Insight into Reverie & autoclaved composites By Simon Farren Presented at US Distributor Sector 111 11 th April 2009.

Insight into Reverie & autoclaved composites

BySimon Farren

Presented at US Distributor Sector 111 11th April 2009

History of ReverieFounded in May of 2000 by Simon Farren, previously on the management team for engineering the Lotus 340R into a production reality.Created to offer affordable autoclaved composites to clients. We design and manufacture a range of quality parts for track days and professional race team consumers for distribution via worldwide dealers emphasizing Lotus enhancing products.

What is Carbon Fiber?• Carbon fiber is a synthetic thread (poly-acrylo-nitrile, rayon or

pitch) heated in an argon atmosphere where carbonization occurs.• Carbonization temperatures can be altered to produce different

strengths and modulus of the carbon fiber.• The very fine carbon threads are left as long fibers along the roll

length (UD fiber) with strength in that axis only or woven together to form a fabric cloth resulting multi-directional strength.

• Carbon fiber can be left dry or pre-impregnated with a thermoset resin to make it pre-preg.

• The cured resin gives the finished part its molded shape, stiffness, rigidity and protection of the stressed fibers.

History Of Carbon Fiber• First developed in 1958 by Dr. Roger Bacon in Cleveland, Ohio,

fibers were manufactured by heating strands of Rayon until they carbonized. This process was inefficient. The resulting fibers contained approximately 20% carbon, which resulted in less strength and stiffness properties.

• Early in the 1960’s, a process was developed using poly-acrylo-nitrile, as a raw material. This produced a carbon fiber, containing55% carbon, compared to 93-95% today.

• Early in 1969, Carr Reinforcements in England first wove a carbon fiber fabric.

Why Composites?• Carbon fiber is typically 3 X stronger than steel yet 4 X lighter. • It’s 7 X stronger than 6061 alloy and 2 X stronger than tensile

modulus, with similar weight.• Tensile modulus (stiffness) ranges from 230 GPa to 441 GPa and

tensile strengths range from 3.5 GPa to 5.9 GPa. • The ultimate strength and the breaking strength are the same for

carbon fiber. Steel yields prior to reaching it’s ultimate strength. • There is no yield to carbon fiber, so parts can be repaired with

lamination to the same shape easily.• Kevlar has a yield strength 7 X higher than steel and about 4 X

lighter than steel. Bullet proof vests are manufactured with it.

Uses Of Composites• Carbon fiber’s weight, stiffness and strength

benefits make it widely used in boat building, aerospace, motorsport and sporting goods.

• Other fibers like Kevlar, Dyneema and fiberglasscan be used independently or incorporated into laminates.

• Resin systems are selected to give the required toughness, temperature range & protect the stressed fibers from damage.

• Modulus & strengths of fibers, thickness and direction of fibers can be varied to give the properties required for the part.

Autoclave Processing Pre-PregsWe process thermoset epoxy pre-pregs using one of two pressurized & temperature computer controlled autoclaves, which are used by Formula One teams.

The use of elevated pressure in the autoclave facilitates a high fiber volume fraction and low void content for maximum strength.

Autoclave Processing Pre-PregsThe UD pre-preg fiber or woven cloth is hand cut or done by machine into the shapes and orientation required for each ply of the component, which form the kit of parts.

Autoclave Processing Pre-PregsA mold tool, either male or female, is required to obtain a good surface finish on one side. Both a male and female compression tool is needed for a dual molded surface.First the tool has a release agent applied to it’s surface to avoid sticking.

Autoclave Processing Pre-PregsEach section of a ply is hand placed into the female mold or over the male mold in the orientations required by the drawing.

Autoclave Processing Pre-PregsSome components require the molds to be multi-pieced and overlapping joints in the pre-preg are often required.

Autoclave Processing Pre-PregsOnce lay-up is complete, a layer of thin release film (approx 15 microns) is applied over the surface of the pre-preg, where the vacuum bag may make contact. This allows the breather layer or bag to release from the cured composite surfaces.

Autoclave Processing Pre-PregsA polyester breather fabric layer is then applied to the outside of the mold and where possible across the component surface. The purpose of this fabric is to allow a full vacuum path over the complete mold and component area.

Autoclave Processing Pre-PregsVacuum bags are applied. They can be a single sheet sealed with tacky tape against the mold’s outer perimeter on a male or female tool or a tubular envelope bag sealed at both ends to vacuum the complete perimeter of the mold tool. Any internal tubular bags or molded latex bladders can be left out of one or both ends of the tubular bag. A vacuum breach fitting goes through the bag surface to allow air to be removed.

Autoclave Processing Pre-PregsThe air is slowly sucked out by a very powerful vacuum pump down to 5 Torr. The pre-preg resin matrix layers are forced together onto the mold surface at nearly one atmosphere (14.7 psi approx). As the air is removed the vacuum bag is carefully manipulated to ensure it does not stretch too tightly over features.

Autoclave Processing Pre-PregsThe component is under full vacuum, any internal tubes or bladders open to atmosphere will be exerting 14.7 psi pressure internally. The mold is now ready for its thermo set process either in an oven to cure at 14.7 psi or in an autoclave to cure at up to 100 psi. The greater the pressure the lower the void content and the higher the strength and greater surface finish.

Autoclave Processing Pre-PregsOnce in the autoclave, the vacuum bag is connected to a vacuum line; a steel wire reinforced line which will not collapse under pressure. Once the autoclave reaches 14.7 psi, the vacuum circuit can be externally vented to atmosphere or left connected to remove volatiles. Most of our component pre-pregs cycle at temperature for 90 minutes at 120°c or 248°f. The pressure used depends on the quality of the mold, if the component is monolithic or features a core material such as foam or honeycomb.

Autoclave Processing Pre-PregsOnce the cure has finished, the mold and component are left to cool. The bagging film is removed and the mold unbolted, if multi-sectioned. The component is carefully released with plastic wedges. The component is now ready to be trimmed to size, secondary bonded and polished or sanded for paint.

Product Design @ ReverieIdentifying a market niche for a new product, either from customers, dealer feedback, demand or via our own research.Each product design is optimized for strength/weight and shaped within constraints of packaging and aerodynamic performance. Materials selected by experience, or where required by mathematical analysis using either hand calculations or computerized FEA.Passionate about improvements

Product Design @ ReverieProducts are designed on CAD where packaging requirements and draft angles can be checked and amended before machining.Products are prototyped and tested at low cost to prove design performance; these results are factored into future design enhancements.

Design to Production @ ReverieMale patterns from foam or clay are either handmade or CNC machined from CAD data out of aluminium block or solid epoxy tooling slabs, which are bonded together to form the cubic block.

Design to Production @ ReverieOnce a male pattern is available, any split lines required for undercuts can be defined by removable weir walls at 90˚ to the surface featuring dowel location holes to ensure alignment. A mold tool can then be hand laid from the pattern with weirs in carbon fiber and autoclave cured . For low volume projects, sometimes a high temperature GRP hand laminated tool is produced.Tools can also be machined direct from alloy.A layup drawing is then produced for the laminating shop.

Reverie In High End Motorsport

WRCWSBFIA GTAMLS

Why Choose a Reverie Part?• Established reputation for high quality.• Exceptional design and product testing.• Autoclaved manufacturing ensuring high fiber to resin ratio and very low voids.• Manufacturing controlled on-site.• Use the highest quality Cytec pre-preg materials.• Excellent customer service, technical data and help.• Chosen by some of the best engine builders and race teams.• Passionate about continuous and constant improvements and

enhancements.