1.  Field of the Invention
This invention relates to the method and apparatus for the manufacture of fiber reinforced structures. 
2.  State of the Art
It is desirable to have inexpensive, strong, lightweight, easily manufactured, dimensionally accurate components in a variety of sizes and geometries for use in aircraft and aerospace applications.  However, meeting such criteria for components is difficult. 
For example, commercial aircraft are typically powered using turbofan type engines.  A turbofan type engine includes a ducted fan, a large diameter axial-flow multi-stage compressor, as the primary source of thrust by the engine while the gas generator portion of the engine provides a smaller amount of the engine's thrust.  Each stage of the ducted fan includes a number of fan blades attached to a rotating fan disc or hub to compress air, the compressed air flowing from the fan and expanding through a nozzle to provide thrust to move the aircraft.  Depending upon the size of the engine, the diameter of each stage of the ducted fan may be approximately one meter to several meters or more in diameter and rotate at several thousand revolutions per minute.  Each fan blade attached to a fan disc or hub being a highly stressed structure due to the forces acting on the blade from compressing the air flowing therearound and from the centrifugal forces acting on the blade during rotation of the engine. 
Since weight is of concern in aircraft engines, it is desirable to provide the lightest engine possible to meet the operational criteria for the aircraft while providing the required aircraft operational safety.  One of the desired operational safety characteristics for a turbofan aircraft engine is that if a fan blade catastrophically fails during engine operation, the blade or pieces of the blade be contained or caught within the fan housing structure to prevent damage to the aircraft, its cargo, and the surrounding engine and aircraft environment.  Typically, aircraft manufactures have required the fan housing be such a structure for the engine thereby making the fan housing one of the heaviest engine components. 
The design of an inexpensive, strong, lightweight, easily manufactured, dimensionally accurate fan housing in a variety of sizes and geometries for use in aircraft is a formidable task.  For instance, the fan housing must be strong enough to contain the energy of a fan blade when the failure occurs at maximum engine speed, must be dimensionally accurate over a range of engine operating conditions, must be easily manufactured at a reasonable cost, must be lightweight, etc.  Typically, fan housings have been metal structures using a variety of reinforcing grids, typically formed of metal.  However, such fan housings are expensive, difficult to manufacture, require extensive tooling to manufacture to close tolerances, and heavy. 
In other instances, some fan housings have been composite type structures including metal components and non-metallic or organic type reinforcing components in an attempt to provide a high strength, lightweight structure capable of containing a broken fan blade.  However, such composite type structures are difficult to construct because the reinforcing structure of non-metallic materials for the fan housing has been difficult and expensive to construct.  Typically, such a non-metallic reinforcing structure has employed an isogrid type structure which is difficult to reliably fabricate in quantities.  The isogrid type structure being efficient in providing reinforcing for the fan housing and the ability of catching a broken fan blade while maintaining its strength and integrity even with a portion missing or broken. 
Typically, such composite isogrid structures have been fabricated by hand using soft imprecise tooling of wood, resilient materials, etc.  which affects the isogrid structure's repeatability in manufacture, dimensional tolerance variation, structural integrity, cost, etc.  Therefore, a need exists for a method and apparatus for the fabrication of composite structures, such as an isogrid structure, to maintain the integrity, reliability, repeatability of manufacture, dimensional control, and cost of the structure.