A low-vacuum laser welding method and apparatus for medium-thick aluminum alloy plates

Abstract

This invention discloses a low-vacuum laser welding device for medium-thick aluminum alloy plates, belonging to the field of metal welding technology, aiming to solve the problems of prominent porosity defects and insufficient mechanical properties in the welding of medium-thick aluminum alloy plates. The device consists of a laser cleaning and oscillating welding integrated module, a low-vacuum welding chamber module, a control system, and a detection module. The laser cleaning module uses a pulsed fiber laser to remove the oxide layer at an optimal energy density of 13.24 J / cm² under nitrogen protection, reducing the surface oxygen content to 9.66%. The low-vacuum welding chamber module constructs a negative pressure environment of 10²-10³ Pa to suppress plasma plumes. The oscillating laser welding module optimizes the stirring of the molten pool by achieving circular oscillation with a frequency of 80 Hz and an amplitude of 1 mm. The control system coordinates and regulates the parameters of each module, and the detection module monitors the weld quality in real time. This device reduces the weld porosity to below 0.032% and the tensile strength to 388.62 MPa (83.16% of the base material), making it suitable for welding medium-thick aluminum alloy plates for aerospace applications.

Description

Technical Field

[0001] This invention relates to a low-vacuum laser welding method and apparatus for medium-thick aluminum alloy plates, belonging to the field of laser processing materials technology. Background Technology

[0002] Aluminum alloys, due to their high specific strength, low density, and good corrosion resistance, have become a core material for lightweight structures in aerospace, rail transportation, and other fields. Among them, 2219 aluminum alloy, as an Al-Cu-Mn alloy, possesses excellent comprehensive mechanical properties at high and low temperatures and resistance to stress corrosion, and also exhibits relatively good weldability, making it widely used in the manufacture of next-generation launch vehicle body structures and fuel tanks. These structural components are mostly medium-thick plates (often exceeding 5mm in thickness), and their welding quality directly determines the structural strength and reliability of aerospace equipment. Currently, the mainstream welding methods for 2219 aluminum alloy medium-thick plates include arc welding (such as MIG and GTAW), friction stir welding (FSW), and conventional laser welding, but these methods all have significant drawbacks. Arc welding suffers from problems such as high heat input, severe welding deformation, and poor weld formation. Furthermore, the joint is prone to porosity and cracks, making it difficult to meet high-precision requirements. Friction stir welding, while reducing defect rates and improving mechanical properties, requires significant equipment investment, is highly sensitive to joint errors, necessitates specialized fixtures to control deformation, and has a slow welding speed (typically not exceeding 0.2 m / min). The weld is also prone to flash, reducing the load-bearing cross-sectional area and limiting its application in complex structures. Conventional laser welding offers advantages such as deep penetration, minimal deformation, and high welding speed. However, the high reflectivity (over 80% for lasers), high thermal conductivity, and low viscosity of aluminum alloys lead to problems such as plasma plume shielding and pinhole instability during welding, resulting in defects such as porosity, shallow penetration, and solidification cracks. Porosity is the most prominent defect, primarily originating from hydrogen released from moisture, oil, and other contaminants adsorbed on the surface oxide layer, as well as the entrapment of metal vapor and shielding gas during welding. These pores can reduce the tensile strength of the weld by 10%-30%, severely weakening the joint's mechanical properties.

[0003] To improve laser welding quality, researchers have proposed improvements such as surface pretreatment and welding environment optimization. Traditional surface pretreatment methods, such as mechanical grinding and chemical cleaning, suffer from low cleaning efficiency, secondary pollution, and damage to the substrate; chemical cleaning also generates waste liquid pollution, which does not meet the requirements of green manufacturing. Regarding the welding environment, the plasma plume generated by laser welding under atmospheric pressure is prone to Rayleigh and Mie scattering, leading to laser beam defocusing and reduced energy utilization. A negative pressure environment can suppress the plasma plume, improving penetration and weld quality. However, existing negative pressure laser welding technologies often lack beam oscillation optimization, resulting in limited effectiveness in suppressing porosity, and there is a lack of dedicated process parameter systems for medium-thick aluminum alloys. Laser oscillation welding technology, through beam scanning, stirs the molten pool, improving melt flow and solute distribution, which helps reduce porosity and refine grains. However, when used alone, it is still limited by surface contaminants and plasma interference, making it difficult to completely solve the defects in medium-thick plate welding. In the existing technology, there is no technical solution that combines low vacuum environment, laser cleaning pretreatment and oscillating laser welding, so it is impossible to achieve synergistic suppression of weld defects and comprehensive improvement of mechanical properties in medium and thick aluminum alloy plates.

[0004] Therefore, developing a new method and device for welding medium-thick aluminum alloy plates that can effectively remove surface contaminants, suppress plasma interference, and optimize molten pool behavior has become a key technical problem that urgently needs to be solved in the aerospace manufacturing field. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing medium-thick plate aluminum alloy welding technology and provide a low-vacuum laser welding method and apparatus for medium-thick plate aluminum alloys. Through the synergistic effect of laser cleaning pretreatment, low-vacuum environment control and oscillating laser welding, multiple effects are achieved, including efficient removal of surface contaminants, suppression of plasma plume, and thorough stirring of the molten pool. This significantly reduces the porosity and crack rate of the weld, refines the microstructure, and improves the tensile strength and microhardness of the joint, thus meeting the high-quality requirements of high-end fields such as aerospace for the welding of medium-thick plate aluminum alloys.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a low-vacuum laser welding method and apparatus for medium-thick aluminum alloy plates, comprising the following modules: an integrated laser cleaning and oscillating welding module, a low-vacuum welding chamber module, a control system, and a detection module. These modules work together to achieve high-quality welding. The laser cleaning module includes a pulsed fiber laser, a scanning mirror system, a gas protection assembly, and a motion platform. The low-vacuum welding chamber module includes a square negative pressure chamber, a vacuum pump group, a pressure control system, and a protective gas supply system. The oscillating laser welding module includes a fiber laser, a scanning galvanometer system, a wire feeder, and a robot motion system. The control system adopts a two-level control system composed of a PLC controller and an industrial computer. The detection module includes a surface quality detection unit and a weld quality detection unit.

[0007] The low-vacuum laser welding method provided by this invention includes a surface pretreatment stage, a low-vacuum environment construction stage, and an oscillating laser welding stage. Surface pretreatment: Select 2219-T87 aluminum alloy sheets with a thickness of 5-20mm, and prepare butt joints or weld joints by machining, controlling the joint gap to 0-0.5mm; wipe the workpiece surface with acetone to remove oil stains, and then let it air dry for later use. Use a pulsed fiber laser to perform laser cleaning on the areas to be welded on the workpiece. The cleaning process is carried out under a nitrogen protective atmosphere, with the nitrogen flow rate controlled at 8-12L / min to avoid secondary oxidation of the surface. The optimized laser cleaning parameters are: wavelength 1064nm, spot diameter 50μm, pulse frequency 500-1000kHz, pulse width 100ns, scanning speed 6000mm / s, line spacing 45μm, spot spacing 30μm, and laser energy density optimized to 13.24J / cm². During the cleaning process, the surface oxide layer and contaminants are removed through photothermal ablation. The thickness of the oxide layer is controlled at 20-22 μm, reducing the surface oxygen content from the original 43.27% to below 9.66% and the surface roughness to below 0.37 μm.

[0008] Low-vacuum environment setup: The cleaned workpiece is fixed in a moving platform within a negative pressure chamber. A vacuum pump is used to reduce the pressure inside the chamber to 10²-10³ Pa. This pressure threshold effectively suppresses plasma plumes and avoids excessive equipment costs. Argon gas is continuously introduced as a protective gas during the welding process at a flow rate of 3-5 L / min to maintain an inert atmosphere inside the chamber and prevent weld oxidation.

[0009] Oscillating Laser Welding: Circular oscillating laser welding is achieved using a fiber laser and scanning galvanometer system. The laser power is adjusted to 3200-5100W according to the thickness of the workpiece, with a wavelength of 1070nm, a spot diameter of 200μm, a collimator focal length of 200mm, a focusing lens focal length of 400mm, and a defocus distance of -4mm. Optimized oscillation parameters are set as follows: oscillation amplitude 1.0mm, oscillation frequency 80Hz, and welding speed 1-2.6m / min. During welding, the laser beam oscillates along a circular trajectory, stirring the molten pool and promoting bubble escape and uniform solute distribution. Simultaneously, a six-axis robot controls the laser head movement to ensure welding trajectory accuracy. The laser head is perpendicular to the workpiece surface, and the wire feeder uses a front-feed method with a wire feed speed of 3m / min, an angle of 55° between the wire feed nozzle and the base material surface, and a wire spacing of 1.5mm.

[0010] The beneficial effects of this invention are as follows: the weld porosity is reduced from 12.77% to below 0.032%, almost eliminating porosity defects; the weld tensile strength reaches 388.62 MPa (83.16% of the base material); the device has high integration and is environmentally friendly; laser cleaning has no chemical pollution; the energy consumption of the low vacuum system is only 1 / 5 of that of the high vacuum equipment, reducing operating costs by 60%; it can be integrated with automated production lines; the process is stable and reliable; spatter is reduced by 90%; the weld has a smooth "fish scale" morphology; and the depth-to-width ratio is increased from 1.5 to 3.0, meeting the manufacturing requirements of key aerospace structures. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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.

[0012] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention; Figure 2 This is a schematic diagram of the internal structure of the low-vacuum welding cavity module; Figure 3 The porosity is given under various environmental pressures, with oscillation frequencies of 0 Hz and 80 Hz. Detailed Implementation

[0013] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. For a thorough understanding of the invention, detailed steps and structures will be set forth in the following description to illustrate the technical solutions of the invention. Preferred embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0014] The low-vacuum laser welding method for medium-thick aluminum alloy plates described in this invention comprises the following detailed steps: Step S1: Workpiece preparation: Material selection and pretreatment: Select aluminum alloy sheet to be welded, preferably 2219-T87 aluminum alloy. Select a sheet with a thickness of 9mm and process it to a size of 160×120×9mm³. Use machining to prepare the weld joint to ensure that the surface of the area to be welded is flat, providing a foundation for subsequent welding and the construction of the negative pressure environment.

[0015] Surface cleaning: Use acetone to thoroughly clean the workpiece to be welded area and its surrounding surface to remove oil, impurities, etc., and then let it air dry naturally to remove soluble contaminants from the surface and avoid additional porosity defects during the welding process.

[0016] Clamping and positioning: The cleaned workpiece is temporarily placed in the processing area. After the laser cleaning pretreatment is completed, the subsequent clamping and fixing operations will be carried out.

[0017] Step S2: Laser cleaning pretreatment Equipment Start-up and Parameter Setting: Start the pulsed fiber laser and debug the equipment to ensure its normal operation. Set the core parameters for laser cleaning: wavelength 1064nm, spot diameter 50μm, pulse frequency 500kHz, pulse width 100ns, scanning speed 6000mm / s, line spacing 45μm, spot spacing 30μm, and laser energy density 13.24J / cm².

[0018] Protective atmosphere setup: Connect the gas protection components, turn on the nitrogen storage tank, and adjust the nitrogen flow rate to 10L / min through the flow controller to ensure that the area to be welded is in a nitrogen protective atmosphere to prevent secondary oxidation of the surface during the cleaning process.

[0019] Laser cleaning process: The laser and motion platform are activated, and the laser spot scans and cleans the area of ​​the workpiece to be welded along a preset path, removing the surface oxide layer and residual contaminants through photothermal ablation. The surface condition is observed in real time during the cleaning process to ensure uniform cleaning.

[0020] Cleaning quality inspection: After cleaning, the oxide layer removal thickness is measured using a digital microscope, the surface oxygen content is detected using an EDS spectrometer, and the surface roughness is measured using a white light interferometer. The standards are: oxide layer removal thickness of approximately 21 μm, oxygen content reduced to below 9.66%, and surface roughness ≤ 0.37 μm.

[0021] Step S3: Device placement and system commissioning: Workpiece clamping: Securely fix the cleaned and qualified plate onto the moving platform inside the square negative pressure chamber (300×400×400mm³), ensuring that the area of ​​the workpiece to be welded is aligned with the center of the anti-reflective coated quartz lens at the top of the negative pressure chamber, to prevent displacement from affecting the welding accuracy during the welding process.

[0022] Optical path alignment: Without turning on the laser, use a low-power visible light indicator to illuminate the workpiece and fine-tune the position of the scanning galvanometer system at the end of the six-axis robot to ensure that the laser beam passes accurately through the anti-reflective coated quartz lens and is focused on the starting position of the workpiece to be welded.

[0023] Gas circuit and equipment connection: Connect the argon storage tank of the protective gas supply system to the negative pressure chamber through the pressure reducing valve and flow regulating valve, and check the gas circuit sealing; connect the vacuum pump group to the vacuum pipeline of the negative pressure chamber to ensure that the gas extraction passage is unobstructed; insert the wire feeding nozzle of the wire feeder into the negative pressure chamber, adjust its angle with the surface of the base material to 55°, and control the wire spacing to 1.5mm.

[0024] Step S4: Establishing and stabilizing the low vacuum environment: Initial vacuuming: Start the vacuum pump set, slowly open the valve on the vacuum pipeline to start evacuating, and gradually increase the evacuation rate to avoid the airflow being too fast and causing surface impurities to contaminate the lens.

[0025] Pressure monitoring and control: The pressure sensor of the pressure control system monitors the pressure in the negative pressure chamber in real time, and the pressure is precisely adjusted to the preset value of 10²Pa through the proportional valve.

[0026] Protective gas introduction and environmental stabilization: Activate the argon protection system and control the argon flow rate to 3L / min via the flow regulating valve to introduce argon into the negative pressure chamber to create a welding protective atmosphere. After the pressure reaches the set value, maintain the closed-loop control mode for 30 seconds to ensure that the pressure fluctuation within the chamber is controlled within ±5Pa. Once the environment stabilizes, proceed to the welding stage.

[0027] Step S5 involves performing oscillating laser welding: Welding parameter settings: Input the optimized welding process parameters into the laser and control system. Laser parameters: power 3200W, wavelength 1070nm, spot diameter 200μm, collimator focal length 200mm, focusing lens focal length 400mm, defocus distance -4mm; Oscillation parameters: the scanning galvanometer system adopts a circular oscillation mode, oscillation amplitude 1.0mm, oscillation frequency 80Hz; Motion and wire feeding parameters: the six-axis robot drives the laser head at a speed of 1m / min, the wire feeder uses 1.2mm diameter 5087 welding wire, and the wire feeding speed is 3m / min.

[0028] Welding Start: After confirming that all parameters are set correctly, the negative pressure environment is stable, and the protective gas is supplied normally, the robot motion system, laser emission system, and wire feeder are triggered simultaneously. The laser head moves at a constant speed along the preset trajectory, and the wire feeder feeds the wire synchronously to carry out the welding operation.

[0029] Process stability control: During the welding process, the vacuum pump unit works continuously to maintain a negative pressure environment, and the robot precisely controls the welding trajectory to ensure the relative position of the laser beam and the welding wire is stable, thus ensuring the quality of the weld formation.

[0030] Step S6: Welding completion and post-processing: Sequential Stop: After the welding trajectory is completed, first turn off the laser emission system and stop wire feeding; maintain the pressure in the negative pressure chamber and the argon gas supply for 30 seconds, and after the weld cools down to below 180°C, stop the vacuum pump group to pump gas and the argon gas supply.

[0031] Remove the device and take out the workpiece: After the pressure in the negative pressure chamber returns to atmospheric pressure, open the chamber door, slowly remove the relevant equipment, and take out the welded workpiece.

[0032] Quality Inspection: The removed workpieces are subjected to comprehensive inspection. The weld porosity is tested by X-ray flaw detector, and the standard value is ≤0.032%. The microstructure is observed by optical microscope to ensure that it is mainly composed of fine equiaxed crystals with a grain size ≤5.28μm. Mechanical property tests are performed. The tensile strength of the weld should reach ≥388.62MPa (83.16% of the base material) and the microhardness should be ≥83.8HV.

Claims

1. A low-vacuum laser welding device for medium-thick aluminum alloy plates, characterized in that, It includes: a laser cleaning and oscillating welding integrated module (1), used to remove the oxide layer and contaminants on the surface of the workpiece to be welded, while generating an oscillating laser beam and realizing wire feeding and welding trajectory control; a low vacuum welding chamber module (2), used to build and maintain the negative pressure environment and protective atmosphere required for welding; a control system (3), which integrates parameter adjustment, equipment start-up and shutdown and status feedback functions to realize the coordinated operation of each module; and a detection module (4), used to monitor the surface quality after cleaning and the weld performance after welding.

2. The apparatus according to claim 1, characterized in that, The laser cleaning and oscillating welding integrated module (1) includes at least a cleaning unit and a welding unit; the cleaning unit: outputs a Gaussian mode laser with a wavelength of 1064nm and a maximum power of 200W; an XY axis galvanometer scanning system with a scanning range of 0-200mm×200mm, a line spacing of 45μm, and a spot spacing of 30μm; a shielding gas supply system with a controlled gas flow rate of 8-12L / min; an electric translation stage with a moving speed of 0-10000mm / s and a load capacity of ≥50kg; the welding unit: has a maximum power of 15kW and a circular oscillation; a wire feeder using 1.2mm diameter 5087 welding wire with a wire feeding speed of 0.5-10m / min, an angle of 55° between the wire feed nozzle and the surface of the workpiece to be welded, and a wire spacing of 1.5mm.

3. The apparatus according to claim 1, characterized in that, The low-vacuum welding chamber module (2) includes at least: a square negative pressure chamber (21) with dimensions of 300×400×400mm³, a top-mounted anti-reflective coated quartz lens (211) with a light transmittance ≥98%, and a side-mounted observation window (212) and pressure sensor interface (213); a vacuum pump group (22) with a pumping speed of 100L / s and a pressure adjustment range of 10-10 5 Pa; Protective gas supply system (23), flow rate adjustment range 0-20L / min.

4. The apparatus according to claim 3, characterized in that, The observation window (212) is made of high-temperature resistant quartz glass with a thickness of 10mm and can withstand temperatures ≥500℃; the anti-reflective coated quartz lens (211) has a light transmittance ≥98%.

5. The apparatus according to claim 1, characterized in that, The control system (3) includes at least: a PLC controller, which is connected to the actuators of the laser cleaning and swing welding integrated module (1) and the low vacuum welding chamber module (2); and a computer, which is equipped with dedicated control software, can store more than 100 sets of process parameters, supports abnormal alarms, and has a response time of ≤1s.

6. The apparatus according to claim 5, characterized in that, The laser (1) has a collimator with a focal length of 200mm and a focusing lens with a focal length of 400mm. After focusing, the diameter of the laser spot is about 200 micrometers. The wire feeder has a wire feeding nozzle with an angle of 55° to the surface of the workpiece to be welded and a wire spacing of 1.5mm.

7. A method for low-vacuum laser welding of medium-thick aluminum alloy plates using the apparatus described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Workpiece preparation: Select 2219-T87 aluminum alloy sheet with a thickness of 5-20mm, wipe the surface with acetone and let it dry; S2: Laser cleaning, start the cleaning unit of the laser cleaning and swing welding integrated module (1) to clean the area to be welded with an energy density of 13.24J / cm²; S3: The device is in place. The workpiece is fixed on the motion platform of the low vacuum welding chamber module (2). The chamber door is closed. The welding unit position of the integrated module (1) is adjusted so that the laser beam is aligned with the area to be welded. S4: Establish a negative pressure environment, start the vacuum pump group, reduce the pressure inside the cavity to 10²-10³Pa, and introduce argon gas for protection; S5: Perform welding, start the welding unit of the laser cleaning and swing welding integrated module (1), and perform welding according to the preset parameters; S6: Process monitoring, the surface quality and weld condition are monitored in real time through the detection module (4); S7: Welding is complete. After cooling, stop the vacuuming and argon gas supply, and remove the workpiece.

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