Numerical Simulation Of The Post Filling Stage Of Microcellular Injection Molding

Microcellular plastics have microcell size ranging from 10 to 100 microns and exhibit light weight, saving material, heat insulation, electrical insulation, excellent mechanical properties. The microcellular plastics are widly used in packaging, construction, transportation, aerospace and bio-engineering fields etc. and have developed rapidly. As a new foaming molding technology , the injection pressure and clamp force requirement is further reduced due to the fact that the microcellular injection molding is not required to packed out the mold. The volumetric shrinkage of the melt is compensated for by the growth of the microcells. Microcellular injection molding has many benefits that conventional injection molding is lacked of and will enlarge the field of optimizing the injection molding process and saving the production cost.The microcellular injection molding process is very complicated. The different stages (cell growth , melt flow and curing shrinkage) involved in this process are interactional. It is difficult to give a comprehensive analysis of satisfaction with the design of molding and process for the designers who only rely on the experience. This paper focuses on developing a mathematical model and numerical simulation for cell growth and melt curing shrinkage during the posting-filling stage of the microcellular injection molding to predict the final cell size distribution and the pressure field . Computer simulation is expected to become an important and required tool to help shorten production cycle time and reduce cost. It can make the molding process build on basis of scientific analysis. This paper mainly includes following works:1.Discuss the process and characteristic of the microcellular injection molding. Discuss and analyze the theory of the polymer-gas solution, nucleation, cell growth and shaping.2.To model the cell growth, the unit-cell model is adopted. A mathematic model was introduced that use the hydrodynamics theory, the Fick law, the Henry law, the idea gas law , and coupled with hydrodynamics and the mass diffusion of dissolved gas .3. A mathematical model ,which describes melt solidification contraction process , is coupled with the cell growth model by hydrodynamics pressure at the outer boundary of unit cell.4.In order to implement the simulation for the posting-filling stage of the microcellular injection molding ,the cell growth are solved using the finite-difference techniques, the temperature and the pressure field are solved using the finite element/ finite-difference method.5.Study the temperature field, the pressure field and cell size distribution during the posting-filling stage of the microcellular injection molding processing for PS/N₂. Finally it can been see that the cell size is gradually decreased from the mold cavity center to the moldwall, and become larger as increasing distance from the gate.