Parasitic vibration attenuation in ultrasonic welding of battery tabs

Abstract

Lithium-ion battery cells of pouch type for battery electric vehicles are often joined by ultrasonic welding. High-frequency vibration generated by the piezoelectric transducer of the welder creates solid-state bonds between the workpieces via interfacial frictional heat. This vibration, however, can cause parasitic vibration of the entire system that is harmful to the structure (such as destroying existing welds). In this study, a modulation of input waveforms of the ultrasonic welder is proposed to reduce such parasitic vibration. A series of vibration models are analyzed: (a) a discrete model of single-degree-of-freedom (SDOF) mass–spring–damper system to understand rigid body dynamics, (b) a continuous model of multi-degree-of-freedom (MDOF) cantilever beam to study an elastic body system, and (c) a battery welding system to study a complex real-world application. Analyses indicate that the waveform modulation (including 180°-phase shift, pause, amplitude stepping, and frequency modulation) can reduce parasitic vibration while improving or maintaining the quality of the weld that is being ultrasonically made.