Laser welding method and laser welding system thereof

Abstract

The invention discloses a laser welding method and a laser welding system thereof, and relates to the field of laser welding, and the laser welding method comprises the following steps: carrying out surface cleaning, nano sand blasting morphology regulation and stress relief annealing pretreatment on a to-be-welded workpiece, and constructing a gradient protective gas atmosphere in a welding area; data are collected in real time through a visual sensor and a laser displacement sensor, and the laser focusing position is dynamically adjusted to achieve accurate tracking; a molten pool is regulated and controlled in a layered mode through multi-band laser, and laser parameters are optimized in real time in combination with plasma spectrum monitoring; ultrasonic vibration is applied in the stable welding stage, and stress is released in cooperation with local cooling; and internal defects are detected through industrial CT after welding, and the defect area is repaired through ultraviolet laser, so that the welding quality is ensured. The method has the advantages that by means of multi-link collaborative optimization, fine pretreatment, gradient shielding gas, dynamic tracking, multi-band laser regulation and control, real-time spectrum monitoring and ultrasonic stress release, the welding process is stable and controllable, and joints are high in quality.

Description

Technical Field

[0001] This invention relates to the field of laser welding, and in particular to a laser welding method and a laser welding system thereof. Background Technology

[0002] Laser welding technology, as a key process in modern precision manufacturing, is increasingly in demand in fields such as automotive, electronics, and aerospace. However, traditional methods have limitations such as large heat-affected zones and insufficient precision. With the development of high-power fiber lasers and ultrafast laser technology, laser welding is gradually evolving towards higher energy density and lower heat input, showing significant advantages, especially in processing difficult-to-weld objects such as dissimilar materials and thin-walled components.

[0003] Currently available laser welding methods often employ traditional pickling or mechanical grinding for surface treatment, making it difficult to precisely control the microstructure and resulting in residual impurities or stress concentration. Shielding gases are typically single gases or simple mixtures, failing to create a gradient atmosphere and easily susceptible to external air interference leading to molten pool oxidation. Welding path tracking relies on a single sensor, resulting in sluggish dynamic response and poor adaptability to workpiece deformation or assembly errors. Lasers are mostly single-band outputs, making it difficult to address the differentiated needs of molten pool formation, stabilization, and finishing stages, easily leading to porosity or cracks. The lack of real-time plasma monitoring feedback results in delayed welding parameter adjustments and insufficient process stability. Internal stress control largely relies on overall annealing, which is inefficient and can negatively impact workpiece performance. Quality inspection is often limited to visual inspection or destructive sampling, making it difficult to detect minute internal defects. Repair often involves secondary welding, which can cause secondary damage, leading to large fluctuations in joint mechanical properties and making it difficult to consistently achieve over 90% of the strength standard of the base material. Summary of the Invention

[0004] To improve existing methods and systems, a laser welding method and system are provided. This method achieves stable and controllable welding process and high-quality joints with satisfactory mechanical properties through multi-stage collaborative optimization, including refined pretreatment, gradient shielding gas, dynamic tracking, multi-band laser control, real-time spectral monitoring, ultrasonic stress release, and full-process quality inspection and repair.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A laser welding method, comprising:

[0007] The welding area of ​​the workpiece to be welded is cleaned to remove oil, oxide layer and impurities. The micro-morphology of the welding area is controlled by nano-level sandblasting process. The pre-treated workpiece is then subjected to stress-relieving annealing.

[0008] An annular shielding gas nozzle is set around the welding area to create a gradient shielding gas atmosphere from the center to the periphery of the welding area;

[0009] The image data of the welding area is collected in real time by a vision sensor, and the height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor. Based on the preset welding path model and the real-time data, the position of the laser focusing lens is adjusted to dynamically track the welding area.

[0010] Layered molten pool control welding is performed by moving a multi-band laser beam along a preset welding path.

[0011] During the welding process, the plasma spectral signal of the welding area is collected in real time by a spectrometer. The intensity ratio of characteristic spectral lines is extracted from the collected spectral signal. When the intensity ratio of characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency or energy ratio is adjusted to make the intensity ratio of characteristic spectral lines return to the preset threshold range.

[0012] During the stable welding stage, ultrasonic vibration is applied to the non-welding area of ​​the workpiece to be welded by an ultrasonic vibration device, and the area affected by ultrasonic vibration is locally cooled by a cooling device to release the internal stress generated during the welding process.

[0013] After welding is completed, the welded joint is inspected for internal defects using industrial CT. If a defect is detected, a laser repair procedure is initiated, in which an ultraviolet laser is used to perform local scanning and welding on the defective area.

[0014] Preferably, the surface cleaning treatment of the welding area of ​​the workpiece to be welded, removing oil, oxide layer and impurities from the surface of the welding area, the micro-morphology control of the surface of the welding area through nano-level sandblasting process, and the stress-relieving annealing treatment of the pretreated workpiece to be welded specifically include:

[0015] Based on the material of the workpiece in the welding area, a targeted pickling solution is selected to remove oil, oxide layer and impurities from the surface of the welding area;

[0016] The cleaned and dried workpiece is fixed on the CNC worktable, and the welding area of ​​the workpiece is sandblasted using a nano-level sandblasting process, while the sandblasting pressure, distance and angle are monitored in real time.

[0017] Five random inspection points were selected in the welding area to measure the surface roughness. The depth of the concave part and the height of the convex part of the concave-convex structure were analyzed by AFM image analysis. If the roughness or ratio did not meet the standard, the sandblasting pressure and scanning speed were adjusted, and the sandblasting process was repeated until it met the requirements.

[0018] The sandblasted workpiece is placed on a ceramic support in a vacuum annealing furnace and undergoes stress-relief annealing through heating, holding, and cooling stages.

[0019] Preferably, the step of setting an annular protective gas nozzle around the welding area to create a gradient protective gas atmosphere from the center to the periphery of the welding area specifically includes:

[0020] An annular protective gas nozzle is provided around the welding area, the annular protective gas nozzle including an inner layer nozzle, a middle layer nozzle and an outer layer nozzle;

[0021] The inner layer uses high-purity argon gas with a purity of ≥99.999%, the middle layer uses argon gas and helium gas with a purity of ≥99.99%, and the outer layer uses compressed air that has been dried and degreased and helium gas with a purity of ≥99.99%.

[0022] When ventilating, first turn on the inner layer of high-purity argon gas, then turn on the middle layer of mixed gas after 30 seconds, and then turn on the outer layer of mixed gas after another 30 seconds. After the airflow in each layer stabilizes for one minute, gradually increase the flow rate of each layer to the preset value.

[0023] By observing the airflow pattern in the welding area using a fume generator, if the inner airflow forms a columnar shape covering the molten pool area, the middle airflow forms a conical transition, and the outer airflow forms an umbrella shape to isolate the outside air, and there is no obvious airflow interference among the three, then the airflow pattern is normal.

[0024] Preferably, the step of acquiring image data of the welding area in real time through a vision sensor, combining it with the height change data of the welding area of ​​the workpiece to be welded detected by a laser displacement sensor, and adjusting the position of the laser focusing lens based on a preset welding path model and the real-time acquired data to dynamically track the welding area specifically includes:

[0025] The image data of the welding area is acquired in real time by a vision sensor and the image pixel coordinates are converted into actual physical coordinates. The height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor.

[0026] The filtered image data is fused with the height change data to generate a set of three-dimensional coordinate data for the welding area.

[0027] Based on the preset welding path model and real-time acquired data, the focus offset deviation is calculated;

[0028] The PID algorithm outputs a control signal based on the deviation value to drive the servo motor to move the focusing lens. After adjustment, new data is collected in real time to dynamically track the welding area.

[0029] Preferably, the step of controlling the molten pool by moving a multi-band laser beam along a preset welding path specifically includes:

[0030] In the initial stage of welding, the proportion of infrared laser energy is increased to 85%-90%, and the proportion of ultraviolet laser energy is reduced to 10%-15%, so that the initial molten pool is quickly formed in the welding area. The temperature of the initial molten pool is controlled at 1800-2200℃, and the depth of the molten pool is 1 / 3-1 / 2 of the thickness of the workpiece to be welded.

[0031] After entering the stable welding stage, the energy ratio of infrared laser and ultraviolet laser is adjusted to 5:5-6:4. The total laser power is adjusted in real time according to the molten pool temperature to stabilize the molten pool temperature at 1600-1900℃ and control the molten pool flow rate at 0.5-1.2mm / s.

[0032] In the final stage of welding, the proportion of infrared laser energy is reduced to 60%-70%, the proportion of ultraviolet laser energy is increased to 30%-40%, and the total laser power is reduced to 60%-70% of the initial power, so that the molten pool cools slowly and the welding speed is reduced to 50%-60% of the initial welding speed in the final stage.

[0033] Preferably, during the welding process, the plasma spectral signal of the welding area is acquired in real time by a spectrometer, and the intensity ratio of characteristic spectral lines is extracted from the acquired spectral signal. When the intensity ratio of characteristic spectral lines exceeds a preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of characteristic spectral lines back to the preset threshold range. This specifically includes:

[0034] During the welding process, the plasma spectral signals of the welding area are collected in real time by a spectrometer, and the collected spectral signals are preprocessed.

[0035] The center wavelength and peak intensity of the characteristic spectral lines are determined by the spectral line peak-finding algorithm, and the intensity ratio of the characteristic spectral lines is extracted. The characteristic spectral lines include atomic spectral lines and ionic spectral lines of metal elements.

[0036] When the intensity ratio of the characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of the characteristic spectral lines back to the preset threshold range. The preset threshold range is determined according to the material of the workpiece to be welded.

[0037] Preferably, in the stable welding stage, applying ultrasonic vibration to the non-welding area of ​​the workpiece to be welded using an ultrasonic vibration device, and locally cooling the area affected by the ultrasonic vibration using a cooling device to release the internal stress generated during the welding process specifically includes:

[0038] During the stable welding stage, high-frequency ultrasonic vibration is applied to the non-welding area of ​​the workpiece, with the vibration direction forming an angle of 45°-60° with the welding direction;

[0039] In the area affected by ultrasonic vibration, anhydrous ethanol is used for precise local cooling to counteract the temperature rise caused by vibration and enhance the effect.

[0040] Preferably, after the welding is completed, the weld joint is inspected for internal defects using an industrial CT scanner. If a defect is detected, a laser repair procedure is initiated, which involves using an ultraviolet laser to perform local scanning welding on the defective area. Specifically, this includes:

[0041] After welding is completed, industrial CT is used to inspect the welded joint for internal defects. If the diameter of internal pores is ≥0.1mm or the length of cracks is ≥0.5mm, the laser repair procedure is initiated, and ultraviolet laser is used to perform local scanning welding on the defective area.

[0042] After repair, perform industrial CT inspection again until the defect is eliminated;

[0043] The welded joint is subjected to tensile strength, bending and hardness tests to ensure that the tensile strength of the welded joint is not less than 90% of the tensile strength of the base material of the workpiece to be welded, the bending angle is ≥120°, and the hardness fluctuation range of the welded joint area is ≤15HV.

[0044] Furthermore, a laser welding system is proposed, comprising:

[0045] Surface pretreatment module: The module integrates pickling, nano-sandblasting and annealing functions to achieve surface cleaning, morphology control and stress relief in the welding area;

[0046] Gradient protective gas control module: The module dynamically adjusts the composition and flow rate of the protective gas through multi-layer annular nozzles to create a gradient gas atmosphere from the center to the periphery;

[0047] Dynamic tracking module: The module integrates data from visual sensors and laser displacement sensors to adjust the position of the laser focusing lens in real time to track the welding path;

[0048] Multi-band laser output module: The module coordinates the energy ratio of infrared and ultraviolet lasers to achieve precise control of the temperature, flow rate and depth of the stratified molten pool;

[0049] Plasma spectral monitoring module: The module analyzes the intensity ratio of plasma characteristic spectral lines in real time and adjusts laser parameters accordingly to stabilize the welding process;

[0050] Ultrasonic stress control module: The module applies directional ultrasonic vibration to the non-welding area and combines it with local cooling to suppress welding internal stress;

[0051] Defect detection and quality verification module: The module locates defects based on industrial CT scan results, triggers a local ultraviolet laser repair program, and automatically performs tensile, bending and hardness tests to verify whether the mechanical properties of the joint meet the standards.

[0052] Processor: The processor is used to handle the calculation process of each formula and the construction calculation process of each model.

[0053] Compared with the prior art, the advantages of the present invention are:

[0054] Surface pretreatment, through targeted pickling, nano-level sandblasting to control microstructure, and stress-relief annealing, reduces the impact of oil stains and oxide layers, improving the basic conditions for welding. A gradient shielding atmosphere, constructed with multiple nozzles, effectively isolates external interference, ensuring a stable molten pool. Dynamic tracking integrates visual and laser displacement sensor data, combined with a PID algorithm to adjust the focusing lens, precisely tracking the welding path. Multi-band laser layered control of energy ratio and temperature adapts to the needs of different welding stages. Plasma spectral monitoring provides real-time feedback for parameter adjustment, ensuring stable welding. During the stabilization stage, ultrasonic vibration combined with localized cooling releases internal stress, reducing the risk of deformation. Post-weld industrial CT inspection and repair, along with mechanical property testing, comprehensively ensure joint quality, guaranteeing that tensile strength, bending angle, and other parameters meet standards. Overall, this achieves efficient, high-quality welding with a wide range of applications and high reliability. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the method proposed in this invention;

[0056] Figure 2 This is a schematic diagram of the welding area pretreatment proposed in this invention;

[0057] Figure 3 This is a schematic diagram of the construction of a gradient protective gas atmosphere proposed in this invention;

[0058] Figure 4 This is a schematic diagram of the dynamic tracking of the welding area proposed in this invention;

[0059] Figure 5 This is a schematic diagram of the layered molten pool control welding proposed in this invention;

[0060] Figure 6 This is a schematic diagram of the characteristic spectral line intensity ratio adjustment proposed in this invention;

[0061] Figure 7 This is a schematic diagram illustrating the stress relief proposed in this invention.

[0062] Figure 8 This is a schematic diagram of the partial scanning welding proposed in this invention. Detailed Implementation

[0063] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0064] A laser welding system, comprising:

[0065] Surface pretreatment module: The module integrates pickling, nano-sandblasting and annealing functions to achieve surface cleaning, morphology control and stress relief in the welding area;

[0066] Gradient protective gas control module: The module dynamically adjusts the composition and flow rate of the protective gas through multi-layer annular nozzles to create a gradient gas atmosphere from the center to the periphery;

[0067] Dynamic tracking module: The module integrates data from visual sensors and laser displacement sensors to adjust the position of the laser focusing lens in real time to track the welding path;

[0068] Multi-band laser output module: The module coordinates the energy ratio of infrared and ultraviolet lasers to achieve precise control of the temperature, flow rate and depth of the stratified molten pool;

[0069] Plasma spectral monitoring module: The module analyzes the intensity ratio of plasma characteristic spectral lines in real time and adjusts laser parameters accordingly to stabilize the welding process;

[0070] Ultrasonic stress control module: The module applies directional ultrasonic vibration to the non-welding area and combines it with local cooling to suppress welding internal stress;

[0071] Defect detection and quality verification module: The module locates defects based on industrial CT scan results, triggers a local ultraviolet laser repair program, and automatically performs tensile, bending and hardness tests to verify whether the mechanical properties of the joint meet the standards.

[0072] Processor: The processor is used to handle the calculation process of each formula and the construction calculation process of each model.

[0073] See Figure 1 As shown, a laser welding method includes:

[0074] Step 1: Clean the surface of the welding area of ​​the workpiece to be welded, remove oil, oxide layer and impurities from the surface of the welding area, control the micro-morphology of the surface of the welding area through nano-level sandblasting process, and perform stress relief annealing on the pre-treated workpiece.

[0075] Step 2: Set up annular shielding gas nozzles around the welding area to create a gradient shielding gas atmosphere from the center to the periphery of the welding area;

[0076] Step 3: Real-time image data of the welding area is acquired through a vision sensor, and height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor. Based on the preset welding path model and the real-time acquired data, the position of the laser focusing lens is adjusted to dynamically track the welding area.

[0077] Step 4: Perform layered molten pool control welding by moving a multi-band laser beam along a preset welding path;

[0078] Step 5: During the welding process, the plasma spectral signal of the welding area is collected in real time by a spectrometer. The intensity ratio of characteristic spectral lines is extracted from the collected spectral signal. When the intensity ratio of characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency or energy ratio is adjusted to make the intensity ratio of characteristic spectral lines return to the preset threshold range.

[0079] Step Six: In the stable welding stage, ultrasonic vibration is applied to the non-welding area of ​​the workpiece to be welded using an ultrasonic vibration device, and the area affected by ultrasonic vibration is locally cooled using a cooling device to release the internal stress generated during the welding process.

[0080] Step 7: After welding is completed, the welded joint is inspected for internal defects using industrial CT. If a defect is detected, the laser repair program is initiated, and ultraviolet laser is used to perform local scanning welding on the defective area.

[0081] See Figure 2 As shown, the welding area of ​​the workpiece to be welded undergoes surface cleaning treatment to remove oil, oxide layer and impurities. The microstructure of the welding area is controlled through nano-level sandblasting. The pre-treated workpiece is then subjected to stress-relief annealing. Specifically, this includes:

[0082] Based on the material of the workpiece in the welding area, a targeted pickling solution is selected to remove oil, oxide layer and impurities from the surface of the welding area;

[0083] The cleaned and dried workpiece is fixed on the CNC worktable, and the welding area of ​​the workpiece is sandblasted using a nano-level sandblasting process, while the sandblasting pressure, distance and angle are monitored in real time.

[0084] Five random inspection points were selected in the welding area to measure the surface roughness. The depth of the concave part and the height of the convex part of the concave-convex structure were analyzed by AFM image analysis. If the roughness or ratio did not meet the standard, the sandblasting pressure and scanning speed were adjusted, and the sandblasting process was repeated until it met the requirements.

[0085] The sandblasted workpiece is placed on a ceramic support in a vacuum annealing furnace and undergoes stress-relief annealing through heating, holding, and cooling stages.

[0086] Specifically, five test points (one at the center and four at 10 mm from the edge) are evenly selected in the welding area. The Ra value of each point is measured using a surface roughness meter, the data is recorded, and the average value is calculated.

[0087] AFM image analysis involves scanning each detection point with an atomic force microscope, selecting a 5μm×5μm sampling area, analyzing the depth of the concave part and the height of the convex part in the image, and calculating the ratio between the two.

[0088] If the average roughness exceeds the target range or the roughness ratio does not meet the requirements, adjust the sandblasting parameters. If the pressure is too low, increase it by 0.02-0.05 MPa; if the scanning speed is too fast, decrease it by 1-2 mm / s. Sandblast the welding area again with the adjusted parameters and repeat the inspection steps until the indicators meet the standards.

[0089] During the heating phase, set the heating rate to 5-10℃ / min and start the heating system; monitor the furnace temperature in real time to avoid excessive heating that could cause workpiece deformation; stop heating when the temperature reaches the target holding temperature.

[0090] During the heat preservation stage, the vacuum level and heat preservation temperature inside the furnace are kept stable. The heat preservation time is set according to the thickness of the workpiece, and the temperature and vacuum level are recorded every 30 minutes during the process.

[0091] Cooling stage and unloading: After the heat preservation is completed, set the cooling rate to 3-5℃ / min and cool down with the furnace. When the temperature inside the furnace drops below 200℃, turn off the vacuum system, slowly introduce inert gas to atmospheric pressure, open the furnace door, and wait for the workpiece to cool naturally to room temperature before taking out the workpiece to complete the stress-relief annealing.

[0092] See Figure 3 As shown, setting an annular shielding gas nozzle around the welding area to create a gradient shielding gas atmosphere from the center to the periphery of the welding area specifically includes:

[0093] An annular protective gas nozzle is provided around the welding area, the annular protective gas nozzle including an inner layer nozzle, a middle layer nozzle and an outer layer nozzle;

[0094] The inner layer uses high-purity argon gas with a purity of ≥99.999%, the middle layer uses argon gas and helium gas with a purity of ≥99.99%, and the outer layer uses compressed air that has been dried and degreased and helium gas with a purity of ≥99.99%.

[0095] When ventilating, first turn on the inner layer of high-purity argon gas, then turn on the middle layer of mixed gas after 30 seconds, and then turn on the outer layer of mixed gas after another 30 seconds. After the airflow in each layer stabilizes for one minute, gradually increase the flow rate of each layer to the preset value.

[0096] By observing the airflow pattern in the welding area using a fume generator, if the inner airflow forms a columnar shape covering the molten pool area, the middle airflow forms a conical transition, and the outer airflow forms an umbrella shape to isolate the outside air, and there is no obvious airflow interference among the three, then the airflow pattern is normal.

[0097] Specifically, after welding begins, continuously observe the airflow pattern displayed by the fume generator, and monitor the gas flow rate of each layer in real time through the flow monitoring device. If abnormal flow rate or change in airflow pattern is found, welding should be stopped in time, the gas parameters should be adjusted, and welding should be continued only after the airflow returns to normal.

[0098] After welding is completed, the gas cylinder valves of each layer are closed in the order of outer layer, middle layer and inner layer. After the residual gas in the pipeline is emptied, the flow control device is turned off. Finally, the gas pipeline is disassembled, the annular protective gas nozzle and surrounding area are cleaned, the equipment status is checked and it is stored properly.

[0099] See Figure 4 As shown, image data of the welding area is acquired in real time by a vision sensor, and height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor. Based on a preset welding path model and the real-time acquired data, the position of the laser focusing lens is adjusted to dynamically track the welding area. Specifically, this includes:

[0100] The image data of the welding area is acquired in real time by a vision sensor and the image pixel coordinates are converted into actual physical coordinates. The height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor.

[0101] The filtered image data is fused with the height change data to generate a set of three-dimensional coordinate data for the welding area.

[0102] Based on the preset welding path model and real-time acquired data, the focus offset deviation is calculated;

[0103] The PID algorithm outputs a control signal based on the deviation value to drive the servo motor to move the focusing lens. After adjustment, new data is collected in real time to dynamically track the welding area.

[0104] Specifically, the preset welding path model is retrieved. This model contains a standard three-dimensional coordinate sequence for the entire welding process, namely the X and Y plane positions that each welding step should reach and the corresponding Z height focal position.

[0105] The real-time generated three-dimensional coordinate data set is compared with the corresponding coordinates in the preset welding path model according to time or welding progress. The position deviation in the plane direction and the focus deviation in the height direction are calculated respectively, and the total focus offset deviation value is obtained by integration.

[0106] The calculated focus offset deviation value is input into the PID controller. The PID algorithm automatically calculates and outputs the corresponding control signal based on the magnitude of the deviation, the cumulative amount of the deviation, and the rate of change of the deviation. The magnitude and direction of the control signal correspond to the rotation amplitude and direction of the servo motor.

[0107] The control signal output by the PID is transmitted to the servo motor. The servo motor starts according to the control signal and drives the transmission mechanism to move, thereby pushing the laser focusing lens to move in the X, Y and Z directions, adjusting the spatial position of the focusing lens, so that the laser focus is re-aligned with the real-time position of the welding area, and offsetting the focus offset deviation.

[0108] After the focusing lens is adjusted, the vision sensor and laser displacement sensor immediately reacquire the latest image data and height data of the welding area. The process of acquisition, calculation, adjustment and reacquisition is repeated to form a closed-loop control, realizing continuous dynamic tracking of the welding area.

[0109] See Figure 5 As shown, the layered molten pool control welding, achieved by moving a multi-band laser beam along a preset welding path, specifically includes:

[0110] In the initial stage of welding, the proportion of infrared laser energy is increased to 85%-90%, and the proportion of ultraviolet laser energy is reduced to 10%-15%, so that the initial molten pool is quickly formed in the welding area. The temperature of the initial molten pool is controlled at 1800-2200℃, and the depth of the molten pool is 1 / 3-1 / 2 of the thickness of the workpiece to be welded.

[0111] After entering the stable welding stage, the energy ratio of infrared laser and ultraviolet laser is adjusted to 5:5-6:4. The total laser power is adjusted in real time according to the molten pool temperature to stabilize the molten pool temperature at 1600-1900℃ and control the molten pool flow rate at 0.5-1.2mm / s.

[0112] In the final stage of welding, the proportion of infrared laser energy is reduced to 60%-70%, the proportion of ultraviolet laser energy is increased to 30%-40%, and the total laser power is reduced to 60%-70% of the initial power, so that the molten pool cools slowly and the welding speed is reduced to 50%-60% of the initial welding speed in the final stage.

[0113] See Figure 6 As shown, during the welding process, the plasma spectral signal of the welding area is acquired in real time using a spectrometer. The intensity ratio of characteristic spectral lines is extracted from the acquired spectral signal. When the intensity ratio of characteristic spectral lines exceeds a preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of characteristic spectral lines back to the preset threshold range. Specifically, this includes:

[0114] During the welding process, the plasma spectral signals of the welding area are collected in real time by a spectrometer, and the collected spectral signals are preprocessed.

[0115] The center wavelength and peak intensity of the characteristic spectral lines are determined by the spectral line peak-finding algorithm, and the intensity ratio of the characteristic spectral lines is extracted. The characteristic spectral lines include atomic spectral lines and ionic spectral lines of metal elements.

[0116] When the intensity ratio of the characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of the characteristic spectral lines back to the preset threshold range. The preset threshold range is determined according to the material of the workpiece to be welded.

[0117] Specifically, based on the material of the workpiece to be welded, the atomic and ionic spectral lines of the target metal element are determined by consulting the spectral manual. Through preliminary trial welding experiments, the intensity ratio of characteristic spectral lines corresponding to qualified welds is collected, and their fluctuation range is statistically analyzed as the preset threshold range. At the same time, the initial laser parameters are determined.

[0118] By calling the spectral peak finding algorithm, the preprocessed spectral curve is analyzed. Based on the preset center wavelength of the characteristic spectral line, the spectral peak near the corresponding wavelength is located, the center wavelength corresponding to the peak is confirmed, and the light intensity value of the peak is read, that is, the peak intensity of the characteristic spectral line.

[0119] If the target spectral line is not found during the peak search process, such as if the spectral line is not obvious due to the plasma concentration being too low, an alarm will be triggered immediately, welding will be suspended, and the position of the spectrometer probe and whether the laser energy is normal will be checked. After troubleshooting, the acquisition will be restarted.

[0120] The intensity ratio of the two is calculated according to the preset combination of characteristic spectral lines. It is usually the atomic spectral line intensity divided by the ion spectral line intensity, or the ratio order is set according to the process requirements. The calculation result is compared with the preset threshold range in real time.

[0121] If the intensity ratio is within the preset threshold range, keep the current laser parameters unchanged and continue welding, while continuously monitoring the trend of intensity ratio changes;

[0122] If the intensity ratio exceeds the threshold range, analyze the cause of the anomaly and adjust the parameters accordingly, including:

[0123] When the intensity ratio is higher than the upper limit, if it is a single-band laser, the laser power should be increased or the pulse frequency should be increased appropriately; if it is a multi-band laser, the proportion of infrared laser energy should be increased to enhance the plasma temperature and ionization degree, reduce the relative intensity of atomic spectral lines, and thus lower the ratio.

[0124] When the intensity ratio is below the lower limit, appropriately reduce the laser power or pulse frequency. If it is a multi-band laser, increase the proportion of ultraviolet laser energy, suppress excessive ionization, and increase the relative intensity of atomic spectral lines to make the ratio rise.

[0125] See Figure 7 As shown, during the stable welding stage, ultrasonic vibration is applied to the non-welding area of ​​the workpiece using an ultrasonic vibration device, and the area affected by the ultrasonic vibration is locally cooled using a cooling device to release the internal stress generated during the welding process. Specifically, this includes:

[0126] During the stable welding stage, high-frequency ultrasonic vibration is applied to the non-welding area of ​​the workpiece, with the vibration direction forming an angle of 45°-60° with the welding direction;

[0127] In the area affected by ultrasonic vibration, anhydrous ethanol is used for precise local cooling to counteract the temperature rise caused by vibration and enhance the effect.

[0128] Specifically, when welding enters a stable phase, the ultrasonic vibration device and cooling device are automatically triggered by the control system or manually activated to ensure synchronous operation. This avoids overheating or premature cooling of the vibration zone due to individual activation, which could affect the vibration effect. The intensity of ultrasonic vibration is characterized by acceleration, which directly affects the internal stress release effect. The formula is as follows:

[0129]

[0130] in, Ultrasonic vibration acceleration, The frequency of ultrasonic vibration. The amplitude of ultrasonic vibration;

[0131] If the ultrasonic vibration device suddenly stops operating, immediately stop the cooling device and observe the state of the weld pool. If there is no abnormality in the weld pool, welding can continue. If stress concentration causes the weld pool to shift, welding must be stopped and the vibration device must be repaired before it can return to a stable state. After repair, restart the vibration and cooling devices.

[0132] If the nozzle of the cooling device is blocked or the ethanol supply is interrupted, immediately stop the ultrasonic vibration device to prevent the vibration area from overheating; disassemble the nozzle to clean the blockage, check whether the pipeline is unobstructed, restart the cooling device after the supply is restored, and restart the ultrasonic vibration device after the temperature of the vibration area drops to the normal range.

[0133] If ethanol splashes into the weld pool due to nozzle displacement, immediately stop welding, vibration and cooling devices, clean the residual ethanol on the surface of the weld pool, and check whether there are pores or cracks in the weld. After repairing the nozzle position, re-weld the area. When re-welding, vibration and cooling should still be turned on according to the requirements of the stable stage.

[0134] See Figure 8 As shown, after welding is completed, the weld joint is inspected for internal defects using industrial CT. If a defect is detected, a laser repair procedure is initiated, which involves using an ultraviolet laser to perform local scanning welding on the defective area. Specifically, this includes:

[0135] After welding is completed, industrial CT is used to inspect the welded joint for internal defects. If the diameter of internal pores is ≥0.1mm or the length of cracks is ≥0.5mm, the laser repair procedure is initiated, and ultraviolet laser is used to perform local scanning welding on the defective area.

[0136] After repair, perform industrial CT inspection again until the defect is eliminated;

[0137] The welded joint is subjected to tensile strength, bending and hardness tests to ensure that the tensile strength of the welded joint is not less than 90% of the tensile strength of the base material of the workpiece to be welded, the bending angle is ≥120°, and the hardness fluctuation range of the welded joint area is ≤15HV.

[0138] Specifically, after welding, the workpiece is first placed in a room temperature environment to cool naturally to avoid CT imaging distortion caused by high temperature detection. After cooling, the slag and dust on the surface of the welded joint are blown away with compressed air, and then the surface oil is wiped with alcohol to ensure that the joint area is free of impurities and does not affect the accuracy of CT scanning.

[0139] After the scan is completed, a three-dimensional tomographic image of the welded joint is generated using CT imaging software, and the internal structure is observed frame by frame: the focus is on checking for defects such as porosity, cracks, and lack of fusion, and the size of the defects is marked using software measurement tools. If a porosity diameter ≥ 0.1m or a crack length ≥ 0.5mm is detected, the three-dimensional coordinates, number and shape of the defects are recorded, and the laser repair program is started; if no defects exceeding the standard are detected, the mechanical performance test is directly initiated.

[0140] Start the ultraviolet laser equipment and perform local scanning welding on the defective area according to the preset parameters. During the repair process, use an industrial camera to observe the state of the molten pool in real time. If the molten pool is too large, reduce the laser power appropriately; if the molten pool is too small, increase the power.

[0141] After all defects exceeding the standard are repaired, the workpiece is sent to the industrial CT inspection platform again. The repaired area is scanned with the same parameters as the first inspection. After generating tomographic images, they are checked frame by frame. If no pores with a diameter ≥0.1mm or cracks with a length ≥0.5mm are detected, the defects are determined to be eliminated and the mechanical performance test is started.

[0142] If defects still exceed the standard, record the defect coordinates again, analyze the reasons why the first repair failed to meet the standard, adjust the laser parameters or reposition and repair again until the second re-inspection is qualified.

[0143] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, the above description focuses on specific embodiments of this specification. Additionally, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0144] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0145] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser welding method, characterized in that, include: The welding area of ​​the workpiece to be welded is cleaned to remove oil, oxide layer and impurities. The micro-morphology of the welding area is controlled by nano-level sandblasting process. The pre-treated workpiece is then subjected to stress-relieving annealing. An annular shielding gas nozzle is set around the welding area to create a gradient shielding gas atmosphere from the center to the periphery of the welding area; The image data of the welding area is collected in real time by a vision sensor, and the height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor. Based on the preset welding path model and the real-time data, the position of the laser focusing lens is adjusted to dynamically track the welding area. Layered molten pool control welding is performed by moving a multi-band laser beam along a preset welding path. During the welding process, the plasma spectral signal of the welding area is collected in real time by a spectrometer. The intensity ratio of characteristic spectral lines is extracted from the collected spectral signal. When the intensity ratio of characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency or energy ratio is adjusted to make the intensity ratio of characteristic spectral lines return to the preset threshold range. During the stable welding stage, ultrasonic vibration is applied to the non-welding area of ​​the workpiece to be welded by an ultrasonic vibration device, and the area affected by ultrasonic vibration is locally cooled by a cooling device to release the internal stress generated during the welding process. After welding is completed, the welded joint is inspected for internal defects using industrial CT. If a defect is detected, a laser repair procedure is initiated, in which an ultraviolet laser is used to perform local scanning and welding on the defective area.

2. The laser welding method according to claim 1, characterized in that, The process involves surface cleaning of the welding area of ​​the workpiece to be welded, removing oil, oxide layer, and impurities. The microstructure of the welding area is then controlled using a nano-level sandblasting process. Finally, the pre-treated workpiece undergoes stress-relief annealing. Specifically, this includes: Based on the material of the workpiece in the welding area, a targeted pickling solution is selected to remove oil, oxide layer and impurities from the surface of the welding area; The cleaned and dried workpiece is fixed on the CNC worktable, and the welding area of ​​the workpiece is sandblasted using a nano-level sandblasting process, while the sandblasting pressure, distance and angle are monitored in real time. Five random inspection points were selected in the welding area to measure the surface roughness. The depth of the concave part and the height of the convex part of the concave-convex structure were analyzed by AFM image analysis. If the roughness or ratio did not meet the standard, the sandblasting pressure and scanning speed were adjusted, and the sandblasting process was repeated until it met the requirements. The sandblasted workpiece is placed on a ceramic support in a vacuum annealing furnace and undergoes stress-relief annealing through heating, holding, and cooling stages.

3. The laser welding method according to claim 1, characterized in that, The step of setting up annular protective gas nozzles around the welding area to create a gradient protective gas atmosphere from the center to the periphery of the welding area specifically includes: An annular protective gas nozzle is provided around the welding area, the annular protective gas nozzle including an inner layer nozzle, a middle layer nozzle and an outer layer nozzle; The inner layer uses high-purity argon gas with a purity of ≥99.999%, the middle layer uses argon gas and helium gas with a purity of ≥99.99%, and the outer layer uses compressed air that has been dried and degreased and helium gas with a purity of ≥99.99%. When ventilating, first turn on the inner layer of high-purity argon gas, then turn on the middle layer of mixed gas after 30 seconds, and then turn on the outer layer of mixed gas after another 30 seconds. After the airflow in each layer stabilizes for one minute, gradually increase the flow rate of each layer to the preset value. By observing the airflow pattern in the welding area using a fume generator, if the inner airflow forms a columnar shape covering the molten pool area, the middle airflow forms a conical transition, and the outer airflow forms an umbrella shape to isolate the outside air, and there is no obvious airflow interference among the three, then the airflow pattern is normal.

4. The laser welding method according to claim 1, characterized in that, The process of acquiring real-time image data of the welding area using a visual sensor, combining this with height change data of the welding area of ​​the workpiece to be welded detected by a laser displacement sensor, and adjusting the position of the laser focusing lens based on a preset welding path model and the real-time acquired data to dynamically track the welding area specifically includes: The image data of the welding area is acquired in real time by a vision sensor and the image pixel coordinates are converted into actual physical coordinates. The height change data of the welding area of ​​the workpiece to be welded is detected by a laser displacement sensor. The filtered image data is fused with the height change data to generate a set of three-dimensional coordinate data for the welding area. Based on the preset welding path model and real-time acquired data, the focus offset deviation is calculated; The PID algorithm outputs a control signal based on the deviation value to drive the servo motor to move the focusing lens. After adjustment, new data is collected in real time to dynamically track the welding area.

5. The laser welding method according to claim 1, characterized in that, The step of controlling the molten pool by moving a multi-band laser beam along a preset welding path specifically includes: In the initial stage of welding, the proportion of infrared laser energy is increased to 85%-90%, and the proportion of ultraviolet laser energy is reduced to 10%-15%, so that the initial molten pool is quickly formed in the welding area. The temperature of the initial molten pool is controlled at 1800-2200℃, and the depth of the molten pool is 1 / 3-1 / 2 of the thickness of the workpiece to be welded. After entering the stable welding stage, the energy ratio of infrared laser and ultraviolet laser is adjusted to 5:5-6:

4. The total laser power is adjusted in real time according to the molten pool temperature to stabilize the molten pool temperature at 1600-1900℃ and control the molten pool flow rate at 0.5-1.2mm / s. In the final stage of welding, the proportion of infrared laser energy is reduced to 60%-70%, the proportion of ultraviolet laser energy is increased to 30%-40%, and the total laser power is reduced to 60%-70% of the initial power, so that the molten pool cools slowly and the welding speed is reduced to 50%-60% of the initial welding speed in the final stage.

6. The laser welding method according to claim 1, characterized in that, During the welding process, the plasma spectral signal of the welding area is collected in real time by a spectrometer. The intensity ratio of characteristic spectral lines is extracted from the collected spectral signal. When the intensity ratio of characteristic spectral lines exceeds a preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of characteristic spectral lines back to the preset threshold range. Specifically, this includes: During the welding process, the plasma spectral signals of the welding area are collected in real time by a spectrometer, and the collected spectral signals are preprocessed. The center wavelength and peak intensity of the characteristic spectral lines are determined by the spectral line peak-finding algorithm, and the intensity ratio of the characteristic spectral lines is extracted. The characteristic spectral lines include atomic spectral lines and ionic spectral lines of metal elements. When the intensity ratio of the characteristic spectral lines exceeds the preset threshold range, the laser power, pulse frequency, or energy ratio is adjusted to bring the intensity ratio of the characteristic spectral lines back to the preset threshold range. The preset threshold range is determined according to the material of the workpiece to be welded.

7. The laser welding method according to claim 1, characterized in that, In the stable welding stage, ultrasonic vibration is applied to the non-welding area of ​​the workpiece using an ultrasonic vibration device, and the area affected by the ultrasonic vibration is locally cooled using a cooling device to release the internal stress generated during the welding process. Specifically, this includes: During the stable welding stage, high-frequency ultrasonic vibration is applied to the non-welding area of ​​the workpiece, with the vibration direction forming an angle of 45°-60° with the welding direction; In the area affected by ultrasonic vibration, anhydrous ethanol is used for precise local cooling to counteract the temperature rise caused by vibration and enhance the effect.

8. The laser welding method according to claim 1, characterized in that, After the welding is completed, the weld joint is inspected for internal defects using industrial CT. If a defect is detected, a laser repair procedure is initiated, which involves local scanning and welding of the defective area using an ultraviolet laser. Specifically, this includes: After welding is completed, industrial CT is used to inspect the welded joint for internal defects. If the diameter of internal pores is ≥0.1mm or the length of cracks is ≥0.5mm, the laser repair procedure is initiated, and ultraviolet laser is used to perform local scanning welding on the defective area. After repair, perform industrial CT inspection again until the defect is eliminated; The welded joint is subjected to tensile strength, bending and hardness tests to ensure that the tensile strength of the welded joint is not less than 90% of the tensile strength of the base material of the workpiece to be welded, the bending angle is ≥120°, and the hardness fluctuation range of the welded joint area is ≤15HV.

9. A laser welding system for implementing a laser welding method as described in any one of claims 1-8, characterized in that, include: Surface pretreatment module: The module integrates pickling, nano-sandblasting and annealing functions to achieve surface cleaning, morphology control and stress relief in the welding area; Gradient protective gas control module: The module dynamically adjusts the composition and flow rate of the protective gas through multi-layer annular nozzles to create a gradient gas atmosphere from the center to the periphery; Dynamic tracking module: The module integrates data from visual sensors and laser displacement sensors to adjust the position of the laser focusing lens in real time to track the welding path; Multi-band laser output module: The module coordinates the energy ratio of infrared and ultraviolet lasers to achieve precise control of the temperature, flow rate and depth of the stratified molten pool; Plasma spectral monitoring module: The module analyzes the intensity ratio of plasma characteristic spectral lines in real time and adjusts laser parameters accordingly to stabilize the welding process; Ultrasonic stress control module: The module applies directional ultrasonic vibration to the non-welding area and combines it with local cooling to suppress welding internal stress; Defect detection and quality verification module: The module locates defects based on industrial CT scan results, triggers a local ultraviolet laser repair program, and automatically performs tensile, bending and hardness tests to verify whether the mechanical properties of the joint meet the standards. Processor: The processor is used to handle the calculation process of each formula and the construction calculation process of each model.

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