Monitoring and Control in Friction Stir Welding

Friction Stir Welding (FSW) is a recently-developed technique where metals are joined together through mechanical stirring. FSW, often performed by robotic welders, is being used in an increasing number of industries such as aerospace, maritime and transportation. FSW has proven to be very effective and has replaced fusion welding and riveting in a number of manufacturing processes. In order to increase FSW’s applicability, it is important that methods for control, fault avoidance, and detection be implemented reliably. Unfortunately, a number of faults occurring in FSW are difficult to detect. A worm-hole fault for instance occurs entirely below the weld surface. What is needed is a non-destructive testing system which can detect fault occurrences in real time and take corrective action. In this work, the use of force feedback is investigated as a means of monitoring gaps in Friction Stir Lap Welding (FSLW). Results are presented which indicate that although the gaps cannot be seen visually before or after the weld, forces can be used to discern even small gaps between the metals.