Stainless steel micro-indentation resistance spot welding process
By using an electrode cap divided into a center and an edge, the current conduction path and heat dissipation are controlled, solving the problems of indentation and weld nugget offset in stainless steel resistance spot welding, and achieving efficient and stable welding results.
Patent Information
- Application Number
- CN202511490941.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-17
- Publication Date
- 2026-01-02
AI Technical Summary
Traditional stainless steel resistance spot welding technology is prone to indentation during the welding process, which leads to stress concentration and weld nugget displacement, affecting the mechanical properties of the welded joint, and is not suitable for complex welding conditions.
The electrode cap is divided into a center and an edge. Electrical isolation is achieved through an insulating coating, which controls the current conduction path and causes the current to generate heat on the contact surface between the edge and the plate. Combined with homogeneous copper-based material and cooling water channels, a flat or annular melt nugget is formed, which reduces the melting penetration and heat accumulation.
It effectively reduces the depth of weld indentation, avoids weld nugget displacement, improves the yield strength of the base material, increases electrode life, and is suitable for different plate sizes and shapes, with stable welding results.
Smart Images
Figure CN121245162A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of welding technology, in particular to a stainless steel micro-indentation resistance spot welding process. BACKGROUND
[0002] 301L austenitic stainless steel cold-rolled series plate is the main material for manufacturing rail trains, and in the welding technology of stainless steel train bodies, resistance spot welding is the most widely used and the most automated welding method. However, when using resistance spot welding technology to weld stainless steel plates, obvious indentations are often left, which can cause the following problems: 1. When the workpiece is under stress or complex stress, stress concentration can occur due to the narrowing of the nugget interface width, which can easily lead to failure and affect the mechanical properties of the welded joint. 2. Deep indentations are not aesthetically pleasing, and for workpieces with appearance requirements, additional costs are required to handle the indentations, and handling the indentations can also result in some loss of mechanical properties.
[0003] The indentation on the surface of the stainless steel resistance spot welding is often caused by two reasons. On the one hand, during the resistance spot welding process, a large amount of heat is generated in the nugget area and the heat affected zone. The yield strength of the workpiece surface material decreases significantly under high temperature. In addition, the upper and lower electrodes exert a large pressure on the workpiece during the welding process. Under the combined action of the two, the workpiece surface is easily deformed and indented. On the other hand, during the pressure maintaining stage of resistance spot welding, the liquid metal in the molten pool rapidly cools to form a nugget, which also shrinks during the cooling process, causing deformation.
[0004] The current traditional micro-indentation resistance spot welding technology on the market often increases the contact area between the electrode cap on one side of the spot welding equipment and the workpiece surface to reduce the unit area pressure of the electrode and workpiece contact surface and to disperse the current. This technology can effectively alleviate the indentation problem of resistance spot welding, but due to the uneven heat dissipation conditions and current distribution on both sides of the upper and lower electrodes, the nugget often shifts to the side with poor heat dissipation conditions and concentrated current distribution, resulting in nugget shift and affecting the mechanical properties of the welded joint. In addition, due to the significant increase in the size of the single-sided electrode, this resistance spot welding process often has certain requirements for the shape and size of the workpiece, and is not suitable for complex welding conditions.
[0005] Furthermore, the micro indentation resistance spot welding technology similar to the composite ceramic filled annular electrode process, although the electrode cap core part is not conductive, changes the distribution of the internal current of the workpiece, reduces the penetration rate to a certain extent, and has a certain mitigation effect on the surface indentation of the stainless steel resistance spot welding joint, but since the filling material and the edge part of the electrode cap are different materials, the composite ceramic filling material has poor heat conduction performance, so it is easy to cause heat accumulation in the center part during welding, which affects the yield strength of the material and increases the shrinkage amount of the molten core during cooling, which limits the control ability of the indentation depth. SUMMARY
[0006] The purpose of the present application is to provide a stainless steel micro indentation resistance spot welding process, which solves the problems of molten core deviation and resistance spot welding workpiece (sheet) welding versatility in traditional micro indentation resistance spot welding technology. The present application can better solve the problem of surface indentation in the process of resistance spot welding of stainless steel materials, and can also control the indentation of the welded joint. It can effectively weld stainless steel sheets of the same thickness, so that it can minimize the indentation depth of the workpiece surface, and the molten core deviation does not occur.
[0007] The above-mentioned purpose of the present application is realized by the following technical solutions: The electrode cap for the stainless steel micro indentation resistance spot welding process is divided into a center part 2 and an edge part 3, and the electrical isolation of the two parts is realized only by an insulating coating 1, so as to effectively control the conduction path of the spot welding current, so that the heat is generated only on the contact area between the edge and the sheet, thereby effectively reducing the penetration rate and making the molten core flat or ring-shaped. The center part 2 and the edge part 3 are made of homogeneous copper-based electrode material and are in contact with the cooling circulating waterway 4, so the center part 2 also has good heat dissipation function, which reduces the temperature of the base material during welding, thereby improving the plasticity of the stainless steel base material during welding and effectively reducing the indentation effect of the welded joint. At the same time, due to the fast heat dissipation of the electrode during welding, it helps to reduce the electrode wear. On this basis, since the contact surface between the electrode cap and the sheet is a plane, the pressure effect of the electrode on the sheet can be dispersed, so that the indentation depth of the welded joint can be further reduced.
[0008] The center part 2 of the electrode cap has a conical taper of 1:10, and the side surface is provided with an insulating coating 1. The outer edge part 3 of the electrode cap is composed of a complete electrode cap by interference fit with the center part 2. The end surface of the outer edge part 3 of the electrode cap is annular and planar, and the inner surface is a circular table matching surface. The lower end surface of the center part 2 and the edge part 3 after assembly is coplanar, and the end surface of the complete electrode cap is in contact with the sheet.
[0009] The center part 2 and the edge part 3 of the electrode cap are made of chromium-zirconium-copper material, and the material of the insulating coating 1 can be zirconium oxide, aluminum oxide or high-temperature insulating polymer material, etc. The insulating coating has high-temperature insulating properties and is processed by spraying technology or pvd technology, etc. The thickness of the insulating coating is selected according to the insulating material.
[0010] The center part 2 and the edge part 3 of the electrode cap are made of the same copper-based electrode material, i.e. chromium-zirconium-copper material, and both parts simultaneously contact the cooling water channel. During the heat generation process of resistance spot welding, the center part 2 and the edge part 3 have excellent heat dissipation conditions, so that the heat does not accumulate in the center part of the electrode and the heat accumulation of the stainless steel base material is effectively reduced, thereby effectively improving the yield strength of the surface of the stainless steel base material under high temperature during the resistance spot welding process, so that plastic deformation does not easily occur under high temperature and high pressure environment.
[0011] The electrode cap is divided into a center part and an edge part, and the electrical isolation of the two parts is realized only by the insulating coating. Due to the shortest current path principle, the current will preferentially flow through the edge parts of the upper and lower electrodes, thereby effectively controlling the current conduction path of spot welding, so that the current presents the characteristics of sparse-dense-sparse-sparse-dense-sparse in the horizontal direction of the base material center, i.e. the heat can be effectively concentrated in the peripheral area of the electrode center. By this way of controlling the current flow path, the morphology of the nugget is controlled, so that the penetration rate can be reduced to a certain extent. Under the joint action of the heat dissipation of the electrode cap, the nugget is controlled to present a flat or ring shape.
[0012] The outer diameter size of the electrode cap is 16-20 mm, and the outer diameter of the center part is smaller than the outer diameter of the electrode cap.
[0013] Another object of the present application is to provide a stainless steel micro-indentation resistance spot welding process, which comprises the following welding steps: Step one: determine the end face radius size of the center part of the electrode cap and the material of the insulating layer according to the material, plate thickness and joint strength requirement of the plate, and ensure that the end face radius size of the core part (center part) of the electrode cap is smaller than the radius of the electrode cap; Step two: the stainless steel plate is pretreated before welding, assembled according to the process requirement of the plate, and the stainless steel micro-indentation resistance spot welding electrode cap is used for both sides of the electrode cap, and the cooling water pipeline is opened; Step three: set the welding current, welding time and electrode pressure according to the material performance and welding joint performance requirement; Step four: place the electrode cap on both sides of the plate stack to constrain the positive and negative electrodes, perform pre-pressing, and the positive electrode approaches the plate until the welding end face is tightly attached to the plate; Step five: after the pre-pressing stage, the current is applied, and the center part of the electrode cap is not conductive due to the existence of the insulating coating, the current is conducted through the contact area between the edge part of the electrode cap and the plate, so that the center current passing area of the plate is melted; Step six: after the end of the power-on stage, the electrode pressure remains unchanged, the melted base material cools down, and a flat or ring-shaped nugget is formed between the plates, and after a period of time (0.5-2s), the electrode cap is removed from the surface of the plate, and the welding process is completed.
[0014] The beneficial effects of the present application are: 1. The indentation effect in the resistance spot welding process can be greatly reduced. In industrial production, due to the spherical electrode, the nugget is located at the center position, and melting occurs first when the current is small, and the pressure stress borne by the center area is significantly greater than that of the other plate surface and the electrode contact area, thereby forming a deep indentation. The present application effectively reduces the problem of excessive concentration of plate surface pressure stress on one hand, and on the other hand, the electrode core (center part) is not conductive due to the insulating layer, so that the spot welding current is dispersed to ensure that the nugget growth area is located outside the center of the joint, reducing the penetration rate, and because the center part and the edge part use the same material, the heat dissipation effect of the electrode is effectively improved, thereby greatly reducing the accumulation of heat in the base material, reducing the proportion of the decrease in the yield strength of the material, and effectively controlling the indentation depth.
[0015] 2. The center insulating part of the electrode cap has good heat dissipation performance. The electrode cap is divided into center and edge parts, and the two parts use the same copper-based electrode material and are connected with a cooling water channel, and the two parts are electrically isolated only by the insulating coating, so as to effectively control the conduction path of the spot welding current. Because the same chromium-zirconium copper material is used, the resistance itself has good heat dissipation performance, and the cooling water channel is connected, which can further reduce the heat accumulation in the welding area of the stainless steel base material, and the problem of large accumulation of heat on the surface of the base material caused by the poor heat dissipation performance of the ceramic filler electrode.
[0016] 3. It will not cause the nugget to deviate. The traditional micro-indentation resistance spot welding technology often increases the contact area between the electrode and the plate to reduce the unit area pressure, and this way the heat dissipation condition of one side is much better than that of the other side, which leads to uneven temperature field distribution in the plate internal nugget area, so that the nugget grows like the side with poor heat dissipation condition, and the nugget deviation phenomenon occurs. In contrast, the present method does not change the size of the single-sided electrode of the nugget, but uses the insulating layer to control the current distribution in the plate to reduce the penetration rate, so the nugget deviation phenomenon caused by uneven temperature field distribution on both sides does not occur.
[0017] 4. It has low requirements for the size and shape of the plate material and has good applicability. In this invention, the outer diameter of the resistance spot welding electrode does not change significantly, conforms to national standard dimensions, and can be applied to both conventional and unconventional plates. The welding scenarios applicable to spherical electrodes can also be applied to this invention, which has good versatility and a wide range of applications.
[0018] 5. Electrode life has been improved to a certain extent. Because the contact surface between the electrode and the plate is flat, the force exerted by the electrode on the plate surface is more balanced, and the heat dissipation and cooling effect is stronger. In addition, the center and edge of the electrode cap are made of homogeneous copper-based material with excellent thermal conductivity and connected to cooling channels, thus reducing heat accumulation in the electrode cap. This helps to reduce indentation at the spot weld joint and overheating wear of the electrode itself, thereby improving electrode life. Attached Figure Description
[0019] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate the invention and are used to explain it, but do not constitute an undue limitation of the invention.
[0020] Figure 1 This is a cross-sectional view of the electrode cap of the present invention; Figure 2 This is a schematic diagram of the end face structure of the electrode cap of the present invention; Figure 3 This is a schematic diagram of the welding process of the stainless steel micro-indentation resistance spot welding electrode cap using the present invention; Figure 4 This is a schematic diagram of the welding process using a traditional spherical electrode cap; Figure 5 This is a schematic diagram of the welding current distribution and weld nugget morphology of the micro-indentation resistance spot welding electrode of the present invention; Figure 6 This is a cross-sectional view of the weld nugget during the actual production process of the stainless steel micro-indentation resistance spot welding process of the present invention. Figure 7 This is a cross-sectional view of the weld nugget during the actual production process of spherical electrode resistance spot welding. Figure 8 This is a comparison diagram of the indentation depth between the stainless steel micro-indentation resistance spot welding process and the spherical resistance spot welding process of the present invention.
[0021] In the figure: 1. Insulating coating; 2. Central part; 3. Edge part; 4. Cooling circulation water channel; 5. Stainless steel sheet; 6. Stainless steel micro-indentation resistance spot welding electrode cap; 7. Spherical electrode cap; 8. Melt nugget; 9. Melt nugget prepared by spherical electrode cap. Detailed Implementation
[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application. In order to make the above-mentioned objects, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.
[0023] Referring to Figures 1 to 8 As shown in the figure, the electrode cap for the stainless steel micro-indentation resistance spot welding process of the present application is divided into a center part 2 and an edge part 3, and the center part 2 and the edge part 3 are electrically isolated by an insulating coating 1, so as to effectively control the conduction path of the spot welding current during the welding process, so that the heat is generated only on the contact surface of the edge part and the plate, thereby effectively reducing the penetration rate and making the nugget flat or ring-shaped. The center part and the edge part of the electrode cap are made of homogeneous copper-based electrode material and are in contact with the cooling water path, so that the center part can also provide good heat dissipation conditions and greatly reduce the temperature of the base material during welding, thereby improving the yield strength of the stainless steel base material during high-temperature welding and effectively reducing the effect of the indentation of the welded joint. At the same time, due to the fast heat dissipation of the electrode during the welding process, the heat is not easy to accumulate, which helps to reduce the electrode wear. On this basis, since the contact surface of the electrode and the plate is a plane, the pressure effect of the electrode on the plate can be dispersed, so that the depth of the indentation of the welded joint can be further reduced.
[0024] The outer diameter of the electrode cap is 16-20 mm, and is divided into a center part 2 and an edge part 3. The outer diameter of the center part 2 is smaller than the outer diameter of the electrode cap, and the two parts are electrically isolated by an insulating coating 1. The insulating coating 1 has good high-temperature insulation properties. The center part 2 and the edge part 3 of the electrode cap are made of homogeneous copper-based electrode material and are in contact with the cooling water path. The end surface of the electrode cap in contact with the plate is a plane. Embodiment
[0025] Referring to Figure 1 and Figure 2 As shown in the figure, in order to realize the stainless steel micro-indentation resistance spot welding process, an electrode cap structure with a non-conductive center part of the electrode is designed. During the spot welding process, the current in the electrode cap cannot pass through the insulating coating 1, so that the center part 2 of the electrode cap is non-conductive. In addition, the material of the center part of the electrode cap and the material of the edge part are homogeneous materials, and the two parts of the electrode cap are in contact with the cooling circulating water path 4 at the same time. The heat generated during the spot welding process can still be conducted through the center part of the electrode cap. Thus, the entire electrode cap maintains good heat dissipation performance.
[0026] The processing method is to process a circular truncated cone shaped through hole in the core of the planar electrode, then embed the electrode core with surface layer insulation treatment and taper into the through hole, remove the copper column processing allowance, and process the same surface morphology as the planar electrode. In order to make the stainless steel micro-indentation resistance spot welding electrode cap and the spherical electrode cap have the same heat dissipation characteristics, both of them adopt chromium zirconium copper material, in order to ensure that the center part 2 and the edge part 3 of the electrode cap can also realize electrical isolation at high temperature, the insulation coating 1 needs to have high temperature insulation characteristics.
[0027] The specific size data of the electrode cap are as follows: the outer diameter of the edge part 3 of the electrode cap is 16 mm, the height is 13 mm, the inner wall diameter is 14.6 mm, the depth is 11 mm, and the inclined taper is 1:10; the bottom surface diameter of the center part 2 of the electrode cap is 5 mm, the height is 12 mm, the taper is designed as 1:10, and the side surface of the center part 2 is provided with the insulation coating 1. Embodiment
[0028] Referring to Figure 3 It can be seen from the drawings that the stainless steel micro-indentation resistance spot welding process of the present application adopts a stainless steel micro-indentation resistance spot welding electrode cap 6, a stainless steel sheet 5 with a thickness of 0.8 mm, and a cooling circulating water path 4.
[0029] Before welding, the stainless steel micro-indentation resistance spot welding electrode cap 6 does not contact the stainless steel sheet 5, the cooling circulating water path 4 is opened, the cooling water contacts the center part 2 and the edge part 3 of the electrode cap, and during the welding pre-pressing, the two stainless steel micro-indentation resistance spot welding electrode caps 6 are closely attached to the stainless steel sheet 5, then the current is applied, and due to the existence of the insulation coating 1, the current in the middle of the sheet presents the characteristics of sparse-dense-sparse-sparse-dense-sparse as shown in the drawings, the current passing area part of the sheet contacted by the edge part of the electrode cap is melted to form a flat or ring-shaped nugget 8, and the nugget 8 has no offset phenomenon. Figure 5
[0030] The welding process uses the following welding parameters: current 10 ka, current time 200 ms, electrode pressure 9 kn, and the nugget morphology of the welding joint formed by resistance spot welding on 0.8 mm thick 301L stainless steel sheet is as shown in the drawings. Figure 6 It can be seen from the drawings that the nugget formed by the stainless steel micro-indentation resistance spot welding process of the present application has a small welding penetration rate, the surface deformation of the base material is small, the nugget presents a ring or flat shape, and there is no obvious nugget offset phenomenon. Figure 6
[0031] Referring to Figure 7 It can be seen from the drawings that the traditional spherical electrode cap 7 is adopted and the current distribution in the sheet is as shown in the drawings. Figure 4 The spot welding process is shown, and the specific welding parameters are as follows: current 10 ka, current time 200 ms, electrode pressure 9 kn, and the nugget morphology of the welded joint formed by resistance spot welding of 0.8 mm equal-thickness 301L stainless steel sheets is shown by Figure 7 It can be seen that, compared with the present application, the base material surface deformation is larger, the nugget 9 prepared by the spherical electrode cap presents an elliptical shape, which is smaller in the horizontal direction and larger in the vertical direction than the nugget prepared in Example 3.
[0032] Referring to Figure 8 As shown, the indentation depth of the welded joint prepared by using 9 ka and 11 ka welding current for the traditional spherical electrode cap 7 and using 10 ka and 13 ka welding current for the stainless steel micro-indentation resistance spot welding electrode cap is compared by three-dimensional optical surface profiler, wherein RAW-S is the indentation three-dimensional profile curve of the traditional stainless steel resistance spot welding process, and RAW-R is the nugget indentation three-dimensional profile curve welded by the stainless steel micro-indentation resistance spot welding process of the present application, it can be obviously seen that the nugget indentation prepared by the micro-indentation resistance spot welding process of the present application is far smaller than that of the traditional resistance spot welding process, which meets the requirement that the indentation depth does not exceed 30% of the thickness of the base material according to the joint venture standard.
[0033] The spot welding method of the present application divides the electrode cap into two parts of center and edge, uses an insulating coating outside the center part to control the distribution of current and reduce the penetration rate, so as to ensure that the nugget growth area is located outside the center of the joint. The two parts of the electrode cap use homogeneous materials with good thermal conductivity to ensure the heat dissipation effect of the electrode cap and improve the yield strength of the stainless steel base material during high-temperature welding. At the same time, since the contact surface between the electrode and the plate is a plane, the depth of the indentation on the surface of the welded joint is further reduced. In addition, a set of resistance spot welding method is designed, which covers the pre-pressing, current welding and cooling three stages, and through adjusting the electrode pressure, current size, welding time and other precise welding parameters, the efficiency and stability of the welding process are ensured. The present application improves the surface performance of the stainless steel resistance spot welding joint, effectively solves the problem of surface indentation in the resistance spot welding process of stainless steel material, and provides a more reliable and efficient welding technology selection for high-end manufacturing fields such as automobiles and rail passenger cars.
[0034] The above only describes the preferred examples of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made to the present application shall be included in the protection scope of the present application.
Claims
1. An electrode cap for a stainless steel micro- indentation resistance spot welding process, characterized by: The electrode cap is divided into a center part (2) and an edge part (3), and electrical isolation between the center part (2) and the edge part (3) is realized through an insulating coating (1), so that the current conduction path of spot welding is controlled, the center current of the plate material in contact with the edge part of the electrode cap melts the base material, and a flat or ring-shaped nugget is formed after cooling; the center part (2) and the edge part (3) are made of homogeneous copper-based electrode material and are in contact with a cooling circulating water channel (4); the center part (2) has a geometric appearance of a circular cone with a taper of 1:10, and the side surface is provided with the insulating coating (1); the edge part (3) of the electrode cap is combined with the center part (2) into an integrated whole through interference fit, the end surface of the edge part (3) is annular and planar, and the inner surface is a circular cone matching surface; the lower end surfaces of the center part (2) and the edge part (3) are coplanar after assembly, the part of the end surface of the electrode cap in contact with the plate material is planar to disperse the pressure on the plate material and reduce the depth of the welding joint indentation.
2. The electrode cap for stainless steel micro- indentation resistance spot welding process as claimed in claim 1, wherein: The outer diameter of the electrode cap is 16-20 mm, and the outer diameter of the center part (2) is smaller than the outer diameter of the electrode cap.
3. The electrode cap for stainless steel micro- indentation resistance spot welding process as claimed in claim 1, wherein: The center part (2) and the edge part (3) of the electrode cap are made of chromium-zirconium-copper material, and the material of the insulating coating (1) is zirconium oxide, aluminum oxide or high-temperature insulating high-molecular material.
4. A stainless steel micro- indentation resistance spot welding process characterized by: The welding process comprises the following steps: Step one: determine the end surface radius size of the center part of the electrode cap and the material of the insulating layer according to the material, plate thickness and joint strength requirement of the plate material, and ensure that the end surface radius size of the center part of the electrode cap is smaller than the radius of the electrode cap; Step two: perform pretreatment on the stainless steel plate before welding, assemble according to the process requirement of the plate material, use stainless steel micro-indentation resistance spot welding electrode caps on both sides of the electrode cap, and open the cooling water pipeline; Step three: set the welding current, welding time and electrode pressure according to the material performance and performance requirement of the welding joint; Step four: place the electrode cap on both sides of the plate stack to constrain the positive and negative electrodes, perform pre-pressing, and move the positive electrode towards the plate until the welding end surface is closely attached to the plate; Step five: after the pre-pressing stage, apply current, the center part of the electrode cap does not conduct due to the existence of the insulating coating, the current is conducted through the contact area between the edge part of the electrode cap and the plate material, so that the center current of the plate material in contact with the edge part of the electrode cap melts the base material; Step six: after the current conduction stage is completed, the pressure remains unchanged, the melted base material cools down, a flat or ring-shaped nugget is formed between the plate materials, the electrode cap is removed from the surface of the plate after 0.5-2 s, and the welding process is completed.