Numerical Simulation Of Co-injection Molding And Rheological Behavior Of Polymer Melt

Co-injection molding,which is also called sandwich injection molding,is an advanced technology to meet the special quality requirements and reduce the cost of materials.It is a promising technique in industrial production.The filling stage is an important phase of co-injection molding;the dynamic interactions of air,skin melt and core melt in the process are very complex.Hence,the mathematical modeling for the filling process of co-injection molding is science engineering problem needed to be solved.The present dissertation focuses on developing three-dimensional model for filling process of co-injection molding,and simulating core penetration and rheological behavior of polymer melt based on Finite Volume Method on the collocated mesh.The major work of this dissertation is summarized as follows:(1)It is difficult to predict the behavior of core penetration in co-injection molding by Hele-Shaw model effectively.A three-dimensional Newtonian-Viscosity-Viscosity multiphase model is set up for solving this problem,in which the governing equations for flow field and interface evolution are coupled.The evolutions of air/skin melt and skin/core melt interfaces governed simultaneously by the same Level Set equation,which is convenient for implementing numerical simulation.The multiphase model is validated by simulating the sequential co-injection molding process of a centrally gated and a line gated rectangular plate.(2)The three-dimensional Newtonian-Viscosity-Viscosity multiphase model is used to simulate the filling process of sequenential co-injection molding for complex cavity in real life.The domain extension method is used to deal with boundary of complex cavity.The multiphase model is validated and the domain extension method is poven effective by simulating the filling stage of the molding process of a cavity with a block insert and then comparing this with available experimental results.Then numerical simulations of sequential co-injection molding of a toothbrush handle are performed,the penetration of core melt is investigated detailedly.All numerical results are consistent with experimental results,which show that the multiphase model can simulate the filling process of sequenential co-injection molding for complex cavity in real life.(3)At present,the elasticity of polymer melt is usually neglected in the investigation of co-injection molding.In this dissertation,the XPP constitutive equation is used to describe the stress-strain relation of polymer melt,two-dimensional and three-dimensional Newtonianviscoelasticity-viscoelasticity model are set up.In order to determine the constitutive equation parameters of material,a viscosity model based on XPP constitutive equation is obtained;meanwhile,the finite volume discretization of governing equations and constitutive equation together with the process of momentum and stress interpolation are deduced detailedly;the dynamic simulation of interface evolution in the filling stage of simultaneous co-injection molding is achieved.It is difficult to conduct simulation for filling process of simultaneous co-injection molding for its complex production process and special nozzle design;no simulated results for interface evolution are published till now.By implementing twodimentional and three-dimension simulations of filling process of simultaneous co-injection molding,the evolution of interface and stress distribution are predicted successfully.(4)In order to uncover the complex rheological behavior of polymer melt,a viscosity model and finite volume discretization of the Rolie-Poly constitutive equation with finite extensibility are deduced detailedly.Numerical simulations are performed to predict molecular orientation and V-shape of polystyrene melt.The microstructure of molecular including molecular orientation and extension is shown vividly by means of stress ellipse.The good predictive capability of Rolie-Poly constitutive equation with finite extensibility for polymer melt is verified in fast flows.