Analysis Of Morphology And Shrinkage Of IPP Micro Injection Molded Parts

With the development of science and technology, micro-electromechanical systems (MEMS) and micro-systems technology (MST) have been successively applied to many fields. Micro-injection molding (MIM) is one of the most important processes for replicating microstructured parts and microparts with high precision. Because of the application in high-grade, precision and advanced fields of micro injection molded parts, the higher property of the parts is demand. The morphology of structure plays a major role in mastering the final properties of the products, therefore, investigation of morphology of the micro parts has important significance.In this work, the iPP microparts with two different thickness were chosen in the study. The influence of processing parameters on morphology and shrinkage of two kinds of microparts was investigated based on the microinjection molding experiments. The work includes:1. The influence of scale effect on morphology of the microparts. By means of polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD), the morphology evolution of micro parts was investigated. PLM observations indicated that morphology along the thickness direction of microparts exhibited a similar skin-core structure as morphology of the traditional injection parts. There are three structures in the microparts including skin frozen layer, shear layer and core layer, and shear layer presented a large fraction of the thickness in micro injection molded parts. The core layer in the traditional injection parts presented a large fraction. There’s hardly any β-crystal in two kinds of microparts. The degree of crystallinity of the microparts is different at different location. The degree of orientation in micro part with thickness of0.5mm is higher that micro parts with thickness of1.0mm.2. The influence of injection speed on morphology of microparts. By means of polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD), the influence of the injection speed on morphology evolution of microparts was investigated. The results show that two kinds of microparts exhibited the similar skin-core structure at low injection speed. With the injection speed increasing, the fraction of shear layer has little change. The micro parts exhibit a specific core-free morphology at high injection speed. And there’s hardly any β-crystal in two kinds of microparts with the injection speed increasing. The degree of crystallinity and orientation are different in the two kinds of micro parts.3. The influence of melt temperature on morphology of the microparts. By means of polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD), the influence of melt temperature on morphology evolution of micro parts was investigated. The results show that three skin-core layer structure in the microparts including skin frozen layer, shear layer and core layer. The micro parts with thickness of0.5mm exhibit a specific core-free morphology. The fraction of shear layer in the micro parts molded under different melt temperature with thickness of1.0mm has little change. There’s hardly any β-crystal in both two kinds of the microparts. The degree of crystallinity and orientation are different in the two kinds of microparts.4. The influence of processing parameters on shrinkage of the microparts.The shrinkage ratio in thickness, width and radial direction of the microparts were calculated. The results indicated that injection speed is the most influential factor on the shrinkage ratio in thickness, width and radial direction of the micropart with the thickness of1.0mm, it’s same to the micropart with the thickness of0.5mm.Generally, the injection speed is the most influential factor of the shrinkage ratio, followed by packing pressure and mold temperature, and the influence of packing time and melt temperature was unobvious.