Numerical Simulation of Ultrasonic Welding for CFRP Using Energy Director

Abstract

An energy director (ED), a sharp, flat- or triangular-shaped resin bead, is usually inserted between CFRPs during ultrasonic welding. In this study, a two-dimensional model was used to conduct finite element analyses for CFRP ultrasonic welding. The effects of the ED shape on the temperature increase, deformation history, and dissipated energy behavior are discussed. The results of the numerical simulations show that the triangular ED more easily increases the temperature than the flat ED does, and thus its use consumes less energy and time than using the flat ED. However, this study indicates that a triangular ED is not always better than a flat ED. In the ED, the temperature is distributed significantly; that is, the temperature range between points is vast. There is the possibility that unexpected chemical reactions such as oxidation occur. It is found that an abrupt temperature increase is caused by a synergic effect. That is, the increase in temperature causes the viscoelastic and frictional dissipated energy to be remarkable, and an increase in dissipated energy increases the temperature. Consequently, it is difficult to optimize the parameters, such as overall pressure, frequency, and welding time, for ultrasonic welding.