3D Simulation Of Filling Stage In Micro-Injection Molding

The micro-injection is a new technology of polymer processing developed from the traditional injection molding. It is one of the branches for the Micro Electro Mechanical System(MEMS).With the development of the MEMS,the micro-injection molding technology is developed and now widely used in the optical communications, image transfer, chemical and biological medicine, information storage, precision machinery and many other fields.However, because of the very small size and volume of micro-plastic parts, the flow behavior of polymer in the filling stage in micro-injection molding has many differences compared with that in the traditional injection molding. Therefore, the theories and mathematical model of polymeric flow used in traditional injection molding could not be applied in micro-injection molding directly. Nowadays incontrovertible theories of polymeric flow in micro-injection molding haven't been established and some study conclusions were made by traditional methods or traditional simulation software, so research results couldn't describe the real mechanism in micro-injection molding. Theories and model of micro-injection molding need be investigated, and the investigation of micro-injection molding simulation is very significant. The scientific method and quantitative analysis for mold design and polymer processing for micro-injection molding can be established based on simulation. The design flaws can be founded and the development of micro-injection molding can be promoted.In this paper, the characteristics of the influencing factors on filling stage in micro-injection molding were analyzed and two factors (microscale viscosity and surface tension) were investigated. The 3D mathematical model of filling analysis in micro-injection molding was established based on the fundamental theories of viscous fluid dynamics and polymer rheology. The microscale modification factor was introduced in Cross-WLF viscosity model to describe the influence of microscale effects.The BrackBill continnum method was used to model surface tension. Based on the above analysis, ANSYS CFX was adopted to simulate the filling stage in micro-injection molding. Simulation of micro-injection molding and traditional injection molding was implemented using CEL(CFX expression language).Four microscale parts (100μm,10μm,1μm,0.1μm) were adopted to research the influence of microscale viscosity and surface tension during the filling stage of micro-injection molding. The results indicate, the simulation result using the microscale viscosity model shows the filling more easily for micro parts; The results indicate, when the part size is less than 10μm, the cross-section of the melt front becomes semicircle with the decrease of the part size.The position of melt front indicates, the surface tension has negative effects on the flow behavior. The surface tension has more and more severely hamper on melt flow with the decrease of the part size.