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One of the problems encountered in fluid-assisted injection-molded parts is the gas or water 'fingering' phenomenon, in which gas (water) bubbles penetrate nonuniformly into the core of the parts and form finger-shape branches. Severe fingerings can lead to significant reductions in part stiffness. This study investigated the fingering phenomenon in fluid-assisted injection-molded disk parts. Experiments were carried out on a reciprocating injection-molding machine equipped with gas- and water-injection units. The material used was virgin polypropylene. A disk cavity with two different thicknesses was used for all experiments. The effects of various processing parameters on the fingering were examined. It was found that the melt short shot size and mold temperature were the principal parameters affecting the formation of part fingerings. In addition, the formation mechanism of part fingerings has also been proposed to better understand the formation of part fingerings. It has been shown that the fluid-assisted filling process is an unstable system by nature. Any small perturbation by material viscosity or by temperature gradient can trigger the unbalance of gas (water) penetrations in the parts and result in fingerings. POLYM. ENG. SCI., 49:2257-2263, 2009. [C] 2009 Society of Plastics Engineers, INTRODUCTION Fluid-assisted injection molding technologies, including gas-assisted (1-3) and water-assisted (4-7) injection moldings, have received extensive attention in recent years, because of the light weight of molded parts, relatively lower [...]

Injection molding has been one of the most important polymer processing methods for the manufacturing of plastic parts. This article discusses an innovative and effective infrared assisted injection molding process, which enables the rapid fabrication of surface-relief plastic diffusers. A mold insert bearing microfeatures is fabricated using a tungsten carbide turning machine. An infrared radiation system, which consists of four 1,000 W halogen infrared lamps and a semi-spherical reflective cover, is employed to provide additional heating for the mold surface that bears microfeatures. Before each molding cycle, the infrared energy is converted into heat at the master mold/plastic plate interface to increase the cavity surface temperature and to facilitate the replication of the microfeatures. After molding, the properties of the fabricated diffusers are verified with an optical microscope, scanning electronic microscope, surface profiler, and hazemeter. The results suggest that with a minimal heating of five seconds, high-performance plastic diffusers may be successfully fabricated. The experimental results in this study suggest that the infrared assisted injection molding can provide an effective way to fabricate high-performance plastic diffusers with a high throughput. [ABSTRACT FROM PUBLISHER]