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 industry for the 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 USW process, especially for the materials with some special properties. 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 ANSYS Workbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process was simulated and analyzed. Firstly, the superelastic constitutive model of NiTi SMAs was constructed. The distribution of temperature and stress field 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 distribution during USW process.

Numerical analysis of ultrasonic spot welding of metal sheets: A review

“…Jedrasiak et al [35] validated the model by comparing the simulated and experimental temperature variation curves. It is in agreement with that reported by Wang et al [32]. Lee et al [9] verified the accuracy of the model by using the surface profiles on the top surface.…”

“…Similarly, Siddiq and Ghassemieh [12,23], Elangovan et al [18,30], Chen et al [31], Du et al [25] and Wang et al [32] have also taken into account the influence of both plastic deformation and friction on heat generation during ultrasonic spot welding. They have considered the heat generated by these two factors together as the heat input in their theoretical and finite element analyses.…”

“…In the case of the friction heat generation at the contact interfaces, the Coulomb friction model is implemented in the model by Chen et al [31]. The model of the heat generation induced by the plastic deformation at the welding interface [18,30,32,33] is taken from the work done by De Vries [34] and given by:…”

“…Shen et al [24] Novel models were developed, which can resolve the issue in the references [17,28,29]. Li et al [8], Siddiq and Ghassemieh [12,23], Elangovan et al [18,30], Chen et al [31], Du et al [25] and Wang et al [32] The friction and plastic deformation are considered as the influence factors.…”

“…Wang et al [32] developed a three-dimensional finite element analysis model using ANSYS WORKBENCH for simulating ultrasonic spot welding of superelastic NiTi shape memory alloy with Cu interlayer. In this paper, it is assumed that only the friction thermal boundary condition and plastic deformation heat flow are introduced between the sheets, top sheet and sonotrode tip, bottom sheet and anvil.…”