JPS62286689A - Electrode for resistance welding - Google Patents

Abstract

PURPOSE:To improve the durability of an electrode by containing SiC whisker of the specific volume rate% at least at the tip part of the electrode. CONSTITUTION:An electrode is formed so as to contain the SiC whisker of 5-25%volume rate at the tip at least of the electrode for resistance welding. The electrode first forms the integrated body of SiC whisker, dries it with pressure, then is manufactured with the high pressure casting method, etc. of impregnating a copper or copper alloy under high temp. and high pressure inside a die. The electrode part containing SiC whisker at the volume rate of 5-25% has an extremely high deformation resistant stiffness in a high temp., preventing the fusion, settling, etc. of the electrode material with the counterpart steel plate. The durability of the electrode is therefore improved remarkably.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Object of the Invention] (i!1 Industrial Application Field) This invention is applicable to resistance welding, mainly spot welding, which is commonly performed in automobile manufacturing processes, etc. This invention relates to a resistance welding electrode used.

(Prior technology) In general, electrodes for resistance welding are required to have excellent electrical conductivity, thermal conductivity, and high-temperature strength, and in the case of spot welding of ordinary steel plates, heat-treated chromium copper is used as the electrode. has been done. During use, the distal end deteriorates or deforms due to deformation and pressure, so dressing is performed periodically. However, when the number of welding operations and the number of welding points are large, such as in an automobile assembly process, dressing must be performed frequently.

On the other hand, in recent years, the amount of surface-treated steel sheets used as a rust prevention measure for car bodies has increased.To spot weld this type of steel sheet, it is necessary to apply a larger current than that of ordinary steel sheets, which means that the electrode tip must be The heat load on the area increases. Furthermore, because the surface layer of the steel plate is fused to the electrode, the tip of the electrode is severely deteriorated and damaged, which increases the frequency of dressing, which is one of the factors that impede productivity.

For this reason, it is desired to develop a more durable electrode material to replace the conventional chromium copper (New edition, Automotive Engineering Handbook, 9th edition, pp. 1-41, 1-47-48, 1982) Published by Japan Society of Automotive Engineers of Japan on May 31st).

Therefore, in recent years, in addition to the conventional heat-treated chromium copper, copper-based composite materials, mainly Cu-AJ1203-based composite materials in which fine alumina particles are dispersed, have been used as electrode materials.

(Problem to be solved by the invention) This Cu-AfL203-based composite material has fine AfL2
It is said to have better heat resistance than chromium copper because it is strengthened by the dispersion of o3 particles and maintains its effect up to high temperatures, but even so, its durability is still not sufficient. There was a problem that.

(Objective of the Invention) This invention was made in view of this background, and is made of conventional heat-treated chromium copper and Cu-A 203-based composite material in which fine alumina particles are dispersed. For resistance welding, it is more durable than electrodes for resistance welding, and there is less deterioration and damage to the electrode tip even when spot welding surface-treated steel sheets with improved rust prevention, making it possible to reduce the frequency of dressing. The purpose is to provide electrodes.

[Structure of the Invention] (Means for Solving the Problems) The resistance welding electrode according to the present invention contains SiC whiskers in a volume percentage of 5 to 25% at least at the tip of the electrode made of copper or copper alloy. It is characterized by the presence of

The resistance welding electrode according to the present invention has a matrix made of copper or a copper alloy as described above, and has Si at least at its tip.
FRM (FA fiber reinforced metal) containing C whiskers
It is characterized by consisting of.

The main causes of deterioration in this type of resistance welding electrode are considered to be sagging and fusion with the mating material (steel plate), and improving deformation resistance and rigidity at high temperatures is the way to improve durability. The electrode is usually water-cooled from the rear end, so the temperature rise at the base is not a problem, but the tip that comes into contact with the steel plate turns green and is exposed to considerable high temperature and pressure, so it must be strengthened by regular heat treatment. There are limits to heat resistance in this method. Therefore, as a method for further improving heat resistance, there is a method of combining heat-resistant substances. The aforementioned Cu-A12o3 dispersion alloy is one such type. In this invention, we focused on the fact that FRM, which is a type of composite material, is effective in improving heat resistance, and applied it as an electrode material.

Among the various thermal fibers for FRM, an inexpensive manufacturing method has been developed for SiC whiskers in recent years, and SiC whiskers are now being stably supplied. This SiC whisker has excellent mechanical properties and heat resistance, and is suitable as a reinforcing fiber for FRM.

Furthermore, since it is relatively easy to wet metal compared to other ceramics #aM1, it also has the advantage of being easy to form into FRM. Furthermore, when converting to FRM using the casting method,
Since molded bodies can be made without a binder, there is also the advantage that contamination with impurities can be avoided.

Therefore, in the resistance welding electrode according to the present invention.

At least the tip portion thereof contains the SiC whisker at a volume percentage of 5 to 25%.

In this case, if the SiC whisker content is less than 5%, it will not have a significant effect on improving heat resistance, and if it exceeds 25%, it will be difficult to uniformly disperse it and the processability will deteriorate. ~25%, and even 10
-15% is desirable, and if only the tip of the electrode, which deteriorates significantly during resistance welding, is made into FRM, durability can be improved, but due to manufacturing reasons, partial FR
If it is difficult to make the electrode M, there is no problem even if the entire electrode is made FRM.

In normal cases, resistance welding electrodes are made from raw materials such as forging and rolling.
After the next processing, it is finished into the final shape.

Therefore, in this case, there are methods to convert the electrode material into FRM, such as plating copper or black stone on SiC whiskers and vacuum hot pressing them in a bundle, but these methods have poor productivity. The manufacturing cost is high and this method is not suitable for products that are produced in large quantities, such as spot welding electrodes used in automobile manufacturing processes.On the other hand, this method has relatively high productivity.

There are high pressure casting methods and powder metallurgy methods.

Among these, the high pressure casting method will be explained.

In this high-pressure casting method, first, SlC whiskers are placed in a suitable dispersion medium and loosened by stirring.
Next, a whisker aggregate is obtained by suctioning through a filter.Next, this whisker aggregate is dried under pressure to obtain a whisker molded body having an arbitrary density. Next, after heating this whisker molded body, it is set in a mold, molten copper or copper alloy is poured into it, and high pressure is applied via a plunger until solidification is completed, thereby forming a molded body with SiC whiskers. The FRM is obtained by impregnating copper or copper alloy.

This high-pressure casting method has high productivity because it can be cast repeatedly if the molded bodies are made separately. However, the molten copper or copper alloy is at high temperature and under high pressure, which reduces the lifespan of the casting mold. There are some problems with this point. Also, SiC
There is also the problem that increasing the content of whiskers is difficult because it increases the penetration resistance of copper or copper alloy.
This is possible if the content is around 20%.

Therefore, the FRM material obtained in this way may be processed as is and used as an electrode for resistance welding, but preferably, the strength can be further improved by applying hot and cold stretching processing. Further, in the case of a heat-treated copper alloy whose matrix contains Cr, Zr, Be, etc., the strength can be further improved by applying the necessary heat treatment.

Next, the powder metallurgy method will be explained.

In this powder metallurgy method, first, Si is prepared in a suitable solvent.
Add whiskers and copper or copper alloy powder to form the matrix, stir, and disperse them uniformly in a solvent Next, after drying, press and heat the mixed powder to obtain a compact. Next, the molded body thus obtained is heated, set on a die, and extruded under high pressure to obtain FRMI.

In this powder metallurgy method, the content of SiC whiskers can be arbitrarily controlled by adjusting the amount added.

However, if the content of SiC whiskers becomes too high, the deformation resistance becomes high, making extrusion difficult.

In addition, with this powder metallurgy method, if the compact is prepared in advance, it can be repeatedly extruded, and if the shape of the die is selected, a rod-shaped material can be obtained, so there are fewer secondary processing steps and productivity is high. .

However, if the matrix is a copper alloy, copper alloy powder must be made, and if heat treatment is to be performed, extrusion must be followed by solution treatment and aging, so the effect of stretching by extrusion is Since it will become thinner, the process will be a little more complicated, as it will have to be stretched again if necessary.

(Example) <Example 1> In this Example 1, F
A prototype RM was produced, then processed into an electrode shape for resistance welding, and its durability was evaluated.

That is, a cap-type resistance welding tip electrode of 16 mm in diameter was machined from an ingot obtained under the molten metal forging conditions shown in Table 1, and Zn-coated steel sheets were successively manufactured using this resistance welding tip electrode as shown in Table 2. Spot welding was performed under the spot welding conditions shown below, and the durability of the electrode was evaluated by the number of welds until no nuggets were formed. For comparison, an electrode containing no SiC whiskers, that is, a pure copper electrode, was also tested in the same manner. The results are shown in Table 3. Test pieces were also cut out from the same ingot and the high temperature hardness was also measured. The results are shown in Table 4. As shown in Table 2 and Spot Welding Conditions in Table 3, the electrode containing SiC whiskers has a greater number of dots until nuggets are no longer formed than the electrode that does not contain SiC whiskers. It can be seen that it has excellent durability. In addition, C in which A2203 particles are dispersed
The inventors have also confirmed through experiments that the electrode is more durable than electrodes made of U material. On the other hand, during resistance welding, the temperature at the tip of the electrode may reach 600 to 900°C;
As shown in the table, it can be seen that materials containing SiC whiskers have high hardness at high temperatures and are excellent in thermal properties.

<Example 2> In this Example 2, an FRM was prototyped by a powder metallurgy method employing the extrusion conditions shown in Table 5, and then carried out, that is, the fifth
A cap-type resistance welding tip electrode with a diameter of 16 mm was processed from the rod-shaped material obtained under the extrusion conditions shown in the table, and using this resistance welding tip electrode, Zn-coated steel sheets were continuously spot welded under the spot welding conditions shown in Table 2. A spot welding experiment was conducted, and the durability of the electrode was evaluated by the number of welds until no nuggets were formed. For comparison, an electrode containing no SiC whiskers, that is, a pure copper electrode, was also tested in the same manner. The results are shown in Table 6, and it can be seen that the electrode containing SiC whiskers has a greater number of dots until nuggets are no longer formed than the electrode containing no SiC whiskers, and exhibits excellent durability.

[Effects of the Invention] As explained above, the resistance welding electrode according to the present invention uses copper or a copper alloy as a matrix and contains 5 to 25% by volume of SiC whiskers at least at the tip of the electrode. Because it is.

The electrode tip containing SiC has excellent heat resistance, which significantly reduces deterioration or deformation of the electrode tip during resistance welding, making it especially suitable for resistance welding of surface-treated steel sheets with improved rust prevention. Even when used for a long time, there is considerably less deterioration and damage to the tip of the electrode, the durability of the electrode is improved, and the frequency of dressing can be reduced, resulting in a very excellent effect of significantly improving productivity.

Claims (1)

[Claims] (1) A resistance welding electrode made of copper or copper alloy, characterized in that the tip of the electrode contains at least 5 to 25% of SiC whiskers by volume.