Computer Simulation of the Inflation Process in Blow Molding

A finite element numerical analysis of parison inflation associated with the extrusion blow molding process has been developed using a novel overlay viscoelastic model. The model uses 2-D six noded overlay isoparametric elements. The analysis is capable of predicting final wall thickness distribution for axisymmetric mold geometries. Experimental studies were carried out on an extrusion blowing molding machine with two axisymmetric molds. High density polyethylene was used in the experiment. The predicted wall thickness distribution is in reasonable agreement with the experimental data. Non-uniformity in the initial thickness and the non-isothermal temperature profile of the parison was found to have the most significant impact on the inflation behavior and the resulting wall thickness. Numerical simulation of a blow molding process can be used to optimize the molds and the molding parameters to achieve a product with ideal thickness distribution.