Abstract
ABSTRACT Magnetorheological finishing (MRF) is a sub-aperture deterministic process for fabricating high-precision optics by removing material and smoothing the surface. The goal of this work is to study the relative contribution of nanodiamonds and water in material removal for MRF of aluminum oxynitride ceramic (ALON) based upon a nonaqueous magnetorheological (MR) fluid. Removal was enhanced by a high carbonyl iron concentration and the addition of nanodiamond abrasives. Sma ll amounts of deionized (DI) water were introduced into the nonaqueous MR fluid to further influence the material removal process. Materi al removal data were collected with a spot-taking machine. Drag force (F d ) and normal force (F n ) before and after adding nanodiamonds or DI water were measured with a dual load cell. Both drag force and normal force were insensitive to the addition of nanodiamonds but increased with DI water content in the nonaqueous MR fluid. Shear stress (i.e., drag force divided by spot area) was calculated, and examined as a function of nanodiamond concentration and DI water concentration. Volumetric removal rate increased with increasing shear stress, which was shown to be a result of increasing viscosity after adding nanodiamonds and DI water. This work demonstrates that removal rate for a hard ceramic with MR F can be enhanced by adding DI water into a nonaqueous MR fluid. Key words: magnetorheological finishing (MRF), viscosity, drag forc e, shear force, normal force, coefficient of friction, nonaqueous fluid, chemical mechanical polishing, aluminum oxynitride (ALON)
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