Nonlinear friction behavior in ultrasonic welding of aluminum alloy to carbon fiber reinforced PA6 composite

Abstract

Accurate prediction of the friction-mediated interaction between workpieces in ultrasonic welding requires nonlinear multi-physical models. Local contact points that are in slip receive a heat flux from friction, which raises the local temperature and therefore, changes the local material stiffness and local stresses. These local changes affect the contact status and the overall dynamics. The effects of vibration amplitude and clamping force on the nonlinear friction behavior in ultrasonic welding of aluminum alloy to carbon fiber reinforced thermoplastic (CFRTP) are particularly important process parameters that can be controlled. Their effect is investigated through a multiphysics coupled model with consideration of the nonlinear contact, nonlinear structural dynamics, and the transient heat conduction. Solutions are obtained by combining the harmonic balance method with the finite element method. Intuitively, large amplitudes promote sliding and higher heating, while large clamping forces can promote sticking and lower heating. Unexpectedly however, results show that the amplitude has a limited influence on the process, while the clamping force has a significant influence. That is because optimal heating results from a balanced manifestation of sticking, sliding and temperature at the interface. In particular, results suggest that a low clamping force with a high vibration amplitude is desirable for the ultrasonic welding of aluminum alloys to CFRTP composites.