Coefficient of friction at interface of lubricated upsetting process

In the lubricated upsetting process, it is well known that the coefficient of friction over the contact surface between the tool and the workpiece is distributed nonuniformly and changes with the reduction in height and the position at the interface. In order to increase the reliability of the numerical simulation of cold forging processes, more precise input data of the coefficient of friction at the tool–workpiece interface have become necessary. In this study, in order to predict the coefficient of friction at the interface lubricated cylinder upset tests are carried out using a specimen of commercially pure aluminum and a liquid lubricant. The displacements of the points located at the interface are measured. The normal stress and the tangential stress acting on the interface are calculated by the finite element method, using the measured displacement. Then, the coefficients of friction are estimated using Amonton–Couloumbʹs friction law. The coefficients of friction depend on the reduction in height and the position at the interface.