Composite structures are used in a wide variety of applications. In aircraft construction, composites are used in increasing quantities to form the fuselage, wings, and other components. The wings of an aircraft are generally hollow structures that require a smooth and dimensionally-accurate outer mold line (OML) surface. The wings may be constructed of composite skin members and may include internal components such as composite ribs, spars, and/or stiffeners to increase the strength and bending stiffness of the wings.
In conventional construction techniques for forming composite structures such as an aircraft wing or a fuselage, composite stiffeners or other internal components may be assembled to a skin member by bonding and/or mechanically fastening. For co-bonding operations, a mandrel may be positioned within an interior of the stiffener to support the stiffener during the application of pressure when bonding the stiffener to the inner surface of the skin member. The mandrel may be formed using a hardenable mixture such as a plaster mixture.
Unfortunately, removal of hardened plaster from the interior of a composite structure may require the use of mechanical force to break up the plaster into smaller pieces. The use of mechanical force may pose a risk to the integrity of the composite structure. In addition, the process of forming the mandrel and removing the hardened plaster material is labor intensive and time consuming. Furthermore, plaster material is a generally non-recyclable material that is discarded as waste after each use.
Inflatable mandrels are also used in conventional processes for manufacturing hollow composite structures. An inflatable mandrel may be positioned within a hollow composite layup that may be supported by a closed female mold. The inflatable mandrel may be inflated to apply an internal compaction pressure on the composite layup against the female mold to consolidate and cure the composite layup. After consolidation and/or curing of the composite layup, the mandrel may be deflated and removed from the cured composite article. Unfortunately, an inflatable mandrel is generally limited in the ability to form the inner surface geometry to a high level of accuracy. In addition, inflatable mandrels may be limited in the temperatures to which they may be exposed. For example, certain composite materials may require curing at temperatures greater than 450 F which may exceed the operating limits of inflatable mandrels.
As can be seen, there exists a need in the art for a tooling system and method that minimizes or eliminates the need for bonding or mechanically fastening an assembly of components to form a hollow composite article. In this regard, there exists a need in the art for a tooling system and method that provides a means for producing unitized, monolithic composite articles having dimensionally-accurate inner and outer mold line surfaces with complex three-dimensional geometry.