Low-stress multi-wavelength laser hybrid welding method for long welding seam of thin plate

Abstract

The invention provides a low-stress multi-wavelength laser hybrid welding method for a long welding seam of a thin plate, which realizes low-stress, low-deformation and long-fatigue-life welding of the long welding seam of the aluminum thin plate through a preset gradient temperature field, multispectral laser collaborative welding and a dynamic cooling technology. The method specifically comprises the following steps: pre-treating the surface of an aluminum sheet, clamping and fixing; a gradient temperature field 20-95 DEG C which transits from low temperature to high temperature is constructed on the two sides of the welding seam, and virtual drawing force is generated through the heat expansion and cold contraction effect to offset welding thermal stress; by means of the cooperative operation effect of three red lasers and three blue lasers, the shape of a welding seam is optimized to be in an X shape from a goblet shape; and the micro-channel water cooling system is synchronously started, and cold-heat dynamic balance is realized in combination with PID temperature control. The method is suitable for efficient welding of 0.3-2.0 mm ultrathin aluminum plates with the thickness of 1 m or above in the fields of thin-wall structures with high airtightness requirements such as power battery trays and spaceflight fuel cabins.

Description

Technical Field

[0001] The present invention relates to the technical field of laser thin plate welding, in particular to a low-stress multi-wavelength laser composite welding method for thin plate long welds. Background Art

[0002] Aluminum and its alloys have low density (about 2.7g / cm 3 ), high specific strength, and excellent corrosion resistance have made it a core material for lightweight aerospace structures (such as fuselage skins and fuel tank bulkheads), high-speed train bodies, new energy vehicle battery trays, and all-aluminum bodies. Residual stress and deformation are common and difficult to resolve in the lap welding of ultra-thin sheets (0.3-2.0mm thick and several meters long).

[0003] Take the common 6061 aluminum alloy as an example. It is a 6 series aluminum alloy widely used in various industrial fields. Its main components are magnesium and aluminum. It has good weldability, machinability and corrosion resistance. However, even in the relatively ideal welding process of 6061 aluminum alloy, it is difficult to avoid the occurrence of these problems. When welding aluminum sheets, traditional metal inert gas welding (MIG) and tungsten inert gas welding (TIG) are difficult to accurately control the heat input, which can easily lead to overheating of the weld area and produce large residual stress and deformation. Although the welding effect can be improved to a certain extent by optimizing welding parameters (such as current, voltage, welding speed, etc.), these problems cannot be fundamentally solved.

[0004] When traditional welding methods are used to weld such aluminum sheets, the high thermal conductivity of aluminum causes rapid heat diffusion, and its low melting point makes the welding heat input window narrow, which easily forms high residual tensile stress in the weld and heat-affected zone, causing wave deformation, angular deformation, and even unstable buckling of the sheet, directly threatening the airtightness and dimensional accuracy of the structure, and affecting the welding quality. At the same time, when using ordinary laser welding, the effective welding width of the upper and lower sheets is narrow, and the service life of the weld is short, which affects the performance of the workpiece.

[0005] At present, the industry has made some attempts to reduce welding residual stress and deformation. Although traditional mechanical methods such as pre-stretching and rolling during welding can alleviate local deformation, they cannot eliminate stress from the thermodynamic root. The pre-stretching method is to apply a certain tensile stress to the plate before welding, so that the plate will produce a strain opposite to the residual stress during the welding process, thereby offsetting part of the residual stress. However, this method requires large pre-stretching equipment and can only be used under specific welding structures and process conditions, and its scope of application is limited. Rolling during welding is to roll the weld and its surrounding areas during the welding process to change the stress distribution and strain state of the plate. However, this method may lead to a decrease in the surface quality of the weld, and requires high operating accuracy, making it difficult to achieve precise control.

[0006] Presetting a temperature field is an effective method for reducing residual stress by creating differential thermal expansion and contraction between the weld and surrounding areas. The basic principle is to locally heat the weld area before welding, creating a temperature gradient. During the welding process, heat distribution in the weld area becomes more uniform, and thermal stress is relieved to a certain extent. However, combining a preset temperature field with laser welding technology—using multiple laser beams and pre-set heating and cooling devices to precisely control the temperature field to achieve low-stress, low-deformation welding of long lap welds of thin aluminum sheets—remains an urgent technical challenge. Furthermore, when welding two thin sheets together, the weld's macroscopic appearance typically takes on a "goblet" shape, with a narrow effective width at the weld's junction. Increasing this effective width, transforming it into an "X" shape to increase the fatigue life of the workpiece, is also an important area of ​​current research.

[0007] Furthermore, several other challenges exist during the welding of thin aluminum sheets. For example, aluminum has a large coefficient of thermal expansion, making it susceptible to significant thermal deformation due to temperature fluctuations during welding. This can lead to irregular weld shapes and reduced dimensional accuracy. Furthermore, aluminum oxidizes rapidly, forming a dense aluminum oxide film at high temperatures. This can hinder weld formation and fusion, reducing weld quality. Traditional welding methods often require rigorous cleaning and protection of the weld area to reduce the effects of the oxide film, but this increases process complexity and cost. Existing single- and dual-laser beam welding suffers from uneven energy distribution in the molten pool and insufficient stress compensation. Single-red and single-blue lasers concentrate energy at a single point, resulting in low penetration and narrow welds. While dual-red and dual-blue lasers improve energy distribution, they provide insufficient stress uniformity control in long welds. Optimizing the number and energy ratio of multiple laser beams to achieve three-dimensional molten pool control and efficient stress compensation is key to improving the quality of long welds in thin aluminum sheets.

[0008] In summary, the existing aluminum sheet welding technology still has many shortcomings in reducing residual stress, reducing deformation, and improving weld quality and fatigue life. It is difficult to meet the urgent needs of high-end manufacturing industries such as aerospace, new energy vehicles, etc. for high-precision and high-performance aluminum sheet welding. Summary of the Invention

[0009] The present invention proposes a low-stress multi-wavelength laser composite welding method for long welds of thin plates. A preset temperature field is used to reduce the wave deformation of the thin plate caused by residual tensile stress after welding. The synergistic energy field of three red and three blue laser beams is coupled with the preset temperature field to achieve low-stress and high fatigue life welding.

[0010] The technical solutions of the present invention are as follows:

[0011] A method for low-stress multi-wavelength laser composite welding of thin plates with long welds, comprising the following steps:

[0012] Step 1: Mechanically polish the surfaces of the two aluminum sheets to remove the Al2O3 oxide film and pre-treat them by ethanol cleaning;

[0013] Step 2: Stack the aluminum sheets up and down and fix them with a multi-point pneumatic clamping device. The gap between the sheets should be ≤0.1mm and the clamping pressure should be 0.5MPa.

[0014] Step 3: Use a 20kHz high-frequency induction coil to preset a gradient temperature field within 30mm on both sides of the weld. The temperature distribution of the gradient temperature field is: 20±2℃ at 0mm from the weld center, 60±3℃ at 10mm, 75±3℃ at 20mm, and 95±5℃ at 30mm, generating a virtual tensile force.

[0015] Step 4: After the semiconductor laser is preheated, use multi-laser beam welding equipment for welding.

[0016] Three beams of 450nm wavelength blue laser, 1000W power, 0.5mm spot diameter, arranged in an equilateral triangle with a spacing of 1mm, focused on the center of the weld;

[0017] Three beams of 1064nm wavelength red laser, 1500W power, 2mm spot diameter, distributed in a 60° fan shape on both sides of the weld; covering a 30mm area on both sides of the weld, so that the edge temperature of the molten pool is maintained at 500℃;

[0018] Welding speed 5m / min;

[0019] Step 5: During the welding process, the copper microchannel water cooling system is started synchronously, with a water inlet temperature of 15±1°C, a flow rate of 0.5L / min·m, and a response time of ≤0.5s.

[0020] Furthermore, the aluminum sheet is 6 series aluminum alloy, has a thickness of 0.5-2.0 mm, and a length ≥1000 mm.

[0021] Furthermore, the heating power of the gradient temperature field is adjusted in three stages: the power is 5kW in the initial stage, and the temperature is quickly raised to 80°C; the power is reduced to 3kW in the middle stage, and finely adjusted to the target temperature; the power is 1kW in the maintenance stage.

[0022] Furthermore, the spot spacing between the red laser beam and the blue laser beam is 0.5 mm, and the timing interval between the red and blue laser beams is ≤10 ms. The blue laser melts through the plate, and the red laser regulates the flow of the molten pool.

[0023] Furthermore, the three red laser beams and the three blue laser beams work together to make the effective weld width ≥3 mm.

[0024] Furthermore, the inner wall of the copper channel of the microchannel water cooling system is nickel-plated with a thickness of 50 μm.

[0025] Furthermore, the microchannel water cooling system PID temperature control cooling: water inlet temperature: 15±1℃ flow rate: 0.5L / min·m, response time: ≤0.5s.

[0026] Furthermore, when the multi-point pneumatic clamping device is used, a flexible silicone gasket with a hardness of 50 Shore A is provided to evenly distribute the pressure.

[0027] Compared with the prior art, the present invention has the following significant advantages:

[0028] 1. Preset temperature field and multi-laser beam coordination: By superimposing the energy fields of three red and three blue lasers with the 20℃-95℃ gradient temperature field, a virtual tensile force is generated to reduce the wave deformation of the thin plate caused by residual tensile stress after welding. The deformation of a 1200mm thin plate is controlled at 0.3±0.05°, thereby improving the dimensional accuracy and stability of the welded structure.

[0029] 2. Improved weld morphology: Under the synergistic effect of three red and three blue lasers, the blue laser melts through the upper plate, and the red laser heats both sides of the lower plate. The molten metal is pulled by thermal convection to form an "X"-shaped weld that is symmetrical up and down, with an effective width of ≥3mm.

[0030] 3. Ultra-fast dynamic cooling: The microchannel water cooling system has a response time of ≤0.5s, which inhibits grain growth in the heat-affected zone and reduces deformation. At the same time, it cooperates with the preset temperature field to achieve a cold-hot stretching effect, further reducing residual stress and improving welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a front view schematic diagram of the welding device of the present invention.

[0032] 1. Cooling device 2. Heating device 3. Flexible silicone gasket 4. Welding workpiece 5. Clamping device 6. Laser

[0033] Figure 2 It is a schematic side view of the welding device of the present invention.

[0034] Figure 3 It is the preset temperature field curve and theoretical stress distribution diagram.

[0035] Figure 4 Schematic diagram of the red and blue laser beam distribution.

[0036] Figure 5 Comparison diagrams of welds obtained using different methods: (a) cross section of ordinary laser weld; (b) cross section of laser weld of Scheme 1; (c) cross section of laser weld of Scheme 2; (d) cross section of laser weld of Scheme 3. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0038] The present invention is a low-stress multi-wavelength laser composite welding method for thin plate long welds.

[0039] The device used in the present invention is as follows Figure 1 As shown, there are a cooling device 1, a heating device 2, a flexible silicone gasket 3, a welding workpiece 4, a clamping device 5, and a laser 6. The laser adopts CML-Hybrid-1500DF-ARC.

[0040] Performing multi-laser beam low-stress welding of long welds on aluminum sheets includes the following steps:

[0041] Step 1: Prepare two aluminum plates and pre-treat their surfaces to remove impurities;

[0042] Step 2: Stack the two aluminum plates together and fix them with clamps;

[0043] Step 3: Preset the temperature field in the weld area and locally heat both sides of the weld;

[0044] Step 4: Adjust the parameters of the 6-laser beam welding equipment according to the specifications of the aluminum alloy ultra-thin plate to ensure that the upper plate is welded through and a stable weld joint is formed with the lower plate; use a semiconductor laser for preheating, and then follow the 6 laser beams for welding;

[0045] Step 5: During the welding process, the weld is cooled rapidly.

[0046] The present invention provides a specific implementation method. In step 1, two 6061 aluminum alloy thin plates with a length greater than 1000 mm and a thickness of 1 mm are polished to remove the Al2O3 oxide film on the surface.

[0047] The present invention provides a specific implementation method. In step three, the preheating module adopts a zoned induction heating method to preheat the 30 mm range on both sides of the weld to 90±5°C (frequency 20kHz), so that the temperature gradient distribution of the area on both sides of the weld is: the temperature gradient from the center of the weld is 0mm→20°C→10mm→60°C→20mm→75°C→30mm→95°C, and the temperature is monitored in real time using a temperature measuring pen or an infrared thermometer.

[0048] The present invention provides a specific embodiment. In step 4, the multi-laser beam welding equipment used for welding has 3 red laser beams and 3 blue laser beams, with a maximum power of 1500W. The welding parameters are: preheating laser power of 1500W, welding laser power of 1000W, and welding speed of 5m / min. The blue laser (450nm) has an 85% absorption rate for aluminum, focusing on the center of the weld to form an "energy column", penetrating the upper plate and forming a molten pool on the lower plate; the red laser (1064nm) covers both sides with a 2mm spot diameter, heating the lower plate through heat conduction, causing the molten pool to expand laterally, while reducing local overheating of the blue laser.

[0049] The present invention provides a specific implementation method. In step 4, the time interval between the red and blue lasers is ≤10ms. The blue laser melts the workpiece first, and the red laser immediately replenishes energy: three blue laser beams are arranged in an equilateral triangle (side length 1mm), with the focal point coinciding with the center of the weld; three red laser beams are distributed in a fan shape (angle 60°), covering a 30mm area on both sides of the weld, so that the temperature of the molten pool edge is maintained at 500°C to prevent stress concentration.

[0050] The present invention provides a specific implementation method, in step 4, the preheating and welding laser beams are separated by 20 mm;

[0051] The present invention provides a specific implementation method, in which a microchannel water cooling system is used for rapid cooling, and a copper microchannel PID temperature control cooling is arranged at the corresponding position on the back of the weld: water inlet temperature: 15±1℃, flow rate: 0.5L / min·m, response time: ≤0.5s.

[0052] The present invention provides a specific embodiment, wherein a multi-point pneumatic clamping device is provided to prevent the sheet from becoming unstable and deforming in a wave-like manner. When the multi-point pneumatic clamping device is used, a flexible silicone gasket with a hardness of 50 Shore A is provided to evenly distribute the pressure.

[0053] Example

[0054] The low-stress multi-wavelength laser hybrid welding method for long welds of aluminum alloy thin plates is carried out using the following steps:

[0055] Step 1: Select two 1200mm long, 1mm thick 6061 aluminum alloy sheets as the workpieces to be welded. Use sandpaper to carefully polish the surfaces of the sheets to completely remove the dense Al2O3 oxide film. After polishing, wipe the surfaces with anhydrous ethanol to remove polishing debris and residual impurities, then let them dry.

[0056] The second step is to stack the two processed aluminum alloy sheets one on top of the other, aligning their edges and securing them with a special clamping device. This clamping device applies even pressure at multiple points, ensuring the sheets are securely fixed while effectively preventing wavy deformation caused by uneven force during welding.

[0057] Step 3: Using zoned induction heating, a preset temperature field is established within a 30mm radius on either side of the weld. The induction heating equipment raises the temperature in this area to 90±5°C (heating frequency 20kHz). The heating power and duration are carefully controlled to achieve a specific temperature gradient distribution on both sides of the weld: the temperature at 0mm from the weld center is 20°C higher than the weld center, 60°C at 10mm, 75°C at 20mm, and 95°C at 30mm. A high-precision infrared thermometer is used to monitor the temperature in real time to ensure that the temperature field meets the preset requirements. The induction heating equipment primarily consists of a high-frequency power supply, an induction coil, and a control system. The high-frequency power supply generates an alternating current at a frequency of 20kHz, providing energy for induction heating. The induction coil is designed based on the shape and size of the heated area on both sides of the weld and is wound from a hollow copper tube. Its shape adapts to the 30mm area on both sides of the weld, generating a uniform alternating magnetic field within this area. During heating, the induction coils are placed on both sides of the weld, maintaining an appropriate distance from the aluminum sheet to ensure effective magnetic field application. The control system precisely adjusts the high-frequency power supply's output power and heating time based on preset temperature requirements. It initially rapidly increases the temperature with a high power output. When the temperature approaches the target temperature of 90±5°C, it reduces the power output and fine-tunes the temperature to stabilize within this range.

[0058] Step 4: Perform welding and provide three laser distribution schemes

[0059] Implementation plan 1: Start the semiconductor laser for preheating. The preheating laser beam and the 6 laser beams for subsequent welding are spaced 20mm apart. After preheating is completed, 3 red laser beams and 3 blue laser beams cooperate to follow up welding. The 3 blue lasers have a wavelength of 450nm, a power of 1000W, a spot diameter of 0.5mm, and are arranged in an equilateral triangle (with a spacing of 1mm) and focused on the center of the weld; the 3 red lasers have a wavelength of 1064nm, a power of 1500W, a spot diameter of 2mm, and are distributed in a 60° fan shape on both sides of the weld. The spot and the blue laser are spaced 0.5mm apart, and the timing interval is ≤10ms. The blue laser serves as the main heat source to melt through the 1mm aluminum plate, and the red laser assists in fusing the lower plate through heat conduction. The energy ratio between the two is 2:3, which matches the "surface melting-bottom layer heat conduction" requirements of the aluminum sheet, and the energy utilization rate is improved compared to a single laser. Low stress and small deformation welding is achieved by coupling the synergistic energy field of 3 red and 3 blue lasers with the preset temperature field. Figure 5 b. An "X"-shaped weld is formed at the weld seam, which is symmetrical up and down. The effective width of the weld seam is increased to 3.36mm, and the fatigue life and overall performance of the weld are improved.

[0060] Implementation 2: Arrange all three red and three blue lasers in an equidistant linear arrangement along the length of the weld, with the laser spacing uniformly set to 1.5mm. This solution simplifies the optical path adjustment, but it will cause uneven energy distribution. During the welding process, the linear arrangement concentrates the energy on a straight line, resulting in insufficient energy coverage on both sides of the weld, resulting in incomplete fusion defects ( Figure 5 c).

[0061] Implementation 3: Let 3 red and 3 blue lasers form two symmetrical rings, with the blue laser in the inner ring (radius 1.2mm) and the red laser in the outer ring (radius 1.8mm) surrounding the weld. Although this solution can make the energy distribution relatively uniform in the circumferential direction, the energy transmission along the depth direction of the weld is poor, and crack defects will appear in the weld ( Figure 5 d).

[0062] Step 5: During welding, the microchannel water cooling system located on the back side of the weld is activated simultaneously. The copper microchannels use PID temperature control, maintaining the inlet water temperature at 15±1°C. The weld area is rapidly cooled at a flow rate of 0.5L / m·min. The system has a response time of ≤0.5s, promptly removing welding heat. Combined with the preset temperature field, it achieves a cold-hot stretching effect and reduces the sheet's corrugated deformation caused by residual tensile stress after welding. The inner wall of the copper microchannel is nickel-plated with a thickness of 50μm to prevent oxidation and corrosion, extend the service life of the cooling system, ensure the stability and reliability of the cooling effect, and thus inhibit grain growth in the heat-affected zone (HAZ), reduce deformation, and improve the fatigue life and overall performance of the weld.

Claims

1. A method for low-stress multi-wavelength laser composite welding of thin plate long welds, characterized in that: The following steps are involved: Step 1: Mechanically polish the surfaces of the two aluminum sheets to remove the Al2O3 oxide film and pre-treat them by ethanol cleaning; Step 2: Stack the aluminum sheets up and down and fix them with a multi-point pneumatic clamping device. The gap between the sheets should be ≤0.1mm and the clamping pressure should be 0.5MPa. Step 3: Use a 20kHz high-frequency induction coil to preset a gradient temperature field within 30mm on both sides of the weld. The temperature distribution of the gradient temperature field is: 20±2℃ at 0mm from the weld center, 60±3℃ at 10mm, 75±3℃ at 20mm, and 95±5℃ at 30mm, generating a virtual tensile force. Step 4: After the semiconductor laser is preheated, use multi-laser beam welding equipment for welding. Three beams of 450nm wavelength blue laser, 1000W power, 0.5mm spot diameter, arranged in an equilateral triangle with a spacing of 1mm, focused on the center of the weld; Three beams of 1064nm wavelength red laser, 1500W power, 2mm spot diameter, distributed in a 60° fan shape on both sides of the weld; covering a 30mm area on both sides of the weld, so that the edge temperature of the molten pool is maintained at 500℃; Welding speed 5m / min; Step 5: During the welding process, the copper microchannel water cooling system is started synchronously, with a water inlet temperature of 15±1°C, a flow rate of 0.5L / min·m, and a response time of ≤0.5s.

2. The method according to claim 1, characterized in that The aluminum sheet is made of 6 series aluminum alloy, has a thickness of 0.5-2.0 mm, and a length of ≥1000 mm.

3. The method according to claim 1, characterized in that The heating power of the gradient temperature field is adjusted in three stages: the power is 5kW in the initial stage, and the temperature is quickly raised to 80°C; the power is reduced to 3kW in the middle stage, and finely adjusted to the target temperature; the power is 1kW in the maintenance stage.

4. The method according to claim 1, wherein The spot spacing between the red laser beam and the blue laser beam is 0.5 mm, and the timing interval between the red and blue laser beams is ≤10 ms. The blue laser melts through the plate, and the red laser regulates the flow of the molten pool.

5. The method according to claim 1 or 4, characterized in that The synergistic effect of 3 red laser beams and 3 blue laser beams makes the effective weld width ≥3mm.

6. The method according to claim 1, characterized in that The inner wall of the copper channel of the microchannel water cooling system is nickel-plated with a thickness of 50 μm.

7. The method according to claim 1, characterized in that Microchannel water cooling system PID temperature control cooling: water inlet temperature: 15±1℃ flow rate: 0.5L / min·m, response time: ≤0.5s.

8. The method according to claim 1, characterized in that When the multi-point pneumatic clamping device is used, a flexible silicone gasket with a hardness of 50 Shore A is set to evenly distribute the pressure.

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