Aerofoil Root Diffusion Bonding for Stress Relief

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Solution Overview

Problem

The existing methods for manufacturing hollow aerofoil blades with roots in ducted fan gas turbine engines face challenges in achieving strong and stress-free joints, particularly in relieving welding-induced stresses and ensuring the structural integrity of thinner sheets.

Innovation Solution

A method involving welding metal sheets together, incorporating a separate root member with a shaped surface, and using diffusion bonding after heating to convert weld joints into strong, stress-relieved bonds, while incorporating a thin sheet for lateral stiffening and using Yttria to prevent diffusion bonding where necessary.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If welding is used to join metal sheets and root, then manufacturing speed and ease of assembly are improved, but welding-induced stresses and potential structural weakness in thin sheets occur

Engineering Contradiction:

Improvemanufacturing speedVSAvoidstructural integrity

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The patent applies parameter changes by transitioning the joint type from welded to diffusion-bonded through controlled heating. The heating step changes the physical and chemical parameters of the metal sheets and root, enabling diffusion bonding that eliminates welding-induced stresses while maintaining manufacturing efficiency. This parameter transformation resolves the contradiction by achieving both strong joints and stress-free structure.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of welding-induced stresses into a beneficial outcome by applying heat treatment. The same heating process that enables diffusion bonding also serves to relieve any residual welding stresses and prevent distortion. This transforms the potential harm of welding into a benefit by using the heating step to both create the diffusion bond and eliminate stress concentration.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Weight of moving object

If thinner sheets are used to reduce weight, then weight reduction is achieved, but structural strength and resistance to deformation deteriorate

Engineering Contradiction:

Improveaerofoil weightVSAvoidstructural strength

Core Design Contradiction:

Weight of moving objectVSStrength

Solution Approach 1:

The patent employs composite material strategies by creating a diffusion-bonded assembly of multiple metal sheets and root. The diffusion bonding process creates a homogeneous composite structure where the joined components act as a unified strong unit. This composite approach allows thinner individual sheets to achieve the required structural strength through the integrated assembly, resolving the contradiction between weight reduction and structural integrity.

Inventive Principle:

Principle #40Composite materials

3Strength

If diffusion bonding is applied to convert weld joints, then welding-induced stresses are relieved and joint strength is improved, but additional heating time and process complexity increase

Engineering Contradiction:

Improvejoint strengthVSAvoidheating time

Core Design Contradiction:

StrengthVSLoss of time

Solution Approach 1:

The patent merges the diffusion bonding process with the existing heating operations in the manufacturing sequence. By integrating the diffusion bonding step with other necessary heating operations (such as those required for super-plastic expansion), the patent eliminates the need for separate, dedicated diffusion bonding time. This merging of operations achieves strong stress-free joints without proportionally increasing total manufacturing time, resolving the contradiction between joint quality and production efficiency.

Inventive Principle:

Principle #5Merging (Combining)

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 method enables the production of hollow aerofoil blades with enhanced structural strength, allowing the use of thinner sheets without compromising the integrity, and eliminates the need for separate stress relief operations, while ensuring a completely hollow design with a root attachment.

Implementation Method 1

heating the assembly to convert the weld joints to diffusion bonds

Methodology Applied

Scientific EffectDiffusion bonding: Diffusion Welding

Data Source

PatentUS8661669B2Method of making and joining an aerofoil and root

Publication Date: 2014.03.04 ROLLS ROYCE PLC

AI summary

A ducted fan gas turbine engine aerofoil is made by electron beam welding together at least two metal sheets (10) and (12) and electron beam welding that sub assembly via an end to a root that has been manufactured in a separate operation, and then heating the whole to a temperature that will convert the electron beam welds to diffusion bonds.