Real-Time Measurement of Friction Stir Tool Motion During Defect Interaction in Aluminum 6061-T6

The objective of this research is to develop a fundamental understanding of the interaction between features on the friction stir tool probe and volumetric sub-surface defects formed during welding. This will guide the development of real-time defect monitoring methods that will promote process adoption in high volume and high-reliability applications. A single-head laser Doppler vibrometer system was used to produce a non-contact measurement of the eccentric motion of a friction stir tool during welding. When features on the tool probe interacted with voided volumes, the tool was momentarily deflected into the voided volume. The distortion signals in the tool position, measured with the laser vibrometer, are correlated with distortions in measured process forces and defect size. The results add understanding to the changes in forces signals that hold potential for defect monitoring and suggest that monitoring may be possible through a motion-based measurement (accelerometer) from the tool side.