Influence Of Processing Parameters On Morphology And Micro Structure Of Micro Injection Molded Parts

The complicated thermal-mechanical history in the micro injection molding process that melt gained is different from that in the macro injection molding process. The thermal-mechanic history in the micro injection molding process and its impact on the structure of micro injection molded parts is crucial to the final properties of part. With the micro cavity size decreased, the change and control of process parameters in the micro-injection molding process to a great extent determine the thermal-mechanic. Therefore, in order to explore mechanism of morphological structure development in the process of micro injection molding and acquire a complete law about the micro-injection molding, the paper studies the influence of process parameters on the morphology and micro structure of the micro parts from the perspective of controlling process parameters. The works and conclusions are as follows:1. Analysis of melt filling and flow behavior in micro injection molding. Based on the micro injection molding experiments, under different process parameters of a set of micro thin wall parts with the thickness of 1.0mm, 0.5mm, 0.2mm, the influence of injection speed, mold temperature and melt temperature on the mold filling of the parts were investigated. The results show that the cavity filling ratio of the micro parts increases apparently as the processing parameters increasing. The size of the cavity is thinner, the harder the filling is. Another result by investigating the influence on the filling under different process parameters show that the most significant process parameter is the injection speed, followed by the mold temperature and melt temperature; and the melt front is unbalance in the filling stage.2. The influence of the process parameters on the morphology evolution of the micro injection molded polyoxymethylenes parts was analyzed. Based on a sequence of micro parts with the thickness of 1.0mm,0.5mm and 0.2mm, the influence of process parameters on the morphology evolution of micro molded parts were investigated by single factor experiments, by means of polarized light microscopy(PLM) and differential scanning calorimetry(DSC), the influence of injection speed, mold temperature and melt temperature on the morphology, crystallinity was investigated. The result indicated that micro injection molded POM parts appears a skin-core layer structure, core layer presents a typical trigonal system, with the thickness of parts decreasing, the ratio of the thickness of skin layer and shear layer is higher, core layer is dominant in the micro parts with the thickness of 1.0mm, while skin layer is dominant in the micro parts with the thickness of 0.2mm. The sequence of the significance of the factors is as injection speed, mold temperature, melt temperature. With the increasing of injection speed, mold temperature and melt temperature, the thickness of skin layer of the micro parts is decreases. The crystallinity of the micro parts has a small increase with the ascending of injection speed and mold temperature, when injection speed upgrade a certain range it declined, and the crystallinity of the micro parts descend with melt temperature increasing. The DSC results show that process parameters have nothing substancial impact on the crystallinity of the micro parts.3. The influence of process parameters on the morphology evolution of micro molded i PP parts was analyzed. The influence of injection speed, mold temperature and melt temperature on morphology and micro structure of the micro PP parts with different thickness was investigated through single factor experiments by PLM. The results show that micro injection molded parts with thickness of 1.0mm presents a skin-core structure which contains frozen layer, shear layer and spherulite layer, and the ratio of thickness of skin layer is smaller relatively; a skin-core structure which contains column crystal layer is observed in the parts with the thickness of 0.2mm, and the ratio of thickness of skin layer is larger relatively. Injection speed is the most important factor influencing on the morphology of the micro parts, mold temperature and melt temperature followed. With the increasing of injection speed, mold temperature and melt temperature, the ratio of the skin thickness declined gradually.4. Influence of the cavity geometric dimension on the structure of the micro injection molded parts. A comparative analysis was made to investigate the morphologies evolution along melt flow direction in micro POM parts and micro PP parts, the thickness of skin layer of POM micro parts increase first then desrease while the thickness of skin layer of micro PP parts decrease along flow direction, and core-free structure appears at the sprue position of micro PP parts; The oblate spherocrystal appears at the interior of skin layer in the micro parts but not where supposed to be the core position in the macro parts, there are some shish-kebab structure like column crystal between skin layer and core layer, which is rarely in macro parts; besides, complete spherocrystal exists between the two symmetric column crystal; the size of column crystal increases along the flow direction.