Spot welded structure and method for manufacturing spot welded structure

Abstract

This spot welding structure comprises: a first lap joint; a second lap joint; a lap part in which one or more ends of a metal plate of the first lap joint and one or more ends of a metal plate of the second lap joint are overlapped; a main nugget joining the first lap joint and the second lap joint in the lap part; a metal plate-form member that is superposed on the first lap joint, the second lap joint, and the lap part; and a plurality of sub-nuggets joining the plate-form member and the first lap joint, and joining the plate-form member and the second lap joint. The number of metal plates to which the main nugget is joined is three. An indentation of the main nugget is provided only to the metal plate included in the first lap joint or the second lap joint. The plate-form member is located outside the main nugget. The sub-nuggets are located outside the lap part.

Description

[Technical Field]

[0001] The present disclosure relates to spot welded structures and methods for manufacturing spot welded structures. This application claims priority based on Japanese Patent Application No. 2023-150978, filed on September 19, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Spot welding is a resistance welding technique in which overlapping base metals are clamped between the tips of electrodes, and a current is passed through them while applying pressure, causing the metals to melt and join with the Joule heat generated. In lap resistance welding such as spot welding, the molten and solidified part that forms at the weld is called a nugget.

[0003] Spot welding is highly efficient and is used to manufacture various mechanical structural parts. For example, in the manufacture of automobiles, thousands of spot welds are formed in each vehicle.

[0004] Patent Document 1 discloses a joint structure for a vehicle body frame in which a side sill is formed by joining together ends of divided panel pieces obtained by dividing the inner panel longitudinally with a reinforcement interposed between them, and in which the flange portions of both panels and the reinforcement are overlapped with each other, spot welds that can be overlapped with each other are formed at one end of each divided panel piece and joined by spot welding, and the flange portion of the outer panel and the flange portion of the reinforcement are overlapped with one of the flange portions of both divided panel pieces in a three-layer configuration and then joined by spot welding.

[0005] The vehicle center pillar structure disclosed in Patent Document 2 has an upper reinforcement disposed in the upper part of the interior space formed by the outer center pillar and the inner center pillar, and a lower reinforcement disposed in the lower part of the interior space. The lower end of the upper reinforcement and the upper end of the lower reinforcement are disposed so as to overlap each other. The two reinforcements are combined with each other, with one different side of each side edge being cut out. The upper main reinforcement portion extends toward the lower main reinforcement portion, and they overlap each other, forming a partition portion that divides the interior space into upper and lower parts.

[0006] The impact energy absorption structure for the upper body of an automobile disclosed in Patent Document 3 is a structure for absorbing impact energy for the upper body of an automobile that is formed into a closed structure by an outer panel and an inner panel and has roof side rails extending in the fore-and-aft direction, and includes two energy absorption panels made of steel plate with a thickness smaller than that of the outer panel and the inner panel. The two energy absorption panels have the same cross-sectional shape and the same plate thickness, are arranged in the fore-and-aft direction of the roof side rail so that adjacent terminal portions overlap, and are joined to the roof side rail at their flanges without joining their web portions.

[0007] In the resistance spot welding method disclosed in Patent Document 4, after the applied pressure reaches a set value, a preliminary current is started at a low current; when the gap is eliminated and all of the overlapping plates are in contact, the electrode position is fixed and then the main current is started; by fixing the electrode position, thermal expansion of the plate assembly after the start of the main current is suppressed, thereby increasing the applied pressure, so that the initial set applied pressure P and the maximum applied pressure Pm satisfy Pm≧1.5×P.

[0008] Patent Document 5 discloses a resistance spot welding method for high-strength thin steel sheets, characterized in that, in performing resistance spot welding while sandwiching overlapping high-strength thin steel sheets between a pair of electrodes and applying a pressure, after welding a first point, the position of the electrodes is moved, and after the first welded point is cooled to a temperature below the Mf point, a second weld is performed so that a part of the second welded point overlaps the first welded point. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-30746 [Patent Document 2] Japanese Utility Model Application Publication No. 5-16559 [Patent Document 3] Japanese Patent Application Publication No. 9-39834 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-290098 [Patent Document 5] Japanese Patent Application Laid-Open No. 2010-172945 Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, there has been an increase in the number of cases where an inner frame structure is applied to the body of an automobile. The inner frame structure is a structure in which the body of an automobile is divided into a framework member (frame) and an outer panel member (outer panel), and the frame of the entire body is assembled first, and then the outer panel is welded. This allows the framework members to be joined even more firmly.

[0011] However, spot welding has the problem of prone to welding defects when welding four or more overlapping plates. In the manufacture of automobile bodies, welding defects are likely to occur at the locations where two frame members and an outer plate member are spot welded. In particular, when the outer plate member is made of thin mild steel, the nugget may not grow all the way to the thin plate. It is difficult to stabilize the quality of spot welding at such joints.

[0012] One way to avoid poor welding of outer plate members is to increase the welding current to promote nugget growth, but spot welding, which uses a large current, is prone to expulsion.

[0013] Furthermore, during the manufacturing of automotive parts, gaps are likely to form between steel sheets due to a phenomenon known as springback. Spot welding of sheet assemblies with gaps between the steel sheets can result in explosions and large blowholes in the nugget. Blowholes reduce the joint strength of the weld.

[0014] Another method for avoiding poor joints of outer plate members is to reduce the number of metal plates included in the joint and thereby reduce the total thickness of the joint. For example, as shown in FIG. 2, it has been common practice to use three overlapping steel plates at the joints between skeletal members. In the conventional technology, only one of the two or more steel plates in the skeletal members (first lap joint 11 and second lap joint 12 in FIG. 2) is the target of joining. Then, the steel plates of the two skeletal members (the metal plate 111 on the upper side of the drawing in FIG. 2 and the metal plate 121 on the lower side of the drawing in FIG. 2) and the outer plate member (the plate-like member 13 in FIG. 2) are overlapped and spot welded to form a nugget (the main nugget 15 in FIG. 2).

[0015] However, in the spot-welded structure shown in Fig. 2, the three-layer structure including the outer plate member at the joint reduces the load transfer efficiency between the frame members, which can result in a decrease in the rigidity of the car body and a decrease in the joint strength.

[0016] None of the techniques disclosed in Patent Documents 1 to 5 assumes an inner frame structure, and does not disclose means for solving the above-mentioned problems.

[0017] In view of the above circumstances, an object of the present disclosure is to provide a spot welded structure that suppresses poor joining of outer plate members and has high load transmission efficiency between frame members, and a method for manufacturing the spot welded structure. [Means for solving the problem]

[0018] The gist of the present disclosure is as follows.

[0019] (1) A spot welding structure according to one embodiment of the present disclosure includes a first lap joint having two or more metal plates, a second lap joint having two or more metal plates, a lap portion where ends of one or more of the metal plates of the first lap joint and ends of one or more of the metal plates of the second lap joint are overlapped, a main nugget that joins the first lap joint and the second lap joint at the lap portion, a metal plate-shaped member overlapped on the first lap joint, the second lap joint, and the lap portion, and a plurality of secondary nuggets that join the plate-shaped member and the first lap joint, and the plate-shaped member and the second lap joint, wherein the number of metal plates joined by the main nugget is three, an indentation of the main nugget is provided only on the metal plates included in the first lap joint or the second lap joint, the plate-shaped member is outside the main nugget, and the secondary nugget is outside the lap portion. (2) Preferably, in the spot welding structure described in (1) above, the distance between the center of the secondary nugget joining the plate-like member and the first lap joint and the center of the secondary nugget joining the plate-like member and the second lap joint is 200 mm or less. (3) Preferably, in the spot welding structure described in (1) or (2) above, one or more of the metal plates of the first lap joint and the second lap joint have a seam processing portion in the lap portion, and two of the three metal plates joined by the main nugget are arranged on approximately the same plane outside the lap portion. (4) Preferably, in the spot welded structure according to any one of (1) to (3) above, the number of joint interfaces between the first lap joint and the second lap joint is two or more. (5) Preferably, in the spot welding structure described in any one of (1) to (4) above, the spot welding structure has a main nugget that joins two of the metal plates of the first lap joint and one of the metal plates of the second lap joint, and a main nugget that joins one of the metal plates of the first lap joint and two of the metal plates of the second lap joint. (6) Preferably, in the spot welding structure described in any one of (1) to (5) above, the spot welding structure further has an adhesive between the plate-shaped member and one or both of the first lap joint and the second lap joint. (7) Preferably, in the spot welding structure described in any one of (1) to (6) above, the spot welding structure further has an additional nugget in the lap portion, the additional nugget joining two or more of the metal plates and the plate-like members included in the lap portion, and an impression of the additional nugget is provided on the plate-like member. (8) Preferably, in the spot welding structure described in any one of (1) to (7) above, the plate-like member is separated from the first lap joint and the second lap joint over the entire lap portion. (9) Preferably, in the spot welding structure described in any one of (1) to (8) above, the first lap joint has a nugget outside the lap portion that joins only the metal plates of the first lap joint, and the second lap joint has a nugget outside the lap portion that joins only the metal plates of the second lap joint. (10) Preferably, in the spot welding structure described in any one of (1) to (9) above, the first lap joint and the second lap joint are frame parts of an automobile, and the plate-like member is an outer panel part of the automobile.

[0020] (11) A manufacturing method of a spot welded structure according to another aspect of the present invention includes the steps of preparing a first lap joint having two or more metal plates and a second lap joint having two or more metal plates; overlapping end portions of one or more of the metal plates of the first lap joint and end portions of one or more of the metal plates of the second lap joint to form a lap portion; primary spot welding the first lap joint and the second lap joint at the lap portion to form a main nugget; overlapping the first lap joint, the second lap joint, and the lap portion on which the main nugget is formed with a metal plate-shaped member; and secondary spot welding the plate-shaped member and the first lap joint, and the plate-shaped member and the second lap joint to form a plurality of secondary nuggets, wherein the number of metal plates to be primary spot welded is three, and the welding points for the secondary spot welding are outside the lap portion. (12) A manufacturing method of a spot welded structure according to another aspect of the present invention includes the steps of preparing a plate assembly in which two of the metal plates that are components of a first lap joint are overlapped at their ends, overlapping an end of one of the metal plates that are components of a second lap joint on the end of the plate assembly to form a lap portion, primarily spot welding two of the metal plates that are components of the first lap joint and one of the metal plates that are components of the second lap joint at the lap portion to form a main nugget and the first lap joint, and welding the second lap joint in which the main nugget is provided. The method includes the steps of: overlapping one of the metal plates and the remaining metal plate of the second lap joint outside the lap portion and spot welding them to form the second lap joint; overlapping a metal plate-shaped member on the lap portion where the first lap joint, the second lap joint, and the main nugget are formed; and secondary spot welding the plate-shaped member and the first lap joint, and the plate-shaped member and the second lap joint to form a plurality of secondary nuggets, wherein the number of metal plates to be primarily spot welded is three, and the welding points for the secondary spot welding are outside the lap portion. (13) Preferably, in the manufacturing method of the spot welded structure described in (11) or (12) above, the distance between the center of the welding point in the secondary spot welding of the plate-shaped member and the first lap joint and the center of the welding point in the secondary spot welding of the plate-shaped member and the second lap joint is 200 mm or less. (14) Preferably, in the manufacturing method of the spot welded structure described in any one of (11) to (13) above, a seam processing portion is provided at the end portion of one or more of the metal plates of the first lap joint and the metal plates of the second lap joint, and when forming the lap portion, two of the three metal plates joined by the main nugget are arranged on approximately the same plane outside the lap portion. (15) Preferably, in the manufacturing method of the spot welded structure described in any one of (11), (13), and (14) above, when forming the lap portion, the lap portion is formed by overlapping two of the metal plates of the first lap joint with one of the metal plates of the second lap joint, and the lap portion is formed by overlapping one of the metal plates of the first lap joint with two of the metal plates of the second lap joint, and the primary spot welding is performed on each of the multiple lap portions. (16) Preferably, the manufacturing method of the spot welded structure described in any one of (12) to (14) above further includes the steps of, after forming the main nugget, overlapping the remaining metal plate of the second lap joint onto one of the metal plates of the second lap joint on which the main nugget is provided, so as to form an additional lap portion in which one of the metal plates of the first lap joint and two of the metal plates that are parts of the second lap joint are overlapped, and further performing primary spot welding on the additional lap portion to further form the main nugget. (17) Preferably, the manufacturing method of the spot welded structure described in any one of (11) to (16) above further includes a step of applying an adhesive between the plate-shaped member and one or both of the first lap joint and the second lap joint after the primary spot welding and before overlapping the plate-shaped member onto the first lap joint, the second lap joint, and the lap portion on which the main nugget is formed. (18) Preferably, the method for manufacturing a spot welded structure according to any one of (11) to (17) above further comprises a step of performing additional spot welding on the lap portion and the plate-shaped member after the secondary spot welding. (19) Preferably, in the method for manufacturing a spot welded structure according to any one of (11) to (18) above, all spot welding of the plate-like member is performed outside the lap portion. (20) Preferably, in the manufacturing method of the spot welded structure described in any one of (11) to (19) above, the first lap joint and the second lap joint are frame parts of an automobile, and the plate-like member is an outer panel part of the automobile. [Effects of the Invention]

[0021] According to the present disclosure, it is possible to provide a spot welded structure that suppresses poor joining of outer plate members and has high load transmission efficiency between frame members, and a method for manufacturing the spot welded structure. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view of a spot welding structure according to one embodiment of the present disclosure. [Figure 2] FIG. 1 is a cross-sectional view of a conventional spot welding structure. [Figure 3] FIG. 1 is a schematic diagram of a weld structure. [Figure 4A] FIG. 1 is a cross-sectional view of an example of a spot welding structure having a welded joint structure. [Figure 4B] FIG. 1 is a cross-sectional view of an example of a spot welding structure having a welded joint structure. [Figure 4C] FIG. 1 is a cross-sectional view of an example of a spot welding structure having a welded joint structure. [Figure 4D] FIG. 1 is a cross-sectional view of an example of a spot welding structure having a welded joint structure. [Figure 4E] FIG. 1 is a cross-sectional view of an example of a spot welding structure having a welded joint structure. [Figure 5A] FIG. 1 is a cross-sectional view of an example of a spot welding structure in which the lap portion is divided into two. [Figure 5B] FIG. 1 is a cross-sectional view of an example of a spot welding structure in which the lap portion is divided into two. [Figure 5C] FIG. 1 is a cross-sectional view of an example of a spot welding structure in which the lap portion is divided into two. [Figure 5D] FIG. 1 is a cross-sectional view of an example of a spot welding structure in which the lap portion is divided into two. [Figure 6] FIG. 1 is a cross-sectional view of an example of a spot weld structure with adhesive. [Figure 7] FIG. 1 is a cross-sectional view of an example of a spot weld structure having an additional nugget. [Figure 8A] FIG. 10 is a schematic diagram of a step of preparing a lap joint in a first manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 8B] 10 is a schematic diagram of a step of overlapping the ends of a lap joint to form a lap portion in a first manufacturing method of a spot welded structure according to one embodiment of the present disclosure. FIG. [Figure 8C] FIG. 10 is a schematic diagram of a step of forming a main nugget by primarily spot welding a lap portion in a first manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 8D] 10A and 10B are schematic diagrams illustrating a step of stacking a metal plate-shaped member on another member in a first manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 8E] 10A and 10B are schematic diagrams illustrating a step of forming a secondary nugget by secondary spot welding a plate-shaped member and another member in a first manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 9A] FIG. 10 is a schematic diagram of a step of preparing a plate assembly corresponding to a first lap joint in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 9B] 10 is a schematic diagram of a step of overlapping the ends of metal plates to form a lap portion in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. FIG. [Figure 9C] FIG. 10 is a schematic diagram of a step of forming a main nugget and a first lap joint by primarily spot welding the lap portion in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 9D] FIG. 10 is a schematic diagram of a step of forming a second rough lap joint in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 9E] 10A and 10B are schematic diagrams illustrating a step of stacking a metal plate-shaped member on another member in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. [Figure 9F] 10 is a schematic diagram of a step of forming a secondary nugget by secondary spot welding a plate-shaped member and another member in a second manufacturing method of a spot welded structure according to one embodiment of the present disclosure. FIG. [Figure 10] FIG. 1 is a schematic diagram of a vehicle body. [Figure 11] 1 is an example cross-section of a spot welded structure according to one aspect of the present disclosure. [Figure 12] 1 is an example cross-section of a spot welded structure according to one aspect of the present disclosure. [Figure 13] 1 is an example cross-section of a spot welded structure according to one aspect of the present disclosure. [Figure 14] 1 is an example cross-section of a spot welded structure according to one aspect of the present disclosure. [Figure 15] 1 is an example cross-section of a spot welded structure according to one aspect of the present disclosure. [Figure 16A] FIG. 1 is a perspective view of a first simulation model (Comparative Example No. 1). [Figure 16B] FIG. 1 is a perspective view of a first simulation model (Comparative Example No. 1). [Figure 16C] FIG. 1 is a side view of a first simulation model (Comparative Example No. 1). [Figure 17A] FIG. 10 is a perspective view of a second simulation model (invention example No. 2). [Figure 17B] FIG. 10 is a perspective view of a second simulation model (invention example No. 2). [Figure 17C] FIG. 10 is a side view of the second simulation model (invention example No. 2). [Figure 18A] FIG. 10 is a perspective view of a third simulation model (invention example No. 3). [Figure 18B]FIG. 10 is a perspective view of a third simulation model (invention example No. 3). [Figure 18C] FIG. 10 is a side view of the third simulation model (invention example No. 3). [Figure 19] FIG. 10 is a schematic diagram for explaining three-point bending conditions. [Figure 20] 10 is a graph showing the results of a simulation. DETAILED DESCRIPTION OF THE INVENTION

[0023] (1. Spot welding structure 1) A spot welding structure 1 according to one embodiment of the present disclosure is applied to, for example, a flange portion of a frame member of an automobile body, and as shown in FIG. 1 etc., includes a first lap joint 11 having two or more metal plates, a second lap joint 12 having two or more metal plates, a lap portion 14 where one or more ends of the metal plates 111 of the first lap joint and one or more ends of the metal plates 121 of the second lap joint are overlapped, a main nugget 15 that joins the first lap joint 11 and the second lap joint 12 at the lap portion 14, and The joint comprises a metal plate-like member 13 overlapped on the lap joint 11, the second lap joint 12, and the lap portion 14, and a plurality of secondary nuggets 16 joining the plate-like member 13 and the first lap joint 11, and the plate-like member 13 and the second lap joint 12, the number of metal plates joined by the main nugget 15 is three, the indentation 151 of the main nugget 15 is only provided on the metal plate included in the first lap joint 11 or the second lap joint 12, the plate-like member 13 is outside the main nugget 15, and the secondary nuggets 16 are outside the lap portion 14.

[0024] (First lap joint 11 and second lap joint 12) The spot-welded structure 1 is a welded structure obtained by further spot-welding the ends of two lap joints. Hereinafter, for ease of explanation, the two lap joints will be referred to as a first lap joint 11 and a second lap joint 12. Either of the two lap joints can be considered the first lap joint 11. For example, if one lap joint is a B-pillar and the other lap joint is a side sill, the B-pillar can be considered the first lap joint 11, or the side sill can be considered the first lap joint 11. In the spot-welded structure 1 illustrated in FIG. 1 and other figures, for convenience, the lap joint on the left side of the drawing is considered the first lap joint 11, and the lap joint on the right side of the drawing is considered the second lap joint 12. Hereinafter, the term "lap joint" refers to both the first lap joint 11 and the second lap joint 12 unless otherwise specified.

[0025] A lap joint is a joint in which parts are placed approximately parallel and overlap each other. In this embodiment, the parts of the lap joint are metal plates. The lap joint is a joint obtained by overlap welding multiple metal plates. An example of a lap joint is a frame member of an automobile body to which an inner frame structure is applied.

[0026] The metal plate can have any shape suitable for spot welding. In other words, the term "metal plate" is a concept that encompasses not only flat metal plates but also flat plate-like regions of metal members having a three-dimensional shape. For example, the flange portion of a hat-shaped member is also considered to be a metal plate. The plate-like member described below is also a concept that encompasses flat plate-like regions of metal members having a three-dimensional shape.

[0027] In the spot welding structure 1 illustrated in Fig. 1, the number of metal plates in the lap joint is two. However, the number of metal plates in the lap joint can be any number equal to or greater than three.

[0028] (Lap portion 14 and main nugget 15) Ends of one or more of the metal plates of the first lap joint 11 and end portions of one or more of the metal plates of the second lap joint 12 are overlapped at a lap portion 14. The first lap joint 11 and the second lap joint 12 are spot welded at the lap portion 14. A main nugget 15 that is formed by spot welding and joins the first lap joint 11 and the second lap joint 12 is provided at the lap portion 14.

[0029] The main nugget 15 joins three metal plates. In FIG. 1 , the main nugget 15 joins one metal plate 111 of the first lap joint 11 and two metal plates 121 of the second lap joint 12. Alternatively, the main nugget 15 may join two metal plates of the first lap joint 11 and one metal plate of the second lap joint 12.

[0030] During spot welding, an indentation is formed so as to overlap the nugget. The indentation is a depression on the surface of the base material caused by the electrode tip as a result of spot welding. The indentation 151 of the main nugget 15 is formed only on the metal plates included in the first lap joint 11 or the second lap joint 12. The indentation 151 of the main nugget is not formed on the plate-like member 13 described below.

[0031] (Plate-shaped member 13) The spot welding structure 1 according to this embodiment has, in addition to two lap joints, a metal plate-like member 13. The plate-like member 13 is made of a metal plate. The plate-like member 13 is overlapped with the first lap joint 11, the second lap joint 12, and the lap portion 14. The plate-like member 13 is, for example, an outer plate member of an automobile body to which an inner frame structure is applied.

[0032] The plate-like member 13 is located outside the above-described main nugget 15. The above-described main nugget 15 does not have the function of joining the plate-like member 13 to the first lap joint 11 or the second lap joint 12. The main nugget 15 is formed by spot welding (primary spot welding, described later) that only targets the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12. Therefore, the indentation 151 of the main nugget 15 is not formed on the plate-like member 13.

[0033] (Sub-Nugget 16) The plate-like member 13 and the first lap joint 11 are joined by a secondary nugget 16. The plate-like member 13 and the second lap joint 12 are also joined by a secondary nugget 16. This ensures that the first lap joint 11, the second lap joint 12, and the plate-like member 13 are all firmly joined together. An impression 161 of the secondary nugget 16 is formed on the plate-like member 13.

[0034] The secondary nugget 16 is provided outside the lap portion 14. Therefore, the secondary nugget 16 does not join the first lap joint 11 and the second lap joint 12. The secondary nugget impression 161 is also necessarily provided outside the lap portion 14.

[0035] (Action and effect) In a conventional spot-welded structure 1 as illustrated in Fig. 2, the main nugget 15 that joins the first lap joint 11 and the second lap joint 12 joins two metal plates and plate-like members. There are only two skeletal members (metal plates) that are directly involved in joining the first lap joint 11 and the second lap joint 12. In this case, it is difficult to sufficiently increase the load transfer efficiency of the spot-welded structure 1.

[0036] In the spot welding structure 1 according to this embodiment as illustrated in FIG. 1 , the main nugget 15 that joins the first lap joint 11 and the second lap joint 12 joins three skeletal members (metal plates). In the spot welding structure 1 according to this embodiment, the plate-shaped member 13 is located outside the main nugget 15. The main nugget 15 is separated from the plate-shaped member 13. Therefore, the number of skeletal members (metal plates) that are directly involved in joining the first lap joint 11 and the second lap joint 12 is three. As a result, the spot welding structure 1 according to this embodiment dramatically improves load transmission efficiency.

[0037] Furthermore, when manufacturing the spot welded structure 1 according to this embodiment, it is not necessary to grow the main nugget 15 up to the plate-shaped member 13. Therefore, it is not necessary to use an excessively large welding current in the spot welding (primary spot welding) for forming the main nugget 15. This makes it possible to suppress the occurrence of expulsion and blowholes, and further increase the joining strength of the main nugget 15.

[0038] Furthermore, in the spot welding structure 1 according to this embodiment, the secondary nugget 16 that joins the plate-shaped member 13 to another member is provided outside the lap portion 14. This makes it possible to suppress poor joining of the plate-shaped member 13.

[0039] The reason for this can be explained by the sheet thickness ratio. The sheet thickness ratio is a value calculated by dividing the total thickness of the sheet assembly to be spot welded by the thickness of the thinner of the metal sheets arranged on the surface of the sheet assembly. When the thicknesses of the metal sheets arranged on the surface of the sheet assembly are the same, the sheet thickness ratio is the value obtained by dividing the total thickness of the sheet assembly by that thickness. The sheet thickness ratio is used as an indicator of the ease of spot welding. The larger the sheet thickness ratio, the more difficult it is to grow a nugget to the metal sheet arranged on the surface of the sheet assembly. If a nugget does not grow to the metal sheet arranged on the surface of the sheet assembly, the metal sheet will not be joined to the adjacent metal sheet. Therefore, the larger the sheet thickness ratio, the more likely it is that poor joining will occur.

[0040] The total thickness of the metal sheet outside the lap portion 14 is smaller than the total thickness of the metal sheet at the lap portion 14. Therefore, the sheet thickness ratio outside the lap portion 14 is smaller than the sheet thickness ratio at the lap portion 14. By providing the secondary nugget 16 outside the lap portion 14, poor joining of the plate-like member 13 can be suppressed extremely effectively.

[0041] When the spot welding structure 1 according to this embodiment is applied to an inner frame structure of an automobile body, the plate-like member 13 becomes an outer plate member of the vehicle body, and the first lap joint 11 and the second lap joint 12 become frame members of the vehicle body. The spot welding structure 1 according to this embodiment can suppress poor joining of the outer plate members and increase the load transmission efficiency between the frame members.

[0042] The most basic aspect of the spot welding structure 1 according to this embodiment has been described above. A more preferred aspect will now be described.

[0043] (Spacing of secondary nuggets) It is preferable that the distance d between the center of the secondary nugget 16 joining the plate-like member 13 and the first lap joint 11 and the center of the secondary nugget 16 joining the plate-like member 13 and the second lap joint 12 is 200 mm or less. This further improves the load transmission efficiency of the spot welded structure 1. The distance d may be 190 mm or less, 180 mm or less, 160 mm or less, or 140 mm or less. The center-to-center distance of the secondary nuggets 16 is determined by measuring the center-to-center distance of the indentations 161 on the secondary nuggets 16.

[0044] A plurality of secondary nuggets 16 may be provided in the first lap joint 11 and the second lap joint 12. In this case, the distance d between the center of the secondary nugget 16 joining the plate-like member 13 and the first lap joint 11 and the center of the secondary nugget 16 joining the plate-like member 13 and the second lap joint 12 means the minimum center-to-center distance of the secondary nuggets 16.

[0045] (Shrinkage structure) The lap portion 14 is preferably a shoulder joint. Generally, a shoulder joint is understood to be a type of joint in which one member and / or part of a lap joint is stepped so that the base material surfaces are substantially flush (JIS Z 3001-1:2018). In the spot welding structure according to this embodiment, it is preferable that one or more of the metal plates 111 of the first lap joint 11 and the metal plates 121 of the second lap joint 12 have a shoulder processed portion in the lap portion 14, and two of the three metal plates joined by the main nugget 15 are arranged on substantially the same plane outside the lap portion 14.

[0046] The seam structure will be described in detail below with reference to Figure 3. In the seam structure of Figure 3, a metal plate 2 having a seam processed portion 21 is stacked on a metal plate 3 not having a seam processed portion. The seam processed portion 21 is formed, for example, by bending the metal plate 2 in a stepped shape. The seam processed portion 21 has a tip portion 211 and a connection portion 212. In the following description, the portion of the metal plate 2 having the seam processed portion 21, excluding the seam processed portion 21, will be referred to as a main body portion 22.

[0047] The tip 211 of the seam processing portion 21 is approximately parallel to the main body portion 22 of the metal plate 2, but is not on the same plane as the main body portion 22 of the metal plate 2. The plane that includes the tip 211 is separated by a predetermined distance x from the plane that includes the main body portion 22. It is preferable that the predetermined distance x is approximately the same as the thickness y of the metal plate 3 that is overlapped with the seam processing portion 21. The tip 211 constitutes the lap portion 14. The tip 211 has a width that is at least large enough to allow spot welding.

[0048] The connection portion 212 of the edge processing portion 21 connects the tip portion 211 of the edge processing portion 21 and the main body portion 22 of the metal plate 2. The connection portion 212 forms a predetermined angle with respect to the tip portion 211 of the edge processing portion 21 and the main body portion 22 of the metal plate 2. As a result, the connection portion 212 separates the plane containing the tip portion 211 of the edge processing portion 21 by a predetermined distance x from the plane containing the main body portion 22 of the metal plate 2. The connection portion 212 may be flat or curved.

[0049] 3, the metal plate 3 is placed in the space between a plane including the tip 211 of the seam processing portion 21 and a plane including the main body 22 of the metal plate 2. One surface of the metal plate 2 having the seam processing portion 21 is placed on approximately the same plane as one surface of the metal plate 3 that is overlapped with the seam processing portion 21.

[0050] Next, a specific example of the welded joint structure in the spot welding structure according to this embodiment will be described with reference to FIG. 1 and FIGS. 4A to 4E.

[0051] 1, a seam 1211 is provided at the ends of the two metal plates 121 of the second lap joint 12. The two metal plates 111 of the first lap joint 11 do not have a seam.

[0052] 1, the metal plate 111 on the upper side of the first lap joint 11 is disposed between the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 and the plate-like member 13. The seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 is disposed between the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 and the metal plate 111 on the upper side of the first lap joint 11. As a result, the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12 are disposed on approximately the same plane.

[0053] In the lap portion 14 of the spot welding structure 1 in Figure 1, (1) the metal plate 111 on the upper side of the first lap joint 11 in the drawing, (2) the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and (3) the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. The main nugget 15 joins the three metal plates of the lap portion 14. The metal plate 111 on the lower side of the first lap joint 11 in the drawing is excluded from the lap portion 14.

[0054] 4A, a seam 1211 is provided only on the end of the metal plate 121 on the lower side of the paper of the second lap joint 12. The two metal plates 111 of the first lap joint 11 and the metal plate 121 on the upper side of the paper of the second lap joint 12 do not have a seam.

[0055] 4A, the two metal plates 111 of the first lap joint 11 are arranged between the plate-like member 13 and the seam-cut portion 1211 of the metal plate 121 on the lower side of the paper of the second lap joint 12. As a result, the metal plates 111 of the first lap joint 11 and the metal plates 121 of the second lap joint 12 are arranged on approximately the same plane.

[0056] 4A, (1) the metal plate 111 on the upper side of the first lap joint 11 in the drawing, (2) the metal plate 111 on the lower side of the first lap joint 11 in the drawing, and (3) the seam processing portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. The main nugget 15 joins the three metal plates of the lap portion 14. The metal plate 121 on the upper side of the second lap joint 12 in the drawing is excluded from the lap portion 14.

[0057] 4B, a seam 1111 is provided at the end of the metal plate 111 on the lower side of the first lap joint 11, and a seam 1211 is provided at the end of the metal plate 121 on the upper side of the second lap joint 12. The metal plate 111 on the upper side of the first lap joint 11 and the metal plate 121 on the lower side of the second lap joint 12 do not have a seam.

[0058] 4B , the metal plate 111 on the upper side of the first lap joint 11 is disposed between the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 and the plate-like member 13. The seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 is disposed between the metal plate 111 on the upper side of the first lap joint 11 and the seam-processed portion 1111 of the metal plate 111 on the lower side of the first lap joint 11. As a result, the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12 are disposed on approximately the same plane.

[0059] 4B, (1) the metal plate 111 on the upper side of the first lap joint 11, (2) the edged portion 1211 of the metal plate 121 on the upper side of the second lap joint 12, and (3) the edged portion 1111 of the metal plate 111 on the lower side of the first lap joint 11 are overlapped in this order. The main nugget 15 joins the three metal plates of the lap portion 14. The metal plate 121 on the lower side of the second lap joint 12 is excluded from the lap portion 14.

[0060] 4C, a seam 1211 is provided only on the end of the metal plate 121 on the upper side of the paper of the second lap joint 12. The two metal plates 111 of the first lap joint 11 and the metal plate 121 on the lower side of the paper of the second lap joint 12 do not have a seam.

[0061] 4C, the two metal plates 111 of the first lap joint 11 are arranged between the seam processing portion 1211 of the metal plate 121 on the upper side of the paper of the second lap joint 12 and the plate-like member 13. As a result, the metal plates 111 of the first lap joint 11 and the metal plates 121 of the second lap joint 12 are arranged on approximately the same plane.

[0062] 4C , (1) the metal plate 111 on the upper side of the first lap joint 11, (2) the metal plate 111 on the lower side of the first lap joint 11, and (3) the seam 1211 of the metal plate 121 on the upper side of the second lap joint 12 are overlapped in this order. The main nugget 15 joins the three metal plates of the lap portion 14. The metal plate 121 on the lower side of the second lap joint 12 is excluded from the lap portion 14.

[0063] The plate-shaped member 13 may have a seam-processed portion. In the spot-welded structure of Fig. 4D, seam-processed portions 1211 are provided on the two metal plates 121 of the second lap joint 12. Furthermore, seam-processed portions 131 are also provided on the plate-shaped member 13. The two metal plates 111 of the first lap joint 11 do not have seam-processed portions.

[0064] 4D, the seam processed portion 1211 of the metal plate 121 on the lower side of the paper of the second lap joint 12 is disposed between the seam processed portion 1211 of the metal plate 121 on the upper side of the paper of the second lap joint 12 and the metal plate 111 on the lower side of the paper of the first lap joint 11. As a result, the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12 are disposed on approximately the same plane.

[0065] In the lap portion 14 of the spot-welded structure 1 in FIG. 4D , the seam 1211 of the metal plate 121 on the upper side of the second lap joint 12 forms a convex portion facing upward in the drawing. However, this convex portion is accommodated in the seam 131 of the plate-shaped member 13. Therefore, no large gap is formed between the plate-shaped member 13 and the main body 1112 of the metal plate 111 of the first lap joint 11 and / or the main body 1212 of the metal plate 121 of the second lap joint 12. In the lap portion 14 of the spot-welded structure 1, a gap may be formed between the plate-shaped member 13 and the first lap joint 11 and / or the second lap joint 12. By providing a gap between the plate-shaped member 13 and the first lap joint 11 and / or the second lap joint 12, the rigidity of the lap portion 14 of the spot-welded structure 1 is improved.

[0066] 4D , (1) the edged portion 1211 of the metal plate 121 on the upper side of the second lap joint 12, (2) the edged portion 1211 of the metal plate 121 on the lower side of the second lap joint 12, and (3) the metal plate 111 on the lower side of the first lap joint 11 are overlapped in this order. The main nugget 15 joins the three metal plates of the lap portion 14. The metal plate 111 on the upper side of the first lap joint 11 is excluded from the lap portion 14.

[0067] A plurality of main nuggets 15 may be provided in the lap portion 14. In the spot welded structure 1 of Fig. 4E, a seam 1211 is provided on the two metal sheets 121 of the second lap joint 12. The two metal sheets 111 of the first lap joint 11 do not have a seam.

[0068] 4E, the metal plate 111 of the first lap joint 11 on the upper side of the drawing sheet is disposed between the seam processing portion 1211 of the two metal plates 121 of the second lap joint 12 and the plate-like member 13. As a result, the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12 are disposed on approximately the same plane.

[0069] In the lap portion 14 of the spot welded structure 1 in Figure 4E, (1) the metal plate 111 on the upper side of the first lap joint 11 in the drawing, (2) the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and (3) the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. There are two main nuggets 15, and the two main nuggets 15 join the three metal plates of the lap portion 14. The metal plate 111 on the lower side of the first lap joint 11 in the drawing is excluded from the lap portion 14.

[0070] In either configuration, the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12 are arranged on approximately the same plane, thereby further increasing the load transmission efficiency.

[0071] 1, 4A, 4C, 4D, and 4E, there is only one joint interface between the first lap joint 11 and the second lap joint 12. However, the number of joint interfaces between the first lap joint 11 and the second lap joint 12 may be two or more. By making the number of joint interfaces between the first lap joint 11 and the second lap joint 12 two or more, the rigidity of the spot welded structure 1 is further improved.

[0072] An example of a spot welded structure 1 having two or more joining interfaces is the spot welded structure 1 shown in Fig. 4B. In the spot welded structure 1 of Fig. 4B, one metal plate 121 of the second lap joint 12 is sandwiched between two metal plates 111 of the first lap joint 11 at the location where the main nugget 15 is formed.

[0073] Another example of a spot welded structure 1 having two or more bonding interfaces is a spot welded structure 1 in which three different metal plates are joined by multiple main nuggets 15, as shown in FIGS. 5A to 5D . Specifically, in the spot welded structure 1 shown in FIGS. 5A to 5D , it is preferable that some of the main nuggets 15 join two metal plates 111 of the first lap joint 11 to one metal plate 121 of the second lap joint 12, and the other main nuggets 15 join one metal plate 111 of the first lap joint 11 to two metal plates 121 of the second lap joint 12. This further improves the load transfer efficiency of the spot welded structure 1. Furthermore, since the number of bonding interfaces between the first lap joint 11 and the second lap joint 12 is two or more, the rigidity of the spot welded structure 1 is further improved.

[0074] In the spot welding structure 1 illustrated in Fig. 5A, the lap portion 14 is divided into two. In the lap portion 14 on the side of the first lap joint 11, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the metal plate 111 on the lower side of the first lap joint 11 in the drawing, and the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. In the lap portion 14 on the side of the second lap joint 12, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. In each of the two lap portions 14, a main nugget 15 is formed that joins the three metal plates.

[0075] 5B , the lap portion 14 is also divided into two. In the lap portion 14 on the first lap joint 11 side, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and the seam-processed portion 1111 of the metal plate 111 on the lower side of the first lap joint 11 in the drawing are overlapped in this order. In the lap portion 14 on the second lap joint 12 side, the main body 1212 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, the metal plate 121 on the lower side of the second lap joint 12 in the drawing, and the seam-processed portion 1111 of the metal plate 111 on the lower side of the first lap joint 11 in the drawing are overlapped in this order. In each of the two lap portions 14, a main nugget 15 is formed that joins the three metal plates.

[0076] 5C , the lap portion 14 is also divided into two. In the lap portion 14 on the side of the first lap joint 11, the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, and the metal plate 111 on the lower side of the first lap joint 11 in the drawing are overlapped in this order. In the lap portion 14 on the side of the second lap joint 12, the seam-processed portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, the seam-processed portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing, and the metal plate 111 on the lower side of the first lap joint 11 in the drawing are overlapped in this order. In each of the two lap portions 14, a main nugget 15 is formed that joins the three metal plates. Additionally, the seam processing portion 1211 of the metal plate 121 on the upper side of the drawing of the second lap joint 12 forms a convex portion in the lap portion 14. The convex portion is housed inside the seam processing portion 131 provided in the plate-like member 13.

[0077] 5D , the lap portion 14 is also divided into two. In the lap portion 14 on the first lap joint 11 side, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the edged portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and the edged portion 1111 of the metal plate 111 on the lower side of the first lap joint 11 in the drawing are overlapped in this order. In the lap portion 14 on the second lap joint 12 side, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the edged portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and the edged portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. In each of the two lap portions 14, a main nugget 15 is formed that joins the three metal plates.

[0078] In either configuration, the lap portion 14 is divided into two, and a main nugget 15 that joins three metal plates is formed in each of the two lap portions 14, thereby forming two joint structures. This further improves the load transmission efficiency. Also, two or more main nuggets 15 may be formed in each lap portion 14. This further improves the load transmission efficiency.

[0079] (Adhesive 17) It is preferable that the spot welding structure 1 further includes an adhesive 17. For example, as shown in FIG. 6 , the adhesive 17 is disposed between the plate-shaped member 13 and one or both of the first lap joint 11 and the second lap joint 12. This further increases the joining strength between the plate-shaped member 13 and other members. Alternatively, the adhesive 17 may be disposed between the metal plate 111 of the first lap joint 11 and the metal plate 121 of the second lap joint 12. This further increases the joining strength of the two lap joints and improves load transfer efficiency. The adhesive 17 may be disposed between the multiple metal plates 111 included in the first lap joint 11, or between the multiple metal plates 121 included in the second lap joint 12. This further increases the joining strength of the first lap joint 11 and / or the second lap joint 12. The type of adhesive 17 is not particularly limited. Examples of the adhesive 17 include epoxy-based, rubber-based, silicone-based, and mixtures thereof. The adhesive may be heat-curable or reactively curable, but when applied to automobile bodies, a heat-curable adhesive that cures during the heat treatment process (140°C to 190°C) of electrodeposition coating is preferred.

[0080] (18 additional nuggets) As shown in FIG. 7 , the spot welded structure 1 may further include an additional nugget 18 in the lap portion 14. The additional nugget 18 joins two or more of the metal plates and plate-like members 13 included in the lap portion 14. The additional nugget 18 is similar to the main nugget 15 in that it is provided in the lap portion 14. However, unlike the main nugget 15, one of the two indentations of the additional nugget 18 is provided in the plate-like member 13. The additional nugget 18 is obtained by spot welding to the lap portion 14 with another plate-like member 13 overlapping the lap portion 14.

[0081] When an additional plate-shaped member 13 is placed on the lap portion 14, the lap portion 14 will include four or more metal plates. Spot welding of such a plate assembly typically tends to cause expulsion. However, the gaps in the lap portion 14 are removed when the main nugget 15 and the sub-nugget 16 are formed. Therefore, expulsion caused by the gaps is suppressed when the additional nugget 18 is formed.

[0082] The additional nugget 18 only needs to join at least two of the metal plates included in the lap portion 14 and the plate-like member 13. The additional nugget 18 does not have to grow into the plate-like member 13. That is, the additional nugget 18 does not have to join the plate-like member 13 to another member. Alternatively, the additional nugget 18 may press the plate-like member 13 to another member. Even if the additional nugget 18 is located outside the plate-like member 13, the additional nugget 18 can still improve the joining strength and load transmission efficiency of the two lap joints. The additional nugget 18 may be provided spaced apart from the main nugget 15. On the other hand, the additional nugget 18 and the main nugget 15 may be partially fused together. Figure 15 shows an example cross section in which the additional nugget 18 and the main nugget 15 are partially fused together.

[0083] On the other hand, the spot welded structure 1 does not have to have the additional nugget 18 in the lap portion 14. That is, the plate-like member may be separated from the first lap joint and the second lap joint over the entire lap portion. By omitting the additional nugget 18, the manufacturing cost of the spot welded structure 1 can be reduced, and the time required to manufacture the spot welded structure 1 can be shortened.

[0084] The first lap joint may have a joint outside the lap portion that joins only the metal plates of the first lap joint. The second lap joint may have a joint outside the lap portion that joins only the metal plates of the second lap joint. The joints are, for example, the nugget 112 of the first lap joint 11 and the nugget 122 of the second lap joint 12 shown in FIG. 1 . The nugget 112 of the first lap joint 11 joins the metal plates 111 of the first lap joint 11, but does not join the first lap joint 11 to another member. The nugget 122 of the second lap joint 12 joins the metal plates 121 of the second lap joint 12, but does not join the second lap joint 12 to another member. The metal plates included in the lap joint may be joined by arc-welded metal, seam-welded metal, laser-welded metal, or a combination thereof.

[0085] (2A. First manufacturing method of spot welded structure 1) A first method for manufacturing a spot welding structure 1 according to another embodiment of the present invention includes, as shown in FIGS. 8A to 8E, (S1) a step of preparing a first lap joint 11 having two or more metal plates and a second lap joint 12 having two or more metal plates; (S2) a step of overlapping one or more ends of the metal plates 111 of the first lap joint and one or more ends of the metal plates 121 of the second lap joint to form a lap portion 14; (S3) a step of primarily spot welding the first lap joint 11 and the second lap joint 12 at the lap portion 14 to form a main nugget 15; (S4) a step of overlapping a metal plate-like member 13 on the lap portion 14 on which the first lap joint 11, the second lap joint 12, and the main nugget 15 are formed; (S5) a step of secondary spot welding the plate-like member 13 and the first lap joint 11, and the plate-like member 13 and the second lap joint 12 to form a plurality of secondary nuggets 16; The number of metal plates to be primarily spot welded is three, and the welding point in the secondary spot welding is outside the lap portion 14.

[0086] A first manufacturing method for a spot welded structure 1 according to another embodiment of the present invention will be described in detail below. Note that the preferred embodiment of the spot welded structure 1 described above can also be applied to the first manufacturing method for the spot welded structure 1 and the second manufacturing method described below. For example, the configuration of the lap portion 14 described with reference to Figures 4A to 4E can also be appropriately adopted in the first and second manufacturing methods for the spot welded structure 1.

[0087] (S1) First, a first lap joint 11 having two or more metal plates and a second lap joint 12 having two or more metal plates are prepared. The process of preparing the lap joints may be a process of manufacturing the first lap joint 11 having two or more metal plates and the second lap joint 12 having two or more metal plates. The process of manufacturing the lap joints may be, for example, a spot welding process shown in FIG. 8A. The process of manufacturing the lap joints may be, for example, a laser welding process, a seam welding process, a lap arc welding process, or the like. On the other hand, lap joints manufactured by others may be used as the first lap joint 11 and the second lap joint 12. An example of the first lap joint and the second lap joint is an automobile frame component, and an example of the plate-like member 13 is an automobile exterior panel component.

[0088] When preparing the first lap joint 11 and the second lap joint 12, it is preferable to shape the ends of these. For example, it is preferable to make only one of the two or more metal plates in the lap joint protrude. By machining the ends of the lap joint or positioning the ends of the metal plates before manufacturing the lap joint, it is possible to make only one of the two or more metal plates in the lap joint protrude. It is also preferable to provide a seam processing portion in at least one of the two or more metal plates. The seam processing portion can be formed by machining the ends of the metal plates before or after manufacturing the lap joint.

[0089] In the first lap joint 11 illustrated in Fig. 8A, only one of the two or more metal plates 111 protrudes. In the second lap joint 12 illustrated in Fig. 8A, only one of the two or more metal plates 121 protrudes, and a seam is provided on both of the two metal plates 121. In addition, various embodiments such as those illustrated in Fig. 1, 4A to 4E, and 5A to 5D can be applied to the ends of the first lap joint 11 and the second lap joint 12.

[0090] (S2) Next, the ends of one or more of the metal plates 111 of the first lap joint and the ends of one or more of the metal plates 121 of the second lap joint are overlapped to form the lap portion 14. As shown in Fig. 8B, an area where three metal plates are overlapped is formed in the lap portion 14. The number of metal plates in the lap portion 14 can be adjusted by appropriately adjusting the shape of the end of the lap joint.

[0091] 4B, the two lap joints are aligned so that the ends of the metal plates are inserted into the spaces formed by the seams. This alignment is also considered to be the overlapping of the ends of one or more of the metal plates 111 of the first lap joint and the ends of one or more of the metal plates 121 of the second lap joint. In other words, all of the actions for forming the lap portion 14 are considered to be the actions of overlapping the ends of the metal plates.

[0092] (S3) After the ends of the first lap joint 11 and the second lap joint 12 are overlapped, the first lap joint 11 and the second lap joint 12 are first spot welded together at the lap portion 14 to form a main nugget 15. At this time, a main nugget impression 151 is formed in the metal plate disposed on the outermost surface of the lap portion 14 by the first spot welding.

[0093] 8C, when forming main nugget 15, the number of metal sheets to be primarily spot-welded is three. Therefore, it is preferable to use the area of ​​lap portion 14 where three metal sheets are overlapped as the welding point for the primary spot welding. The number of times primary spot welding may be one, two or more.

[0094] (S4) Following the primary spot welding, a metal plate-like member 13 is placed over the lap portion 14 where the first lap joint 11, the second lap joint 12, and the main nugget 15 have been formed. One of the pair of indentations formed by the primary spot welding is covered by the plate-like member 13.

[0095] (S5) After the plate-like member 13 and the other members are overlapped, the plate-like member 13 and the first lap joint 11, and the plate-like member 13 and the second lap joint 12 are secondarily spot welded to form multiple minor nuggets 16. The welding points of the secondary spot welding are outside the lap portion 14. Secondary spot welding is performed at least once on the plate-like member 13 and the first lap joint 11, and also at least once on the plate-like member 13 and the second lap joint 12. Therefore, secondary spot welding is performed at least two times. The total number of secondary spot weldings may be three or more.

[0096] (Action and effect) In the first manufacturing method of the spot welded structure 1 according to this embodiment, three metal plates are overlapped at the joining portion of the two lap joints. Therefore, the first manufacturing method according to this embodiment can firmly join the two lap joints. Furthermore, the spot welded structure 1 obtained by the first manufacturing method according to this embodiment has excellent load transmission efficiency.

[0097] Furthermore, by overlapping three metal sheets at the joints of the two lap joints, the occurrence of expulsion is suppressed. Generally, in spot welding of sheet pairs with a large total thickness, a high welding current is required to grow the nugget. However, a high welding current is likely to cause expulsion. In particular, in cases where there is a gap between the metal sheets, expulsion caused by a high current is likely to form large blowholes in the nugget. In the first manufacturing method according to this embodiment, by limiting the number of metal sheets to be primarily spot-welded to three, the total thickness of the sheet pair to be primarily spot-welded can be reduced, thereby suppressing the occurrence of expulsion.

[0098] Additionally, in the first manufacturing method according to this embodiment, the welding point in the secondary spot welding for joining the plate-shaped member 13 to the other member is located outside the lap portion 14. Therefore, in the first manufacturing method according to this embodiment, the total thickness of the plate assembly in the secondary spot welding is also reduced. This also suppresses the occurrence of expulsion in the secondary spot welding. In addition, poor joining between the plate-shaped member 13 and the other member is avoided.

[0099] (2B. Second manufacturing method of spot welded structure 1) A second manufacturing method of a spot welding structure 1 according to another embodiment of the present invention includes, as shown in FIGS. 9A to 9F, (s1) a step of preparing a plate assembly in which two of the metal plates that are components of a first lap joint are overlapped at their ends; (s2) a step of overlapping an end of one of the metal plates that is a component of the second lap joint onto an end of the plate assembly to form a lap portion; (s3) a step of primarily spot welding two of the metal plates that are components of the first lap joint and one of the metal plates that are components of the second lap joint at the lap portion to form a main nugget and a first lap joint; (s4) a step of overlapping and spot welding one metal plate of the second lap joint provided with the main nugget and the remaining metal plates of the second lap joint outside the lap portion to form a second lap joint; (s5) placing a metal plate-like member on the lap portion where the first lap joint, the second lap joint, and the main nugget are formed; (s6) a step of secondarily spot welding the plate-like member and the first lap joint, and the plate-like member and the second lap joint to form a plurality of secondary nuggets; The number of metal plates to be spot-welded in the first step is three, and the welding point in the second step is outside the lap portion.

[0100] A second manufacturing method for a spot welded structure 1 according to another embodiment of the present invention will be described in detail below. The second manufacturing method differs from the first manufacturing method in that the first lap joint and the second lap joint are not formed before the primary spot welding. However, in other respects, the second manufacturing method is very similar to the first manufacturing method. In particular, the first manufacturing method and the second manufacturing method are identical in terms of the process of stacking the plate-like members and subsequent processes. Therefore, in the following description of the second manufacturing method, details that overlap with those of the first manufacturing method may be omitted. Suitable aspects of the first manufacturing method can be applied to the second manufacturing method.

[0101] (s1) First, as shown in Fig. 9A, a plate set is prepared by overlapping two metal plates at their edges. These two metal plates are parts of a first lap joint. However, at this point, the metal plates of the first lap joint are not joined together.

[0102] (s2) Next, as shown in Figure 9B, the end of another metal plate is overlapped on the end of the plate set to form a lap. The other metal plate is part of a second lap joint. However, at this point, the metal plates of the second lap joint are also not joined.

[0103] (s3) Then, as shown in Figure 9C, two of the metal plates that are components of the first lap joint and one of the metal plates that are components of the second lap joint are primarily spot welded at the lap portion. This brings the number of metal plates that are primarily spot welded to three. A main nugget is formed by the primary spot welding. Furthermore, a first lap joint is formed by the primary spot welding, which has two metal plates and a main nugget that joins the two metal plates.

[0104] (s4) 9D, one metal plate of the second lap joint where the main nugget is provided is overlapped with the remaining metal plate of the second lap joint outside the lap portion, and the overlapping portion is then spot welded to form the second lap joint.

[0105] 9D, the second lap joint has only two metal plates. However, a second lap joint having three or more metal plates can be produced by spot welding two or more metal plates to the one metal plate of the second lap joint provided with the main nugget.

[0106] In addition, to increase the joining strength of the first lap joint, additional spot welding may be performed on the first lap joint as shown in Fig. 9D. When additional spot welding is performed, an additional metal plate may be added, so that the number of metal plates in the first lap joint can be three or more.

[0107] (s5, s6) Then, as shown in Figure 9E, a metal plate-shaped member is placed on the lap portion where the first lap joint, second lap joint, and main nugget have been formed. Furthermore, as shown in Figure 9F, the plate-shaped member and the first lap joint, and the plate-shaped member and the second lap joint are secondarily spot welded to form multiple sub-nuggets. The welding points for the secondary spot welding are outside the lap portion. In the second manufacturing method, the process of welding the plate-shaped member to another member by placing it on top of another member is substantially the same as in the first manufacturing method.

[0108] (Action and effect) As with the first manufacturing method, in the second manufacturing method of the spot welded structure 1 according to this embodiment, three metal plates are overlapped at the joint between the two lap joints. Also, as with the first manufacturing method, in the second manufacturing method according to this embodiment, the welding point in the secondary spot welding for joining the plate-shaped member 13 to the other member is located outside the lap portion 14. Therefore, according to the second manufacturing method according to this embodiment, a spot welded structure with excellent load transmission efficiency is obtained. Furthermore, the second manufacturing method can suppress the occurrence of expulsion. Additionally, according to the second manufacturing method, poor joining between the plate-shaped member 13 and the other member is avoided.

[0109] The most basic aspects of the first and second manufacturing methods for the spot welding structure 1 according to this embodiment have been described above. More preferred aspects will be described below. Unless otherwise specified, the preferred aspects described below are applicable to both the first and second manufacturing methods.

[0110] (Spacing between welding points) It is preferable that the distance between the center of the weld point in the secondary spot welding of the plate-like member 13 and the first lap joint 11 and the center of the weld point in the secondary spot welding of the plate-like member 13 and the second lap joint 12 be 200 mm or less. This allows the distance d between the center of the secondary nugget 16 joining the plate-like member 13 and the first lap joint 11 and the center of the secondary nugget 16 joining the plate-like member 13 and the second lap joint 12 to be 200 mm or less. This further improves the load transmission efficiency of the spot welding structure 1. The distance between the centers of the weld points may be 190 mm or less, 180 mm or less, 160 mm or less, or 140 mm or less.

[0111] It should be noted that there are cases where secondary spot welding is performed two or more times on the first lap joint 11 and the second lap joint 12. In this case, the distance between the center of the welding point in the secondary spot welding of the plate-like member 13 and the first lap joint 11 and the center of the welding point in the secondary spot welding of the plate-like member 13 and the second lap joint 12 means the minimum value of the center-to-center distance of the welding points.

[0112] (Shrinkage structure) A seam may be provided at the end of one or more of the metal sheets 111 of the first lap joint 11 and the metal sheets 121 of the second lap joint 12, and when forming the lap portion 14, two of the three metal sheets joined by the main nugget 15 may be arranged on approximately the same plane outside the lap portion 14. By arranging the metal sheets 111 of the first lap joint 11 and the metal sheets 121 of the second lap joint 12 on approximately the same plane, the load transmission efficiency is further improved. Specific examples of the seam structure are the same as the preferred aspects of the spot welding structure 1 according to this embodiment, as exemplified in Figures 1 and 4A to 4E.

[0113] (Multiple primary spot welds) In the first manufacturing method, primary spot welding may be performed on the lap portion 14 multiple times. In this case, as shown in FIG. 4E, the sheet combinations may be the same in the multiple primary spot weldings. On the other hand, as shown in FIG. 5A and the like, the sheet combinations may be different in the multiple primary spot weldings. Specifically, when forming the lap portion 14, a lap portion 14 formed by overlapping two metal sheets 111 of the first lap joint 11 with one metal sheet 121 of the second lap joint 12, and a lap portion 14 formed by overlapping one metal sheet 111 of the first lap joint 11 with two metal sheets 121 of the second lap joint 12 may be formed, and primary spot welding may be performed on each of these multiple lap portions 14.

[0114] In the second manufacturing method, primary spot welding may also be performed multiple times on the lap portion 14. In this case, as shown in Fig. 4E, the sheet combinations may be the same in the multiple primary spot weldings. On the other hand, as shown in Fig. 5A etc., the sheet combinations may be different in the multiple primary spot weldings.

[0115] In the second manufacturing method, in order to perform multiple primary spot welding operations on different sheet pairs, the primary spot welding must be performed in two stages. This is because only one of the metal sheets of the second lap joint is included in the lap portion during the first primary spot welding. Therefore, during the first primary spot welding, a main nugget is formed that joins the two metal sheets 111 of the first lap joint 11 and the one metal sheet 121 of the second lap joint 12. Next, another metal sheet 121 of the second lap joint 12 is overlapped on the one metal sheet 121 of the second lap joint 12 to form an additional lap portion in which the one metal sheet 111 of the first lap joint 11 and the two metal sheets 121 of the second lap joint 12 overlap. Then, primary spot welding is performed on the additional lap portion to form a main nugget that joins the one metal sheet 111 of the first lap joint 11 and the two metal sheets 121 of the second lap joint 12.

[0116] Either manufacturing method can be used to manufacture a spot welded structure 1 having a main nugget 15 that joins two metal sheets 111 of the first lap joint 11 to one metal sheet 121 of the second lap joint 12, and a main nugget 15 that joins one metal sheet 111 of the first lap joint 11 to two metal sheets 121 of the second lap joint 12. This further improves the load transfer efficiency of the spot welded structure 1. The lap portion 14 when performing multiple primary spot welding operations can have the configurations shown in, for example, FIGS. 5A to 5D.

[0117] (Application of adhesive 17) The secondary spot welding may be a method in which a weld bond, i.e., an adhesive 17, is applied to the joint interface before spot welding. Specifically, the manufacturing method of the spot welded structure 1 may further include a step of applying adhesive 17 between the plate-shaped member 13 and one or both of the first lap joint 11 and the second lap joint 12 after the primary spot welding and before overlapping the plate-shaped member 13 onto the lap portion 14 in which the first lap joint 11, the second lap joint 12, and the main nugget 15 are formed. This makes it possible to manufacture a spot welded structure 1 in which adhesive 17 is applied between the plate-shaped member 13 and one or both of the first lap joint 11 and the second lap joint 12, as illustrated in FIG. 6 . This further increases the joint strength between the plate-shaped member 13 and another member.

[0118] (additional spot welding) The method for manufacturing the spot welded structure 1 may further include a step of performing additional spot welding on the lap portion 14 and the plate-shaped member 13 after the secondary spot welding. This makes it possible to manufacture a spot welded structure 1 that further has an additional nugget 18 in the lap portion 14, as shown in FIG. 7 .

[0119] When an additional plate-shaped member 13 is placed on the lap portion 14, the lap portion 14 includes four or more metal plates. The metal plates here include the metal plates that make up the plate-shaped member 13. Spot welding of such a plate assembly typically tends to result in expulsion. However, the gaps in the lap portion 14 are removed when the main nugget 15 and the sub-nugget 16 are formed. Therefore, expulsion caused by the gaps is suppressed during additional spot welding.

[0120] The additional spot welding only needs to join at least two of the metal plates included in the lap portion 14 and the plate-like member 13. The additional spot welding does not have to grow the additional nugget 18 into the plate-like member 13. That is, the additional nugget 18 does not have to join the plate-like member 13 to another member. Alternatively, the additional nugget 18 may press the plate-like member 13 to another member. Even if the additional nugget 18 is located outside the plate-like member 13, the additional nugget 18 can still improve the joining strength and load transmission efficiency of the two lap joints. The welding point of the additional spot welding may be separated from or overlap with the welding point of the primary spot welding.

[0121] On the other hand, the manufacturing method of the spot welded structure 1 does not have to include the step of performing additional spot welding. That is, all spot welding of the plate-like member may be performed outside the lap portion. By omitting the additional spot welding, the manufacturing cost of the spot welded structure 1 can be reduced and the time required to manufacture the spot welded structure 1 can be shortened.

[0122] Although the embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical concept of the invention. A more preferred example of the spot welding structure 1 according to this embodiment and its manufacturing method will be described below. The preferred example described below is applicable to both the spot welding structure 1 and its manufacturing method.

[0123] (plate thickness ratio) The thickness ratio of the lap portion 14 is the value obtained by dividing the total thickness of the three metal plates and the plate-shaped member 13 at the location where the main nugget 15 is provided by the thickness of the plate-shaped member 13. The thickness ratio of the lap portion 14 is preferably within a range of 6.0 to 11.0. The larger the thickness ratio of the lap portion 14, the thinner the plate-shaped member 13 can be, thereby reducing the weight of the spot-welded structure 1. Generally, the larger the thickness ratio, the more difficult it is to join the plate-shaped members 13. However, in the spot-welded structure 1 according to this embodiment and its manufacturing method, the plate-shaped members 13 are firmly joined outside the lap portion 14. Therefore, it is not essential that the plate-shaped members 13 be welded at the lap portion 14. Even if the thickness ratio of the lap portion 14 is large, poor joining of the plate-shaped members 13 does not become a problem.

[0124] The thickness ratio of the secondary nugget forming portion is the total thickness of the metal plates and plate-shaped member 13 at the location where the secondary nugget 16 is provided, divided by the thickness of the plate-shaped member 13. The thickness ratio of the secondary nugget forming portion is preferably within the range of 3.0 to 6.0, and more preferably has an upper limit of 5.5. The smaller the thickness ratio of the secondary nugget forming portion, the more likely it is that poor joining of the plate-shaped member 13 will be avoided.

[0125] The plate thickness ratio is determined by measuring the thickness of the metal plate and plate-like member 13 in a cross section that passes through the center of the indentation and is perpendicular to the surface of the plate-like member 13. If the thickness of the metal plate and plate-like member 13 has been reduced by the indentation, the thickness measured at a location that is not affected by the indentation is used to calculate the plate thickness ratio.

[0126] (Types of metal plates and plate-like members 13) The type of metal plate of the lap joint is not particularly limited. The type of metal plate constituting the plate-shaped member 13 is also not particularly limited. In the spot welded structure 1 and its manufacturing method according to this embodiment, any material that can be spot welded can be used as the metal plate of the lap joint and the metal plate constituting the plate-shaped member 13. A suitable material can be used depending on the application of the spot welded structure 1. Examples of metal plates include steel plates, aluminum plates, and stainless steel plates.

[0127] A suitable example of the metal plate is a steel plate. In particular, it is preferable that one or more of the metal plates be high-strength steel plates. For example, when the spot welded structure 1 is an automobile body, by using one or more of the metal plates as high-strength steel plates, the thickness of the metal plates can be reduced while ensuring the strength of the spot welded structure 1. By reducing the thickness of the metal plates, the weight of the spot welded structure 1 can be reduced.

[0128] When the metal plates are steel plates, it is preferable that the plate-shaped member 13 be mild steel and that at least one of the metal plates included in the lap joint be a high-strength steel plate. For example, it is preferable that the Vickers hardness of the plate-shaped member 13 be 150 HV or less, 140 HV or less, 130 HV or less, or 120 HV or less. It is preferable that the tensile strength of the plate-shaped member 13 be 440 MPa or less, 400 MPa or less, or 370 MPa or less. It is preferable that the hardness of at least one of the metal plates included in the lap joint be 300 HV or more, 380 HV or more, or 440 HV or more. It is preferable that the tensile strength of at least one of the metal plates included in the lap joint be 980 MPa or more, 1200 MPa or more, or 1350 MPa or more. The plate-shaped member 13 can be disposed on the outermost surface of the spot-welded structure 1, and is therefore suitable, for example, for use as an exterior component of an automobile. Using thin mild steel for the plate-shaped member 13 can improve the formability of the plate-shaped member 13 and enhance the aesthetic appearance of the automobile. The metal plates included in the lap joint are suitable for, for example, automobile frame parts. By using high-strength steel plates for one or more of the metal plates included in the lap joint, the collision safety of the automobile can be improved.

[0129] (Surface treatment of metal plate and plate-like member 13) One or more of the plate-shaped member 13 and the metal plate may have a surface treatment layer. Examples of the surface treatment layer include a chemical conversion coating layer and a plating layer. The chemical conversion coating layer and the plating layer may have a composition suitable for the composition of the underlying metal plate. For example, when the metal plate or the plate-shaped member 13 of the lap joint is a steel plate, the plating layer is preferably a zinc-based plating layer and an aluminum-based plating layer. A zinc-based plating layer is a plating layer having a Zn content of 30% by mass or more. Examples of zinc-based plating layers include a hot-dip galvanized layer, a galvannealed hot-dip galvanized layer, an electrogalvanized layer, a zinc-aluminum-magnesium plating layer, and a hot-stamped hot-dip galvanized layer. An aluminum-based plating layer is a plating layer having an Al content of 20% by mass or more. An example of a steel plate having an aluminum-based plating layer is a hot-stamped aluminum-silicon-plated steel plate. A layer of Al oxide, Ti oxide, or zinc oxide may be provided on the surface of the aluminum plated plate after hot stamping.

[0130] (Thickness of metal plate) There are no particular limitations on the thickness of the metal plates in the lap joint and the thickness of the plate-like member 13. For example, the thickness of the plate-like member 13 is preferably 0.5 to 1.1 mm. The thickness of the metal plates in the lap joint is preferably 0.9 to 2.6 mm.

[0131] (nugget diameter) The diameter of the main nugget 15 is not particularly limited, but is preferably, for example, 3√t or more, 4√t or more, or 5√t or more. This increases the joining strength of the main nugget 15. On the other hand, from the viewpoint of suppressing the heat input and further preventing the generation of spatter, it is preferable that the diameter of the main nugget 15 be 9√t or less, 8√t or less, or 7√t or less. The numerical range of the diameter of the main nugget 15 can also be applied to the sub nugget 16, the additional nugget 18, the nugget 112 of the first lap joint, and the nugget 122 of the second lap joint.

[0132] The nugget diameter refers to the diameter of the nugget measured along the joint interface in a cross-sectional test of the weld. t refers to the sheet thickness of the thinner of the two steel sheets constituting the joint interface at which the nugget diameter was measured. When the number of steel sheets joined by the nugget is three or more and there are two or more joint interfaces, it is preferable that the nugget diameter be within the above-mentioned range at each joint interface, and it is even more preferable that the nugget diameter be within the above-mentioned range at all joint interfaces.

[0133] (Application) The spot welding structure 1 according to this embodiment is not particularly limited in its application. A suitable application is a joint in an automobile body to which an inner frame structure is applied. FIG. 10 shows a joint in an automobile body 4. For example, by applying the spot welding structure 1 according to this embodiment to flanges at joints in the frame parts of the automobile body, such as a joint 41 between an A-pillar lower and a side sill, a joint 42 between a B-pillar and a side sill, a joint 43 between a B-pillar and a roof rail, a joint 44 between an A-pillar lower and an A-pillar upper, a joint 45 between an A-pillar upper and a roof rail, a joint between a C-pillar and a roof rail, and a joint 46 between a C-pillar and a side sill, an automobile body with high load transmission efficiency can be realized.

[0134] Examples of cross sections of spot welding according to the present disclosure are shown in FIGS. In the spot welded joint 1 shown in FIG. 11 , the first and second plates from the bottom at the left edge of the page are two metal plates that make up a first lap joint. The first and second plates from the bottom at the right edge of the page are two metal plates that make up a second lap joint. The location where the second nugget from the right is provided is a lap portion where an end of one of the metal plates of the first lap joint and an end of two or more of the metal plates of the second lap joint overlap. The second nugget from the right is a main nugget that joins the first lap joint and the second lap joint at the lap portion. The top plate on the page is a plate-like member that overlaps the first lap joint, the second lap joint, and the lap portion. The first nugget from the right is a secondary nugget that joins the plate-like member and the first lap joint, and the first nugget from the left is a secondary nugget that joins the plate-like member and the second lap joint. The number of metal plates joined by the main nugget is three. The main nugget indentation is only provided on the metal plates included in the first lap joint or the second lap joint. The plate-like member is located outside the main nugget. The secondary nugget is located outside the lap portion. The second nugget from the left in Figure 11 does not correspond to either the main nugget or the sub-nugget of the spot welding structure according to this embodiment. The location where the second nugget from the left is provided corresponds to the lap portion where the end of one of the metal plates of the first lap joint and the end of one of the metal plates of the second lap joint are overlapped. Since this nugget is provided in the lap portion, it does not correspond to the sub-nugget. On the other hand, since the plate-like member is joined to this nugget, this nugget does not correspond to the main nugget. However, adding such an additional nugget to the spot welded structure according to this embodiment is naturally permitted. Furthermore, as described above, the spot welded joint of FIG. 11 has all the characteristic features of the spot welded joint according to this embodiment. Therefore, even if the spot welded joint of FIG. 11 has an additional nugget, it is still considered to be a spot welded joint according to this embodiment. If the second nugget from the left on the page is ignored, the spot welded joint 1 shown in FIG. 11 has a configuration similar to that of FIG. 4A flipped left and right. The spot welded joint 1 shown in FIG. 12 has the same configuration as that shown in FIG. The spot welded joint 1 shown in FIG. 13 has a configuration similar to that of FIG. 5A, flipped left and right. The spot welded joint 1 shown in FIG. 14 has the same configuration as that shown in FIG. 5B. The spot welded joint 1 shown in FIG. 15 has a configuration similar to that of FIG. 7, but flipped left and right.

[0135] (Example) The effects of one embodiment of the present disclosure will be explained more specifically through experiments using simulations. However, the following conditions are merely one example of conditions adopted to confirm the effects of the present disclosure. The present disclosure is not limited to this one example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and achieve the purpose.

[0136] The following three simulation models, No. 1 to No. 3, were created, and a simulation assuming three-point bending was performed on each of the created models. Models No. 1 to No. 3 are models assuming structural members in which hat-shaped members (metal plates) made of steel plates with thicknesses of 1.2 mm and 1.6 mm and tensile strengths of 1500 MPa are combined, with the flanges spot-welded. The outer plate member (plate-shaped member 13) is made of steel plate with a thickness of 0.65 mm and tensile strength of 270 MPa.

[0137] The spot welding structure of Comparative Example No. 1 is shown in FIGS. 16A to 16C. The spot welding structure of Comparative Example No. 1 simulates a conventional spot welding structure. Note that the outer plate member (plate-shaped member 13) is not shown in FIG. 16A. As shown in FIG. 16C, the spot welding structure of Comparative Example No. 1 targets only one of the two steel plates in each of the first lap joint 11 and the second lap joint 12. The spot welding structure of Comparative Example No. 1 is a model in which three steel plates—the steel plates of two frame members (the metal plate 111 and the metal plate 121 on the upper side of the drawing in FIG. 16C) and the outer plate member (the plate-shaped member 13)—are spot-welded together to form a nugget (main nugget 15). Note that the holes in FIGS. 16A and 16B represent spot welds in the simulation model.

[0138] The spot welding structure 1 of Example No. 2 is shown in FIGS. 17A to 17C. The spot welding structure 1 of Example No. 2 simulates the spot welding structure of the present disclosure. Note that the outer plate member (plate-like member 13) is not shown in FIG. 17A. As shown in FIG. 17C, in the spot welding structure 1 of Example No. 2, the main nugget 15 that joins the first lap joint 11 and the second lap joint 12 joins three metal plates. In the spot welding structure 1 of Example No. 2, the metal plate 111 on the upper side of the page in FIG. 17C, the metal plate 112 on the upper side of the page, and the metal plate 112 on the lower side of the page are stacked in this order. In the spot welding structure 1 of Example No. 2, the plate-like member 13 is located outside the main nugget 15. The main nugget 15 is separated from the plate-like member 13. Therefore, there are three metal plates directly involved in joining the first lap joint 11 and the second lap joint 12. The spot welding structure of Example No. 2 has the same configuration as that shown in Figure 1. Note that the parts that look like holes in Figures 17A and 17B indicate spot welds on a simulation model.

[0139] The spot welding structure 1 of Example No. 3 is shown in Figures 18A to 18C. The spot welding structure 1 of Example No. 3 simulates the spot welding structure of the present disclosure. Note that the outer plate member (plate-shaped member 13) is not shown in Figure 18A. In the spot welding structure 1 of Example No. 3, the lap portion 14 is divided into two. In the lap portion 14 on the side of the first lap joint 11, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the metal plate 111 on the lower side of the first lap joint 11 in the drawing, and the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. In the lap portion 14 on the side of the second lap joint 12, the metal plate 111 on the upper side of the first lap joint 11 in the drawing, the seam-cut portion 1211 of the metal plate 121 on the upper side of the second lap joint 12 in the drawing, and the seam-cut portion 1211 of the metal plate 121 on the lower side of the second lap joint 12 in the drawing are overlapped in this order. A main nugget 15 joining the three metal plates is formed in each of the two lap portions 14. In the spot welding structure 1 of Example No. 3, the plate-shaped member 13 is located outside the main nugget 15. The main nugget 15 is separated from the plate-shaped member 13. Therefore, in each of the two lap portions 14, there are three metal plates directly involved in joining the first lap joint 11 and the second lap joint 12. The spot welding structure of Example No. 3 has a configuration similar to that shown in FIG. 5A. In addition, the parts that look like holes in FIGS. 18A and 18B indicate spot welds on the simulation model.

[0140] The simulation model was a long structural member as shown in Figure 19. The basic conditions for the simulation assuming three-point bending were as follows: In Nos. 1 and 2, the impactor was pressed against the position in the longitudinal direction of the structural member where the main nugget 15 was formed, and in No. 3, the impactor was pressed against the position midway between the two main nuggets 15 in the longitudinal direction of the structural member. Total length of structural member L: 800mm Spot welding: 50mm pitch Support point: R30 Distance between support points: 700mm Impactor: R50

[0141] The results of the simulation are shown in FIG. Compared to the maximum load of Comparative Example No. 1, the maximum load of Inventive Example No. 2 was improved by 22%, and the maximum load of Inventive Example No. 3 was improved by 50%. [Explanation of symbols]

[0142] 1 Spot welded structure 11 First lap joint 111 First lap joint metal plate 1111 First lap joint cutting section 112 First lap joint nugget 12 Second lap joint 121 Second lap joint metal plate 1211 Second lap joint cutting section 122 Second lap joint nugget 13 Plate-shaped members 131 Cutting part of plate-shaped member 14 Wrap section 15 Main Nugget 151 Main nugget impression 16 Vice Nuggets 161 Secondary nugget impression 17 Adhesive 18 additional nuggets 181 Additional nugget impressions 2 Metal plate with a cutout 21 Cutting section 211 Tip 212 Connection 22 Main body 3 Metal plate without a cutout 4. Body 41 Joint between A-pillar lower and side sill 42 B-pillar and side sill joint 43 B-pillar and roof rail joint 44 Joint between lower A-pillar and upper A-pillar 45 Upper A-pillar and roof rail joint 46 C-pillar and side sill joint

Claims

1. a first lap joint having two or more metal plates; a second lap joint having two or more metal plates; a lap portion where end portions of one or more of the metal plates of the first lap joint and end portions of one or more of the metal plates of the second lap joint are overlapped; a main nugget that joins the first lap joint and the second lap joint at the lap portion; a metal plate-like member overlapped on the first lap joint, the second lap joint, and the lap portion; a plurality of secondary nuggets joining the plate-like member and the first lap joint, and the plate-like member and the second lap joint; Equipped with The number of the metal plates to which the main nugget is joined is three, The main nugget impression is provided only on the metal plates included in the first lap joint or the second lap joint, the plate-like member is located outside the main nugget, The secondary nugget is located outside the lap portion. Spot welded construction.

2. 2. The spot welding structure according to claim 1, wherein the distance between the center of the secondary nugget joining the plate-like member and the first lap joint and the center of the secondary nugget joining the plate-like member and the second lap joint is 200 mm or less.

3. At least one of the metal plates of the first lap joint and the metal plates of the second lap joint has a seam processing portion in the lap portion, Two of the three metal plates joined by the main nugget are arranged on approximately the same plane outside the lap portion.

3. The spot welding structure according to claim 1 or 2.

4. 3. The spot welding structure according to claim 1, wherein the number of bonding interfaces between the first lap joint and the second lap joint is two or more.

5. The spot welded structure is The main nugget joins the two metal plates of the first lap joint and the one metal plate of the second lap joint; and The main nugget joins one of the metal plates of the first lap joint and two of the metal plates of the second lap joint.

3. The spot welding structure according to claim 1, further comprising:

6. The spot welded structure according to claim 1 or 2, further comprising an adhesive between the plate-shaped member and one or both of the first lap joint and the second lap joint.

7. The spot welded structure further includes an additional nugget in the lap portion, The additional nugget joins two or more of the metal plate and the plate-like member included in the lap portion, The plate-like member has an indentation of the additional nugget.

3. The spot welding structure according to claim 1 or 2.

8. The plate-like member is separated from the first lap joint and the second lap joint over the entire lap portion.

3. The spot welding structure according to claim 1 or 2.

9. The first lap joint has a nugget that joins only the metal plates of the first lap joint outside the lap portion, The second lap joint has a nugget that joins only the metal plates of the second lap joint outside the lap portion.

3. The spot welding structure according to claim 1 or 2.

10. the first lap joint and the second lap joint are frame parts of an automobile, The plate-like member is an outer panel part of the automobile.

3. The spot welding structure according to claim 1 or 2.

11. Providing a first lap joint having two or more metal plates and a second lap joint having two or more metal plates; overlapping end portions of one or more of the metal plates of the first lap joint and end portions of one or more of the metal plates of the second lap joint to form a lap portion; a primary spot welding step of welding the first lap joint and the second lap joint together at the lap portion to form a main nugget; a step of overlapping a metal plate-shaped member on the lap portion on which the first lap joint, the second lap joint, and the main nugget are formed; a step of secondary spot welding the plate-like member and the first lap joint, and the plate-like member and the second lap joint, to form a plurality of secondary nuggets; Equipped with The number of the metal plates to be primarily spot welded is three, The welding point in the secondary spot welding is outside the lap portion. A method for manufacturing spot welded structures.

12. A step of preparing a plate set in which two of the metal plates that are components of the first lap joint are overlapped at their ends; A step of overlapping an end portion of one of the metal plates that is a component of a second lap joint onto the end portion of the plate assembly to form a lap portion; a step of primarily spot welding two of the metal plates that are components of a first lap joint and one of the metal plates that are components of the second lap joint at the lap portion to form a main nugget and the first lap joint; a step of overlapping and spot welding one of the metal plates of the second lap joint on which the main nugget is provided and the remaining metal plates of the second lap joint outside the lap portion to form the second lap joint; a step of overlapping a metal plate-shaped member on the lap portion on which the first lap joint, the second lap joint, and the main nugget are formed; a step of secondary spot welding the plate-like member and the first lap joint, and the plate-like member and the second lap joint, to form a plurality of secondary nuggets; Equipped with The number of the metal plates to be primarily spot welded is three, The welding point in the secondary spot welding is outside the lap portion. A method for manufacturing spot welded structures.

13. 13. The method for manufacturing a spot welded structure according to claim 11 or 12, characterized in that the distance between the center of the welding point in the secondary spot welding of the plate-shaped member and the first lap joint and the center of the welding point in the secondary spot welding of the plate-shaped member and the second lap joint is 200 mm or less.

14. A cutting portion is provided on the end portion of one or more of the metal plates of the first lap joint and the metal plates of the second lap joint, When forming the lap portion, two of the three metal plates joined by the main nugget are arranged on approximately the same plane outside the lap portion.

13. The method for manufacturing a spot welded structure according to claim 11 or 12.

15. When forming the lap portion, the lap portion is formed by overlapping two of the metal plates of the first lap joint with one of the metal plates of the second lap joint, and the lap portion is formed by overlapping one of the metal plates of the first lap joint with two of the metal plates of the second lap joint, The primary spot welding is performed on each of the plurality of lap portions. The method for manufacturing a spot welded structure according to claim 11.

16. After forming the main nugget, a step of overlapping the remaining metal plates of the second lap joint onto the one metal plate of the second lap joint on which the main nugget is provided, so as to form an additional lap portion in which one metal plate of the first lap joint and two metal plates that are components of the second lap joint are overlapped; a step of performing a primary spot welding on the additional lap portion to further form the main nugget; The method for manufacturing a spot welded structure according to claim 12, further comprising:

17. 13. The method for manufacturing a spot welded structure according to claim 11 or 12, further comprising a step of applying an adhesive between the plate-shaped member and one or both of the first lap joint and the second lap joint after the primary spot welding and before overlapping the plate-shaped member onto the first lap joint, the second lap joint, and the lap portion on which the main nugget is formed.

18. The method for manufacturing a spot welded structure according to claim 11 or 12, further comprising the step of performing additional spot welding on the lap portion and the plate-like member after the secondary spot welding.

19. 13. The method for manufacturing a spot welded structure according to claim 11 or 12, wherein spot welding of the plate-like member is entirely performed outside the lap portion.

20. the first lap joint and the second lap joint are frame parts of an automobile, The plate-like member is an outer panel part of the automobile.

13. The method for manufacturing a spot welded structure according to claim 11 or 12.

Images