A friction stir weld strengthening device and method based on grinding and laser shot peening

Abstract

The present invention relates to the technical field of post-processing strengthening of friction stir welding joints, and specifically discloses a friction stir weld strengthening device and method based on grinding and laser shot peening. The device mainly includes a motion component, a weld grinding and laser shot peening composite strengthening processing head; the motion component further includes a processing platform and a six-axis robot; the weld grinding and laser shot peening composite strengthening processing head further includes a processing head crossbeam, a galvanometer laser head, a laser full-reflecting mirror, a front grinding wheel, and a rear grinding wheel. The present invention organically combines grinding and surface strengthening, fully utilizes the friction heat during the grinding process, enhances the plasticity of the high-strength aluminum alloy in the grinding area, and can directly use laser shot peening without an absorption layer and a constraint layer to strengthen the surface, which is conducive to obtaining significant microstructure optimization and a residual stress field with a higher amplitude and greater depth, thereby obtaining a friction stir welding joint with a smooth surface and high performance.

Description

Technical Field

[0001] The present invention relates to the technical field of post-processing strengthening of friction stir welding joints, and more particularly to a device and method for strengthening friction stir welds based on grinding and laser shot peening. Background Art

[0002] High-strength aluminum alloys are widely used in the manufacture of medium and large components in the fields of aerospace and rail transportation due to their advantages such as high specific strength and light weight. During the production of aluminum alloys, it is necessary to control the distribution of the strengthening phase through a sophisticated heat treatment process to obtain a widely distributed nano-scale strengthening phase to improve the strength. However, the nano-scale precipitated phase is very susceptible to spheroidization or growth due to external heat input, resulting in a decrease in performance. Therefore, traditional fusion welding will cause severe softening of the weld joint due to excessive heat input. As a solid-phase welding method, stir friction welding can greatly reduce the welding heat input compared to fusion welding, and can completely eliminate the inevitable porosity defects in fusion welding, and can obtain high-performance welded joints. It has been widely used in the connection and production of high-strength aluminum alloy structures.

[0003] The basic principle of friction stir welding (FSW) is to insert a stirring tip with a pin under external force into the edges of the materials to be joined. The pin rotates under downward pressure, causing plastic deformation of the metals on both sides. Frictional heat is generated, promoting metal fusion and completing the joint. Due to the characteristics of this technique, some material inevitably squeezes out of the edge of the stir tip and accumulates, forming flash on both sides of the weld, affecting weld aesthetics and subsequent painting. Furthermore, the downward pressure causes the shoulder of the stir tip to sink a certain distance into the material, ultimately creating a concave step in the weld's stir zone. This creates a discontinuous component surface and can easily lead to stress concentration and damage during service. Therefore, in actual production, post-weld grinding is required to remove flash and the concave step. Furthermore, the heat and plastic deformation of the stir tip during FSW significantly alter the microstructure of high-strength aluminum alloys. This can include significant dissolution of precipitates in the stir zone and coarsening of grains and precipitates in the thermomechanically affected zone. Consequently, the final joint strength remains lower than that of the parent metal. For medium and large welded components, it is usually difficult to use post-weld heat treatment for overall strengthening. Surface strengthening methods can be used to further improve the mechanical properties of welded joints.

[0004] Laser peening utilizes shock waves generated by a high-energy pulsed laser to bombard the material surface, inducing intense plastic deformation at high strain rates. This results in grain refinement, high dislocation density, and high residual compressive stresses. Numerous studies have demonstrated that laser peening can significantly improve the overall mechanical properties of welded joints. Conventional laser peening requires the application of absorbent and constraining layers to the material surface to enhance the transmission of shock waves into the material, thereby improving the strengthening effect. However, when applied to medium- and large-scale friction stir welded components, the application of absorbent and constraining layers significantly reduces production efficiency. Direct laser peening without absorbent and constraining layers results in insufficient impact force, resulting in minimal plastic deformation on the material surface. This leads to less pronounced surface microstructural evolution, a smaller depth of residual compressive stress, and ablation of the surface, damaging surface integrity and increasing surface roughness. Experiments have demonstrated that increasing the pulsed laser power density can effectively enhance the strengthening effect of laser peening without absorbent and constraining layers, achieving microstructural strengthening comparable to that achieved with conventional laser peening. However, the surface ablation caused by high energy density will form residual tensile stress within 0 to 100 μm on the material surface and produce pits hundreds of microns deep, significantly reducing the fatigue performance of the material.

[0005] Furthermore, existing research indicates that simultaneous heating of the material during laser peening can soften the material, thereby increasing the plastic deformation induced by laser peening of the non-absorbing layer and constrained layer on the material surface, leading to more significant microstructural evolution and increased depth of residual compressive stress. The necessary post-weld grinding process generates frictional heating at the grinding location, which can be directly applied to simultaneous laser peening of the non-absorbing layer and constrained layer. However, due to the good thermal conductivity of aluminum alloys and the relatively small amount of grinding, it is difficult to maintain a stable temperature field behind the grinding area for laser peening of the non-absorbing layer and constrained layer. Furthermore, considering the shortcomings of laser peening of the non-absorbing layer and constrained layer, a subsequent grinding process is required to remove the surface ablation layer and residual tensile stress. The coupled temperature fields generated by the pre- and post-grinding heating produce a more stable surface heating area for laser peening of the non-absorbing layer and constrained layer, which can improve the process integration and strengthening effect. However, there are currently no composite processing devices or joint strengthening methods that organically combine grinding and laser peening. Summary of the Invention

[0006] In response to the shortcomings of existing post-processing and strengthening devices and methods for friction stir welding high-strength aluminum alloy joints, the present invention proposes a friction stir weld strengthening device and method based on grinding and laser shot peening. The joint surface is ground by double grinding wheels to generate local heating, forming a relatively stable high-temperature area, so that the joint surface has a certain softening effect, and high-energy density non-absorption layer and constraint layer laser shot peening are simultaneously performed between the double grinding wheels to strengthen the joint surface. By generating significant surface plastic deformation, the microstructure of the near-surface area of ​​the joint is improved, and high-amplitude and large-depth residual compressive stress is formed. Then, the surface ablation layer and surface residual tensile stress generated by high-energy density non-absorption layer and constraint layer laser shot peening are removed synchronously, thereby greatly improving the joint strength and fatigue performance, making full use of the frictional heat generated in the grinding process, and solving the problems of insufficient laser shot peening strengthening capacity of the non-absorption layer and constraint layer and poor strengthened surface quality, thereby improving the processing efficiency of laser shot peening for large aluminum alloy friction stir welding joints.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A friction stir weld strengthening device based on grinding and laser shot peening, comprising a motion component, a weld grinding and laser shot peening composite strengthening processing head;

[0009] The motion assembly includes a processing platform and a six-axis robot. The workpiece to be strengthened by friction stir welding is placed and fixed on the processing platform. The motion end of the six-axis robot is fixed with the weld grinding and laser shot peening composite strengthening processing head. A pressure sensor for monitoring the downward pressure of the six-axis robot is also provided between the motion end of the six-axis robot and the weld grinding and laser shot peening composite strengthening processing head.

[0010] The weld grinding and laser shot peening composite strengthening processing head includes a processing head beam, a galvanometer laser head, a laser full reflector, a front grinding wheel, and a rear grinding wheel. The processing head beam is fixed to the moving end of the six-axis robot. The front grinding wheel, the laser full reflector, the rear grinding wheel, and the galvanometer laser head are respectively fixedly connected below the processing head beam from front to back. The laser full reflector is tilted and faces the light outlet of the galvanometer laser head. The front grinding wheel and the rear grinding wheel can be driven and grind the weld surface under the action of downward pressure. The pulsed laser beam is focused by the galvanometer laser head to generate a focused laser beam. The focused laser beam is irradiated on the weld surface after total reflection by the laser full reflector and moves perpendicular to the weld.

[0011] Preferably, the weld grinding and laser shot peening composite strengthening processing head is fixed to the moving end of the six-axis robot through a processing head connector; the stir friction welding workpiece to be strengthened is fixed to the processing platform using a fixture installed on the processing platform.

[0012] Preferably, the front grinding wheel is fixed to the processing head crossbeam through a front grinding wheel connecting rod, the rear grinding wheel is fixed to the processing head crossbeam through a rear grinding wheel connecting rod, and the front grinding wheel and the rear grinding wheel are located at the same height; the front grinding wheel is driven by a front grinding wheel drive motor, and the rear grinding wheel is driven by a rear grinding wheel drive motor; the galvanometer laser head is fixed to the processing head crossbeam through a galvanometer laser head connecting rod, the laser total reflector is fixed to the processing head crossbeam through a laser total reflector connecting rod, and the pulsed laser beam enters the galvanometer laser head through the galvanometer laser head incident hole.

[0013] A friction stir weld strengthening method based on grinding and laser shot peening, using the above-mentioned friction stir weld strengthening device based on grinding and laser shot peening, specifically comprising the following steps:

[0014] 1) Fix the workpiece to be reinforced with friction stir welding on the processing platform and select the width of the front and rear grinding wheels according to the width of the weld;

[0015] 2) Controlling the six-axis robot to drive the weld grinding and laser shot peening composite strengthening processing head to move, move the front and rear grinding wheels above the weld and align them with the weld, drive the front grinding wheel to rotate and adjust the speed of the front grinding wheel, and use the six-axis robot to drive the weld grinding and laser shot peening composite strengthening processing head downward to press the front and rear grinding wheels against the weld surface. The pressure is monitored in real time by a pressure sensor, so that the front and rear grinding wheels and the weld surface contact to reach positive pressure, and then the front grinding wheel removes the flash and concave steps on the weld surface;

[0016] 3) Adjust the single pulse energy, pulse width and frequency of the pulsed laser beam entering the galvanometer laser head. The galvanometer laser head focuses the pulsed laser beam to form a focused laser beam that irradiates the laser total reflector, and then reflects it to the area where the front grinding wheel has completed grinding. The focused light spot moves back and forth perpendicular to the weld along the light spot movement path. The friction heat generated during the grinding process is used to perform high-energy-density laser shot peening on the non-absorption layer and the constraint layer of the grinding area;

[0017] 4) driving the post-grinding grinding wheel to rotate and adjusting the speed of the post-grinding grinding wheel to simultaneously grind the high-energy-density non-absorption layer and the constrained layer laser peening area;

[0018] 5) The forward speed is determined based on the spot diameter, overlap rate, and spot movement speed. The weld grinding and laser shot peening composite strengthening processing head is driven by a six-axis robot to move parallel to the weld direction, and the weld surface grinding-laser shot peening-grinding process is completed simultaneously to obtain a high-strength aluminum alloy friction stir welding joint with high-quality surface and high performance.

[0019] Preferably, in step 1), the width of the front and rear grinding wheels needs to be 10% to 20% larger than the width of the weld to ensure that the burrs on both sides of the weld and the concave steps at the edge of the weld can be completely covered.

[0020] Preferably, in step 2), the rotation speed of the front grinding wheel is set to 800~2000r / min to ensure that the front grinding wheel and the weld surface can quickly generate sufficient friction heat and prevent excessive grinding from damaging the weld geometry; the positive pressure of the front and rear grinding wheels in contact with the weld surface is 100N~500N, which can ensure that the front and rear grinding wheels are in close contact with the weld surface.

[0021] Preferably, in step 3), the single pulse energy of the pulsed laser beam entering the galvanometer laser head is 15 to 25 J, the pulse width is 10 to 15 ns, and the frequency is 5 to 10 Hz.

[0022] Preferably, in step 3), the diameter of the focused light spot is 2 to 8 mm, and the reciprocating motion speed of the light spot is 5 to 15 mm / s; the light spot overlap rate is controlled to be 30% to 80% by matching the pulse laser frequency with the light spot motion speed; the width of the laser shot peening area without the absorption layer and the constraint layer is the same as the width of the front and rear grinding wheels; the irradiation position of the focused light spot is 10 to 20 mm away from the grinding area of ​​the front grinding wheel to ensure that there is sufficient friction heat to heat up the surface.

[0023] Preferably, in step 4), the rotation speed of the post-grinding grinding wheel is set to 200-500 r / min to ensure that the post-grinding grinding wheel can quickly remove the ablation layer and surface residual tensile stress generated by high-energy density non-absorption layer and constraint layer laser shot peening, generate friction heat to continue heating the strengthened area, and prevent excessive grinding from removing excessive surface strengthening layer.

[0024] Preferably, in step 5), after the focused spot completes a line of laser shot peening in the polished area, the weld grinding and laser shot peening composite strengthening processing head is driven forward by a six-axis robot to perform stepping motion with a movement distance of 0.2 to 5 mm.

[0025] The working principle of the present invention is as follows: first, the front grinding wheel removes the flash and concave steps on the surface of the stir friction welding joint under the action of downward pressure, and generates friction heat to locally heat the weld surface, and then the galvanometer laser head focuses the pulsed laser beam to irradiate the grinding area for scanning, the pulsed laser focused spot generates a plasma explosion, and the shock wave is transmitted to the inside of the material, completing the high-energy density laser shot peening of the non-absorption layer and the constraint layer on the weld surface, and finally the post-grinding wheel removes the surface ablation layer and the surface residual tensile stress generated by the high-energy density laser shot peening of the non-absorption layer and the constraint layer, and heats the weld surface again to ensure that the temperature of the strengthening area is stable, so that the weld surface is softened, which is more conducive to increasing the plastic deformation of the high-energy density laser shot peening of the non-absorption layer and the constraint layer on the surface, thereby generating high-amplitude and large-depth residual compressive stress, and can also induce more violent dislocation movement to produce obvious grain refinement and high-density dislocation structure, thereby obtaining a stir friction welding joint with a smooth surface and high performance.

[0026] Compared with the prior art, the friction stir weld strengthening device and method based on grinding and laser shot peening of the present invention has the following advantages:

[0027] 1. Grinding the surface of the friction stir welding joint is a necessary process in the actual production process. The conventional post-weld surface strengthening process and the grinding process are independent of each other. The present invention organically combines grinding and surface strengthening. The designed composite strengthening processing head can be directly assembled in the original grinding system, and the system integration is high.

[0028] 2. The present invention makes full use of the friction heat during the grinding process to enhance the plasticity of the high-strength aluminum alloy in the grinding area. Laser shot peening without an absorption layer and a constraint layer can be directly used to strengthen the surface, which is conducive to obtaining significant microstructure optimization and a residual stress field with a higher amplitude and greater depth.

[0029] 3. Friction stir welding is usually used to manufacture large components. Compared with traditional laser shot peening, the present invention eliminates the process of arranging an absorption layer and a constraint layer on the weld surface. In addition, the surface ablation layer and surface residual tensile stress generated by high-energy density laser shot peening without an absorption layer and a constraint layer can be eliminated simultaneously. The surface quality of the resulting joint is extremely high, and the processing efficiency is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0031] Figure 1This is a schematic diagram of the overall structure of the friction stir weld strengthening device based on grinding and laser shot peening of the present invention.

[0032] Figure 2 It is a structural schematic diagram of the weld grinding and laser shot peening composite strengthening processing head in the present invention.

[0033] Figure 3 The figure is a flow chart of the friction stir weld strengthening method based on grinding and laser shot peening according to the present invention.

[0034] Figure 4 Schematic diagram of the motion path of the pulsed laser focused spot during the laser shot peening process of the present invention.

[0035] Figure 5 These are macroscopic cross-sectional photographs of the aluminum alloy friction stir welded joint obtained in Example 1 of the present invention before and after surface grinding and strengthening.

[0036] Figure 6 The tensile curves of the aluminum alloy friction stir welded joint obtained in Example 1 of the present invention before and after surface grinding and strengthening are compared.

[0037] Figure 7 This is the surface residual stress state of the aluminum alloy friction stir welding joint obtained by Example 1 of the present invention.

[0038] Figure 8 The surface micromorphology of the aluminum alloy friction stir welding joint obtained by Example 1 of the present invention is shown.

[0039] Figure 9 The fatigue life of the aluminum alloy friction stir welding joint obtained by using Example 1 of the present invention.

[0040] In the figure: 1-processing platform, 2-six-axis robot, 3-workpiece to be strengthened by friction stir welding, 4-pressure sensor, 5-processing head crossbeam, 6-galvanometer laser head, 7-laser full-reflection mirror, 8-front grinding wheel, 9-rear grinding wheel, 10-pulsed laser beam, 11-focused laser beam, 12-weld, 13-focused spot, 14-processing head connector, 15-tooling fixture, 16-front grinding wheel connecting rod, 17-rear grinding wheel connecting rod, 18-front grinding wheel drive motor, 19-rear grinding wheel drive motor, 20-galvanometer laser head connecting rod, 21-galvanometer laser head incident hole, 22-laser full-reflection mirror connecting rod, 23-flash, 24-recessed step, 25-laser shot peening area without absorption layer and constraint layer, 26-front grinding wheel grinding area DETAILED DESCRIPTION

[0041] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0042] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0044] like Figure 1-Figure 2 As shown, the present invention discloses a friction stir weld strengthening device based on grinding and laser shot peening, which mainly includes a motion component and a weld grinding and laser shot peening composite strengthening processing head.

[0045] Specifically, the motion component includes a processing platform 1 and a six-axis robot 2. The workpiece 3 to be strengthened by friction stir welding is placed and fixed on the processing platform 1. The moving end of the six-axis robot 2 is fixed with a weld grinding and laser shot peening composite strengthening processing head, and a pressure sensor 4 for monitoring the downward pressure of the six-axis robot is also provided between the moving end of the six-axis robot 2 and the weld grinding and laser shot peening composite strengthening processing head.

[0046] More specifically, the weld grinding and laser shot peening composite strengthening processing head is fixed to the moving end of the six-axis robot 2 through the processing head connector 14; the workpiece 3 to be strengthened by the stir friction welding is fixed to the processing platform 1 using a fixture 15 installed on the processing platform 1.

[0047] Therefore, during composite strengthening, the friction stir welding workpiece 3 to be strengthened is placed on the processing platform 1 and fixed with a fixture 15. The weld grinding and laser shot peening composite strengthening processing head is fixed to the moving end on the front side of the six-axis robot 2 through the processing head connector 14. The weld grinding and laser shot peening composite strengthening processing head is driven by the six-axis robot 2 to perform stepping motion, and the downward force is monitored by the pressure sensor 4.

[0048] The weld grinding and laser shot peening composite strengthening processing head includes a processing head beam 5, a galvanometer laser head 6, a laser full reflector 7, a front grinding wheel 8, and a rear grinding wheel 9. The processing head beam 5 is fixed to the moving end of the six-axis robot 2. The front grinding wheel 8, the laser full reflector 7, the rear grinding wheel 9, and the galvanometer laser head 6 are fixedly connected to the bottom of the processing head beam 5 from front to back. The laser full reflector 7 is tilted and faces the light outlet of the galvanometer laser head 6; the front grinding wheel 8 and the rear grinding wheel 9 can be driven and grind the surface of the weld 12 under the action of downward pressure; the pulsed laser beam 10 is focused by the galvanometer laser head 6 to generate a focused laser beam 11. The focused laser beam 11 is irradiated on the weld surface after total reflection by the laser full reflector 7 and moves perpendicular to the weld 12, performing high-energy density laser shot peening strengthening on the weld surface without absorption layer and constraint layer.

[0049] More specifically, the front grinding wheel 8 is fixed to the processing head beam 5 through the front grinding wheel connecting rod 16, and the rear grinding wheel 9 is fixed to the processing head beam 5 through the rear grinding wheel connecting rod 17, and the front grinding wheel 8 and the rear grinding wheel 9 are located at the same height to ensure that both of them are close to the weld surface at the same time; the front grinding wheel 8 is driven by the front grinding wheel drive motor 18, and the rear grinding wheel 9 is driven by the rear grinding wheel drive motor 19; the galvanometer laser head 6 is fixed to the processing head beam 5 through the galvanometer laser head connecting rod 20, and the laser full reflector 7 is fixed to the processing head beam 5 through the laser full reflector connecting rod 22, and the pulsed laser beam 10 enters the galvanometer laser head 6 through the galvanometer laser head incident hole 21.

[0050] Combine Figure 1-Figure 4 (A in the figure indicates the grinding forward direction, and B indicates the reciprocating motion path of the light spot). The present invention discloses a stir friction weld strengthening method based on grinding and laser shot peening. The stir friction weld strengthening device based on grinding and laser shot peening is applied. The specific steps are as follows:

[0051] 1) The workpiece 3 to be subjected to enhanced friction stir welding is fixed to the processing platform 1 by a fixture 15 to keep the workpiece stable. Then, according to the weld width, a front grinding wheel 8 and a rear grinding wheel 9 are selected that are 10% to 20% larger than the weld width to ensure that they can completely cover the flash 23 on both sides of the weld, the recessed step 24 at the weld edge, and the high-energy-density non-absorption layer and constraint layer laser peening area 25. The front grinding wheel 8 and the rear grinding wheel 9 are fixed to the processing head beam 5 by the front grinding wheel connecting rod 16 and the rear grinding wheel connecting rod 17 respectively.

[0052] 2) Control the six-axis robot 2 to drive the weld grinding and laser shot peening composite strengthening processing head to move, move the front grinding wheel 8 and the rear grinding wheel 9 to the top of the weld and align with the weld 12, start the front grinding wheel drive motor 18, and adjust the front grinding wheel speed to 800-2000r / min to ensure that the front grinding wheel 8 and the weld surface can quickly generate sufficient friction heat and prevent excessive grinding from damaging the weld geometry; drive the weld grinding and laser shot peening composite strengthening processing head downward by the six-axis robot 2 to press the front and rear grinding wheels on the weld surface, monitor the pressure in real time through the pressure sensor 4, and make the positive contact pressure between the front and rear grinding wheels and the weld surface 100N-500N to ensure that the grinding wheels are in close contact with the weld surface, and remove the burrs 23 and the recessed steps 24 on the weld surface by the front grinding wheel 8;

[0053] 3) Adjusting the single pulse energy of the pulsed laser beam 10 to 15-25 J, the pulse width to 10-15 ns, and the frequency to 5-10 Hz, the pulsed laser beam 10 enters the galvanometer laser head 6 through the galvanometer laser head incident hole 21; starting the galvanometer laser head 6, focusing the pulsed laser beam 10 to form a focused laser beam 11 that irradiates the laser total reflector 7, and then reflects it to the area where the front grinding wheel completes grinding, forming a focused light spot 13 with a diameter of 2-8 mm, and the focused light spot 13 reciprocates perpendicular to the weld 12 along the light spot movement path B at a speed of 5-15 mm / s The width of the movement range is the same as the width of the grinding wheel (that is, the width of the laser shot peening area without the absorption layer and the constraint layer is the same as the width of the front and rear grinding wheels). The distance d between the focused light spot 13 and the grinding area 26 of the front grinding wheel is 10 to 20 mm, ensuring that the laser transmission is not interfered with by the grinding wheel and that there is sufficient frictional heat on the surface to heat up. The frictional heat generated during the grinding process is used to perform high-energy-density laser shot peening of the non-absorption layer and the constraint layer on the grinding area. At the same time, the spot movement speed is matched with the pulse laser frequency to control the spot overlap rate to 30% to 80%;

[0054] 4) starting the rear grinding wheel drive motor 19, adjusting the rear grinding wheel speed to 200-500 r / min, and simultaneously grinding the high-energy-density non-absorbing layer and constrained layer laser peening area 25 to remove surface ablation and surface tensile stress generated by the high-energy-density non-absorbing layer and constrained layer laser peening, while generating frictional heat to heat the high-energy-density non-absorbing layer and constrained layer laser peening area 25 to ensure a stable temperature field and prevent excessive grinding from removing excessive surface strengthening layer;

[0055] 5) According to the spot diameter, overlap rate and spot movement speed, it is ensured that after the pulse spot completes a line of laser shot peening in the polished area, the weld grinding and laser shot peening composite strengthening processing head is driven by the six-axis robot 2 to perform a stepping motion with a movement distance of 0.2 to 5 mm in the polishing forward direction A parallel to the weld direction, and the weld surface polishing-laser shot peening-polishing process is completed synchronously to obtain a high-strength aluminum alloy friction stir welding joint with high-quality surface and high performance.

[0056] The present invention discloses a friction stir weld strengthening method based on grinding and laser shot peening. First, a six-axis robot 2 is used to drive a front grinding wheel 8 to grind the surface of a friction stir welded high-strength aluminum alloy weld to remove the burrs 23 and the recessed steps 24 on the weld surface. The grinding wheel and the joint surface generate heat by friction. The galvanometer laser head 6 moving synchronously at the rear focuses a pulsed laser beam 10 on the polished area to perform high-energy-density laser shot peening strengthening on the weld surface without an absorption layer and a constraint layer, inducing severe plastic deformation on the joint surface, generating high-density dislocations and refining grains, and forming high-amplitude and large-depth residual compressive stress. The rear grinding wheel behind the strengthening area is used to strengthen the weld surface. 9. The ablation layer and surface residual tensile stress generated by high-energy-density laser shot peening of the non-absorption layer and the constraint layer are removed simultaneously. The friction heat generated by the simultaneous grinding of the front and rear grinding wheels heats the weld surface, and a high-temperature zone with a relatively stable temperature is formed between the two grinding wheels, which softens the surface of the aluminum alloy weld. This significantly enhances the laser shot peening effect of the non-absorption layer and the constraint layer, resulting in more significant grain refinement and high-amplitude, large-depth residual compressive stress field, thereby improving the strength and fatigue properties of the aluminum alloy friction stir welded joint, and finally obtaining an aluminum alloy friction stir welded joint with high surface quality and excellent comprehensive mechanical properties.

[0057] Example 1:

[0058] In this embodiment, the workpiece to be strengthened is a 2219 aluminum alloy friction stir welded plate with a thickness of 7 mm. The weld width is 20 mm, and there are flashes 23 and recessed steps 24 on both sides of the weld.

[0059] First, the workpiece 3 to be reinforced with friction stir welding is fixed on the processing platform 1 through the fixture 15 to keep the workpiece stable. Then, according to the width of the weld, the front grinding wheel 8 and the rear grinding wheel 9 with a width of 22 mm are selected, and the front grinding wheel 8 and the rear grinding wheel 9 are fixed to the processing head beam 5 through the front grinding wheel connecting rod 16 and the rear grinding wheel connecting rod 17 respectively. Control the six-axis robot 2 to drive the weld grinding and laser shot peening composite strengthening processing head to move, move the front grinding wheel 8 and the rear grinding wheel 9 above the weld and align with the weld 12, start the front grinding wheel drive motor 18, adjust the front grinding wheel speed to 1000r / min, and drive the weld grinding and laser shot peening composite strengthening processing head downward through the six-axis robot 2 to press the front and rear grinding wheels on the weld surface. Monitor the pressure in real time through the pressure sensor 4, so that the positive contact pressure between the front and rear grinding wheels and the weld surface is 300N, ensuring that the grinding wheel is in close contact with the weld surface. The front grinding wheel 8 removes the burrs 23 and the concave steps 24 on the weld surface, and generates friction heat to heat the weld surface.The single pulse energy of the pulse laser beam 10 is adjusted to 20J, the pulse width is 15ns, and the frequency is 5Hz. The pulse laser beam 10 enters the galvanometer laser head 6 through the galvanometer laser head incident hole 21. The galvanometer laser head 6 is started, and the pulse laser beam 10 is focused to form a focused laser beam 11 that irradiates the laser total reflector 7. The laser beam is then reflected to the area where the front grinding wheel has completed grinding, forming a focused light spot 13 with a diameter of 5mm. The laser spot is reciprocated perpendicular to the weld seam 12 along the reciprocating motion path of the light spot at a speed of 12.5mm / s. The motion range is 22mm, and the distance between the focused spot 13 and the area 26 being polished by the front grinding wheel is 12mm, ensuring that the laser transmission is not interfered with by the grinding wheel. The friction heat generated during the grinding process is used to perform high-energy-density laser shot peening on the non-absorption layer and the constraint layer of the grinding area. The spot overlap rate is 50%. After starting, the grinding wheel drive motor 19 is adjusted to a speed of 300r / min, and the high-energy-density laser shot peening area 25 of the non-absorption layer and the constraint layer is simultaneously performed. Grinding removes surface ablation and surface tensile stress generated by high-energy-density laser peening of the non-absorbing layer and the constrained layer. At the same time, frictional heat is generated to heat the high-energy-density laser peening area 25 of the non-absorbing layer and the constrained layer to ensure a stable temperature field and prevent excessive grinding to remove excessive surface strengthening layer. Under the action of frictional heat generated by the front and back grinding, the weld surface softens. Under the action of high-energy-density laser peening of the non-absorbing layer and the constrained layer, significant plastic deformation occurs, resulting in grain refinement, a high-density dislocation structure, and a high-amplitude, large-depth residual compressive stress field. According to the spot diameter, overlap rate, and spot movement speed, after the pulse spot completes a line of laser peening in the polished area, the six-axis robot 2 drives the weld grinding and laser peening composite strengthening processing head to perform a stepping motion of 2.5 mm in the grinding forward direction parallel to the weld direction, thereby simultaneously completing the weld surface grinding-laser peening-grinding process, thereby obtaining a high-strength 2219 aluminum alloy friction stir welded joint with high surface quality and excellent mechanical properties.

[0060] Combine Figure 4 It can be seen that the flash 23 and the concave step 24 on the surface of the aluminum alloy friction stir welded joint obtained by the weld surface grinding and laser shot peening strengthening device and method provided by the present invention completely disappear, the surface is smooth, and the strength is significantly improved.

[0061] Combine Figure 5 It can be seen that the yield strength of the aluminum alloy friction stir welded joint obtained by the weld surface grinding and laser shot peening strengthening device and method provided by the present invention is significantly improved, and the tensile strength is slightly improved.

[0062] Combine Figure 6It can be seen that the surface of the aluminum alloy friction stir weld joint obtained by the weld surface grinding and laser shot peening strengthening device and method provided by the present invention is completely transformed into high-amplitude residual compressive stress. If there is no post-grinding grinding wheel 9 to grind the high-energy density non-absorption layer and constraint layer laser peening area 25, the surface of the aluminum alloy friction stir weld joint will still have high-amplitude residual tensile stress due to laser ablation.

[0063] Combine Figure 7 It can be seen that if the post-grinding grinding wheel 9 is not used to grind the high energy density non-absorption layer and constraint layer laser peening area 25, obvious ablation will occur on the joint surface and the surface quality will be extremely low.

[0064] Combine Figure 8 It can be seen that the fatigue life of the aluminum alloy friction stir welding joint obtained by the weld surface grinding and laser shot peening strengthening device and method provided by the present invention is greatly improved. If there is no post-grinding grinding wheel 9 to grind the high-energy density non-absorption layer and constraint layer laser shot peening area 25, the surface quality of the joint is extremely poor and residual tensile stress exists, and the fatigue life is reduced.

[0065] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0066] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A friction stir weld strengthening device based on grinding and laser shot peening, characterized in that: Includes motion components, weld grinding and laser shot peening composite strengthening processing head; The motion assembly includes a processing platform and a six-axis robot. The workpiece to be strengthened by friction stir welding is placed and fixed on the processing platform. The motion end of the six-axis robot is fixed with the weld grinding and laser shot peening composite strengthening processing head. A pressure sensor for monitoring the downward pressure of the six-axis robot is also provided between the motion end of the six-axis robot and the weld grinding and laser shot peening composite strengthening processing head. The weld grinding and laser shot peening composite strengthening processing head includes a processing head beam, a galvanometer laser head, a laser full reflector, a front grinding wheel, and a rear grinding wheel. The processing head beam is fixed to the moving end of the six-axis robot. The front grinding wheel, the laser full reflector, the rear grinding wheel, and the galvanometer laser head are respectively fixedly connected below the processing head beam from front to back. The laser full reflector is tilted and faces the light outlet of the galvanometer laser head. The front grinding wheel and the rear grinding wheel can be driven and grind the weld surface under the action of downward pressure. The pulsed laser beam is focused by the galvanometer laser head to generate a focused laser beam. The focused laser beam is irradiated on the weld surface after total reflection by the laser full reflector and moves perpendicular to the weld.

2. The friction stir weld strengthening device based on grinding and laser shot peening according to claim 1, characterized in that: The weld grinding and laser shot peening composite strengthening processing head is fixed on the moving end of the six-axis robot through a processing head connector; the workpiece to be strengthened by friction stir welding is fixed on the processing platform using a tooling fixture installed on the processing platform.

3. The friction stir weld strengthening device based on grinding and laser shot peening according to claim 1, characterized in that: The front grinding wheel is fixed to the processing head crossbeam through the front grinding wheel connecting rod, and the rear grinding wheel is fixed to the processing head crossbeam through the rear grinding wheel connecting rod, and the front grinding wheel and the rear grinding wheel are located at the same height; the front grinding wheel is driven by the front grinding wheel driving motor, and the rear grinding wheel is driven by the rear grinding wheel driving motor; the galvanometer laser head is fixed to the processing head crossbeam through the galvanometer laser head connecting rod, and the laser total reflector is fixed to the processing head crossbeam through the laser total reflector connecting rod, and the pulsed laser beam enters the galvanometer laser head through the galvanometer laser head incident hole.

4. A friction stir weld strengthening method based on grinding and laser shot peening, characterized in that: The friction stir weld strengthening device based on grinding and laser shot peening according to any one of claims 1 to 3 is applied, and the specific steps are as follows: 1) Fix the workpiece to be reinforced with friction stir welding on the processing platform and select the width of the front and rear grinding wheels according to the width of the weld; 2) Controlling the six-axis robot to drive the weld grinding and laser shot peening composite strengthening processing head to move, move the front and rear grinding wheels above the weld and align them with the weld, drive the front grinding wheel to rotate and adjust the speed of the front grinding wheel, and use the six-axis robot to drive the weld grinding and laser shot peening composite strengthening processing head downward to press the front and rear grinding wheels against the weld surface. The pressure is monitored in real time by a pressure sensor, so that the front and rear grinding wheels and the weld surface contact to reach positive pressure, and then the front grinding wheel removes the flash and concave steps on the weld surface; 3) Adjust the single pulse energy, pulse width and frequency of the pulsed laser beam entering the galvanometer laser head. The galvanometer laser head focuses the pulsed laser beam to form a focused laser beam that irradiates the laser total reflector, and then reflects it to the area where the front grinding wheel has completed grinding. The focused light spot moves back and forth perpendicular to the weld along the light spot movement path. The friction heat generated during the grinding process is used to perform high-energy-density laser shot peening on the non-absorption layer and the constraint layer of the grinding area; 4) driving the post-grinding grinding wheel to rotate and adjusting the speed of the post-grinding grinding wheel to simultaneously grind the high-energy-density non-absorption layer and the constrained layer laser peening area; 5) The forward speed is determined based on the spot diameter, overlap rate, and spot movement speed. The weld grinding and laser shot peening composite strengthening processing head is driven by a six-axis robot to move parallel to the weld direction, and the weld surface grinding-laser shot peening-grinding process is completed simultaneously to obtain a high-strength aluminum alloy friction stir welding joint with high-quality surface and high performance.

5. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 1), the width of the front and rear grinding wheels must be 10% to 20% larger than the weld width.

6. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 2), the rotation speed of the front grinding wheel is set to 800-2000 r / min, and the positive pressure between the front and rear grinding wheels and the weld surface is 100N-500N.

7. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 3), the single pulse energy of the pulse laser beam entering the galvanometer laser head is 15 to 25 J, the pulse width is 10 to 15 ns, and the frequency is 5 to 10 Hz.

8. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 3), the diameter of the focused light spot is 2 to 8 mm, and the reciprocating motion speed of the light spot is 5 to 15 mm / s; the light spot overlap rate is controlled to be 30% to 80% by matching the pulse laser frequency with the light spot motion speed; the width of the laser shot peening area without the absorption layer and the constraint layer is the same as the width of the front and rear grinding wheels; the irradiation position of the focused light spot is 10 to 20 mm away from the grinding area of ​​the front grinding wheel.

9. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 4), the rotation speed of the post-grinding grinding wheel is set to 200-500 r / min.

10. The method for strengthening friction stir welds based on grinding and laser shot peening according to claim 4, characterized in that: In step 5), after the focused spot completes a line of laser shot peening in the polished area, the weld grinding and laser shot peening composite strengthening processing head is driven forward by the six-axis robot to perform stepping motion with a movement distance of 0.2 to 5 mm.

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