T-Shaped Stringer Manufacturing with Variable Angle Invar Tooling
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Solution Overview
Problem
The existing methods for manufacturing 'T' shaped stringers for aircraft, which need to be placed on inclined surfaces, face issues with fitment due to varying angles between the stringer web and foot, leading to low-quality unions and potential structural problems, as conventional methods either require additional pieces or result in visible folds when adapting the stringer geometry.
Innovation Solution
A manufacturing method involving hot-forming of carbon fiber laminates into 'L' shaped semi-stringers, placing them together to form a 'T' shape, using invar alloy angles with non-90° geometry, and employing a heating device and roller to adjust the stringer feet's geometry within a gap, ensuring precise fitment on curved surfaces without contact during curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If invar alloy angles with 90° geometry are used for curing, then the manufacturing process is simple, but the stringer does not fit perfectly on curved surfaces causing deviations from theoretical position
Solution Approach 1:
The patent applies different geometry angles to different parts of the curing tool. The invar alloy angle is designed with varying angles (not uniform 90°) to match the specific curvature requirements at different locations on the curved skin, allowing precise fitting while maintaining manufacturing simplicity
Solution Approach 2:
The patent changes the geometric parameters of the invar alloy angle from fixed 90° to variable angles that correspond to the specific curvature of the skin. This parameter adjustment allows the stringer to fit perfectly on curved surfaces while maintaining the simplicity of using standard invar alloy curing tools
2Adaptability or versatility
If two L semi-stringers are placed at different heights to accommodate curved surfaces, then the stringer can fit the surface, but free spaces are created between stringer feet and surface resulting in low quality union
Solution Approach 1:
The patent changes the angle parameter of the invar alloy curing tool to match the skin curvature, which allows the stringer feet to maintain full contact with the surface at the correct height, eliminating free spaces and ensuring high quality union while preserving adaptability to curved surfaces
Solution Approach 2:
Instead of adjusting the stringer height to fit the surface, the patent inverts the approach by adjusting the curing tool angle to match the surface curvature, thereby maintaining proper stringer positioning and full surface contact
3Manufacturing precision
If stringer feet are bent after curing to adapt to surface geometry, then the fit is improved, but folds are created which are visible and complicate assembly of additional elements
Solution Approach 1:
The patent applies the correct angle geometry to the invar alloy curing tool before the curing process begins, which pre-establishes the proper stringer angle and position during manufacturing. This preliminary action eliminates the need for post-curing bending operations, thereby avoiding visible folds and assembly complications while achieving precise surface fit
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 method ensures perfect fitment of stringers on inclined surfaces, eliminating the need for additional pieces, reducing distortions, and enhancing mechanical properties by avoiding wrinkles, thus increasing the reliability and strength of the assembled stringers.
Implementation Method 1
moving a heating device over the stringer feet surface
Implementation Method 2
sliding a roller over said stringer feet surface
Data Source
AI summary
Method of manufacturing “T” shaped stringers (1) with an angle different from 90° between the web (2) and the foot (3) whereby the “T” shaped stringers have a stringer web and a stringer foot. The method comprises, after placing together two hot-formed “L” shaped semi-stringers to form a “T” shaped stringer, placing the “T” shaped stringer inside an invar alloy angle leaving a gap between the stringer web and the invar alloy angle. Afterwards, a heating device (7) is moved over the stringer feet (3) surface and a roller (8) slides over said stringer feet (3) surface to adapt the geometry of the stringer feet to the geometry of the invar alloy angle. The resulting “T” shaped stringer is co-bonded on a cured skin with an adhesive line between the stringer and the cured skin, and finally the obtained “T” shaped stringer is cured.