Adaptive torque control of friction stir welding for the purpose of estimating tool wear

In this paper, an adaptive torque controller for friction stir welding (FSW) that can estimate parameters such as probe radius which may be changing throughout the welding process is presented. Implementing an adaptive controller with this capability would be of interest to industry sectors in which FSW is performed on high melting point alloys or metal matrix composites (MMC). Welding these materials has shown a greatly accelerated rate of tool wear. Simulations were conducted to examine how extreme tool wear would affect controller performance and how accurately the controller could estimate the probe radius. A simplified wear model consisting of a linear decrease in probe radius was used to verify controller performance. Next, a wear model consistent with wear patterns seen in the welding of highly abrasive materials was developed. Results indicate that torque is controlled effectively while a change in system dynamics is experienced, as would be expected with adaptive control, but also that the tool profile is accurately estimated after an initial identification period.