Effects of knurl tooth angle on mechanical and thermal behaviors of aluminum ultrasonic welding

Ultrasonic welding (USW) has been receiving more and more attentions in material joining field due to its advantages of cleanness and high efficiency. The knurl tooth angle (KTA), as a key factor of horn knurl geometry (HKG), has significant influences on the contact and friction behavior of the joint formation. Although there have been some researches on the simulation of ultrasonic welding, the 3D finite element (FE) model considering the influence of KTA has not been reported. In this study, the FE models of different KTAs are established to reveal the effects of KTA on joint formation. The simulation result shows that the KTA greatly influences the process parameters of the USW after 0.025 s. The gaps of the faying interface and local stress concentration in the sonotrode-workpiece contact area, caused by KTAs less than 120 degrees, are the main reasons for the strength reduction of the joint. The higher average equivalent plastic strain and temperature of the welding area, formed by KTAs greater than 130 degrees, are turned out to be the main reasons for the formation of more bonds. The simulation has been verified by experiments, and the results provide guidance to improve the quality of the joint.