| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 100 === In recent years, computing, Communication and Consumer Electronics industry is changing rapidly and requires an increased demand for thin-wall product. Thin-wall injection molding process requires high injection speed during filling stage and high packing pressure during the packing/holding stage. The high injection speed will be made high shear rate at region near wall of injection mold. Consequently, the molecular chain will be broken because of excessive molecular chain stretching. Moreover, high shear rate will lead to potential for shear degradation due to high shear heating. The effect of high shear rate can be found in mechanical and aesthetical properties of thin-wall product such as scraped surface.
This study investigates influence of injection molding processing conditions on the melt shear effect and the finished surface qualities of Light Guide Plate (LGP) such as roughness, gloss, and hardness property. In this work, an amorphous polycarbonate (PC) was injected into the 6-inches LGP two plate injection mold system with cavity thickness of 1 mm. The on-line measurement shear effect system created to obtain the shear rate, and shear stress where a pressure transducer was installed at location which is near gate, and a temperature sensor was located far from gate into the two plate injection mold system. Time interval between the pressure and temperature sensors was used to calculate shear rate, shear stress and viscosity of flow in-mold. This study can be found out an optimal injection molding process parameter by using Taguchi method. The surface hardness of LGP was measured by scratch test. The surface roughness of LGP is tested by FORM TALYSURF from Taylor Hobson Precision. And the gloss of LGP is assessed by gloss meter.
As the results show that the injection speed and the mold temperature are two key factors which influenced on the surface qualities of the plastic products. The Taguchi method also show that the packing pressure is significantly effected on the surface hardness of plastic parts about 72%, and the injection speed is highly influenced on the surface roughness about 72.22%. Furthermore, the multi-factors Taguchi method is presented injection speed and packing pressure is significantly influenced on surface qualities of plastic products about 38.42%, and 33.42% respectively.
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