Technologies framework for Automated Dry Fibre Placement

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Technologies framework for Automated Dry Fibre Placement

Host Institution: The University of Bristol, The University of Nottingham

Lead Investigator: Anthony Evans, Carwyn Ward, Eric Kim, Kevin Potter, Mike Elkington, Thomas Turner

Aims

Automated Fibre Placement (AFP) technology has been adopted within the aerospace industry for the manufacture of carbon fibre reinforced components, such as wing spars, wing box covers and fuselage barrel segments. AFP has the ability to control fibre orientation as a result of its fibre steering capabilities by directing fibres onto a complex geometry or curved surface. The robustness, low wastage and repeatability through automation result in a desirable process for high quality high volume manufacture. AFP eliminates the labour intensive hand lay-up methodology that significantly increases production times. Traditionally, AFP uses thermoset or thermoplastic prepreg slit tapes, using the tack of the matrix material to adhere the fibres into position. However, these materials are expensive, require accurate temperature control during storage and deposition, to ensure sufficient adhesive properties are not effected by aging, and require further consolidation processing, such as by autoclave. The latter further increases initial equipment cost and operation cost as well as cycle times in comparison to liquid composite moulding (LCM) processes. Therefore, automated dry fibre placement (ADFP) has become of particular interest with the aim of reducing cost and cycle times whilst maintaining the high quality and low wastage of fibre placement technologies.

The overall aims are to understand the rate and quality limiting effects in the ADFP process and develop models to increase understanding of the critical factors. The project consists of several work packages:

  1. The process design package will determine hardware effects and control of the deposition apparatus whilst developing lab scale equipment to demonstrate these.
  2. The material design package will investigate the fundamental tow/ tape/NCF structure, optimising the binder content (type and volume) for tack and the prevention of fibre fuzzing during deposition.
  3. The deposition process work package will quantify the tack properties with respects to rate and temperature of dry fibre systems as well as the studying the compaction and topology to predict behaviour of single tows or ply stacks and their interactions with the deposition roller.
  4. The infusion process package will quantify the permeability effects of the fibre architecture post deposition.
  5. Finally, the part design package will part geometric effects in terms of processing rate and quality of the preforms.

 

Progress

A range of dry fibre AFP materials are commercially available (or available in developmental quantities) that are processable using the Coriolis AFP machine at the National Composites Centre using laser heating to activate the binders. The material variants include both slit tape and towpreg, with the majority of products being towpregs.

These materials have been assessed against a set of requirements based on the factors such as:

  • strength of bonding to tool substrates and previously laid down plies
  • minimum steering radius
  • bulk factor
  • volume fraction as laid and under pressure
  • in and out of plane permeability with and without deliberately induced course to course gaps
  • the generation of fluff in process (leading to machine downtime)

No significant improvement in steering radius is seen from the use of current commercially available dry fibre tapes compared to the use of impregnated tapes None of the materials tested to date have an ideal set of properties and significant opportunity exists to generate improved dry fibre AFP forms, which will be a feature of the work to be carried out in this project. Alternative approaches to conventional AFP can be used to generate very significantly tighter steering radii for both dry fibre and prepregged reinforcements from relatively low cost reinforcement forms.

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