(A) study on the modelling and suboptimal control of the resistance spot welding process

Abstract

Even though the resistance spot welding has been widely used in industry with many advantages, an on-line feedback controller based upon process dynamics is yet to be developed. This is mainly due to the fact that analytical process model as well as on-line measuring technique for weld quality are not available at present to design a feedback controller. In this thesis, analytical models are developed to predict the temperature and voltage distributions during the nugget formation, incorporating with thermoelectric interaction at the interface in the weldment. Based upon this analysis, a reduced order model is established to predict the nugget growth behavior with welding cycles, employing the approximate integral method. The electric conductance is introduced to detect a nugget size and the correlation between the conductance and the nugget size is investigated numerically and experimentally. Based upon these developments, a suboptimal controller is designed, focusing on the regulation of nugget geometry and minimizing control energy needed for welding.