JPS591074A - Electrode for resistance welding - Google Patents

Abstract

PURPOSE:To improve abrasion resistance and service life, by providing a coating layer conisting of chromium on the surface of an electrode for resistance welding to be brought into contact with a member to be welded. CONSTITUTION:A chromium coating layer 2 is formed on the forward end part of an electrode 1 in the range wider than the contact surface 21 with a member to be welded. A material having high electrical and thermal conductivity like a copper alloy and having high binding force to the layer 2 is used for the elecrode 1. The thickness of the layer 2 is preferably 20mum-70mum. If galvanized steel plates are subjected to resistance welding by using such electrode, the formatin of the brass occuring in the reaction between the zinc in the steel plates and the copper in the base material of the electrode is prevented. As a result, the abrasion of the electrode owing to the deformation by softening of brass is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a long-life resistance welding electrode.

In resistance welding, the workpiece to be welded is placed between electrodes.

This is a welding method in which a large current is passed between the electrodes while pressurizing the parts to be welded, and a nugget is formed by the Geel heat generated at the joint of the parts to be welded, and the parts to be welded are joined together. Used for welding.

However, when using the nine-point method for welding galvanized steel sheets with excellent corrosion resistance, the following problems occurred. That is,
In resistance welding of galvanized steel sheets, which requires large currents, the electrode surface is heated to high temperatures.

However, brass produced by the reaction between the copper of the electrode base material and the zinc on the steel plate has a low melting temperature and high-temperature strength. Therefore, if resistance welding is performed using an electrode with brass formed on its surface, the brass will soften and deform, causing significant deformation and wear and tear on the electrode itself.

As a result, the contact surface with the workpiece increases and the current density decreases.

Proper nugget formation becomes difficult. therefore.

Galvanized steel sheet resistance welding electrode material is a good conductor of electricity and heat, and has great high-temperature strength.

In addition, the material needed to be resistant to metallurgical reactions with zinc.

The present invention aims to solve these problems and provide a resistance welding electrode that has a long service life.

The present invention provides a coating layer (hereinafter referred to as "chromium") made of chromium on at least the surface of an electrode member that comes into contact with a member to be welded.

A resistance welding electrode is provided with a chromium coating layer.

Resistance welding galvanized steel sheets using the electrode of the present invention:
It is possible to prevent the formation of brass due to the reaction between the zinc in the W4 plate and the copper of the electrode base material. As a result, it is possible to avoid the conventional wear and tear of the electrode mainly due to softening and deformation of brass. Furthermore, since a chromium coating layer with excellent high-temperature strength and strong bonding with the electrode base material is provided on the electrode surface, the electrode life can be extended by a large amount.

The material of the electrode member of the present invention may be a copper alloy.

Use a material with excellent electrical and thermal conductivity and strong bonding strength with the chromium coating layer. Among them, 0.5nium,
It may also be a copper alloy in which beryllium or titanium is replaced.

A chromium coating layer refers to a coating layer made of pure chromium!
In addition to chromium, it may contain trace amounts of elements as impurities.

Elements as impurities are silicon and aluminum.

Magnesium, nickel, iron, etc. ◎ As a general rule, it is sufficient to form the chromium coating layer on the surface of the electrode member only on the surface of the electrode member that comes into contact with the member to be welded. However, in reality, during welding, molten zinc is often extruded or scattered and comes into contact with the exposed copper alloy of the electrode member, producing brass. Therefore, in order to prevent this, it is desirable to form a chromium coating layer over a slightly wider area, starting from the center of the part of the surface of the electrode that comes into contact with the material to be welded.

The thickness of the coating layer is preferably from 20 μm to 70 μm.

If the thickness of the coating layer is thinner than 20μm, with a small number of dots,
The coating layer on the surface of the electrode is worn out and it is impossible to prevent the exposed copper of the electrode base material from reacting with the zinc of the material to be welded. However, if the thickness exceeds 70 μm, the coating layer itself generates heat and cracks when energized, resulting in uneven contact between the electrode and the member to be welded.

As a result, a good nugget shape cannot be obtained and the quality of the welded part is unstable.

Methods for forming the chromium coating layer include plating methods, thermal spraying methods, vapor deposition methods, and
Any method such as ion derating method or sputtering method may be used.

Among others, a simple method such as electroplating can also be used to form a coating layer that is firmly bonded to the electrode member.

Hereinafter, nine aspects of the present invention will be described in detail.

Embodiment FIGS. 1 to 4 show a resistance welding electrode according to the present invention. 1 and 2 show the entire flat chip for the lower electrode and its longitudinal section, and FIGS. 8 and 4 show the entire domed chip for the upper electrode, and It shows its longitudinal section.

) - A chromium coating layer 2 is formed on the tip of the electrolyte over a wider area than the contact surface 21 with the workpiece to be welded. - The coating layer is formed using chromic acid (Crot) 250 f/l.

Consisting of 2.6 f/l of sulfuric acid (HISO4) and 5 f/l of sodium silicofluoride (NazSiFg),
Use a plating bath with a bath temperature of 50°C, and a current density of 4OA/dm.
It was done by electroplating under '. In this way, the thickness of each chromium coating layer was 9071 m.

2871 m + 5071 m 160 p m @
A chip of the present invention of 70/Z m was prepared.

And to measure the lifetime of these chips.

Spot welding was carried out using two stacked heat-worked galvanized steel plates with a thickness of 08 t as the welded parts, and a beer test was conducted at every 20 welding points. The relationship between the resulting chromium coating layer and chip life is shown in FIG. 5.The welding conditions in this case were a welding current of 12.000A.

~ Energizing Psyche/L/I O# (60Hs, ), Pressure 2
00 kg, and the hitting speed was 5 seconds/point. In addition, the tip life is determined according to the one-point welding work standard (JISZ-8611), and the first number of dots at which the effective nugget diameter becomes smaller than sJτ (number is the thickness of the galvanized steel sheet) + 4.51 is determined as the φmade life. .

At the same time, as a comparative example, a chip made of the same electrode base material as that of the present invention but without any chromium coating layer, and a chip with 15 tt m t and 160 /J, respectively.
A chip provided with a chromium coating layer of rn was prepared. Then, the same workpieces were spot welded under the same welding conditions as in the present invention, and the life of the tip was measured. The results are shown in FIG.

The lifespan of chips without a chromium coating layer on the surface is 80
He only had 0 RBIs. However, the life of a chip having a coating layer with a thickness of 201 t m was as high as 400 dots, and as the thickness of the coating layer increased, the chip life improved and showed the highest life of 680 dots at 50 μm. However, when the coating layer becomes thicker than 50 μm, the life of the chip decreases, and at a thickness of 160 μm, the life of the chip is comparable to that of a chip without any coating layer.

As is clear from the above, the resistance welding electrode of the present invention has the following characteristics:
Since it has excellent wear resistance and excellent bonding between the coating layer and the electrode member, when used for resistance welding of galvanized steel sheets, it can exhibit a lifespan about twice that of conventional electrodes.

[Brief explanation of drawings]

1 and 8 are perspective views of the resistance welding electrode of the present invention, FIGS. 2 and 4 are longitudinal sectional views of the resistance welding electrode of the present invention, and FIG. 6 is a perspective view of the electrode surface of the electrode. FIG. 3 is a diagram showing the relationship between the thickness of the chromium coating layer and the life of the chip. 1...Electrode member, 2...Chromium coating layer. 21...Contact surface with the workpiece to be welded Applicant Toyota Central Research Institute Co., Ltd. Agent Figure 5 70

Claims (2)

[Claims] (1) A resistance welding electrode characterized in that a coating layer made of chromium is provided on at least the surface of the electrode member that comes into contact with the member to be welded. (2) The resistance welding electrode according to claim 1, wherein the thickness of the coating layer made of chromium is 20 μm to 7 Q It m.