MANUFACTURING METHOD FOR FASTENING STRUCTURE

Abstract

In a casting step, a first member is cast by die casting. In the driving step after the casting step, a self-piercing rivet is driven into, from a second member side, an overlapping part in which the second member overlaps the first member, while heat from casting remains in the first member. As a result, the self-piercing rivet is driven into the first member in a state that the ductility is higher than that at the normal temperature. Therefore, the first member is less likely to crack during the driving step.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2023-045967 filed on Mar. 22, 2023 incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a manufacturing method for a fastening structure.

2. Description of Related Art

The following Japanese Unexamined Patent Application Publication No. 2010-188383 (JP 2010-188383 A) discloses a technique for joining (fastening) a pair of joined plate materials that overlaps each other by using a self-piercing rivet. To briefly explain the prior art, the self-piercing rivet is used to join the joined plate materials by boring a hole in the joined plate materials by using a hollow leg part. In this prior art, the ductility of the joint to be joined using the self-piercing rivet is increased by heating the joint, thereby suppressing the occurrence of breakage (cracking) at the joint.

SUMMARY

By the way, among the objects to be joined (fastened) with the self-piercing rivet, the member that comes into contact with the tip side of the self-piercing rivet may be a die casting product. Although the above-mentioned prior art may be applied in such a case, there is room for improvement in terms of improving manufacturing efficiency.

In consideration of the above facts, an object of the present disclosure is to obtain a manufacturing method for a fastening structure that can improve manufacturing efficiency while suppressing cracking in a die casting product that is caused by driving of a self-piercing rivet when a member that is in contact with a tip side of the self-piercing rivet among the objects to be fastened with the self-piercing rivet is the die casting product.

A manufacturing method for a fastening structure of the present disclosure according to claim 1 includes a casting step for casting a first member by die casting, and a driving step for driving a self-piercing rivet into, from a second member side, an overlapping part in which the second member overlaps the first member, while heat from casting remains in the first member after the casting step.

According to the above configuration, the first member is cast by die casting in the casting step. In the driving step after the casting step, a self-piercing rivet is driven into, from a second member side, an overlapping part in which the second member overlaps the first member, while heat from casting remains in the first member. As a result, the self-piercing rivet is driven into the first member in a state that the ductility is higher than that at the normal temperature. Therefore, the first member is less likely to crack during the driving step. That is, cracking of the first member can be suppressed by effectively utilizing the heat applied to the first member during casting of the first member. In addition, in this manufacturing method for a fastening structure, the driving step is executed without waiting until the first member cools down after the casting step. Therefore, the time until the first member cools down can be effectively utilized, and a manufacturing time of the fastening structure can be shortened.

In the manufacturing method for a fastening structure of the present disclosure according to claim 2, in the configuration according to claim 1, a part of the first member overlapped by the second member is heated from a support member that supports the first member from a side opposite to a side on which the self-piercing rivet is to be driven into the overlapping part in the driving step.

According to the above configuration, a part of the first member overlapped by the second member is heated from a support member that supports the first member from a side opposite to a side on which the self-piercing rivet is to be driven into the overlapping part in the driving step. Therefore, the ductility of the first member in the driving step can be further increased, and the first member becomes even more difficult to crack in the driving step. Further, since the heat from the casting remains in the first member, the amount of heating required to ensure good ductility of the first member can be suppressed.

As explained above, according to the manufacturing method for a fastening structure of the present disclosure, when the member 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 casting product, the manufacturing method for a fastening structure has an excellent effect of making it possible to improve manufacturing efficiency while suppressing cracking in the die casting product that is caused by driving of the self-piercing rivet.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a sectional view showing a part of a fastening structure manufactured by a manufacturing method for a fastening structure according to an embodiment;

FIG. 2 is a sectional view showing a state before a self-piercing rivet is driven into the overlapping part of the first member and the second member;

FIG. 3 is a sectional view showing an example of a molding die used in a casting step in a manufacturing method for a fastening structure according to an embodiment, together with a first member;

FIG. 4 is a cross-sectional view showing an example of a fastening device used in a driving step in a manufacturing method for a fastening structure according to an embodiment, together with a first member, a second member, and a self-piercing rivet; and

FIG. 5 is a cross-sectional view showing a driving step in a manufacturing method for a fastening structure according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

A manufacturing method for a fastening structure according to an embodiment of the present disclosure will be described using FIGS. 1 to 5.

FIG. 1 shows a part of a fastening structure 10 manufactured by the manufacturing method for a fastening structure according to the present embodiment in a cross-sectional view. The fastening structure 10 includes a first member 12, a second member 14, and a self-piercing rivet 16.

The first member 12 and the second member 14 are both made of metal. More specifically, the first member 12 is made of aluminum alloy, for example, and the second member 14 is made of steel, for example. Moreover, the first member 12 is a die casting product formed by die casting. The first member 12 and the second member 14 are, for example, members for a vehicle.

The self-piercing rivet 16 is made of special steel such as chromium molybdenum steel. The self-piercing rivet 16 includes a head 16A and a cylindrical leg portion 16B extending from the head 16A. As shown in FIG. 2, before the self-piercing rivet 16 is driven into the overlapping part 40 of the first member 12 and the second member 14, the inner diameter of the distal end side of the leg portion 16B increases toward the distal end. It is being gradually expanded. The reason why the distal end side of the leg portion 16B is formed in this way is to make it easier to deform the distal end side of the leg portion 16B in the direction of expanding the diameter when driving the self-piercing rivet 16 into the member.

Next, an example of an apparatus used in the method of manufacturing the fastening structure 10 (see FIG. 1) will be described with reference to FIGS. 3 and 4.

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

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

As shown in FIG. 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 driving side of the self-piercing rivet 16. The die 32 is made of steel, for example, and has a general support surface 32A that supports the first member 12 from below. Further, the die 32 is formed with a recess 32B that comes into contact with the deformed portion when the first member 12 is deformed by driving the self-piercing rivet 16. The recess 32B is recessed with respect to the general support surface 32A, and is formed in a circular shape in a plan view.

Furthermore, the die 32 has a built-in heater 34, and this heater 34 is provided at a position corresponding to the recess 32B. Note that the heater 34 is schematically shown in the figure. The heater 34 is connected to a power source (not shown), and can raise its temperature by being energized. The heater 34 is configured to be energized by a user's operation or by automatic control.

The fastening device 30 also includes a cylinder 36 and a punch 38. The cylinder 36 is formed into a cylindrical shape, and the self-piercing rivet 16 can be inserted into the cylinder 36. Further, the cylinder 36 is arranged so that its axis corresponds to the center of the recess 32B of the die 32, and the first member 12 and the second member 14 supported by the die 32 are placed on the general support surface 32A side of the die 32. to press against. The punch 38 is a cylindrical member that is movable in the axial direction within the cylinder 36 by a drive device (not shown), and configured to be able to press the self-piercing rivet 16 inserted into the cylinder 36 from above. In addition, in the figure, the direction in which the punch 38 presses the self-piercing rivet 16 is indicated by an arrow P.

Next, a manufacturing method for a fastening structure will be described with reference to FIGS. 3 to 5. This manufacturing method for a fastening structure includes a casting step and a driving step.

As shown in FIG. 3, in the casting step, the first member 12 is molded by die casting. More specifically, in this casting step, the first molding mold 22 and the second molding mold 24 are closed, and molten metal (aluminum alloy in this embodiment) is press-fitted into the cavity 26. The first member 12 is molded by solidifying the molten metal press-fitted into the cavity 26, and then the first molding mold 22 and the second molding mold 24 are opened to mold the first member 12. It is taken out from the molding die 20.

In the driving step after the casting step, as shown in FIG. 5, the self-piercing rivet 16 is driven into, from the second member 14 side, the overlapping part 40 in which the second member 14 overlaps the first member 12, while heat from casting remains in the first member 12 shown in FIG. 4. An example of this driving step will be explained in more detail.

First, as shown in FIG. 4, the first member 12 is supported by the general support surface 32A of the die 32, and the second member 14 is superimposed on the first member 12. In this embodiment, as an example, an 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.

Next, the die 32 is heated by energizing the heater 34 and causing the heater 34 to generate heat. Note that the timing to start energizing the heater 34 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-piercing rivet 16 inside the cylinder 36 is pushed from above with the punch 38.

As a result, as shown in FIG. 5, the self-piercing rivet 16 goes down, the leg portion 16B of the self-piercing rivet 16 penetrates the second member 14, and the first member 12 pressed by the self-piercing rivet 16 and the second member 14 deforms toward the recess 32B side of the die 32. A portion of the first member 12 is deformed along the recess 32B, and the distal end side of the leg portion 16B of the self-piercing rivet 16 bites into the first member 12 while being deformed to expand in diameter. At this time, the deformed portion of the first member 12 that overlaps with the second member 14 is heated from the recess 32B of the die 32 by the heat generated by the heater 34. Thereafter, the cylinder 36 and the punch 38 are raised, and the fastening structure 10 shown in FIG. 1 is taken out from the fastening device 30.

In this embodiment, the driving step shown in FIG. 5 is performed while the heat from the forming process remains in the first member 12, so the first member 12 is in a state where the ductility is higher than that at room temperature. The self-piercing rivet 16 is driven in. Therefore, the first member 12 becomes difficult to break during the driving step. That is, cracking of the first member 12 can be suppressed by effectively utilizing the heat applied to the first member 12 during molding of the first member 12.

Further, in this embodiment, in the driving step, the portion of the first member 12 that overlaps with the second member 14 is heated from the recess 32B of the die 32 by the heat generated by the heater 34, so that the ductility of the first member 12 can be further increased during the driving step, and the first member 12 becomes even more difficult to crack during the driving step. Moreover, since the heat from the molding process remains in the first member 12, the amount of heating required to ensure good ductility of the first member 12 can be suppressed.

Moreover, in this embodiment, the manufacturing time of the fastening structure 10 (see FIG. 1) can be shortened. To further explain this point, for example, when the first member 12 is a large part, it takes time for the first member 12 molded by die casting to cool down, but in this embodiment, since the first member 12 and the second member 14 are fastened (joined) without waiting for the molding heat of the first member 12 to cool down, the time until the molding heat of the first member 12 cools down can be effectively utilized. Note that the first member 12 may be a patch instead of a large component.

Furthermore, in this embodiment, the casting step and the driving step are performed in locations close to each other, so that the effort required for transportation can be reduced. Thereby, productivity can be improved. This effect is particularly great when the first member 12 is a large component.

As explained above, according to the manufacturing method for a fastening structure of the present embodiment, when the member to be fastened with the self-piercing rivet 16 that is in contact with the tip side of the self-piercing rivet 16 is a die casting product, It becomes possible to improve manufacturing efficiency while suppressing cracking of the die casting product due to driving of the self-piercing rivet 16.

As a modification of the above embodiment shown in FIGS. 1 to 5, in the manufacturing method for a fastening structure, a configuration may also be adopted in which after the casting step and before driving the self-piercing rivet (16) into the overlapping part (40), a heating step of separately heating a portion of the first member (12) that overlaps with the second member (14) from the side opposite to the second member (14) side is further included. In such a modification, the easily-breakable portion of the first member (12) is heated separately, so that the ductility of the easily-breakable portion of the first member (12) is further increased.

Further, in the above embodiment, the first member 12 is heated from the recess 32B of the die 32 in the driving step, but as a modification of the above embodiment, for example, a heater (34) built in the die (32) is also arranged near the general support surface (32A) of the die (32), and the first member (12) is heated from the general support surface (32A) and the recess (32B) of the die (32). Good too.

Further, 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.

The above-mentioned embodiments and the above-mentioned modified examples can be appropriately combined and implemented.

Although an example of the present disclosure has been described above, it goes without saying that the present disclosure is not limited to the above example, and various modifications other than the above can be carried out without departing from the spirit of the present disclosure.

Claims

1. A manufacturing method for a fastening structure, the manufacturing method comprising: a casting step for casting a first member by die casting; anda driving step for driving a self-piercing rivet into, from a second member side, an overlapping part in which the second member overlaps the first member, while heat from casting remains in the first member after the casting step.

2. The manufacturing method according to claim 1, wherein a part of the first member overlapped by the second member is heated from a support member that supports the first member from a side opposite to a side on which the self-piercing rivet is to be driven into the overlapping part in the driving step.