MODELLING OF CRYSTALLIZATION IN INJECTION MOLDING. A 3D APPROACH
Jean-Marc HAUDIN, Mathieu BARRE, Thierry COUPEZ
Ecole des Mines de Paris
FRANCE
Keywords: Modelling, Injection molding, Crystallization
Structure development is more and more a key issue in polymer processing with a view to master the final properties of the products. Among the phenomena involved, crystallization plays a major role. It generally occurs under complex, inhomogeneous and coupled mechanical and thermal conditions, especially in the case of injection molding.
Numerical simulation is very useful tool to understand and predict these coupled phenomena in the injection-molding process. Many papers have been devoted to the incorporation of a crystallization model into codes based first on the Finite Difference method, and then on the Finite Element method using the Hele-Shaw approximations. Conversely, few studies concern the implementation of a crystallization kinetics into 3D FE codes, which do not require any geometrical or kinematic assumption.
Written in C++, Rem3D is a 3D code dedicated to injection molding. To treat crystallization, a new class (Phase) has been introduced into the Rem3D environment. The solution of the kinetic equation uses a new solver derived from the existing convection-diffusion one. The kinetic law of Ozawa modified to take into account non-constant cooling rate and flow has been chosen for the calculations.
The numerical simulation of the filling stage gives a very good prediction of the solidified layer, in agreement with previous experimental measurements.
In parallel with this overall model, we have developped a microscopic approach. The growth rate of the morphological entities (spherulites) is related to the gradient of transformation. The structure development is described by a pseudo-convection model. The formation of spherulitic patterns is correctly described by this model.