Modelling and simulation of freeform surface generation in ultra-precision raster milling

Abstract

Optical freeform surfaces are large-scale surface topologies with shapes generally possessing non-rotational symmetry with submicrometric form accuracy and nanometric surface finish. Due to the geometrical complexities, the prediction of form accuracy in ultraprecision raster milling of ultra-precision freeform surfaces is more difficult than conventional machining. Nowadays, the achievement of submicrometre form accuracy still depends largely on the experience and skills of the machine operators through an expensive trial-and-error approach. This paper presents a model-based simulation system for the prediction of form accuracy in ultra-precision raster milling of optical freeform surfaces. The system takes into account the cutting mechanics, cutting strategy, and the kinematics of the cutting process. Experimental work has been undertaken to verify the system and the predicted results agree well with the experimental results. The successful development of the model-based simulation system allows the optimum cutting parameters and cutting strategies to be determined without the need to conduct massive and costly trial-and-error cutting tests.