Investigation of the effects of process parameters on the glass-to-mold sticking force during precision glass molding

Compression glass molding is a promising manufacturing process for high precision, low cost glass optical elements. However, the conditions during glass molding are known to cause sticking between the glass workpiece and the mold surface. Materials for glass molds need to have high hardness and heat resistance, therefore cemented carbide or ceramics are often used. To mitigate the adhesion problem, a thin coating layer of inert materials is deposited on the mold surface. In this research, two different coatings. Pt-Ir and TiAlN, were applied to both tungsten carbide and silicon wafer substrates and then tested in a real molding environment. Experiments based on the design of experiment or DOE revealed factors which significantly affect the sticking force under the described forming conditions including compression hold time, cooling time and compression force. The morphology of the coatings in this research was also carefully investigated using white light interferometry and scanning electron microscopy The methodology developed in this research can be readily applied to quantitatively test the effectiveness of different thin film coatings thus providing the optics industry a solution for high performance molding process design. Results on both WC-Co and silicon substrates also support the notion that different engineering materials can be used for mold fabrication if proper coating is applied.