Modelling of the injection stretch blow moulding of PET containers via a Pressure-Volume-time (PV-t) thermodynamic relationship

A 2-D isothermal finite element simulation of the injection stretch-blow moulding (ISBM) process for polyethylene terephthalate (PET) containers has been developed via the commercial finite element package ABAQUS/standard. In this work, the blowing air to inflate the PET preform was modelled via two different approaches; a direct pressure input (as measured in the blowing machine) and a constant mass flow rate input (based on a Pressure-Volume-time relationship). These two methods were tested with a simplified stretch blow moulding process where a preform was blown with and without a stretch rod in free air (no mould). The results clearly show that simulation with a constant mass flow rate as input gave an excellent prediction of volume vs. time curve and preform shape evolution when compared with the direct pressure approach. In addition to this, rapid inflation of the PET preform (~0.03s) was found to occur in the direct pressure approach which was not observed in reality. This result reveals that the constant mass flow rate approach is more appropriate in modelling the blowing stage in ISBM process.