Influence Of Processing Parameters On The Crystallinity And Thickness Distribution Of Medical Injector In Plastic Injection Molding

Thin-wall injection molding technology have a stronger different with conventional injection molding technology. Due to the wall thickness of plastic part is very thin, the molten polymer will be cooled very quickly in the dynamic molding process, and looking towards solidification, it makes the production difficult, easy to form a variety of molding defects, seriously affected the quality of the plastic parts. Thermoplastic injection molding is a complex molding process with highly non-linear and time-varying effect of multi-processing parameters, each processing parameter have different degrees of influence on quality of the molded parts. Therefore, it is necessary to research and analyze the effect of molding processing parameters on quality of plastic parts.In this paper, the basic flow of molten polymer in mold filling was simulated by using advantage plastic injection molding analysis CAE software MOLDFLOW, it is wildly used around the world. The effect of the main processing parameters(melt temperature, mold temperature, injection time and packing pressure) on the distribution of maximum shear rate in thin wall injection molding were investigated. It turned out that the maximum shear rate closed to the gate location is much higher than other location. On the scale from 0~10mm, with the increase of distance, maximum shear rate decrease rapidly, the change of the maximum shear rate is not obvious from 10 mm to the end of the part in flow direction. In thickness direction, the maximum shear rate at core layer is a minimum, increased gradually from core layer to the sub-skin layer, and up to its maximum at the position from the skin layer of 0.1mm, and then it decreased again. Finally, the crystallinity was predicted based on the distribution of maximum shear rate.Taking one-time syringe barrel as research object, melt temperature, mold temperature, injection time and packing pressure were selected as the design variable, with the perpendicular shrinkage and core shift as the response optimization goals. The non-linear second order response surface mathematical model which described the relationship between the design variable and the response optimization goals were established by using CAE numerical simulation technique, central composite design of response surface and data analysis software Design-Expert8.0 in combination. The effect of parameters selected on core shift of the one-time syringe barrel was analyzed. Optimal injection molding processing parameters sequence was obtained by using multi-objective optimization algorithm, and the validation was done by CAE finite element numerical simulation and practical production test. Finally, the one-time syringe barrel which meets with the quality requirements of enterprises were produced successfully.