| Résumé | An outstanding problem in extrusion blow-molding process of polymers is the precise prediction of the parison shape inside the part along the pinch-off weld. Such a prediction is highly relevant for producing components with an accurate wall thickness distribution along the parting line as blow-molded parts often fail at the parison pinch-off weld of the mold parting line. In this paper, we report on the numerical study of the parison pinch-off modeling in extrusion-blow molding using a coupled level set (LS)-arbitrary Lagrangian–Eulerian (ALE) method. The deformation of the parison-free surface during the mold closing stage is approximated by means of the level set technique on a deforming mesh domain caused by the simultaneous mold halves displacement. The multi-mode Phan-Thien and Tanner (mPTT) constitutive equation is employed to model the parison deformation in the pressure zone, the flash pocket, and along the pinching edge. The developed LS–ALE approach is first validated on a benchmark squeeze flow problem between two parallel coaxial disks for both Newtonian and viscoelastic fluids before the numerical simulation results for the pinch-off problem are discussed. We report numerical experiments related to the mold closing velocity effects on the parison shape behavior and parison wall thickness distribution along the pinch-off weld for a high-density polyethylene (HDPE). For this viscoelastic polymer, the parison exhibits a rounded shape along the pinch-off weld line inside the part, and this rounding becomes more pronounced as the mold closing velocity increases, in accordance with experimental observations. Whereas, for a Newtonian fluid, the parison displays an angular V-shape along the pinch-off weld inside the part and does not depend on the mold closing speed. The parison thickness along the weld line is increased by 126% for the HDPE studied while it only increases by 72% for a Newtonian fluid with the same zero shear-rate viscosity. The predicted parison wall thickness distribution around the pinching zone represents an important step in optimizing both processing conditions and the mold pinch-off design. |
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