A tool and method for enhancing load bearing of a friction stir spot welded joint of dissimilar materials

Abstract

The application discloses a tool and a welding method for realizing load enhancement of a heterogeneous material backfill type friction stir spot welding joint, and relates to a tool and a welding method for realizing heterogeneous material backfilling. In order to solve the problems of low joint load capacity, large performance discreteness and poor service reliability caused by the difficulty in increasing the connection area in the prior art, the tool is improved to realize horizontal movement, and the tool is made to move along a circular path during welding, so that the effective connection area is increased. The specific welding process is as follows: after the pressing ring, the stirring sleeve and the stirring needle are leveled, the tool is moved to a starting position of welding, the stirring sleeve is lowered and the stirring needle is retracted at the same time; under the program control of the equipment, the whole tool starts to move along a circular path for welding, and after one circle is completed, the tool returns to the center area of the circle; the stirring sleeve is lifted and the stirring needle is lowered at the same time, the material in the cavity formed by the relative movement of the stirring sleeve and the stirring needle is fully backfilled, and the welding is completed. The application belongs to the technical field of friction stir welding.

Description

Technical Field

[0001] This invention relates to a welding tool and welding method for backfilling heterogeneous materials, belonging to the field of friction stir welding technology. Background Technology

[0002] Driven by the development of lightweight, energy-saving, and high-performance automotive, rail transportation, and high-end equipment industries, heterogeneous composite structures of aluminum alloys and high-strength steel have become a core solution for achieving weight reduction, efficiency improvement, and structural efficiency enhancement. Aluminum / steel dissimilar material joining technology, as a key link in composite structure manufacturing, directly determines the load-bearing capacity, service life, and safety reliability of components. Refill Friction Stir Spot Welding (RFSSW), with its advantages of solid-state bonding, low heat input, keyless operation, and regular forming, effectively avoids defects such as porosity, cracks, and excessive intermetallic compounds (IMCs) caused by fusion welding. It has become the preferred process for efficient spot welding of aluminum / steel dissimilar thin plates, showing broad industrial application prospects in body panels, frame assemblies, and cabin structures. However, due to the significant differences in thermal properties, mechanical properties and metallurgical compatibility between aluminum and steel, the joint strength of aluminum-steel backfill friction stir welding joints is generally low and the mechanical properties are highly variable, making it difficult to meet the dynamic load and fatigue durability requirements of vehicles and equipment. This has become a major obstacle to the large-scale promotion of this technology. The connection area, as a core geometric factor determining the joint's load-bearing capacity, is significantly positively correlated with the failure load. Increasing the effective connection area can expand the load transfer range, reduce the average interface stress, smooth the stress gradient, reduce defect-induced local stress peaks, and enhance the continuity of the interface's mechanical interlocking and metallurgical bonding, thereby weakening the stress concentration effect. Simultaneously, it improves the interface bonding uniformity without significantly increasing heat input, thus enhancing the joint's load-bearing capacity and structural stability. However, due to limitations in the power output, rigidity, and precision of existing equipment, the size of the RFSSW welding fixture is difficult to increase. Furthermore, increasing the fixture size would lengthen the material flow path and increase backfill resistance, resulting in insufficient material backfilling in the cavity formed by the relative movement of the stirring pin and the stirring sleeve. This leads to defects such as surface annular grooves, incomplete interface welding, and voids, severely reducing the joint's mechanical properties. CN117359084A improves the strength reduction and functional loss caused by the disorder of grain size and composition in the weld joint of heterogeneous materials by gradually backfilling the material to the weld area in stages by controlling the rotation and dwell of the stirring sleeve and stirring needle at different backfill depths. CN117680805A compensates for the volume loss of metal material during the backfilling and spot welding process by pre-fabricating the material before welding. On the other hand, since the volume of the pre-backfilled material is larger than the space to be filled generated by the sleeve retraction, it increases the internal pressure of the plastic metal inside the sleeve, which helps to avoid the formation of voids and thus improves the joint strength and strength stability. CN110216367A takes aluminum alloy plates as the object, pre-processes an annular groove or trench matching the spot welding tool in the center of its overlapping area, and puts in graphene of matching volume. Then, another aluminum alloy plate is placed underneath, and the spot welding tool is aligned before welding. This method uses the strong plastic flow during the stirring friction process to make the graphene uniformly dispersed, thereby strengthening and toughening the weak areas inside the joint and improving the joint strength. However, the above-mentioned inventions have limited effect on improving the load-bearing capacity of welded joints, and new methods are still needed to achieve a breakthrough in improving the load-bearing capacity of joints.

[0003] This invention aims to address the problems of low joint load-bearing capacity, large performance dispersion, and poor service reliability caused by the difficulty in increasing the effective connection area in existing technologies. It provides an aluminum-steel backfill friction stir spot welding technology solution that offers stable forming, high load-bearing capacity, good consistency, and suitability for mass production. Compared with traditional processes, this invention improves the welding fixture structure to enable lateral movement, thereby increasing the effective connection area at the aluminum-steel interface, thus enhancing the joint load-bearing capacity and structural stability. Simultaneously, it maintains the technical advantages of low heat input, keyhole-free operation, and high efficiency, meeting the requirements for connection strength and structural reliability in lightweight aluminum / steel composite components. This invention has significant engineering application value and industrialization prospects. Summary of the Invention

[0004] To address the problems of low joint load-bearing capacity, large performance dispersion, and poor service reliability caused by the difficulty in increasing the connection area in the prior art, this invention proposes a welding tool and welding method to enhance the load-bearing capacity of heterogeneous material backfill friction stir spot welded joints.

[0005] The technical solution adopted by the present invention to solve the above problems is as follows: The welding tool for realizing the load-bearing enhancement of the heterogeneous material backfill friction stir spot welding joint includes a stirring pin, a stirring sleeve is fitted on the lower part of the stirring pin, and a clamping ring is fitted on the lower part of the stirring sleeve.

[0006] Furthermore, the clamping ring is divided into an end cone structure, a middle outer diameter enlargement structure, and an upper mounting structure from bottom to top. The outer wall of the middle outer diameter enlargement structure is provided with a ball screw mounting hole, a ball is provided in the ball screw mounting hole, and a ball screw is provided outside the ball.

[0007] Furthermore, the outer wall of the end cone structure is provided with a discharge hole.

[0008] The steps of the welding method for achieving load-bearing enhancement of heterogeneous material backfill friction stir spot weld joints according to the present invention include: Step 1, Clamping: Secure the plates to be welded tightly to the workbench in an overlapping manner, with the steel plate at the bottom and the aluminum plate at the top; Step 2, Zeroing: After the top ball screw is installed, make sure that the bottom of the clamping ring, stirring sleeve and stirring needle are all on the same horizontal plane, and set the zero point a of the stirring sleeve and stirring needle; then press the clamping ring down onto the aluminum plate. When the pressure is 4~7KN, set this point as the welding start point b. Step 3, Welding Stage 1: The rotation speeds of the stirring sleeve and the stirring pin are respectively... , The stirring sleeve is The stirring needle plunges downwards into the aluminum plate at a speed that allows it to penetrate the aluminum plate simultaneously. The speed retracts upwards until the stirring sleeve plunges to the set depth. Then, at this point, the stirring needle retracts upward a distance of... The stirring sleeve and stirring needle no longer move relative to each other and remain stationary at this point. time; Step 4, Second Welding Stage: Under the control of the welding equipment, the entire welding tool performs circular welding along the programmed path and at a speed v. After completing the circular path, it returns to the center of the circular path along a straight line, reaching the final welding position c, where it stops. time; Step 5, Welding Stage 3: The entire welding tool remains stationary after reaching the final welding position c. After a certain time, the mixing sleeve is... The stirring needle retracts upwards at a speed that allows it to move upwards at the same time. The stirring sleeve and stirring pin descend at a certain speed. After they return to zero point a, they stop rotating, the welding tool is lifted as a whole, and the entire welding process is completed.

[0009] Furthermore, the rotation speed of the stirring jacket in step 3 The stirring needle speed is 100~5000 rpm. The descent speed of the mixing sleeve is 100~5000 rpm. The retraction speed of the stirring needle is 0.1~2 mm / s. The set depth of the mixing sleeve The distance is 1~10mm, and the retraction distance of the stirring needle is also... Duration of stay The range is 0~5s; R is the outer diameter of the stirring sleeve, and r is the outer diameter of the stirring needle.

[0010] Furthermore, in step 4, the welding tool moving speed v is 0.1~10mm / s, and the dwell time is... The duration is 0~5s.

[0011] Furthermore, in step 5, the upward retraction speed of the stirring sleeve... The downward thrust speed of the stirring needle is 0.1~2 mm / s. R is the outer diameter of the stirring sleeve, and r is the outer diameter of the stirring needle.

[0012] The beneficial effects of this invention are: 1. By using a circular path (or other shaped path) during the welding process, the size limitations of the stirring sleeve and stirring pin of the backfill friction stir equipment can be overcome. A larger area interface welding can be achieved in one welding process with a smaller stirring sleeve and stirring pin, resulting in a welded joint with a larger connection area. On the one hand, this can expand the selection range of welding equipment, and on the other hand, it can improve the load-bearing capacity and structural stability of the joint. At the same time, it can maintain the technical advantages of low heat input, no keyhole, green and efficient technology, and obtain a backfill friction stir spot welded joint with stable formation, high strength, good consistency and suitable for mass production.

[0013] 2. During the welding process, due to the relatively long size of the stirring sleeve and stirring pin, they will be subjected to lateral forces and deform as they move along the circumferential weld (or other shaped paths). This will cause the stirring sleeve to come into direct contact with the clamping ring and cause friction. The steel ball set screw installed in the clamping ring can provide support for the stirring sleeve during the welding process, thereby reducing the degree of deformation when it moves along the circumferential weld. At the same time, the rolling of the top ball can also reduce the friction between the clamping ring and the stirring sleeve. In addition, the tapered design at the end of the clamping ring can also avoid large-area contact friction between the clamping ring and the stirring sleeve during lateral displacement.

[0014] 3. This invention is applicable to the reliable connection between most "soft" and "hard" dissimilar materials, such as aluminum / titanium, magnesium / titanium, magnesium / steel, polymer / metal, etc. Attached Figure Description

[0015] Figure 1 This is a schematic cross-sectional view of the welding fixture assembly structure; Figure 2 This is a partial schematic diagram of the cross-sectional structure of the welding tool and the plate being welded; Figure 3 This is a schematic diagram of the circular path welding process in aluminum / steel welding; Figure 4 This is a schematic diagram of the circular path welding process in aluminum / steel welding; Figures 1 to 4 In the middle, 1-compression ring, 11-end cone structure, 12-increased outer diameter structure in the middle, 13-upper mounting structure, 101-discharge hole, 102-top ball screw mounting hole, 111-lower end face of end cone structure, 2-stirring sleeve, 3-stirring needle, 4-top ball screw, 401-ball bearing, 5-aluminum plate, 6-steel plate. Detailed Implementation

[0016] Specific implementation method one: as follows Figures 1 to 2 As shown, the welding tool for enhancing the load-bearing capacity of the backfill friction stir spot welding joint of heterogeneous materials described in this embodiment includes a stirring pin (3), a stirring sleeve (2) is fitted on the lower part of the stirring pin (3), and a clamping ring (1) is fitted on the lower part of the stirring sleeve (2).

[0017] In some embodiments, the clamping ring 1 is divided into three parts from bottom to top: an end cone structure 11, a middle outer diameter enlargement structure 12, and an upper mounting structure 13. The end cone structure 11 has a taper of 15°~45°. The wall thickness at the lower end face 111 of the end cone structure is 2~3mm. The inner diameter of the lower end of the end cone structure 11 is 0.1~0.2mm larger than the outer diameter of the stirring sleeve 2. The tapered design at the end can also avoid large-area contact friction between the clamping ring and the stirring sleeve during lateral displacement. The outer diameter at the upper end is 2~4mm larger than the outer diameter at the lower end. There are 6~12 discharge holes 101 with a diameter of 1~2mm distributed circumferentially at 1~3mm from the lower end face of the end cone structure 11. The middle outer diameter enlargement structure 12 is located 2~5mm above the discharge holes 101. Its length is 10~20mm and its wall thickness is 5~10mm. There are 4~8 ball screw mounting holes 102 distributed circumferentially at 3~6mm from the lower end face to realize the installation limit of the ball screw 4. The top of the top ball screw 4 has a built-in ball 401. The ball 401 is embedded in the top of the screw, will not fall out and can rotate freely. The diameter of the ball 401 is 1mm smaller than the diameter of the unthreaded end of the screw. The diameter of the threaded end of the top ball screw 4 is 4~6mm and the length is 3~4mm. The diameter of the unthreaded end is 1~2mm smaller than that of the threaded end.

[0018] After the top ball screw 4 is installed, the gap between its top ball 401 and the stirring sleeve 2 is 0~0.1mm. Since the stirring sleeve 2 and the stirring pin 3 are both relatively long, in the second stage of welding, the stirring sleeve 2 and the stirring pin 3 will be deformed by lateral force during the process of moving through the circumferential weld (or other shaped path), which will cause the stirring sleeve 2 to come into direct contact with the clamping ring 1 and cause friction. On the one hand, this will lead to a sharp increase in frictional heat, which will rapidly increase the welding heat input and cause a decrease in the performance of the welded joint. On the other hand, the wear of the contact friction area between the stirring sleeve 2 and the clamping ring 1 will be aggravated, affecting the service life of the welding tool. Therefore, the top ball screw 4 installed in the clamping ring 1 can not only provide support for the stirring sleeve 2 during the welding process, thereby reducing the degree of deformation caused by it moving through the circumferential weld, but also reduce the friction between the clamping ring 1 and the stirring sleeve 2 by the rolling of its top ball 401. In addition, the tapered design at the end of the clamping ring 1 can also avoid a large area of ​​contact friction between the clamping ring and the stirring sleeve during lateral displacement.

[0019] Specific implementation method two: such as Figures 1 to 4 The steps of the welding method for achieving load-bearing enhancement of heterogeneous material backfill friction stir spot weld joint described in this embodiment include: Step 1: Clamping: Secure the plates to be welded tightly to the workbench in an overlapping manner, with the steel plate at the bottom and the aluminum plate at the top; Step 2: Zeroing: After the top ball screw 4 is installed, make the bottom of the clamping ring 1, stirring sleeve 2 and stirring needle 3 all at the same horizontal position, and set it as the zero point a of stirring sleeve 2 and stirring needle 3; then press the clamping ring 1 down onto the aluminum plate. When the pressure is 5~7KN, set this point as the welding start point b. Step 3: Welding Stage 1: The rotation speeds of the stirring sleeve 2 and the stirring pin 3 are respectively... , The stirring sleeve 2 is used as The stirring needle 3 plunges downwards into the aluminum plate at a speed that allows it to penetrate the aluminum plate at the same time. The speed retracts upwards until the stirring sleeve 2 plunges to the set depth. Then, at this point, the stirring needle 3 retracts upward a distance of... The stirring sleeve 2 and the stirring needle 3 no longer move relative to each other and remain stationary at this point. time; Step Four: Second Stage of Welding: Under the control of the welding equipment, the entire welding tool performs circular welding according to the programmed path and speed v. After completing the circular path, it returns to the center of the circle along a straight line, reaching the final welding position c, where it stops. time; Step 5: Welding Stage 3: The entire welding tool remains stationary after reaching the final welding position c. After a certain time, the stirring sleeve 2... The stirring needle 3 is pulled upwards at a speed that allows it to retract. As the stirring sleeve 2 and stirring needle 3 descend at a certain speed, they eventually return to zero point a. After this, the stirring sleeve 2 and stirring needle 3 stop rotating, the welding fixture is lifted as a whole, and the entire welding process is completed.

[0020] The thickness of aluminum plate 5 is 1~10mm.

[0021] Among them, the rotational speed of the stirring jacket The range is 100~5000 rpm, the speed of the stirring needle. The range is 100~5000 rpm, the downward speed of the stirring jacket. The range is 0.1~2mm / s, and the retraction speed of the stirring needle is... The set depth of the mixing sleeve The range is 1~10mm, and the retraction distance of the stirring needle 3 is also measured. Duration of stay The range is 0~5s; R is the outer diameter of the stirring sleeve 2, and r is the outer diameter of the stirring needle 3.

[0022] The welding tool's moving speed v ranges from 0.1 to 10 mm / s, and the dwell time... The range is 0~5s; the welding path can be multiple turns or any other shape that meets the requirements.

[0023] Among them, the upward retraction speed of the stirring sleeve The range is 0.1~2mm / s, and the downward thrust speed of the stirring needle is... R is the outer diameter of the stirring sleeve, and r is the outer diameter of the stirring needle.

[0024] Various shapes of path welding can be achieved during the welding process, and a large range of joint welding can be achieved using a small-sized stirring sleeve and stirring pin.

[0025] This invention can not only realize the welding of aluminum / steel dissimilar materials, but also the combination of other "soft and hard" dissimilar materials, such as aluminum / titanium, magnesium / titanium, magnesium / steel, polymer / metal, etc.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A welding tool for enhancing the load-bearing capacity of a backfill-type friction stir spot weld joint of heterogeneous materials, characterized in that, It includes a stirring needle (3), a stirring sleeve (2) is fitted on the lower part of the stirring needle (3), and a clamping ring (1) is fitted on the lower part of the stirring sleeve (2).

2. The welding tool for enhancing the load-bearing capacity of a backfill-type friction stir spot weld joint of heterogeneous materials according to claim 1, characterized in that, The clamping ring (1) is divided into an end cone structure (11), a middle outer diameter enlargement structure (12) and an upper mounting structure (13) from bottom to top. The outer wall of the middle outer diameter enlargement structure (12) is provided with a ball screw mounting hole (102). A ball (401) is provided inside the ball screw mounting hole (102), and a ball screw (4) is provided outside the ball (401).

3. The welding tool for enhancing the load-bearing capacity of a backfill-type friction stir spot weld joint of heterogeneous materials according to claim 1, characterized in that, The outer wall of the end cone structure (11) is provided with a discharge hole (101).

4. A welding method based on the welding tool according to any one of claims 1 to 3, characterized in that, The specific steps include: Step 1, clamping: Secure the plates to be welded tightly on the workbench in an overlapping manner, with the steel plate (6) at the bottom and the aluminum plate (5) at the top; Step 2, Zeroing: After the top ball screw (4) is installed, make the bottom of the clamping ring (1), stirring sleeve (2) and stirring needle (3) all on the same horizontal plane, and set the zero point a of the stirring sleeve (2) and stirring needle (3); then press the clamping ring (1) down onto the aluminum plate (5). When the pressure is 4~7KN, set this point as the welding start point b; Step 3, Welding Stage 1: The rotation speeds of the stirring sleeve (2) and the stirring pin (3) are respectively , The stirring sleeve (2) is used as The needle plunges downwards into the aluminum plate (5) at a speed that is simultaneously stirred by the stirring needle (3) at a speed that is... The speed retracts upward until the stirring sleeve (2) plunges to the set depth. Then, at this time, the stirring needle (3) retracts upward a distance of... The stirring sleeve (2) and the stirring needle (3) do not move relative to each other and remain at this point. time; Step 4, Second Welding Stage: Under the control of the welding equipment, the entire welding tool performs circular welding along the programmed path and at a speed v. After completing the circular path, it returns to the center of the circular path along a straight line, reaching the final welding position c, where it stops. time; Step 5, Welding Stage 3: The entire welding tool remains stationary after reaching the final welding position c. After a certain time, the stirring sleeve (2) with The stirring needle (3) is pulled upwards at a speed of [speed not specified], while simultaneously [speed not specified]. The speed of the plunger is such that after the stirring sleeve (2) and stirring needle (3) return to zero point a, the stirring sleeve (2) and stirring needle (3) stop rotating, the welding tool is lifted as a whole, and the entire welding process is completed.

5. The welding method for enhancing the load-bearing capacity of a heterogeneous material backfill-type friction stir spot weld joint according to claim 4, characterized in that, The rotational speed of the stirring sleeve (2) in step 3 The rotation speed of the stirring needle (3) is 100~5000 rpm. The descent speed of the stirring sleeve (2) is 100~5000 rpm. The retraction speed of the stirring needle (3) is 0.1~2 mm / s. The set depth of the stirring sleeve (2) The distance is 1~10mm, and the retraction distance of the stirring needle (3) is also 1~10mm. Duration of stay The value is 0~5s; R is the outer diameter of the stirring sleeve (2), and r is the outer diameter of the stirring needle (3).

6. The welding method for enhancing the load-bearing capacity of a heterogeneous material backfill-type friction stir spot weld joint according to claim 4, characterized in that, In step 4, the welding tool moving speed v is 0.1~10mm / s, and the dwell time is... The duration is 0~5s.

7. The welding method for enhancing the load-bearing capacity of a heterogeneous material backfill-type friction stir spot weld joint according to claim 4, characterized in that, The upward retraction speed of the stirring sleeve (2) in step 5 The downward thrust speed of the stirring needle (3) is 0.1~2 mm / s. R is the outer diameter of the stirring sleeve (2), and r is the outer diameter of the stirring needle (3).

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