Title:
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The evolution and automation of sheet prepreg layup
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It became evident that Preshearing had simplified the layup process to such an extent that
automation had become a more feasible option. Subsequently, a two stage automated process
was developed. The preshearing was applied using a custom built press with blank holders
around the perimeter to control shearing and prevent wrinkling by applying in-plane tension.
A short study on the deformation of prepreg material showed that by heating the prepreg, the
deformation could be held in the ply for over an hour after preshearing. Once the plies had been
presheared they were passed on to a robotic layup cell based around an industrial six axis robot.
Inspired by the way the human laminators used their hands alongside additional hard tools to
adapt to different mould features, three bespoke end effectors were developed to tackle
different geometric features. A large cylindrical roller was used to consolidate flat and convex
regions, while a second ' discus ' shaped roller with a 60° angle at its outer edge was used to
tackle tight concave corners. A third end effector was required to tackle tight doubly curved
convex corners. A number of hard plastic based tools were trialled, but a hybrid of a silicone
wedged tip with an aluminium core provided the right balance of high pressure and conformity.
In combination, these three end effectors successfully completed a series of increasingly
complex layup tasks. The robotic system was then combined with plies which had been
presheared in the press, and an entire sample panel ply was laid-up without any human
interaction other than transferring the ply from the press to the mould. Two complete three ply
panels were laid-up with the automated system and cured into finished parts. The quality of
these layups compared favourably to an additional example made by hand.
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