JP6900692B2 - Joining method using rivets and equipment used for its implementation - Google Patents

Description

The present invention relates to a joining method and apparatus using rivets, and more particularly to a method and apparatus for joining a plurality of steel plates including one or more high-strength steel plates having a tensile strength of 780 MPa or more.

Conventionally, in the automobile field, spot welding is often used for assembling car bodies and attaching parts, and joining of a plurality of steel plates including high-strength steel plates is also performed by spot welding.
However, in a spot-welded joint containing a steel plate having a tensile strength of 780 MPa or more, the toughness of the nugget decreases, and the stress in the peeling direction concentrates the stress on the nugget end, so that even if the tensile strength of the steel plate increases. , There is a problem that the cross tensile strength (CTS) does not increase or decreases.

As one of the technologies to solve this problem, a technique of mechanically joining without melting the base material, that is, a technique of superimposing a plurality of metal plates to be joined and pressing the metal plates with a plate presser while holding the metal plates together. There is a technology to drive rivets with a punch and join multiple metal plates with rivets.
However, in this technology, since the rivet is driven, the deformation of the metal plate on the opposite side (die side) to the metal plate in contact with the punch becomes very large, and the metal plate on the die side cracks. In addition, when tensile stress is applied in the peeling direction, the rivet comes off and fracture occurs, and there is a problem that sufficient values cannot be obtained in the tensile strength in the shearing direction and the peeling direction.

As a technique for solving such a problem, in Patent Document 1, first, steel plates 2 and 3 including high-strength steel plates are mechanically joined by a self-piercing type rivet 7 through a riveting machine (see FIG. 7a). ), Next, a technique is disclosed in which a joint portion including a rivet is heated and pressurized through a spot welder to form a welded spot microstructure metallurgically bonded to the portion (see FIG. 7b).

Further, in Patent Document 2, in the method of joining dissimilar metals between the iron-based metal plate 3 and the aluminum-based metal plate 2, the iron-based metal rivet 7 is pushed in while being pressed by an electrode from the aluminum-based metal plate side, and the rivet is rivet. The aluminum metal plate 2 is pierced by No. 7, the tip portion 7c of the rivet is brought into contact with the iron metal plate 3 (see FIG. 8a), and the rivet 7 and the iron metal plate 3 are pressed by the electrodes while the rivet 7 and the iron metal plate 3 are pressed. A technique of resistance-welding the tip 7c of a rivet and an iron-based metal plate 3 by energizing between the metal plate 3 (see FIG. 8b) and joining the iron-based metal plate and the aluminum-based metal plate via the rivet. Is disclosed.

Special Table 2007-521964 Japanese Patent No. 29544476

The techniques of Patent Documents 1 and 2 attempt to solve the problems of spot welding and rivet joining, but the technique of Patent Document 1 has a problem that the steps of rivet driving and resistance welding are two steps. There is. Further, in Patent Document 2, pin driving and resistance welding are continuously performed in one step, but this is an effective technique for welding a joint including an aluminum-based metal plate, and at least when only a steel plate is used. Welding is not considered.

Therefore, an object of the present invention is to provide a joining method and an apparatus thereof capable of forming a joint having a sufficiently high peel strength by using a high-strength steel plate having a tensile strength of 780 MPa or more.

In the present invention, in order to solve such a problem, a self-piercing type using energization heating is continuously combined with a solid rivet bonding with a sharp tip and a fusion bonding (or solid phase bonding) by energization heating. The above problem was solved by performing it in one step.
The gist of such an invention is as follows.

(1) A method of joining a plurality of stacked steel sheets including at least one high-strength steel sheet having a tensile strength of 780 MPa or more by using a self-piercing rivet, a punch and a die.
After the steel plate is preheated by energizing between the plate retainer and the die while pressurizing the steel plate with the punch, which is arranged coaxially with the punch on the outside of the punch.
As the rivet, with a solid rivet having a sharp tip made of steel, by energizing between the rivet while pressing the rivet with punch die, of the steel sheet while heating the steel sheet to be the joint A joining method characterized in that a rivet is pushed to a predetermined position in the thickness direction, and then energization is continued while pressurizing the rivet with a punch to perform solid-phase bonding or melt-bonding at least between steel sheets.

( 2 ) The joining method according to (1) above, wherein steel having a C: 0.15% by mass or less is used as the rivet.
(3) In the step of energizing between the rivet and the die while pressurizing the rivet with the punch.
After energizing and pressurizing with the first current and the first pressurizing, the energizing and pressurizing is performed with a second current higher than the first current and a second pressurizing higher than the first pressurizing (1). ) Or (2).

(4) A joining device used to carry out the joining method described in (1) above.
One side has a punch and a tubular plate retainer coaxially provided on the outside of the punch, and the other side has a die that supports the steel plate to be joined facing the punch. And
The plate retainer and die, and the punch and die are connected to the power supply device, respectively.
When the plate retainer comes into contact with the steel plate, the plate retainer and the die are energized to preheat the steel plate, and then when the rivet comes into contact with the steel plate, the punch and the die are energized to heat the steel plate. A joining device characterized by being configured.

(5) A joining device used to carry out the joining method described in (3) above.
One side has a punch and a tubular plate retainer coaxially provided on the outside of the punch, and the other side has a die that supports the steel plate to be joined facing the punch. And
The plate retainer and die, and the punch and die are connected to the power supply device, respectively.
When the plate retainer comes into contact with the steel plate, the plate retainer and the die are energized to preheat the steel plate, and then
When the rivet comes into contact with the steel sheet, the punch and the die are energized to further heat the steel sheet, and
When the punch and the die are energized to further heat the steel sheet, after energizing and pressurizing with the first current and the first pressing force, the second current higher than the first current and the first pressing force A joining device characterized in that it is configured to be energized and pressurized with a high second pressing force.

According to the present invention, since the steel sheets are joined by using both mechanical joining by rivets and metallurgical joining using heat, it is possible to form a joint having sufficiently high peel strength by using a high-strength steel sheet. ..
In addition, since energization heating is used, it is easy to drive rivets even if a high-strength steel plate is used, and since a pointed rivet is used, a high current is not required for heating and the time required for joining is sufficiently short. it can.
Further, by using steel having a low carbon content for the rivet, the toughness of the joint can be improved and delayed fracture can be suppressed.

It is the schematic of the apparatus used in the joining method of this invention. It is the schematic which shows an example of the procedure of the joining method of this invention. It is a figure which shows an example of the shape of a rivet. It is a figure which shows another aspect of the die set. It is the schematic of the apparatus used for carrying out the method of this invention. It is a figure which shows an example of the pattern of the pressing force and the electric current used in the joining method of this invention. It is a figure for demonstrating the prior art. It is a figure for demonstrating another prior art.

The present invention uses a high-strength steel plate by continuously performing joining by driving using energization heating of a self-piercing type rivet and melt joining (or solid-phase joining) by energization heating in one step. It is possible to manufacture a joint product with high joint strength.
First, a basic embodiment of the present invention will be described with reference to the drawings.

In carrying out the present invention, the punch 4 and the cylindrical plate retainer 5 provided coaxially with the punch are arranged on one side facing each other, which is outlined in FIG. 1, and the other side. A joining device 1 having a die set 6 for supporting the steel plates 2 and 3 to be joined (hereinafter, may be simply referred to as steel plates) facing the punch is used. The die set 6 includes a die 6a facing the rivet 7 and a pressing portion 6b facing the plate pressing 5.
Further, as shown in FIG. 3, the rivet 7 to be driven into the steel plate is composed of a shaft portion 7a and a head portion 7b having a brim portion like a general rivet, is made of steel, is solid, and is a rivet. The tip portion, that is, the tip portion 7c of the shaft portion 7a is pointed like a nail.

The punch 4 and the die 6a are made of a material that can be energized and are both connected to the power supply device 8. When the punch and the die come into contact with the steel plate, an electric circuit is formed. The plate retainer 5 is electrically insulated from other members so that a current does not flow even if it comes into contact with the steel plate.

FIG. 1 shows an example in which the die side is arranged on the upper side and the punch side is arranged on the lower side, but the die side may be arranged on the lower side and the punch side may be arranged on the upper side.

Joining is performed by the following procedure using the above device.
The steel plates 2 and 3 to be joined are overlapped, carried between the die set 6 of the joining device 1 and the plate retainer 5, and placed on the plate retainer 5 (see FIG. 1). The rivet 7 is set on the punch 4 in advance.
The steel plates 2 and 3 include one or more high-strength steel plates having a tensile strength of 780 MPa or more. The number of steel plates to be stacked is two in FIG. 1, but it can be about 3 to 5.

Next, the die set 6 is moved to the steel plate side, the steel plate is sandwiched between the die set 6 and the plate retainer 5 to hold the steel plate (see FIG. 2a), and then the punch 4 is moved to the steel plate side through the plate retainer 5. , The rivet 7 located at the tip of the punch is extruded toward the steel plate, the tip 7c of the rivet is brought into contact with the steel plate 2 (see FIG. 2b), and the rivet 7 is further pressed by the punch 4 so that the tip bites into the steel plate 2 (see FIG. 2b). See FIG. 2c).

At that time, after the tip 7c of the rivet comes into contact with the steel plate 2, an electric current flows between the punch 4 and the die 6a, so that a current flows through the tip of the rivet and the steel plate, and the rivet and the steel plate are energized and heated.
Since the rivet tip 7c is sharp, current and stress are concentrated on the rivet tip and the steel plate in contact with the rivet tip during energization, and the temperature of the steel plate rises sharply. Therefore, the material of the steel sheet easily plastically flows, and even if a high-strength steel sheet is used as the material to be joined, rivets can be easily driven.

Further, the rivet 7 is pressed by the punch 4 to allow the tip of the rivet to penetrate into the steel plate. When the brim of the head portion 7a of the rivet 7 reaches the surface of the steel plate, the drilling of the rivet is stopped, and the steel plate between the rivet 7 and the die 6a is pressurized in a heated state. Further, the steel plate between the die 6a and the die 6a is also pressurized via the brim (see FIG. 2d).
The punch may be cooled when driving the rivet while energizing between the rivet and the die. In that case, softening of the rivet can be suppressed and the rivet can be driven more stably.

After the brim of the head portion 7b of the rivet 7 reaches the inner surface of the steel plate 2, the pressure applied to the rivet 7, the amount of current applied, the energization time, etc. are adjusted to be between the steel plate on the die side and the rivet. Is solid-phase bonded (see FIG. 2e) and melt-bonded between the steel plate on the die side and the rivet (see FIG. 2f).

(I) When the steel plate and the rivet on the die side are solid-phase bonded The pressure is applied between the steel plate and the rivet while the steel plate and the rivet are energized and heated, and the steel plate is also pressurized through the brim. At this time, by continuing energization heating while adjusting the pressing force and current value so that the boundary between the rivet and the steel plate and the mating surface between the steel plates do not melt, between the rivet and the steel plate and between the steel plates. Mutual diffusion of metal elements progresses, and both are solid-phase bonded (see FIG. 2e).

(Ii) When the steel plate on the die side and the rivet are melt-bonded The tip of the rivet and the steel plate in contact with the tip are brought into contact with each other by increasing the energizing current between the rivet and the steel plate or increasing the pressing force. Both melt to form a nugget. As a result, the rivet steel plates and the steel plates are melt-bonded by the nugget 9 (see FIG. 2f).
In this case, as shown in FIG. 4, it is preferable to reduce the area of the portion of the die 6a facing the rivet 7 so that the current is concentrated and flows in a narrow region of the steel sheet.
When there are three or more steel plates, it is preferable to drive the rivets until the tip of the rivet reaches the inner surface of the steel plate on the die side. Further, melt joining in which the joining between the die steel sheets is performed more reliably is preferable.

As a result of the above, the laminated steel sheets are joined by both mechanical joining by rivets and solid-state joining or melt joining using heat, and a high-strength steel sheet can be used to form a joint having sufficiently high peel strength. it can.

In the above embodiment, the case where the punch 4 and the die 6a are energized has been described. Further, the plate retainer 5 is also connected to the power supply device, the plate retainer 5 and the die 6a are energized, and the steel plates 2 and 3 are connected. Can be preheated.
In this case, with the steel plate sandwiched between the die set 6 and the plate retainer 5 as shown in FIG. 2a, energization is applied between the plate retainer 5 and the die 6a to prepare the steel plate before the rivet tip 7c comes into contact with the steel plate 2. Energize and heat. Next, the punch 4 is moved to the steel plate side through the plate retainer 5, and after the tip 7c of the rivet comes into contact with the steel plate 2, an electric current is applied between the punch 4 and the die 6a, so that a current flows through the rivet tip and the steel plate to form the rivet. The steel sheet is energized and heated, and thereafter, the steel sheet is joined in the same manner as described above.

It is effective to carry out such an invention by a joining device 11 capable of performing two-stage pressing as outlined in FIG.
In the figure, a die 6a assembled to the die set 6 is arranged at the lower end of a shank 12 which is moved up and down by a driving device (not shown) above the steel plates 2 and 3 to be joined. Further, below, the punch 4 is fixed to the straight holder 13 which is similarly moved up and down by a driving device (not shown) so as to face the die 6a, and the plate retainer 5 is arranged on the outside of the punch 4 to be straight. The plate retainer 5 is supported by the adapter 14 fixed to the holder 13 via the gas spring 15.

When the punch 4 is driven toward the die 6a during the joining operation, the plate retainer 5 also moves toward the die 6a via the adapter 14, first abuts on the steel plate, and pressurizes and holds the steel plate together with the die set 6. .. When the punch 4 moves further upward to drive the rivet 7, the gas spring 15 compresses and the pressing force of the plate retainer 5 further increases, so that the mating surfaces of the steel plates 2 and 3 are brought into close contact with each other. There is. Therefore, the current is concentrated on the mating surface.

The energization of the steel plate is performed by the conduction between the punch 4 and the die 6a when the rivet 7 comes into contact with the steel plate 3. Therefore, the punch 4 and the die 6a are connected to the power supply device 8 (see FIG. 1), respectively. Further, when the plate retainer 5 before the rivet 7 contacts the steel plate 3 comes into contact with the steel plate 3, the plate retainer 5 and the die 6a are energized through the steel plate, and the plate retainer 5 is also supplied with power to preheat the steel plate. It can also be connected to the device 8. In this case, the temperature of the steel sheet can be raised faster.

When the punch 4 drives the rivet 7, the drive device is provided with a drive control means for controlling the movement of the punch 4 so that the rivet 7 is loaded with a pressing force having a predetermined pattern as described later. Further, the power supply device 8 is energized between the punch 4 and the die 6a when the rivet 7 comes into contact with the steel plate, and while the punch 4 is driving the rivet 7, a predetermined value as described later is provided between the punch 4 and the die 6a. An energization control means for controlling the flow of the pattern current is provided. Further, when the plate retainer 5 and the die 6a are connected to the power supply device, the energization control means energizes the plate retainer 5 and the die 6a through the steel plate when the plate retainer 5 comes into contact with the steel plate to prepare the steel plate. Control the current to heat up.

The basic aspects of the present invention have been described above, and the individual requirements and preferable requirements of the present invention will be further described.

(Steel sheet to be joined)
The steel plate is formed of two steel plates in the above example, but may be three or more steel plates depending on the form of the structural parts to be joined. Such a steel plate may have at least a plate-shaped portion at least in part and may have a portion in which the plate-shaped portions are stacked on each other, and the entire steel plate does not have to be a plate. Further, the method is not limited to the one composed of separate steel plates, and the end portions of one steel plate bent and formed into a tubular shape may be overlapped.

The plurality of steel plates shall include at least one steel plate of 780 MPa class or higher. In particular, by using steel plates of 780 MPa class or higher for all steel plates, members having high joint strength can be manufactured, so that thin steel plates can be used, and weight reduction of parts can be achieved.

(rivet)
The rivet is composed of a head having a shaft portion and a brim portion like a general rivet, and is solid, and the tip portion of the shaft portion is pointed like a nail. The tip may be pre-rounded because it is immediately heated and softened when it comes into contact with the steel sheet and is energized.

The material of the rivet is not particularly limited as long as it is steel, but it is preferable to use steel having a low carbon content. By using a rivet made of steel having a low carbon content, the hardness of the joint can be suppressed, so that the toughness of the joint is excellent and the joint strength such as tensile shear strength and cross tensile strength can be improved. Further, when forming a nugget, a nugget portion having a low carbon content can be formed. Further, since the hardness of the joint portion is lowered, it is possible to suppress delayed fracture (hydrogen embrittlement) which may occur in the spot welded portion of the high-strength steel plate. For this purpose, steel having a C: 0.15% or less is particularly preferable.

(Die set)
The die set is arranged so as to face the punch and the plate retainer, and holds the steel plate between the punch and the plate retainer during the driving of the rivet, and the surface opposite to the driving surface of the steel plate with respect to the driving of the rivet. Consists of a die that supports the steel plate so that it does not deform. The die also acts as an electrode when the steel sheet is energized and heated through the rivet.
The material of the presser foot may be tool steel, but the die is preferably copper or a copper alloy.

(Punch)
The punch 4 may be entirely made of ordinary tool steel, but since it also acts as an electrode for energizing the rivet, the end portion in contact with the rivet is made of copper or a copper alloy having high electrical conductivity. Is preferable.
When driving the rivet, if the temperature of the rivet rises too much due to energization, the punch is cooled by passing it through a cooling pipe inside or from the outside so that the punch can be cooled.

(Plate presser)
In the example of FIG. 5, an example in which the plate retainer is supported by a gas spring is shown, but instead of the gas spring, a resin molded body made of an air cylinder, a compression coil spring, and a urethane resin having appropriate elasticity can be used.

(Conditions for pressurization and energization)
The patterns of the pressing force by the punch when driving the rivet into the steel plate and the current for energizing and heating the steel plate are as follows: (a) A pattern in which the pressing force is constant and the current (its effective value) is constant as in normal spot welding. (See FIG. 6a) and (b), when the temperature of the rivet tip and the steel plate rises, a pattern of changing to a higher pressing force and a current in two steps can be exemplified.
The case (b) is suitable for hot-dip joining between the steel plate on the die side and the rivet, and the joining time can be shortened.

When the current and the pressing force are changed in two steps, the timing of changing (increasing) the current should be approximately the same as the timing of increasing the pressing force. If the time that is constant at the first current of the first stage is the first energization time and the time that is constant at the second current of the second stage is the second energization time, the first stage pressurization (first pressurization) ) Is held for a little longer than the first energization time in consideration of the stability of the pressing force as in the case of spot welding. Specifically, it may be set as [holding time of first pressing force = squeeze time + first energizing time]. Here, the squeeze time is the time from the time when the pressing force rises to the start of energization.
Further, the time for holding the second pressing force in the second stage is set to be slightly longer than the second energizing time in order to ensure the joining. Specifically, it may be set as [holding time of second pressing force = second energizing time + holding time]. Here, the holding time is the time from the end of energization to the stop of holding the pressure.

The feasibility and action / effect of the present invention will be described below with reference to Examples.
As the test steel, two steel plates made of S45C steel having a plate thickness of 1.6 mm and a steel plate strength of 1.8 GPa class were used, and these steel plates were overlapped and spot welded or rivet-joined according to the present invention.

In spot welding, the pressing force, current, and energizing time were adjusted so that the nugget diameter was about 6 mm.
On the other hand, in the rivet joining, it is made of steel with a C content of 0.12% by mass, the diameter is 6 mm, the length under the neck (shaft) is 2.5 mm, the opening angle of the tip is 120 °, and the brim is attached. Using rivets, joining was performed under the condition that the pressing force and the current were constant (see FIG. 6a) or the pressing force and the current value were changed in two steps (see FIG. 6b).
When the current and the pressing force were changed in two steps, the timing of changing (increasing) the current was set to be approximately the same as the timing of increasing the pressing force.
Under all conditions, the squeeze time was 0.5 sec and the holding time was 0.2 sec.
Each condition is shown in Table 1.

The quality of the obtained joint was judged by the joint strength (cross tensile strength = CTS).
The results are shown in Table 1, where the CTS outperformed that of spot welded joints under all conditions of riveting. It can be seen that when the two-stage energization is adopted for the rivet joining, the CTS is improved and the time required for the joining is shortened as compared with the case of the one-stage energization.

1 Joining device 2, 3 Overlapping steel plate to be joined 4 Punch 5 Plate presser 6 Die set 6a Die 6b Presser part 7 Rivet 7a Rivet shaft part 7b Rivet head 7c Shaft tip 8 Power supply device 9 Nugget 11 Joining device 12 Shank 13 Straight holder 14 Adapter 15 Gas spring

Claims (5)

A method of joining a plurality of stacked steel sheets including at least one high-strength steel sheet having a tensile strength of 780 MPa or more by using a self-piercing rivet, a punch and a die.
After the steel plate is preheated by energizing between the plate retainer and the die while pressurizing the steel plate with the punch, which is arranged coaxially with the punch on the outside of the punch.
As the rivet, said steel sheet using a solid rivet having a sharp tip made of steel, by energizing between the rivet and the die while pressing the rivet in the punch, while heating the steel sheet to be the joint A joining method characterized in that a rivet is pushed to a predetermined position in the thickness direction of the steel sheet, and then energization is continued while pressurizing the rivet with a punch to perform solid-phase bonding or melt-bonding at least between steel sheets. The joining method according to claim 1, wherein a steel having a C content of 0.15% by mass or less is used as the rivet. In the step of energizing between the rivet and the die while pressurizing the rivet with the punch.
Claim 1 is characterized in that after energization and pressurization with a first current and a first pressurization, energization and pressurization is performed with a second current higher than the first current and a second pressurization higher than the first pressurization. Or the joining method according to 2. A joining device used to carry out the joining method according to claim 1 , which has a punch and a tubular plate retainer coaxially provided on the outside of the punch on one side facing each other. On the other side, it has a die that supports the steel plate to be joined against the punch.
The plate retainer and die, and the punch and die are connected to the power supply device, respectively.
When the plate retainer comes into contact with the steel plate, the plate retainer and the die are energized to preheat the steel plate, and then
A joining device characterized in that when the rivet comes into contact with a steel sheet, the punch and the die are energized to further heat the steel sheet. A joining device used to carry out the joining method according to claim 3.
One side has a punch and a tubular plate retainer coaxially provided on the outside of the punch, and the other side has a die that supports the steel plate to be joined facing the punch. And
The plate retainer and die, and the punch and die are connected to the power supply device, respectively.
When the plate retainer comes into contact with the steel plate, the plate retainer and the die are energized to preheat the steel plate, and then
When the rivet comes into contact with the steel sheet, the punch and the die are energized to further heat the steel sheet, and
When the punch and the die are energized to further heat the steel sheet, after energizing and pressurizing with the first current and the first pressing force, the second current higher than the first current and the first pressing force A joining device characterized in that it is configured to be energized and pressurized with a high second pressing force.

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