Effects of surface-topography directionality and lubrication condition on frictional behaviour during plastic deformation

Abstract

Surface-topography, friction and plasticity form a complex system at the interface of a plastic deformation operation. Surface-topography before deformation affects the frictional behaviour at the interface, which in turn affects the level and distribution of plastic deformation. The surface-topography after deformation operations is determined by a combination of the initial surface-topography, the frictional behaviour at the interface and the level and distribution of the plastic deformation. Friction testing with the asymmetric friction upsetting (AFU) test machine and subsequent surface-topography analysis help to further clarify the relationship between surface-topography, interface friction and plasticity. The frictional conditions during testing are controlled via lubricant viscosity, film thickness, surface roughness, and deformation velocity. High and low viscosity lubricants are used in conjunction with a range of test speeds to produce frictional conditions in the boundary, mixed and hydrodynamic lubrication regimes. The effect of initial surface-topography was examined by preparing five different initial specimen surfaces and recording the surface-topographies before testing. Five surface conditions were used: as received, etched, coarse ground perpendicular to test direction, coarse ground parallel to test direction and polished. A correlation between surface-topography directionality and frictional resistance has previously been observed by testing specimens with grooves machined into the surface at a range of angles [A newly developed test method for characterization of frictional conditions in metal forming, in: Proceedings of the Eighth International Conference on Metal Forming, Krakow, 2000, pp. 91–97; Steel Res. 69 (1998) (4–5) 154–160; Beurteilung des Schmierungsverhaltens unterschiedlich texturierter Oberflächen mit Hilfe des Streifenziehversuches, Diplomarbeit Universität, Gesamthochschule Duisburg, 1996]. In the current work coarse grinding is used in place of machined grooves. The scale of the effect from the surface-topography directionality is compared to the scale of the effect of lubricants, arithmetic roughness value and friction regime. Results indicate that arithmetic roughness value and lubrication regime have greater influence than directionality. These results can be explained via the application of lubrication regime theory and the importance of each component in determining the lubrication condition.