Single-Sided Friction Stir Welding for Stable Large Metal Blanks
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Solution Overview
Problem
Friction stir welding in large metallic structures results in undesirable abnormal grain growth (AGG) during heat treatment and aging, leading to unstable microstructures and reduced mechanical properties, which complicates the formation of large aerospace components.
Innovation Solution
A single-sided friction stir welding process with a backing plate is employed, where the welding tool extends into the backing plate, followed by its removal, to maintain a stable microstructure and high joint efficiency, allowing for subsequent forming and heat treatment without AGG.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If friction stir welding is performed on large metallic structures, then joining capability is achieved, but abnormal grain growth occurs during heat treatment leading to unstable microstructure
Solution Approach 1:
The friction stir welding is performed in a predetermined state (such as solution heat treated or as-extruded) before the final heat treatment and aging processes. This preliminary welding approach allows the weld to be formed when the material is more ductile and less prone to abnormal grain growth, avoiding the AGG issue that occurs when welding is performed after solution heat treatment
Solution Approach 2:
The patent changes the state parameters of the material at different stages of the process. Specifically, it performs friction stir welding in a predetermined state (solution heat treated or as-extruded) rather than in the final state, and uses different tool rotational speeds and feed rates depending on the material state to control the weld microstructure and prevent abnormal grain growth
2Strength
If friction stir welding is performed after solution heat treatment, then welding is achieved, but abnormal grain growth occurs in the weld center reducing mechanical properties
Solution Approach 1:
The friction stir welding is performed as a preliminary operation before the final heat treatment and aging processes. By welding in a predetermined state (solution heat treated or as-extruded) rather than in the final state, the weld is formed when the material is more ductile and less prone to abnormal grain growth, ensuring better microstructure control and mechanical properties
Solution Approach 2:
The patent applies different tool rotational speeds and feed rates depending on the material state and weld location. For example, it uses lower rotational speeds (50-150 rpm) and slower feed rates (0.5-2.5 ipm) in the weld center region to prevent excessive heat input and abnormal grain growth, while using higher speeds at the edges to ensure proper weld formation
3Stability of the object's composition
If large monolithic plate stock is used to avoid welding, then uniform properties are achieved, but manufacturing cost and material availability become prohibitive
Solution Approach 1:
The patent divides large structures into smaller plates that can be friction stir welded together. By performing welding in a predetermined state before final heat treatment, the segmented construction becomes feasible without sacrificing mechanical properties, making manufacturing of large structures economically viable
Solution Approach 2:
The patent changes the material state parameters to enable welding of large structures. By performing friction stir welding in a predetermined state (solution heat treated or as-extruded) rather than in the final state, and using controlled tool parameters, the welded joints achieve mechanical properties comparable to monolithic structures, making segmented construction a viable alternative
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 achieves high strength welds with greater than 95% joint efficiency, maintaining a stable microstructure and preventing abnormal grain growth, enabling the use of narrower commodity plates for large aerospace structures.
Implementation Method 1
Friction stir welding is a solid-state joining process that provides a method of joining metal components without melting of the workpiece material
Implementation Method 2
subjecting the welded blank to a solution heat treatment, followed by quenching and aging
Data Source
AI summary
A method for forming a large metallic component, a friction stir welded component and a friction stir welded blank are provided. The method includes positioning a first metallic plate and a second metallic plate in an abutting arrangement. The first metallic plate and the second metallic plate have corresponding faying surfaces at a point of abutment. A backing plate is attached spanning the point of abutment adjacent the faying surfaces. The first metallic plate is friction stir welded to the second metallic plate to form a friction stir weld along the faying surfaces. The backing plate receives an end of a friction stir welding tool curing the friction stir welding. The backing plate is removed to form a welded blank. The welded blank is formed into a component form. The component is heat treated and aged to form the large metallic component. The friction stir weld in the welded blank has a stable microstructure having little or no abnormal grain growth during elevated temperature forming, heat treatment and aging.