Study On The Surface Morphology Changing And Tribological Properties At Plastic Deformed Interface

The workpiece and tool and lubricant at the interface form a complex,multivariable, and time-dependent tribological system in sheet metal forming. Inorder to investigate the effect of surface topography on the tribological behavior insliding contact interface formed on strip drawing, a new friction test device wasbuilt. The sample used was Aluminum sheet with three kinds of texture of regularmicro-cavity surface, unidirectional groove surface and random surface. The frictiontests were performed under high contact pressures at different sliding velocities withlubricant. The three dimensional surface topography of samples before and afterfriction tests were measured with non-contact optical profilometer, and variations ofsurface topography of samples were analyzed by using3D surface parameters of the3D average surface roughness（Sa）, void volume in center zone （Vvc）and voidvolume in valley zone（Vvv）. Using image threshold segmentation based onmaximum between class variance method, the real contact area ratio is calculatedthrough the Matlab programming. Experimental results show that regularmicro-cavity surface has a lower friction coefficient than unidirectional groovesurface and random surface. At a relatively low contact pressures, the frictioncoefficient of the three kinds of surfaces decreases with the increase of contactpressure, and at a relatively high contact pressures, the friction coefficient of thethree kinds of surface increases with the increase of contact pressure. The frictioncoefficient of the three kinds of surface is significantly dependent on the slidingspeed at a certain contact pressure.3D surface parameter are changed before andafter the test because of the impact of working conditions on the surfacemorphology, reflect the mechanism of surface morphology variations at a certainextent. The real contact area ratio increases with the increasing contact pressure, anddecreases with the increasing sliding speed. Surface topography, contact pressureand sliding speed are shown to be crucial factors to variations of tribologicalbehavior in the interface during sliding.Along with experiment, the finite element method based on fractal theory andANSYS is used to analyze plastic deformation of rough surface contact interface atthe whole process. The deformation of the surface asperities under differentconditions of contact pressure and sliding speed were simulated and the test results were compared to further analyze the mechanism of plastic deformation of theinterface morphology changes in the surface.