A circumferentially strong backfilling friction stir spot welding repair tool and method

Abstract

The application belongs to the technical field of welding, and particularly relates to a circumferential strong-pressure backfill type friction stir spot welding repair tool and method. The repair tool comprises coaxially arranged compression rings, sleeves and stirring needles. The upper part of the side surface of the sleeve is provided with m symmetrical threads, and the symmetrical threads change left / right rotation directions every 90 degrees. The lower part of the side surface of the sleeve is provided with k large-angle threads. The end surface of the sleeve is uniformly provided with n gradient threads. During repair, the workpiece to be repaired is polished and filled with a T-shaped filler rod. Then, the repair tool is pressed onto the upper surface of the workpiece to be repaired and the T-shaped filler rod. The outer diameter D4 of the sleeve is smaller than the inner diameter D2 of the T-shaped filler rod. Then, the preheating, down-embedding, backfilling, evacuating and polishing stages are performed, so that the repair of the entire workpiece is completed. The application promotes the metallurgical combination of the interface between the filler material / base material and the interface between the sleeve and the exit line, further enhances the combination of the interface, and improves the connection quality of the welding spot.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a circumferentially high-pressure backfill-type friction stir spot welding repair tool and method. Background Technology

[0002] Metal structural components in aerospace and other fields inevitably develop various defects during use, such as corrosion pits in aircraft skin and out-of-tolerance holes in aerospace structures. These defects affect the performance of the metal structural components and, in severe cases, even lead to product scrapping. Therefore, green repair of defective metal structural components is of great significance. Currently, methods for repairing defects in metal materials mainly include traditional fusion welding, electrical discharge alloying, and laser multilayer coating. Among these, the mechanism of fusion welding repair is based on material melting, but excessive local heat input can easily cause coarse microstructure and cannot avoid the generation of secondary defects such as porosity and cracks. Electrical discharge alloying and laser multilayer coating are only suitable for surface defect repair of metal structural components, limiting their application. As a novel solid-state repair technology, refilled friction stir spot welding (RFSSWR) has advantages in the green repair of volumetric defects. However, a certain volume loss of metal is inevitable during the RFSSWR process, resulting in insufficient remaining ductile metal to fill the gaps left by the retraction of the stirring tool during the backfilling stage. This leads to surface annular groove defects and weak bonding at the thermo-mechanically affected zone / stirring zone interface, affecting weld quality. To address these issues, researchers have proposed many improvement methods and measures to enhance the quality of RFSSWR repair.

[0003] Chinese invention patent CN110640392A discloses a method for repairing defects in aluminum alloy welds based on RFSSW equipment. First, a cylindrical hole is machined on the workpiece to be repaired according to the size and location of the defect, and the defective area is removed. Simultaneously, a cylindrical part with the same diameter and depth as the cylindrical hole is machined and inserted into the cylindrical hole. Then, the rotation of the sleeve and stirring pin is controlled, causing friction with the workpiece to generate heat and soften it. Finally, the movement of the sleeve and stirring pin of the backfill friction stir spot welding (RFSSW) equipment is controlled to complete the repair. While this method is effective in eliminating defects such as porosity, cracks, and inclusions, the consistent diameter and depth of the machined cylindrical part with the cylindrical hole leads to surface annular groove defects caused by material loss during the RFSSW process. This results in severe thinning of the weld joint in the repair area, compromising the weld quality.

[0004] Chinese invention patent CN116197518A discloses a friction stir spot welding weld and a method and apparatus for weld repair. This method involves machining the weld cross-section into an inverted Ω shape (narrower at the top and wider at the bottom), and utilizing a specially designed first and second stirring pin structure to sequentially engage the bevel, perform hot-melt filling, and then reverse and withdraw. This ensures that the weld filler is less likely to detach under stress and that the welded surface exhibits good mechanical properties. However, this method requires a high level of skill in machining the inverted Ω shape (narrower at the top and wider at the bottom) and does not consider the high heat generated by the two welding processes, which can lead to enlarged grains in the weld area, affecting the mechanical properties and load-bearing capacity of the weld joint.

[0005] Chinese invention patent CN111687595A discloses a method for repairing engine disk dents using pre-placed material friction stir spot welding. This method involves filling the dents in the engine disk with powdered material or pre-placed block material, and then repairing the damaged area using friction stir spot welding, achieving a denser repair area and less blade deformation. However, this invention fails to consider that excessive pre-placed block material and high operating speeds can lead to bulging and damage in the repair area, affecting the joint welding quality and, in severe cases, causing damage to the repaired component. Summary of the Invention

[0006] To avoid surface annular groove defects and weak weld interface connections during backfill friction stir spot welding repair, and to improve the weld joint forming quality and joint strength, this invention provides a circumferentially high-pressure backfill friction stir spot welding repair tool and method, specifically employing the following technical solution:

[0007] A circumferentially high-pressure backfill friction stir spot welding repair tool includes a clamping ring, a sleeve, and a stirring needle arranged coaxially. The upper part of the side of the sleeve is provided with m symmetrical threads, and the symmetrical threads change left / right rotation direction every 90°. The lower part of the side of the sleeve is provided with k large helix angle threads. The end face of the sleeve is uniformly provided with n gradient threads.

[0008] Where m>2, the width of the symmetrical thread = depth = 1.0mm~3.0mm, the symmetrical thread includes left-hand thread and right-hand thread, and the inclination angle β of the left-hand thread or right-hand thread is 20°~60°; the symmetrical thread provided on the side of the sleeve occupies 2 / 3~4 / 5 of the total height of the sleeve.

[0009] When k>2, the direction of the large helix angle thread matches the direction of the sleeve rotation. When the sleeve rotation is counterclockwise, the large helix angle thread is right-handed; when the sleeve rotation is clockwise, the large helix angle thread is left-handed. The width and depth of the large helix angle thread are the same, ranging from 0.5mm to 2mm, and the inclination angle θ is from 30° to 75°.

[0010] Where n>2, the direction of the gradient thread is designed from the outside to the inside. The width of the gradient thread = depth = 0.2mm to 4mm, and the width gradually narrows from the inside to the outside. The outer arc length b and the inner arc length c of the gradient thread are: c = A × b, A = 2 to 3. The radius of curvature of the gradient thread is adjusted according to the actual process conditions.

[0011] A circumferentially high-pressure backfill-type friction stir spot welding repair method, specifically as follows:

[0012] Hole-making stage: Grind the defective part of the workpiece to be repaired, and make the defect form a pre-made hole with a minimum diameter of D3 while ensuring the minimum enlargement of the defective part volume.

[0013] Filling stage: Prepare a T-shaped filler rod, the height of which is higher than the surface of the workpiece to be repaired;

[0014] Preheating stage: The stirring needle, sleeve and clamping ring are pressed down as a whole onto the surface of the workpiece to be repaired and the T-shaped filler rod, and the workpiece to be repaired is pressed and fixed. At the same time, the outer diameter D4 of the sleeve is smaller than the inner diameter D2 of the T-shaped filler rod, and the sleeve and stirring needle start to rotate at a speed of ω1 to preheat the surface of the workpiece to be repaired and the T-shaped filler rod.

[0015] During the insertion phase: the sleeve and the stirring needle maintain the same rotation speed ω1. The sleeve rotates and inserts into the T-shaped filler rod, while the stirring needle rotates and retracts. The metal to be welded is squeezed into the cavity of the sleeve. The insertion speed of the sleeve and the retraction speed of the stirring needle are both ν1.

[0016] Backfilling stage: The sleeve and stirring needle maintain the same rotation speed ω2. While the sleeve rotates and retracts at speed ν1, the stirring needle rotates and plunges down at speed ν2, backfilling the plastic metal in the sleeve cavity onto the upper surface of the workpiece to be repaired.

[0017] Withdrawal phase: The sleeve and stirring needle rotate at a certain speed ω3, and the sleeve and stirring needle are withdrawn from the surface of the workpiece to be repaired at a speed ν3, returning to the original set position;

[0018] Grinding stage: Remove the workpiece to be repaired and grind off any protruding excess metal material on the upper surface of the workpiece to ensure that the upper surface of the workpiece to be repaired is flat.

[0019] Furthermore, the material of the T-shaped filler rod is the same as that of the workpiece to be repaired. The height of the T-shaped filler rod is h2 = h1 + t, where h1 is the depth of the pre-drilled hole and t = 0.1 mm to 0.5 mm. The inner diameter of the T-shaped filler rod is D2 and the outer diameter is D1, where D2 = D3 – 0.05 mm, D1 = 1.2 × D3, and D3 is the diameter of the pre-drilled hole. The outer diameter of the sleeve is D4 = D2 - 0.2 mm. The end face of the clamping ring is provided with a groove, the groove diameter is D5 = D1 + 0.04 mm, and the depth is a = t + 0.01 mm.

[0020] Furthermore, during the preheating stage, the rotational speed ω1 of the sleeve and stirring needle ranges from 600 rpm to 1200 rpm.

[0021] Furthermore, during the insertion phase, the insertion speed ν1 of the sleeve and the retraction speed of the stirring needle ranges from 0.5 mm / min to 1.5 mm / min.

[0022] Furthermore, during the backfilling stage, the rotation speed ω2 of the sleeve and stirring needle ranges from 900 rpm to 1500 rpm, and the downward thrust speed ν2 of the stirring needle ranges from 3.0 mm / min to 5.0 mm / min.

[0023] Furthermore, during the withdrawal phase, the rotational speed ω3 of the sleeve and stirring needle ranges from 600 rpm to 800 rpm, and the withdrawal speed ν3 of the sleeve and stirring needle ranges from 2.0 mm / min to 3.0 mm / min.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. The sleeve diameter of this invention is smaller than the filler rod diameter. Therefore, in the repair area, there is not only a sleeve exit line interface but also a filler material / base material interface. The material that accumulates due to the change in sleeve thread direction at the center of symmetry exerts a significant compressive force on the surrounding material. During the backfilling stage, the symmetrical threads drive the material upward and downward, converging and impacting at the center of symmetry, thus exerting a significant compressive force on the surrounding material. The synergistic effect of the large helix angle thread on the sleeve side and the gradually changing thread on the end face enhances the horizontal impact of the material, thereby promoting the metallurgical bonding between the filler material / base material interface and the sleeve exit line interface, further strengthening the interface bonding and improving the connection quality of the weld.

[0026] 2. The backfill-type friction stir spot welding method used in this invention employs a T-shaped filler rod. The volume of the filler material is larger than the defect volume, which can compensate for the volume loss of metal during the backfill spot welding process and avoid the generation of surface annular groove defects. At the same time, since the volume of the pre-backfill material is larger than the space to be filled generated by the sleeve retraction, it can increase the internal pressure of the plastic metal inside the sleeve, which is beneficial to avoid the generation of holes and ensure the welding quality of the joint.

[0027] 3. The crossbeam section of the T-shaped filler rod can achieve zero-thinning welding and avoid annular grooves. It can also ensure that the material is strongly squeezed out of the interface after the sleeve leaves the upper surface of the workpiece during the backfilling stage, thus improving the welding quality.

[0028] 4. Because the sleeve diameter is smaller than the filler rod diameter, a small-diameter weld point is obtained, which reduces the impact of heat generation on the strength of the workpiece to be welded, and at the same time achieves high-quality repair of volumetric defects with lower heat input. Compared with the large-diameter sleeve of the existing conventional RFSSW repair process, the sleeve diameter is larger than the filler rod diameter. Although there is no filler material / base material interface, the increase in sleeve diameter leads to high heat input, which contradicts the green characteristics of the repair. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the sleeve of the circumferentially high-pressure backfill friction stir spot welding repair tool of the present invention;

[0030] Figure 2 This is a schematic diagram of the symmetrical thread structure of the sleeve of the circumferentially high-pressure backfill friction stir spot welding repair tool of the present invention.

[0031] Figure 3 This is a diagram showing the arrangement of the tapered threads on the end face of the sleeve of the circumferentially high-pressure backfill friction stir spot welding repair tool of the present invention.

[0032] Figure 4 This is a diagram showing the arrangement of the large helix angle threads on the sleeve of the circumferentially high-pressure backfill friction stir spot welding repair tool of the present invention.

[0033] Figure 5 This is a schematic diagram of the clamping ring structure of the circumferentially high-pressure backfill friction stir spot welding repair tool of the present invention;

[0034] Figure 6 This is a schematic cross-sectional view of the filling stage of the circumferential high-pressure backfill friction stir spot welding repair method of the present invention.

[0035] Figure 7 This is a schematic diagram of the preheating stage of the backfill-type friction stir spot welding repair method using circumferential high pressure according to the present invention.

[0036] Figure 8 This is a schematic diagram of the jacking stage of the backfilling friction stir spot welding repair method using circumferential high pressure according to the present invention;

[0037] Figure 9 This is a schematic diagram of the backfilling stage of the backfilling stage of the circumferential high-pressure backfilling friction stir spot welding repair method of the present invention.

[0038] Figure 10 This is a schematic diagram of the removal stage of the backfill-type friction stir spot welding repair method using circumferential high pressure according to the present invention.

[0039] Figure 11 for Figure 9 Schematic diagram of material flow during the backfilling stage;

[0040] In the attached diagram: 1. Workpiece to be repaired; 2. T-shaped filler rod; 3. Stirring needle; 4. Sleeve; 5. Clamping ring; 51. Groove; 6. Pad; 7. Sleeve exit line; 8. Filler material / base material interface; 9. Symmetrical thread; 91. Right-hand thread; 92. Left-hand thread; 10. Gradient thread; 11. Large helix angle thread. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0042] like Figures 1-5 As shown in Figure 7, a circumferentially high-pressure backfilling friction stir spot welding repair tool includes a coaxially arranged clamping ring 5, sleeve 4, and stirring needle 3. The upper part of the sleeve 4 has m symmetrical threads 9, where m>2. The symmetrical threads 9 include left-hand threads 92 and right-hand threads 91. The symmetrical threads 9 change their left / right direction every 90°, achieving material convergence and impact at the center of symmetry during backfilling, giving the surrounding material a large compressive force. The width and depth of the symmetrical threads 9 are 1.0mm to 3.0mm, and the inclination angle β of the left-hand or right-hand threads is 20° to 60°. The symmetrical threads 9 occupy 2 / 3 to 4 / 5 of the total height of the sleeve 4. The lower part of the sleeve 4 has k large-helix angle threads 11, where k>2. The direction of the large-helix angle threads 11 is the same as the direction of rotation of the sleeve 4. In this configuration, when the sleeve 4 rotates counterclockwise, the large helix angle thread 11 is right-handed; when the sleeve 4 rotates clockwise, the large helix angle thread 11 is left-handed, thus causing the material to accumulate downwards. The width and depth of the large helix angle thread 11 are the same, ranging from 0.5mm to 2mm, and the inclination angle θ is from 30° to 75°. The end face of the sleeve 4 is uniformly provided with n gradually changing threads 10, where n>2. The rotation direction of the gradually changing threads 10 is designed from the outside to the inside, enabling the material to flow out horizontally and at high speed during the backfilling process. The width and depth of the gradually changing threads 10 are 0.2mm to 4mm, and the width gradually narrows from the inside to the outside. The outward arc length b and the inward arc length c of the gradually changing threads 10 are defined as follows: c = A × b, where A = 2 to 3. The radius of curvature of the gradually changing threads 10 is adjusted according to the actual process conditions.

[0043] like Figures 6-11 As shown, a circumferentially high-pressure backfill-type friction stir spot welding repair method is specifically as follows:

[0044] Hole-making stage: Grind the defective part of the workpiece 1 to be repaired, and make the defect form a pre-made hole with a minimum diameter of D3 while ensuring the minimum enlargement of the defective part volume.

[0045] Filling stage: Prepare T-shaped filler rod 2. The material of T-shaped filler rod 2 is the same as that of workpiece 1 to be repaired. The height of T-shaped filler rod 2 is higher than the surface of workpiece 1 to be repaired. Use acetone and ethanol to clean the oxides and oil stains of the area to be welded and the filler material to expose the fresh material surface. The height of T-shaped filler rod 2 is h2 = h1 + t, where: h1 is the depth of the pre-drilled hole, t = 0.1mm ~ 0.5mm, the inner diameter of T-shaped filler rod 2 is D2, and the outer diameter is D1, where: D2 = D3 - 0.05mm, D1 = 1.2 × D3, and D3 is the diameter of the pre-drilled hole.

[0046] Preheating stage: The stirring needle 3, sleeve 4 and clamping ring 5 are pressed down as a whole onto the upper surface of the workpiece 1 to be repaired and the T-shaped filler rod 2. The workpiece 1 to be repaired is placed on the pad 6 and pressed and fixed. At the same time, the outer diameter D4 of the sleeve 4 is smaller than the inner diameter D2 of the T-shaped filler rod 2. The outer diameter of the sleeve D4 = D2 - 0.2mm, so that it forms the sleeve exit line 7 and the interface 8 of the filler material / base material. The end face of the clamping ring 5 is provided with a groove 51, which cooperates with the T-shaped filler rod. The groove diameter D5 = D1 + 0.04mm and the depth a = t + 0.01mm. The sleeve 4 and stirring needle 3 are rotated at a speed of ω1 to preheat the surface of the workpiece 1 to be repaired and the T-shaped filler rod 2. The speed ω1 of the sleeve 4 and stirring needle 3 is in the range of 600rpm to 1200rpm.

[0047] During the insertion phase: the sleeve 4 and the stirring needle 3 maintain the same rotation speed ω1. The sleeve 4 rotates and inserts into the T-shaped filling rod 2, while the stirring needle 3 rotates and retracts. The metal to be welded is squeezed into the cavity of the sleeve 4. The insertion speed of the sleeve 4 and the retraction speed of the stirring needle 3 are both ν1. The range of the insertion speed ν1 of the sleeve 4 and the retraction speed of the stirring needle 3 is 0.5mm / min to 1.5mm / min.

[0048] Backfilling stage: The sleeve 4 and the stirring needle 3 maintain the same rotation speed ω2. While the sleeve 4 rotates and retracts at a speed ν1, the stirring needle 3 rotates and plunges down at a speed ν2, backfilling the plastic metal in the cavity of the sleeve 4 onto the upper surface of the workpiece 1 to be repaired. The rotation speed ω2 of the sleeve 4 and the stirring needle 3 is in the range of 900rpm~1500rpm, and the plunging speed ν2 of the stirring needle 3 is in the range of 3.0mm / min~5.0mm / min.

[0049] Withdrawal phase: The sleeve 4 and the stirring needle 3 rotate at a certain speed ω3. The sleeve 4 and the stirring needle 3 are withdrawn from the surface of the workpiece 1 to be repaired at a speed ν3 and return to the original set position. The rotation speed ω3 of the sleeve 4 and the stirring needle 3 is in the range of 600rpm~800rpm, and the withdrawal speed ν3 of the sleeve 4 and the stirring needle 3 is in the range of 2.0mm / min~3.0mm / min.

[0050] Grinding stage: Remove the workpiece 1 to be repaired and grind the excess metal material protruding from the upper surface of the workpiece 1. During grinding, the grinding area needs to be cooled in real time to reduce the impact of the high temperature generated by grinding on the performance of the welded joint and ensure that the upper surface of the workpiece to be repaired is flat.

[0051] Example 1

[0052] A circumferentially high-pressure backfill-type friction stir spot welding repair tool consists of three coaxially arranged parts: a clamping ring 5, a sleeve 4, and a stirring needle 3. A schematic diagram of the repair tool structure is shown below. Figures 1-5 As shown.

[0053] In this embodiment, both the workpiece 1 to be repaired and the T-shaped filler rod 2 are made of 2024 aluminum alloy. The stirring needle 3 has a diameter of 3mm, the outer diameter of the sleeve 4 is D4 = 4.75mm, and the outer diameter of the clamping ring 5 is 15mm. The upper part of the side of the sleeve 4 has 6 symmetrical threads 9, of which right-hand threads 91 and left-hand threads 92 are alternately arranged at 90° intervals. The width and depth of the symmetrical threads are both 2.0mm, and the inclination angle β of the right-hand threads 91 and the left-hand threads 92 is 45°. The symmetrical threads 9 occupy 3 / 4 of the entire sleeve height. The lower part of the side of the sleeve 4 has 4 large helix angle threads 11. The large helix angle threads are right-handed, with a width and depth of 1.5mm and an inclination angle θ = 60°. The end face of the sleeve 4 has 5 evenly distributed gradient threads. The width and depth of the gradient threads are 1.8mm, the outward arc length b = 2mm, and the inward arc length c = 4mm.

[0054] The repair process includes six stages: hole making, filling, preheating, drilling, backfilling, removal, and polishing.

[0055] like Figures 6-11 As shown, a circumferentially high-pressure backfill-type friction stir spot welding repair method is specifically as follows:

[0056] Hole-making stage: The defect position of the workpiece 1 to be repaired is adjusted to form a pre-made hole with a depth of h1 = 4mm and a diameter of D3 = 5mm;

[0057] Filling stage: Prepare T-shaped filler rod 2, and the height of the T-shaped filler rod 2 is higher than the surface of the workpiece to be repaired. The height of the T-shaped filler rod 2 is h2 = 4.3 mm, the inner diameter D2 = 4.95 mm, and the outer diameter D1 = 6 mm.

[0058] Preheating stage: The stirring needle 3, sleeve 4 and clamping ring 5 are pressed down as a whole onto the upper surface of the workpiece 1 to be repaired and the T-shaped filler rod 2, and the workpiece 1 to be repaired is pressed and fixed. At the same time, the outer diameter D4 of the sleeve 4 is smaller than the inner diameter D2 of the T-shaped filler rod 2. The outer diameter D4 of the sleeve 4 is 4.75mm. The sleeve 4 and the stirring needle 3 are rotated counterclockwise at a speed of ω1 = 900rpm to preheat the surface of the workpiece 1 to be repaired and the T-shaped filler rod 2.

[0059] During the insertion phase: the sleeve 4 and the stirring needle 3 maintain the same rotation speed ω1 = 900 rpm. The sleeve 4 rotates and inserts into the T-shaped filling rod 2, while the stirring needle 3 rotates and retracts. The metal to be welded is squeezed into the cavity of the sleeve 4. The speed of insertion of the sleeve 4 and retraction of the stirring needle 3 are both ν1 = 1.0 mm / min.

[0060] Backfilling stage: The sleeve 4 and the stirring needle 3 maintain the same rotation speed ω2=1000rpm. While the sleeve 4 rotates and retracts at a speed ν1=1.0mm / min, the stirring needle 3 rotates and thrusts down at a speed ν2=3.0mm / min, backfilling the plastic metal in the cavity of the sleeve 4 onto the upper surface of the workpiece to be repaired.

[0061] Withdrawal phase: The sleeve 4 and the stirring needle 3 rotate at a certain speed ω3 = 800 rpm. The sleeve 4 and the stirring needle 3 are withdrawn from the surface of the workpiece 1 to be repaired at a speed ν3 = 2.0 mm / min and return to the original set position.

[0062] Grinding stage: Remove the workpiece 1 to be repaired, and grind the excess metal material protruding from the upper surface of the workpiece 1 to ensure that the upper surface of the workpiece 1 to be repaired is flat.

[0063] At this point, the entire repair process is complete. The surface of the repaired workpiece is not thinned. At the same time, due to the strong extrusion of the material during the repair process, the repaired area can promote the metallurgical bonding between the repaired material and the base material, thereby improving the forming quality and the load-bearing capacity after repair.

[0064] Example 2

[0065] A circumferentially high-pressure backfill-type friction stir spot welding repair tool consists of three coaxially arranged parts: a clamping ring 5, a sleeve 4, and a stirring needle 3. A schematic diagram of the repair tool is shown below. Figures 1-5 As shown.

[0066] In this embodiment, both the workpiece 1 to be repaired and the T-shaped filler rod 2 are made of 5083 aluminum alloy. The stirring needle 3 has a diameter of 2mm, the outer diameter of the sleeve 4 is D4 = 3.75mm, and the outer diameter of the clamping ring 5 is 10mm. The upper part of the side of the sleeve 4 has 5 symmetrical threads 9, of which right-hand threads 91 and left-hand threads 92 are alternately arranged at 90° intervals. The width and depth of the symmetrical threads are both 1.5mm, and the inclination angle β of the right-hand threads 91 and the left-hand threads 92 is 60°. The symmetrical threads 9 occupy 4 / 5 of the entire sleeve height. The lower part of the side of the sleeve 4 has 6 large helix angle threads 11. The large helix angle threads are right-handed, with a width and depth of 2.0mm and an inclination angle θ = 75°. The end face of the sleeve 4 has 4 evenly distributed gradient threads. The width and depth of the gradient threads are 3.0mm, the outward arc length b = 3mm, and the inward arc length c = 6mm.

[0067] The repair process includes six stages: hole making, filling, preheating, drilling, backfilling, removal, and polishing.

[0068] like Figures 6-11 As shown, a circumferentially high-pressure backfill-type friction stir spot welding repair method is specifically as follows:

[0069] Hole-making stage: The defect position of the workpiece 1 to be repaired is adjusted to form a pre-made hole with a depth of h1 = 3mm and a diameter of D3 = 4mm;

[0070] Filling stage: Prepare T-shaped filler rod 2, and the height of the T-shaped filler rod 2 is higher than the surface of the workpiece to be repaired. The height of the T-shaped filler rod 2 is h2 = 3.3 mm, the inner diameter D2 = 3.95 mm, and the outer diameter D1 = 4.8 mm.

[0071] Preheating stage: The stirring needle 3, sleeve 4 and clamping ring 5 are pressed down as a whole onto the upper surface of the workpiece 1 to be repaired and the T-shaped filler rod 2, and the workpiece 1 to be repaired is pressed and fixed. At the same time, the outer diameter D4 of the sleeve is smaller than the inner diameter D2 of the T-shaped filler rod, the outer diameter D4 of the sleeve 4 is 3.75mm, and the sleeve 4 and stirring needle 3 are started to rotate at a speed of ω1 = 800rpm to preheat the surface of the workpiece 1 to be repaired and the T-shaped filler rod 2.

[0072] During the insertion phase: the sleeve 4 and the stirring needle 3 maintain the same rotation speed ω1 = 800 rpm. The sleeve 4 rotates and inserts into the T-shaped filling rod 2, while the stirring needle 3 rotates and retracts. The metal to be welded is squeezed into the cavity of the sleeve 4. The insertion speed of the sleeve 4 and the retraction speed of the stirring needle 3 are both ν1 = 1.5 mm / min.

[0073] Backfilling stage: The sleeve 4 and the stirring needle 3 maintain the same rotation speed ω2=1100rpm. While the sleeve 4 rotates and retracts at a speed ν1=1.5mm / min, the stirring needle 3 rotates and thrusts down at a speed ν2=3.2mm / min, backfilling the plastic metal in the cavity of the sleeve 4 onto the upper surface of the workpiece to be repaired.

[0074] Withdrawal phase: The sleeve 4 and the stirring needle 3 rotate at a certain speed ω3 = 700 rpm. The sleeve 4 and the stirring needle 3 are withdrawn from the surface of the workpiece 1 to be repaired at a speed ν3 = 2.2 mm / min and return to the original set position.

[0075] Grinding stage: Remove the workpiece 1 to be repaired, and grind the excess metal material protruding from the upper surface of the workpiece 1 to ensure that the upper surface of the workpiece 1 to be repaired is flat.

[0076] At this point, the entire repair process is complete. The surface of the repaired workpiece is not thinned. At the same time, due to the strong extrusion of the material during the repair process, the repaired area can promote the metallurgical bonding between the repaired material and the base material, thereby improving the forming quality and the load-bearing capacity after repair.

Claims

1. A circumferentially high-pressure backfill friction stir spot welding repair method, wherein the backfill friction stir spot welding repair tool includes a coaxially arranged clamping ring, sleeve and stirring needle, the upper part of the side of the sleeve is provided with m symmetrical threads, the symmetrical threads change left / right rotation direction every 90°; the lower part of the side of the sleeve is provided with k large helix angle threads; the end face of the sleeve is uniformly provided with n gradient threads; Its features are, The specific method is as follows: Hole-making stage: Grind the defective part of the workpiece to be repaired, and make the defect form a pre-made hole with a minimum diameter of D3 while ensuring that the volume of the defective part is minimized. Filling stage: Prepare a T-shaped filler rod, the height of which is higher than the surface of the workpiece to be repaired; Preheating stage: The stirring needle, sleeve and clamping ring are pressed down as a whole onto the surface of the workpiece to be repaired and the T-shaped filler rod, and the workpiece to be repaired is pressed and fixed. At the same time, the outer diameter D4 of the sleeve is smaller than the inner diameter D2 of the T-shaped filler rod, and the sleeve and stirring needle start to rotate at a speed of ω1 to preheat the surface of the workpiece to be repaired and the T-shaped filler rod. During the insertion phase: the sleeve and the stirring needle maintain the same rotation speed ω1. The sleeve rotates and inserts into the T-shaped filler rod, while the stirring needle rotates and retracts. The metal to be welded is squeezed into the cavity of the sleeve. The insertion speed of the sleeve and the retraction speed of the stirring needle are both ν1. Backfilling stage: The sleeve and stirring needle maintain the same rotation speed ω2. While the sleeve rotates and retracts at speed ν1, the stirring needle rotates and plunges down at speed ν2, backfilling the plastic metal in the sleeve cavity onto the upper surface of the workpiece to be repaired. Withdrawal phase: The sleeve and stirring needle rotate at a certain speed ω3, and the sleeve and stirring needle are withdrawn from the surface of the workpiece to be repaired at a speed ν3, returning to the original set position; Grinding stage: Remove the workpiece to be repaired and grind off any protruding excess metal material on the upper surface of the workpiece to ensure that the upper surface of the workpiece to be repaired is flat.

2. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, Where m>2, the width and depth of the symmetrical thread are 1.0 mm to 3.0 mm, the symmetrical thread includes left-hand thread and right-hand thread, and the inclination angle β of the left-hand thread or right-hand thread is 20° to 60°; the symmetrical thread provided on the side of the sleeve occupies 2 / 3 to 4 / 5 of the total height of the sleeve.

3. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, When k>2, the direction of the large helix angle thread matches the direction of the sleeve rotation. When the sleeve rotation is counterclockwise, the large helix angle thread is right-handed; when the sleeve rotation is clockwise, the large helix angle thread is left-handed. The width and depth of the large helix angle thread are the same, ranging from 0.5 mm to 2 mm, and the inclination angle θ is from 30° to 75°.

4. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, Where n>2, the direction of the gradient thread is designed from the outside to the inside. The width of the gradient thread is equal to the depth, which is 0.2 mm to 4 mm, and the width gradually narrows from the inside to the outside. The outer arc length b and the inner arc length c of the gradient thread are: c = A × b, where A = 2 to 3. The radius of curvature of the gradient thread is adjusted according to the actual process conditions.

5. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, The material of the T-shaped filler rod is the same as that of the workpiece to be repaired. The height of the T-shaped filler rod is h2 = h1 + t, where h1 is the depth of the pre-drilled hole and t = 0.1~0.5mm. The inner diameter of the T-shaped filler rod is D2 and the outer diameter is D1, where D2 = D3 – 0.05mm, D1 = 1.2×D3, and D3 is the diameter of the pre-drilled hole. The outer diameter of the sleeve is D4 = D2 - 0.2mm. The end face of the clamping ring is provided with a groove, the groove diameter is D5 = D1 + 0.04mm, and the depth is a = t + 0.01mm.

6. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, During the preheating stage, the rotational speed ω1 of the sleeve and stirring needle is in the range of 600 rpm to 1200 rpm.

7. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, During the insertion phase, the insertion speed ν1 of the sleeve and the withdrawal speed of the stirring needle ranges from 0.5 mm / min to 1.5 mm / min.

8. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, During the backfilling stage, the rotation speed ω2 of the sleeve and stirring needle is in the range of 900 rpm to 1500 rpm, and the downward speed ν2 of the stirring needle is in the range of 3.0 mm / min to 5.0 mm / min.

9. The circumferential high-pressure backfill-type friction stir spot welding repair method according to claim 1, characterized in that, During the withdrawal phase, the rotational speed ω3 of the sleeve and stirring needle ranges from 600 rpm to 800 rpm, and the withdrawal speed ν3 of the sleeve and stirring needle ranges from 2.0 mm / min to 3.0 mm / min.

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