The use of chalcogenide glass in the thermal infrared domain is an emerging alternative to commonly used crystalline materials such as germanium. The main advantage of chalcogenide glass is the possibility of mass production of complex shaped geometries with replicative processes such as precision glass molding. Thus costly single point diamond turning processes are shifted to mold manufacturing and do not have to be applied to every single lens produced. The usage of FEM-Simulation is mandatory for developing a molding process for complex e.g. non rotational symmetric chalcogenide glass lenses in order to predict the flow of glass. This talk will present state of the art modelling of the precision glass molding process for chalcogenide glass lenses, based on thermal- and mechanical models. Input data for modelling are a set of material properties of the specific chalcogenide glass in conjunction with properties of mold material and wear protective coatings. Specific properties for the mold-glass interaction such as stress relaxation or friction at the glassmold interface cannot be obtained from datasheets and must be determined experimentally. A qualified model is a powerful tool to optimize mold and preform designs in advance in order to achieve sufficient mold filling and compensate for glass shrinkage. Application of these models in an FEM-Simulation “case study” for molding a complex shaped non-rotational symmetric lens is shown. The outlook will examine relevant issues for modelling the precision glass molding process of chalcogenide glasses in order to realize scaled up production in terms of multi cavity- and wafer level molding.
Precision Glass Molding (PGM) is a manufacturing method which enables cost efficient production of highly complex glass optics in medium to high quantities. The produced glass optics can be intended for applications in a spectral range from 180 nm ultraviolet to 13 μm thermal infrared. However, it is necessary to choose the glass type according to their intended task and wavelength domain. Typical glass types used for PGM are low Tg optical glasses. Fused silica and chalcogenide glasses expand applications to UV and IR. The use of different glass types entails a variation of the necessary temperature range in which the glass can be processed. The processing temperature of these glasses varies between 200 and 1400 °C. To ensure an economical processing, mold materials and mold manufacturing technologies are varied according to the task at hand. The application of PVD thin film coatings is one of the methods commonly used for prolonging the molds service lifetime. However, the specific coating has to be selected suitable for the glass type and mold material. To illustrate the differences in molding optical grade low Tg glass, fused silica and chalcogenide glass a representative process chain for PGM is described and peculiarities for each glass category is presented in regards to the state of the art. Finally an outlook on ongoing and future issues for applied research in the filed of PGM is given.