Elucidation of material removal mechanism in float polishing

Float polishing (FP) is a non-contact polishing method in which a thin layer of fluid is maintained between the workpiece and precision lap by hydrodynamic pressure effect. While it is known to consistently produce atomically flat surfaces with little or no sub-surface damage, the characteristics of polishing fluid flow and material removal have not been studied in-depth. In this research, the underlying mechanism in FP is investigated by means of computational fluid dynamics (CFD) and molecular dynamics (MD) simulation. It is revealed that a fluid gap few microns in height is generated by the wedge effect of slurry. The near wall flow condition is further investigated by direct observation and tracing of cavitation bubbles. Abrasive particle trajectory tracing is carried out with a well calibrated CFD model, and suggests that single abrasive particles move almost parallel to the workpiece surface at a relative speed of around 0.5 mm/s. Next, single abrasive particle interactions with the surface of a Ni crystal are simulated by MD to predict the required conditions in terms of kinetic energy for effective smoothing of the surface. Finally, it is concluded that the material removal mechanism in FP is dependent on a minimum size of nano-abrasive agglomerates of several 100 nm, and the existence of two types of smoothing phenomena: atomic removal and atomic transfer.