A manufacturing process method of a precision die-casting cold plate

Abstract

The present application relates to the technical field of electronic equipment heat dissipation, and particularly relates to a manufacturing process method of a precision die-casting liquid cooling cold plate. The process splits the cold plate into a die-casting shell and an independent cover plate, and designs a partitioned allowance for the blank. The shell is formed by vacuum die casting, the cavity is pre-vacuumized to below 10 kPa, and a die-casting part with a density of 97% to 99% is obtained. The cover plate is processed from a rust-proof aluminum alloy sheet. The shell and the cover plate are connected by friction stir welding, and the welding deformation is controlled by cooperating with a partitioned profiling and a hydraulic follow-up reverse deformation tool. The finished product is obtained after secondary aging treatment, finishing and sealing detection. The present application solves the problems of insufficient density of the die-casting cold plate, difficult control of welding deformation and substandard sealing reliability.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation technology for electronic devices, and more specifically to a molding process for a precision die-cast liquid cooling plate for high-power electronic equipment. Background Technology

[0002] With the rapid development of high-power electronic equipment towards higher integration and miniaturization, the heat flux density of chips and power modules continues to rise, making traditional air cooling methods insufficient to meet heat dissipation demands. Liquid cooling technology, with its high specific heat capacity and forced convection heat transfer capability, offers 10-25 times higher heat dissipation efficiency than air cooling, and has become a core technology solution for thermal management of high-power electronic equipment. As the core heat exchange component in a liquid cooling system, the manufacturing quality of the liquid cooling plate directly determines the reliability and lifespan of the entire heat dissipation system.

[0003] Currently, there are two main technical approaches to manufacturing liquid-cooled cold plates: The first approach is integral machining, which involves using CNC milling to directly machine the internal flow channel structure from a single piece of aluminum alloy blank, and then sealing it with a cover plate. The advantage of this approach is its high degree of freedom in flow channel design, allowing for relatively complex flow channel configurations. However, this approach has the following prominent problems: First, it involves a large amount of material removal, with a material utilization rate typically less than 30%, resulting in high manufacturing costs and long production cycles; second, for large-sized cold-rolled plates, the uneven distribution of residual stress after removing a large amount of material from the entire piece can easily lead to product deformation; third, the surface roughness of the flow channel is limited by the tool path, making it difficult to achieve optimal heat exchange; and fourth, the limited travel of the equipment prevents the machining of ultra-large cold-rolled plates.

[0004] The second approach is die casting, which involves using high-pressure die casting to form the complex flow channel structure within the shell in a single process, followed by sealing via welded cover plates. This approach offers the advantage of efficiently forming complex structures, high material utilization, and suitability for mass production. However, existing die-casting cold-plate processes also face significant technical challenges: (1) Insufficient internal density of die castings. In the traditional die casting process, high-speed filling can cause gas to be trapped in the mold cavity, forming porosity and shrinkage cavities inside the casting, especially in areas with varying wall thickness and at the far end. Internal pores not only reduce the mechanical strength and thermal conductivity of the casting, but may also become a source of crack initiation during subsequent welding and use, seriously affecting product reliability.

[0005] (2) Welding deformation of long welds is difficult to control. The welds of the cover plates of die-cast cold plates are usually long (up to hundreds of millimeters or even more than one meter). The uneven heat input generated during friction stir welding causes significant thermal deformation between the shell and the cover plate, and the flatness of the large surface after welding is difficult to meet the assembly requirements. Traditional rigid fixing fixtures cannot adapt to the thermal deformation characteristics of large thin-walled castings, often resulting in defects such as weld edge collapse and local warping.

[0006] (3) Inadequate sealing reliability. Liquid cooling plates in high-power electronic equipment typically need to withstand working pressures of over 2.0 MPa and operate reliably within a temperature range of -50℃ to +65℃, while also passing rigorous vibration and impact tests. The combined effect of micropore defects inside die-cast parts and residual welding stress can easily lead to sealing failures under harsh operating conditions.

[0007] In summary, the existing manufacturing process for die-cast cold plates still has significant shortcomings in terms of internal density control, welding deformation suppression, and sealing reliability assurance, and a systematic process solution is urgently needed. Summary of the Invention

[0008] This invention addresses the technical problems existing in the current die-cast cold plate manufacturing process, such as insufficient internal density, difficulty in controlling welding deformation of long welds, and substandard sealing reliability. It provides a manufacturing process method for precision die-cast cold plates. Through the systematic integration of processes such as structural decomposition and partitioned allowance design, vacuum die casting, friction stir welding and anti-deformation tooling coordinated control, and post-weld aging treatment, it achieves the manufacturing of precision die-cast liquid-cooled cold plates with high density, low deformation, and high sealing reliability.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A manufacturing process for precision die-cast cold plate includes the following steps: Step 1: Structural Disassembly and Blank Allowance Design: The liquid cooling plate is disassembled into two parts: a die-cast shell body and an independent cover plate. The shell blank is designed with zoned allowances as follows: A rough machining allowance of 0.5mm and a post-weld finishing machining allowance of 0.75mm are reserved on the front large surface (the mounting surface in contact with the heating element), for a total allowance of 1.25mm; a machining allowance of 0.5mm is reserved on the reverse boss and welded lap surface; no machining allowance is reserved on the internal flow channel surface, and secondary machining is strictly prohibited to ensure the original cast state of the flow channel surface and heat exchange efficiency; no allowance is reserved on other non-mating surfaces to achieve near-net-shape forming.

[0010] Structural optimization: A draft angle of 1°~3° is added to the heat dissipation boss and weight reduction groove to facilitate demolding and reduce stress concentration; the structural transition uses a rounded transition of R1 or more to avoid stress concentration and poor filling at sharp corners; the through hole is designed as a tapered hole to facilitate demolding and improve dimensional accuracy.

[0011] Mold flow simulation and gating system optimization: Numerical simulation technology is used to simulate and analyze the die casting filling process. The position, cross-sectional size, number and layout of the gating gate, and position and capacity of the overflow groove are optimized in multiple rounds to ensure smooth aluminum liquid filling, smooth venting, and uniform temperature field, and to minimize air entrapment and cold shut defects.

[0012] Step 2: Die casting of the shell, which includes the following sub-steps: 2.1 Smelting and Degassing: Aluminum alloy materials are used for smelting. During the smelting process, inert gas is first introduced for refining to remove hydrogen and non-metallic inclusions from the melt. Then, vacuum degassing is performed to further reduce the gas content of the melt.

[0013] 2.2 Vacuum Die Casting: After mold closing, the mold cavity is pre-evacuated to a vacuum level below 10 kPa, significantly reducing the amount of residual gas in the cavity. A large die casting machine of 1600t or higher is used for die casting, with the die casting specific pressure controlled at 50~70 MPa and the gate filling speed controlled at 40~50 m / s. Under these process parameters, molten aluminum rapidly fills the cavity under high pressure, and the vacuum environment effectively suppresses gas entrapment, resulting in high-density die castings.

[0014] 2.3 Aging treatment: After the die casting is trimmed, stress-relieving annealing is performed at a temperature of 200~250℃ for 3~5 hours to eliminate residual casting stress, stabilize the dimensions of the casting, and prevent deformation caused by stress release during subsequent processing and welding.

[0015] Step 3: Cover Plate Preparation: The cover plate is prepared using 5A05 rust-resistant aluminum alloy sheet through machining. 5A05 alloy possesses excellent corrosion resistance and weldability, and exhibits good compatibility with the AlSi-based aluminum alloy of the die-cast shell through friction stir welding. The cover plate blank thickness is 3.2mm, and the overlap width of the large surfaces is not less than 2.5mm to ensure sufficient support area and weld strength during the welding process.

[0016] Step 4: Friction stir welding connection, which specifically includes the following sub-steps: 4.1 Stirring Head and Welding Parameters: A double-ring right-hand threaded stirring head is used, with a shoulder diameter of 8mm and a stirring pin length of 3.5mm. The welding speed is 100~150mm / min, the spindle speed is 1000~1500r / min, and the stirring head tilt angle is 2°~3°. Within the above parameter range, the frictional heat generated by friction stir welding fully plasticizes the base material without melting it, resulting in a dense, forged structure in the weld, free from weld porosity defects.

[0017] 4.2 Welding tooling: Zoned profiling and hydraulic follow-up anti-deformation tooling are adopted to control thermal deformation during the welding of long welds. Said tooling comprises a plurality of zoned profiling stainless steel support blocks (preferably 18 blocks), each support block is machined according to the profiling contour of the shell bottom surface, and fits well with the outer surface of the shell. A stainless steel gasket with a thickness of 0.1~1mm is padded under each support block. By adjusting the thickness of gaskets at different positions, a preset anti-deformation amount can be applied to the shell to offset welding thermal deformation. The tooling is also equipped with a hydraulic follow-up pressure plate, which applies a dynamic pressing force near the welding area during the welding process, and adjusts the pressing position in real time as the stirring head moves. In addition, the tooling is provided with spring pins and a side positioning module to ensure the relative positioning accuracy of the shell and the cover plate.

[0018] 4.3 Welding sequence: A welding sequence of welding the serpentine flow channel cover plate first, and then welding the plug cover plates at both ends is adopted. The weld in the serpentine flow channel area is the longest and produces the largest cumulative deformation. Preferential welding allows a certain degree of stress release and orthopedic treatment on the flow channel weld area through the welding thermal cycle of shorter welds during the subsequent welding of the plug cover plates.

[0019] Step 5, Post-weld treatment and finish machining, which specifically comprises the following sub-steps: 5.1 X-ray flaw detection: X-ray flaw detection is performed on the welded assembly, and the inspection standards are as follows: no cracks in the weld, the size of internal pores is not more than 0.2mm, and the flatness of the large surface of the welded assembly is not more than 0.5mm.

[0020] 5.2 Secondary aging treatment: Secondary aging treatment is performed on the assembly that passes the flaw detection, the treatment temperature is 200~250°C, and the holding time is 3~5 hours. The purpose of secondary aging is to eliminate the welding residual stress generated during friction stir welding, stabilize the structure of the weld area and the heat affected zone, and improve the dimensional accuracy and the reliability of long-term use.

[0021] 5.3 Finish machining: Finish machining is performed on the front large surface, removing 0.75mm of post-weld finishing allowance, to reach the flatness and surface roughness required by the drawing. At the same time, features such as mounting holes and port interfaces are finish machined to the final dimensional accuracy.

[0022] 5.4 Sealing test: Sealing test is carried out by means of a combination of air pressure leak detection and water pressure pressure holding detection. First, air pressure leak detection is carried out, the detection pressure is 0.6-1.6MPa, and it is qualified if there is no pressure drop after 15min of pressure holding; then water pressure pressure holding detection is carried out, the detection pressure is 2.5MPa, and it is qualified if there is no leakage after 15min of pressure holding. The double detection ensures the sealing reliability of the product under high-pressure working conditions.

[0023] The beneficial effects of the present invention are as follows: (1) High internal density of die castings. By controlling the vacuum degree of the mold cavity to below 10 kPa through vacuum die casting process, combined with the dual melt treatment of inert gas refining and vacuum degassing, the entrapment of gas and oxide inclusions are effectively eliminated, the density of die castings reaches more than 98%, and the internal pore size in key areas is controlled to below 0.2 mm, which significantly improves the mechanical properties and thermal conductivity of the castings.

[0024] (2) Excellent welding deformation control. By applying a preset anti-deformation amount through a combination of partitioned contour support blocks and adjustable shims, and with the dynamic clamping of the hydraulic follow-up pressure plate, precise control of thermal deformation during friction stir welding of long welds is achieved. The flatness of the large surface after welding reaches less than 0.4mm, meeting the requirements of precision assembly.

[0025] (3) High weld quality and reliable sealing. Friction stir welding adopts a solid-state bonding method, and the weld is free of fusion porosity defects. The tensile strength of the weld reaches 189~201MPa, which is close to the strength of the base material. After double sealing tests of air pressure leak detection and water pressure holding, there was no leakage at air pressure of 0.6-1.6MPa and water pressure of 2.5MPa for 15 minutes, respectively, which meets the stringent requirements of high-power electronic equipment.

[0026] (4) Excellent overall reliability. The product has passed the GJB 150.16A vibration and shock test and the high and low temperature storage test of -50℃ to +65℃, which verifies its long-term reliable operation capability under extreme environmental conditions.

[0027] (5) The process system is systematic and highly repeatable. This invention systematically integrates key processes such as vacuum die casting, partitioned allowance design, friction stir welding and anti-deformation tooling coordinated control. The processes cooperate and support each other to form a complete precision die casting cold plate manufacturing process system, which has good repeatability and mass production applicability. Attached Figure Description

[0028] Figure 1 This is a three-dimensional structural diagram of the liquid-cooled cold plate in an embodiment of the present invention, wherein 1(a) is the top surface, 1(b) is the bottom surface, and 1(c) is the side surface.

[0029] Figure 2 This is a flowchart of the precision die-casting cold plate forming process in an embodiment of the present invention.

[0030] Figure 3 This is a distribution diagram of the contour support blocks in an embodiment of the present invention.

[0031] Figure 4 The stainless steel gasket is shown in this embodiment of the invention.

[0032] Figure 5 This is an internal quality inspection diagram of the die-cast shell in an embodiment of the present invention.

[0033] Figure 6 This is a weld quality inspection diagram in an embodiment of the present invention, wherein 6(a) is a high-magnification metallographic diagram of the weld. Figure 6 (b) is a diagram of the X-ray detection results.

[0034] The numbers in the diagram are: 1-Die-cast cold plate shell; 2-Cover plate; 3-Cold plate plug; 4-Stainless steel gasket. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0036] This embodiment uses a complex flow channel and a double-sided deep cavity liquid-cooled plate as an example for description. The plate has external dimensions of approximately 460mm × 170mm × 55mm and an average wall thickness of 3mm. However, the scope of protection of this invention is not limited to this specific size and structure.

[0037] 1. Material Selection The die-cast shell is made of AlSi8 eutectic aluminum alloy with the following properties: thermal conductivity 150 W / (m·K), tensile strength 200 MPa, yield strength 150 MPa, and elongation 2%. The cover plate is made of 5A05 rust-proof aluminum alloy sheet with a thickness of 3.2 mm.

[0038] 2. Die-cast shell forming Reference Figure 1 The three-dimensional structure shown and Figure 2 The process flow shown is as follows: 1) Blank allowance: According to the design in step one, the total allowance of the front surface is 1.25mm, the allowance of the back boss and overlapping surface is 0.5mm, and no allowance is left on the inner surface of the flow channel.

[0039] 2) Optimized design: such as Figure 1 As shown, the heat dissipation boss and weight reduction groove have an increased draft angle of 1° and a transition fillet radius of R1 or more; the 16 through holes are designed as tapered holes (φ7.1 / φ6.6mm) with a draft angle of 1°.

[0040] 3) Smelting and degassing: Argon refining combined with vacuum degassing is adopted.

[0041] 4) Vacuum die casting: On a 1600t die casting machine, the cavity is evacuated to 10kPa, the specific pressure is 60MPa, the gate cross-sectional area is 630mm², and the filling speed is 48m / s.

[0042] 5) Aging treatment: Keep warm at 220℃ for 4 hours.

[0043] 6) Results: The flatness of the front side of the 10 blanks was 0.261~0.366mm, and the flatness of the back side was 0.313~0.373mm, both ≤0.4mm; the density was 97%~99%; the internal quality was as follows. Figure 5As shown, it meets the requirements for critical areas in GB / T 15114—2023.

[0044] 3. Cover plate processing The structural position of cover plate 2 is as follows Figure 1 As shown. The 5A05 sheet is machined and formed, with a large surface overlap width of ≥2.5mm and a blank thickness of 3.2mm.

[0045] 4. Friction stir welding 1) Process parameters: φ8mm shoulder of stirring head, double ring, 3.5mm long right-hand thread of stirring needle; welding speed 120mm / min, rotation speed 1200r / min, tilt angle 2.5°.

[0046] 2) Fixture: 18 partitioned contour support blocks are arranged at the bottom, as shown in the diagram. Figure 3 As shown; each piece has four 0.1~0.8mm stainless steel shims pre-placed underneath (e.g. Figure 4 As shown, determined through iteration); a hydraulic follow-up pressure plate is installed above; and spring pins are used for side positioning.

[0047] 3) Welding sequence: such as Figure 1 As shown, first weld the serpentine flow channel cover plate, then weld the end caps 3 at both ends.

[0048] 4) Results: The flatness of the large surface after welding is ≤0.4mm; the high-magnification metallographic image of the weld is as follows: Figure 6 As shown in (a), X-rays are as follows Figure 6 As shown in (b), the results show that the weld has no cracks and the porosity is ≤0.2mm; the tensile strength of the weld is 189~201MPa.

[0049] 5. Post-processing and testing Post-weld processing and inspection procedures are as follows: Figure 2 As shown: 1) Secondary aging: Keep warm at 220℃ for 4 hours.

[0050] 2) Finishing: Achieve drawing accuracy ±0.05mm and flatness 0.1mm.

[0051] 3) Sealing test: First, pressurize with 0.6MPa air pressure for 15 minutes, then pressurize with 2.5MPa water pressure for 15 minutes. All 10 finished products showed no leakage or deformation.

[0052] 4) Environmental testing: Randomly selected finished products were subjected to vibration and impact tests and high and low temperature storage tests (-50℃~+65℃, 65℃ / 48h, -50℃ / 24h). All passed, and there were no abnormalities in size and sealing.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A manufacturing process for a precision die-cast cold plate, characterized in that, Includes the following steps: Step 1: Structural Decomposition and Blank Allowance Design: The liquid cooling plate is decomposed into a shell and a cover plate; the shell is partitioned with allowance design, where the front is the heat dissipation surface, and its machining allowance is the sum of the rough machining allowance and the post-weld finishing allowance; the back includes the flow channel boss and the cover plate welding overlap surface, and its machining allowance is the rough machining allowance; no machining allowance is reserved on the internal flow channel surface and it is die-cast in one piece; no allowance is reserved on other non-mating surfaces; draft angles are added to the flow channel boss and the shell weight reduction area, and fillets are set at the structural transitions; the gating system is iteratively optimized through mold flow simulation; Step 2, Shell Die Casting: Inert gas refining combined with vacuum degassing is used during aluminum alloy melting; vacuum die casting is used for forming, the mold cavity is pre-vacuumed to below 10 kPa, the die casting specific pressure is 50~70 MPa, and the gate filling speed is 40~50 m / s; the die casting is subjected to stress-relieving annealing after trimming. Step 3, Cover plate preparation: The cover plate is made of rust-proof aluminum alloy sheet and machined into shape. The overlap width of the cover plate is not less than 2.5mm. Step 4, Friction Stir Welding Connection: The cover plate is welded to the shell using friction stir welding. During the welding process, the deformation is controlled by a partitioned contour support and a hydraulic follow-up anti-deformation fixture. The fixture includes several partitioned contour support blocks. Each support block is equipped with a shim underneath to adjust the support height and a hydraulic follow-up pressure plate to achieve dynamic clamping of the welding area. Step 5, Post-weld treatment and finishing: Non-destructive testing is performed on the welded components, followed by secondary aging treatment to eliminate residual welding stress, then finishing, and finally sealing test to obtain the finished precision die-cast liquid cooling plate.

2. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The roughing allowance is 0.5 mm, and the finishing allowance after welding is 0.75 mm.

3. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The draft angle mentioned in step one is 1°~3°, and the fillet radius at the structural transition is R1 or higher.

4. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The stress-relief annealing process in step two is carried out at a temperature of 200-250°C for 3-5 hours.

5. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The process parameters for friction stir welding described in step four are as follows: a double-ring right-hand threaded stirring head is used, with a shoulder diameter of 8 mm, a stirring pin length of 3.5 mm, a welding speed of 100~150 mm / min, a spindle speed of 1000~1500 r / min, and a stirring head tilt angle of 2°~3°.

6. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The number of partitioned contour support blocks in step four is 12 to 24, the thickness of the gasket is 0.1 to 1 mm, and both the support blocks and the gasket are made of stainless steel.

7. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The welding sequence described in step four is as follows: first weld the cover plate of the serpentine flow channel area, and then weld the cover plates of the end cap areas.

8. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The non-destructive testing described in step five is X-ray testing, and the testing standards are: no cracks in the weld, hole size ≤ 0.2 mm, and flatness of the welded assembly ≤ 0.5 mm.

9. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The temperature for the secondary aging treatment in step five is 200~250℃, and the holding time is 3~5 hours.

10. The manufacturing process of the precision die-cast cold plate according to claim 1, characterized in that, The sealing test described in step five includes air pressure leak detection and water pressure holding test, wherein the air pressure leak detection pressure is 0.6-1.6MPa and the water pressure holding test pressure is 2.5MPa.

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