JPH0446684A - Spot resistance welding electrode - Google Patents

Abstract

PURPOSE:To remarkably prolong the service life of electrodes by forming a recessed part on the tip of a positive electrode side electrode and forming a projecting part on the tip of a negative electrode side electrode. CONSTITUTION:Since the recessed part 6a is formed on the tip of the positive electrode side electrode 6, the tip of the positive side electrode 6 changes from a recessed shape into a projecting shape by a thermoelectric effect as the number of weldings increases. As a result, in the first half of continuous welding work, a normal nugget is generated by abutting of the projecting part 7a of the negative electrode side electrode 7 on material to be welded and in the second half of continuous welding work, a normal nugget is generated by abutting of the positive electrode side electrode 6 whose tip is deformed into the projecting shape on material to be welded. Consequently, since either of the tips of both electrodes to come into contact with the materials to be welded is formed into the projecting shape, concentration of an electric current on a weld zone is maintained extending for a long period of time and the need for electrode replacement and electrode dressing with high frequency can be also eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode used in DC spot resistance welding, and particularly to an electrode structure that improves the life of the electrode.

[Prior Art] In recent years, DC spot resistance welding machines with less loss have come to be used in place of AC spot resistance welding machines in order to reduce power consumption and the like in various production lines.

However, in DC spot resistance welding, there is a phenomenon in which heat generation in the weld zone is biased toward the positive electrode side, so the problem is that the positive electrode or the negative electrode is more likely to be heated than the negative electrode, resulting in large softening deformation and short electrode life. There was. Therefore, in order to maintain the quality of the welded part, electrode dressing or electrode replacement must be performed frequently, leading to a decrease in work efficiency.

Therefore, in order to deal with the above-mentioned problems regarding electrode life, a technique has been proposed in which polarity switching is used to average out the bias in electrode deterioration and improve the life of the electrode (Japanese Patent Laid-Open No. 1-118376). Public bulletin).

[Problems to be Solved by the Invention] However, in the case of the method of switching the polarity of the electrode as in the above-mentioned publication, there is a limit to the improvement of the electrode life, and a sufficient effect cannot be expected. Furthermore, since a mechanical switch or the like is required for polarity exchange, equipment costs increase and equipment space is restricted.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an electrode that can significantly improve the life of the electrode in DC spot resistance welding without changing the polarity.

[Means for Solving the Problems] A spot resistance welding electrode according to the present invention that meets this objective has a recess formed at the tip of the positive electrode connected to the positive electrode of a DC spot welding transformer, and It consists of a negative electrode connected to the negative electrode of a welding transformer, with a convex portion formed at the tip.

[Function] In the spot resistance welding electrode configured in this way, a recess is formed at the tip of the positive electrode, so as the number of welding increases, the tip of the positive electrode becomes susceptible to thermoelectric effects. deforms from a concave shape to a convex shape. Therefore, in the first half of continuous welding work, a normal nugget is generated due to the contact between the convex part of the negative electrode and the non-weld material, and in the second half of continuous welding work, a normal nugget is generated on the positive electrode side, which has a convex tip and is deformed. A normal nugget is generated by contact between the electrode and the non-weld material.

In this way, one of the tips of both electrodes that comes into contact with the non-welded material is formed into a convex shape, so the concentration of current at the welding part is maintained for a long period of time, and there is no need for frequent electrode replacement or electrode dressing. becomes.

[Examples] Hereinafter, preferred embodiments of the spot resistance welding electrode according to the present invention will be described with reference to the drawings.

1 to 3 show one embodiment of the present invention. In FIG. 1, numeral 1 indicates a DC spot welding transformer. A primary side terminal 2 of the DC spot welding transformer 1 is connected to a welding power source (not shown) via a control device 3. The secondary terminal of the DC spot welding transformer 1 includes a positive terminal 4a and a negative terminal 4b.

A positive electrode 6 is connected to the positive terminal 4a via a secondary cable 5a. A negative electrode 7 is connected to the negative terminal 4b via a secondary cable 5b. For example, in the case of a stationary spot welding machine, the positive electrode 6 is
It is composed of a movable electric electrode connected to a pressurizing means (path shown), and the negative electrode 7 is composed of a fixed electrode. Also,
In the case of a portapull spot welding machine, the positive electrode 6 and the negative electrode 7 are composed of movable electrodes driven by a common pressure means.

The positive electrode 6 and the negative electrode 7 are arranged on the same axis, and the machine 10 to be welded is located between the positive electrode 6 and the negative electrode 7. In this embodiment, the material to be welded 10 consists of two galvanized steel plates 10a and 10b. A recess 6a is formed at the tip of the positive electrode 6 that can come into contact with one galvanized steel plate 10a. Recess 6
a is formed in a hemispherical shape concave in the axial direction. A protrusion 7a is formed at the tip of the negative electrode 7 that can come into contact with the other galvanized steel plate 10b. The convex portion 7a is
It is formed into a hemispherical shape that protrudes in the axial direction.

FIG. 2 shows the shapes of the positive electrode and negative electrode of this example and the shape of a comparative example (conventional electrode). As shown in the figure, the electrode shape in this example is such that the diameter of the positive electrode 6 is 16#, the curvature R of the tip is 40#, and the diameter d of the tip is 6 m. The diameter d- of the recess 6a is 4M, and the curvature R- of the recess 6a is 2.
It is 5m. In the negative electrode 7, the diameter is 16#, the curvature R of the tip is 40#, and the diameter d of the tip is 6M. The diameter d LL of the convex portion 7a is 4M
The curvature RII of the recessed portion 7a is 25#.

Note that the curvature r from the tip to the outer peripheral surface of both electrodes is set to 8 degrees.

Incidentally, as shown in FIG. 2, the electrode used in Comparative Example 1.2 only has no recesses 6a and 7a at its tip, and the shape of the other parts is the same as that of this example. be.

Next, the operation of the above spot resistance welding electrode will be explained.

Using the above electrode, welding current 10.5 KA, energization time 0.2 sec, pressing force 196 ON, dot speed 1 point/point.
The life of each electrode was measured under welding conditions of 3 IA/min and a cooling water flow rate of 3 IA/min. In addition, as the welding machine, an inverter type DC spot resistance welding machine was used in the present example and Comparative Example 2, and a single-phase AC resistance welding machine was used in Comparative Example 1. Also,
As the materials to be welded, an alloyed hot-dip galvanized steel plate with a thickness of 0.8 m and a bare steel plate with a thickness of 0.8 m were used.

FIG. 3 shows the relationship between the number of welding points and the nugget diameter when each steel plate is continuously welded at 20 points alternately. As shown in Figure 3, the number of welding points in this example is approximately 2300.
It can be seen that the nugget diameter decreases dramatically when the value exceeds . On the other hand, it can be seen that in Comparative Example 1, when the number of welding points exceeds about 1000, the nugget diameter decreases rapidly. Comparative example 2
In this example, the polarity of the electrode was changed every 5 points, but as shown in FIG. 3, although the life was improved somewhat compared to Comparative Example 1, it was still far short of that of the present invention. In other words, the present invention can provide about twice the electrode life as compared to the conventional polarity conversion method.

When continuous spot welding involves welding galvanized steel plates together using direct current, or welding galvanized steel plates together and bare steel plates together, the tip of the positive electrode may deform into a convex shape due to the thermoelectric effect. At the same time, since the tip of the negative electrode is deformed into a concave shape, the contact area between the electrode and the material to be welded increases. As a result, the current density at the welding part may decrease from the initial set value, and the dispersed welding current may generate a ring-shaped or horseshoe-shaped irregular nugget.
By making the tip of the negative electrode 7 concave from the beginning and making the tip of the negative electrode 7 convex, it is possible to suppress the progress of electrode wear due to the thermoelectric effect and to concentrate the welding current between the tips of the electrodes. It becomes possible.

[Effects of the Invention] As explained above, when using the spot resistance welding electrode according to the present invention, a recess is formed at the tip of the positive side electrode connected to the positive electrode of a DC spot welding transformer, and DC spot welding is performed. Since a convex portion is formed at the tip of the negative electrode that is connected to the negative electrode of the transformer, it is possible to suppress the progress of electrode wear due to the thermoelectric effect, greatly extending the life of the electrode. Therefore, the current density in the weld zone can be maintained high for a long period of time, and a desired nugget can be formed even in continuous spot welding operations.

Furthermore, since there is no need to change the polarity of the electrodes, there is no need for a mechanical switch or the like for changing the polarity, which is advantageous in terms of equipment costs and equipment space.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the vicinity of a spot resistance welding electrode according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the electrode shape of FIG. 1 and a comparative example, and FIG. FIG. 3 is a characteristic diagram showing the relationship between the number of welding points and the nugget diameter in a comparative example. 1...DC slot 4a...Positive terminal 4b...Negative terminal 6...Positive side electrode 6a...-Recessed portion 7... ... Negative electrode side welding transformer 7a ... Convex portion 10 ... Material to be welded

Claims (1)

[Claims] 1. A recess is formed at the tip of the positive electrode connected to the positive electrode of the DC spot welding transformer, and a convex portion is formed at the tip of the negative electrode connected to the negative electrode of the DC spot welding transformer. An electrode for spot resistance welding featuring: