Technical field
[0001]
　The present invention relates to a spot welding method for a plurality of steel plates containing plated steel sheet, particularly, it relates to suitable spot welding method on a plurality of steel plates including galvanized high strength steel sheet for automobiles.
Background technique
[0002]
　In recent years, in the automotive field, lower fuel consumption and CO 2 in order to reduce emissions, and that the weight of the vehicle body, for the improvement of collision safety, are required to increase the strength of the vehicle body member. To satisfy these requirements, it is effective to use a high strength steel sheet such as a vehicle body member, various parts.
[0003]
　From the viewpoint of the vehicle body high proof Sabika, it is necessary to configure an excellent steel plate member corrosion resistance. Zinc-plated steel sheet, it is widely known corrosion resistance is good. From the viewpoint of weight reduction and increased strength in the galvanized steel sheet used for automotive, galvanized high strength steel sheet with high strength steel sheet is being used to be plated.
[0004]
　Such as the mounting of the vehicle body of the assembly and parts of motor vehicles, mainly, it is spot welding is used. Doing spot welding galvanized high strength steel sheet, cracks from the outer surface of the steel sheet in contact with the electrode for spot welding in the thickness direction may occur.
[0005]
　Figure 1 shows a schematic of a crack spot welding point in the case of performing spot welding galvanized high strength steel sheet. Figure 1 is a thickness direction of the cross section. Doing spot welding galvanized high strength steel sheet 1, cracks 3 progresses toward the surface of the steel sheet 1 in contact with the electrodes in the molten-solidified portion 2 (nugget) (hereinafter referred to as "electrode immediately below the crack") and, the steel plate 1 cracks 6 that evolves from the point of contact between the shoulder of the electrode crack 5 (hereinafter referred to as "shoulder crack") which develop into the heat affected zone 4, from the outside of the portion where the electrode and the steel sheet 1 comes into contact with the heat-affected zone 4 ( hereinafter referred to as "electrode outer cracking") is known to occur.
[0006]
　Or less, particularly when it is not necessary to distinguish, the combined "electrode immediately below the cracking", "shoulders cracking" and "electrode outer cracking", referred to as "outer cracking". Further, as the combined "shoulders cracking" and "electrode outer cracking", "cracking of the welded portion near the outer periphery".
[0007]
　These cracks are said to be cracking due to the so-called liquid metal embrittlement. That, is said to thermal expansion of the electrode pressurizing force and the steel sheet, tensile stress due to shrinkage by acting on the welding portion is caused to lower the grain boundary strength galvanized metal melted from entering the grain boundaries of the steel sheet ing.
[0008]
　The automobile body, cracking of the welds and the strength of the joint is reduced significantly. Cracking of welded portions, suppressing technology is known by a method of controlling the chemical composition and structure of the steel sheet.
[0009]
　For example, Patent Document 1, it adjusts the chemical composition of the steel sheet, and the austenite phase generated during spot welding to fine crystal grains, and having a crystal grain and intricate metal structure of another phase in discloses that molten zinc complicates the diffusion and penetration path of the molten zinc into the crystal grain boundary is less likely to penetrate, to prevent liquid metal embrittlement cracks during welding.
[0010]
　Further, Patent Document 2, only complicates the grain boundaries by the organization control of the steel sheet, which teaches that it is not to be sufficiently inhibited cracking of welded portions, to adjust the component composition of the steel sheet, heat the grain boundary oxidation depth between rolled steel sheet and 5μm or less, by performing Fe-based electroplating the cold-rolled steel plate prior galvannealed treatment, the intergranular corrosion depth of the galvannealed steel sheet by the 5μm below discloses the suppressing the occurrence of cracks in the welded portion of the galvannealed steel sheet.
CITATION
Patent Literature
[0011]
Patent Document 1: JP 2006-265671 Patent Publication
Patent Document 2: JP 2008-231493 Patent Publication
Patent Document 3: JP-A 05-277552 JP
Summary of the Invention
Problems that the Invention is to Solve
[0012]
　Thus, measures for cracking of a region of contact between the steel sheet and the electrodes are discussed. However, in the spot welded joint of the part of galvanized steel sheet, or in the spot welded joint of the part of the non-plated steel plate and zinc-plated steel sheet, still or the cracking of a region of contact between the steel sheet and the electrode occurs, cracks may not be obtained the desired tensile strength even when not occur.
[0013]
　The present inventors have found that cracking of a region of contact between the steel sheet and the electrode was investigated why desired tensile strength can not be obtained in the case does not occur. 2 and 3 are schematic crack spot welds, shows the thickness direction of the cross section including the nugget.
[0014]
　As shown in FIG. 2, the desired tensile strength can not be obtained spot welded joint, overlapping surface corona bond directly outside crack 7 or the steel sheet be 8 crack during nugget corona bond occurs there were.
[0015]
　Further, as shown in FIG. 3, the desired tensile strength in the spot welded joint of three or more steel sheets can not be obtained, there is the crack 9 in the nugget progress from the corona bonded to the nugget has occurred .
[0016]
　Hereinafter, if it is not necessary to distinguish, corona bonding straight outer cracking, cracking during nugget corona bonding, and the cracks in the nugget are collectively referred to as "inner cracking".
[0017]
　Overlapping surface cracking or of such steel, cracks contact points of the aforementioned steel sheet and the electrode, when performing spot welding on galvanized high strength steel sheet, does not occur routinely. Therefore, in the case where the crack is generated, it is desired to prevent cracking by a simple method.
[0018]
　In view of such circumstances, and an object thereof is to provide a spot welding method in which liquid metal embrittlement cracks may easily prevented in spot welding of coated steel sheet.
Means for Solving the Problems
[0019]
　The present inventors have investigated the relationship between occurrence factor of the liquid metal embrittlement cracks of weld points were found that were likely to occur such as in the case of the following (a) ~ (g).
[0020]
　(A) If the axis is welded at an angle to be 3 ° or more from the perpendicular to the surface of the steel sheet.
[0021]
　(B) If the axis is welded by using an angled electrode has a more than 5 ° from the perpendicular to the surface of the steel sheet
[0022]
　(C) If axial to welding using a welding gun to flex more than 3 ° from the perpendicular to the surface of the steel sheet during welding
[0023]
　(D) if the relative displacement of the axis of the opposing welding electrodes are welded while occurred over 0.5mm
[0024]
　(E) superimposing when welding a weld portion having a minimum clearance of 0.5mm to the surface
[0025]
　(F) when the position of the pressing direction of the welding electrode on the fixed side to the steel sheet is welded while having the above clearance 0.2mm
[0026]
　(G) If the intensity ratio is welded a plate assembly comprising a steel sheet of more than 2.5 times
[0027]
　The present inventors have found that when such, in the welding process, the crack generation position, a tensile stress portion is caused to be high, the grain boundaries of the steel sheet of the relevant section, plating metal penetrates the melted, generating cracks It was considered to be allowed to.
[0028]
　The present inventors have studied means for preventing liquid metal embrittlement cracks. As a result, prior to the actual spot welding, to remove at least the electrode on the surface of the side in contact with, coated plated on the inside of the region of the weld heat affected zone, it prevents external cracking, also, at least a plating coated on both sides of the superimposed surface of the steel plate, the outer periphery is heat-affected zone outer edge, the inner periphery is coated in an annular (ring) shaped region comprised between 0.8 times the nugget diameter by removing the plating, conceived to prevent the inner cracking superimposed surface of the steel plate, thereby completing the invention.
[0029]
　The present invention has been made based on the above findings, and its gist is as follows.
[0030]
　(1) A method of plating a welding point of the at least one surface is spot welded sandwiched between the welding electrode facing the plurality of steel plates superimposed containing more than one sheet of coated steel sheet,
　before spot welding, plating comprising the step of removing,
　in the step of removing the plating, the range in which plating is removed, at least, in a circle to be the weld heat affected zone outer edge which is formed on the welding electrode side of a plurality of steel plates periphery are superimposed spot welding method characterized in that a.
[0031]
　(2) After the spot welding, spot welding method (1), wherein a part or the whole of the plating is removed portion, applying a sealer.
[0032]
　(3) Test spot welding before removing the plating, to confirm the presence or absence of cracks in the welded portion, when they check cracking of the welding electrode of the plurality of steel plates superimposed, it was confirmed cracks spot welding method (1) or (2), characterized in that the removal of the plating surface of the steel sheet.
[0033]
　(4) a plurality of steel plates plated welds superimposed containing more than one sheet of coated steel plate of at least one surface to a method of spot welding sandwiched between opposed welding electrodes,
　before spot welding, plating comprising the step of removing,
　in the step of removing the plating, range, the plating is removed
　in a circle the more the wide HAZ outer edge which is formed on the superposed faces of a plurality of steel plates superimposed periphery spot welding method characterized in that a.
[0034]
　(5) A method of plating a welding point of the at least one surface is spot welded sandwiched between the welding electrode facing the plurality of steel plates superimposed containing more than one sheet of coated steel sheet,
　before spot welding, plating wherein the step of removing,
　in the step of removing the plating, the range in which plating is removed,
　it is a wider the HAZ outer edge periphery is formed on the superposed faces of a plurality of steel plates superimposed,
inner and wherein the peripheral share the position and the center of the plan that is central to the nugget formed in the surface superposition of the steel sheet, and circle ring is a circle having a diameter of 0.8 times the nugget diameter spot welding method to.
[0035]
　(6) before spot welding, or spot welding method to a part or the whole of the plating is removed portion, above, wherein applying a sealer or adhesive (4) to (6).
[0036]
　(7) Test spot welding before removing the plating, to confirm the presence or absence of cracks in the welded portion, when they check cracking of a plurality of steel plates superimposed, the confirmed steel sheet cracks cracks spot welding method (4) or (5) or (6), characterized in that the removal of plating on the superimposed of superposed and generated surface steel sheet surface.
[0037]
　(8) the spot welding, (a) if the axis of the welding electrode is welded at an angle to be 3 ° or more from the perpendicular to the surface of the steel sheet, (b) the surface of the axis of the welding electrode is steel welding gun to flex less than 3 ° from perpendicular to the case, (c) the surface of the axis of the electrode is a steel sheet during the welding of welding using an angled electrode has a more than 5 ° from the perpendicular to the when welding using, with (d) If the axis relative shift of the core opposite the welding electrode is welded in a state that occurred more than 0.5mm, (e) superimposing surfaces of the gap than 0.5mm when welding weld points, more than 2.5 times the case, and (g) the intensity ratio of welding while having a clearance position of the pressing direction is 0.2mm or more welding electrodes of the fixed-side with respect to (f) steel when welding plates set containing steel sheet
under conditions including any one or more of Spot welding method (3) or (7), wherein the testing spot welding when dividing.
[0038]
　(9) In the above test spot welding, wherein, characterized in that also plated steel plates occurrence of cracks was not confirmed is removed (3), spot welding method (7), or (8).
[0039]
　(10) the removal of the plating, mechanical removal, and any one of the spot welding method of (1) to (9), which comprises carrying out at least one method of evaporation removal.
[0040]
　(11) any one spot welding method of (1) to (10), wherein the plating is zinc-plated.
Effect of the invention
[0041]
　According to the present invention, in the spot welding, it is possible to prevent the occurrence of liquid metal cracking conveniently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042]
FIG. 1 is a cross-sectional view of a plate thickness direction schematically showing the crack spot welding point in the case of performing spot welding galvanized high strength steel sheet.
FIG. 2 is a cross-sectional view of a plate thickness direction including the nugget.
3 is a cross-sectional view of a plate thickness direction including the nugget.
It is a cross-sectional view of FIG. 4 angle with and indicating the state of the welding plate thickness direction.
5 is a cross-sectional view of the thickness direction showing a state of using the angled electrodes are welded.
6 is a cross-sectional view of the thickness direction showing a state of using the easily bent welding gun are welded.
7 is a thickness direction of the cross-sectional view showing a welding by which the state remains resulted relative displacement of the axis of the opposing welding electrodes.
[8] the mating surfaces is a cross-sectional view of the thickness direction showing a state where the welding portions are welded with a gap.
9 is a thickness direction of the cross-sectional view showing a state where the position of the pressing direction is welded remain inadequate welding electrode for a plurality of steel plates.
It is a sectional view showing a state of welding FIG. 10 three leaf sets.
[11] In two-plate sets of spot welding, a cross-sectional view in the thickness direction illustrating the scope of the zinc-based plating to remove when they check cracking.
[Figure 12] three plates set of spot welding, which is a thickness direction cross-sectional view illustrating a range of zinc-based plating is removed when checking the internal cracking superimposed surface of the steel plate.
DESCRIPTION OF THE INVENTION
[0043]
　Spot welding method of the present invention (hereinafter referred to as "welding method of the present invention") is a steel sheet plated is coated on the welding portion of one surface in a plurality of steel plates containing more than one prior to spot welding, the welding point If the cracks are expected to occur, a method for removing a plating prior to spot welding.
[0044]
　Cracking is actually trying to spot welding, plating can be confirmed tested spot welding at a plurality of steel plates including one or more sheets of coated steel sheets.
[0045]
　In particular, if the spot welding is carried out under conditions corresponding to one or more of the following (a) ~ (g), before actually starting the production performing spot welding, it is possible to perform the test spot welding in the same plate pair preferable.
[0046]
　(A) If the axis is welded at an angle to be 3 ° or more from the perpendicular to the surface of the steel sheet
[0047]
　(B) If the axis is welded by using an angled electrode has a more than 5 ° from the perpendicular to the surface of the steel sheet
[0048]
　(C) If axial to welding using a welding gun to flex more than 3 ° from the perpendicular to the surface of the steel sheet during welding
[0049]
　(D) if the relative displacement of the axis of the opposing welding electrodes are welded while occurred over 0.5mm
[0050]
　(E) superimposing when welding a weld portion having a minimum clearance of 0.5mm to the surface
[0051]
　(F) when the position of the pressing direction of the welding electrode on the fixed side to the steel sheet is welded while having the above clearance 0.2mm
[0052]
　(G) If the intensity ratio is welded a plate assembly comprising a steel sheet of more than 2.5 times
[0053]
　First, the case that the testing spot welding preferably of (a) ~ (g) (cracking Factor), will be described with reference to the drawings.
[0054]
　(A) If the axis is welded at an angle to be 3 ° or more with respect to the surface of the steel plate of the welding electrode
　4 is welded at an angle to the axis becomes 3 ° or more with respect to the surface of the steel sheet it is a cross-sectional view of the thickness direction showing a state you are. Weld members shown in FIG 4 is composed of steel sheet 1a and the steel plate 1b. Steel 1a has a rising portion W, is a steel cross-sectional hat shape. In the vicinity of such a rising portion W, the case of spot welding the steel plate 1a and the steel plate 1b, the space around the welding portion becomes narrow, which may be part of a spot welding gun interfering with the rising portion W.
[0055]
　To avoid this interference, there is a case where the welding electrodes 10a, angularly 10b. Electrodes 10a, 10b, the axial core 11a, 11b is steel 1a, to the surface 1b, the not the vertical. Electrodes 10a, 10b of the distal end surface and the steel sheet 1a, in the state in which a is in contact 1b, is inclined in a direction away electrode 10a of the spot welding is from the rising portion W.
[0056]
　Axis 11a of the welding electrode, if 11b is welded at an angle to be 3 ° or more from the vertical to the steel sheet 1a, 1b surface, in particular, steel sheet 1a, the overlapping surface of the 1b corona bond straight outer or corona cracking is likely to occur when the bond of the nugget. This, when welding in a state that not exposed to vertically electrode to the surface of the steel sheet, the tensile stress is generated by the spring back to the corona bond straight outer or corona in the bond at the electrode release, because causing internal cracks.
[0057]
　(B) the axis of the welding electrode may be welded using an angled electrode has a more than 5 ° from the perpendicular to the surface of the steel sheet
　state Figure 5, which is welded by using an angled electrode is a cross-sectional view of the thickness direction illustrating the. Weld members shown in FIG. 5 consists of steel sheet 1a and the steel plate 1b. Steel 1a has a rising portion W, is a steel cross-sectional hat shape. In the vicinity of such a rising portion W, the case of spot welding the steel plate 1a and the steel plate 1b, the space around the welding portion becomes narrow, sometimes arm or the like of the spot welding gun from interfering with the rising portion W.
[0058]
　To avoid this interference, angled electrodes 10a, 10b are used. Angled electrodes 10a, 10b, the axial core 11a, 11b is steel 1a, to the surface 1b, the not the vertical. Angled electrodes 10a, 10b of the distal end surface and the steel sheet 1a, in the state in which a is in contact 1b, is inclined in a direction away from the rising portion W electrodes of the spot welding.
[0059]
　Axial 11a, 11b is steel 1a, angled electrodes 10a which is a more than 5 ° from the perpendicular to the surface 1b, the case of welding using 10b, in particular, angled electrodes 10a, 10b and the steel plate 1a, cracking of the electrode immediately below the cracking and weld near the outer periphery to the contact portion is likely to occur with 1b. This not hit is perpendicular to the electrodes to the surface of the steel sheet, with the parallel stress component on the surface of the steel sheet occurs, the plated metal during welding is for melting.
[0060]
　If axial in (c) welding to weld using a welding gun to flex more than 3 ° from the perpendicular to the surface of the steel sheet
　6 are attached is liable welding gun (electrode at the tip of the welding gun deflection ) is a sectional view of the thickness direction showing a state of welding using. Welding electrodes 10a, 10b shown in FIG. 6, the axial core 11a, 11b is steel 1a, to the surface 1b, the not become perpendicular, in parallel tip surface to the surface of the steel sheet 1a, 1b not. The welding gun by pressure due to welding (not shown) deflects the welding electrodes 10a, the distal end side of 10b is displaced in a direction away from the holder (not shown) to hold the welding electrode.
[0061]
　Axis 11a of the welding electrode, if 11b is welded using a welding gun to flex more than 3 ° from perpendicular to the steel sheet 1a, 1b surface, in particular, the electrode immediately below the cracking region of contact between the electrode and the steel sheet or, it is likely to occur cracking of the welded portion near the outer periphery. The welding gun during welding is bent, as in the case of using an angled electrode, no longer hit the vertical electrodes to the steel sheet surface, occurs parallel stress component on the surface of the steel sheet, the plating metal is melted during the welding stress the outer cracking occurs in the high part.
[0062]
　(D) if the relative displacement of the axis of the opposing welding electrodes are welded while occurred above 0.5mm
　Figure 7 is welded while resulting in relative displacement of the axis of the opposing welding electrodes it is a cross-sectional view of the thickness direction showing a state. As shown in FIG. 7, the welding electrodes 10a, 10b is the mounting of the electrode chip failure, each axis 11a, which may cause relative misalignment 12 (hereinafter referred to as "electrode misalignment") to 11b. Further, in easily bent welding gun shown in FIG. 6, when the upper and lower deflection is not uniform, deviation of the axis is generated with angle occurs in the electrode.
[0063]
　Opposing welding electrodes 10a, if the electrode misalignment 12 of 10b is welded remains above 0.5 mm, in particular, cracking or corona bonding directly outside overlapped surface of the steel sheet, cracks during nugget corona bond, in nugget cracking is likely to occur. If the axis of the electrode is shifted, so that the welding in a state of stress to shear the steel occurs. Then, while power for the welding, and when energized to release the finished electrode, and high stress occurs, cracking or corona bonding straight out, cracking during nugget corona bond, cracks in the nugget occur.
[0064]
　(E) superimposing the case of welding the welding parts having a minimum clearance of 0.5mm to the surface
　8 is a cross-sectional view of the thickness direction showing a state of welding a weld portion having a gap mating surfaces . As shown in FIG. 8, the steel sheet 1a, during 1b, such as when another member 13 is inserted, the steel sheet 1a of overlapping surfaces of the welding location, that the gap 14 (hereinafter "Itasuki" during 1b ) may be formed.
[0065]
　If Itasuki 14 welding point is welded remains above 0.5 mm, in particular, a corona bond straight out of the crack is likely to occur on the rear overlapping the steel sheet. When there is a gap, it is welded in a state where tensile stress is standing on the surface of the mating surface side of the steel plate. Energized for welding, although the temperature of the steel sheet increases the tensile stress is relaxed, after application end, the steel begins to cool Standing strong tensile stress, the stress of the occurrence limit cracks before the plating metal solidifies it exceeds corona bond straight out of the crack will occur when.
[0066]
　(F) when the position of the pressing direction of the welding electrode on the fixed side to the steel sheet is welded while having more clearance 0.2mm
　Figure 9, while the wrong position in the pressing direction of the welding electrode for a plurality of steel plates a plate thickness direction of the cross section showing a state of welding. In spot welding, in order to correct the position of the pressing direction of the welding electrode for a plurality of steel plates, and welding teaches that position the robot welding electrodes of the fixed side is brought into contact with the steel plate, the pressure welding by providing equalization mechanism between the robot and the spot welding gun so that it can move freely in the direction is carried out.
[0067]
　However, if not provided or if the equalizing mechanism of the teachings failure to the robot, as shown in FIG. 9, it has a faulty position in the pressing direction of the welding electrode 10b of the fixed side to the steel sheet 1b, the steel sheet 1b and the welding electrode 10b will be welded while there is a clearance 15, the tensile stress is generated in the weld.
[0068]
　If this order clearance 15 is welded remains above 0.2 mm, in particular, cracking or corona bonding directly outside overlapped surface of the steel sheet, cracks tend to occur during nugget corona bond.
[0069]
　(G) If the intensity ratio is welded a plate assembly comprising a steel sheet of more than 2.5-fold
　Figure 10 is a mild steel plate in the middle, upper and lower high strength steel plate provided showing a state of welding the plate thickness direction of the it is a cross-sectional. In spot welding welding 3 ply is often performed. However, when the difference in the tensile strength of the steel sheet to be welded is large, for example, the case of FIG. 10, in the spot welding process, mild steel plate in the middle low strength is thickened at ambient extruded from immediately below the electrode. In this case, so as to displace the upper and lower high-strength steel sheets vertically, the high strength steel sheet surface, parallel pulling tension stress on the surface of the steel sheet is produced.
[0070]
　When the intensity difference of the steel sheet is more than 2.5 times, in particular, crack or during nugget corona bonded to the mating surface of the steel sheet, is likely to occur cracks in the nugget.
[0071]
　It will now be described welding method of the present invention.
[0072]
　First, plating providing a plurality of steel plates including one or more steel plates which are coated on at least the welding location. For example, zinc-based plated is coated on both sides, tensile strength 780MPa or more, C content is 0.15 mass% or more, to prepare a steel sheet having a thickness of 0.5 ~ 3.0 mm 2 or more sheets.
[0073]
　Then, in the actual production, the (a) ~ the cracking factor (g) under conditions comprising one or more when it comes to performing spot welding, may be carried out in advance test spot welding.
[0074]
　The test spot welding, resulting in actual production, the (a) under conditions comprising one or more of the cracking factor ~ (g), by superimposing two or more steel plates, from both sides, two or more steel plates so as to sandwich and energized while pressing the electrode made of a copper alloy, to form a molten metal, by heat conduction to the heat removal and the steel plate by water-cooled electrode after the end of energization, rapidly cooling the molten metal and solidifying, during the steel plate to form a nugget oval cross section.
[0075]
　After the test spot welding, to confirm the presence or absence of the occurrence of cracks in the welded portion. Cracking of the welding electrode side of the superposed plurality of steel plates, namely check of external cracking, for example, it can be performed by visual contact points. Confirmation of the outer cracking, as shown in FIG. 1, to include a nugget, and cut in the thickness direction is performed to check the cross-section. Small cracks by using a magnifying glass can also be confirmed.
[0076]
　Overlapping surface cracking of the steel sheet, confirmation of the inner cracking i.e., for example, to include nuggets as shown in FIGS. 2 and 3, is cut in the thickness direction is performed to check the cross-section. Small cracks by using a magnifying glass can also be confirmed.
[0077]
　Cracking of the welded portion was observed, when performing spot welding a plurality of steel plates under conditions comprising cracking factor, before spot welding, to carry out the removal of the plating preferred.
[0078]
　HAZ, nugget, to determine the amount of corona bond, through the center of the portion recess by spot welding, and cut in the thickness direction, polished, etched with chemicals such as nital.
[0079]
　Then, plating is superposed two or more steel plates which are removed, and the spot welding conditions to adjust the current based on the welding conditions of the test spot welding. The adjustment of the current value, so that the nugget diameter of the target is obtained, is for correcting the variation of the required current value due to the removal of the plating typically require adjustment to low current side. Thus, the generation position of the cracks in the welded portion, since the molten zinc is not present, it is possible to prevent the occurrence of liquid metal cracking overlapping surfaces of the contact points and steel with the electrodes of the steel sheet.
[0080]
　Next, the welding method of the present invention, furthermore, will be sequentially described necessary requirements and preferred features.
[0081]
　
　plurality of steel plates to be spot welded, if a plurality of steel plates containing plating welded portion of at least one surface at least one of the coated steel sheet, not limited in particular. For example, the steel sheets plated is coated on the surface on the side in contact with the steel sheet and the electrode combination and the combination of steel sheets plated with steel sheet and the electrode is plated on the surface of the side contacting the coated steel sheet is uncoated plating overlapping surfaces of the surface and the steel sheet on the side where the steel sheet and the electrodes are in contact with a combination of steel sheets coated are exemplified. Further, considering the corrosion resistance of the welded joint, it is preferable that plating overlapping surfaces of the surface and the steel sheet on the side in contact with the steel sheet and the electrode is covered.
[0082]
　Welding method of the present invention, an alloy containing zinc is plated is suitable for spot welding of steel sheet, including zinc-based plated steel sheet. However, according to the principles of the present invention, even in the case of other plating such as Cu-plated, it is clear it is possible to obtain the same effect.
[0083]
　If plating zinc-based coated on steel plates to be welded, as long as a plating including zinc, is not particularly limited. For example, a plating species, galvannealed, galvanized, electro-galvanized, zinc-nickel electroplating are exemplified. It can also include plating of zinc-aluminum-magnesium system.
[0084]
　As a plurality of steel plates to be spot welded, in FIGS. 1 and 2, has been described the two steel plates, depending on the form of structural parts to be joined, a plurality of steel plates or three as shown in FIG. 3 it can be. The thickness of each steel sheet spot welding, but the present invention is not particularly limited, for example, may be 0.5 ~ 3.0 mm. Further, the thickness of the sum of a plurality of steel plates, but the present invention is not particularly limited, for example, may be 1.0 ~ 7.0 mm.
[0085]
　Further, a plurality of steel plates to be spot welded, and component composition, and the metal structure, not particularly limited. However, steel galvanized were coated on overlapping surfaces of the side surface or the steel plate to contact steel sheet and the electrode, or the steel sheet galvanized is superimposed over the steel sheet and the galvanized coating in contrast, and low-alloy TRIP steel sheet, when the tensile strength using a steel sheet containing C not less than 0.15 mass% at least 780 MPa, since the cracking of the welded portions tends to occur, in the welding method of the present invention, in particular, it is effective for such steel sheet.
[0086]
　Further, the steel sheet has a plate-shaped portion on at least a portion, as long as it has a portion where the plate-like portion is stacked superposed each other or even entirely without a plate. The plurality of steel plates is not limited to those composed of separate steel plate, or a superposition of those molding a single steel plate into a predetermined shape, such as tubular.
[0087]
　
　Next, a description will be given of the test spot welding. Test spot welding is preferably carried out when satisfying the actual one or more of the above occurring in the production (a) ~ (g).
[0088]
　Test spot welding, at conditions including cracking factors mentioned above (a) ~ (g) generated in the plate set and the actual production of the target is performed in the welding conditions used in actual production.
[0089]
　Welding conditions, employing a welding conditions used in actual production. For example, the electrode assumes the Domurajiasu type tip diameter 6 ~ 8 mm, pressure 2.5 ~ 8.0kN, energizing time 5-99 cycles, it is possible to supply current 4 ~ 15 kA. However, the applied current value, it is desirable to employ the current value before and after setting in actual production. In the test of energization current of pinpoint, there is a miss cracking welding point. This welding surface of the electrode wear during repeated, when a current density decreases even at the same current value becomes a nugget diameter close to the minimum nugget diameter for a target, and the tensile stress generated in the welded portion of the plated metal This is to correspond to the melting range is changed.
[0090]
　
　in the spot welded joint obtained by the test spot welding, to confirm the presence or absence of cracks in the welded portion. How to check occurrence of this crack is not limited in particular, performed in the observation and penetrant inspection visually observed and the thickness direction of the cross section including the molten-solidified portion, a tensile test spot welded joint can be carried out by, for example, determined by whether or not a predetermined tensile strength can be obtained by. Or, in addition to the observation of the thickness direction of the cross section including the spot welds, it may be confirmed by performing X-ray transmission test.
[0091]
　Electrode immediately below the fracture point of contact between the steel sheet and the electrode is generated directly below the electrode contact points between the steel sheet and the electrode (near the center), the shoulder cracking and electrodes outside cracks generated in the vicinity weld periphery.
[0092]
　Cracking during nuggets overlapping surface corona bond straight outer and corona bonding of the steel sheet, overlapping surfaces of steel sheets plated is coated, or plated are superimposed with coated steel plate plated steel sheets uncoated generated in the mating surfaces. Then, among these overlapping surface, it generated in the corona bond and its vicinity. Also, cracks in the nugget in the spot welded joint of three or more steel plates, produced toward the nugget from the corona bond.
[0093]
　
　welding method of the present invention, prior to spot welding, and removing the plated steel plate to be welded. Removal range plating, depending on the position of the crack was confirmed in the test spot welding, it is in the range of less.
[0094]
　(Contact portion with the case confirmed the cracks around the steel plate and the electrode)
　when they check out cracks by the test spot welding, the range of the plating to be removed, at least, outside cracking of a plurality of steel plates superimposed is confirmed in steel sheet, a coated plated to the welding electrode side, the outer periphery is a range within a circle as the weld heat affected zone outer edge of the welding electrode. Thereby, overlapping several generation factors of cracks, even strong stress is generated on the surface of the side in contact with the electrodes of the steel sheet, occurrence of external crack because the plated metal melted does not exist eliminated.
[0095]
　Outside cracking, the electrode immediately below the crack, shoulder cracks, there are electrodes outside cracking. For example, when the axis of the electrodes from the electrode directly under cracking was not observed did not remove the plating of the portion in contact, when the repeating spot welding, an alloy of copper molten plating metal or plating metal and the electrode, There through the electrodes, cracking adheres to the steel sheet surface was removed to occur again cracking occurs. Therefore, even if any was one only cracks occur, the outer periphery is necessary to remove the plating of all the regions in the circle as the weld heat affected zone outer edge of the welding electrode.
[0096]
　Illustrating the range of the plating to specifically remove with reference to FIG. Figure 11 is a cross-sectional view in the thickness direction illustrating the scope of the plating to be removed when checking the cracking of the contact surface and the superimposed surfaces of the steel plate and steel plate electrodes with two leaf pairs. In Figure 11, the steel plate 101 is welded superimposed, nugget formation planned portion 102, a corona bond formation planned portion 103, portion 105 of the electrode immediately below the cracking is expected locations electrode shoulder fracture is expected 106, electrode It shows a portion 107 of the outer cracking is expected by the dotted line.
[0097]
　11, the heat affected zone outer edge formation planned position 104 is also shown by dotted lines. Removal area of the plating to prevent external cracks, the diameter D to the outer circumference and heat-affected zone outer HAZ1 and within a circle. HAZ outer edge to be formed position of the steel sheet is a position where the steel sheet is heated to about 700 ° C.. Therefore, the plating metal in the range in the welding process melts and has sufficient liquidity. Therefore, in order to prevent the outer cracking, be removed plating only portions cracking occurs because the spread wet sites plated metal around is removed, is removed effect the plating is lost.
[0098]
　For convenience aim accuracy of the welding position, a range for removing the plating, for example, D HAZ1 such as within a circle having a diameter of × 1.5, the diameter D HAZ1 may be wider than the circle. However, since the corrosion resistance decreases, it should be as narrow as possible.
[0099]
　The heat affected zone edge position, the distance from the nugget center Cn different in the thickness direction. This contrast is the side in contact with the steel plate electrodes are cooled by the electrode, because the mating surfaces are in does not work this cooling action. Range of diameters D to remove the plating for outer-break preventing HAZ1 , it is preferable to determine in the heat affected zone outer edge of the vicinity of the electrode surface of the steel sheet.
[0100]
　Further, in order to determine the heat-affected zone outer edge to be formed position can performed observing a section of the test spot welds using a corrosive liquid such as nital.
[0101]
　(Overlapping surface cracking (when confirming the internal crack) of steel sheet)
　when they check test by spot welding cracks or corona bonding straight outside during nugget nugget or corona bonding cracks, the range of the plating to be removed, a superposition surface of the steel plate to be welded, the diameter of the more wide HAZ outer edge of the overlapped outer peripheral surface D HAZ2 the range within the circle is. By removing the plating of this range, overlapping several generation factors of cracks, even strong stress is generated in the overlapping surfaces of the steel plate, inner cracks does not occur because the plated metal melted is not present.
[0102]
　Further, it is rather wide weld affected zone outer edge outer peripheral range of removing the plating is formed on the superposed faces of a plurality of steel plates superimposed, the nugget the inner circumference is formed on the overlapping surface of the steel plate center sharing position the center of the made schedule, may be in the range of a circle within the ring is a circle having a diameter of 0.8 times the nugget diameter. Plated in a circle having a diameter of 0.8 times the nugget diameter, the substantially inner cracks is because not contribute.
[0103]
　By limiting the scope of removing such plating, a change in welding conditions caused by the removal of the plating can be suppressed as much as possible.
[0104]
　Illustrating the range of the plating which specifically removed using FIGS. 11 and 12. Figure 11 is a cross-sectional view in the thickness direction illustrating the scope of the plating to be removed when checking cracking of overlapping surfaces of the steel plate in two leaf pairs. In Figure 11, the steel plate 101 is welded superimposed shows nugget formation planned portion 102, a corona bond formation planned portion 103, a portion 108 where the crack in the corona bond straight outer anticipated by dotted lines.
[0105]
　FIG. 12 shows locations occurrence of nugget Sai cracking corona bond is predicted 109, a portion 110 of cracking in the nugget is predicted by a dotted line.
[0106]
　Inner cracks in the welding process, to generate a plating metal melted at between steel sheet remains at the site of action of the tensile stress.
[0107]
　Corona Bond straight out of the crack is melted in the corona bond formation planned portion, a plating metal discharged by the electrode pressure, inside the heat-affected zone in the molten plating metal corona bond straight outer were located outside the corona bond tensile stress in the wet state is generated in action.
[0108]
　Cracking and cracking during nugget corona bond in the corona bond melts in the vicinity of the outer edge of the nugget to be formed position, plating metal was melted in the molten plating metal and the corona bond formation planned portion discharged by the electrode pressurization, Corona in a state of being confined within the bond tensile stress is generated acts.
[0109]
　That is, inner cracks in the welding process, caused plated metal melted at the heat affected portion, and then melted at overlapping surfaces of the steel plate by hot dipping metal discharged in the forward direction (outward direction) away from the center of the nugget . Therefore, the de-plating is not only near the inner cracking position, outer and heat affected zone from the nugget center, it is necessary to perform together range including the nugget to be formed a position close to the nugget center. Here, the molten plating metal, after evaporation and vaporization, liquefied plated metal The present invention also includes.
[0110]
　When confirming the internal cracks, the range of the plating to be removed is a superposition surface of the steel plate to be welded, D is a circle equivalent diameter of more wide periphery of the weld heat affected zone outer edge of the overlapping surface HAZ2 have a and, the range of the circle around the center Cn of the nugget formation planned portion 102. Note that the circle equivalent diameter of the weld heat affected zone outer edge, in the heat affected zone outer edge of the overlapping surfaces of two steel plates superimposed, is that the diameter of the wider towards the area and the circle having the same area.
[0111]
　Removal of the plating, it is necessary to the superimposed steel plates, for both plating. If you have superimposed plated steel plates, be removed only plating occurred steel cracked, plated metal melted from steel superimposed party is to be supplied. Inner Thus, by removing the plating of this range of plating, overlapping several generation factors of cracks, even a strong tensile stress is generated in the overlapping surfaces of the steel plate, the plating metal melted absence cracking does not occur.
[0112]
　Also, a range for removing the plating, outer periphery about the center Cn of the nugget formation planned portion 102, D as the diameter HAZ2 or D, HAZ3 a circle having the inner periphery is formed on the overlapping surface of the steel plate around the center Cn of the nugget formation planned portion 102 may be a range within ring is a circle of 0.8 times the diameter of the nugget Dn formed on surfaces superposed in diameter. Plating within the circle is 0.8 times the diameter of the nugget, the substantially inner cracks is because not contribute.
[0113]
　Plating metal is coated on a circle outside the 0.8 times the circle equivalent diameter Dn of nugget formation planned portion is often the rate to be discharged into the corona bond in the welding process. Therefore, in order to suppress internal cracks must be reliably remove the plating is covered in this range. On the other hand, the plating metal is coated in 0.8 times the circle equivalent circle diameter Dn of nugget formation planned portion, because the proportion that is discharged into the corona bond is small, it is not actively removed.
[0114]
　Furthermore, by leaving without removing the plating within the circle is 0.8 times the diameter of the nugget diameter Dn, it is possible to prevent the welding conditions vary greatly by removing the plated metal.
[0115]
　Incidentally, when the removal area of ​​the plating becomes large, there is a possibility that corrosion occurs from the removal location, blindly, but is not preferred to remove the plating, plating beyond the range defined in the present invention in order to prevent weld cracking It does not prevent the removal.
[0116]
　Considering the positional accuracy of the spot welding, the heat affected zone outer edge formation planned portion of the circle equivalent diameter D HAZ2 , or D HAZ3 may be removed plating coated on a range beyond, but because the corrosion resistance decreases, removed If you want, an effort to improve the positional accuracy of the spot welding, the heat affected zone outer edge formation planned portion of the circle equivalent diameter D HAZ2 , or D HAZ3 when all 5.0 times the parts of it.
[0117]
　The plating to be removed, the circle equivalent diameter D HAZ2 or D, HAZ3 all 2.0 times or less parts, more preferably, may be all of 1.5 times or less parts.
[0118]
　Also, equivalent circle of HAZ outer form planned portion diameter D HAZ2 , D HAZ3 , circle equivalent diameter Dn of nugget formation planned portion, prior to spot welding the plurality of steel plates, determines the welding conditions at the coupon (test specimen) a circle equivalent diameter observed when the. Also in the actual spot welding, although not necessarily the identical weld length, as long as removal area of the plating of the welding method of the present invention, it is possible to cover this error sufficiently.
[0119]
　
　In spot welding of a plurality of steel plates including steel plates plated is removed at a particular position, when checking cracking of overlapping surface cracks and steel contact points between the steel sheet and the electrode , adjust the time of the test spot welding, the current value so that the nugget diameter is the same. Thereby, it is possible to secure the strength of spot welded joint was originally targeted.
[0120]
　
　by removing the plating, corrosion resistance of the overlapping surfaces of welded portions and the steel plate of the steel plate and the electrode may become insufficient. Therefore, upon removal of the plating of the contact planned portion of the steel plate and the welding electrode is removed after spot welding, a part or the whole of the plating is removed portion is coated with a sealer, the plating of the superimposed surface of the steel plate when, before spot welding, a part or the whole of the plating is removed portion, it is preferable to apply a sealer or adhesive.
[0121]
　Sealer or adhesive is not particularly limited and may be a known to be used in vehicle assembly. Further, it is also effective in ensuring the corrosion resistance to be mixed with metal particles made of zinc sealer or adhesive.
[0122]
　
　As a method for removing the plating may be employed at least one of the mechanical removal, and evaporated off. The mechanical removal can be ground by byte rotation. At this time, Sadamari rotation center when ground by byte with projections in a circle equivalent center of such contact planned portion can be removed accurately plating. By sufficiently small projections, by welding, it is possible to fill the hole formed in the projection.
[0123]
　Evaporation removal beyond that must be removed, circular, illuminated ring, a laser having a light collecting shape such as a square in the plating, a method of evaporating off. According to this, it is possible to selectively remove low-boiling metals that cause liquid metal embrittlement, such as zinc or magnesium.
[0124]
　Irradiation of the laser, it is important to ensure that the reflected light does not return to the oscillator at an angle. From the viewpoint of environmental protection, it is preferable to provide a device for sucking the vaporized metal. Further, the laser was focused to a few tens of [mu] m, it may be ablating. Further, by irradiating the plasma, it can be removed by evaporation plating.
Example
[0125]
　Next, a description will be given of an embodiment of the present invention. Conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0126]
　Table 1 shows the steel sheet used. Galvanized steel sheet A ~ E are the galvannealed steel sheet, a zinc plating is coated on both sides.
[0127]
[Table 1]

[0128]
　The steel sheets shown in Table 1 2-3 sheets using subjected to spot welding.
[0129]
　Test No. 1, with the axis of the welding electrode is in the 3 ° from the perpendicular to the surface of the steel sheet, which is a comparative example in which spot welding without removing the galvanized. Spot welding, from both sides, in Domurajiasu electrode tip diameter 6 mm, sandwiched two steel plates, while pressing at a pressure 4 kN, weld time 18 cycles were performed with the electric current 9 kA. As a result, a corona bond directly outside the inner cracking was confirmed.
[0130]
　The subsequent examples, the conditions of the spot welding is the same as Test No. 1.
[0131]
　Test Nos. 2 to 6, receives the results of Test No. 1 is an example in which the spot welding to remove galvanized.
[0132]
　Test No. 7 using the angled electrodes becomes 5 ° from the vertical to the surface of the shaft is a steel sheet during welding, with the gap of the overlapping surface exists 0.5 mm, without removing the galvanized is a comparative example in which spot welding. In Test No. 7, a corona bond directly outside the inner cracking was confirmed.
[0133]
　Test No. 8 receives the result of Test No. 7 is an example of performing a spot welding by removing the galvanized.
[0134]
　Test No. 9, in combination with a large steel sheet strength ratio is a comparative example in which spot welding without removing the galvanized. In Test No. 9, the inner cracking was observed during nugget coronavirus bond.
[0135]
　Test No. 10 to 12, receives the results of Test No. 9, an example in which the spot welding to remove galvanized.
[0136]
　Test No. 13, in a state the axis of the opposing welding electrodes were relatively 0.5mm offset, and, in a state where the position of the welding electrode pressurizing direction of the fixed side to the steel sheet is in the 0.2 mm, zinc without removing the plating is a comparative example in which spot welding. In Test No. 13, the inner cracking was progress in the nugget from the corona bond was confirmed.
[0137]
　Test No. 14 to 17, receives the results of Test No. 9, an example in which the spot welding to remove galvanized.
[0138]
　Test No. 18, the shaft core during welding using the welding gun to flex so that 3 ° from the perpendicular to the surface of the steel sheet, which is a comparative example in which spot welding without removing the galvanized. In Test No. 18, the outer cracking was observed directly under the electrode and the shoulder.
[0139]
　Test No. 19-20, receives the results of Test No. 18 is an example in which the spot welding to remove galvanized.
[0140]
　Test No. 21, using a welding gun to flex so that 3 ° from the perpendicular to the surface of the shaft is a steel sheet during welding, further, the welding portion where the gap of the overlapping surface has more than 0.5 mm, is a comparative example in which spot welding without removing the galvanized. In Test No. 21, the outer cracks was confirmed in the electrode outward.
[0141]
　The removal of zinc-based plating, using evaporation removal, or mechanical removal.
[0142]
　The evaporated off, and then heated for galvanizing laser, by plasma.
[0143]
　Removal of galvanized with evaporation by laser, the laser was focused to a diameter 9.5 mm, 0.1 seconds at the output 1 kW, irradiating the galvanized to remove galvanized removal range.
[0144]
　Removal of galvanized using laser ablation, the laser was focused to a diameter 40 [mu] m, an average output 9W, the number of repetitions 50 kHz, at a pulse width (time reporting the laser) 20 ns, 10 shots at the same point, galvanized irradiating the to remove the galvanized by scanning the entire area of ​​the removal area.
[0145]
　Removed with plasma, current 200A, discharged at a voltage 20V, 0.2 seconds, and heated galvanized. Plasma, since the energy density is distributed, the aim galvanized range is completely removed, the surrounding was also partially removed.
[0146]
　In mechanical removal, by grinding using rotary tool to remove the zinc plating of the removal area.
[0147]
　Test piece, was confirmed cracks welding point and combined cycle corrosion test to verify the corrosion resistance (CCT test). The results are shown in Tables 2-4 to. Incidentally, the sign of cracking factor in Tables 2-4 correspond to be preferable to carry out the test spot welding as described above (cracking Factor).
[0148]
　CCT test, based on the Corrosion testing method for automobile (JASOM609-91), the processing of 8 hours per cycle was repeated 30 cycles was performed. 1 cycle, salt spray test (2 hours, 5% NaCl, 35 ℃), dried (4 hours, 30% RH, 60 ℃), consisting of a wet test (2 hours, 95% RH, 50 ℃).
[0149]
　Evaluation, those that do not seen a change in the peripheral spot weld between the steel plate "◎", "○" what occurrence of white rust is observed, and what red rust is occurring as "×". Further, confirmation of the cracks, to include a nugget, by cutting the test piece in the thickness direction was carried out to confirm the cross-section.
[0150]
　As a result of spot welding to remove the zinc plating were as follows.
[0151]
　Test Nos. 2 to 3,8,10,14 ~ 15, 19 ~ 20, 22 ~ 23 removes the galvanized range defined in the present invention, as a result of spot welding, the generation of cracks in the weld no, corrosion resistance was good. At a position to remove the test No. 2 in galvanizing an adhesive is applied, because applying a sealer after welding the plating removal unit in Test No. 20, it showed particularly good corrosion resistance.
[0152]
　Test No. 4-6, were carried out the removal of zinc plating, removal range is narrow, inner cracks in the corona bond straight outer occurs.
[0153]
　Test Nos. 11 to 12 have been carried out the removal of zinc plating, removal range is narrow, inner cracks in the nugget corona bond occurs.
[0154]
　Test No. 16 to 17, although the removal of zinc plating was performed, the removal area is narrow, inner cracks were developed in the nugget from the corona bond occurs.
[0155]
[Table 2]

[0156]
[table 3]

[0157]
[Table 4]

Industrial Applicability
[0158]
　According to the present invention, in the spot welding, it is possible to prevent the occurrence of liquid metal cracking conveniently. Accordingly, the present invention has high industrial applicability.
DESCRIPTION OF SYMBOLS
[0159]
　1, 1a, 1b steel
　2 nugget
　third electrode immediately below the cracking
　4 HAZ
　5 shoulder cracking
　sixth electrode outer cracks
　7 corona bond straight out of the crack
　8 cracking during nugget corona bond
　cracks in 9 nugget
　10a, 10b electrode
　11a , 11b shaft core
　12 electrodes misalignment
　13 member
　14 Itasuki
　15 clearance
　101 steel
　102 nugget formation planned portion
　103 corona bond formation scheduled position
　104 HAZ outer edge formation planned position
　105 electrode immediately below the cracking planned portion
　106 electrode shoulder cracking planned portion
　107 electrode outer cracking planned portion
　108 corona bond straight outer cracking planned portion
　109 nugget Sai cracking planned portion corona bond
　110 nugget cracking planned portion
　center Cn nugget formation planned portion
　Dc corona bond to be formed circle locations equivalent diameter
　Dn nugget to be formed Circle equivalent diameter of at
　D HAZ1　　diameter ranging removing the plating to avoid external cracking
　DHAZ2　　2 ply board sets range of diameters for removing plating to avoid internal cracking in
　D HAZ3　　diameter range for removing plating to avoid internal cracking in three leaf set
　W rising portion

The scope of the claims
[Claim 1]
　A method plating welded portion of at least one surface spot welding sandwiching welding electrode facing the plurality of steel plates superimposed containing more than one sheet of coated steel sheet,
　prior to spot welding, to remove the plating includes the step,
　in the step of removing the plating, the range in which plating is removed, at least, be in the circle as a weld heat affected zone outer edge which is formed on the welding electrode side of a plurality of steel plates periphery are superimposed spot welding method comprising.
[Claim 2]
　After spot welding, a part or the whole of the plating is removed portion, the spot welding method according to claim 1, wherein applying the sealer.
[Claim 3]
　Test spot welding before removing the plating, to confirm the presence or absence of cracks in the welded portion, when they check cracking of the welding electrode of the plurality of steel plates superimposed, the confirmed steel sheet surface cracks spot welding method according to claim 1 or 2, characterized in that the removal of plating.
[Claim 4]
　A method plating welded portion of at least one surface spot welding sandwiching welding electrode facing the plurality of steel plates superimposed containing more than one sheet of coated steel sheet,
　prior to spot welding, to remove the plating It includes the step,
　in the step of removing the plating, plating the range to be removed,
　to be within a circle the more the wide HAZ outer edge which is formed on the superposed faces of a plurality of steel plates superimposed periphery spot welding method comprising.
[Claim 5]
　A method plating welded portion of at least one surface spot welding sandwiching welding electrode facing the plurality of steel plates superimposed containing more than one sheet of coated steel sheet,
　prior to spot welding, to remove the plating includes the step,
　in the step of removing the plating, the range in which plating is removed,
　it is a wider the HAZ outer edge periphery is formed on the superposed faces of a plurality of steel plates superimposed, inner circumference above spots, characterized in that sharing position the center of the plan that is central to the nugget formed in the superimposed surface of the steel plate, and the ring is a circle having a diameter of 0.8 times the nugget diameter welding method.
[Claim 6]
　Before spot welding, spot welding method according to claim 4 or 5 in a part or the whole of the plating is removed portion, characterized by applying a sealer or adhesive.
[Claim 7]
　Test spot welding before removing the plating, to confirm the presence or absence of cracks in the welded portion, when they check cracking of a plurality of steel plates superimposed, cracking surface of the confirmed steel cracked spot welding method according to any one of claims 4-6, characterized in that the removal of plating on the steel sheet superposed surfaces superimposed with.
[8.]
　The spot welding,
　　(a) if the axis of the welding electrode is welded at an angle to be 3 ° or more from the perpendicular to the surface of the steel sheet,
　　with respect to (b) the surface of the axis of the welding electrode is steel when welding using an angled electrode consists perpendicular to 5 ° or more,
　　by using the welding gun to flex more than 3 ° from perpendicular to the (c) the surface of the axis of the electrode during welding steel plates when welding Te,
　　when, welding in a state caused or relative deviation of the axis is 0.5mm in (d) opposite the welding electrode
　　to the welding parts having (e) superimposing surfaces of the gap than 0.5mm when welding,
　　when, and welding while having a clearance position of the pressing direction is 0.2mm or more welding electrodes of the fixed-side with respect to (f) steel
　　including steel sheets of more than 2.5 times (g) intensity ratio when welding plates of sets
line under conditions comprising any one or more of Spot welding method according to claim 3 or 7, characterized in that the test spot welding when.
[Claim 9]
　In the above test spot welding, spot welding method according to claim 3, 7 or 8, characterized in that also plated steel plates occurrence of cracks was not confirmed removed.
[Claim 10]
　The removal of plating, mechanical removal, and spot welding method according to any one of claims 1 to 9, characterized in that at least one of the evaporation removal.
[Claim 11]
　Spot welding method according to any one of claims 1 to 10, wherein the plating is zinc-plated.