JPH0494877A - Dc resistance spot welding method - Google Patents

Abstract

PURPOSE:To greatly improve deterioration of the service life of electrodes in performing DC resistance spot welding by performing welding by making arrangement so that the galvanized surface treated face and the surface nontreated face come into contact with a plus side electrode and a minus side electrode, respectively. CONSTITUTION:As a result of carrying out a continuous spot test of an ordinary cold rolled steel sheet and a molten alloyed galvanized steel sheet by using DC inverter welding equipment, the electrodes are worn out and finally made into ringlike nuggets and the service life of the electrodes expires by combination of unevenness by the polarity on both steel sheets. When the galvanized steel sheet and the cold rolled steel sheet come into contact with the plus side electrode and the minus side electrode, respectively, the tip shape of both electrodes is formed into a projecting type and worn out and the service life of the electrodes is improved remarkably. Consequently, deterioration of the service life of the electrodes which is a defect of DC inverter welding can be greatly improved only by limiting the polarity of the welding electrodes and the service life of the electrodes can be remarkably improved even in comparison with the case of AC welding.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention can improve production efficiency by extending the life of electrodes in all industries that implement resistance spot welding, such as the automobile and home appliance industries. The present invention relates to a direct current resistance spont welding method.

<Prior Art> In order to reduce the weight and power consumption of electrical equipment, DC resistance spot welding machines have recently come into widespread use in place of the AC resistance spot welding machines that have been widely used in the past. In particular, inverter-type DC resistance spot welding machines have a large output current relative to the weight of the welding transformer, so the welding transformer can be made smaller and lighter, and is attracting attention as a robot-mounted welding machine. However, in DC resistance welding, a polarity effect appears when one member of the electrode wears out, and the life of the electrode often deteriorates significantly compared to AC resistance welding.

Therefore, in DC resistance welding, the current situation is to frequently dress or replace the electrode to prevent wear and tear. Methods have been proposed to average out the bias.

<Problems to be Solved by the Invention> Frequent dressing or replacement of the electrode will maintain a constant current density at the tip of the electrode, making it possible to form an appropriate weld, but this is not possible at sites where production efficiency is important. This is a method that is industrially impractical as it reduces the production efficiency. Also, JP-A-1-118
The method disclosed in Japanese Patent No. 376 requires modification or installation of the welding machine and is complicated, so it is not a good idea.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC resistance spont welding method that solves the problems of the prior art and can dramatically extend the life of the electrode.

<Means for Solving the Problems> In the present invention, as a result of extensive testing of the polarity effects peculiar to DC resistance welding on electrode wear, we have found that the form of electrode wear for each polarity differs depending on the surface condition of the steel plate in contact with the electrode. Based on this knowledge, by controlling the combination of the electrode polarity and the steel plate in contact with it, they were able to significantly improve the electrode life.

In the present invention, when a cold-rolled steel sheet and a zinc-based surface-treated steel sheet or a zinc-based single-sided surface-treated steel sheet are stacked together and DC resistance spot welded using -U, the positive side electrode has a zinc-based surface treatment surface, and the negative side electrode has a non-surface treated surface. This is a DC resistance spot welding method characterized in that welding is performed in a position where the treated surfaces are in contact with each other.

<Function> Table 1 schematically shows the results of a continuous dot test of ordinary cold-rolled steel sheets and melt-type alloyed galvanized steel sheets using a DC inverter welding machine and the polarity effect of electrode wear.

Due to the polarity of both steel plates, the electrodes wear out due to the combination of unevenness, and eventually form a ring-shaped nugget and reach the end of the electrode's life. However, the wear pattern due to polarity is completely opposite for both steel sheets, and the positive side electrode (Φ side electrode) wears in a concave shape in the cold-rolled steel sheet, and the negative side electrode (O side electrode) wears in a concave shape in the galvanized steel sheet. discovered a phenomenon.

In order to improve the life of the electrode, it is important that the convex t-shaped portions of both the ■ and ○ side electrodes are worn out, thereby maintaining the current density at the tip of the electrode and making it possible to achieve a long life. However, in the case of welding a combination of cold-rolled steel sheets and galvanized steel sheets, the results of investigating the influence of the electrode polarity arrangement on the electrode life and the wear pattern of the electrodes were investigated in the second study.
Shown in the table.

<Example> The present invention was implemented using a DC inverter welding machine. As a zinc-based surface-treated steel sheet, melt-type alloyed galvanized steel sheet (
Weight 45/45 g/nT), melt-type non-alloy galvanized steel sheet (IKJ weight 60/60 g/nT)
, electrogalvanized steel sheet (eye; J clear 30/30 g /
nf ), electrolytic zinc nickel plated steel sheet (mei τJ
Amount 30/30 g/rrO1 organic resin coated electrolytic zinc nickel plating @ plate (resin l g/n'f, ZnN
i 30/30g/n() and 5P as a cold rolled steel plate
CB was used. All plate thicknesses are 0.7 mm.

Table 3 shows electrode shapes and welding conditions, and Table 4 shows examples and comparative examples of the present invention.

The form of electrode wear is determined by the polarity of the electrode and the type of steel in contact with the electrode. When the ■ side electrode is in contact with a galvanized steel plate and the θ side electrode is in contact with a cold rolled steel plate, the tips of both electrodes will have a convex shape. wear and electrode life is significantly improved.

Table 4 Electrode life: Number of dots where nugget diameter < 4.5A (L cut ￥) No matter which combination of zinc-based surface treated steel sheet and cold rolled steel sheet, if welding is carried out using the method of the present invention, the number of dots will be 7.
Il! It can be seen that the electrode life is improved day by day, and even compared to AC welding, the electrode life is improved by about twice as much.

Further, Table 5 shows Examples and Comparative Examples in which steel plates with only the lunar surface subjected to the same surface treatment as above were welded together.

can do. This makes it possible to utilize the advantages of DC inverter welding and to weld the resistance sprocket 1 with high production efficiency.

Claims (1)

[Claims] When cold-rolled steel sheets and zinc-based surface-treated steel sheets or zinc-based single-sided surface-treated steel sheets are stacked together and resistance spot welded using direct current, the positive side electrode has the zinc-based surface treatment side, and the negative side electrode has the non-surface treated side. A DC resistance spot welding method characterized by performing welding in a contacting arrangement.