Efficient mold manufacturing for precision glass molding

Abstract

Precision glass molding is an efficient near net shape fabrication method for high volume production of aspherical optical glass components. Up until now, the mold manufacturing is still the most cost- and time-consuming process partly due to the fact that the shrinkage error of glass has to be compensated for by means of multiple molding trials and mold modifications (this process is sometimes called mold iteration). The main reason for shrinkage is the different thermal expansions of mold and glass materials during forming and cooling, many other factors such as uneven cooling speed and stress relaxation affect molding process and thus lead to complex form deviation in final geometry. In this paper, an efficient mold manufacturing process with integrated numerical simulation is presented in the form of a case study of an industrial molding example. Taking into account the shrinkage error predicted by process simulation, revised molds are manufactured directly with compensated design. After molding test with the compensated molds, the surface figure of the molded glass lenses was in good agreement with the desired shape within ±1 μm, which matched the original accuracy requirement and no further mold compensation was needed. Based on the result of this work, it is clear that numerical simulation can be used as an efficient tool to predict the final geometrical shape of precision molded glass components, which leads to an efficient mold manufacturing with lower production cost and a shorter cycle time.