Precision Glass Moulding - Process Chain

Process Chain

In order to ensure the desired quality the parts are measured between each process step. Additionally, the parts are handled and transported carefully between the processing and metrology steps.

1. Hotforming of gobs: The precision glass moulding process yields the best results in both quality and cost if it works with precise preforms. These are usually acquired by pressing or hotforming of "gobs" of molten glass. This step is done by continuous glass melting and moulding in single-sided metal moulds. This process is only suitable for high production volumes. For smaller production volumes, the preforms have to be manufactured by mechanical material-removing steps from blocks or slices of raw glass.
2. Precision glass moulding: In this step the preform is directly formed into an optical glass lens. It is necessary to clean the glass preform and the mould before starting the process, but there is no polishing or post-machining required.
3. Lens coating: An antireflection coating is applied to the finished lenses. The lenses are first cleaned, and then loaded into a fixture. The fixture, containing a large number of lenses, is placed in the coating machine. After finishing the process the glass lenses are removed from the holder and the holder is cleaned by sand-blasting or other techniques. Usually the optical coating is done by one of two methods: physical vapour deposition (PVD), in which oxide materials evaporate and are deposited on the lens, and plasma-enhanced chemical vapor deposition (PECVD). Chemical reactions take place in a vacuum and the reaction product is deposited on the lens. The lenses are coated for two reasons:
   1. Manipulate or improve the optical transmission / reflection
   2. Enhance the mechanical, chemical or electrical properties