Production and Analysis of Injection Molded Micro-Optic Components

Injection molding is a manufacturing technique that, through filling of a mold cavity (typically made from steel or aluminum alloys) with molten polymer, produces plastic parts. The geometry of the mold cavity is identical to the desired part shape, after taking into account thermal shrinkage. This manufacturing process is an economical and reliable way to mass-produce a variety of parts. Traditionally, part volumes are approximately 0.05 to 0.5 m3, but a new class of socalled micro-parts, with volumes on the order of 1 mm3 and features on the order of 10 m, are being injection molded with mixed results. The interest in micro-part production is not confined to the academy; market estimates for the years 2000–2002 indicate that 40 billion U.S. dollars will be spent on micro-system devices (1). In addition, current reports indicate that by 2005 the annual revenue will increase from 2 billion to upwards of 12 billion U.S. dollars in the MEMS field alone, and the biotechnology industry will likely grow even faster (2). As polymer use becomes more prevalent in the fields of micro-systems and MEMS, injection molded microparts will be in demand. While the manufacture of micro-parts enjoys much success, the computer simulation of their production is not as fortunate. Conventional-scale part simulation programs exist and are quite accurate, but do not yield acceptable results at the small scale. This has led many researchers to attack the problem of micropart simulation, but until these current simulations are commensurate with those for larger-scale parts, the problem requires more attention. This presents a gap between the areas of simulation and production of micro-parts; this paper discusses research conducted in these two areas, which attempts to fill this gap (3). Specifically, the research presented in this paper simulated injection molding manufacture of an optic part, shown in Fig. 1, made from three different polymers, and predicted the influence of the manufacturing conditions on the numerical values of certain optical quality criteria. These predicted values were compared to measured values obtained from physical parts.