Breakaway Mold Fasteners for Composite Part Release During Cooling

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Solution Overview

Problem

The fabrication of composite parts in molds is hindered by differential thermal contraction between mold pieces and composite materials, which can cause damage, and existing solutions like using low-CTE materials like BME or Invar are costly.

Innovation Solution

A system using mold pieces with a higher coefficient of thermal expansion than the composite part, coupled with breakaway fasteners made of materials like polytetrafluoroethylene, that break under tension or shear forces during cooling to facilitate the removal of the composite part.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If mold pieces are made of materials with higher CTE than the composite part, then the mold pieces contract more during cooling which can damage the pieces or composite part, but using breakaway fasteners allows the mold pieces to be decoupled safely

Engineering Contradiction:

Improvemold material selectionVSAvoidthermal contraction damage

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The mold is divided into multiple mold pieces that are coupled together with breakaway fasteners. This segmentation allows the mold pieces to contract independently during cooling and enables safe decoupling when the fasteners break due to differential thermal contraction, preventing damage to the composite part while maintaining manufacturing ease with high-CTE materials like aluminum

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The breakaway fasteners are designed as disposable components that are intentionally made weaker than the mold pieces and composite part. These fasteners are replaced after each use, allowing the use of inexpensive high-CTE mold materials without risk of damage, as the fasteners sacrifice themselves to protect the valuable composite part

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Object-affected harmful factors

If bolts are loosened during cooling to prevent damage, then thermal contraction damage is reduced, but the operation becomes difficult

Engineering Contradiction:

Improvethermal contraction damageVSAvoidbolt adjustment difficulty

Core Design Contradiction:

Object-affected harmful factorsVSEase of operation

Solution Approach 1:

The breakaway fasteners are designed to automatically break and decouple the mold pieces themselves during the cooling process due to differential thermal contraction. This self-service mechanism eliminates the need for manual intervention to loosen bolts, making the operation easy while preventing thermal contraction damage

Inventive Principle:

Principle #25Self-service

3Object-affected harmful factors

If mold pieces are made of low-CTE materials like BME or Invar to match composite part CTE, then thermal contraction damage is prevented, but the cost increases significantly

Engineering Contradiction:

Improvethermal contraction damageVSAvoidmaterial cost

Core Design Contradiction:

Object-affected harmful factorsVSQuantity of substance

Solution Approach 1:

The system changes the approach from matching CTE parameters to utilizing CTE differential. By designing breakaway fasteners with lower strength than the mold pieces and composite part, the system allows high-CTE mold materials to be used safely, dramatically reducing material costs while preventing damage through controlled fastener failure rather than CTE matching

Inventive Principle:

Principle #35Parameter changes

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

Enables cost-effective fabrication of composite parts by using less expensive materials like aluminum for mold pieces, leveraging thermal expansion differences to decouple mold pieces and release the composite part without damage.

Implementation Method 1

The mold pieces has a higher coefficient of thermal expansion than the composite part, such that when the mold and the composite material are heated during curing and then cooled, the mold pieces contract more than the composite part

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Implementation Method 2

This differential contraction exerts a tension or sheering force on the breakaway fasteners which causes them to break and thereby decouple the mold pieces

Methodology Applied

Scientific EffectFracture mechanics: Fracture Mechanics

Data Source

PatentUS11988237B2System including breakaway fasteners for fabrication of composite parts

Publication Date: 2024.05.21 SPIRIT AEROSYSTEMS INC

AI summary

A system including mold pieces coupled together with breakaway bolts or other fasteners for facilitating the fabrication of composite parts for, e.g., aerospace vehicles. First and second mold pieces are coupled together to form a mold within which the composite part is fabricated from a composite material. A coefficient of thermal expansion of the mold pieces is higher than a coefficient of thermal expansion of the composite part. One or more breakaway fasteners couple together the mold pieces while the mold pieces and the composite material are heated, and then purposefully break and thereby decouple the mold pieces and release the composite part when the mold pieces are cooled. The fasteners may be constructed from polytetrafluoroethylene, may include a structural weakness to ensure breakage, may break into two or more pieces when under a tension or a sheering force, or may include threads that sheer when under a tension force.