A NOVEL BALL END MAGNETORHEOLOGICAL FINISHING PROCESS

摘要

A novel ball end magnetorheological finishing process was developed for performing stable and controllable finishing operation on flat as well as 3D free form features of magnetic or non-magnetic materials. The main innovation in this process was generating a magnetic flux density at the end of a cylindrical tool that facilitates the shaping of the magnetorheological polishing fluid in a fashion to resemble like a ball nose cutter. A 4-axis motion controller program directs the resembled polishing fluid to follow the surface to be finished. This paper focuses on the various stages of the development of a novel finishing process. This leads to significant improvement in process performance in terms of smooth controllable functionality, percentage reduction in surface roughness, surface textures at microscopic level of the workpiece surfaces. In the initial stage of development, the magnetorheological cylindrical finishing tool was made to rotate as a whole during the finishing operation with all its constituent components like inner core, magnetic coil and outer core. In this stage, there was no provision of cooling magnetic coil because magnetic coil was rotated with the rotation of the finishing tool during finishing operation. Therefore, it was difficult to incorporate any cooling arrangement over the outer surface of magnetic coil to cool it continuously. Hence, the tool was limited to shorter time of finishing operation due to continuous heating of magnetic coil. Also, some other additional limitations were noticed such as constraint on magnetic coil to produce higher magnetic field, noise and vibration during the finishing operation. These limitations resulted in low effectiveness of finishing operation. To overcome these specific limitations which were observed after initial development of finishing setup, the limitations were overcome by redesigning of cylindrical finishing tool with stationary magnetic coil(integrated with cooling coils) and only central core was allowed to rotate during operation without the outer core. This resulted in smooth rotational motion of the tool without much noise and vibration during finishing operation. The experiments were performed on flat magnetic material workpiece using the modified magnetorheological cylindrical finishing tool. The surface finish obtained was 23.7 nm from the initial surface roughness of 126.1 nm in 30 min with continuous cooling of magnetic coil.