Abstract: The numerical model with Giesekus constitutive equation was established for the 3-D isothermal coextrusion flow within a die with the square shaped cross section. The simulation of the moving interface between two polymer melts was performed using Polyflow. The numerical results were compared with the experimental data of Karagiannis et al. and the numerical error was discussed. The analysis shows that the interface position in coextrusion could be predicted at a relatively high order of accuracy for the numerical model with viscoelastic constitutive equation and slight-slip wall boundary condition, The interface obtained from simulation is a little higher than the real interface obtained from experiment. The simulation error at the center part of the die is less than that beside the wall. Surface tension on interface and wall boundary condition is the main factor which affects the accuracy of the simulation on moving interface in coextrusion process.

Key words: viscoelastic, coextrusion, interface position, numerical simulation