Effects of Contact Pressure and Strain on Friction in Sheet-Metal Forming©

Abstract

The authors suggested a boundary friction model which treats the combined influence of surface roughening (due to inhomogeneous deformation) and surface smoothing (due to asperity flattening) on the real area of contact in the presence of plastic strain. Predictions using the new model for sheet metal forming indicate that the friction coefficient tends to decrease with strain for low pressures (when roughening is of dominant importance) and tends to increase with strain for high pressures (when asperity flattening prevails). This behavior was confirmed experimentally by friction measurements for 6022-T4 aluminum sheet stretched over A2 steel pins of different diameters with a commercial lubricant. Average coefficients of friction predicted by the model were in good agreement with those measured experimentally.