On-line condition monitoring of friction stir spot welding tool using vibration measurements

Friction stir welding and spot welding (FSW/FSSW) tool condition plays a vital role on joint quality and successful completion of welding process. Detecting FSW tool pin cracking or fracture during welding is not possible by visual monitoring of the weld, as the tool pin is submerged in the butted or lapped joints. Even if the pin is fractured, the tool shoulder can still process the surface of the workpiece, giving false indication about the progress of the weld. Monitoring systems that can detect the condition of the tool can help operators or automated FSW machines in taking corrective actions to avoid continuation of the welding process with a damaged pin. These systems can also alert the operators to the necessity of replacing the tool. Researchers in the past have developed several methodologies in monitoring manufacturing processes (e.g. machining) utilizing force, temperature measurements, acoustic emission and vibration monitoring. Vibration is directly related to a machine's structural dynamics and its working health conditions giving it an advantage over other techniques in detecting structural related problems such as cracking.