Abstract:

The development of lightweight car body technology has led to widespread usage of high-strength steel in automotive industry， which brings new challenges to the resistance spot welding （RSW） process in car body welding and manufacturing. The occurrence of common abnormal working conditions， such as electrode axis off normal （ON） can negatively impact the consistency of RSW process. In this paper， the influence mechanism of ON condition on spot welding process is revealed by comparing multi-sensor process signals， weld surface morphology， nugget size and joint formation process under standard and ON conditions. The results indicate that compared with the standard condition， the ON condition increases the initial contact area of the sheet-sheet interface， which leads to a slower temperature rise of sheets， a later peak in resistance signal and a delayed nucleation time. In the welding process， the contact area of sheet-sheet and electrode-sheet interface increases， which leads to the decrease of dynamic resistance signal and heat generation， so the nugget size and electrode displacement signal are smaller than the standard condition. Furthermore， the larger contact area along the length direction leads to more heat generation， ultimately resulting in a larger nugget dimension and indentation size in this particular direction. This study can provide theoretical support for the optimization of high-strength steel resistance spot welding process in actual production environment and online quality monitoring of spot welding under complex working conditions.

Key words: resistance spot welding, high strength steel, electrode misalignment, influence mechanism