Adaptive model-based temperature control in friction stir welding

The welding temperature strongly affects the quality of friction stir welds. Thus, a novel approach for a closed-loop temperature control system was developed and is described in this paper. A model-based ℒ1 adaptive controller was implemented to control the welding temperature during friction stir welding (FSW). This control structure was selected due to its fast adaption to fluctuations in the behavior of the controlled system while guaranteeing robustness of the closed-loop system. A semi-analytical process model, which links the process torque and the welding temperature, was developed and included in the control structure. Thereby, the dynamics of the closed-loop system could be improved. The developed control strategy was compared to the state-of-the-art strategies. The results showed that the developed control structure provides the possibility to reduce the settling time of the closed-loop system while avoiding stability problems. Finally, the effectiveness of the controller was shown during FSW of aluminum to copper.