Magnetic field assisted abrasive based micro-/nano-finishing

Micro-/nano-machining (abbreviated as MNM) processes are classified mainly in two classes: traditional and advanced. Majority of the traditional MNM processes are embedded abrasive or fixed geometry cutting tool type processes. Conversely, majority of the advanced MNM processes are loose flowing abrasive based processes in which abrasive orientation and its geometry at the time of interaction with the workpiece is not fixed. There are some MNM processes which do not come under the abrasive based MNM category, for example, laser beam machining, electron beam machining, ion beam machining, and proton beam machining. This paper gives a comprehensive overview of various flowing abrasive based MNM processes only. It also proposes a generalized mechanism of material removal for these processes. The MNM processes discussed in this paper include: Abrasive Flow Finishing (AFF), Magnetic Abrasive Finishing (MAF), Magnetorheological Finishing, Magnetorheological Abrasive Flow Finishing, Elastic Emission Machining (EEM) and Magnetic Float Polishing. EEM results in surface finish of the order of sub-nanometer level by using the nanometer size abrasive particles with the precisely controlled forces. Except two (AFF and EEM), all other processes mentioned above use a medium whose properties can be controlled externally with the help of magnetic field. This permits to control the forces acting on an abrasive particle hence the amount of material removed is also controlled. This class of processes is capable to produce surface roughness value of 8 nm or lower. Using better force control and still finer abrasive particles, some of these processes may result in the sub-nanometer surface roughness value on the finished part. Understanding the mechanism of material removal and rotation of the abrasives in these processes will help in rationalization of some of the experimental observations which otherwise seem to be contradicting with the established theories. It also explains why a magnet used in MAF should have a slot in it even though the area under the slot has “non-machining” zone. It elaborates based on the experimental observations why to use pulse D.C. power supply in MAF in place of smooth D.C. power supply.