JP7117814B2 - Ground electrode for indirect spot welding - Google Patents

Description

The present invention relates to ground electrodes for indirect spot welding.

In the automobile assembly process, a vehicle body is assembled by joining a plurality of parts made of metal plates by spot welding. As spot welding, direct spot welding is often used in which a plurality of metal plates are sandwiched between a pair of electrodes and energized. However, depending on the shape of the part, a plurality of metal plates cannot be sandwiched between a pair of electrodes, and there are restrictions on the parts to which direct spot welding can be applied. As spot welding used in the vehicle body assembly process, there is series spot welding in which a pair of electrodes are pressed against a plurality of metal plates from one side and energized to weld two locations simultaneously. However, this series spot welding also requires two adjacent welding points, so there are restrictions on the locations where welding can be performed.

Therefore, there is indirect spot welding as spot welding that is not subject to the above restrictions. In indirect spot welding, the parts to be joined of a plurality of metal plates are pressed from one side by a welding electrode, and a ground electrode is brought into contact with a part different from the parts to be joined. Weld. In such indirect spot welding, there are few structural restrictions on the applied portion, and the degree of freedom in design can be expanded.

In indirect spot welding, it is necessary to bring the ground electrode into contact with the member to be welded over a wider range in order to prevent current with excessive current density from flowing through the ground electrode. However, if the ground electrode is made of, for example, a plate material, the ground electrode and the member to be welded come into point contact due to the contact between the rigid bodies, causing a localized large current to flow, resulting in damage to the ground electrode and damage to the member to be welded. There was a problem that it would cause cracking and melt-down.

In order to address such a problem, for example, in the conductive electrode for indirect welding disclosed in Patent Document 1, a sheet material formed by knitting conductive wires is provided at the contact portion with the member to be welded. Due to the flexibility of the sheet material, the member to be welded and the sheet material can be brought into contact with each other at many points, so that local large current flow can be prevented.

Japanese Utility Model Laid-Open No. 62-142481

Even if the electrode formed by weaving copper wires as in Patent Document 1 prevents the flow of current with an excessive current density, the temperature of the copper wire becomes high due to the application of pressure during welding, and the copper wire becomes hot. The ground electrode may be damaged, such as by melting or burning out the wire.

In view of such circumstances, an object of the present invention is to provide a ground electrode for indirect spot welding that can ensure a wide contact range and can suppress damage due to overheating and pressure during welding.

In order to solve the above problems, the present invention provides an indirect spot comprising a tubular knitted body having a first portion and a second portion formed by knitting conductive linear bodies, and a plate-shaped intermediate member. The ground electrode for welding, wherein the intermediate member is interposed between the first portion and the second portion, and the side of the first portion opposite to the intermediate member side is abutted by a member to be abutted It is characterized by being a contact part which contacts a contact part .

According to the present invention, by configuring the knitted body with a plurality of layers, it is advantageous in terms of strength as compared with the case of a single layer. Further, by inserting the intermediate member between the layers of the knitted body, overheating of the knitted body can be prevented. As a result, damage to the ground electrode can be suppressed.

As the ground electrode, the intermediate member can be a conductive plate member. Thereby, the knitted body and the intermediate member can be brought into contact with each other at a plurality of points, thereby increasing the number of energization paths in the knitted body and improving the conductivity in the knitted body. As a result, the amount of heat accumulated in the knitted body can be reduced, and overheating of the knitted body can be prevented.

According to the present invention, it is possible to prevent overheating of the knitted body and suppress breakage of the ground electrode by configuring the knitted body with a plurality of layers and inserting an intermediate member between the layers of the knitted body. .

FIG. 4 is a cross-sectional view showing a state in which indirect spot welding is applied to a component made up of a plurality of metal plates; 4 is a plan view showing a contact portion of the ground electrode of the embodiment; FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2; FIG. 4 is a cross-sectional view showing a member to be welded after welding;

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

This embodiment shows an indirect spot welding method performed in the assembly process of an automobile body. Specifically, for example, a case of welding a frame component (member to be welded) 50 of a vehicle body as shown in FIG. 1 is shown. This skeleton component 50 is a frame-like component extending in the direction perpendicular to the plane of FIG. The frame component 50 is composed of a first metal plate 1 having a substantially flat plate shape, a second metal plate 2 having a hat-shaped cross section, and the first metal plate 1 and the second metal plate 2. and a third metal plate 3 having a hat-shaped cross section disposed in the hollow portion.

The first metal plate 1 and the flange portion 2a of the second metal plate 2 are joined via a pre-welded point Q1 welded in advance by direct spot welding. The bottom portion 2b of the second metal plate 2 and the flange portion 3a of the third metal plate 3 are joined via a pre-welded point Q2 welded in advance by direct spot welding.

The top plate portion 3b of the third metal plate 3 and the first metal plate 1 are joined by the indirect spot welding method according to one embodiment of the present invention. Specifically, the portion to be joined P between the first metal plate 1 and the top plate portion 3b of the third metal plate 3 is pressed from one side in the thickness direction (upper side in the figure) with the welding electrode 10, With the ground electrode 30 in contact with the abutted portion R, which is a portion different from the to-be-joined portion P of the frame component 50, the to-be-joined portion P is welded by energizing between the two electrodes 10 and 30. . In the illustrated example, the ground electrode 30 is brought into contact with the bottom portion 2b of the second metal plate 2 from below. The ground electrode 30 is held at the tip of the conductive holding member 20 .

This indirect spot welding method is connected to the indirect spot welding apparatus having the welding electrode 10 and the ground electrode 30 described above, and the indirect spot welding apparatus. It is carried out in an installation with a controller that controls the value. The indirect spot welding apparatus includes pressurizing means for axially driving the welding electrode 10 to pressurize the metal plate. An air cylinder or an electric cylinder can be used as the pressurizing means, and an air cylinder is used in this embodiment.

Next, a more detailed configuration of the ground electrode 30 will be described with reference to FIGS. 2 and 3. FIG.

As shown in FIGS. 2 and 3, the ground electrode 30 has a knitted body 31 and a copper plate 32 as an intermediate member.

The knitted body 31 is formed by flat knitting a copper wire 40, which is a conductive linear body, and has a structure having a plurality of layers. More specifically, the knitted body 31 of this embodiment is formed in a tubular shape and has a two-layer structure including an upper layer portion 31a and a lower layer portion 31b. The upper portion of the upper layer portion 31a is a contact portion that contacts the contact portion R of the frame component 50 (see FIG. 1).

The copper plate 32 is a plate-shaped member inserted between the upper layer portion 31a and the lower layer portion 31b and provided over the longitudinal direction of the knitted body 31 (horizontal direction in FIG. 2).

An example of a method for manufacturing the ground electrode 30 of this embodiment will be described below.
First, the braided body 31 is formed by softening the copper wire 40 by, for example, loosening the commercially available flat braided copper wire by hand. By inserting a copper plate 32 into the knitted body 31, the ground electrode 30 of the present embodiment can be formed. Then, the ground electrode 30 is fixed to the holding member 20 by an appropriate method.

By inserting the sheet-like copper plate 32 between the upper layer portion 31a and the lower layer portion 31b, the copper plate 32 and each layer of the knitted body 31 can be brought into contact with each other at many points. As a result, it is possible to increase the number of energization paths in the ground electrode 30 during welding, promote heat conduction from the ground electrode 30 to the holding member 20 side, reduce the amount of heat accumulated inside the knitted body 31, and reduce the amount of heat accumulated inside the knitted body 31. A cooling effect on the body 31 can be obtained. In addition, although the knitted body 31 is configured to be easily elastically deformed as described above, the ground electrode 30 can be kept in a constant shape by inserting the regular-shaped copper plate 32 between the layers of the knitted body 31. be able to. As a result, the area of contact with the contacted portion R can be controlled within a certain range, and the current density during welding can be stabilized within a certain range. Furthermore, in order to insert the copper plate 32 between the layers of the knitted body 31, it is necessary to provide a gap about the thickness of the copper plate 32 between the upper layer portion 31a and the lower layer portion 31b. In other words, the flat braided copper wire is loosened to the extent that this gap is formed, which can be used as a guideline for loosening the flat braided copper wire, and at the same time, the copper wire can be reliably softened to a certain level or higher.

By bringing the knitted body 31 into contact with the contacted portion R (see FIG. 1), the ground electrode 30 can be brought into contact with the contacted portion R at many points. That is, by weaving the copper wires 40 to form the knitted body 31, the knitted body 31 can be made elastic. As a result, when the ground electrode 30 comes into contact with the contacted portion R, the upper layer portion 31a elastically deforms so as to follow the contacted surface of the contacted portion R due to the surface pressure received by the upper layer portion 31a. , a plurality of copper wires 40 constituting the knitted body 31 can be brought into contact with the contacted portion R. That is, the ground electrode 30 can be brought into contact with the abutted portion R at a large number of locations, and the ground electrode 30 can be substantially brought into surface contact with the abutted portion R. As shown in FIG. In particular, in this embodiment, by loosening the commercially available flat braided copper wire and softening the copper wire 40, the knitted body 31 can be more easily elastically deformed, and the contact portion with the contacted portion R is increased. be able to.

For example, unlike the present invention, the abutting portion of the ground electrode 30 with respect to the abutted portion R has a configuration in which a rigid body or simply copper wires 40 are arranged in parallel in a plane, that is, a configuration that hardly deforms elastically. Since the second metal plate 2, which is a member to be contacted, is also a rigid body, the ground electrode 30 and the second metal plate 2 are locally in contact with each other. In this way, if the contact area of the ground electrode 30 with the contacted portion R is small, a current with an excessive current density will flow during welding, and damage such as cracking or melting of the ground electrode 30 will occur. . In addition, welding quality becomes unstable, such as burn-through, cracking, and the like, occurring in the members to be welded, that is, the second metal plate 2 and the like that constitute the frame component 50 . On the other hand, in the present embodiment, as described above, by making the knitted body 31 elastically deformable, the contact range between the ground electrode 30 and the second metal plate 2 is expanded, and excessive current density is prevented. It can prevent current from flowing. Therefore, the quality of welding can be stabilized, and breakage of the ground electrode can be suppressed.

As a result of the indirect spot welding of this embodiment, that is, the cross section after welding when the ground electrode 30 is brought into contact with the contacted portion R, the welding electrode 10 is pressurized and energized, and the to-be-joined portion P is welded. An example of is shown in FIG.

As shown in FIG. 4, a sufficiently large nugget N is formed across the first metal plate 1 to be welded and the top plate portion 3b, and the first metal plate 1 and the top plate portion 3b are can be welded. At this time, by using the ground electrode 30 of the present embodiment, the current flow and current density are stabilized particularly on the ground side, and burn-through of the welded member and breakage of the ground electrode do not occur.

By providing the abutted portion R at a position corresponding to the already welded point Q2, that is, at the plate-to-plate portion, as in the present embodiment, the abutted portion R is set at a position where the heat capacity of the frame component 50 is large. It is possible to suppress overheating of the ground electrode 30 and the contacted portion R more reliably.

In addition, by configuring the knitted body 31 to have a multi-layer structure, it is possible to improve flexibility and durability compared to a single-layer structure, and it is possible to provide a gap for inserting the copper plate 32 between the multiple layers. .

As the intermediate member, unlike the present embodiment, an insulating member can also be used. However, when an insulating member is used, it becomes impossible to conduct electricity through the intermediate member in the knitted body 31, so the insulating member can be used only when the current density does not become excessive. For example, as shown in FIG. 3, in the knitted body 31 of the present embodiment, when the copper plate 32 is replaced with an insulating member, the copper plate 32 is avoided and the upper layer portion 31a and the lower layer portion 31b of the knitted body 31 are connected. A current flows from the upper layer portion 31a to the lower layer portion 31b via 31c, and the current density may become excessive. Therefore, when an insulating member is used as an intermediate member, it is necessary to provide a separate current path by partially disposing a conductive member. By using an insulating member as the intermediate member, the range of material selection for the intermediate member is widened, such as selecting a member with a higher cooling effect. For example, it is possible to obtain a cooling effect for the knitted body 31 by using a rubber tube in which cooling water is flowed as an intermediate member.

When a conductive member is used as the intermediate member as in the present embodiment, it is preferable to use a member having thermal conductivity equal to or higher than that of the knitted body 31 . In this embodiment, a metal plate, particularly a copper plate, is used.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

In the above embodiments, the linear body is flat-knitted as the knitted body, but the knitting method is not limited to this, and any knitting method may be used as long as the knitted body can have appropriate elasticity. For example, the knitted body can be formed by weaving the filaments in an appropriate weaving method such as rubber knitting or purl knitting. Moreover, the linear body is not limited to a copper wire, and any member that is conductive and can provide appropriate elasticity and strength can be appropriately selected.

REFERENCE SIGNS LIST 1 first metal plate 2 second metal plate 3 third metal plate 3a flange portion 3b top plate portion 10 welding electrode 20 holding member 30 earth electrode 31 knitted body 31a upper layer portion 31b lower layer portion 32 copper plate (intermediate member)
40 copper wire (conductive linear body)
50 skeleton parts (members to be welded)
P Part to be joined R Part to be contacted N Nugget

Claims (1)

a cylindrical knitted body having a first portion and a second portion formed by knitting conductive linear bodies;
A ground electrode for indirect spot welding , comprising a plate-like intermediate member,
The intermediate member is interposed between the first portion and the second portion,
A ground electrode for indirect spot welding , wherein a side opposite to the intermediate member side of the first portion is a contact portion that contacts a contact portion of a contact member .

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