NUMERICAL-SIMULATION OF BLOW MOLDING - VISCOELASTIC FLOW-ANALYSIS OF PARISON FORMATION

The simulation of the parison formation process in blow molding has be en studied. The flow field was divided into two regions, namely, the e xtrudate swell region near the die Lip and the parison formation regio n after the exit swell. In the swell region, we predicted the swelling ratio and residual stress distribution for high Weissenberg numbers f or steady planar swell using the 1-mode Giesekus model. In the parison formation region, the now is assumed to be an unsteady unaxial elonga tional flow including drawdown and recoverable swell and is modeled us ing the 10-mode Giesekus model. We calculated the time course of paris on length and thickness distribution, and compared the calculation res ults of parison length with experimental data. It; was found that the predicted values agreed rather well with the experimental values. The calculation results could especially predict the shrink-back, which is the phenomenon where the parison length becomes shorter after the ces sation of extrusion, and it was found that this was caused by the reco verable swell of the parison, which depends on the tensile stress gene ration in the die. Various flow rates and die geometries were studied and confirmed the reliability and usefulness of the method.