Large-size aluminum alloy honeycomb panel long-weld seam welding method

Abstract

The application discloses a large-size aluminum alloy honeycomb plate long-welding seam welding method and belongs to the technical field of aluminum alloy precision welding. The method reduces hydrogen sources from the source by laser cleaning and argon passivation before welding, provides high-precision back support and protection for the long-welding seam by adopting an electronic gear hard synchronous follow-up back support, controls the molten pool cooling rate and the welding seam atmosphere state through two independent feedback loops, and carries out online ultrasonic impact in the plastic interval of 300 DEG C to 500 DEG C of the welding seam, so that multiple effects of grain refinement, stress relief and hydrogen escape are realized. The method can realize automatic welding of the ultralong butt welding seam of the aluminum alloy honeycomb plate with a single length of greater than or equal to 6 m, the welding seam is free of excessive heat cracks, the size of pores is small, and welding efficiency and quality consistency are significantly improved. The method can be widely applied to the fields of rail transit, aerospace, building curtain walls and the like.

Description

Technical Field

[0001] This invention belongs to the field of precision welding technology for aluminum alloys, and specifically relates to a welding method for long welds in large-size aluminum alloy honeycomb panels. Background Technology

[0002] Aluminum alloy honeycomb panels, as a lightweight, high-strength, sound-insulating, heat-insulating, and highly flat sandwich structure material, are widely used in rail transit vehicle bodies, aerospace cabins, and high-end building curtain walls. With the development of large-scale and integrated equipment, the demand for large-size aluminum alloy honeycomb panels with ultra-long welds of no less than 3m and no less than 6m in length per panel is constantly increasing, making the fully automated welding of their butt welds the most important processing step.

[0003] Currently, there are still several technical challenges in welding long seams of large-size aluminum alloy honeycomb panels: First, the solubility of hydrogen in liquid aluminum alloy is much higher than in solid aluminum alloy. During the welding of long seams, factors such as uneven pre-weld treatment, secondary oxidation of the base material, local failure of shielding gas, and intrusion of environmental moisture can easily lead to random hydrogen porosity along the entire weld. Existing processes mostly adopt single-point control measures such as pre-weld cleaning and in-weld protection, which cannot effectively control the hydrogen source throughout the long weld. Second, commonly used aluminum alloys have a wide brittle temperature range. When welding ultra-long seams continuously, heat accumulation leads to significant differences in the solidification behavior of the molten pool along the weld direction. Welding stress continues to accumulate, easily causing crystallization cracks and liquefaction cracks in the middle and end sections of the weld. Existing processes mostly improve crack tendency by adjusting welding parameters and post-weld offline treatment, but cannot achieve synchronous control of solidification behavior and stress throughout the long weld. Third, the thin-walled sandwich structure of the honeycomb panel results in the absence of rigid solid support on the back of the weld, leading to poor stability of the molten pool and a tendency to sink and burn through. Insufficient back protection further exacerbates porosity and crack defects. Existing follow-up back support devices mostly adopt a position feedback following method, that is, the back support is driven to move by detecting the position of the welding torch through a sensor. This method has the problems of large following error and response lag. The synchronization accuracy further decreases under long stroke, making it difficult to meet the high-precision synchronization requirements of ten-meter-long welds.

[0004] In existing technologies, ultrasonic impact stress relief treatment is used. However, most existing technologies are carried out after the weld has cooled to room temperature. It is generally believed in the industry that impact at high temperatures will damage the weld formation that has not yet fully solidified. Therefore, existing ultrasonic impact processes are all offline room temperature treatments after welding, which cannot achieve grain refinement, stress relief and hydrogen escape at the same time when the weld is in the plastic temperature range.

[0005] Furthermore, while electronic gear hard synchronization is a mature synchronization technology in the servo drive field, it has not yet been applied to the follow-up control of welded back supports. Existing measures for preventing porosity and cracks in aluminum alloy welding are mostly single-process optimizations, and a comprehensive and systematic quality control system for long welds in large-size honeycomb panels has not yet been formed. The poor quality consistency and high defect rate of long welds throughout the process restrict the large-scale application of large-size aluminum alloy honeycomb panels. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a welding method for long welds in large-size aluminum alloy honeycomb panels, achieving low-defect, high-efficiency automated welding of long welds in large-size aluminum alloy honeycomb panels.

[0007] The method of this invention is implemented using a long-stroke gantry welding machine, which is a conventional piece of equipment in the welding field. Its main components are as follows: Welding actuator: This refers to the gantry-type long-stroke linear travel mechanism of the equipment, which consists of a servo motor, linear guide rails, and mounting slides. It is a conventional travel mechanism for welding large-sized workpieces. Its function is to carry welding-related functional units and travel at a constant speed along the length of the weld. Its travel servo axis serves as the active motion axis of the entire system, providing position and timing references for the synchronous movement of each unit. This invention can adopt the aforementioned welding actuator from the prior art.

[0008] The multi-heat source system consists of two independent conventional devices: a pre-pulsed laser and a laser-MIG composite welding head. Both are fixedly mounted on the same mounting slide of the welding actuator, arranged front-to-back along the welding direction, and move synchronously with the traveling mechanism. The pre-pulsed laser performs secondary film removal and preheating at the bevel, while the laser-MIG composite welding head serves as the main welding unit, responsible for the main weld deposition. This invention does not involve structural improvements to the aforementioned heat source devices, but rather improvements to their arrangement, parameter matching, and operating methods.

[0009] The follow-up flexible back support device consists of a back support slider, a flexible copper backing, a back gas chamber, and a walking servo mechanism. It is a common back support device used in the welding field. The working principle is that the back support slider fits against the back of the weld, providing rigid support to prevent the molten pool from sinking, while the back gas chamber is filled with inert gas to provide gas protection for the back weld. The walking servo mechanism drives the back support slider to move along the weld.

[0010] The molten pool condition monitoring module consists of two conventional detection devices: a high-speed industrial camera and an infrared thermometer. These are mounted on the slide of the welding actuator and aligned with the molten pool area. The high-speed industrial camera is used to acquire data on the molten pool morphology, weld width, and solidification front position, while the infrared thermometer is used to acquire data on the molten pool temperature field distribution. Together, they constitute the signal acquisition end of the first feedback control loop in the technical solution of this invention.

[0011] Weld atmosphere monitoring module: It consists of two conventional oxygen and humidity integrated sensors, one arranged inside the front protective gas cover and the other arranged in the back gas chamber of the back support device. They collect oxygen content and humidity data on the front and back sides of the weld, respectively, and constitute the signal acquisition end of the second feedback control loop in the technical solution of this invention.

[0012] Online defect detection module: It adopts a conventional commercially available ultrasonic phased array detection probe, which is fixed to the tail of the welding actuator and moves synchronously with the walking mechanism to scan the internal defects of the weld seam immediately after welding.

[0013] The above are the hardware facilities involved in the technical solution of the present invention, but not all of them. All the equipment facilities involved in the solution of the present invention that are not mentioned above are hardware facilities in the prior art that are clearly known to those skilled in the art.

[0014] The welding method of the present invention specifically includes the following steps: S1. Pre-welding treatment: Dry pulsed laser cleaning is performed on the weld butt groove and the area 20mm to 30mm on both sides. The laser energy is used to peel off the Al2O3 oxide film on the surface of the base material, while vaporizing and removing oil and adsorbed water vapor. After cleaning, high-purity argon gas with a purity of not less than 99.999% is immediately introduced above the cleaning area to form a laminar flow protective gas curtain to isolate the air until welding starts. This inhibits secondary oxidation and hydrogen adsorption on the exposed surface of the base material after cleaning, reducing the source of porosity and inclusion defects from the source.

[0015] S2. Plate clamping and follow-up back support positioning: Clamp and fix the pre-treated honeycomb plate on the tooling platform, adjust the weld butt gap to no more than 0.15mm and the misalignment to no more than 10% of the plate thickness; attach the pad surface of the follow-up flexible back support device to the back of the weld, and align it coaxially with the welding torch mounted on the welding actuator.

[0016] During welding, the back support device and welding torch achieve full-range tracking via electronic gear hard synchronization. Specifically, the welding actuator's servo axis is the driving axis, and the back support device's servo axis is the driven axis. Both axes are connected to the same motion controller's real-time industrial bus and share the same hardware clock source as the timing reference. The servo driver's built-in electronic gear function sets the transmission ratio between the two axes to 1:1. Position and speed commands for the driving axis are simultaneously sent to both axis drivers via the bus in synchronous frames. The driven axis requires no additional position detection or calculation correction and directly follows the driving axis in a constant-speed synchronous motion. Compared to the traditional software-based position tracking method of "welding torch position detection - controller calculation - back support drive tracking," this method eliminates detection lag and calculation errors, achieving a full-stroke synchronization accuracy of less than ±0.02mm, a synchronization response time of less than 1ms, and almost no accuracy degradation over long strokes. The back support device integrates a back-side protective gas path, continuously supplying inert protective gas to the back of the weld during tracking, while simultaneously providing rigid support to the weld, improving the stability of the molten pool in thin-walled structures and reducing back-side oxidation.

[0017] S3. System Calibration and Control Model Preset: The coaxiality of the multi-heat source system arranged sequentially along the welding direction is calibrated, and the molten pool condition monitoring module and weld atmosphere monitoring module are calibrated; the threshold values ​​of welding process parameters and the control range of molten pool condition are preset, and a control model for welding parameters, molten pool condition and defect tendency is established.

[0018] The coaxiality calibration described above involves placing a graduated reference target plate on the tooling platform, with the center line of the target plate coinciding with the preset weld center line; sequentially activating the center mark of the front laser, the laser indicator spot of the main welding unit, and the impact head of the ultrasonic impact unit; adjusting the lateral position and pitch angle of each unit to ensure that all action centers fall on the center line of the target plate, guaranteeing that the coaxiality deviation between the action center of each functional unit and the weld center line along the welding direction is less than 0.1 mm.

[0019] The specific operations for the above sensor calibration are as follows: the high-speed camera and infrared thermometer in the molten pool condition monitoring module are calibrated using a standard blackbody furnace to ensure that the molten pool temperature measurement error is less than ±5℃; the oxygen content sensor in the weld atmosphere monitoring module is calibrated using a standard concentration of argon-oxygen mixed gas, and the humidity sensor is calibrated using a standard humidity generator to ensure accurate detection of atmosphere parameters.

[0020] The control model is a parameter mapping table established based on multiple sets of process experimental data from the aforementioned tests. It includes the correspondence between welding current, laser power, welding speed and molten pool cooling rate and defect tendency under different base material grades and plate thicknesses, serving as the parameter benchmark for feedback adjustment.

[0021] S4. Dual-path feedback control fully automatic welding: Upon starting welding, the multi-heat source system moves synchronously along the weld seam with the welding actuator, simultaneously executing the following processes: S4.1. The pre-pulsed laser performs real-time secondary defilm removal and preheating on the weld bevel, removing the ultra-thin oxide film newly formed on the surface of the base material during the interval between cleaning and welding. At the same time, the base material in the bevel area is preheated to 150°C to 220°C to reduce the solidification temperature gradient of the molten pool.

[0022] The solidification temperature gradient of the molten pool, as referred to here, is the temperature change per unit distance perpendicular to the weld width during the solidification process. In conventional welding without preheating, the temperature at the center of the molten pool is approximately 2000℃, while the base metal on both sides of the bevel is at room temperature. This extreme temperature difference and high temperature gradient cause heat to dissipate rapidly laterally into the base metal, leading to the directional growth of coarse columnar grains along the heat dissipation direction. Furthermore, the difference in thermal expansion and contraction across different parts of the weld results in high thermal stress during solidification, making it prone to hot cracking. Preheating with a laser to raise the base temperature of the bevel base metal reduces the overall temperature difference between the molten pool and the surrounding base metal, lowers the temperature gradient, and makes lateral heat dissipation from the molten pool more uniform. This inhibits the directional growth of columnar grains, reduces the unevenness of lateral weld shrinkage, and decreases the tendency for hot cracking.

[0023] S4.2 The main welding unit uses laser and electric arc hybrid welding for weld deposition, and achieves closed-loop control of the solidification behavior of the molten pool through the first feedback control loop.

[0024] The aforementioned first feedback control loop consists of a molten pool condition monitoring module, a computational controller, a laser power supply, a welding power supply, and a walking servo mechanism. All hardware components are standard equipment in the welding control field. Its working principle is as follows: Real-time data on the molten pool temperature field distribution, weld depth, weld width, and solidification front advance speed are collected at a sampling frequency of no less than 1000Hz. The computational controller compares the measured molten pool cooling rate with a preset control range, using feedforward and PID feedback adjustment to dynamically adjust welding parameters such as laser power, welding current, welding speed, and wire feed speed. When the cooling rate exceeds the upper limit, the laser power is appropriately increased or the welding speed is decreased; when the cooling rate falls below the lower limit, the laser power is appropriately decreased or the welding speed is increased, stabilizing the molten pool cooling rate between 120℃ / s and 200℃ / s. Within this cooling rate range, the molten pool solidification rate is moderate, ensuring sufficient time for dissolved hydrogen to diffuse and escape while avoiding excessive grain coarsening. Simultaneously, it ensures consistent molten pool solidification at both the beginning and end of the weld, suppressing hot cracking.

[0025] S4.3. Control of the inert protective atmosphere of the weld is achieved through the second feedback control loop.

[0026] The aforementioned second feedback control loop consists of a weld atmosphere monitoring module, a computational controller, and a multi-channel gas flow regulating valve. All hardware components are standard equipment in the field of welding atmosphere control. Its operation is as follows: Oxygen content and humidity data are collected in real-time within the protective shield on the front side of the weld and the gas chamber on the back side using a sampling frequency of no less than 100Hz. The computational controller compares the measured values ​​with preset thresholds and dynamically adjusts the flow rate and outlet angle of the shielding gas in the inner and outer layers of the front side and the back side. When the oxygen content or humidity exceeds the threshold, the shielding gas flow rate is increased accordingly. The flow rate is automatically increased by 30% during the arc initiation and arc termination phases to ensure that the oxygen content in the weld area is less than 50ppm and the humidity is less than 100ppm throughout the entire weld area, isolating the molten pool from external oxygen and water vapor, and suppressing hydrogen porosity and oxidation defects.

[0027] The first feedback control loop and the second feedback control loop are two parallel and independent systems. They share the position and timing reference of the welding actuator and independently regulate the formation mechanism of two different defects, hot cracks and hydrogen porosity, respectively. There is no control relationship between them. At the same time, the control parameter ranges of the two are matched. The cooling rate range set by the first loop ensures that hydrogen has sufficient diffusion time, while the low oxygen and low humidity environment ensured by the second loop can reduce the hydrogen source. The two work together to achieve effective prevention and control of defects throughout the long weld.

[0028] S4.4 The rear-mounted ultrasonic impact unit moves synchronously with the welding actuator, performing real-time synchronous impact on the high-temperature weld within 0.5s to 2s after welding, where the temperature is in the plastic range of 300℃ to 500℃. In this temperature range, the weld metal has completely solidified and is in a good plastic state. The impact treatment can simultaneously achieve three effects: first, it promotes weld grain refinement through plastic deformation, increasing the proportion of equiaxed grains; second, it breaks the stress accumulation in the brittle temperature range, releasing residual welding stress; and third, it promotes the diffusion and escape of residual hydrogen inside the weld, further reducing the tendency for porosity defects.

[0029] S5. Post-weld online inspection and feedback correction: After welding is completed, the online defect detection module scans and inspects the weld along the walking mechanism, and feeds back the defect location and type data to the control system. The control system drives the welding execution mechanism to return to the defect location and performs on-site repair welding to correct the defect area that exceeds the standard, so as to realize the fully automated production process.

[0030] This invention, through the synergistic effect of the aforementioned technical features, simultaneously addresses multiple aspects such as molten pool stability support, end-to-end atmosphere protection, welding stress control, and hydrogen escape, significantly reducing weld defect rate and improving welding efficiency. Experimental verification shows that compared to solutions using only high-temperature online ultrasonic impact, only electronic gear synchronous follow-up support, or only dual-path feedback control, this solution achieves a more significant reduction in weld defect rate and a smaller decrease in strength at the weld joint. Attached Figure Description

[0031] Figure 1 This is a flowchart of the welding method described in this invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. This method can be implemented using conventional long-stroke gantry welding equipment, and all welding methods employing the following process steps fall within the protection scope of the present invention.

[0033] Example 1 This embodiment targets large-size 5052 aluminum alloy honeycomb panels for rail transit vehicle bodies. The size of a single panel is 12m × 1.5m, the thickness of the top and bottom panels is 2mm, the aluminum honeycomb core size is 6mm, the foil thickness is 0.08mm, the continuous length of the butt weld is 12m, and the welding technical requirements are: the weld has no excessive hot cracks, no pores larger than 0.2mm, the weld is uniformly formed, and the overall flatness of the panel is less than 0.5mm / m.

[0034] First, the weld bevel and the 25mm area on both sides are cleaned with dry pulsed laser with a laser power of 120W, a scanning speed of 8m / min, and a repetition frequency of 30kHz to remove the surface oxide film and adsorbed water vapor. After cleaning, the surface roughness Ra of the base material reaches 0.5μm or less. Immediately after cleaning, 99.999% high-purity argon gas is introduced to form a protective gas curtain until welding is started.

[0035] The pre-treated honeycomb panel is clamped and fixed on the tooling platform, and the butt joint gap is adjusted to 0.1mm and the misalignment is 0.08mm. The follower flexible back support is attached to the back of the weld and coaxially aligned with the MIG welding torch mounted on the welding actuator. Electronic gear hard synchronization is adopted. The driving shaft is the gantry welding torch travel axis, and the driven shaft is the back support travel axis. The two axes are connected to the real-time bus, and the electronic gear ratio is set to 1:1. They share the same system time. The actual full-stroke synchronization accuracy is ±0.015mm and the synchronization response time is 0.8ms. Argon gas is synchronously introduced into the gas path inside the back support to provide an inert gas atmosphere protection on the back.

[0036] A reference target plate is placed on the tooling platform. The lateral positions of the front laser, laser-MIG composite welding head, and rear ultrasonic impact head in the multi-heat source system are adjusted so that the indicator light spots of the three are all aligned with the center line of the weld, with a coaxiality deviation of less than 0.08 mm. The infrared thermometer in the molten pool condition monitoring module is calibrated using a standard blackbody furnace, the oxygen content sensor in the weld atmosphere monitoring module is calibrated using a standard gas, and the humidity sensor is calibrated using a standard humidity source. The preset molten pool cooling rate control range is 150℃ / s~180℃ / s, the protective gas oxygen content threshold is 30ppm, and the humidity threshold is 80ppm. The welding parameters and molten pool condition control model of the 5052 aluminum alloy base material in this embodiment are loaded into the control system.

[0037] Welding begins, and the welding actuator moves along the weld seam at a speed of 1.2 m / min. The multi-heat source system and the ultrasonic impact unit move synchronously, and the following processes are performed simultaneously: The pre-pulse laser has a power of 60W, a spot diameter of 0.8mm, and a distance of 15mm from the composite welding head. It preheats the bevel to 180℃ to reduce the solidification temperature gradient of the molten pool. The main welding adopts fiber laser-MIG hybrid welding with a laser power of 2500W, a welding current of 200A, and ER5356 welding material with a diameter of 1.2mm. The first feedback loop has a sampling frequency of 2000Hz, which collects the molten pool temperature and solidification rate in real time. The laser power and welding speed are dynamically adjusted through feedforward and PID algorithm to stabilize the molten pool cooling rate at 150℃ / s~180℃ / s. The weld front protection uses a double-layer laminar flow hood, with an inner layer of argon gas flow rate of 25 L / min and an outer layer of 15 L / min. The inert shielding gas flow rate on the weld back is 20 L / min. During the arc initiation and arc termination phases, the flow rate increases by 30%, i.e., the inner layer of argon gas flow rate is 32.5 L / min, the outer layer is 19.5 L / min, and the inert shielding gas flow rate on the weld back is 26 L / min. The second feedback loop has a sampling frequency of 200 Hz, which collects oxygen content and humidity data on both sides in real time and dynamically fine-tunes the gas flow rate to ensure that the oxygen content in the weld area is ≤30 ppm and the humidity is ≤80 ppm. The ultrasonic impact unit is activated 1 second after welding and at a weld temperature of 400℃. There are 3 impact heads with arc surfaces, arranged along the width of the weld. The impact frequency is 20kHz, the amplitude is 20μm, the impact pressure is 70N, and the impact area covers the weld and the heat-affected zone of 5mm on both sides.

[0038] After welding is completed, the ultrasonic phased array probe of the online defect detection module scans the entire weld seam along with the walking mechanism. No defects exceeding the standard are found, and no repair welding is required.

[0039] Testing revealed that the 12m long weld completed in this embodiment had no excessive hot cracks, the maximum porosity was less than 0.1mm, and there were no defects exceeding the standard; the weld penetration deviation at the beginning and end was less than 0.15mm, and the overall flatness of the plate was less than 0.3mm / m; the total welding time was 10 minutes, which greatly improved the welding efficiency compared with traditional manual TIG welding of the same specification; the weld joint strength coefficient was 0.92, which is basically close to the strength of the base material.

[0040] Example 2 This embodiment targets large-size 6061-T6 aluminum alloy honeycomb panels for building curtain walls. Each panel measures 8m x 2m, with top and bottom panel thicknesses of 1.5mm and a continuous butt weld length of 8m. Compared to Embodiment 1, the process parameters in this embodiment are adjusted as follows: The pre-welding laser cleaning power was 80W, and the scanning speed was 10m / min; the preheating laser power was 40W, and the preheating temperature was 160℃; the main welding laser power was 2000W, the welding current was 160A, the welding speed was 1.5m / min, and the molten pool cooling rate was controlled between 160℃ / s and 190℃ / s; ultrasonic impact was performed 0.8s after welding at a weld temperature of 420℃, with an impact frequency of 25kHz and an amplitude of 15μm, and the shielding gas flow rate during the arc initiation and termination phases was increased by 30%. The remaining steps were the same as in Example 1.

[0041] Testing revealed that the 8m long weld completed in this embodiment had no excessive hot cracks or excessive porosity, the flatness of the plate was no greater than 0.35mm / m, and the joint strength coefficient was 0.89, meeting the requirements for use in high-end building curtain walls.

[0042] Example 3 This embodiment is for large-size 7075-T6 aluminum alloy honeycomb panels used in aerospace cabins. The size of a single panel is 6m × 1m, the thickness of the top and bottom panels is 3mm, and the continuous length of the butt weld is 6m. The process parameters are adjusted compared to Embodiment 1 as follows: The pre-welding laser cleaning power was 150W, and the scanning speed was 6m / min; the preheating laser power was 80W, and the preheating temperature was 200℃; the main welding laser power was 4000W, the welding current was 280A, the welding speed was 0.9m / min, and the molten pool cooling rate was controlled between 130℃ / s and 160℃ / s; ultrasonic impact was performed 1.5s after welding, at a weld temperature of 360℃, with an impact frequency of 18kHz and an amplitude of 25μm. ER5183 aluminum alloy welding wire was used, and the first feedback adopted feedforward plus PID feedback regulation. The remaining steps were the same as in Example 1.

[0043] Testing revealed that the 6m long weld completed in this embodiment had no excessive hot cracks, a maximum porosity of 0.08mm, and a weld joint strength coefficient of 0.88, meeting the requirements for use in aerospace cabins.

[0044] Comparative Example 1 This comparative example uses traditional manual TIG welding. The welding object is the same 12m long 5052 aluminum alloy honeycomb panel as in Example 1. Before welding, the bevel is ground with a mechanical wire brush, and the back is unprotected. After welding, it is cooled to room temperature and then subjected to ultrasonic impact. Inspection revealed three pores larger than 0.3mm in the weld, several microcracks exceeding the standard, one of which was approximately 15mm long. The total welding time was 96 minutes, and the joint strength coefficient was 0.65, significantly lower than the base material strength.

[0045] Comparative Example 2 This comparative example uses conventional laser-MIG hybrid welding. The welding object is the same as in Example 2: a large-size 6061-T6 aluminum alloy honeycomb panel for a building curtain wall. Welding parameters are fixed, without dual-path feedback adjustment. A standard position-following back support is used on the back, with a following error of 0.2mm. After welding and cooling to room temperature, ultrasonic impact testing is performed. Inspection revealed two pores larger than 0.2mm, one microcrack approximately 8mm long, and a weld penetration deviation of 0.5mm between the beginning and end, indicating poor quality consistency. The joint strength coefficient was 0.72.

[0046] Comparative Example 3 This comparative example employs an automated welding process with a follow-up back support. The welding object is the same as that in Example 3: a large-size 7075-T6 aluminum alloy honeycomb panel for aerospace cabins. The welding process includes preheating with a laser and ultrasonic impact after the weld has cooled to room temperature, without dual-path feedback adjustment. Inspection revealed one pore larger than 0.2 mm in the weld, a tendency for microcracks in the middle section of the weld, and the inconsistency in quality caused by heat accumulation in the long weld was not effectively resolved. The joint strength coefficient was 0.78.

[0047] Comparative Example 4 The welding object in this comparative example is the same as in Example 1, except that the ultrasonic impact time was adjusted to 0.3 seconds after welding, and the other parameters are the same as in Example 1. Testing showed that the temperature in the weld impact zone was 550℃. At this point, the weld metal had not fully solidified, and the impact resulted in poor weld surface formation, with two microcracks approximately 5mm long and numerous porosity defects. The joint strength coefficient was 0.75, failing to meet the quality requirements.

[0048] Comparative Example 5 The welding object in this comparative example is the same as in Example 1, except that the ultrasonic impact time was adjusted to 3 seconds after welding. At this time, the weld temperature had dropped to 250°C, which is below the plastic range. The other parameters are the same as in Example 1. Testing showed that ultrasonic impact could only eliminate some residual surface stress and could not refine the internal grains of the weld. Multiple microcracks were present inside the weld, and there were also many pores. The joint strength coefficient was 0.76, which did not meet the quality requirements.

[0049] Comparative Example 6 The welding object in this comparative example is the same as that in Example 1, except that the cooling rate of the molten pool is adjusted to 100℃ / s, and the other parameters are the same as those in Example 1. Inspection revealed that the weld grains were coarse, the heat-affected zone was wide, there was one crystallization crack approximately 10mm long, and multiple defects exceeding the standard (porosity, microcracks, uneven surface). The joint strength coefficient was 0.7, failing to meet the quality requirements.

[0050] The above embodiments and comparative examples demonstrate that the process parameter range selected in this invention is a reasonable range verified by experiments. When the parameters exceed the range of this invention, the weld quality will significantly decrease. Using the technical solution of this invention can effectively improve the welding quality and efficiency of long welds in large-size aluminum alloy honeycomb panels.

Claims

1. A method for welding long welds in large-size aluminum alloy honeycomb panels, used for welding ultra-long butt welds in large-size aluminum alloy honeycomb sandwich panels, characterized in that, Includes the following steps: S1. Pre-welding treatment: Dry pulsed laser cleaning is performed on the weld bevel and both sides to remove the Al2O3 oxide film, oil and adsorbed water vapor on the surface; after cleaning, high-purity argon gas is introduced to form a passivation protective gas curtain until welding starts, which inhibits secondary oxidation and hydrogen adsorption on the base material surface. S2. Plate clamping and positioning: Fix the pre-treated honeycomb panel onto the tooling platform and adjust the gap and misalignment of the weld joint; attach the follow-up flexible back support device to the back of the weld and align it coaxially with the welding actuator. During the welding process, the back support device and the welding torch follow each other throughout the process through electronic gear hard synchronization, while providing back support and inert gas protection for the weld. S3. Setting up the welding control model: The coaxiality of the multi-heat source system arranged sequentially along the welding direction is calibrated, and the molten pool condition monitoring module and weld atmosphere monitoring module are calibrated; the threshold values ​​of welding process parameters and the control range of molten pool condition are preset, and a control model composed of welding parameters, molten pool condition and defect tendency is established. S4. Dual-feedback loop controlled welding: When welding is started, the multi-heat source system moves synchronously along the weld seam with the welding actuator, simultaneously executing the following processes: S4.

1. The pre-pulsed laser performs real-time secondary defilm removal and preheating on the weld bevel, breaking the newly formed ultra-thin oxide film before welding, and preheating the base material in the bevel area to 150°C to 220°C to reduce the solidification temperature gradient of the molten pool. S4.2 The main welding unit uses laser and arc composite welding to deposit welds. Through the first feedback control loop, the molten pool temperature, penetration depth and solidification rate data are collected in real time and compared with the preset threshold. The relevant welding parameters are dynamically adjusted to control the molten pool cooling rate between 120℃ / s and 200℃ / s to ensure the consistency of the solidification behavior of the molten pool of the entire weld. S4.

3. The oxygen content and ambient humidity data of the front and back of the weld are collected in real time through the second feedback control loop, and the supply of inert protective gas on the front and back is dynamically adjusted to control the oxygen content and humidity of the weld area throughout the process, and to isolate the molten pool from contact with external oxygen and water vapor. S4.

4. For high-temperature welds with temperatures in the plastic range of 300℃ to 500℃ within 0.5s to 2s after welding, an ultrasonic impact unit is used for real-time synchronous impact to achieve weld grain refinement, elimination of welding residual stress, and escape of residual hydrogen. S5. Post-weld online inspection and feedback correction: After welding is completed, the online defect detection module scans and inspects the weld throughout the process, and feeds back the defect location and type data to the control system. Areas with defects exceeding the standard are repaired by on-site welding.

2. The welding method according to claim 1, characterized in that, In step S1, the power of the pulsed laser cleaning is 50W to 200W, the scanning speed is 5m / min to 10m / min, the repetition frequency is 20kHz to 50kHz, and the surface roughness Ra of the substrate after cleaning is less than 0.6μm.

3. The welding method according to claim 1, characterized in that, In step S4.1, the power of the pre-pulse laser is 30W to 100W, the spot diameter is 0.5mm to 1mm, and the distance between it and the main welding unit is 10mm to 20mm.

4. The welding method according to claim 1, characterized in that, In step S4.2, the laser and arc hybrid welding is fiber laser and MIG arc hybrid welding, with a laser power of 1500W to 6000W, a welding current of 120A to 300A, a welding speed of 0.8m / min to 2m / min, and an aluminum alloy welding wire that matches the base material with a diameter of 1.0mm to 1.6mm.

5. The welding method according to claim 1, characterized in that, In step S4.3, the inert protective gas on the front side adopts a double-layer laminar flow protective cover, with the inner layer argon flow rate being 20L / min to 30L / min, the outer layer argon flow rate being 10L / min to 20L / min, and the back inert protective gas flow rate being 15L / min to 25L / min; the inert protective gas flow rate is increased by 30% accordingly during the arc initiation and arc termination phases.

6. The welding method according to claim 1, characterized in that, In step S4.4, the impact head of the ultrasonic impact unit is an arc surface that matches the weld surface. Multiple impact heads are arranged along the width direction of the weld. The impact frequency is 15kHz to 30kHz, the impact amplitude is 10μm to 30μm, the impact head pressure is 50N to 100N and is adjustable. The impact area covers the weld and the heat-affected zone of 5mm on both sides.

7. The welding method according to claim 1, characterized in that, In step S4.2, the first feedback control loop adopts a feedforward plus PID feedback adjustment method to adjust the main welding parameters in advance according to the preheating temperature of the laser; in step S4.3, the second feedback control loop adjusts the shielding gas flow rate in segments according to the weld position.

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