Experimental and theoretical investigation into surface roughness and residual stress in magnetorheological finishing of OFHC copper

Highly finished copper surface without any appreciable residual stress is in high demand in electronics, space, and optical industries. Conventional finishing processes are not suitable for the finishing of copper owing to its extremely lower hardness. In the present study, wheel based magnetorheological finishing (MRF) process is used to attain nanolevel surface roughness of oxygen-free high conductivity (OFHC) copper. The wheel speed, working gap and feed rate are selected as the main controlling process parameters. Areal surface roughness ( S a ), normal force, tangential force and residual stress are studied as the response parameters. The measurement of residual stress has a significant importance as it may affect the optical properties of the finished surface. The residual stresses and phases of all the finished surfaces are analysed using X-ray diffraction (XRD) technique. A theoretical model is proposed to predict the surface roughness of the MRF processed surfaces. It is observed that a nanolevel surface roughness with lower residual stress can be attained by performing MRF with a higher working gap, and lower wheel speed and feed rate. In the present study, a minimum surface roughness ( S a ) of 15.5 nm and compressive residual stress of 6.9 MPa are attained on the OFHC copper surface.