Elastohydrodynamic Lubrication Modeling of Hydrodynamic Nanopolishing Process

Abstract

Nanopolishing processes are used in medical, industrial, telecommunication, optics, and military fields. Hydrodynamic polishing (HDP) is one of the prominent nanopolishing methods in creating nanopolished surfaces on hard and profiled surfaces, where rigid tool-based methods like diamond turning, grinding, and honing have many limitations. This work is focused on modeling of hydrodynamic polishing method. In this method, a film of abrasive suspension is formed between the work-piece surface and a rotating soft tool, which helps in nanopolishing. The past experimental research gives an insight into the process but the process has not been explicitly modeled. Consequently, besides experimental characterization, a numerical/mathematical model of hydrodynamic polishing process is important. This paper presents a model of the HDP process which takes into account the polishing process variables, such as, contact load, spindle speed, tool and work-piece material properties/geometry, and abrasive suspension properties. The response of the model is the pressure distribution and the abrasive film thickness in the polishing zone. To model the elastohydrodynamic process encountered in HDP, the pressure and the film thickness profiles of lubricated isothermal point contacts have been evaluated using the multilevel multi-integration (MLMI) scheme coded in C programming language. Finally, load, tool stiffness, speed, and particle concentration in the suspension have been implicitly correlated to the surface roughness (SR) to evolve a semi-empirical model for surface roughness as a function of mean film thickness and mean pressure. Empirical models for mean film thickness and mean pressure have also been developed as a function of process variables. These models have been developed from a Taguchi L27 orthogonal array wherein the mean pressure/film thickness values have been determined from the model and the average surface roughness values have been measured experimentally. It has been observed that the load does not affect the surface roughness significantly and mean pressure does not change with the change in abrasive size and spindle speed. Abrasive particle concentration has been found to be the most important parameter and it affects the surface roughness significantly.