Superplastic Forming Titanium Assemblies Markoff Reduction
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Solution Overview
Problem
Conventional superplastic forming and diffusion bonding methods face limitations in producing structural assemblies with a wide range of desired dimensions, particularly when thicker middle sheets are required, as they often result in markoff deformation of outer sheets, restricting the production of complex geometries and assemblies with specific thickness ratios.
Innovation Solution
The method involves using titanium sheets with different grain sizes, where the first sheet has a larger grain size than the second sheet, allowing the second sheet to be superplastically formed at a lower temperature without forming the first sheet, and both sheets are diffusion bonded, enabling the production of assemblies with reduced or eliminated markoff and increased thickness ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional superplastic forming is performed on multi-sheet packs, then complex geometries can be formed, but markoff deformation occurs on outer sheets
Solution Approach 1:
The patent applies parameter changes by heating the pack to different temperatures for different sheets. Specifically, the pack is heated to a first temperature to superplastically form the first sheet, then heated to a second temperature (higher than the first) to superplastically form the second sheet, while the first sheet remains substantially unformed at the second temperature. This differential temperature approach allows complex geometry formation without markoff deformation on outer sheets.
2Strength
If thicker middle sheets are used in conventional SPF/DB, then structural strength is improved, but markoff deformation increases on outer sheets
Solution Approach 1:
The patent resolves this contradiction by implementing differential temperature heating. The pack is heated to a first temperature sufficient to superplastically form the middle sheet (enabling use of thicker sheets for strength), then heated to a second higher temperature to form the outer sheets. This allows thick middle sheets to provide structural strength while the controlled sequential forming prevents markoff deformation on outer sheets.
3Strength
If conventional diffusion bonding is performed before superplastic forming, then bonding strength is achieved, but geometric flexibility is restricted
Solution Approach 1:
The patent applies dynamics by making the forming process adaptive and sequential rather than static and simultaneous. The pack undergoes superplastic forming at different temperatures in sequence - first the inner sheet at a lower temperature, then the outer sheets at a higher temperature. This dynamic, multi-stage approach enables greater geometric flexibility and complex configurations while maintaining bonding strength, as each sheet can be formed to its optimal geometry before the next forming stage.
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 enables the formation of structural assemblies with reduced markoff and increased thickness ratios, allowing for a greater range of dimensions and complex geometries, while maintaining the stiffness of the outer sheets and reducing thermal stresses on tooling.
Implementation Method 1
heating the pack to at least a superplastic forming temperature of the second sheet, and superplastically forming the second sheet to a predetermined configuration
Implementation Method 2
both sheets are diffusion bonded
Data Source
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AI summary
A method of superplastic forming of titanium packs and an associated assembly is provided. The titanium packs can include sheets (14, 16) having different granular structures so that the different sheets (14, 16) are adapted to superplastically form at different temperatures. One or more of the sheets (14, 16) can be formed at a temperature that is below the superplastic forming temperature of another sheet (14, 16) in the pack. In some cases, the occurrence of markoff can be reduced or eliminated. An airframe comprising an aircraft structure manufactured by this method is also described.