Theoretical Modeling And Numerical Simulation Of The Filling Flow Of Micro Injection Molding

Along with the development of the micro electromechanical system technology, micro injection molding has been widely used in a wide range of applications including micro mechanics, micro optical and biomedical field in recent years. For the small structure size and little volume of micro plastics parts, the traditional injection mold design theory has lost its meaning of direction in some sense. A new design theory for micro injection mold should be built according to the characteristics of micro injection molding on micro scale.Using the melt filling theory on macro scale for reference, after compared the micro injection molding technology with the traditional one, some possible effect factors on micro filling process are analyzed, such as mold and melt temperature, non-isothermal feature, cavity venting, surface roughness, surface tension and gravity and inertia force of melt, viscoelasticity and the melt compressibility etc. The mechanism of each factor under micro filling conditions is also analyzed. Then some suppositions and predigestions for these factors are proposed in reason combined with the characteristics of micro injection molding. The wall slip and surface tension are determined to be included in the micro-filling model to consider the effect of those former factors generally.Based on the relative theory of polymer rheology and hydromechanics, the mechanisms of wall slip and surface tension on micro channels are analyzed thoroughly, and two kinds of wall slip boundary conditions are imported according to different mechanisms. On the basis of the analysis of surface tension, a continuum surface force (CSF) model is also imported which interprets surface tension as a volume force and adds it into the momentum conservation equation. Based on this model, the continuity, momentum and energy conservation equation are deduced which suit for describe the melt filling behavior of micro injection molding.Aimed at wall slip and surface tension factors, which should be considered in micro-filling model, some steady and transient flow in micro channels considered the two factors are simulated respectively employing Polyflow and FIDAP. Some results considered wall slip and surface tension like the velocity, pressure and viscosity distribution of melt filling are obtained. The results are also analyzed to confirm the rationality of the micro melt filling model.