JPS60255297A - Electrode tip for spot welding - Google Patents

Abstract

PURPOSE:To extend considerably the life of electrode tips in the spot welding stage of materials to be welded by the electrode tips by sticking Al to a specific thickness on the surfaces of the electrode tips in contact with the materials. CONSTITUTION:Galvanized steel sheets 1, 2 having galvanized layers 3 are partially superposed and the electrode tips 5, 6 are disposed on the superposed parts in contact therewith. Electricity is then conducted to the tips 5, 6 to spot-weld the sheets 1, 2. Al or Al alloys 7, 8 are preliminarily stuck to >=0.8mu onto the surfaces of the tips 5, 6 in contact with the sheets 1, 2. The alloys 7, 8 which consist essentially of Al and are added with 1 or >=2 kinds among about 3-40% Si, about 1-10% Cu, about 0.1-5% Mg and about 0-3% Mn in combination are preferable. The Zn-Al alloy is thus positively formed on the surfaces of the tips 5, 6 and the life thereof is improved.

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]

Electrode tip K Ou for spot welding of galvanized steel sheets
-Or gold alloy alumina-dispersed copper is often used, but it has the disadvantage that the life of the electrode tip is inferior to that of cold-rolled steel sheets.

As is well known, the life of the electrode tip in spot welding of galvanized steel sheets is determined by the fact that the zinc layer on the surface of the steel sheet melts due to the welding heat and adheres to the tip surface, and the zn-pe + Zn-0u alloy is deposited on the surface layer of the electrode tip due to thermal diffusion. Form. In the continuous spot welding process, this 7. Damage to the electrode tip is promoted by repeated formation and falling off of the n-Fe+Zn-Qu alloy layer. The life of the electrode tip of a galvanized steel sheet is shortened as the plating thickness increases. On the other hand, compared to the hot-dip plating method, the electroplating method has drawbacks such as a poorer electrode tip life despite thinner plating because the surface of the plating layer is more active.

However, with the invention described in JP-A-56-151180 (it is known that Ni and Mn are added to the electrode of Qu-Pase to improve its 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 an A/1. Or At alloy 0.
The electrode tip life span is improved by allowing the electrode to adhere to a thickness of 8 μm or more.

[Configuration 9 of the Invention] Next, the present invention will be explained with reference to the drawings. In Fig. 1, galvanized steel plates 1 and 2 are placed on the overlapping part of the electrode tip 5.
, 6 are arranged in contact with each other as shown in the figure, and current is applied between the electrode tips 5 and 6 to spot weld the plated steel plates 1.degree.2. The present invention uses At in the spot welding electrode tips 5 and 6.
Alternatively, by adhering At alloy 7.8 to suppress the adhesion of surrounding components of the steel plate plating to the electrode tips 5 and 6,
This can dramatically improve the life of the electrode tip 5.6.

That is, in the case of a galvanized steel sheet using a general Ou-based electrode tip, when continuous spot welding is performed, the plating component 3 in the plating layer, which is melted by the welding heat, adheres to the electrode tip 5.6. 9 reaction to form an alloy layer of non-uniform thickness at the tip of the electrode tip 5.6. This alloy layer becomes thicker due to the increase in the number of dots, so that the electrode tips 5 and 6 are broken.
This will damage the electrode tip 5.6, significantly shorten the life of the electrode tip 5.6, impair normal nugget formation, and reduce weldability.

Therefore, the inventors conducted various studies to improve the continuous dot performance during welding, and as a result A7. It has also been discovered that the above-mentioned difficulties can be advantageously solved by attaching At alloy 7.8 to the part of the electrode tip 5.6 that contacts the object to be welded.

Here, the thick-filled steel sheet refers to a steel sheet coated with zinc or zinc-based PE or Ni by hot-dip plating or electroplating.

This refers to an alloy-plated steel sheet containing one or more of 00, Mn, Ou, 5flP, etc., or a multi-layer plated steel sheet thereof, and the present invention can be effectively applied to these steel sheets. .

The mechanism for improving the life of the electrode tip according to the present invention is that At or At alloy attached to the surface of the electrode tip reacts with the object to be welded, causing damage to the electrode tip.
Of course, it becomes an obstacle that suppresses the reaction of n and □u.
The form of the alloy layer formed on the surface of At or At alloy is
The tail has a mold shape (navel) that is advantageous for nugget formation.
Second, it is possible to actively suppress a decrease in current density due to damage, softening, and deformation of the electrode tip.

Usually, an electrode chip is made by depositing the components constituting the galvanized layer during continuous dots and performing an alloying reaction to form Zn-Fe, Zn, etc. on the surface and inside of the electrode chip.
An alloy layer of -Fe-Ou, Zll-OH, Ou-Zn, etc. 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. Also, the electrode tip softens due to welding heat,
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 solves the above problems by attaching At or an At alloy to the surface of an electrode chip and actively forming a zn-At alloy layer on the surface.

In general, an alloy layer has a lower electrical conductivity than cupht, so forming an excessively large amount of the alloy layer is not preferable because it increases heat generation between the electrode tip and the plate, causing the tip to soften and deform. However, when the damage to the electrode tip or the state of alloy layer formation as described above is disadvantageous to nugget formation, as in the case of a galvanized steel sheet, the expansion of the energized area must be suppressed in some way. To solve this problem, the electrode tip components must be selected so that the alloy layer formed on the electrode tip has a navel-shaped shape.

As a result of studying electrode tip materials with the above-mentioned characteristics, it was found that attaching At or At alloy to the surface of these electrode tips shortens the life of the electrode tips, compared to commonly used single substances such as ou-Qr and alumina-dispersed copper. It is effective in improving the However, if A4 straddles A2 alloy alone, the electrical conductivity is lower than that of O, etc., and the electrode tip tends to soften and deform. Therefore, a composite type of A4 or At alloy and □U or Ou gold alloy is the best. It has been found.

The At alloy attached to the electrode tip is based on A1,
5i (3-40%), Cu (1-10%).

It is effective to use one or a combination of two or more of Mg (0.1-5X) and Mfl (0-3%). The thickness of the At or A7 alloy coated on the electrode tip must be 0.8 μm or more. Electroplating is a method for attaching At or At alloy to the electrode tip.

Hot-dip plating, PVI) (ion plating.

It may also be attached by methods such as vapor deposition, snogging) or by machining a cast and forged product into a cab shape and then fitting or screwing it together.

〔Effect of the invention〕

By applying the present invention, the electrode tip replacement period when using galvanized steel sheets can be significantly extended. Furthermore, it has the effect of reliably improving weldability, such as increasing the number of consecutive welding points and improving the quality of welded joints.

〔Example〕

Next, examples of the present invention will be given along with comparative examples.

Note-1) Melt plating: Plating thickness 120/100 (g
/m') - Double-sided lead-plated steel plate-2) Electroplating: Plating thickness 25/25 (g/n?
), double-sided galvanized steel sheet - 3) Weldability was evaluated by a continuous workability test and the number of dots that could form nuggets. The welding conditions are as follows.

-4) Examples 1.2.3 are chrome copper chips, 4.5.
6 uses alumina dispersed copper chips.

(1) Pressure force: 250Kgf (molten metal @).

200Kgf (electroplating) (2) Initial pressure time: 22H2 (3) Welding time: 8H2 (4) Holding time: 5Hz (5) Welding current: 11KA (6) Steel type: Mild steel plate (force plate thickness: 0.8+5 (8) Tip tip diameter = 5.7φ (conical crest shape) The number of continuous hits was determined as the end point with the nugget diameter of 6 m as the lower limit.

[Brief explanation of the drawing]

41Ll! FIG. 1 is an explanatory diagram showing one row of the present invention. Agent Patent Attorney Masaaki Akizawa 2 others

Claims (1)

[Claims] (1) An electrode tip for spot welding in which A/= or At alloy is adhered to a thickness of 0.8 μm or more on the surface of the electrode tip that comes into contact with the object to be welded.