Abstract
Injection compression molding (ICM) provides enhanced optical performances of molded polymer optics in terms of birefringence and transmission of light compared to Injection molding (IM). Nevertheless, ICM requires case-dedicated process optimization to ensure that the required high accuracy geometrical replication is achieved, particularly especially in the case of surface micro-features. In this study, two factorial designs of experiments (DOE) were carried out to investigate the replication capability of IM and ICM on a micro structured Fresnel lens. A laser scanning confocal microscope was employed for the quality control of the optical components. Thus, a detailed uncertainty budget was established for the dimensional measurements of the replicated Fresnel lenses, considering specifically peak-to-valley (PV) step height and the pitch of the grooves. Additional monitoring of injection pressure allowed for the definition of a manufacturing signature, namely, the process fingerprint for the evaluation of the replication fidelity under different process conditions. Moreover, considerations on the warpage of parts were related to a manufacturing signature of the molding processes. At last, the global part mass average and standard deviation were measured to correlate local geometrical replication performances with global part quality trends.
Highlights
Fresnel lenses are well-known optical devices with enhanced illumination properties combined with a compact and lightweight design
For mobile communication and electronic devices, as well as automotive and medical applications, the dimensions of the grooves lie in the micrometer scale and define the Fresnel lens optical performances [1,2,3,4]
Even though injection molding (IM) and injection compression molding (ICM) are established processes, it appears that they are still not clearly understood in the literature with regard to which process conditions provide the optimal results in terms of micro-geometrical replication for complex polymer optical systems
Summary
Fresnel lenses are well-known optical devices with enhanced illumination properties combined with a compact and lightweight design. The major advantage of ICM consists of the opportunity to reduce stresses in the part, as compression action provides an in-thickness holding effect on the cavity, ensuring a uniform distribution of stresses inside the cavity, while the part solidifies [6,7,8] For this reason, ICM has been extensively favored to IM in the production of optical components. The four different manufacturing signatures (micro-replication accuracy, warpage, injection pressures, and part mass) were applied, providing a methodology for the optimization of IM and ICM These four manufacturing signatures are employed, and their respective results are compared simultaneously as drivers of the optimization process for micro-structured optical parts manufacturing. The methodology, based on a metrological approach, provides a robust guideline for the effective molding of high precision polymer optics
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