A 2D isothermal finite element simulation of the injection stretch-blow molding (ISBM) process for polyethylene terephthalate (PET) containers has been developed through the commercial finite element package ABA-QUS/standard. In this work, the blowing air to inflate the PET preform was modeled through 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). The results from these two approaches were validated against free blow and free stretch-blow experiments, which were instrumented and monitored through highspeed video. Results show that simulation using a constant mass flow rate approach gave a better prediction of volume vs. time curve and preform shape evolution when compared with the direct pressure approach and hence is more appropriate in modeling the preblowing stage in the injection stretch-blow molding process.
The injection stretch blow moulding process involves the inflation and stretching of a hot preform into a mould to form bottles. A critical process variable and an essential input for process simulations is the rate of pressure increase within the preform during forming, which is regulated by an air flow restrictor valve. The paper describes a set of experiments for measuring the air flow rate within an industrial ISBM machine and the subsequent modelling of it with the FEA package AbaqusABAQUS. Two rigid containers were inserted into a Sidel SBO1 blow moulding machine and subjected to different supply pressures and air flow restrictor settings. The pressure and air temperature were recorded for each experiment enabling the mass flow rate of air to be determined along with an important machine characteristic known as the 'dead volume'. The experimental setup was simulated within the commercial FEA package AbaqusABAQUS/Explicit using a combination of structural, fluid and fluid link elements that idealize the air flowing through an orifice behaving as an ideal gas under isothermal conditions. Results between experiment and simulation are compared and show a good correlation.
In spite of intensive research, computational modeling of the injection stretch blow molding (ISBM) still cannot match the accuracy of other polymer processes such as injection molding. There is a lack of understanding of the interdependence among the machine parameters set up by the operators, process parameters, material behavior, and the resulting final thickness distribution and performance of the molded product. The work presented in this paper describes a set of instrumentation tools developed for investigation of the ISBM process in an industrial setting. Results are presented showing the pressure and air temperature evolution inside the mold, the stretch rod force and displacement history, and the moment of contact of the polymer with seven discrete locations on the mold. C 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E771-E783, 2013; View this article online at wileyonlinelibrary.com.
International audienceA 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
The work presented in this paper takes advantage of newly developed instrumentation suitable for in-process monitoring of an industrial stretch blow molding machine. The instrumentation provides blowing pressure and stretch-rod force histories along with the kinematics of polymer contact with the mold wall. A design of experiments pattern was used to qualitatively relate machine inputs with these process parameters and the thickness distribution of stretch blow molded PET (polyethylene terephtalate) bottles. Material slippage at the mold wall and thickness distribution is also discussed in relation to machine inputs. The key process indicators defined have great potential for use in a closed loop process control system and validation of process simulations. C 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E436-E450, 2013; View this article online at wileyonlinelibrary.com.
ISBM is currently experiencing an increasing demand and only a scientifically based understanding can manage the stringent market conditions. Therefore, a better understanding of the interdependence between the machine parameters set up by the operators, process parameters or material behaviour under the initial conditions and the bottle final thickness distribution in an industrial setting is mandatory. Comprehensive measurements of various parameters on an industrial machine allowed a more complete assessment of the process. In addition, the temperature of the pre-form was measured on both inside and outside surfaces which revealed significant difference. Particular care was given to the understanding of the air flow during blowing. In this sense a simple thermodynamic model is proposed and implemented in an ISBM simulation. The followed indicators were the kinematics of the bubble expansion and pressure and force histories.
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