Composite Tooling CTE Control via Invar Substructure

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Solution Overview

Problem

Aerospace manufacturing faces challenges with thermal expansion mismatches between tooling and composite parts, leading to dimensional inaccuracies, sagging, and wrinkling due to differing coefficients of thermal expansion, which existing technologies have not adequately addressed.

Innovation Solution

Incorporating substructure such as headers and gussets into composite tooling to constrain diametric growth, reducing the thickness of the face-sheet, and introducing inner skin to control thermal expansion, thereby limiting hat wall rotation and reducing the effective coefficient of thermal expansion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If carbon/epoxy tooling is used to form composite parts, then the tooling can provide other manufacturing advantages, but the tooling experiences excessive thermal expansion during autoclaving causing dimensional inaccuracies and part sagging

Engineering Contradiction:

Improvemanufacturing advantagesVSAvoiddimensional accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent uses a hybrid tooling system combining carbon/epoxy composite with invar alloy components. The invar alloy is strategically placed in regions experiencing high thermal expansion to compensate for the carbon/epoxy material's excessive expansion during autoclaving, achieving both manufacturing advantages and dimensional accuracy

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the thermal expansion parameters of the tooling by selecting materials with specific CTE characteristics. Invar alloy with its low CTE is combined with carbon/epoxy to create a tooling system whose overall thermal expansion matches that of the composite part, eliminating dimensional mismatches

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If invar alloy tooling is used to match CTE with composite parts, then dimensional control is improved, but wrinkles appear in the formed part due to insufficient expansion to eliminate bulk factor wrinkles

Engineering Contradiction:

Improvedimensional controlVSAvoidsurface smoothness

Core Design Contradiction:

Manufacturing precisionVSShape

Solution Approach 1:

The patent applies different material properties to different regions of the tooling. Carbon/epoxy composite is used in areas requiring high expansion to eliminate wrinkles, while invar alloy is used in areas requiring dimensional stability, creating local quality variations that simultaneously address both dimensional control and surface smoothness

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If carbon/epoxy mandrel thickness is reduced to control thermal expansion, then diametric growth is minimized, but the mandrel may become structurally weaker

Engineering Contradiction:

Improvethermal expansion controlVSAvoidmandrel structural strength

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The patent creates a composite mandrel structure combining carbon/epoxy layers with invar alloy reinforcement. This hybrid construction provides the necessary structural strength even when the overall mandrel thickness is reduced, while the invar components constrain thermal expansion and maintain dimensional accuracy

Inventive Principle:

Principle #40Composite materials

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 minimizes thermal expansion, preventing wrinkles and sagging, and ensuring accurate dimensional control of parts, allowing for the production of high-quality aerospace components with improved shape and size consistency.

Implementation Method 1

It is commonly known that materials expand and contract with changes in temperature. A commonly used quantifier of this natural phenomenon is the coefficient of thermal expansion or CTE.

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

When a material is heated, its linear dimensions increase approximately in proportion to the temperature. However, upon cooling the mandrel and the part, the resultant structure of the part experiences undesirable sagging

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Implementation Method 3

Methodology Applied

Scientific EffectMechanical constraint:

Implementation Method 4

Dissimilar materials typically have different CTEs, and the union of dissimilar materials can impart a residual thermal loading effect between the materials, as they will expand and contract at different rates

Methodology Applied

Scientific EffectDifferential thermal expansion: Thermal Expansion

Data Source

PatentEP2185832B1Coefficient of thermal expansion control structure

Publication Date: 2016.09.21 THE BOEING CO

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Figure 2A~2B

AI summary

The present invention is directed to the incorporation of a substructure into tooling for constructing composite structures in order to control thermal expansion of the tooling during aerospace manufacturing processes. Substructure, such as headers and/or gussets, is added to the tooling to constrain the growth of the laminate expansion and/or control the diametric growth of the tool during the curing cycle. The thickness of the face-sheet of the tooling also may be reduced in order to further reduce the effective coefficient of thermal expansion (CTE) of the tooling.