An electrode pair for resistance spot welding

Abstract

The application discloses an electrode pair for resistance spot welding and relates to the technical field of resistance spot welding. The electrode pair comprises a first electrode and a second electrode which are structurally identical. The first electrode and the second electrode both comprise a center electrode, a ceramic sleeve and an outer electrode which are sequentially nested from inside to outside. The end of the center electrode close to an electrode contact surface and the end of the ceramic sleeve close to the electrode contact surface are in the same plane. The end of the center electrode away from the electrode contact surface and the end of the outer electrode away from the electrode contact surface are in the same plane. The inner wall height of the outer electrode is equal to the height of the center electrode. The inner wall height of the outer electrode is less than the outer wall height of the outer electrode. The height of the ceramic sleeve is less than the height of the center electrode. The height difference between the inner wall and the outer wall of the outer electrode can improve the heat distribution of the welding interface, improve the reliability of the welding and prolong the service life of the electrode.

Description

Technical Field

[0001] This invention relates to the field of resistance spot welding technology, and in particular to an electrode pair for resistance spot welding. Background Technology

[0002] Resistance spot welding is a welding technique that uses two electrodes pressed together at both ends of the workpieces. Direct current (DC) or alternating current (AC) is applied, and a low voltage with a high current rapidly generates Joule heat, melting the metal and achieving a metallurgical bond. Resistance spot welding offers advantages such as high efficiency, low cost, good connection quality, ease of operation, and simple automation, and has been widely used in the automotive, aerospace, and electronics industries. However, current resistance spot welding techniques suffer from several drawbacks. When welding dissimilar materials or different thicknesses of the same material, the varying heat generation and dissipation due to different materials or thicknesses cause temperature field shifts, resulting in the weld nugget deviating from the workpiece interface. Furthermore, the workpiece, under the combined effects of electrode pressure and thermal stress, can warp and deform, affecting welding accuracy and quality. Additionally, some metals (such as titanium and aluminum) readily react with oxygen or nitrogen in the air at high temperatures, producing brittle hard phases. Moreover, welding dissimilar materials can also generate intermetallic compounds, which are prone to brittle fracture, reducing connection strength and welding reliability.

[0003] To address the aforementioned issues, patent application number 201510638161.8 proposes using different materials for the upper and lower electrodes and incorporating grooves to generate a ring current, thereby suppressing the growth of intermetallic compounds and improving connection strength. Patent application number 201911153165.1 proposes a thin-film insulating core non-conductive electrode capable of forming a ring current to obtain a ring-shaped weld nugget, thus reducing weld indentations and deformation and improving joint performance. Patent application number 201611123840.2 proposes two electrodes with different cross-sectional structures: a positive electrode with a spherical end face and two concentric circular grooves, and a negative electrode with a flat end face, which can improve the heat distribution at the aluminum-steel interface and enhance connection reliability. While these patents partially solve the problem of obtaining a ring-shaped weld nugget, the groove design is prone to stress concentration and wear, and the thin-film insulating core is also susceptible to wear, reducing electrode lifespan.

[0004] Therefore, there is an urgent need to develop an electrode pair and welding method for resistance spot welding of dissimilar materials or plates of unequal thickness, so as to improve the welding quality. Summary of the Invention

[0005] The purpose of this invention is to provide an electrode pair for resistance spot welding that can improve the heat distribution at the welding interface, increase the reliability of welding, and extend the service life of the electrodes.

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

[0007] An electrode pair for resistance spot welding, the electrode pair being applied to an interface to be welded; the interface to be welded is obtained by contacting a plane of a first plate with a plane of a second plate.

[0008] The electrode pair includes:

[0009] First electrode and second electrode;

[0010] The first electrode and the second electrode have the same structure;

[0011] The first electrode is disposed on the electrode contact surface of the first plate; the electrode contact surface is a plane of the first plate or the second plate that is away from the interface to be welded;

[0012] The second electrode is disposed on the electrode contact surface of the second plate;

[0013] The first electrode includes:

[0014] The center electrode, ceramic sleeve, and outer electrode are nested sequentially from the inside out.

[0015] The ends of the central electrode near the electrode contact surface, the ceramic sleeve near the electrode contact surface, the central electrode away from the electrode contact surface, the ceramic sleeve away from the electrode contact surface, and the outer electrode away from the electrode contact surface are all planar.

[0016] The end of the central electrode near the electrode contact surface and the end of the ceramic sleeve near the electrode contact surface are on the same plane;

[0017] The end of the central electrode away from the electrode contact surface and the end of the outer electrode away from the electrode contact surface are on the same plane;

[0018] The height of the inner wall of the outer electrode is equal to the height of the central electrode;

[0019] The height of the inner wall of the outer electrode is less than the height of the outer wall of the outer electrode;

[0020] The height of the ceramic sleeve is less than the height of the central electrode.

[0021] Optionally, the outer wall of the outer electrode near the electrode contact surface is rounded.

[0022] Optionally, the central electrode has a cylindrical structure;

[0023] Both the ceramic sleeve and the outer electrode are cylindrical structures.

[0024] The central electrode, the ceramic sleeve, and the outer electrode are arranged coaxially.

[0025] Optionally, the central electrode has a square columnar structure;

[0026] Both the ceramic sleeve and the outer electrode are square cylindrical structures;

[0027] The central electrode, the ceramic sleeve, and the outer electrode are arranged coaxially.

[0028] Optionally, the materials of the central electrode and the outer electrode are copper alloys.

[0029] Optionally, the ceramic sleeve is made of one of alumina, silicon carbide, or silicon nitride.

[0030] Optionally, the welding method of the electrode pair is at least one of the first welding method and the second welding method;

[0031] The first welding method involves connecting both the center electrode of the first electrode and the outer electrode of the second electrode to a power source.

[0032] The second welding method involves connecting both the center electrode of the second electrode and the outer electrode of the first electrode to a power source.

[0033] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0034] This invention provides an electrode pair for resistance spot welding, comprising a first electrode and a second electrode with identical structures. Both the first and second electrodes include a center electrode, a ceramic sleeve, and an outer electrode nested sequentially from the inside out. The ends of the center electrode and the ceramic sleeve near the electrode contact surface are on the same plane. The ends of the center electrode and the outer electrode away from the electrode contact surface are also on the same plane. The inner wall height of the outer electrode is equal to the height of the center electrode. The inner wall height of the outer electrode is less than the outer wall height of the outer electrode. The height of the ceramic sleeve is less than the height of the center electrode. This invention, by setting a height difference between the inner and outer walls of the outer electrode, can improve the heat distribution at the welding interface, increase welding reliability, and extend electrode lifespan. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of an electrode pair structure for resistance spot welding according to Embodiment 1 of the present invention;

[0037] Figure 2 This is a first schematic diagram of spot welding of annular coaxial electrodes in Embodiment 1 of the present invention;

[0038] Figure 3 This is a second schematic diagram of spot welding of annular coaxial electrodes in Embodiment 1 of the present invention;

[0039] Figure 4 This is a first schematic diagram of conventional electrode spot welding in Embodiment 1 of the present invention;

[0040] Figure 5 This is a second schematic diagram of conventional electrode spot welding in Embodiment 1 of the present invention;

[0041] Figure 6 This is a first schematic diagram of dual-power resistance spot welding in Embodiment 1 of the present invention;

[0042] Figure 7 This is a second schematic diagram of dual-power resistance spot welding in Embodiment 1 of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The purpose of this invention is to provide an electrode pair for resistance spot welding that can improve the heat distribution at the welding interface, increase the reliability of welding, and extend the service life of the electrodes.

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] like Figures 1-3As shown, this embodiment provides an electrode pair for resistance spot welding. The electrode pair is applied to the interface to be welded. The interface to be welded is obtained by contacting a plane of a first plate with a plane of a second plate. The electrode pair includes a first electrode and a second electrode. The first electrode and the second electrode have the same structure. The first electrode is disposed on the electrode contact surface of the first plate. The electrode contact surface is a plane of the first or second plate away from the interface to be welded. The second electrode is disposed on the electrode contact surface of the second plate. The first electrode includes a central electrode, a ceramic sleeve, and an outer electrode nested from the inside to the outside. The ends of the central electrode near the electrode contact surface, the ceramic sleeve near the electrode contact surface, the central electrode away from the electrode contact surface, the ceramic sleeve away from the electrode contact surface, and the outer electrode away from the electrode contact surface are all planes. The ends of the central electrode near the electrode contact surface and the ceramic sleeve near the electrode contact surface are on the same plane. The ends of the central electrode away from the electrode contact surface and the outer electrode away from the electrode contact surface are on the same plane. The inner wall height of the outer electrode is equal to the height of the central electrode. The inner wall height of the outer electrode is less than the outer wall height of the outer electrode. The height of the ceramic sleeve is less than the height of the central electrode. The outer electrode has a rounded corner on the end closest to the electrode contact surface. Both the center and outer electrodes are made of copper alloy. The ceramic sleeve is made of alumina, silicon carbide, or silicon nitride.

[0048] Specifically, the central electrode has a cylindrical structure; the ceramic sleeve and the outer electrode both have cylindrical structures; the central electrode, ceramic sleeve, and outer electrode are coaxially arranged. Alternatively, the central electrode has a square columnar structure; the ceramic sleeve and the outer electrode both have square cylindrical structures; the central electrode, ceramic sleeve, and outer electrode are coaxially arranged.

[0049] The electrode pair is welded in at least one of a first welding method and a second welding method; the first welding method is that the center electrode of the first electrode and the outer electrode of the second electrode are both connected to the power source; the second welding method is that the center electrode of the second electrode and the outer electrode of the first electrode are both connected to the power source.

[0050] Specifically, the present invention mainly includes an upper electrode and a lower electrode, wherein the upper outer electrode and the lower outer electrode are cylindrical, the upper insulating ceramic sleeve and the lower insulating ceramic sleeve are cylindrical, and the upper center electrode and the lower center electrode are cylindrical. Further, the outer and center electrodes are made of materials with low resistivity, high hardness, and high temperature resistance, such as commonly used copper alloys, and the insulating ceramic sleeve is made of high-temperature resistant insulating materials such as alumina, silicon carbide, and silicon nitride. Figure 1 Taking the central electrode as a cylindrical rod, the outer electrode as a cylindrical cylinder, and the insulating ceramic sleeve as a cylindrical cylinder as an example, it is not limited to these. For example, the central electrode is square, the ceramic sleeve and the outer electrode are U-shaped, or other special shapes with special requirements.

[0051] like Figure 3The upper and lower center electrodes and the ceramic sleeve have flat end faces. The lower end faces of the upper and lower outer electrodes are inclined at a certain angle towards the electrode center (0-10° relative to the horizontal plane), and the inner and outer sides are rounded to prevent stress concentration on the plate when in contact with it. The coaxial annular sealed electrode has its center and outer electrodes concentrically assembled, with a transition fit between them and the ceramic sleeve (length less than the electrode length to allow for cooling water channels). The end of the ceramic sleeve near the plate is generally flush with the end of the center electrode near the plate, and both are higher than the lowest point h of the outer electrode. h is 0.1-2 mm, depending on the plate thickness, material strength, and required density of the melt nugget. The ceramic sleeve serves to insulate and seal the cooling water channels.

[0052] This invention, by setting a central electrode and outer electrodes, allows one of the outer electrodes to be connected in parallel with one of the upper or lower central electrodes, thus forming an additional current loop within the plate material on the side with the parallel outer electrode. The additional loop current generates heat, altering the heat distribution and causing the weld nugget to move towards the plate interface. Therefore, this invention can control the position of the weld nugget by distributing the electrode current, ensuring that the center of the weld nugget is located at the plate interface. By setting the outer electrode lower than the central electrode, this invention creates a sealed welding area under electrode pressure, preventing oxygen, nitrogen, and other elements from the air from entering the molten zone and reacting with the liquid metal. The outer electrode tip is tilted at a certain angle θ (10°-20°) towards the center, preventing molten titanium metal from flowing out of the molten zone along the plate interface while the electrode pressure forges the weld nugget to reduce metallurgical defects. It also helps to avoid sputtering to some extent. Therefore, this invention can seal the molten zone and forge it to improve the welding quality of the weld nugget.

[0053] Resistance spot welding of plates of different materials with the same thickness: such as Figure 4 and Figure 5 When material 4 and material 5 are different, for example, material 4 is a titanium alloy and material 5 is an aluminum alloy, the resistivity of titanium alloy is greater than that of aluminum alloy, and the thermal conductivity of titanium alloy is less than that of aluminum alloy. In traditional resistance spot welding, such as... Figure 2 As shown, according to Kirchhoff's current law, the current in titanium alloy and aluminum alloy is equal. Therefore, within a certain welding time, the heat generated in the titanium alloy sheet is greater than that in the aluminum alloy sheet. Furthermore, due to the better thermal conductivity of aluminum alloy, it facilitates heat exchange between the lower electrode 11 and the air, ultimately resulting in a significantly lower temperature inside the aluminum alloy sheet compared to the titanium alloy sheet. After welding, this manifests as the weld nugget shifting towards the interface between the aluminum and titanium alloys, moving closer to the titanium alloy side. Figure 4 As shown, this resulted in different weld penetration rates on the two sides of the plates, with the aluminum alloy having insufficient weld penetration and the titanium alloy having excessive weld penetration. Furthermore, the plates underwent significant warping deformation due to electrode pressure and thermal stress, such as... Figure 5As shown. To solve the problem of weld nugget misalignment in resistance spot welding of plates of different materials with the same thickness, the coaxial ring electrode spot welding method is as follows:

[0054] 1. Determine the electrode dimensions. The cross-sectional dimensions of a coaxial ring electrode are generally based on those of a traditional electrode; that is, the sum of the cross-sectional areas of the central electrode and the outer electrodes is approximately equal to the cross-sectional area of ​​the traditional electrode. Additionally, consider the weld penetration rate and the weld nugget size (minimum weld nugget size is D = 4t). 0.5 (t is the plate thickness) Adjust the ratio between the cross-sectional area of ​​the center electrode and the cross-sectional area of ​​the outer electrode.

[0055] 2. Determine the welding current and welding time. Taking material 1 (titanium alloy) and material 2 (aluminum alloy) as examples, titanium alloys generally use a small current and long welding time (soft specification), while aluminum alloys generally use a large current and short welding time (hard specification). There are two options: Figure 2 When the lower outer electrode 8 is energized with a current in the same direction as the upper central electrode 1, under the premise of determining a welding time that minimizes the impact on the two materials, it is possible to apply a small current to the titanium alloy and a large current to the aluminum alloy. A soft specification of small current and long time is used for the titanium alloy side, while a large current and short time are used for the aluminum alloy side. That is, the titanium alloy side is energized first and then the aluminum alloy side is energized (at this time, compared with the traditional spot welding time and spot welding current, the heat transfer between them needs to be considered to correct the welding time and welding current).

[0056] 3. Determine the electrode pressure, the tilt angle of the outer electrode end face, and the height difference h between the lowest points of the center electrode and the outer electrode. The electrode pressure primarily considers the yield strength and surface roughness of the welding material to ensure that, within an acceptable indentation depth, the outer electrode surrounds the welding zone, forming a sealed area. The end face tilt angle primarily considers the movement of the electrode towards the weld nugget interface, which is converted into the movement of material in the heat-affected zone towards the center of the weld nugget, thus forging the weld nugget and eliminating defects during solidification. The purpose of the center electrode being lower than the lowest point h of the outer electrode is to ensure that, while the outer electrode forms a sealed area with higher pressure, the center electrode maintains appropriate pressure to prevent excessively low inter-plate resistance (inter-plate resistance is one of the main sources of welding heat).

[0057] 4. Perform resistance spot welding according to the process parameters determined above.

[0058] When welding plates of unequal thickness, the thicker plate has higher resistance and generates more heat while dissipating less, while the thinner plate has lower resistance and generates less heat while dissipating more, causing the weld nugget to be biased towards the thicker plate. The welding method for plates of unequal thickness is exactly the same as the welding method in Example 1.

[0059] When obtaining an annular weld nugget by dual-power welding of the same plate and thickness, Zhang Xu et al. chose to apply an external magnetic field to solve the problem of brittle joint caused by the easy reaction of TA1 pure titanium with oxygen in the air during resistance welding. Experimental results show that the external magnetic field can effectively increase the weld nugget diameter and improve the load-bearing capacity of TA1 joints. At the same time, the dimple size of the tensile fracture surface is larger, showing better plasticity and toughness (Zhang Xu, Luo Zhen, Bi Jing et al. Influence of external magnetic field on the quality of resistance spot welding of TA1 industrial pure titanium [J]. Journal of Tianjin University (Natural Science and Engineering Technology Edition), 2019, 52(05): 110-114.). It can be seen that the magnetic field has a certain influence on the welding quality. Oersted's discovery of the current magnetic effect explains that a magnetic field is generated around a current-carrying conductor, and Ampere further pointed out that the direction of the magnetic field follows the right-hand screw rule. Traditional resistance spot welding, such as Figure 2 As shown, there is only one set of electrodes; therefore, the direction and magnitude of the current determine the direction and magnitude of the generated magnetic field. And as... Figure 6 and Figure 7 The coaxial ring electrode shown has two sets of electrodes. Therefore, while achieving the same current density as a traditional electrode, the principle of magnetic field superposition allows for the connection of two power sources to the coaxial ring electrode, enabling free adjustment of the magnitude and direction of the magnetic field near the welding area, while simultaneously obtaining a ring-shaped weld nugget. The specific steps are as follows, using a 1mm thick TC4 titanium plate as an example:

[0060] 1. Determine the electrode dimensions. The cross-sectional dimensions of a coaxial ring electrode are generally based on those of a traditional electrode; that is, the sum of the cross-sectional areas of the central electrode and the outer electrodes is approximately equal to the cross-sectional area of ​​the traditional electrode. Additionally, consider the weld penetration rate and the weld nugget size (minimum weld nugget size is D = 4t). 0.5 (t is the plate thickness) Adjust the ratio between the cross-sectional area of ​​the center electrode and the cross-sectional area of ​​the outer electrode. Given the total current, the ratio of the cross-sectional areas of the center and outer electrodes is determined. Then, based on the current-carrying capacity of the electrode materials, the cross-sectional area of ​​the center electrode is determined, thus determining the cross-sectional area of ​​the outer electrode. Once both cross-sectional areas are determined, the dimensions of the ceramic sleeve are naturally obtained.

[0061] 2. Determine the welding current and welding time. Based on existing experience or relevant literature, a welding current of 9 kA and a welding time of 0.24 s are selected. When using dual-power welding, the two currents can be evenly distributed, i.e., each current is 4.5 kA. This achieves the maximum magnetic induction intensity when the currents are in the same direction, and the magnetic induction intensity is 0 when the currents are opposite. Furthermore, the ratio of the two currents can be adjusted arbitrarily according to the direction of the magnetic field and the magnitude of the magnetic induction intensity.

[0062] 3. Determine the electrode pressure, the inclination angle of the outer electrode end face, and the height difference h between the lowest points of the center electrode and the outer electrode. The electrode pressure primarily considers the yield strength and surface roughness of the welding material to ensure that, within an acceptable indentation depth, the outer electrode surrounds the welding zone, forming a sealed area. The end face inclination angle primarily considers the movement of the electrode towards the weld nugget interface, which is converted into the movement of material in the heat-affected zone towards the center of the weld nugget, thus forging the weld nugget and eliminating defects during solidification. The purpose of the center electrode being lower than the lowest point h of the outer electrode is to ensure that, while the outer electrode forms a sealed area with higher pressure, the center electrode maintains an appropriate pressure to prevent excessively low inter-plate resistance (inter-plate resistance is one of the main sources of welding heat). The selected electrode pressure is 1900N, at which point the pressure of the center electrode is lower than 1900N, while the pressure of the outer electrode is greater than 1900N.

[0063] 4. Perform resistance spot welding according to the process parameters determined above.

[0064] In addition to forming an additional current loop, the outer electrode of this invention also provides support. Its lowest point is located in and outside the heat-affected zone (HAZ) and is lower than the central electrode. Therefore, the pressure on the outer electrode is greater, its contact resistance is lower, and this reduces the HAZ during welding. Consequently, the plate material outside the electrode will not warp due to the reduced volume of the molten zone, using the HAZ or solid-liquid coexistence zone as a fulcrum. Thus, this invention can reduce warping deformation during plate welding and improve welding accuracy. By setting two electrodes, one above and one below, while maintaining the same current density as traditional electrodes, the coaxial ring electrode uses a two-power-connection scheme. The current path is between the central and outer electrodes, and the area with the highest current density is between the central and outer electrodes, thus ultimately obtaining a ring-shaped weld nugget. Furthermore, according to the principle of magnetic field superposition, the induced magnetic fields generated by the two current loops can be superimposed, thereby allowing free adjustment of the strength and direction of the magnetic field in the welding area. Therefore, this invention, using two power sources, can obtain a ring-shaped weld nugget and an adjustable magnetic field.

[0065] In summary, this invention can regulate the temperature distribution during welding of plates of unequal thickness or dissimilar materials, eliminate the phenomenon of weld nugget displacement, form a closed welding area to prevent the material from reacting with elements in the air and to forge the weld nugget to improve welding quality, reduce the heat-affected zone to prevent plate warping and deformation, and improve welding accuracy, and regulate the magnetic field of the welding area to obtain a ring-shaped weld nugget.

[0066] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0067] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An electrode pair for resistance spot welding, characterized in that, The electrode pair is applied to the interface to be welded; The interface to be welded is obtained by contacting one plane of the first plate with one plane of the second plate. The electrode pair includes: First electrode and second electrode; The first electrode and the second electrode have the same structure; The first electrode is disposed on the electrode contact surface of the first plate; the electrode contact surface is a plane of the first plate or the second plate that is away from the interface to be welded; The second electrode is disposed on the electrode contact surface of the second plate; The first electrode includes: The center electrode, ceramic sleeve, and outer electrode are nested sequentially from the inside out. The ends of the central electrode near the electrode contact surface, the ceramic sleeve near the electrode contact surface, the central electrode away from the electrode contact surface, the ceramic sleeve away from the electrode contact surface, and the outer electrode away from the electrode contact surface are all planar. The end of the central electrode near the electrode contact surface and the end of the ceramic sleeve near the electrode contact surface are on the same plane; The end of the central electrode away from the electrode contact surface and the end of the outer electrode away from the electrode contact surface are on the same plane; The height of the inner wall of the outer electrode is equal to the height of the central electrode; The height of the inner wall of the outer electrode is less than the height of the outer wall of the outer electrode; The height of the ceramic sleeve is less than the height of the central electrode; The end of the outer electrode near the electrode contact surface is inclined at an angle to the center of the electrode. The ceramic sleeve end near the plate is flush with the end of the central electrode near the plate, and both are higher than the lowest point h of the outer electrode; the outer wall of the end of the outer electrode near the electrode contact surface is rounded. The dual-power resistance spot welding method of the electrode pair is as follows: the two output terminals of the first power supply are electrically connected to the center electrode of the first electrode and the outer electrode of the second electrode, respectively; the two output terminals of the second power supply are electrically connected to the center electrode of the second electrode and the outer electrode of the first electrode, respectively, to form two cross-connected current loops; the first power supply and the second power supply supply power to the two current loops simultaneously, and the ratio of the current values ​​and the relative direction of the two currents are adjustable. The sum of the cross-sectional areas of the central electrode and the outer electrode matches the cross-sectional area of ​​a conventional electrode.

2. The electrode pair for resistance spot welding according to claim 1, characterized in that, The central electrode has a cylindrical structure; Both the ceramic sleeve and the outer electrode are cylindrical structures. The central electrode, the ceramic sleeve, and the outer electrode are arranged coaxially.

3. An electrode pair for resistance spot welding according to claim 1, characterized in that, The central electrode has a square columnar structure; Both the ceramic sleeve and the outer electrode are square cylindrical structures; The central electrode, the ceramic sleeve, and the outer electrode are arranged coaxially.

4. An electrode pair for resistance spot welding according to claim 1, characterized in that, The materials of the central electrode and the outer electrode are copper alloys.

5. An electrode pair for resistance spot welding according to claim 1, characterized in that, The ceramic sleeve is made of one of the following materials: alumina, silicon carbide, or silicon nitride.

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