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Continued...
Due to this process constraint, spring-back after CAF is very high
compared to other metal forming processes, with up to 80% of the initial elastic
deformation being recovered after processing.
The main benefits of creep forming are the accuracy and
repeatability that can be achieved, as well as the ability to produce multiple
curvatures on thick topologically complex components. Unlike shot peening, which
can require several stages to achieve the required shape, CAF produces
components that are very close to net shape in a single procedure. At Broughton,
the process is also virtually automatic, requires little labour input and allows
each wing skin to be processed in 24 hours to meet Airbus's throughput
requirements.
The CAF process used at Broughton has three distinct phases.
First, a fully machined flat wing skin panel is loaded and located by means of a
guide system on to a generally concave form tool, whose surface has been
designed to compensate for post-process spring-back. Next, a vacuum bag is
fitted to seal the component against the continuous surface of the form tool,
and air is removed from under the bag, creating an atmospheric pressure
differential that produces a clamping action, forcing the panel towards the tool
surface.
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