Experimental investigation of unbonded magnetic abrasive polishing (UMAP) of silicon nitride balls.

摘要

Scope and method of study. New polishing technique know as "Unbonded Magnetic Abrasive Polishing (UMAP)" was designed and built in-house, to investigate polishing of Si3N4 balls in an economical way. UMAP is based on the combination of underling principles of magnetic float polishing (MFP), magnetic abrasive finishing (MAF) and V-groove lapping. Balls to be finished were loaded between an acrylic polishing plate and a beveled top plate attachment to the spindle by spring action. This set up was placed in a non-magnetic chamber mounted horizontally on a lathe. The chamber was filled with a mixture of loose abrasive grit, iron powder, and non-magnetic viscous fluid (a mixture of glycerin, de-ionized water and rust inhibitor). Magnetic field gradient generated around the balls concentrates abrasive particles in the polishing region. Polishing action was achieved by the motion of the balls around the inner surface of the chamber. This action occurs due to relative movement of the polishing plate and the spindle rotating in opposite directions.;Findings and conclusions. A bevel of ≤ 25° with the groove was essential for improving the sphericity. Also, the surface finish improves rapidly without the need for machining this groove. Material removal rate (MRR) up to 1.2 μm/min/ball with an average sphericity of 0.77 μm and a surface finish of 11.6 nm were obtained. The best ball measurements achieved were 0.5 μm sphericity and 10.4 nm surface finish.