Recent advances in the study of the magnetorheological finishing (MRF) have allowed for the characterization of the dynamic yield stress of the magnetorheological (MR) fluid, as well as the nanohardness (H(nano)) of the carbonyl iron (CI) used in MRF. Knowledge of these properties has allowed for a more complete study of the mechanisms of material removal in MRF. Material removal experiments show that the nanohardness of CI is important in MRF with nonaqueous MR fluids with no nonmagnetic abrasives, but is relatively unimportant in aqueous MR fluids or when nonmagnetic abrasives are present. The hydrated layer created by the chemical effects of water is shown to change 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 atomic force microscope scans demonstrate that, when added to a MR fluid, nonmagnetic abrasives (cerium oxide, aluminum oxide, and diamond) are driven toward the workpiece surface because of the gradient in the magnetic field and hence become responsible for material removal. Removal rates increase with the addition of these polishing abrasives. The relative increase depends on the amount and type of abrasive used.

Magnetorheology and sedimentation behavior of an aqueous suspension of surface modified carbonyl iron particlesAn original procedure and device used for the estimation of a sedimentation constant of magnetorheological fluids have been developed. Experiments that vary the volume concentration and particle size of the dispersed phase, as well as the viscosity of the dispersion medium, show the flexibility of the proposed procedure. A procedure for using this device to estimate the yield stress of these fluids is also described. The results given by our device are shown to be in good agreement with flow curves generated by a commercial rheometer.

One suitable way to polish optics of complex shapes is by using a jet of abrasive fluid. In doing so, the energy required for polishing is supplied by the radial spread of the jet, which impinges upon a surface to be polished. Generally, the jet instability results in a non-deterministic polishing process. A method of jet stabilization has been proposed, developed, and demonstrated whereby the round jet of magnetorheological (MR) fluid is magnetized by an axial magnetic field as it flows out of the nozzle. It has been experimentally shown that in this case a stable and reproducible material removal function can be achieved at a distance of several tens of centimeters from the nozzle. At the same time, the interferometrically derived distribution of material removal for the MR jet coincides well with the distribution of the fluid power density calculated using CFD modeling. Polishing results support the assertion that the MR jet finishing process may produce high precision surfaces on glasses and single crystals.

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