DIFFERENT-MATERIAL JOINING METHOD

Abstract

A different-material joining method for joining a first member molded by die casting to a second member formed of a material having a greater ductility than the first member using a self-piercing rivet, the different-material joining method including: energizing a joint portion where the first member and the second member have been superimposed on each other; and driving the self-piercing rivet into the joint portion from the second member side while energizing the joint portion.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese Patent Application No. 2025-033834, filed on Mar. 4, 2025, the disclosure of which is incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to a different-material joining method.

Related Art

Japanese Patent Application Laid-Open (JP-A) No. 2020-63486, discloses an aluminum alloy member manufacturing method that forms a softened portion where only a localized portion of an aluminum alloy casting is softened by energizing from an electrode through the casting while pressing the localized portion of the casting with the electrode.

However, when another member is to be joined by driving a self-piercing rivet into the softened portion of the casting obtained by the manufacturing method disclosed in JP-A No. 2020-63486, it takes a certain amount of time from when Joule heating is performed to the localized portion of the casting until the self-piercing rivet is driven. There is accordingly a concern that the temperature of the localized portion of the casting may drop, and cracks may be generated in the joint portion of the casting, when driving the self-piercing rivet.

SUMMARY

The present disclosure provides a different-material joining method that may suppress generation of cracks in a joint portion of a casting, when joining the casting and another member together by a self-piercing rivet.

A first aspect of the present disclosure is a different-material joining method for joining a first member molded by die casting to a second member formed of a material having a greater ductility than the first member using a self-piercing rivet, the different-material joining method including: energizing a joint portion where the first member and the second member have been superimposed on each other; and driving the self-piercing rivet into the joint portion from the second member side while energizing the joint portion.

In the first aspect of the present disclosure, the self-piercing rivet is driven from the second member side while energizing the self-piercing rivet and the first member. This means that the self-piercing rivet can be driven prior to the temperature of the first member dropping, due to driving being performed at the same time as heating. This may suppress generation of crack in the joint portion of the first member formed by die casting a less ductile material.

In a second aspect of the present disclosure, in the first aspect, the joint portion may be started prior to driving of the self-piercing rivet is started, and energizing the joint portion may be ended after driving of the self-piercing rivet is finished.

In the second aspect of the present disclosure, energizing the self-piercing rivet and the first member is started prior to driving of the self-piercing rivet, and energizing the self-piercing rivet and the first member is ended after driving of the self-piercing rivet. Accordingly, cracking of the first member that may occur during driving, may be prevented by the first member being heated during driving.

In a third aspect of the present disclosure, in the second aspect, a power source may be connected to a driving member that drives the self-piercing rivet when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

In the third aspect of the present disclosure, the power source is connected to the driving member that energize and drives the self-piercing rivet. An electrode member is accordingly able to energize the self-piercing rivet, and at the same time, drive the self-piercing rivet. Accordingly, there is no need to provide a new member to perform energizing of the self-piercing rivet. Moreover, the energy conversion efficiency by energizing may be raised, compared to a configuration in which a new member is provided for energizing. Thus, manufacturing cost may also be reduced.

In a fourth aspect of the present disclosure, in the third aspect, the power source may be connected to a support member that supports the joint portion when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

In the fourth aspect of the present disclosure the power source is connected to the support member that supports the joint portion when driving and energizing the self-piercing rivet. Since the support member can energize the first member while supporting the first member, there is no need to provide a new member to energize the first member. Moreover, the energy conversion efficiency by energizing may be raised, compared to a configuration in which a member is newly provided for energizing. Thus, manufacturing cost may also be reduced.

In a fifth aspect of the present disclosure, in the first aspect, the first member may be part of a vehicle body structural member.

In the fifth aspect of the present disclosure, the first member is part of a vehicle structural member molded by die casting. This means that even in cases in which the member to be joined is a large product employed in a vehicle, the joint portion can be heated efficiently by energizing the self-piercing rivet and the first member, enabling suppression of crack generation in the joint portion of the first member formed of a less ductile material.

In a sixth aspect of the present disclosure, in the fifth aspect, the first member may be the vehicle body structural member configured from an integrally molded die casting of a pair of wheel arches disposed at each vehicle width direction outside and a support member for supporting the pair of wheel arches.

In the sixth aspect of the present disclosure, the first member is a vehicle body structural member configured from the integrally molded die casting of the wheel arches and the support member for supporting the pair of wheel arches. This thereby enables the joint portion to be heated efficiently by energizing the self-piercing rivet and the first member, even in cases in which the member to be joined is a particularly large product from out of components employed in a vehicle, enabling suppression of crack generation in the joint portion of the first member formed of a less ductile material.

The above aspects of the different-material joining method of the present disclosure may suppress generation of crack in a joint portion of a casting, when driving a self-piercing rivet.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in detail based on the following figures, wherein:

FIG. 1 is a cross-sectional view illustrating part of a joint structure manufactured by a different-material joining method according to an exemplary embodiment of the present disclosure;

FIG. 2 is a cross-sectional view illustrating a state prior to driving a self-piercing rivet into a joint portion between a first member and a second member;

FIG. 3 is a schematic diagram illustrating a self-piercing rivet joining device employed in a different-material joining method according to an exemplary embodiment of the present disclosure;

FIG. 4 is a cross-sectional view illustrating a state prior to start of energizing, in a different-material joining method according to an exemplary embodiment of the present disclosure;

FIG. 5 is a cross-sectional view illustrating a state after end of energizing, in a different-material joining method according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Description follows regarding a different-material joining method according to an exemplary embodiment of the present disclosure, with reference to FIG. 1 to FIG. 5.

FIG. 1 illustrates a cross-section of part of a joint structure 10 joined by a different-material joining method according to the present exemplary embodiment. The joint structure 10 includes members-to-be-joined 50, configured by a first member 12 and a second member 14, and a self-piercing rivet 16. The self-piercing rivet 16 is driven into a joint portion 40, where the first member 12 and the second member 14 have been superimposed in a plate thickness direction, by driving from the second member 14 side. The number of members-to-be-joined 50 is not particularly limited as long as there are plural thereof (i.e. two or more), and is typically two.

The first member 12 and the second member 14 are both made from metal. Moreover, the second member 14 is configured from a substance having greater ductility than the first member 12. More specifically, the first member 12 is, as an example, formed from an aluminum alloy, and the second member 14 is, as an example, formed from a steel. Moreover, the first member 12 is, as an example, a die cast product molded by die casting. The first member 12 and the second member 14 are, for example, members employed in a vehicle.

The self-piercing rivet 16 is made from a special steel, such as a chromium molybdenum steel or the like, and includes a head 16A, and a leg 16B that extends in a circular cylinder shape from the head 16A. In a state of the self-piercing rivet 16 prior to being driven into the joint portion 40 between the first member 12 and the second member 14, as illustrated in FIG. 2, an inner diameter of the tip side of the leg 16B gradually widens on progression toward the tip of the self-piercing rivet 16. The tip side of the leg 16B is formed in this manner in order to facilitate deformation of the tip side of the leg 16B in a direction of widening diameter when the self-piercing rivet 16 is being driven into the joint portion 40.

Next, description follows regarding an example of a self-piercing rivet joining device employed in a joining method of the joint structure 10, with reference to FIG. 3.

FIG. 3 illustrates an example of a driving section 20 and an energizing section 30 in a self-piercing rivet joining device.

As illustrated in FIG. 3, the driving section 20 includes a die 18 serving as a support member to support the first member 12 from the opposite side to the driven side where the self-piercing rivet 16 is being driven. The die 18 includes a support face 18A to support the first member 12 from the lower side. Moreover, an opening 18B is formed to the die 18 for contacting a plastically deformed portion when the first member 12 has been plastically deformed by driving the self-piercing rivet 16. The opening 18B is formed in a circular shape in plan view, indented with respect to the support face 18A.

The joint portion 40, with the first member 12 at the lower side, is supported on the support face 18A of the die 18 while the self-piercing rivet 16 is being driven into the joint portion 40.

The driving section 20 includes a cylinder 22 and a punch 24. The cylinder 22 is formed in a circular cylinder shape that enables the self-piercing rivet 16 to be inserted therein. The cylinder 22 is disposed such that an axial center thereof is aligned with a central portion of the opening 18B of the die 18, and such that a lower end face thereof presses the joint portion 40 supported by the die 18 against the support face 18A side of the die 18. Note that, at least an inner face and a lower end face of the cylinder 22 are insulated. This thereby enables current, that flows due to energizing by the energizing section 30, to be prevented from flowing in the cylinder 22. This may suppress a drop in energy conversion efficiency.

The punch 24 is configured by a circular pillar shaped member that moves along the axial direction inside the cylinder 22 by the drive device, and presses the self-piercing rivet 16 inserted inside the cylinder 22 from the upper side. Note that, a direction of movement of the punch 24 is indicated by an arrow in the drawings.

The punch 24 and the die 18 are formed from materials that can be energized, and also functions as electrode members that passes electrical power supplied from a power source 32, as current, to the self-piercing rivet 16 and the first member 12. There is accordingly no need to provide a new member for energizing, since the self-piercing rivet 16 can be energized and driven at the same time. Moreover, in comparison to a configuration in which a new member is provided for energizing, the energy conversion efficiency may be raised due to current not passing through another member. Thus, manufacturing cost may also be reduced.

Next, description follows regarding the energizing section 30.

The energizing section 30 is configured including the power source 32, a wiring 34 and a wiring 36, and a switch S.

The switch S is provided to the wiring 34 that connects the power source 32 and the die 18. The wiring 36 connects the power source 32 and the punch 24. Current passes between the punch 24 and the die 18 via the self-piercing rivet 16 and the joint portion 40, in a case in which the switch S is closed when the punch 24 contacts the self-piercing rivet 16, the die 18 contacts the first member 12, and the first member 12 contacts the second member 14.

Next, description follows regarding energizing and driving the self-piercing rivet 16, with reference to FIG. 4 and FIG. 5. FIG. 4 is a cross-sectional view illustrating a state prior to start of energizing in the different-material joining method according to an exemplary embodiment of the present disclosure. FIG. 5 is a cross-sectional view illustrating a state after end of energizing in the different-material joining method according to an exemplary embodiment of the present disclosure.

In a state prior to start of energizing, as illustrated in FIG. 4, the support face 18A of the die 18 supports the first member 12, and the second member 14 is stacked on the first member 12. Next, the first member 12 and the second member 14 are clamped between the lower end face of the cylinder 22 and the support face 18A of the die 18.

Next, when energizing, an electrical circuit is formed by contacting the punch 24, the self-piercing rivet 16, the second member 14, the first member 12, and the die 18, against each other, after the switch S has been closed. Thus, energizing is started. However, a configuration may be adopted in which energizing is started by closing the switch S after the punch 24, the self-piercing rivet 16, the second member 14, the first member 12, and the die 18 have contacted with each other. Energizing is thereby started.

Next, driving of the self-piercing rivet 16 is started. The self-piercing rivet 16 placed inside the cylinder 22 is pressed from above by the punch 24. The leg 16B of the self-piercing rivet 16 penetrates into the second member 14, and the second member 14 starts to deform.

Next, due to the self-piercing rivet 16 being pressed from above by the punch 24, the leg 16B of the self-piercing rivet 16 pierces through the second member 14, and the first member 12 pressed by the self-piercing rivet 16, and the second member 14, plastically deform toward the opening 18B side of the die 18. Part of the first member 12 deforms so as to conform to the opening 18B, and the tip side of the leg 16B of the self-piercing rivet 16 digs into the first member 12 while deforming so as to increase in diameter.

Due to continuously applying the current, an area spanning from portions of the second member 14 contacting the leg 16B of the self-piercing rivet 16, to portions of the first member 12 contacting the die 18, is heated by the passing current. Namely, current flows from the die 18 to the self-piercing rivet 16 via the portions contacting the head 16A, and flows from the leg 16B to the support face 18A of the die 18 via contacting portions of the second member 14 and the first member 12. The entire area of the second member 14 and the first member 12 penetrated by the tip of the leg 16B of the self-piercing rivet 16 is accordingly heated, enabling efficient heating and softening of the area to be joined by the self-piercing rivet 16.

Next, the punch 24 reaches the lowest point of the stroke in its axial direction movement inside the cylinder 22. Accordingly, the self-piercing rivet 16 is driven into the joint portion 40, and driving is ended.

Next, the electrical circuit is disconnected by the switch S being opened, and energizing is ended. However, a configuration may be adopted in which the electrical circuit is disconnected and energizing is ended by raising the punch 24, and by the punch 24 being separated from the head 16A of the self-piercing rivet 16.

Thereafter, the cylinder 22 and the punch 24 are raised, and the joint structure 10 as illustrated in FIG. 1 is taken out from the driving section 20.

In the present exemplary embodiment, the area spanning from the portions of the second member 14 contacting the leg 16B of the self-piercing rivet 16, to the portions of the first member 12 contacting the die 18, is heated by passing current. Thus, areas of the first member 12 and the second member 14 to be joined by the self-piercing rivet 16 can be efficiently heated and softened. Thus, the present exemplary embodiment may suppress generation of crack in the joint portion 40 of the first member 12.

In the present exemplary embodiment, energizing is started prior to driving the self-piercing rivet 16, and the joint portion 40, including the self-piercing rivet 16, is heated and softened. This thereby enables the joint portion 40 to plastically deform, after plastic deformation of the self-piercing rivet 16, and thus, cracks may be suppressed from being generated. Moreover, in the present exemplary embodiment, the energizing section 30 performs energizing from the start of driving the self-piercing rivet 16 to the end of driving. Accordingly, cracking of the joint portion 40 of the first member 12 that may occur during driving, may be prevented by the joint portion 40 being heated during driving.

Moreover, since energizing is performed directly in the self-piercing rivet 16, the entire joint portion 40 is heated even in cases in which the first member 12 is configured from a material with a low ductility. Thus, generation of crack in the joint portion 40 of the first member 12, may be suppressed.

In the present exemplary embodiment the first member 12 is a vehicle structure member molded by die casting. Moreover, the first member 12 is a large die cast product employed in a vehicle configured from a low ductility aluminum alloy. The joint portion 40 can be heated by energizing the self-piercing rivet 16 and the first member 12, even in cases in which the first member 12 is such a vehicle structure member molded by die casting. Thus, generation of crack in the joint portion 40 of the first member 12, which is a die cast product, may be suppressed.

Moreover, heating of the joint portion 40 can be performed by energizing the self-piercing rivet 16 and the first member 12, even in a particularly large die cast products employed in a vehicle, such as front side member or a rear side member or the like, and generation of crack in the joint portion 40 of the first member 12 may be suppressed.

Moreover, in the present exemplary embodiment, the first member 12 is a vehicle body structural member configured from an integrally molded die casting of a pair of wheel arches disposed at each vehicle width direction outside and a support member to support the pair of wheel arches. Note that, the vehicle body structural member may be a vehicle body structural member at the vehicle front side, or may be the vehicle body structural member at the vehicle rear side, and the pair of wheel arches and the support member are not necessarily integrally molded.

Moreover, in the present exemplary embodiment, the punch 24 presses the self-piercing rivet 16 and also energizes the self-piercing rivet 16. Similarly, the die 18 supports the first member 12 and also energizes the first member 12. This accordingly mean that a new member does not need to be provided for energizing. Moreover, the energy conversion efficiency from energizing can be raised compared to a configuration in which a new member is provided for energizing, enabling the manufacturing cost to be reduced.

Note that, in the present exemplary embodiment, the start of energizing, the start of driving, the end of driving, and the end of energizing, proceed in this sequence. However, there is no limitation thereto. Driving may be started after start of energizing, and driving may be ended after end of energizing. Moreover, energizing may be started after start of driving, and energizing may be ended after end of driving. Moreover, energizing may be started after start of driving, and driving may be ended after end of energizing.

In the present exemplary embodiment, the electrode member for energizing the self-piercing rivet also functions as the die 18. However, there is no limitation thereto. An electrode member may be provided separately from the die 18.

In the present exemplary embodiment, the electrode member for energizing the first member 12 also functions as the punch 24. However, there is no limitation thereto. An electrode member may be provided separately from the punch 24.

Supplements

Note that appropriate combinations of the following configurations may be employed as the different-material joining method according to the present disclosure.

Configuration 1

A different-material joining method for joining a first member molded by die casting to a second member formed of a material having a greater ductility than the first member using a self-piercing rivet, the different-material joining method comprising:

• • energizing a joint portion where the first member and the second member have been superimposed on each other in a plate thickness direction; and
  • driving the self-piercing rivet into the joint portion from the second member side while energizing the joint portion.

Configuration 2

Energizing the joint portion is started prior to driving of the self-piercing rivet is started, and energizing the joint portion is ended after driving of the self-piercing rivet is finished.

Configuration 3

A power source is connected to a driving member that drives the self-piercing rivet when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

Configuration 4

The power source is connected to a support member that supports the joint portion when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

Configuration 5

The first member is part of a vehicle body structural member.

Configuration 6

The first member is the vehicle body structural member configured from an integrally molded die casting of a pair of wheel arches disposed at each vehicle width direction outside and a support member for supporting the pair of wheel arches.

Although examples of exemplary embodiments of the present disclosure have been described above, exemplary embodiments of the present disclosure are not limited to the above, and obviously appropriate combinations of exemplary embodiments and various modified examples may be implemented to obtain various embodiments within a scope not departing from the spirit of the present disclosure.

Claims

1. A different-material joining method for joining a first member molded by die casting to a second member formed of a material having a greater ductility than the first member using a self-piercing rivet, the different-material joining method comprising:

energizing a joint portion where the first member and the second member have been superimposed on each other; and

driving the self-piercing rivet into the joint portion from the second member side while energizing the joint portion.

2. The different-material joining method of claim 1, wherein energizing the joint portion is started prior to driving of the self-piercing rivet is started, and energizing the joint portion is ended after driving of the self-piercing rivet is finished.

3. The different-material joining method of claim 2, wherein a power source is connected to a driving member that drives the self-piercing rivet when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

4. The different-material joining method of claim 3, wherein the power source is connected to a support member that supports the joint portion when driving the self-piercing rivet into the joint portion, and energizes the joint portion.

5. The different-material joining method of claim 1, wherein the first member is part of a vehicle body structural member.

6. The different-material joining method of claim 5, wherein the first member is the vehicle body structural member configured from an integrally molded die casting of a pair of wheel arches disposed at each vehicle width direction outside and a support member for supporting the pair of wheel arches.