Numerical Simulation of Ultrasonic Spot Welding of Superelastic NiTi Alloys: Temperature Distribution and Deformation Behavior

Abstract Ultrasonic spot welding (USW) has attracted increasing attention due to its high-throughput solid-state bonding mechanism, which shows great potential in the semiconductor and automotive industries for joining of metal sheets. However, the short welding cycle makes it challenging to effectively monitor the temperature history and deformation of the workpieces during the process. In this study, a three-dimensional (3D) finite element analysis model for USW of superelastic NiTi shape memory alloy (SMA) with Cu interlayer was developed using ansysworkbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process were simulated and analyzed. First, a superelastic constitutive model for NiTi SMAs was constructed. The distribution of temperature and stress fields was then obtained by thermal-stress analysis using the direct coupling method, and the superelasticity of SMAs was observed. The simulation results showed that the highest temperature occurred in the center of the welding area during USW, which is proportional to the welding time and inversely proportional to the clamping pressure. In addition, the maximum stress occurred at the center of the contact surface between upper NiTi and Cu interlayer. After that, the validity of the simulation results was verified by setting up a thermocouple temperature measurement platform to collect the temperature data, which exhibited a good agreement with the simulated results. The simulation procedure demonstrates its potential to predict temperature and stress distributions during the USW process.