Numerical Simulation Investigation Of Water-Assisted Co-Injection Molding Process Based On The Finite Volume Method

Water-assisted co-injection molding technology is a new advanced polymer injection technology in recent years. Water assisted co-injection molding technology combined total of water assisted injection molding technology and co-injection molding technology, a number of advantages: a very short cooling time and cycle time; parts thinner and more uniform wall thickness, cross-sectional size can be larger; ensure the high surface quality at the same time, the inner surface of hollow parts are smooth; water medium of cheap easy to get; the core of waste plastics for recycling waste plastics to a partial solution to the problem; to high-performance (corrosion resistance and heat resistance, decorative appearance) or soft contact materials for the shell, common materials for the core production of high performance, low-cost injection molding surface; unique properties of integrated layers of materials, production of multi-functional complex injection molded parts.At first,water-assisted co-injected molding technology partially filled mold cavity with the first kind of melt as the material of production's shell, and then partially filled the sencond melt as the core of the material,then using water auxiliary devices inject high pressure water, melt fills the whole mold cavity through the thrust of water,then using water keep pressure, finally getting the hollow plastic products with a composite structure.Howerver, water-assisted co-injection molding, experimental study and theory study. still small both at home and abroad.So this paper studys theory and numerical simulation about the main products of.water-assisted co-injected molding-- the of tubular products.According to the theory of fluid dynamics and polymer rheology theory and the base of the water-assisted injection molding and co-injection molding,it establishes a mathematical model by reasonable assumptions and simplified which is suitable for water-assisted co-injection and two demension axialsymmetry mathematical model which takes up little computer resouse.were used for water assisted injection molding process of filling flow front tracking method of the interface—Volume Of Fluid(VOF). what is more, basing on the finite volume method (FVM) scatter the mathematical model , quested a efficient numerical solution (PISO),by single factor method,with the Fluent pltform which is a software widely used in the field of fluid dynamics, analysising the factors influence of water-assisted co-injection filling process, and revealed the mechanism of their formation.The research suggests:1) With the inner layer of melt consistency coefficient, melt flow index of the inner layer, the inner melt injection increasing, the inner layer melts and water penetration depth decreas , the width increases.2) With the inner melt injection temperature increasing, inner melt and the water penetration depth increase, penetration width is reduced.3) With the water temperature increaseing, the inner layer melts and the water penetration depth increases, the inner wall thickness increased, residual melt and the penetrating width of the water decreases.4) With the water injection rate increasing, the inner melt is essentially the same penetration depth, penetration width reduces, residual wall thickness increases, the water penetration depth increases, and the width decreases.5) With the cortex or inner layer of melt increasing,with the distance between injection volume and the inner melt front increasing, or with the front water interface distance from the inner front of the interface increasing will cause short shots of water. With the inner layer of the cortex or the amount of melt injection decreasing,between the front of the interface melt and the front of the interface with the cortex from the melt decreases, or water front of the interface with the inner front of the interface distance decreases.It is easy to create the inner layer melt front Breakthrough cortex melt front, or inner layer of melt water breakthrough in front of the interface ahead of the interface conditions.6) The wall temperature has no effect. on the water filling process of secondary co-injection and molding effect,7) With the delay of the water injection increases, the inner melt and the penetration depth of the water increase, the width decreases, the residual cortical thickness of the melt increases.8) The water inlet is too large or too small will led to the initial stage of injection water through the width of large, then decreases and the water interface is very sharp convex edge phenomenon.9) The use of cortical melt overflow method needs more injection pressure than a short shot method, inconsuming more energy and wasting cortical material.