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

Abstract

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.

Developing magnetorheological finishing (MRF) technology for the manufacture of large-aperture optics in megajoule class laser systems

“…MRF 15,16,17,18,19,20,21 is an advanced polishing technique that can finish optics without propagating the subsurface damage layer. The technique also removes preexisting subsurface damage under the correct conditions.…”

Magnetorheological Finishing: A Review

“…The material removal is enhanced by nonmagnetic abrasive particles, which are constitutes of the slurry and forced out to the polishing interface by a magnetic field gradient. When the MR fluid mixed with abrasives flows over specimen surface, the shear stress of the fluid generates a drag force to move the abrasives, which results in material removal Shorey, Jacobs et al 2001) Fig1.aMagnetorheological finishing bMagnetorheological Finishing Machine In MRF, the magnetic-field-dependent yield stress and viscosity of magnetorheological polishing (MRP) fluid are controlled by controlling magnetizing current in the electromagnet coils producing magnetic field across the finishing zone. The MRP fluid comprises of carbonyl iron particles (CIPs) and very fine abrasives dispersed in the carrier fluid, which exhibits unique reversible change in its rheological properties on the application and removal of external magnetic field.…”

Effect of surface treatment on magnetorheological characteristics of core-shell structured soft magnetic carbonyl iron particles

“…The MR fluid can return to its original liquid-like state reversibly when the magnetic field is removed. Accordingly, the MR fluids have been applied in various engineering fields, including shock absorbers, torque transducer, and polishing technology [9][10][11].…”