scope:

Description of Driving Event:

To cure a large laminate structural part, the part is wrapped in layers of material that maintain a vacuum on the part and allow a portion of the resin to bleed away from the part. For this part, the stack up of bag layers is: peel ply, perforated release film, bleeder, solid release film, breather, and then vacuum bag. The function of these layers is:

• Peel ply - Layer of no-sticking material that allows the bagging to be removed after cure; Provides flow path for the applied vacuum

• Perforated release film - Allows for the appropriate volume of resin bleed by having the specified bleed holes at the specified spacing

• Bleeder cloth - Soaks up resin as the vacuum process pulls it from the composite structure to permit part cure

• Solid release film (non perforated) - Protect the vacuum bag from the resin

• Breather - Polyester material allows a vacuum to be maintained throughout the entire part without pinching off in any area

• Vacuum bag - Provide the pressure barrier between the high pressure in the curing chamber and the vacuum drawn on the part

• Vacuum Sealer Tape - Seals the joints in the bagging material to complete the bags.

The scrapped part was the third unit of this part to be built. The part is conical in shape, so flat sheets of bagging material did not drape nicely over the part. During the original two builds, the manufacturing crew cut the bagging materials into gore sections and taped them together to achieve a good fit to the part. The criticality of cutting bagging materials into gore sections was unknown and un-documented. On the third build of this part, the manufacturing crew wrapped the flat sheets around the part then taped the one joint. During the cure of the third part, wrinkles formed when vacuum was applied to the bags. At the wrinkles areas, additional holes formed in the perforated release film and holes formed in the solid release film. These new holes in the bagging material allowed excessive resin to bleed through the perforated release film and also to bleed through the solid release film. The resin in contact with the vacuum bag cured, permitting stress concentrations to form on the vacuum bag. The vacuum bag failed at 231 minutes into the cure and at 329 deg F, causing the part to be nonconforming.