Streamline Carbon supplies many orders from the Formula 1 industry, as well as our current road/track car range where we specialise in the French car market along with many other bespoke moulds and products for all kinds of applications in between.

For your benefit we have tried to highlight the pros and cons if you like of the more common methods used in the production of carbon fibre parts. We still invest a lot of time and materials into product development as there are so many different attributes to creating moulds and composite products, development of our production techniques will forever evolve. In addition, materials used and preferred production techniques are all relevant to client requirements such as strength, weight and finish.

What is carbon fibre ?
Carbon Fibre is a synthetic thread that is heated to such a degree that total carbonisation takes place. The very fine threads in carbon fibre are either left as long fibres along the roll length (known as uni directional fibre) with good strength in that axis, or they are woven together to form fabric cloth giving multi-directional strength with the classic woven appearance most people associate with carbon fibre parts.

There are many woven styles of cloth available including plain, twill (2×2 and 4×4) and satin weaves. The Carbon Fibre is then usually left dry to be used in resin infusion processes or wet laminating (wet lay), or it is also impregnated with an epoxy resin to make pre-preg (pre-impregnated).

Both these processes rely on the resin curing either via a catalyst or heat cured (oven or high pressure autoclave) The cured resin is formed into a mould to give the finished part its moulded shape, stiffness and rigidity.

What is wet lay carbon fibre ?

The manufacturer will most likely use the cheaper polyester resin material, a single layer of dry carbon cloth with the rest being glass fibre cloth. The mould may have a clear gel coat applied (brushed or sprayed) before brushing in polyester resin followed by placing the carbon cloth with more resin then the glass fibre and letting cure naturally.

The problem with this method is a resin rich part as there really is no control over the amount of resin used. The weave pattern is also vulnerable to being disturbed. If there are any contour changes there will be voids filled with resin. Generally on anything other than a flat part this method proves to be more unsuccessful, with the only real gain proving to be a carbon weave on show and a glossy finish offered by the clear gel coat.

What is pre-impregnated autoclaved carbon fibre ?

Carbon fibre cloth is pre-impregnated (aka pre-preg) with resin and is laminated into the mould, usually applying short bursts of heat assistance to help follow the contours of the mould. The mould is wrapped in a release film and then breather material before being placed into a vacuum bag and ‘debaulked’ by use of compressor withdrawing all of the air from inside the bag.

This ensures the carbon fibre is pushed down into the mould and does not leave any voids. This process is carried out after each ply of material is laminated into the mould. The mould is then placed into an autoclave (high pressure cooker) and the vacuum bag is connected to an air line located inside the autoclave. Pressures in excess of 100psi along with heat are then applied(both low and high temperatures can be used depending on the materials used).

The length of cure cycle is dictated by the type of pre-preg material used and the structural make up of the moulds themselves. This is the top end of carbon parts production as it uses autoclaves costing many tens of thousands of pounds.

Typically, pre-preg carbon offers a very low resin content in contrast to the volume of carbon fibre material, thus producing a stronger and lighter part, hence why high end motorsport circles lend their choice of methods to pre-preg and also why you will rarely find anything ‘wet lay’ about a carbon fibre part on a Formula 1 vehicle.

What’s the difference between oven-cured and autoclaved carbon?

The use of pre-impregnated materials gives a greater guarantee that products will contain just the right percentage of resin. There are two manufacturing methods for pre-preg carbon: oven cure under vacuum and autoclave. In both methods carbon is manually wrapped around the model to obtain a single-piece that is a jointless handmade product with maximum compactness.

An autoclave applies both an ideal heat and pressure to the product placed inside of it. This technology is shared with the motorsport industry and guarantees a finished product of maximum lightness and elevated mechanical characteristics which exalt the properties of carbon.  Working carbon parts in an autoclave is considered superior because it exhalts the compactness of the laminate and reduces the possibility of vacuums and airpockets due to the application of an equal pressure accross the product. It’s also a far more expensive method of producing parts!

The lower pressure during oven cure and different curing steps affect resin viscosity and fibre distribution. In essence this can mean that oven cure is a very hit and miss affair where porosity is your worst enemy. You can’t necessarily get enough pressure with vacuum alone which results in poor consolidation. This means the finished carbon surface may contain pin holes as a result of this type of process. As such oven curing is only suitable for certain parts depending on their intended application and final finish.

Summary

To conclude, ‘Wet Lay’ is ideal for the customer that has a low budget but hankers after the carbon weave to be on show, but not entirely concerned about strength or weight, a cheaper carbon/glass fibre/polyester bonnet will most likely meet their requirements.

Those with a larger budget can accommodate the lighter, stronger and more durable products produced using pre-preg carbon material cured in an autoclave.