Optimization by the C-NEM Method of the Stretch-Blow Molding Process of a PET Bottle Near T g

Abstract

The stretch-blow molding process of poly(ethylene terephthalate) bottles generates some important modifications in the mechanical properties of the material. Considering, the range of temperature (T > T g ) that is usually used, the material has a very high viscosity and shows a strain hardening effect linked to the microstructure evolution. A simple visco-plastic model had been identified from experimental results of uniaxial and biaxial tensile tests [1]. In the present work, we use this model and a numerical technique to simulate the inflation of a preform under an internal pressure and also submitted to the elongation of a stretch rod. The finite elements method has a poor efficiency in the stretch-blow molding process because the final material strain is up to 300%. This strain level generates strong element distortions and necessitates to often re-mesh. In order to carry out simulations with strain higher than 300%, the constrained natural elements method (C-NEM [2]) is used. In fact, the C-NEM method allows simulation with high strain level without re-meshing. The original "mesh" can be use from the beginning to the end of the simulation. So the properties of the material can be recorded in each node, without loss of information. In a first approach C-NEM are applied to simulate and optimize stretch-blowing of a PET preform by using axis symmetric assumption, the mold is not taking into account.

Finite Element Analysis of PMMA Stretch Blow Molding

“…Each geometry is characterized by a given pair ( , ) (given in Table 1). The thicknesses are in agreement with the results obtained by Cosson et al [7] and Yang et al [11]. The simulation results are superimposed to the measured data of an existing bubble.…”

“…The "optimal" distribution of the thickness should be obtained for ≃ 2.1 ∘ C and ≃ 4.2 mm. It gives a light bubble with a uniform distribution of the thickness in addition to a better mechanical quality [7,8].…”

“…These simulations focused on the optimisation of the side wall thickness of the bottle by adjusting the variations of histories of plunger movement and gas pressure. Cosson et al [7] used the so-called constrained natural elements method to simulate and optimize the stretch blowing of a PET preform by assuming an axisymmetrical and viscoplastic preform model under an internal pressure. The thickness of the bottle is linked to the variation of the stretch rod speed and time where the blow pressure is applied.…”

Measuring and modelling air mass flow rate in the injection stretch blow moulding process

“…An aspect of their work has focused on developing a blow moulding simulation based on the Constrained Natural Elements Method (C-NEM) which has the advantage of not requiring any re-meshing even when the elements are subjected to high strains [3]. The simulation is still at an early stage of development and no correlation between simulation and experiment is available.…”

Experimental investigation and numerical simulation of liquid supported stretch blow molding

“…Several workgroups already applied FE-tools to investigate the SBM process and related forming processes [5][6][7][8][9][10][11][12][13]. One of the key features in these simulations is the PET material characterization.…”