High Aspect Ratio Micro-structural Parts Injection Molding Filling Behavior

Injection molded parts with high aspect ratio micro structures are one of the most important micro injection molded parts, they are extensively applied in machine, photoelectric and communication, automation, biomedicine, communication testing and so on. The filling field characteristics of injection molded parts with high aspect ratio micro structures were investigated by the ways of theoretical analysis, numerical simulation and experiments, then the filling characteristic and the factors which might affect filling length of micro structures were analyzed. The main researches and conclusions were as follows.Firstly, when fluid flows in micro runners, the impact factors were analyzed, and the filling model of micro structures was set up on the basis of the Navier-Stokes equation with considering the effects of surface tension. In order to study the effect of surface tension on its flow field, the filling model of micro structures was set up by using continuum surface force model and flow front transition equation, and then the effect of surface tension was regarded as boundary condition of flow front according to theory of dynamic contact angle.Secondly, the filling behavior was simulated by the computational fluid dynamics software CFD-ACE in 2D physics model of injection molded parts with high aspect ratio micro structures. Furthermore, in order to investigate the impact on the filling behavior from surface tension, surface tension and contact angle were imported into simulation for the first time. The results had shown that there were speed volutions in the micro structures, and the influence of surface tension on micro flow filling was very little in the 200μm hydraulic diameter runners. Flow fields in symmetry rectangle micro structure were the most uniformity, the un-symmetry trapezium micro structure's was less uniformity, and the un-symmetry rectangle micro structure's was the least of uniformity. As a result, symmetry structures were advised in designing parts with micro structures.Lastly, the filling process was simulated by the software of MoldFlow. In order to study the filling length of micro structures, the effect factors were investigated. The result had shown that the filling lengths of micro structures were affected by material viscosity, melt temperature, mold temperature, cavity pressure, parts dimension and shape. It was namely that, when viscosity was lower, cavity pressure, melt and mold temperature were higher, cavity dimension was smaller, micro structures were bigger and be more near to the end of cavity, then the filling length of micro structures were longer. But the filling length of micro structures had not related to the aspect ratio of micro structure, in other words, when the micro structures had same section dimension and different aspect ratio, its filling lengths almost were equality.