The gloss transition defect of injection-molded surfaces should be mitigated because it creates a poor impression of product quality. Conventional approaches for the suppression of the gloss transition defect employ a trial-and-error approach and additional equipment. The causes of the generation of a low-gloss polymer surface and the surface change during the molding process have not been systematically analyzed. This article proposes the causes of the generation of a low-gloss polymer surface and the occurrence of gloss transition according to the molding condition. The changes in the polymer surface and gloss were analyzed using gloss and topography measurements. The shrinkage of the polymer surface generates a rough topography and low glossiness. Replication to the smooth mold surface compensates for the effect of surface shrinkage and increases the surface gloss. The surface stiffness and melt pressure influence the degree of mold surface replication. The flow front speed and mold temperature are the main factors influencing the surface gloss because they affect the development rate of the melt pressure and the recovery rate of the surface stiffness. Therefore, the mold design and process condition should be optimized to enhance the uniformity of the flow front speed and mold temperature.

Since the 3D printing technology was applied to metallic materials, the conformal cooling channel has been widely utilized for injection mold with a higher cooling efficiency. The conformal cooling channel provides higher degree of freedom in shape and size. It is more effective to apply it to convex core accumulating more heat than the concave side. However, there has not been a standard design method for the conformal cooling channel. Depending upon channel design, the cooling efficiency would not be improved. Sometimes dead flow zones could be made in the channel. Currently every engineer makes the cooling channel design of his own. In this work, we proposed an automated optimum design method for the conformal cooling channel. In the proposed design method, whole product surface is divided into smaller domains with equal thermal energy by Voronoi diagram algorithm. Then cooling channels are installed along the centers of the domains by a binary branching algorithm. The objective of the optimization was the minimization of the product surface temperature deviation. The cooling channels are branching out over the product surface through the evolutionary steps until the objective was satisfied. The injection molding CAE analysis was done by Moldflow, and the optimization by PIAnO. The sample product was an eye-glass lens product.

The vent of the injection mold is an essential part for mold operation. It makes it possible for the incoming gas during filling to be ventilated out of mold preventing molding defects such as burn mark or short shot. Many additives such as flame retardants, UV stabilizer or lubricants are compounded to resins to enhance products quality and processing capability. The resins are likely to produce a large amount of gas during processing. The gas includes organic substances that can easily condense and be accumulated on the surface of the vent, which reduces the vent to make it difficult for the gas to be ventilated easily. The mold with the clogged vent should be cleaned regularly. If the cleaning time could be predicted by monitoring, it can make mold operators to set up the working schedule with proper preparation ahead. In this work, how to measure the temperature and pressure changes of the gas in the cavity during filling is examined to make the vent clogging to be monitored efficiently. The gas in the cavity during filling is compressed adiabatically in a moment due to the fast filling speed. As the vent gets clogged, the adiabatic compression would become severe. When the adiabatic compression occurs, the temperature and pressure of the gas in the cavity will increase sharply. We developed temperature and pressure sensors to detect the adiabatic compression in the cavity. A sensitivity of the sensors was tested in a compression chamber. We developed and tested methods to measure the temperature and pressure changes in the chamber in this work. We discussed the problems to affect the sensitivity and the long-term reliability of the sensors.