Contoured Composite Stiffener Creep Forming
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Solution Overview
Problem
The challenge in manufacturing contoured composite laminate stiffeners is the tendency of plies to wrinkle during the forming process, which affects the performance of the stiffener and is not adequately addressed by existing production methods.
Innovation Solution
A method involving constrained creep forming, where a multi-ply composite charge is heated and formed into a die cavity, then constrained and slowly contoured to reduce or eliminate ply wrinkling by allowing slippage and relaxation of residual stresses, using flexible cauls and controlled pressure to maintain even forming pressure and prevent significant compression stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the composite charge is formed to a desired contour at a high rate, then productivity is improved, but ply wrinkling occurs due to excessive compression stresses
Solution Approach 1:
The patent applies parameter changes by controlling the forming rate to be slow enough that friction or shear resistance between resin and fibers remains low, allowing slippage to occur and preventing significant compression stresses that cause wrinkling. This parameter control resolves the contradiction between productivity and surface quality.
2Manufacturing precision
If the composite charge is formed to a desired contour at a slow rate, then ply wrinkling is reduced, but productivity decreases
Solution Approach 1:
The patent optimizes the forming rate parameter to a specific range that is slow enough to prevent wrinkling but maintains acceptable productivity. This parameter optimization resolves the contradiction between manufacturing precision and productivity.
3Ease of manufacture
If conventional forming methods are used, then the process is simple, but ply wrinkling occurs which affects stiffener performance
Solution Approach 1:
The patent modifies the forming process by controlling the rate parameter to prevent wrinkling while maintaining process simplicity. This resolves the contradiction between ease of manufacture and reliability.
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 significantly reduces or eliminates ply wrinkling, enabling the production of stiffeners with more severe contours and smooth surface finishes, improving the quality and performance of contoured composite laminate stiffeners.
Implementation Method 1
heating the composite charge
Implementation Method 2
constrained creep forming it to a desired contour
Implementation Method 3
friction or shear resistance between resin and fibers of the plies remains low enough that slippage can occur
Implementation Method 4
forming the stiffener to the contour is performed at a rate that allows relaxation of residual stresses in the stiffener
Data Source
AI summary
A composite laminate stiffener is formed to contour with reduced ply wrinkling using constrained creep forming. The tooling apparatus is provided with flexible cauls which constrain the stiffener during the contour forming process. The creep forming is carried out at a slow enough rate so that friction or shear resistance between the resin and fibers of the plies remains low enough that slippage can occur and significant compression stresses are not generated rate, allowing relaxation of residual stresses in the stiffener.