A non-marking resistance spot welding electrode pair and welding method

Abstract

This invention discloses a non-marking resistance spot welding electrode pair and welding method, applicable to welding scenarios with high surface quality requirements, such as automotive exterior parts, curved rail transit components, and precision electronic components. The electrode pair consists of a flat electrode on one side and a curved electrode on the other. The flat electrode's end face is a smooth plane, which increases the contact area and reduces pressure, achieving a non-marking weld surface without obvious indentations or burns. However, the flat electrode tends to disperse current, leading to insufficient heat input and a small weld nugget. The curved electrode uses a spherical surface with a specific curvature or an end face with concentric convex rings, which effectively concentrates the current, increases the local current density, compensates for the current diffusion problem of the flat electrode, and ensures the weld nugget size and joint strength. The two work together to optimize the current and heat field distribution, achieving non-marking welding on one side while meeting the weld nugget quality requirements. This structure is simple, requires no complex additional devices, and is suitable for easily marked materials such as coated plates and aluminum alloys, showing promising industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of welding, specifically relating to a non-marking resistance spot welding electrode pair and welding method, which is particularly suitable for welding applications with high requirements for workpiece surface quality, such as the connection of automotive exterior parts, curved roof plates of rail transit vehicles, and precision electronic components. Background Technology

[0002] Resistance spot welding, as a highly efficient and automated joining process, is widely used in automotive manufacturing, rail transportation, and electronic component assembly. However, traditional spot welding technology has significant limitations: when no visible weld marks are required on one side of the workpiece (such as exterior parts, coated plates, or curved structures), conventional electrodes struggle to balance surface quality and weld strength. While using dual-planar electrodes can reduce indentation, the dispersed current density leads to insufficient heat input, substandard weld nugget size (typically requiring a weld nugget diameter of at least 5mm), and reduced joint strength. Convex electrodes, although concentrating the current, are prone to leaving excessively deep indentations or burns on the workpiece surface, affecting aesthetics and corrosion resistance.

[0003] Patent CN205520139U discloses a non-marking spot welding electrode cap, which features a flat surface at the end of the upper or lower electrode cap's ball, increasing the contact area between the electrode cap and the workpiece and resulting in a smooth weld surface. Patent CN202367342U discloses a non-marking spot welding electrode system consisting of a fixed electrode and a movable electrode. The fixed electrode is made of plate-shaped chromium-zirconium copper material and is mounted on a bracket via elastic connectors. Marking reduction is achieved through material selection and flexible mounting. The chromium-zirconium copper plate provides high conductivity and wear resistance, and the plate-shaped design increases the contact area. The elastic connectors compensate for positional deviations, ensuring tight contact between the electrode and the workpiece and avoiding marks caused by poor contact. However, this method is unusable when the weld overlap is small.

[0004] Therefore, there is an urgent need to develop an electrode pair and welding method that is simple in structure and can synergistically optimize current distribution and pressure distribution. Summary of the Invention

[0005] The purpose of this invention is to provide a non-marking resistance spot welding electrode pair and welding method to solve the contradiction in the prior art of achieving non-marking welding on one side of a workpiece while simultaneously ensuring the weld nugget size meets the requirements. Specifically, it aims to overcome the dual defects of traditional double-plane electrodes, which can reduce indentation but lead to current dispersion and insufficient weld nugget, and traditional convex electrodes, which can concentrate current but are prone to leaving excessively deep indentations or burns on the workpiece surface, thereby achieving the dual goals of non-marking welding on one side of the workpiece and meeting the weld nugget size requirements.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A non-marking resistance spot welding electrode pair is characterized by comprising a flat electrode and an arc-shaped electrode. Through the synergistic cooperation of their end face structures, the current lines are concentrated while reducing the non-marking side pressure of the workpiece, thus optimizing the thermal field distribution.

[0008] The electrode pair consists of a flat electrode and an arc-shaped electrode. The welding end face of the flat electrode is a smooth plane, and its diameter must meet specific geometric requirements to ensure pressure dispersion and reduce indentation when in contact with the non-marking side of the workpiece. The welding end face of the arc-shaped electrode is a spherical surface with a radius of curvature within a certain range (e.g., 40–100 mm). The raised structure concentrates the current, compensating for the current diffusion effect caused by the flat electrode. The diameter D of the flat electrode end face and the radius of curvature R of the arc-shaped electrode must meet proportional constraints to balance pressure distribution and current density. High-performance alloys such as chromium-zirconium-copper can be selected as electrode materials to ensure conductivity and wear resistance.

[0009] The diameter D of the welding end face of the flat electrode satisfies: D≥8.5√t (where t is the plate thickness).

[0010] The radius of curvature R of the arc-shaped electrode satisfies: 40mm≤R≤100mm.

[0011] The arc-shaped electrode welding end face can be a smooth sphere or the welding end face has a concentric convex ring with a height of h, and the height h of the convex ring and the radius of curvature R of the arc surface satisfy: h = R / 500.

[0012] The relationship between the diameter D of the flat electrode end face and the radius of curvature R of the arc electrode is: D ≥ R / 5.

[0013] This invention achieves a significant improvement in welding quality and efficiency through the complementary design of flat and curved electrode end face morphologies. The flat electrode, with its large contact surface, effectively disperses pressure, preventing indentations or burrs on the coated material surface and ensuring a smooth, unmarked weld joint. Simultaneously, the curved electrode, with its convex end face, focuses the current lines, compensating for current diffusion caused by the flat electrode, ensuring sufficient heat input, and maintaining a stable weld nugget diameter that meets standard requirements (e.g., ≥5mm). This electrode combination has a simple structure, requires no additional complex devices, and has excellent process adaptability. It is particularly suitable for high-quality welding of automotive exterior parts, curved roof panels for rail transit, and precision electronic components. It also demonstrates outstanding advantages in joining coated materials with easily marked materials such as aluminum alloys, and has broad industrial application prospects.

[0014] Furthermore, in some embodiments, the diameter of the welding end face satisfies D≥8.5√t, and the radius of curvature of the arc electrode welding end face is 40mm-100mm, where t is the thickness of the thinnest plate in the aluminum alloy plate being welded.

[0015] Furthermore, in some embodiments, the diameter of the welding end face is 8mm-20mm.

[0016] According to another aspect of the present invention, a welding method is provided, which uses the non-marking resistance welding electrode provided in any of the foregoing embodiments to perform aluminum alloy welding.

[0017] During welding, the workpiece is placed between a flat electrode and a curved electrode, with the flat electrode contacting the non-marking side and the curved electrode contacting the other side. Pressure is applied and current is supplied through the welding clamp. The low pressure on the flat electrode side avoids surface damage, while the high current density on the curved electrode side ensures sufficient weld nugget growth. Key process parameters (such as current, time, and pressure) need to be controlled in a coordinated manner, for example, by using a multi-pulse energizing mode to suppress spatter and stabilize the weld nugget size.

[0018] Furthermore, in some embodiments, the diameter D of the flat electrode welding end face satisfies D≥8.5√t, where t is the thickness of the thinnest plate in the aluminum alloy plate being welded; the electrode pressure used during welding is 2kN-6kN.

[0019] Furthermore, in some embodiments, the aluminum alloy plate being welded is configured as a 6-series aluminum alloy.

[0020] Furthermore, in some embodiments, the welding current is 18kA-45kA, and the welding time is 60ms-200ms.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) An asymmetrical configuration of "flat electrode + curved electrode" is adopted. The flat electrode side achieves "physical non-marking" by dispersing pressure through large-area contact, while the curved electrode side achieves "electrical compensation" through a protruding structure limited by the radius of curvature. The two work together to solve the technical contradiction that "non-marking" and "full core" are mutually exclusive.

[0023] 2) The coupling relationship between the diameter D of the flat electrode end face and the radius of curvature R of the arc electrode is proposed (D ≥ R / 5), and the plate thickness t is introduced to constrain the diameter of the flat electrode end face (D ≥ 8.5√t), so that the electrode design is upgraded from empirical qualitative to parameter quantitative, ensuring that the optimized current field and stress field distribution can be obtained under different plate thickness conditions.

[0024] 3) A concentric convex ring structure is introduced on the arc electrode, and a quantitative relationship between the height h of the convex ring and the radius of curvature R is established (h = R / 500). Based on the traditional spherical focusing, the local current density is further enhanced. At the same time, the indentation is avoided by precise size control, which reflects the refined design concept of micro-morphology control.

[0025] In summary, achieving an asymmetric current density distribution during welding—with a higher current density on the curved electrode side than on the flat electrode side—ensures preferential nucleation and growth of the weld nugget on the curved electrode side while avoiding surface burns caused by current concentration on the flat electrode side. The electrode structure is simple, requiring no additional complex devices or control systems, and can be directly applied to existing resistance spot welding equipment, demonstrating promising industrial application prospects and economic benefits. It is particularly suitable for coated plates and aluminum alloys prone to weld marks. Through synergistic control of the current and stress fields, problems such as coating damage and surface oxide film damage can be effectively avoided, expanding the application range of resistance spot welding in fields requiring high surface quality. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the flat electrode structure in Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the arc-shaped electrode in Embodiment 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the indentation morphology of the weld joint surface after welding using the electrode of the present invention in Example 1, wherein (a) is a macroscopic morphology diagram of the weld joint surface of the electrode of the present invention, (b) is a height distribution diagram of the part within the red frame in (a), and (c) is a line graph of the height distribution of the part within the red line in (b).

[0029] Figure 4 This is a schematic diagram simulating the current distribution across the weld nugget cross section in Example 1;

[0030] Figure 5 This is a schematic diagram of the deformation simulation structure of the weld nugget section in Example 1;

[0031] Figure 6 This is a schematic diagram of the welding electrode structure using a traditional symmetrical arc surface electrode pair in Comparative Example 1.

[0032] Figure 7 The diagram shows the indentation morphology of the weld joint surface after welding using a conventional symmetrical arc surface electrode in Comparative Example 1. (a) is a macroscopic morphology diagram of the weld joint surface of the electrode of the present invention, (b) is a height distribution diagram of the part within the red frame in (a), and (c) is a line graph showing the height distribution of the part within the red line in (b).

[0033] Figure 8 This is a schematic diagram simulating the current distribution across the weld nugget cross-section using a conventional symmetrical arc-shaped electrode pair in Comparative Example 1.

[0034] Figure 9 This is a schematic diagram simulating the deformation of the weld nugget cross section using a traditional symmetrical arc-shaped electrode pair in Comparative Example 1;

[0035] Figure 10This is a schematic diagram of the welding electrode structure using a large radius of curvature symmetrical arc surface electrode pair in Comparative Example 2.

[0036] Figure 11 The diagram shows the indentation morphology of the weld joint surface after welding using a large radius of curvature symmetrical arc surface electrode in Comparative Example 2. (a) is a macroscopic morphology diagram of the weld joint surface of the electrode of the present invention, (b) is a height distribution diagram of the part with red frame in (a), and (c) is a line graph of the height distribution of the part with red line in (b).

[0037] Figure 12 This is a schematic diagram simulating the current distribution across the weld nugget cross-section of a large-radius symmetrical arc-shaped electrode pair used in Comparative Example 2.

[0038] Figure 13 This is a schematic diagram simulating the deformation of the weld nugget section in Comparative Example 2 using a large radius of curvature symmetrical arc surface electrode pair;

[0039] Figure 14 This is a schematic diagram of the welding apparatus used in an embodiment of the present invention.

[0040] Meaning of the reference numerals in the attached figures:

[0041] 1-Electrode body; 2-Flat electrode welding end face; 3-Curved electrode welding end face; 4-Electrode side; 5-Upper electrode; 6-Lower electrode; 7-Upper plate; 8-Lower plate; 9-Weld nugget; 10-Cold water pipe. Detailed Implementation

[0042] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the accompanying drawings are schematic diagrams, and therefore the apparatus and device of the present invention are not limited to the size or scale of the schematic diagrams.

[0043] Example 1

[0044] In Example 1, the structure of the welding electrode pair is as follows: Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of a flat electrode structure, including an electrode body 1. The top of the electrode body 1 is a flat electrode welding end face 2, which is a smooth circular plane. Figure 2This is a schematic diagram of an arc-shaped electrode structure, including an electrode body 1, a flat electrode welding end face 2, and an arc-shaped electrode welding end face 3 connecting the electrode body 1 and the flat electrode welding end face 2. The arc-shaped electrode welding end face 3 is an arc surface or a conical surface, and the flat electrode welding end face 2 is a smooth spherical surface. During welding, the flat electrode welding end face 2 is the part of the electrode body 1 that contacts the aluminum alloy material being welded. The radius of curvature R of the flat electrode welding end face 2 is 40 mm. In a further preferred embodiment, the welding electrode also satisfies the following: the diameter of the flat electrode welding end face 2 satisfies D ≥ 8.5√t (where t is the thickness of the thinnest plate in the aluminum alloy sheet being welded), specifically 8 mm-20 mm (i.e., the circular diameter of the flat electrode welding end face 2 is 8 mm-20 mm). Furthermore, the diameter D of the flat electrode welding end face 2 satisfies D ≥ R / 5. The electrode uses a chromium-zirconium-copper electrode, and the welding parameters are: electrode pressure 4.0 kN, welding time 100 ms, and welding current 30 kA. The welded workpiece uses 1.5mm thick 6016 wrought aluminum alloy.

[0045] Adopting such Figure 14 The welding apparatus shown places the workpiece to be welded between a flat electrode and an arc-shaped electrode, with the flat electrode contacting the non-marked side of the workpiece (i.e., the side requiring a flat surface) and the arc-shaped electrode contacting the other side; an electrode pressure of 4.0 kN is applied through the welding clamp to clamp the workpiece between the two electrodes; welding is performed by energizing with a welding current of 30 kA and a welding time of 100 ms (using a single-pulse energizing mode); the current flowing through the workpiece generates resistance heat to form a weld nugget 9.

[0046] After welding, the surface morphology of the weld point is shown in Figure 3. Using a white light interferometer, it can be seen that the indentation depth of the electrode welding surface is 14 μm, and the indentation is slightly convex (i.e., the electrode contact area is slightly higher than the surrounding base material). Figure 4 This is a schematic diagram simulating the welding nugget cross-section current in Example 1. As can be seen from the figure, the current density on the flat electrode side is relatively dispersed, while the current concentration is present on the arc electrode side. Figure 5 This is a schematic diagram of the deformation simulation of the weld nugget section in Example 1. As can be seen from the figure, there is almost no deformation on the flat electrode side.

[0047] Example 2:

[0048] This embodiment is basically the same as Embodiment 1, except that the arc electrode welding end face 3 adopts a concentric convex ring structure. The height h of the convex ring and the radius of curvature R satisfy h=R / 500, that is, h=0.08mm (when R=40mm), and there are 3 convex rings, which are evenly distributed.

[0049] The welding parameters and other conditions remained the same as in Example 1.

[0050] Welding results:

[0051] Surface quality: The indentation depth on the flat electrode side is about 12 μm, and it still has a slightly convex shape. The surface quality is better than that of Example 1.

[0052] The size of the melt core is 5.5 mm, which is an increase compared to Example 1, indicating that the convex ring structure further enhances the current focusing effect.

[0053] Current distribution: Simulations show that a local current density peak (approximately 380 A / mm²) appears at the tip of the convex ring, which is conducive to the preferential nucleation of the melt nucleus at the contact point of the convex ring and its expansion to the surrounding area.

[0054] Example 3:

[0055] This embodiment examines the effect of the radius of curvature R of the arc-shaped electrode. The same materials and methods as in Example 1 are used, but the value of R is changed. Three sets of experiments are set up with R=60mm, R=80mm and R=100mm. The diameter D of the flat electrode is adjusted accordingly to satisfy D≥R / 5.

[0056] Group R(mm) D(mm) Indentation depth (μm) Melt core diameter (mm) Deformation amount (μm) 3-1 60 14 16 5.3 32 3-2 80 16 18 5.1 35 3-3 100 20 20 4.9 38

[0057] The results show that within the range of R=40-100mm, the indentation depth can be ≤20μm and the melt nugget diameter can be ≥4.9mm. Among them, the smaller R is more effective in current focusing and the melt nugget size is slightly larger; the larger R is more effective in pressure on the flat electrode side and the indentation is shallower. When R exceeds 100mm (see Comparative Example 2), the current focusing effect weakens and the risk of the melt nugget diameter decreasing to the point of not meeting the standard increases.

[0058] Example 4

[0059] This embodiment examines the adaptability under different plate thicknesses. 6016 aluminum alloy was used, with plate thicknesses set to 1.0 mm, 2.0 mm, and 3.0 mm, respectively. Electrode parameters were designed based on D≥8.5√t and D≥R / 5, and welding parameters were optimized and adjusted according to the plate thickness.

[0060] Plate thickness (mm) R(mm) D(mm) Pressure (kN) Current (kA) Time (ms) Indentation (μm) Melting nugget (mm) 1.0 40 10 2.5 22 80 10 4.5 2.0 60 14 4.5 32 120 18 5.4 3.0 80 18 6.0 42 180 25 6.1

[0061] Experimental results show that, under different plate thicknesses, by reasonably matching electrode parameters and welding processes, the dual goals of single-sided non-marking (indentation depth ≤ 25 μm) and weld nugget size meeting the standard (weld nugget diameter ≥ 4.5√t) can be achieved.

[0062] Comparative Example 1:

[0063] The electrode pair uses traditional arc-shaped symmetrical electrodes, meaning the upper and lower electrodes have the same parameters and specifications, such as... Figure 6As shown in Figure 7, the electrode curvature radius is 100 mm, and the electrode end diameter also satisfies D ≥ 8.5√t (where t is the thickness of the thinnest plate in the aluminum alloy being welded). The electrode material is also chromium-zirconium copper, and the welding parameters are also 4.0 kN electrode pressure, 100 ms welding time, and 30 kA welding current. The workpiece used for welding is 1.5 mm thick 6016 wrought aluminum alloy. After welding, the surface morphology of the weld point is shown in Figure 7. It can be seen that the surface indentation of the weld point has both upward convex and downward concave parts, with the upward convex height being about 17 μm and the downward concave depth being about 84 μm. Figure 8 The figure shows a simulation diagram of the welding nugget cross-section current in Comparative Example 1. As can be seen from the figure, there is current concentration on both sides of the upper and lower electrodes. Figure 9 The figure shows a schematic diagram of the deformation of the weld nugget section in Comparative Example 1. As can be seen from the figure, there is deformation on both sides of the upper and lower electrodes, and the deformation is about 144 μm. The workpiece is severely warped as a whole.

[0064] Comparative Example 2

[0065] In Comparative Example 2, the electrode pair used as follows Figure 10 The arc-shaped symmetrical electrode shown has identical parameters for both the upper and lower electrodes. The electrode radius of curvature is 300 mm, and the electrode end diameter also satisfies D ≥ 8.5√t (where t is the thickness of the thinnest plate in the aluminum alloy being welded). The electrode material is also chromium-zirconium copper, and the welding parameters are the same: electrode pressure 4.0 kN, welding time 100 ms, and welding current 30 kA. The workpiece used is a 1.5 mm thick 6016 wrought aluminum alloy. After welding, the surface morphology of the weld point is shown in Figure 11. It can be seen that the surface indentation of the weld point has both upward-protruding and downward-recessed parts, with the upward protrusion reaching a height of approximately 12 μm and the downward recess reaching a depth of approximately 40 μm. Figure 12 The figure shows a simulation diagram of the welding nugget cross-section current in Comparative Example 2. As can be seen from the figure, the current concentration on both sides of the upper and lower electrodes is significantly reduced. Figure 13 The figure shows a schematic diagram of the deformation of the weld nugget cross section in Comparative Example 2. As can be seen from the figure, there is deformation on both sides of the upper and lower electrodes, and the amount of deformation is about 103 μm. Although it is smaller than that in Comparative Example 1, it still affects the surface quality.

[0066] Comparative Example 3:

[0067] This comparative example uses a double-plane electrode pair, meaning both the upper and lower electrodes are flat electrodes with an end face diameter D = 16 mm, and the material is chromium-zirconium copper. The welding parameters are the same as in Example 1.

[0068] Welding results:

[0069] Surface quality: The indentation on the flat electrode side is extremely shallow (about 8μm), with excellent surface quality that meets the requirements for a mark-free surface.

[0070] The weld nugget size is only 3.8 mm in diameter, which is far below the standard requirement. Tensile tests show that the failure load is only 2.5 kN, indicating that the joint strength is seriously insufficient.

[0071] Current distribution: Simulation shows that the current density is dispersed on both the upper and lower electrode sides, with a peak value of only 120A / mm². Insufficient heat input leads to incomplete growth of the melt nucleus.

[0072] The above comparison results fully demonstrate that only by adopting the asymmetrical configuration of "flat electrode + arc surface electrode" as described in this invention and meeting the corresponding geometric parameter constraints can the technical effects of achieving a scratch-free surface on one side of the workpiece and meeting the weld nugget size requirements be simultaneously realized. Simply increasing the radius of curvature of the arc surface electrode (Comparative Example 2) can reduce indentation, but it will lead to current dispersion and insufficient weld nugget; simply using double flat electrodes (Comparative Example 3) can achieve scratch-free results, but the weld nugget is severely insufficient; and the traditional symmetrical arc surface electrode (Comparative Example 1) causes indentation on both sides.

[0073] Another embodiment of the present invention provides a welding method for welding aluminum alloys using the welding electrode provided in the above embodiments. Both the embodiments and comparative examples of the present invention employ this welding method in welding experiments. A schematic diagram of the welding process is shown below. Figure 14 As shown, in a preferred embodiment, the diameter D of the flat electrode welding end face 2 is ≥ 8.5√t (where t is the thickness of the thinnest plate in the aluminum alloy sheet being welded); the electrode pressure used during welding is 2kN-6kN. This welding method is particularly suitable for welding wrought aluminum alloys. In a further preferred embodiment, the welding current is 18kA-45kA, and the welding time is 60ms-200ms.

[0074] As can be seen from the detailed descriptions of the above embodiments and comparative examples, this invention successfully solves the long-standing technical challenge in the field of resistance spot welding where achieving both "scratchy surface" and "full-size weld nugget" is mutually exclusive through the asymmetrical configuration of flat and curved electrodes and the quantitative constraints of geometric parameters. This technical solution is simple in structure, highly effective, and adaptable to various processes, showing broad application prospects in fields such as automobile manufacturing, rail transportation, and precision electronics.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art will recognize that improvements or modifications can be made based on the above description within the scope of the disclosed concept, such as adjustments to the selection of electrode materials, specific dimensions, and optimization of welding parameters. However, all such improvements or modifications should fall within the protection scope of the appended claims.

Claims

1. A non-marking resistance spot welding electrode pair, characterized in that, include: A flat electrode has a welding end face (2) at its end for contacting the non-marking side of the workpiece. The welding end face (2) is a smooth plane and its diameter D is greater than 8.5√t, where t is the thickness of the thinnest plate in the workpiece to be welded. An arc-shaped electrode has a welding end face (3) at its end for contacting the other side of the workpiece. The welding end face (3) is a convex surface with a radius of curvature R of 40 mm to 100 mm. The diameter D of the welding end face (2) of the flat electrode and the radius of curvature R of the welding end face (3) of the arc electrode satisfy the following relationship: D ≥ R / 5; During welding, the flat welding end face (2) of the flat electrode is in contact with the non-mark side surface of the workpiece, and the convex curved welding end face (3) of the arc electrode is in contact with the other side surface of the workpiece. Through the synergistic cooperation of the two electrode end face structures, the pressure on the non-mark side surface of the workpiece is reduced, and the current lines are concentrated towards the arc electrode side, so as to form a non-mark weld point on one side of the workpiece and obtain a weld nugget (9) with the required size. The arc-shaped electrode welding end face (3) has several concentric convex rings; The height h of the convex ring of the arc electrode welding end face (3) and the radius of curvature R of the arc electrode welding end face (3) satisfy the following relationship: h = R / 500.

2. A welding method using the non-marking resistance spot welding electrode pair as described in claim 1, characterized in that, Includes the following steps: The workpiece to be welded is placed between the flat electrode and the arc electrode, so that the flat welding end face (2) of the flat electrode contacts the non-marked side of the workpiece, and the convex curved welding end face (3) of the arc electrode contacts the other side of the workpiece. Apply pressure to clamp the workpiece between the flat electrode and the arc-shaped electrode; When welding is performed by applying electricity, the current flowing through the workpiece generates resistance heat, forming a weld nugget. The flat electrode disperses pressure through its flat end face, reducing the pressure on the non-marked side of the workpiece. At the same time, the arc-shaped electrode concentrates current through its convex curved end face, making the local current density on the arc-shaped electrode side higher than that on the flat electrode side.

3. The welding method according to claim 2, characterized in that, During the welding process, by controlling the welding current, energizing time and electrode pressure parameters, the current distribution and thermal field morphology are optimized, and the workpiece surface is free of marks on one side and the weld nugget size meets the standard simultaneously.

4. The welding method according to claim 2, characterized in that, The applied electrode pressure is 2kN to 6kN, the welding current is 18kA to 45kA, and the welding time is 60ms to 200m.

5. The welding method according to claim 2, characterized in that, The workpiece material is a coated sheet or an aluminum alloy.

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