Why X-rays and ultrasounds play a vital role in F1

Previously in F1 Racing, we've looked at composite materials and investigated the plethora of different fibres, weaves and resins that allow these materials to be accurately tuned to the many different requirements of strength and stiffness required in a Formula 1 car.

While the process of forming metallic components through casting, fabricating, machining and even 3D printing is relatively well understood, the process of manufacturing carbon composite items is somewhat complex, so now we will try and de-mystify some of those complexities.

A composite component will be of one of two distinct forms. Either a solid monolithic, relatively thin structure, such as a brake duct, where the carbon fibre plies are formed together to produce an item that resembles something made out of sheet metal, or, more commonly, a composite structure consisting of two thin skins that carry the loads in the component but which are separated by a core material, which is typically a honeycomb structure but can also be a very light foam.

The manufacturing process for composite components starts, as always, in the designer's Computer Aided Design (CAD) system.

The design starts as a 3D model of the finished component and detail will be added to this as the design evolves through stress analysis. The designer decides what types of carbon and resin systems to use, exactly how many plies and what orientation of those plies is needed.

The 3D model forms the basis of the pattern from which moulds for the component will be made. The pattern is a solid representation of the finished component usually machined from an epoxy tooling block material.

An engineer will pass the virtual CAD model through a process called tool pathing, which programmes the large 5-axis machines that cut the tooling block to the required shape.

Once machined, the surface must be brought to a high gloss finish. This is still largely done by hand sanding with wet and dry paper followed by the application of a high gloss epoxy paint.

The pattern will then be inspected using laser scanning or a 3D coordinate measuring machine, as any errors at this point will be reproduced in every component made.

The next stage of the process is to make the mould itself.

These are normally made from carbon, which may sound extravagant but has the advantage that when the items are finally cured at high temperature, the mould will expand at the same rate as the carbon fibre component inside it.

The pre-preg used will, however, be one of the cheaper varieties and many plies will be laid to make a very rigid mould that is an inverse of the final component.

If the mould is large, such as for the monocoque (below), a stiffening frame will be incorporated in the lay-up. After the initial cure, the mould will be solid but will then be post-cured at a higher temperature to enhance its robustness for further use.

With moulds finished the production work can start.

The first stage is to lay the pre-impregnated carbon cloth in the mould. This is done by highly skilled laminators who follow the precise design that has been determined by the designer and verified by the stress engineers.

The orientation of the plies is particularly important so some experimentation sometimes has to be made with how the material is draped into the mould. The pre-preg can be a little reluctant to get into sharp corners and the laminators will often use a domestic hair drier to heat the resin, hence lowering its viscosity and allowing the material to become more pliable.

Several layers, known as plies, may be built up in this way. Each one must be placed precisely to the instructions contained in the laminating book and sometimes lasers or augmented reality type video systems help the laminator align the plies exactly.

Sometimes it is necessary to ensure the material is well consolidated with no air bubbles between plies. This will be done by applying a vacuum and moderate heat to the laminate to force the plies together and into the mould. This is a process known as debulking.

With all the plies in place the final cure can be carried out.

Firstly, the carbon fibre in the mould is covered with a release film. This in turn is covered in a cotton wool-like breather fabric and finally a vacuum bag, which is sealed to the mould with a putty-like tape.

Vacuum line attachments are pushed through the vacuum bag and the whole assembly put in an autoclave, in effect a huge oven that can be pressurised. With a vacuum drawn on the work the cure cycle begins. This involves bringing the temperature and pressure up in a controlled manner.

Typically this is a two-stage process with an intermediate temperature and pressure allowing the resin to flow and for gasses to escape before finally consolidating the materials and fully wetting the fibres. A typical cure cycle might slowly heat the assembly to 175 degrees centigrade with around 6 bar pressure in the autoclave. This will be held for some time before both pressure and temperature are ramped down.

If a core is to be used then this can either be incorporated in a single hit of outer laminate, core and inner laminate, or assembled into a pre-cured outer laminate.

A film adhesive will be placed between the core and the skins to ensure adhesion.

To apply loads into the structure, inserts may also be co-cured into the structure. These will be typically aluminium or solid carbon and a foaming adhesive may be used to ensure a bond to the skins and core.

Once cooled, the component will be released from the mould and cleaned up before undergoing dimensional checks.

If the component is structural, for example a wing or suspension leg, it will also undergo X-ray or ultrasonic scanning to check for consolidation, before being subjected to a mechanical proof strength test and finally being fitted to the car.

The rise in composite technology in F1 has brought improved safety and lightweight structural efficiency.

While the material may have been invented in the aerospace sector, it is F1 that has pushed its limits in both material science and application, to the point where it is now also a viable material for lightweighting road vehicles for reduced fuel consumption.