| Popis: |
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. |
