JP2002160074A - Electrode for resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for resistance welding which has high conductivity and is excellent in welding quality, durability, and resistance to sticking. SOLUTION: An electrode 10 for resistance welding has an electrode body 12 which contains a holding part 14 and an electrode tip 16. The periphery of the electrode tip 16 is surrounded with a supporting member 20 in a hollow cylindrical shape. The supporting member 20 has higher rigidity than that of the electrode body 12. The electrode body 12 is prevented from deforming by the supporting member 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for resistance welding, and more particularly, to an electrode for resistance welding having high conductivity, high durability and improved sticking resistance.

[0002]

2. Description of the Related Art When welding members to be welded such as galvanized plywood, a resistance welding method has been widely used. In this resistance welding method, for example, a member to be welded such as the galvanized plywood is partially overlapped and positioned between a pair of electrodes provided to face each other, and the pair of electrodes is pressed against the overlapped portion. To generate Joule heat by the electric resistance of the metal plate to weld the welded portion.

[0003] In particular, when welding a steel sheet which has been subjected to a surface treatment such as galvanization as described above, this resistance welding method involves:
Thousands of amperes of current are passed between the pair of electrodes. For this reason, the electrode is required to be a material having good conductivity, excellent heat resistance, and high heat conductivity. That is, since the electrode material itself is required to have excellent properties of electrical conductivity, heat resistance and thermal conductivity, pure copper has been conventionally mainly used as an electrode material. However, since the electrode is made of pure copper, it cannot be said that the electrode has excellent durability. Specifically, as a result of pressing the steel plate, the shape of the tip of the electrode is deformed, the current density flowing through this current becomes unstable,
There is a concern that welding quality will deteriorate and inconveniences such as peeling will be exposed.

[0004] In order to overcome this difficulty, an electrode material which is made of copper as a base and which is made of a precipitation-strengthened alloy by adding chromium, zirconium, beryllium or the like to copper has been adopted. In this case, for example, assuming that the conductivity of pure copper is 100, when an electrode made of a composite material to which an alloy such as chromium, zirconium, and beryllium is added is employed, the conductivity is expressed as a relative value. Conductivity (IAC
S%) from 85% to about 20%.

Further, in this resistance welding, since the electrodes are used continuously under high temperature and high pressure conditions, the initial material properties deteriorate with time. That is, when a precipitation strengthened alloy is used, it is pointed out that chromium, zirconium, beryllium, and the like are re-dissolved by heat generated during resistance welding, resulting in a further decrease in conductivity and further deterioration in durability. ing.

Therefore, in order to overcome the problems inherent in electrode materials using such precipitation strengthened alloys, oxide dispersion strengthened alloys in which oxides are dispersed have been developed. As this oxide, aluminum oxide, silicon oxide, and zirconium oxide are known to be particularly effective for electrodes. However, as described above, aluminum oxide, silicon oxide, oxide dispersion strengthened alloys such as zirconium oxide,
If high conductivity is to be expected from the viewpoint of an electrode, the durability is inferior, and consequently, since the materials exhibit contradictory material properties, an electrode having both high durability and adhesion resistance to a workpiece is obtained. Was difficult.

[0007] In view of these drawbacks, a so-called composite electrode has been devised in which partially different materials are combined as electrodes. According to this composite electrode, an alloy material based on copper having high hardness is incorporated at the tip of the electrode in contact with the workpiece by press-fitting or the like, that is, durability is improved by combining different materials. (See JP-A-9-76074).

[0008]

However, in this kind of electrode, the performance of the electrode is promoted by the press-fitted alloy material, and the expected effect cannot be expected. Furthermore, the welding current flows through the low electric resistance area around the electrode during resistance welding, and as a result, the nugget of the work to be welded is formed in a donut shape, so that a product excellent in welding quality cannot always be obtained. Has also been pointed out.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned disadvantages.
An object of the present invention is to provide an electrode for resistance welding that has excellent conductivity and also excellent resistance to electrode sticking to a workpiece.

[0010] The present invention is based on the following findings.

According to the applicant, the conductivity (IACS%)
When a correlation with the sticking force (Kgf) was obtained by an experiment, it was confirmed that a positive correlation was present. That is, it was confirmed that despite the highest conductivity, pure copper had the lowest sticking force. On the other hand, it is known that the conductivity of the electrode and the calorific value of the electrode have a relationship of Q = I × 2R. However, it was also confirmed that when the IACS was 50% or less, the calorific value increased sharply, the temperature of the electrode itself rose, and the work and the electrode were welded, that is, the adhesion resistance was not sufficient.

However, as described above, pure copper has low durability. As a result, when the welding process is continued, the tip of the electrode is deformed due to crushing or the like, and penetration of the stacked workpieces becomes insufficient. As a result, poor welding occurs, and the possibility that the objects to be welded peel off from each other after welding increases. The reason is that the electrode tip is crushed and the electrode tip area becomes 50
Assuming that the resistance increases, the current density flowing between the electrode tips is reduced by about 30%, resulting in an insufficient amount of Joule heat required for resistance welding. Therefore, it was confirmed that the amount of penetration between the objects to be welded was insufficient, and the possibility that the objects to be welded peeled from each other was increased.

On the other hand, according to electrodes having the same conductivity, it has been confirmed that a material having higher durability has a longer life. Here, the long life is based on a criterion that the life of the electrode has expired in a state where the tensile strength of the work to be welded has become less than a predetermined value. Therefore, in order for a material having higher durability to have a longer life, the amount of deformation of the electrode tip with time is small.
It is necessary that a sufficient and sufficient current density can be ensured for resistance welding.

From the above findings, the applicant of the present invention has used the electrode material of high conductivity for the shaft portion at the tip of the electrode, and tried to reduce the amount of temporal deformation of the electrode material of high conductivity as much as possible. Then, a composite electrode having a structure in which the periphery of the electrode material is protected by a material having high durability has been developed.

[0015]

An electrode for resistance welding according to the present invention is an electrode for resistance welding in which an electrode is connected to a tip of a holder and a member to be welded is resistance-welded through the electrode.
The outer shape of the electrode is formed in a tapered shape so as to be directed to the member to be welded, and the tapered electrode body is formed of a copper material, and the central portion of the electrode body is made of a material having higher rigidity than the electrode body. It is characterized by being surrounded by a hollow cylindrical member made of

In this case, it is preferable that the conductivity of the electrode is 75% or more in IACS. More preferably, the electrode body is made of pure copper, and the material of the hollow cylindrical member is made of a copper-impregnated iron alloy, zirconium boride, or a beryllium copper alloy.

[0017]

FIG. 1 shows an electrode 10 for resistance welding according to an embodiment of the present invention. The resistance welding electrode 10 has an electrode body 12, the electrode body 12 extending in a columnar holding portion 14 attached to an electrode holder (not shown), and further extending downward from FIG. And an electrode tip 16. As is easily understood from FIG. 1, an annular hole 18 that reaches the holding portion 14 is provided at the electrode tip 16. In this case, the conductivity of the electrode body 12 is 75% or more in IACS. IACS
At about 50%, a part of the electrode material is welded to a member to be welded such as a galvanized steel sheet in a thin film at the time of welding, and the electrode body is easily consumed by repeating the welding process. Further, there is a possibility that the electrode is welded to the member to be welded at an early stage of the welding process, and the electrode falls out of the electrode holder.

In the electrode structure according to the present embodiment, an annular support member (hollow cylindrical member) 20 is provided in the hole 18. The support member 20 is moved from the holding portion 14 to the electrode tip 16.
To the end. In this case, the support member 20 is preferably made of a material that is more durable than the material constituting the electrode body 12, and for example, a copper-impregnated iron alloy, a beryllium copper alloy, zirconium boride, or ceramics can be used. is there.

In the above configuration, a welding current of several hundreds of amperes flows from the holding portion 14 constituting the electrode body 12 to the electrode tip 16 during welding. This welding current flows between a pair of opposing electrodes, and the current concentrates on a welded member (not shown), for example, a welded portion of a laminated galvanized steel sheet, generating Joule heat and forming a nugget on the welded member. Is done. As a result, a welded product having a high tensile strength, that is, an improved peel resistance is obtained. In other words, a current having a sufficiently high current density flows through the electrode tip 16, thereby generating sufficient Joule heat required for resistance welding to carry out the welding process of the member to be welded.

[0020]

EXAMPLE In Example 1 of the present invention, the electrode body 12 was made of pure copper, and the support member 20 was made of a copper-impregnated iron alloy.
On the other hand, a zinc steel plate was used as a member to be welded. The sheet thickness was about 0.7 mm, and two sheets of this about 0.7 mm zinc steel sheet were stacked. Then, 11 KA was passed through the electrode body 12 as a welding current. The pressure applied between the electrodes was set to 250 kgf. During this time, the electrode body 12 is
Cool with about 2 l of cooling water per minute.

As comparative examples, an electrode using alumina-dispersed copper (Comparative Example 1) and an electrode using chromium copper (Comparative Example 2) were employed.

When the durability and the sticking resistance test were performed, according to the electrode main body 12 of Example 1, no deformation was observed at the electrode tip even when the number of continuous hitting points approached about 3000 times. In addition, the sticking force was about 2 kgf. On the other hand, in Comparative Example 1, deformation was recognized at the electrode tip when the number of continuous hits was 1,000, and the sticking force was 55
Kgf was confirmed. Further, in Comparative Example 2, when the number of continuous hitting points reached 700, deformation of the electrode tip was recognized, and at that time, the sticking force was 60 kgf (see FIGS. 3 and 4).

Further, in the second embodiment, the electrode body 12 is made of pure copper, and the support member 20 is made of beryllium copper alloy. In the third embodiment, the electrode body 12 is made of pure copper, and the support member 20 is made of zirconium boride. Adopted. The members to be welded, welding conditions, and cooling conditions were the same as those in Example 1.

When the durability (life) and the sticking resistance tests were performed, the electrode of Example 2 had a continuous hit number of 2400.
No deformation at the tip of the electrode was observed at all, and the sticking force was about 5 kgf. In the electrode of Example 3, no deformation was observed at the tip of the electrode even when the number of continuous hitting points reached 1600, and the sticking force was about 7 kgf.

In Examples 1, 2 and 3, the conductivity of the electrode body 12 was 100% IACS.

[0026]

According to the present invention, as described above, the central portion of the electrode body of the resistance welding electrode is surrounded by the highly rigid support member (hollow tubular member). Therefore, the welding current flows with high conductivity in the central part of the electrode body, while durability and anti-sticking properties are ensured by the support member surrounding the central part of the electrode body.
As a result, the life of the electrode itself is prolonged, and the electrode density is stabilized, so that a high-quality welded product can be stably obtained over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional explanatory view of a resistance welding electrode according to the present embodiment.

FIG. 2 is a partially cutaway perspective view of the resistance welding electrode shown in FIG.

FIG. 3 is a first embodiment in which the resistance welding electrode shown in FIG. 1 is employed.
7 is a graph showing results of comparison between Comparative Examples 1 to 3 and Comparative Examples 1 and 2 in terms of the relationship between the electrical conductivity and the sticking force.

FIG. 4 is a first embodiment employing the resistance welding electrode shown in FIG. 1;
9 is a graph showing the results of comparison of Nos. 1 to 3 and Comparative Examples 1 and 2 with the number of continuous hits until the tip deformation rate reaches 3%.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Electrode for resistance welding 12 ... Electrode main body 14 ... Holding part 16 ... Electrode tip 18 ... Hole 20 ... Supporting member (hollow cylindrical member)

Claims (4)

[Claims] 1. An electrode for resistance welding in which an electrode is connected to a tip of a holder and a member to be welded is resistance-welded through the electrode, wherein the outer shape of the electrode is formed to be tapered so as to be directed to the member to be welded. An electrode for resistance welding, wherein the tapered electrode body is formed of a copper material, and a center portion of the electrode body is surrounded by a hollow cylindrical member made of a material having higher rigidity than the electrode body. . 2. The resistance welding electrode according to claim 1, wherein
An electrode for resistance welding, wherein the conductivity of the electrode is 75% or more in IACS. 3. The resistance welding electrode according to claim 1, wherein the electrode body is made of pure copper. 4. The resistance welding electrode according to claim 1, wherein said hollow cylindrical member is made of a copper-impregnated iron alloy, zirconium boride, or a beryllium copper alloy. Electrode for resistance welding.