Composite Stringer Co-Curing Tool Assembly
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Solution Overview
Problem
The aircraft industry faces challenges with the use of precured stringers, which require costly cure tooling, vacuum bagging, and autoclave operations, and result in weighty bonded joints that are difficult to inspect, necessitating a more efficient method for forming and installing composite stringers on aircraft skins.
Innovation Solution
A method and apparatus that form and compact uncured or partially cured stringers directly onto the skin using a tool assembly, allowing co-curing with the skin to create a strong joint, reducing production time and eliminating the need for extensive tooling and equipment, by using a tray with forming blocks and a bladder to position and compact the stringer against the skin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If precured stringers are used, then stringer stiffness and handleability are improved, but production cost and equipment requirements increase
Solution Approach 1:
The stringer is pre-formed on a mandrel to the desired shape and dimensions before installation on the skin. This preliminary forming action allows the stringer to achieve sufficient stiffness for handling and positioning without requiring complete precuring in an autoclave, thereby reducing equipment requirements while maintaining the necessary mechanical properties for installation
Solution Approach 2:
The invention extracts the stringer formation process from the autoclave curing process. By forming the stringer shape on a mandrel before installation and then co-curing it with the skin in a single autoclave operation, the complex precuring equipment is eliminated while maintaining stringer stiffness requirements
2Strength
If structural adhesives are used to attach stringers to skin, then bonded joint strength is improved, but aircraft weight and inspection difficulty increase
Solution Approach 1:
The stringer attachment process is merged with the skin curing process. The stringer is positioned on the skin in an uncured or partially cured state, and both components are co-cured together in a single autoclave operation. This merging eliminates the need for separate structural adhesive bonding operations, reducing aircraft weight while maintaining joint strength through direct composite bonding
3Strength
If precuring operations are performed, then stringer structural integrity is improved, but production time and recurring cost increase
Solution Approach 1:
The stringer formation and skin curing operations are merged into a single co-curing process. The pre-formed stringer is installed on the uncured or partially cured skin, and both are cured together in one autoclave cycle. This eliminates separate precuring and bonding operations, significantly reducing production time while maintaining stringer structural integrity through the co-curing process
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 results in a hands-free, efficient process that decreases production time and costs, while producing a superior joint with reduced weight and inspection challenges, by co-curing the stringer with the skin, thus addressing the limitations of traditional methods.
Implementation Method 1
Compacting the preformed stringer may include displacing a first portion of the tool assembly toward the skin while holding a second portion of the tool assembly substantially stationary. Displacing the first portion of the tool assembly may be performed by expanding a bladder to react against the first and second portions of the tool assembly.
Implementation Method 2
The method may further comprise vacuum bagging and co-curing skin and the compacted stringer.
Implementation Method 3
The method may further comprise vacuum bagging and co-curing skin and the compacted stringer.
Data Source
AI summary
A hands-free method and related apparatus are used to shape, place and compact a composite stringer on a composite skin of an aircraft. A composite charge is placed on a tool assembly that used to shape the charge into a preformed stringer. With the stringer held on the tool assembly, the tool assembly is used to move the preformed stringer into proximity with the skin and both place and compact the stringer against the skin. Following compaction of the stringer, the tool assembly is removed and the skin and the stringer are co-cured.