For the 2007 limited edition of its Royal Oak Offshore Alinghi Team Chronograph (made in 2007 pieces, pictured), Audemars Piguet chose a material that had never before been used in watchmaking, which it called 'forged carbon', to distinguish it from the better-known 'carbon fibre'.
The name 'forged carbon' comes from the similarity between the process of making this material and the method of forging metals, as we see below.
Chosen for its properties of strength and lightness, forged carbon is made from a carbon 'thread' approximately 2 millimetres in diameter, itself composed of several thousand carbon fibres with a diameter of 7 microns. The fibres, cut into segments of around 4/5 centimetres, are placed inside a steel mould (pictured), where they are then heated to a high temperature and compressed with a pressure of 300 kg/cm2. This operation makes it possible to create a component, in this case the watch case, as hard as titanium (according to the company's technicians), totally non-deformable, very light and easily machined with the same tools that are used precisely for titanium.
From wikipedia: "Forging or forging is an industrial production process of plastic transformation of metal pieces of various cross-sections, usually brought to a red-hot state at the change of shape of the iron crystal from alpha to gamma and worked by repeated shaking of a hammer, forging press, etc."
The above descriptions show the similarities between the two processes.
The difference with carbon fibre is in the different arrangement of the fibres, which in 'forged carbon' are not oriented in a precise direction, but fused to form a solid structure. For carbon fibre structures, on the other hand, a 'fabric' is first constructed by weaving the carbon filaments together. These fabrics, which are soft as cloth before passing through an oven to harden the carbon (here too, a certain amount of pressure as well as heat intervenes), are placed in moulds that will give them their final shape, overlapping in such a way as to orient several filaments along the main stress lines to which the finished parts are subjected.
In both processes, the fibres are mixed with a resin, which has the task of binding the fibres.
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