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Plastics Lens Molding by Vibro-Thermoforming
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Yokoi, Hidetoshi / Fujiki, Ryuichi / Yagi, Toshio / Orito, Naoto
This paper describes a new method of manufacturing plastic lenses. Injection molding is the process usually employed to produce plastic lenses. In spite of its popularity, this method presents some problems such as long molding times, adverse optical influence due to molecular orientation near the gate zone and the high cost of the mold. In order to solve these problems, we have developed a new technique to manufacture plastic lenses-called Vibro-Thermoforming-which is a derivation of Vibro-Punching. This is based on a reciprocating half-blanking process with a concentration of thermal energy produced by local deformation. Lenses are then formed from the thermo-softened material. This process can be used for manufacturing lenses from PMMA sheets in 31.5 seconds. The interference fringe number is about 0.3, the resulting surface roughness in Rmax is 0.04ƒÊm and the birefringence index is approximately the same as for injection molding.
Key words: Vibro-Thermoforming / Plastic lens / Lens molding / Vibro-Punching