PATH FORCE CONTROL FOR FRICTION STIR WELDING PROCESSES

In Friction Stir Welding (FSW) processes, force control can be used to achieve good welding quality. This paper presents the systematic design and implementation. on of a FSW path force controller The path force is modeled us, a nonlinear function of the FSW process parameters (i.e., plunge depth, tool traverse rate, and tool rotation speed). An equipment model, which includes a communication delay is constructed to relate the commanded and measured tool rotation speed Based on the dynamic process and equipment models, a feedback controller fir the path force is designed using the Polynomial Pole Placement technique. The controller is implemented in a Smith Predictor-Corrector structure to compensate for the inherent equipment communication delay and the controller parameters are tuned to achieve the best closed loop response possible given equipment limitations. In the path force controller implementation, a constant path force is maintained, even in the presence of gaps, and wormhole generation during the welding process is eliminated by regulating the path force.