Effect of process parameters on the joint strength in ultrasonic welding of Cu and Ni foils

Abstract

ABSTRACTManufacturing of battery packs for electric vehicles requires joining at different levels such as cell level, unit level, and module level, which include the joining of highly conductive and dissimilar layers of thin metal foils. Conventional welding techniques such as fusion welding, resistance spot welding, and laser beam welding are not appropriate for the joining of multiple layers of metal foils with a comparatively thicker tab because they face difficulties in producing large weld nuggets and generate weld defects such as brittle phases. Ultrasonic welding, a solid-state technique, has been found to be the most successful joining process for battery pack manufacturing. Several studies focused on the joining of two layers of dissimilar materials while very few have successfully characterized the welding performance of multi-layer ultrasonic metal welding. In this study, a set of weld attributes was introduced, and weld parameters have been optimized for sound quality joints using optical microscopy and nanoindentation based on those attributes. Different failure types were associated with weld quality based on microscopic images of fractured specimens. A correlation between weld parameters and weld attributes (i.e., bond density and post weld thickness) was developed to provide some insights into their interdependencies.