A study of ultra-precision raster milling of optical freeform surfaces

Freeform surface has been widely applied to various optical components which require a surface quality with submicrometer form accuracy and nanometric surface finish. Currently the achievement of such ultra-precision surface quality relies largely on the skills and experience of the operator based on a trial-and-error approach, which is a time consuming and expensive process. Ultra-precision raster milling is an enabling technology to generate freeform surfaces with the optical surface quality without any subsequent processing. This paper presents the fundamental knowledge about ultra-precision raster milling, including the cutting mechanism, cutting strategies, cutting path plans, tool path generation and hence a slide motion error model has been established to predict the form error generation. A series of experimental studies have been undertaken and the prediction results were found to agree well with the measured values.