Process Optimization in Glass Polishing Based on a Material Removal Model

In the industrial world there are different production processes for the manufacturing of spectacle lens. Nowadays casting is the most common lens manufacturing method. Here, the mould production is based on three stages: grinding, polishing and hardening, where, in the second step, different sets of process parameters play a key role in quality, time and cost. To optimize the polishing process of moulds a model for the correlation between the material removal and the process parameters is proposed. The model is developed for CNC ball polishing of free-form surfaces, where the pad, made of a polyurethane layer superimposed to a rubber bulk, moves along a scanning path, in a suspension of cerium oxide. The material removal can be derived through pressure and sliding velocity between polishing pad and workpiece and consequently can be related to the CAD-CAM-CNC parameters e.g. tool and workpiece shape, dimension and modulus of elasticity, feed rate, feed step, tool rotational speed and radial tool deformation. The model has been validated on ground glass flat samples polished varying the process parameters and it shows a satisfactory estimation of material removal as a function of the process parameters.