Curvature error estimation in ground and polished surfaces of glass moulds

The design and fabrication of moulds for the production of opthalmic lenses require the appropriate selection of CAD-CAM parameter being used to drive the grinding and polishing CNC manufacturing of the workpiece. In a past study, a theoretical-empirical model of the grinding operation was developed to correlate working parameters with macro- and micro-geometric errors characterising the grinded surface. The reliability of the estimate of the comprehensive geometric error in grinding is essential for the planning of the successive polishing operation, which is responsible for the compliance to functional requirements. In the present work, an algorithm for the assessment of curvature profile errors was developed and applied to experimental data from grinded and polished surfaces. Furthermore, the analisys of the evolution of the surface roughness and curvature error has lead to the preliminar definition of a methodology for the identification of optimal duration of the polishing operation in terms of expected geometric quality of the finished surface.