Coefficient of friction at interface of lubricated upsetting process

► In this paper, the direct observation method of the interface between tool and workpiece of the edge surface in upsetting of the cylinder specimen developed firstly by the authors is used in order to measure the displacement of the position at the interface. ► We can first present that the coefficients of friction calculate by the finite element method using the measured displacement depend on the reduction in height and the position at the interface.