A Coupled Thermal-Mechanical Analysis of Ultrasonic Bonding Mechanism

A three-dimensional (3-D) finite element model has been developed to simulate the coupled thermal-mechanical fields in ultrasonic welding of aluminum foils. Transient distributions and evolution of the in-process variables, including normal stress, shear stress, slide distance, heat generation, temperature, and plastic deformation on the contact interface, and their interactions have been studied in detail. The von Mises plastic strain from the simulation has been correlated with the measured bonded area of ultrasonic joints. A possible mechanism for ultrasonic bond formation is proposed. The severe, localized, plastic deformation at the bond region is believed to be the major phenomenon causing bond formation in ultrasonic welding.