The Numerical Simulation On Extrusion Blow Molding Mechanism

Extrusion blow molding (EBM) is an advanced molding technology of molding polymer hollow production. The molding process is very complicated for the mutual effect of parison swell and sag in molding process. So the mechanism of EBM is difficult to understand. In this situation, the research on simulation on the parison formation phase and parison inflation phase of polymer EBM process were conducted in this paper. The influences of process parameters and polymer viscoelastic rheological parameters on parison die swell and sag in parison molding process were systematically studied, and the influences of parison die swell and sag on parison inflation molding process were also studied in this paper. The following main achievements were yielded:Based on process characteristics of EBM process, theories of polymer rheology, hydrokinetics and thermodynamics etc, the full 3D,non-isothermal, steady, viscoelastic theoretical model of describing EBM process was established under reasonable assumption.On the basis of the mixed finite element stable discrete techniques of Galerkin method, Penalty function method, EVSS method, Mini-Element method and SUPG. method, corresponding stable finite element numerical model with fast convergence were established for high non-linearity 3D viscoelastic theoretical model of EBM. Finally, with above numerical model systems, the finite element numerical simulation of viscoelastic polymer EBM was implemented.The influencing rules of process parameters and polymer viscoelastic rheological parameters on parison die swell and sag in parison formation process were analyzed by means of the finite element numerical simulation on parison formation process in EBM, and the mechanism of parison die swell was disclosed by theoretical analysis. The research results showed that the parison die swell mainly depend on the intensity of the melt secondary flow which is arose by normal stress difference.For the annular parison in this paper, the bigger of normal stress difference, the stronger of the melt secondary flow, and the parison die swell would be bigger. Based on above research results, the relations of parison die swell and sag with the wall thickness and radius of parison after extrusion from die were estabished.Based on the research results on influencing of the process parameters and polymer viscoelastic rheological parameters on parison die swell and sag in parison formation process, the influence rules of parison die swell and sag on parison inflation process were studied. And the theoretical relation model of the wall thickness influence-factor, radius influence-factor of EBM parts with the parison die swell and sag were established. Finally the science theoretical basis was supplied in which the extrusion blow molding design method of integrating parison formation process and parison inflation process can be established.