Study and implementation of a force stepper and a part fit-up solver algorithm for a servo controlled MFDC spot welder

The goal of this research is to study the effect of a time-varying electrode force on the weld nugget size for mid frequency direct current (MFDC) resistance spot welding (RSW) systems. Using SORPAS^TM, a software for simulation and optimization of resistance welding process, simulations were performed for MFDC RSW with changing force profiles and weld times. Additionally, an algorithm was developed to automatically detect a bad stack fit-up and correct it by applying an additional compensating force. This was implemented on a resistance spot welding gun fitted with a 4.5 KW servo motor along with a built-in resolver, a Unidrive^TM motor controller and a real time embedded program. The simulation and experimental results are presented and compared with results obtained using a constant current (CC) welding process with constant force profile.