Development of a flexible and reliable numerical simulation for precision glass molding of complex glass optics

摘要

In the last two decades, precision glass molding is gradually becoming a competitive hot-replicating manufacturing technology for precision glass optical components such as aspherical lenses, lens arrays and freeform lenses. During the process, however, different factors may cause shrinkage errors on the final lens shape and index drop which affect the optical performance of the final molded lens. Currently, such errors have to be compensated by time-consuming and cost intensive iteration loops featuring tryout molding and mold revising. In order to avoid this iteration process in precision glass molding, an integrated numerical simulation tool developed at Fraunhofer IPT is introduced in this paper based on several case studies, which can be used to provide optimized mold design, process design and automated mold compensation of the mold insert. In this process simulation, the entire molding process, including the heating, molding and cooling steps, are precisely described by a combined thermal and structural model. Generalized Maxwell Model is used to describe the complex stress and structural relaxation behavior of the glass, and detailed test series are conducted to acquire precise knowledge about the material properties of optical glass. In this way, the deformation of glass pre-forms during the molding phase and thermal shrinkage of the molded glass optics during the cooling phase can be precisely predicted in the process simulation. Based on this information, a compensated contour layout for mold inserts, as well as an optimized process parameter set can be defined in advance and directly applied to the initial mold inserts during manufacturing, so that the challenging practical integration is eliminated. Further more, a 3D process simulation has also been successfully developed for the prediction of pitch error of molded glass wafer optics. With the motivation to adapt this simulation approach to the requirements of industrial applications, a Graphical User Interface was also developed. With this GUI, The customer will be able to use this interface to perform simulations of his own without technical knowledge of the finite element method (FEM). The positive feedback from customer shows that the developed flexible and reliable numerical simulation is a useful tool to reduce the development cost and enhance the performance of precision glass molding for industrial application.