Masatsune Kondo

Degradation mechanism of electrode tip during alternate resistance spot welding of zinc coated and uncoated steel sheets

Abstract The operation life and degradation mechanism of electrode during resistance spot alternating current welding of zinc coated galvannealed steel sheets were investigated. The electrode life in alternate resistance spot welding of zinc coated and uncoated steel sheets was extremely short in comparison with welding only on zinc coated steel sheets. During alternate resistance spot welding, the ring shaped nuggets were formed easily. This is attributable to the sticking of the alloy layers formed on the electrode top during the previous welding of zinc coated steel, to the uncoated steel surface at the following welding, so that notable wear took place, and the surface profile of electrode tip became flat. Additionally, an accumulation of highly resistant carbonaceous substance layer at the centre of electrode top caused an annular flow of welding current to hinder the nugget formation.

Degradation mechanism of electrode tip during resistance spot welding of aluminium alloy sheets

Abstract This study investigated the electrode life and the electrode degradation characteristics during continuous resistance spot welding of aluminium alloy sheets. When a long welding time and dome radius type electrode were used, the electrode life was extended more than that when a short welding time and radius type electrode are used. The electrode tip is considered to degrade by the following mechanism: an Al–Cu alloy layer is formed at the electrode tip during continuous welding, and then it peels off from the electrode tip transferring to the surface of aluminium alloy sheet. Its peeling makes the electrode tip indented and finally the electrode tip flattens with increasing diameter of electrode tip. In order to eliminate the direct contact between electrode and worksheet, a special Cu foil insert device for resistance spot welding of aluminium alloy sheets was developed and an extremely long electrode life was achieved.

Degradation mechanism of electrode tip during alternate resistance spot welding of zinc-coated galvannealed and uncoated steel sheets

This study investigated the electrode life and the electrode degradation mechanism during alternate resistance spot welding of galvannealed steel sheets and bare steel sheets. As a result, it was found that the electrode life in this type of welding was extremely short in comparison to welding of only galvannealed steel sheets. The reason for this short life is explained by the sticking of the alloy layers formed on the electrode top to the bare steel sheet surface, so that the narrower and sharper shape the original electrode top is the better to prolong the life. Although the ring-shaped nuggets were not formed during alternate resistance DC welding, the electrode degradation mechanism is similar to that during the resistance DC welding of only galvannealed steel sheets.