A metal sheet self-piercing riveting forming device and method

Abstract

The application discloses a metal plate self-punching riveting forming device and method, and belongs to the field of metal plate connection. The device comprises a frame type bearing base, a bottom bearing workbench, left and right guide columns, an electromagnetic force driven movable cross beam, left and right elastic compression reset springs, a high-temperature-resistant plate compression bearing cross beam, a self-punching riveting concave die embedding bearing cross beam, an upper fixed cross beam, a hydraulic cylinder and a top rod, an electromagnetic force driven punch rod guide sleeve and punch rod, an electromagnetic coil supporting base and an electromagnetic coil, and a concave die positioning base and a concave die. The high-temperature-resistant plate compression bearing cross beam inlaying plate heating coil preheats the plate in situ, the same electromagnetic coil linkage synchronously provides the edge compression load, completes the riveting forming and the current is adjustable, and the independent hydraulic cylinder drives the concave die positioning. The application improves the forming quality and joint reliability of the high-strength metal plate self-punching riveting.

Description

Technical Field

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

[0002] Self-Piercing Riveting (SPR) is a cold-forming mechanical joining process for joining sheet metal without the need for pre-drilling. A punch pushes a rivet through the upper sheet and into the lower sheet, but not through it. The rivet tail expands radially within the die, creating a mechanical interlock, thus joining the upper and lower sheets. This process is easily automated and suitable for joining dissimilar metals and materials such as aluminum and high-strength steel.

[0003] However, existing self-piercing riveting processes and equipment still have the following shortcomings when applied to high-strength metal sheets:

[0004] (1) High-strength plates have high deformation resistance and poor plasticity. The rivet insertion and tail expansion resistance are large, which can easily lead to insufficient tail expansion and excessive locking gap, resulting in joint interlocking failure.

[0005] (2) When the clamping area of ​​the pressure ring on the plate is insufficient, the plate in the un-clamped area will flow irregularly, wrinkle and warp, causing the rivet to shift under force, form asymmetry and uneven force, reducing the life of the joint.

[0006] (3) The tilting of the plate will generate lateral force, causing the insertion trajectory to deviate, the tail to expand asymmetrically, and the joint to become loose and fall off. Summary of the Invention

[0007] This invention aims to solve problems such as insufficient expansion due to large deformation resistance of the sheet metal during self-piercing riveting of high-strength metal sheets, wrinkling, warping and force offset of the sheet metal due to insufficient pressure area, and lateral force and eccentric loosening due to sheet metal tilting. It improves the riveting quality and joint reliability, and increases forming efficiency and process adjustability.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] A self-piercing riveting forming device for metal sheets includes a frame-type load-bearing base 1, a bottom load-bearing worktable 2, a left guide post for the crossbeam guide 3, a right guide post for the crossbeam guide 13, an electromagnetically driven movable crossbeam 4, a left elastic pressing and returning spring 5, a right elastic pressing and returning spring 18, a high-temperature resistant sheet metal pressing and bearing crossbeam 6, a self-piercing riveting die insert bearing crossbeam 7, an upper fixed crossbeam 9, a hydraulic cylinder 10, a hydraulic cylinder push rod 11, an electromagnetically driven punch guide sleeve 16, an electromagnetically driven punch 19, an electromagnetic coil support base 20, an electromagnetic coil 21, a self-piercing riveting forming die positioning base 24, and a self-piercing riveting forming die 25.

[0010] The bottom support workbench 2 is fixed above the frame-type load-bearing base 1. The left guide column 3 and the right guide column 13 of the crossbeam are installed in the through holes on both sides of the bottom support workbench 2 and are fixed to the upper fixed crossbeam 9. The upper fixed crossbeam 9 is equipped with a hydraulic cylinder 10 in the center. The lower end of the hydraulic cylinder push rod 11 is fixed to the concave mold inlaid with the support crossbeam 7.

[0011] Electromagnetic force drives the movable crossbeam 4, the high-temperature plate pressing and bearing crossbeam 6 and the concave mold inlaid bearing crossbeam 7 to slide through the crossbeam guide left guide post 3 and the crossbeam guide right guide post 13, and are connected by the left elastic pressing and returning spring 5 and the right elastic pressing and returning spring 18. The bottom bearing worktable 2 is provided with an electromagnetic coil support base 20 and an electromagnetic coil 21.

[0012] The high-temperature resistant plate is pressed into the annular groove in the middle of the bearing beam 6. The plate heating coil 26 is installed in the groove to preheat the plate in situ. The concave mold is installed to press the bearing beam 7 to the upper plate 14.

[0013] The punch guide sleeve 16 is fixed below the high-temperature resistant plate pressing bearing beam 6, and the punch 19 is fixed on the electromagnetic force driven movable beam 4 and slides along the punch guide sleeve 16; the self-punching riveting forming die positioning base 24 is installed in the dovetail groove below the die mounting bearing beam 7, and a stepped hole is provided in the middle of the self-punching riveting forming die positioning base 24 for installing the die 25;

[0014] The electromagnetic coil 21 generates electromagnetic force when energized, driving the movable crossbeam 4 upward. This electromagnetic force is transmitted to the high-temperature resistant plate pressing and bearing crossbeam 6 through the left elastic pressing and returning spring 5 and the right elastic pressing and returning spring 18, so that the pressing load and the riveting of the punch 19 are completed synchronously by the same electromagnetic power source. This drives the self-piercing riveting rivet 17 set on the upper surface of the punch 19 to complete the self-piercing riveting, and the forming load is adjusted by the current of the electromagnetic coil 21.

[0015] Preferably, the self-piercing riveting die positioning base 24 is provided with a front end cover 12 and a rear end cover 22 on its front and rear sides, respectively, and is locked by a front end cover locking nut 8 and a rear end cover locking nut 23, respectively, to restrict the self-piercing riveting die positioning base 24 from moving in the front and rear directions.

[0016] Preferably, the punch guide sleeve 16 has a groove inside, which limits the riveting stroke when the punch 19 moves up until the lower surface of the groove is coplanar with the upper surface of the punch 19.

[0017] Using the above-mentioned self-piercing riveting forming device for metal sheets, the present invention also provides a method for self-piercing riveting forming of metal sheets, comprising the following steps:

[0018] (1) Clamping die steps: Insert the self-punching riveting die 25 into the stepped hole of the self-punching riveting die positioning base 24, and insert the positioning base back into the dovetail groove below the die mounting bearing beam 7 and lock it.

[0019] (2) Lifting and preheating steps: Drive the hydraulic cylinder push rod 11 to move upward and drive the concave mold insert bearing beam 7 to move upward. Place the cleaned upper plate 14 and lower plate 15 on the upper surface of the high temperature resistant plate pressing bearing beam 6, and preheat the plate in place through the plate heating coil 26.

[0020] (3) Pressing step: Drive the hydraulic cylinder push rod 11 to move down and drive the die-mounted bearing beam 7 to move down and press the upper plate 14. Continue to press down so that the upper plate 14, the lower plate 15 and the high temperature plate pressing bearing beam 6 move down together, compressing the left elastic pressing return spring 5 and the right elastic pressing return spring 18.

[0021] (4) Electromagnetic riveting steps: When the electromagnetic coil 21 is energized, the electromagnetic force drives the movable crossbeam 4 to move upward along the guide post and compress the spring, so that the high temperature resistant plate presses the bearing crossbeam 6 with the load of the spring and clamps the plate with the die-mounted bearing crossbeam 7. At the same time, the movable crossbeam drives the punch 19 to move upward quickly, pushes the rivet to pierce the lower plate 15 and causes the legs to expand radially and embed into the upper plate 14 under the constraint of the die 25. The head presses the lower surface of the lower plate 15 and the forming load is adjusted by the magnitude of the current of the electromagnetic coil 21.

[0022] (5) Reset and take out the parts: the power is cut off to make the electromagnetic force disappear, the movable crossbeam is reset under the spring force, and the hydraulic cylinder push rod 11 moves up to take out the riveted and formed components.

[0023] Preferably, in the lifting and preheating step, the upper plate 14 and the lower plate 15 are preheated for 5 to 10 minutes by the plate heating coil 26.

[0024] Preferably, after the clamping step and before the electromagnetic riveting step, the hydraulic cylinder 10 stops when it descends to the point where the upper surface of the punch rod 19 is coplanar with the lower surface of the inner groove of the punch rod guide sleeve 16, the position of the die-mounted bearing beam 7 is recorded, and then the rivet is placed on the upper surface of the punch rod 19.

[0025] Preferably, in the electromagnetic riveting step, the forming load is adjusted by adjusting the current of the electromagnetic coil 21.

[0026] The beneficial effects of this invention are:

[0027] Compared with the prior art, the present invention has the following beneficial effects (expected values, actual effects are subject to measured data):

[0028] (1) The heating coil 26 of the plate is embedded in the pressing bearing beam 6 and preheats the plate in situ, reducing the deformation resistance of the high-strength metal plate, facilitating the rivet insertion and good tail expansion, forming a stable interlock, and improving the forming quality (expected value, actual effect is subject to actual measurement data).

[0029] (2) The upper plate 14 and the lower plate 15 have a large contact area with the die-mounted bearing beam 7 and the high-temperature plate pressing bearing beam 6, respectively, which effectively constrains the plates around the riveting area. During the forming process, the plates do not flow irregularly, wrinkle or warp, and the joint is subjected to uniform force. It can also ensure that the plate is perpendicular to the axis of the punch 19 and that there is no lateral force when it is pressed in (expected value, actual effect is subject to actual measurement data).

[0030] (3) The same electromagnetic source applies the pressure load through the spring and completes the riveting almost simultaneously, eliminating the timing misalignment caused by step control, resulting in fast forming speed and high efficiency; the forming load can be adjusted by controlling the current, making operation convenient (expected value, actual effect is subject to actual measurement data).

[0031] (4) The design of the detachable die 25 allows for easy replacement of dies 25 with different inner hole shapes according to the sheet material; the die 25 is positioned by an independent hydraulic cylinder 10, which is decoupled from the pressing / riveting action and has strong adaptability (expected value, actual effect is subject to actual measurement data). Attached Figure Description

[0032] Figure 1 Main view;

[0033] Figure 2 for Figure 1 Sectional view along axis AA;

[0034] Figure 3 for Figure 1 BB-direction sectional view;

[0035] Figure 4 for Figure 1 CC-direction sectional view;

[0036] Figure 5 For comparison, the process simulation results are used;

[0037] Figure 6 These are the process simulation results of the present invention;

[0038] Reference numerals: 1-Frame-type load-bearing base, 2-Bottom load-bearing worktable, 3-Left guide post of crossbeam, 4-Electromagnetic force driven movable crossbeam, 5-Left elastic clamping and reset spring, 6-High temperature resistant plate clamping load-bearing crossbeam, 7-Self-piercing riveting die inlay load-bearing crossbeam, 8-Front end cap locking nut, 9-Upper fixed crossbeam, 10-Hydraulic cylinder, 11-Hydraulic cylinder push rod, 12-Front end cap, 13-Right guide post of crossbeam, 14-Upper plate to be riveted, 15-Lower plate to be riveted, 16-Electromagnetic force driven punch guide sleeve, 17-Self-piercing riveting rivet, 18-Right elastic clamping and reset spring, 19-Electromagnetic force driven punch, 20-Electromagnetic coil support base, 21-Electromagnetic coil, 22-Rear end cap, 23-Rear end cap locking nut, 24-Self-piercing riveting die positioning base, 25-Self-piercing riveting die, 26-Plate heating coil; Detailed Implementation

[0039] The invention will be further described below with reference to its specific structure.

[0040] like Figures 1-4 As shown, the frame-type load-bearing base 1 serves as the overall load-bearing foundation, with the bottom load-bearing worktable 2 fixed above it. The left guide post 3 and the right guide post 13 of the crossbeam are installed in the through holes on both sides of the bottom load-bearing worktable 2 and the top of the upper fixed crossbeam 9 is fixed. A hydraulic cylinder 10 is installed in the center of the upper fixed crossbeam 9. The lower end of the hydraulic cylinder push rod 11 is fixedly connected to the self-piercing riveting die insert load-bearing crossbeam 7. The hydraulic cylinder 10 independently drives the die insert load-bearing crossbeam 7 to rise and fall along the guide post, thereby positioning the die 25 and decoupling it from the pressing / riveting action.

[0041] The electromagnetic force drives the movable crossbeam 4, the high-temperature resistant plate pressing and bearing crossbeam 6, and the self-piercing riveting die-mounted bearing crossbeam 7. The crossbeam slides through the left guide post 3 and the right guide post 13, and is connected by the left elastic pressing and returning spring 5 and the right elastic pressing and returning spring 18. The upper surface of the bottom bearing workbench 2 is provided with an electromagnetic coil support base 20 and an electromagnetic coil 21. The upper end face of the electromagnetic coil support base 20 is in contact with the lower surface of the electromagnetic force driven movable crossbeam 4, and the electromagnetic force drives the movable crossbeam 4 to move upward under the action of electromagnetic force.

[0042] A circular groove is opened in the middle of the high-temperature resistant plate pressing bearing beam 6, and a plate heating coil 26 is installed in the groove for in-situ preheating of the upper plate 14 and the lower plate 15. The upper surface of the beam is used to support the lower plate 15. The lower surface of the self-piercing riveting die is pressed against the upper plate 14, and the upper plate 14 is stacked on the lower plate 15.

[0043] The electromagnetic force driven punch guide sleeve 16 is fixed to the center below the high-temperature resistant plate pressing bearing beam 6, and the electromagnetic force driven punch 19 is fixed to the center above the electromagnetic force driven movable beam 4 and slides along the through hole of the guide sleeve; the upper surface of the punch 19 is provided with a self-piercing riveting rivet 17, and the inside of the guide sleeve is provided with a groove, which limits the riveting stroke when the upper surface of the punch 19 and the lower surface of the groove are coplanar. The self-piercing riveting forming die positioning base 24 is installed in the dovetail groove below the self-piercing riveting die inlaid bearing beam 7, and its stepped hole is fitted with the self-piercing riveting forming die 25; the front end cover 12 and the rear end cover 22 are respectively provided on the front and rear sides of the positioning base, and are locked by the front end cover locking nut 8 and the rear end cover locking nut 23 respectively, so as to restrict the movement of the positioning base in the front and rear directions, and facilitate the replacement of dies 25 with different inner hole shapes.

[0044] The self-piercing riveting forming method using the above-mentioned device includes the following steps:

[0045] First, loosen the locking nut, remove the front cover 12 and the rear cover 22, pull out the self-punching riveting forming die positioning base 24, install the die 25 with the required inner hole shape, and then insert the positioning base back into the dovetail groove and lock it.

[0046] In the second step, the hydraulic cylinder push rod 11 moves upward, driving the self-punching riveting die-mounted load-bearing beam 7 to move upward along the guide post.

[0047] The third step is to turn on the power supply of the panel heating coil 26, and stack the cleaned upper panel 14 and lower panel 15 on the upper surface of the high-temperature resistant panel pressing bearing beam 6. The panel is preheated in situ by the panel heating coil 26 for 5-10 minutes, with the upper panel 14 on top and the lower panel 15 on the bottom.

[0048] In the fourth step, the hydraulic cylinder push rod 11 moves downward, driving the die-mounted bearing beam 7 to move downward. Its lower surface presses against the upper plate 14 and continues to move downward, pushing the upper plate 14, the lower plate 15 and the high-temperature resistant plate to move downward together with the bearing beam 6. The left elastic pressing return spring 5 and the right elastic pressing return spring 18 are compressed.

[0049] Fifth step: When the upper surface of punch 19 is coplanar with the lower surface of the inner groove of punch guide sleeve 16, the hydraulic cylinder 10 stops, the position of the die insert bearing beam 7 is recorded at this time, and then the rivet is placed on the upper surface of punch 19.

[0050] Step 6: Connect the power supply to the electromagnetic coil 21. The same electromagnetic source generates electromagnetic force to drive the movable crossbeam 4 to move upward along the guide post and compress the left elastic clamping return spring 5 and the right elastic clamping return spring 18. This causes the high-temperature resistant plate to clamp the bearing crossbeam 6 with the load of the spring and the die-mounted bearing crossbeam 7 to clamp the upper plate 14 and the lower plate 15 (integrated pressing edge). This electromagnetic force is transmitted in conjunction with the left elastic clamping return spring 5 and the right elastic clamping return spring 18, so that the pressing edge load and the riveting of the punch 19 are completed synchronously by the same electromagnetic power source. The movable crossbeam drives the punch 19 to move upward quickly, pushing the rivet to pierce the lower plate 15 and causing the legs to expand radially and embed into the upper plate 14 under the constraint of the die 25. The head presses the lower surface of the lower plate 15. The forming load is adjusted by adjusting the current of the electromagnetic coil 21.

[0051] Step 7: After riveting is completed, the power is turned off, the electromagnetic force disappears, and the movable crossbeam moves down and resets under the spring force.

[0052] Step 8: The hydraulic cylinder push rod 11 moves upward and the riveted assembly is removed.

[0053] 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.

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] 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 of 0.222mm meets the safety threshold of greater than 0.2mm, 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 better than that of the control process.

[0059] 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 resistance reduction with synchronous edge pressing riveting, enhancing the inventiveness of this invention compared to existing step-by-step processes. The above description is only a preferred embodiment of this 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 this invention, and these improvements and substitutions should also be considered to fall within the protection scope of this invention.

Claims

1. A self-piercing riveting forming device for metal sheets, characterized in that, Includes a frame-type load-bearing base (1), a bottom load-bearing worktable (2), a left guide column for the crossbeam (3), a right guide column for the crossbeam (13), an electromagnetically driven movable crossbeam (4), a left elastic pressing and resetting spring (5), a right elastic pressing and resetting spring (18), a high-temperature resistant plate pressing and bearing crossbeam (6), a self-piercing riveting die-mounted bearing crossbeam (7), an upper fixed crossbeam (9), a hydraulic cylinder (10), a hydraulic cylinder push rod (11), an electromagnetically driven punch guide sleeve (16), an electromagnetically driven punch (19), an electromagnetic coil support base (20), an electromagnetic coil (21), a self-piercing riveting forming die positioning base (24), and a die (25); The bottom support workbench (2) is fixed above the frame-type load-bearing base (1). The left guide column (3) and the right guide column (13) of the crossbeam are installed in the through holes on both sides of the bottom support workbench (2) and are fixed to the upper fixed crossbeam (9). A hydraulic cylinder (10) is provided in the center of the upper fixed crossbeam (9). The lower end of the hydraulic cylinder push rod (11) is fixed to the concave mold inlaid support crossbeam (7). The electromagnetic force drives the movable crossbeam (4), the high temperature resistant plate pressing bearing crossbeam (6) and the concave mold inlaid bearing crossbeam (7) to slide through the crossbeam guide left guide post (3) and the crossbeam guide right guide post (13), and are connected by the left elastic pressing return spring (5) and the right elastic pressing return spring (18). The bottom bearing worktable (2) is provided with an electromagnetic coil support base (20) and an electromagnetic coil (21). The high-temperature resistant plate is pressed into the bearing beam (6) with a circular groove in the middle. The plate heating coil (26) is installed in the groove to preheat the plate in situ. The bearing beam (7) is installed in the concave mold to press the upper plate (14). The punch guide sleeve (16) is fixed below the high temperature resistant plate pressing bearing beam (6), and the punch (19) is fixed on the electromagnetic force driven movable beam (4) and slides along the punch guide sleeve (16); the self-punching riveting forming die positioning base (24) is installed in the dovetail groove below the die mounting bearing beam (7), and a stepped hole is provided in the middle of the self-punching riveting forming die positioning base (24) for installing the die (25). The electromagnetic coil (21) generates electromagnetic force when energized, driving the movable crossbeam (4) to move upward. This electromagnetic force is transmitted to the high-temperature plate pressing bearing crossbeam (6) through the left elastic pressing return spring (5) and the right elastic pressing return spring (18), so that the pressing load and the riveting of the punch (19) are completed synchronously by the same electromagnetic power source, driving the self-piercing riveting rivet (17) set on the upper surface of the punch (19) to complete the self-piercing riveting, and adjusting the forming load through the current of the electromagnetic coil (21).

2. The self-piercing riveting forming device for metal plates according to claim 1, characterized in that, The self-piercing riveting die positioning base (24) has a front end cover (12) and a rear end cover (22) on its front and rear sides, respectively, and is locked by the front end cover locking nut (8) and the rear end cover locking nut (23) to restrict the self-piercing riveting die positioning base (24) from moving in the front and rear directions.

3. The self-piercing riveting forming device for metal sheets according to claim 1, characterized in that, The punch guide sleeve (16) has a groove inside, which limits the riveting stroke when the punch (19) moves up until the lower surface of the groove is coplanar with the upper surface of the punch (19).

4. A method for self-piercing riveting forming of metal sheets, employing the self-piercing riveting forming apparatus for metal sheets as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Clamping die steps: Insert the self-punching riveting die (25) into the stepped hole of the self-punching riveting die positioning base (24), and insert the positioning base back into the dovetail groove below the die mounting bearing beam (7) and lock it. (2) Lifting and preheating steps: Drive the hydraulic cylinder push rod (11) to move upward and drive the concave mold mounting bearing beam (7) to move upward. Place the cleaned upper plate (14) and lower plate (15) on the upper surface of the high temperature plate pressing bearing beam (6), and preheat the plate in place through the plate heating coil (26). (3) Pressing step: Drive the hydraulic cylinder push rod (11) downward to drive the die insert bearing beam (7) downward and press the upper plate (14). Continue to press down so that the upper plate (14), the lower plate (15) and the high temperature plate pressing bearing beam (6) move down together, compressing the left elastic pressing return spring (5) and the right elastic pressing return spring (18). (4) Electromagnetic riveting steps: Powering the electromagnetic coil (21) causes the electromagnetic force to drive the movable crossbeam (4) to move upward along the guide post and compress the spring, so that the high-temperature plate presses the bearing crossbeam (6) and clamps the plate with the die-mounted bearing crossbeam (7) through the upward load of the spring. At the same time, the movable crossbeam drives the punch (19) to move upward quickly, pushing the rivet to pierce the lower plate (15) and causing the legs to expand radially and embed into the upper plate (14) under the constraint of the die (25). The head presses the lower surface of the lower plate (15) and the forming load is adjusted by the magnitude of the current of the electromagnetic coil (21). (5) Reset and take out the parts: the power is cut off so that the electromagnetic force disappears, the movable crossbeam is reset under the spring force, and the hydraulic cylinder push rod (11) moves up to take out the riveted and formed components.

5. The self-piercing riveting forming method for metal plates according to claim 4, characterized in that, In the lifting and preheating step, the upper plate (14) and the lower plate (15) are preheated for 5 to 10 minutes by the plate heating coil (26).

6. The self-piercing riveting forming method for metal plates according to claim 4, characterized in that, After the clamping step and before the electromagnetic riveting step, the hydraulic cylinder (10) descends to the point where the upper surface of the punch (19) is coplanar with the lower surface of the groove inside the punch guide sleeve (16), and the position of the die-mounted bearing beam (7) is recorded. Then, the rivet is placed on the upper surface of the punch (19).

7. The self-piercing riveting forming method for metal plates according to claim 4, characterized in that, In the electromagnetic riveting step, the forming load is adjusted by adjusting the current of the electromagnetic coil (21).

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