Innovative process for precise grinding of optical free-form elements

Abstract

The aim of the presented article is to share experience gained throughout the course of two projects focused on precise grinding of a free-form glass optical element with the objective of achieving a surface shape error of less than approximately 10 μm PV before the subsequent polishing phases. Compared to spheres or aspheres machining, it is considerably more demanding, mainly due to the impossibility of using rotationally symmetric shape corrections. The developed and tested process combines a mechanical engineering approach based on the use of the current Computer Aided Design and Computer Aided Manufacturing software with their respective strengths and weaknesses and an optical engineering approach, for which the employment of CNC machines featuring precise control but low flexibility is typical. Therefore, attention is paid mainly to the description of particular process steps like CAD construction and CNC grinding step programming with regard to the necessary software and data handling, as well as the required parametrisation of the used machine equipment.