Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

• A freeform surface component is nanofinished using magnetorheological fluid.
• The selected process is rotational-magnetorheological abrasive flow finishing.
• The selected process parameters are abrasive particle size and extrusion pressure.
• Surface roughness ranging from 35 to 78 nm is achieved at various locations.

Freeform complex surfaces have become an inevitable part of many devices to perform specific functions. Some of these components require nanolevel surface roughness value to meet the desired requirements in their applications. Finishing of freeform surfaces to nanometer surface roughness value is always difficult for any process. Rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been applied so far for finishing internal surfaces of relatively simple geometry. In this work, an attempt has been made to improve external topography of freeform surfaces using this process. Large hydrodynamic pressure coupled with magnetic fluid is the principal idea behind these experiments. A smooth mirror like finished surface is achieved with improved finishing rate (nanometer/min) by controlling two motions (axial and rotational) simultaneously on stainless steel workpiece similar to knee joint implant. Magnetorheological polishing fluid with different mesh sizes of abrasive particles and at different extrusion pressures is used to reduce final surface roughness value, to increase uniformity of surface finish on the freeform surface and to enhance finishing rate. Surface roughness ranging from 35 to 78 nm is achieved at various locations as compared to larger variation in Ra value obtained in the earlier research work.