Penetrator formation mechanisms during high-frequency electric resistance welding

In this study, welding phenomena involved in penetrator formation during high-frequency electric resistance welding were investigated. High-speed cinematography of the phenomena revealed that molten metal bridges, which formed between neighboring strip edges near the apex point, travel along a narrow gap toward the welding point at a speed much faster than that of the strip. Frequency of formation, travel distance, and speed of the bridge were affected mainly by the heat input power into the strip. Among the variables of the bridge traveling behavior, standard deviation of the travel distance appeared to have a strong relationship with defect density in weldments. Based on observation, a new mechanism of the penetrator formation during HF ERW process was proposed.