A secondary degassing laser remelting sealing method for a VC uniform temperature plate

Abstract

The present application relates to VC uniform temperature plate manufacturing technical field, disclose a kind of VC uniform temperature plate secondary degassing laser remelting sealing method, the method comprises: the vacuum degassing of VC uniform temperature plate sealed cavity of having been injected liquid is extracted, while heating VC uniform temperature plate body, make non-condensable gas gather to the upper portion of injection pipe, maintain continuous vacuum condition, along the circumferential pulse spot welding of injection pipe root portion is formed first annular sealing weld, subsequently heating injection pipe area, make its internal residual non-condensable gas gather to top, carry out continuous laser seal welding above first annular sealing weld and form second annular sealing weld, complete sealing, wherein second annular sealing weld partially overlaps the upper edge of first annular sealing weld.The present application is cooperated by twice heating degassing and double laser seal welding, effectively removes residual non-condensable gas, realizes low thermal damage, high airtightness of injection port sealing, and is suitable for the high reliability sealing manufacturing of ultrathin VC uniform temperature plate.

Description

Technical Field

[0001] This invention relates to the field of VC vapor chamber manufacturing technology, and in particular to a method for secondary degassing and laser remelting sealing of VC vapor chambers. Background Technology

[0002] As electronic devices rapidly evolve towards higher performance and thinner designs, efficient chip heat dissipation has become a key bottleneck restricting product reliability and user experience. VC vapor chambers, with their excellent two-dimensional heat transfer capabilities and flexible form factor adaptability, are widely used in compact but heat-generating electronic devices such as smartphones, high-performance laptops, servers, and graphics cards, becoming a core heat dissipation component for solving localized hotspots.

[0003] The VC vapor chamber needs to maintain a high vacuum environment to ensure the efficient operation of the working fluid's gas-liquid phase change cycle. Currently, the mainstream sealing process involves evacuating the cavity through the injection tube after liquid injection, and then sealing the injection port using physical extrusion or laser welding. However, one degassing operation is insufficient to completely remove the trace amounts of non-condensable gases adsorbed on the inner wall of the cavity and dissolved in the working fluid. These residual gases not only severely restrict the subsequent service life of the product, but may also precipitate at the sealing welding temperature, causing weld porosity defects and directly affecting the weld airtightness.

[0004] Among existing sealing technologies, pressure welding can quickly achieve initial sealing, but its long-term sealing reliability is insufficient. While laser welding can form a high-strength weld with metallurgical bonding, the laser process window is narrow for ultra-thin and heat-sensitive VC vapor chambers, making it difficult to balance welding quality and product yield. Therefore, how to achieve a highly reliable airtight seal while effectively eliminating residual non-condensable gases and ensuring low thermal damage has become a pressing technical problem to be solved in the VC vapor chamber manufacturing field.

[0005] Existing technologies include improved solutions for cutting off gas-containing injection pipe sections after laser sealing, as well as attempts to use a composite process of pressure welding and laser welding. However, these solutions have not yet solved the problems of circumferential weld start-stop defects, poor welding quality consistency, and surface defects after sealing. Therefore, there is an urgent need for a process method that can systematically solve the problems of secondary degassing and high-reliability sealing of VC heat exchange plates. Summary of the Invention

[0006] The purpose of this invention is to provide a method for secondary degassing and laser remelting sealing of a VC vapor chamber plate in order to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for secondary degassing and laser remelting sealing of a VC heat exchanger plate, comprising the following steps: S1, a VC heat exchange plate is provided and fixed on a clamp, the VC heat exchange plate has a sealed cavity and an injection port, the injection port is connected to an injection pipe; S2, connect the injection pipe to the vacuum pumping system to perform vacuuming and degassing treatment on the sealed cavity, and at the same time heat the body of the VC heat spreader to collect the remaining non-condensable gas in the sealed cavity to the upper part of the injection pipe. S3, while maintaining the continuous operation of the vacuum pumping system, pulse spot welding is performed along the circumferential direction of the connection root between the liquid injection pipe and the VC heat exchange plate shell using laser welding equipment to form the first annular sealing weld. S4. While maintaining the continuous operation of the vacuum pumping system, the injection pipe area is heated to allow the residual non-condensable gas in the injection pipe to gather at the top of the injection pipe. At the same time, the output mode of the laser welding equipment is adjusted to perform continuous laser sealing welding above the first annular sealing weld to form a second annular sealing weld. The second annular sealing weld partially overlaps and covers the upper edge of the first annular sealing weld, thus completing the sealing.

[0008] The beneficial effects of the technical solution provided by this invention include at least the following: This invention provides a secondary degassing and laser remelting sealing method for a VC vapor chamber plate. Through a gradient degassing strategy based on segmented heating, it effectively solves the technical problem of difficult removal of residual non-condensable gases. In the first heating process, heating the VC vapor chamber plate body causes the trace gases adsorbed on the inner wall of the cavity and dissolved in the working fluid to desorb upon heating. Driven by the macroscopic pressure difference, these gases migrate along the injection pipe towards the vacuum pump and are extracted. In the second heating process, after the first weld isolates the cavity, heating the injection pipe area establishes a temperature gradient along its axial direction. The thermal diffusion effect causes the residual gas in the injection pipe to converge towards its top. The two heating processes work synergistically to gradually remove residual gas from the cavity to the top of the injection pipe, significantly reducing the gas partial pressure in the weld area during final sealing, avoiding porosity defects, and improving the heat transfer performance and service life of the vapor chamber plate.

[0009] This invention designs a dual-sealing architecture of pulse spot welding root sealing + continuous laser sealing coverage, which takes into account both heat damage control and long-term sealing reliability of ultra-thin wall welding. Pulse spot welding establishes the first annular sealing weld at the root of the injection tube with single-pulse low heat input. Continuous laser sealing welds form a second annular sealing weld above the first weld, achieving a dense and long-lasting seal. At the same time, the second weld partially overlaps and covers the upper edge of the first weld, so that the two welds form a metallurgical transition interface in the overlapping area. This achieves a strong metallurgical bond and retains the sealing redundancy of the bottom unremelted area, forming a dual-sealing structure.

[0010] This invention significantly improves the circumferential consistency of the weld and the quality stability of mass production by using a start-stop control strategy for the circumferential weld and infrared temperature measurement closed-loop feedback control. The two welds overlap circumferentially at their starting and ending points, and the start-stop zone of the second weld is configured on the opposite side of the start-stop zone of the first weld, effectively eliminating the start-stop joint of the circumferential weld and avoiding the risk of local leakage caused by the superposition of weak points. On this basis, this invention introduces anti-interference infrared temperature measurement to monitor and dynamically adjust the molten pool temperature in real time, effectively overcoming the quality fluctuations caused by batch differences and heat accumulation effects in open-loop control, and reducing the scrap rate.

[0011] This invention further improves the surface quality and long-term reliability of the weld by performing laser scanning and remelting on the product after sealing. This reduces the surface roughness of the weld to the industry standard Ra≤1.6μm, eliminating microscopic defects on the surface without changing the main sealing structure of the weld, reducing the risk of fatigue crack initiation under long-term thermal cycling and alternating stress, and improving the appearance quality of the product. Attached Figure Description

[0012] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a flowchart of a method provided in an embodiment of the present invention. Detailed Implementation

[0014] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a VC vapor chamber plate secondary degassing laser remelting and sealing method proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0016] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0017] The following describes in detail, with reference to the accompanying drawings, a specific scheme for a secondary degassing and laser remelting sealing method for a VC vapor chamber provided by the present invention.

[0018] Please see Figure 1 The diagram illustrates a flowchart of a method for secondary degassing and laser remelting sealing of a VC vapor chamber plate according to an embodiment of the present invention. The method includes the following steps: S1, a VC heat exchange plate is provided and fixed on the fixture. The VC heat exchange plate has a sealed cavity and an injection port. The injection port is connected to an injection pipe. S2, connect the injection pipe to the vacuum pumping system to perform vacuuming and degassing treatment on the sealed cavity, and at the same time heat the body of the VC heat spreader to collect the remaining non-condensable gas in the sealed cavity to the upper part of the injection pipe. S3, under the condition of maintaining continuous operation of the vacuum pumping system, pulse spot welding is performed along the circumferential direction of the connection root between the liquid injection pipe and the VC heat exchange plate shell using laser welding equipment to form the first annular sealing weld. S4. While maintaining the continuous operation of the vacuum pumping system, the injection pipe area is heated to allow the residual non-condensable gas in the injection pipe to gather at the top of the injection pipe. At the same time, the output mode of the laser welding equipment is adjusted to perform continuous laser sealing welding above the first annular sealing weld to form the second annular sealing weld. The second annular sealing weld partially overlaps and covers the upper edge of the first annular sealing weld, thus completing the sealing.

[0019] It should be noted that, as a prerequisite for the application of this invention, the VC heat spreader has been quantitatively filled with working fluid through the injection port before implementing this method, and the injection pipe is kept open to the outside after injection for subsequent vacuuming process. The method of this invention is implemented on the basis of the VC heat spreader that has been filled with working fluid.

[0020] In one embodiment of the present invention, the shell material of the VC heat spreader is copper or copper alloy, the Vickers hardness of the shell after annealing is HV 60~HV 90, the wall thickness of the shell is 0.2mm~0.5mm, and the initial leakage rate of the sealed cavity before vacuuming and degassing is not higher than 1×10⁻⁶. -6 Pa·m 3 / s; The injection tube is made of copper or copper alloy, with an inner diameter of 1.0mm to 3.0mm, a wall thickness of 0.15mm to 0.4mm, and a height of 5mm to 15mm above the surface of the VC heat spreader.

[0021] It should be noted that, in this embodiment, the shell material and dimensional parameters of the VC heat spreader, and the material and dimensional parameters of the injection tube are the preferred implementation criteria applicable to the method of the present invention, and their selection is based on the following: The commonly used materials for the shell and injection pipe of the VC heat spreader are copper or copper alloys (such as oxygen-free copper, phosphorus deoxidized copper, etc.). The Vickers hardness of the shell after annealing is controlled between HV 60 and HV 90. If the hardness is < HV 60, the shell is prone to thermal deformation under the thermal cycle of laser welding, resulting in weld misalignment or cavity warping. If the hardness is > HV 90, the material has a high degree of cold work hardening, the fluidity of the molten pool decreases during welding, and microcracks are prone to appear in the solidification structure of the weld.

[0022] The wall thickness of the VC heat spreader shell is 0.2mm~0.5mm and the wall thickness of the injection tube is 0.15mm~0.4mm. The heat capacity and heat conduction path of the two are similar during the laser welding process, which avoids uneven welding at the connection root due to excessive thickness difference. If the shell wall thickness is <0.2mm, the heat input window of pulse spot welding is too narrow, and the fluctuation of welding parameters can easily lead to weld burn-through. If the shell wall thickness is >0.5mm, the heat input required for pulse spot welding increases significantly, the heat-affected zone expands, and the capillary structure layer of the inner wall of the shell is easily damaged.

[0023] The inner diameter of the injection tube is 1.0mm~3.0mm to balance vacuum conduction and gas collection efficiency. If the inner diameter is <1.0mm, the flow resistance of gas in the injection tube increases, the pumping rate is limited, and the small inner volume of the tube is not conducive to the full collection of non-condensable gases. If the inner diameter is >3.0mm, the heat capacity of the injection tube itself increases, and more heat input is required to achieve sufficient penetration during pulse spot welding and continuous laser sealing. The thermal expansion of the tube wall during heating increases, affecting the welding positioning accuracy.

[0024] The height of the injection tube extending from the shell surface is 5mm to 15mm. This provides sufficient operating space for vacuuming, pulse spot welding, secondary heating and gas removal, and continuous laser sealing. If the extension height is less than 5mm, it will be difficult to limit the lower boundary of the heating area during the secondary heating and gas removal process. Furthermore, the operating space is too small, making it inconvenient to adjust the posture of the laser welding equipment. If the extension height is greater than 15mm, the top of the injection tube may vibrate or wobble due to the cantilever effect during vacuuming and heating, affecting the stability of the welding process.

[0025] In this embodiment, based on the helium mass spectrometry leak detection standard commonly used in the field of vapor chamber manufacturing, the initial leakage rate of the sealed cavity before vacuuming and degassing is limited to no more than 1×10⁻⁶. -6 Pa·m 3 / s, the initial leakage rate is detected after the VC heat spreader is clamped and fixed and before the vacuum degassing process is started.

[0026] In one embodiment of the present invention, the steps of connecting the injection pipe to the vacuum pumping system to perform vacuum degassing on the sealed cavity, and simultaneously heating the body of the VC heat spreader, include: After connecting the injection tube to the vacuum pumping system, start the vacuum pumping system and pump the sealed cavity at a rate of 5~20L / min until the vacuum level inside the sealed cavity reaches 1×10⁻⁶. -3 Pa~5×10 -3 Pa; While the vacuum pumping system is running, the heating device is activated to heat the VC heat spreader body to 60~120℃ in a contact or non-contact manner. At this time, the temperature of the injection pipe area is lower than the temperature of the VC heat spreader body, so that the residual non-condensable gas in the sealed cavity expands due to heat and gathers along the injection pipe to the upper part of the injection pipe under the pressure difference.

[0027] It should be noted that in this embodiment, the vacuum pumping system evacuates the sealed cavity at a pumping rate of 5~20 L / min. This pumping rate range is matched to the inner diameter of the injection pipe. If the pumping rate is <5 L / min, the gas flow rate in the injection pipe is insufficient to carry out the gas molecules escaping from the cavity in time, resulting in a decrease in vacuum efficiency and a prolonged process cycle. If the pumping rate is >20 L / min, the gas flow rate in the injection pipe is too high, causing a scouring effect on the inner wall of the injection pipe and potentially excessively extracting the working fluid vapor, affecting the amount of working fluid retained inside the heat spreader. Experimental verification shows that the target vacuum balance point is 5 × 10⁻⁶. -3 Pa ~ 1×10 -3 Pa, vacuum degree less than 5×10 -3 At a pressure of Pa, the partial pressure of the gas inside the cavity is relatively high. Even after subsequent sealing, residual gas may still be released at the operating temperature of the heat exchanger, affecting heat transfer performance. The vacuum level is higher than 1×10⁻⁶. -3 If the pressure is too high (Pa), the pumping time will be extended, affecting production efficiency.

[0028] Due to its slender structure, the injection tube has good heat dissipation conditions, and its natural temperature is usually lower than that of the VC heat exchanger. The heating device acts on the VC heat exchanger and does not actively heat the injection tube area, further increasing the temperature difference and making the injection tube a "cold end" in the gas migration path, forming a temperature gradient between it and the VC heat exchanger. In this embodiment, the VC heat spreader is heated to 60~120°C to use thermal energy to desorb the trace amounts of gas originally adsorbed on the inner wall of the sealed cavity or dissolved in the working fluid and escape into the gas phase space. At the same time, the volume of the gas increases after being heated and expanded, and the gas pressure in the sealed cavity increases relatively. This creates a macroscopic pressure difference between the gas and the low-pressure zone formed by the vacuum pumping system at the top of the injection pipe, driving the gas to flow along the injection pipe toward the vacuum pump and be extracted. If the heating temperature is below 60°C, the thermal activation energy is insufficient to fully desorb the adsorbed gas. If the heating temperature is above 120°C, the saturated vapor pressure of the working fluid liquid inside the heat spreader increases significantly, forming working fluid vapor that is extracted by the vacuum system, resulting in working fluid loss and affecting the vacuum degree of the sealed cavity.

[0029] The above-mentioned heating treatment and vacuuming treatment are carried out simultaneously. Based on a room temperature of 20°C, under heating conditions of 60~120°C, the volume expansion coefficient of non-condensable gases is about 1 / 273, the mean free path of gas molecules increases, and the diffusion coefficient increases by about 1.5~2 times. Combined with a pumping rate of 5~20L / min, the residual gas concentration in the sealed cavity can be reduced to the target level within 30~60s.

[0030] In one embodiment of the present invention, the step of forming a first annular sealing weld by performing pulse spot welding along the circumferential direction of the connection root between the injection pipe and the VC heat exchanger shell using a laser welding device includes: The laser welding equipment is set to operate in pulse mode, with the peak power of the emitted pulsed laser set to 200W~400W, the pulse width to 2ms~5ms, the pulse frequency to 5Hz~20Hz, the duty cycle to 10%~40%, the spot diameter of the output laser beam to 0.3mm~0.8mm, and the defocusing amount to -1mm~+1mm. Using a pulsed laser welding device, the laser moves circumferentially along the connection root between the injection pipe and the VC heat exchanger shell at a step speed of 0.5 mm / s to 2.0 mm / s. Each time the laser moves a distance equal to the diameter of a laser spot, a laser pulse is output. The overlap rate between adjacent pulsed molten pools is 30% to 60%, forming a continuous annular closed weld seam composed of overlapping discrete pulsed molten pools. This serves as the first annular sealing weld seam, with the starting and ending points of its welding trajectory overlapping 0.5 mm to 2.0 mm circumferentially.

[0031] It should be noted that in this embodiment, a discrete molten pool is formed by circumferentially overlapping pulsed lasers to construct the first annular sealing weld. Its core function is to establish an airtight seal in the heat-sensitive area with low heat input, providing vacuum isolation for subsequent steps. The design basis of its process parameters is as follows: The single-pulse energy is determined by both the peak power and the pulse width. In this embodiment, the peak power is 200W~400W and the pulse width is 2ms~5ms, corresponding to a single-pulse energy of 0.4J~2.0J. This is based on the absorption rate of copper alloy for 1064nm wavelength laser (approximately 5%~10% at room temperature, which can increase to 15%~25% with temperature rise) and the thermal diffusivity (approximately 1.17×10). -4 m 2 The above single pulse energy, within a duration of 2ms to 5ms, can achieve a thermal diffusion depth of approximately 0.15mm to 0.35mm, which matches the wall thickness of the injection tube (0.15mm to 0.4mm) and the shell wall thickness (0.2mm to 0.5mm). This allows the molten pool to penetrate 60% to 80% of the injection tube wall thickness without penetrating it.

[0032] The overlap rate of adjacent pulsed melt pools is determined by both the pulse frequency and the stepping speed. The center distance Δ between adjacent pulses is calculated as follows: Δ = v / f; In the formula, v is the stepping speed and f is the pulse frequency. In this embodiment, the overlap rate of adjacent pulse molten pools is 30% to 60%, corresponding to a Δ value of 40% to 70% of the spot diameter. Combined with a stepping speed of 0.5 mm / s to 2.0 mm / s and a pulse frequency of 5 Hz to 20 Hz, Δ is controlled within the range of 0.025 mm to 0.4 mm. In addition, a duty cycle of 10% to 40% is used to allow the molten pool to cool sufficiently within the pulse interval, preventing heat accumulation that could cause thermal deformation at the root of the injection tube.

[0033] The typical width of the annular joint at the root of the injection tube is 0.2mm to 0.6mm. In this embodiment, the spot diameter is 0.3mm to 0.8mm to ensure that the laser energy acts on both the outer wall of the injection tube and the wall of the shell hole simultaneously, achieving double-sided metallurgical bonding. The defocusing amount is -1mm to +1mm to make the laser beam form an irradiation area on the workpiece surface that is slightly larger than the focal point. Within ±1mm, the spot diameter variation does not exceed 10% to 20%, and the melting depth fluctuation is controlled within ±15% to adapt to the small height changes on the annular trajectory.

[0034] The energy of the first and last pulses at the moment of laser start-up and shutdown is about 5% to 15% lower than that of the middle pulse, which corresponds to a smaller molten pool size. In this embodiment, the non-overlapping gap is eliminated by making the termination point extend 0.5mm to 2.0mm beyond the starting point (corresponding to 5% to 30% of the circumferential arc length of the injection tube outer diameter of 2 to 5mm), thus ensuring the continuous closure of the weld in the entire circumference.

[0035] In one embodiment of the present invention, the step of heating the injection tube area includes: Before continuous laser sealing, the outer wall of the injection tube is locally heated by a heating device. The heating temperature is 120℃~180℃, the heating rate is 5℃ / s~15℃ / s, and the temperature is held for 2s~10s after reaching the heating temperature. The lower boundary of the heating area is located 0.5mm~2.0mm above the first annular sealing weld, and the upper boundary extends to the top of the injection tube. During the heat treatment process, the temperature at the top of the injection tube is higher than the temperature at the root of the injection tube, and the axial temperature gradient between the top and root of the injection tube is 10℃ / mm~30℃ / mm. The heat treatment continues during the continuous laser sealing process until the second annular sealing weld solidifies and forms.

[0036] It should be noted that in this embodiment, under the premise that the first annular sealing weld has been formed and the sealed cavity has been isolated, the injection pipe area is subjected to a second independent heating treatment. At this time, the vacuum pumping system only acts on the inside of the injection pipe. Unlike the macroscopic pressure difference driven by the vacuum pump in the first heating treatment, this step uses the thermal diffusion effect driven by the temperature gradient as the core mechanism.

[0037] In this embodiment, the heating device locally heats the outer wall of the injection tube at a temperature of 120°C to 180°C, so that the residual gas molecules in the injection tube can obtain sufficient kinetic energy and migrate along the temperature gradient direction, while avoiding excessively high temperatures that could cause oxidation of the injection tube wall before laser welding.

[0038] In this embodiment, the heating rate is controlled within the range of 5℃ / s to 15℃ / s. This aims to prevent excessive thermal stress from being generated on the injection tube wall while it is rapidly heated. For thin-walled copper tubes with a wall thickness of 0.15mm to 0.4mm, if the heating rate exceeds 20℃ / s, the temperature difference between the inner and outer walls of the tube can reach 15 to 25℃, and the resulting thermal stress may exceed the yield strength of the material, leading to deformation of the injection tube. If the heating rate is lower than 5℃ / s, the process waiting time will be extended, affecting production efficiency. After heating, the tube is held at the temperature for 2s to 10s to ensure that the temperature distribution along the axial and circumferential directions of the injection tube wall is uniform, ensuring that the temperature at the top of the injection tube is stable and controllable.

[0039] The first annular sealing weld has the function of locking the vacuum level of the sealed cavity. If the lower boundary of the heating area is lower than the upper edge of the first weld (i.e., directly covering the first weld or located below it), heat conduction will cause the temperature of the first weld to rise to more than 100°C, which may lead to the release of residual stress inside or changes in the weld structure, thereby affecting its long-term sealing reliability. Combining the fact that the injection tube wall thickness is only 0.15mm~0.4mm and the material has high thermal conductivity (the thermal conductivity of copper is approximately 401W / (m·K), and the thermal diffusivity is approximately 1.17×10⁻⁶), the solution is suitable for use in injection tubes. -4 m 2 During the heating period (heating time plus holding time), when the heat is conducted axially along the injection pipe to the first weld position, it is attenuated by a distance of 0.5~2.0mm and reduced to below 80~100℃, thereby ensuring that the first weld is not affected by this heating step.

[0040] Thermal diffusion effect refers to the migration of molecules of different components in a gas mixture in different directions under the influence of a temperature gradient. Non-condensable gases such as hydrogen and nitrogen tend to migrate towards higher temperatures. In this embodiment, a temperature gradient with a high temperature at the top and a low temperature at the bottom is established along the axial direction of the injection tube, causing the residual non-condensable gas molecules in the injection tube to migrate towards the top and converge along the temperature gradient direction. Calculated with an injection tube extension height of 5mm to 15mm, a temperature gradient of 10℃ / mm to 30℃ / mm means that the theoretical temperature difference between the top and bottom of the injection tube is 50 to 450℃. Actual testing has verified that the actual temperature difference at the bottom of the injection tube, due to its proximity to the first weld and the influence of residual heat from pulse spot welding and subsequent laser sealing welding, is usually controlled within the range of 100 to 250℃, which is sufficient to drive the migration of light gas molecules such as hydrogen and nitrogen towards the top.

[0041] In this embodiment, the heat treatment continues during the continuous laser sealing process until the second annular sealing weld solidifies and forms. This is to maintain the temperature advantage at the top of the injection tube during the continuous sealing process, so that the local heat generated by the laser welding will not disrupt the temperature gradient distribution along the axial direction of the injection tube. This ensures that the weld pool solidification front (solid-liquid interface) is always in a low gas partial pressure state, preventing gas from being drawn into the weld pool and forming porosity defects during weld solidification.

[0042] In one embodiment of the present invention, the step of adjusting the output mode of the laser welding equipment and performing continuous laser sealing welding above the first annular sealing weld to form a second annular sealing weld includes: Switch the laser welding equipment to continuous mode, set the power of the emitted continuous laser to 150W~350W, the welding speed to 5mm / s~15mm / s, and the defocusing amount to -0.5mm~+0.5mm; Continuous laser sealing is performed circumferentially above the first annular sealing weld. Its welding trajectory is coaxial with the welding trajectory of the first annular sealing weld. The starting point and the ending point overlap 1.0mm~3.0mm in the circumferential direction, and the starting point and the ending point are located within 90°~180° on the opposite side of the ending point of the first annular sealing weld. During continuous laser sealing, the power of the initial welding section linearly increases from zero to the continuous laser power within 0.5s to 1.5s, while the power of the final welding section exponentially decreases from the continuous laser power to zero within 0.3s to 0.8s. The continuous laser sealing process is carried out under a protective atmosphere, which is argon or nitrogen, and the gas flow rate of the protective atmosphere is 8L / min~15L / min.

[0043] It should be noted that in this embodiment, after the first annular sealing weld has been formed and the residual non-condensable gas in the injection pipe has been driven to the top of the injection pipe by the second heating, the remelting and sealing operation is performed. The design basis of its process parameters and control strategy is as follows: Taking the absorption rate of copper alloy to 1064nm wavelength laser (approximately 5%~10% at room temperature, which can increase to 15%~25% with increasing temperature) as an example, a power of 150W~350W combined with a welding speed of 5mm / s~15mm / s produces a linear energy density of approximately 10~70J / mm, which is sufficient to form a sufficient penetration depth of 60%~90% of the wall thickness on the wall of the injection tube with a wall thickness of 0.15mm~0.4mm. At the same time, it avoids excessive heat input that could cause the molten pool to penetrate the tube wall or damage the capillary structure layer of the inner wall of the shell.

[0044] Welding speeds of 5 mm / s to 15 mm / s balance production efficiency and weld pool stability. If the welding speed is below 5 mm / s, the heat input per unit length is too high, the weld pool exists for a longer time, and the risk of weld pool collapse increases. If the welding speed is above 15 mm / s, the weld pool cools too quickly, and porosity may remain in the weld or solidification cracks may occur. The defocusing amount of -0.5mm to +0.5mm allows the laser beam to form an irradiation area on the workpiece surface that is slightly larger than the focal spot. While ensuring energy density, it expands the process tolerance window for possible small height changes on the circular trajectory, avoiding defocusing errors caused by workpiece clamping deviations or welding thermal deformation.

[0045] Because the laser experiences power ramp-up and attenuation during startup and shutdown, if the starting point and the ending point are exactly connected but not overlapping, weak areas with incomplete welding or insufficient penetration may appear at the joint. In this embodiment, by overlapping the starting point and the ending point by 1.0mm to 3.0mm in the circumferential direction, the ending segment covers and remelts the starting segment, ensuring the continuity of the seal.

[0046] The first annular sealing weld also has quality fluctuation zones caused by pulse start-stop at its start and end points. In this embodiment, by configuring the start-stop zone of the second weld on the opposite side that is 90°~180° away from the start-stop zone of the first weld, the potential weak points of the two welds do not overlap in the circumferential direction, thus avoiding the superposition of weak points that lead to a decrease in local sealing performance.

[0047] In this embodiment, the power of the initial welding stage linearly increases from zero to continuous laser power within 0.5s to 1.5s. The purpose is to eliminate the impact effect on the molten pool caused by the sudden increase in power at the moment of laser ignition. The power of the final welding stage exponentially decays from continuous laser power to zero within 0.3s to 0.8s. The purpose is to allow the molten pool to naturally converge and solidify as the laser power gradually decreases, avoiding molten pool collapse and weld shrinkage caused by a sudden drop in power. The exponential decay is beneficial for the gas in the molten pool to escape fully before solidification, while reducing the concentration of residual stress at the final welding end.

[0048] The role of the protective atmosphere is to create a local protective environment around the weld pool and heat-affected zone, preventing the copper alloy from reacting with oxygen in the air at high temperatures, which would cause instability in the welding process. A gas flow rate of 8 L / min to 15 L / min corresponds to an airflow velocity of about 2 to 5 m / s, which is sufficient to displace the air above the welding area. At the same time, it avoids the purging effect of excessive flow rate on the weld pool, which could cause disturbance of the weld pool or the protective gas to be entrained into the weld pool, forming pores.

[0049] In one embodiment of the present invention, the continuous laser sealing process further includes the following steps: The infrared radiation wavelength of the infrared thermometer is set to 1.6μm~2.2μm, the measurement response time is no more than 50ms, and the temperature measurement accuracy is ±5℃. The infrared thermometer is used to measure the temperature of the edge area of ​​the injection tube break and the upper edge area of ​​the first annular sealing weld in real time. The controller acquires the temperature measured by the infrared thermometer at a sampling frequency of no less than 10Hz, and compares the measured temperature with a preset target temperature window after each sampling. The lower limit of the target temperature window is 85%~90% of the melting point temperature of the injection tube material, and the upper limit is 110%~120% of the melting point temperature of the injection tube material. When the measured temperature is below the lower limit, the controller will adjust the continuous laser power upward in increments of 1% to 3% per step until the measured temperature returns to the target temperature window. When the measured temperature is above the upper limit, the controller will adjust the continuous laser power downward in increments of 1% to 3% per step until the measured temperature returns to the target temperature window.

[0050] It should be noted that in this embodiment, a closed-loop control system is used to monitor and dynamically adjust the weld pool temperature in real time during continuous laser sealing welding through infrared temperature feedback. Specifically: In this embodiment, the laser wavelength used for continuous laser sealing is preferably 1064nm or 1070nm. The plasma radiation generated during the welding process is mainly distributed in the 200nm~800nm ​​band. By setting a narrowband filter with a bandwidth of 100nm~200nm in the 1.6μm~2.2μm band which does not overlap with the above-mentioned interference bands, the interference of laser reflected light and plasma radiation on the temperature measurement signal can be effectively filtered out, ensuring that the infrared thermometer only collects the thermal radiation signal of the molten pool and the heat-affected zone itself.

[0051] Based on a welding speed of 5mm / s to 15mm / s, the time required for the laser beam to move 1mm is 67ms to 200ms, and the response time is ≤50ms. That is, the temperature measuring instrument can complete the response and output of a temperature signal within a distance of about 0.25mm to 0.75mm of the laser beam movement. Furthermore, the width of the target temperature window in this embodiment is approximately 20% to 35% of the melting point temperature of the injection tube material (for example, with the melting point of copper being 1083°C, the target temperature window width is approximately 216°C to 378°C). The relative error corresponding to a measurement accuracy of ±5°C is approximately 1.3% to 2.3%, and misjudgment will not be caused by measurement error.

[0052] The lower limit of the target temperature window is 85%~90% of the melting point temperature of the injection pipe material, and the upper limit is 110%~120%. Taking copper's melting point of 1083℃ as an example, the lower limit of the target temperature window is 920℃~975℃ and the upper limit is 1191℃~1300℃. The width of the target temperature window is approximately 216℃~378℃. If the molten pool temperature is lower than the lower limit of the target temperature window, the melting degree of the injection pipe wall is insufficient, making it difficult to form sufficient metallurgical bonding and failing to guarantee the weld strength and airtightness. Conversely, if the molten pool temperature is higher than the lower limit of the target temperature window, the molten pool is overheated, which may produce metal vapor ejection and splashing. During the solidification process, it is easy to form coarse columnar crystal structure and shrinkage defects, reducing the density and mechanical properties of the weld. In addition, this target temperature window also provides sufficient adjustment buffer space for closed-loop control—the window width of 216℃~378℃ is much larger than the temperature change caused by each step of 1%~3% power adjustment, which can effectively avoid temperature oscillations during power adjustment and ensure the stability of the control system.

[0053] When the measured temperature is lower than the lower limit of the target temperature window or higher than its upper limit, the controller adjusts the continuous laser power in increments or decrements of 1% to 3% per step. With a laser power of 150W to 350W, the adjustment amount per step is 1.5W to 10.5W, and the corresponding change in the molten pool temperature is about 5 to 15℃. Field tests have verified that in most cases, the temperature can be brought back to the target temperature window within 2 to 4 steps of adjustment. With a sampling frequency of 10Hz, the total adjustment time is 200 to 400ms.

[0054] In one embodiment of the present invention, the second annular sealing weld partially overlaps and covers the upper edge of the first annular sealing weld, specifically: The second annular sealing weld partially overlaps with the first annular sealing weld, and the width of the overlapping area along the axial direction of the injection pipe is 30% to 70% of the width of the first annular sealing weld. The first annular sealing weld is partially remelted by the second annular sealing weld in the overlapping area, with the remelting depth being 20% ​​to 50% of the height of the first annular sealing weld. In the overlapping area, the second annular sealing weld melts from the outside to the inside of the injection pipe wall to 60% to 90% of the wall thickness. The melting front of the second annular sealing weld in the overlapping area crosses the original interface between the first annular sealing weld and the injection pipe wall, and penetrates inward by 0.05 mm to 0.15 mm. The bottom area of ​​the first annular sealing weld that has not been remelted retains its original pulse spot welding solidification structure, and forms a metallurgical transition interface with the continuous welding solidification structure of the second annular sealing weld in the overlapping area.

[0055] It should be noted that, in this embodiment, the width of the overlapping area between the second and first annular sealing welds along the axial direction of the injection pipe is 30% to 70% of the width of the first annular sealing weld. The width of the first annular sealing weld is determined by the diameter of the pulse spot welding spot (typically 0.3mm to 0.8mm) and the molten pool spreading effect, with a typical width of approximately 0.4mm to 1.0mm. Therefore, the actual width of the overlapping area is approximately 0.12mm to 0.7mm; the remelting depth of the overlapping area is equal to the width of the first annular weld. The height of the sealing weld is 20% to 50% of the total height. The height of the first annular sealing weld is determined by its penetration depth. According to the aforementioned steps, the height of the first annular sealing weld is approximately 60% to 80% of the wall thickness of the injection pipe, i.e., 0.09 mm to 0.32 mm. Therefore, the remelting depth is approximately 0.02 mm to 0.16 mm. This allows the bottom of the first weld to retain its original pulse spot welding solidification structure, forming a gradual transition rather than a sharp interface with the upper continuous weld remelting zone. This is beneficial for the uniform transmission of stress and redundant assurance of sealing performance.

[0056] The second annular sealing weld, within the overlapping area, melts from the outside to the inside of the injection pipe wall to 60%~90% of the pipe wall thickness. Calculated with an injection pipe wall thickness of 0.15mm~0.4mm, the actual melting depth is approximately 0.09mm~0.36mm. Under the condition of wall thickness fluctuation of ±0.05mm, this melting depth range provides a process tolerance window of approximately 0.05mm~0.1mm, ensuring that defects such as weld penetration or insufficient melting depth will not occur within the normal process fluctuation range.

[0057] The second annular sealing weld, at its melting front in the overlapping area, crosses the original interface between the first annular sealing weld and the injection pipe wall, penetrating inward by 0.05mm to 0.15mm. This penetration depth depends on the heat input of the second continuous laser sealing weld being sufficient to allow the molten pool to break through the surface oxide film and original solidification structure interface of the first weld and enter the internal region of the first weld for remelting. If the penetration depth is less than 0.05mm, a layered interface with the original interface as the boundary still exists between the two welds. Oxides or pores may remain at this layered interface, affecting the metallurgical bonding strength. If the penetration depth is greater than 0.15mm, the thickness of the unremelted area at the bottom of the first weld may be insufficient, weakening the sealing redundancy effect.

[0058] In one embodiment of the present invention, after sealing is completed, the following steps are also included: Maintain the laser welding equipment in continuous mode, set its continuous laser power to 40%~70% of the power used in continuous laser sealing welding, laser scanning speed to 1.2~2.0 times the welding speed used in continuous laser sealing welding, and defocusing amount to +2mm~+5mm; Under the condition of maintaining an inert gas protective atmosphere, at least one laser scanning remelting modification is performed along the circumference of the second annular sealing weld to form a smooth remelting modification layer on the surface of the second annular sealing weld. The remelting depth of the remelting modification layer is 0.02 mm to 0.08 mm, and the surface roughness Ra is not higher than 1.6 μm.

[0059] It should be noted that the purpose of the laser scanning remelting and finishing step after sealing is to improve the surface quality of the second annular sealing weld, rather than to provide an airtight seal. This finishing step uses low heat input to remelt and spread the weld surface layer, thereby eliminating microscopic surface defects that may occur during the sealing process and improving the fatigue resistance and appearance quality of the weld. The design basis for its process parameters is as follows: The power of the modification welding is 40% to 70% of that used in continuous laser sealing welding. The heat input density is significantly lower than that in the sealing welding stage. It can only melt a very thin layer on the surface of the weld without changing the solidification structure and sealing structure of the weld body. At the same time, the laser scanning speed is 1.2 to 2.0 times that of the sealing welding speed, which further reduces the heat input per unit length, ensuring that the remelted modification layer is extremely shallow and solidifies quickly, reducing the impact of heat accumulation on the weld body.

[0060] Positive defocusing (+2mm~+5mm) causes the laser beam to form a defocused spot on the weld surface. Compared to the near-focus defocusing of -0.5mm~+0.5mm during the sealing stage, positive defocusing of +2mm~+5mm increases the spot diameter to 2~5 times that during sealing, and reduces the surface energy density to 4%~25% of that during sealing. This creates a wide, low-power-density thermal zone on the weld surface, allowing the weld surface to be uniformly heated and remelted rather than locally deep-melted. Combined with a laser scanning speed of 1.2~2.0 times, the melting depth of the remelted decorative layer is precisely controlled within the range of 0.02mm~0.08mm, which is sufficient to melt the microscopic protrusions and depressions on the weld surface without touching the sealing section of the weld body.

[0061] At least one laser scan is performed along the circumference of the second annular sealing weld for remelting and modification. In actual production, one or more scans can be performed depending on the actual morphology of the weld surface. Usually, one scan can eliminate most of the microscopic defects on the surface. If there are obvious spatters or ripples on the weld surface after sealing, 2 to 3 scans can be performed to gradually optimize it. When scanning multiple times, the overlap of adjacent scan trajectories in the circumferential direction should not be less than 20% of the spot diameter to ensure that the entire circumference is covered.

[0062] After modification, the surface roughness of the weld is reduced from the typical value Ra 3.2μm~6.3μm after sealing to Ra≤1.6μm. This helps to reduce the risk of fatigue crack initiation caused by thermal cycling stress at surface scratches or pits during long-term use, while improving the appearance quality of the product. This surface roughness index can be measured by a stylus profilometer or an optical profilometer. Ra≤1.6μm is the arithmetic mean deviation value measured at a sampling length of 0.8mm according to the ISO 4287 surface roughness standard, which is the commonly used surface quality evaluation benchmark in this field.

[0063] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for secondary degassing and laser remelting sealing of a VC heat exchanger plate, characterized in that, The method includes: S1, a VC heat exchange plate is provided and fixed on a clamp, the VC heat exchange plate has a sealed cavity and an injection port, the injection port is connected to an injection pipe; S2, connect the injection pipe to the vacuum pumping system to perform vacuuming and degassing treatment on the sealed cavity, and at the same time heat the body of the VC heat spreader to collect the remaining non-condensable gas in the sealed cavity to the upper part of the injection pipe. S3, while maintaining the continuous operation of the vacuum pumping system, pulse spot welding is performed along the circumferential direction of the connection root between the liquid injection pipe and the VC heat exchange plate shell using laser welding equipment to form the first annular sealing weld. S4. While maintaining the continuous operation of the vacuum pumping system, the injection pipe area is heated to allow the residual non-condensable gas in the injection pipe to gather at the top of the injection pipe. At the same time, the output mode of the laser welding equipment is adjusted to perform continuous laser sealing welding above the first annular sealing weld to form a second annular sealing weld. The second annular sealing weld partially overlaps and covers the upper edge of the first annular sealing weld, thus completing the sealing.

2. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 1, characterized in that: The shell of the VC heat spreader is made of copper or copper alloy. The Vickers hardness of the shell after annealing is HV60~HV90, and the wall thickness is 0.2mm~0.5mm. The initial leakage rate of the sealed cavity before vacuuming and degassing is no higher than 1×10⁻⁶. -6 Pa·m 3 / s; The injection tube is made of copper or copper alloy, with an inner diameter of 1.0mm to 3.0mm, a wall thickness of 0.15mm to 0.4mm, and a height of 5mm to 15mm above the surface of the VC heat spreader.

3. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 1, characterized in that: The steps of connecting the injection pipe to the vacuum pumping system to perform vacuuming and degassing of the sealed cavity, and simultaneously heating the body of the VC heat spreader, include: After connecting the injection tube to the vacuum pumping system, start the vacuum pumping system and pump the sealed cavity at a pumping rate of 5~20L / min to achieve a vacuum level of 1×10⁻⁶ within the sealed cavity. -3 Pa~5×10 - 3 Pa; While the vacuum pumping system is running, the heating device is activated to heat the VC heat spreader body to 60~120℃ in a contact or non-contact manner. At this time, the temperature of the injection pipe area is lower than the temperature of the VC heat spreader body, so that the residual non-condensable gas in the sealed cavity expands due to heat and gathers along the injection pipe to the upper part of the injection pipe under the pressure difference.

4. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 1, characterized in that: The step of forming the first annular sealing weld by performing pulse spot welding along the circumferential direction of the connection root between the injection pipe and the VC heat exchanger shell using laser welding equipment includes: The laser welding equipment is set to operate in pulse mode, with the peak power of the emitted pulsed laser set to 200W~400W, the pulse width to 2ms~5ms, the pulse frequency to 5Hz~20Hz, the duty cycle to 10%~40%, the spot diameter of the output laser beam to 0.3mm~0.8mm, and the defocusing amount to -1mm~+1mm. The pulsed laser welding equipment moves circumferentially along the connection root between the injection pipe and the VC heat exchanger shell at a step speed of 0.5 mm / s to 2.0 mm / s. Each time the laser moves a distance equal to the diameter of a laser spot, a laser pulse is output. The overlap rate between adjacent pulsed molten pools is 30% to 60%, forming a continuous annular closed weld seam composed of discrete pulsed molten pools overlapping each other. This serves as the first annular sealing weld seam, and the starting and ending points of its welding trajectory overlap 0.5 mm to 2.0 mm circumferentially.

5. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 1, characterized in that: The steps for heating the injection pipe area include: Before continuous laser sealing, the outer wall of the injection tube is locally heated by a heating device at a temperature of 120℃~180℃ and a heating rate of 5℃ / s~15℃ / s. After reaching the heating temperature, the temperature is held for 2s~10s. The lower boundary of the heating area is located 0.5mm~2.0mm above the first annular sealing weld, and the upper boundary extends to the top of the injection tube. During the heat treatment process, the temperature at the top of the injection tube is higher than the temperature at the root of the injection tube, and the axial temperature gradient between the top of the injection tube and the root of the injection tube is 10℃ / mm~30℃ / mm. The heat treatment continues during the continuous laser sealing process until the second annular sealing weld solidifies and forms.

6. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 1, characterized in that: The step of adjusting the output mode of the laser welding equipment to perform continuous laser sealing welding above the first annular sealing weld to form the second annular sealing weld includes: Switch the laser welding equipment to continuous mode, set the power of the emitted continuous laser to 150W~350W, the welding speed to 5mm / s~15mm / s, and the defocusing amount to -0.5mm~+0.5mm; The continuous laser sealing weld is performed circumferentially above the first annular sealing weld, and its welding trajectory is coaxial with the welding trajectory of the first annular sealing weld. The starting point and the ending point overlap 1.0mm~3.0mm in the circumferential direction, and the starting point and the ending point are located within the range of 90°~180° on the opposite side of the ending point of the first annular sealing weld in the circumferential direction. During the continuous laser sealing process, the power of the initial welding section linearly increases from zero to the continuous laser power within 0.5s to 1.5s, and the power of the final welding section exponentially decreases from the continuous laser power to zero within 0.3s to 0.8s. The continuous laser sealing process is carried out under a protective atmosphere, which is argon or nitrogen, and the gas flow rate of the protective atmosphere is 8L / min to 15L / min.

7. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 6, characterized in that: The continuous laser sealing process also includes the following steps: The infrared radiation wavelength of the infrared thermometer is set to 1.6μm~2.2μm, the measurement response time is no more than 50ms, and the temperature measurement accuracy is ±5℃. The infrared thermometer measures the temperature of the edge area of ​​the injection tube break and the upper edge area of ​​the first annular sealing weld in real time. The controller acquires the temperature measured by the infrared thermometer at a sampling frequency of not less than 10Hz, and compares the measured temperature with a preset target temperature window after each sampling. The lower limit of the target temperature window is 85%~90% of the melting point temperature of the injection tube material, and the upper limit is 110%~120% of the melting point temperature of the injection tube material. When the measured temperature is lower than the lower limit, the controller adjusts the continuous laser power upward in increments of 1% to 3% per step until the measured temperature returns to the target temperature window. When the measured temperature is higher than the upper limit, the controller adjusts the continuous laser power downward in increments of 1% to 3% per step until the measured temperature returns to the target temperature window.

8. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 4, characterized in that: The second annular sealing weld partially overlaps and covers the upper edge of the first annular sealing weld, specifically: The second annular sealing weld partially overlaps with the first annular sealing weld, and the width of the overlapping area along the axial direction of the injection pipe is 30% to 70% of the width of the first annular sealing weld. The first annular sealing weld is partially remelted by the second annular sealing weld in the overlapping area, and the remelting depth is 20% to 50% of the height of the first annular sealing weld. The second annular sealing weld melts from the outside to the inside of the injection pipe wall within the overlapping area to 60% to 90% of the injection pipe wall thickness, and the melting front of the second annular sealing weld in the overlapping area crosses the original interface between the first annular sealing weld and the injection pipe wall, and penetrates inward by 0.05 mm to 0.15 mm. The bottom region of the first annular sealing weld that has not been remelted retains its original pulse spot welding solidification structure, and forms a metallurgical transition interface with the continuous welding solidification structure of the second annular sealing weld in the overlapping region.

9. The method for secondary degassing and laser remelting sealing of a VC heat exchanger plate according to claim 6, characterized in that: After sealing, Includes the following steps: The laser welding equipment is kept in continuous mode, and its power for emitting continuous laser is set to 40% to 70% of the power used for continuous laser sealing welding, the laser scanning speed is 1.2 to 2.0 times the welding speed used for continuous laser sealing welding, and the defocusing amount is +2mm to +5mm. Under the condition of maintaining the inert gas protective atmosphere, at least one laser scanning remelting modification is performed along the circumference of the second annular sealing weld to form a smooth remelting modification layer on the surface of the second annular sealing weld. The remelting depth of the remelting modification layer is 0.02 mm to 0.08 mm, and the surface roughness Ra is not higher than 1.6 μm.

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