3D finite element modeling of the stretch blow molding process

International audienceThe stretch blow molding process of PET bottles is a two-step process. First, a cold tube-shape preform is heated using an infrared oven above PET glass transition temperature (about 80°C) in order to reach the forming temperature. The softened preform is then simultaneously stretched and inflated with a rod and air pressure. The final wall thickness of the bottle is both related to heating parameters as well as stretch blow molding ones. It leads to a complex thermo-mechanical problem for which specific numerical models must be developed. In this work, a complete 3D finite element modeling of the stretch blow molding process has been developed including both infrared heating and forming steps. The energy transfer between the infrared oven and the irradiative surface of the preform is modeled using a ray tracing method. In the same time, the amount of radiation intensity absorbed by the polymer is approximated with a Rosseland model. Owing to that, the radiation heat transfer results in a pure conductive heat transfer. All the thermal computations will be compared to the so-called PLASTIRAD control volume software [MON2001] and to a temperature analytical model. Considering the deformation step, a Mooney-Rivlin hyperelastic model has been implemented in Forge3® software in order to account for the PET rheological behavior. The numerical model is developed using a velocity pressure formulation and P1+/P1 tetrahedral finite elements. In order to validate the hyperelastic behavior, computations are compared to a Mooney-Rivlin analytical model of a free inflation tube. This model enables to obtain the tube internal radius versus a given pressure on the internal surface