Numerical Simulation For Water Penetration In Water-Assisted Injection Molding Based On Two-Phase Flow Principle

The Water-assisted Injection Molding(WAIM), which is based on the Gas-assisted Injection Molding(GAIM), is a kind of the new technology to manufacture hollow plastic parts. Compared with the GAIM technology, the inner wall of the WAIM product is more smooth and its wall thickness is more uniform. In addition, this technology can avoid the ‘finger’ effect that the GAIM often exists.Therefore, the WAIM technology has already been applied to the manufacture and processing of cars, household appliances and medical products, such as clutch pedal,feed rollers of printer, conduct pipe for medium of washing machine, hollow needle,expander used to the surgical operation and so on. Before manufacturing the actual mould, it is useful to conduct numerical simulation for the WAIM to assess the rationality of the mould structure and molding process, predict the product’s defects,so as to reduce the test times, and finally improve the manufacture efficiency.In the past, the numerical simulation is mainly based on the capillary CA perturbation method and the volume of fluid(VOF) method to trace the evolution of the penetrate interface and predict the residual wall thickness and penetrate length.However, this method cannot simulate the inside and outside wall thicknesses and undulating penetrate interface, and can’t predict the influence of the thermal conductivity of water on the residual wall thickness either. Therefore, this article built a set of equations and boundary condition of the plastic melt and water flows in the process of penetrate based on the principle of two phase flow. At the same time, the continuity equation and momentum equation and energy equation were discretized based on finite volume method according to the characteristics of water penetration.Based on the numerical results we analyzes the mechanism of penetration, and explore the influence regularity of the process conditions on the penetration interface.The chief results in this thesis are concluded as follow:(1) If the pressure of the water for injection is constant, the average insideresidual wall thickness of the products decreases 3.8% the initial melt temperature increases 10℃, while the average outside residual wall thickness decreases 2.3%.(2) When the initial melt temperature keeps constant, the viscosity of melt reduces and the residual wall thickness decreases with the increase of the speed of the water for injection, the shear rate increases, While the shear rate increases as the pressure of the water for injection increases, the viscosity of melt reduces and the residual wall thickness decreases.(3) The inside residual wall thickness decreases along with the direction of fluid flow at the crooked gallery, at the same time the outside residual wall thickness increases gradually.(4) For the variable cross-section products, the law of the influence of the initial temperature of melt on the penetration ratio is different. For the contraction of cross section. The penetration ratio decreases with the increase of the initial temperature of melt, while the effect of the initial melt temperature becomes smaller at the other cross section.The results of this thesis is an important of reference significance in the aspect of machining of the Water-Assisted Injection Molding...