A welding method and system for reducing heat-affected zone of laser welding and refining structure

Abstract

The present invention belongs to the field of laser welding technology, and specifically discloses a welding method and system for reducing the heat affected zone of laser welding and refining the organization. The method includes: pre-treating the surface of the workpiece to be welded; S2 setting the welding process parameters and the working parameters of the conformal condensation plate; S3 integrating an ultrasonic generator, and the laser head and the ultrasonic generator are arranged at intervals; S4 welding the workpiece in a vacuum environment according to the set welding process parameters, the laser head moves according to a preset path and speed, the conformal condensation plate works, and the ultrasonic generator is turned on at the same time to perform ultrasonic vibration on the weld of the workpiece; S5 recrystallization annealing of the workpiece at a specified temperature. The present invention accurately controls the welding energy distribution, and at the same time assists the accompanying condensation plate with adaptive temperature adjustment and the accompanying ultrasonic treatment of the weld, thereby optimizing and controlling the laser welding forming and quality, improving the uniformity of organizational performance, so as to reduce the heat affected zone of laser welding and refine the organization.

Description

Technical Field

[0001] The present invention belongs to the field of laser welding, and more specifically, relates to a welding method and system for reducing a laser welding heat-affected zone and refining a structure. Background Art

[0002] During the melting welding process, the metal material melts under the action of the heat source to form a weld. Between the weld metal and the base material, there is a certain range of area affected by the heat of the welding process, which is called the heat-affected zone. Due to the effect of the welding heat cycle, the structure morphology of the weld zone and the heat-affected zone is different from that of the base material, and often shows coarse structure, which in turn affects the service performance of the welded joint. In many practical engineering applications, there are often certain requirements for the width of the heat-affected zone and the structure morphology of the weld. Therefore, reducing the width of the heat-affected zone and refining the weld zone structure are of great significance to improving the service performance of the welded joint.

[0003] Welding heat input has an important influence on the width of the welding heat affected zone and the microstructure of the weld. In recent years, research has confirmed that vacuum laser welding can significantly reduce the heat input of laser welding. Under the same welding heat input, vacuum laser welding can achieve more than twice the penetration depth of conventional laser welding. Chinese patent CN106271061B discloses an unconventional low-temperature gas shielded laser welding method, which adopts a low-temperature gas shielded laser welding method. On the basis of conventional laser welding, the welding shielding gas supply device is improved. However, this method uses low-temperature shielding gas to protect and cool the molten pool and its vicinity. The atmosphere environment has high requirements and is difficult to control. At the same time, it is still necessary to groove the parent material and cannot meet the one-time forming of the connection of medium and thick plates. The process is relatively complicated. Patent document CN201210002191.6 discloses a vacuum laser welding device and method. The process means of this method are too briefly described, and the swing laser tuning energy field is not used, and the microstructure uniformity and performance consistency of the thick welded joint in the thickness direction cannot be guaranteed.

[0004] Based on the above defects and shortcomings, this field urgently needs to propose a welding method that reduces the heat affected zone of laser welding and refines the structure. The welding substrate can be directly cooled at any time, and the process parameters of vacuum laser welding can be optimized. A composite process of impact vibration and heat treatment recrystallization annealing is performed after welding to achieve the goal of reducing the width of the welding heat affected zone and refining the grain size of the weld. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a welding method and system for reducing the heat affected zone of laser welding and refining the organization. In combination with the characteristics of vacuum laser welding itself and the control of its welding process parameters, a welding method for reducing the heat affected zone of laser welding and refining the organization is designed accordingly. Through a high vacuum environment and a swinging laser tuning energy field, the laser output power is synchronously regulated during the swinging process. At the same time, the accompanying condensation plate with adaptive temperature adjustment is assisted to cool the welding substrate at any time, and the ultrasonic vibration impact is used to carry out accompanying treatment of the weld, so as to accurately control the welding energy distribution, and then optimize and control the laser welding forming and quality, improve the uniformity of organizational performance, reduce the heat affected zone of laser welding and refine the organization, and can achieve one-time forming with higher welding quality. It can effectively suppress the generation of feather and spatter, improve welding stability, and effectively reduce common defects such as pores, depressions, and back weld nodules.

[0006] Therefore, the use of vacuum laser welding and the use of a cold zone substrate during welding can significantly reduce the welding heat input, increase the cooling rate, and perform a composite process of impact vibration and heat treatment recrystallization annealing after welding, which can achieve the goal of reducing the width of the welding heat affected zone and refining the weld grain size.

[0007] To achieve the above object, according to one aspect of the present invention, a welding method for reducing the heat affected zone of laser welding and refining the structure is proposed, comprising the following steps:

[0008] S1 pre-treats the surface of the workpiece to be welded, and then places the pre-treated workpiece on a workbench, while a conformal condensation plate is arranged between the workpiece and the workbench;

[0009] S2 sets welding process parameters according to the material and thickness of the workpiece, and also sets working parameters of the conformal condensation plate;

[0010] S3: an ultrasonic generator is integrated on a laser head for welding, and the laser head and the ultrasonic generator are arranged at intervals;

[0011] S4 provides a vacuum environment during the welding process, and welds the workpiece in the vacuum environment according to the set welding process parameters. The laser head moves according to the preset path and speed, the conformal condensation plate works, and the ultrasonic generator is turned on to perform ultrasonic vibration on the weld of the workpiece;

[0012] S5 After the workpiece welding is completed and all welds are subjected to ultrasonic vibration, the workpiece is subjected to recrystallization annealing at a specified temperature.

[0013] As further preferred, in step S2, the welding process parameters include vacuum pressure, laser power, welding speed and defocus, wherein:

[0014] The vacuum pressure is 100 to 10000 Pa, the laser power of the laser is 3500 to 5500 W, the welding speed is 0.3 to 1.8 m / min, and the defocusing amount is -10 to 10 mm.

[0015] As further preferred, in step S2, the operating temperature range of the conformal condensation plate is -50°C to 20°C, and the flow rate of the coolant is adaptively adjusted according to the temperature of the workpiece and the temperature of the conformal condensation plate.

[0016] As a further preference, in step S3, the laser head performs welding according to a swinging walking path, which is achieved by the swinging of the galvanometer inside the laser head, so as to convert the light spot output by the laser head into a swinging light spot. The trajectory of the swinging light spot movement is generally one or more of a straight line, a circle, an 8-shape, an ∞-shape, a square or a triangle. Special graphics can be achieved by programming to control the swinging of the galvanometer inside the laser head.

[0017] As a further preference, the swing amplitude of the swing light spot is 0.4 to 10 mm, which is achieved by controlling the coordinated high-speed movement of the galvanometer inside the laser head on the X and Y axes.

[0018] As further preferred, in step S5, the workpiece is placed in a heat treatment furnace for recrystallization annealing at 550-750°C.

[0019] As further preferred, in step S2, the maximum thickness of the workpiece is determined by the upper limit of the laser head power and does not exceed 200 mm.

[0020] As a further preferred embodiment, the pretreatment includes: smoothing the front and back sides of the workpiece where the welding part is to be welded, and grinding, pickling or laser cleaning the surface of the workpiece where the welding part is to be welded.

[0021] According to another aspect of the present invention, there is also provided a welding system for reducing the heat affected zone of laser welding and refining the structure, comprising:

[0022] Pre-welding pretreatment mechanism, to pre-treat the surface of the workpiece to be welded;

[0023] Welding tooling, used to place the pre-treated workpiece on the welding platform in the vacuum chamber;

[0024] A conformal condensation plate is provided between the welding fixture and the workpiece and is used to cool the weld of the workpiece in real time;

[0025] The swing laser path planning mechanism is used to place the laser head in the vacuum chamber according to the actual situation, adjust the swing laser spot shape to the required shape, align the spot with the welding starting point, and determine that the spot walking path covers the entire weld gap through the walking mechanism or weld tracking device;

[0026] Laser oscillation welding parameter control module, used to set corresponding welding process parameters such as welding speed, welding power, and defocus according to actual welding requirements, and adjust oscillation parameters such as laser oscillation mode, oscillation frequency, and oscillation amplitude according to weld performance requirements and welding gap adaptability, and optimize and control the laser energy distribution during welding until welding is completed;

[0027] The laser welding mechanism comprises a laser head, which is communicatively connected with the laser swing welding parameter control module and the swing laser path planning mechanism, and is used for vacuum laser welding of the workpiece;

[0028] An ultrasonic generating device, arranged at a distance from the laser head, for ultrasonically vibrating the weld of the workpiece;

[0029] The recrystallization annealing mechanism is used to perform recrystallization annealing at a specified temperature on the workpiece after the welding of the workpiece is completed and all welds are subjected to ultrasonic vibration.

[0030] As a further preference, the operating temperature range of the conformal condensation plate is -50°C to 20°C.

[0031] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0032] 1. The present invention uses a high vacuum environment and a swinging laser tuning energy field to synchronously adjust the laser output power during the swinging process, and at the same time assists the accompanying condensation plate with adaptive temperature adjustment to cool the welding substrate at any time, and the ultrasonic vibration impact performs accompanying treatment on the weld, so as to accurately control the welding energy distribution, and then optimize and control the laser welding forming and quality, improve the uniformity of organizational performance, reduce the laser welding heat affected zone and refine the organization, achieve one-time forming, have higher welding quality, effectively suppress the generation of feather and spatter, improve welding stability, and effectively reduce common defects such as pores, depressions, and back weld nodules.

[0033] 2. The swinging laser spot shape of the present invention is the laser swinging walking path. The swinging of the laser is realized by controlling the coordinated high-speed motion of the galvanometer inside the laser head on the X and Y axes. The swinging spot shape is generally one or more of a straight line, a circle, an 8-shape, an ∞-shape, a square or a triangle. Special graphics can be realized by programming to control the swinging of the galvanometer inside the laser head, and the laser energy distribution in the welding process is optimized and regulated by the swinging laser regulation method.

[0034] 3. Compared with conventional single laser vacuum welding, the present invention adds a means of swinging laser for energy field tuning, which improves the stability of vacuum laser welding and has the effect of weld shaping, making the upper and lower widths of the weld joint more consistent, so that the organizational properties of the weld joint in the thickness direction are more uniform, thereby improving the welding quality.

[0035] 4. The vacuum chamber of the present invention delivers dry high-purity inert gas into the chamber when the pressure reaches below 1000Pa, and controls the dynamic balance of air intake and exhaust in the chamber to be adjusted to a specified vacuum environment condition. The high vacuum environment can double the welding depth.

[0036] 5. The present invention seeks the nonlinear mapping relationship between welding process parameters and weld quality, thereby finding the optimal welding process parameters according to welding quality, plate thickness, etc., optimizing and regulating laser welding forming and quality, improving the uniformity of organizational performance, reducing the heat affected zone of laser welding and refining the organization. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of a welding method for reducing the heat-affected zone of laser welding and refining the structure according to a preferred embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of the structure of a device involved in a welding method for reducing the heat-affected zone of laser welding and refining the structure of the present invention;

[0039] Figure 3 Schematic diagram of the microstructure of the joint obtained by welding using the method of the present invention;

[0040] Figure 4 It is the microstructural characteristics of different areas of the joint after welding using the method of the present invention.

[0041] In all the drawings, the same reference numerals represent the same technical features, specifically: 1-laser head, 2-vacuum chamber, 3-connecting seat, 4-ultrasonic generating device, 5-workpiece to be processed, 6-tooling fixture, 7-conformable condensation plate. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] like Figure 1 and Figure 2 As shown, a welding method for reducing the heat affected zone of laser welding and refining the structure provided by an embodiment of the present invention includes the following steps:

[0044] S1 pre-treats the surface of the workpiece to be welded, and then places the pre-treated workpiece on a workbench, while a conformal condensation plate is arranged between the workpiece and the workbench.

[0045] During the pretreatment process, the front and back sides of the workpiece to be welded are processed flat, and the surface of the workpiece to be welded is polished, pickled or laser cleaned. More specifically, the workpiece to be welded is processed to the required accuracy as required, and the surface oxide film is removed by sandpaper polishing, and then immersed in acetone and ultrasonically cleaned to remove oil stains. The polished or cleaned workpiece to be welded is fixed on the welding fixture and placed on the workbench in the vacuum chamber.

[0046] In this embodiment, the laser head used for welding is placed in a vacuum chamber, so that the workpiece to be welded and the laser head are located in a set vacuum environment. A workbench is provided in the vacuum chamber, and a welding tool is provided on the workbench, which is used to place the pre-treated workpiece on the welding workbench in the vacuum chamber. Correspondingly, a conformal condensation plate is also provided between the workbench and the workpiece for real-time cooling of the weld of the workpiece. In a preferred embodiment of the present invention, the conformal condensation plate includes a plate body and a coolant flow channel provided in the plate body, and the temperature and flow rate of the coolant are controlled so that the refrigeration working temperature range provided by the conformal condensation plate is -50°C to 20°C. Of course, the above is only a specific embodiment of the present invention. In the present invention, the flow rate of the coolant is adaptively adjusted according to the temperature of the workpiece and the temperature of the conformal condensation plate. In this way, the welding substrate is directly cooled at any time to achieve the goal of reducing the width of the welding heat affected zone and refining the grain size of the weld.

[0047] S2 sets welding process parameters according to the material and thickness of the workpiece, and also sets working parameters of the conformal condensation plate.

[0048] In a preferred embodiment of the present invention, the welding process parameters include vacuum pressure, laser power, welding speed and defocus, wherein the vacuum pressure is 100 to 10000 Pa, the laser power of the laser is 3500 to 5500 W, the welding speed is 0.3 to 1.8 m / min, and the defocus is -10 to 10 mm.

[0049] Of course, the above is only the welding process parameter range of the preferred embodiment of the present invention. In the present invention, the welding process parameters are optimized and calculated according to the existing vacuum welding welding process parameters and weld parameters to obtain the optimal welding process parameters.

[0050] In one embodiment of the present invention, the weld parameters are first extracted based on a large number of weld photos. The weld parameters include weld width, weld area fine grain size, weld depth and bubble number. An evaluation function of welding quality is constructed based on the above weld parameters:

[0051] A(x)=∑α i W i

[0052] Where A(x) is the evaluation function, W i is the i-th weld parameter, α i is the weight of the i-th weld parameter, which is a constant.

[0053] Then, a training data set is established according to the historical welding process parameters and the corresponding plate thickness, and the training data set is used as the input of the support vector machine model, and the corresponding welding quality parameters are used as the output of the support vector machine model. The support vector machine model is optimized and trained to obtain the nonlinear mapping relationship between the vacuum welding parameters, the corresponding plate thickness and the weld parameters. The nonlinear mapping relationship between the vacuum welding parameters, the corresponding plate thickness and the weld parameters and the above-mentioned evaluation function are used as the objective function, and the welding process parameters and the corresponding plate thickness are used as constraints to construct a neural network model, and the welding process parameters are multi-objective optimized according to the set iteration termination conditions to obtain the optimal welding process parameter set corresponding to the plate thickness. In a preferred embodiment of the present invention, the neural network model can adopt the NSGA-II model.

[0054] Among them, the Gaussian kernel function is selected to build the support vector machine model. The Gaussian kernel function expression is as follows:

[0055]

[0056] Among them, x and d are input variables, x i is the i-th sample data, x j is the jth sample data, σ 2 is the core width parameter, d' is the plate thickness, w1 is the first weight, and w2 is the second weight.

[0057] At the same time, in the above optimization process, the Gaussian kernel function is selected to construct the support vector machine model. Five-fold cross validation is used for parameter optimization to determine the optimal parameter combination of the penalty parameter of the support vector machine model and the Gaussian kernel function kernel width parameter to obtain the optimized trained support vector machine model.

[0058] The working parameters of the conformable condensation plate can be directly set according to the vacuum welding parameters. In a preferred embodiment of the present invention, a temperature sensor is provided on the conformable condensation plate to directly detect the temperature of the workpiece and the conformable condensation plate, and the working temperature is adjusted according to the temperature of the workpiece and the conformable condensation plate, so as to directly cool the welding substrate at any time.

[0059] S3: An ultrasonic generator is integrated on a laser head for welding, and the laser head and the ultrasonic generator are arranged at an interval. In this step, the laser head performs welding according to a swinging walking path, which is achieved by the swinging of the internal galvanometer of the laser head, so as to convert the light spot output by the laser head into a swinging light spot. The trajectory of the swinging light spot is generally one or more of a straight line, a circle, an 8-shaped, an ∞-shaped, a square or a triangle. Special graphics can be achieved by programming to control the swinging of the internal galvanometer of the laser head.

[0060] Preferably, the swing amplitude of the swing light spot is 0.4-10 mm, which is achieved by controlling the coordinated high-speed movement of the galvanometer inside the laser head on the X and Y axes.

[0061] Specifically, Figure 2 As shown, the laser welding mechanism also includes a laser driving base and a laser driving assembly. A laser head 1 and an ultrasonic generating device 4 are provided on the laser driving base. The laser head 1 and the ultrasonic generating device 4 are arranged at intervals. In this way, after the laser head welds the workpiece, the ultrasonic generating device 4 performs ultrasonic vibration impact on the weld, which can remove the extremely small pores generated during the welding process on the one hand, and refine the weld grain size on the other hand, and reduce the welding heat affected area.

[0062] In the present invention, the laser head 1 and the ultrasonic generator 4 work independently without affecting each other, that is, the laser head 1 is in front, and the workpiece is laser welded according to the preset motion trajectory, and the ultrasonic generator 4 is in the back, and the molten pool at the welding point is subjected to ultrasonic vibration impact. Further, in order to achieve the situation where the trajectory of the swinging spot movement is circular, 8-shaped, ∞-shaped, square or triangular, in the present invention, the interval distance between the laser head 1 and the ultrasonic generator 4 is an integer number of cycles, so that the laser head 1 and the ultrasonic generator 4 have the same motion trajectory.

[0063] S4 provides a vacuum environment during the welding process. According to the set welding process parameters, the workpiece is welded in the vacuum environment. The laser head moves according to the preset path and speed, the conformal condensation plate works, and the ultrasonic generator is turned on to perform ultrasonic vibration on the weld of the workpiece. In this step, the vacuum environment plus the swinging laser and the ultrasonic generator accelerate the flow of the molten pool, which is conducive to the escape of pores and effectively eliminates metallurgical pores generated during the welding process.

[0064] S5 After the workpiece welding is completed and all welds are subjected to ultrasonic vibration, the workpiece is subjected to recrystallization annealing at a specified temperature.

[0065] According to another aspect of the present invention, a welding system for reducing the heat affected zone of laser welding and refining the structure is also proposed, including: a pre-welding pretreatment mechanism for pre-treating the surface of the workpiece to be welded; a welding tool for placing the pre-treated workpiece on a welding workbench in a vacuum chamber; a conformal condensation plate provided between the welding tool and the workpiece for real-time cooling of the weld of the workpiece; an oscillating laser path planning mechanism for placing the laser head in the vacuum chamber according to actual conditions, adjusting the shape of the oscillating laser spot to a required shape, aligning the spot with the starting point of welding, and determining through a walking mechanism or a weld tracking device that the spot walking path covers the entire weld gap; a laser oscillating welding parameter control module for adjusting the shape of the oscillating laser spot to a required shape according to actual conditions, aligning the spot with the starting point of welding, and determining through a walking mechanism or a weld tracking device that the spot walking path covers the entire weld gap; and a laser oscillating welding parameter control module for adjusting the shape of the oscillating laser spot to a required shape according to actual conditions. The corresponding welding process parameters such as welding speed, welding power and defocus amount are set as required, and the swing parameters such as laser swing mode, swing frequency and swing amplitude are adjusted according to the weld performance requirements and the adaptability of the welding gap, so as to optimize and control the laser energy distribution during the welding process until the welding is completed; the laser welding mechanism includes a laser head, which is communicated with the laser swing welding parameter control module and the swing laser path planning mechanism, and is used for vacuum laser welding of the workpiece; an ultrasonic generating device is arranged at intervals from the laser head, and is used for ultrasonically vibrating the weld of the workpiece; a recrystallization annealing mechanism is used to perform recrystallization annealing at a specified temperature on the workpiece after the welding of the workpiece is completed and all welds are ultrasonically vibrated.

[0066] The above system also includes a control mechanism, which is used to communicate with the follow-up condensation plate, the swing laser path planning mechanism, the laser swing welding parameter control module, the laser welding mechanism and the ultrasonic generating device to control the coordinated work of the entire mechanism. Furthermore, in the present invention, the control mechanism is also integrated with the optimization algorithm designed by the above method, and the welding process parameters and weld parameters of each welding are collected and stored at the same time, so that when the data reaches a certain amount, the optimization algorithm is updated using historical data and new data.

[0067] In the above system, the operating temperature range of the conformal condensation plate is -50°C to 20°C.

[0068] In the above system, the laser welding mechanism also includes a laser driving base and a laser driving assembly. A laser head 1 and an ultrasonic generating device 4 are provided on the laser driving base. The laser head 1 and the ultrasonic generating device 4 are arranged at intervals. In this way, after the laser head welds the workpiece, the ultrasonic generating device 4 performs ultrasonic vibration impact on the weld, which, on the one hand, removes the extremely small pores generated during the welding process, and on the other hand, refines the grain size of the weld and reduces the welding heat affected zone.

[0069] In the above system, the laser head 1 and the ultrasonic generator 4 work independently without affecting each other, that is, the laser head 1 is in front, and the workpiece is laser welded according to the preset motion trajectory, and the ultrasonic generator 4 is in the back, and the molten pool at the welding point is subjected to ultrasonic vibration impact. Further, in order to achieve the situation where the trajectory of the swinging spot movement is circular, 8-shaped, ∞-shaped, square or triangular, in the present invention, the interval distance between the laser head 1 and the ultrasonic generator 4 is an integer number of cycles, so that the movement trajectory of the laser head 1 and the ultrasonic generator 4 is consistent.

[0070] In the above system, a temperature sensor is provided on the conformal condensation plate for directly detecting the temperature of the workpiece and the conformal condensation plate, and adjusting the working temperature according to the temperature of the workpiece and the conformal condensation plate to directly cool the welding substrate at any time.

[0071] Example 1

[0072] Step 1: During welding, the laser can be CO2 gas laser, YAG solid laser, semiconductor laser, or fiber laser.

[0073] Step 2: Fix the polished or cleaned workpiece 5 on the welding fixture 6 and place it on a workbench in the vacuum chamber 2 , on which a conformable condensation plate 7 is installed.

[0074] Step 3: Use a special fixture 3 to fix the ultrasonic generator 4 on the laser head 1, so that after the laser welding is completed, it can achieve post-welding ultrasonic vibration impact by controlling the laser head without light.

[0075] Step 4: Evacuate the vacuum chamber 2 to a vacuum pressure of 100 to 10000 Pa.

[0076] Step 5: Vacuum laser welding, specifically:

[0077] S51: According to the thickness of the workpiece 5 to be welded, the laser power is 3500-5500 W, the welding speed is 0.3-1.8 m / min, and the defocus is -10-10 mm.

[0078] S52: The temperature range of the conformal condensation plate 7 is -50°C to 20°C.

[0079] S53: Immediately after welding, the ultrasonic generator 4 is turned on to use ultrasonic vibration to weld the seam.

[0080] Step 6: After welding, break the air, take out the welded specimen and put it into the heat treatment furnace for recrystallization annealing at 550-750℃.

[0081] In the above embodiment, the size and form of the vacuum chamber 2 can be adjusted according to actual needs, and the specified vacuum degree should be between 100 and 10000 Pa.

[0082] Example 2

[0083] In this embodiment, a vacuum swing laser welding method is used to weld a 20 mm thick aluminum alloy joint. The laser uses a TRUMPF high-power laser with a maximum power of 10,000 W. The laser head is an IPG swing laser welding head. Other equipment includes a KUKA robot, a vacuum system, and a vacuum chamber.

[0084] Step 1: Use laser cleaning method to remove the oxide film on the surface of the workpiece to be welded;

[0085] Step 2: Place the workpiece to be welded after grinding, pickling or laser cleaning on the welding workbench in the vacuum chamber, and place a traveling condensation plate on the workbench. The area of ​​the traveling condensation plate should at least cover the aluminum alloy joint. Then fix it with a fixture suitable for the structure and size of the weldment.

[0086] Step 3: Adjust the shape of the oscillating laser spot to a circular spot, align the center of the spot with the center of the starting weld point, and adjust the walking mechanism of the welding platform in the vacuum chamber to ensure that the walking path of the spot covers the entire weld gap, and the weld gap is 2mm.

[0087] Step 4: Close the vacuum chamber door, open the electronically controlled damper valve of the vacuum chamber, and turn on the vacuum pump group. When the vacuum chamber is evacuated to a pressure below 1kPa, open the protective gas inlet valve to deliver dry high-purity inert gas into the chamber. Set automatic adjustment to dynamically balance the inlet and exhaust of the chamber to a vacuum degree of 1000Pa in preparation for welding.

[0088] Step 5: Set the welding speed to 0.3m / min, welding power to 9000W, defocus to -5mm, swing laser frequency to 150Hz, swing amplitude to 0.3mm, and the temperature range of the conformal condensation plate 7 to -50℃~20℃. At the same time, turn on the ultrasonic generator 4 immediately after welding to use ultrasonic vibration welding.

[0089] Step 6: After welding, break the air, take out the welded specimen and put it into the heat treatment furnace for recrystallization annealing at 750℃.

[0090] It will be easily understood by those skilled in the art that 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A welding method for reducing the heat affected zone of laser welding and refining the structure, characterized in that: The following steps are involved: S1 pre-treats the surface of the workpiece to be welded, and then places the pre-treated workpiece on a workbench, while a conformal condensation plate is arranged between the workpiece and the workbench; S2 sets welding process parameters according to the material and thickness of the workpiece, and also sets working parameters of the conformal condensation plate; In this step, the weld parameters are extracted based on the weld photos. The weld parameters include weld width, weld area fine grain size, weld depth, and bubble number. The evaluation function of welding quality is constructed based on the above weld parameters: In the formula, is the evaluation function, is the i-th weld parameter, is the weight of the i-th weld parameter; A training data set is established according to historical welding process parameters and corresponding plate thicknesses, the training data set is used as input of a support vector machine model, and corresponding weld parameters are used as output of the support vector machine model, and the support vector machine model is optimized and trained to obtain a nonlinear mapping relationship between welding process parameters, corresponding plate thickness, and weld parameters; The nonlinear mapping relationship between welding process parameters, corresponding plate thickness and weld parameters and the above evaluation function are used as the objective function, and the welding process parameters and corresponding plate thickness are used as constraints to construct the NSGA-II neural network model. The welding process parameters are multi-objective optimized according to the set iteration termination conditions to obtain the optimal welding process parameter set corresponding to the plate thickness. Among them, the Gaussian kernel function is selected to build the support vector machine model. The Gaussian kernel function expression is as follows: in, , is the input variable, is the i-th sample data, is the jth sample data, is the kernel width parameter, d’ is the plate thickness, is the first weight, is the second weight; S3: an ultrasonic generator is integrated on a laser head for welding, and the laser head and the ultrasonic generator are arranged at intervals; S4 provides a vacuum environment during the welding process, and welds the workpiece in the vacuum environment according to the set welding process parameters. The laser head moves according to the preset swing path and speed, the conformal condensation plate works, and the ultrasonic generator is turned on to perform ultrasonic vibration on the weld of the workpiece; S5 After the workpiece welding is completed and all welds are subjected to ultrasonic vibration, the workpiece is subjected to recrystallization annealing at a specified temperature.

2. A welding method for reducing the heat affected zone of laser welding and refining the structure according to claim 1, characterized in that: In step S2, the welding process parameters include vacuum pressure, laser power, welding speed and defocus, wherein: The vacuum pressure is 100 to 10000 Pa, the laser power of the laser head is 3500 to 5500 W, the welding speed is 0.3 to 1.8 m / min, and the defocusing amount is -10 to 10 mm.

3. The welding method for reducing the heat affected zone of laser welding and refining the structure according to claim 1, characterized in that: In step S2, the operating temperature range of the conformal condensation plate is -50°C to 20°C, and the flow rate of the coolant is adaptively adjusted according to the temperature of the workpiece and the temperature of the conformal condensation plate.

4. The welding method for reducing the heat affected zone of laser welding and refining the structure according to claim 1, characterized in that: In step S4, the laser head performs welding according to the swinging walking path, which is achieved by the swinging of the galvanometer inside the laser head to convert the light spot output by the laser head into a swinging light spot. The trajectory of the swinging light spot movement is generally one or more of a straight line, a circle, an 8-shape, an ∞-shape, a square or a triangle. Special graphics can be achieved by programming to control the swinging of the galvanometer inside the laser head.

5. A welding method for reducing the heat affected zone of laser welding and refining the structure according to claim 4, characterized in that: The swing amplitude of the swing light spot is 0.4-10 mm, which is achieved by controlling the coordinated high-speed movement of the galvanometer inside the laser head on the X and Y axes.

6. A welding method for reducing the heat affected zone of laser welding and refining the structure according to any one of claims 1 to 5, characterized in that: In step S5, the workpiece is placed in a heat treatment furnace for recrystallization annealing at 550-750°C.

7. A welding method for reducing the heat affected zone of laser welding and refining the structure according to any one of claims 1 to 5, characterized in that: In step S2, the maximum thickness of the workpiece is determined by the upper limit of the laser head power and does not exceed 200 mm.

8. A welding method for reducing the heat affected zone of laser welding and refining the structure according to any one of claims 1 to 5, characterized in that: The pretreatment includes: smoothing the front and back sides of the workpiece to be welded, and grinding, pickling or laser cleaning the surface of the workpiece to be welded.

9. A welding system for reducing the heat affected zone of laser welding and refining the structure, used to implement a welding method for reducing the heat affected zone of laser welding and refining the structure as claimed in any one of claims 1 to 8, characterized in that: include: Pre-welding pretreatment mechanism, to pre-treat the surface of the workpiece to be welded; Welding tooling, used to place the pre-treated workpiece on the welding workbench in the vacuum chamber; A conformal condensation plate is provided between the welding fixture and the workpiece and is used to cool the weld of the workpiece in real time; The swing laser path planning mechanism is used to place the laser head in the vacuum chamber according to the actual situation, adjust the swing laser spot shape to the required shape, align the spot with the welding starting point, and determine that the spot walking path covers the entire weld gap through the walking mechanism or weld tracking device; The laser oscillation welding parameter control module is used to set corresponding welding process parameters according to actual welding requirements. The welding process parameters include welding speed, laser power, and defocus. At the same time, the oscillation parameters are adjusted according to the weld performance requirements and the adaptability of the welding gap. The oscillation parameters include laser oscillation mode, oscillation frequency, and oscillation amplitude. The laser energy distribution during the welding process is optimized and regulated until the welding is completed. The laser welding mechanism comprises a laser head, which is communicatively connected with the laser swing welding parameter control module and the swing laser path planning mechanism, and is used for vacuum laser welding of the workpiece; An ultrasonic generating device, arranged at a distance from the laser head, for ultrasonically vibrating the weld of the workpiece; The recrystallization annealing mechanism is used to perform recrystallization annealing at a specified temperature on the workpiece after the workpiece welding is completed and all welds are subjected to ultrasonic vibration.

10. A welding system for reducing the heat affected zone of laser welding and refining the structure according to claim 9, characterized in that: The working temperature range of the conformal condensation plate is -50°C to 20°C.

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