A metal sheet self-piercing riveting device and method

Abstract

The application discloses a metal plate self-punching riveting device and method, and belongs to the technical field of metal plate connection. The device adopts a fixed punch rod inverted configuration, uses electromagnetic force to synchronously provide a blank holder and a riveting load, and is provided with a plate heating coil for preheating the plate in situ. The device effectively prevents wrinkles, warping and lateral deviation in the forming process by constraining the plate through a large-area beam. The preheating function reduces the deformation resistance of high-strength plates, which is beneficial to forming a stable interlocking structure. The application solves the problems of coordination difficulty between the blank holder and the riveting, poor riveting quality of high-strength plates and the like in the traditional process, and has the advantages of fast forming speed, adjustable load, high coaxiality and strong joint reliability, and the like. The riveting quality and service life of the metal plate are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of metal sheet joining technology, specifically relating to a self-piercing riveting (SPR) device and method for metal sheet joining. Background Technology

[0002] Self-Piercing Riveting (SPR) is a mechanical joining process for multi-metal sheets. It eliminates the need for pre-drilled pilot holes, simplifying the process and making it widely used in the assembly of various metal components. The process works by using pressure from the equipment to drive a rivet into stacked sheets in a single press. The rivet and sheet undergo simultaneous plastic deformation, forming a self-locking interlocking structure within the die cavity, achieving a high-strength connection. The core components of the complete self-piercing riveting equipment include a punch, a blank holder, a die, and specialized rivets. The blank holder first clamps the sheet, restricting the free flow of metal during the forming stage and ensuring dimensional accuracy. Then, the punch pushes the rivet through the upper sheet and embeds it into the lower sheet, but without penetrating it. Finally, under the bidirectional pressing action of the punch and die, the rivet tail expands outward from within the lower sheet, forming a stable mechanical interlock and completing the reliable assembly of multiple sheet materials.

[0003] During riveting production, various riveting defects are easily generated due to factors such as sheet metal properties, tooling conditions, and clamping accuracy, which reduce the strength and reliability of the joint. When the strength of the plates to be riveted is high, the material's resistance to deformation is large and its plasticity is poor, which will significantly increase the resistance to rivet insertion and tail expansion. This can easily lead to insufficient rivet tail expansion, excessive gaps in the locking structure, and poor fit between the plate and the rivet. In severe cases, insufficient rivet upsetting can directly cause the riveted joint to fail. When the pressure ring has insufficient pressure area, it cannot effectively constrain the plate around the riveting area. During the rivet pressing process, the plate in the unpressed area will exhibit irregular flow, wrinkling, and warping. At the same time, it will cause the rivet to be subjected to force offset, resulting in asymmetrical riveting, uneven joint stress, and a significant reduction in the service life of the component. If the plate is placed at an angle and is not perpendicular to the punch axis, the rivet will generate a lateral component force when it is pressed down, causing the insertion trajectory to deviate. At the same time, it will cause the rivet tail to expand asymmetrically in the lower plate, resulting in riveting eccentricity, inconsistent joint tightness, and other problems. This will cause the interlocking structure to be subjected to unbalanced stress, which can easily lead to joint loosening and detachment, seriously affecting the quality and safety of the component. Summary of the Invention

[0004] To address the challenges in riveting high-strength plates, such as high deformation resistance, insufficient pressure area leading to wrinkling and warping, lateral force, and difficulties in coordinating pressure load and riveting forming, this invention provides a self-piercing riveting device and method for metal plates. It uses a large-area crossbeam to constrain the plate, in-situ preheating to reduce deformation resistance, and a fixed punch rod combined with electromagnetic force to provide an inverted configuration that synchronously provides pressure and riveting loads, thereby improving the riveting quality and joint reliability of high-strength plates.

[0005] To solve the above problems, the present invention provides a self-piercing riveting device for metal plates, including a frame-type load-bearing base 1, a bottom load-bearing worktable 2, a left small guide post 8, guide posts 9 and 14, a right small guide post 15, a fixed punch 22, elastic clamping and reset springs 3 and 20, a high-temperature resistant plate clamping load-bearing beam 4, a self-piercing riveting die-mounted load-bearing beam 6, an upper fixed beam 10, and a hydraulic cylinder driven beam 16.

[0006] The bottom support worktable 2 is fixedly mounted on the frame-type load-bearing base 1, and the through holes on both sides are fitted with guide posts 9 and 14; the fixed punch 22 is fixedly connected to the bottom support worktable 2 and is axially fixed, and the self-punching riveting 19 is placed on the upper surface of the fixed punch 22.

[0007] Elastic compression and reset springs 3 and 20 are sleeved on the outer surface of guide posts 9 and 14, with their two ends abutting against the bottom bearing workbench 2 and the high-temperature resistant plate pressing bearing crossbeam 4, respectively. An upper plate 17 and a lower plate 18 are stacked between the two crossbeams. The upper ends of guide posts 9 and 14 are fixed to the upper fixed crossbeam 10. A hydraulic cylinder 11 is fixedly installed at the center of the upper fixed crossbeam 10, and its hydraulic cylinder push rod 12 is fixedly connected to the hydraulic cylinder drive crossbeam 16 to drive it to move up and down along the guide posts 9 and 14.

[0008] The self-piercing riveting die 23 is detachable and is installed below the self-piercing riveting die insert bearing beam 6 and directly above the fixed punch 22; the electromagnetic coil support base 7 is fixedly installed below the hydraulic cylinder drive beam 16 and is equipped with an electromagnetic coil 24; the plate heating coil 28 is used for in-situ preheating; the left small guide post 8 and the right small guide post 15 are fixedly installed in the outer through hole of the self-piercing riveting die insert bearing beam 6 and pass through the outer through hole of the hydraulic cylinder drive beam 16; the upper ends of the left small guide post 8 and the right small guide post 15 are provided with bosses to limit the range of movement of the hydraulic cylinder drive beam 16 relative to the small guide posts;

[0009] During operation, the electromagnetic coil 24 is energized to generate electromagnetic force, which drives the high-temperature resistant plate to press against the bearing beam 4, the self-piercing riveting die-mounted bearing beam 6, the upper plate 17, the lower plate 18, and the self-piercing riveting die 23 to move downward along the guide posts 9 and 14. This causes the upper and lower plates to be fitted into the self-piercing riveting rivets 19 on the upper surface of the fixed punch 22 and pierced. Under the constraint of the self-piercing riveting die 23, the legs of the rivets expand radially and embed into the upper plate, while the head presses against the lower plate. The fixed punch 22 and the electromagnetic force are from the same source and provide the pressing and riveting forming force simultaneously.

[0010] Preferably, the self-piercing riveting die 23 is detachably mounted below the self-piercing riveting die mounting support beam 6 via a self-piercing riveting die positioning base 27; the self-piercing riveting die positioning base 27 is mounted in a dovetail groove below the self-piercing riveting die mounting support beam 6, and has stepped holes to accommodate the self-piercing riveting die 23.

[0011] Preferably, the self-piercing riveting forming die positioning base 27 is provided with a front end cover 13 and a rear end cover 25 on the front and rear sides respectively, and is locked by the front end cover locking nut 5 and the rear end cover locking nut 26 respectively to restrict its front and rear movement.

[0012] Preferably, the heating coil 28 of the plate is embedded in the annular groove on the upper surface of the high-temperature resistant plate pressing bearing beam 4.

[0013] Preferably, a punch guide sleeve 21 is fixedly installed at the center of the lower surface of the high-temperature resistant plate pressing the bearing beam 4. The punch guide sleeve 21 has a through hole and groove that match the fixed punch 22. When the lower surface of the groove inside the punch guide sleeve 21 is coplanar with the upper surface of the fixed punch 22, the downward stroke of the hydraulic cylinder driving the beam 16 is limited.

[0014] The present invention also provides a self-piercing riveting method for metal plates using the above-mentioned self-piercing riveting device, comprising the following steps:

[0015] (1) Insert the self-punching riveting die 23 into the self-punching riveting die positioning base 27, and place the positioning base below the self-punching riveting die mounting bearing beam 6.

[0016] (2) Start the hydraulic cylinder 11, and drive the hydraulic cylinder to move the crossbeam 16 and the self-piercing riveting die-mounted bearing crossbeam 6 upward by the hydraulic cylinder push rod 12, thereby raising the die-mounted bearing crossbeam 6.

[0017] (3) Place the cleaned lower plate 18 to be riveted and the upper plate 17 to be riveted on the upper surface of the high temperature resistant plate pressing bearing beam 4, and turn on the plate heating coil 28 to preheat in place for 5~10 minutes, wherein the upper plate 17 is located above the lower plate 18.

[0018] (4) The hydraulic cylinder push rod 12 moves down, driving the self-punching riveting die insert bearing beam 6 to press down, so that the high temperature resistant plate presses the bearing beam 4 to move down, and the left elastic pressing return spring 3 and the right elastic pressing return spring 20 are pressed until the force is balanced.

[0019] (5) The hydraulic cylinder drives the crossbeam 16 to drive the electromagnetic coil support base 7 to continue to descend until the lower surface of the electromagnetic coil support base 7 contacts the upper surface of the self-piercing riveting die-mounted support crossbeam 6, thereby pushing the upper component to continue to descend until the upper surface of the fixed punch 22 is coplanar with the lower surface of the inner groove of the punch guide sleeve 21, the hydraulic cylinder 11 stops and records the position.

[0020] (6) Place the self-piercing riveting 19 on the upper surface of the fixed punch 22, connect the electromagnetic coil 24, and the electromagnetic force drives the high temperature resistant plate to press the bearing beam 4, the self-piercing riveting die insert bearing beam 6, the upper plate 17, the lower plate 18 and the self-piercing riveting forming die 23 to move down along the guide posts 9 and 14. The two springs are compressed more to achieve edge pressing. The self-piercing riveting 19 pierces the upper and lower plates. Its legs expand radially and embed into the upper plate under the constraint of the self-piercing riveting forming die 23, and its head presses the lower surface of the lower plate to complete the riveting.

[0021] (7) Disconnect the electromagnetic coil 24, the electromagnetic force disappears, the upper component moves upward to reset, and the hydraulic cylinder 11 drives the lifting and removal of the riveting component.

[0022] Preferably, in step 3, the in-situ preheating time of the plate heating coil 28 on the stacked plates is 5 to 10 minutes.

[0023] Preferably, in step 5, when the upper surface of the fixed punch 22 is coplanar with the lower surface of the inner groove of the punch guide sleeve 21, the current position of the hydraulic cylinder drive beam 16 is recorded as the reference for the riveting stroke.

[0024] Preferably, in step 6, the pressure load and riveting forming load are adjusted simultaneously by adjusting the magnitude of the energizing current of the electromagnetic coil 24.

[0025] The beneficial effects of this invention are:

[0026] (1) The self-punching riveting die insert bearing beam has a large contact area with the upper plate to be riveted and the high temperature resistant plate pressing bearing beam and the lower plate to be riveted. It can effectively constrain the plate around the riveting area. During the forming process, the plate will not flow irregularly, wrinkle or warp, and the joint will be subjected to uniform force. At the same time, it can ensure that the plate is perpendicular to the punch axis and no lateral force is generated when the rivet is pressed in.

[0027] (2) The device is equipped with a plate heating coil. For high-strength metal plates, in-situ preheating can reduce the deformation resistance of the metal plates, which is conducive to forming a good interlocking structure and improving the riveting quality.

[0028] (3) Unlike the previous method of controlling the edge pressure load and riveting forming separately, this device uses electromagnetic force as the driving force to provide the edge pressure load of the plate and complete the riveting forming of the plate at the same source. The forming speed is fast and the efficiency is high. The forming load can be adjusted by controlling the current, and the operation is convenient.

[0029] (4) The detachable die design allows for easy replacement of dies with different inner hole shapes according to the sheet material, making it highly adaptable.

[0030] (5) The inverted configuration with the fixed punch rod and the bottom bearing worktable has the following non-obvious technical effects compared with the follow-up configuration of "moving crossbeam driving the punch rod to move upward": the fixed punch rod makes the rivet axis and the guide axis naturally coaxial, eliminating the follow-up guidance error of the punch and improving the coaxiality of the rivet and the plate; the downward movement of the upper component is completed in the same electromagnetic force closed loop for pressing and riveting, the force control is more precise, and the current is adjustable, i.e., the load is adjusted; the motion mass center of gravity of this downward configuration is lower, the spring pre-stored energy requirement is smaller, and the movement is more stable. The expected value and the actual effect are subject to the measured data. Attached Figure Description

[0031] Figure 1 This is a front view of a self-piercing riveting device for metal sheets.

[0032] Figure 2 for Figure 1 A sectional view along the AA direction.

[0033] Figure 3 for Figure 1 BB-direction sectional view.

[0034] Figure 4 for Figure 1 CC-direction sectional view.

[0035] Figure 5 For comparison, the process simulation results are used;

[0036] Figure 6 These are the process simulation results of the present invention;

[0037] The markings used in the above figures are as follows: 1-Frame-type load-bearing base, 2-Bottom load-bearing worktable, 3-Left elastic compression and return spring, 4-High temperature resistant plate compression load-bearing crossbeam, 5-Front end cap locking nut, 6-Self-piercing riveting die-mounted load-bearing crossbeam, 7-Electromagnetic coil support base, 8-Left small guide post, 9-Left side guide post, 10-Upper fixed crossbeam, 11-Hydraulic cylinder, 12-Hydraulic cylinder push rod, 13-Front end cap, 14-Right side guide post. 15-Right small guide post, 16-Hydraulic cylinder driven crossbeam, 17-Upper plate to be riveted, 18-Lower plate to be riveted, 19-Self-piercing riveting rivet, 20-Right elastic clamping return spring, 21-Punch rod guide sleeve, 22-Fixed punch rod, 23-Self-piercing riveting die, 24-Electromagnetic coil, 25-Rear end cap, 26-Rear end cap locking nut, 27-Self-piercing riveting die positioning base, 28-Plate heating coil. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. In this embodiment, steel plates are selected as the upper plate 17 to be riveted and the lower plate 18 to be riveted. The device includes: a frame-type load-bearing base 1, a bottom load-bearing worktable 2, a left elastic compression and return spring 3, a high-temperature resistant plate compression and load-bearing crossbeam 4, a front cover locking nut 5, a self-piercing riveting die inlaid load-bearing crossbeam 6, an electromagnetic coil support base 7, a left small guide post 8, a left side guide post 9, an upper fixed crossbeam 10, a hydraulic cylinder 11, a hydraulic cylinder push rod 12, a front cover 13, a right side guide post 14, a right small guide post 15, a hydraulic cylinder drive crossbeam 16, an upper plate to be riveted and formed 17, a lower plate to be riveted and formed 18, a self-piercing riveting rivet 19, a right elastic compression and return spring 20, a punch guide sleeve 21, a fixed punch 22, a self-piercing riveting die 23, an electromagnetic coil 24, a rear cover 25, a rear cover locking nut 26, a self-piercing riveting die positioning base 27, and a plate heating coil 28.

[0039] The bottom support worktable 2 is fixedly installed above the frame-type load-bearing base 1. The left guide post 9 and the right guide post 14 are respectively fixedly installed in the through holes on both sides of the bottom support worktable 2. The fixed punch 22 is fixedly connected to the bottom support worktable 2 and is axially fixed.

[0040] The left elastic compression return spring 3 and the right elastic compression return spring 20 are respectively sleeved on the outer surfaces of the left guide post 9 and the right guide post 14, with their lower ends abutting against the bottom bearing worktable 2. The through holes on both sides of the high-temperature resistant plate pressing bearing beam 4 are respectively sleeved on the left guide post 9 and the right guide post 14 and are located on the upper ends of the two springs. A punch guide sleeve 21 is fixedly installed in the center of its lower surface. The punch guide sleeve 21 has through holes and grooves that match the fixed punch 22. The plate heating coil 28 is installed in the annular groove in the middle of the upper surface of the high-temperature resistant plate pressing bearing beam 4.

[0041] The through holes on both sides of the self-piercing riveting die-mounted support beam 6 and the hydraulic cylinder driven beam 16 are respectively fitted onto the left guide post 9 and the right guide post 14. Between the high-temperature resistant sheet metal pressing support beam 4 and the self-piercing riveting die-mounted support beam 6, there are stacked lower sheet metal 18 and upper sheet metal 17 to be riveted. An electromagnetic coil support base 7 is fixedly installed below the hydraulic cylinder driven beam 16, and the electromagnetic coil support base 7 is equipped with an electromagnetic coil 24.

[0042] The left small guide post 8 and the right small guide post 15 are fixedly mounted in the outer through hole of the self-piercing riveting die-mounted bearing beam 6 and pass through the outer through hole of the hydraulic cylinder drive beam 16. A boss is provided at the upper end of each guide post to limit the relative movement range of the hydraulic cylinder drive beam 16. The upper fixed beam 10 is fixedly connected to the left guide post 9 and the right guide post 14. The hydraulic cylinder 11 is fixedly mounted in the center of the upper fixed beam 10, and its hydraulic cylinder push rod 12 is fixedly connected to the hydraulic cylinder drive beam 16.

[0043] The self-piercing riveting die positioning base 27 is installed in the dovetail groove below the self-piercing riveting die mounting support beam 6, and the stepped hole in the middle accommodates the self-piercing riveting die 23; the front cover 13 and the rear cover 25 are placed on the front and rear sides of the positioning base 27 and locked by the front cover locking nut 5 and the rear cover locking nut 26, and the self-piercing riveting die 23 is located directly above the fixed punch 22.

[0044] The experimental procedure using this device is as follows:

[0045] Unscrew the front cover locking nut 5 and the rear cover locking nut 26, remove the front cover 13 and the rear cover 25, pull out the self-piercing riveting forming die positioning base 27, and install the self-piercing riveting forming die 23; insert the positioning base 27 into the dovetail groove below the self-piercing riveting die mounting load-bearing beam 6, and lock and limit it with the end covers 13 and 25 and the locking nuts 5 and 26 at both ends.

[0046] Start the hydraulic cylinder 11, the hydraulic cylinder push rod 12 moves upward, driving the hydraulic cylinder drive beam 16 to move upward along each guide post; when the hydraulic cylinder drive beam 16 contacts the upper limit boss of the left small guide post 8 and the right small guide post 15, it drives the small guide post and the self-piercing riveting die-mounted bearing beam 6 to move upward synchronously.

[0047] Turn on the heating coil 28 of the plate, place the cleaned lower plate 18 to be riveted and the upper plate 17 to be riveted on the upper surface of the high temperature resistant plate pressing bearing beam 4, and preheat in place for 5-10 minutes, with the upper plate 17 located above the lower plate 18.

[0048] Start the hydraulic cylinder 11 to make the hydraulic cylinder push rod 12 move downward, which drives the self-punching riveting die-mounted load-bearing crossbeam 6 to move downward synchronously; when its lower surface contacts the upper surface of the upper plate 17, the high-temperature resistant plate presses the load-bearing crossbeam 4 to move downward, and the left elastic pressing return spring 3 and the right elastic pressing return spring 20 are compressed; when the force is balanced, each beam stops moving.

[0049] The hydraulic cylinder drives the crossbeam 16 to continue moving the electromagnetic coil support base 7 downward. When the lower surface of the electromagnetic coil support base 7 contacts the upper surface of the self-piercing riveting die-mounted support crossbeam 6, it pushes the upper component to continue moving downward. When the upper surface of the fixed punch 22 is coplanar with the lower surface of the groove inside the punch guide sleeve 21, the hydraulic cylinder 11 stops and records the position of the hydraulic cylinder driven crossbeam 16.

[0050] The self-piercing riveting rivet 19 is placed on the upper surface of the fixed punch 22. The electromagnetic coil 24 is turned on, and the electromagnetic force drives the high-temperature resistant plate to press against the bearing beam 4, the self-piercing riveting die-mounted bearing beam 6, the upper plate 17 and the lower plate 18, and they move down along the guide post. The two springs are compressed further to achieve edge pressing. The tip of the rivet 19 contacts and pierces the lower plate 18. Its legs are supported and constrained by the upper plate 17 and the self-piercing riveting die 23 and expand radially, embedding into the interior of the upper plate 17. The head presses against the lower surface of the lower plate 18, completing the riveting.

[0051] After riveting is completed, the electromagnetic coil 24 is disconnected, the electromagnetic force disappears, and the upper component moves upward to reset; the hydraulic cylinder 11 is started to lift and remove the riveting assembly consisting of the upper plate 17, the lower plate 18 and the rivet 19.

[0052] To demonstrate that the synergistic effect of the "in-situ preheating + integrated edge pressing and riveting with the same electromagnetic source" combination of this invention is not a simple additive effect, the applicant conducted a simulation comparison analysis with the process of this invention using "no preheating + step-by-step edge pressing and riveting" (control process) under the same sheet material grade and process conditions. Table 1 corresponds to... Figure 5 According to the process simulation results, Table 2 corresponds to Figure 6 The simulation results of the process of this invention.

[0053] Table 1

[0054]

[0055] Table 2

[0056]

[0057] The simulation results of the control process show that although the gap between the plates is small, the residual thickness at the bottom is large, and the lateral interlocking is slightly higher, the rivet tail opening ratio is close to 1. The rivet foot mainly compresses the plate vertically, and the outward curling deformation is insufficient. The vertical interlocking is inadequate, and an ideal hook-shaped mechanical internal lock is not formed, resulting in poor joint pull-out resistance. The simulation results of the present invention show that the rivet tail undergoes sufficient outward curling expansion, the vertical interlocking is significantly improved, the residual thickness at the bottom is 0.286mm, which meets the safety threshold of greater than 0.2mm, and no bottom plate penetration occurs. A typical and reliable SPR hook-lock structure is formed, and the quality of the core internal lock structure of the joint is superior to that of the control process.

[0058] The expected results show that the radial expansion of the rivet tail is significantly better and the interlocking is more uniform and stable using the process of this invention. The above comparative data are used to illustrate the synergistic effect of in-situ softening and drag reduction and synchronous edge pressing riveting, enhancing the inventiveness of this invention compared to existing step-by-step processes.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the principle of the present invention, and these improvements and substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A self-piercing riveting device for metal plates, characterized in that, It includes a frame-type load-bearing base (1), a bottom load-bearing worktable (2), a left small guide post (8), guide posts (9, 14), a right small guide post (15), a fixed punch (22), an elastic clamping and reset spring (3, 20), a high-temperature resistant plate clamping load-bearing crossbeam (4), a self-piercing riveting die-mounted load-bearing crossbeam (6), an upper fixed crossbeam (10), and a hydraulic cylinder driven crossbeam (16). The bottom support worktable (2) is fixedly mounted on the frame-type load-bearing base (1), and the through holes on both sides are fitted with guide posts (9, 14); the fixed punch (22) is fixedly connected to the bottom support worktable (2) and is axially fixed, and the self-punching riveting rivet (19) is placed on the upper surface of the fixed punch (22); Elastic compression and reset springs (3, 20) are sleeved on the outer surface of guide posts (9, 14), with their two ends abutting against the bottom bearing worktable (2) and the high-temperature resistant plate pressing bearing crossbeam (4) respectively. The upper plate (17) and the lower plate (18) are stacked between the two crossbeams. The upper end of the guide posts (9, 14) is fixed to the upper fixed crossbeam (10). The hydraulic cylinder (11) is fixedly installed at the center of the upper fixed crossbeam (10), and its hydraulic cylinder push rod (12) is fixedly connected to the hydraulic cylinder drive crossbeam (16) to drive it to move up and down along the guide posts (9, 14). The self-piercing riveting die (23) is detachable and is installed below the self-piercing riveting die mounting support beam (6) and directly above the fixed punch (22); the electromagnetic coil support base (7) is fixed below the hydraulic cylinder drive beam (16) and is equipped with an electromagnetic coil (24); the plate heating coil (28) is used for in-situ preheating; the left small guide post (8) and the right small guide post (15) are fixedly installed in the outer through hole of the self-piercing riveting die mounting support beam (6) and pass through the outer through hole of the hydraulic cylinder drive beam (16); the upper ends of the left small guide post (8) and the right small guide post (15) are provided with bosses to limit the movement range of the hydraulic cylinder drive beam (16) relative to the small guide post; During operation, the electromagnetic coil (24) is energized to generate electromagnetic force, which drives the high-temperature resistant plate to press the bearing beam (4), the self-piercing riveting die to install the bearing beam (6), the upper plate (17), the lower plate (18), and the self-piercing riveting die (23) to move downward along the guide posts (9, 14). This causes the upper and lower plates to be fitted into the self-piercing riveting rivets (19) on the upper surface of the fixed punch (22) and pierced. Under the constraint of the self-piercing riveting die (23), the legs of the rivets expand radially and embed into the upper plate, while the head presses the lower plate. The fixed punch (22) and the electromagnetic force are from the same source and provide the pressing and riveting forming force.

2. The self-piercing riveting device for metal plates according to claim 1, characterized in that, The self-piercing riveting die (23) is detachably mounted below the self-piercing riveting die mounting support beam (6) via a self-piercing riveting die positioning base (27); the self-piercing riveting die positioning base (27) is mounted in a dovetail groove below the self-piercing riveting die mounting support beam (6), and it is provided with stepped holes to accommodate the self-piercing riveting die (23).

3. The self-piercing riveting device for metal plates according to claim 1, characterized in that, The self-piercing riveting forming die positioning base (27) has a front end cover (13) and a rear end cover (25) on its front and rear sides, respectively, and is locked by the front end cover locking nut (5) and the rear end cover locking nut (26) to restrict its forward and backward movement.

4. The self-piercing riveting device for metal plates according to claim 1, characterized in that, The heating coil (28) of the plate is embedded in the annular groove on the upper surface of the high temperature resistant plate pressing bearing beam (4).

5. The self-piercing riveting device for metal plates according to claim 1, characterized in that, A punch guide sleeve (21) is fixedly installed at the center of the lower surface of the high temperature resistant plate pressing bearing beam (4). The punch guide sleeve (21) has a through hole and groove that match the fixed punch (22). When the lower surface of the groove inside the punch guide sleeve (21) is coplanar with the upper surface of the fixed punch (22), the downward stroke of the hydraulic cylinder driving beam (16) is limited.

6. A method for self-piercing riveting of metal plates, employing the self-piercing riveting device for metal plates as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Insert the self-punching riveting die (23) into the self-punching riveting die positioning base (27), and place the positioning base below the self-punching riveting die mounting load-bearing crossbeam (6); (2) Start the hydraulic cylinder (11), and drive the hydraulic cylinder to move the crossbeam (16) and the self-piercing riveting die-mounted bearing crossbeam (6) upward by the hydraulic cylinder push rod (12), thereby raising the die-mounted bearing crossbeam (6). (3) Place the cleaned lower plate (18) to be riveted and the upper plate (17) to be riveted on the upper surface of the high temperature plate pressing bearing beam (4), and turn on the plate heating coil (28) to preheat in place for 5~10 minutes, wherein the upper plate (17) is located above the lower plate (18). (4) The hydraulic cylinder push rod (12) moves down, driving the self-punching riveting die insert bearing beam (6) to press down, so that the high temperature resistant plate presses the bearing beam (4) to move down, and the left elastic pressing return spring (3) and the right elastic pressing return spring (20) are pressed until the force is balanced. (5) The hydraulic cylinder drives the crossbeam (16) to drive the electromagnetic coil support base (7) to continue to descend until the lower surface of the electromagnetic coil support base (7) contacts the upper surface of the self-piercing riveting die-mounted support crossbeam (6), and then pushes the upper component to continue to descend until the upper surface of the fixed punch (22) is coplanar with the lower surface of the groove inside the punch guide sleeve (21), the hydraulic cylinder (11) stops and records the position; (6) Place the self-piercing riveting rivet (19) on the upper surface of the fixed punch (22), turn on the electromagnetic coil (24), and the electromagnetic force drives the high temperature plate to press the bearing beam (4), the self-piercing riveting die insert bearing beam (6), the upper plate (17), the lower plate (18) and the self-piercing riveting forming die (23) to move down along the guide post (9, 14). The two springs are compressed more to achieve the pressing edge. The self-piercing riveting rivet (19) pierces the upper and lower plates. Its legs are radially expanded and embedded in the upper plate under the constraint of the self-piercing riveting forming die (23), and the head presses the lower surface of the lower plate to complete the riveting. (7) Disconnect the electromagnetic coil (24), the electromagnetic force disappears, the upper component moves upward to reset, and the hydraulic cylinder (11) drives the lifting and removal of the riveting component.

7. The self-piercing riveting method for metal plates according to claim 6, characterized in that, In step (3), the heating coil (28) preheats the stacked plates in situ for 5 to 10 minutes.

8. The self-piercing riveting method for metal plates according to claim 6, characterized in that, In step (5), when the upper surface of the fixed punch (22) is coplanar with the lower surface of the groove inside the punch guide sleeve (21), the current position of the hydraulic cylinder drive beam (16) is recorded as the reference for the riveting stroke.

9. The self-piercing riveting method for metal plates according to claim 6, characterized in that, In step (6), the pressure load and riveting forming load are adjusted synchronously by adjusting the current of the electromagnetic coil (24).

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