Real-Time Quality Monitoring in Friction Stir Welding : The Use of Feedback Forces for Nondestructive Evaluation of Friction Stir Welding

The focus of the book is to demonstrate a feasibility study for detecting wormhole defects using the frequency spectrum, phase space, and time spectrum of feedback forces in real-time. It is asserted here that the oscillations of the feedback forces are related to the dynamics of the plasticized material flow and that the feedback forces can provide useful information for detecting wormhole defects. Two real-time feedback-force evaluation algorithms are developed for assessing the weld quality. A probability of detection analysis is conducted to compare the wormhole-detection performance of the two algorithms. Both algorithms detect defects greater than 0.5 mm with 95% mean probability of detection, and both algorithms evaluate 3-second-long time series segments in less than 0.1 seconds. The present study not only demonstrates the possibility of identifying weld quality in real-time but also provides evidence that the oscillations of the feedback forces are related to the material flow. In general, the book introduces a real-time approach for providing important feedback information about weld quality to a control system for Friction Stir Welding.