Low-expansion heterogeneous cell printing method based on uniform metal micro-droplet spraying

Abstract

The invention discloses a low-expansion heterogeneous cell printing method based on uniform metal micro-droplet spraying, and belongs to the technical field of heterogeneous cell printing. According to the method, uniform metal micro-droplet spraying, prefabricated metal micro-rod embedding and a laser micro-domain heating technology are fused, and firstly, continuous metal straight lines are printed on a substrate through micro-droplet spraying to serve as cell element bottom edges and positioning structures; then the pretreated heterogeneous metal micro-rod is embedded into the positioning structure in an interference mode, and a triangular frame is formed; and then metal micro-droplets are quantitatively deposited at the connecting end of the micro-rod, laser parameters optimized based on a thermodynamic model are adopted for micro-domain heating, the micro-droplets are molten to form a liquid-bridge-shaped metallurgical bonding part, weak-rigidity nodes capable of achieving concentrated thermal deformation are formed, and finally printing of the low-expansion heterogeneous cell elements is completed. According to the preparation method, high-strength reliable connection of the micro-scale heterogeneous material and active regulation and control of thermal deformation behaviors are achieved, and a low-expansion lattice structure with excellent dimensional stability can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous cell printing technology, specifically relating to a low-expansion heterogeneous cell printing method based on uniform metal microdroplet jetting. Background Technology

[0002] As spacecraft evolve towards miniaturization and high integration, advanced micro-spacecraft need to integrate multiple functional units within limited structural space, such as microwave communication modules, optical payloads, and radar systems, to simultaneously perform multiple tasks including communication, remote sensing, and navigation. In the complex space environment, these spacecraft often face severe temperature fluctuations, and structural materials are prone to thermal expansion and deformation under temperature changes, potentially leading to the failure of critical functional units. Therefore, constructing lightweight structural systems with low thermal expansion characteristics and high thermal stability has become a key technological requirement in the design and manufacturing of micro-spacecraft.

[0003] In the fabrication of low thermal expansion heterogeneous lattice structures, existing technologies mainly include two approaches: one is based on traditional machining and assembly methods, and the other is based on additive manufacturing methods for printing heterogeneous materials.

[0004] Traditional machining methods, such as wire EDM to manufacture parts of different materials, followed by assembly using mortise and tenon joints, interference fits, or laser spot welding, while capable of combining materials, have significant limitations at the microscale: the assembly process demands extremely high dimensional accuracy, making it difficult to avoid assembly stress; and controlling the morphology of laser welds is challenging, easily introducing defects such as microcracks and porosity. These process-level issues lead to insufficient bonding strength at heterogeneous interfaces, increased thermal resistance, and ultimately affect the overall thermal stability and load-bearing reliability of the structure.

[0005] Emerging additive manufacturing methods offer new approaches to the integrated molding of heterogeneous materials. For example, uniform metal microdroplet jetting technology can achieve the interactive deposition molding of bimetallic materials. This method overcomes the precision problems of traditional assembly to some extent by constructing triangular cells with near-zero thermal expansion. However, this method still faces the following technical bottlenecks: The interface connection mechanism is simple: it relies solely on the wetting and solidification of aluminum microdroplets on the surface of titanium rods to achieve connection. At the microscale, the interfacial metallurgical reaction is insufficient, the bonding strength is limited, and it is difficult to accurately control the thickness of the reaction layer and the phase composition.

[0006] Lack of active deformation control: The deformation of the structure under thermal load depends on the stiffness matching of the material itself. The lack of a controllable "weak stiffness" or "liquid bridge" mechanism at the nodes leads to uneven distribution of thermal stress, and local stress concentration may cause microcracks.

[0007] Insufficient process integration: The precise positioning of microrods, pre-processing of interface micro-morphology (such as beveling), and precise delivery of local energy (such as laser micro-domain heating) are not systematically integrated with microdroplet printing, making it difficult to achieve the construction and performance control of heterogeneous interfaces with micron-level precision.

[0008] In summary, the core bottleneck of current low-expansion heterogeneous cell manufacturing technology lies in how to achieve high-strength, low-stress metallurgical connections between heterogeneous metal materials at the microscale, and how to precisely control the deformation behavior of cells under thermal loads through active design of node structures, thereby ensuring that the structure possesses both low expansion characteristics and high reliability. Existing technologies have not yet systematically resolved the contradiction between micro-connection strength, interface stability, and structural deformation coordination.

[0009] Therefore, achieving effective connections between heterogeneous metal materials while enabling rapid and efficient manufacturing has become a problem that needs to be solved. Developing a low thermal expansion heterogeneous cell printing method is of great significance for the miniaturization, lightweighting, and functional integration of spacecraft. Summary of the Invention

[0010] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides a low-expansion heterogeneous cell printing method based on uniform metal microdroplet jetting. This method combines three manufacturing paradigms: uniform metal microdroplet jetting additive manufacturing, positioning and assembly of prefabricated heterogeneous metal microrods, and laser-guided micro-domain local metallurgical bonding. This allows for the fabrication of high-strength connections and controllable thermal deformation structures of heterogeneous materials at the microscale. Specifically, by combining "microrod positioning on a substrate" with "laser-guided micro-domain heating liquid bridge connection," high-strength, low-stress connections of heterogeneous materials (aluminum / titanium) are achieved. The liquid bridge structure forms "weak-stiffness nodes," concentrating deformation at these nodes and keeping the microrods under only tension and compression, thus improving the structural thermal stability. This invention solves the problem of precisely controlling the deformation behavior of cells under thermal loads, thereby ensuring that the structure possesses both low expansion characteristics and high reliability.

[0011] The technical solution of this invention is: a low-expansion heterogeneous cell printing method based on uniform metal microdroplet jetting, the specific steps of which are as follows: Step 1: Select two metal microrods made of the first metal material, and perform beveling and surface pretreatment on the ends of the metal microrods to be connected. Step 2: Select a second metal material as the printing material. Using a uniform metal droplet jetting device, deposit droplets of the second metal material on a metal substrate with low thermal conductivity. By controlling the deposition position and path of the droplets, a positioning structure for positioning the metal microrods is formed on the substrate. At the same time, process parameters are controlled to achieve complete metallurgical interfusion between the deposited droplets, forming a continuous and uninterrupted uniform metal straight line. Step 3: The pre-treated metal microrods are embedded into the positioning structure with their ends to be connected facing a preset direction, so that the metal microrods and the substrate form an interference fit fixed connection; at the same time, the two metal microrods and the metal straight line as the base structure form the basic framework of the triangular cell. Step 4: Control the uniform metal droplet ejection device to deposit a predetermined volume of the second metal material droplets at the connection ends of the two fixed metal micro rods to form a pre-deposited droplet pile; Step 5: Use a laser beam to heat the pre-deposited microdroplet stack and the ends of the adjacent metal microrods in a micro-domain, so that the microdroplets of the second metal material are fully melted and spread, forming a liquid bridge-like metallurgical joint between the ends of the adjacent metal microrods, thereby forming a weak stiffness node at the vertex that can be deformed in a concentrated manner. Step 6: Use a laser beam to heat the two ends of the metal straight line and the ends of the adjacent metal microrods in a micro-domain, so that the two ends of the metal straight line partially melt and spread, forming a liquid bridge-like metallurgical joint between the ends of the metal straight line and the adjacent metal microrods, thereby forming a weak stiffness node at both ends of the bottom edge that can be deformed in a concentrated manner. Complete the printing of a low-expansion heterogeneous cell structure containing three weak stiffness nodes.

[0012] A further technical solution of the present invention is: in step 1, the surface pretreatment includes: sequentially performing organic solvent degreasing, hot water cleaning, and acid washing to remove oxide scale, and finally storing the treated microrods in anhydrous ethanol.

[0013] A further technical solution of the present invention is: in step 2, the process parameters of uniform metal droplet spraying are controlled so that the spraying temperature is higher than the surface melting temperature of the substrate, so that a single metal droplet can locally melt the substrate surface and achieve partial embedding; and can melt the overlapping part of the deposited droplets to achieve mutual melting and bonding between droplets.

[0014] A further technical solution of the present invention is: in step 2, the positioning structure printed on the substrate is a boss structure, and the position and contour of the boss structure are pre-planned according to the positioning position and angle of the metal microrod; the continuous and uninterrupted uniform metal straight line constitutes the bottom edge structure of the heterogeneous cell.

[0015] A further technical solution of the present invention is: before performing step 2, it further includes a step of designing the cell structure based on the target thermal expansion properties. Based on the coefficients of thermal expansion of the first and second metal materials, and the designed coefficient of thermal expansion of the target cell in the height direction, the vertex angle of the triangular cell is determined using the following formula. :

[0016] in, The coefficient of thermal expansion of a heterogeneous unit cell in the height direction. The coefficient of thermal expansion of the printing material is the second metallic material. The coefficient of thermal expansion of the first metallic microrod is given. The angle of the apex of the heterogeneous unit cell.

[0017] A further technical solution of the present invention is: in step 4, a predetermined volume of microdroplets is deposited between the upper ends of two metal microrods; In step 5, laser micro-domain heating forms a liquid bridge-like metallurgical joint between the upper ends of the two metal microrods, constituting the vertex node of the triangular cell. In step 6, laser micro-domain heating forms a liquid bridge-like metallurgical junction between the bottom ends of the two metal microrods and the two ends of the metal straight line, constituting the two bottom corner nodes of the triangular cell.

[0018] A further technical solution of the present invention is as follows: In step 4, the microdroplets of a predetermined volume are determined by: calculating the minimum metal volume required to form a stable liquid bridge based on the design spacing at the upper ends of adjacent microrods, the radius of the second metal microdroplet, and the theoretical model of liquid bridge formation, thereby determining the number of microdroplets to be deposited.

[0019] A further technical solution of the present invention is: in step 4, the predetermined volume is determined in the following way: Based on the design spacing D between the upper ends of the two microrods and the design radius at the narrowest point of the liquid bridge. and the characteristic radius of the cross-section of the microrod Calculate the theoretical metal volume V required to form the target liquid bridge:

[0020] Based on the theoretical volume V and the volume of a single second metal droplet, the number of droplets n to be deposited is determined so that the total volume of deposited metal is not less than V.

[0021] A further technical solution of the present invention is: in step 5, the parameters of laser micro-domain heating are determined by the following thermodynamic calculations: Based on the total mass of the pre-deposited droplet pile m Specific heat capacity of the second metal material C 1. Latent heat of fusion L and from the initial temperature T 1 liter to melting temperature T 2. Required temperature rise, calculate the heat required to melt the microdroplet pile. Q 1:

[0022] Based on the total mass of the pre-deposited droplet pile m Specific heat capacity of the first metal material C 2. Calculate the heat required to raise the temperature of the target area. Q 2;

[0023] in, The power of the laser. This refers to the irradiation time.

[0024] A printing system for implementing the method includes: A uniform metal droplet ejection device for generating and depositing droplets of a second metal material; A motion platform is used to support and precisely move the substrate; A laser micro-area heating device is used to generate and focus a laser beam to heat a specified micro-area. A visual positioning system is used to monitor the position of metal microrods, droplet deposition points, and laser application points in real time. The controller is communicatively connected to the uniform metal droplet ejection device, the motion platform, the laser micro-domain heating device, and the visual positioning system. It is used to integrate and control the droplet ejection trajectory, platform motion, and laser parameters, and to perform online calibration based on visual feedback.

[0025] Beneficial effects The beneficial effects of this invention are as follows: This invention effectively solves the common problem of difficult bonding of metals with high thermal property differences, such as aluminum and titanium, at the micrometer scale through a composite process combining "substrate positioning" and "laser micro-domain heating liquid bridge metallurgical connection." This method not only achieves precise mechanical positioning of the microrod, avoiding assembly gaps, but also, through the precise delivery of laser energy, melts, spreads, and forms a liquid bridge at the end of the titanium rod, achieving metallurgical bonding at the interface.

[0026] The "liquid bridge type weak stiffness node" designed in this invention is formed after laser micro-domain heating, and its stiffness is significantly lower than that of the metal microrods that serve as the inclined sides. When the structure is heated, thermal stress will be preferentially guided and concentrated at these controllable weak stiffness nodes, causing them to undergo elastic deformation, thereby effectively "absorbing" and "releasing" strain energy. This ensures that the metal microrods, which serve as the main load-bearing units, basically maintain a state of pure tension or compression, avoiding additional stress caused by bending deformation and overall structural instability.

[0027] This invention seamlessly integrates three manufacturing paradigms—uniform droplet jetting (droplet fabrication and deposition), precision mechanical embedding (microrod positioning), and laser micro-domain heating (local connection)—to form a synergistic micro-additive manufacturing system. Uniform droplet jetting enables efficient and precise shaping of substrate structures; visual positioning and motion control ensure micron-level positioning accuracy for microrod embedding and droplet deposition; and laser micro-domain heating achieves localization and minimization of energy, avoiding thermal deformation caused by overall heat input. This combination of processes, each with its own function and working synergistically, ensures manufacturing precision while also possessing good process flexibility, making it suitable for the automated and mass production of complex heterogeneous cell arrays. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of adjusting the jetting step distance for metal microdroplets; Figure 2 This is a schematic diagram of the positioning structure printing and elastic deformation nodes; Figure 3 This is a schematic diagram of the embedded metal microrod; Figure 4 This is a schematic diagram of printing pre-fused metal droplets; Figure 5 This is a schematic diagram of micro-domain heating of pre-fused metal droplets; Figure 6 This is a schematic diagram of the prepared low-expansion heterostructure; Figure 7 This is a diagram showing the geometric parameters of the liquid bridge structure between two microrods; Figure 8 This is a physical image of a low-expansion heterogeneous cell; Figure 9 It is a low-expansion heterogeneous cell stress cloud diagram.

[0029] Figure labeling: 1. Single aluminum microdroplet, 2. Printed substrate, 3. Uniform straight line, 4. Positioning structure, 5. Cell bottom edge, 6. Metal microrod, 7. Pre-fused metal microdroplet, 8. Laser, 9. Heterogeneous cell. Detailed Implementation

[0030] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0031] In existing technology, the literature "Wei K, Chen H, Pei Y, et al. Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit[J]. Journal of the Mechanics and Physics of Solids.2016, 86: 173-191." proposes a mechanically interlocking tenon and mortise structure to manufacture low thermal expansion lattice units. Parts of different materials are cut from thin metal sheets using electrical discharge machining (EMD), and the parts are connected by interference fits to achieve the fabrication of low-expansion lattice units. This connection method requires strict dimensional tolerances, and assembly stress is difficult to avoid. The literature “Gdoutos, E., Shapiro, AA, Daraio. Thin and thermally stable periodic metastructures. [C]. Exp. Mech. 2013. 53, 1735–1742.” proposes to fabricate unit cell structures and then splice them together, allowing for arbitrary expansion of the cell structure. Laser spot welding is used for the connection, improving the level of automated production. However, experimental data shows that controlling the weld point morphology is difficult, inevitably introducing welding defects.

[0032] To address the problems existing in current technologies, this invention proposes a low-expansion heterogeneous cell printing method based on uniform metal microdroplet jetting, the specific steps of which are as follows: Step 1: Select two metal microrods made of the first metal material, and perform beveling and surface pretreatment on the ends of the metal microrods to be connected. Step 2: Select a second metal material as the printing material. Using a uniform metal droplet jetting device, deposit droplets of the second metal material on a metal substrate with low thermal conductivity. By controlling the deposition position and path of the droplets, a positioning structure for positioning the metal microrods is formed on the substrate. At the same time, process parameters are controlled to achieve complete metallurgical interfusion between the deposited droplets, forming a continuous and uninterrupted uniform metal straight line. Step 3: The pre-treated metal microrods are embedded into the positioning structure with their ends to be connected facing a preset direction, so that the metal microrods and the substrate form an interference fit fixed connection; at the same time, the two metal microrods and the metal straight line as the base structure form the basic framework of the triangular cell. Step 4: Control the uniform metal droplet ejection device to deposit a predetermined volume of the second metal material droplets at the connection ends of the two fixed metal micro rods to form a pre-deposited droplet pile; Step 5: Use a laser beam to heat the pre-deposited microdroplet stack and the ends of the adjacent metal microrods in a micro-domain, so that the microdroplets of the second metal material are fully melted and spread, forming a liquid bridge-like metallurgical joint between the ends of the adjacent metal microrods, thereby forming a weak stiffness node at the vertex that can be deformed in a concentrated manner. Step 6: Use a laser beam to heat the two ends of the metal straight line and the ends of the adjacent metal microrods in a micro-domain, so that the two ends of the metal straight line partially melt and spread, forming a liquid bridge-like metallurgical joint between the ends of the metal straight line and the adjacent metal microrods, thereby forming a weak stiffness node at both ends of the bottom edge that can be deformed in a concentrated manner. Complete the printing of a low-expansion heterogeneous cell structure containing three weak stiffness nodes.

[0033] Specifically, In step 4, a predetermined volume of microdroplets is deposited between the upper ends of two metal microrods; In step 5, laser micro-domain heating forms a liquid bridge-like metallurgical joint between the upper ends of the two metal microrods, constituting the vertex node of the triangular cell. In step 6, laser micro-domain heating forms a liquid bridge-like metallurgical junction between the bottom ends of the two metal microrods and the two ends of the metal straight line, constituting the two bottom corner nodes of the triangular cell.

[0034] The present invention also proposes a printing system for implementing the method, comprising: A uniform metal droplet ejection device for generating and depositing droplets of a second metal material; A motion platform is used to support and precisely move the substrate; A laser micro-area heating device is used to generate and focus a laser beam to heat a specified micro-area. A visual positioning system is used to monitor the position of metal microrods, droplet deposition points, and laser application points in real time. The controller is communicatively connected to the uniform metal droplet ejection device, the motion platform, the laser micro-domain heating device, and the visual positioning system. It is used to integrate and control the droplet ejection trajectory, platform motion, and laser parameters, and to perform online calibration based on visual feedback.

[0035] The above technical solution will be further analyzed below with reference to the accompanying drawings and examples: In one embodiment, refer to Figure 1-6 As shown, a method for printing low-expansion heterogeneous cells based on uniform metal microdroplet technology and laser micro-domain heating technology includes the following steps: Step 1: Select a cross-section of 500. × 500 The metal microrods have pre-beveled edges at the interface and their surfaces pre-treated. Suitable metal materials include Invar alloy, pure titanium, and titanium alloys. The pre-treatment process is as follows: a) Fix the metal microrod with a special fixture and process a bevel at a specified angle on the beveling platform.

[0036] b) After soaking and wiping in acetone until a metallic luster appears, rinse with hot water at 30°C to remove grease from the surface of the microrod.

[0037] c) Prepare an aqueous solution with a mass fraction of 40% HNO3 + 5% HF, and soak in the solution for 3 to 5 minutes to remove the oxide scale.

[0038] d) Remove the processed metal microrods and store them in anhydrous ethanol.

[0039] Step 2: Select the nozzle (diameter denoted as...) Cast aluminum was selected as the printing material for uniform microdroplet technology, placed in a crucible, and heated to the jetting temperature. , making Above the material's melting point By adjusting the injection voltage and pulse width, stable injection of a single aluminum microdroplet can be achieved. Step 3: Select a metal material with low thermal conductivity K as the printing substrate 2, such as nickel, titanium, stainless steel, etc. Step 4: Conduct microdroplet jet deposition experiments and make preliminary adjustments to the printing step size of the moving platform. and injection temperature and substrate temperature To increase the spray temperature Higher than the substrate melting temperature This allows individual metal droplets to locally melt the substrate surface and partially embed themselves, while ensuring that the metal droplets can melt the overlapping portions of the deposited metal droplets, achieving mutual melting and bonding between the metal droplets. This ensures that the metal droplets are deposited as a uniform, straight line without breaks. Figure 1 As shown; Step 5: Determine the angle of the cell using formula (1). ; Enter the angle in the print program generation system. Microrod length micro rod width d Generate a printing program for metal microrod positioning structures; (1) In the formula, The coefficient of thermal expansion of a heterogeneous unit cell in the height direction. The coefficient of thermal expansion of the metal printed at the bottom edge. is the coefficient of thermal expansion of the inclined metal microrod. The vertex angle of the heterogeneous unit cell; when When the value is equal to 0, the angle of the triangular cell with zero expansion can be obtained. .

[0040] Step Six: Place the metal substrate on the moving platform, control the platform to move using a motion controller, and print the positioning structure 4 and the cell bottom edge 5 on the metal substrate, as shown. Figure 2 As shown; Step 7: Embed the metal microrods 6 between the printed positioning structures 4, ensuring a tight interference fit. Figure 3 As shown; Step 8: Calculate the distance between the upper ends of the two metal microrods according to formulas (2) and (3). D 300 This ensures the volume range of aluminum droplets where liquid bridges exist, and then the number of aluminum droplets to be deposited can be calculated according to formula (4). n According to the length of the metal microrod Adjust the printing program so that the jetting device prints at the tip of the metal microrod 6. n (2~4) pre-fused metal droplets 7, columnar in shape, such as Figure 4 As shown; (2) (3) (4) In the formula, V The volume of the liquid bridge is mm. 3 ; D The distance between the two microrods is mm; The radius of the narrowest point of the liquid bridge is mm; The width of the microrod is in mm; v To make the volume of the liquid bridge dimensionless; r The radius of the aluminum droplet is mm; n This represents the number of deposited metal droplets; cosh It is a hyperbolic cosine.

[0041] Step 9: Adjust the laser 8's output mode to continuous output, such as... Figure 5 As shown; calculate the heat required for pre-droplet melting according to formulas (5) and (6). Q 1. Irradiate the middle part of the microrod end near the droplet, calculate the energy required to heat the titanium rod according to formula (7), and determine the light power. (30 ~ 100W); Emission time (500 ~ 1000) ); incident angle is By adjusting the laser parameters, the pre-fused aluminum microdroplets were fully melted and spread, forming the theoretically calculated liquid bridge structure at the ends of the two titanium rods.

[0042] (5) (6) (7) In the formula: m The mass of aluminum droplets is (g). r The radius of the aluminum droplet is (mm). ρ Density of aluminum droplets (g / cm³) 3 ). Q 1. Heat required for droplet melting (J); Q 2. Heat generated by heating the titanium rod (J); C 1 represents the specific heat capacity of the aluminum alloy (kJ / (kg·℃)); C 2 represents the specific heat capacity of the titanium alloy (kJ / (kg·℃)); L The latent heat of fusion of aluminum (kJ / kg); T 1 represents the initial temperature (°C); T 2 represents the melting temperature of the aluminum material (°C); The output power of the laser (W); The laser emission time is denoted as μs.

[0043] Step 10: Complete the printing of the low thermal expansion heterogeneous cell 9, as shown below. Figure 6 As shown.

[0044] In one embodiment, low-expansion heterogeneous cellular structure printing Step 1: Raw material preparation and surface treatment.

[0045] Cast aluminum 104 was selected as the printing material, with a cross-section of 500 mm. × 500 TC4 microrods were used as the embedding material, and TA2 was selected as the substrate 2 for printing heterogeneous deformable multi-cell structures. To ensure good bonding at the aluminum / titanium interface, the titanium microrods 6 underwent surface pretreatment: a 30°–60° bevel was created at the connecting end to improve the wettability of the molten aluminum; oily solvents were used to remove surface oil, followed by an acid solution to remove the surface oxide layer. After treatment, the titanium microrods 6 were stored in anhydrous ethanol to prevent re-oxidation.

[0046] Step 2: Determine the geometric parameters of the low-expansion cell.

[0047] First, combining with formula (1) in the previous embodiment, the thermal expansion coefficient of material TC4 is 8.6 ppm / ℃ and the thermal expansion coefficient of material cast aluminum 104 is 23 ppm / ℃. The angle of the low-expansion cell can be calculated from the thermal expansion matching relationship. The angle is 40-50°. Enter the angle in the print program generation system. Microrod length micro rod width d This generates a printing program for metal microrod positioning structures, providing geometric control for subsequent printing.

[0048] Step 3: Aluminum microdroplet printing and positioning structure formation.

[0049] Referring to Figure 1, select the diameter 700 The nozzle was used to heat cast aluminum 104 in a crucible to 600-900°C. The spray voltage was adjusted to 1-5V and the pulse width to 200-1000μs to ensure stable spraying of aluminum microdroplets 1, depositing a uniform straight line 3 without breaks. The diameter of the aluminum microdroplets was approximately 500-700 μm. .

[0050] Referring to Figure 2, the printing step size of the aluminum microdroplets is adjusted to be between 400 and 600 μm. The positioning structure 4 of the titanium microrods and the cell aluminum edge 5 are printed on the titanium substrate to ensure continuous printing path and good interlayer bonding.

[0051] Step 4: Embedding and positioning of titanium microrods.

[0052] Referring to Figure 3, the treated titanium microrods 6 are removed under a micro-oxygen environment and embedded into the printed positioning structure 4. It is ensured that the embedding of the titanium microrods 6 is an interference fit to ensure tight bonding and precise positioning. After embedding, the overall flatness is checked to ensure stability in the subsequent deposition process.

[0053] Step 5: Aluminum liquid deposition and liquid bridge formation.

[0054] Referring to Figures 4 and 7, adjust the substrate position and perform zero-point positioning for jetting. Calculate the distance between the two microrods according to formulas (2) and (3). D 300 To ensure the presence of liquid bridges, the volume range of aluminum droplets is determined, and then the number of aluminum droplets to be deposited is calculated according to formula (4). n (2 to 4 droplets). By precisely controlling the number and position of jets, pre-fused aluminum microdroplets 7 are deposited on the tip of titanium microrods 6 to form stable liquid bridges, thus completing the printing process.

[0055] Step 6: Effective connection between laser micro-domain heating and the interface.

[0056] Referring to Figure 5, the laser 8 emission mode is adjusted to continuous emission. Combining formulas (5), (6), and (7), the laser power is calculated. P 0 is 30 ~ 100W, light emission time With a latency of 500 to 1000 ms, laser micro-domain heating is performed under these parameters. Pre-fused aluminum microdroplets 7 are wetted downwards by capillary force and fill the gaps at the ends of titanium rods 6, forming a continuous reaction layer structure. This reaction layer is less than 10 μm thick and mainly consists of the TiAl3 phase, enabling stable connections between the two titanium microrods and between the titanium rods and the aluminum edge, thus forming a node structure with elastic deformation capabilities.

[0057] Step 7: Structural sampling and performance verification.

[0058] Reference Figure 6 As shown, the final printed structure is achieved by using wire cutting technology to remove the printed low-expansion heterogeneous cell structure 9. The manufactured cell is shown in the reference image. Figure 8 Its cell stress distribution is as follows Figure 9 As shown in Table 1, the measurement results demonstrate that the cells manufactured by this method can achieve low expansion performance and absorb thermal stress at elastic deformation nodes, significantly improving the overall thermal stability and reliability of the structure.

[0059] Table 1. Measured values ​​of the samples and corresponding coefficients of thermal expansion.

[0060] Measurement results show that the final coefficient of thermal expansion of the test sample reaches 2.32 × 10⁻⁶. -6 K -1 Furthermore, multiple sets of measurement results and their average values ​​indicate that the absolute value of the thermal expansion coefficient of the test specimen is less than 5 × 10⁻⁶. -6 K -1 It can be determined that it has low thermal expansion properties.

[0061] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for printing low-swelling heterogeneous cells based on uniform metal microdroplet ejection, characterized by, The specific steps are as follows: Step 1, select two metal micro rods of a first metal material, and perform beveling and surface pretreatment on the ends to be connected of the metal micro rods; Step 2, select a second metal material as the printing material, use a uniform metal micro droplet jetting device to deposit micro droplets of the second metal material on a metal substrate with low thermal conductivity characteristics, and form a positioning structure for positioning the metal micro rods on the substrate by controlling the deposition position and path of the micro droplets; at the same time, control the process parameters to realize complete metallurgical intermelting between the deposited micro droplets to form a continuous and uninterrupted uniform metal straight line; Step 3, embed the pretreated metal micro rods into the positioning structure with their ends to be connected facing a predetermined direction, so that the metal micro rods are fixedly connected with the substrate in an interference fit; at the same time, the two metal micro rods and the metal straight line as the bottom edge structure form the basic framework of a triangular cell; Step 4, control the uniform metal micro droplet jetting device to deposit a predetermined volume of micro droplets of the second metal material on the ends to be connected of the two fixed metal micro rods to form a pre-deposited micro droplet pile; Step 5, use a laser beam to perform micro-domain heating on the pre-deposited micro droplet pile and the adjacent ends of the metal micro rods to fully melt and wet spread the micro droplets of the second metal material, forming a liquid bridge-shaped metallurgical bonding part between the adjacent ends of the metal micro rods, thereby forming a weak stiffness node at the vertex that can concentrate deformation; Step 6, use a laser beam to perform micro-domain heating on the two ends of the metal straight line and the adjacent ends of the metal micro rods, causing the two ends of the metal straight line to partially melt and wet spread, forming a liquid bridge-shaped metallurgical bonding part between the adjacent ends of the metal micro rods, thereby forming a weak stiffness node at the two ends of the bottom edge that can concentrate deformation; Complete the printing of a low-expansion heterogeneous cell structure containing three weak stiffness nodes.

2. The method of claim 1, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In step 1, the surface pretreatment includes: sequentially performing organic solvent oil removal, hot water cleaning, and pickling to remove oxide scale, and finally storing the treated micro rods in anhydrous ethanol.

3. The method of claim 1, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In step 2, the process parameters of uniform metal micro droplet jetting are controlled so that the jetting temperature is higher than the surface melting temperature of the substrate, so that a single metal micro droplet can locally melt the substrate surface and partially embed; and can melt the overlapping part of the deposited micro droplets to realize intermelting bonding between the droplets.

4. The method of claim 3, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In step 2, the positioning structure printed on the substrate is a boss structure, and the position and contour of the boss structure are pre-planned according to the positioning position and angle of the metal micro rods; the continuous and uninterrupted uniform metal straight line constitutes the bottom edge structure of the heterogeneous cell.

5. The method of claim 1, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. Before step 4 is performed, a step of designing the cell structure according to the target thermal expansion performance is further included: According to the thermal expansion coefficients of the first metal material and the second metal material, and the design thermal expansion coefficient of the target cell in the height direction, the top angle of the triangular cell is determined by the following relationship : wherein, is a thermal expansion coefficient of the heterogeneous unit cell in the height direction, is a thermal expansion coefficient of the second metal material printing material, is a thermal expansion coefficient of the first metal material metal micro rod, is an apex angle of the heterogeneous unit cell.

6. The method of claim 4, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In step 4, the predetermined volume of micro droplets is deposited between the upper ends of the two metal micro rods; In step 5, laser micro-domain heating forms a liquid bridge-shaped metallurgical bonding part between the upper ends of the two metal micro rods, forming a vertex node of the triangular cell; In step 6, laser micro-domain heating is performed between the bottom ends of the two metal micro rods and the two ends of the metal straight line, respectively, to form a liquid bridge-shaped metallurgical bonding part, thereby forming two bottom corner nodes of the triangular cell.

7. The method of claim 6, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In the step 4, the predetermined volume of the micro-droplet is determined by calculating the minimum metal volume required for forming a stable liquid bridge according to the designed spacing of the adjacent micro-rods, the radius of the micro-droplet of the second metal material, and a theoretical model of liquid bridge formation, and then determining the number of micro-droplets to be deposited.

8. The method of claim 7, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In the step 4, the predetermined volume is determined by: According to the designed distance D between the upper ends of the two metal micro-rods, the designed radius of the liquid bridge at the narrowest part and the characteristic radius of the cross-section of the metal micro-rods , the theoretical metal volume V required to form the target liquid bridge is calculated: According to the theoretical volume V and the volume of a single micro-droplet of the second metal material, the number n of micro-droplets to be deposited is determined so that the total volume of the deposited metal is not less than V.

9. The method of claim 6, wherein the method is a low-swelling heterogeneous cell printing method based on uniform metal microdroplet ejection. In the step 5, the parameters of laser micro-domain heating are determined by thermodynamic calculation: According to the total mass of the pre-deposited droplet stack m , the specific heat capacity of the second metal material C 1, the latent heat of fusion L , and the temperature rise required from the initial temperature T 1 liter to the melting temperature T 2, the heat required to melt the droplet stack is calculated Q 1: According to the total mass of the pre-deposited droplet stack m , the specific heat capacity of the first metal material C 2 and the target temperature rise, the heat required to raise the temperature of the region Q 2; wherein is the power of the laser, is the irradiation time.

10. A printing system for carrying out the method of any one of claims 1-9, characterized by Including: A uniform metal micro-droplet spraying device for generating and depositing micro-droplets of the second metal material; A motion platform for carrying and accurately moving the substrate; A laser micro-domain heating device for generating and focusing a laser beam to heat a specified micro-region; A visual positioning system for real-time monitoring of the position of the metal micro-rod, the deposition point of the micro-droplet, and the action point of the laser; A controller in communication with the uniform metal micro-droplet spraying device, the motion platform, the laser micro-domain heating device, and the visual positioning system for integrated control of the micro-droplet spraying trajectory, the platform motion, the laser parameters, and online calibration according to the visual feedback.

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