Analysis Of Formability And Morphology Of IPP Micro Injection Molded Parts

The melt in the micro injection molding process exhibit different processing characteristics compared with the conventional injection molding, and molded by the high temperature, high pressure and high shear in the micro-cavity, which would result in the size dependence of the viscosity, wall slip, and the effect of surface tension increase in the flow channel. Material experienced more complicated mechanics history and thermal history experienced compared, with traditional injection molding, these special behavior will affect the crystallization of the polymer at different stages. In addition, the characterization of the morphological structure also exists certain difficulties due to the size of micro-injection molded parts is very small. Therefore, there is an urgent need to study the morphology of the micro-injection molded parts to control the morphology of micro products, improve the performance of micro-products. The paper work and relevant conclusions are as follows:1. Analysis of molding ability and flow phenomena of micro parts in micro injection molding. Based on the micro-injection molding experiments of a set of micro thin wall parts with thickness of100μm,200μm,500μm and lmm, the influence of the process parameters on the molding ability of the parts with different thicknesses were investigated. The process operation windows of the parts with different thickness were obtained, and the mechanism of flow imbalance phenomena and the variation of the shape of melt flow front in molding process were analyzed. The result showed that the cavity filling rate increased as the injection speed, mold temperature and melt temperature increased, the influence of the process parameters on mold filling from big to small in turn was the injection speed, mold temperature, melt temperature. It is more difficult to achieve the filling completely with the decrease of product thickness, and the process operating window will be narrowed. The process window analysis showed that the mold temperature and injection speed are closely related.2. Comparative analysis of the typical morphology of the micro injection parts. By means of polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD), the influence of injection speed, melt temperature and mold temperature on the morphology was investigated. The result showed that the form of distribution of the parts with the thickness of lmm was typical skin-core structure; frozen layers and spherulite structure for the parts with the thickness of200μm can not be observed, and there were almost all the shear layer which is shish-kebab structure, while the column crystal structure in the core can also be observed at special conditions; a skin-core structure which contains column crystal layer and shear layer are observed in the parts with the thickness of100μm, and the proportion of column crystal layer and spherulites layer changes along the flow direction.3. The influence of process parameters on the morphology evolution of micro injection molding parts were analyzed. By means of polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD), the influence of injection speed, melt temperature and mold temperature on the morphology, the internal crystal type, degree of crystallinity and orientation of different thickness micro injection parts was investigated. The result showed that the effect of injection speed is maximum, mold temperature and melt temperature is following. And the product size is thinner, the more significant effect of process conditions on the crystallization behavior and crystal morphology for micro-products.4. Some special phenomenon in the analysis of micro injection parts morphology. The study of the morphology of the location of the gate, near the gate and at the weld line showed that a large number of irregular regions shish-kebab crystal morphology exist at the location of the gate; the formation of a whirlpool near the due to the inertia of the viscous fluid; the high-speed fluid in the bottom of the boss by shearing to form a highly oriented crystal structure. The core layer of the spherulites disappear and trans crystalline generated and increases along the flow direction of the morphological evolution gradually. The special form of the weld surfaces was observed in the melt which converge to the vanes by the center disk.