Detection of terminal oscillation pattern in ultrasonic metal welding

Oscillation pattern of the mating parts during the ultrasonic welding process can provide reliable information about the fixation of the parts in the machine and possibly the bond quality. The present work is a very first attempt to in situ capture the oscillation pattern of the terminal. Terminals, made of a brass alloy, are the mating substrate in the process of ultrasonic welding of multi-strand single core aluminum cables in the automotive industry. In this research work, the time signal of the terminal oscillations is captured through piezoelectric transducers. Frequency spectrum of the time signal shows an excitation frequency of 20.3 kHz, which represents the operating frequency of the welding sonotrode. This spectrum also illustrates the novel discovery of the presence of higher-order harmonics at multiples of 2, 3, 4, and 5, i.e. 40.6, 60.9, 81.2 and 101.5 kHz, respectively. Moderate modifications of the geometry of the conventional terminal as well as changes of the terminal fixation in the ultrasonic welding machine are carried out in order to investigate the effect of these two important phenomena on the oscillation pattern of the terminal during welding. Observation of the frequency spectrum of the oscillations shows that terminal fixations during the ultrasonic welding process can strongly affect its vibration pattern, whereas the moderate geometry modifications do not show significant influences on the terminal oscillations. Results of the present study provide new insights into the fundamental understanding of the substrate vibration pattern and the possibilities to affect this pattern for the benefit of manufactured products using ultrasonic welding.