Sheet lap joint resistance welding process and multi-sheet group ring lap joint resistance welding process

Abstract

The invention discloses a sheet overlapping resistance welding process. The sheet overlapping resistance welding process comprises the following steps: a, setting the contours of overlapping edges of two adjacent overlapped sheet workpieces to be matched and consistent when the two adjacent overlapped sheet workpieces are blanked; b, the edges of the two sheets are in lap joint with each other and placed on the lower electrode, and it is guaranteed that the lap joint width is consistent; c, after the upper electrode descends and pressurizes, current is conducted, and nuggets are formed between the sheet workpieces; and d, maintaining the pressure until the nugget is completely cured. The upper electrode and the lower electrode completely cover a welded lap joint area, the lap joint area is rapidly heated and gradually melted under the action of electrified large current, and the thickness of the lap joint part is gradually thinned under the action of pressure, so that the lap joint edges of the sheet are completely fused into a whole, and the strength of the sheet is not lower than that of a sheet body. The welding process can be used for welding the sheet-shaped workpieces prepared in a segmented mode into the large annular workpieces, namely the multi-sheet ring assembling lap joint electric resistance welding process, the material cost of the large annular workpieces can be greatly saved through the process, and meanwhile the equipment investment for manufacturing large stamping parts is reduced.

Description

Technical Field

[0001] The present invention relates to a resistance welding process for sheet lap joints, in particular to a resistance welding process for sheet lap joints with reduced thickness of the welded part, and also to a resistance welding process for multi-sheet group ring lap joints with reduced thickness of the welded part. Background Art

[0002] In industrial production, large sheet metal parts are usually required, such as the door ring of an automobile, which is initially a ring-shaped sheet with a hollow interior and can be stamped and processed into a formed door ring including parts such as the A-pillar, B-pillar, and door sill. The hollow sheet of the door ring can be processed by punching with a whole piece of steel, but its low material utilization rate leads to high costs. Usually, in order to save materials, the door ring can be divided into multiple segments for separate material preparation, and then each segment is welded together in sequence to form a sheet-shaped integral door ring, and then subsequent forming processing is carried out.

[0003] Currently, the following solutions are usually adopted for door ring splicing:

[0004] 1. Divide the door ring into n pieces, and use laser non-fill wire butt welding for the first n - 1 connections; a lap margin of 16 mm to 40 mm is reserved in advance at the last connection, and the last connection is welded by resistance spot welding or laser lap welding. This method has low efficiency, complex process which will increase the process cost, the two plate surfaces of the resistance welding lap joint are uneven, the welding quality is unstable, the rejection rate is relatively high, the overall strength of the spot welding lap joint is low, and local detachment is likely to occur during subsequent forming processing and use, affecting the structural strength of the component.

[0005] 2. Enclose the door ring into a ring structure; two adjacent sub-sheet materials overlap by 15 mm to 30 mm and are connected to each other by spot welding, and the number of welding points is at least 4 or more. This method has obvious disadvantages. The two plate surfaces of the resistance welding lap joint are uneven, the overlaps at each weld are not in the same plane, the connection strength of the spot welding lap joint is low, and the strength of the component after welding cannot be guaranteed; because the welding lap width is relatively large, the weld overlap causes a relatively large amount of material waste.

[0006] 3. Place each sheet material with different thicknesses on the workbench in sequence, adjust the height to ensure that the weld end faces of each sheet material with different thicknesses are butt-joined flush, and then use the laser welding process to splice them together in sequence to form a door ring. Its disadvantages are: the laser welding efficiency is not high, and the welding process is more complex; sheet materials with different thicknesses need to be provided with a support part at the bottom to adjust the height, the process is cumbersome and complex, and the adjustment process is inconvenient. If it is not adjusted to be completely coplanar, it will affect the welding quality, the consistency is not high, and the yield rate is relatively low.

[0007] In addition to the above-mentioned spot welding and laser welding, the welding processes for splicing or overlapping two adjacent sheets together include projection welding and seam welding. Projection welding generally welds the surfaces between two workpieces to make them butt-joined, such as fixing a nut to a metal plate. This process requires the surface of the metal component to be pre-set / processed to form a continuous or intermittent raised line before resistance welding can be performed to melt the raised line / intermittent point, thereby completing the welding process. The workpiece body after welding does not melt, and the two sheets have a misalignment in the thickness direction after overlap welding, which cannot achieve the effect of the two workpieces being on the same side after welding. If spot welding overlaps, point connections can be formed in the local area where the current passes, but the connection strength of the welding is low, the processing efficiency is low, and the thickness direction misalignment between the workpieces is different. Seam welding: Two pairs of roller electrode wheels are used to clamp the two sheet workpieces stacked up and down and energize them, and the workpieces are gradually pushed forward to implement resistance welding of a continuous extension line trajectory, which can achieve welding connection on the overlapping edges. However, it has obvious disadvantages. The workpiece needs to be slowly advanced during the welding process, resulting in low welding efficiency. The structure of the welding electrode is complex, the welding position is easily deformed, a large overlap width needs to be reserved, and deep fusion in the thickness direction cannot be achieved, making it difficult to eliminate the misalignment in the thickness direction. Summary of the invention

[0008] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a sheet lap resistance welding process that can reduce the thickness of the welded part and ensure the welding strength for subsequent stamping and bending forming. The present invention also provides a multi-sheet ring lap resistance welding process that can reduce the thickness of the welded part and form an integral hollow ring sheet.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a sheet overlap resistance welding process, which includes the following steps: a. When cutting two adjacent overlapping sheet workpieces, the contours of their overlapping edges are set to match each other; b. The edges of the two sheets to be welded are overlapped and placed on the lower electrode, and the overlapping widths of the two sheets at various locations on the edges are ensured to be consistent; c. The upper electrode completely covers and presses the overlapping edge downward to apply pressure, and then sufficient current is passed between the upper and lower electrodes, and the overlapping area of the two sheet workpieces is melted by resistance heat to form a molten core; d. During the melting process of the overlapping area, the upper electrode maintains pressure so that the sheet on the upper side continues to move downward, and the overlapping widths at various locations on the edges of the overlapping workpieces remain the same until the molten core is completely solidified to complete the welding.

[0010] As an improvement to the technical solution of the sheet lap resistance welding process of the present invention, during the welding process of step d, the sheets are allowed to gradually slide sideways along the lap width direction while keeping the lap width consistent at all locations.

[0011] As an improvement to the technical solution of the sheet lap resistance welding process of the present invention, before completing the welding in step d, pressure needs to be continuously applied to the upper electrode and power supply needs to be maintained until the surfaces on at least one same side of the two sheet workpieces coincide with each other.

[0012] As an improvement to the technical solution of the sheet lap resistance welding process of the present invention, the welding power supply is an intermediate frequency resistance welding power supply or an energy storage resistance welding power supply; the thickness of the two sheet workpieces is 1.2 mm - 2.0 mm; the lap width between the two sheets is 0.5 mm - 2.0 mm, the welding pressure is 150 N / mm 2 above, and the welding current is 2.2 KA / mm 2 above.

[0013] As an improvement to the technical solution of the sheet lap resistance welding process of the present invention, the lap edge contour of adjacent sheets in step a is linear.

[0014] As an improvement to the technical solution of the sheet lap resistance welding process of the present invention, the lap edge contour of adjacent sheets in step a is arc-shaped, and the angle between the tangent at any point on the edge contour to be welded and the line connecting the two ends of the edge contour to be welded is less than 15°.

[0015] To solve the technical problems of the present invention, the specific technical solution adopted is: a multi-sheet group ring lap resistance welding process, surrounding multiple sheets into a ring, using the sheet lap resistance welding process described in the foregoing technical solution, successively welding adjacent sheets with the same lap width to form an integral sheet with no misalignment in the thickness direction, and the length of the lap edge of the sheet is less than 700 mm.

[0016] As an improvement to the technical solution of the multi-sheet group ring lap resistance welding process of the present invention, when overlapping and lapping two adjacent sheets, first hold the two sheets to be welded with their edges to be welded parallel and clamp them in a transfer fixture and transport them to the side of the welding electrode station, lower the first sheet and fix it with the first clamping head of the positioning fixture; move one of the sheets to overlap the edges of the two sheets, lower the second sheet so that the two sheets overlap and the lap width is consistent, and fix the second sheet with the second clamping head of the positioning fixture; synchronously move the two sheets to above the lower electrode by moving the positioning fixture.

[0017] As an improvement to the technical solution of the multi-sheet group ring lap resistance welding process of the present invention, position multiple sheets to be grouped into a ring so that the welding edges are parallel, and use an upper suction cup manipulator to transfer multiple sheets to be grouped into a ring to the welding station; the positioning fixture includes multiple groups of lower suction cups.

[0018] The beneficial effects of the present invention are as follows: In the sheet overlapping resistance welding process, the butt overlapping edges of the two sheet workpieces to be welded are set to have the same contour so that their overlapping contours match and are placed overlapping up and down. The overlapping width is the same everywhere at the welding edge. The upper and lower electrodes completely cover the overlapping part to be welded, and the upper electrode descends to apply pressure to the workpiece. The misaligned overlapping part rapidly heats up due to resistance heat under the action of a large electric current and gradually melts, and a molten effect appears uniformly along the overlapping edge. Under the pressing action of the upper electrode, the thickness of the overlapping part of the sheets gradually thins under the pressure. After the overlapping edges of the two sheets melt and solidify, they are fused together to ensure the welding strength between the two sheets, and the strength is not lower than that of the sheet body itself.

[0019] The above-mentioned sheet overlapping resistance welding process can be used to quickly weld the segmented prepared sheet workpieces end to end to form a ring-shaped workpiece, obtaining a multi-sheet group ring overlapping resistance welding process. This process can greatly save the material cost of large ring-shaped parts and reduce the equipment investment for manufacturing large stamping parts at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1a 、 Figure 1b 、 Figure 1c 、 Figure 1d 、 Figure 1e FIGS. 18-22 are schematic structural diagrams of five states of the overlapping welding change process of two sheet workpieces with the same thickness in a sheet overlapping resistance welding process of the present invention.

[0021] Figure 2a 、 Figure 2b FIGS. 24-25 are schematic structural diagrams of two states of the overlapping welding change process of two sheet workpieces with different thicknesses in a sheet overlapping resistance welding process of the present invention.

[0022] Figure 3 FIG. 27 is a schematic structural diagram of the sectionalized structure of a door ring in a door ring welding embodiment of a multi-sheet group ring overlapping resistance welding process of the present invention.

[0023] Figure 4 FIG. 31 is a planar structural diagram of the vertical projection of the sectionalized door ring and the electrode.

[0024] Figure 5 FIG. 35 is a planar state structural diagram of a transfer fixture clamping each sectionalized part of the door ring.

[0025] Figure 6 is Figure 5 a schematic three-dimensional state structural diagram of the transfer fixture clamping each sectionalized part of the door ring shown in FIG.

[0026] Figure 7 a schematic diagram of the shape of the arc-shaped contour of the welding edge. DETAILED DESCRIPTION OF THE INVENTION

[0027] The specific implementation manners of the present invention will be further described below in conjunction with the accompanying drawings.

[0028] As Figures 1a to 1e , Figure 2a , Figure 2b shown, a sheet overlapping resistance welding process of the present invention includes the following steps:

[0029] a. During blanking, the overlapping edges of two sheet workpieces 12 that need to be overlapped and welded adjacent to each other are processed into the same matching profiles; the profiles are linear or arc-shaped, and it should be ensured that the overlapping width consistency between the two workpieces is not significantly affected when the workpieces move in the direction perpendicular to the edges. For example, when the workpieces move outward and the overlapping width is halved, the overlapping widths at various places can remain consistent, so that the overlapping width consistency can still be maintained when side-slip and offset occur during the welding process, that is, the current density can reach basically the same at the welding part / overlapping edge, so as to maintain the same welding effect at various places.

[0030] The arc-shaped edge profile of the welding edge refers to a slowly changing and smooth edge. As Figure 7 shown, it can be defined that the included angle α between the tangent line at any point on the profile of the edge to be welded and the connecting line at both ends of the welding edge profile is less than 15°, preferably less than 10°, and the smaller the included angle, the better. It is better to choose a linear edge profile for the welding edge, so that it will not shift in a direction not perpendicular to the profile edge, thus better maintaining the consistency of the edge overlapping width.

[0031] b. Place the edges of the two sheets to be welded on the lower electrode 18 in an overlapping manner, as Figure 1a shown, and ensure that the overlapping widths of the two sheets are consistent at each edge; the overlapping width refers to the size of the overlapping part between the upper and lower sheet workpieces 12 in the direction perpendicular to the edge. Different overlapping widths will cause differences in the local welding effects of the workpieces, resulting in poor welding. To ensure the consistency of the welding effect and the yield rate of the product, it is necessary to accurately ensure the overlapping width when the workpieces are overlapped.

[0032] c. The upper electrode 16 completely covers and presses down on the overlapping edge to apply synchronous pressure to all parts of the welding edge, and then pass a sufficient current between the upper and lower electrodes. As Figure 1b , Figure 1c , Figure 1d shown, discharge in the overlapping area between the two sheet workpieces 12 and use the resistance heat to melt and form a fusion core; make the overlapping area of the sheet workpieces 12 partially molten and can be pushed forward and further melted under the action of pressure. The larger the overlapping width, the greater the current required to be applied, and the larger the edge width size available for side-slip. On the contrary, the smaller the overlapping width, the smaller the current required to be digested, and the smaller the corresponding size available for side-slip.

[0033] d. During the melting process in the lap joint area, the upper electrode maintains pressure, causing the sheet workpiece on the upper side to move downward continuously, and keeping the lap width the same at each edge of the lapped workpieces until the fusion core is completely solidified, so that the current density is the same at each edge of the welded lap joint, thus ensuring a consistent welding effect and completing the welding. As shown in Figure 1e shown.

[0034] Based on the above welding process steps, as shown in Figures 1a to 1e shown, in the welding process of edge lap welding of two sheet workpieces 12, when blanking, the butt lap joint parts of the two sheet workpieces 12 are set to have the same contour so that their lap contours match and are placed overlapping up and down. The lap width is the same at each welding edge. The upper and lower electrodes 16 / 18 completely cover the welded lap joint area, and the upper electrode descends to apply pressure to the workpiece. The overlapped area with misalignment overlaps and rapidly heats up and gradually melts due to the resistance heat under the action of a large current, and a molten effect appears uniformly along the lap edge. Under the pressing action of the upper electrode 16, the thickness of the overlapped part of the sheet is continuously thinned, so that the thickness of the welded part can be thinned. After the molten and solidified parts at the lap edges of the two sheets are completely fused together, the welding strength between the two sheet workpieces 12 is ensured, and its strength is not lower than that of the sheet body. The existing projection welding process only forms a fusion core for melting and welding at the projection points, with less energy required. The lap welding process of the present invention is a surface lap overlapping welding process, which requires a larger welding current, and the cross-sectional area of the welding electrode is larger, enabling it to pass a large current, and the strength of the welded workpiece is higher.

[0035] Compared with seam welding and projection welding, the lap welding process is the overall simultaneous welding of the lap joint area, requiring a relatively large welding pressure. When welding high-strength workpieces, a gantry can be used to ensure the pressure intensity of the welding pressure. This lap welding process can greatly shorten the time cycle for welding a long strip edge seam. For a product that requires welding multiple long strip edge seams for a finished product, its welding cycle is significantly reduced, and it can quickly complete the edge-to-edge lap work between workpieces with a higher connection strength at the welding part, which is convenient for subsequent stamping forming processing without loosening or cracking at the welded connection position. After lap welding, the thickness of one sheet workpiece is melted, so that it is easier to bend and deform during subsequent stamping forming processing, and the bending amount is reduced due to the reduced thickness, and the stress concentration phenomenon is weakened, and it is also easier to achieve subsequent annealing if necessary.

[0036] Among them, during the welding process of step d, as shown in Figure 1c , Figure 1dAs shown, it is allowed that the sheets gradually generate lateral sliding offset in the lateral direction along the overlapping width direction and keep the overlapping width consistent everywhere. In fact, during welding, under the action of pressure, the workpiece will generate a small lateral sliding displacement, that is to say, the overlapping width at the overlapping part of the welding edge will be reduced equally, and the overlapping width at each place after reduction will continue to be consistent, so as to continue to have the same current density passing through the welding part and ensure the welding consistency. Among them, the total lateral sliding amplitude is less than 0.6 times of the initial overlapping width, and generally a better fusion part can be formed, thus ensuring the welding firmness. It is possible to set that at least one side of the positioning fixture has a small lateral buffer and yielding distance, so that the workpiece can move laterally during the welding process. During the welding process, usually the sheet on the lower side can be clamped to prevent sliding and completely positioned, so that the small displacement of the workpiece only occurs on the sheet on the upper side.

[0037] In addition, before completing the welding in step d, it is necessary to continuously apply pressure to the upper electrode and keep it energized until at least one same-side surface of the two sheet workpieces coincides with each other, as Figures 2a to 2b shown, that is, in the thickness direction of the welding part, the thickness equivalent of the overlap of one of the sheets should be completely eliminated. For example, if the thinner sheet is on the upper side, usually the upper side surfaces of the two sheet workpieces 12 finally coincide, and the welding part is completely fused together, which can quickly fuse and solidify to complete the welding at one time, and can also obtain the butt welding effect without misalignment in the thickness direction, rather than the usual lap joint with a slight contact welding effect of thickness superposition, so as to obtain a welded product with better integrity. Among them, the thicknesses of the two sheet workpieces can be the same or different. After welding two sheets with the same thickness, the upper and lower surfaces coincide; after welding two sheet workpieces with different thicknesses, if the relatively thinner workpiece is on the upper side, the upper surfaces of the two sheet workpieces coincide in the same plane, and vice versa.

[0038] Among them, the welding power supply is an intermediate frequency resistance welding power supply or an energy storage resistance welding power supply, which can quickly release a large-power welding current, so that a molten area can be formed under its action on the lap joint with a certain length and width, and the effect of resistance welding can be achieved.

[0039] Among them, the thickness of at least one of the sheet workpieces 12 is 1.2 mm - 2.0 mm, so that its thickness can at least melt the thickness of one of the sheets during the process of applying current by resistance welding. According to the melting properties of the sheet materials, the overlapping width between the two sheet workpieces 12 is 0.5 mm - 2.0 mm. When welding sheets that are easy to melt and have less lateral sliding, a smaller misaligned overlapping width can be set, so as to save welding energy consumption and ensure that the entire thickness direction of at least one sheet workpiece 12 is melted and fused with the other sheet workpiece 12; the welding pressure is 150 N / mm 2 Above, the welding current is 2.2 KA / mm 2Above, sufficient welding pressure and current density enable it to ensure that the sheets are in contact with each other and can pass sufficient current to quickly form a fusion nucleus, enabling the contact parts of the sheets to be quickly melted at one time, and then reducing the thickness of the sheets at one time to complete the welding.

[0040] The present invention also includes a multi-sheet group ring lap resistance welding process. As Figure 3 shown, multiple sheets are lapped end to end to form a ring, and the sheet lap resistance welding process described in the foregoing technical solution is used to form a state where the edges of adjacent sheets overlap vertically up and down. As Figure 1a shown in the state, an appropriate lap width is obtained, and then referring to Figures 1b to 1e , Figure 2a , Figure 2b shown, after applying welding pressure, welding current is passed through to weld adjacent sheets with the same lap width in sequence, so that after they are melted and welded together, at least one sheet thickness is reduced at the welding part to form an integral sheet without misalignment in the thickness direction. When preparing the sheets, a margin for the sliding of the pressed side during the welding process is reserved in advance at the welding edge, so that it forms a ring before the last edge of the welding is completed, and the overlapping part only has a meltable lap width, and the overlapping edge widths are consistent. Lap resistance welding can be completed for workpiece butt joints by the above process as long as the length of the lap edge of the sheet is less than 700 mm.

[0041] This welding process can be used to complete the welding process of the car door ring. As Figure 3 shown, the door ring is divided into 5 sections for material preparation, and then the two ends of the five door ring workpieces are lapped in sequence to form a ring end to end. The two welding edges of each workpiece are one on top and one at the bottom, or the two ends of some workpieces are both set as the lapped lower edges, and the two ends of the adjacent workpieces are both set as the lapped upper edges, and there must be an odd number of workpieces with the two welding edges being lapped edges one on top and one at the bottom, as Figure 1a shown. As Figure 3 , Figure 4 shown, the complete door ring is divided into B-pillar and patch panel 21, upper side frame 22, A-pillar 23, sill panel 24, B-pillar lower plate 25. After being divided into five door ring workpieces, there will be five weld seams. The above-mentioned sheet lap welding process is used for welding at each weld seam, and welding upper and lower electrodes 16 / 18 are required for welding each weld seam. Each weld seam is sequentially energized and pressurized for resistance welding to melt and weld it. After welding, an integral door ring will be formed. If the thicknesses of each door ring workpiece are equal, the upper and lower sides of the door ring are on the same plane. If the thicknesses of the door ring workpieces are not equal, at least the thickness of the thinner door ring workpiece sheet is reduced so that one side of the two workpieces is on the same plane, thus ensuring that the overall structure of the door ring has high strength.

[0042] The above multi-sheet group ring lap resistance welding process realizes the welding of the door ring, making the process simple and cost-effective. It not only solves the problem of the cumbersome process of using spot welding and laser welding in combination in the past, but also can complete the welding quickly at one time, thus greatly improving the processing efficiency, and can ensure the consistency of the welds. Compared with the way of overlapping spot welding of workpieces, since the overlapping part is fused and the lap width is smaller, reduced to one-fifth to one-tenth of the original, the structural strength of the welded finished workpiece and the material utilization rate of the workpiece are improved. After welding, the door ring is not a structure with double-layer thickness of overlapping lap joints, but one side is guaranteed to be in the same plane, with better integrity and fewer defects, and the structural strength of the welded finished product is higher. When welding sheets with different thicknesses by overlapping each other, the multi-sheet group ring lap resistance welding process can ensure that one side of the door ring after welding is in the same plane without adjusting the height of the supporting parts of sheets with different thicknesses, eliminating the process steps and complex tooling for adjusting the height of the supporting parts, directly eliminating the possibility of incomplete coplanarity, and improving the welding quality and the yield rate of the door ring. This welding process can quickly weld the segmented prepared sheet-shaped workpieces end to end into a ring-shaped workpiece, which can greatly save the material cost of large ring-shaped parts, and at the same time reduce the equipment investment for manufacturing large stamping parts, truly saving workpiece materials, having a fast welding speed, and good strength at the welding position of the workpiece.

[0043] Among them, when overlapping and lapping two adjacent sheets, pre-position the workpieces, and then keep the edges to be welded parallel between the two sheets to be welded first. As Figure 5 , Figure 6 shown, clamp them on the same transfer fixture 31 and transport them to the side of the welding electrode station, which is convenient for ensuring the parallelism of their welding edges to ensure the consistency of the lap width during welding. The transfer fixture 31 moves downward and places the first sheet and fixes it with the first clamping head of the positioning fixture. Before the positioning fixture fixes the sheet workpiece, the clamping head of the transfer fixture 31, usually the magnetic chuck 33, does not release the workpiece, realizing the transfer and precise positioning and clamping of one workpiece; there can be an edge gap between the two sheets during pre-positioning and transportation, which is convenient for setting parallelism. Then move one of the sheets so that the edges of the two sheets overlap, and the moving direction is perpendicular to the welding edge. Usually, the more stable sheet can be moved to ensure the accuracy of the moving position. Then lower the second sheet so that the two sheets overlap and the lap width is the same, and fix the second sheet with the second clamping head of the positioning fixture. Then the corresponding magnetic chuck 33 of the transfer fixture 31 releases the workpiece; move the two sheets synchronously to above the lower electrode by moving the positioning fixture and start the upper electrode to discharge and apply pressure to perform welding. When multiple sheets are overlapped and lapped at the edges, first transfer, position, and clamp the sheet workpiece serving as the lower welding edge. After the clamping is completed, move it between the corresponding upper and lower electrodes 16 / 18. The positions of multiple sets of electrodes are set to match the positions of the welding and fusing edges. Then, without moving the workpiece again, energize and pressurize each set of electrodes one by one to complete the welding.

[0044] Specifically, a plurality of sheets to be grouped into a ring are positioned and arranged such that the corresponding welding edges of the corresponding adjacent sheet workpieces are parallel to each other. As Figure 5 , Figure 6 shown, a manipulator / transfer fixture 31 having an upper magnetic chuck 33 is used to transfer a plurality of sheets to be grouped into a ring to a welding station, complete the pre-positioning of the workpieces, align the welding edges to be machined in parallel, and realize the transfer of the workpieces, providing a pre-guarantee for the consistency of the lap width of the welding edges of the workpieces; the positioning fixture includes a plurality of lower magnetic chucks. Through the pre-fixation of the magnetic chucks, the workpieces can be accurately positioned during the transfer process, without vibrating and deviating in angle or dimension. The magnetic chuck is usually an electromagnetic chuck, which generates magnetic suction force when powered on to suck and position or transfer the workpiece.

[0045] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention.

Claims

1. A sheet lap resistance welding process, characterized in that, The method includes the following steps: a. When cutting two adjacent overlapping sheet workpieces, the outlines of their overlapping edges are set to match exactly; b. The corresponding edges to be welded of the two sheets are overlapped with each other and placed on the lower electrode, and it is ensured that the overlapping widths of the two sheets are the same at each edge; c. The upper electrode completely covers and presses down on the overlapping edge to apply pressure, and then a sufficient current is passed between the upper and lower electrodes. The overlapping area of the two sheet workpieces is melted by resistance heat to form a fusion nucleus; d. During the melting process of the overlapping area, the upper electrode maintains pressure so that the upper sheet follows and continuously moves downward, and the overlapping widths at each edge of the overlapping workpieces are kept the same until the fusion nucleus is completely solidified to complete the welding.

2. The sheet lap resistance welding process according to claim 1, wherein: During the welding process of step d, it is allowed that the sheets gradually slide and shift laterally along the overlapping width direction and the overlapping widths at each place are kept the same.

3. The sheet overlapping resistance welding process according to claim 1, wherein: Before completing the welding in step d, pressure needs to be continuously applied to the upper electrode and power supply needs to be maintained until at least one same-side surface of the two sheet workpieces coincides with each other.

4. The sheet lap resistance welding process according to claim 4, wherein: The welding power source is an intermediate frequency resistance welding power source or an energy storage resistance welding power source; the thickness of the two sheet workpieces is 1.2 mm - 2.0 mm; the lap width between the two sheets is 0.5 mm - 2.0 mm, and the welding pressure is 150 N / mm 2 or more, and the welding current is 2.2 KA / mm 2 or more.

5. The sheet overlapping resistance welding process according to claim 1, characterized in that: In step a, the overlapping edge outline of the adjacent sheets is linear.

6. The sheet lap resistance welding process according to claim 1, characterized in that: In step a, the overlapping edge outline of the adjacent sheets is arc-shaped, and the angle between the tangent line at any point on the edge outline to be welded and the connecting line at both ends of the edge outline to be welded is less than 15°.

7. A multi-sheet group ring lap resistance welding process, characterized in that: Multiple sheets are surrounded into a ring, and the sheet overlapping resistance welding process described in claims 1 to 5 is used. Adjacent sheets are overlapped and welded with the same width in sequence to form an integral sheet without misalignment in the thickness direction, and the length of the overlapping edge of the sheet is less than 700 mm.

8. The multi-sheet group loop lap resistance welding process according to claim 7, characterized in that: When overlapping and joining two adjacent sheets, first, the two sheets to be welded are clamped between the same transfer fixture while keeping the edges to be welded parallel and transported to the side of the welding electrode station. The first sheet is placed down and fixed by the first clamping head of the positioning fixture; One of the sheets is moved so that the edges of the two sheets overlap, the second sheet is placed down so that the two sheets overlap and the overlapping widths are the same, and the second sheet is fixed by the second clamping head of the positioning fixture; The two sheets are synchronously moved to above the lower electrode by moving the positioning fixture.

9. The multi-sheet group lap resistance welding process according to claim 8, characterized in that: Multiple sheets to be grouped into a ring are positioned so that the corresponding adjacent welding edges are parallel to each other, and the multiple sheets to be grouped into a ring are transferred to the welding station by using the upper suction cup manipulator; the positioning fixture includes multiple groups of lower suction cups.

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