Modelling the heat during the injection stretch blowing moulding: Infrared heating and blowing modelling

International audienceThe effects of temperature, initial heating conditions or self heating during the process, are very important during the injection stretch blow moulding (ISBM) process of PET bottles. They control the preform temperature distribution and strongly affect the blowing kinematics via the important influence of temperature on mechanical behaviour. The temperature affects the orientation induced by biaxial stretching, which in turn, affects mechanical properties of PET. Therefore, thermal proprieties are one of the most important variables in the ISBM. In order to achieve accurate simulation of the ISBM process, it is necessary to: (i) measure the initial temperature distribution of the preform when the blowing operation begins; (ii) follow the history of the temperature field and consequently to identify the thermal proprieties of the PET; (iii) to model the behaviour law of PET coupled to the thermal laws. In this work, we modelled the PET behaviour in ISBM strian rate and temperature conditions by a thermo-viscohyperelastic model which has been inspired from Figiel and Buckley 2009 [1] and already presented by Luo et al. 2011 [2]. A procedure is proposed for the identification of the thermal parameters from experimental results of a test where PET sheets are heated using infrared (IR) lamps. The Monte Carlo method is used to provide the parameters best fit from the temperature evolution measured on the face in front of the lamps and from the rear face. The beginning of the temperature evolution gives information on the IR flux and the final stage of the heating gives information on the convection exchange. Difference between the front and the rear faces gives information on the PET conductivity. Using a finite element approach implemented in Matlab, the coupled thermo-visco-hyperelastic model has been used to simulate the ISBM process. The results from the computer simulation can be compared with the temperature profiles measured by thermal imaging