Characterization of deformation in injection molded parts after packing and cooling

Residual stresses which are developed in injection molded parts affect dime nsional accuracy and mechanical properties of the final products. To predic t the residual stresses in injection molded parts, three stages of injectio n molding, i. e., filling, packing, and cooling, must be taken into conside ration for the thermal and flow analyses. Flow field anaysis for filling an d postfilling stages has been carried out by using the control volume based FEM/FDM hybrid method. The generalized Hele-Shaw flow is assumed. Compress ibility of the polymer melt is considered during packing and cooling stages . Modified Cross model is employed to reflect the dependency of the viscosi ty upon shear rate and temperature. An equation of state proposed by Tait o ffers an efficient means to describe pvt-relationship of the polymer. Varia tions in temperature and pressure fields are obtained over all stages by th e numerical flow analysis and used as input data for the stress analysis of the part. Plane stress elements, such as shell elements, are used for fini te element stress analysis of injection molded parts with appropriate bound ary conditions both in the mold and after ejected from the mold. The numeri cal analysis yields useful information which is relevant to the mechanical properties of the final products, e. g., residual stress distribution, shap e of deformation, displacement field, and strain distribution.