Experiments and observations regarding the mechanisms of glass removal in magnetorheological finishing

Recent advances in the study of the magnetorheological finishing (MRF) have allowed for the characterization of the dynamic yield stress of the magnet orheological (MR) fluid, as well as the nanohardness (H-nano) of the carbon yl iron (CI) used in MRF. Knowledge of these properties has allowed for a m ore complete study of the mechanisms of material removal in MRF. Material r emoval experiments show that the nanohardness of CI is important in MRF wit h nonaqueous MR fluids with no nonmagnetic abrasives, but is relatively uni mportant in aqueous MR fluids or when nonmagnetic abrasives are present. Th e hydrated layer created by the chemical effects of water is shown to chang e the way material is removed by hard CI as the MR fluid transitions from a nonaqueous MR fluid to an aqueous MR fluid. Drag force measurements and at omic force microscope scans demonstrate that, when added to a MR fluid, non magnetic abrasives (cerium oxide, aluminum oxide, and diamond) are driven t oward the workpiece surface because of the gradient in the magnetic field a nd hence become responsible for material removal. Removal rates increase wi th the addition of these polishing abrasives. The relative increase depends on the amount and type of abrasive used. (C) 2001 Optical Society of Ameri ca OCIS codes: 220.5450, 220.4610.