Simulation Of Flow Induced Stress In Injection Molding

Injection molding is a widely used manufacturing process for the manufacture of complex shaped, thin walled polymer products. It consists of filling, packing and cooling stages. During the whole process, the polymer experiences a complex deformation and temperature history that affect the finial properties of products.As a consequence of the development of computer aided engineering (CAE), the ultimate aim of numerical simulation of injection molding process is not only to analysis the process stage but also to calculate the mechanical, optical properties of the products. There are number of various factors which can influence the properties of products. Among them, the "frozen-in" molecular orientation and the residual stress play an important role.Residual stress in injection molded products stem from two main sources. First, shear stresses and normal stresses develop during the viscoelastic flow of polymer melt in both the filling and packing stage of the injection molding process. These two kinds of stresses can not relax entirely and are "frozen-in" the products because the temperature drop rapidly during cooling stages, and are regarded as residual flow induced stress. Flow induced stress mainly affects the mechanical and optical properties and corresponds with the molecular orientation. Second resource is thermal induced stress. During the cooling stage, the part's deformation is constrained by the wall of cavity. As the temperature of every section of the part drops below the glass transaction at different time, the part develops different deformation in every section of the part and causes the so-called thermal induced stress.The study on filling stage has been mature, but only a few study focus on the stresses developed in filling and packing stage, while the major study on residual stress focus on the thermal induced stress, the flow induced stress is fewer too. Most of the previous studies use the pure viscous constitutive equation by neglecting viscoelastic effects. This method can simulate the shear stresses but can not predict the flow induced stress.In this paper, a numerical method for solving the viscoelastic flow is proposed, the viscoelastic flow of the polymer melt in both the filling and packing stage of injection molding process can be simulated and the flow induced stress developed in this process can also be calculated. The main works are shown as follow:...