Method for manufacturing fastening structure

Abstract

To provide a manufacturing method of a fastening structure which can suppress, when a member fastened by a self-piercing rivet and contacting with a tip side of the self-piercing rivet is a die cast product, cracking of a die cast product caused by implantation of the self-piercing rivet to be capable of improving producibility.SOLUTION: A manufacturing method of a fastening structure comprises the steps of: forming a first member 12 through die casting at a molding process; and implanting a self-piercing rivet 16 from a second member 14 side into an overlapped part 40 where the second member 14 is overlapped with the first member 12 while heat generated at the formation of the first member 12 remains at an implantation process after the molding process. Thereby, the self-piercing rivet 16 is implanted into the first member 12 at high ductility state relative to a state at the normal temperature so that the first member 12 becomes hard to crack at the implantation process.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a fastening structure. [Background technology]

[0002] Patent Document 1 listed below discloses a technique for joining (fastening) a pair of overlapping plate materials with a self-piercing rivet. Briefly describing this prior art, a self-piercing rivet uses a hollow leg to drill holes in the pair of plate materials to join them. In this prior art, the ductility of the joint is increased by heating the joint joined by the self-piercing rivet, thereby reducing the risk of fracture (cracks) at the joint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-188383 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when joining (fastening) objects with a self-piercing rivet, the part that comes into contact with the tip of the self-piercing rivet may be a die-cast product. In such cases, the above-mentioned prior art may be applicable, but there is room for improvement in terms of improving manufacturing efficiency.

[0005] In consideration of the above, an object of the present invention is to provide a method for manufacturing a fastening structure that can improve manufacturing efficiency while suppressing cracking of the die-cast product caused by driving the self-piercing rivet, when the component that comes into contact with the tip side of the self-piercing rivet among the objects to be fastened with the self-piercing rivet is a die-cast product. [Means for solving the problem]

[0006] The method for manufacturing a fastening structure of the present invention described in claim 1 includes a molding step of molding a first member by die-casting, and a driving step of driving a self-piercing rivet into a portion where a second member is overlapped on the first member from the side of the second member after the molding step, while heat from the molding process remains in the first member.

[0007] According to the above configuration, the first member is formed by die casting in the molding step. In the driving step following the molding step, a self-piercing rivet is driven from the second member into the overlapping portion where the second member is superimposed on the first member while heat from molding remains in the first member. As a result, the self-piercing rivet is driven into the first member when the first member is in a state where it is more ductile than at room temperature, making the first member less likely to crack in the driving step. In other words, the heat imparted to the first member during molding can be effectively utilized to prevent cracking of the first member. Furthermore, in this method for manufacturing a fastened structure, the driving step is performed without waiting for the first member to cool after the molding step, making effective use of the time it takes for the first member to cool and shortening the manufacturing time of the fastened structure.

[0008] The method for manufacturing a fastening structure of the present invention described in claim 2 is configured as described in claim 1, and in the driving process, the portion of the first member that overlaps with the second member is heated from a support member that supports the first member from the side opposite the driving side of the self-piercing rivet.

[0009] According to the above configuration, during the driving step, the portion of the first member that overlaps with the second member is heated by a support member that supports the first member from the side opposite the driving side of the self-piercing rivet. This further increases the ductility of the first member during the driving step, making the first member even less likely to crack during the driving step. Furthermore, because heat from its forming remains in the first member, the amount of heat required to ensure good ductility of the first member can be reduced. [Effects of the Invention]

[0010] As described above, the method for manufacturing a fastening structure of the present invention has the excellent effect of making it possible to improve manufacturing efficiency while suppressing cracking of the die-cast product caused by driving the self-piercing rivet, when the component that is in contact with the tip side of the self-piercing rivet among the objects to be fastened with the self-piercing rivet is a die-cast product. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a portion of a fastening structure manufactured by a fastening structure manufacturing method according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a state before a self-piercing rivet is driven into the overlapping portion of the first member and the second member. [Figure 3] 1 is a cross-sectional view showing an example of a molding die used in a molding step in a method for manufacturing a fastening structure according to one embodiment, together with a first member. [Figure 4] 1 is a cross-sectional view showing an example of a fastening device used in a driving step in a manufacturing method for a fastened structure according to one embodiment, together with a first member, a second member, and a self-piercing rivet. FIG. [Figure 5] 1 is a cross-sectional view showing a driving step in a manufacturing method of a fastening structure according to one embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] A method for manufacturing a fastening structure according to one embodiment of the present invention will be described with reference to FIGS.

[0013] 1 shows a cross-sectional view of a portion of a fastened structure 10 manufactured by the method for manufacturing a fastened structure according to this embodiment. The fastened structure 10 has a first member 12, a second member 14, and a self-piercing rivet 16.

[0014] The first member 12 and the second member 14 are both made of metal. More specifically, the first member 12 is made of an aluminum alloy, for example, and the second member 14 is made of steel, for example. The first member 12 is a die-cast product formed by die-casting. The first member 12 and the second member 14 are, for example, vehicle components.

[0015] The self-piercing rivet 16 is made of special steel such as chrome-molybdenum steel and includes a head 16A and a leg 16B that extends cylindrically from the head 16A. As shown in Fig. 2, before the self-piercing rivet 16 is driven into the overlapping portion 40 of the first member 12 and the second member 14, the inner diameter of the tip of the leg 16B gradually increases toward the tip. The tip of the leg 16B is shaped in this manner to make it easier to deform the tip of the leg 16B in the direction that expands the diameter when the self-piercing rivet 16 is driven into the members.

[0016] Next, an example of an apparatus used in a method for manufacturing the fastening structure 10 (see FIG. 1) will be described with reference to FIGS.

[0017] 3 shows an example of a molding die 20 of a mold device used in the molding step in the manufacturing method of a fastening structure. The molding die 20 includes a first molding die 22 and a second molding die 24. When the first molding die 22 and the second molding die 24 are closed, a molding cavity 26 is formed between the first molding die 22 and the second molding die 24. Molten metal (aluminum alloy in this embodiment) is injected into the cavity 26.

[0018] Fig. 4 shows an example of a fastening device 30 used in the driving step in the manufacturing method of a fastened structure. In this embodiment, the fastening device 30 shown in Fig. 4 is installed in a location relatively close to the molding die 20 shown in Fig. 3.

[0019] As shown in Figure 4, the fastening device 30 includes a die 32 as a support member that supports the first member 12 from the side opposite to the side where the self-piercing rivet 16 is driven. The die 32 is made of, for example, steel, and has a general support surface 32A that supports the first member 12 from below. The die 32 also has a recess 32B that comes into contact with the deformed portion of the first member 12 when the first member 12 is deformed by driving the self-piercing rivet 16. The recess 32B is recessed relative to the general support surface 32A and is circular in plan view.

[0020] The die 32 also has a built-in heater 34, which is provided at a position corresponding to the recess 32B. The heater 34 is shown schematically in the drawing. The heater 34 is connected to a power source (not shown) and is capable of increasing its temperature by energizing it. The heater 34 is configured to be energizable by user operation or automatic control.

[0021] The fastening device 30 also includes a cylinder 36 and a punch 38. The cylinder 36 is cylindrical and allows the self-piercing rivet 16 to be inserted therein. The cylinder 36 is positioned so that its axis corresponds to the center of the recess 32B of the die 32, and presses the first member 12 and the second member 14 supported by the die 32 against the general support surface 32A of the die 32. The punch 38 is a cylindrical member that can be moved axially within the cylinder 36 by a driving device (not shown), and is configured to press the self-piercing rivet 16 inserted into the cylinder 36 from above. In the drawing, the direction in which the punch 38 presses the self-piercing rivet 16 is indicated by arrow P.

[0022] Next, a method for manufacturing a fastening structure will be described with reference to Figures 3 to 5. This method for manufacturing a fastening structure includes a molding step and a driving step.

[0023] 3, in the molding step, the first member 12 is molded by die casting. More specifically, in this molding step, the first molding die 22 and the second molding die 24 are closed together, and molten metal (aluminum alloy in this embodiment) is forced into the cavity 26. The molten metal forced into the cavity 26 is then solidified to form the first member 12, after which the first molding die 22 and the second molding die 24 are opened and the first member 12 is removed from the molding die 20.

[0024] In the driving step after the molding step, while heat from the molding process remains in first member 12 shown in Fig. 4, self-piercing rivet 16 is driven from the second member 14 side into overlapping portion 40 where second member 14 is overlapped on first member 12, as shown in Fig. 5. An example of this driving step will be described in more detail.

[0025] 4, the first member 12 is supported on the general support surface 32A of the die 32, and the second member 14 is placed on top of the first member 12. In this embodiment, as an example, the end portion of the first member 12 is supported by the die 32. Next, the first member 12 and the second member 14 are sandwiched between the lower end surface of the cylinder 36 and the general support surface 32A of the die 32.

[0026] Next, the heater 34 is energized to generate heat, thereby heating the die 32. Note that the timing at which energization of the heater 34 begins may be before the first member 12 and the second member 14 are sandwiched between the lower end surface of the cylinder 36 and the general support surface 32A of the die 32. Next, the self-pierce rivet 16 inside the cylinder 36 is pressed from above with the punch 38.

[0027] As a result, as shown in Figure 5, the self-piercing rivet 16 is lowered, the leg 16B of the self-piercing rivet 16 pierces the second member 14, and the first member 12, pressed by the self-piercing rivet 16 and the second member 14, is deformed toward the recess 32B of the die 32. A portion of the first member 12 deforms along the recess 32B, and the tip side of the leg 16B of the self-piercing rivet 16 is expanded in diameter and deformed as it bites into the first member 12. At this time, the heat generated by the heater 34 heats the deformed portion of the first member 12 that overlaps with the second member 14 from the recess 32B of the die 32. The cylinder 36 and punch 38 are then raised, and the fastened structure 10 shown in Figure 1 is removed from the fastening device 30.

[0028] 5 is performed while heat from the forming process remains in the first member 12, so the self-piercing rivet 16 is driven into the first member 12 when it is in a state where it is more ductile than at room temperature. This makes the first member 12 less likely to crack during the driving process. In other words, the heat imparted to the first member 12 during the forming process of the first member 12 can be effectively used to prevent cracking of the first member 12.

[0029] In addition, in this embodiment, in the driving step, the heater 34 generates heat from the recess 32B of the die 32 to heat the portion of the first member 12 that overlaps with the second member 14, so that the ductility of the first member 12 in the driving step can be further increased, making the first member 12 even less likely to crack in the driving step. In addition, because heat from the forming process remains in the first member 12, the amount of heat required to ensure good ductility of the first member 12 can be reduced.

[0030] Furthermore, in this embodiment, the manufacturing time of the fastening structure 10 (see FIG. 1 ) can be shortened. To further explain this point, for example, if the first member 12 is a large part, it takes time for the first member 12 formed by die casting to cool. However, in this embodiment, the first member 12 and the second member 14 are fastened (joined) together without waiting for the molding heat of the first member 12 to cool, so that the time until the molding heat of the first member 12 cools can be effectively utilized. Note that the first member 12 may not be a large part, but may be a patch.

[0031] In addition, in this embodiment, the molding process and the driving process are performed in close proximity to each other, which reduces the labor required for transportation, thereby improving productivity. This is particularly effective when the first member 12 is a large component.

[0032] As described above, according to the manufacturing method of the fastening structure of this embodiment, when the member that is to be fastened with self-piercing rivet 16 and that comes into contact with the tip side of self-piercing rivet 16 is a die-cast product, it is possible to improve manufacturing efficiency while suppressing cracks in the die-cast product that are caused by driving in self-piercing rivet 16.

[0033] 1 to 5, the method for manufacturing a fastening structure may further include a heating step, after the molding step and before the self-piercing rivet 16 is driven into the overlapping portion 40, of separately heating the portion of the first member 12 that overlaps with the second member 14 from the side opposite to the second member 14. In this type of modification, the fragile portion of the first member 12 is heated separately, further increasing the ductility of the fragile portion of the first member 12.

[0034] In addition, in the above embodiment, the first member 12 is heated from the recess 32B of the die 32 during the driving process. However, as a variation of the above embodiment, for example, the heater (34) built into the die (32) may also be arranged near the general support surface (32A) of the die (32), and the first member (12) may be heated from the general support surface (32A) and the recess (32B) of the die (32).

[0035] As a modification of the above embodiment, a configuration may be adopted in which the first member 12 is not heated from the die 32 serving as a support member in the driving step.

[0036] The above-described embodiment and the above-described modifications can be implemented in appropriate combinations.

[0037] Although one example of the present invention has been described above, the present invention is not limited to the above, and it goes without saying that the present invention can be implemented in various modified forms within the scope of the gist of the present invention. [Explanation of symbols]

[0038] 10 Fastening structure 12 First member 14 Second member 16 Self-piercing rivets 32 Die (support member) 40 Overlapping section

Claims

1. a molding step of molding the first member by die casting; a driving step of driving a self-piercing rivet into an overlapping portion where a second member is overlapped on the first member from the second member side after the molding step while heat generated during molding remains in the first member; A method for manufacturing a fastening structure comprising:

2. 2. The method for manufacturing a fastening structure according to claim 1, wherein in the driving step, a portion of the first member that overlaps with the second member is heated from a support member that supports the first member from the side opposite to the driving side of the self-piercing rivet.

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