Not unacceptable but hard to mould are bi-concave lenses, steep meniscus lenses, and lenses with severe features (e.g. Precision glass moulding can be used to produce a large variety of optical form elements such as spheres, aspheres, free-form elements and array-structures.Ĭoncerning the curvature of the lens elements, the following statements can be drawn: Acceptable lens shapes are most bi-convex, plano-convex and mild meniscus shapes. Tool and mould design Lens shapes Shape of optical element Enhance the mechanical, chemical or electrical properties. Manipulate or improve the optical transmission / reflection.Chemical reactions take place in a vacuum and the reaction product is deposited on the lens. 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). After finishing the process the glass lenses are removed from the holder and the holder is cleaned by sand-blasting or other techniques. The fixture, containing a large number of lenses, is placed in the coating machine. The lenses are first cleaned, and then loaded into a fixture. Lens coating: An antireflection coating is applied to the finished lenses.It is necessary to clean the glass preform and the mould before starting the process, but there is no polishing or post-machining required. Precision glass moulding: In this step the preform is directly formed into an optical glass lens.For smaller production volumes, the preforms have to be manufactured by mechanical material-removing steps from blocks or slices of raw glass. This process is only suitable for high production volumes. This step is done by continuous glass melting and moulding in single-sided metal moulds. These are usually acquired by pressing or hotforming of "gobs" of molten glass. Hotforming of gobs: The precision glass moulding process yields the best results in both quality and cost if it works with precise preforms.Additionally, the parts are handled and transported carefully between the processing and metrology steps. In order to ensure the desired quality the parts are measured between each process step. The mold materials also have to be suitable for machining into the precise surface profiles. The tools used must withstand high temperatures and pressures, and need to be resistant to chemical interaction with the glass. The process is executed on a specialized moulding machine, which precisely controls the temperature, travel, and force during the process. When the lens has cooled to the point where it can be handled, it is removed from the tool. After moulding has been completed, the glass is cooled down and the working environment is filled with nitrogen.When the final thickness of the part has been achieved, the pressing switches over to a force-controlled process.After reaching the working temperature, which is between the transition temperature and the softening point of the glass, the moulds close further and start pressing the glass in a travel-controlled process.Infrared lamps are used for heating in most systems. The tool system is nearly closed (no contact of the upper mould) and the entire system of mould, die and glass is heated up.Oxygen is removed from the working area by filling with nitrogen and/or evacuation of the process chamber.The glass blank is loaded into the lower side of the moulding tool.The precision glass moulding process consists of six steps: Temperature (in ☌), travel (in mm), and force (in N) during the process.
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