In-situ observation of the bond formation process during ultrasonic metal welding of Al/Cu joints using Laser Doppler Vibrometry

In recent years, ultrasonic metal welding (USMW) has gained considerable research attention due to the increasing application of lithium-ion batteries in electric vehicles. Although USMW is widely used in battery manufacturing, the fundamental understanding and monitoring of the welding process needs to be investigated to ensure the process robustness. Therefore, this work aims to establish in-situ observation of the bond formation process by using Laser-Doppler Vibrometry (LDV). The acquired velocity data was analyzed in the time and time-frequency domains. Based on the relative motion, a five-stage model was developed to describe the welding process. The changes in system dynamics led to the formation of sidebands in the frequency domain. Additionally, the power consumption was recorded by the welding system, which had a good correlation with the system dynamics. The results provided the scientific understanding behind the bond formation process and suggested relevant signals for in-process monitoring.