Modeling of surface roughness in ball end magnetorheological finishing (BEMRF) process

A new precision finishing process called the ball end magnetorheological finishing (BEMRF) process was developed for super finishing of complex 3D surfaces. This process is based on magnetorheological polishing (MRP) fluid whose rheological behaviour varies with the magnitude of the applied magnetic field. The magnetically energized MRP fluid is used at the tip of a rotating tool to finish workpiece of different materials and shapes. The MRP fluid is a mixture of abrasives and magnetizable carbonyl iron particles (CIP) in a carrier medium. To improve the in-depth understanding of the BEMRF process, this work deals with the theoretical investigations into modeling of surface roughness and mechanism of material removal associated with ferromagnetic workpiece. Since it is very difficult to understand the complex structure of the magnetically energized MRP fluid during finishing operation, microstructure of the constituents of the MRP fluid has been proposed. A theoretical model of magnetically induced normal and shear forces acting on the abrasive is also proposed in the present study. Based on these forces, the material removal process and wear behaviour during finishing operation have been analyzed. While the normal force model explains the penetration of abrasives into the workpiece surface, the shear force model aids in the understanding of three body wear mechanism between the abrasives and the workpiece surface. A mathematical model has been developed to evaluate the surface roughness. Using the developed model, the theoretical value of surface roughness is computed. The close agreement of theoretical and experimental results validates the proposed model.