Transfer function analysis of welding stage models in Ultrasonic Metal Welding
Ultrasonic Metal Welding (USMW) is a welding process in which two thin metal “workpieces” are welded together. The concept is simple: the workpieces – in our case, sheets of copper- are placed on the anvil, and compressed against each other by the sonotrode. The sonotrode then vibrates horizontally at 20 kHz, leading to friction at the interfaces between the workpieces, anvil and sonotrode. Under the effect of heat and compression, a bond forms between the workpieces. However, the bond strength fluctuates between otherwise similar welds, and these fluctuations are still not understood. In an effort to control these fluctuations, the literature has analysed USMW and described it as happening in stages. The exact stages, and the mechanical models they suggest, differ from one source to another. In this project, the mechanical models suggested in the literature are investigated experimentally: the vibrations of the sonotrode and anvil are measured along the direction of welding. The measurement data is divided into welding stages, and different transfer functions were fitted to the data. The results are then analysed to track the development of the weld, and compared to the literature models.