Friction coefficients of battery metals and the usage in ultrasonic welding simulations

Ultrasonic welding is one of the mainstream joining technologies for an automotive battery pack where battery cells are welded mostly in series with bus-bars on interconnect circuit boards in battery electric vehicles (BEV). Mathematical simulations, such as Finite Element Analysis, have been used to simulate the ultrasonic welding for process and joint quality optimizations. Since friction-generated heat plays a critical role in ultrasonic welding, accurate friction coefficient measurement is essential to the fidelity of such simulations. This paper describes the experimental results of friction coefficients for such materials, as well as the effects of surface conditions, sliding frequencies, and normal loads on the friction coefficient. It was found that the average friction coefficient between a Cu bus-bar and a Cu tab is 1.2, while between a Cu bus-bar and an Al tab is 0.6. The finite element analysis of the battery tab welding process using the measured friction data is depicted.