Manufacturing method of stud

Abstract

To provide a manufacturing method of a stud capable of achieving both downsizing of a flange in the stud and increasing the size of a projection.SOLUTION: In a manufacturing method of a stud 10, a shape of a body 10a of the stud 10 is made to be a columnar shape, a flange 10b is made to have a minimum size for locking a distal end portion of an inside electrode 121, the flange 10b extending in a right angle direction with respect to a central axis of the body 10a with respect to a lower end part 10c welded to a welded member 5 of the body 10a, one projection part is formed in a central part so as to have substantially the same size as the flange 10b, the lower end part 10c of the stud 10 is reduction pressed by using a mold having three recessed parts formed in a peripheral edge part outer than the central part, a recessed groove part 10e is formed in a center portion of the lower end part 10c, and three projecting projections 10d are formed in a peripheral edge portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a stud that is attached to a metallic member to be welded, such as a steel plate, by resistance welding. [Background technology]

[0002] Resistance welding is a metal joining method in which metals such as steel plates are overlapped, the welding point is sandwiched between electrodes, pressure is applied, and an electric current is passed through, causing the metals to melt and bond together using Joule heat generated by the contact resistance at the welding point. In addition to joining steel plates together, resistance welding is also used to join studs to steel plates (see, for example, Patent Document 1). The stud shown in Patent Document 1 has a flange formed on the end that is welded to the steel plate, and one or more projections formed on the bottom surface. Studs include stud screws that are threaded on the outside, stud bosses that are threaded on the inside, and studs that are not threaded on either the outside or inside. Needless to say, those that are threaded on the outside are stud screws (male), and those that are threaded on the inside are stud bosses (female).

[0003] 10 is a diagram showing the state when a stud 300 with a projection 302 formed thereon is fusion-bonded to a steel plate (member to be welded) 360. As shown in the figure, during welding, the tip of the electrode 350 abuts against the flange 301 of the stud 300, and pressure and electricity are applied in this state. As a result, current i flows from the electrode 350 to the projection 302, melting the bottom surface of the stud 300 around the projection 302, and melting and bonding it to the steel plate 360. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-035706 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a stud with a flange such as that shown in Figure 10, it is desirable to make the flange as small as possible, as there is a risk that the flange may physically interfere with objects located around the stud's installation position. However, if the flange is made small, the area for forming the projection becomes smaller, and the amount of metal material in the stud itself becomes less, making it difficult to form a projection with a sufficient prominence. In this way, if the flange is made small, it becomes difficult to make the projection large.

[0006] The projection is mainly formed using a machine tool called a "multi-stage former." This multi-stage former repeatedly strikes the projection-forming portion of the surface of one end of the stud body to form a raised projection.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide a method for manufacturing a stud that can simultaneously achieve a smaller flange and a larger projection in the stud. [Means for solving the problem]

[0008] The present invention relates to a method for manufacturing a stud, which is a method for manufacturing a stud. The stud is held by a coaxial electrode having an inner electrode and an outer electrode, each of which is formed in a cylindrical shape and arranged coaxially. The stud is held by the inner electrode, and is pressed while in contact with the tip of the inner electrode. When an electric current is supplied between the stud and the welded members and the stud, the Joule heat generated at the welding point of the welded members melts and bonds the stud to the welded members. The stud body has a cylindrical shape, and a flange extending perpendicular to the central axis of the body from one end of the body that is welded to the welded members is of the minimum size that can engage with the tip of the inner electrode. Furthermore, the one end of the stud body is pressed using a pressing die that is approximately the same size as the flange, has one convex portion in the center, and at least one concave portion on the periphery outward from the center, to form a concave groove in the center of the one end of the stud body, and at least one convex projection on the periphery outward from the center.

[0009] According to the above method, a concave groove is formed in the central portion of one end of the stud body, and at least one convex projection is formed in the peripheral portion. By using a pressure press to form the concave groove and the at least one convex projection, they can be formed at the same time.

[0010] By forming a recessed groove in the center of one end of the stud body, the metal that was present before the groove was formed is forced outward (i.e., to the peripheral edge of one end of the stud body). This forced metal is added to the raised convex projection formed on the peripheral edge. This raised projection is larger than when a projection is formed with a multi-stage former. In other words, a multi-stage former forms a raised projection by striking the stud body in the axial direction, whereas a pressing press using a die forms a raised projection by forcing an amount of metal material equivalent to the recess outward, making it possible to obtain a larger raised projection than with a multi-stage former. Furthermore, since a sufficiently large projection can be formed, the flange can be made smaller.

[0011] In this way, the present invention can simultaneously achieve a small flange size and a large projection size. [Effects of the Invention]

[0012] According to the present invention, it is possible to simultaneously achieve a reduction in the size of the flange on the stud and an increase in the size of the projection formed on the flange. [Brief explanation of the drawings]

[0013] [Figure 1] 1A is a side view of a stud according to an embodiment of the present invention, FIG. 1B is a front view of the stud, and FIG. 1C is a cross-sectional view of a flange. [Figure 2] FIG. 2 is a cross-sectional view illustrating the generation of projections on the stud of FIG. 1; [Figure 3] A side view showing the appearance of the welding gun of a coaxial electrode type resistance welding device that handles the stud shown in Figure 1. [Figure 4] FIG. 4 is a cross-sectional view showing the structure of a coaxial electrode used in the resistance welding device of FIG. [Figure 5] A diagram showing the arrangement of projections on the flange of the stud in Figure 1 [Figure 6] 2A and 2B are diagrams showing the appearance of a first modified example of the stud of FIG. 1, in which (a) is a front view and (b) is a cross-sectional view taken along the line AA in (a). [Figure 7] 1. FIG. 4 is a diagram showing the appearance of a second modified example of the stud of FIG. 1, where (a) is a side view, (b) is a front view, and (c) is a partial cross-sectional view. [Figure 8] 1. FIG. 4 is a diagram showing the appearance of a third modified example of the stud of FIG. 1, where (a) is a side view, (b) is a front view, and (c) is a partial cross-sectional view. [Figure 9] 1. FIG. 1 shows the appearance of a fourth modified example of the stud of FIG. 1, where (a) is a side view, (b) is a front view, and (c) is a cross-sectional view. [Figure 10]A diagram showing the state when a stud with a projection is fused and bonded to a steel plate. DETAILED DESCRIPTION OF THE INVENTION

[0014] A stud according to one embodiment of the present invention will now be described. First, before describing the stud according to this embodiment, a resistance welding device for welding the stud to the workpiece (steel plate) will be described.

[0015] Fig. 3 is a side view showing a welding gun 100 of a coaxial electrode type resistance welding device (not shown) that handles studs according to this embodiment. Fig. 4 is a cross-sectional view showing a coaxial electrode 120 handled by the welding gun 100. In Fig. 4, the hatched portion indicates the coaxial electrode 120.

[0016] In FIG. 3 , the welding gun 100 includes a gun body 101, a conducting electrode 102, an insulating member 103, an ounce copper plate 104, and a coaxial electrode 120. The gun body 101 is formed in a generally L-shape, and the coaxial electrode 120 is disposed at one end 101a. The other end 101b of the gun body 101 is connected to a resistance welding device body 130. The conducting electrode 102 is disposed on the back surface of the gun body 101 and forms a current path downstream of the coaxial electrode 120. The insulating member 103 is disposed between the gun body 101 and the conducting electrode 102 to provide insulation between the gun body 101 and the conducting electrode 102. The ounce copper plate 104 is formed by stacking multiple copper foils and connects the conducting electrode 102 to the coaxial electrode 120, forming part of the current path downstream of the coaxial electrode 120.

[0017] 4, the coaxial electrode 120 includes an inner electrode 121, an outer electrode 122, a holding member 123, and an insulating member 124. The inner electrode 121, the outer electrode 122, the holding member 123, and the insulating member 124 are each formed in a cylindrical shape, and are coaxially arranged on the inner circumferential surface side of the outer electrode 122 in the order of the insulating member 124, the holding member 123, and the inner electrode 121.

[0018] The inner electrode 121 is made of a conductive metal such as chromium copper, and is sized to accommodate the main body 10a of the stud 10 (excluding the flange 10b). The tip of the inner electrode 121 is tapered slightly narrower than the remaining portion. The length of the inner electrode 121 is approximately the same as the length of the outer electrode 122.

[0019] The outer electrode 122 is made of a conductive metal such as chromium copper, like the inner electrode 121, and is sized to accommodate the inner electrode 121, the holding member 123, and the insulating member 124. The tip portion of the outer electrode 122 is thicker than the other portions. The holding member 123 holds the inner electrode 121. The holding member 123 is made of a conductive metal such as chromium copper, like the inner electrode 121, and is sized so that its inner circumferential surface is in close contact with the outer circumferential surface of the inner electrode 121. The length of the holding member 123 is approximately the same as that of the insulating member 124.

[0020] The insulating member 124 is intended to provide insulation between the inner electrode 121 and the outer electrode 122, and is formed to a size such that its inner surface is in close contact with the outer surface of the holding member 123 and its outer surface is in close contact with the inner surface of the outer electrode 122.

[0021] As shown in Fig. 5, the stud 10 has three convex portions ("projections" described below) 10d on the bottom surface of the flange 10b. In Fig. 4, the stud 10 is welded to a workpiece (steel plate) 5 placed on a mounting table 6 while being held by an inner electrode 121. Note that in this disclosure, the stud 10 is a stud screw with an external thread, but it may also be a stud boss with an internal thread, or one that is not threaded on either the external or internal side.

[0022] When welding the stud 10 to the workpieces 5, pressure is applied to the coaxial electrode 120 from the resistance welding device main body 130 side, and current is supplied. The current supplied from the resistance welding device main body 130 side flows from the inner electrode 121 through the flange 10b of the stud 10 to the workpieces 5, and then flows from the workpieces 5 through the outer electrode 122 to the resistance welding device main body 130 side. As mentioned above, three projections 10d are provided on the bottom side of the flange 10b, and current flows concentrated in each projection 10d. Joule heat is generated by the contact resistance between each projection 10d and the workpieces 5, and this Joule heat melts and bonds the metals of the stud 10 and the workpieces 5 together.

[0023] Next, the stud 10 will be described in detail. 1 shows the appearance of a stud 10, with (a) being a side view, (b) being a front view, and (c) being a partial cross-sectional view. In the figure, the stud 10 has a cylindrical body 10a, and a flange 10b extending perpendicular to the central axis of the body 10a is formed at one end (hereinafter referred to as the "lower end") 10c of the body 10a. Threads (not shown) are formed on the outer surface of the body 10a, excluding the lower end 10c.

[0024] Here, the end portion on one end side of the main body 10a of the stud 10 is called the "lower end portion" because the stud 10 is used with the side on which the projection 10d is provided facing downward.

[0025] In addition to the three projections 10d mentioned above, the lower end 10c of the main body 10a is formed with one approximately triangular recessed portion (hereinafter referred to as the "groove portion") 10e set inside the three projections 10d.

[0026] The flange 10b is formed to be large enough to engage the tip of the inner electrode 121 so as not to physically interfere with objects present around the attachment position of the stud 10. The groove 10e is formed in the central portion of the lower end portion 10c of the main body 10a. The three projections 10d are positioned on the periphery outside the groove 10e so that their centers are on the same circumference (the circle indicated by the dashed dotted line).

[0027] In manufacturing the stud 10, a pressing die (not shown) is used so that the groove 10e in the flange 10b and the three projections 10d can be formed simultaneously. This die has a flat surface that is approximately the same size as the flange 10b, and in the center of this flat surface, a convex portion (not shown) that is the inverse of the groove 10e is formed, and in the peripheral portion, a concave portion (not shown) that is the inverse of the projection 10d is formed. There are three concave portions (not shown) that are the inverse of the shape of the projection 10d, and they are positioned so that their centers are on the same circumference.

[0028] The one concave portion and three convex portions of the mold and the one groove portion 10e and three projections 10d on the flange 10b of the stud 10 have a "positive" and "negative" relationship in terms of a photograph. By using this mold to press down against the lower end portion 10c of the body 10a of the stud 10, the groove portion 10e is formed in the center of the lower end portion 10c, and the three projections 10d are formed in the peripheral portion. At this time, the groove portion 10e and the three projections 10d are formed at the same time.

[0029] By forming a groove 10e in the center of the lower end 10c of the stud 10, the metal that was present before the formation of the groove 10e can be pushed outward (i.e., toward the peripheral edge of the lower end 10c of the stud 10). This pushed-out metal contributes to the raised projection formed on the peripheral edge. This raised projection is larger than when the projection is formed using a multi-stage former. Figure 2 is a cross-sectional view showing the direction of movement of the metal when the groove 10e is formed. As shown in the figure, when the groove 10e is formed, the metal moves in the direction indicated by the dashed arrow. In this way, the metal pushed toward the projection 10d contributes to the raised projection 10d.

[0030] While a multi-stage former creates a raised projection by striking the stud body in the axial direction, a reduction press creates a raised projection by moving an amount of metal material equivalent to the recess outward, so a larger raised projection can be expected than with a multi-stage former. Furthermore, the ability to create a sufficiently large raised projection also makes it possible to make the flange smaller.

[0031] The stud 10 is manufactured by forming the body 10a of the stud 10 into a cylindrical shape, and by forming a flange 10b extending perpendicular to the central axis of the body 10a at the lower end 10c of the body 10a, which is welded to the workpiece 5, of the minimum size that can engage the tip of the inner electrode 121, and further by using a mold that is approximately the same size as the flange 10b and has one convex portion formed in the center and three concave portions formed on the periphery outside the center, the lower end 10c of the stud 10 is pressed down using this mold, forming a concave groove portion 10e in the center of the lower end 10c and three convex projections 10d on the periphery.

[0032] As described above, the stud 10 of the present disclosure forms a concave groove 10e in the center of the lower end 10c. This allows the metal that existed before the formation of the groove 10e to be pushed outward (i.e., toward the peripheral edge of the lower end 10c of the stud 10). This pushed-out metal then contributes to the raised projection 10d formed on the peripheral edge. By adding the metal that was present in the groove 10e to the raised projection 10d, the raised projection becomes larger than when a projection is formed using a multi-stage former. In this way, a projection with a large raised projection can be obtained. Furthermore, since a projection with a sufficiently large raised projection can be formed, the flange can be made smaller. In other words, it is possible to simultaneously achieve a smaller flange and a larger projection.

[0033] Although the stud 10 of the present disclosure has three projections 10d, there is no limitation on the number of projections, and it may be two or less, or four or more.

[0034] Furthermore, in the stud 10 of the present disclosure, the groove 10e formed in the lower end 10c has a substantially triangular shape, but is not limited to this shape. In short, any shape is acceptable as long as it can push the metal that was present before the groove 10e was formed toward the side where the projection 10d is formed (toward the peripheral edge of the lower end 10c).

[0035] Modified examples of the stud 10 will now be described. (First Modification) FIG. 6 shows the appearance of a stud 11 of a first modified example, with (a) being a front view and (b) being a cross-sectional view taken along line AA in (a). In the figure, the stud 11 of the first modified example has a groove 11e formed in the lower end 11c of the main body 11a that resembles the shape of a three-groove screw. In the groove 11e, metal that existed before its formation also contributes to the protruding projection 11d formed on the peripheral edge. In FIG. 6, the reference symbol "11b" denotes a flange.

[0036] (Second Modification) FIG. 7 shows the appearance of a stud 12 of a second modified example, with (a) being a side view, (b) being a front view, and (c) being a partial cross-sectional view. In this figure, the stud 12 of the second modified example has a circular groove 12e formed in the lower end 12c of the main body 12a, resulting in a ring-shaped (annular) projection 12d protruding from the groove 12e. The metal that existed before the groove 12e was formed becomes part of the projection 12d. In FIG. 7, the reference symbol "12b" denotes a flange.

[0037] (Third Modification) FIG. 8 shows the appearance of a stud 13 of a third modified example, with (a) being a side view, (b) being a front view, and (c) being a partial cross-sectional view. In this figure, the stud 13 of the third modified example has a lattice-shaped groove 13e formed on the bottom side of the lower end 13c of the main body 13a. This lattice-shaped groove 13e is a collection of small, rectangular grooves 13e. Note that because the outer periphery of the stud 13 is circular, not all of the grooves 13e are rectangular, but this point will be ignored. By forming multiple rectangular grooves 13e, it is possible to obtain multiple sufficiently large, raised rectangular projections 13d.

[0038] (Fourth Modification) FIG. 9 shows the appearance of a stud 14 of a fourth modified example, with (a) being a side view, (b) being a front view, and (c) being a cross-sectional view. In this figure, the stud 14 of the fourth modified example has three protruding, arc-shaped projections 14d formed at regular intervals along the circumferential direction on the peripheral edge of the bottom side of the lower end 14c of the main body 14a. The cross-sectional shape of each of the three projections 14d is semicircular. Inside the three projections 14d, there is a circular groove 14e. The metal that existed before the groove 14e was formed becomes part of the three projections 14d. In FIG. 9, the symbol "14c" indicates the lower end.

[0039] Note that the cross-sectional shape of each of the three projections 14d may be a semicircular shape, or may be a triangular shape, a rectangular shape, a concave shape, etc. In other words, various shapes may be used, such as a shape that contacts the workpiece at one point, a shape that contacts at two or more points, or a shape that contacts over an area. [Industrial Applicability]

[0040] The present invention is applicable to studs that are attached to metallic workpieces, such as steel plates, using resistance welding. [Explanation of symbols]

[0041] 5. Welded parts 6 Mounting table 10, 11, 12, 13, 14 studs 10a, 11a, 12a, 13a main body 10b, 11b, 12b, 13b flanges 11c, 10c, 12c, 13c lower end 10d, 11d, 12d, 13d, 14d projection 10e, 11e, 12e, 13e, 14e Groove 100 welding gun 101 Gun body 120 coaxial electrode 121 Inner electrode 122 Outer electrode 130 Resistance welding device body

Claims

[Claim 1] A method for manufacturing a stud, which has a coaxial electrode having an inner electrode and an outer electrode each formed in a cylindrical shape and arranged coaxially, is held by the inner electrode, and while the stud is in contact with the tip of the inner electrode and pressurized, an electric current is supplied between the stud and the members to be welded, and the stud is fused and bonded to the members to be welded by Joule heat generated at the welding point of the members to be welded, The stud body is cylindrical in shape, and a flange extending perpendicular to the central axis of the body from one end of the body that is welded to the workpiece is of a minimum size that can engage the tip of the inner electrode, Furthermore, using a pressing die having substantially the same size as the flange and having one convex portion formed in the center and at least one concave portion formed in the periphery outside the center, the end portion on said one end side of the stud body is pressed down to form a concave groove in the center portion of the end portion on said one end side of the stud body, and to form at least one convex projection in the periphery outside the center portion. Stud manufacturing method.

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