The surface effect of ultrasonic vibration in double cup extrusion test

Ultrasonic vibration has been widely studied because of its excellent utility and performance in the plastic forming of metals. The mechanism and effects of ultrasonic vibration on material flow and deformation have therefore become a focus for current research. The mechanisms of ultrasonic vibration as it acts on materials include the volume effect and the surface effect. Double Cup Extrusion (DCE) testing is an ideal method for studying the surface effect but there have been few studies and some conclusions from those studies have been contradictory. For the present study, a new ultrasonic vibration-assisted DCE device was specifically designed and used for the experiment. In the tests, friction factors were calibrated and analyzed using the finite element method (FEM). The results show that ultrasonic vibration can effectively improve interface friction conditions in DCE. By changing ultrasonic loadings, an explanation was found for the 'illusion' that ultrasonic vibration increased interface friction, as had previously been reported. It was also shown that ultrasonic vibration exhibits a significant size effect, which can efficiently offset the negative size effect of friction in the micro-forming process. Further, it was found that the ultrasonic effect is influenced by the wall thickness of the formed part-the smaller the wall thickness, the more significant the effect of ultrasonic vibration.