In ultrasonic metal welding of battery tabs, high-frequency ultrasonic energy is used to generate an oscillating shear force at the interface between metal sheets to produce solid-state bonds between the sheets clamped under a normal force. Experimental results show that the weld quality of battery tabs strongly depends on the vibrational properties of the weld parts and fixtures in addition to welding parameters such as weld frequency, amplitude, and clamping normal force. This chapter discusses the fundamental aspects of dynamics and vibrations involved in ultrasonic welding.
Using discrete mass-spring-damper models for ultrasonic welding, the basic concepts of vibration and the principle of work and energy are discussed to enable the readers to understand subsequent materials presented in Chapter 11. The underlying characteristics of energy dissipation by friction at weld interface and material damping are described along with the mechanical work by the harmonic force at sonotrode weld tip. It is shown that, in addition to the friction force at weld interface, the ratio between the welding frequency and natural frequencies of the weld parts plays a critical role in determining the amount of work (which is the energy used for weld formation) performed by the friction force at weld interface.
The longitudinal vibration of a bar with variable cross section and its resonance behavior are the basis of sonotrode design in power ultrasonics. An introductory discussion on the frequency response analysis by finite element method of a half wavelength sonotrode is presented.
10.2Energy Dissipation at Frictional Interface
10.3Dynamics of a Sonotrode