Experimental Investigations of Axial Force Control for Friction Stir Welding Based on Multi-Level Fuzzy Control

Friction stir welding (FSW) is a promising welding technology and is being extensively researched because it can produce high-quality joints. However, attendant process variability such as improper clamping, uneven workpiece flatness and other process variations changes is known to lead to joints with inconsistent material properties. A large number of studies have indicated that axial force control can be used to achieve good welding quality. This work describes the development of a closed-loop control system which is equipped with a custom real-time wireless force dynamometer for friction stir welding. A multi-level adaptive fuzzy PID control approach for maintaining constant axial force is designed. Implementation of the control scheme is conducted on a vertical milling machine configured for FSW using an open architecture controller. The experimental results demonstrate that the controller maintains the constant axial force and shows desirable dynamic behavior, even when the disturbance is encountered during the welding process.