JP6060579B2 - Resistance spot welding method - Google Patents

Description

  The present invention relates to a method for resistance spot welding of a workpiece in which a plurality of steel plates are overlapped, particularly a plate assembly having a large plate thickness ratio (= total thickness / thickness of the thinnest plate).

  In general, a resistance spot welding method, which is a kind of a lap resistance welding method, is used for joining stacked steel plates. For example, in the manufacture of automobiles, several thousand spots are welded per vehicle. This welding method is a method in which two or more steel plates are overlapped, and the surface is directly sandwiched between the upper and lower electrodes and a high current welding current is applied between the upper and lower electrodes for a short time to join them. A spot-like weld is obtained by utilizing resistance heat generated by passing a high-current welding current. This point-like weld is called a nugget and is a part where both steel plates melt and solidify at the contact points of both steel plates when current is passed through both steel plates. The

  Looking at the parts structure of an automobile, for example, a center pillar employs a structure in which a reinforcement is sandwiched between an outer and an inner. In this structure, unlike the case of spot welding of a simple two-ply steel plate, it is required to superimpose three or more steel plates for spot welding.

  Furthermore, recently, with the demand for further improvement in collision safety of the car body, reinforcement and other strength has been increased, and a thin outer (thin plate) has been placed on the outside, and the thickness has been increased on the inside. Often, it is necessary to spot weld a plate assembly that combines thick inners and reinforcements (thick plates). Here, among the steel plates assembled in a plate, a steel plate having a relatively small thickness is referred to as a thin plate, a steel plate having a relatively large thickness is referred to as a thick plate, and the following is also the same description. To do.

  In such a plate assembly having a large plate thickness ratio (= total thickness of the plate assembly / thickness of the thinnest plate), spot welding was performed with a constant pressure and welding current as in the prior art. In this case, it is known that a nugget of a necessary size is difficult to be formed between the thin plate and the thick plate on the outermost side (the side in contact with the electrode tip), and it is difficult to obtain a sound joint. This tendency is particularly strong when the plate thickness ratio exceeds 5.

  This is because the temperature hardly rises between the outermost thin plate and the thick plate due to cooling by the electrode tip. The nugget is formed by volume resistance heat generation due to the specific resistance of the steel plate from the center between the electrodes, but between the thick plate and the thick plate located near the center between the electrodes while the nugget grows to a thin plate The nugget grows at a large size, and it is difficult to obtain a nugget of the required size between the thin and thick plates without the occurrence of splattering. The thin plate is easy to peel off.

  Further, when the outermost thin plate is the outer, formability is more important than strength, so the steel plate used is often mild steel. On the other hand, the thick plate is a strength reinforcing member, and a high-tensile steel plate is often used. In such a plate assembly, the position where heat is generated is biased toward the high-tensile steel plate having a high specific resistance, so that nuggets are more difficult to be formed between the thick plate and the thin plate (mild steel).

  In order to deal with such a problem, for example, in Patent Document 1, in a plate assembly having a large plate thickness ratio in which a thin plate is further overlapped with two superposed thick plates, the thin plate is generally partially positioned at a position to be welded. In addition to forming a seat surface that is one step higher than the center, the electrode that opposes the thin plate is formed with a spherical tip at the tip, and in the first half of welding, the seat surface of the thin plate is crushed with a low applied pressure, so A technique for obtaining a necessary nugget between a thin plate and a thick plate by welding the plates and then welding the two thick plates with a high pressure force has been proposed.

  Further, in Patent Document 2, in a method in which a workpiece in which a thin plate with low rigidity is superimposed on two thick plates with high rigidity is sandwiched between a pair of electrode tips, the thin plate with the smallest rigidity is brought into contact. By making the tip diameter of the electrode tip smaller than the tip diameter of the electrode tip contacting the thick plate, the contact area between the thin plate and the electrode tip is made smaller than the contact area between the thick plate and the electrode. A technique for obtaining a nugget between a thin plate and a thick plate has been proposed.

  Further, in Patent Document 3, in a method of spot welding a workpiece to be welded having a large thickness ratio, after applying a first pressing force to the workpiece and flowing a welding current, the energization is temporarily stopped and the workpiece to be welded is applied. With the body sandwiched between them, a second pressing force larger than the first pressing force is applied and a welding current is flowed again. Preferably, the current value of the welding current in the first step is set to a first value. While changing from the first stage to the third stage, the current value of the second stage is made smaller than the current values of the first stage and the third stage, the joint strength of the welded body having a large plate thickness ratio is increased. The spot welding method of improving is proposed.

JP 2003-071569 A JP 2003-251468 A JP 2004-358500 A

  However, in the resistance spot welding method described in Patent Document 1, when there is a gap between the thick plate and the thick plate, the first portion of the energization period in which the nugget is formed between the thin plate and the thick plate is directly below the electrode. When contact occurs between the thick plate and the thick plate, there is a problem in that the current density rapidly increases and scattering occurs.

  Moreover, in the resistance spot welding method described in Patent Document 2, the thin plate and the electrode tip are formed by making the tip diameter of the electrode tip that contacts the thin plate having the smallest rigidity smaller than the tip diameter of the electrode tip that contacts the thick plate. Nugget is obtained between the thin plate and the thick plate by making the contact area with the plate smaller than the contact area between the thick plate and the electrode, but the contact area between the thin plate and the electrode tip is small. As a result, there is a problem that the range in which pressure is applied becomes narrow, and when a large nugget is formed between the thick plate and the thick plate, scattering occurs.

  In addition, in the resistance spot welding method described in Patent Document 3, it is possible to form a nugget between a thin plate and a thick plate. However, if a sheet gap exists between the steel plates, it becomes difficult to form the nugget, and a peeling test is performed. It is considered difficult to obtain a sound joint between the thin plate and the thick plate.

  The present invention has been made in view of the above circumstances, and in a plate assembly having a large plate thickness ratio in which a thin plate is overlaid on at least one of two or more thick plates overlaid with a large plate thickness, An object of the present invention is to provide a resistance spot welding method capable of obtaining sound joints between a thin plate and a thick plate and between a thick plate and a thick plate even when there is a gap between the plate and the plate.

  In order to achieve the above-mentioned problems, the present inventors diligently studied various factors affecting nugget formation in resistance spot welding. First, when spot welding is performed in the case of a large plate thickness ratio in which a thin plate is overlapped with one of two or more thick plates that are overlapped, it is difficult to form a nugget of a necessary size between the thin plate and the thick plate. It has been known that, in order to solve this problem, it is effective to reduce the applied pressure in the first stage of welding and increase the applied pressure during welding.

  That is, when high pressure is applied from the first stage of welding, the current-carrying area between the electrode and thin plate, between the thin plate and thick plate, and between the thick plate and thick plate becomes large, and the current density becomes low, so it is difficult to generate heat. In the case of a plate assembly having a large thickness ratio, the space between the thin plate and the thick plate is close to the electrode, so that it is cooled and is in a state where it is more difficult to generate heat. For this reason, even if a nugget of a necessary size is formed between the thick plate and the thick plate, no nugget is formed between the thin plate and the thick plate, and the thin plate is easily peeled off when a destructive test is performed.

  On the other hand, when welding is performed at a low pressure in the first stage of welding, the current-carrying area between the electrode and the thin plate, between the thin plate and the thick plate, and between the thick plate and the thick plate is small, and the current density is high and the heat is easily generated. In particular, by setting the applied pressure low so that the contact diameter between the electrode and the thin plate is reduced, the current density at the contact portion between the electrode and the thin plate increases, but the heat generation between the electrode and the thin plate is caused by the cooling action of the electrode. In the first half of energization, the heat generation in the vicinity of the electrode slightly away from the electrode is the largest. In a plate assembly with a large plate thickness ratio, the heat generation area near the electrode and the boundary between the thin plate and the thick plate are close to each other. By reducing the diameter and increasing the current density, a nugget is formed between the thin plate and the thick plate.

  However, if the pressure is kept low, the melted portion formed in the vicinity of the electrode grows up to the surface of the steel plate even when the current is applied for a long time, and surface scattering occurs. Further, since the applied pressure is small between the thick plate and the thick plate, scattering occurs before the necessary nugget diameter is obtained.

  Therefore, by starting welding with a low pressure and increasing the pressure during welding, the above problems can be solved, and even between a thin plate and a thick plate, even between a thin plate and a thick plate, We thought that welding to form a nugget with a diameter required for the welding would be possible. A nugget is formed between a thin plate and a thick plate by applying a high current for a short time with a low pressure in the first stage of welding. After that, by increasing the applied pressure in the latter stage of welding, the nugget formation near the electrodes was stopped due to the expansion of the current-carrying area between the electrode and the thin plate and the increase of the cooling action by the electrodes. The heat generation area moves, and a nugget is formed between the thick plate and the thick plate. In addition, since the pressurizing force is large, the pressurization area by the electrode is widened, and even if the nugget grows greatly, it becomes difficult for scattering to occur.

  As described above, even in a plate assembly having a large plate thickness ratio, resistance spot welding that can obtain nuggets of a necessary size between the thin plate and the thick plate and between the thick plate and the thick plate is possible.

  However, if there is a gap between the stacked steel sheets, the gap does not disappear in the low-pressure welding in the first half of welding, so the welding current is in a remote position such as the adjacent welding point. Shunt to the contact point. In this case, the welding current density immediately below the electrode is lower than that without a gap, and it is difficult to form a nugget between the thin plate and the thick plate. On the other hand, if the welding conditions at low pressure in the first stage of welding are matched with a gap, if there is no gap, or if the gap does not collapse during welding, The current density between them becomes excessive, and scattering occurs.

  Therefore, the present inventors have further studied, and it is possible to form a nugget between a thin plate and a thick plate and between a thick plate and a thick plate even in a plate assembly having a large plate thickness ratio regardless of the presence or absence of a plate gap. And found a technique.

  It is provided with a convex part on at least one of the two stacked thick plates so that a gap is formed between the thick plate and the thick plate, and a resin having no electrical conductivity is applied between the thick plate and the thick plate. After that, the above method is applied. Between the stacked thin plates and the thick plates, the plate gap between the thin plates and the thick plates is crushed and contacted directly under the electrodes even at a low pressure in the first stage of welding, and a high current density can be obtained. On the other hand, the rigidity between the two thick plates overlapped with each other increases due to the provision of the convex portion, and in the low pressure welding in the first stage of welding, the gap between the thick plates is large. By applying a resin that is not easily crushed and has no electrical conductivity between the thick plate and the thick plate, the resin accumulates in the gap provided between the thick plate and the thick plate, and the pressure applied during the first half of welding is low. Even if deformation occurs during welding, no current flows between the thick plate and the thick plate directly under the electrode. The electric current between the thick plate and the thick plate always flows through the contact portion between the steel plates on the outside of the protrusion or the welding point that has already been welded, and it is difficult for scattering to occur during welding at a low pressurizing force before the welding. After that, by increasing the applied pressure in the second half of welding, the resin that does not have electrical conductivity between the thick plate and the thick plate is pushed out from directly under the electrode. And a nugget can be formed between the plank and the plank.

  In addition, reducing the diversion in a place other than just below the electrode between the thin plate and the thick plate is effective for forming a nugget between the thin plate and the thick plate during welding under low pressure in the first stage of welding. It is not essential to apply a resin between the thin plate and the thick plate, but it is more preferable to apply a resin having no conductivity. By applying a non-conductive resin between the thin plate and the thick plate, the resin is extruded under pressure by the electrode just below the electrode to secure a current path, and the outside of the thin plate is made of non-conductive resin. Since the thick plates are insulated, it is easy to increase the current density immediately below the electrode between the thin plates and the thick plates, and it is easy to form a healthy nugget.

  In the conventional resistance spot welding method, it is necessary to grow a nugget formed near the center between the electrodes until the gap between the thin plate and the thick plate is melted, and an excessive current is required. On the other hand, in the case of the above method, a sound joint can be formed between the thin plate and the thick plate in the first stage of welding. What is necessary is just to select an appropriate welding current value according to the applied pressure in the latter stage of welding. It is necessary to apply sufficient pressure to crush the gap between the thick plates and extrude the resin without conductivity, and this depends on the strength of the steel plate and the rigidity of the gap.

  The present invention has been conceived based on the above concept and has the following characteristics.

  [1] When carrying out resistance spot welding while applying a pressing force by sandwiching a plate assembly in which a steel plate with a thinner plate thickness is further superposed on one of two stacked steel plates with a greater thickness, Protruding portions are provided on at least one of the two thick steel plates so that a gap is formed between the two thick steel plates immediately below the two thick steel plates. Between the steel plates, a non-conductive resin is interposed, and the welding process is divided into the first and second stages, and the resin interposed between the two or more thick steel plates in the first stage of welding is directly under the electrode. Welding is performed for a short time with a low pressure that is not extruded from, and welding is performed with a sufficiently high pressure so that the resin intervening between the two or more thick steel plates is extruded from directly below the electrode in the latter stage of welding. Resistance spot characterized by performing Contact method.

  [2] The resistance spot welding method according to [1], wherein welding is performed with a non-conductive resin interposed between the thin steel plate and the thick steel plate that are stacked on one side. .

  According to the present invention, in the case of resistance spot welding a plate assembly having a large plate thickness ratio in which a thin steel plate is superposed on at least one of two superposed thick steel plates, between the thin plate and the thick plate, It is possible to perform resistance spot welding that forms a sound joint between the thick plate and the thick plate.

It is a figure which shows the state (plate assembly) before the welding start in one Embodiment of this invention. It is a figure which shows the nugget formation state of the welding first term in one Embodiment of this invention. It is a figure which shows the nugget formation state of the welding latter stage in one Embodiment of this invention. It is a figure which shows the state (plate assembly) before the other welding start in one Embodiment of this invention. It is a figure which shows the state (plate assembly) before the other welding start in one Embodiment of this invention. It is a figure which shows the board assembly in the Example of this invention. It is a figure which shows the shape of the steel plate (thick board) which has the convex part used in the Example of this invention.

  One embodiment of the present invention is described below.

  In one embodiment of the present invention, as shown in FIG. 1, a thin steel plate (thin plate) 11 is superposed on the upper surfaces of two superposed thick steel plates (thick plates) 12, 13. Further, the plate thickness ratio is large such that there is a plate gap (the first plate gap 31 between the thin plate 11 and the thick plate 12 and the second plate gap 32 between the thick plate 12 and the thick plate 13) between the steel plates. When a plate assembly (workpiece) is sandwiched between a pair of electrodes (electrode tips) 16 and 17 and is subjected to resistance spot welding while applying pressure, the thick plate 12 includes a gap between the thick plate 12 and the thick plate 13 immediately below the electrodes. A plate assembly (work) 10A in which a convex portion 20 facing upward is provided so that a gap 33 is formed, and a non-conductive resin 14 is applied between the two thick plates 12 and 13. Then, welding is performed.

  Then, the welding process is divided into the first half and the second half. In the first half of welding, the first plate gap 31 is crushed by pressurizing with a low pressure, and welding is performed at a high current for a short time. As shown, a nugget 18 is formed between the thin plate 11 and the thick plate 12. In this low pressure pre-welding pre-welding period, the non-conductive resin 14 applied to the gap 32 is pushed out from between the steel plates on the outside of the projection 20, and the welding current passes through the outside 21 of the projection 20. Then flow. On the other hand, in the convex part 20, the resin 14 accumulates in the gap 33 to be formed, and remains without being extruded from directly below the electrode. As a result, even if the temperature of the welded portion rises during welding in the first half of welding and the gap 33 formed in the convex portion 20 is deformed in a direction to be crushed, the resin 14 having no conductivity causes the thickness at the convex portion 20 to increase. The welding current does not flow linearly between the plates 12 and 13, and the occurrence of scattering here can be suppressed.

  Then, after the energization in the first half of welding was completed, the applied pressure was increased in the second half of welding to crush the gap 33 formed in the convex portion 20, and the applied non-conductive resin 14 was pushed out between the electrodes. Thereafter, by energization, a nugget 19 is also formed between the thick plate 12 and the thick plate 13 as shown in FIG.

  Here, the resin 14 to be used is not particularly limited as long as it does not have conductivity. For example, the resin 14 used as a sealant in the manufacture of an automobile or an adhesive used in a weld bond method may be used. In the case of an adhesive, the effect of improving the fatigue characteristics and corrosion resistance of the welded portion can be obtained, and the effect of increasing the rigidity of the part can be obtained. For example, a thermosetting epoxy resin adhesive can be applied.

  Thus, in this embodiment, by applying a low pressure in the first stage of welding, only the current density in the plate gap 31 is increased to form the nugget 18, and then the pressure is increased in the second stage of welding. By extruding the non-conductive resin 14 accumulated in the gap 33 formed in the convex portion 20 in such a manner that a current flows linearly between the electrodes, a thickness ratio with the gaps 31 and 32 is provided. Nuggets 18 and 19 having the required nugget diameter can be formed between the thin plate 11 and the thick plate 12 and between the thick plate 12 and the thick plate 13, respectively, even with a large plate assembly, and welding to form a sound joint is possible. It becomes.

  As described above, in order to form the melted portion (nugget) 18 between the thin plate 11 and the thick plate 12, by passing a high welding current with a low pressurizing force in the first stage of welding, between the thin plate 11 and the thick plate 12 near the electrode. It is important to heat the neighborhood intensively. If the applied pressure exceeds 2.0 kN, the thick plate 12 becomes high temperature when a high current is passed, and the strength is lowered. Therefore, the plate gap 32 between the thick plate 12 and the thick plate 13 is greatly deformed, As a result, the thin plate 11 is also greatly deformed, the contact area between the thin plate 11 and the thick plate 12 is greatly enlarged, the current density is lowered, and it is difficult to form the nugget 18 between the thin plate 11 and the thick plate 12. Or because the resin 14 having no electrical conductivity between the thick plate 12 and the thick plate 13 is pushed out and the current flows linearly between the electrodes, the contact portion between the thick plate 12 and the thick plate 13 at once. The current density increases, and scattering occurs. Therefore, it is preferable that the applied pressure in the first stage of welding is 2.0 kN or less, more preferably 1 kN or less. Furthermore, reducing the applied pressure after several cycles of energization in the first half of welding is effective in suppressing deformation of the thick plates 12 and 13 during energization.

  In the above description, the plate assembly 10A has the thick plate 12 provided with the upwardly projecting protrusions 20. However, at least the thick plate 12 and the thick plate 12 are formed so that a gap 33 is formed between the thick plate 12 and the thick plate 13. It suffices to provide the convex portion 20 on either one of the thick plates 13, and as shown in FIG. 4, a plate assembly 10B in which the convex portion 20 facing downward is provided on the thick plate 13, or as shown in FIG. As described above, the thick plate 12 may be provided with the convex portion 20 facing upward, and the thick plate 13 may be provided with the convex portion 20 facing downward.

  The first gap 31 is preferably coated with a resin having no conductivity. Since the thin plate 11 is thin, it can be crushed even with a low applied pressure in the first stage of welding. At this time, the non-conductive resin applied to the first gap 31 is pushed out from directly under the electrode, and the energized area directly under the electrode. , And the formation of the nugget 18 in the initial stage of welding can be made easier.

  The tip of the electrode tip 16 on the thin plate 11 side is a curved surface, and the tip of the electrode tip 17 on the thick plate 13 side is a flat or thin plate 11 side having a diameter of about the required nugget diameter between the thick plate 12 and the thick plate 13. More preferably, the electrode tip 16 is a curved surface having a larger radius of curvature.

  By making the tip of the electrode tip 16 on the thin plate 11 side a curved surface and making the tip of the electrode tip 17 on the thick plate 13 side flatter, the amount of pushing of the electrode 16 into the thin plate 11 is reduced at a low pressure, and the current-carrying area is reduced. Therefore, the current density between the thin plate 11 and the thick plate 12 becomes high, and the nugget 18 is easily formed between the thin plate 11 and the thick plate 12. In addition, by making the tip of the electrode 16 on the thin plate 11 side a curved surface, increasing the pressing force during welding increases the range in which the electrode tip 16 on the thin plate 11 side can apply the pressing force, thereby suppressing the occurrence of scattering. Thus, a nugget 19 having a necessary diameter between the thick plate 12 and the thick plate 13 can be formed.

  By the way, the welding apparatus used in the present invention can be any type of pressurizing mechanism (such as an air cylinder or servomotor) as long as it sandwiches a portion to be welded by a pair of upper and lower electrode tips, and pressurizes and energizes. There are no particular restrictions on the type (stationary, robot gun), type of power source (single-phase AC, AC inverter, DC inverter), etc.

  Moreover, the steel plate to be welded can be applied regardless of the strength level (soft steel, high-tensile steel plate), and can also be applied to a hot press material or a warm press material. Moreover, it can be applied not only to a bare steel plate but also to many types of plated steel plates such as an electrogalvanized steel plate, a hot dip galvanized steel plate, an alloyed hot dip galvanized steel plate, and an Al-based plated steel plate.

  In order to confirm the effect of the present invention, the present invention example and the comparative example were carried out.

  The plate assemblies are the plate assemblies A to G shown in Table 1, and are shown by the basic plate assemblies a to e shown in FIGS. 6A to 6E and the steel plate / plate thickness configurations shown in Table 1. is there. Here, each of the basic plate assemblies a to e is a three-layer stack of (thin plate 11 + thick plate 12 + thick plate 13), of which the basic plate assemblies a to c are shown in FIGS. 6 (a) to (c). As shown, at least one of the thick plate 12 and the thick plate 13 has a convex portion 20 as shown in FIG. 7 so that a gap 33 is formed between the thick plate 12 and the thick plate 13. . On the other hand, as shown in FIG. 6 (d), the basic plate assembly d has a convex portion 20, but the downward convex portion 20 has a gap between the thick plate 12 and the thick plate 13. The base plate assembly e is a plate assembly in which the thick plates 12 and 13 do not have the convex portion 20, as shown in FIG. 6 (e).

  The first stage welding is the first stage of welding and the second stage welding is the second stage of welding. In each case, the shape of the upper and lower electrode tips, the welding pressure in the first stage of welding (first stage), the energizing time, the welding current Welding was performed under the conditions shown in Table 2 for the welding pressure (second stage), the energization time, and the welding current in the latter stage of welding. In addition, the first and second stages of welding are the first stage of welding, and the third stage of welding is the second stage of welding. In each case, the shape of the upper and lower electrode tips, the first stage of welding (first stage, second stage) Welding was performed under the conditions shown in Table 3 for the applied pressure, energizing time, welding current, applied pressure in the latter stage (third stage), energizing time, and welding current. The resin 14 was a thermosetting epoxy resin adhesive, and the presence or absence of application in each plate gap was described. The welding conditions were set such that the nugget diameter between the thick plate 12 and the thick plate 13 was 4√t (t: the thickness of the thinner one of the two thick plates 12 and 13 (mm)) mm. The welding machine used was a single-phase AC servo motor pressure resistance spot welder.

  Tables 2 and 3 show the results of evaluating the joints in each case. The evaluation is based on the evaluation based on the presence or absence of the occurrence of scattering and the peel test specified in JIS Z 3001, and the case where the plug is formed between the thin plate 11 and the thick plate 12 is good (◯), and the plug is not formed. What fractured at the interface was regarded as defective (x).

  As a result, in the example of the present invention, the plug rupture occurs between the thin plate 11 and the thick plate 12, resulting in good welding. Or, peeling occurred between the thin plate 11 and the thick plate 12, and a good weld joint could not be obtained. Thereby, the effectiveness of the present invention can be confirmed.

  Although the case where the nugget diameter between the thick plate 12 and the thick plate 13 is 4√t is evaluated here, in the case of carrying out the present invention, the nugget diameter between the thick plate 12 and the thick plate 13 is May be performed with the nugget diameter required between the thick plate and the thick plate.

10A Board assembly (work)
10B Board assembly (work)
10C Board assembly (work)
11 First steel plate (thin plate)
12 Second steel plate (thick plate)
13 Third steel plate (thick plate)
14 Non-conductive resin 16 Thin plate side electrode (electrode chip)
17 Thick plate side electrode (electrode tip)
18 Nugget between thin plate and thick plate 19 Nugget between thick plate and thick plate 20 Convex portion 21 Outside of convex portion 31 First plate gap 32 Second plate gap 33 Clearance by convex portion

Claims (2)

  When carrying out resistance spot welding with a pair of electrodes sandwiched between a pair of two thick steel plates and a thin steel plate with a pair of electrodes, A convex portion is provided on at least one of the two thick steel plates so that a gap is formed between the two thick steel plates, and between the two thick steel plates. In this process, a non-conductive resin is interposed, and the welding process is divided into the first and second stages, and the resin interposed between the two or more thick steel plates is pushed out from directly under the electrode in the first half of welding. Welding for a short time with a low applied pressure, and welding with a sufficiently high applied pressure so that the resin interposed between the two or more thick steel plates is pushed out from directly under the electrode in the latter stage of welding. Features of resistance spot welding .   The resistance spot welding method according to claim 1, wherein welding is performed by interposing a resin having no electrical conductivity between the thin steel plate and the thick steel plate that are stacked on one side.

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