Influence of Surface Topography Deformation on Friction at Sliding Contact Interface in Metal Forming

In order to obtain a better understanding of the frictional behavior at sliding contact interface in metal forming, a novel friction test apparatus was built up. A series of strip drawing friction tests using aluminum 1050 sheet specimens with two types of texturing topographies were conducted at different contact pressures and sliding speeds. The three dimensional surface topographies of specimens before and after tests were measured. Such three dimensional surface parameters as real contact area ratio, closed void area ratio and open void area ratio, were used to describe the variations of surface topography of specimens. Experimental results show that the friction coefficient decreases with increasing nominal contact pressure and sliding speed. The initial surface topography of the specimens has a definite influence on the friction behavior. The three dimensional surface topographies and parameters of the specimens vary regularly with contact conditions. Based on mechani- cal-rheological model, it is found that depending on the surface topography deformation, different mechanisms determine the friction behavior. The dependence of the friction coefficient on nominal contact pressure and sliding speed can be attributed to micro-plasto-hydrodynamic lubrication and hydrodynamic entrainment in the inlet at the interface respectively.