Evaluation of Rheological Properties of Magnetorheological Polishing Fluid and Their Effect on Surface Finish in Ultra Precision Finishing Processes

Magnetorheological finishing (MRF) process for automated lens finishing and Magnetorheological abrasive flow finishing (MRAFF) for internal geometries rely on unique smart behavior of MRP-fluid. The rheological properties of MRP-fluid depend on carbonyl iron particle (CIP) and silicon carbide (SiC) particle size, their volume concentration, magnetic properties and applied magnetic field strength. To study the effect of particle size on rheological properties of MRP-fluid, a hydraulically driven specially designed capillary rheometer is fabricated. The best surface finish improvement was obtained with MRP-fluid containing approximately equal diameter of abrasive particles and CIPs. Least improvement was noticed with smaller CIPs and bigger abrasive combinations used. This is because the smaller size CIPs are incapable of providing the necessary finishing forces for bigger abrasive particles, which results in weak bonding strength.