Specification
Title of invention: Spot welding method
Technical field
[0001]
　The present disclosure relates to a spot welding method for performing resistance spot welding on a plate set including a plurality of stacked metal plates.
Background technology
[0002]
　Resistance spot welding is mainly used for joining a plurality of metal plates which are overlapped with each other in assembling a vehicle body of an automobile or mounting parts. In this spot welding, a pair of electrode tips whose tip is pressed against the plate assembly is used.
[0003]
　In spot welding, electricity is applied while pressing the electrode chips so that the metal plates are sandwiched from both sides of the overlapped metal plates to form molten metal, and after the energization, heat removal by the electrode chips and metal plates are performed. The molten metal is cooled and solidified by heat conduction to itself, and a molten and solidified portion (nugget) having an elliptical cross section is formed between the metal plates.
[0004]
　In automobile bodies, difficult-to-weld parts have recently appeared in order to reduce the weight. As a typical example thereof, a thin plate/thick plate/thick plate three-layer spot welded portion is formed by thinning an outer plate around a door called a side member and thickening a reinforcement of a B pillar which is a skeletal member. In the present application, the metal plate having the smallest thickness is referred to as a thin plate, and the metal plate having a thickness greater than that is referred to as a thick plate among the plurality of metal plates stacked.
Prior art documents
Patent literature
[0005]
Patent Document 1: Japanese Patent Laid-Open No. 2011-11259
Patent Document 2: Japanese Patent Laid-Open No. 2012-66284
Patent Document 3: Japanese Patent Laid-Open No. 2006-55898
Summary of the invention
Problems to be Solved by the Invention
[0006]
　In spot welding such as thin plate/thick plate/thick plate three-ply stacking found in automobile bodies and the like, the metal plate having the smallest thickness is generally arranged on the outermost side of the laminate because it is easy to process. In this case, the thick plate/thick plate interface is easily melted, but the thin plate/thick plate interface is difficult to melt and stable spot welding is difficult.
[0007]
　In spot welding, since the melting starts from the center of the plate assembly farthest from the water-cooled electrode, the thin plate/thick plate interface is difficult to melt. Furthermore, since thin plates are generally made of mild steel and thick plates are generally made of high-strength steel, the use of such a combination of plates results in a large contact area between the thin plate and the electrode tip and a contact between the thick plate and the electrode tip. Since the area becomes smaller, the current density on the thin plate side becomes smaller, and the thin plate/thick plate interface becomes more difficult to melt. Furthermore, since mild steel has a higher electric conductivity than high-strength steel, it is less likely to generate heat, and it is difficult to melt the thin plate/thick plate interface.
[0008]
　Therefore, the upper limit of the plate thickness ratio is generally defined to be about 4 to 5, which is one of the factors that hinders the degree of freedom in design.
[0009]
　In order to perform spot welding of a thin plate/thick plate combination having such a large plate thickness ratio, a technique of providing a pressure member for pressing the electrode tip and the metal plate in the welding electrode (Patent Documents 1 and 2) , And a technique (Patent Document 3) in which pressurization is performed by two-stage pressing force and electricity is conducted by two-stage current value.
[0010]
　However, in Patent Documents 1 and 2, a predetermined distance is provided between the electrode tip and the pressure rod in order to provide a contact diameter difference between the thin plate/thick plate interface and the thick plate/thick plate interface. Is required, and the device becomes large in the width direction of the plate assembly, and it is difficult to perform spot welding on a narrow place, for example, a flange having a width of about 10 to 20 mm. Further, since the polarity of the current is different between the electrode tip and the pressure lot, the electric control for energizing becomes complicated. Also in Patent Document 3, it is necessary to change the pressing force and the current value during welding, which complicates the spot welding method and complicates the configuration of the spot welding apparatus.
[0011]
　Therefore, even with a plate set having a plate thickness ratio of 5 or more in which the thinnest metal plate is arranged on the outermost surface, dust can be generated at the thin plate/thick plate interface by using a compact welding device with easy electric control. There is a demand for a spot welding method capable of performing spot welding by forming a desired nugget diameter while suppressing the above.
Means for solving the problem
[0012]
　The gist of the present disclosure is as follows.
　(1) A spot welding method in which resistance spot welding is performed on a plate assembly in which a plurality of metal plates having a plate thickness ratio of 5 or more are stacked, and a
　metal plate having the thinnest plate thickness is arranged on the outermost surface. Prepare a plate set of 5 or more, and
　the first electrode tip and the second electrode tip are arranged so that the first electrode tip is arranged on the side where the thinnest metal plate is arranged. The two electrode chips are arranged so as to be arranged on the opposite side of the plate set so as to face each other with the plate set interposed therebetween, and
　the first pressing member, which is an insulator, of the first electrode chip is arranged .
　The first electrode is arranged around the first electrode tip so that the pressing force applied to the plate assembly from the first electrode tip is smaller than the pressing force applied to the plate assembly from the second electrode tip. The tip and each tip of the first pressure member, and the tip of the second electrode tip are pressed against the plate assembly to apply a pressing force, and
　the first electrode tip and the first tip. A current is applied between the first electrode tip and the second electrode tip while pressing each tip of the pressure member and the tip of the second electrode tip against the plate assembly to apply a pressing force. Flowing to perform welding of the plate set
　.
　(2) disposing a second pressure member, which is a conductor, around the second electrode tip;
　The first electrode tip and the first electrode tip are arranged so that the pressing force applied to the plate assembly from the first electrode tip is smaller than the pressing force applied to the plate assembly from the second electrode tip. Each tip of the pressure member and the tip of the second electrode tip are pressed against the plate assembly to apply a pressing force, and the tip of the second pressure member is brought into contact with or pressed against the plate assembly. Applying a pressing force, and pressing the
　tip portions of the first electrode tip and the first pressing member and the tip portion of the second electrode tip against the plate assembly to apply a pressing force, and Current is applied between the first electrode tip, the second electrode tip and the second pressure member while applying pressure by pressing or pressing the tip end of the pressure member to the plate assembly. Flowing, and performing the welding of the plate assembly,
　the spot welding method according to (1).
　(3) The spot welding method according to (1) or (2), wherein the average distance between the body portion of the first electrode tip and the first pressure member is 0.5 mm or less.
　(4) The spot welding method according to (2), wherein the average distance between the body portion of the second electrode tip and the second pressure member is 0.5 mm or less.
　(5) When the first electrode tip and the second electrode tip are brought into contact with the plate assembly with a pressure force of zero
　(electrodes of the first electrode tip and the second electrode tip) (
　Interval distance)≦(total thickness of each metal plate forming the plate set×1.1 times) , the pressing force of the second pressure member is reduced to 0.43 kN or less, (2) or The spot welding method according to (4).
Effect of the invention
[0013]
　According to the spot welding method of the present disclosure, even if a plate set in which a metal plate having the thinnest plate thickness is arranged on the outermost surface has a plate thickness ratio of 5 or more, a thin plate/thick plate can be obtained by using a compact welding device that is easily electrically controlled. Spot welding can be performed by forming a desired nugget diameter while suppressing the occurrence of dust at the interface of the plate.
Brief description of the drawings
[0014]
FIG. 1 is a schematic sectional view showing an example of a welding apparatus that can be used in the spot welding method of the present disclosure.
FIG. 2 is a schematic sectional view showing an example of a welding apparatus that can be used in the spot welding method of the present disclosure.
[FIG. 3] FIG. 3 is a schematic cross-sectional view showing a mode in which the tip portion of the pressing member is pressed against the plate assembly and the tip portion of the electrode tip is arranged at a position separated from the plate assembly.
[Fig. 4] Fig. 4 is a schematic cross-sectional view showing a mode in which the tip portion of the electrode tip and the tip portion of the pressure member are pressed against the plate assembly.
FIG. 5 is a schematic cross-sectional view showing a current flow when a current is applied between the first electrode tip and the second electrode tip.
FIG. 6 is a schematic cross-sectional view showing a current flow when electricity is applied between the first electrode tip and the second electrode tip and the second pressure member.
FIG. 7 is a schematic diagram illustrating a method for measuring a nugget diameter.
FIG. 8 is a schematic cross-sectional view of an example of the welding device of the present disclosure when a pneumatic cylinder is used as the second drive device.
FIG. 9 is a schematic cross-sectional view when the pressure member of the welding device in FIG. 8 is moved.
FIG. 10 is a cross-sectional photograph of a plate assembly that has been spot-welded in the example.
FIG. 11 is a perspective view schematically showing a spot-welded flange.
FIG. 12 is a schematic cross-sectional view showing an example of a mode in which the plate assembly is pressed by the first electrode tip, the second electrode tip, the first pressure member and the second pressure member. is there.
[Fig. 13] Fig. 13 is a schematic cross-sectional view showing a state in which spacers are arranged at opposite ends between thick plates/thick plates to simulate a state with a plate gap between the thick plates/thick plates. is there.
FIG. 14 is a graph showing the relationship between the average distance between the electrode and the pressing member and the appropriate current range in Examples 4 to 9 and Comparative Examples 3 to 4.
FIG. 15 is a graph showing the relationship between the average distance between the electrode and the pressing member and the appropriate current range in Examples 2 and 10 to 14 and Comparative Examples 5 to 10.
MODE FOR CARRYING OUT THE INVENTION
[0015]
　The present disclosure is a spot welding method in which resistance spot welding is performed on a plate assembly in which a plurality of metal plates having a plate thickness ratio of 5 or more are stacked, and a metal plate having the thinnest plate thickness is arranged on the outermost surface. Preparing a plate set having a ratio of 5 or more; the first electrode tip and the second electrode tip being arranged such that the first electrode tip is arranged on the side on which the thinnest metal plate is arranged. The second electrode chip is arranged on the opposite side of the plate set so as to face each other with the plate set interposed therebetween, and the first pressing member, which is an insulator, is disposed on the first electrode chip. The first electrode tip so that the pressure applied to the plate assembly is smaller than the pressure applied to the plate assembly from the second electrode tip. The tip of the electrode tip and the first pressure member, and the tip of the second electrode tip are pressed against the plate assembly to apply a pressing force, and the first electrode tip and the first tip. While pressing each tip of the pressure member and the tip of the second electrode tip against the plate assembly to apply a pressing force, a current is applied between the first electrode tip and the second electrode tip. Is applied to perform the welding of the plate set.
[0016]
　FIG. 12 is a schematic cross-sectional view showing an example of a mode in which the plate assembly is pressed by the first electrode tip, the second electrode tip, the first pressure member and the second pressure member.
[0017]
　As shown in FIG. 12, the pressing force applied from the first electrode tip 2a to the plate assembly 16 is F1, the pressing force applied from the first pressing member 3a to the plate assembly 16 is F2, and the second electrode chip 2b. The pressing force applied to the plate assembly 16 by the above is F3, and the pressing force applied by the second pressing member 3b to the plate assembly 16 is F4.
[0018]
　According to the spot welding method of the present disclosure, the pressurizing force F1 of the electrode tip on the thin plate side can be made smaller than the pressurizing force F3 of the electrode tip on the thick plate side, and the current value of the electrode tip on the thin plate side is smaller than in the past. Therefore, even when spot welding is performed on a plate assembly having a plate thickness ratio of 5 or more, it is possible to suppress the occurrence of dust and to secure a wide appropriate current range for forming a desired nugget diameter. ..
[0019]
　For example, the pressing force F1 of the electrode chip on the thin plate 15a side is 2.5 kN, the pressing force F2 of the surrounding pressurizing member of the insulator is 1.5 kN, and the pressing force F3 of the electrode chip on the thick plate 15c side is 4. It can be 0 kN. As described above, by using the pressing member around the thin plate-side electrode chip, the pressing force F1 of the thin plate-side electrode chip is made small and the pressing force F3 of the thick plate-side electrode chip is made large, thereby deforming the thin plate. Can be made smaller, the contact area with the electrode can be made smaller, and the current-carrying diameter can be made smaller, so that the current density on the thin plate side becomes large and heat is easily generated.
[0020]
　According to the method of the present disclosure, since the electrode tip and the pressing member can be arranged in proximity to each other, the apparatus for performing the method of the present disclosure becomes compact, and the device can be installed in a narrow space, for example, as shown in FIG. Spot welding can be easily performed on a flange having a width of about 10 to 20 mm. Further, by disposing the electrode tip and the pressing member in close proximity to each other, the proper current range can be increased. FIG. 11 is a perspective view schematically showing a spot-welded flange. Further, since the current value and the energization direction can be constant, it is not necessary to control the polarity of the current or switch the current in multiple stages. Furthermore, it is not necessary to change the pressure applied to the plate assembly during spot welding, and constant pressure can be applied.
[0021]
　According to the method of the present disclosure, the conventional welding apparatus can be used by changing only the electrode tip and the pressing member.
[0022]
　The appropriate current range is a current value range from a minimum current value at which a nugget having a reference diameter is formed to a maximum current value at which a nugget having a reference diameter or more is formed without occurrence of dust. The appropriate current range is preferably 1.5 kA or more, more preferably 1.8 kA or more, still more preferably 1.9 kA or more, although it depends on the presence or absence of a plate gap and the size thereof described later. The reference diameter is equal to 4√t (t is the thickness of the thinnest metal plate). The reference diameter is also referred to as a reference nugget diameter. As will be described later, the proper current range becomes narrower when there is a plate gap or when the plate gap is larger.
[0023]
　In the spot welding method of the present disclosure, as illustrated in FIG. 12, as a member to be welded, a plate assembly having a plate thickness ratio of 5 or more that is stacked such that the thin metal plate 15a is arranged on the outermost surface. To prepare. The plate thickness ratio is a value obtained by dividing the total thickness of each metal plate forming the plate set by the thickness of the thinnest metal plate, and the following formula: plate thickness ratio
　=(of each metal plate forming the plate set The total thickness)/(thickness of the thinnest metal plate)
　.
[0024]
　The plurality of metal plates includes two or more metal plates, and can be three or more metal plates depending on the form of the structural component to be joined.
[0025]
　The spot welding method of the present disclosure can be particularly suitably used for welding three metal plates that are superposed such that the thinnest metal plate is arranged on the outermost surface.
[0026]
　Each metal plate is not particularly limited, and may be steel plates having various component compositions, or metal members other than the steel plates, such as aluminum and stainless steel.
[0027]
　Preferably, the metal plate (thin plate) having the thinnest plate thickness is mild steel of 270 MPa or less, and the other metal plates (thick plates) are high-strength steel of 590 MPa or more, 980 MPa or more, 1180 MPa or more, or 1480 MPa or more. The method of the present disclosure can be suitably used for spot welding of plate combinations of the above combinations. For example, according to the method of the present disclosure, 0.75 mm thick and 270 MPa alloyed hot dip galvanized steel sheet, 1.6 mm thick and 590 MPa alloyed hot dip galvanized steel sheet, and 2.3 mm thick and 590 MPa alloyed hot dip galvanized steel sheet. Even in the case of spot welding a plate set having a plate thickness ratio of 6.2 in which plated steel plates are superposed, it is possible to suppress the occurrence of dust and to secure a wide appropriate current range for forming a desired nugget diameter.
[0028]
　Regardless of the presence or absence of the second pressure member, the plate thickness of each metal plate is not particularly limited as long as the plate thickness ratio is 5 or more, and is, for example, 0.5 to 3.2 mm or 0.7. It can be up to 2.8 mm. Preferably, the thinnest metal plate has a thickness of 0.7 to 1.0 mm or 0.7 to 0.9 mm, and the other metal plates have a thickness of 1.6 to 2.3 mm or 1.8. Is about 2.2 mm. The thickness of the plate assembly including the plurality of metal plates (thickness of the entire plate assembly) is not particularly limited, and may be, for example, 1.0 to 7.0 mm, 2.0 to 6.0 mm or 2.4 to 5 It can be 0.0 mm.
[0029]
　According to the spot welding method of the present disclosure, a plate assembly having a plate thickness ratio of 5 or more, preferably 6 or more, and more preferably 7 or more can be spot welded regardless of the presence or absence of the second pressing member. The upper limit of the plate thickness ratio does not have to be specified in particular, but the upper limit of the plate thickness ratio may be 20, 15 or 10, for example. According to the spot welding method of the present disclosure, since the pressing force F1 of the electrode tip on the thin plate side is small and the pressing force F3 of the electrode tip on the thick plate side is large, the current density on the thin plate side can be increased. The position of the nugget diameter can be shifted to the thin plate side, and a plate assembly having a large thick plate ratio in the above range can be spot-welded.
[0030]
　The metal plate may have a surface treatment film such as plating formed on both sides or one side, or may not have a surface treatment film formed thereon. The metal plate may have a plate-shaped portion at least in part and may have a portion in which the plate-shaped portions are stacked on top of each other, and may not be entirely plate-shaped, such as shaped steel. Good. The plurality of metal plates are not limited to those composed of separate metal plates, and may be a stack of one metal plate formed into a predetermined shape such as a tubular shape.
[0031]
　As illustrated in FIG. 12 or FIG. 1, the first electrode tip 2a is arranged on the side on which the thinnest metal plate 15a is arranged, and the second electrode tip 2b is arranged on the opposite side of the plate assembly. As opposed to being arranged, they are arranged opposite to each other. That is, the first electrode tip and the second electrode tip are arranged so as to face each other so as to sandwich a plate set in which a plurality of metal plates having a plate thickness ratio of 5 or more are stacked.
[0032]
　As illustrated in FIG. 12 or FIG. 1, the first electrode tip 2a and the second electrode tip 2b can be driven in the axial direction of the electrode tip and can be stopped at an arbitrary position. It is possible to press the tip portion 2a2 and the tip portion 2b2 of the second electrode tip 2b against the plate assembly to sandwich the plate assembly therebetween. The electrode tip can be moved relative to the pressure member.
[0033]
　A current can be passed through the first electrode tip and the second electrode tip at a predetermined current value and a predetermined number of cycles. The energization of the plate set by the electrode tip can be changed according to the strength and thickness of the metal plate included in the plate set. For example, a current of 4 to 15 kA should be applied at an energization time of 5 to 50 cycles (power supply frequency 50 Hz). You can
[0034]
　The electrode tip is not particularly limited and may be a known one, but is preferably made of Cu, Cu—Cr alloy, or alumina-dispersed Cu. The electrode tip preferably has a body portion having a cylindrical shape of 2 to 16 mm, and a DR type (dome radius type), CF type (conical/planar type), CR type (conical/radius type) having a tip diameter of 6 to 8 mm. ), DF (dome/planar), or D-shaped tip. In the example of FIG. 12, the first electrode tip 2a has a body portion 2a1 and a tip portion 2a2, and the second electrode tip 2b has a body portion 2b1 and a tip portion 2b2. The electrode tip preferably has a circular cross section in a direction perpendicular to the pressing direction.
[0035]
　As illustrated in FIG. 12 or FIG. 1, the first pressure member 3a, which is an insulator, is arranged around the first electrode tip 2a. The first pressing member can be driven in the axial direction of the electrode tip and can be stopped at an arbitrary position, and the tip end portion of the first pressing member can be pressed against the plate assembly to apply a pressing force F2. .. The material of the first pressure member, which is an insulator, is not particularly limited as long as it has heat resistance and also has predetermined mechanical characteristics capable of pressing the plate assembly, but is preferably Is a resin, more preferably an engineering plastic, even more preferably an aromatic resin group polyetherketone resin (PEEK) or a polyamide resin.
[0036]
　The shape of the first pressing member is preferably a cylindrical shape that is point-symmetrical about the first electrode tip, and a part of the cylindrical shape is missing, but most of the shape is point-symmetrical about the first electrode tip. Is a partial cylindrical shape having a cylindrical shape of, or a point-symmetrical or line-symmetrical cylindrical shape having a number of angles of 5 or more around the first electrode tip, more preferably the cylindrical shape or It has a partially cylindrical shape, and more preferably the cylindrical shape. The first pressing member having the above-mentioned shape can be arranged around the first electrode tip, and presses the plate assembly in point symmetry or line symmetry about the first electrode tip, The pressure applied to the first electrode tip can be reduced uniformly. The area of ​​the first pressing portion to be pressed may be 40% or more, 50% or more, or 75% or more of the circumference of the first electrode tip. Further, if necessary, this region may be shaped so as to form the entire circumference of the first electrode chip, that is, 100%.
[0037]
　The first pressing member preferably has a constant inner diameter in the pressing direction. Accordingly, the electrode tip and the pressing member can be moved independently without interfering with each other. In order to move in this way, it is preferable that the first pressure member has a cylindrical shape. More preferably, the distance (spacing) from the outer periphery of the contact surface of the first electrode tip with the metal plate to the inner diameter of the first pressure member is more than 5 mm or more than 6 mm.
[0038]
　The inner diameter of the first pressure member is preferably close to the diameter of the first electrode tip within the operable range. The average distance between the body of the first electrode tip 2a and the first pressure member is preferably 0.5 mm or less, more preferably 0.3 mm or less, even more preferably 0.2 mm or less, and even more preferably 0. It is less than or equal to 1 mm. The average distance between the body portion of the first electrode tip and the first pressure member is the outer diameter of the body portion 2a1 of the first electrode tip 2a and the inner diameter of the first pressure member 3a shown in FIG. Is an average distance D1 in the direction perpendicular to the pressing direction. By setting the average distance between the body portion of the first electrode tip and the first pressure member within the above range, the appropriate current range can be increased. The first pressure member, which is an insulator, may or may not be in contact with the first electrode tip.
[0039]
　The thickness (thickness) of the first pressing member 3a in the direction perpendicular to the pressing direction can be, for example, 1 to 7 mm or 1 to 5 mm. The first pressing member may be a cylindrical body having an upper limit of outer diameter of 30 mm, 25 mm, or 20 mm and a lower limit of outer diameter of 10 mm or 15 mm. The lower limit of the outer diameter of the first pressure member is the outer diameter of the first electrode tip.
[0040]
　The pressing force F1 applied to the plate assembly from the first electrode tip is smaller than the pressing force F3 applied to the plate assembly from the second electrode tip, so that Each tip and the tip of the second electrode tip are pressed against the plate assembly to apply a pressing force.
[0041]
　Since the sum of the pressing forces F1 and F2 applied to the plate assembly from the first electrode tip and the first pressure member is equal to the pressing force F3 applied to the plate assembly from the second electrode tip, the first pressing force is applied. When the pressing force F2 is applied to the plate assembly from the pressure member, the pressing force F1 applied to the plate assembly from the first electrode tip can be reduced by that amount. Accordingly, the pressing force F1 applied to the plate set from the first electrode tip can be made smaller than the pressing force F3 applied to the plate set from the second electrode tip.
[0042]
　Preferably, the ratio of the pressing force F1 applied to the plate set from the first electrode tip to the plate set F3 applied from the second electrode tip to the plate set is (10 to 95):100. That is, it is preferable that the pressing force F1 is 10 to 95% of the pressing force F3 regardless of the presence or absence of the second pressing member. The upper limit of the ratio of the pressing force F1 to the pressing force F3 may be 90%, 85%, 80% or 70%. The lower limit of the ratio of the pressing force F1 to the pressing force F3 may be 20%, 30% or 40%. More preferably, the pressing force F1 applied to the plate set from the first electrode tip is smaller than the pressing force F3 applied to the plate set from the second electrode tip by 1.5 to 2.5 kN. As described above, since the pressing force F1 applied to the plate set from the first electrode tip is smaller than the pressing force F3 applied to the plate set from the second electrode tip, the pressing force F2 to the plate set from the first pressing member is applied. Is applied to balance the pressure applied by sandwiching the plate assembly.
[0043]
　The pressing force F2 applied to the plate set from the first pressing member can be changed according to the strength and thickness of the metal plate included in the plate set, and is, for example, 0.0 to 6.0 kN, or 1.5 to It can be 4.5 kN.
[0044]
　The pressing force F3 applied to the plate set from the second electrode tip can be changed according to the strength and thickness of the metal plate included in the plate set, and is, for example, 0.0 to 6.0 kN, or 1.5 to 4 It can be 0.5 kN.
[0045]
　In the spot welding method of the present disclosure, preferably, a second pressure member, which is a conductor, is arranged around the second electrode tip, and a pressing force applied from the first electrode tip to the plate assembly. F1 is smaller than the pressing force F3 applied to the plate assembly from the second electrode tip, the tip portions of the first electrode tip and the first pressure member, and the second electrode. Pressing the tip of the tip against the plate assembly to apply a pressure force F1, F2, F3 and contacting or pressing the tip of the second pressure member against the plate assembly to apply a pressure force F4; The tip portions of the first electrode tip and the first pressure member and the tip portion of the second electrode tip are pressed against the plate assembly to apply pressing forces F1, F2, F3 and to apply the second pressing force. An electric current is applied between the first electrode tip, the second electrode tip, and the second pressure member while applying the pressing force F4 while contacting or pressing the tip end of the pressure member with the plate assembly. And welding the plates.
[0046]
　As illustrated in FIG. 12 or FIG. 1, by using the insulating pressure member 3a on the thin plate 15a side and the conductive pressure member 3b on the thick plate 15c side, the pressing force of the electrode chip 2a in contact with the thin plate 15a is used. F1 is small, the pressing force F3 of the electrode tip 2b in contact with the thick plate 15c is large, the energization diameter for energizing the thin plate 15a from the electrode tip 2a in contact with the thin plate 15a is small, and the energization diameter for energizing the thick plate 15c is small. Since the width can be increased, the current density on the thin plate 15a side can be increased.
[0047]
　For example, the pressing force F1 of the electrode chip 2a on the side of the thin plate 15a is 2.5 kN and the pressing force F2 of the surrounding pressing member 3a of the insulator is 1.5 kN, and the pressing force F3 of the electrode chip 2b on the side of the thick plate 15c is F3. Can be set to 3.9 kN and the pressing force F4 of the pressure member 3b around it can be set to 0.1 kN.
[0048]
　As illustrated in FIG. 12, even when the tip end portion of the second pressurizing member is pressed to apply the pressing force F4, the pressing force F1 applied to the plate set from the first electrode tip is applied to the plate from the second electrode tip. The tip portions of the first electrode tip and the first pressure member and the tip portions of the second electrode tip and the second pressure member are set so as to be smaller than the pressing force F3 applied to the set. Apply pressure by pressing it against the plate assembly.
[0049]
　The tip of the second pressing member is brought into contact with the plate assembly with the pressing force being substantially zero, or is pressed to apply the pressing force F4, and the plate member is also electrically heated from the second pressing member. be able to. Even when spot-welding a plate set in which a plurality of metal plates having a plate thickness ratio of 5 or more are stacked by electrically heating the plate set from the second pressing member in addition to the second electrode tip, It is possible to more stably form a desired nugget diameter without generating dust. By using a conductive pressure member on the thick plate side, the current density on the thick plate side can be lowered, the position of the nugget diameter can be shifted to the thin plate side, and the plate thickness ratio is 5 or more, preferably Is capable of spot welding plate sets having a large plate ratio of 6 or more, more preferably 7 or more.
[0050]
　The energization of the plate set by the second pressure member can be changed according to the strength and thickness of the metal plate included in the plate set. A current can be passed.
[0051]
　The material of the second pressing member, which is an electric conductor, is heat-resistant and has a predetermined mechanical characteristic capable of contacting the plate assembly or pressing the plate assembly. Although not particularly limited, Cu, Cu—Cr alloy, or alumina-dispersed Cu is preferable. The second electrode tip and the second pressure member may be made of the same material, although they may be made of different materials.
[0052]
　The second pressure member can be driven in the axial direction of the electrode tip and stopped at an arbitrary position, and the tip end portion of the second pressure member can be pressed against the plate assembly to apply a pressure F4. ..
[0053]
　The shape of the second pressing member is preferably a cylindrical shape that is point-symmetrical about the second electrode tip, and a part of the cylindrical shape is missing, but most of the shape is point-symmetrical about the second electrode tip. Is a partial cylindrical shape having a cylindrical shape, or a regular polygonal cylindrical shape having 5 or more corners, which is point-symmetrical or line-symmetrical about the second electrode tip, and more preferably the cylindrical shape or It has a partially cylindrical shape, and more preferably the cylindrical shape. The second pressure member having the above-mentioned shape can be arranged around the second electrode tip, and contacts the plate assembly in point symmetry or line symmetry about the second electrode tip, or It is possible to pressurize the plate set to make the current-carrying diameter for energizing the thick plate 15c more evenly around the second electrode tip, and reduce the current density on the thick plate side. The area of ​​the second pressurizing portion to be pressed may be 40% or more, 50% or more, or 75% or more of the circumference of the second electrode tip. Further, if necessary, this region may be shaped so as to form the entire circumference of the second electrode tip, that is, 100%.
[0054]
　The second pressure member preferably has a constant inner diameter in the pressure direction. Accordingly, the electrode tip and the pressing member can be moved independently without interfering with each other. In order to move in this way, it is preferable that the second pressure member has a cylindrical shape. More preferably, the distance (spacing) from the outer circumference of the contact surface of the second electrode tip with the metal plate to the inner diameter of the second pressure member is more than 5 mm or more than 6 mm.
[0055]
　The inner diameter of the second pressure member is preferably close to the diameter of the second electrode tip within the operable range. The average distance between the body of the second electrode tip and the second pressure member is preferably 0.5 mm or less, more preferably 0.3 mm or less, even more preferably 0.2 mm or less, and even more preferably 0. It is 1 mm or less. The average distance between the body portion of the second electrode tip and the second pressure member is defined by the outer diameter of the body portion 2b1 of the second electrode tip and the inner diameter of the first pressure member 3b shown in FIG. Is an average distance D2 in the direction perpendicular to the pressing direction. By setting the average distance between the body portion of the second electrode tip and the second pressure member within the above range, it is possible to further increase the appropriate current range.
[0056]
　The thickness (wall thickness) of the second pressure member 3b in the direction perpendicular to the pressure direction can be, for example, 1 to 7 mm or 1 to 5 mm. The second pressure member may be a cylindrical body having an upper limit of outer diameter of 30 mm, 25 mm, or 20 mm and a lower limit of outer diameter of 10 mm or 15 mm. The lower limit of the outer diameter of the second pressure member is the outer diameter of the second electrode tip.
[0057]
　The average distance between the body of the first electrode tip and the first pressure member and the average distance between the body of the second electrode tip and the second pressure member may be set separately. it can.
[0058]
　The pressing force F4 applied to the plate assembly from the second pressure member can be, for example, 0.0 to 6.0 kN, or 1.5 to 4.5 kN. The metal plates that make up the plate set may be deformed, such as warped, due to springback that occurs during press working. In that case, a gap (also called a plate gap) may exist between the stacked plate sets. is there. When the metal plates are deformed, the thickness of the plate set becomes larger than the total thickness of the metal plates forming the plate set because there is a gap between the stacked plate sets. A gap is more likely to exist between the relatively hard thick plate and the thick plate than between the relatively soft thin plate and the thick plate. If the thickness of the plate set is larger than the total thickness of the metal plates that make up the plate set, there will be a gap between the stacked plate sets, but there will be no gap between the stacked plate sets. In the case where the gap is small or the gap is small, even if the pressure F4 of the second pressure member is reduced, the pressure F1 of the first electrode tip, the pressure F2 of the first pressure member, and By applying the pressing force F3 of the second electrode tip to the plate set, the metal plates forming the plate set can be brought into contact with each other at the welding location. Therefore, when there is no gap between the superposed plate sets or when the gap is small, the pressing force F4 of the second pressurizing member is reduced within the range in which dust can be prevented from occurring. It is preferable to concentrate the pressure on the electrode tip to increase the contact area between the second electrode tip and the thick plate.
[0059]
　If there is no gap between the plate sets, or if there is a small gap, the first electrode tip and the second electrode tip are brought into contact with the plate set with substantially no pressing force before welding. When it is made to exist, it means the condition that (distance between electrodes of the first electrode tip and the second electrode tip)≦(total thickness of each metal plate constituting the plate set×1.1 times) is satisfied.
[0060]
　When both the first electrode tip and the second electrode tip are brought into contact with the plate assembly with the applied pressure being substantially zero (distance between the electrodes of the first electrode tip and the second electrode tip)≦ When (total thickness of each metal plate constituting the plate set×1.1 times) is satisfied, the pressing force F4 of the second pressing member is preferably 0.43 kN or less, more preferably 0.10 kN or less, It is preferably lowered to 0.00 kN. Alternatively, the pressing force F4 of the second pressing member is set to 40% or less, 30% or less, 20% or less of the total of the pressing force F3 of the second electrode tip and the pressing force F4 of the second pressing member. % Or less.
[0061]
　On the other hand, when there is a large gap between the superposed plate sets, it is preferable that the pressing force F4 applied to the plate sets by the second pressure member be more than 0.43 kN. In the case where there is a large gap between the plate sets, the first electrode tip and the second electrode tip when welding are brought into contact with the plate set with substantially no applied pressure before welding. The distance between the electrodes and the second electrode tip is more than 1.1 times, preferably 1.5 times or less, more preferably 1.4 times or less, of the total thickness of the metal plates forming the plate assembly. It is preferably 1.3 times or less, and more preferably 1.2 times or less.
[0062]
　The second pressure member, which is a conductor, may or may not be in contact with the second electrode tip. The second electrode tip and the second pressure member can be connected to a power source to which the first electrode tip is connected, and the current can be shunted to reduce the current of the electrode tip. The current is divided according to the material and cross-sectional area of ​​the second electrode tip and the second pressure member.
[0063]
　Preferably, the respective tip portions of the first pressure member and the second pressure member are pressed against the plate assembly to apply the pressing forces F2 and F4, and then the respective tip portions of the first electrode tip and the second electrode tip. Is pressed against the plate assembly to apply the pressing forces F1 and F3. Thereby, the tact time of spot welding can be reduced.
[0064]
　An example of the configuration of the spot welding apparatus that can be used in the method of the present disclosure will be described with reference to the drawings.
[0065]
　FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a spot welding apparatus when spot welding is performed on a plate assembly including a plurality of metal plates.
[0066]
　The welding device shown in FIG. 1 has a first electrode tip 2a and a second electrode tip 2b (hereinafter also referred to as a pair of electrode tips) whose tip is pressed against the plate assembly 16 and the periphery of the first electrode tip 2a. , A first pressing member 3a, which is an insulator whose tip is pressed against the plate assembly 16, a power source 17 connected to the pair of electrode chips, and a first drive mechanism 18 connected to the pair of electrode chips. , A second drive mechanism 19 connected to the first pressurizing member 3a, and a pressing force control unit 20 connected to the first drive mechanism 18 and the second drive mechanism 19.
[0067]
　The power supply 17 can supply a current to the electrode chip at a predetermined current value and a predetermined number of cycles. The energization of the plate set by the electrode tip can be changed according to the strength and thickness of the metal plate included in the plate set. For example, a current of 4 to 15 kA should be applied at an energization time of 5 to 50 cycles (power supply frequency 50 Hz). You can
[0068]
　The first drive mechanism 18 can drive the pair of electrode tips in the axial direction of the electrode tip and stop them at arbitrary positions, and can also provide a pressing force for pressing the pair of electrode tips against the plate assembly 16. The second drive mechanism 19 drives the first pressing member 3a in the axial direction of the electrode tip and stops it at an arbitrary position, and applies a pressing force for pressing the first pressing member 3a against the plate assembly 16. You can
[0069]
　The first drive mechanism and the second drive mechanism are independently, preferably pneumatic cylinders, hydraulic cylinders, springs, ball screws, electric cylinders, actuators, gear drives, or rack and pinion, more preferably pneumatic cylinders, hydraulics. It is a cylinder or an electric cylinder. The drive mechanism may be selected according to the actual construction environment.
[0070]
　The pneumatic cylinder does not contaminate others even if air leaks, and maintenance is easy. The hydraulic cylinder is resistant to heat and can obtain a large amount of power. Electric cylinders do not require piping and can be controlled with high accuracy.
[0071]
　The pressing force control unit 20 independently controls the pressing force applied by the first drive mechanism 18 and the pressing force applied by the second drive mechanism 19. The pressurizing force control unit 20 applies each pressurizing force so that the pressurizing force applied from the first electrode tip 2a and the first pressurizing member 3a is equal to the pressurizing force applied from the second electrode tip 2a. Control the pressure.
[0072]
　The first drive mechanisms 18 connected to the pair of electrode chips may be separately configured as a pair or may be integrally configured.
[0073]
　The plate set 16 including a plurality of metal plates is sandwiched from both sides by the pair of electrode chips and the first pressing member 3a. In FIG. 1, a mode in which a plate set 16 of three metal plates 15a, 15b, and 15c is sandwiched is illustrated. The metal plate 15a has the smallest plate thickness among the three metal plates, and the plate thickness ratio of the plate set of the three metal plates 15a, 15b, and 15c is 5 or more.
[0074]
　The welding apparatus shown in FIG. 2 has a first electrode tip 2a and a second electrode tip 2b (hereinafter also referred to as a pair of electrode tips) whose tip is pressed against the plate assembly 16 and a periphery of the first electrode tip 2a. Is arranged around the first pressing member 3a and the second electrode tip 2b, which are insulators whose front end is pressed against the plate assembly 16, and whose front end is pressed against the plate assembly 16. The second pressure member 3b, the power source 17 connected to the pair of electrode chips, the first drive mechanism 18 connected to the pair of electrode chips, the first pressure member 3a and the second pressure member 3b. A second drive mechanism 19 connected thereto, and a pressing force control unit 20 connected to the first drive mechanism 18 and the second drive mechanism 19 are provided.
[0075]
　The first drive mechanism 18 can drive the pair of electrode tips in the axial direction of the electrode tip and stop them at arbitrary positions, and can also provide a pressing force for pressing the pair of electrode tips against the plate assembly 16. The second drive mechanism 19 drives the first pressure member 3a and the second pressure member 3b in the axial direction of the electrode tip and stops them at arbitrary positions, and the first pressure member 3a and the second pressure member 3b. It is possible to apply a pressing force for pressing the pressurizing member 3b of FIG.
[0076]
　The pressing force control unit 20 independently controls the pressing force applied by the first drive mechanism 18 and the pressing force applied by the second drive mechanism 19. In the pressing force control unit 20, the pressing force applied from the first electrode tip 1a and the first pressing member 3a is the same as the pressing force applied from the second electrode tip 2a and the second pressing member 3b. The respective pressures are controlled so that
[0077]
　The first drive mechanisms 18 connected to the pair of electrode chips may be separately configured as a pair or may be integrally configured.
[0078]
　Similar to FIG. 1, the pair of electrode chips and the first pressing member 3a and the second pressing member 3b sandwich the plate set 16 including a plurality of metal plates from both sides.
[0079]
　When performing spot welding, the tip portions of the pair of electrode tips are pressed against the plate assembly 16. At this time, the tip of the electrode tip and the tip of the pressing member may be pressed against the plate assembly 16 at the same time or at different timings. Referring to FIG. 2 as an example, the tip portions of the pair of electrode chips and the tip portions of the first pressure member 3a and the second pressure member 3b (hereinafter, also referred to as a pair of pressure members) are simultaneously set to the plate assembly 16. The pair of pressure members may be pressed against the plate assembly 16 and then the pair of electrode tips may be pressed against the plate assembly 16. Alternatively, the pair of electrode tips may be assembled together. It is also possible to press against 16 and then press the tips of the pair of pressing members against the plate assembly 16.
[0080]
　Preferably, as shown in FIG. 3, before performing spot welding, the tip portions of the pair of pressure members are pressed against the plate assembly 16 so that the tip portions of the pair of electrode tips are separated from the plate assembly 16. Deploy. FIG. 3 is a schematic cross-sectional view showing a mode in which the tip portions of the pair of pressure members are pressed against the plate assembly 16 and the tip portions of the pair of electrode chips are arranged at positions separated from the plate assembly 16. When the tip portions of the pair of pressure members are pressed against the plate assembly 16 and the tip portions of the pair of electrode chips are arranged at positions separated from the plate assembly 16, the tip portions of the pair of electrode chips are, for example, 0 to 5 mm, Alternatively, it may be arranged at a position 1 to 3 mm away from the plate assembly.
[0081]
　As shown in FIG. 3, the tip portions of the pair of pressing members are pressed against the plate assembly 16, the tip portions of the pair of electrode chips are arranged at positions separated from the plate assembly 16, and then the pair of electrode chips is mounted. As shown in FIG. 4, the pair of electrode chips can be brought into contact with the metal plate 15 by moving them relative to the pair of pressure members. FIG. 4 is a schematic cross-sectional view showing a mode in which the tip portions of the pair of electrode tips and the tip portions of the pair of pressing members are pressed against the plate assembly 16.
[0082]
　Since the plate assembly 16 can be pressed with a desired pressing force by the pair of pressure members before the pair of electrode chips are brought into contact with the plate assembly 16 in FIG. 3, the pair of electrode chips in FIG. An electric current can be applied at the same time when the plate assembly 16 is brought into contact with the plate assembly 16, and the tact time of spot welding can be shortened. Also in FIGS. 3 and 4, the spot welding apparatus includes the power supply 17 and the pressure control unit 20, but they are not shown.
[0083]
　As indicated by the solid line arrow in FIG. 4, the metal plate 15a/metal plate 15b/metal plate 15c is energized between the first electrode tip 2a, the second electrode tip 2b and the second pressure member 3b. Molten metal can be formed on the superposed surfaces of.
[0084]
　As shown in FIG. 4, the first electrode tip and the second electrode tip are pressed against the plate assembly 16, the first pressure member is pressed against the plate assembly 16, and the second pressure member is attached to the plate assembly 16. In a state where they are in contact with each other or pressed against each other, electric current is applied between the first electrode tip 2a, the second electrode tip 2b and the second pressure member 3b to overlap the metal plate 15a/metal plate 15b/metal plate 15c. Molten metal can be formed on the mating surfaces. Pressure is applied from the first pressurizing member 3a so that the pressure applied from the first electrode tip to the plate assembly is smaller than the pressure applied from the second electrode tip to the plate assembly. Since current is applied between the first electrode tip 2a, the second electrode tip 2b, and the second pressure member 3b, the current density at the interface of the metal plate 15a/metal plate 15b can be increased, and the plate thickness can be increased. Even in the case of spot welding a plate assembly having a ratio of 5 or more, it is possible to secure a wide appropriate current range for forming a desired nugget diameter while suppressing the occurrence of dust. The pressing force of the second pressing member is within a range in which the pressing force applied from the first electrode tip to the plate assembly is smaller than the pressing force applied from the second electrode tip to the plate assembly and does not cause dust. It may be increased or may be set to zero depending on the strength and thickness of the metal plate included in the plate assembly.
[0085]
　After the completion of energization, the molten metal is rapidly cooled and solidified by heat removal by cooling the pair of electrode tips and heat conduction to the periphery of the welded portion of the plate assembly 16, and the metal plate 15a/metal plate 15b/ A nugget having an elliptical cross section can be formed between the metal plates 15c. After forming the nugget, the electrode tip and the pressing member can be separated from the metal plate, and the welding device can be returned to the state in the welding standby state.
[0086]
　FIG. 5 is a schematic cross-sectional view showing the flow of current when electricity is applied between the first electrode tip and the second electrode tip, and FIG. 6 shows the first electrode tip, the second electrode tip and the second electrode tip. The cross-sectional schematic diagram which shows the flow of an electric current when energizing between the 2 pressure members is shown.
[0087]
　In FIG. 5, a current flows only between the first electrode tip and the second electrode tip as shown by the arrow, but in FIG. 6, the second pressing member made of a conductor is provided as a plate as shown by the arrow. Since it is in contact with the set 16, it is possible to conduct electricity between the first electrode tip, the second electrode tip and the second pressure member. Therefore, it is possible to more stably form the nugget at the interface between the thin plate 15a and the thick plate 15b.
[0088]
　The method for confirming the nugget diameter was as shown in FIG. FIG. 7 is an enlarged photograph of a cross section obtained by cutting the center of the spot-welded portion of the plate assembly that has been spot-welded, embedding and polishing it, and then performing metal flow etching. The nugget is the melted and solidified portion in FIG. 7, and the nugget diameter at the interface between the thin plate and the thick plate is indicated by a dashed arrow, and the nugget diameter at the interface between the thick plate and the thick plate is indicated by a solid arrow.
[0089]
　FIG. 8 shows a schematic cross-sectional view of an example of a welding device that can be used in the spot welding method of the present disclosure when a pneumatic cylinder is used as the second drive mechanism. The first drive mechanism is preferably a pneumatic cylinder, but may be a hydraulic cylinder, an electric cylinder or the like. Although the first drive mechanism is omitted in FIG. 8, when the first drive mechanism is a pneumatic cylinder, it may have the same configuration as the pneumatic cylinder of the second drive mechanism illustrated in FIG. 8.
[0090]
　The first electrode tip 2a is attached to the rod-shaped shank 1. The shank 1 is attached to a holder (not shown) attached to the spot welding gun. The first pressing member 3a is arranged around the first electrode tip 2a. The power supply and the pressure control unit are not shown.
[0091]
　Except for the pressure member, the welding device is provided with a pair of electrode chips, and is used by placing a plurality of stacked metal plates so as to face each other. Since they are the same, one of the welding devices will be described below. This is substantially the same when the second pressure member is not used and when it is used.
[0092]
　The shank 1 and the first electrode tip 2 a can move relative to the pneumatic cylinder 4. The shank 1 is fixed to the pneumatic cylinder 4 by a screw adapter 12 made of Cu-1 mass% Cr and a nut 13.
[0093]
　The pneumatic cylinder 4, which is the second drive mechanism, includes a substantially cylindrical cylinder housing 5 into which the shank 1 is inserted, a circular rod cover 6 that closes the cylinder housing 5, and the inside of the cylinder housing 5 in the axial direction of the shank 1. And a piston rod 7 that moves to. The piston rod 7 has a cylindrical rod portion 7a into which the shank 1 is inserted, a ring portion 7b formed on the outer periphery of the lot portion 7a, and is made of SUS304 or the like.
[0094]
　The cylinder housing 5 has a side (hereinafter referred to as "inside") on which the pressing member 3 is attached to the piston rod 7 and a rod cover 6 side (hereinafter referred to as "outside") with respect to the ring portion 7b of the piston rod 7. ) Has ports 8 and 9a for supplying and discharging air for moving the piston rod 7. The cylinder housing 5 is made of SUS304 or the like.
[0095]
　The rod cover 6 has a lower cover 6a for limiting the moving range of the piston rod 7, and an upper cover 6b having a port 9b for supplying/exhausting air outside the rod portion 7a of the piston rod 7, and the SUS304 or the like. Is formed by. The lower cover 6a and the upper cover 6b are fixed by a cap nut 10.
[0096]
　The cylinder housing 5, the piston rod 7, and the lower cover 6a are provided with O-rings 11a, 11b, and 11c, respectively, which prevent compressed air between the inside and outside of the ring portion 7b of the piston rod 7. By suppressing the movement and supplying/exhausting the compressed air through the port 8 and the ports 9a and 9b, the piston rod 7 and the pressing member 3 connected to the tip thereof can be moved and stopped.
[0097]
　The flow of current during spot welding will be described with reference to FIG. In the spot welding, a current flows through the electrode tip 2 through the shank 1 as indicated by the solid arrow. As a result, the welded portion of the metal plate is heated and a nugget is formed.
[0098]
　The direction of the current (the direction of the arrow) is not particularly limited and may be the opposite direction.
[0099]
　FIG. 9 shows a schematic cross-sectional view when the first pressure member 3a of the welding device of FIG. 8 is moved to the outside.
[0100]
　The first pressurizing member 3a moves through the piston rod 7 by supplying and discharging compressed air through the port 8 and the ports 9a and 9b. As shown in FIG. 9, the piston rod 7 is moved by compressed air to a position limited by the inner cover 6a and stopped.
[0101]
　The material of the shank is not particularly limited as long as it can hold the electrode tip and can apply a pressing force from the electrode tip to the plate assembly. For example, the shank is made of Cu—Cr alloy or the like and has a cooling pipe inside thereof. be able to. The holder is not particularly limited as long as the shank 1 can be assembled, but is made of, for example, a Cu—Cr alloy, and can have a cooling pipe therein.
Example
[0102]
　(Example 1)
　0.75 mm thick and 270 MPa alloyed galvanized steel sheet (thin plate), 1.6 mm thick and 590 MPa alloyed galvanized steel sheet (thick plate), and 2.3 mm thick and 590 MPa alloyed Hot-dip galvanized steel sheets (thick plates) were overlapped to prepare a plate set having a total thickness of each metal plate of the plate set of 4.65 mm and a plate thickness ratio of 6.2. The vertical and horizontal dimensions of the steel sheet were 30 mm×100 mm.
[0103]
　As the first electrode tip and the second electrode tip, a DR type tip 40R and an electrode tip having a tip diameter of 6 mm and a Cu-1% Cr alloy diameter of 13.0 mm were prepared. A cylindrical insulator (MC nylon (registered trademark) (engineering plastic)) having an inner diameter of 13.2 mm and an outer diameter of 16.0 mm is prepared as a first pressure member to be arranged around the first electrode tip. did.
[0104]
　The first electrode tip and the second electrode tip are arranged so that the first electrode tip is arranged on the thin plate side and the second electrode tip is arranged on the opposite side (thick plate side) of the plate assembly. , The plate assembly was placed so as to face each other.
[0105]
　A first pressure member was arranged around the first electrode tip. The average distance between the body of the first electrode tip and the first pressure member was 0.10 mm. Using a spring, the pressing force F2 of the first pressing member is 0.86 kN and the pressing force F1 of the first electrode tip is 3.06 kN on the thin plate side, and only the second electrode tip is on the thick plate side. And the pressing force F3 of the second electrode tip was set to 3.92 kN. Spot welding was performed with a single current flow of 31 cyc (energization for 0.62 seconds) while changing the current value while applying the above pressing force. The distance between the electrodes of the first electrode tip and the second electrode tip when the first electrode tip and the second electrode tip are brought into contact with the plate assembly with zero pressure before welding is the plate assembly. Was less than or equal to the total thickness of each of the metal plates forming 1.1×1.1 times. The obtained proper current range was 3.0 kA. The distance between the electrodes is the tip of the first electrode tip and the second electrode tip when the first electrode tip and the second electrode tip are brought into contact with the plate assembly with the pressing force being substantially zero before welding. It was obtained by measuring the distance between the tip of the electrode tip.
[0106]
　(Example 2) In
　order to evaluate a more severe condition, an experiment was also conducted under conditions simulating the case where a plate gap exists between thick plates. Specifically, as shown in FIG. 13, spacers are arranged at opposite ends of the thick plate/thick plate to simulate the state with the plate gap between the thick plates/thick plates. The spacer had a thickness of 2 mm, and the gap had a 40 mm span and a height of 2 mm. Hereinafter, the case where the spacers are arranged is referred to as "with spacers", and the case where the spacers are not arranged is referred to as "without spacers". Note that, in FIG. 13, the illustration of the first pressure member and the second pressure member is omitted. A cylindrical Cu-1% Cr alloy having an inner diameter of 17.0 mm and an outer diameter of 20.0 mm was prepared as a second pressure member to be arranged around the second electrode tip.
[0107]
　As described above, the spacer is provided, and the second pressure member is arranged around the second electrode chip, and the average distance between the body portion of the second electrode chip and the second pressure member is 2. The pressurizing force F2 of the first pressurizing member is 1.37 kN, the pressurizing force F1 of the first electrode tip is 2.55 kN on the thin plate side, and the second plate is set on the thick plate side. Spot welding was performed in the same manner as in Example 1 except that the pressing force F4 of the pressing member was 0.43 kN and the pressing force F3 of the second electrode tip was 3.49 kN. The distance between the electrodes of the first electrode tip and the second electrode tip when the first electrode tip and the second electrode tip are brought into contact with the plate assembly with zero pressure before welding is the plate assembly. Was more than 1.1 times the total thickness of the metal plates constituting the above. When spot welding was performed while changing the current value, a proper current range of 1.5 kA was obtained. In the following Examples and Comparative Examples, in the case of no spacer, when the first electrode tip and the second electrode tip were brought into contact with the plate assembly with zero pressure before welding (first electrode The relationship between the distance between the tip and the second electrode tip)≦(total thickness of each metal plate forming the plate set×1.1 times) was satisfied, but in the case of having a spacer, the above relationship was satisfied. Didn't.
[0108]
　FIG. 10 shows a cross-sectional photograph of the plate assembly that was spot-welded in Example 2. When the current value was 9.0 to 10.5 kA, the nugget diameter at the thin plate/thick plate interface was 5.26 to 6.92 mm. The standard nugget diameter was 4√t=4×√0.75=3.2 mm, and a nugget diameter equal to or larger than the standard nugget diameter was obtained, and no dust was generated. When the current value is 11.0 to 11.5 kA, the nugget diameter at the thin plate/thick plate interface is 7.29 to 5.97 mm, and although a nugget diameter larger than the reference nugget diameter is obtained, dust is generated. Occurred. Therefore, a proper current range of 9.0 to 10.5 kA, 1.5 kA, was obtained.
[0109]
　(Example 3) With a
　spacer, on the thin plate side, the pressing force F2 of the first pressing member was 1.37 kN, and the pressing force F1 of the first electrode tip was 2.55 kN (total 3.92 kN). Spot welding was performed in the same manner as in Example 1 except for the above. When spot welding was performed while changing the current value, an appropriate current range of 1.2 kA was obtained.
[0110]
　(Comparative Example 1)
　Pressing members were not used on each of the thin plate side and the thick plate side, and only the first electrode tip and the second electrode tip were used, and the pressurizing forces F1 and F3 were set to 3.92 kN, respectively. Other than the above, spot welding was performed under the same conditions as in Example 1. When spot welding was performed while changing the current value, a proper current range of 0.5 kA was obtained.
[0111]
　(Comparative Example 2)
　Spot welding was performed under the same conditions as in Comparative Example 1 except that a spacer was provided. When spot welding was performed while changing the current value, the proper current range was 0.0 kA.
[0112]
　Table 1 shows the presence/absence of spacers, the pressures F1, F2, F3, and F4 of Examples 1 to 5 and Comparative Examples 1 and 2, the average distance between the electrode and the pressing member, and the obtained appropriate current range.
[0113]
[table 1]

[0114]
　(Examples 4 to 9) Using the
　cylindrical first pressure member having the inner diameter and the outer diameter shown in Table 2, the distance between the first electrode tip and the first pressure member was 0.10 mm. , 0.25 mm, 0.40 mm, 0.60 mm, 0.90 mm, and 1.50 mm, and spot welding was performed under the same conditions as in Example 1 except that a spacer was arranged as in Example 2. went. Table 2 shows the proper current range obtained in each example.
[0115]
[Table 2]

[0116]
　(Examples 10 to 14) Using the
　cylindrical second pressure member having the inner diameter and the outer diameter shown in Table 3, the distance between the second electrode tip and the second pressure member was set to 0.10 mm. , 0.25 mm, 0.40 mm, 0.60 mm, and 0.90 mm, spot welding was performed under the same conditions as in Example 2. Table 3 shows the proper current range obtained in each example.
[0117]
[Table 3]

[0118]
　(Comparative Examples 3 to 4)
　Instead of the first pressure member, a third pressure member having a cylindrical shape having an inner diameter and an outer diameter shown in Table 4 and made of Cu-1% Cr alloy was used. Spot welding was performed under the same conditions as in Example 4 except that the distance between the first electrode tip and the third pressure member was 0.25 mm and 0.90 mm. Table 2 shows the proper current range obtained in each example.
[0119]
[Table 4]

[0120]
　(Comparative Examples 5 to 6)
　Instead of the second pressurizing member, a cylindrical shape having an inner diameter and an outer diameter shown in Table 5 and made of an insulator (MC nylon (registered trademark) (engineering plastic)) Spot welding was performed under the same conditions as in Example 2 except that the distance between the second electrode tip and the fourth pressure member was set to 0.25 mm and 0.90 mm using the pressure member of No. 2. .. Table 2 shows the proper current range obtained in each example.
[0121]
[Table 5]

[0122]
　(Comparative Examples 7 to 8)
　Instead of the first pressure member, a third pressure member having a cylindrical shape having the same dimensions as the first pressure member and made of Cu-1% Cr alloy is used. In addition, by using the cylindrical second pressure member having the inner diameter and the outer diameter shown in Table 6, the distance between the second electrode tip and the second pressure member was set to 0.25 mm and 0.90 mm. Other than the above, spot welding was performed under the same conditions as in Example 2. Table 2 shows the proper current range obtained in each example.
[0123]
[Table 6]

[0124]
　(Comparative Examples 9 to 10)
　Instead of the first pressure member, a third pressure member having a cylindrical shape having the same dimensions as the first pressure member and made of Cu-1% Cr alloy is used. Further, in place of the second pressure member, a fourth pressure member having a cylindrical shape having an inner diameter and an outer diameter shown in Table 7 and made of an insulator (MC nylon (registered trademark) (engineering plastic)) is used. Then, spot welding was performed under the same conditions as in Example 2 except that the distance between the second electrode tip and the fourth pressure member was 0.25 mm and 0.90 mm. Table 7 shows the proper current range obtained in each example.
[0125]
[Table 7]

[0126]
　FIG. 14 is a graph showing the relationship between the average distance between the electrode and the pressing member and the appropriate current range in Examples 4 to 9 and Comparative Examples 3 to 4. FIG. 15 is a graph showing the relationship between the average distance between the electrode and the pressing member and the appropriate current range in Examples 2 and 10 to 14 and Comparative Examples 5 to 10.
Explanation of symbols
[0127]
　1 shank
　2a first electrode tip
　2a1 first electrode tip body
　2a2 first electrode tip tip
　2b second electrode tip
　2b1 second electrode tip body
　2b2 second electrode tip tip
　3a 1st pressurizing member
　3b 2nd pressurizing member
　4 Pneumatic cylinder
　5 Cylinder housing
　6 Rod cover
　6a Lower cover
　6b Upper cover
　7 Piston rod
　7a Rod part
　7b Ring part
　8 Port
　9a, 9b port
　10 Cap nut
　11a, 11b, 11c O-ring
　12 Screw adapter
　13 Nut
　14 Insulation sleeve
　15a Thinnest metal plate (thin plate)
　15b, 15c Thick metal plate (thick plate)
　16 Plate Assembly
　17 Power Supply
　18 First Driving Mechanism
　19 Second Driving Mechanism
　20 Pressurizing Force Control Section
　21 Molten Metal
　23 Spacer
　30 Steel Plate Member
　31 Flange
　32 Flange
　33 Spot Weld Section
　D1 Body of First Electrode Tip and First Average distance
　D2 between the pressure member and the average distance
　F1 between the body portion of the second electrode tip and the second pressure member F1 The pressing force
　F2 applied to the plate assembly from the first electrode tip . Pressure
　F3 applied to the plate assembly from the pressing member F3 Pressurization force applied to the plate assembly from the second electrode tip
　F4 Pressure applied to the plate assembly from the second electrode member
The scope of the claims
[Claim 1]
　A spot welding method in which resistance spot welding is performed on a plate assembly in which a plurality of metal plates having
　a plate thickness ratio of 5 or more are stacked, and a plate thickness ratio in which a metal plate having the thinnest plate thickness is arranged on the outermost surface is 5 or more. Preparing a plate set of
　the first electrode tip and the second electrode tip so that the first electrode tip is arranged on the side where the thinnest metal plate is arranged. Arrangement so that the chip is arranged on the opposite side of the plate set so as to face each other with the plate set interposed therebetween, and
　the first pressing member, which is an insulator, is arranged around the first electrode chip. to it,
　the first pressing force from the electrode tip is added to the plate set is such that said second electrode tip is smaller than the pressure exerted on the plate assembly, the first electrode tip and the Pressing each tip of the first pressure member and the tip of the second electrode tip against the plate assembly to apply a pressing force, and
　the first electrode tip and the first pressure member. While pressing each tip portion and the tip portion of the second electrode tip against the plate assembly to apply a pressing force, a current is caused to flow between the first electrode tip and the second electrode tip, Performing a welding of the plate assembly
　.
[Claim 2]
　A second pressure member, which is a conductor, is arranged around the second electrode tip, and the
　pressing force applied to the plate set by the first electrode tip is changed from the second electrode tip to the plate. The tip of each of the first electrode tip and the first pressure member and the tip of the second electrode tip are pressed against the plate assembly so as to be smaller than the pressure applied to the assembly. And contacting or pressing the tip of the second pressure member to the plate assembly to apply pressure,
　and the tip of each of the first electrode tip and the first pressure member, The tip portion of the second electrode tip is pressed against the plate assembly to apply a pressing force, and the tip portion of the second pressing member is contacted with the plate assembly or pressed to apply a pressing force.
　The spot welding method according to claim 1 , further comprising: applying a current between the first electrode tip and the second electrode tip and the second pressure member to weld the plate assembly .
[Claim 3]
　The spot welding method according to claim 1 or 2, wherein an average distance between the body portion of the first electrode tip and the first pressure member is 0.5 mm or less.
[Claim 4]
　The spot welding method according to claim 2, wherein an average distance between the body portion of the second electrode tip and the second pressure member is 0.5 mm or less.
[Claim 5]
　When the first electrode tip and the second electrode tip are brought into contact with the plate assembly with a pressing force of zero
　(inter-electrode distance between the first electrode tip and the second electrode tip)
　The pressurization force of the said 2nd pressurizing member is reduced to 0.43 kN or less, when <= (total thickness of each metal plate which comprises the said plate group x 1.1 times) is materialized, The claim 2 or 4. Spot welding method.