Estimation of wear behaviour for structures of ultrasonic welding sonotrodes by finite element simulations

Ultrasonic welding has proven to be a promising joining process for creating high-performance multi-material systems. The design of the sonotrode coupling surface affects the resulting bonding strength just as much as wear, which is particularly important for welding complex materials such as titanium alloys. In this work structurings of sonotrode tip surfaces (STS) were designed to increase the joint strength and enhance the tool longeveity. Their suitability for ultrasonic welding, taking tribology into account, was examined using finite element model simulations of the simplified sonotrode movement contacting the upper joining partner. The upper joining partner was defined as Ti6Al4V, which is a challenging joining partner, but of high relevance e.g. in aerospace and the chemical industry. The comparison of the weldability and wear was made based on the simulated von Mises stresses and the plastic deformations in the upper joining partner and the contact stress on the STS. The simulations showed lower contact stresses and higher plastic deformations for a pyramidal flat STS than for a round groove STS. This is consistent with experimental results where the pyramidal flat structure had higher bond strength and lower wear, validating the simulation model. Based on these investigations, a pyramidal flat STS was assessed to be the most suitable, but a hemispherical structure also showed a promising behaviour and should be manufactured and experimentally investigated in the future.