Study on Optimization of Ultrasonic Welding Process Parameters of Al-Cu Bimetallic Busbar for use in Battery Electric Vehicle (EV)

The battery is the power source of an Electric Vehicle (EV) and improving its operational efficiency is one of the requirements to achieve the required product performance and quality. There are numerous electrical connections in the assembly of a battery pack from cell to module and further module to the battery pack. These connections such as Tab-toTab (i.e., cell-to-cell joining to connect the battery cells in series or parallel) and Tab-to-Busbars can be made through various methods such as soldering, crimping, resistance welding, fusion welding, etc. Still, all these conventional joining methods have some mechanical, metallurgical, electrical, and economic constraints that limit the overall process efficiency. One of the factors includes poor weld quality, voids, cracks, pores, and other defects in the weld zone that affect the battery performance. The Ultrasonic Welding (UW) technique can overcome many issues that persist in conventional methods. In this work, we describe the study of the UW zone's mechanical, thermal, and electrical properties based on the mechanical and microstructural analysis using design and validation processes such as lap shear strength tests, Optical Microscopy (OM), and Scanning Electron Microscopy (SEM). Here we attempted the Ultrasonic Welding of Copper and Aluminum of different thicknesses. The thickness of the intermetallic layer in the heataffected zone could be observed with the help of SEM. A 3D thermomechanical model was also developed with ABAQUS to investigate the coupled mechanical and thermal behavior of materials in ultrasonic welding. Results were validated with experimental results, which can be employed to analyze battery pack performance. This study provides important insight into Al and Cu UW for electric vehicle battery assembly as a basis for future research directions in the field.