Mechanical analysis of ultrasonic welding considering knurl pattern of sonotrode tip

Ultrasonic welding is attracting increasing attention in dissimilar material joining. The knurl pattern of sonotrode tip strongly affects the contact status and friction coefficient at the sonotrode/workpiece interface and thus plays a significant role on joint formation. Finite element models, with/without consideration of geometrical feature of sonotrode tip, were constructed to reveal the role of sonotrode geometry during ultrasonic welding process of copper to aluminum. The coupled thermal-mechanical fields and high-strain-rate deformation of metallic materials were incorporated in the models. The simulated results showed that the serrated knurl pattern of sonotrode tip greatly influenced the in-process variables (including stress, strain and displacement) at the contact surfaces of specimens. The localized concentration of plastic strain caused by the specific design of serrated tip knurl pattern, turned out to be the major cause for joint formation. Based on the evolution of average state variables in the bond area, ultrasonic welding process could be divided into three periods. Specimen deformation and material flow mainly occurred in the initial period of welding process. The simulated results were further verified by comparing specimen deformation and temperature evolution with experimental results. (C) 2015 Elsevier Ltd. All rights reserved.