Study On Numerical Simulation Of Co-injection Molding

As a new injection molding technology, co-injection molding is of great significance in resolving the recycling of waste plastics, producing cost-effective plastic products and achieving the functional diversification in plastic products.The principle of co-injection molding technology is to inject different polymers melt into the mold cavity simultaneously or sequentially. In the mold cavity, the melt filling the mold as multiphase-multilayer filling flow. Melt finally solidified to be skin/core composite injection molded parts. The melt first injected forms skin of composite, the melt injected afterward forms core of composite.In co-injection molding, the breakthrough phenomenon of core melt, the penetration length of core melt, uniformity of distribution for core melt and warpage of goods are important issues. Previous studies impossible to provide a comprehensive, rapid, dynamic and visual engineering analysis results for this special molding technology. This thesis used polypropylene (PP), polyamide (PA), Polyolefin elastomers (POE) and polyethylene (PE) materials, and made simulation analysis on co-injection module of Moldflow Plastics Insight 5.0 (MPI 5.0) Software. In this thesis, the content of the study are as follows:(1) By changing the molding materials and molding process parameters, analyzing the influence of viscosity ratio of core/skin melt, melt temperature, mold temperature and melt flow rate on breakthrough phenomenon of core melt. To provide the basis for how to avoid breakthrough phenomenon of core melt in the process of co-injection.(2) Analyzing the influence of viscosity ratio of core/skin melt, melt temperature, mold temperature and melt flow rate on the penetration length of core melt. In the premise that core melt didn't breakthrough skin melt, to guide material selection and adjust molding process parameters in order to obtain core melt in the maximization and cut the cost of injection molding products.(3) Analyzing the influence of viscosity ratio of core/skin melt, melt temperature, mold temperature and melt flow rate on distribution of core melt. Understanding how these important parameters affect uniformity of goods. (4) Analyzing the influence of melt temperature, mold temperature and melt flow rate on deflection of goods. Though deflection analysis, understanding how to adjust process parameters to reduce parts deflection and improve product quality and product value.In this thesis, co-injection molding simulation analysis showed that: viscosity ratio of core/skin melt has a great impact on breakthrough phenomenon, penetration length and distribution of core melt. As viscosity ratio of core/skin melt increased, the trend for breakthrough phenomenon of core melt weaken, the penetration length of core melt decreases and the uniformity of core melt debases. Melt temperature has some impact on breakthrough phenomenon, penetration length and distribution of core melt and deflection of goods. And the core melt temperature and skin melt temperature have opposite direction impact. As core melt temperature increased, the trend for breakthrough phenomenon of core melt boosts up, the penetration length of core melt increases, the uniformity of core melt enhances and the deflection of goods increases. Increased skin melt temperature has an opposite result. As mold temperature increased, the trend for breakthrough phenomenon of core melt weaken, the penetration length of core melt decreases, the uniformity of core melt debases and the deflection of goods increases. But this impact is small. Melt flow rate has prominent impact on the four issues in this thesis. As melt flow rate increased, the trend for breakthrough phenomenon of core melt weaken, the penetration length of core melt decreases, the uniformity of core melt debases and the deflection of goods increases.In fact, melt temperature and melt flow rate have more complicated impact on issues mentioned above. The influence related to materials. If the viscosity of material is sensitive to melt temperature or shear rate, the impact of melt temperature or melt flow rate would be significant, and vice versa. If the impact of trend or size on two materials of one combination changed, the impact of melt temperature and melt flow rate on breakthrough phenomenon of core melt, the penetration length, the uniformity of core melt and deflection of goods would been changed. These problems require we continue to lucubrate.