Foam-Stiffened Hollow Composite Stringer Manufacturing
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Solution Overview
Problem
The use of inflatable bladders in manufacturing composite aircraft stringers can lead to defects such as deflation during the curing process, resulting in improperly formed stringers due to issues like improper shape, ply movement, ply wrinkling, or porosity, which necessitates re-manufacturing.
Innovation Solution
A method and apparatus for manufacturing a hollow composite stringer using a foam core with a mandrel, where the foam is formed with channels, allowing for the creation of a hollow structure that remains as part of the stringer, providing additional benefits like increased impact resistance and reduced weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If inflatable bladders are used to support the internal structure of composite stringers during curing, then the stringer shape can be maintained, but the bladders may deflate during the curing process resulting in defects such as improper shape, ply movement, ply wrinkling, or porosity
Solution Approach 1:
The patent removes the bladder from the curing process entirely. Instead of using an inflatable bladder to support the stringer shape, the method uses a rigid mold that directly forms the hollow stringer shape during curing. The bladder function is extracted and replaced by the mold structure itself, eliminating the reliability issue of bladder deflation while maintaining shape accuracy.
Solution Approach 2:
The patent introduces a rigid mold as an intermediary between the composite material and the final stringer shape. This mold serves as the supporting structure during curing, replacing the bladder's support function. The mold provides stable geometric constraints without the deflation risks associated with inflatable bladders.
2Shape
If bladders are used to form hollow sections in composite stringers, then the hollow structure can be created, but the process requires additional equipment and increases manufacturing complexity
Solution Approach 1:
The patent extracts the hollow section formation process from the bladder-based method. Instead of inserting and inflating bladders, the method uses a rigid mold with the desired hollow geometry that directly shapes the composite material during curing. This eliminates the need for bladder insertion equipment, inflation systems, and associated complexity.
Solution Approach 2:
The patent inverts the traditional approach by forming the hollow shape through the mold cavity rather than inflating an internal bladder. Instead of adding material around a bladder, the composite material is laid up directly against the mold's hollow-forming surfaces, creating the hollow section as a negative space defined by the mold geometry.
3Manufacturing precision
If traditional metal-forming techniques are used to create hat stringers, then tight constant angular bends and straight legs can be achieved, but the weight of the aircraft increases
Solution Approach 1:
The patent uses composite materials (fiber-reinforced polymers) to replace traditional metal hat stringers. The composite material is molded into the required hat section shape with precise angular bends during the curing process. This achieves the structural precision of metal forming while significantly reducing weight, as composites have higher strength-to-weight and stiffness-to-weight ratios than metals.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach eliminates the need for inflatable bladders, reduces the risk of defects, and offers improved structural properties, acoustical benefits, and simplified fabrication while minimizing weight and handling requirements.
Implementation Method 1
A foam core is formed within the first channel. A set of channels is created within the foam core to form the hollow composite part.
Implementation Method 2
A curing process is a process that toughens or hardens a polymer material in the composite stringer.
Data Source
AI summary
A method and apparatus for a composite stringer. A method is used for manufacturing a hollow composite stringer. Foam is formed with a mandrel installed into the foam. A composite material and the foam is laid up onto a tool in a form of a stringer. The composite material and the foam in the form of the stringer is cured to form a cured stringer. The mandrel from the foam is removed to form the hollow composite stringer.