Numerical Simulation of Injection Stretch Blow Moulding: Comparison with Experimental Free Blow Trials

The aim of this study is to develop validated simulations of the stretch blow moulding process. This paper describes experimental studies where a preform is inflated into free air (free blow trials) and the subsequent development of simulations based on the experimental data. The free blow trials were monitored via video and instrumentation was use to measure the pressure vs. time in the process. One of the key conclusions from these trials was that the pressure inside the preform is not an input variable but is in fact an output variable highly dependent on the preform temperature, timing of the application of pressure and the nominal line pressure. This effect was also shown to be hugely significant when considering the development of simulations of the manufacturing process. Two free blow simulations were developed 1: where the pressure was applied directly as measured and 2: where the application of pressure was calculated by the simulation based on a specified flow rate of air. The results clearly show the need for method 2 to accurately predict the evolution of preform shape history.