Flow field analysis of the thin fluid film in disc hydrodynamic polishing

Abstract

Nowadays, large aspheric surfaces, including non-rotationally-symmetric surfaces, are increasingly used in ground and space-based astronomical instruments. The fabrication of these surfaces with sub-micrometric form accuracy and nanometric surface finish, especially for hard and difficult-to-machine materials, has always been a challenge to the optics industry. To efficiently produce ultra-smooth surfaces without the subsurface damage and surface scratches, a novel Disc Hydrodynamic Polishing (DHDP) is proposed by the combination of Elastic Emission Machining (EEM) and Fluid Jet Polishing (FJP). Firstly, the polishing tool for DHDP was carefully designed and the feasibility of the proposed method was experimentally verified. It is interesting to find that the liquid film acts as a carrier of abrasive grains between the polishing tool and polished surface. Then, computational fluid dynamics (CFD) was used to study the effects of process parameters on the slurry film flow in disc hydrodynamic polishing. Finally, preliminary experiments are conducted to verify the CFD simulations. The experimental data reasonably agree with the simulation results. The results also show that increasing rotation speed has no influence on the film thickness for polishing tool without grooves, but leads to increased film thickness for polishing tool with grooves. The film thickness increases as the inlet pressure is increased for these two polishing tools.