Development of Resistance Spot Welding Applying Pulsed High Current for High Strength Steel Sheet

In the automotive indsutry, the applications of high strength steels(HSS) have been increasing for weight reduction of vehcles. However, carbon equivalent of HSS tends to be higher and it leads to more brittle nugget which is easily cracked through the nugget and lower cross tension strength.

 The aim of the paper is to demonstrate that pulsed current pattern can improve the joint strength of 1180MPa steel. The distribution of current density and temperature by high current was evaluated and it was revealed that the appropriate high current heated up HAZ more than nugget. From the fact, we clarify that the pulsed current pattern, the combination of short holding and short high current, can improve cross tension strength of HSS and it’s realized by much shorter extention of the total weld cycle than conventional temper pattern. It means that both high reliablity and high efficiency can be accomplished by the pulsed current pattern.