Characterization and monitoring of tool wear in ultrasonic metal welding

In manufacturing lithium-ion battery packs for electrical vehicles such as the Chevy Volt, it is critical to create reliable interconnections between battery cells, module-to-module, and module-to-control unit. Such joint connections must possess reliable electrical conductivity and sufficient mechanical strength to ensure battery performance. Ultrasonic metal welding has been adopted for battery tab joining in lithium-ion battery pack manufacturing due to its advantages in joining dissimilar and conductive materials [1]. Ultrasonic metal welding is a solid-state joining process which uses ultrasonic vibration to generate oscillating shears between metal sheets clamped under pressure [2]. A typical ultrasonic metal welding system is shown in Fig. 1. It is reported that welding tool replacement is a major production cost in vehicle battery production. Specifically, the high production costs due to tool replacement and maintenance can be divided into three major categories [3]: (1) costs due to machine down-time; (2) costs for fabricating, reworking, or refurbishing the replaced tool elements; and (3) costs for removing worn tools and installing new tools before and after tool replacement. Fig. 1 A typical ultrasonic metal welding system [2]