Theoretical analysis of magnetorheological finishing of HVOF sprayed WC-Co coating

WC-Co coating with nano-level surface finish is required for some special components in aircraft, automobile and forming industries. In the present study, magnetorheological finishing (MRF) of WC-Co coating is performed. Theoretical models of finishing forces (both normal and tangential force), material removal rate (MRR), surface roughness and surface temperature are proposed for better understanding of the finishing mechanism. During the MRF process, MR fluid gets compressed as it passes through the converging gap. The theory of rolling process is utilized to model the squeezing effect of the MR fluid. The side spreading of the MR fluid ribbon is confirmed by the finite element analysis (FEA) of the magnetic flux distribution in the working gap. The effect of the side spreading is also considered in the force model. It is observed that the squeezing force, magnetic force, and shear force have major contribution in producing overall finishing forces. In the proposed MRR model, the effects of the mechanical properties, shear stress, and hydrodynamic pressure are incorporated. A surface roughness model is proposed by considering the progressive interactions of the active abrasive particles with the surface asperities. The micro-cutting actions and the interfacial friction between the ribbon and work piece surface result in, an increase in surface temperature. The temperature rise of the finishing zone is modelled based on the one-dimensional heat conduction theory. All the proposed models are experimentally verified and good correlations are observed with the experimental values. By performing MRF with diamond abrasives, areal surface roughness (S-a) of the coating is reduced to 130 nm.