A low-stress friction stir welding joint with a built-in heat source

Abstract

This invention belongs to the field of friction stir welding technology and discloses a low-stress friction stir welding head with a built-in heat source. The welding head mainly consists of three systems: a rotating spindle, a main stirring head, and a power supply device. The main stirring head is installed below the rotating spindle and includes multiple components such as a shoulder, stirring pin, and a spiral heating device. The power supply device is fixed to the outer shell of the rotating spindle, supports the conductive head via a support arm, and is connected to the graphite conductive ring of the main stirring head, energizing and heating it. The stirring head of this invention has an integrated structure, and its built-in spiral heating device can directly provide additional heat to the stirring head, replacing the single heat source of friction heat in traditional friction stir welding with multiple heat sources, reducing the requirement for rotational speed, thereby reducing the stress generated by high-speed rotation in friction stir welding. Furthermore, the built-in heat input can be controlled by adjusting the frequency of the alternating current, allowing parameters to be adjusted according to specific welding requirements, increasing the controllability of the welding heat source.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, and more particularly to a low-stress friction stir welding joint with a built-in heat source. Background Technology

[0002] Friction stir welding is a solid-state welding technique that uses a rotating stirring tool (usually composed of needle-like tools) to generate frictional heat at the workpiece contact surface, heating the workpiece to near its plastic state. The tool's rotation and longitudinal feed force stir and bond the materials. Throughout the welding process, the metal remains in a solid state, achieving bonding through mechanical stirring. Due to its unique welding principle, superior weld quality, and broad application prospects, it has received extensive research in recent years.

[0003] The welding quality and efficiency of friction stir welding are affected by a variety of factors, including tool design, welding parameters, and material properties. The friction stir welding process requires rigid support and secure clamping, and relies on the high heat input generated by high-speed rotation. Therefore, it has drawbacks such as being unsuitable for high-melting-point metals and requiring high assembly precision. Furthermore, as the rotational speed increases, significant tensile stress tends to appear below the blade shoulder in friction stir welding, adversely affecting weld quality. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a low-stress friction stir welding head with a built-in heat source. This welding head is connected to an external motor, and by supplying a high-frequency alternating current to the graphite conductive ring, spiral heating ring, and spiral heating rod inside the stirring head, it achieves two heat source inputs: frictional heat and eddy current heat generation. This reduces the required rotational speed of the stirring head, thereby reducing the stress generated during welding. Furthermore, the built-in temperature sensor of this invention can monitor the temperature of the weld surface in real time, thereby improving the controllability of temperature and rotational speed in friction stir welding.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A low-stress friction stir welding head with a built-in heat source is characterized by comprising three systems: a rotating spindle, a main stirring head, and a power supply device.

[0007] Preferably, the rotating spindle consists of a housing, a rotating shaft, and a clamping head. The housing is fixed and does not rotate, the rotating shaft and the clamping head are integrated, and the clamping head is clamped to the main stirring head and fixed with a nut, so that the rotating shaft drives the main stirring head to rotate at high speed together.

[0008] Preferably, the main stirring head consists of three parts: a clamping front end, a power supply middle part, and a heating tail end. The clamping front end is tightly connected to the clamping head of the rotating spindle. The power supply middle part consists of a limiting shoulder, a graphite conductive ring, and an internal conductive wire. The limiting shoulder limits the clamping depth of the clamping front end. The graphite conductive ring transmits current to the internal conductive wire. The heating tail end consists of a shaft shoulder, a stirring needle, a spiral heating ring, a fixing nut, and a spiral heating rod. The spiral heating ring is located inside the shaft shoulder and is connected to the internal conductive wire to achieve current transmission for heating. The spiral heating rod is located inside the stirring needle, and its tail end is connected to the internal conductive wire to achieve current transmission. The spiral copper wire is heated after being energized. The spiral copper wire is located at the lower part of the spiral heating rod and is coiled on the heating shaft. A temperature sensor is located on the spiral heating rod to detect the temperature of the weld center.

[0009] Preferably, the power supply device comprises a fixing device, a support arm, and a conductive head. The fixing device is fixed to the outer surface of the housing and supports the power supply device. One end of the support arm is tightly connected to the fixing device, and the other end supports the conductive head. The conductive head comprises a conductive head housing, an internal spring, and a conductive needle. The internal spring and the conductive needle are both located inside the conductive head housing. The internal spring is placed at the thin end of the conductive needle to support the conductive needle. The thin end of the conductive needle is connected to an external power source to transmit current. The thick end of the conductive needle is connected to the graphite conductive ring through an opening in the conductive head housing. After the power is turned on, the current is transmitted through the conductive head to the conductive graphite ring, and then supplies power to the spiral heating ring and spiral heating rod through the internal conductive wire. The spiral heating ring and spiral heating rod can provide a large amount of heat input to the heating tail end of the main stirring head, thereby reducing the required rotational speed of the main stirring head and reducing the tensile stress generated on the shoulder due to high-speed rotation during welding. On the other hand, the reduced rotational speed can also improve the surface forming quality of the weld and reduce flash.

[0010] Preferably, the clamping front end is integrated with the power supply middle part, and the power supply middle part is connected to the heating tail end by a fixing nut. Two cylindrical threaded holes are present on both sides of the bottom end of the power supply middle part. Two cylindrical threaded holes are also present on both sides of the upper part of the heating tail end. The fixing nut can be used to securely connect the power supply middle part and the heating tail end through these threaded holes. The spiral heating ring is installed in a groove at the connection point between the power supply middle part and the heating tail end. Considering the need for periodic replacement of the welding head in friction stir welding and the associated costs, this welding head allows for the replacement of only the heating tail end and the recycling of the spiral heating ring. The grooves on both sides of the upper part of the heating tail end can be used to house the fixing nut, preventing it from being exposed and thus adversely affecting the friction stir welding process.

[0011] Preferably, the heating operation of the spiral heating ring and spiral heating rod is based on the principle of electromagnetic induction. According to Joule's law, when current flows through a conductor, it does work inside the conductor and is converted into heat energy due to the conductor's resistance. Eddy currents, as currents generated by electromagnetic induction, convert electrical energy into heat energy when flowing inside the conductor due to the resistance. The strength of the eddy currents is related to the frequency of the magnetic field change; the higher the frequency of the alternating current, the stronger the induced current and the more heat is generated.

[0012] Preferably, the conductive head in the power supply device is connected to an external power source, with one end connected to the positive terminal and the other end connected to the negative terminal. High-frequency alternating current is transmitted through the conductive head to the graphite conductive ring built into the main stirring head. The current flows through the conductive wire to the spiral heating ring and the spiral heating rod, achieving electrical input from the outside to the inside and from top to bottom.

[0013] Preferably, the spiral heating rod is equipped with the temperature sensor, which can monitor the temperature of the weld surface in real time. Simultaneously, based on actual temperature requirements and the temperature feedback from the temperature sensor, the amount of heat input can be controlled by changing the frequency of the high-frequency current.

[0014] Preferably, the taper angle of the shoulder is 80–100°, thereby increasing the contact area between the shoulder and the plate to be welded, thus increasing frictional heat generation and enhancing the coating effect on the weld metal of the shoulder surface.

[0015] Preferably, during the friction stir welding process, the upper housing of the rotating spindle is connected to and fixed to the welding robot. The rotating shaft inside the rotating spindle housing is connected to the rotating shaft of the welding robot, and the lower clamping head clamps the main stirring head, realizing the matching relationship between the robot's rotating shaft, the rotating spindle, and the main stirring head.

[0016] Preferably, the graphite conductive ring has good conductivity and lubricity, which can ensure the stability of power supply during friction stir welding.

[0017] Preferably, the outer shell of the conductive head is insulated and non-conductive, and the built-in spring has elastic potential energy, which can squeeze the conductive needle outward and push the conductive needle to keep in close contact with the graphite conductive ring at all times to ensure stable power supply.

[0018] Preferably, when the rotation speed of conventional friction stir welding is too high, it can easily cause large stress in the joint, reducing the weld quality; when the rotation speed is too low, the heat generated by the friction between the tip of the stirring pin and the material in that area is insufficient to allow the material on both sides of the weld to be sufficiently thermoplasticized and fully fused, easily forming a thin line resembling a crack at the root of the weld, resulting in a weak connection. Therefore, this invention achieves the goal of reducing the rotation speed and stress while ensuring sufficient heat to achieve fusion of the welded materials by using the additional heat input provided by the spiral heating ring and spiral heating rod.

[0019] Preferably, during the welding process, the temperature sensor provides real-time feedback on the weld surface temperature. When the temperature is too high, the heat input can be reduced by decreasing the input frequency of the high-frequency alternating current or decreasing the rotation speed of the main stirring head; conversely, when the temperature is too low, the frequency of the high-frequency alternating current or the rotation speed can be increased. Specific process parameters need to be adjusted and matched according to the actual welding process.

[0020] Based on the above technical solution, the advantages and benefits of the present invention are as follows:

[0021] This invention provides a low-stress friction stir welding head with a built-in heat source. The welding head mainly consists of three systems: a rotating spindle, a main stirring head, and a power supply device. The main stirring head is installed below the rotating spindle and includes multiple components such as a graphite conductive ring, a shoulder, a stirring pin, a fixing nut, and a spiral heating device. The power supply device is fixed to the housing of the rotating spindle, supports the conductive head via a support arm, and is connected to the graphite conductive ring of the main stirring head. The conductive head is held in close contact with the graphite conductive ring by a built-in spring, energizing and heating it. The stirring head of this invention has an integrated structure, and its built-in spiral heating device can directly provide additional heat to the stirring head, replacing the single heat source of friction heat in traditional friction stir welding with multiple heat sources, reducing the required rotational speed and thus reducing the stress generated by high-speed rotation in friction stir welding. Simultaneously, the spiral heating rod has a built-in temperature sensor that can monitor the temperature of the weld surface in real time. In actual welding, based on the welding process requirements and the temperature feedback from the temperature sensor, this invention can adjust the frequency of the alternating current to regulate the built-in heat input, adjusting parameters according to specific welding needs and increasing the controllability of the welding heat source. The connection between the power supply section and the heating end nut in the main stirring head allows for cost control and the recycling of heating components. In summary, this invention offers several advantages over existing friction stir welding heads and has a wider range of applications. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of a low-stress friction stir welding joint with a built-in heat source.

[0023] Figure 2 This is a cross-sectional view of a low-stress friction stir welded joint with a built-in heat source.

[0024] Figure 3 This is a cross-sectional view of the rotating spindle structure;

[0025] Figure 4 This is a cross-sectional view of the main stirring head structure;

[0026] Figure 5 This is a cross-sectional view of the power supply device structure;

[0027] Figure 6This is a schematic diagram of the welding process of friction stir welding joints.

[0028] 1-Rotary spindle: 11 Housing; 12 Rotary shaft; 13 Clamping head

[0029] 2-Main stirring head: 21 Clamping front end; 22 Power supply middle section: 221 Limiting shoulder; 222 Graphite conductive ring; 223 Internal conductive wire; 23 Heating tail end: 231 Shaft shoulder; 232 Stirring needle; 233 Spiral heating ring; 234 Fixing nut; 24 Spiral heating rod: 241 Spiral copper wire; 242 Heating shaft; 243 Temperature sensor

[0030] 3-Power supply device: 31 Fixing device; 32 Support arm; 33 Conductive head: 331 Conductive head housing; 332 Internal spring; 333 Conductive pin Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not the entire structure.

[0032] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0034] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0035] The present invention will be further illustrated by a specific embodiment below.

[0036] This example demonstrates the use of a low-stress friction stir welding head with a built-in heat source to perform friction stir welding on alloy workpieces.

[0037] Specifically, such as Figure 1 As shown, a low-stress friction stir welding head with a built-in heat source is characterized by comprising three systems: a rotating spindle 1, a main stirring head 2, and a power supply device 3.

[0038] Specifically, such as Figure 3 As shown, the rotating spindle 1 consists of a housing 11, a rotating shaft 12, and a clamping head 13. The housing 11 is fixed and does not rotate. The rotating shaft 12 and the clamping head 13 are integrated. The clamping head 13 is clamped to the main stirring head 2 and fixed with a nut, so that the rotating shaft 12 drives the main stirring head to rotate at high speed.

[0039] Specifically, such as Figure 4 As shown, the main stirring head 2 consists of three parts: a clamping front end 21, a power supply middle part 22, and a heating tail end 23. The clamping front end 21 is tightly connected to the clamping head 13 of the rotating spindle 1. The power supply middle part 22 consists of a limiting shoulder 221, a graphite conductive ring 222, and an internal conductive wire 223. The limiting shoulder 221 limits the clamping depth of the clamping front end 21. The graphite conductive ring 222 transmits current to the internal conductive wire 223. The heating tail end 23 consists of a shaft shoulder 231, a stirring needle 232, a spiral heating ring 233, and a fixing nut. 234. A spiral heating rod 24 is composed of a spiral heating ring 233 located inside the shoulder 231 and connected to the internal conductive wire 223 to achieve current transmission for heating. The spiral heating rod 24 is located inside the stirring needle 232, and its tail end is connected to the internal conductive wire 223 to achieve current transmission. The spiral copper wire 241 is heated after being energized. The spiral copper wire 241 is located at the lower part of the spiral heating rod 24 and is coiled on the heating shaft 242. The temperature sensor 243 is located on the spiral heating rod and is used to detect the temperature of the weld center.

[0040] Specifically, such as Figure 5As shown, the power supply device 3 consists of a fixing device 31, a support arm 32, and a conductive head 33. The fixing device 31 is fixed to the outer surface of the housing 11 to support the power supply device 3. One end of the support arm 32 is tightly connected to the fixing device 31, and the other end supports the conductive head 33. The conductive head 33 consists of a conductive head housing 331, an internal spring 332, and a conductive needle 333. The internal spring 332 and the conductive needle 333 are both located inside the conductive head housing 331. The internal spring 332 is placed at the thin end of the conductive needle 333 to support the conductive needle 333. The thin end of the conductive needle 333 is connected to an external power source to transmit current. The thick end of the conductive needle 333 is connected to the graphite conductive ring 222 through the opening of the conductive head housing 331. After the power is turned on, the current is transmitted through the conductive head 33 to the conductive graphite ring 222, and then to the spiral heating ring 233 and spiral heating rod 24 through the internal conductive wire 223. The spiral heating ring 233 and the spiral heating rod 24 can provide a large amount of heat input to the heating tail end 23 of the main stirring head 12, thereby reducing the required rotational speed of the main stirring head 12 and reducing the tensile stress generated on the shoulder due to high-speed rotation during welding. On the other hand, the reduction in rotational speed can also improve the surface forming quality of the weld and reduce flash.

[0041] Specifically, the clamping front end 21 is integrated with the power supply middle part 22, and the power supply middle part 22 is connected to the heating tail end 23 by a fixing nut 234. Two cylindrical threaded holes are present on both sides of the bottom end of the power supply middle part 22. Two cylindrical threaded holes are also present on both sides of the upper part of the heating tail end 23. The fixing nut 234 can securely connect the power supply middle part 22 and the heating tail end 23 through these threaded holes. The spiral heating ring 233 is installed in a groove at the connection point between the power supply middle part 22 and the heating tail end 23. Considering the need for periodic replacement of the welding head in friction stir welding and cost factors, this welding head allows for the replacement of only the heating tail end 23 and the recycling of the spiral heating ring 233. The grooves on both sides of the upper part of the heating tail end 23 can be used to house the fixing nut 234, preventing the fixing nut 234 from being exposed and thus adversely affecting the friction stir welding process.

[0042] Specifically, the heating operation of the spiral heating ring 233 and the spiral heating rod 24 is based on the principle of electromagnetic induction. According to Joule's law, when current flows through a conductor, it does work inside the conductor and is converted into heat energy due to the conductor's resistance. Eddy currents, as currents generated by electromagnetic induction, convert electrical energy into heat energy when flowing inside the conductor due to the resistance. The strength of eddy currents is related to the frequency of magnetic field changes; the higher the frequency of the alternating current, the stronger the induced current and the more heat is generated.

[0043] Specifically, the conductive head 33 in the power supply device 3 is connected to an external power source, with one end connected to the positive terminal and the other end connected to the negative terminal. The high-frequency alternating current is transmitted through the conductive head 33 to the graphite conductive ring 222 built into the main stirring head 2, and the current flows through the conductive wire 223 to the spiral heating ring 233 and the spiral heating rod 24, realizing the electrical input from the outside to the inside and from the top to the bottom.

[0044] Specifically, the spiral heating rod 24 is equipped with the temperature sensor 243, which can monitor the temperature of the weld surface in real time. Simultaneously, based on actual temperature requirements and the temperature feedback from the temperature sensor 243, the amount of heat input can be controlled by changing the frequency of the high-frequency current.

[0045] Specifically, the cone angle of the shoulder 231 is 80 to 100°, thereby increasing the contact area between the shoulder 231 and the plate to be welded, so as to increase the frictional heat generation and at the same time increase the coating effect on the weld metal of the shoulder surface.

[0046] Specifically, the graphite conductive ring 222 has good conductivity and lubricity, which can ensure the stability of power supply during friction stir welding.

[0047] Specifically, the conductive head shell 331 is insulated and non-conductive, and the built-in spring 332 has elastic potential energy, which can squeeze the conductive needle 333 outward, pushing the conductive needle 333 to keep in close contact with the graphite conductive ring 222 at all times, so as to ensure stable power supply.

[0048] Specifically, during the friction stir welding process, the upper outer shell 11 of the rotating spindle 1 is connected and fixed to the welding robot. The rotating shaft 12 inside the rotating spindle shell is connected to the rotating shaft of the welding robot, and the lower clamping head 13 clamps the main stirring head 2, realizing the matching relationship between the robot rotating shaft, the rotating spindle, and the main stirring head.

[0049] Specifically, such as Figure 6 As shown, the specific welding process of the low-stress friction stir welding joint with built-in heat source is as follows. The welded plates are 2219 aluminum alloy, and the butt joint is a flat plate butt joint, with the welding head placed at the joint of the two plates. During the welding process, due to the heating effect of the spiral heating ring 233 and the spiral heating rod 24, the stirring pin 232 carries a large amount of heat, providing sufficient heat input to the aluminum alloy plates. Furthermore, the rotating spindle 1, with its clamping head 13 fixing the main stirring head 2, rotates at high speed under the drive of the welding robot. The stirring pin 232 contacts the aluminum alloy plates, generating a large amount of heat and softening the aluminum alloy, thus connecting the two plates.

[0050] Specifically, in conventional friction stir welding, excessively high rotation speeds can easily lead to significant stress at the joint, reducing weld quality. Conversely, excessively low rotation speeds result in insufficient heat generated by friction between the stirring pin tip and the material in that area, preventing adequate thermoplasticization and fusion of the materials on both sides of the weld. This can easily lead to the formation of a crack-like line at the weld root, resulting in a weak connection. Therefore, this invention utilizes the additional heat input provided by the spiral heating ring 233 and the spiral heating rod 24 to reduce rotation speed and stress while ensuring sufficient heat for fusion of the aluminum alloy sheet.

[0051] Specifically, during the welding process, the temperature sensor provides real-time feedback on the temperature of the stirring pin. When the temperature is too high, the heat input can be reduced by decreasing the input frequency of the high-frequency alternating current or decreasing the rotation speed of the main stirring head 2; conversely, when the temperature is too low, the frequency of the high-frequency alternating current or the rotation speed can be increased. Specific process parameters need to be adjusted and matched according to the actual welding process.

[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low-stress friction stir welding joint with a built-in heat source, characterized in that, It includes three systems: a rotating spindle (1), a main stirring head (2), and a power supply device (3). The rotating spindle (1) consists of a housing (11), a rotating shaft (12), and a clamping head (13). The housing (11) is fixed and does not rotate. The rotating shaft and the clamping head are integrated. The clamping head (13) is clamped to the main stirring head (2) and fixed with a nut, so that the rotating shaft (12) drives the main stirring head to rotate at high speed. The main stirring head (2) consists of three parts: a clamping front end (21), a power supply middle part (22), and a heating tail end (23). The clamping front end (21) is tightly connected to the clamping head (13) of the rotating spindle (1). The power supply middle part (22) consists of a limiting shoulder (221), a graphite conductive ring (222), and an internal conductive wire (223). The limiting shoulder (221) limits the clamping depth of the clamping front end (21). The graphite conductive ring (222) transmits current to the internal conductive wire (223). The heating tail end (23) consists of a shaft shoulder (231), a stirring needle (232), and a spiral heating ring (233). The assembly consists of a fixing nut (234) and a spiral heating rod (24). The spiral heating ring (233) is located inside the shoulder (231) and connected to the internal conductive wire (223) to achieve current transmission for heating. The spiral heating rod (24) is located inside the stirring needle (232), and its tail end is connected to the internal conductive wire (223) to achieve current transmission. The spiral copper wire (241) is heated after being energized. The spiral copper wire (241) is located at the lower part of the spiral heating rod (24) and is coiled on the heating shaft (242). The temperature sensor (243) is located on the spiral heating rod and is used to detect the temperature of the weld center. The power supply device (3) consists of a fixing device (31), a support arm (32), and a conductive head (33). The fixing device (31) is fixed to the outer surface of the outer shell (11) to support the power supply device (3). One end of the support arm (32) is tightly connected to the fixing device (31), and the other end supports the conductive head (33). The conductive head (33) consists of a conductive head shell (331), an internal spring (332), and a conductive needle (333). The internal spring (332) and the conductive needle (333) are both located inside the conductive head shell (331). The internal spring (332) is placed at the thin end of the conductive needle (333) to support the conductive needle (333). The thin end of the conductive needle (333) is connected to an external power source. The conductive needle (333) is connected to the graphite conductive ring (222) through the opening of the conductive head shell (331). After the power is turned on, the current is transmitted to the graphite conductive ring (222) through the conductive head (33) and then to the spiral heating ring (233) and the spiral heating rod (24) through the internal conductive wire (223). The spiral heating ring (233) and the spiral heating rod (24) can provide a large amount of heat input to the heating end (23) of the main stirring head (2), thereby reducing the demand on the rotation speed of the main stirring head (2) and reducing the tensile stress generated by the shaft shoulder due to high speed rotation during the welding process. On the other hand, the reduction in rotation speed can also improve the surface forming quality of the weld and reduce flash.

2. The low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The clamping front end (21) is integrated with the power supply middle part (22). The power supply middle part (22) and the heating tail end (23) are connected by a fixing nut (234). There are two cylindrical threaded holes on both sides of the bottom end of the power supply middle part (22), and there are also two cylindrical threaded holes on both sides of the upper part of the heating tail end (23). At the same time, the fixing nut (234) can fasten the power supply middle part (22) and the heating tail end (23) through the threaded holes. The spiral heating ring (233) is installed. In the groove at the connection between the power supply middle part (22) and the heating tail end (23), considering the need for periodic replacement of the welding head and cost factors in friction stir welding, this welding head can realize the replacement of only the heating tail end (23) and the recycling of the spiral heating ring (233). The grooves on both sides of the upper part of the heating tail end (23) can be used to house the fixing nut (234) to prevent the fixing nut (234) from being exposed, thereby having an adverse effect on the friction stir welding process.

3. The low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The heating operation of the spiral heating ring (233) and the spiral heating rod (24) is based on the principle of electromagnetic induction. According to Joule's law, when current passes through a conductor, due to the resistance of the conductor, the current does work inside the conductor and is converted into heat energy. Eddy current, as a current generated by electromagnetic induction, will convert electrical energy into heat energy due to the resistance when it flows inside the conductor. The strength of eddy current is related to the frequency of magnetic field change. The higher the frequency of alternating current, the stronger the induced current and the more heat is generated.

4. The low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The conductive head (33) in the power supply device (3) is connected to an external power source, with one end connected to the positive terminal and the other end connected to the negative terminal. The high-frequency alternating current is transmitted through the conductive head (33) to the graphite conductive ring (222) built into the main stirring head (2). The current flows through the conductive wire (223) to the spiral heating ring (233) and the spiral heating rod (24), realizing the electrical input from the outside to the inside and from the top to the bottom.

5. A low-stress friction stir welding joint with a built-in heat source according to claim 3, characterized in that, The spiral heating rod (24) is equipped with the temperature sensor (243), which can monitor the temperature of the weld surface in real time. At the same time, according to the actual temperature requirements and the temperature feedback of the temperature sensor (243), the heat input can be controlled by changing the frequency of the high-frequency current.

6. A low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The cone angle of the shoulder (231) is 80-100°, thereby increasing the contact area between the shoulder (231) and the plate to be welded, so as to increase the frictional heat generation and at the same time increase the coating effect on the weld metal of the shoulder surface.

7. A low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The graphite conductive ring (222) has good conductivity and lubricity, which can ensure the stability of power supply during friction stir welding.

8. A low-stress friction stir welding joint with a built-in heat source according to claim 1, characterized in that, The conductive head shell (331) is insulated and non-conductive, and the built-in spring (332) is elastic, which can squeeze the conductive needle (333) towards the thicker section, pushing the conductive needle (333) to keep in close contact with the graphite conductive ring (222) at all times, so as to ensure stable power supply.

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