Development of resistance spot welding technology applying multi-stage adaptive control for narrow pitch spot welding

Narrow pitch spot welding causes decrease in nugget diameter due to shunting to existing- welds under conventional resistance spot welding. This study aims to develop new resistance spot welding technology for ensuring required nugget diameter regardless of weld spacing. Adaptive control based on real-time feedback of heat quantity was applied for welding of mild steel sheets. However, expulsion occurred from steel sheet surface around the contact edge with electrode when weld spacing was shortened to 10mm. To solve this problem, a new adaptive control method was developed. The method includes 2-stage adaptive control, in which heat quantity is controlled independently in each stage to obtain proper nugget diameter. It is effective to set relatively low heat quantity compared to conventional method in the 1st stage to ensure current pass between steel sheets, and then to apply enough current-flow to obtain proper nugget diameter in the 2nd stage. This method can decrease shunt current flow to existing-welds, and excess increase in welding current and over-heating around contact edge with electrode was suppressed. Appropriate nugget diameter can be consequently ensured without expulsion from steel sheet surface even with 10mm weld spacing.