Identification of Coulomb's friction coefficient in real contact conditions applied to a wire drawing process

Coulomb's friction coefficient in cold win drawing is determined via a new upsetting sliding test procedure which takes into account the bulk properties in the contact surface vicinity of both coating and substrate. The test is performed on the real workpiece directly from the drawing plant, thereby the physical and chemical properties of the interface are respected. The test parameters are defined from two simple graphs in order to simulate as well the effective local strain and the contact pressure of the studied forming process. Thus, both the mechanical contact conditions and the associated mechanisms of adhesion or separation and fracture are representative. During the test both the normal and the tangential forces are recorded and the mechanical analysis of the contact area easily enables the calculation of the mean Coulomb's friction coefficient. This result is directly usable for the finite element simulation of the drawing process and leads to a very good agreement in regards to the experimental drawing force. Moreover, the analysis of the deformed part of the tested workpiece enables the selection of lubricant coatings and also prevention of some eventual defects. (C) 1997 Elsevier Science S.A.