A method for preparing a composite heat exchange structure

Abstract

This application provides a method for preparing a composite heat exchange structure, belonging to the field of heat exchange equipment processing technology. The method includes: preparing a heat exchange substrate; forming a grafting portion on the heat exchange substrate using a material removal manufacturing process to obtain a shaped substrate; based on the shaped substrate, forming an additive portion on the surface of the grafting portion using an additive manufacturing process to construct a composite heat exchange unit; and processing a heat exchange auxiliary structure on the surface of the composite heat exchange unit using an additive manufacturing process and / or a surface treatment process. This application achieves the adaptation and integration of material removal and additive manufacturing technologies, retains the excellent thermal conductivity and mechanical properties of the machined substrate, improves the interfacial bonding strength between the additive structure and the substrate, and balances the forming freedom, processing accuracy, and cost of complex heat exchange structures, thus meeting the needs of large-scale preparation of various high heat flux density heat exchange structures.

Description

Technical Field

[0001] This application relates to the field of heat exchange equipment processing technology, specifically to a method for preparing a composite heat exchange structure. Background Technology

[0002] The increasing integration and power density of electronic devices have led to a year-on-year increase in heat dissipation requirements under high heat flux density conditions, which in turn places higher demands on the heat exchange performance, molding accuracy and reliability of the supporting heat exchange structures.

[0003] Existing heat exchange structure fabrication technologies face insurmountable technical problems in practical engineering applications, specifically as follows: In traditional material removal manufacturing, CNC machining is currently the most widely used preparation method. However, it has poor accessibility for machining complex topologies and high aspect ratio micro-channels. For closed channels and irregular curved surface heat exchange structures, only a process route of separate machining followed by welding assembly can be adopted. This route is not only cumbersome and has poor forming consistency, but more importantly, the weld interface is prone to sealing failure and increased contact thermal resistance, which cannot meet the stability requirements of heat exchange structures under long-term hot and cold cycling conditions.

[0004] In emerging additive manufacturing, metal 3D printing technology can achieve one-piece molding of complex heat exchange structures and avoid the sealing failure problem caused by separate welding. However, it also has significant problems. On the one hand, for heat exchange structures with large size and thick wall, additive molding requires a large amount of material, has a long molding cycle, and has high manufacturing costs, making it difficult to achieve large-scale application. On the other hand, the mechanical properties of the additively molded heat exchange substrate are significantly different from those of traditional machined substrates, making it impossible to simultaneously achieve both structural formability and basic heat exchange performance.

[0005] In summary, existing methods for fabricating heat exchange structures cannot simultaneously meet the comprehensive requirements of low cost, high precision, high reliability, and high performance in high heat flux density heat exchange scenarios. Summary of the Invention

[0006] This application addresses the problems existing in the prior art by providing a method for preparing a composite heat exchange structure that is suitable for large-scale applications of high heat flux density electronic devices.

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing a composite heat exchange structure, including: preparing a heat exchange substrate; A shaped substrate is obtained by forming multiple convex and / or concave grafting portions on the heat exchange substrate through a material removal manufacturing process; the grafting portions include multiple grafting joints, and the formed grafting joints are convex or concave portions on the heat exchange substrate. Based on the molded substrate, an additive part is formed on the grafting joint using an additive manufacturing process. The additive part includes an additive joint. The additive joint is connected to the grafting joint. The grafting part and the corresponding additive part constitute a composite heat exchange unit. On the surface of the composite heat exchange unit, heat exchange auxiliary structures are processed by additive manufacturing and / or surface treatment processes.

[0008] Optionally, the heat exchange auxiliary structure includes micro / nano structures on the surface of the composite heat exchange unit; The micro / nano structures are fabricated through surface treatment processes; these processes include laser ablation, chemical deposition, chemical ablation, electrochemical blasting, or sandblasting. The micro / nano structure is formed on at least a portion of the heat exchange wall surface of the composite heat exchange unit.

[0009] Optionally, the distribution density of the micro / nano structure can be varied in a gradient along a preset direction by adjusting processing parameters or by segmented processing. By adjusting processing parameters or using segmented processing, the aspect ratio of the micro / nano structure is made to vary in a gradient along a preset direction. The gradient change can be linear or nonlinear.

[0010] Optionally, the heat exchange auxiliary structure further includes a sealing structure, the sealing structure being manufactured by: The sealing structure is integrally formed on the top surface or upper edge of the composite heat exchange unit using an additive manufacturing process. The bottom surface of the sealing structure forms a flow channel with the side surface of the composite heat exchange unit.

[0011] Optional, also includes: After processing some or all of the composite heat exchange units, a sealing structure is integrally formed with the additive part by additive manufacturing process. After the sealing structure is formed, cleaning work is carried out using the additive manufacturing process; After the cleaning process, the micro-nano structure is processed using a surface treatment process.

[0012] Optionally, the surface treatment process is chemical deposition or chemical ablation; The surface treatment process involves fabricating the micro / nano structure using a segmented processing method, including: Based on the gradient change, the processing area of ​​the surface treatment process is segmented to obtain multiple segmented processing areas; The micro / nano structure is obtained by chemically depositing or chemically ablating the multiple segmented processing areas using a progressive segmented accumulation method.

[0013] Optionally, the material removal manufacturing process includes milling, and the processing of the molded substrate includes: The surface of the heat exchange substrate to be processed is flattened, and a processing coordinate system is established; Based on the machining coordinate system, the planarized surface to be machined is orthogonally parallel milled using a dual-angle forming milling cutter to obtain the shaped substrate.

[0014] Optionally, the additive manufacturing process is a powder-spread metal laser selective melting manufacturing process, and the processing of the additive part includes: A three-dimensional model of the additive part is constructed, and the three-dimensional model is sliced ​​and layered and scan path is planned to obtain slice data and scan path data; Based on the slice data and the scanning path data, layer-by-layer powder spreading and laser selective melting are performed to form the additive part layer by layer on the surface of the grafting part.

[0015] Compared with the prior art, this application has the following advantages: This application combines a material removal manufacturing process with an additive manufacturing process to form an additive part on the grafting surface and construct a composite heat exchange unit. This achieves the integration of material removal and additive manufacturing, retains the excellent thermal conductivity and mechanical properties of the machined substrate, and improves the interfacial bonding strength between the additive structure and the substrate, thus solving the problem of insufficient reliability. Furthermore, by processing heat exchange auxiliary structures on the surface of the composite heat exchange unit, the requirements for the forming freedom and processing accuracy of complex heat exchange structures are met, while reducing manufacturing costs and forming cycle. This can meet the comprehensive requirements of low cost, high precision, high reliability, and high performance in high heat flux density heat exchange scenarios. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of the method in this application; Figure 2 This is a top perspective view of the cold plate in a specific embodiment of this application; Figure 3 This is a schematic diagram of the internal structure of the cold plate in a specific embodiment of this application; Figure 4 This is a perspective view of the composite heat exchange unit structure in a specific embodiment of this application; Figure 5 This is a longitudinal sectional view of the composite heat exchange unit structure in a specific embodiment of this application; Figure 6 This is a perspective view of the grafting portion in a specific embodiment of this application; Figure 7 This is a perspective view of the additive manufacturing part in a specific embodiment of this application; Figure 8 This is a longitudinal sectional view of the additive manufacturing section in a specific embodiment of this application; Figure 9 This is a partial transverse sectional view of the cold plate in a specific embodiment of this application; Figure 10 This is a perspective view of the molded substrate in a specific embodiment of this application; Figure 11 This is a schematic diagram of laser ablation in this application; Figure 12 This is a schematic diagram of the composite heat exchange unit in Example 1.

[0018] In the picture: 1. Heat exchange substrate; 101. Molded substrate; 2. Seal the top cover; 3. Target bonding surface, 301. Composite heat exchange unit, 3011. Grafting part, 30111. Grafting joint, 3012. Additive part, 30121. Additive joint, 30122. Heat exchange wall, 311. First segment, 312. Second segment, 313. Third segment, 314. Fourth segment, 315. Fifth segment; 4. Pulsed laser; 5. Microchannels. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this application, it should be understood that the relative relationship indicated by terms such as "upper" and "lower" is based on the position shown in the drawings, and is used for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, and therefore should not be construed as a limitation of this application.

[0022] In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically defined.

[0023] like Figure 1 As shown, this application provides a method for preparing a composite heat exchange structure. This method is adaptable to various heat exchange products employing composite structure designs. For ease of understanding, a typical heat exchange structure adapted to this method will be described first. An example composite heat exchange structure is shown below. Figures 2-9 As shown, it includes a heat exchange substrate 1, which is made of a metal material with high thermal conductivity, providing a basic load-bearing structure and a heat conduction path for the heat exchange structure. Multiple convex and / or concave grafting portions 3011 are formed on the target mating surface 3 of the heat exchange substrate 1. The grafting portions 3011 are integrally formed with the heat exchange substrate 1 through a material removal manufacturing process, retaining the convex and / or concave portions on the target mating surface 3 as the grafting joint portions 30111, specifically as follows... Figure 6 As shown. Each grafting portion 3011 has one or more grafting joint portions 30111 formed on it, providing a mechanically interlocking joint interface for subsequent additive molding. At least one grafting joint portion 30111 of the grafting portion 3011 has an additive portion 3012 formed on its surface. The additive portion 3012 is covered or stacked on the grafting portion 3011 by an additive manufacturing process. The additive portion 3012 is provided with an additive joint portion 30121 and a heat exchange wall surface 30122. The additive joint portion 30121 is connected to the grafting joint portion 30111 to form a joint interface for fixing the additive portion 3012 and the grafting portion 3011. The heat exchange wall surface 30122 is the exposed surface of the additive portion 3012 after processing, and it is in contact with the working fluid. It is understood that in some embodiments of this application, the additive bonding portion 30121 is not only connected to the grafting bonding portion 30111, but also, since the target bonding surface 3 and the grafting portion 3011 are made of the same material, it means that the additive bonding portion 30121 can be connected to part of the target bonding surface 3 and form a corresponding bonding interface, thereby achieving full coverage of the grafting portion 3011 by the additive bonding portion 3012.

[0024] The grafting part 3011 and the corresponding additive part 3012 together construct a composite heat exchange unit 301, and the side of the composite heat exchange unit 301 is a heat exchange wall surface 30122; a working fluid flow space can be formed between adjacent composite heat exchange units 301, that is, an open or closed flow channel. The surface of the composite heat exchange unit 301 can also be provided with heat exchange auxiliary structures, including but not limited to micro-nano structures for enhancing heat exchange and sealing structures for forming closed flow channels. The heat exchange auxiliary structures are formed by additive manufacturing process and / or surface treatment process.

[0025] Specifically, the heat exchange structure described in this application is a sealed cold plate, and the sealing structure of its heat exchange auxiliary structure is a sealed top cover 2, as shown in the reference. Figure 9As shown, a cold plate with microchannels 5 inside is constructed by combining the bottom surface of the sealed top cover 2 with the side surface (partial heat exchange wall surface 30122) of the composite heat exchange unit 301 of multiple arrays and the target bonding surface 3 on the heat exchange substrate 1.

[0026] It is understood that the above structure is merely an example for ease of description and explanation. In other embodiments of this application, the composite heat exchange unit 301 may adopt an open design, i.e., without a sealing structure such as a sealed top cover 2. Furthermore, the distribution of the composite heat exchange unit 301 may include continuous / segmented linear, curved, or polygonal distributions. The heat exchange wall surface 30122 on its outer surface may also be processed into an irregular curved surface, such as a Triply Periodic Minimal Surface (TPMS). This application does not impose specific limitations. Moreover, all raw materials and equipment used in this application, unless otherwise specified, are conventional commercially available products and general-purpose equipment in the field of heat exchange equipment processing, without any special customization.

[0027] Therefore, the method for preparing the composite heat exchange structure of this application mainly includes the following steps: I. Preparation of heat exchange substrate 1; First, based on the heat dissipation requirements of the target heat exchange scenario, the design and fabrication of the heat exchange substrate 1 are completed. The dimensions of the heat exchange plane that directly contacts the heat source are determined first, ensuring that the heat exchange plane can completely cover the heat-generating area of ​​the heat source. Then, based on the actual installation conditions, auxiliary dimensions such as the thickness of the heat exchange substrate 1 and the installation positioning structure are determined, thus completing the design of the heat exchange substrate 1.

[0028] During the manufacturing stage, CNC machining is used to pre-process the heat exchange substrate 1. Its shape is processed through rough milling and fine milling. After fine milling, the surface roughness and flatness of the target mating surface 3 of the substrate are controlled within the processing requirements, providing a reference plane for the subsequent processing of the grafting part.

[0029] After the heat exchanger substrate blank is machined, the surface of the heat exchanger substrate 1 to be machined is precision leveled, and then the heat exchanger substrate 1 is cleaned, including: First, use an alkaline degreasing agent to ultrasonically clean the surface at 50℃-60℃ for 15-20 minutes to remove cutting oil and impurities; then use anhydrous ethanol to ultrasonically clean the surface for 10 minutes to remove residual degreasing agent; finally, dry the surface with compressed air and store it in a dry environment for later use to avoid surface oxidation affecting subsequent bonding performance.

[0030] II. Forming of the grafting portion and preparation of the forming substrate 101; After the initial preparation of the heat exchange substrate 1 is completed, multiple grafting portions 3011 with outward convexity and / or inward concavity are formed on the target bonding surface 3 of the heat exchange substrate 1 by a material removal manufacturing process, thereby obtaining the molded substrate 101.

[0031] Specifically, taking the grafting part 3011 of the convex quadrangular pyramid structure as an example, the material removal manufacturing process adopts CNC milling. Before machining, the heat exchange substrate 1 is clamped in the fixture of the CNC machining center. A dial indicator is used to align the target mating surface 3 of the substrate, ensuring that the parallelism between the target mating surface 3 and the machine tool table is controlled within 0.01mm. After clamping, the fixture is locked. A machining coordinate system is established in the CNC system of the machine tool, defining the target mating surface 3 of the heat exchange substrate 1 as the Z-axis zero point, and the two mutually perpendicular horizontal directions as the X and Y directions. The X and Y directions are parallel to the two adjacent straight edges of the heat exchange substrate 1, respectively, ensuring that the machining coordinate system coincides with the geometric datum of the substrate.

[0032] After establishing the coordinate system, tool selection and clamping are performed. For the grafting section 3011 of the array-type quadrangular pyramid structure, a double-angle forming milling cutter is selected. The milling cutter cutting edge includes two symmetrical inclined planes, and the included angle between the two inclined planes is equal to the vertex angle of the target quadrangular pyramid. The included angle ranges from 60° to 120°, with a 90° included angle preferred. The tip radius of the milling cutter is no greater than 0.05mm, with a tip radius of no greater than 0.03mm preferred, to ensure the forming accuracy of the quadrangular pyramid structure. After tool clamping, the length and radius compensation settings of the tool are completed using an in-machine tool setter.

[0033] After completing the preparation work, perform orthogonal parallel milling to form the array of square pyramidal grafting parts 3011. The specific steps are as follows: Several parallel first V-shaped grooves are machined along the X direction. All first V-shaped grooves have the same depth and groove spacing. One-cut forming milling is used to achieve the target depth in one cut, avoiding tool marks and dimensional deviations caused by multiple cuts. Several parallel second V-grooves are machined along the Y direction. The second V-grooves are orthogonal to the first V-grooves in the horizontal projection. The depth, groove spacing and cutting strategy of the second V-grooves are exactly the same as those of the first V-grooves, so that the intersection of the projections of the center lines of the second V-grooves and the center lines of the first V-grooves in the XY plane forms a regular grid. After the first and second orthogonal V-grooves intersect, they form an array of square pyramidal microstructures on the workpiece surface. The base of the pyramid is square, and the four inclined surfaces are formed by splicing the inclined surfaces of two sets of orthogonal V-grooves, thus completing the processing of the grafting part 3011. Figure 10 As shown.

[0034] During the processing, the ratio of the height of the grafting part 3011 to the height of any section in the target composite heat exchange unit 301 is controlled to be less than or equal to 0.9, so as to ensure that the subsequent additive part 3012 can completely cover the grafting part 3011, and the outer contour of the composite heat exchange unit 301 is precisely controlled by the additive manufacturing process.

[0035] In other embodiments, for the grafting portion 3011 of the conical, cylindrical, cuboid, or toothed structure, the corresponding forming milling cutter is used to complete the machining by contour milling, and the machining accuracy requirements are the same as those for the above-mentioned quadrangular pyramid structure.

[0036] After the grafting part is processed, the forming substrate is subjected to precision inspection. The key dimensions such as the array spacing, height, and cone angle of the grafting part are inspected using an image measuring instrument to ensure that the dimensional deviation is within ±0.02mm. After passing the inspection, the forming substrate is cleaned a second time to remove cutting debris and oil stains from the surface. After cleaning, it is dried for later use.

[0037] III. Molding of Additive Manufacturing Section and Construction of Composite Heat Exchange Unit; After the molding substrate 101 is prepared, an additive part 3012 is formed on the grafting joint 30111 of the grafting part 3011 by an additive manufacturing process based on the molding substrate 101, so that the additive part 3012 covers the surface of the grafting part 3011, and a composite heat exchange unit 301 is constructed by the grafting part 3011 and the corresponding additive part 3012.

[0038] The additive manufacturing process employs a powder-layout metal laser selective melting manufacturing process, and the specific steps are as follows: First, 3D modeling and design optimization are carried out. A 3D model of the additive part 3012 is constructed in computer-aided design software to ensure that the additive bonding part 30121 of the additive part 3012 and the grafting bonding part 30111 are completely matched and can completely cover the outer surface of the grafting part 3011. At the same time, the model is optimized according to the self-supporting design principle.

[0039] After model optimization, slicing and path planning are performed. The slicing software is used to slice the 3D model along the Z-axis. The layer thickness is set to 20μm to 50μm according to the molding accuracy and metal powder particle size. The 3D model is decomposed into two-dimensional thin layers. Then, a laser scanning path is generated for each layer, and the rotation angle of the interlayer scanning path is set to reduce the accumulation of interlayer stress.

[0040] After completing the slicing and path planning, preparations for printing are carried out. Metal powder of the same material as the heat exchange substrate 1 is selected. The powder is a gas-atomized powder with high sphericity and low oxygen content. Before use, it is dried in a vacuum drying oven to remove moisture from the powder, and then agglomerated particles are removed by sieving.

[0041] The molding substrate 101 is fixed in the molding cavity of the additive manufacturing equipment as a printing substrate. After fixing, the parallelism between the substrate and the molding platform is controlled within 0.05mm.

[0042] Close the molding chamber door, perform vacuuming and inert gas filling inside the chamber, repeat 2-3 times to reduce the oxygen content inside the chamber to below 100ppm, and prevent oxidation of the metal powder during high-temperature melting.

[0043] After completing the preparation work, key process parameters such as laser power, scanning speed, scanning spacing, and layer thickness are set according to the molding material and feature dimensions. Layer-by-layer powder spreading and selective melting molding are then performed. The steps include: The powder feeding cylinder rises to a preset height, and the powder spreading device pushes a layer of uniform metal powder to the substrate area of ​​the forming platform. The high-power laser beam selectively scans and irradiates the powder layer according to the planned path. After the powder absorbs energy and melts, it quickly solidifies and achieves metallurgical bonding with the lower substrate or the already formed layer. After one layer is formed, the forming platform is lowered by one layer thickness. The powder spreading and scanning process is repeated to stack the layers one by one until the entire additive part 3012 is processed, so that the additive part 3012 completely covers the outer surface of the grafting part 3011, and together with the grafting part 3011, they form a composite heat exchange unit 301.

[0044] After the additive manufacturing process 3012 is completed, the part is removed after it has completely cooled to room temperature in the molding cavity. Unmelted metal powder on the surface and in the internal flow channels is removed by vibration and high-pressure inert gas blowing to ensure that the microchannels 5 are unobstructed and free of residue.

[0045] IV. Fabrication of heat exchange auxiliary structures; After the composite heat exchange unit 301 is formed, a heat exchange auxiliary structure is fabricated on the composite heat exchange unit 301 using additive manufacturing and / or surface treatment processes. Depending on the type of heat exchange auxiliary structure and processing requirements, this application provides two process routes, as follows: Process route 1: First, surface treatment is performed to fabricate the micro / nano structure, and then additive molding is used to seal the structure; This route is compatible with visually accessible surface treatment processes such as laser ablation and spraying. Visually accessible surface treatment processes refer to processes such as laser ablation and electrochemical spraying that can only process the exposed surface of the workpiece. The specific steps are as follows: After all composite heat exchange units 301 are processed, the additive manufacturing process cleaning is carried out first. Ultrasonic cleaning is used to thoroughly remove residual powder and debris from the surface and interior of the parts. After cleaning, the parts are dried for later use.

[0046] After cleaning, micro-nano structures are processed on the heat exchange wall surface 30122 through surface treatment. The micro-nano structures are distributed on the heat exchange wall surface in the form of micro-pits, micro-pillars or micro-grooves, which can significantly increase the vaporization core points in the working fluid boiling process and improve heat exchange performance.

[0047] Specifically, taking laser ablation technology as an example, refer to Figure 11As shown, a pulsed laser 4 is used. The posture of the laser head is adjusted so that the laser beam axis forms a 5° angle with the normal of the side wall to be processed, so as to avoid laser reflection damage to the equipment. The fixed parameters for laser processing are set as follows: laser power 32W, scanning speed 0.3m / s, number of ablation cycles 5, spot diameter 50μm, and defocusing amount 0.

[0048] For micro / nano structures with gradient distributions, fabrication is carried out using a method of adjusting fabrication parameters, including: Along the preset working fluid flow direction, all heat exchange walls 30122 of the composite heat exchange unit 301 are divided into multiple continuous processing sections. Processing parameters are constant within each section, while parameters gradually change linearly between sections. This causes the distribution density and aspect ratio of the micro / nano structures to decrease linearly or non-linearly along the working fluid inlet to outlet direction. After processing, the parts are ultrasonically cleaned to remove surface ablation slag and debris, completing the micro / nano structure processing. The distribution density of the micro / nano structures is the number of micro / nano structures per unit area; the aspect ratio of the micro / nano structures is the ratio of their depth to their width, which can be represented by a local average value in specific statistics.

[0049] At this point, if an open structure is being processed, cleaning and stress relief work is performed, resulting in a heat exchange device without a sealed top cover 2, which can be used for immersion heat exchange. If the cold plate in the aforementioned example is being processed, subsequent process steps are continued.

[0050] After the micro-nano structure is fabricated, the part is clamped again in the forming cavity of the additive manufacturing equipment. Using the same powder-spreading metal laser selective melting process as mentioned above, a sealing cover 2 is integrally formed on the top of the composite heat exchange unit 301. The sealing structure and the additive part 3012 below form a complete metallurgical bond. During the processing, the span of the suspended part of the sealing structure is controlled to not exceed 8mm to ensure that the cavity is formed smoothly without the need for additional auxiliary support.

[0051] After the sealing structure is formed, post-processing steps such as powder cleaning and washing are performed again.

[0052] Process route 2: First, additively form the sealing structure, then perform surface treatment to process the micro / nano structure; This route is compatible with fully wetted surface treatment processes such as chemical deposition and chemical ablation. Fully wetted surface treatment processes refer to processes such as chemical deposition and chemical ablation that can process surfaces inside closed flow channels; the specific steps are as follows: After all composite heat exchange units 301 are processed, there is no need to interrupt the additive manufacturing process. The same set of equipment and processes are used to continue to form the sealing cover 2 layer by layer on the top of the composite heat exchange unit 301, so that the sealing structure and the additive part 3012 are completely integrally formed, forming a continuous metallurgical bond, avoiding positioning deviation and poor bonding problems caused by secondary clamping.

[0053] After the sealing structure is formed, the parts are removed after cooling to room temperature in the molding cavity. The complete cleaning process includes: first, preliminary powder removal is completed by vibration and high-pressure gas blowing; then, ultrasonic cleaning combined with high-pressure fluid flushing is used to thoroughly clean the inside of the closed flow channel to ensure that there is no residual powder or impurities in the flow channel. After cleaning, the parts are dried for later use.

[0054] After cleaning, micro- and nanostructures are fabricated in microchannel 5 through surface treatment processes. For micro- and nanostructures with gradient distribution, a progressive segmented accumulation method in the segmented processing method is used to achieve molding, including: First, based on the preset gradient change, the flow channel is segmented along the working fluid flow direction to obtain multiple continuous segmented processing zones; Then, by controlling the wetting section of the processing medium in the flow channel, the first segment processing area on the inlet side of the working medium is wetted only for processing. Then, the number of wetting segments is gradually increased, so that the total processing time of each segment decreases gradually along the flow direction of the working medium. Finally, the distribution density of micro-nano structures and the gradient change of the aspect ratio decreasing linearly along the flow direction of the working medium are achieved.

[0055] After processing, the inside of the flow channel is neutralized, cleaned, and dried to complete the fabrication of the micro-nano structure.

[0056] After the heat exchange auxiliary structure is processed, the parts undergo final post-processing, such as stress-relieving annealing or aging treatment, to eliminate residual thermal stress generated during the processing.

[0057] Similarly, if an open structure is fabricated, there is no need to fabricate a sealed top cover 2. Instead, a fully wetted surface treatment process such as chemical deposition and chemical ablation can be directly performed. Finally, cleaning and stress relief work are carried out to obtain a heat exchange device without a sealed top cover 2, which can be used for immersion heat exchange.

[0058] Example 1; This embodiment takes the processing of the aforementioned cold plate as an example. The flow channel coverage area is 45mm × 54mm, and the composite heat exchange unit 301 has a conical cross-section with protruding ridges. Figure 12 As shown, the composite heat exchange unit 301 is divided into 5 sections, including the first section 311, the second section 312, the third section 313, the fourth section 314, and the fifth section 315. The length of each section of the composite heat exchange unit 301 is 10mm, and the spacing between each section is 1mm. Specifically, the micro-nano structure is processed by segmented laser processing.

[0059] First, the heat exchange substrate 1 is prepared, the base of the copper cold plate is processed, and a micro pyramid array with a depth of 0.5 mm is prepared by using a double-angle forming milling cutter with an included angle of 90° in the horizontal and vertical milling method. Finally, the cone-shaped microchannel layer is printed on the base by powder-spreading 3D printing. The composite heat exchange unit 301 is designed with a cone angle of 45° and the height increases linearly along the working fluid flow direction. The printing material is copper.

[0060] The composite heat exchange unit 301 has an isosceles triangle cross-section with a 45° apex angle and a base width that gradually increases along the flow direction. The specific design parameters are as follows: The initial cross-section width of the first segment 311 is 1mm, and the final cross-section width is 1.3mm. The initial cross-section width of the second segment 312 is 1.3mm, and the final cross-section width is 1.6mm. The initial cross-section width of the third segment 313 is 1.6mm, and the final cross-section width is 1.9mm. The initial cross-section width of the fourth segment 314 is 1.9mm, and the final cross-section width is 2.2mm. The initial cross-section width of the fifth segment 315 is 2.2mm, and the final cross-section width is 2.5mm.

[0061] Next, the laser ablation parameters were set. Pulsed laser 4 was a nanosecond pulsed fiber laser with a wavelength of 1064 nm and a maximum power of 40 W. Fixed parameters were set as follows: laser power 32 W, scanning speed 0.3 m / s, 5 ablation cycles, spot diameter approximately 50 μm, and defocusing amount 0. Gradient ablation was performed along the flow direction, with the following ablation parameters: The first segment has an ablation spacing of 300 μm, a scanning spacing of 15 μm, and an aspect ratio of 0.4 to 0.6. The second segment has an ablation spacing of 350 μm, a scanning spacing of 18 μm, and an aspect ratio of 0.35 to 0.5. The third segment has an ablation spacing of 400 μm, a scanning spacing of 21 μm, and an aspect ratio of 0.3 to 0.45. The fourth segment has an ablation spacing of 450 μm, a scanning spacing of 24 μm, and an aspect ratio of 0.25 to 0.4. The fifth segment has an ablation spacing of 500 μm, a scanning spacing of 27 μm, and an aspect ratio of 0.2 to 0.35.

[0062] In this embodiment, the micro-nano structure is a micro-cavity within a porous trench structure formed by laser ablation on the surface of the channel wall. The trench width is approximately equal to the ablation spacing, and the trench depth is 50 μm to 100 μm. The diameter of the micro-pits within the trench is 20 μm to 50 μm and they are randomly distributed. The density of the micro-pits is inversely proportional to the scanning spacing.

[0063] Specifically, this embodiment achieves a gradient increase in trench width from 300μm to 500μm, a gradient decrease in micropit density from approximately 4400 pits / mm² to approximately 1400 pits / mm², and a gradient decrease in micropit depth-to-width ratio from approximately 0.6 to approximately 0.3 by continuously increasing the ablation spacing.

[0064] Furthermore, during the laser ablation process in this embodiment, the laser head is adjusted to form a 5° angle with the channel wall normal and scanned section by section along the channel length. The filling method is grating filling. The processing parameters are constant within each section and linearly change between sections. After processing, ultrasonic waves are used to remove residual slag.

[0065] Compared with cold plates of the same structure and size without micro / nano structures, the technical effects of this embodiment are as follows: A. In terms of heat transfer performance, uniform laser ablation can increase the heat transfer coefficient of the two phases by 70% to 150%. In this embodiment, gradient ablation maintains an optimal spacing of 300 μm in the inlet region to ensure rapid boiling start-up. The outlet region gradually transitions to 500 μm to avoid excessive bubble aggregation, which can further delay the start of film boiling and increase the critical heat flux density.

[0066] B. Regarding flow resistance characteristics, laser ablation reduces the average pressure drop of the microchannel by 10% to 30%. In this embodiment, by reducing the density of micro-pits and the aspect ratio in the outlet area, the pressure drop can be further reduced by 8% to 12%, effectively mitigating the risk of gas blockage.

[0067] C. In terms of flow stability, laser ablation of the surface can significantly suppress periodic backflow and rewetting flow, reduce fluctuations in wall temperature and pressure drop. The gradient design in this embodiment maintains strong boiling in the inlet region and suppresses excessive vaporization in the outlet region, further improving the flow stability of the entire channel.

[0068] Finally, it should be noted that the above content is only used to illustrate the technical solution of this application, and is not intended to limit the scope of protection of this application. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this application shall not depart from the substance and scope of the technical solution of this application.

Claims

1. A method for preparing a composite heat exchange structure, comprising: Preparation of heat exchange substrate; The feature is that a plurality of convex and / or concave grafting portions are formed on the heat exchange substrate by a material removal manufacturing process to obtain a shaped substrate; the grafting portion includes a plurality of grafting joints, and the formed grafting joints are convex or concave portions on the heat exchange substrate. Based on the molded substrate, an additive part is formed on the grafting joint using an additive manufacturing process. The additive part includes an additive joint. The additive joint is connected to the grafting joint. The grafting part and the corresponding additive part constitute a composite heat exchange unit. On the surface of the composite heat exchange unit, heat exchange auxiliary structures are processed by additive manufacturing and / or surface treatment processes.

2. The method for preparing the composite heat exchange structure according to claim 1, characterized in that, The heat exchange auxiliary structure includes micro-nano structures on the surface of the composite heat exchange unit; The micro / nano structures are fabricated through surface treatment processes; these processes include laser ablation, chemical deposition, chemical ablation, electrochemical blasting, or sandblasting. The micro / nano structure is formed on at least a portion of the heat exchange wall surface of the composite heat exchange unit.

3. The method for preparing the composite heat exchange structure according to claim 2, characterized in that, By adjusting processing parameters or using segmented processing, the distribution density of the micro-nano structure is processed to vary in a gradient along a preset direction. By adjusting processing parameters or using segmented processing, the aspect ratio of the micro / nano structure is made to vary in a gradient along a preset direction. The gradient change can be linear or nonlinear.

4. The method for preparing the composite heat exchange structure according to claim 3, characterized in that, The heat exchange auxiliary structure also includes a sealing structure, the processing of which includes: The sealing structure is integrally formed on the top surface or upper edge of the composite heat exchange unit using an additive manufacturing process. The bottom surface of the sealing structure forms a flow channel with the side surface of the composite heat exchange unit.

5. The method for preparing the composite heat exchange structure according to claim 4, characterized in that, Also includes: After processing some or all of the composite heat exchange units, cleaning work is carried out using additive manufacturing processes; After the cleaning process, the micro / nano structure is processed using a surface treatment process; After the micro-nano structure is fabricated, a sealing structure integrally formed with the additive part is fabricated using an additive manufacturing process.

6. The method for preparing the composite heat exchange structure according to claim 5, characterized in that, The surface treatment process is laser ablation, electrochemical spraying, or sandblasting. The surface treatment process involves processing the micro / nano structure by adjusting processing parameters. Processing parameters include processing power, processing distance, number of processing cycles, and processing speed.

7. The method for preparing the composite heat exchange structure according to claim 4, characterized in that, Also includes: After processing some or all of the composite heat exchange units, a sealing structure is integrally formed with the additive part by additive manufacturing process. After the sealing structure is formed, cleaning work is carried out using the additive manufacturing process; After the cleaning process, the micro-nano structure is processed using a surface treatment process.

8. The method for preparing the composite heat exchange structure according to claim 7, characterized in that, The surface treatment process is chemical deposition or chemical ablation; The surface treatment process involves fabricating the micro / nano structure using a segmented processing method, including: Based on the gradient change, the processing area of ​​the surface treatment process is segmented to obtain multiple segmented processing areas; The micro / nano structure is obtained by chemically depositing or chemically ablating the multiple segmented processing areas using a progressive segmented accumulation method.

9. The method for preparing the composite heat exchange structure according to claim 1, characterized in that, The material removal manufacturing process includes milling, and the processing of the molded substrate includes: The surface of the heat exchange substrate to be processed is flattened, and a processing coordinate system is established; Based on the machining coordinate system, the planarized surface to be machined is orthogonally parallel milled using a dual-angle forming milling cutter to obtain the shaped substrate.

10. The method for preparing the composite heat exchange structure according to claim 1, characterized in that, The additive manufacturing process is a powder-spread metal laser selective melting manufacturing process, and the processing of the additive part includes: A three-dimensional model of the additive part is constructed, and the three-dimensional model is sliced ​​and layered and scan path is planned to obtain slice data and scan path data; Based on the slice data and the scanning path data, layer-by-layer powder spreading and laser selective melting are performed to form the additive part layer by layer on the surface of the grafting part.

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