Fusible Tin Mandrel for CMC Internal Cavities

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Solution Overview

Problem

Conventional methods for creating internal cavities in ceramic matrix composite (CMC) articles face challenges such as distortion, longer processing times, and difficulties in forming complex shapes due to the use of fugitive resins and metallic mandrels, which can alter cavity dimensions and require slow pyrolysis cycles.

Innovation Solution

A method using a fusible mandrel made of elemental tin or a tin alloy that melts during the burnout process, allowing it to be drained without reacting with the CMC preform, thereby creating a hollow cavity without distortion and enabling complex shapes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If conventional steel mandrels are used to form internal cavities, then the cavity shape can be defined, but the mandrel cannot be removed from the preform due to being captured by shoulders

Engineering Contradiction:

Improvecavity shapeVSAvoidmandrel removal

Core Design Contradiction:

ShapeVSEase of manufacture

Solution Approach 1:

The mandrel material is changed from conventional steel to a fusible material (low-melting-point alloy or wax) that undergoes a phase change during processing. This parameter change allows the mandrel to be easily removed by melting and draining, solving the mandrel removal problem while maintaining complex cavity shape definition capabilities

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention utilizes phase transition of the mandrel material from solid to liquid state during the burnout process. The fusible mandrel melts at elevated temperatures and drains from the preform, leaving a clean cavity without requiring physical removal operations. This phase transition approach resolves the contradiction between maintaining shape definition and enabling easy removal

Inventive Principle:

Principle #36Phase transitions

2Ease of manufacture

If fugitive polymeric resins are used as mandrels, then the mandrel can be removed by volatilization, but the CMC preform distorts during heating due to high thermal expansion coefficients

Engineering Contradiction:

Improvemandrel removalVSAvoidpreform distortion

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The mandrel material is changed from polymeric resin to inorganic fusible material (low-melting-point alloy or wax) with thermal expansion characteristics matched to the CMC preform. This parameter change eliminates the thermal expansion mismatch problem while maintaining the ability to remove the mandrel through melting and draining during the burnout process

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The fusible mandrel is designed as a temporary, consumable component that is intentionally sacrificed during processing. It melts and drains away during burnout, leaving no residue that could cause distortion. This disposable approach solves both the removal ease and precision problems by eliminating the mandrel entirely after it serves its shaping function

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Shape

If fugitive resins are used with larger-size CMC components, then cavities can be formed, but the amount of gases increases requiring slower pyrolysis cycles which increases processing time

Engineering Contradiction:

Improvecavity formationVSAvoidprocessing cycle time

Core Design Contradiction:

ShapeVSProductivity

Solution Approach 1:

The mandrel material is changed from polymeric resin to inorganic fusible material that melts and drains during burnout rather than requiring complete pyrolysis and volatilization. This parameter change dramatically reduces the volume of gases that must escape during processing, allowing faster heating rates and shorter processing cycles while still achieving complete mandrel removal and clean cavity formation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The removal mechanism is changed from gas-phase volatilization (requiring slow pyrolysis) to liquid-phase draining (enabling faster processing). The fusible mandrel melts and drains through gravity and capillary action during burnout, eliminating the need for slow gas evolution that plagues polymeric resin removal. This substitution of removal mechanism resolves the contradiction between cavity formation and processing speed

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 eliminates processing time issues and distortion, allowing for precise and complex cavity formation in CMC articles for weight reduction and cooling purposes without the limitations of conventional mandrels or fugitive resins.

Implementation Method 1

The mandrel material melts during a thermal treatment of the CMC preform

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 2

the resulting molten material does not wet or react with constituents of the CMC preform and is drained off leaving behind an internal cavity

Methodology Applied

Scientific EffectGravity-driven flow: Gravitation

Data Source

PatentUS10011043B2Method of producing an internal cavity in a ceramic matrix composite

Publication Date: 2018.07.03 GENERAL ELECTRIC CO

AI summary

A process for producing an internal cavity in a CMC article and mandrels used therewith. The process entails incorporating a mandrel made of a fusible material that is melted and drained during a thermal treatment of a CMC preform to form the CMC article. The mandrel material is preferably non-wetting and non-reactive with any constituents of the CMC preform during the thermal treatment. The mandrel is preferably tin or an alloy of tin.