Double-acting electrode for spot welding, spot welding device, and method for manufacturing spot-welded member

Abstract

To provide a double-acting type electrode for spot welding capable of suppressing sheet separation and ruggedness of a surface of a member with a simple structure in spot welding of a plate set consisting of a plurality of thin plates,a spot welding device, and a method of manufacturing a spot welding member.SOLUTION: A double-acting type electrode for spot welding comprises: a rod-like electrode; an adapter supporting a base end of the rod-like electrode; a sleeve surrounding the rob-like electrode and configured to move between a first position and a second position along the axis of the rod-like electrode; a coil spring pressing the sleeve from the base end side toward a tip side of the rod-like electrode along the axis of the rod-like electrode; and a positioning mechanism connected to the sleeve and configured to adjust the first position of the sleeve along the axis of the rod-like electrode, wherein the first position is a position where the tip of the sleeve protrudes toward the tip side of the tip of the rod-like electrode, and the positioning mechanism can adjust the quantity of protrusion of the sleeve from the rod-like electrode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a double-action electrode for spot welding, a spot welding device, and a method for manufacturing a spot-welded member. [Background technology]

[0002] Spot welding is one of the manufacturing methods for lap welded components obtained by lap welding metal sheets. Spot welding is a welding method in which multiple metal sheets are sandwiched between two water-cooled copper electrodes, and electricity is passed through them while they are pressed by the electrodes, causing the metal sheets to melt and solidify. Spot welding is simple, and spot welding machines are inexpensive. Therefore, spot welding is used in various technical fields.

[0003] However, spot welding has a problem in that it is prone to sheet separation (a gap between plates that occurs around a nugget as a result of welding in lap resistance welding). Sheet separation occurs particularly notably in spot welding of thin plates.

[0004] Furthermore, in spot welding of a sheet assembly in which a thin plate is arranged on the surface of the sheet assembly, poor joining of the thin surface plate is also a problem. The steel plate arranged on the outermost surface of the sheet assembly is difficult to form a nugget due to the heat dissipation effect of the water-cooled electrode. In addition, when the number of steel plates constituting the sheet assembly is large, the electrode pressure must be increased. The larger the electrode pressure, the larger the contact area between the steel plate arranged on the outermost surface of the sheet assembly and the electrode, and the greater the amount of heat dissipation by the electrode.

[0005] In order to prevent poor joints, the outermost steel sheet of the plate assembly must be melted. To achieve this, it is necessary to increase the welding current and reduce the electrode pressure. However, reducing the electrode pressure makes it easier for splashing to occur. Therefore, when spot welding multiple thin metal sheets, for example, four or more sheets, it is necessary to find an optimum range within an extremely narrow range for the welding current and electrode pressure. Even if the optimum values ​​for the welding current and electrode pressure to avoid poor joints are found, it is not possible to suppress sheet separation.

[0006] As a technique for suppressing sheet separation, for example, Patent Document 1 discloses a composite electrode used for resistance spot welding of a sheet assembly including a plurality of stacked metal sheets, the composite electrode including a rod-shaped electrode body having a tip surface contacting and pressed against the sheet assembly, a rigid body having a through hole into which the electrode body is inserted and having a tip surface contacting and pressed against the sheet assembly, the rigid body including a conductor not electrically connected to the electrode body, and an elastic body connected to the rear end of the rigid body and applying a pressing pressure to the rigid body as the electrode body and the rigid body are pressed against the sheet assembly, the distance between the outer periphery of the tip surface of the electrode body and the inner periphery of the tip surface of the rigid body being 0.3 mm or more and 7 mm or less. According to the composite electrode described in Patent Document 1, it is possible to expand the appropriate current range and improve the strength of the welded joint in spot welding of ultra-high tensile steel used in transportation machines such as automobiles and industrial machines.

[0007] On the other hand, when spot welding is applied to welding of a plate assembly in which the outermost surface is a thin plate, in addition to the problem of sheet separation, there is a problem that unevenness is likely to occur on the surface of the spot weld. The unevenness is formed at the contact part between the electrode and the material to be welded and in the vicinity thereof. For example, in a welded joint obtained using the spot welding device disclosed in Patent Document 1, unevenness occurs on the inner peripheral edge of the tip of the rigid body.

[0008] In the technical fields of transportation machinery such as automobiles and industrial machinery to which the invention described in Patent Document 1 is applied, unevenness formed on the surface of spot welds is not considered to be a particular problem. Therefore, in the invention described in Patent Document 1, suppressing unevenness on the surface of spot welds is not considered an issue, and no specific means for suppressing unevenness is disclosed. However, in order to apply spot welding to technical fields with strict requirements for dimensional accuracy of components, a technology capable of suppressing unevenness on the surface of spot welds is desired. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6288097 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a double-acting electrode for spot welding, a spot welding device, and a method for manufacturing spot-welded components that can suppress sheet separation and unevenness on the surfaces of components with a simple structure when spot welding a plate assembly consisting of multiple thin plates. [Means for solving the problem]

[0011] The gist of the present invention is as follows.

[0012] (1) A double-acting electrode for spot welding according to one embodiment of the present invention comprises a rod-shaped electrode, an adapter supporting a base end of the rod-shaped electrode, a sleeve surrounding the rod-shaped electrode and configured to be movable along the axial direction of the rod-shaped electrode between a first position at a tip side of the rod-shaped electrode and a second position at the base end side of the rod-shaped electrode, a coil spring pushing the sleeve from the base end side toward the tip side of the rod-shaped electrode along the axial direction of the rod-shaped electrode, and a positioning mechanism connected to the sleeve and configured to adjust the first position of the sleeve along the axial direction of the rod-shaped electrode, wherein the first position is a position where the tip of the sleeve protrudes toward the tip side relative to the tip of the rod-shaped electrode, and the positioning mechanism can adjust the amount of protrusion of the sleeve from the rod-shaped electrode. (2) In the double-acting electrode for spot welding described in (1) above, the sleeve may have a threaded portion at its base end, and the positioning mechanism may be composed of a sleeve base having a threaded portion that screws into the threaded portion of the sleeve, and a sleeve fixing member that fixes the sleeve to the sleeve base, and the pitch of the threaded portion of the sleeve base may be 1.0 mm or less. (3) In the double acting electrode for spot welding described in (1) or (2) above, the sleeve may be made of metal. (4) In the double-acting electrode for spot welding described in any one of (1) to (3) above, the rod-shaped electrode may be cylindrical, the sleeve may be cylindrical, and the difference between the radius of the inner circumference of the sleeve and the radius of the outer circumference of the rod-shaped electrode may be 0.2 mm or more and 0.3 mm or less. (5) In the double acting spot welding electrode according to any one of (1) to (4) above, the coil spring may have a spring constant of 0.05 kN / mm to 0.30 kN / mm. (6) In the double-action spot welding electrode according to any one of (1) to (5) above, the tip of the rod-shaped electrode may be R-shaped with a radius of curvature of R20 to R120. (7) A spot welding device according to another aspect of the present invention includes a pair of double-acting electrodes according to any one of (1) to (6) above. (8) A method for manufacturing a spot-welded component according to another aspect of the present invention includes a step of spot welding a plate assembly consisting of two or more metal plates using a pair of double-acting electrodes described in any one of (1) to (6) above. (9) In the manufacturing method of spot-welded components described in (8) above, the plate assembly may be composed of four or more of the metal plates, and the thickness of the metal plates arranged on one or both surfaces of the plate assembly may be 0.7 mm or less. (10) In the manufacturing method of a spot-welded component described above in (8) or (9), during the spot welding, a protrusion amount of the tip of the rod-shaped electrode from the tip of the sleeve when the sleeve is in the first position may be 2 mm or more and 10 mm or less. (11) In the method for producing a spot-welded component according to any one of (8) to (10) above, a pressure holding time Th in msec after the end of the spot welding may satisfy the following formula 1: 15×(Σhi) 2 ≦Th≦50×(Σhi) 2 …(Formula 1) Here, Σhi in the formula 1 is the total thickness (unit: mm) of the metal plates constituting the plate assembly. (12) In the manufacturing method of a spot-welded member described in any one of (8) to (11) above, in one or both of the double-acting electrodes, the amount of protrusion of the tip of the rod-shaped electrode relative to the tip of the sleeve when the sleeve is in the first position may be adjusted so that the neutral position of the pair of rod-shaped electrodes provided in the pair of double-acting electrodes coincides with the neutral position of the pair of sleeves provided in the pair of double-acting electrodes. Effect of the Invention

[0013] According to the present invention, it is possible to provide a double-acting electrode for spot welding, a spot welding device, and a method for manufacturing spot-welded components that can suppress sheet separation and unevenness on the surfaces of components with a simple structure when spot welding a plate assembly consisting of multiple thin plates. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view of an example of a dual-acting electrode according to the present embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of an example of a rod-shaped electrode without a sleeve attached. [Diagram 3] FIG. 13 is a cross-sectional view of an example of a sleeve and a positioning mechanism. [Figure 4] FIG. 2 is a schematic diagram showing a state immediately before spot welding using the double-acting electrode according to the embodiment; [Diagram 5] FIG. 2 is a schematic diagram showing a state during spot welding using the double-acting electrode according to the present embodiment. [Figure 6] This is a cross-sectional photograph of a weld formed by ordinary spot welding two steel plates (thin plates with a plate thickness of 0.7 mm). [Figure 7A] This is a cross-sectional photograph of a weld formed by ordinary spot welding eight steel plates (thin plates with a plate thickness of 0.7 mm). [Figure 7B] FIG. 7B is a photograph of sheet separation around the weld of FIG. 7A. [Figure 8]1 is a cross-sectional photograph of a spot-welded member produced using a double-acting electrode having a sleeve surrounding a rod-shaped electrode, without adjusting the amount of sleeve protrusion. [Figure 9] 13 is a cross-sectional photograph of a spot-welded member obtained by spot welding after fine-tuning the amount of sleeve protrusion using a double-acting electrode having a rod-shaped electrode, a sleeve, and a sleeve positioning mechanism. [Figure 10] 13 is a cross-sectional photograph of a spot-welded member obtained by spot welding after fine-tuning the amount of sleeve protrusion using a double-acting electrode having a rod-shaped electrode, a sleeve, and a sleeve positioning mechanism. [Figure 11A] FIG. 1 is a cross-sectional view of a weld obtained by spot welding with a pressure holding time of 300 msec (60 Hz, 18 cycles). [Figure 11B] FIG. 1 is a cross-sectional view of a weld obtained by spot welding with a pressure holding time of 500 msec (60 Hz, 30 cycles). [Figure 11C] FIG. 1 is a cross-sectional view of a weld obtained by spot welding with a pressure holding time of 700 msec (60 Hz, 42 cycles). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a double-action electrode for spot welding (hereinafter, sometimes simply referred to as a "double-action electrode"), a spot welding device, and a method for manufacturing a spot-welded member according to the present invention will be described in detail.

[0016] As illustrated in FIG. 1, a double-acting electrode 1 according to one embodiment of the present invention comprises a rod-shaped electrode 11, an adapter 12 supporting the base end of the rod-shaped electrode 11, a sleeve 13 surrounding the rod-shaped electrode 11 and configured to be movable along the axial direction of the rod-shaped electrode 11 between a first position at the tip side of the rod-shaped electrode 11 and a second position at the base end side of the rod-shaped electrode 11, a coil spring 14 pushing the sleeve 13 from the base end side toward the tip side of the rod-shaped electrode 11 along the axial direction of the rod-shaped electrode 11, and a positioning mechanism 15 connected to the sleeve 13 and configured to be capable of adjusting the first position of the sleeve 13 along the axial direction of the rod-shaped electrode 11.

[0017] 2 shows an example of the rod-shaped electrode 11 and the adapter 12. The rod-shaped electrode 11 is an electrode for spot welding. The type of electrode is not particularly limited, and any spot welding electrode to which a positioning mechanism 15 described later can be connected can be appropriately used as the rod-shaped electrode 11 of the double-acting electrode 1 according to this embodiment. Specifically, a spot welding electrode having a shank 112 that can prevent a sleeve base 152 of the positioning mechanism 15 described later from falling off is preferably used.

[0018] 1 and 2 is a so-called cap-type electrode that is composed of a shank 112 and a cap tip 111 that is placed on the tip of the shank 112. On the other hand, the rod-shaped electrode 11 may be an integrated electrode. The shape of the tip of the electrode is not particularly limited.

[0019] The adapter 12 is a member that supports the base end of the rod-shaped electrode 11. The rod-shaped electrode 11 is attached to a spot welding device via the adapter 12. The adapter 12 and the rod-shaped electrode 11 may be integrally formed as one member. When the adapter 12 and the rod-shaped electrode 11 are one member, it is preferable to prevent a sleeve base 152 of the positioning mechanism 15, which will be described later, from falling off by a portion other than the shank 112, for example, a cap tip 111.

[0020] 3 shows the sleeve 13, the coil spring 14, and the positioning mechanism 15. The sleeve 13 is one of the extremely important components for sheet separation and suppressing unevenness on the surface of the welded member. The sleeve 13 has a cylindrical shape, and the rod-shaped electrode 11 is inserted therein. In this way, the sleeve 13 is attached to the double-acting electrode 1 so as to surround the rod-shaped electrode 11.

[0021] The sleeve 13 is configured to be movable between a first position at the tip end side of the rod electrode 11 and a second position at the base end side of the rod electrode 11 along the axial direction of the rod electrode 11. For example, in the double-acting electrode 1 illustrated in FIG. 1 and FIG. 3, a shank 112 and a sleeve base 152 are used to move the sleeve 13. The shank 112 has a protrusion 1121 having a function of preventing the sleeve base 152 from falling off. The sleeve base 152 is formed with a hole 1522 for inserting the rod-shaped shank 112. In addition, the sleeve base 152 is disposed between the adapter 12 and the protrusion of the shank 112 with the shank 112 inserted into the hole. This allows the sleeve base 152 to slide relative to the shank 112. The sleeve 13 fixed to the sleeve base 152 is movable relative to the rod electrode 11 along the axial direction of the rod electrode 11.

[0022] The first position and the second position refer to both ends of the range in which the sleeve 13 can move along the axial direction of the rod-shaped electrode 11. For convenience, of the two ends of the range in which the sleeve 13 can move, the one on the tip side of the rod-shaped electrode 11 (i.e., the side in contact with the material to be welded) is referred to as the first position, and the one on the base side of the rod-shaped electrode 11 (i.e., the side connected to the adapter 12) is referred to as the second position.

[0023] The sleeve 13 is pushed from the base end side to the tip end side of the rod-shaped electrode 11 by the coil spring 14 described later, so that the sleeve 13 is disposed in the first position unless a particular external force is applied (see FIG. 1). The positioning of the first position will be described later. The sleeve position when the sleeve 13 is pushed to the base end side to the maximum (for example, when the coil spring 14 is pushed to the maximum) is the second position. Naturally, when the sleeve 13 is in the second position, the second position needs to be determined so that the tip of the sleeve 13 is located at the same position as the tip of the rod-shaped electrode 11 or located closer to the base end than the tip of the rod-shaped electrode 11. This is because, if the tip of the sleeve 13 in the second position protrudes beyond the tip of the rod-shaped electrode 11, the rod-shaped electrode 11 cannot be brought into contact with the non-weld object, and spot welding cannot be performed.

[0024] When a pair of double-acting electrodes 1 is pressed against the plate assembly with the tip of the sleeve 13 protruding beyond the tip of the rod-shaped electrode 11, the sleeve 13 is pushed in until the tip of the rod-shaped electrode 11 contacts the plate assembly, and the plate assembly can be clamped with a pressure force according to the length to which the sleeve 13 is pushed in (i.e., the protrusion amount P described below).

[0025] Since the sleeve 13 is arranged to be movable coaxially with the rod electrode 11, deformation of the metal plates around the spot welding point can be suppressed. This makes it possible to keep the contact area between the tip of the rod electrode 11 and the outermost metal plate of the sheet assembly small. In this case, the current density can be increased and heat transfer from the outermost metal plate to the rod electrode 11 can be suppressed. Therefore, a nugget can be formed that reaches the outermost metal plate. In addition, since the pressure range can be widened even in the center of the sheet assembly in the sheet thickness direction, a nugget can be formed on a large number of sheets with small welding deformation without causing expulsion.

[0026] Furthermore, the sleeve 13 is used to press the periphery of the welding point where the rod-shaped electrode 11 contacts, suppressing deformation of the steel sheet and thereby suppressing sheet separation. In the double-acting electrode 1 according to this embodiment, a sleeve 13 that is movable in the axial direction of the rod-shaped electrode 11 is provided around the rod-shaped electrode 11, and the sleeve 13 is pushed toward the tip side of the rod-shaped electrode 11 by a coil spring 14, thereby making it possible to press the periphery of the welding point with a simple mechanism.

[0027] The coil spring 14 is a member that directly or indirectly connects the adapter 12 and the sleeve 13, and presses the sleeve 13 from the base end side along the axial direction of the rod-shaped electrode 11 toward the tip side of the rod-shaped electrode 11. This allows the coil spring 14 to generate a force that causes the sleeve 13 to press against the material to be welded during spot welding.

[0028] In the double-acting electrode 1 illustrated in Fig. 1, the coil spring 14 is disposed between the sleeve base 152 and the adapter 12 with the shank 112 of the rod-shaped electrode 11 passing through its center. This causes the coil spring 14 to push the sleeve base 152 away from the adapter 12. In turn, the coil spring 14 pushes the sleeve 13 fixed to the sleeve base 152 toward the tip side of the rod-shaped electrode 11.

[0029] Incidentally, the coil spring 14 can be replaced with an equivalent elastic body or other member as long as the sleeve 13 can be pressed toward the tip side of the rod-shaped electrode 11 along the axial direction of the rod-shaped electrode 11. However, from the viewpoint of simplifying the structure of the double-acting electrode 1 and making it easy to handle, it is most preferable to use the coil spring 14.

[0030] The positioning mechanism 15 is a member connected to the sleeve 13 and configured to position the first position of the sleeve 13 along the axial direction of the rod-shaped electrode 11. As a result, the first position of the sleeve 13 is a position where the tip of the sleeve 13 protrudes toward the tip side relative to the tip of the rod-shaped electrode 11. In other words, when the sleeve 13 is in the first position, the tip of the sleeve 13 protrudes relative to the tip of the rod-shaped electrode 11. In addition, by using the positioning mechanism 15, the protrusion amount P of the sleeve 13 can be adjusted. Here, the protrusion amount P of the sleeve 13 is the distance between the tip of the sleeve 13 and the tip of the rod-shaped electrode 11 measured along the axial direction of the rod-shaped electrode 11 when the sleeve 13 is in the first position (i.e., when no external force is applied to the sleeve 13).

[0031] The protrusion amount P of the sleeve 13 is closely related to the force with which the sleeve 13 presses the workpiece during spot welding. The product of the protrusion amount P and the spring constant of the coil spring 14 is the pressing force of the sleeve 13. Therefore, the pressing force of the sleeve 13 can be controlled by controlling the protrusion amount P.

[0032] The double-acting electrode having the sleeve 13, the coil spring 14, and the positioning mechanism 15 allows fine adjustment of the positional relationship between the rod-shaped electrode 11 and the sleeve 13 during spot welding. This makes it possible to suppress sheet separation and also to suppress unevenness on the surface of the spot-welded member. The mechanism behind this is believed to be as follows.

[0033] When spot welding is performed using a pair of double-acting electrodes having sleeves, the sheet assembly is pressurized by both the rod-shaped electrodes and the sleeve. Here, the neutral position between the tips of the pair of electrodes may deviate from the neutral position between the tips of the pair of sleeves. The deviation of the neutral position is considered to be caused by dimensional errors of each member within the tolerance, or by asymmetric wear of the electrode tips with respect to the polarity when welding using a DC power source. In particular, when plating steel sheets are welded with a DC power source, asymmetric wear often occurs on the front and back sides of the sheet assembly, and therefore the present invention is particularly useful.

[0034] The inventors presumed that this slight deviation in the neutral position was a disturbance that caused asymmetric unevenness on the surface of the spot-welded component. Then, by performing spot welding with the neutral position between the tips of the pair of electrodes and the neutral position between the tips of the pair of sleeves aligned using positioning mechanism 15, it was possible to suppress asymmetric unevenness on the surface of the spot-welded component.

[0035] Also, when the thicknesses of the two metal sheets on the surface of the sheet assembly are different, it may be preferable to weld the nugget so that it is offset to one surface, rather than forming an even nugget shape on both sides. In this case, other conditions may be preferable than making the neutral position of the electrode tip coincident with the neutral position of the sleeve tip. Even in this case, if a double-acting electrode with a sleeve positioning mechanism is used, the welding conditions can be easily set.

[0036] The configuration of the positioning mechanism 15 is not particularly limited. For example, the sleeve may have a threaded portion at its base end, and the positioning mechanism may be composed of a sleeve base having a threaded portion that screws with the threaded portion of the sleeve, and a sleeve fixing member that fixes the sleeve to the sleeve base. This configuration will be described in detail below.

[0037] 1 and 3 has a sleeve fixing member (lock nut) 151 and a sleeve base 152. The sleeve 13 has a male thread portion 131 at its base end, and the sleeve base 152 has a female thread portion 1521 configured to screw into the male thread portion 131 of the sleeve 13. By rotating the sleeve 13, the tip position of the sleeve 13 can be finely adjusted along the axial direction of the rod-shaped electrode 11, thereby finely adjusting the protrusion amount P. The lock nut 151 is a member that fixes the sleeve 13 to the sleeve base 152.

[0038] According to the inventor's research, the pressure force, which depends on the product of the protrusion amount P and the spring constant, has a very large effect on the unevenness of the surface of the spot-welded member. On the other hand, the spring constant of the coil spring varies. For example, according to the standard for spring constant set forth in JIS B 2704-2 2009, even for a first-class spring, if the number of effective turns is more than 3 and not more than 10, the spring constant is allowed to have an error of ±5%, and if the number of effective turns is more than 10, an error of ±4% is allowed. Therefore, the spring constants of the two coil springs provided on the pair of double-acting electrodes 1 are usually slightly different even if they have the same length and type. If the protrusion amount P of the pair of double-acting electrodes 1 is the same and spot welding is performed, the pressing force by the pair of sleeves 13 is likely to be different. On the side where the sleeve 13 weakly contacts the metal plate, the nugget formed on the outermost metal plate of the plate assembly becomes smaller and the indentation becomes deeper. On the other hand, on the side where the sleeve 13 strongly hits the metal sheet, the nugget becomes larger and the indentation becomes shallower. This phenomenon becomes more noticeable when a large nugget is formed, since the metal sheet directly under the electrode is heated over a wide area and loses strength.

[0039] In order to absorb the variation in the spring constant and generate the same pressing force on the front and back of the plate assembly, the protrusion amount P should be adjustable as precisely as possible. For the above reasons, the pitch of the female thread portion 1521 of the sleeve base 152 is preferably 1.0 mm or less. When the female thread portion 1521 is a hexagonal thread with a pitch of 1.0 mm, the protrusion amount P can be adjusted in units of about 0.08 mm, so that the unevenness of the surface can be more reliably suppressed. By using the six vertices and six sides of the hexagonal thread, the rotation angle of the hexagonal thread can be adjusted in units of about 30 degrees. Therefore, when the female thread portion 1521 is a hexagonal thread with a pitch of 1.0 mm, the protrusion amount P can be adjusted in units of about 0.08 mm (1.0 mm ÷ (360 degrees ÷ 30 degrees)). It is more preferable that the pitch of the female thread portion 1521 of the sleeve base 152 is 0.5 mm or less. However, as described later, in spot welding using a pair of double-acting electrodes according to this embodiment, it is not necessary to make the pressing forces of the sleeve 13 the same, and there may be situations in which they should be made different. Even in such cases, the configuration that allows fine adjustment of the protrusion amount P is advantageous.

[0040] On the other hand, the positioning mechanism 15 may be other than those illustrated in FIG. 1 and FIG. 3. For example, a female thread may be provided on the inner surface of the sleeve 13, and a male thread may be provided on the sleeve base 152 to be screwed therewith. Also, instead of providing a thread, the protrusion amount P can be precisely adjusted by inserting a metal foil between the sleeve 13 and the sleeve base 152. In addition, a suitable positioning mechanism 15 may be appropriately adopted depending on the purpose. However, according to the study of the present inventor, the screw-type positioning mechanism 15 is considered to be the most suitable. The screw-type positioning mechanism 15 has a simple and small structure, so that the double-acting electrode 1 can be attached to an existing spot welding machine. Also, the screw-type positioning mechanism 15 allows the protrusion amount P to be easily adjusted in a short time.

[0041] A more preferred embodiment of the double-acting electrode 1 according to this embodiment will now be described.

[0042] The material of the sleeve 13 is not particularly limited, and any material capable of forming a rigid body that is substantially undeformed by an external force can be appropriately adopted. The sleeve 13 is preferably made of metal, and more preferably made of copper alloy. By making the sleeve 13 of metal, the heat resistance of the sleeve 13 can be ensured. In particular, when the number of metal plates constituting the plate assembly to be welded is large, the amount of heat input for welding becomes large, and the time required for welding also becomes long. Therefore, it is important to ensure the heat resistance of the sleeve 13. Furthermore, the sleeve 13 made of metal has the advantage that it is easy to cool. In addition, when the positioning mechanism 15 is a screw type, the sleeve 13 made of metal has the advantage that the pitch of the screw portion can be made small, and the adjustment accuracy of the protrusion amount P can be further improved. The sleeve 13 is more preferably made of metal having a melting point of 800° C. or more and a yield strength of 50 MPa or more. Examples of such metals include steel, stainless steel, and copper alloy.

[0043] It is permissible to pass current through the sleeve 13. The current shunt to the sleeve 13 is not so large. According to the results of experiments conducted by the present inventors, even if current is passed through the sleeve 13 during spot welding, it does not adversely affect the surface quality and other characteristics of the spot-welded member. Therefore, it is not necessary to use an insulating material for the sleeve 13, and it is also not necessary to provide an insulating material between the sleeve 13 and the rod-shaped electrode 11. On the other hand, if the heat resistance of the sleeve 13 is not important, the sleeve 13 may be made of an insulating nonmetallic material, or an insulating member that electrically insulates the sleeve 13 from the rod-shaped electrode 11 may be provided on the double-acting electrode 1.

[0044] The shapes of the rod-shaped electrode 11 and the sleeve 13 are not particularly limited, but when the sleeve 13 is cylindrical, for example, it is preferable that the difference between the radius of the inner circumference of the sleeve 13 and the radius of the outer circumference of the rod-shaped electrode 11 is about 0.2 mm or more and 0.3 mm or less. The closer the difference between the radius of the inner circumference of the sleeve 13 and the radius of the outer circumference of the rod-shaped electrode 11 is, the more effective it is at suppressing the lifting of the metal plate around the welding point. On the other hand, by making the difference between the radius of the inner circumference of the sleeve 13 and the radius of the outer circumference of the rod-shaped electrode 11 0.2 mm or more, it is possible to prevent the sleeve 13 from galling. When the sleeve 13 is a regular polygon, for example, it is preferable that the difference between the radius of the inscribed circle of the sleeve 13 and the radius of the rod-shaped electrode 11 is about 0.2 mm or more and 0.3 mm or less.

[0045] In FIG. 2 and other figures, the sleeve 13 is cylindrical and surrounds the cylindrical rod-shaped electrode 11. However, the sleeve 13 does not need to be completely cylindrical. That is, the sleeve 13 does not necessarily need to surround the entire circumference of the rod-shaped electrode 11. It is sufficient that the contact area between the sleeve 13 and the metal plate is arranged symmetrically with respect to the axis of the electrode, and that the angle that the total of the contact areas between the sleeve 13 and the metal plate makes with the axis of the electrode is 180° or more. Also, as long as the total of the contact areas between the sleeve 13 and the metal plate is arranged axially symmetrically with respect to the rod-shaped electrode 11 at 180° or more, the area may be divided into multiple areas.

[0046] The spring constant of the coil spring 14 is not particularly limited, but is preferably, for example, 0.05 kN / mm to 0.30 kN / mm. Repeated spot welding causes wear (destruction) at the tip of the rod-shaped electrode 11, and the overall length of the rod-shaped electrode 11 gradually shortens. This increases the amount of spring deflection, and the sleeve pressurizing force increases, while the electrode pressurizing force decreases. In this case, by setting the spring constant to a predetermined value or less, it is possible to suppress fluctuations in the sleeve pressurizing force and the electrode pressurizing force caused by the collapse of the tip of the rod-shaped electrode 11. For example, if the coil spring 14 of the rod-shaped electrode 11 has a spring constant of 0.30 kN / mm, the change in the pressurizing force caused by the spring is within 0.015 kN for a fluctuation of 0.05 mm in the amount of spring deflection. This makes it possible to reduce the frequency of electrode maintenance required to maintain the welding conditions. For this reason, the upper limit of the spring constant is preferably about 0.30 kN / mm.

[0047] On the other hand, the lower limit of the spring constant is preferably about 0.05 kN / mm. The smaller the deflection amount relative to the total length of the spring, the longer the spring life. Also, the smaller the total length of the spring itself, the more compact the double-acting electrode can be, improving convenience. Therefore, it is preferable to set the spring constant to 0.05 kN / mm or more so that a predetermined sleeve pressure can be secured even with a small deflection amount (i.e., protrusion amount P). For example, when welding with a sleeve pressure of 0.20 kN, a spring with a spring constant of 0.05 kN / mm will have a deflection amount of 4 mm. If the total length of the spring is 20 mm, the deflection rate will be 20%, and a service life of more than 1 million times can be expected.

[0048] The tip shape of the rod-shaped electrode 11 is not particularly limited. The tip shape of the rod-shaped electrode 11 may be, for example, a DR type (dome radius) or a CR type (cone radius) with a tip diameter of φ6 or φ8. On the other hand, from the viewpoint of more reliably suppressing indentation, it is preferable that the tip shape of the rod-shaped electrode 11 is an R type (radius) with a curvature radius of R20 to R120. The material of the rod-shaped electrode 11 is also not particularly limited. Examples of the material of the tip of the rod-shaped electrode 11 include chromium copper, chromium zirconium copper, beryllium copper, alumina dispersion strengthened copper, copper tungsten, etc., but any material can be used as long as it functions as an electrode.

[0049] A spot welding apparatus according to another embodiment of the present invention has a pair of the above-mentioned double-acting electrodes 1. Also, a manufacturing method for spot-welded components according to another embodiment of the present invention includes a step of spot welding a sheet set X consisting of two or more metal sheets using the pair of the above-mentioned double-acting electrodes 1. Fig. 4 shows the state of the pair of double-acting electrodes 1 immediately before spot welding, and Fig. 5 shows the state of the pair of double-acting electrodes 1 during spot welding. During spot welding, the sleeve 13 is pushed in and presses the periphery of the spot welding point.

[0050] According to the spot welding device and the manufacturing method of the spot-welded member of the present embodiment, spot welding can be performed while pressing the periphery of the spot welding point from both sides of the sheet assembly X using the sleeve 13. This makes it possible to suppress sheet separation.

[0051] Furthermore, according to the spot welding device and the manufacturing method for the spot-welded member of the present embodiment, the protrusion amount P of the sleeve 13 of each of the pair of double-acting electrodes 1 can be finely adjusted, thereby finely adjusting the pressing force of the sleeve 13. This makes it possible to suppress unevenness on the surface of the spot-welded member.

[0052] For example, the protrusion amount P (i.e., the distance between the tip of the sleeve 13 and the tip of the rod-shaped electrode 11 measured along the axial direction of the rod-shaped electrode 11 when the sleeve 13 is in the first position) may be adjusted in one or both of the double-acting electrodes 1 so that the neutral position of the pair of rod-shaped electrodes 11 included in the pair of double-acting electrodes 1 coincides with the neutral position of the pair of sleeves 13 included in the pair of double-acting electrodes 1. The neutral position of the pair of rod-shaped electrodes 11 is a position where the tips of the pair of rod-shaped electrodes 11 come into contact with each other when the pair of double-acting electrodes 1 are brought close to each other without two or more metal plates (sheet assembly X) to be welded being set in a spot welding device. Similarly, the neutral position of the pair of sleeves 13 is a position where the tips of the pair of sleeves 13 come into contact with each other when the pair of double-acting electrodes 1 are brought close to each other without the sheet assembly X being set in a spot welding device.

[0053] If the neutral positions of the pair of rod-shaped electrodes 11 and the pair of sleeves 13 do not match, the shape of the nugget will be non-uniform on the front and back of the sheet assembly, which may result in significant unevenness on the surface of the spot-welded member. On the other hand, by finely adjusting the protrusion amount P of each of the pair of double-acting electrodes 1 so that the neutral positions of the pair of rod-shaped electrodes 11 and the pair of sleeves 13 match, the shape of the nugget can be made uniform on the front and back of the sheet assembly, and unevenness on the surface of the spot-welded member can be suppressed.

[0054] However, depending on the configuration of the sheet group X, it may be better to make the shape of the nugget uneven on the front and back of the sheet group. For example, if the thickness of the metal sheet on the first surface of the sheet group X is smaller than the thickness of the metal sheet on the second surface of the sheet group X, poor joining of the metal sheet on the first surface side can be suppressed by displacing the nugget toward the first surface side of the sheet group X. According to the spot welding device and the manufacturing method for a spot-welded member of this embodiment, the nugget position can be displaced by finely adjusting the protrusion amount P of each of the pair of double-acting electrodes 1.

[0055] The conditions for spot welding are not particularly limited. Various welding conditions according to the configuration of the plate assembly (type, thickness, plate thickness ratio, etc. of the metal plates) can be applied to the manufacturing method of the spot-welded member according to the present embodiment. Particularly suitable conditions will be described below as examples.

[0056] In the manufacturing method of the spot-welded member according to the present embodiment, the plate assembly may be composed of four or more metal plates, and the thickness of the metal plates arranged on one or both surfaces of the plate assembly may be 0.7 mm or less. Such plate assembly is highly susceptible to sheet separation and unevenness. However, in the manufacturing method of the spot-welded member according to the present embodiment, the periphery of the spot welding point is pressed using a pair of sleeves 13 capable of finely adjusting the protrusion amount P, so that the above-mentioned problem does not occur. The material of the plate assembly is not particularly limited. For example, the manufacturing method of the spot-welded member according to the present embodiment can be applied to a plate assembly composed of various metal plates such as steel plates, stainless steel plates, and aluminum plates.

[0057] In the manufacturing method of the spot-welded member according to the present embodiment, the protrusion amount P of the tip of the rod-shaped electrode relative to the tip of the sleeve when the sleeve 13 moves to the first position during spot welding may be set to 2 mm or more and 10 mm or less. By setting the protrusion amount P to 2 mm or more, the change in the amount of spring deflection caused by the crushing of the tip of the rod-shaped electrode 11 can be reduced. This makes it possible to further suppress the change in welding conditions when performing spot welding continuously. For example, when the protrusion amount P is set to 1 mm, if the reduction in the total length of the rod-shaped electrode 11 due to the crushing of the tip of the rod-shaped electrode 11 is 0.05 mm, the change in the sleeve pressing force is 5%. On the other hand, when the protrusion amount P is set to 2 mm, if the reduction in the total length of the rod-shaped electrode 11 due to the crushing of the tip of the rod-shaped electrode 11 is 0.05 mm, the change in the sleeve pressing force is suppressed to 2.5%.

[0058] On the other hand, by reducing the protrusion amount P, the overall length of the spring can be kept small, thereby reducing the size of the double-acting electrode 1. From this viewpoint, it is desirable for the protrusion amount P to be 10 mm or less.

[0059] In the manufacturing method of a spot-welded member according to the present embodiment, a pressure holding time Th (unit: msec) after the end of spot welding may satisfy the following formula 1. 15×(Σhi) 2 ≦Th≦50×(Σhi) 2 (Formula 1) Here, Σhi in formula 1 is the total thickness, in mm, of the metal plates that make up the plate assembly. The "pressure holding time" is the time from the end of current flow to the point at which the electrode is released and the pressure starts to decrease. When a large number of metal plates make up the plate assembly, the total plate thickness of the plate assembly becomes large, the heat input during spot welding increases, and the distance between the center of the total plate thickness and the electrode becomes long. For this reason, even if a water-cooled electrode is in contact with the weld, it takes a long time for the molten metal to solidify. From the viewpoint of preventing shrinkage cavities from occurring in the nugget, 15×(Σhi) 2 It is preferable to set the welding conditions so as to satisfy the relationship Th≦50×(Σhi). On the other hand, if Th is too long, the work efficiency decreases. Therefore, Th≦50×(Σhi) 2 It is preferable to set the welding conditions so as to satisfy the relationship: EXAMPLES

[0060] The effects of one embodiment of the present invention will be explained more specifically with reference to an example. However, the conditions in the example are merely an example of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to this example of conditions. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0061] (1. Example of an electrode without a sleeve) Figure 6 is a cross-sectional photograph of a weld formed by ordinary spot welding two steel plates (thin plates with a plate thickness of 0.7 mm). The welding conditions were as follows: Single-phase AC power frequency (Freq.): 50Hz ·Electrode (φ16): DR type tip φ6 R40 Welding current: 6.2kA Current upslope time (UP.T): 2 cycles Welding time to form a nugget (WT): 7 cycles Current downslope time (DW.T): 0 cycles - Pressure retention time after current is turned off (Ho.T): 10 cycles Pressure: 2.0kN

[0062] According to the cross-sectional photograph shown in Figure 6, a molten solidified part called a nugget is formed between the steel sheets, and it can be seen that the two steel sheets are welded together. In addition, a gap is generated between the steel sheets around the nugget. This gap is the sheet separation. Figure 7A is a cross-sectional photograph of a weld formed by ordinary spot welding eight steel plates (thin plates with a plate thickness of 0.7 mm, as in Figure 6). Figure 7B is a photograph of the sheet separation around the weld. The welding conditions were as follows: Single-phase AC power frequency (Freq.): 50Hz ·Electrode (φ16): DR type tip φ6 R40 Welding current: 5.3kA Current upslope time (UP.T): 2 cycles Welding time to form a nugget (WT): 28 cycles Current downslope time (DW.T): 0 cycles - Pressure retention time after current is turned off (Ho.T): 10 cycles Pressure: 6.0kN

[0063] When the number of steel plates was eight, the impression depth (the depth of the depression caused by the electrode, measured in the direction of the applied pressure, also known as indentation) and sheet separation were significantly larger than those of the spot-welded component in Figure 6. As such, in spot welding of a sheet assembly of four or more metal plates with a thin metal plate arranged on the outermost surface, it is difficult to weld all of the steel plates while suppressing welding deformation such as indentation and sheet separation. Furthermore, if the welding deformation becomes too large, a problem occurs in that it is no longer possible to ensure the dimensional accuracy of the spot-welded component obtained by welding.

[0064] Furthermore, in the weld shown in Fig. 7A, the nugget does not reach the steel sheet arranged on the outermost surface of the sheet assembly. In other words, the steel sheet on the outermost surface of the sheet assembly is not welded to the adjacent steel sheet. Therefore, the joining strength of the steel sheet on the outermost surface shown in Fig. 7A is extremely low.

[0065] (2. An example where the electrode has a sleeve and a coil spring, but the sleeve is not positioned.) Figure 8 shows a cross-sectional photograph of a spot-welded component manufactured using a double-acting electrode with a sleeve surrounding a rod-shaped electrode. The spot-welded component in Figure 8, like that in Figure 7A, was obtained from a plate assembly in which eight thin plates with a thickness of 0.7 mm were stacked. However, unlike that in Figure 7A, in manufacturing the spot-welded component in Figure 8, a sleeve was used to press the periphery of the weld point to prevent the steel plate from lifting up. However, in manufacturing the spot-welded component in Figure 8, no special adjustment was made to the amount of sleeve protrusion. The welding conditions for the welded component in Figure 8 were as follows: Single-phase AC power frequency (Freq.): 60Hz ·Electrode (φ13): R type R40 Welding current: 6.0kA Current upslope time (UP.T): 0 cycles Welding time to form a nugget (WT): 18 cycles Current Downslope Time (DW.T): 42 cycles - Pressure retention time after current is turned off (Ho.T): 0 cycles Total pressure: 3.5kN (electrode pressure: 2.75kN, sleeve pressure: 0.75kN) Spring length: 30mm Spring constant: 81.7N / mm (0.08kN / mm) Spring deflection: 14 mm (in this example, the spring is pre-deflected by 10 mm and assembled, and the sleeve protrusion is 4 mm)

[0066] As described above, the spot-welded component of Fig. 7A, which was manufactured using an electrode without a sleeve, had a very large indentation depth and also had significant sheet separation (see Fig. 7B). On the other hand, the spot-welded component of Fig. 8, in which a sleeve was used to press the periphery of the weld point, had a small indentation depth and also had suppressed sheet separation.

[0067] However, even in the spot-welded component shown in Fig. 8, unevenness was formed above and below the nugget (particularly below the nugget). This unevenness occurred near the outer circumferential circle of the tip surface of the rod-shaped electrode, i.e., inside the area where the sleeve was pressed. Such unevenness is particularly likely to occur in a sheet assembly consisting of four or more thin plates. Simply pressing the periphery of the weld point makes it difficult to suppress unevenness on the surface of the component in spot welding of a sheet assembly consisting of multiple thin plates.

[0068] (3. Example of adjusting the protrusion amount P by positioning the sleeve) Figure 9 shows a cross-sectional photograph of a spot-welded component obtained by spot welding using a double-acting electrode having a rod-shaped electrode, a sleeve, and a sleeve positioning mechanism, after fine-tuning the sleeve protrusion amount. The welding conditions for the welded component in Figure 9 were the same as those for Figure 8. However, the sleeve protrusion amount was fine-tuned so that the sleeve pressure was the same on the front and back of the plate assembly. As a result, the spot-welded component in Figure 9 has an even flatter surface than the one in Figure 8.

[0069] It should be noted here that the unevenness occurring in the welded portion in FIG. 8 is formed inside the sleeve. The inner diameter of the sleeve used to form the welded portion in FIG. 8 and FIG. 9 was 13.5 mm, and the diameter of the nugget formed in this welded portion was about 5.9 mm at the center of the total plate thickness. Therefore, the unevenness occurring at the upper limit of the nugget in FIG. 8 was on the inside of the sleeve. Initially, the inventors predicted that a means other than the sleeve should be used to suppress the unevenness inside the sleeve. However, contrary to this prediction, the surface quality on the inside of the sleeve could be improved by controlling the protrusion amount of the sleeve. The reason for this is unclear at present, but it is presumed that this is because the amount of bending of the steel plate was further reduced by applying pressure evenly.

[0070] Figure 10 shows a cross-sectional photograph of a spot-welded component obtained by spot welding a different sheet assembly from that shown in Figure 9 after finely adjusting the sleeve protrusion amount in the same manner as in Figure 9. The sheet assembly was made of eight stacked cold-rolled mild steel sheets with no plating, each 0.7 mm thick. The welding conditions were as follows: Single-phase AC power frequency (Freq.): 50Hz ·Electrode (φ13): R type R40 Welding current: 9.6kA Squeeze: 50 cycles Current upslope time (UP.T): 4 cycles Welding time to form a nugget (WT): 15 cycles Current downslope time (DW.T): 0 cycles - Pressure retention time after current is turned off (Ho.T): 50 cycles Pressure: 3.8kN (electrode pressure 3.2kN, sleeve pressure 0.6kN) Sleeve protrusion: Approx. 6mm for both double-acting electrodes

[0071] As shown in the cross-sectional photograph in Figure 10, even when welding thin mild steel plates, sheet separation and unevenness on the surface of the parts could be suppressed by fine-tuning the amount of sleeve protrusion before spot welding.

[0072] (4. Example of further optimizing pressure holding time) Figures 11A to 11C show cross-sectional photographs of welds to which various pressure holding times were applied. The sheet assemblies forming the welds in Figures 11A to 11C were all made of eight stacked steel sheets with a sheet thickness of 0.7 mm. In other words, Σhi of the sheet assembly was 5.6 mm. Under welding conditions where the pressure holding time Th was 470 msec or more and 1568 msec or less, the above formula 1 was satisfied. Other welding conditions were as follows: Single-phase AC power frequency (Freq.): 60Hz ·Electrode (φ13): R type R40 Welding current: 6.3kA Current upslope time (UP.T): 2 cycles Welding time to form a nugget (WT): 18 cycles Current downslope time (DW.T): 0 cycles Pressure holding time (Ho.T) of the weld in Figure 11A: 300msec (18 cycles) Pressure holding time (Ho.T) of the welded part in Figure 11B: 500 msec (30 cycles) Pressure holding time (Ho.T) of the weld in Figure 11C: 700 msec (42 cycles) Total pressure: 4.0kN (electrode pressure: 3.64kN, sleeve pressure: 0.36kN)

[0073] As shown in these photographs, by setting the holding time within the appropriate range, it was possible to suppress the occurrence of sheet separation and unevenness, as well as the occurrence of shrinkage cavities. [Explanation of symbols]

[0074] 1. Double-acting electrode for spot welding 11 Rod-shaped electrode 111 Cap Tip 112 Shank 1121 Convex 12 Adapters 13 Sleeve 131 Male thread 14 Coil spring 15 Positioning mechanism 151 Lock nut 152 Sleeve Base 1521 Female thread 1522 holes P protrusion amount X board set

Claims

1. A rod-shaped electrode; An adapter for supporting a base end of the rod-shaped electrode; a sleeve surrounding the rod-shaped electrode and configured to be movable along an axial direction of the rod-shaped electrode between a first position on a tip end side of the rod-shaped electrode and a second position on a base end side of the rod-shaped electrode; a coil spring that connects the adapter and the sleeve, is exposed to the outside, and pushes the sleeve from a base end side toward a tip side of the rod-shaped electrode along the axial direction of the rod-shaped electrode; a positioning mechanism connected to the sleeve and configured to be able to adjust the first position of the sleeve along the axial direction of the rod-shaped electrode; Equipped with the first position is a position where a tip of the sleeve protrudes toward a tip side relative to a tip of the rod-shaped electrode, and the amount of protrusion of the sleeve from the rod-shaped electrode is adjustable by the positioning mechanism; Double acting electrode for spot welding.

2. A rod-shaped electrode, An adapter for supporting a base end of the rod-shaped electrode; a sleeve surrounding the rod-shaped electrode and configured to be movable along an axial direction of the rod-shaped electrode between a first position on a tip end side of the rod-shaped electrode and a second position on a base end side of the rod-shaped electrode; a coil spring that pushes the sleeve from a base end side toward a tip end side of the rod-shaped electrode along the axial direction of the rod-shaped electrode; a positioning mechanism connected to the sleeve and configured to be able to adjust the first position of the sleeve along the axial direction of the rod-shaped electrode; Equipped with the first position is a position where a tip of the sleeve protrudes toward a tip side relative to a tip of the rod-shaped electrode, and the positioning mechanism is capable of adjusting an amount of protrusion of the sleeve from the rod-shaped electrode; the sleeve having a threaded portion at a proximal end thereof; the positioning mechanism includes a sleeve base having a threaded portion that screws into the threaded portion of the sleeve, and a sleeve fixing member that fixes the sleeve to the sleeve base, The pitch of the threaded portion of the sleeve base is 1.0 mm or less. Double acting electrode for spot welding.

3. 3. The double action electrode for spot welding according to claim 1, wherein the sleeve is made of metal.

4. The rod electrode is cylindrical, and the sleeve is cylindrical, 4. The double-action electrode for spot welding according to claim 1, wherein a difference between a radius of an inner circumference of the sleeve and a radius of an outer circumference of the rod-shaped electrode is 0.2 mm or more and 0.3 mm or less.

5. 5. The double-action electrode for spot welding according to claim 1, wherein the coil spring has a spring constant of 0.05 kN / mm to 0.30 kN / mm.

6. 6. The double-action electrode for spot welding according to claim 1, wherein the tip of the rod-shaped electrode has an R-shape with a radius of curvature of R20 to R120.

7. A spot welding device comprising a pair of double-action electrodes according to any one of claims 1 to 6.

8. A method for manufacturing a spot-welded member, comprising a step of spot-welding a plate set consisting of two or more metal plates using a pair of double-acting electrodes according to any one of claims 1 to 6.

9. The plate assembly is composed of four or more of the metal plates, The thickness of the metal plate arranged on one or both surfaces of the plate assembly is 0.7 mm or less. The method for manufacturing a spot-welded component according to claim 8 .

10. 10. The method for manufacturing a spot-welded member according to claim 8, wherein, during the spot welding, when the sleeve is in the first position, a protrusion amount of the tip of the sleeve relative to the tip of the rod-shaped electrode is 2 mm or more and 10 mm or less.

11. The method for manufacturing a spot-welded member according to any one of claims 8 to 10, characterized in that a pressure holding time Th (unit: msec) after completion of the spot welding satisfies the following formula 1: 15 × (Σhi) ２ ≤ Th ≤ 50 × (Σhi) ２ (Equation 1) Here, Σhi in the formula 1 is the total thickness (unit: mm) of the metal plates constituting the plate assembly.

12. 12. The method for manufacturing a spot welded member according to claim 8, wherein in one or both of the double-acting electrodes, a protrusion amount of a tip of the sleeve relative to a tip of the rod-shaped electrode when the sleeve is in the first position is adjusted so that a neutral position of a pair of rod-shaped electrodes provided in the pair of double-acting electrodes coincides with a neutral position of a pair of sleeves provided in the pair of double-acting electrodes.

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