mechanical pinning and metallurgical bonding are formed at the same time, realizing the strong bond between aluminum microdroplets and printing substrate.

[0062] 5) Piezoelectric jet printing of spiked cone structure

[0063] In step 2), the pneumatic jetting device prints the corresponding spike unit on the first layer of large droplets according to the predetermined printing trajectory, thus completing the printing of the spike structure.

[0064] Furthermore, for ease of fabrication, in step 1), the oblique cone array microstructure is a square oblique cone;

[0065] The side length of the bottom of the square oblique pyramid is 0.5 mm, and the height is 0.3 mm.

[0066] Further, in step 3), the aluminum alloy printing substrate is a 70 mm × 70 mm × 1 mm 6061 aluminum alloy printing substrate.

[0067] Further, in step 4), the induction heating furnace is heated to 800°C and then kept at that temperature for 5 minutes.

[0068] The nozzle diameter used in the piezoelectric jetting device is 1mm, and the diameter of the large droplets ejected is 2mm. In actual operation, it is sufficient as long as the large droplets ejected can cover the inclined cone.

[0069] Furthermore, in step 5), the injection frequency of the pneumatic injection device is 5~10Hz;

[0070] The nozzle diameter used in the pneumatic injection device is 0.4 mm, and the diameter of the ejected droplets is 0.5 mm.

[0071] The present invention also provides an anti-detachment micro-spike cone array for fixing thermal protection materials formed in situ using the above method.

[0072] Furthermore, this invention also provides a method for connecting thermal protection materials to an aircraft shell, characterized by the following steps:

[0073] S1. Using the above method, an anti-detachment micro-spike cone array is printed in situ on the aircraft shell;

[0074] S2. Using a mold, heat protection material is poured onto the outside of the aircraft shell, which has been printed with an anti-detachment micro-spike cone array. After curing, the heat protection material is fixedly connected to the aircraft shell.

[0075] Furthermore, in S2, the heat protection material is phenolic resin.

[0076] The concept and principle of this invention:

[0077] To address the shortcomings of existing adhesive bonding between thermal protection materials and aircraft shells, this invention aims to achieve a stable connection between thermal protection materials and aircraft shells using an anti-detachment structure. However, if a traditional aluminum microdroplet printing anti-detachment structure is used, the substrate temperature needs to be heated to above 400°C for stable molding, which will have a thermal impact on the aircraft shell, causing problems such as annealing softening or microstructure coarsening. But if the temperature is lowered (e.g., below 200°C) to reduce the impact on the substrate microstructure, the problem of droplets being difficult to deposit on the substrate arises.

[0078] To address this, the present invention optimizes the anti-detachment structure, making it consist of three parts: a substrate surface microstructure, a first layer of large droplets, and a spiked structure. First, a micro-milling process is used to process an oblique cone array microstructure on the surface of the substrate. Then, at a substrate temperature of approximately 190°C, a piezoelectric jetting device is used to deposit large droplets corresponding to the oblique cone array microstructure to form a droplet array. Each large droplet encapsulates a microstructure and partially fuses with it, resulting in mechanical interlocking and metallurgical bonding, providing a foundation for the successful deposition of subsequent small droplets. Finally, a pneumatic jetting device is used to print spiked structures composed of small droplets onto the large droplets. By increasing the printing frequency of subsequent small droplets (5Hz~10Hz), the next small droplet can be formed before the previous small droplet has completely solidified.

[0079] The advantages of this invention are:

[0080] To achieve a reliable connection between the thermal protection layer and the aircraft shell surface, this invention proposes an in-situ printing method for an anti-detachment micro-spike cone array of metal microdroplets for fixing thermal protection materials. Specifically, this method utilizes metal microdroplet jetting technology to achieve in-situ growth of a barbed cone structure on the surface of an aluminum alloy skin shell, thereby forming a connection interface between the thermal protection layer and the aircraft shell that combines metallurgical bonding and mechanical interlocking. This method can significantly improve the interface bonding strength while achieving controllable structural growth, providing a new and feasible technical approach for the structural design of aircraft thermal protection systems.

[0081] 1. This invention proposes a thermal protection layer connection strategy based on a barbed cone structure. By printing a barbed cone structure in situ on the surface of an aluminum alloy, the ablation-resistant material can be reliably fixed during service by relying on the mechanical interlocking of the barbs, significantly improving the bonding stability between the thermal protection layer and the metal substrate, and providing a novel manufacturing technology for ablation-resistant thermal protection systems in ultra-high temperature service environments.

[0082] 2. This invention prefabricates a microburr structure on the surface of an aluminum alloy substrate and initially deposits it with larger droplets. The microburr structure provides effective mechanical interlocking and forms a metallurgical bonding layer through local melting and diffusion with the large droplets. This achieves a dual connection mechanism of mechanical interlocking and metallurgical bonding, significantly improving the interfacial bonding strength and anti-detachment performance.

[0083] 3. Through the above connection mechanism, a high-strength bond of 6061 aluminum alloy droplets on the surface of the aluminum alloy substrate at 190 ℃ was successfully achieved. This not only breaks through the bottleneck problem of unstable molding at temperatures below 350 ℃ in traditional aluminum microdroplet printing, but also effectively avoids the thermal impact of high temperature on the overall substrate structure. It does not cause annealing softening or coarsening of the aluminum alloy skin, thus ensuring the mechanical property stability and service reliability of the substrate. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the microstructure on the substrate surface in this invention;

[0085] Figure 2 This is a flowchart of the printing strategy of the present invention;

[0086] Figure 3 This is a schematic diagram of the unit spike structure prepared in this invention;

[0087] Figure 4 It is a discretized droplet model with an oblique cone;

[0088] Figure 5 This is a schematic diagram showing the bonding between a large droplet and the microstructure on the substrate surface;

[0089] Figure 6 This is a schematic diagram of the spike-cone structure deposited on the surface of a large droplet;

[0090] Figure 7 These are photos of the compression test site;

[0091] Figure 8 The quasi-static compressive force-time response curve of the spike array sample is shown in Figure 1.

[0092] Figure 9 The quasi-static compressive force-time response curve of the spike array sample is shown in Figure 2.

[0093] Figure 10 The quasi-static compressive force-time response curve of the spike array sample is shown in Figure 3. Detailed Implementation

[0094] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0095] Example 1:

[0096] like Figure 2 As shown, the in-situ printing method for anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials includes:

[0097] Step 1: Determine the structure and geometric parameters of the anti-detachment micro-needle cone array.

[0098] The anti-detachment spike array consists of three parts: the microstructure of the substrate surface, the first layer of large droplets, and the spike structure.

[0099] The substrate surface microstructure is designed as an oblique cone array microstructure, such as Figure 1 As shown, the process employed is micro-milling. Geometric parameters include a bottom side length of 0.5 mm and a height of 0.3 mm. By optimizing the micro-milling trajectory planning and cutting parameters, a uniformly sized and distributed array of inclined cones can be obtained, providing a reliable foundation for subsequent large droplet anchoring and bonding.

[0100] The first layer of large droplets, corresponding to the droplet array anchored on the oblique conical array microstructure, was deposited using a piezoelectric aluminum microdroplet jet printing device, and its diameter was 2 mm. During the deposition process, the large droplets interacted with the microstructure on the substrate surface, achieving stable spreading and initial anchoring at a substrate temperature of approximately 190 °C (mainly manifested in the large droplets including the microstructure, mutual melting with the microstructure, and metallurgical bonding), providing support for the subsequent growth of the spiked conical structure.

[0101] The spiked structure is an array of spiked units corresponding to the droplet array. The number of spiked units in the array along both the X and Y axes is 18, with an array spacing of 4 mm (the positions of the substrate surface microstructure, the first layer of large droplets, and the spiked structure correspond one-to-one), and the number of units along the Z axis is 3. Each spiked unit consists of an aluminum pillar and aluminum branches, such as... Figure 3 , 4 As shown, the geometric parameters include a single-layer aluminum column height of 7 mm, a total height of 21.14 mm, an angle of 45° between the aluminum branches and the horizontal plane, and a branch length of 2 mm.

[0102] Step 2: Based on the parameters given in Step 1, calculate the corresponding printing parameters according to the aforementioned formulas (2)-(5), and perform micro-milling trajectory planning for the microstructure on the substrate surface, the first layer of large droplet printing trajectory planning, and the spiked cone structure printing trajectory planning.

[0103] The micro-milling trajectory planning for the microstructure on the substrate surface is as follows: Based on the printing node coordinates and the printing spacing of the aluminum cylinders, a three-dimensional model of the oblique cone array microstructure is established in SolidWorks software, and the model is exported as a STEP format file; then the file is imported into Fusion 360 software, and process parameters such as tool type, cutting path, cutting depth, feed rate and spindle speed are set to generate G-code suitable for CNC micro-milling equipment.

[0104] The printing trajectory planning for the first layer of large droplets is as follows: Based on the arrangement parameters of the spiked unit array and the printing spacing, the deposition coordinate position of each first layer of large droplets is calculated; the calculated deposition coordinates are used to generate a PMAC printing trajectory file using trajectory planning software, thereby realizing the deposition path control and printing trajectory generation of the first layer of large droplets.

[0105] The printing trajectory planning for the spiked cone structure includes: discretizing the three-dimensional lattice model of the designed structure and converting it into a droplet model suitable for metal microdroplet 3D printing; establishing a droplet position function based on this, and exporting the spatial coordinate data of each droplet into G-code.

[0106] Step 3: Polishing the substrate and preparing microstructures

[0107] Select a 6061 aluminum alloy substrate with dimensions of 70×70×1mm, and use 800MU, 1200MU and 1600MU sandpaper to remove the oxide layer on the surface of the 6061 aluminum alloy substrate in sequence to ensure that the surface roughness Ra of the substrate is within 0.8~1.6μm;

[0108] Run the microstructure milling trajectory code of the substrate surface in step two. The CNC milling machine mills the surface of the 6061 aluminum alloy substrate according to the predetermined trajectory to obtain a clean printing substrate with surface microstructure. Then place it in an argon environment glove box with an oxygen content of no more than 20PPM.

[0109] Step 4: First layer of large droplet piezoelectric jet printing

[0110] The piezoelectric aluminum microdroplet jet printing device is located in an argon-filled glove box with an oxygen content of less than 20 ppm. The induction heating furnace is turned on to heat the crucible to 800°C, so that the aluminum alloy in the crucible melts and reaches the printing temperature. The flatbed heater is turned on to heat the printing substrate to 190°C. At this temperature, the strength and hardness of the aluminum alloy are improved, which can avoid the substrate annealing and softening caused by overheating.

[0111] Import the first-layer large droplet printing trajectory file obtained in step two into the PMAC host computer software. Then, replace the nozzle with a 0.8 mm diameter nozzle and turn on the piezoelectric aluminum microdroplet jet printing device. Jet large droplets according to the predetermined printing trajectory, allowing the large droplets to deposit and fuse on the microburr structure (i.e., the oblique conical microstructure). Upon deposition on the microburr surface, the large droplets simultaneously generate fluid encapsulation and remelting effects, resulting in both mechanical pinning and metallurgical bonding. This achieves a strong, non-detachable bond between the aluminum microdroplets and the printing substrate. Figure 5 As shown.

[0112] Step 5: Pneumatic jet printing of the spiked cone structure

[0113] Replace the nozzle with a 0.5 mm diameter nozzle, then import the thorn cone structure printing trajectory from step two into the PMAC host computer. Turn on the pneumatic aluminum microdroplet jet printing device and set the jetting frequency to 5~10Hz. Print the thorn cone structure on the first layer of large droplets according to the predetermined printing trajectory, completing the printing of the multi-layer thorn cone structure. Figure 6 As shown.

[0114] Example 2:

[0115] like Figure 2 As shown, the in-situ printing method for anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials includes:

[0116] Step 1: Determine the structure and geometric parameters of the anti-detachment micro-needle cone array.

[0117] The anti-detachment spike array consists of three parts: the microstructure of the substrate surface, the first layer of large droplets, and the spike structure.

[0118] The substrate surface microstructure is designed as an oblique cone array microstructure and processed using micromilling. Geometric parameters include a bottom side length of 0.5 mm and a height of 0.3 mm. By optimizing the micromilling trajectory planning and cutting parameters, a uniformly sized and distributed oblique cone array can be obtained, providing a reliable foundation for subsequent large droplet anchoring and bonding.

[0119] The first layer of large droplets, corresponding to the droplet array anchored on the oblique conical array microstructure, was deposited using a piezoelectric aluminum microdroplet jet printing device, and its diameter was 2 mm. During the deposition process, the large droplets interacted with the microstructure on the substrate surface, achieving stable spreading and initial anchoring at a substrate temperature of approximately 190 °C, providing support for the subsequent growth of the spiked conical structure.

[0120] The spiked structure is an array of spiked units corresponding to the droplet array. The number of spiked units in the X and Y axes is 18 each, with an array spacing of 4 mm, and the number of units in the Z axis is 3. Each spiked unit consists of an aluminum column and branches. The geometric parameters include a single-layer aluminum column height of 7 mm and a total height of 20.87 mm; an angle of 60° between the aluminum branches and the horizontal plane; and a branch length of 2 mm.

[0121] Step 2: Based on the parameters given in Step 1, calculate the corresponding printing parameters according to the aforementioned formulas (2)-(5), and perform micro-milling trajectory planning for the microstructure on the substrate surface, the first layer of large droplet printing trajectory planning, and the spiked cone structure printing trajectory planning.

[0122] The micro-milling trajectory planning for the microstructure on the substrate surface is as follows: Based on the printing node coordinates and the printing spacing of the aluminum cylinders, a three-dimensional model of the oblique cone array microstructure is established in SolidWorks software, and the model is exported as a STEP format file; then the file is imported into Fusion 360 software, and process parameters such as tool type, cutting path, cutting depth, feed rate and spindle speed are set to generate G-code suitable for CNC micro-milling equipment.

[0123] The printing trajectory planning for the first layer of large droplets is as follows: Based on the arrangement parameters of the spiked unit array and the printing spacing, the deposition coordinate position of each first layer of large droplets is calculated; the calculated deposition coordinates are used to generate a PMAC printing trajectory file using trajectory planning software, thereby realizing the deposition path control and printing trajectory generation of the first layer of large droplets.

[0124] The printing trajectory planning for the spiked cone structure includes: discretizing the three-dimensional lattice model of the designed structure and converting it into a droplet model suitable for metal microdroplet 3D printing; establishing a droplet position function based on this, and exporting the spatial coordinate data of each droplet into G-code.

[0125] Step 3: Polishing the substrate and preparing microstructures

[0126] Select a 6061 aluminum alloy substrate with dimensions of 70×70×1mm, and use 800MU, 1200MU and 1600MU sandpaper to remove the oxide layer on the surface of the 6061 aluminum alloy substrate in sequence to ensure that the surface roughness Ra of the substrate is within 0.8~1.6μm;

[0127] Run the microstructure milling trajectory code of the substrate surface in step two. The CNC milling machine mills the surface of the 6061 aluminum alloy substrate according to the predetermined trajectory to obtain a clean printing substrate with surface microstructure. Then place it in an argon environment glove box with an oxygen content of no more than 20PPM.

[0128] Step 4: First layer of large droplet piezoelectric jet printing

[0129] The piezoelectric aluminum microdroplet jet printing device is located in an argon-filled glove box with an oxygen content of less than 20 ppm. The induction heating furnace is turned on to heat the crucible to 800°C, so that the aluminum alloy in the crucible melts and reaches the printing temperature. The flatbed heater is turned on to heat the printing substrate to 190°C. At this temperature, the strength and hardness of the aluminum alloy are improved, which can avoid the substrate annealing and softening caused by overheating.

[0130] Import the first-layer large droplet printing trajectory file obtained in step two into the PMAC host computer software. Then, replace the nozzle with a 0.8 mm diameter nozzle and turn on the piezoelectric aluminum microdroplet jet printing device. Jet large droplets according to the predetermined printing trajectory, allowing the large droplets to deposit and fuse on the microburr structure. Upon deposition on the microburr surface, the large droplets simultaneously generate fluid encapsulation and remelting effects, resulting in both mechanical pinning and metallurgical bonding, achieving a strong and secure bond between the aluminum microdroplets and the printing substrate.

[0131] Step 5: Pneumatic jet printing of the spiked cone structure

[0132] Replace the nozzle with a nozzle with a diameter of 0.5 mm, then import the thorn cone structure printing trajectory from step two into the PMAC host computer, turn on the pneumatic aluminum microdroplet jet printing device, and set the jetting frequency to 5~10Hz. According to the predetermined printing trajectory, the thorn cone structure will be printed on the first layer of large droplets, and the multi-layer thorn cone structure will be printed.

[0133] If the anti-detachment micro-spike cone array is used to fix the thermal protection material, the above method is first used to print it in situ on the aircraft shell, and then the thermal protection material (phenolic resin) is poured into the outside of the aircraft shell with the anti-detachment micro-spike cone array printed on it using a mold. After curing, the thermal protection material is fixedly connected to the aircraft shell.

[0134] To verify the load-bearing capacity and structural reliability of the anti-detachment micro-thorn cone array in actual use, this invention follows... Figure 7 Three sets of compression tests were conducted on the anti-detachment micro-spiked cone array. At the start of compression, as the push rod contacted the spiked structure, the pressure rose sharply, reaching a peak of 65-68 N, followed by a slight decrease, indicating structural deformation and a reduction in pressure. The pressure then continued to rise until it reached the limit of the universal testing machine's range. At this point, the electric displacement stage stopped moving and slowly retracted, causing a sharp drop in pressure. Figure 8-10 As shown, the measurement results indicate that the maximum pressures of the three test groups were 68.20 N, 66.31 N, and 67.48 N, respectively, and the minimum pressures were -9.61 N, -10.91 N, and -11.69 N, respectively. The extreme pressure values ​​were 77.81 N, 77.22 N, and 79.17 N, respectively, corresponding to compressive strengths of 3.71 MPa, 3.68 MPa, and 3.77 MPa, respectively.

[0135] Thus, it can be seen that the anti-detachment micro-spike array has the load-bearing capacity and structural reliability in actual use: as an interface anti-detachment structure, the spike array will be subjected to normal compressive loads under conditions such as thermal protection material pressing and curing, assembly clamping, and service thermal expansion and contraction and vibration impact. The above-mentioned compressive strength test can fully prove that the microstructure is not easily flattened or completely detached under pressure, thus having engineering application feasibility. It can achieve a tight connection and collaborative load-bearing between the thermal protection material and the aircraft shell, thereby meeting the comprehensive requirements of aircraft for lightweight, aerodynamic performance and thermal protection.

[0136] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for in-situ printing of metal microdroplets in a micro-spike array for fixing thermal protective materials, characterized in that, Includes the following steps: 1) Determine the structural and geometric parameters of the anti-detachment micro-thorn cone array. The anti-detachment micro-spiky cone array includes a substrate surface microstructure, a first layer of large droplets, and a spike structure; The substrate surface microstructure is an oblique cone array microstructure, which is formed by micro-milling. The geometric parameters include the radial dimension and height of the bottom surface of the oblique cone. The first layer of large droplets is a droplet array anchored on the oblique conical array microstructure, and the whole is printed by a piezoelectric jetting device; the geometric parameters include the radius R of the large droplets. The spiked structure is an array of spiked units corresponding to the growth on the droplet array. The spiked unit includes an aluminum column and aluminum branches, and is printed as a whole by a pneumatic jetting device. The geometric parameters include the radius r of the small droplet, the number of spiked units in the array along the X, Y, and Z axes in space, the printing spacing a of the aluminum column, the height h of the aluminum column, the solidification angle θ of the aluminum branch, the length l of the aluminum branch, and the total height H of the aluminum column in the Z-axis direction. 2) Complete trajectory planning Micro-milling trajectory planning for microstructures on substrate surface: Based on the coordinates of the printed nodes and the printing spacing of the aluminum cylinders, the three-dimensional model of the oblique cone array microstructure is first completed in the 3D modeling software, and the model is exported as a STEP format file. Then, the STEP format file is imported into the CAM software, the tool type and cutting parameters are set, and G-code for CNC milling is generated. Printing trajectory planning for the first layer of large droplets: Based on the printing spacing of the aluminum cylinders, the deposition position of each large droplet in the droplet array is calculated, and the deposition position is generated as a PMAC printing trajectory using trajectory planning software; Printing trajectory planning for spiked cone structures: The 3D lattice model of the designed structure is discretized and transformed into a droplet model suitable for micro-droplet 3D printing; a droplet position function is established, and the spatial coordinates of each droplet are exported as G-code to achieve printing path control; 3) Polishing the substrate and preparing microstructures 3.1) Grind the substrate to remove the surface oxide layer, ensuring that the surface roughness Ra of the substrate is 0.8-1.6μm; 3.2) Run the micro-milling trajectory code of the microstructure on the substrate surface in step 2). The CNC milling machine mills the substrate surface according to the predetermined trajectory to prepare the required oblique cone array microstructure. Then, place the substrate in an argon environment glove box, wherein the oxygen content of the glove box is not higher than 20ppm. 4) First-layer large droplet piezoelectric jet printing 4.1) Preheating of the piezoelectric injection device The piezoelectric injection device is located in an argon-filled glove box with an oxygen content of less than 20 ppm. Turn on the induction heating furnace to heat the crucible, so that the aluminum alloy inside the crucible melts and reaches the printing temperature; Turn on the flatbed heater to heat the printing substrate temperature in step 3) to 190°C; 4.2) The printing trajectory code of the first layer of large droplets in step 2) is executed. The piezoelectric jetting device sprays large droplets according to the predetermined printing trajectory, so that the large droplets are deposited on the oblique cone array microstructure and fused with it. 5) Pneumatic jet printing of spiked cone structure In step 2), the pneumatic jetting device prints the corresponding spike unit on the first layer of large droplets according to the predetermined printing trajectory, thus completing the printing of the spike structure.

2. The in-situ printing method for anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials according to claim 1, characterized in that: In step 1), the oblique cone array microstructure adopts a four-sided oblique cone; The side length of the bottom of the square oblique pyramid is 0.5 mm, and the height is 0.3 mm.

3. The method for in-situ printing of anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials according to claim 1 is characterized in that: In step 3), the aluminum alloy printing substrate is a 6061 aluminum alloy printing substrate with dimensions of 70 mm × 70 mm × 1 mm.

4. The in-situ printing method for anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials according to claim 1, characterized in that: In step 4), the induction heating furnace is heated to 800℃ and then held at that temperature for 5 minutes; The nozzle diameter used in the piezoelectric jetting device is 1 mm, and the diameter of the ejected large droplets is 2 mm.

5. The method for in-situ printing of anti-detachment micro-spike cone array metal microdroplets for fixing thermal protective materials according to claim 1 is characterized in that: In step 5), the injection frequency of the pneumatic injection device is 5~10Hz; The nozzle diameter used in the pneumatic injection device is 0.4 mm, and the diameter of the ejected droplets is 0.5 mm.

6. A micro-barb cone array for fixing thermal protective materials to prevent them from falling off, characterized in that: In-situ printing is performed using any of the methods described in claims 1-5.

7. A method for connecting thermal protection materials to an aircraft shell, characterized in that, Includes the following steps: S1. Using any of the methods described in claims 1-5, an anti-detachment micro-spike cone array is printed in situ on the aircraft shell; S2. Using a mold, heat protection material is poured onto the outside of the aircraft shell, which has been printed with an anti-detachment micro-spike cone array. After curing, the heat protection material is fixedly connected to the aircraft shell.

8. The method according to claim 7, characterized in that: In S2, the heat protection material is phenolic resin.

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