Friction Stir Welding Titanium for Superplastic Forming
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Solution Overview
Problem
Current methods for welding titanium sheets to form blanks for superplastic forming often result in inconsistencies, such as fractures and uneven properties, due to differences in grain composition and superplastic strain between the weld nuggets and the parent material, leading to undesired characteristics in the final component.
Innovation Solution
A method involving friction stir welding to create weld nuggets with a desired thickness ratio between 1.1 to 1.25, using a welding machine with an anvil and pin tool, and subsequent superplastic forming process to ensure the weld nuggets and parent material have substantially the same characteristics, with controlled strain rates and grain composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If friction stir welding is used to join metal sheets, then thermal distortion is avoided and welding strength is improved, but inconsistencies in grain composition and superplastic strain occur between weld nuggets and parent material
Solution Approach 1:
The patent applies local quality by creating a shim with a specific thickness (0.002 to 0.006 inches) that is placed only at the weld location between metal sheets. This localized thickness variation compensates for the inherent thickness reduction in weld nuggets during superplastic forming, ensuring that the weld area achieves the same final thickness and superplastic strain characteristics as the parent material, while the rest of the sheets maintain their original properties.
2Area of stationary object
If multiple metal sheets are welded together to form a large blank, then the component size requirement is met, but fractures and uneven properties occur due to welding inconsistencies
Solution Approach 1:
The patent applies preliminary action by placing the shim between the metal sheets before the friction stir welding process. This pre-positioned shim anticipates and compensates for the thickness reduction that will occur in the weld nugget during subsequent superplastic forming, preventing fractures and ensuring uniform properties throughout the final component.
3Strength
If the die section is heated to affect mechanical properties, then fatigue performance is improved, but the welding process becomes more complex
Solution Approach 1:
The patent merges the welding process with the superplastic forming process by integrating the shim placement into the welding setup and utilizing the superplastic forming step to simultaneously achieve both component shaping and weld nugget thickness adjustment. This combined approach achieves the desired mechanical properties and uniform characteristics in a single integrated process flow.
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 ensures consistent properties and reduced superplastic strain in weld nuggets, preventing premature necking and maintaining the strength and fatigue characteristics of the parent material, resulting in a component with uniform characteristics.
Implementation Method 1
Heat and mechanical energy are applied to the metal sheets to join the metal sheets at the edges. The heat and mechanical energy cause portions of the metal sheets to form a continuous metallic region joining the two metal sheets.
Implementation Method 2
With friction stir welding, edges of two metal sheets are brought together. Heat and mechanical energy are applied to the metal sheets to join the metal sheets at the edges.
Implementation Method 3
The die section may be heated to a temperature that affects the mechanical properties, fatigue performance, and/or other characteristics of the metal and the welded portions of the blank.
Implementation Method 4
Superplasticity is the ability of a material to elongate in a uniform manner beyond about 100 percent of the length of the material. This uniform elongation of the material reduces the amount of necking of the material as compared to non-uniform elongation.
Implementation Method 5
The pressurized gas may be introduced through the lid section. The die section may be heated to a temperature that affects the mechanical properties, fatigue performance, and/or other characteristics of the metal and the welded portions of the blank.
Data Source
AI summary
A component is formed by welding a plurality of sheets of metal to form a blank with a number of weld nuggets, placing the blank between a die section and a lid section, heating the die section to heat the blank, and introducing a pressurized gas between the lid section and the die section to press the blank into a mold in the die section to form a component. The number of weld nuggets has a desired thickness ratio between about 1.1 to about 1.25 such that the plurality of sheets of metal and the component formed have a number of characteristics that are substantially the same.