Zero defects manufacturing in injection compression molding of polymer Fresnel lenses

Fresnel lenses are polymer optics with reduced dimensions and higher illumination properties. Their structured profile involves high precision replication techniques when industrial scale manufacturing is concerned. Injection Compression Molding (ICM) is the state of the art replication technology to ensure mass production of polymer optics. The opportunity to perform a compression phase on the polymer melt while injected into the cavity, ensures a more homogenous replication of the part, enhancing birefringence and transparency among all the optical properties. However, it is not common to find studies concerning the technological signature of ICM components. The optical transparency of polymer optics as long as the complexity of Fresnel lens profile, are big challenges for metrology making this knowledge expensive and rarely investigated. In this study, absolute dimensions of Fresnel lenses step heights are correlated with respect to ICM process conditions. In a first experimental plan, the effect of packing and compression is individually evaluated on two different materials. In the case compression is performed without packing, the form replication accuracy of the micro structures fails, showing deviations up to 10 times the nominal dimension. On a secondary experimental campaign, packing pressure and compression gap are optimized together to identify the most favorable replication condition. The results show a second order interaction between compression gap and packing pressure. The average replication increases by 1.4 %, 2 µm, when both a high level of compression gap and packing pressure are selected.