2–12 Nanofinishing Process for 3D Freeform Surfaces Using Ball End MR Finishing Tool Anant Kumar Singh, Sunil Jha and P.M.Pandey Department of Mechanical Engineering, Indian Institute of Technology, New Delhi 110016, India suniljha@mech.iitd.ac.in Abstract. A new precision finishing process for nanofinishing of 3D freeform surfaces using ball end MR finishing tool is developed. The newly developed finishing process is useful to finish ferro magnetic as well as non-magnetic materials of 3D freeform surfaces using specially prepared magnetorheological polishing (MRP) fluid. The smart behaviour of MR-polishing fluid is utilized to precisely control the finishing forces, hence final surface finish. The existing MR finishing devices and methods are likely to incapable of finishing of 3D freeform surfaces due to restriction on relative movement of finishing medium and work piece. In this newly developed finishing device, the ball end MR finishing tool is used for finishing of different kinds of 3D surfaces where there are no such limitations of relative movement of finishing medium and workpice.It can finish the work surfaces as same as the machining of 3D freeform surfaces by CNC ball end milling cutter and open a new era of its applications in future. The developed process may have its potential applications in aerospace, automotive and molds manufacturing industries. A computer controlled experimental setup is designed to study the process characteristics and performance. Maxwell simulations were done on ferro magnetic as well as non ferro magnetic materials of 3D surfaces to observe the ball end shape of magnetic field intensity at the tip of the MR finishing tool. Keywords: Magnetorheological fluid; MR polishing; strength of magnetic field; Magnetorheological (MR) finishing tool 1. Introduction The traditional methods of finishing processes like grinding, lapping, honing etc. are labor intensive, comparatively less controllable for finishing operations in the manufacturing of precision parts. These processes generally employ a rigid tool that subjects the workpiece to substantial normal stresses which may cause microcracks and other defects resulting in reduced strength and reliability of the machined parts. Among these, finishing of complex 3D shapes and obtaining surface finish of nano-meter order on advanced materials is still a challenging task.To minimize the subsurface damage it is necessary to finishing the materials under gentle conditions, i.e., by applying very low forces. The precise control of finishing forces is an important consideration for fine finishing with close tolerances and without damaging surface topography. In the last decade, many advanced fine finishing processes have been developed to precisely control the abrading forces such as Magnetic Abrasive Finishing (MAF) [1], Magnetic Float Polishing (MFP) [2], Magnetorheological Jet Finishing (MRJF) [3], Magnetorheological Abrasive Flow Finishing (MRAFF) [4], and Magnetorheological Finishing (MRF) [5] in which the magnetic field is used to control the abrading forces. But the applications of these processes are limited to specific geometries only such as concave, convex, flat and aspherical shapes due to restriction on relative movement of finishing medium and work piece. These are incapable of finishing of 3D intricate shaped surfaces. To overcome the above mentioned problem a new precision finishing process for nanofinishing of 3D surfaces using ball end MR finishing tool is developed. The newly developed finishing process is useful to finish ferro magnetic as well as non-magnetic materials of 3D surfaces using specially prepared magnetorheological polishing (MRP) fluid. The MRP-fluid used is comprised of carbonyl iron powder particles and silicon carbide abrasives dispersed in the viscoplastic base of grease and heavy paraffin liquid; it exhibits change in rheological behaviour in presence of external magnetic field. This smart behaviour of MR-polishing fluid is utilized to precisely control the finishing forces, hence final surface finish. In this process a small hemi spherical ball end of MR polishing fluid is formed by indigenous setup and this ball is used to abrade/erode the material from work surface. The movement to the ball is provided by computer controlled 3-axis motion controller. This MR finishing ball may be visualized similar to ball end of a milling cutter movement on a 3 axis vertical CNC machine. The MR finishing tool tip of stiffened ball end of MR polishing fluid is likely to have very much flexibility to move over different kinds of 3D surfaces and it can finish the work surfaces as same as the machining of 3D surfaces by CNC ball end milling cutter