A design tool for selection and optimization of surface finish in mixed lubrication

This paper presents a deterministic approach developed recently for the numerical simulation of mixed EHD lubrication in rolling/sliding point contacts based on 3-D roughness measured and digitized directly from real engineering surfaces. The computer program has been proven to be robust for the entire transition from full film to mixed EHL and all the way down to boundary lubrication, or even dry contact. The simulation is capable of giving detailed results at asperity scale (or entire distribution) for the hydrodynamic and/or contact pressure, film thickness (or gap), surface and asperity deformation, subsurface stresses, friction and flash temperature at the interface, as well as load sharing between the hydrodynamic film and asperity contacts. Example cases with eight different types of surface finish, including ground, shaved, honed, chemically polished and mechanically super-finished, are analyzed under the same operating conditions. Results are compared with those from ideally smooth surfaces. Different lubrication modes due to different surface finishing processes have been observed. The effect of surface roughness/topography on the lubrication and surface contact characteristics is found to be significant. The detailed results are apparently useful for performance evaluation, efficiency and life improvement, problem diagnosis, failure prevention and production cost minimization. The computer program developed appears to be a useful engineering tool for design optimization and selection of surface finish processes.