JPS5841950B2 - Overlap resistance welding method for surface-treated steel sheets - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for overlapping resistance welding of surface-treated steel sheets,
More details include zinc, aluminum, cadmium, tin,
The present invention relates to a method for overlapping resistance welding of metal materials coated with other metals, alloys, or mixtures of these and organic substances, which can be resistance welded.

As is well known, surface-treated steel sheets with excellent corrosion resistance and aesthetic appearance are used in a wide variety of applications, but there are many problems when stacking and resistance welding these sheets, and various studies have been conducted to solve these problems. However, a satisfactory solution has not yet been found.

Here, as a typical example, conventional problems in spot welding of galvanized steel sheets are explained as follows.

First, the zinc on the surface of the steel sheet melts during welding, so zinc adheres to the welding electrode, and furthermore, zinc oxides and the like accumulate, resulting in significant contamination of the electrode tip, and the electrical conductivity decreases. , the power supply becomes unstable.

Secondly, since this staining and wear is severe, the electrodes must be frequently shaped, which reduces continuous workability.

Thirdly, since zinc melts on the surface of the continuous part of the galvanized steel sheet during welding and is pushed out around the weld, the amount of zinc on the surface of the weld is extremely reduced and the corrosion resistance is reduced.

Examples include.

Various attempts have been made to date to compensate for these shortcomings.

For example, a well-known method is to use a composite electrode in which a material with high high temperature strength such as tungsten is attached to the tip of a copper electrode, but this is intended to reduce deformation of the electrode tip. , corrosion resistance of spot welds is not particularly considered.

In addition, a method is known, for example, from Japanese Patent Publication No. 44-24733, in which a copper alloy tape is sandwiched between the welding electrode and the workpiece, and the tape is moved after a certain number of welding cycles to protect the welding electrode. Neither method can be expected to maintain the corrosion resistance of the welded part.

Furthermore, as a method of maintaining the corrosion resistance of spot welds, there is a method of placing a solder film (or fine powder) on the spot surface together with solder and welding, for example, as disclosed in Japanese Patent Publication No. 39-4220.
However, in this method, the solder is melted along with the zinc, so staining and wear of the electrode tip is unavoidable.

Although various attempts have been made to overcome the various problems mentioned above, the current situation is that these problems have not been completely solved.

The present invention solves at once the above-mentioned conventional problems in lap resistance welding of metal-coated steel plates by means completely different from such known methods.

Specifically, the present invention involves inserting a thin piece of a conductive metal material between the welding electrode and the material to be welded, so that the electrode has less contamination purity than the material to be welded, and has a corrosion resistance suitable for the purpose of use. This is a lap resistance welding method for surface-treated steel plates, which is characterized by welding small pieces together, and is an attempt to provide a new method that can achieve its purpose extremely effectively.

Next, the present invention will be explained in detail with reference to the drawings.

The drawings illustrate the principle of the present invention, and when welding materials 2, 2' having coated metals 3, 3' with a pair of welding electrodes 1, 1', welding electrodes 1 and coated metals 2, 2'. A thin metal piece 5 is sandwiched between the welded material 2 and the metal 3.

Similarly, welding electrode 1'g,! A thin metal piece 5' is also placed in I, and by applying pressure and electricity to this, the materials to be welded 2 and 7 are welded.
A nugget 4 is formed in between to complete the welding.

At this time, the materials to be welded 2, 2' and the metal thin pieces 5, 5@ form a slight nugget, or they appear to be crimped or brazed together through the coated metal 3, 3'. Sufficient bonding is achieved for the purpose of the invention.

The thin metal pieces 5', 5 may be made of any material as long as it is electrically conductive, causes less contamination of the electrodes than the coated metals 3, 3', and can be expected to have a corrosion resistance of □ suitable for the purpose of use.

In short, as shown in Fig. 1, the thin pieces exist as one with the material to be welded after the covering metal has been pushed away by welding, and prevent the bare metal of the welded part from being exposed. What is necessary is to select a material that can provide corrosion resistance that is comparable to that of the covering parts other than the welded parts.

Preferred materials may include iron-based alloys such as stainless steel, nickel-gold, silver, copper, and alloys thereof, depending on the type of coating metal, but may be selected from appropriate materials as required.

There is no particular limit to the thickness of the metal piece, but if it is too thin, the thin piece may break, and if it is too thick, not only is the material wasted, but it also remains as an extra protrusion on the surface of the welded material, so it is not practical. range from 10 to 1000
A thickness of approximately μ is desirable, and a suitable thickness may be selected depending on the thickness of the object to be welded.

According to the method of the present invention, the welding electrodes 1.1/1 do not come into direct contact with the coated metals 3, 3', respectively, so the welding electrodes 1.1/ are not contaminated and always have a uniform surface of the small metal pieces 5, 5'. Since the welding condition is only in contact with the welding material, welding conditions are stable and continuous workability is improved.

Also, the material to be welded 2. Since the small metal pieces 5, 5' having corrosion resistance are joined to the surface of the welded portion z, the corrosion resistance of the welded portion surface does not deteriorate as in the conventional case.

As is clear from the above description, the role of the metal thin pieces is not as a material to be welded, but as an electrode protection material and a corrosion prevention material.

Note that the drawing only shows the principle and does not particularly show the feeding method of the small metal pieces, but one possible feeding method is, for example, by sequentially moving a metal foil tape and placing it on or near the electrode immediately before welding. The tape may be processed into small metal pieces using a cutting jig or punching jig and then fed, or previously prepared small metal pieces may be placed at the welding location using various conventional feeding methods. .

From the above, the shape of the metal piece is not particularly limited, and may be approximately the same shape as the tip of the electrode,
Alternatively, the area may be made larger than the electrode tip area, and the excess portion around the periphery may be peeled off after welding is completed.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Examples The method of the present invention and the conventional method were carried out under the conditions shown in Table 1.

The results are shown in Table 2. * Spot welding is performed continuously, and a tensile shear test according to JIS-23136 is performed at a fixed number of points.

Until the shear strength is judged to be insufficient for practical use. Weldability was investigated by the number of welding points at Ru.

As is clear from the results in Table 2, the continuous workability in the conventional method was 1800 points, while in the method of the present invention it was 860 points.
0 points, indicating an electrode life approximately 5 times longer than that of the conventional method.

In addition, in the salt spray test of spot welds, with the conventional method, the entire surface became red rust in three days because almost all the zinc on the surface was gone, but with the method of the present invention, the spot welds are covered with small pieces of stainless steel foil. Even in a 10-day salt spray test, there was almost no change, showing good corrosion resistance.

As described above, the method of the present invention significantly improves continuous workability compared to the conventional method, and also makes it possible to have extremely excellent corrosion resistance on the surface of the welded part, which contributes to the industry. There is something very dog-like.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is an explanatory view showing an aspect of spot welding according to the method of the present invention. 1.11...Welding electrode, 2,2'...
Material to be welded, 3゜31...Coated metal, 4...
... Nugget, 5,51... Thin metal piece.

Claims (1)

[Claims] 1. A surface-treated steel sheet characterized by inserting a thin piece of a conductive metal material, which has less contamination purity on the electrode than the welding material and has corrosion resistance, between the welding electrode and the material to be welded. Lap resistance welding method.