Study On Numerical Simulation For Water-Assisted Injection Molding

Water-assisted injection molding (WAIM) process has been proved to be a new type of injection molding technology that could be widely used with advantages of shorter cycle time and higher quality. However, the dynamic interaction of polymer melt and water tends to be much more complicated since water is taken as fluid medium. On the other hand, WAIM involves processing parameters in terms of melt temperature, water temperature, water inlet pressure, etc. which directly influence rheological properties of polymer, material distribution and molding quality. Therefore it's necessary to conduct research on water penetration mechanism and influence of processing parameters on molding quality, which provides helpful guidance for the production.According to process characteristics, simulation for filling process of WAIM is implemented based on Hele-Shaw flow model with general Newtonian fluid equations involved. The main work of the thesis is as follows:1. WAIM technology and theoretical model are described including basic principle, advantages and disadvantages, equipment and material required. The theoretical study and experimental research of WAIM are briefly introduced.2. Research on effect of water channel structure on water penetration behavior is conducted. Based on two-dimensional mesh models with typical water channel structures, evolution of dynamic interaction of polymer melt and water is analyzed. Additionally, the influence of various water channel structures on water penetration behavior is studied including dimensional transitions, different structure in the corner. 3. Hollowed core ratio is taken as the quantitative indictor which reflects the residual wall thickness. Based on single-factor analysis, process variables are studied in terms of their influence on the residual wall thickness of WAIM parts: melt temperature, water inlet pressure, mold temperature, water injection delay time, water temperature and melt short shot size.4. Technical advantages are compared between WAIM and GAIM. An automotive cooling pipe is adopted as the analyzed example. Numerical simulation for GAIM process is carried out by MOLDFLOW software. Water penetration behavior in WAIM process is calculated by FLUENT software. It's found that higher molding quality is presented in WAIM process according to comparison of two groups of results.