No abstract

Injection molding is one of the most widely‐used processes for the production of plastic parts, due to the utilization of diverse materials, the complex product‐shape moldability, and the rapid mass production. In relation to the environmental issues, light‐weight technology and green molding solutions are becoming more important. Microcellular injection molding technology is one of the green molding solutions for saving materials, as well as reducing the weight of molded parts. However, the molding process brings about some defects, including a sliver flow mark on the surface and uneven mechanical properties that are caused by the uneven cell size and their distribution within the part. Dynamic molding temperature control technology seems to be an effective way of improving the product quality. Until recently, there has been very little discussion about high‐efficiency cooling methods. A new complex mold for a cooling system has been designed. The basis cooling ability of different materials was investigated. The complex mold design has a faster cooling rate, and it has a greater surface temperature uniformity. This cooling technology was used to improve the quality of microcellular injection molded parts, which improves the glossy finish by about 73%. The results show that the faster cooling rate brings about the more uniform cell size with higher cell density from 9.43E+11 to 1.92E+12 cells/cm3. Otherwise, the cell size reduced from 192.92 to 84.97 μm.

Microcellular injection molding technology (MuCell) using supercritical fluid (SCF) as a foaming agent is one of the important green molding solutions for reducing the part weight, saving cycle time, and molding energy, and improving dimensional stability. In view of the environmental issues, the successful application of MuCell is becoming increasingly important. However, the molding process encounters difficulties including the sliver flow marks on the surface and unstable mechanical properties that are caused by the uneven foaming cell sizes within the part. In our previous studies, gas counter-pressure combined with dynamic molding temperature control was observed to be an effective and promising way of improving product quality. In this study, we extend this concept by incorporating additional parameters, such as gas pressure holding time and release time, and taking the mold cooling speed into account to form a P(pressure)-T(temperature) path in the SCF PT diagram. This study demonstrates the successful control of foaming cell size and uniformity in size distribution in microcellular injection molding of polystyrene (PS). A preliminary study in the molding of elastomer thermoplastic polyurethanes (TPU) using the P-T path also shows promising results.

Centrifugal force has been found to be an excellent method to control fluidic flow in biochips. Most micro-fluidics researchers already use the computer to simulate micro-fluidics flow behavior to save time and reduce mistakes. In this study, the overflow design accurately fixes the liquid volume with less than 5% error. Centrifugal force driven micro-fluidics system is designed with both simulation and experiment. The 3D simulations to utilize computational fluid dynamic software (CFD) to simulate the fluid flow and calculate burst frequency at different capillary switching and several dimension of micro-channels (300, 400, 500μm wide and each 200μm deep). For mercurochrome, the simulation results (384, 360, 348 rpm) shows burst frequency matches experimental results (468, 426, 402rpm) and accurately predicts measured trends followed the effect of channel width. This study also demonstrates the centrifugal application of an advanced computational fluidic dynamics model for the design and analysis of a centrifugal force driven micro-fluidics system.