Contoured Composite Hat Stiffener Forming
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Solution Overview
Problem
The existing methods for fabricating contoured composite stiffeners, such as hat stringers, often result in undesired wrinkling due to material compression, leading to increased labor costs and reduced production rates as hand rework is required to eliminate wrinkling.
Innovation Solution
A method and apparatus that involve punch forming a composite laminate charge into a die, where a portion of the charge is pinched and compressed to maintain tension in the remainder, preventing ply wrinkling during contouring, and utilizing a sequential contouring approach starting at the apex to minimize bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the composite stiffener is highly contoured using traditional punch forming, then the desired contour shape is achieved, but portions of the charge are placed in compression resulting in ply wrinkling
Solution Approach 1:
Instead of allowing the entire charge to be in compression during contouring, the invention applies tension to a portion of the charge (such as the flanges or cap) while contouring. This inverted approach of using tension rather than compression prevents ply wrinkling while still achieving the desired highly contoured shape.
Solution Approach 2:
The invention applies different mechanical conditions to different portions of the charge during contouring. Specifically, one portion is placed in tension while other portions are contoured. This local differentiation of mechanical states (tension in some areas, compression in others) allows the contoured shape to be achieved without wrinkling in the tensioned regions.
2Manufacturing precision
If hand rework is performed to eliminate wrinkling, then the quality of the stiffener is improved, but labor costs increase and production rate decreases
Solution Approach 1:
The invention applies tension to portions of the charge during the contouring process itself, preventing wrinkling before it occurs. This preliminary preventive action eliminates the need for subsequent hand rework to remove wrinkles, thereby maintaining high production rates while ensuring quality.
3Shape
If the charge is compressed during contouring, then the contour is formed, but ply wrinkling occurs requiring additional processing
Solution Approach 1:
The invention changes the mechanical parameter (stress state) applied to portions of the charge during contouring. By switching from compression to tension in specific regions, the contour can be formed without the harmful effect of compression-induced wrinkling, thereby eliminating the need for additional processing steps.
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 effectively reduces or eliminates ply wrinkling, enhancing the production efficiency and reducing labor costs by maintaining tension in the composite stiffener as it is contoured, resulting in wrinkle-free, highly contoured composite laminate stiffeners.
Implementation Method 1
forming the cap and the webs using a punch to drive the charge into the die cavity
Implementation Method 2
A portion of the charge is placed in tension by compressing either the flanges or the cap
Implementation Method 3
A portion of the charge is placed in tension by compressing either the flanges or the cap
Implementation Method 4
A contour is formed into a composite charge while the portion of the charge is being held in tension
Data Source
AI summary
A flexible punch and die are used to form a flat composite laminate charge into a stiffener having a desired cross sectional shape. A desired contour is formed in the stiffener by bending the punch and die. Ply wrinkling is avoided during contouring by maintaining those portions of the stiffener subject to wrinkling in tension as the contouring is being performed. Bridging of the plies during the contouring process is avoided by first contouring those sections of the stiffener that are subject to wrinkling, and then contouring the remaining sections of the stiffener.