On-line evaluation of electrode wear by servo gun in resistance spot welding

More galvanized steels are being used in auto body assembly to improve safety and fuel efficiency of automobiles. However, spot welding these materials will result in a short electrode life due to serious and inconsistent electrode wear. Electrode radial wear during the electrode life test is the main factor leading to unacceptable nugget size. This paper firstly studied the feedback characteristics of servo guns to detect electrode axial wear online based on the developed system of an integrated servo gun with robot. Then a mathematical model of a spherical electrode was established to evaluate radial wear by detecting axial wear online at different electrode wear stages. The model was verified by experiments for welding different galvanized steels. It was shown that evaluation results of the model agreed well with the experiment results. The model revealed that a smaller radius of electrode face at beginning welds would result in a higher electrode wear rate. The method of evaluating electrode wear online based on the model also offered a guidance to determine the suitable time for tip dressing in real production.