Superplastic Forming Venting Grooves for Stronger Diffusion Bonds
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Solution Overview
Problem
The existing superplastic forming/diffusion bonding processes face challenges in achieving effective diffusion bonding between core and skin sheets due to gas entrapment, which can reduce the strength and fatigue performance of the bonded structures, particularly in aerospace applications where complex internal structures are required.
Innovation Solution
The process involves forming venting grooves on the surfaces of the skin or core sheets to facilitate gas withdrawal during the bonding process, improving the removal of gas from the cavity between the sheets and enhancing the intimate contact between them, thereby improving diffusion bonding. This is achieved by injecting gases to urge the sheets against each other and maintaining pressure while withdrawing gas from the cavity to prevent entrapment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If gas is injected between skin sheet and core sheet to form a cavity, then superplastic forming is enabled, but gas entrapment occurs during diffusion bonding
Solution Approach 1:
Venting grooves are pre-formed on the bonding surfaces of skin or core sheets before the diffusion bonding process. These grooves provide predetermined pathways for gas to escape during bonding, preventing gas entrapment that would otherwise occur when gas is injected to form the cavity during superplastic forming.
Solution Approach 2:
The venting grooves act as intermediary channels that facilitate the transition of gas from the cavity space to the external environment. These grooves mediate between the gas pressure needed for cavity formation and the need for gas removal during bonding, allowing both functions to coexist without conflict.
2Strength
If gas pressure is maintained to form diffusion bond, then bonding strength is improved, but gas entrapment reduces bonding quality
Solution Approach 1:
Venting grooves are pre-formed on the bonding surfaces to create escape pathways before bonding begins. This preliminary structure ensures that when gas pressure is applied to achieve intimate contact and strong bonding, the gas can simultaneously escape through the grooves rather than becoming trapped at the bonding interface.
3Ease of manufacture
If venting grooves are formed on sheet surfaces, then gas withdrawal is facilitated, but sheet manufacturing complexity increases
Solution Approach 1:
Rather than modifying the entire sheet structure, venting grooves are created as localized features only on the specific surfaces that will be diffusion-bonded. This localized modification provides the necessary gas withdrawal function while minimizing the overall complexity increase of the sheet components.
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 introduction of venting grooves improves the diffusion bonding process by reducing gas entrapment, enhancing the strength and fatigue properties of the bonded structures, particularly in the flange portion, and allowing for better mechanical fastener locations within fully bonded regions.
Implementation Method 1
maintaining gas pressure of the second gas on the side of the core sheet remote from the skin sheet, thereby forming a diffusion bond between the skin sheet and the core sheet
Implementation Method 2
injecting a first gas between the first surface of the core sheet and the second surface of the skin sheet to urge the skin sheet against an internal face of the mould
Implementation Method 3
heating the pack to a temperature at which the sheets are capable of superplastic deformation
Data Source
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AI summary
A process and apparatus for forming a structure comprising: a) forming a pack (200) from a skin sheet (16, 18) and a core sheet (10, 12), wherein venting grooves (182) are formed in a surface of a sheet that is adjacent to the other sheet; b) placing the pack (200) in a mould (20) and heating the pack (200); c) injecting a first gas between the core and skin sheets to urge the skin sheet (16, 18) against the mould (20); d) injecting a second gas on the side of the core sheet (10, 12) remote from the skin sheet (16, 18) to urge the core sheet (10, 12) against the skin sheet (16, 18); e) maintaining gas pressure of the second gas thereby diffusion bonding the sheets; and f) withdrawing some or all of the first gas from the cavity (30).