JPS60187482A - Electrode tip for spot welding - Google Patents

Abstract

PURPOSE:To extend the life of electrode tips to contact with galvanized steel sheets which are materials to be welded by plating >=1 kinds among Al, Ni, Ti to the surfaces of said tips. CONSTITUTION:A titled electrode tip for spot welding is constituted by plating >=1 kinds among Al, Ni and Ti to the surfaces of electrode tips 5, 6 to contact with materials to be welded. Galvanized steel sheets 1, 2 which are the above- mentioned materials to be welded are superposed and the tips 5, 6 are disposed on the superposed parts in contact therewith. An alloy layer is formed by the Al, Ni, Ti components on the surfaces of the tips 5, 6 as a medium in the stage of such welding, by which the life of the tips 5, 6 is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode tip suitable for spot welding of galvanized steel sheets.

[Prior art]

Cu- is applied to the electrode tip for spot welding of zinc-plated copper plate.
Cr alloys and alumina-dispersed steels are often used, but they have the disadvantage that the lifespan of electrode tips is inferior to that of cold-rolled steel sheets.

As is well known, the life of an electrode tip in spot welding of galvanized steel sheets is affected by the fact that the zinc layer on the surface of the steel sheet melts due to welding heat, adheres to the tip surface, and stains due to thermal diffusion. Forms an alloy. In the continuous spot bath welding process, the formation and falling off of this Zn-Fe or Zn-Cu alloy layer is repeated, thereby promoting damage to the electrode tip. The life of the electrode tip of a galvanized steel sheet becomes shorter as the plating thickness increases. On the other hand, compared to the hot-dip plating method, the electroplating method has drawbacks such as poor electrode tip life despite thin plating because the surface of the plating layer is active. However, as in the invention described in Japanese Patent Application Laid-Open No. 56-1jl180 (it is known that Cu-based electrodes contain Ni, Si, and Mn to improve their physical properties and mechanical properties,
The above drawbacks cannot be overcome.

[Purpose of the invention]

The present invention has been made to advantageously solve these difficulties, and is characterized by the presence of At and Ni on the surface of the electrode tip that comes into contact with the object to be welded.

It is plated with one or more components of Tl to improve the life of the electrode tip.

[Structure and operation of the invention]

Next, the present invention will be explained based on the drawings. When welding the galvanized steel sheets 1.2 by overlapping them in FIG. , 2 are spot welded. In the present invention, an electrode tip 5.6 for spot welding is plated with 1'8i or more of At, Ni or T1, and a steel plate plating layer is formed at a portion of the electrode tip 5.6 that contacts the plated steel plates 1 and 2. By making the adhesion to the electrode tips and the accompanying alloying reaction uniform, the life of the electrode tips 5 and 6 can be dramatically improved.

That is, in the case of a galvanized steel sheet that has been used with a general Cu-based electrode tip, when continuous spot welding is performed, the plating component 3 in the plating layer melted by the welding heat becomes the electrode tip 5.6. It adheres to and warps to form an alloy layer with a non-uniform thickness at the tip of the electrode chip 7'5.6. This alloy layer is
Due to the increase in the number of dots, the electrode tip 5
, 6, significantly shortening the life of the electrode tips 5, 6 and impairing normal slit formation.
This will reduce weldability.

Therefore, as a result of various studies conducted by the present inventors in order to improve the continuous dot performance during welding, the above-mentioned results were obtained by plating the electrode tips 5 and 6 with one or more of At, Ni, and TI. The plated steel sheet referred to here refers to a steel sheet that has been coated by hot-dip plating or electroplating, and is coated with zinc or zinc as a main component by these plating methods. Fe, Ni.

One or two of Cor Mn r Cu + S n etc.
It refers to alloy-plated steel sheets or multilayer-plated steel sheets containing more than 100% of the alloys, and can be effectively applied to these steel sheets. In addition, it can be applied not only to single or mixed dots but also to mixed dots with a cold-rolled steel sheet.

Although the mechanism of the improvement in the life of the electrode tip according to the present invention is not clear, the At
It is thought that the Ni or Ti components serve as a medium to form an alloy layer that is effective for extending the life of the electrode tip. That is, the electrode tip is made by depositing the components constituting the plating layer of the galvanized steel sheet during continuous dotting and causing an alloying reaction.
An alloy layer such as Fe-Cu% Zn-Cu% Cu-Zn is formed. The formed alloy layer has a thick non-uniform distribution in the center where the current density flowing between the plates is low at the center of the contact area. In addition, the electrode tip softens due to bath heating,
In the process of increasing the contact area between the electrode tip and the plate and lowering the current density, the non-uniformity of the thickness of the alloy layer described above is further promoted, and nugget formation is significantly inhibited.

It is important to prevent such a state from occurring in order to improve the life of the electrode tip.

The present invention provides Zn-Fa with a uniform thickness on the surface of the electrode chip,
In order to actively form a Zn-Fe-Cu alloy layer, A1. , Nl or Tlr plating. Generally, alloy layers have lower electrical conductivity than Cu, so excessive formation of an alloy layer increases heat generation between the electrode tip and plate, causing chip softening and deformation. So I don't like it. However, when the damage to the electrode tip or the state of alloy layer formation is as described in (5) above, as in the case of galvanized steel sheets, if the form is unfavorable to nugget formation, it is difficult to obtain a uniform alloy layer on the surface of the electrode tip. It is effective to identify conditions that promote moderate alloying.

As a result of studying electrode chip materials having the above-mentioned characteristics, we found that the surface of the electrode chip, such as commonly used Cu-Cr or alumina-dispersed copper, should be plated with one or more of At, TI, and Ni. is effective in improving electrode life.

Among these, those plated with Ti are the most excellent in that they can improve the electrode life without deteriorating the quality of the joint. At plating can be done at low cost and is therefore highly economical. When welding high-strength steel plates, Nf-plated ones tend to allow N1 to penetrate into the welded parts.
It is not suitable for steel plates with a tensile strength of 60 to 9 f/rrm2 class or higher because it may form a locally brittle structure.

When plating electrode tips, it is effective to use a plating stick with a thickness of 300 to 8000X, assuming that it improves the life of the electrode tip and does not impair the workability of spot bath welding. be.

Examples of methods for plating At, Ni or TI on the electrode tip include electroplating, PVD (ion blasting, vapor deposition, sputtering, etc.), and diffusion plating.

〔Effect of the invention〕

By applying the present invention, it is possible to significantly extend the electrode tip replacement period when using galvanized steel sheets, and to reliably improve weldability, such as increasing the number of continuous points and improving the quality of welded joints. There is an effect that can be achieved.

〔Example〕

Next, examples of the present invention will be listed together with comparative examples.

(7)

[Brief explanation of drawings]

FIG. 1 is an FFL diagram showing one example of the present invention. 1.2... Galvanized steel sheet, 3... Galvanized layer,
4... Plating original plate, 5.6... Electrode chip. (9) Figure 1

Claims (1)

[Claims] At, Ni, TI on the surface of the electrode tip that comes into contact with the workpiece
An electrode tip for spot welding plated with one or more of the following.