The Out-of-Roundness of the Internal Surfaces of Stainless Steel Tubes Finished by the Rotational-Magnetorheological Abrasive Flow Finishing Process

This article reports the experimental findings about the improvement in out-of-roundness (OOR) of stainless steel tubes finished by Rotational-Magnetorheological Abrasive Flow Finishing (R-MRAFF) process. In this process, a rotating motion is provided to the magnetorheological polishing (MRP) medium by means of a rotating magnetic field, and simultaneously, a reciprocating motion is provided to the polishing medium by a hydraulic unit. By controlling these two motions, nano level uniform smooth mirror like finished surface has been achieved and simultaneously OOR of internal surface of tube is reduced. Experiments are planned according to the central composite rotatable design of response surface methodology based on the selected range of process parameters obtained from the preliminary experiments. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting OOR improvement is calculated. It has been found that R-MRAFF process potentially reduces roundness error of axisymmetric parts (maximum improvement in OOR = 2.04 mu m) improving their reliability and wear resistance. The present study shows that, OOR improves with an increase in the rotational speed of the magnet up to an optimum value beyond which the improvement in OOR reduces. From the scanning electron micrographs and atomic force micrographs it has been found that the abrasive cutting marks in R-MRAFF process generate cross-hatch pattern which helps in oil retention in cylindrical workpieces to reduce friction.