Tooling Development for Intersecting "I" Grid Stiffened Structures

For several decades, the manufacture of composite aircraft structures has been advancing towards the unitization of multiple parts to reduce weight and cost. Research and development efforts at Boeing Philadelphia have been aimed at advancing the production readiness level of a technology called Intersecting "I" Grid Stiffened Structures, intended for the unitization rotorcraft fuselages or other applicable primary structure. The design unitizes both the longitudinal and circumferential structural members, while maintaining a continuous load path through the intersection in both directions. The intersecting design presents a significant challenge regarding tooling development, as multiple trapped cavities are created. Program objectives, such as exploiting automated material placement, add further restrictions to any tooling solution. A metallic tooling concept was designed, built, and evaluated through the fabrication of demonstration articles. A brief history of the program development effort to-date is explained, followed by a description of the tooling and a summary of its strengths and weaknesses.