Steel-aluminum hybrid structure current-assisted friction stir welding and riveting machine and method

Abstract

The application provides a steel-aluminum mixed structure current-assisted friction stir welding riveting connection robot and method, the robot comprises a mechanical arm and a welding gun, the mechanical arm has multiple degrees of freedom, and the welding gun is arranged at an execution end of the mechanical arm; a steel-aluminum plate connection piece is placed on a bottom die, a bottom die electrode ring is arranged in the bottom die, an inside of a mounting shell is provided with a welding gun electrode ring, and the bottom die electrode ring and the welding gun electrode ring can be electrified to generate current. The drill bit of the application is detachable and consumes less material, and the current generated by the electrode ring and the friction stir welding riveting of the welding gun are matched, so that the steel-aluminum plate connection piece can further generate heat during drilling, the heat deficiency when the welding nut and the steel-aluminum plate connection piece are rubbed is made up, the steel-aluminum plate connection piece is partially plasticized, the welding resistance is weakened, and the mechanical properties of the connection position are further improved; meanwhile, the application also has the advantages of simple process, high joint connection efficiency, welding integration, high automation degree and the like.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding and riveting technology, and in particular to a current-assisted friction stir welding and riveting robot and method for steel-aluminum hybrid structures. Background Technology

[0002] With the increasing prominence of fuel consumption and gas emissions issues, lightweighting has gradually become a leading trend in the automotive and aerospace industries. Reducing the weight of materials used is an effective way to achieve lightweighting. Aluminum alloys replacing or partially replacing steel materials will become the main direction for lightweighting technology implementation in the aerospace and transportation industries, and can effectively realize industrial lightweight design.

[0003] Currently, the methods for joining plates in industrial production include friction stir welding and riveting. However, friction stir welding has obvious defects when joining steel and aluminum materials. The high welding temperature can easily produce brittle intermetallic compounds on the weld surface of the plates and can easily cause metal accumulation at the joint. At the same time, it is difficult for the rivet to penetrate the lower plate during the welding process, which reduces the mechanical properties of the joint.

[0004] Riveting, as a cold forming joining process, offers high connection strength and good joint sealing, and can connect dissimilar materials and materials that are difficult to weld. However, traditional riveting requires pre-drilling of the connecting parts, making the process complex, time-consuming, and inefficient. Furthermore, the traditional riveting process operates at very low temperatures, resulting in only a mechanical connection between the rivet and the sheet metal, failing to create a high-temperature metallurgical connection and leading to poor mechanical properties of the joint. Summary of the Invention

[0005] The purpose of this invention is to address the problems mentioned in the background art by providing a current-assisted friction stir welding and riveting composite connection scheme for steel-aluminum hybrid structures, so as to improve the connection quality and mechanical properties of current-assisted friction stir welding and riveting joints in steel-aluminum hybrid structures, while also improving the connection efficiency of plates.

[0006] To achieve the above objectives, the present invention provides a current-assisted friction stir welding and riveting robot with a steel-aluminum hybrid structure, comprising a robotic arm and a welding and riveting gun, wherein the robotic arm has multiple degrees of freedom of motion and the welding and riveting gun is disposed at the end of the robotic arm.

[0007] The welding and riveting gun includes a mounting housing, a welding and riveting drill bit assembly, a slide bar fastening assembly, a transmission rod, a spindle transmission assembly, and a spindle drive assembly. A welding and riveting nut is placed inside the mounting housing. The welding and riveting drill bit assembly is located at the front end of the mounting housing and is used for drilling. The welding and riveting nut is located behind the welding and riveting drill bit assembly inside the mounting housing. The transmission rod is located behind the welding and riveting drill bit assembly inside the mounting housing and is capable of moving back and forth and rotating circumferentially, driving the welding and riveting nut and the welding and riveting drill bit assembly to rotate and advance. The spindle transmission assembly and the spindle drive assembly are both located inside the mounting housing. The spindle transmission assembly is used to drive the transmission rod to rotate circumferentially, and the spindle drive assembly is used to drive the transmission rod to move back and forth.

[0008] A bottom mold is provided on which steel and aluminum sheet connectors to be connected are placed. The bottom mold has a through hole and a bottom mold electrode ring is provided inside the through hole. A welding and riveting gun electrode ring is provided inside the mounting housing. The welding and riveting gun electrode ring is in contact with the transmission rod and can generate current through the bottom mold electrode ring and the welding and riveting gun electrode ring.

[0009] Furthermore, the welding and riveting gun also includes a nut supply belt, which is filled with a plurality of welding and riveting nuts and is used to continuously supply the welding and riveting nuts into the mounting housing.

[0010] Furthermore, the outer surface of the welding nut is provided with a conical stirring texture, which is used to stir the plate during drilling.

[0011] Furthermore, the welding and riveting drill bit assembly includes a drill bit, an external threaded shaft, and an internal threaded shaft. The first end of the external threaded shaft is detachably connected to the internal threaded shaft via a thread. The second end of the internal threaded shaft is provided with a transmission internal threaded hole, which is used for transmission connection with the transmission rod.

[0012] The drill bit is connected to the external threaded shaft, and the contact area between the drill bit and the external threaded shaft is provided with a horseshoe-shaped bevel. The drill bit and the external threaded shaft are connected by a rotational reset pin.

[0013] Furthermore, the contact portion of the external threaded shaft is provided with a U-shaped sliding groove, and the contact portion of the drill bit is provided with a square protrusion, which cooperates with the U-shaped sliding groove.

[0014] Furthermore, the slide bar fastening assembly includes a split-type fastening clamp, a transmission guide rod, and a sliding guide rod. The split-type fastening clamp and the transmission guide rod are rotatably connected via a connecting pin. The transmission guide rod is connected to the sliding guide rod. The split-type fastening clamp is provided with a guide rod, which is provided with a slot and a sliding protrusion. The sliding guide rod is slidably connected to the inner wall of the mounting housing. A return spring is connected to the end of the sliding guide rod. The mounting housing is provided with a sliding channel, in which the guide rod is slidably inserted. The return spring is also provided in the sliding channel and is connected to the guide rod. A housing groove is also provided in the sliding channel, which cooperates with the slot.

[0015] Furthermore, the front part of the transmission rod is provided with a small-diameter external thread and a large-diameter external thread in sequence. The small-diameter external thread corresponds to the transmission internal thread hole, and the large-diameter external thread corresponds to the inner hole of the welding nut.

[0016] Furthermore, the spindle transmission assembly includes a rotary motor, a helical screw, and a helical gear. The rotary motor is connected to the helical screw, the helical screw meshes with the helical gear, and the helical gear is connected to the transmission rod via a key.

[0017] Furthermore, the spindle drive assembly includes a linear motor, the output end of which is connected to the transmission rod, and the transmission rod is capable of rotating freely relative to the output end of the linear motor.

[0018] This invention also provides a current-assisted friction stir welding method for steel-aluminum hybrid structures, applicable to the current-assisted friction stir welding robot for steel-aluminum hybrid structures as described above, comprising the following steps:

[0019] S1, the robotic arm controls the welding and riveting gun to move to the designated position;

[0020] S2, connect the welding and riveting gun electrode ring of the welding and riveting gun to the bottom mold electrode ring in the bottom mold, the main spindle drive assembly controls the transmission rod to perform uniform linear feed motion, and the main spindle transmission assembly controls the transmission rod to perform uniform rotational motion, maintaining coordination;

[0021] S3, the transmission rod is first screwed into the welding nut, and then screwed into the transmission internal thread hole of the welding drill bit assembly for synchronous movement. The welding nut touches the transmission guide rod and drives the transmission guide rod to rotate. The transmission guide rod drives the sliding guide rod to move horizontally. After the sliding guide rod disengages from the slot, the split fastening clamp is in an elastic opening and closing state.

[0022] S4, the drill bit contacts the steel-aluminum plate connector and begins drilling until it penetrates the steel-aluminum plate connector. During the synchronous advance, the welding nut rotates at a constant speed and feeds into the drill hole of the steel-aluminum plate connector. It generates heat through friction with the steel-aluminum plate connector. The current of the welding nut electrode ring and the bottom mold electrode ring promotes the heating of the steel-aluminum plate connector, causing local plasticization at the drilled position of the steel-aluminum plate connector.

[0023] S5, the welding nut continues to rotate and feed at a constant speed, the molten metal flows homogenized along the conical stirring texture, and forms a dense solid weld under the squeezing action of the welding nut;

[0024] S6, the main spindle transmission assembly and the main spindle drive assembly move in opposite directions at a constant speed, driving the transmission rod, drill bit and welding nut to move in opposite directions. The welding nut is tightened and deformed, forming a mechanical interlock with the steel-aluminum plate connector. When the welding drill bit assembly exits the welding nut, the drill bit rotates relative to the rotating reset pin and exits. After the welding drill bit assembly exits the welding nut, the slide rod fastening assembly is reset under the action of the reset spring, clamping the welding drill bit assembly. Then the transmission rod separates from the welding drill bit assembly until it runs to the initial position, completing the current-assisted stirring friction welding connection of the steel-aluminum plate connector.

[0025] S7, the robotic arm returns to its initial position, and the robotic arm and welding / riveting gun are shut down.

[0026] The above-described solution of the present invention has the following beneficial effects:

[0027] The steel-aluminum hybrid structure current-assisted friction stir welding and riveting robot and method provided by this invention, through the coordination of the friction stir welding and riveting of the welding and riveting gun and the current generated by the electrode ring, enables the steel-aluminum plate connector to generate more heat during the drilling process, which compensates for the insufficient heat generated by the friction between the welding nut and the steel-aluminum plate connector, promotes local plasticization of the steel-aluminum plate connector, weakens the welding and riveting resistance, and further improves the mechanical properties of the connection position. The process is simple, time-saving, and has high efficiency in installing welding and riveting nuts, high work efficiency, high joint connection efficiency, high degree of integration of drilling, welding, riveting and pulling, and high degree of welding and riveting integration and automation. In addition, the drill bit of the welding and riveting machine is detachable, with less wear and tear during drilling and convenient replacement.

[0028] Other beneficial effects of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0030] Figure 2 This is a schematic diagram of the welding and riveting gun, bottom mold, and steel-aluminum sheet connector of the present invention.

[0031] Figure 3This is a schematic diagram of the welding nut of the present invention;

[0032] Figure 4 This is a schematic diagram of the welding and riveting drill bit assembly of the present invention;

[0033] Figure 5 for Figure 4 Enlarged view of point A;

[0034] Figure 6 This is a schematic diagram of the external threaded shaft of the present invention;

[0035] Figure 7 This is a schematic diagram of the drill bit of the present invention;

[0036] Figure 8 This is a schematic diagram of the slide bar fastening assembly of the present invention;

[0037] Figure 9 for Figure 8 Enlarged view of point B;

[0038] Figure 10 This is a schematic diagram of the split-type fastening clamp of the present invention;

[0039] Figure 11 This is a schematic diagram of the method flow of the present invention;

[0040] Figure 12 for Figure 11 Enlarged view of point C.

[0041] [Explanation of Labels in the Attached Image]

[0042] 100-Robotic arm; 200-Welding and riveting gun; 210-Mounting housing; 220-Welding and riveting drill bit assembly; 221-Drill bit; 222-External threaded shaft; 223-Internal threaded shaft; 224-Horseshoe-shaped bevel; 225-U-shaped sliding groove; 226-Square protrusion; 227-Rotation reset pin; 228-Transmission internal threaded hole; 230-Slide rod fastening assembly; 231-Split-type fastening clamp; 232-Transmission guide rod; 233-Guide rod; 234-Slot; 235-Sliding protrusion; 236 - Sliding guide rod; 237 - Return spring; 238 - Connecting pin; 240 - Transmission rod; 250 - Main spindle transmission assembly; 251 - Rotary motor; 252 - Helical thread screw; 253 - Helical gear; 260 - Main spindle drive assembly; 261 - Linear motor; 270 - Nut supply belt; 280 - Welding gun electrode ring; 300 - Welding nut; 301 - Conical stirring texture; 400 - Steel-aluminum sheet connector; 401 - Intermetallic compound; 500 - Bottom mold; 501 - Bottom mold electrode ring. Detailed Implementation

[0043] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, 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 invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] like Figure 1 As shown, an embodiment of the present invention provides a current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure, including a robotic arm 100 and a welding and riveting gun 200. The robotic arm 100 has six or more degrees of freedom, which are not specifically limited here. The welding and riveting gun 200 is disposed at the end effector of the robotic arm 100 to be aligned with the required position on the steel-aluminum sheet connector 400 under the movement of the robotic arm 100.

[0047] At the same time, such as Figure 2As shown, the riveting gun 200 includes a mounting housing 210, a riveting drill bit assembly 220, a slide bar fastening assembly 230, a transmission rod 240, a spindle transmission assembly 250, and a spindle drive assembly 260. The riveting gun 200 also contains riveting nuts 300 and includes a nut supply belt 270 filled with several riveting nuts 300 for continuously supplying the riveting gun 200 with these nuts. It should be noted that the outer surface of the riveting nut 300 is provided with a conical stirring texture 301. Figure 3 As shown, the plate is stirred during drilling by the conical stirring texture 301, forming an intermetallic compound 401 to enhance the strength of the welded joint.

[0048] At the same time, such as Figures 4-7 As shown, in this embodiment, the welding and riveting drill assembly 220 includes a drill bit 221, an external threaded shaft 222, and an internal threaded shaft 223. The first ends of the external threaded shaft 222 and the internal threaded shaft 223 are detachably connected by threads. The contact area between the drill bit 221 and the external threaded shaft 222 is a horseshoe-shaped inclined surface 224. The contact area of ​​the external threaded shaft 222 is also provided with a U-shaped sliding groove 225, and the contact area of ​​the drill bit 221 is provided with a square protrusion 226. The drill bit 221 and the external threaded shaft 222 are connected by a rotating reset pin 227. During feeding, the welding and riveting drill assembly 220 maintains coaxial operation with the drill bit 221 and the external threaded shaft 222 due to the horseshoe-shaped inclined surface 224. When the welding and riveting drill assembly 220 retracts from the welding and riveting nut 300 (i.e., the welding and riveting joint), the drill bit 221 rotates relative to the rotating reset pin 227, preventing interference at the welding and riveting joint and ensuring retraction. After the drill bit 221 is removed from the welded joint, the reset pin 227 is rotated to reset the drill bit 221. The second end of the internal thread shaft 223 is provided with a transmission internal thread hole 228, which is connected to the transmission rod 240 through the transmission internal thread hole 228.

[0049] At the same time, such as Figures 8-10As shown, in this embodiment, the slide bar fastening assembly 230 includes a split-type fastening clamp 231, a transmission guide rod 232, and a sliding guide rod 236 to open, close, and securely position the welding and riveting drill bit assembly 220. The split-type fastening clamp 231 and the transmission guide rod 232 are rotatably connected via a connecting pin 238, and the transmission guide rod 232 is connected to the sliding guide rod 236. The split-type fastening clamp 231 is provided with a guide rod 233, which has a slot 234 and a sliding protrusion 235. The sliding guide rod 236 is slidably connected to the inner wall of the mounting housing 210 and is equipped with a return spring 237 to ensure that the sliding guide rod 236 can be inserted into the slot 234 during retraction. The mounting housing 210 is provided with a sliding channel. The guide rod 233 corresponds to the sliding channel and is slidably inserted into the sliding channel. A return spring 237 is also provided in the sliding channel, which is connected to the guide rod 233, so that the split-type fastening clamp 231 clamps the welding and riveting drill bit assembly 220 in its natural state. The sliding channel of the mounting housing 210 is further provided with a housing groove, which cooperates with the slot 234 to maintain the position range of the split-type fastening clamp 231.

[0050] In this embodiment, the transmission rod 240 is provided with an external thread corresponding to the transmission internal thread hole 228. The transmission rod 240 can pass through the welding nut 300 and be screwed into the transmission internal thread hole 228, thereby driving the welding nut 300 and the welding drill assembly 220 to move and rotate. Specifically, the front part of the transmission rod 240 is provided with a small-diameter external thread and a large-diameter external thread in sequence. The small-diameter external thread corresponds to the transmission internal thread hole 228, and the large-diameter external thread corresponds to the inner hole of the welding nut 300.

[0051] In this embodiment, the spindle drive assembly 250 includes a rotary motor 251 and a helical screw 252. The rotary motor 251 is connected to the helical screw 252 to drive the helical screw 252 to rotate. The helical screw 252 meshes with a helical gear 253, driving the helical gear 253 to rotate. The helical gear 253 is connected to the rear part of the transmission rod 240 via a key to rotate synchronously and transmit torque.

[0052] In this embodiment, the spindle drive assembly 260 includes a linear motor 261. The output end of the linear motor 261 is connected to the rear end of the transmission rod 240 to drive the transmission rod 240 to move back and forth. Since the transmission rod 240 needs to rotate synchronously when moving back and forth, a threaded cover is provided at the rear end of the transmission rod 240 in this embodiment. It is installed at the rear end of the transmission rod 240 via a threaded connection. The output end of the linear motor 261 passes through a bearing and is inserted into the threaded cover, with a retaining nut. The size of the retaining nut is larger than the bore size of the bearing, thus ensuring that the output end of the linear motor 261 remains fixed to the transmission rod 240 while ensuring continuous rotation of the transmission rod 240.

[0053] In this embodiment, the steel-aluminum sheet connector 400 to be connected is placed on the bottom mold 500. The bottom mold 500 has a through hole, and a bottom mold electrode ring 501 is provided at the through hole position. Correspondingly, a welding and riveting gun electrode ring 280 is provided inside the mounting housing 210. The welding and riveting gun electrode ring 280 is in contact with the transmission rod 240. During operation, the bottom mold electrode ring 501 and the welding and riveting gun electrode ring 280 are energized. The generated current promotes the heating of the steel-aluminum sheet connector 400, which locally plasticizes the drilling position of the steel-aluminum sheet connector 400, further ensuring the subsequent molding of the intermetallic compound 401.

[0054] Based on the same inventive concept, this embodiment also provides a current-assisted friction stir welding and riveting method for steel-aluminum hybrid structures, such as... Figure 11 As shown, the specific steps include the following:

[0055] S1, the robotic arm 100 controls the welding and riveting gun 200 to move to the designated position.

[0056] S2, the welding and riveting gun electrode ring 280 of the welding and riveting gun 200 is connected to the bottom mold electrode ring 501 in the bottom mold 500. The main spindle drive assembly 260 controls the transmission rod 240 to perform uniform linear feed motion, and the main spindle transmission assembly 250 controls the transmission rod 240 to perform uniform rotation motion, maintaining coordination.

[0057] S3, the transmission rod 240 is first screwed into the welding nut 300, and then screwed into the transmission internal thread hole 228 of the welding drill bit assembly 220 for synchronous movement. The welding nut 300 touches the transmission guide rod 232 and drives the transmission guide rod 232 to rotate. The transmission guide rod 232 drives the sliding guide rod 236 to move horizontally. After the sliding guide rod 236 is disengaged from the slot 234, the split fastening clamp 231 is in an elastic opening and closing state.

[0058] S4, the drill bit 221 touches the steel-aluminum plate connector 400 and begins drilling until it penetrates the steel-aluminum plate connector 400. During the synchronous advance, the welding nut 300 rotates at a constant speed and is fed into the drill hole of the steel-aluminum plate connector 400. It generates heat through friction with the steel-aluminum plate connector 400. The current of the welding gun electrode ring 280 and the bottom mold electrode ring 501 promotes the heating of the steel-aluminum plate connector 400, causing local plasticization at the drilled position of the steel-aluminum plate connector 400.

[0059] S5, the welding nut 300 continues to rotate and feed at a constant speed, the molten metal flows homogenized along the conical stirring texture 301, and forms a dense solid phase weld (i.e. the aforementioned intermetallic compound 401) under the extrusion action of the welding nut 300.

[0060] S6, the spindle transmission assembly 250 and the spindle drive assembly 260 move in opposite directions at a uniform speed, driving the transmission rod 240, drill bit 221, and welding nut 300 to move in opposite directions. The welding nut 300 is stretched and deformed, forming a mechanical interlock with the steel-aluminum plate connector 400. When the welding drill bit assembly 220 retracts from the welding nut 300, the drill bit 221 rotates relative to the rotational reset pin 227, preventing the drill bit 221 from interfering with the welding nut 300 and being unable to retract. Figure 12 As shown, after the welding and riveting drill bit assembly 220 is disengaged from the welding and riveting nut 300, the slide bar fastening assembly 230 is reset with the cooperation of the return spring 237, clamping the welding and riveting drill bit assembly 220. Subsequently, the transmission rod 240 separates from the welding and riveting drill bit assembly 220 until it runs to the initial position, completing the current-assisted stirring friction welding and riveting connection of the steel-aluminum plate connector 400.

[0061] S7, the robotic arm 100 is reset to its initial position, and the controllers and power supply of the robotic arm 100 and welding gun 200 are turned off.

[0062] As described above, the current-assisted friction stir welding and riveting robot and method for steel-aluminum hybrid structures provided in this embodiment, through the friction stir welding and riveting of the welding and riveting gun 200 and the current generated by the electrode ring, enables the steel-aluminum plate connector 400 to generate more heat during the drilling process, which makes up for the insufficient heat when the welding and riveting nut 300 rubs against the steel-aluminum plate connector 400, promotes the local plasticization of the steel-aluminum plate connector 400, weakens the welding and riveting resistance, and improves the mechanical properties of the connection position.

[0063] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A current-assisted friction stir welding and riveting robot with a steel-aluminum hybrid structure, characterized in that, It includes a robotic arm and a welding and riveting gun, the robotic arm having multiple degrees of freedom of motion, and the welding and riveting gun being disposed at the end effector of the robotic arm; The welding and riveting gun includes a mounting housing, a welding and riveting drill bit assembly, a slide bar fastening assembly, a transmission rod, a spindle transmission assembly, and a spindle drive assembly. A welding and riveting nut is placed inside the mounting housing. The welding and riveting drill bit assembly is located at the front end of the mounting housing and is used for drilling. The welding and riveting nut is located behind the welding and riveting drill bit assembly inside the mounting housing. The transmission rod is located behind the welding and riveting drill bit assembly inside the mounting housing and is capable of moving back and forth and rotating circumferentially, driving the welding and riveting nut and the welding and riveting drill bit assembly to rotate and advance. The spindle transmission assembly and the spindle drive assembly are both located inside the mounting housing. The spindle transmission assembly is used to drive the transmission rod to rotate circumferentially, and the spindle drive assembly is used to drive the transmission rod to move back and forth. A bottom mold is provided on which steel and aluminum sheet connectors to be connected are placed. The bottom mold has a through hole and a bottom mold electrode ring is provided inside the through hole. A welding and riveting gun electrode ring is provided inside the mounting housing. The welding and riveting gun electrode ring is in contact with the transmission rod. Current can be generated between the bottom mold electrode ring and the welding and riveting gun electrode ring. The welding and riveting drill bit assembly includes a drill bit, an external threaded shaft, and an internal threaded shaft. The first end of the external threaded shaft is detachably connected to the first end of the internal threaded shaft via a thread. The second end of the internal threaded shaft is provided with a transmission internal threaded hole, which is used for transmission connection with the transmission rod. The drill bit is connected to the external threaded shaft, and the contact portion between the drill bit and the external threaded shaft is provided with a horseshoe-shaped bevel. The drill bit and the external threaded shaft are connected by a rotational reset pin. The contact portion of the external threaded shaft is also provided with a U-shaped sliding groove, and the contact portion of the drill bit is also provided with a square protrusion, which cooperates with the U-shaped sliding groove. The transmission rod first screws into the welding nut, and then into the transmission internal thread hole of the welding drill bit assembly for synchronous movement. The drill bit touches the steel-aluminum plate connector and begins drilling until it penetrates the steel-aluminum plate connector. During the synchronous advancement process, the welding nut rotates at a constant speed and is fed into the drill hole of the steel-aluminum plate connector. When the welding drill bit assembly retracts from the welding nut, the drill bit rotates relative to the rotating reset pin.

2. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The welding and riveting gun also includes a nut supply belt, which is filled with a plurality of welding and riveting nuts and is used to continuously supply the welding and riveting nuts into the mounting housing.

3. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The outer surface of the welding nut is provided with a conical stirring texture, which is used to stir the plate during drilling.

4. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The slide bar fastening assembly includes a split-type fastening clamp, a transmission guide rod, and a sliding guide rod. The split-type fastening clamp and the transmission guide rod are rotatably connected via a connecting pin. The transmission guide rod is connected to the sliding guide rod. The split-type fastening clamp is provided with a guide rod, which is provided with a slot and a sliding protrusion. The sliding guide rod is slidably connected to the inner wall of the mounting housing. A return spring is connected to the end of the sliding guide rod. The mounting housing is provided with a sliding channel, in which the guide rod is slidably inserted. The return spring is also provided in the sliding channel and is connected to the guide rod. A housing groove is also provided in the sliding channel, which cooperates with the slot.

5. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The front part of the transmission rod is provided with a small-diameter external thread and a large-diameter external thread in sequence. The small-diameter external thread corresponds to the internal thread hole of the transmission rod, and the large-diameter external thread corresponds to the inner hole of the welding nut.

6. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The main shaft transmission assembly includes a rotary motor, a helical screw, and a helical gear. The rotary motor is connected to the helical screw, the helical screw meshes with the helical gear, and the helical gear is connected to the transmission rod via a key.

7. The current-assisted friction stir welding and riveting robot for a steel-aluminum hybrid structure according to claim 1, characterized in that, The spindle drive assembly includes a linear motor, the output end of which is connected to the transmission rod, and the transmission rod is capable of rotating freely relative to the output end of the linear motor.

8. A method for current-assisted friction stir welding and riveting of a steel-aluminum hybrid structure, applied to a robot for current-assisted friction stir welding and riveting of a steel-aluminum hybrid structure as described in any one of claims 1-7, characterized in that, Includes the following steps: S1, the robotic arm controls the welding and riveting gun to move to the designated position; S2, connect the welding and riveting gun electrode ring of the welding and riveting gun to the bottom mold electrode ring in the bottom mold, the main spindle drive assembly controls the transmission rod to perform uniform linear feed motion, and the main spindle transmission assembly controls the transmission rod to perform uniform rotational motion, maintaining coordination; S3, the transmission rod is first screwed into the welding nut, and then screwed into the transmission internal thread hole of the welding drill bit assembly for synchronous movement. The welding nut touches the transmission guide rod and drives the transmission guide rod to rotate. The transmission guide rod drives the sliding guide rod to move horizontally. After the sliding guide rod is disengaged from the slot, the split fastening clamp is in an elastic opening and closing state. S4, the drill bit contacts the steel-aluminum plate connector and begins drilling until it penetrates the steel-aluminum plate connector. During the synchronous advance, the welding nut rotates at a constant speed and feeds into the drill hole of the steel-aluminum plate connector. It generates heat through friction with the steel-aluminum plate connector. The current of the welding nut electrode ring and the bottom mold electrode ring promotes the heating of the steel-aluminum plate connector, causing local plasticization at the drilled position of the steel-aluminum plate connector. S5, the welding nut continues to rotate and feed at a constant speed, the molten metal flows homogenized along the conical stirring texture, and forms a dense solid weld under the squeezing action of the welding nut; S6, the main spindle transmission assembly and the main spindle drive assembly move in opposite directions at a constant speed, driving the transmission rod, drill bit and welding nut to move in opposite directions. The welding nut is tightened and deformed, forming a mechanical interlock with the steel-aluminum plate connector. When the welding drill bit assembly exits the welding nut, the drill bit rotates relative to the rotating reset pin and exits. After the welding drill bit assembly exits the welding nut, the slide rod fastening assembly is reset under the action of the reset spring, clamping the welding drill bit assembly. Then the transmission rod separates from the welding drill bit assembly until it runs to the initial position, completing the current-assisted stirring friction welding connection of the steel-aluminum plate connector. S7, the robotic arm returns to its initial position, and the robotic arm and welding / riveting gun are shut down.

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