Measurement of Friction Coefficient by Backward Extrusion with Rotating Tool Under Severe Forming Conditions

AbstractIn cold forging processes, friction between materials and dies strongly influences material flow, forging load and damage to the dies. Therefore, several methods to evaluate friction have been proposed. However those methods are not well simulated for the severe conditions occurring in actual forging processes. In this study, a new method to evaluate friction coefficients is proposed. The method applies backward extrusion, which enables us to create high pressure, large surface area expansion and a long sliding distance, for the measurements. The unique feature of the die set used in this method is a rotating punch at a very slow angular velocity. By a combination of measured load and torque, friction coefficients can be monitored throughout the measurement process. Friction coefficients were measured for four types of lubrications; mineral oil, cold forging oil, bonderizing and dry-in-place. With these results, the proposed method enables us to measure friction coefficients under severe forming conditions