Modeling and Analysis of Rotational Magnetorheological Abrasive Flow Finishing Process

Abstract

Magneto rheological abrasive flow finishing (MRAFF) is used to finish complex internal and external geometries with the help of magnetorheological polishing fluid. Such finishing operations play a crucial role in manufacturing process of machine parts. The cost escalates sharply when the requirement is to achieve surface roughness values near nano levels. The need for finishing is to avoid power losses due to friction, increase the wear resistance and to provide a long serviceable life to the equipment. MRAFF is a time consuming process and any effort to reduce the process time even marginally saves production time and cost of the finished product. Researchers have often strived to improve finishing rate and MRR. An attempt has been made to overcome the said limitations, a new finishing process called rotational magneto rheological abrasive flow finishing (R-MRAFF) is developed, which is a combination of rotational abrasive flow machining (R-AFM) and magneto rheological finishing (MRF), for nano finishing of parts even with complicated geometry for a wide range of industrial applications. Rotational magneto rheological abrasive flow finishing (R-MRAFF) process provides better control over rheological properties of abrasive laden magneto rheological finishing medium. Magneto rheological (MR) polishing fluid comprises of carbonyl iron powder and silicon carbide abrasives dispersed in the viscoplastic base of grease and mineral oil. It exhibits change in rheological behaviour in presence of external magnetic field. This smart behaviour of MR-polishing fluid and centrifugal force due to rotation of rams is utilized to precisely control the finishing forces, hence final surface finish. In the present work, an attempt has been made to analyze the total force acting on the single grain at different magnetic field strength and rotational speed and a model for the prediction of volumetric material removal and surface roughness has also been presented. A three dimensional modeling is done to calculate force acting on the single grain. In order to rotate the magnetoreheological polishing fluid (MRPF), rams of the machining system are joined together with the help of a connecting rod. Modeling was done on brass work piece at different magnetic field strengths and at different rotational speeds to observe its effect on final surface roughness and volumetric material removal. No measurable changes in surface roughness a observed after finishing at zero magnetic field and at zero rotational speed. However, for the same number of cycles, the roughness reduces gradually with the increase of magnetic field and rotational speed. This validates the role of centrifugal force and rheological behaviour of magneto rheological polishing fluid in performing finishing action. The present study shows that with the rotation of MR polishing fluid, an extra component of centrifugal force (Fc) adds up to the resultant force which increases the volumetric removal rate and surface finish as compared to other finishing processes.