Numerical Simulation And Experimental Analysis Of The Filling Process Of Micro Parts In Injection Molding

Micro injection molding is attracting more and more attention for its great potential in low-cost, high efficiency and accuracy, mass production, and also the plastic has the advantages of corrosion resistance, oxidation resistance, high specific strength, etc. The filling process is the core of the micro injection molding. While structure dimension and volume of micro plastic parts are extremely small, the conventional injection molding theories and methods lose the guiding significance. So, it is very necessary to research the filling process of micro plastic parts in injection molding.In this paper, a micro cell culture dish was used for study. Theoretical analysis, numerical simulation and experimental method were used to research the heat transfer coefficient and process parameters of filling process.Firstly, according to the characteristics of micro injection molding, control equation, constitutive equation and heat transfer coefficient model were established from reference to the research methods of conventional injection molding and the assumptions for the basic equations of viscous fluid dynamics.Secondly, rheological data were measured by double-bowl barrel capillary rheometer. The Cross-WLF viscosity model parameters were also fitted by Pareto Genetic Algorithm, which supplied accurate model parameters for the simulation of filling process.Thirdly, the influence of heat transfer coefficient and process parameters on filling stage was obtained with 3D mesh model in Moldflow soft. The results indicate that heat transfer coefficient has great effects on the maximum injection pressure and fill percentage. Injection velocity is the main factor for the fill percentage in micro injection molding, the next is melt temperature and mold temperature. When the needed maximum injection pressure is less than the set one and injection volume is more than the part's whole volume, injection pressure and injection volume produce no impact on fill percentage.Lastly, experiment proved the importance of vacuum-pumping for the quality of micro plastic parts. The influence sequence and optimal level combination of process parameters were obtained by Orthogonal Experiment method, and the full micro plastic part was attained. The experimental results show that melt temperature is the most important, injection velocity, pack pressure, mold temperature and pack time are the next. The simulation results are basically consistent with experiment, which indicates that the simulation method of micro injection molding with 3D mesh model is feasible and valid.