Once the engine and chassis designers have agreed upon a general specification and outline of the chassis, 3-D computer-aided drawings (CAD) are made. The same raw data that produced the drawings is then used for computeraided manufacture (CAM). Before the carbon fibre tub is constructed, mirror-image moulds are made, and before that can be done, patterns need to be built to form the moulds. Blank slabs of a man-made material called Ureol are typically used for this. These slabs are machined into the required forms, directed by the CADCAM information.
The various patterns bolted together form a dummy Formula One tub, complete with nose cone. A scanner goes over this, taking measurements, which are compared to the original CAD drawing for accuracy. The dry sheets of carbon fibre are laid out over the pattern. A resin is impregnated within them. This resin releases and bonds under the pressure and temperature of an autoclave, thereby holding the whole thing together in the required shape. Holes and recesses are introduced into the moulds by tooling blocks that replicate suspension and engine mounting points.
With the moulds completed, the carbon fibre is laid up over them, but in a much more complex formation than was used to create the moulds. A calculation technique called finite stress analysis will have shown the engineers where the strength needs to be and so extra layers are laid in at the appropriate places.
Multiple layers mean several stints in the autoclave before the final high-pressure, high-temperature run of around 2.5 hours. Bonded together, the final tub weighs around 30kg.
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