Modeling of surface roughness effect on dry contact friction in metal forming

Abstract

Interfacial conditions such as friction and roughness substantially affect the process characteristics of metal forming. This study developed a dry friction model that accounted for the adhesion and interference effects of surface roughness. A sliding friction coefficient was suggested to provide fundamental information about the interfacial conditions of the contact surface. The proposed model was easily verified by published experiments and predicted values agreed with experimental results. Accordingly, friction coefficient μ clearly increased as relative roughness R m (= roughness of tool $$ R_a^T $$ /roughness of workpiece $$ R_a^M $$ , measured as interference effect) increased. Simulations confirmed that the friction coefficient μ decreased as dimensionless stress S m (= contact pressure p m /tensile strength $$ \sigma_u^0 $$ ) increased at small strain hardening exponent n-values. Under the conditions of large n and small R m values, the friction coefficient μ initially decreased and then increased. It then slightly decreased as dimensionless stress S m increased. However, this trend became less apparent as relative roughness R m increased since friction coefficient μ simply decreased.