Wall shear model for mechanical annular polishing

The applications and the functionalities required for polished glass are countless. Therefore, the polishing process must be designed with extreme care to eliminate surface defects. In this work, the variables affecting the polishing processes for glass are analysed using computational fluid dynamics (CFD) to understand the detailed mechanics of the material removal rate process. The flow field induced by the rotation of the polishing tool, typically used in the annular polishing process, is simulated over a range of tool speeds at various offset (gap between the surface and bonnet) values. Furthermore, to elucidate the additional impact of the particles on the flow field, simulations are performed for both water and abrasive slurry flows. Findings show that reducing the offset distance between the tool and the glass surface significantly increased the shear stress, with the peak value obtained in the region that is in the closest proximity to the rotating tool. The shear stress profile from CFD simulations is compared against experimental profile data for material loss, which displayed good qualitative agreement, especially in the near bonnet region. From the analysis, a power law expression is developed for the estimation of the local shear stress on the workpiece for a given set of process parameters. An R² value of 0.9385 was obtained, showing good correlation between the developed model and CFD results. As such, this equation can be used to estimate shear stress caused by the flowing slurry at various points on the glass surface with confidence during the polishing process.