Development of a new program control setting of welding current and electrode force for single-side resistance spot welding

For the indirect-type single-side resistance spot welding, the new program control setting of welding current and electrode force were developed in order to increase the welding current range, suppress the expulsion, and promote the weld nugget growth. Welding experiments verified that the occurrence of expulsion and formation of molten nugget were significantly influenced by the contacting conditions at the interface between the electrode tip and upper sheet and at the faying surface between the sheets and the resulted heat generation at the early stage of welding. Focusing on better controlling the contacting conditions at the early stage, the two-stage program control setting of welding current and electrode force was developed and successfully improved the weldability, increasing the welding current range, compared with constant current and force setting. Numerical simulations were conducted to study the welding phenomena and clarified the effect of two-stage current and force setting on the suppression of expulsion and promotion of nugget growth.