Auxetic Supports for Aircraft Nacelle Panel Sintering

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Solution Overview

Problem

The increase in temperature during sintering causes deformation of aircraft propulsion unit nacelle panels due to the expansion of fugitive materials used in honeycomb structures, leading to skin deformation.

Innovation Solution

Incorporating auxetic supports made of thermoplastic materials within the honeycomb cavities, which maintain dimensions below a predetermined value upon heating, and using TiAl-based powdery intermetallic alloys for the skins and honeycomb structure, consolidated through sintering without melting, to prevent deformation and improve mechanical properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional fugitive materials are used to fill honeycomb cavities, then the cavities are supported during manufacturing, but the materials expand during sintering causing skin deformation

Engineering Contradiction:

Improveskin deformationVSAvoidthermal expansion control

Core Design Contradiction:

Manufacturing precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent applies parameter changes by selecting fugitive materials with specific thermal expansion characteristics and adjusting their physical state through temperature control. The material is chosen to have low thermal expansion coefficient and is maintained in a solid state during sintering to prevent expansion-induced deformation of the skin.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent directly addresses thermal expansion by selecting fugitive materials with low thermal expansion coefficients and controlling the temperature range during sintering to minimize expansion. The material is specifically chosen to expand minimally under sintering conditions, preventing skin deformation while still providing cavity support.

Inventive Principle:

Principle #37Thermal expansion

2Reliability

If fugitive material is used to support cavities, then cavity collapse is prevented, but material removal becomes necessary adding process complexity

Engineering Contradiction:

Improvecavity supportVSAvoidsupport removal process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies this principle by using inexpensive, easily removable fugitive materials such as water-soluble polymers or low-melting-point materials. These materials serve their support function temporarily during manufacturing and are then easily removed through simple processes like water washing or low-temperature heating, avoiding complex removal operations.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent implements this principle by selecting fugitive materials that can be easily discarded through simple removal processes. The materials are chosen specifically for their ease of removal via water dissolution, low-temperature melting, or other simple methods, converting a potentially complex removal process into a straightforward operation.

Inventive Principle:

Principle #34Discarding and recovering

3Weight of moving object

If TiAl-based powdery intermetallic alloy is used for skins and honeycomb structure, then mass is reduced and high-temperature performance is improved, but hot cracking occurs during melting

Engineering Contradiction:

Improvepanel massVSAvoidhot cracking

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The patent applies phase transitions by carefully controlling the thermal processing to avoid the melting phase of TiAl material. The sintering process is conducted below the melting point, utilizing solid-state diffusion and bonding mechanisms to consolidate the powder while avoiding liquid-phase formation that causes hot cracking.

Inventive Principle:

Principle #36Phase transitions

Solution Approach 2:

The patent uses parameter changes by optimizing sintering temperature, holding time, and atmospheric conditions to achieve dense consolidation of TiAl powder without reaching melting temperatures. The process parameters are specifically tuned to promote solid-state bonding while preventing hot cracking, maintaining both weight reduction and structural integrity.

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

The method effectively preserves the inner volume of cavities and prevents skin deformation during temperature increases, while reducing material usage and avoiding hot cracking, resulting in panels with reduced mass and improved high-temperature performance.

Implementation Method 1

the supports are auxetic so that, under the effect of an increase in temperature, their dimension between the first and the second skins remains below a predetermined value

Methodology Applied

Scientific EffectNegative thermal expansion: Negative Thermal Expansion

Implementation Method 2

the step of making the first skin and the honeycomb structure comprises consolidation of the compound by sintering

Methodology Applied

Scientific EffectSintering: Sintering

Data Source

PatentUS11142343B2Method of manufacturing a panel for an aircraft propulsion unit nacelle

Publication Date: 2021.10.12 SAFRAN SA

AI summary

A method for manufacturing a panel includes disposing one or several supports in a respective cavity(ies) in a honeycomb structure having a first skin and a second skin clasping the honeycomb structure. The supports are made of a fugitive material such as a thermoplastic and are auxetic so that, under the effect of an increase in temperature, their dimension between the first and the second skins remains below a predetermined value.