Injection stretch blow moulding (ISBM) is the most common processing method of producing thin-walled poly (ethylene) terephthalate (PET) containers. With numerous processing parameters and complex deformation, there is still a certain amount of expert knowledge required to successfully convert a PET preform into a useable bottle, capable of passing rigorous post-process testing. The purpose of this work is to develop an accurate simulation of the bottle forming procedure through extensive examination of the input parameters and how they affect the preform deformation and bottle characteristics. By removing the bottle mould, a free-stretch-blow analysis was performed over a large process window. This procedure utilised the digital image correlation (DIC) method with a patterned preform heated using an oil bath. A corresponding simulation was constructed using ABAQUS/Explicit FE solver and a constitutive viscoelastic user material subroutine. A comparison between the experimental and predicted values of internal cavity pressure, stretch-rod force and surface strain was performed resulting in reduced accuracy at low flow rate, sequential-type deformations. Free-stretch-blow trials also highlighted the need for adequate preform storage as increased moisture content affects the deformation behaviour. Reapplying the bottle mould and using the same process parameters revealed that the simulation had difficulties in predicted accurate bottle thickness, particularly at higher flow rate. An insufficient contact friction model was concluded and more insight into the heat transfer and back pressure between the polymer and mould was required. Results from the simulation also demonstrated that the previously assumed incompressible behaviour of PET during bottle formation is incorrect. A novel method of measuring strain levels in all three directions was devised to reveal that deformation mode greatly affects the value of Poisson's ratio. Insight into the ISBM process and development of the simulation has been advanced through this work and key areas of further improvement have been revealed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:677457 |
| Date | January 2015 |
| Creators | Nixon, James |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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