Mold Design for Complex Optical Plastics Components

A key condition for the successful manufacturing of optical plastics parts and a major challenge at the same time is to develop high-performance injection and injection-compression molds. Particularly in the field of optics, the stringent requirements placed on part dimensions and the homogeneity of the internal properties lead to a large number of requirements in terms of the mold concept.

In order to meet these requirements, a modularly-designed injection-compression mold has been developed. The mold features a cone-alignment to ensure a precise centering of the two mold inserts to each other. In injection-compression molding processes, it is necessary to seal the cavity before the polymer is injected. Therefore, a spring-supported sealing ring is implemented that seals the cavity after the two mold inserts are aligned. In this position, the mold is not closed completely and it is possible to mold polymer optics using both injection molding and injection-compression molding.

A second mold has been designed with two cavities to ensure symmetrical forces and hence to increase the reproduction accuracy. Injection-compression molding can be performed either via the closing movement of the injection molding machine or the movement of internal hydraulic pistons. Using this concept it is possible to compare the two compression techniques. During the compression process a gate closure prevents the melt from flowing back into the plasticizing unit. Furthermore, the mold features a parting line locker, which is needed when the compression cores are moved by the machine movement.