Detection of an electromotive force during resistance spot welding and its correlation with nugget growth

This article presents a report on an electromotive force that appears in the electromagnetically open circuit during resistance spot welding. We measured the potential drop between the Cu electrodes during the supply of an alternating current while keeping the area surrounding the electrical lines available for the potential drop measurement. We detected a unique electromotive force in the opposite direction to the back electromotive force induced by the change in the current. Here, we demonstrate that the change in the electromotive force is closely associated with nugget growth and the generation of spatter during welding. Based on the temperature measurement around the Cu electrode, we observed a temperature ripple during the welding process and consider this as the driving force behind the electromotive force.