Low-stress friction stir welding head with built-in heat source

Abstract

The invention belongs to the technical field of friction stir welding, and discloses a low-stress friction stir welding head with a built-in heat source. The welding head mainly comprises a rotating main shaft, a main stirring head and a power supply device. The main stirring head is installed below the rotating main shaft and comprises a plurality of assemblies such as a shaft shoulder, a stirring needle and a spiral heating device. And the power supply device is fixed on the shell of the rotating main shaft, supports the conductive head through a supporting arm, is connected with the graphite conductive ring of the main stirring head and is used for electrifying and heating the graphite conductive ring. The stirring head is of an integrated structure, the spiral heating device arranged in the stirring head can directly provide extra heat for the stirring head, a single heat source of friction heat of original friction stir welding is replaced with a multi-heat-source mode, the requirement for the rotating speed is lowered, and therefore stress generated by high-speed rotation in friction stir welding is lowered. And regulation and control of built-in heat input can be achieved by adjusting the frequency of the alternating current, parameters are adjusted according to specific welding requirements, and the controllability of a welding heat source is improved.

Description

Technical Field

[0001] The invention relates to the technical field of friction stir welding, and in particular to a low-stress friction stir welding joint with a built-in heat source. Background Art

[0002] Friction stir welding is a solid-state welding technology that generates friction heat on the contact surface of the workpiece through a rotating stirring tool (usually composed of a needle-shaped tool), heats the workpiece to a state close to the plastic state of the material, and stirs and connects the materials through the rotation and longitudinal feed force of the tool. During the entire welding process, the metal remains in a solid state, and the material connection is achieved through mechanical stirring. Due to its unique welding principle, superior welding quality and broad application prospects, it has been widely studied in recent years.

[0003] The welding quality and efficiency of friction stir welding are affected by many factors, including tool design, welding parameters, material properties, etc. The friction stir welding process requires rigid support and firm clamping, and relies on high heat input brought by high-speed rotation. Therefore, it is not suitable for high-melting-point metals and has high assembly precision requirements. On the other hand, as the rotation speed increases, large tensile stress is prone to appear under the friction stir welding shoulder, which has an adverse effect on the welding quality. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low-stress friction stir welding welding head with a built-in heat source. The welding head is connected to an external motor, and a high-frequency alternating current is passed through the graphite conductive ring, spiral heating ring, and spiral heating rod inside the stirring head to realize the input of two heat sources, friction heat and eddy current heat generation, thereby reducing the demand for the rotation speed of the stirring head, thereby reducing the stress generated during the welding process. On the other hand, the built-in temperature sensor of the present invention can monitor the temperature of the weld surface in real time, thereby improving the controllability of the temperature and rotation speed of the friction stir welding.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A low-stress friction stir welding joint 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 shell, a rotating shaft and a chuck. The shell is fixed and does not rotate, the rotating shaft and the chuck are integrated, and the chuck 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.

[0008] Preferably, the main stirring head consists of three parts, including 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 limit shoulder, a graphite conductive ring, and an internal conductive wire. The limit 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 transfer 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 transfer. 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 center temperature of the weld.

[0009] Preferably, the power supply device is composed of a fixing device, a support arm, and a conductive head. The fixing device is fixed to the outer surface of the shell and is used to support the power supply device. One end of the support arm is tightly connected to the fixing device, and another end supports the conductive head. The conductive head is composed of a conductive head shell, an internal spring, and a conductive needle. The internal spring and the conductive needle are both located inside the conductive head shell. The internal spring is placed at the thin end of the conductive needle and is used to support the conductive needle. The thin end of the conductive needle is connected to an external power source to transfer current. The thick end of the conductive needle is connected to the graphite conductive ring through the opening of the conductive head shell. After the power is turned on, the current is transferred to the conductive graphite ring through the conductive head, and the spiral heating ring and the spiral heating rod are powered through the internal conductive wire. The spiral heating ring and the spiral heating rod can provide a large amount of heat input for the heating tail end of the main stirring head, thereby reducing the demand for the rotation speed of the main stirring head and reducing the tensile stress of the shoulder caused by high-speed rotation during welding. On the other hand, the reduction in rotation 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 and the heating tail end are connected by a fixing nut. There are two cylindrical threaded holes on both sides of the bottom end of the power supply middle part. There are also two cylindrical threaded holes on both sides of the upper part of the heating tail end, and the fixing nut can fasten the power supply middle part and the heating tail end through the threaded holes. The spiral heating ring is installed in the groove at the connection between the power supply middle part and the heating tail end. Taking into account the irregular replacement of the welding head and the cost factors required for stir friction welding, this welding head can achieve 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 embed the fixing nut to prevent the fixing nut from being exposed, thereby adversely affecting the stir friction welding process.

[0011] Preferably, the heating work of the spiral heating ring and the spiral heating rod 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 the current generated by electromagnetic induction, will convert electrical energy into heat energy due to the existence of resistance when flowing inside the conductor. The intensity 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 generated.

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

[0013] Preferably, the spiral heating rod is provided with the temperature sensor, which can monitor the temperature of the weld surface in real time. At the same time, according to the actual temperature demand and the temperature feedback of the temperature sensor, the 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, thereby increasing frictional heat generation and increasing the cladding effect of the weld metal on the shoulder surface.

[0015] Preferably, during the friction stir welding process, the upper housing of the rotating spindle is connected 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 chuck clamps the main stirring head to achieve a matching relationship between the robot rotating shaft, the rotating spindle, and the main stirring head.

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

[0017] Preferably, the conductive head shell 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 always be in close contact with the graphite conductive ring to ensure stable power supply.

[0018] Preferably, when the speed of conventional friction stir welding is too high, it is easy to cause greater stress in the joint and reduce the quality of the weld; when the speed is too low, the heat generated by the friction between the tip of the stirring needle and the material in the area is not enough to fully plasticize and fuse the materials on both sides of the weld, and it is easy to form a thin line similar to a crack at the root of the weld, which is easy to form a weak connection. Therefore, the present invention uses the additional heat input provided by the spiral heating ring and the spiral heating rod to reduce the speed and stress, while ensuring sufficient heat to achieve the fusion of the welded plates.

[0019] Preferably, during the welding process, the temperature sensor feeds back the weld surface temperature in real time. When the temperature is too high, the heat input can be reduced by reducing the input frequency of the high-frequency alternating current or reducing the speed of the main stirring head; conversely, when the temperature is too low, the frequency of the high-frequency alternating current or the speed can be increased. The specific process parameters need to be regulated 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] The present invention provides a low-stress friction stir welding welding head with a built-in heat source. The welding head mainly includes 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 needle, a fixing nut, and a spiral heating device. The power supply device is fixed on the rotating spindle housing, supports the conductive head through a support arm, and is connected to the graphite conductive ring of the main stirring head. The conductive head is close to the graphite conductive ring through a built-in spring, and is powered and heated. The stirring head of the present invention is an integrated structure, and its built-in spiral heating device can directly provide additional heat for the stirring head, replace the original single heat source of friction stir welding friction heat with a multi-heat source mode, reduce the demand for rotation speed, and thus reduce the stress generated by high-speed rotation in friction stir welding. At the same time, the spiral heating rod has a built-in temperature sensor, which can monitor the temperature of the weld surface in real time. In the actual welding process, based on the requirements of the welding process and the temperature feedback of the temperature sensor, the present invention can realize the regulation of the built-in heat input by adjusting the frequency of the alternating current, adjust the parameters according to the specific welding requirements, and increase the controllability of the welding heat source. The connection between the power supply middle part and the nut at the heating tail end of the main stirring head can realize cost control and recycling of the heating component. In summary, the present invention has multiple advantages over the original friction stir welding joint and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It 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 It is a cross-sectional view of a low-stress friction stir welding joint with a built-in heat source;

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

[0025] Figure 4 It is the structural cross-section of the main mixing head;

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

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

[0028] 1- Rotating spindle: 11 housing; 12 rotating axis; 13 chuck

[0029] 2- Main stirring head: 21 clamping front end; 22 power supply middle: 221 limit 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 needle DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific implementation cases described herein are only used to explain the present invention, rather than to limit the present invention. It is also necessary to explain that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0032] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] In the description of this embodiment, the terms "upper", "lower", "right", etc., directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0035] The present invention is further described below by a specific embodiment.

[0036] This example is to achieve friction stir welding of alloy workpieces through the low stress friction stir welding joint with built-in heat source mentioned above.

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

[0038] Specifically, Figure 3 As shown, the rotating spindle 1 is composed of a shell 11, a rotating shaft 12 and a clamping head 13. The shell 11 is fixed and does not rotate, the rotating shaft 12 and the clamping head 13 are integrated, and the clamping head 13 is clamped with 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, Figure 4 As shown, the main stirring head 2 is composed of three parts, including 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 is composed of a limit shoulder 221, a graphite conductive ring 222, and an internal conductive wire 223. The limit 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 is composed of a shaft shoulder 231, a stirring needle 232, a spiral heating ring 233, and a fixing nut. 234, a spiral heating rod 24, the spiral heating ring 233 is located inside the shoulder 231 and is connected to the internal conductive wire 223 to achieve current transfer 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 transfer, 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, and the temperature sensor 243 is located on the spiral heating rod to detect the center temperature of the weld.

[0040] Specifically, Figure 5As shown, the power supply device 3 is composed 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 one end supports the conductive head 33. The conductive head 33 is composed of a conductive head housing 331, a built-in spring 332, and a conductive needle 333. The built-in spring 332 and the conductive needle 333 are both located inside the conductive head housing 331. The built-in spring 332 is placed at the thin end of the conductive needle 333 to support the conductive needle 333. The conductive needle 333 The thin end 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 to the conductive graphite ring 222 through the conductive head 33, and the spiral heating ring 233 and the spiral heating rod 24 are powered 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 for the heating tail end 23 of the main stirring head 12, thereby reducing the demand for the rotation speed of the main stirring head 12 and reducing the tensile stress of the shoulder caused by high-speed rotation during welding. On the other hand, the reduction in rotation 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 means of a fixing nut 234. There are two cylindrical threaded holes on both sides of the bottom of the power supply middle part 22. There are also two cylindrical threaded holes on both sides of the upper part of the heating tail end 23, and the fixing nut 234 can fasten the power supply middle part 22 to 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 factors such as the irregular replacement of the welding joint required for stir friction welding and the cost, the present welding joint 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 embed the fixing nut 234 to prevent the fixing nut 234 from being exposed, thereby adversely affecting the stir friction welding process.

[0042] Specifically, the heating work 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 is a current generated by electromagnetic induction. When it flows inside a conductor, it converts electrical energy into heat energy due to the existence of resistance. The intensity of the eddy current 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.

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

[0044] Specifically, the spiral heating rod 24 is provided 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 demand and the temperature feedback of the temperature sensor 243, the heat input size can be controlled by changing the frequency of the high-frequency current.

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

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

[0047] Specifically, the conductive head housing 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 always closely contact the graphite conductive ring 222 to ensure stable power supply.

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

[0049] Specifically, Figure 6 As shown, the specific welding process of the low-stress friction stir welding joint with built-in heat source is as follows. Among them, the welded plate is 2219 aluminum alloy, the docking method is flat-plate docking, and the welding head is placed at the docking point 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 needle 232 itself carries a large amount of heat and can provide sufficient heat input to the aluminum alloy plate. In addition, the rotating spindle 1 is equipped with a chuck 13 to fix the main stirring head 2, and is driven by the welding robot to rotate at a high speed. The stirring needle 232 contacts the aluminum alloy plate to generate a large amount of heat and soften the aluminum alloy to connect the left and right plates.

[0050] Specifically, when the speed of conventional friction stir welding is too high, it is easy to cause greater stress in the joint, reducing the quality of the weld; when the speed is too low, the heat generated by the friction between the tip of the stirring needle and the material in the area is not enough to fully plasticize and fuse the materials on both sides of the weld, and it is easy to form a thin line similar to a crack at the root of the weld, which is easy to form a weak connection. Therefore, the present invention uses the additional heat input provided by the spiral heating ring 233 and the spiral heating rod 24 to reduce the speed and stress, while ensuring sufficient heat to achieve the fusion of the aluminum alloy plate.

[0051] Specifically, during the welding process, the temperature sensor feeds back the temperature of the stirring needle in real time. When the temperature is too high, the heat input can be reduced by reducing the input frequency of the high-frequency alternating current or reducing the speed of the main stirring head 2; conversely, when the temperature is too low, the frequency of the high-frequency alternating current or the speed can be increased. The specific process parameters need to be regulated 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 embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A low stress friction stir welding joint with a built-in heat source, characterized in that: The invention comprises three systems: a rotating main shaft (1), a main stirring head (2) and a power supply device (3). The rotating main shaft (1) is composed 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, and 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) is composed of three parts, including 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 main shaft (1). The power supply middle part (22) is composed of a limit shoulder (221), a graphite conductive ring (222), and an internal conductive wire (223). The limit 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) is composed of a shaft shoulder (231), a stirring needle (232), a spiral heating ring (233), and a plurality of other parts. ), a fixing nut (234), and a spiral heating rod (24); the spiral heating ring (233) is located inside the shaft shoulder (231) and is connected to the internal conductive wire (223) to achieve current transfer 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 transfer; 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 center temperature of the weld. The power supply device (3) is composed 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) and is used to support the power supply device (3); one end of the support arm (32) is tightly connected to the fixing device (31), and another end supports the conductive head (33); the conductive head (33) is composed 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) and is used to support the conductive needle (333); The thin end of the needle (333) is connected to an external power source to transmit current, and 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 to the conductive graphite ring (222) through the conductive head (33), and the spiral heating ring (233) and the spiral heating rod (24) are powered 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 for the heating tail end (23) of the main stirring head (12), thereby reducing the demand for the rotation speed of the main stirring head (12) and reducing the tensile stress of the shoulder caused by high-speed rotation during welding. 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 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), and 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 of the power supply middle part (22). There are also two cylindrical threaded holes on both sides of the upper part of the heating tail end (23), and 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). Taking into account the irregular replacement of the welding joint required for stir friction welding and factors such as cost, this welding joint can achieve 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 embed the fixing nut (234) to prevent the fixing nut (234) from being exposed, thereby adversely affecting the stir friction welding process.

3. The low stress friction stir welding joint with 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 an electric current passes through a conductor, due to the resistance of the conductor, the electric current does work inside the conductor and is converted into heat energy. Eddy current is an electric current generated by electromagnetic induction. When it flows inside a conductor, it converts electric energy into heat energy due to the existence of resistance. The intensity of the eddy current 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.

4. The low stress friction stir welding joint with 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, one end of which is connected to a positive electrode, and the other end of which is connected to a negative electrode. A 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), thereby realizing electrical input from outside to inside and from top to bottom.

5. The low stress friction stir welding joint with built-in heat source according to claim 3, characterized in that: The spiral heating rod (24) is provided 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 demand and the temperature feedback of the temperature sensor (243), the frequency of the high-frequency current can be changed to control the heat input.

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

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

8. The low stress friction stir welding joint with built-in heat source according to claim 1, characterized in that: The conductive head housing (331) is insulated and non-conductive, and the built-in spring (332) is elastic and can press the conductive needle (333) toward the thick section, pushing the conductive needle (333) to always be in close contact with the graphite conductive ring (222), thereby ensuring stable power supply.

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