Development of novel transportation shells for use in high volume composite part manufacture: the clamshell concept

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During the manufacture of composite parts utilising direct impregnation/Liquid Composite Moulding techniques, the dry laminate is held to shape utilising tackifiers (or 'binders'). This allows the dry material to become what is termed a 'preform'. Preforming of the dry material serves two key purposes: firstly, it allows the preform to hold its shape before full impregnation has taken place. This helps to prevent generation of defects in the preform due to handling and transportation of the preform, alongside allowing a decrease in bulk factor and the possibility of damage to the tool. Secondly, preforming allows more efficient utilisation of equipment; the infusion equipment can be dedicated just to infusion/cure, as opposed to shaping as well. This is opposed to the manufacturing techniques utilised traditionally with prepreg materials, and is crucial to the upscaling of any manufacturing process towards a high-volume, automated assembly line type process.However, the use of binders to stabilise the preform also provides a number of problems. A key issue when utilising binder materials is the large time cost of 'activation' and cooling of the binder materials, contributing to over half of the time cost of a typical HP-RTM part. It follows therefore that the removal of this can vastly reduce takt time for these parts and allow significant increases in the volumes of parts it is possible to produce. Further, the use of binder materials has also been shown to reduce the permeability of the cloth, leading to lower impregnation, as well as lowering the quality of the final part by introducing material other than the fibre or matrix within the bulk structure. As such, it can be seen that removal of these stabilisers can lead to both drastic increases in production volume and an increase in the quality of the final part. A novel method of achieving this is the focus of the work set out here.In order to achieve binder removal, a new concept termed the "Clamshell Concept" has been envisioned. This concept aims to include no form of traditional binder whatsoever. Instead, a pre-made external shell structure shall be utilised to hold and clamp the preform into shape. This then will allow transportation of the preform from the preforming station to the infusion station without the introduction of defects. Further, the shell can then be utilised to form the matrix material for the system, through an infusion method into the dried preform. This concept will allow the removal of the use of binders, both allowing an increase in final part quality and manufacture volumes. Tradition high volume plastic forming processes can be employed (e.g. injection moulding) to form the thin shells, and as such these should be able to be manufactured rapidly and with less cost. Variations of this concept can also be explored, including reusable shells that can be washed out and utilised many times, or shells designed to give a specific surface finish.The PhD projection undertaken will aim to investigate the feasibility of both the process and possible materials for this concept. Objectives include (but are not limited to):* Research current and potential future manufacturing processes and determine a set of guidelines* Research suitable materials that can be used to form the shell* Develop and characterise the material choices* Demonstrate the feasibility of the processing concepts utilising this shell* Determine the infusion methods to be used and work towards optimising these* Investigate methods of automating this conceptAs such, it can be seen that investigation of this concept is taking place to discover if this concept is capable of providing a disruptive step change in the performance of high-volume manufacture techniques.