| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 103 === It is in a dilemma to set the mold temperature with conventional injection molding, If want to get better mechanical properties or surface quality, higher mold temperature shall be used, but the cooling time was increased. To decrease the cycle time and apply lower mold temperature, often make the surface properties poor or increase internal residual stress.
This study developed a mold temperature adjustment technology with electric heating and water cooling. The mold surface temperature was defected with the temperature sensor installed in the mold. The mechanical property, appearance quality and crystallization of molded parts (ASTM tensile and flexural specimen with 3.2mm thickness) were analyzed with the variation of mold temperature. 3D-CAE was applied to calculate the cross section melt temperature profile. According to the melt temperature variation, the mold temperature can be adjusted to keep the mold temperature higher and cool the mold temperature efficiently. Differential Scanning Calorimetry (DSC), universal testing machine were used to detect crystallinity, mechanical properties, respectively.
The results show that the High Density Polyethylene (HDPE) was used for an example, compare mold temperature was kept at 75 ℃ with mold temperature was dynamic from105℃ to 75℃ in the injection molding, when the same cooling time was applied, dynamic injection molding can increase crystallinity significantly on the surface of the molded parts. This phenomenon also increases the tensile strength of the molded parts, reduces flexural strength, subsequently. Mold temperature adjustment technology can be used for other crystalline plastics, such as Nylon (PA) Polyoxymethylene (POM), etc., depend on its crystallization temperature and crystallization rates to adjustment the mold temperature, achieve the purpose of increasing product quality without increasing the cooling time.
|
|---|
