Evaluation of mold materials for precision glass molding
Driven by the wide range of applications in the fields of laser technology, biomedicine and consumer electronics, etc., the demand for high-quality lenses with complex geometries and small dimensions is rapidly rising. Since grinding and polishing of such lenses is neither practically nor economically viable, Precision Glass Molding (PGM) has become a popular production method. PGM is a replicative technology for producing high-precision optical lenses in medium or high volumes. During the one-cycle molding process, a glass preform is heated until the viscous state and afterwards pressed into the desired shape using two high-precise molding tools. This process permits the direct and efficient manufacture of high shape accuracy and surface quality optics without any mechanic post-processing step. The efficiency of PGM processes depend primarily on the lifetime of the high-precision molding tools. Therefore, various investigations focus on enhancing the molding tool lifetime. This work focuses on the evaluation of suitable mold materials for PGM, whereby different substrate materials as well as protective coatings are considered. At this, three different kinds of glass with varying molding temperature were investigated: common optical glass, infrared transmissive chalcogenide glass, and fused silica. The molding temperature of common optical glass ranges from 400°C to 700°C, whereas chalcogenide glass is molded at around 250°C. Fused silica requires a more challenging molding temperature of about 1400°C. Due to the varying molding temperatures, different mold materials can be evaluated for each of the investigated glasses.