Method for manufacturing a rivet joint, rivet joint and automotive component

Abstract

This invention relates to a method for manufacturing a rivet joint, the rivet joint itself, and automotive components. One embodiment of the method for manufacturing a rivet joint includes: passing the shaft portion of a steel rivet having a shaft portion and a head through a through hole in multiple overlapping sheet metals; clamping the rivet axially between a pair of electrodes; applying pressure and electricity to the rivet through the pair of electrodes to form a deformed portion at the front end of the shaft portion; and cooling the rivet, wherein the Vickers hardness HB of the cooled rivet head satisfies 130≤HB≤330, and the Vickers hardness HA of the deformed portion, the thickness TA of the deformed portion, the Vickers hardness HJ of the axial center and radial center portion of the shaft portion, the diameter DJ of the shaft portion, the Vickers hardness HB of the head, and the thickness TB of the head satisfy HJ×DJ≥4.7×HB×TB and HA×TA≥1.3×HB×TB.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a rivet joint, the rivet joint itself, and automotive components.

[0002] This application is based on and claims priority to Japan Patent Application No. 2021-156655 filed on September 27, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] The application of high-strength steel sheets is being promoted to improve the lightweighting and crash safety of automobiles. However, a problem exists in spot-welded joints made of high-strength steel sheets: when the tensile strength of the base steel sheet exceeds 780 MPa, the cross tensile strength (CTS) decreases. Furthermore, when the tensile strength of the steel sheet exceeds 1500 MPa, there is a tendency for both the cross tensile strength and the tensile shear strength (TSS) to decrease.

[0004] When the strength of a spot weld decreases, the weld may fracture when the component deforms due to impacts or other severe conditions. Therefore, even if the strength of the steel plate is increased, the overall load-bearing capacity of the component may be insufficient. Thus, there is a need for joining methods that improve the strength of joints made of high-strength steel plates.

[0005] As one method to improve the cross tensile strength of a joint, the inventors focus on riveting. Riveting is a joining method as follows: a through hole is formed in a steel plate, a rivet having a head and a shaft is inserted into the through hole, the front end of the rivet's shaft is plastically deformed and flattened at room temperature, and then the steel plate is riveted together through the rivet's head and the plastically deformed portion. The joint obtained by riveting is called a riveted joint.

[0006] Regarding manufacturing methods for riveted joints, techniques such as the following have been disclosed.

[0007] Patent Document 1 discloses a method for joining two or more components together using fasteners. The method is characterized in that each component has a hole, and the components are configured such that the holes overlap to receive the fastener within the holes. The fasteners disposed within the holes are deformed by mechanical pressure and heating, thereby joining the components together. In this method, the fasteners are essentially heated only during the deformation phase, and heat transfer from the fasteners to the joined components is minimized. The fasteners and any of the components are made of the same or similar alloys contained in an intermetallic alloy group, thereby achieving the joining.

[0008] Patent document 2 discloses a riveting method in which the head and front end of a rivet are sandwiched between a pair of electrodes and pressed while being heated by electricity. The method is characterized by a padding portion provided between the back of the rivet head and the material to be riveted for riveting. The padding portion has a small cross-sectional area and has a height such that the shaft portion of the rivet is fully and tightly filled into the rivet hole or, after which, the back of the head contacts the material to be riveted.

[0009] Patent document 3 discloses a method for fastening a rivet, which involves clamping the rivet with an electrode, heating it by resistance heating through an electric current, and then pressing it into shape. The method is characterized in that, after heating by an electric current, the head electrode on the forming side is temporarily separated from the rivet, so that the heating extends to the front end of the rivet.

[0010] Patent document 4 discloses a method for joining components using rivets via electric riveting. The method is characterized by forming at least a portion of a rivet hole, which is formed through at least two components to be joined, into a tapered shape. The rivet is then fitted into this hole, and an electric riveting process is used to expand and deform the rivet's shaft into the shape of the tapered hole. The thermal contraction of the rivet after electric riveting ensures a tight, gapless fit between the rivet's shaft and the tapered hole. Here, the rivet temperature during electric riveting is 700–900°C.

[0011] Patent document 5 discloses a rivet fastening method that uses rivets to join multiple workpieces. The method is characterized by clamping a rivet that passes through multiple workpieces between a pair of electrodes and energizing it under pressure. The rivet softens by heating up due to its own resistance caused by the energization, and the ends of the rivet are riveted.

[0012] Patent document 6 discloses a strain-free composite joining method, characterized in that two riveted parts having annular flanges around a hole are placed opposite each other and joined by resistance spot welding using resistance heating. Then, a pin is inserted into the hole and the pin is heated and pressured using resistance heating to perform riveting.

[0013] Patent document 7 discloses a method for joining high-strength steel plates with excellent tensile and fatigue properties. The method is characterized by using a high-strength steel plate with a tensile strength of 430 to 1000 MPa as the material to be joined, driving a rivet into the overlapping material to make it penetrate through, and deforming the front end of the penetrating rivet to mechanically join the plates.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Publication No. 2006-507128

[0017] Patent Document 2: Japanese Patent Application Publication No. 55-27456

[0018] Patent Document 3: Japanese Patent Application Publication No. 53-78486

[0019] Patent Document 4: Japanese Patent Application Publication No. 61-165247

[0020] Patent Document 5: Japanese Patent Application Publication No. 10-205510

[0021] Patent Document 6: Japanese Patent Application Publication No. 3-216282

[0022] Patent Document 7: Japanese Patent Application Publication No. 2000-202563 Summary of the Invention

[0023] The problem that the invention aims to solve

[0024] The inventors have not identified any examples of riveting joints applied to high-strength sheet metal (especially high-strength metal sheets or steel sheets). Manufacturing rivets from high-strength materials commensurate with the strength of the sheet metal incurs processing costs. Furthermore, when riveting is used to join sheet metal, the number of components increases, raising the manufacturing cost of the joint. On the other hand, the advantages of riveting high-strength sheet metal are unknown. For these reasons, the joining method for high-strength sheet metal is specifically designed as welding (especially spot welding), and there are no examples of riveting joints. For instance, in any of Patent Documents 1-8, the joined materials are all low-strength materials. In particular, the joining method described in Patent Document 8, which involves driving a rivet into a sheet metal without a through hole and making it pass through, cannot be applied to high-strength steel sheets with a tensile strength exceeding 1000 MPa.

[0025] However, the inventors have discovered that the cross tensile strength of a joint (riveted joint) obtained by riveting high-strength steel plates is significantly higher than that of a spot-welded joint. Since riveting mechanically joins steel plates, no embrittlement occurs at the joint, it can be considered that the cross tensile strength (CTS) of the joint made of high-strength steel plates can be maintained at a high level.

[0026] On the other hand, the inventors also discovered that the tensile shear strength of a riveted joint is not necessarily stable, and is therefore lower than that of a spot-welded joint. It can be argued that the lower tensile shear strength of the rivet's shaft portion is due to its lower hardness compared to the spot-welded portion. Furthermore, since there is a gap between the rivet and the sheet metal, the smaller cross-sectional area of ​​the region where shear stress is applied in the riveted joint compared to that in the spot-welded joint also contributes to the reduced tensile shear strength.

[0027] For example, none of Patent Documents 1 through 8 has explored methods for improving TSS. In these documents, the reduction of TSS is not considered a problem, and the mechanism of TSS reduction in riveted joints is not investigated. Furthermore, the inventors have found that the joint strength (TSS and CTS, etc.) of riveted joints obtained by applying these techniques to high-strength steel plates is insufficient. For example, in the joining method described in Patent Document 8, which involves driving a rivet into a plate without a through hole and making it pass through, it is necessary to increase the carbon content and hardenability of the rivet to achieve high strength. However, in such rivets, the hardness distribution after riveting tends to become inappropriate. Therefore, rivet breakage is likely to occur.

[0028] In view of the above, the objective of the present invention is to provide a method for manufacturing a rivet joint that can achieve a stable increase in tensile shear strength (TSS), a rivet joint with a stable increase in TSS, and an automotive component.

[0029] The main points of this invention are as follows.

[0030] (1) A method for manufacturing a riveting joint according to one aspect of the present invention includes: passing the shaft portion of a steel rivet having a shaft portion and a head through a through hole in multiple overlapping plates; clamping the rivet between a pair of electrodes in the axial direction of the rivet; applying pressure and energizing the rivet through the pair of electrodes to form a deformed portion at the front end of the shaft portion; and cooling the rivet, wherein the Vickers hardness HB (HV) of the head of the cooled rivet satisfies 130≤HB≤330, and the Vickers hardness HA (HV) of the deformed portion of the cooled rivet, the thickness TA (mm) of the deformed portion, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following formulas 1 and 2.

[0031] HJ×DJ≥4.7×HB×TB:Equation 1

[0032] HA×TA≥1.3×HB×TB: Equation 2.

[0033] (2) In the manufacturing method of the rivet joint described in (1) above, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet after cooling, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head shall satisfy the following formula 3.

[0034] HJ×DJ≥5.3×HB×TB: Equation 3.

[0035] (3) In the manufacturing method of the rivet described in (1) or (2) above, the Vickers hardness HA (HV) of the deformed part of the rivet after cooling is 310≤HA≤600, and the Vickers hardness HJ (HV) of the part of the shaft of the rivet after cooling, which is the center of the axial direction and the center of the radial direction, is 310≤HJ≤590.

[0036] (4) The manufacturing method of the rivet joint described in any of (1) to (3) above may also include projection welding of the head of the rivet and the plate adjacent to the head.

[0037] (5) In the manufacturing method of the rivet joint described in (4) above, the Vickers hardness HP (HV) of the projection weld portion formed by the projection weld and the Vickers hardness HB (HV) of the head of the rivet after cooling may satisfy the following formula 4.

[0038] 1.4×HB≤HP≤3.2×HB: Equation 4.

[0039] (6) In any of the above-described (1) to (5) manufacturing methods of the rivet joint, one or more of the above-described plates may be high-strength steel plates with a tensile strength of 1180 MPa or higher.

[0040] (7) In any of the manufacturing methods of the rivet joint described in (1) to (6) above, the C content of the rivet is 0.08 to 0.40% by mass.

[0041] (8) In any of the above (1) to (7) manufacturing methods of the rivet joint, the C content, Mn content and B content of the rivet shall satisfy 0.16≤C+(1 / 30)Mn+5B≤0.50.

[0042] (9) Another aspect of the riveting joint of the present invention comprises: multiple overlapping plates, each having a through hole; and a steel rivet having a shaft portion, and a head and a deformed portion disposed at both ends of the shaft portion, the shaft portion passing through the through hole to rivet the multiple plates, wherein the Vickers hardness HB (HV) of the head of the rivet satisfies 130≤HB≤330, and the Vickers hardness HA (HV) of the deformed portion of the rivet, the thickness TA (mm) of the deformed portion, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following formulas A and B.

[0043] HJ×DJ≥4.7×HB×TB:Formula A

[0044] HA×TA≥1.3×HB×TB: Formula B.

[0045] (10) In the rivet joint described in (9) above, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head may satisfy the following formula C.

[0046] HJ×DJ≥5.3×HB×TB:Formula C.

[0047] (11) In the rivet joint described in (9) or (10) above, the Vickers hardness HA (HV) of the deformed part of the rivet satisfies 310≤HA≤600, and the Vickers hardness HJ (HV) of the axial center and radial center of the shaft part of the rivet satisfies 310≤HJ≤590.

[0048] (12) In any of the above (9) to (11), the rivet joint may also have a projection weld portion that joins the head of the rivet with the plate adjacent to the head.

[0049] (13) In the riveted joint described in (12) above, the Vickers hardness HP (HV) of the projection weld and the Vickers hardness HB (HV) of the head of the rivet may satisfy the following formula D.

[0050] 1.4×HB≤HP≤3.2×HB: Formula D.

[0051] (14) In any of the above (9) to (13), the riveting joint may be one of the above plates, which is a high-strength steel plate with a tensile strength of 1180 MPa or more.

[0052] (15) In any of the above (9) to (14), the C content of the rivet may be 0.08 to 0.40% by mass.

[0053] (16) In any of the above (9) to (15), the C content, Mn content and B content of the above rivet can also be such that 0.16≤C+(1 / 30)Mn+5B≤0.50.

[0054] (17) Another aspect of the present invention is an automotive component having a rivet joint described in any one of (9) to (16) above.

[0055] (18) The automotive components described in (17) above can also be bumpers or B-pillars.

[0056] The effects of the invention

[0057] According to the present invention, a method for manufacturing a rivet joint that can achieve a stable increase in tensile shear strength (TSS), a rivet joint with a stable increase in TSS, and an automotive component are provided. Attached Figure Description

[0058] Figure 1A This is a cross-sectional schematic diagram illustrating the manufacturing method of the rivet joint according to this embodiment.

[0059] Figure 1B This is a cross-sectional schematic diagram illustrating the manufacturing method of the rivet joint according to this embodiment.

[0060] Figure 1C This is a cross-sectional schematic diagram illustrating the manufacturing method of the rivet joint according to this embodiment.

[0061] Figure 1D This is a schematic diagram showing the manufacturing method of the rivet joint according to this embodiment and the cross-sectional view of the rivet joint obtained therefrom.

[0062] Figure 2A This is a schematic diagram of the stress distribution when tensile shear stress is applied to a rivet joint.

[0063] Figure 2B This is a schematic diagram of the cross-section of a rivet joint when the shaft breaks due to tensile and shear stress.

[0064] Figure 2C This is a schematic diagram of the cross-section of a rivet joint when the deformed part breaks due to tensile and shear stress.

[0065] Figure 2D This is a schematic diagram of the cross-section of a rivet joint when the head breaks due to tensile and shear stress.

[0066] Figure 3 This is a cross-sectional view showing the size of the through hole according to the different rivet joints of each plate.

[0067] Figure 4 This is a cross-sectional view of a rivet joint that also has adhesive disposed around the through hole.

[0068] Figure 5 It is a three-dimensional view of a bumper that uses rivets and other joining methods.

[0069] Figure 6A This is a cross-sectional diagram of the plate and rivets before projection welding.

[0070] Figure 6BThis is a cross-sectional diagram of the plate and rivets after projection welding is completed.

[0071] Figure 7 This is an enlarged cross-sectional view of the projection weld.

[0072] Figure 8 This is a cross-sectional view showing an example of a mechanism used to prevent rivets from interfering with other components.

[0073] Figure 9 This is a cross-sectional view showing an example of a mechanism used to prevent rivets from interfering with other components.

[0074] Figure 10 This is a cross-sectional view showing an example of a mechanism used to prevent rivets from interfering with other components.

[0075] Figure 11 This is a cross-sectional view of the B-pillar, which is an example of an automotive component in this embodiment.

[0076] Figure 12 This is a cross-sectional view of a bumper, which is an example of an automotive component in this embodiment. Detailed Implementation

[0077] The inventors have conducted extensive and repeated research on a method for obtaining a rivet joint with a consistently improved tensile shear strength (TSS). As a result, a correlation was found between the fracture site of the rivet and the TSS of the rivet joint. When the rivet's shaft fractures due to tensile shear stress, the TSS of the rivet joint decreases. Furthermore, it was found that when the rivet's shaft fractures due to tensile shear stress, the amount of deformation of the rivet joint during the period from the application of tensile shear stress until the rivet fractures is smaller. Moreover, the inventors found that when the deformed portion of the rivet fractures due to tensile shear stress, the TSS value is unstable. Furthermore, the inventors discovered that by controlling the shape and hardness of the rivet, so that the rivet fractures from the head rather than from the shaft or deformed portion, the TSS of the rivet joint can be consistently improved.

[0078] like Figures 1A to 1D As shown, a method for manufacturing a riveted joint (hereinafter, sometimes simply referred to as a riveting joining method) according to one aspect of the present invention, based on the above insights, comprises:

[0079] (S1) The shaft portion 121 of the steel rivet 12 (electrically heated rivet) having a shaft portion 121 and a head 122 is passed through the through hole 111 of the overlapping multiple sheets 11.

[0080] (S2) Clamp the rivet 12 between a pair of electrodes A in the axial direction of the rivet 12;

[0081] (S3) Pressurize and energize the rivet 12 by a pair of electrodes A to form a deformable part 123 at the front end of the shaft 121;

[0082] (S4) Cool the rivet 12.

[0083] Here, the Vickers hardness HB (HV) of the head 122 of the cooled rivet 12 satisfies 130 ≤ HB ≤ 330. Furthermore, the shape and hardness of the cooled rivet 12 satisfy the following Equations 1 and 2.

[0084] HJ×DJ≥4.7×HB×TB:Equation 1

[0085] HA×TA≥1.3×HB×TB: Equation 2

[0086] Here, as Figure 1D As shown, the meanings of the symbols contained in Equations 1 and 2 are as follows.

[0087] HA: Vickers hardness (in HV) of the deformed portion 123 of rivet 12 after cooling.

[0088] TA: In mm, the thickness of the deformed portion 123 of the rivet 12 after cooling.

[0089] HJ: Vickers hardness, measured in HV, at the axial and radial center of the shaft portion 121 of the rivet 12 after cooling.

[0090] DJ: In mm, the diameter of the shaft 121 of rivet 12 after cooling.

[0091] HB: Vickers hardness (in HV) of the head 122 of rivet 12 after cooling.

[0092] TB: In mm, the thickness of the head 122 of rivet 12 after cooling.

[0093] The manufacturing method will now be described in detail.

[0094] First, such as Figure 1A As shown, the shaft portion 121 of the steel rivet 12 is passed through the through hole 111 of the overlapping sheets of plates. Next, as... Figure 1B As shown, rivet 12 is clamped between a pair of electrodes A along its axial direction. Plate 11 serves as the base material for the riveting joint 1. Rivet 12 has a shaft portion 121 and a head 122, the front end of which is plastically deformed due to riveting to form a deformed portion 123. The head 122 serves to clamp (rivet) plate 11 together with the deformed portion 123.

[0095] The composition of the plate 11 is not particularly limited. For example, it is preferable to use a steel plate, especially a high-strength steel plate (e.g., a steel plate with a tensile strength TS of approximately 590 MPa or more), as this can improve the strength of the rivet joint 1. Furthermore, the riveting method of this embodiment does not cause embrittlement of the high-strength steel plate that leads to a decrease in CTS. Therefore, when the riveting method of this embodiment is applied to the joining of high-strength steel plates, a rivet joint 1 with a higher CTS can be provided. When the tensile strength of the high-strength steel plate is 980 MPa or more, the superiority of the riveting method of this embodiment over spot welding becomes more significant regarding CTS. Regarding the strength level of the plate 11, the tensile strength is more preferably 1180 MPa or more, and even more preferably 1500 MPa or more. The upper limit of the tensile strength of the plate 11 is not particularly limited, but it may be, for example, 2700 MPa or less.

[0096] In addition, the sheet material 11 can also be an aluminum sheet, a CFRP sheet, or a titanium sheet, etc. Unlike welding-based joints, in the riveting joint of this embodiment, the material of the sheet material 11 can also be different. For example, it can be a combination of steel sheet and aluminum sheet or a combination of steel sheet and CFRP sheet. There is no particular requirement for the arrangement of the sheet materials, but in the case of sheet materials of different materials, from the viewpoint of avoiding melting of the sheet material with a lower melting point, it is preferable to arrange the sheet material with a lower melting point on the rivet head side. Various surface treatments can also be applied to the sheet material 11. For example, the sheet material 11 can also have a GA coating, a GI coating, an EG coating, a Zn-Al coating, a Zn-Mg coating, a Zn-Ni coating, a Zn-Al-Mg coating, an Al coating, a Zn-based coating (Zn-Fe, Zn-Ni-Fe) alloyed with the base metal by hot stamping, and an Al-based coating (Al-Fe-Si), etc.

[0097] The thickness of the sheet material 11 is not particularly limited, and can be, for example, 0.5mm to 3.6mm. The thickness of the sheet material 11 can also vary. The number of sheets 11 is also not particularly limited. In the description of the riveting connection in this embodiment, it is assumed that the number of sheets 11 is two, but the number can also be three or more. Examples of preferred combinations include two sheets of sheet material with a thickness of approximately 1.6mm and approximately 2.3mm overlapping, or three sheets of sheet material with thicknesses of 0.75mm, 1.8mm, and 1.2mm overlapping. Examples of preferred combinations of sheets include two sheets of sheet material with thicknesses of approximately 0.6mm to 2.9mm overlapping, or three sheets of sheet material with thicknesses of 0.6mm to 1.6mm, 0.6mm to 2.9mm overlapping, and three sheets of sheet material with thicknesses of 0.6mm to 2.9mm overlapping. Sheet metal can also be molded into finished products through cold or hot stamping, cold roll forming, or hydroforming. In addition, sheet metal can also be formed into tubular shapes.

[0098] The configuration of the through hole 111 through which the rivet 12 is inserted is not particularly limited. From the viewpoint that the rivet 12 passes through the through hole 111 without stopping, it is preferable that the diameter of the through hole 111 is larger than the diameter of the shaft portion of the rivet 12 before riveting.

[0099] The through hole 111 can be circular, for example. Alternatively, it can be a polygon such as a quadrilateral, pentagon, hexagon, or octagon. The corners of these polygons can also have curvature. Furthermore, the through hole 111 can be elliptical or have a convex or concave portion within a circle. By making the through hole 111 a shape other than a circle, it is possible to prevent the sheet metal from rotating around the rivet in the through hole after riveting, or to reduce loosening of the joint, which is therefore more preferable.

[0100] The through hole 111 for the rivet 12 can be formed by any method, such as laser cutting, die punching, or drilling. When the sheet 11 is a hot-stamped steel sheet, it is preferable to form the through hole 111 by hot die punching or laser cutting.

[0101] The size of the through hole 111 can also be constant in the depth direction of the plate 11. Alternatively, a stepped or tapered shape with different sizes in the depth direction can be applied to the through hole 111. Furthermore, the central axes of the through holes 111 between multiple joined materials can also be inconsistent.

[0102] The diameter of the through hole 111 in the multiple sheets 11 (when the through hole 111 is not circular, it is the equivalent circle diameter) can be as follows: Figure 1B It can be the same as shown, or as... Figure 3 The difference is not shown. By varying the size of the through holes 111, a stress-relieving effect and improved efficiency in the rivet 12 insertion process can be expected. The degree of variation in the diameter of the through holes 111 is not particularly limited; for example, it is preferable that the diameter difference of the through holes 111 in adjacent plates 11 is in the range of 0.3 mm to 3 mm. From the viewpoint of facilitating the rivet 12 insertion process, it is preferable to increase the diameter of the through hole in the plate opposite to the side that serves as the rivet entry point (the side where the rivet head is located). This prevents the tip of the rivet 12 from becoming blocked in the through hole 111.

[0103] Furthermore, the minimum diameter of the through hole 111 is preferably 0.1 mm to 5 mm larger than the maximum diameter of the shaft portion of the rivet through which it is inserted. This is because if the diameter is less than 0.1 mm, insertion permeability deteriorates; if it is greater than 5 mm, it becomes difficult to adequately fill the gap in the through hole 111. A range of 0.3 mm to 3 mm is more preferred, and a range of 0.5 mm to 2.3 mm is most preferred. Furthermore, the offset of the central axis of the through holes 111 between the plurality of joined materials is preferably within 1.5 mm, and more preferably within 0.75 mm.

[0104] The rivet 12 is made of steel. This ensures excellent joint strength of the rivet joint 1. Other components of the rivet 12 are not particularly limited in the stage prior to riveting. A suitable configuration can be selected so that the shape and hardness of the riveted rivet 12, as described later, satisfy a prescribed relationship. Preferred examples of the configuration of the rivet 12 will be described later.

[0105] Next, as Figure 1C As shown, the rivet 12 is clamped between a pair of electrodes A along its axial direction. Then, pressure and electricity are applied to the rivet 12 via the pair of electrodes A. This causes the rivet 12 to generate resistance heating, softening it and flattening the front end of the shaft portion 121 of the rivet 12 (so-called riveting). As a result, a deformed portion 123 is formed at the front end of the shaft portion 121.

[0106] In the riveting assembly of this embodiment, it is preferable to apply pressure to the rivet 12 using electrode A before energizing the rivet 12. When energizing begins while under pressure, the shaft portion 121 softens and the front end of the shaft portion 121 deforms. At this time, a molten portion may also be generated inside the rivet 12. In this case, the assembly is performed in the following sequence: clamping the rivet 12 between electrodes A, applying pressure to the rivet 12, energizing the rivet 12, and then cooling the rivet 12. However, the timing of starting to heat the rivet 12 and the timing of starting to apply pressure to the rivet 12 are not limited to the preferred example described above.

[0107] Furthermore, in conventional riveting, it is permissible to heat and soften the rivet 12 before inserting the shaft portion 121 of the rivet 12 through the through hole 111 of the plate 11. In the manufacturing method of the riveting joint of this embodiment, the rivet 12 may also be heated, and then the shaft portion 121 of the rivet 12 is inserted through the through hole of the plate 11. After insertion, a pair of electrodes A are energized to generate resistance heating in the rivet 12, softening the rivet 12, deforming the front end of the shaft portion of the rivet, and cooling the rivet. Before insertion, it is sometimes preferable to soften the rivet before insertion, especially when the diameter of the rivet shaft portion is large or the rivet is hard.

[0108] Rivet 12 is cooled after pressure and energization. Therefore, in Figure 1D The cooled steel rivet 12 shown undergoes quenching hardening. The shape and hardness of the cooled rivet 12 must satisfy Equations 1 and 2 below.

[0109] HJ×DJ≥4.7×HB×TB:Equation 1

[0110] HA×TA≥1.3×HB×TB: Equation 2

[0111] Furthermore, in the cooled rivet 12, HB contained in Equations 1 and 2 above must also satisfy 130≤HB≤330.

[0112] The symbol "HA" represents the Vickers hardness of the deformed portion 123 of the rivet 12 after cooling, expressed in HV. Hereinafter, this value HA will be referred to as the "Vickers hardness of the deformed portion 123". The Vickers hardness of the deformed portion 123 is measured in a cross-section of the rivet joint 1 through the shaft of the cooled rivet 12. In this cross-section, the surface of the plate 11 in contact with the deformed portion 123 is considered the boundary between the deformed portion 123 and the shaft portion 121. Furthermore, the measurement position for the Vickers hardness HA of the deformed portion 123 is set at the center of the thickness direction of the deformed portion 123 at both ends of the shaft portion 121. Additionally, the thickness direction of the deformed portion 123 is the same as the axial direction of the rivet 12. For example, in... Figure 1D In the diagram, the point marked with the symbol "HA" is the measurement location for the Vickers hardness HA of the deformed part 123. At this measurement location, the Vickers hardness HA of the deformed part 123 is obtained by measuring the Vickers hardness with a load of 0.5 kgf.

[0113] The symbol "TA" represents the thickness of the deformed portion 123 of the rivet 12 after cooling, in mm. Hereinafter, this value TA will be referred to as the "thickness of the deformed portion 123". The thickness of the deformed portion 123 is obtained by measuring the thickness of both ends of the shaft portion 121 along the axial direction of the rivet 12 in the cut surface of the rivet joint 1 through the shaft of the cooled rivet 12. For example, in... Figure 1DIn the diagram, the arrow marked with the symbol "TA" indicates the measurement location of the thickness TA of the deformed part 123.

[0114] exist Figure 2A The diagram shows the stress distribution when tensile shear stress is applied to riveted joint 1. Figure 2A In the diagram, the white arrows indicate the direction of the tensile shear stress applied to the plate 11, and the black arrows indicate the location and direction of the stress applied by the plate 11 to the rivet 12. Figure 2A As shown, the Vickers hardness HA and thickness TA of the aforementioned deformed portion 123 are measured at the location where the stress is greatest in the deformed portion 123 when the rivet 12 is pulled out from the through hole 111 in the direction from the deformed portion 123 toward the head 122. Therefore, when controlling the fracture mode of the rivet 12, it is most appropriate to use the hardness and thickness of the deformed portion 123 obtained at the aforementioned measurement location.

[0115] The symbol "HJ" represents the Vickers hardness, in units of HV, at the axial and radial center of the shaft portion 121 of the cooled rivet 12. Hereinafter, this value HJ will be referred to as the "Vickers hardness of the shaft portion 121". The Vickers hardness of the shaft portion 121 is measured in a cross-section of the rivet joint 1 through the shaft of the cooled rivet 12. In this cross-section, the surface of the plate 11 that contacts the shaft portion 121 is considered the boundary between the shaft portion 121 and the deformed portion 123, and the surface of the plate 11 that contacts the head 122 is considered the boundary between the shaft portion 121 and the head 122. Furthermore, the position located on the central axis of the shaft portion 121 and at the center of the aforementioned two boundaries is taken as the measurement position for the Vickers hardness HJ of the shaft portion 121. For example, in Figure 1D The point marked with the symbol "HJ" is the measurement location for the Vickers hardness HJ of shaft 121. At this measurement location, the Vickers hardness HJ of shaft 121 is obtained by measuring the Vickers hardness under a load of 0.5 kgf. However, if defects such as cracks or porosity exist at the Vickers hardness measurement location, the measurement should be performed at a location at least 0.2 mm away from the defect.

[0116] The symbol "DJ" represents the diameter of the shaft portion 121 of the rivet 12 after cooling, in mm. Hereinafter, this value DJ will be referred to as the "diameter of the shaft portion 121". When the cooled shaft portion 121 is cylindrical, the diameter of the shaft portion 121 is the minimum width of the shaft portion 121 measured in a direction perpendicular to the axial direction at the cut surface of the rivet head 1 through the shaft of the cooled rivet 12.

[0117] For example, in Figure 1DIn the diagram, the arrow marked with the symbol "DJ" indicates the measurement position of the diameter DJ of the shaft portion 121. With the diameter of the through hole 111 and the diameter of the shaft portion 121 before riveting remaining constant along the axial direction, the diameter of the shaft portion 121 after riveting increases as it approaches the deformed portion 123. This is because, through riveting, the shaft portion 121 expands significantly near the deformed portion 123 to fill the gap between the shaft portion 121 and the through hole 111; on the other hand, the shaft portion 121 hardly expands near the head 122. Therefore, in Figure 1D In this case, the boundary between the head 122 and the shaft portion 121 becomes the measurement position of the diameter DJ of the shaft portion 121. However, when the through hole 111 is tapered, or when the diameters of the through holes 111 provided on multiple plates 11 are different, the position where the width of the shaft portion 121 is the smallest may not be consistent with the boundary between the head 122 and the shaft portion 121.

[0118] If the shaft portion 121 is not cylindrical after cooling, its diameter cannot be determined from the cross-section of the shaft passing through the rivet 12. In this case, firstly, observe the cross-section of the shaft passing through the rivet 12 to determine the position where the diameter of the shaft portion 121 is minimized. Next, at the position where the diameter of the shaft portion 121 is minimized, cut the shaft portion 121 perpendicular to the axis of the rivet 12. The equivalent circle diameter of the cross-section perpendicular to the axis of the rivet 12 is considered as the diameter DJ of the shaft portion 121.

[0119] The location where the Vickers hardness HJ of the aforementioned shaft portion 121 is measured represents the Vickers hardness of the shaft portion 121. Furthermore, the location where the diameter DJ of the aforementioned shaft portion 121 is measured is the location in the shaft portion 121 most prone to fracture. Therefore, when controlling the fracture mode of the rivet 12, using the hardness and diameter of the shaft portion 121 obtained at the aforementioned measurement locations is most appropriate.

[0120] The symbol "HB" represents the Vickers hardness of the head 122 of the rivet 12 after cooling, expressed in HV. Hereinafter, this value HB will be referred to as the "Vickers hardness of the head 122". The Vickers hardness of the head 122 is measured in a cross-section of the rivet joint 1 through the shaft of the cooled rivet 12. In this cross-section, the surface of the plate 11 in contact with the head 122 is considered the boundary between the head 122 and the shaft 121. Furthermore, the measurement location for the Vickers hardness HB of the head 122 is defined as the central portion of the head 122 in the thickness direction at both ends of the shaft 121. Additionally, the thickness direction of the head 122 is the same as the axial direction of the rivet 12. For example, in... Figure 1D In the diagram, the point marked with the symbol "HB" is the measurement location for the Vickers hardness HB of head 122. At this measurement location, the Vickers hardness HB of head 122 is obtained by performing a Vickers hardness test with a load of 0.5 kgf.

[0121] The symbol "TB" represents the thickness of the head 122 of the rivet 12 after cooling, in mm. Hereinafter, this value TB will be referred to as the "thickness of the head 122". The thickness of the head 122 is obtained by measuring the thickness of the head 122 at both ends of the shaft portion 121 along the axial direction of the rivet 12 in the cut surface of the rivet joint 1 through the shaft of the cooled rivet 12. For example, in... Figure 1D In the diagram, the arrow marked with the symbol "TB" indicates the measurement location of the thickness TB of the head 122.

[0122] like Figure 2A As shown, the Vickers hardness HB and thickness TB of the head 122 are measured at the location in the head 122 where the stress is greatest when the rivet 12 is pulled out from the through hole 111 in the direction from the head 122 toward the deformed portion 123. Therefore, using the hardness and thickness of the head 122 obtained at the above-mentioned measurement location is most appropriate when controlling the fracture mode of the rivet 12.

[0123] In the cooled rivet 12, it is necessary to control the shape and hardness of the shaft 121, head 122 and deformable part 123 in order to satisfy Formula 1 and Formula 2.

[0124] HJ×DJ≥4.7×HB×TB:Equation 1

[0125] HA×TA≥1.3×HB×TB: Equation 2

[0126] Equations 1 and 2 are both specifications designed to prevent fracture of the shaft portion 121 and promote fracture of the head portion 122. Specifically, in Equation 1, the Vickers hardness HB and thickness TB of the head portion 122 are specified to be sufficiently small compared to the Vickers hardness HJ and diameter DJ of the shaft portion 121. Furthermore, in Equation 2, the Vickers hardness HB and thickness TB of the head portion 122 are specified to be sufficiently small compared to the Vickers hardness HA and thickness TA of the deformed portion 123. As a result, fracture preferentially occurs in the head portion 122.

[0127] Alternatively, the lower limit of HJ×DJ can be set to 5.3×HB×TB. That is, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft 121 of the rivet 12 after cooling, the diameter DJ (mm) of the shaft 121, the Vickers hardness HB (HV) of the head 122, and the thickness TB (mm) of the head 122 can also satisfy the following formula 3.

[0128] HJ×DJ≥5.3×HB×TB:Equation 3

[0129] Under the condition of satisfying Equation 3 above, the fracture of shaft 121 can be further suppressed. The lower limit value of HJ×DJ can also be set to 5.0×HB×TB, 5.5×HB×TB or 5.8×HB×TB.

[0130] Alternatively, the lower limit of HA×TA can be set to 1.5×HB×TB. This can further suppress the fracture of the shaft 121. The lower limit of HA×TA can also be set to 1.8×HB×TB, 2.0×HB×TB, or 2.5×HB×TB.

[0131] The reasons for the fracture occurring at the head 122 will be explained below. The inventors have conducted extensive research on a method for obtaining a rivet joint with a consistently increased tensile shear strength (TSS). As a result, a correlation was found between the fracture site of the rivet 12 and the TSS of the rivet joint 1. When the shaft portion 121 of the rivet 12 fractures due to tensile shear stress, the TSS of the rivet joint 1 decreases. Furthermore, it was found that when the shaft portion 121 of the rivet 12 fractures due to tensile shear stress, the amount of deformation of the rivet joint 1 during the period from the application of tensile shear stress until the rivet 12 fractures is smaller. Moreover, the inventors also found that when the deformed portion 123 of the rivet 12 fractures due to tensile shear stress, the TSS value is unstable. Furthermore, the inventors found that by controlling the shape and hardness of the cooled rivet 12, so that the rivet 12 fractures at the head 122 instead of at the shaft portion 121 or the deformed portion 123, the TSS of the rivet joint 1 can be consistently increased.

[0132] exist Figures 2A to 2D The diagram shows a cross-sectional view of the rivet 1 under applied tensile shear stress. Figures 2A to 2D In this configuration, the upper plate 11 is pulled to the left, and the lower plate 11 is pulled to the right. As a result, a stress towards the left is applied to the upper part of the shaft portion 121 through the inner wall of the upper through hole 111, and a stress towards the right is applied to the lower part of the shaft portion 121 through the inner wall of the lower through hole 111. Furthermore, a stress towards the lower part is applied to the head 122 through the outer periphery of the lower through hole 111, and a stress towards the upper part is applied to the deformable portion 123 through the outer periphery of the upper through hole 111. This is because a stress similar to pulling the rivet 12 from the through hole 111 is applied to both the head 122 and the deformable portion 123.

[0133] Figure 2B This is a schematic diagram of the rivet joint 1 when the shaft 121 becomes the fracture starting point. Figure 2C as well as Figure 2D These are schematic diagrams of the riveting joint 1 when the deformed portion 123 and the head 122 become the fracture starting point. According to the inventors' experimental results, when the shaft portion 121 becomes the fracture starting point, as... Figure 2BAs shown, the plate 11 hardly deforms before fracture, thus the amount of deformation from the initial application of shear stress to fracture is small. On the other hand, if the deformed portion 123 or the head 122 becomes the fracture initiation point, such as Figure 2C as well as Figure 2D As shown, the plate 11 deforms before fracture, and the rivet 12 tilts, resulting in a large amount of deformation from the start of shear stress until fracture. Furthermore, the TSS when the deformed portion 123 or the head 122 becomes the fracture initiation point is greater than the TSS when the shaft portion 121 becomes the fracture initiation point.

[0134] However, when the deformed portion 123 fractures, the TSS (Total Stability Score) deviates. The deformed portion 123, formed during riveting, has an inconsistent shape and uneven hardness due to significant plastic deformation. This could be a cause of the TSS deviance when the deformed portion 123 fractures. The inventors investigated eliminating the TSS deviance by increasing the size of the deformed portion 123, but in this case, cracks occurred in the deformed portion 123 during riveting. On the other hand, when the head 122 fractures, the TSS consistently remains at a high value.

[0135] According to the inventors' experimental results, it can be confirmed that by controlling the shape and hardness of the shaft portion 121, the head 122, and the deformable portion 123 in a manner that satisfies Formulas 1 and 2, the head 122 is most prone to breakage in the cooled rivet 12. Therefore, in the manufacturing method of the rivet joint 1 of this embodiment, riveting and cooling need to be performed in a manner that satisfies Formulas 1 and 2.

[0136] Furthermore, in the cooled rivet 12, the Vickers hardness HB of the head 122 needs to satisfy 130 ≤ HB ≤ 330. If the Vickers hardness HB of the head 122 exceeds 330, the fracture initiation point of the rivet 12 may be outside the head 122. On the other hand, if the Vickers hardness HB of the head 122 is less than 130, the TSS of the rivet joint 1 decreases. Based on the above reasons, the Vickers hardness HB of the head 122 is 130 or higher and 330 or lower. Alternatively, the Vickers hardness HB of the head 122 can be set to 135 or higher, 150 or higher, or 180 or higher. Alternatively, the Vickers hardness HB of the head 122 can be set to 300 or lower, 280 or lower, or 250 or lower.

[0137] As long as the riveting and quenching of the rivet 12 are carried out in a manner that satisfies the above requirements, the energizing conditions are not particularly limited. The shape and hardness of the cooled rivet 12 can be controlled by the chemical composition of the rivet 12, the strength of the rivet 12, the size of the rivet 12, the pressure and energizing conditions applied to the rivet 12, and the cooling conditions of the rivet 12. Preferred examples of these conditions are described below.

[0138] First, an example of the chemical composition of rivet 12 will be explained. Regarding the chemical composition of rivet 12, for example, it is sufficient that the C content, Mn content, and B content per unit mass % are 0.16 ≤ C + (1 / 30)Mn + 5B ≤ 0.50 or less. By setting C + (1 / 30)Mn + 5B to 0.16 or more, the hardness of rivet 12 can be ensured. On the other hand, by setting C + (1 / 30)Mn + 5B to 0.50 or less, the toughness of rivet 12 can be ensured. Alternatively, C + (1 / 30)Mn + 5B can be set to 0.18 or more, 0.20 or more, or 0.25 or more. Alternatively, C + (1 / 30)Mn + 5B can be set to 0.48 or less, 0.45 or less, or 0.35 or less.

[0139] Alternatively, the carbon content of the rivet 12 can be set to 0.08 to 0.40% by mass. This allows for the formation of a hardened portion in the rivet 12, further improving the joint strength of the rivet joint 1. The carbon content of the rivet 12 can also be set to 0.10% by mass or more, 0.15% by mass or more, or 0.17% by mass or more. Alternatively, the carbon content of the rivet 12 can be set to 0.350% by mass or less, 0.30% by mass or less, or 0.25% by mass or less.

[0140] Next, an example of the shape of the rivet 12 before riveting will be described. Hereafter, unless otherwise specified, all descriptions relating to the example of the shape of the rivet 12 relate to the rivet 12 before the deformed portion 123 is formed by applying pressure and electricity.

[0141] From the viewpoint of ensuring joint strength, the diameter (or equivalent circle diameter of the shaft portion 121 of the rivet 12 before riveting) can be 3 mm or more. Furthermore, if the diameter of the shaft portion 121 is too large, the current density decreases and the rivet becomes difficult to soften. Therefore, the upper limit of the diameter of the shaft portion 121 can be set to 12 mm or less. The length of the shaft portion 121 (the value after deducting the thickness of the head 122 from the length of the rivet 12) needs to be greater than the total thickness of the plate 11. When the rivet 12 has a head 122, it is preferably set within the following range. Additionally, the values ​​included in the following formula are values ​​before riveting.

[0142] Total sheet thickness + shaft diameter × 0.3 ≤ shaft length ≤ Total sheet thickness + shaft diameter × 2.0

[0143] By making the length of the shaft portion 121 of the rivet 12 greater than the total thickness of the sheet metal 11 plus the diameter of the shaft portion 121 × 0.3, the size of the riveted portion (deformed portion 123) after the front end of the shaft portion 121 is deformed can be ensured, thereby further improving the joint strength. By setting the length of the shaft portion 121 to be less than or equal to the total thickness of the sheet metal 11 plus the diameter of the shaft portion 121 × 2.0, manufacturing efficiency can be improved.

[0144] Furthermore, the diameter of the shaft portion 121 can be constant. On the other hand, the rivet 12 can also have a shape in which the diameter of the shaft portion 121 decreases towards the front end of the shaft portion 121 (a so-called conical shape). The conical portion can be formed entirely throughout the shaft portion 121 or only near the front end of the shaft portion 121. A rivet 12 with a conical shape is easier to insert into the through hole 111, and is therefore preferred. In addition, the front end of the shaft portion 121 can be either flat or hemispherical. When the front end of the shaft portion 121 is made hemispherical, it is easier for the shaft portion 121 to insert into the through hole 111, and is therefore preferred.

[0145] The head 122 of the rivet 12 can be any shape other than a typical flange. For example, the head 122 can be hemispherical (so-called round head), disc-shaped (so-called flat head), or have a flat surface and a conical root (so-called countersunk head). The top view of the head 122 can be a polygon, such as a circle, quadrilateral, or hexagon. A positioning recess can also be provided in the center of the electrode side of the head 122. Furthermore, a recess surrounding the shaft portion 121 (so-called undercut support portion) can be provided in the support portion (the surface in contact with the joined material) of the head 122. This recess gives the head 122 elasticity, thereby further increasing the riveting force of the rivet 12. Additionally, one or more protrusions can be provided in the support portion (the surface in contact with the joined material) of the head 122. These protrusions further increase the riveting force of the rivet 12 by pressing into the joined material or forming a joint with the joined material during riveting. Examples of protrusion shapes include circular, polygonal, and annular shapes surrounding the shaft. Additionally, Figure 1D The cross-sectional shape of the head 122 of the rivet 12 illustrated in the example is quadrilateral, but even if the cross-sectional shape of the head 122 is other than this, such as hemispherical, the method for measuring the Vickers hardness HB and the thickness TB of the head 122 is as described above.

[0146] The rivet 12 uses its head 122 to rivet the plate 11. Therefore, the diameter of the head 122 is preferably 1.5 mm or more larger than the diameter of the through hole 111. More preferably, the diameter of the head 122 is 3.0 mm or more larger than the diameter of the through hole 111. Furthermore, the thickness of the head 122 is preferably 0.8 mm to 5 mm. If the thickness of the head 122 is less than 0.8 mm, sufficient joint strength cannot be obtained. On the other hand, if the thickness of the head 122 exceeds 5 mm, the fracture initiation point may be outside the head 122.

[0147] The rivet 12 can be manufactured, for example, by cutting and machining the coiled wire or by cold forging. From a productivity point of view, cold forging is preferred for machining the cut coiled wire. The rivet 12 can be used directly in its machined state, but if joint strength is particularly important, the machined or cold-forged rivet can be subjected to heat treatment such as quenching and tempering. This heat treatment increases the overall hardness of the rivet 12, including the head 122, thereby further improving the joint strength.

[0148] Rivet 12 may not require surface treatment, but surface treatment may be performed if corrosion resistance is required. For example, rivet 12 may be coated with zinc, aluminum, chromium, nickel, or chromate.

[0149] Next, an example of the energizing and pressurizing conditions for the rivet 12 will be explained. The rivet 12 is preferably energized to the point of hardening. However, the temperature required for hardening varies depending on the composition of the rivet 12 (e.g., carbon content and carbon equivalent). Therefore, the heating temperature can be appropriately selected based on the composition of the rivet 12. For example, it is preferable that the maximum temperature reached by the shaft portion 121 of the rivet 12 exceeds 900°C. However, if the A3 point of the rivet 12 is low, the maximum temperature reached by the shaft portion 121 can be less than 900°C. Furthermore, regarding the head 122 of the rivet, since hardening is not necessary, its maximum temperature can be above 900°C or below 900°C. Additionally, the maximum temperature reached by the shaft portion 121 of the rivet 12 can be estimated by observing the metal microstructure of its cross-section. For example, if the rivet 12 is made of an iron alloy and a martensitic structure is formed in the shaft portion, it can be estimated that the maximum temperature reached by the shaft portion of the rivet 12 is approximately 900°C or higher. Furthermore, if the rivet 12 is made of an iron alloy and a molten solidified portion is formed in the shaft portion 121, it can be estimated that the maximum temperature reached by the shaft portion 121 of the rivet 12 is 1530°C or higher.

[0150] After the plates 11 are overlapped, rivets 12 are inserted into the through holes 111, for example, using a rivet supply device. Then, for example, a spot welding machine is used to apply pressure to the rivets while simultaneously heating them with an electric current. Alternatively, after the plates 11 are overlapped, rivets 12 are positioned on the electrode A of a spot welding robot, which has a mechanism for holding the head 122 of the rivets, for example, using a rivet supply device. Then, by moving the spot welding robot, the rivets 12 on the electrode A are inserted into the through holes 111. Then, the rivets are applied pressure to the rivets while simultaneously heating them with an electric current. The specific energizing conditions (current value, voltage value, and energizing time, etc.) for heating the rivets 12 to the temperature required for quenching, as well as the pressure conditions for the rivets 12, are not particularly limited and can be appropriately selected according to the shape and material of the rivets 12. Those skilled in the art can study the optimal pressure and energizing conditions corresponding to the shape and material of the rivets 12 by applying pressure and electricity to the rivets 12 under various conditions.

[0151] Applying pressure and energizing the rivet 12 is preferably performed using a pair of electrodes A. The configuration of the pair of electrodes A is not particularly limited. For example, electrodes used for spot welding can apply pressure and energize, and therefore can also be used for rivet joining in this embodiment. The shape of the electrodes A can be appropriately selected according to the shape of the rivet 12. For example, the electrodes A can also be flat electrodes, single R-type, CF-type, and DR-type, etc. Examples of materials for the electrodes A include chromium copper, alumina-dispersed copper, and chromium-zirconium copper, which have excellent conductivity. Furthermore, it is preferable to have a mechanism on one side of the pair of electrodes A that holds the rivet head until joining by means of a magnet, a mechanical holding mechanism, or a vacuum. Examples of materials for the electrodes A include chromium copper, alumina-dispersed copper, and chromium-zirconium copper, which have excellent conductivity. Moreover, the shape and material of the pair of electrodes A can also be different.

[0152] Examples of power sources for welding machines include single-phase AC, DC inverters, and AC inverters. Examples of welding torch types include fixed-position, C-type, and X-type torches. The pressure applied by the electrode to the rivet is, for example, 150 kgf to 1000 kgf. The pressure is preferably 250 kgf to 600 kgf. To obtain a good joint without cracks, it is preferable to increase the pressure as the rivet's shaft diameter increases. The pressure setting can be constant, but it can also be varied during energization as needed. From the viewpoint of obtaining a good joint, it is preferable that the direction of electrode pressure on the rivet is at an angle of 10° or less relative to the axial extension direction of the rivet. More preferably, the angle between the pressure direction and the axial direction of the rivet is 4° or less.

[0153] The energizing time is, for example, 0.15 seconds to 2 seconds. The energizing time is preferably 0.2 seconds to 1 second. The number of energizing cycles can be once (so-called single energizing), but multi-stage energizing (two-stage, three-stage, etc.) is also possible as needed. Furthermore, pulse energizing, uphill energizing with a gradually increasing current, and downhill energizing with a gradually decreasing current are also possible. Additionally, a higher current can be flowed in the first half of the energizing process to rapidly heat the rivet, and the current can be reduced in the second half to deform it. Furthermore, when the rivet's shaft diameter is large, it is preferable to flow a lower current value for a longer period in the first half of the energizing process than in the second half, thereby heating the rivet uniformly, and then increasing the current value in the second half to deform the rivet. On the other hand, as described above, the rivet 12 can also be heated by a mechanism other than resistance heating. In this case, the mechanism for applying pressure to the rivet 12 for riveting is not limited to a pair of electrodes A. By combining the energizing conditions and the cooling conditions described later, it is easy to obtain a hardness distribution that satisfies Equations 1 and 2.

[0154] The softened rivet 12 is pressurized to deform the front end of its shaft portion 121, and then the rivet 12 is cooled. This allows multiple sheets of sheet metal 11 to be joined together by riveting the rivet 12. Specifically, the multiple sheets of sheet metal 11 are riveted together using the head 122 of the rivet 12 and the flattened front end (i.e., the deformed portion 123) of the shaft portion 121. Furthermore, by cooling the rivet 12, the austenite generated in the metal structure of the rivet 12 during heating undergoes a martensitic phase transformation. This allows a hardened portion to be formed in the center of the shaft portion 121, increasing the Vickers hardness (i.e., the Vickers hardness HJ of the shaft portion 121) of the cooled rivet 12 at its axial and radial center.

[0155] By heating and cooling the rivet 12 as described above, the Vickers hardness HJ (HV) of the shaft portion 121 of the rivet 12 after cooling can be made to be 310 or higher and 590 or lower. Setting the Vickers hardness HJ of the shaft portion 121 to 310 or higher easily satisfies Equation 1 above. On the other hand, setting the Vickers hardness HJ of the shaft portion 121 to 590 or lower prevents embrittlement of the shaft portion 121 and further improves the TSS of the rivet joint 1. The Vickers hardness HJ of the shaft portion 121 can also be set to 320 or higher, 350 or higher, or 400 or higher. Alternatively, the Vickers hardness HJ of the shaft portion 121 can be set to 570 or lower, 550 or lower, or 530 or lower.

[0156] Furthermore, the Vickers hardness HA (HV) of the deformed portion 123 of the cooled rivet 12 can be set to 310 or higher and 600 or lower. By setting the Vickers hardness HA of the deformed portion 123 to 310 or higher, it is easy to satisfy Equation 2 above. On the other hand, by setting the Vickers hardness HA of the deformed portion 123 to 600 or lower, embrittlement of the deformed portion 123 can be avoided, and the TSS of the rivet joint 1 can be further improved. The Vickers hardness HA of the deformed portion 123 can also be set to 320 or higher, 350 or higher, or 400 or higher. The Vickers hardness HA of the deformed portion 123 can be set to 580 or lower, 550 or lower, or 530 or lower.

[0157] The cooling conditions for the rivet 12 are not particularly limited, but for example, the cooling rate of the rivet 12 between 800 and 500°C can be specified as 50°C / second or more, more preferably 100°C / second or more, and most preferably 150°C / second or more. As a result, a martensitic phase transformation occurs in the center of the shaft portion 121 of the rivet 12, and it is easy to obtain a hardness distribution that satisfies Formula 1 and Formula 2.

[0158] To ensure that the cooling conditions of the rivet 12 are within the aforementioned range, it is preferable to accelerate the cooling of the rivet 12. For example, accelerated cooling can be achieved by extending the holding time of electrode A. The holding time refers to the time from the end of the current flow for joining until the electrode is released. Refrigerant flows inside electrode A. After energizing, the rivet 12 can be accelerated by bringing electrode A into contact with it. By accelerating the cooling of the rivet 12, it can be hardened, further improving the joint strength. However, if the holding time (holding time) for accelerating cooling is too long, productivity decreases. Therefore, the holding time is preferably set to 3 seconds or less after energizing is completed. The holding time is more preferably 0.01 seconds or more and 1.00 seconds or less. The holding time is most preferably 0.10 seconds or more and 0.80 seconds or less.

[0159] In the manufacturing method of the rivet joint according to this embodiment, other joining methods may also be used in combination. By combining two or more different joining methods, the joining strength of the rivet joint can be further improved.

[0160] For example, the riveting joining method of this embodiment may further include joining multiple plates 11 by one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding (e.g., MAG welding, MIG welding, CO2 welding, and plasma welding). Welding can be performed before or after riveting joining. From the viewpoint of improving the assembly accuracy of the components, it is preferable to perform riveting joining after welding. In the case of spot welding, riveting joining can be performed simply after spot welding. Alternatively, riveting joining can be performed after spot welding, followed by spot welding.

[0161] Furthermore, the riveting method of this embodiment may further include: applying adhesive 13 around the periphery of at least the through hole 111 between multiple sheets 11, and then overlapping the multiple sheets 11. Thus, as Figure 4 As shown, the sheet 11 is bonded. The thickness of the adhesive is not particularly specified, but can be 0.03 mm or more and 1.5 mm or less. If it is too thin, poor adhesion will occur; if it is too thick, the bond strength will decrease. The adhesive 13 needs to be applied before overlapping multiple sheets 11 and before the rivet 12 is passed through the sheets 11. In the case of thermosetting adhesives, the adhesive 13 can also be cured by heating for coating curing on an electrodeposition coating production line after the rivet is joined. In the case of reaction-curing adhesives, the adhesive 13 is cured over time after the rivet is joined. Furthermore, in spot welding of the sheet 11, it is sometimes necessary to separate the area coated with adhesive 13 from the spot weld area to prevent bursting. However, in the rivet joining method of this embodiment, bursting does not occur, thus having the advantage that the area coated with adhesive 13 is not limited. By using both the rivet 12 and the adhesive 13, the rigidity of the joint can be further improved. Furthermore, by using rivets 12 and adhesive 13 together, contact corrosion of the overlapping surfaces can be prevented in the joining of dissimilar metals and the joining of metal and CFRP. In addition to adhesive 13, a sealant can also be applied between the plates 11. The sealant improves the water resistance and corrosion resistance of the rivet joint 1. Furthermore, in the case of joining dissimilar metals and joining metal and CFRP, at least one side of the metal plate can be chemically converted and coated before rivet joining. This further suppresses contact corrosion between dissimilar materials and improves corrosion resistance.

[0162] like Figure 6A as well as Figure 6B As shown, the manufacturing method of the rivet joint may further include: projecting a weld on the head 122 of the rivet 12 and the plate 11 adjacent to the head 122. The resulting rivet joint 1 has a welded portion 14 that joins the head 122 to the plate 11. The welded portion 14 further disperses the stress when tensile shear stress is applied to the rivet joint 1, thereby further improving the TSS of the rivet joint 1.

[0163] Furthermore, projection welding can be performed either before or after the plates 11 are aligned. For example, as... Figure 6A as well as Figure 6BAs shown, one approach is to first pass the shaft portion 121 of the rivet 12 through the through hole 111 of a sheet metal 11, then perform projection welding on the head 122 of the rivet 12 to the sheet metal 11, and then pass the shaft portion 121 of the rivet 12 through the through holes 111 of the remaining sheet metal 11. In this case, the sheet metal 11 is overlapped after projection welding. This allows the shaft portion 121 to pass through the through holes 111 of multiple overlapping sheet metal 11s. Alternatively, multiple sheet metal 11s can be overlapped first, then the shaft portion 121 can be passed through the through holes 111 of multiple sheet metal 11s, and then the head 122 of the rivet 12 can be projection welded to the sheet metal 11. In this case, projection welding is performed after the sheet metal 11s are overlapped. The timing of the projection welding can be appropriately selected based on the manufacturing apparatus of the rivet joint 1.

[0164] There are no particular limitations on the conditions for projection welding. For example, projection welding is preferably performed in such a way that the Vickers hardness HP (HV) of the projection weld portion 14 and the Vickers hardness HB (HV) of the head 122 in the cooled rivet 12 satisfies the following formula 4.

[0165] 1.4×HB≤HP≤3.2×HB: Equation 4

[0166] Here, as Figure 7 As shown, HP refers to the Vickers hardness of the weld projection 14 measured at a point 0.2 mm away from the contact surface between the head 122 and the plate 11 towards the head 122. Furthermore, the weld projection 14 can be composed of weld metal or a solid-state bonding surface. In either case, the measurement location for the Vickers hardness HP of the weld projection 14 is as described above.

[0167] By setting the Vickers hardness HP of the projection weld 14 to 1.4 × HB or higher, the head 122 is less likely to separate from the plate 11 when tensile shear stress is applied to the rivet joint 1. This further improves the stress relief effect of the projection weld 14. On the other hand, by setting the Vickers hardness HP of the projection weld 14 to 3.2 × HB or lower, low-temperature cracking of the projection weld 14 can be suppressed, further improving the stress relief effect of the projection weld 14. Furthermore, when projection welding is performed between the rivet 12 and the plate 11, such as... Figure 6A As shown, a protrusion 1221 is preferably provided on the support surface of the head 122 of the rivet 12 before projection welding. The support surface is the surface of the head 122 that contacts the plate 11.

[0168] Next, another embodiment of the riveting joint of the present invention will be described. For example... Figure 1DAs shown, the riveting joint 1 of this embodiment includes: multiple overlapping plates 11, each having a through hole 111; and a rivet 12, having a shaft portion 121, and a head 122 and a deformable portion 123 provided at both ends of the shaft portion 121. The shaft portion 121 passes through the through hole 111 and rivets the multiple plates 11. Here, the Vickers hardness HB (HV) of the head 122 of the rivet 12 satisfies 130≤HB≤330, and the Vickers hardness HA (HV) of the deformable portion 123 of the rivet 12, the thickness TA (mm) of the deformable portion 123, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion 121, the diameter DJ (mm) of the shaft portion 121, the Vickers hardness HB (HV) of the head 122, and the thickness TB (mm) of the head 122 satisfy the following formulas A and B.

[0169] HJ×DJ≥4.7×HB×TB:Formula A

[0170] HA×TA≥1.3×HB×TB:Formula B

[0171] The composition of the multiple sheet metal plates 11 is not particularly limited. Furthermore, the composition of the through holes 111 formed in the sheet metal plates 11 for the insertion of rivets 12 is also not particularly limited. These specific examples are detailed in the description of the manufacturing method of the rivet joint according to this embodiment.

[0172] The diameters of the through holes 111 in the multiple sheets 11 (or equivalent circle diameter if the through hole 111 is not circular) can be the same or different. By varying the size of the through holes 111, stress relief and efficiency improvements in the rivet 12 insertion process can be expected. The degree of difference in the diameter of the through holes 111 is not particularly limited, but for example, it is preferable that the diameter difference of the through holes 111 in adjacent sheets 11 is in the range of 0.3 mm to 3 mm.

[0173] Rivet 12 is a component whose shaft portion 121 passes through the through hole 111 and rivets multiple sheets of metal 11 together. Therefore, rivet 12 has a head 122 and a deformable portion 123 provided at both ends of the shaft portion 121. The shaft portion 121 is inserted into the through hole 111 of the multiple sheets of metal 11, and the head 122 and the deformable portion 123 clamp the multiple sheets of metal 11, thereby riveting the multiple sheets of metal 11 together. The deformable portion 123 is formed by flattening the front end of the shaft portion 121. Furthermore, the head 122 and the deformable portion 123 can be easily distinguished, for example, based on metal flow and the degree of surface oxidation. Alternatively, the portion with the higher Vickers hardness can be considered the deformable portion 123.

[0174] Specific examples of the composition (shape, material, and surface treatment, etc.) of the rivet 12 are detailed in the description of the manufacturing method of the rivet joint according to this embodiment. For example, the carbon content of the rivet 12 is preferably 0.08 to 0.40% by mass. The carbon content of the rivet 12 may also be 0.10% by mass or more, 0.15% by mass or more, or 0.17% by mass or more. The carbon content of the rivet 12 may also be 0.350% by mass or less, 0.30% by mass or less, or 0.25% by mass or less. Furthermore, the C content, Mn content, and B content per unit mass% of the rivet 12 may also satisfy 0.16 ≤ C + (1 / 30)Mn + 5B ≤ 0.50. C + (1 / 30)Mn + 5B may also be 0.18 or more, 0.20 or more, or 0.25 or more. C + (1 / 30)Mn + 5B may also be 0.48 or less, 0.45 or less, or 0.35 or less.

[0175] In rivet 12, the Vickers hardness HA of the deformed part 123, the thickness TA of the deformed part 123, the Vickers hardness HJ of the shaft part 121, the diameter DJ of the shaft part 121, the Vickers hardness HB of the head 122, and the thickness TB of the head 122 satisfy the following formulas A and B.

[0176] HJ×DJ≥4.7×HB×TB:Formula A

[0177] HA×TA≥1.3×HB×TB:Formula B

[0178] The methods for determining the values ​​contained in these formulas are the same as those described in the manufacturing method of the rivet joint. According to the inventors' experimental results, it can be confirmed that by controlling the shape and hardness of the shaft portion 121, the head 122, and the deformed portion in a manner that satisfies Formula A and Formula B, the head 122 is most prone to breakage in the cooled rivet 12.

[0179] Alternatively, the lower limit of HJ×DJ can be set to 5.3×HB×TB. That is, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion 121 of the cooled rivet 12, the diameter DJ (mm) of the shaft portion 121, the Vickers hardness HB (HV) of the head 122, and the thickness TB (mm) of the head 122 can also satisfy the following formula C.

[0180] HJ×DJ≥5.3×HB×TB:Formula C

[0181] Under the condition of satisfying the above formula C, the fracture of shaft 121 can be further suppressed. The lower limit value of HJ×DJ can also be set to 5.0×HB×TB, 5.5×HB×TB, or 5.8×HB×TB.

[0182] Alternatively, the lower limit of HA×TA can be set to 1.5×HB×TB. This can further suppress the fracture of the shaft 121. The lower limit of HA×TA can also be set to 1.8×HB×TB, 2.0×HB×TB, or 2.5×HB×TB.

[0183] Furthermore, in rivet 12, the Vickers hardness HB of the head 122 needs to satisfy 130 ≤ HB ≤ 330. If the Vickers hardness HB of the head 122 exceeds 330, the fracture initiation point of rivet 12 may be outside the head 122. On the other hand, if the Vickers hardness HB of the head 122 is less than 130, the TSS of the rivet joint 1 decreases. Based on the above reasons, the Vickers hardness HB of the head 122 is set to 130 or higher and 330 or lower. Alternatively, the Vickers hardness HB of the head 122 can be set to 135 or higher, 150 or higher, or 180 or higher. Alternatively, the Vickers hardness HB of the head 122 can be set to 300 or lower, 280 or lower, or 250 or lower.

[0184] The interior of the rivet 12 can also be hardened. Therefore, the Vickers hardness HJ (HV) of the axially oriented and radially oriented portion of the rivet 12, i.e., the Vickers hardness HJ of the shaft portion 121, can be 310 or higher and 590 or lower. By setting the Vickers hardness HJ of the shaft portion 121 to 310 or higher, it is easy to satisfy the above formula A. On the other hand, by setting the Vickers hardness HJ of the shaft portion 121 to 590 or lower, embrittlement of the shaft portion 121 can be avoided, and the TSS of the rivet joint 1 can be further improved. The Vickers hardness HJ of the shaft portion 121 can also be set to 320 or higher, 350 or higher, or 400 or higher. The Vickers hardness HJ of the shaft portion 121 can also be set to 570 or lower, 550 or lower, or 530 or lower.

[0185] Furthermore, the Vickers hardness HA (HV) of the deformed portion 123 of the rivet 12 can be set to 310 or higher and 600 or lower. By setting the Vickers hardness HA of the deformed portion 123 to 310 or higher, it is easy to satisfy the above formula B. On the other hand, by setting the Vickers hardness HA of the deformed portion 123 to 600 or lower, embrittlement of the deformed portion 123 can be avoided, and the TSS of the rivet joint 1 can be further improved. The Vickers hardness HA of the deformed portion 123 can also be set to 320 or higher, 350 or higher, or 400 or higher. The Vickers hardness HA of the deformed portion 123 can also be set to 580 or lower, 550 or lower, or 530 or lower.

[0186] One or more of the sheet metal 11 can be steel plates. In particular, when the sheet metal 11 and the rivet 12 are made of high-strength steel (e.g., steel with a tensile strength of 980 MPa or higher), the strength of the rivet joint 1 can be significantly improved. Furthermore, unlike spot welds, the rivet 12 does not cause the steel to become brittle, thus preventing a decrease in CTS (Complex Strength Tolerance). Moreover, unlike conventional rivets, the rivet 12 of the rivet joint in this embodiment has a higher TSS (Tolerance to Steel Strain), making it suitable for joining high-strength steel plates.

[0187] Furthermore, the rivet joint 1 may further have an adhesive 13 disposed around at least the through hole 111 between the multiple plates 11. The rivet joint 1 may further have one or more welded parts selected from the group consisting of spot welded parts, laser welded parts, and arc welded parts. As described above, by combining multiple joining methods, the joint strength of the rivet joint 1 can be further improved. The rivet joint 1 may further have a sealant disposed between the multiple plates 11. This can improve the water resistance and corrosion resistance of the rivet joint 1. In addition, as an adhesive layer, a resin adhesive tape such as an ionomer can also be used. In addition, the sealant can also be applied in a manner that covers the head and / or deformed part of the rivet. This can prevent water from entering from the gap between the head and / or deformed part of the rivet and the metal or CFRP.

[0188] exist Figure 5 An example of a riveted joint 1 (bumper) using rivets 12 and other joining methods is shown. Figure 5 As shown, the rivet 12 of this embodiment can also be used in areas where the stress of the load is expected to increase during a collision. Figure 5 The black circle portion in the middle) is joined, and other joining methods are used in other parts (e.g., spot welded part 2 formed by low-cost spot welding) ( Figure 5 (The white circle part in the middle).

[0189] In the riveting joint 1 of this embodiment, the rivet 12 has a head 122 and a deformable portion 123 disposed at both ends of the shaft portion 121. Here, it is also possible to... Figures 8-10 As shown, in a cross-sectional view parallel to the axis of the shaft portion 121 of the rivet 12, the top surface of the head 122 and / or the deformed portion 123 is positioned closer to the shaft portion 121 than a position 0.6 mm away from the surface of the plate 11 near the rivet 12 towards the side away from the shaft portion 121, in the direction along the axis of the shaft portion 121. Here, the surface (outer surface) of the plate 11 refers to the surface of the plate 11 that does not contact other plates. Therefore, it is possible to suppress the head 122 and / or the deformed portion 123 from protruding from the plate 11 (or, to suppress the height of the protrusion to within 0.6 mm), and to suppress interference between the head 122 and / or the deformed portion 123 and other components.

[0190] exist Figure 8 as well as Figure 10 In the example, the top surface of the deformed portion 123 of the rivet 12 is positioned closer to the shaft portion 121 than the surface 112 (outer surface) of the plate near the rivet 12. Figure 9 In the example, the top surfaces of the head 122 and the deformed portion 123 of the rivet 12 are located relative to the plates near the rivet 12, on the side closer to the axis 121 than the surfaces 112 (outer surfaces) of these plates. Here, the surface 112 (outer surface) of the plates refers to the surface of each plate that does not contact other plates. Furthermore, in Figures 8-10 In this configuration, the top surface of the head 122 and / or the deformable portion 123 is positioned closer to the shaft portion 121 than the outer surface of the plate surface 112 near the rivet 12, but the top surface of the head 122 and / or the deformable portion 123 can also extend a maximum of 0.6 mm beyond the plate surface 112. That is, in Figures 8-10 Even if the top surface of the head 122 and / or the deformed part 123 protrudes 0.6 mm from the dotted line, the effect of suppressing interference with other components can still be achieved.

[0191] Before or after joining the sheet metal 11 using the above method, the sheet metal 11 can also be stamped, thereby positioning the top surface of the head 122 and / or the deformed portion 123 further from the shaft portion 121 than a position 0.6 mm away from the surface 112 of the sheet metal 11 near the rivet 12. Figure 8 In the example, the plate 11 disposed on the deformable part 123 side of the two plates 11 deforms towards the deformable part 123 side near the rivet 12. Figure 9 In the example, the plate on the head 122 side of the two plates deforms towards the head 122 side near the rivet 12, and the plate on the deformed part 123 side of the two plates deforms towards the deformed part 123 side near the rivet 12. Figure 10 In the example, the plate 11 located on the deformable portion 123 side of the two plates 11 deforms towards the deformable portion 123 side near the rivet 12, and the plate 11 located on the head 122 side deforms correspondingly to the other plate 11 near the rivet 12. Furthermore, Figures 8-10 The dashed lines indicate the surfaces that correspond to surface 112 of the board.

[0192] The rivet joint 1 may further include a projection weld 14 that joins the head 122 of the rivet 12 with the plate 11 adjacent to the head 122. The projection weld 14 further disperses the stress when tensile shear stress is applied to the rivet joint 1, thereby further improving the TSS of the rivet joint 1.

[0193] The Vickers hardness HP (HV) of the projection weld 14 and the Vickers hardness HB (HV) of the head 122 of the rivet 12 can also satisfy the following formula D.

[0194] 1.4×HB≤HP≤3.2×HB:Formula D

[0195] Here, HP is the Vickers hardness of the weld projection 14, measured at a point 0.2 mm away from the contact surface between the head 122 and the plate 11 towards the head 122. Furthermore, the weld projection 14 can be composed of weld metal or a solid-state bonding surface. In either case, the measurement location for the Vickers hardness HP of the weld projection 14 is as described above. HP is measured using a Vickers hardness test with a load of 0.5 kgf.

[0196] By setting the Vickers hardness HP of the projection weld 14 to 1.4 × HB or higher, the head 122 is less likely to separate from the plate 11 when tensile shear stress is applied to the riveting joint 1. This further improves the stress mitigation effect of the projection weld 14. On the other hand, by setting the Vickers hardness HP of the projection weld 14 to 3.2 × HB or lower, cracking of the projection weld 14 can be suppressed, further improving the stress mitigation effect of the projection weld 14.

[0197] Other automotive components of the present invention have the riveted joint of this embodiment. Therefore, the automotive component of this embodiment has higher joint strength. The automotive component of this embodiment is, for example, a bumper and B-pillar, components that are important for ensuring collision safety. Figure 11 The diagram shows a cross-sectional view of the B-pillar, an example of a vehicle component according to this embodiment. Figure 12 The diagram shows a cross-sectional view of a bumper, which is an example of an automotive component according to this embodiment. Alternatively, the A-pillar, lower side beam, floor beam, front longitudinal beam, rear longitudinal beam, front suspension tower cover, tunnel reinforcement, front bulkhead, torque box, seat frame, seat rails, battery housing frame, and the joints between these pillars (the joint between the B-pillar and the lower side beam, the joint between the B-pillar and the roof longitudinal beam, and the joint between the roof crossbeam and the roof longitudinal beam) can also be considered automotive components according to this embodiment.

[0198] Example

[0199] Various steel rivets of different compositions, shapes, and processing methods were inserted into through holes in two hot-stamped high-strength steel plates with a tensile strength of 2400 MPa. Then, these rivets were pressurized and energized using a spot welding machine to create a riveted joint. For some rivets, projection welding was performed to join their heads to the steel plates.

[0200] The steel plate is 1.6 mm thick. Its composition is 0.45C-0.5Mn with added Si, Cr, Ti, Nb, and B. The electrodes used for riveting are made of a Cr-Cu alloy. The rivet joining conditions and projection welding conditions are described below.

[0201] ●Conditions of rivet engagement

[0202] • Pressure applied: 400 kgf

[0203] • Power-on time: Adjustable within the range of 0.30 seconds to 0.50 seconds.

[0204] • Current value: Adjustable within the range of 5kA to 10kA

[0205] • Holding time: 0.5 seconds

[0206] ● Projection soldering conditions

[0207] • Pressure applied: 400 kgf

[0208] • Power-on time: 0.1 seconds

[0209] • Current value: Adjustable within the range of 10kA to 13kA

[0210] The Vickers hardness HA, thickness TA, shaft hardness HJ, shaft diameter DJ, head Vickers hardness HB, and head thickness TB of various riveting joints obtained by the above method were measured and recorded in Table 1. For riveting joints with projection welding, the Vickers hardness HP of the projection weld was also measured by the above method and recorded in Table 1. Furthermore, Table 2 shows the determination results of whether the above values ​​satisfy the following formula.

[0211] HJ×DJ≥4.7×HB×TB:Equation 1 (Equation A)

[0212] HA×TA≥1.3×HB×TB:Equation 2 (Equation B)

[0213] 1.4×HB≤HP≤3.2×HB:Equation 4 (Equation D)

[0214] The tensile shear strength (TSS) of various rivet joints obtained by the above method was evaluated by tensile shear test. The tensile shear test was conducted according to JIS Z 3136:1999 "Test piece size and test method for shear test of resistance spot weld and projection weld joints". Rivet joints that meet the following two conditions are considered to have a consistently increased TSS.

[0215] (Condition 1) TSS exceeds 1.3 × DJ × TB

[0216] (Condition 2) The fracture formed by the tensile shear test is located at the head of the rivet.

[0217] In addition, the fracture site of the rivet after the test can be observed to confirm whether the fracture is located at the head of the rivet or at the deformed part.

[0218] A rivet joint that meets condition 1 can be considered to have high resistance to tensile shear stress. In addition, TSS is greatly affected by the shape of the rivet, so when judging whether TSS has improved, the pass / fail benchmark is set as a function of the diameter DJ of the shaft 121 and the thickness TB of the head 122.

[0219] Furthermore, a rivet joint that satisfies condition 2 can be considered to have a stable increase in tensile shear stress. Regarding rivets where the fracture occurs at the deformed portion of the rivet, it is presumed that the TSS deviates after multiple tensile shear tests; therefore, even if the TSS satisfies condition 1 above, it is not considered to have a stable increase in TSS.

[0220] [Table 1]

[0221] HA(HV) HJ(HV) HB(HV) HP(HV) TA(mm) DJ(mm) TB (mm) 1 435 445 205 - 2.0 3.8 1.2 2 441 438 212 - 2.2 5.9 2.0 3 425 420 195 - 3.1 8.2 2.8 4 592 585 301 - 2.2 6.0 2.0 5 521 531 278 - 2.2 6.0 2.0 6 385 372 172 - 2.2 6.0 2.0 7 318 319 156 - 2.2 6.0 2.0 8 430 420 135 - 2.3 5.9 1.9 9 527 537 321 - 2.2 6.2 1.9 10 435 448 198 - 2.6 6.0 2.0 11 452 438 186 - 1.2 6.0 2.0 12 453 433 149 471 2.2 6.0 2.0 13 378 377 260 378 2.5 6.9 1.8 14 515 550 355 - 1.6 6.6 1.9 15 142 137 105 - 2.2 6.0 2.0 16 354 365 240 - 1.2 7.0 2.0 17 320 320 97 - 2.2 5.9 2.0 18 439 433 224 458 2.2 5.0 1.8 19 153 158 131 155 2.4 8.0 1.8 20 618 589 230 - 2.3 6.0 2.0

[0222] [Table 2]

[0223]

[0224] For rivet joints with a Vickers hardness HB (HV) of 130 to 330 that satisfy Equation 1 and Equation 2, the TSS is steadily increased.

[0225] On the other hand, in Example 14, where the Vickers hardness HB of the head is excessive and does not satisfy Equation 2, the fracture portion forms at the deformed portion. Although Example 14 has a high TSS, it is presumed that a deviation in TSS will occur when multiple rivet joints are manufactured under the conditions of Example 14.

[0226] In Example 15, where the Vickers hardness HB of the head is insufficient and Equation 1 is not satisfied, the fracture occurs at the axial portion, resulting in an extremely low TSS.

[0227] In Example 16, which does not satisfy Equation 2, the fracture portion forms in the deformed portion, resulting in a lower TSS.

[0228] In Example 17, where the Vickers hardness HB at the head was insufficient, the TSS was low. Although the TSS of Example 17 was higher than that of Example 15 because the fracture occurred at the head, the TSS of Example 17 did not meet the acceptance criteria due to the insufficient Vickers hardness HB at the head.

[0229] Explanation of symbols

[0230] 1: Rivet joint; 11: Plate; 111: Through hole; 112: Plate surface; 12: Rivet; 121: Shaft; 122: Head; 1221: Protrusion; 123: Deformed part; 13: Adhesive; 14: Projection weld; 2: Spot weld; A: Electrode; HA: Vickers hardness of deformed part 123; TA: Thickness of deformed part 123; HJ: Vickers hardness of shaft 121; DJ: Diameter of shaft 121; HB: Vickers hardness of head 122; TB: Thickness of head 122.

Claims

1. A method for manufacturing a riveted joint, comprising: The shaft portion of the steel rivet, which has a shaft portion and a head, is passed through a through hole in multiple overlapping sheets of sheet metal. The aforementioned rivet is clamped between a pair of electrodes along its axial direction; By applying pressure and energizing the rivet using a pair of electrodes, a deformable portion is formed at the front end of the shaft portion; and The rivets are cooled. The Vickers hardness HB (HV) of the head of the rivet after cooling satisfies 130 ≤ HB ≤ 330. The Vickers hardness HA (HV) of the deformed portion of the rivet after cooling, the thickness TA (mm) of the deformed portion, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following Equations 1 and 2. HJ×DJ≥4.7×HB×TB:Equation 1 HA×TA≥1.3×HB×TB: Equation 2.

2. The manufacturing method of the riveted joint according to claim 1, wherein, The Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet after cooling, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following formula 3. HJ×DJ≥5.3×HB×TB: Equation 3.

3. The method for manufacturing a riveted joint according to claim 1 or 2, wherein, After cooling, the Vickers hardness HA (HV) of the deformed portion of the rivet satisfies 310 ≤ HA ≤ 600. The Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet after cooling is 310 ≤ HJ ≤ 590.

4. The method for manufacturing a riveted joint according to claim 1 or 2, wherein, The manufacturing method of the above-mentioned rivet joint further includes projection welding of the head of the rivet and the plate adjacent to the head.

5. The method for manufacturing a riveted joint according to claim 4, wherein, In the cooled rivets, the Vickers hardness HP (HV) of the projection weld portion formed by the projection weld and the Vickers hardness HB (HV) of the head satisfy the following formula 4. 1.4×HB≤HP≤3.2×HB: Equation 4.

6. The method for manufacturing a riveted joint according to claim 1 or 2, wherein, One or more of the aforementioned plates are high-strength steel plates with a tensile strength of 1180MPa or higher.

7. The method for manufacturing a riveted joint according to claim 1 or 2, wherein, The carbon content of the above rivets is 0.08–0.40% by mass.

8. The method for manufacturing a riveted joint according to claim 1 or 2, wherein, The C, Mn, and B contents of the above rivets satisfy 0.16≤C+(1 / 30)Mn+5B≤0.

50.

9. A riveting joint, comprising: Multiple overlapping sheets of material, each with through holes; and A steel rivet has a shaft portion, and heads and deformed portions located at both ends of the shaft portion. The shaft portion passes through the through hole to rivet together multiple sheets of sheet metal. The Vickers hardness HB (HV) of the head of the aforementioned rivet satisfies 130 ≤ HB ≤ 330. The Vickers hardness HA (HV) of the deformed portion of the rivet, the thickness TA (mm) of the deformed portion, the Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following formulas A and B. HJ×DJ≥4.7×HB×TB:Formula A HA×TA≥1.3×HB×TB: Formula B.

10. The riveting joint according to claim 9, wherein, The Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet, the diameter DJ (mm) of the shaft portion, the Vickers hardness HB (HV) of the head, and the thickness TB (mm) of the head satisfy the following formula C. HJ×DJ≥5.3×HB×TB:Formula C.

11. The riveting joint according to claim 9, wherein, The Vickers hardness HA (HV) of the deformed portion of the rivet described above satisfies 310 ≤ HA ≤ 600. The Vickers hardness HJ (HV) of the axial center and radial center of the shaft portion of the rivet satisfies 310 ≤ HJ ≤ 590.

12. The riveting joint according to claim 9, wherein, The aforementioned rivet joint also includes a projection weld portion that joins the head of the rivet to the plate material adjacent to the head.

13. The riveting joint according to claim 12, wherein, The Vickers hardness HP (HV) of the aforementioned projection weld and the Vickers hardness HB (HV) of the aforementioned head of the aforementioned rivet satisfy the following formula D. 1.4×HB≤HP≤3.2×HB: Formula D.

14. The riveting joint according to claim 9, wherein, One or more of the aforementioned plates are high-strength steel plates with a tensile strength of 1180MPa or higher.

15. The riveting joint according to claim 9, wherein, The carbon content of the above rivets is 0.08–0.40% by mass.

16. The riveting joint according to claim 9, wherein, The C, Mn, and B contents of the above rivets satisfy 0.16≤C+(1 / 30)Mn+5B≤0.

50.

17. An automotive component, wherein, The riveting joint is provided according to any one of claims 9 to 16.

18. The automotive component according to claim 17, wherein, The aforementioned automotive components are bumpers or B-pillars.

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