Contoured Composite Hat Stringer Cap Wrinkling Reduction

Solution Overview

Problem

Existing methods for forming contoured composite hat stringers often result in buckling or wrinkling of the cap, which can compromise the structural performance of the stringer and increase production costs.

Innovation Solution

A method and apparatus that utilize a cap pinch bladder to constrain the cap of the hat stringer during forming, transferring stress away from the cap and reducing the likelihood of buckling or wrinkling. The apparatus includes a tool set with a punch and segmented dies that can be contoured to match the desired shape of the stringer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If conventional forming methods are used to create contoured hat stringers, then the desired contoured shape is achieved, but buckling or wrinkling occurs in the cap during forming

Engineering Contradiction:

Improvecontoured shapeVSAvoidcap surface quality

Core Design Contradiction:

ShapeVSManufacturing precision

Solution Approach 1:

The cap is pre-formed on a cap mandrel to the desired contour shape before the main forming operation. This preliminary contouring establishes the final cap shape while avoiding stress concentration that would cause wrinkling during subsequent forming operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The forming process is divided into separate operations: first forming the cap on a dedicated mandrel, then forming the hat section in the die cavity. This segmentation allows each component to be formed independently without inducing wrinkles in the cap during the main forming operation.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If the composite charge is formed into a die cavity using a punch or inflatable bladder, then the hat stringer takes the desired cross-sectional shape, but stresses are locally created within the composite charge that result in buckling or wrinkling

Engineering Contradiction:

Improveforming processVSAvoidstructural performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The cap is pre-formed on a cap mandrel to the desired contour shape before the main forming operation. This preliminary contouring establishes the final cap shape while avoiding stress concentration that would cause wrinkling during subsequent forming operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A cap mandrel serves as an intermediary tool that holds the cap in the desired contoured shape during forming. The mandrel provides support and guidance, allowing the cap to be formed to the correct shape without developing wrinkles or buckles.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If contouring is performed during stringer formation, then the desired contoured stringer is produced, but stresses concentrate in the contoured regions causing buckling or wrinkling of the cap

Engineering Contradiction:

Improvecontoured designVSAvoidcap surface quality

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The cap is pre-formed on a cap mandrel to the desired contour shape before the main forming operation. This preliminary contouring establishes the final cap shape while avoiding stress concentration that would cause wrinkling during subsequent forming operations.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP3970939B1Constrained forming of contoured composite hat stringers

Publication Date: 2025.03.05 THE BOEING CO

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AI summary

Cap wrinkling in a contoured composite hat stringer is reduced by constraining the cap as the hat stringer is being formed from a flat composite charge. The cap is constrained by an inflatable bladder placed in a tool set used to form the composite charge.