Force-Temperature Coupled Controller for Friction Stir Welding of Hybrid M/C

In this paper, a force-temperature coupled controller is proposed to overcome welding quality deterioration owing to heat accumulation in the workpiece during friction stir welding (FSW) with force control alone. The temperature of the weld joint must be controlled to compensate for the force-control problem. To this end, we developed and tested an intelligent tool holder that can receive temperature feedback. Additionally, system modeling for temperature control was experimentally obtained using a system identification method. The feedback controller uses a proportional-integral (PI) controller, and the root-locus method is employed for its design. An experiment was conducted to test the force-temperature coupled control system. The results confirmed that force control is stable in the axial movement range of the tool within ±0.15 mm. This is because the temperature controller appropriately reduced the tool’s rotational speed to maintain the weld joint temperature in the 400℃ range.