Fluid Structure Interaction in Injection Stretch Blow Moulding

The Injection Stretch Blow Moulding (ISBM) process is the main method used to mass-produce PET bottles for the carbonated soft drink and water industries, an industry worth 6 billion pounds in the UK. The process begins with injection moulding of a preform which is subsequently re-heated above its glass transition temperature and formed into a hollow mould by a combination of axial stretching by a stretch rod and radial stretching by internal air pressure. The existing industrial state of the art in the process involves trial and error approaches on a single cavity ISBM machine to determine appropriate machine settings for industrial production. This process is wasteful in terms of time, energy and material and restricts processors in their ability to lightweight containers which for both economic and environmental reasons is a major goal of the industry. Researchers are developing numerical simulations to try and overcome this empirical approach and replace it with a more scientific method whereby one can predict the process conditions and their effect on material thickness distribution and final material properties in advance, thus enabling the optimum preform design and process conditions to be obtained. However success to date has been limited. One of the major causes is that current simulations do not model the correct physical behaviour of the transient pressure history inside the preform as it is inflated into the bottle mould. The project will build on recent results from a European project (Apt_Pack) in which it was demonstrated that one of the most fundamental process variables in the ISBM process is the mass flow rate of air that enters the preform as it inflates. It is this that is ultimately responsible for the pressure inside the preform and thus primarily controls the rate of inflation of the preform, the final thickness distribution and the properties of the formed container. The transient pressure history depends on the supply pressure, the mass flow rate of air and the rate of inflation of the preform. As a result, the only sensible approach to modelling this is to have a coupled fluid structure interaction whereby the pressure is calculated based on the volume of the expanding preform and the mass flow rate of air entering the preform. The main aim of this project will be to conduct a parallel experimental and modelling program to understand and accurately quantify the air flow within the injection stretch blow moulding process and evaluate how it can be best incorporated within an ISBM process simulation.

Who will benefit from the research and how? The entire ISBM industrial supply chain will benefit from the research. This includes material suppliers, machine manufactures, converters, end users and the consumer. Each will feel the benefits of simulation technology in different ways. Consumers will benefit from lighter packaging which is more environmentally friendly - a very important benefit considering the current focus on the impact of plastic packaging on the environment. The end users (e.g. P&G and Danone) can use it to design novel added value packaging in a more efficient way. The converters will be able to offer services to their customers for light weighting containers thus making them more competitive. In addition they will be able to move away from the trial and error techniques they traditionally use which will enable them to produce products with a shorter lead time and less material and energy waste. As highlighted in the case for support this can potentially save them millions of pounds per year. The machine manufacturers will use the simulation to gain a better understanding of the process thus enabling them to design the next generation of stretch blow moulding machines. In addition they could offer simulation as a value added service to their customers to enhance the sales of their machines. Material suppliers could also get a better understanding of the complex modes of deformation that occur during the ISBM process thus enabling them to design tailored grades of PET or new materials such as nanocomposites and biomaterials. It is possible that a spinoff company can be generated offering simulation and associated instrumentation services to the ISBM industry. This would have direct benefit to the UK economy through job and wealth creation. The timescale of the impacts on industry are expected to be 2 to 3 years after completion of the project. This will allow for the further investment required to develop commercial versions of software and accompanying instrumentation. The PDRA working on the project will develop skills in instrumentation and modelling that will be applicable to any industrial sector, especially in the high tech automotive and aerospace industry where people with CFD, FEA and corresponding experimental validation skills are highly sought after. Actions to ensure they have opportunity to benefit The project has 2 multinational end users and 2 converters as project partners so they will feel direct benefit immediately. Through tele conferences and physical meetings they will have early access to the results. Other companies will be made aware of the results through presentations at international conferences, journal publications and magazine articles. In addition a stand at the international plastics fair The K Show will be taken by QUB to promote this research and other research activities ongoing on ISBM within the School. This will ensure that other members of the supply chain are made aware of the project and its results. It is expected a further collaborative project will be necessary to translate the results from this scientific project to a commercial product. The partners will be expecting to contribute private funding (potentially as a 5 way collaboration) to exploit the results from this project in a commercial manner. With regards to the formation of a new company, funding will be applied for through the InvestNI Proof of Concept programme to produce commercial prototypes. After the completion of the proof of concept, additional funding from InvestNI and Venture Capitalists will be sought to form a new company. The benefit to the consumer will take place once the industry has exploited the use of the software.