Composite materials ProcessingGetting the process right

Alex WhatleyMarine Innovation Service ManagerFalmouth Marine School

Overview

• Falmouth Marine School• The Marine Innovation Service• The push to move to closed mould processes• Implications of changing processes• Summary

• Dedicated marine specialist campus of Cornwall College, covering boatbuilding, marine engineering, marine science and leisure & water sports

• Courses from NVQ to Degree level (validated by University of Plymouth)

• Full time courses, apprenticeships and employer responsive programs

• www.falmouthmarineschool.ac.uk

• Technical Consultancy Service – not training• Knowledge Transfer /Knowledge Exchange• Marine specialism• Strong composite materials focus• Other technologies covered• Service currently underwritten by ERDF

Composite materials – an overview

• 2 or more materials combined to make hybrid material; Reinforced concrete, plywood, cob...

• Marine industry use fibre reinforced composites (FRP)• Reinforcements (fibres), consolidated in a matrix system

(resin)• Fibres most commonly glass, but also aramid (Kevlar),

carbon or natural (e.g. flax, jute or hemp)• Resins most commonly polyester, but also vinlyester, epoxy

or bio resins (e.g. linseed oil derived)• Cores used to increase bending stiffness – can be wood,

foam, paper/metal honeycombs

Composite processing - basic

• Resin is dispensed into a bucket• Catalyst measured, added and mixed• Resin applied to fibres in the mould using a brush or

foam roller• Resin and fibres consolidated using metal paddle

roller or plastic squeegee• MESSY AND SMELLY! Polyester resin gives off styrene

gas, which is a suspected carcinogen• Lowest quality processing method – inconsistent

weight and mechanical properties

Composite processing - intermediate• Use of vacuum to get better consolidation

over hand rolling; pressure approx 10 tons/m2

• Resin infusion uses this pressure to push resin through dry laminate stack

• Fibres are laid dry into mould – better control of fibre orientation

• Mechanical mixing and dispensing of resin and catalyst further increases quality and reduces waste (= monetary and environmental cost)

Composite processing – high tech

• Pre-pregs – fibre is pre-impregnated with catalysed resin and then deep frozen to pause chemical reaction

• Resin film infusion – plies of fibres are interspersed with films of resin and then deep frozen to pause chemical reaction

• Both require processing under a vacuum bag at elevated temperature to reactivate resin curing process

• High material and capital cost, but optimal weight and mechanical performance

Why change?

• Higher quality product:• Greater repeatability of weight and mechanical

properties in each moulding• Opportunity to optimise structure – reduction of weight

for same or better strength and stiffness• Easier to mould complex shapes and structures• Higher tech design and build process allows innovation• Potentially quicker processing times, needed for

business expansion or more economic production• Better working environment – lower styrene emissions

Processing options – large structures

• In 2007, the National Composites Network funded a feasibility study/cost comparison of material choice and processing methods for Rustler Yachts Ltd in Falmouth and the lessons learnt were applied to the new R33

• The report looked at the following build programs:– Wet lay/vacuum consolidation– Resin infusion– Resin film infusion– Pre-impregnated fabrics

Study outputs

• Pre-pregs were discounted on grounds of cost – both materials and processing (oven)

• Wet lay/vacuum consolidation does not give significant enough differences in working conditions from the existing processes to be considered

• This leaves resin infusion and resin film infusion, including the SP Sprint system

• A cost and weight comparison was carried out, based on the specific boat (a yet to be developed 37ft model)

• Current wet lay/hand consolidation• Low material cost, high labour cost per unit• High structural weight

• Resin Infusion• Higher material cost, lower labour cost per unit• Lower structural weight - 56.1% of current lay-up

• Resin Film Infusion• Much higher material cost than resin infusion and

no reduction in labour cost• Lowest structural weight - 49.8% of current lay-up

• Wet lay-up• Nett Weight of composite structure 8,231kg• Projected Weight inc 10% margin 9,055kg• Cost of composite Materials £25,036• Projected cost including margin £27,539• Labour (GBP) 535hrs @ £30/hr £16,050• £68,625• Cost/weight = 100%• • Resin infusion• Nett Weight of composite structure 4,620kg• Projected Weight inc 10% margin 5,082kg• Cost of composite Materials £35,517• Projected cost including margin £39,069• Labour (GBP) 400hrs @ £30/hr £12,000• £86,586• Cost/weight = 126%• • Resin film infusion• Nett Weight of composite structure 4 098kg• Projected Weight inc 10% margin 4,508kg• Cost of composite Materials £41,570• Projected cost including margin £45,727• Labour (GBP) 400hrs @ £30/hr £12,000• Amortized oven cost £2,000• £101,297• Cost/weight = 148%

Who changes?

• Not a high end, expensive process• Applicable in a range of projects• Rustler Yachts – new 33ft model• J Boats Inc – whole range, built in USA/France• Cornish Crabbers have developed a 12ft

dinghy which was designed from the outset to be built in resin infusion - desire to move all models to infusion over the next 5 years

Scalable process

• Princess Yachts in Plymouth are infusing hulls up to 40m in a single process – 6 tonnes of resin in one shot!

Processing options – Smaller units

• Resin Transfer Moulding (RTM) and Vacuum RTM (RTM light) allows double sided moulding to be produced in ‘one hit’

• Ideal where customer sees both sides of the product – would otherwise be built in 2 parts and bonded together

• True closed mould process – two solid moulds with engineered cavity between them into which fibre is loaded

• RTM uses mechanical clamping, VRTM uses vacuum as primary clamping force

• Resin injected into cavity

Hurdles/changes/implications

• Capital investment– Mould design to accommodate vacuum system– Vacuum pumps and monitoring equipment

• Consumables cost– Vac bags, sealing tape, pipe work etc

• ‘Clean space’ on shop floor amongst other ongoing projects

• Staff development• Getting the details right

The learning curve

• Understanding key processing principles is one thing, but practical application is another!

• Small section trials and practice runs• Help and support is available– Marine Innovation Service– National Composites Centre (Bristol)– Supply chain e.g. equipment specialists Composite

Integration Ltd, material supply companies etc…– Specialist training courses such as Composite Skills

Alliance to develop shop floor staff

Video ShowcaseFMS dinghy build

Summary

• Driver to change processing method has to come from a sound business plan

• Choice of processing has to be relevant to the end product

• You don’t need to make sweeping changes... incremental introduction of process change allows analysis of impact

• Bolting on higher technology can work, but new projects with technology built in from day one give greater flexibility

Summary

• Of all the closed mould processes for large structures, resin infusion offers the lowest financial outlay for laminate quality and working environment improvement

• However – developments of low temperature pre-pregs continue to bring these materials within reach of the most basic ovens (500C)

• The learning curve is steep – don’t try and reinvent the wheel as there is plenty of help out there, from other businesses to the supply chain

Alex WhatleyMarine Innovation Service Manageralex.whatley@cornwall.ac.uk07771907266www.marineinnovationservice.co.uk

Next event:Wednesday 13th February 2013Composite Workshop, Ponsharden