Several methods to evaluate frictio

Several methods to evaluate friction have been proposed by the Japan Society for Technology of Plasticity (1993).
However these methods are not well simulating severe conditions occurring in actual forging processes. If friction
coefficients, which are the values to represent friction conditions, can be measured under similar conditions to
actual cold forging processes, that makes it possible to select a suitable lubricant for each forging process and
improve calculation accuracy in computer aided engineering. Hansen and Bay (1986) proposed a measurement
method for friction coefficients using a punch consisting of two parts; an inner punch and an outer ring punch. The
outer ring punch rotates to measure both load and torque for calculating the friction coefficient. They showed the
measured results under low pressure with aluminum. Danno et al. (1983) and Kitamura et al. (1996) applied
backward extrusion to evaluate severe friction conditions with steel. They measured forming load, and then they
examined performance of lubricants based on the measured load. However, they did not measure friction
coefficients. The authors proposed an improved backward extrusion equipment with a rotating punch for torque
measurement to adapt the existing method to severe friction conditions in Sawamura et al. (2012).