Original Date: 10/14/1988
Revision Date: 01/18/2007

Bell Helicopter Textron, Inc. (BHTI) is using closed cavity tooling for curing composite primary rotor system components, and for fabricating main rotor system yokes. This process guarantees repeatability, assures control of finished dimensions, and reduces secondary machining operations.

To assure the success of this approach, BHTI has established several manufacturing practices. The most critical of these are the accurate sizing of prepreg details, the tandem use of mechanical pressure and vacuum pressure techniques at ambient and higher temperature conditions during lay-up in order to optimize compaction, and the strict control of resin content and fiber area/weight.

Sizing of details is accomplished by using an automated controlled belt winding of prepreg roving and precision cutting of details from broadgood prepreg with chisel cutters fitted to a computer controlled Gerber cutting machine. Ambient temperature and mechanically induced compaction are accomplished with customized, pressurized rubber bladders.

The flexibility of this approach allows compaction at various stages during the lay-up in the curing tool at pressures up to 40 psi. Heat compaction using vacuum is performed in the curing tool at 130-140 degrees F for two hours. It is applied twice during lay-up. This procedure progressively controls bulk factor and resin bleedout. The strict control of resin content and fiber area/weight is accomplished by the kitting of details of known resin and fiber content. This balancing approach compensates for the variation in resin and fiber content of prepreg material as it is received from the supplier.

For more information see the Point of Contact for this survey.