Double-Sided Friction Stir Welding for Uniform Through-Thickness Flow
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Solution Overview
Problem
Conventional friction stir welding methods face challenges in achieving uniform plastic flow and temperature distribution across the thickness of metal sheets, leading to defects and reduced welding speed when applied to structural steel sheets.
Innovation Solution
A double-sided friction stir welding method where a pair of rotating tools with controlled gap, diameter, and tilt angle are used to apply uniform temperature and shear stress across the metal sheets, ensuring effective plastic flow and increased welding speed by rotating the tools in opposite directions and adjusting their configuration to optimize the gap and shoulder dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional friction stir welding is applied to metal sheets, then welding can be performed on low-melting point metal sheets, but poor plastic flow occurs locally at the joint due to temperature and plastic flow differences in the thickness direction
Solution Approach 1:
The welding process is segmented into two simultaneous operations: one rotating tool applies friction heat to soften the metal, while a second rotating tool stirs the softened portion to generate plastic flow. This segmentation of heating and stirring functions into separate tools resolves the contradiction by ensuring both adequate temperature and uniform plastic flow distribution throughout the joint thickness.
Solution Approach 2:
The invention transitions from single-sided welding to double-sided welding, utilizing tools rotating in opposite directions from both faces of the metal sheets. This dimensional change ensures symmetric heat distribution and plastic flow generation across the thickness direction, eliminating the poor plastic flow that occurs with single-sided welding.
2Productivity
If the rotating tool is moved while rotated to join metal sheets continuously, then substantially infinitely long members can be welded, but the shape and size of the metal materials are limited when materials are rotated
Solution Approach 1:
Instead of rotating the metal materials as in conventional friction welding, the invention inverts the approach by rotating the welding tools while keeping the metal sheets fixed. This inversion allows continuous welding of infinitely long members and removes shape and size limitations on the workpieces.
3Reliability
If friction stir welding is applied to structural steel sheets, then solidification cracking and hydrogen cracking can be avoided, but welding speed increases and defects occur due to temperature and plastic flow differences
Solution Approach 1:
The invention changes the welding parameters by using two rotating tools with specific rotational speeds, directions, and configurations. The first tool provides friction heat at a controlled rate, while the second tool stirs at an optimized speed to generate sufficient plastic flow. This parameter optimization enables high welding speeds while maintaining uniform temperature and plastic flow distribution, preventing defects in structural steel sheets.
4Device complexity
If a single rotating tool is used for friction stir welding, then the process is simple, but uniform temperature and plastic flow distribution across the thickness direction cannot be achieved
Solution Approach 1:
The welding system is segmented into two specialized rotating tools: one dedicated to friction heating and another dedicated to stirring and plastic flow generation. This functional segmentation achieves uniform temperature and plastic flow distribution across the thickness direction, overcoming the limitations of a single-tool approach while maintaining process efficiency.
Solution Approach 2:
The invention moves from single-sided to double-sided welding with tools rotating in opposite directions from both faces of the workpiece. This dimensional change ensures symmetric heat and plastic flow distribution through the thickness, achieving uniform welded state that cannot be obtained with a single tool.
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 ensures a uniform welded state, reduces defects, and enhances welding speed and strength, making it suitable for structural steel sheets.
Implementation Method 1
moving the pair of rotating tools along the butt joint or the lap joint in a welding direction while the pair of opposed rotating tools are rotated to thereby soften a portion of the metal sheets by heat of friction between the rotating tools and the metal sheets
Implementation Method 2
stirring the softened portion with the rotating tools to generate plastic flow to thereby join the metal sheets together
Data Source
AI summary
There is provided a friction stir welding method in which, when double-sided friction stir welding is performed, enough plastic flow to obtain a welded state uniform in the thickness direction of metal sheets can be obtained, in which an increase in welding speed is achieved while the occurrence of defects during welding is prevented, and in which sufficient strength and improvement in welding workability can be achieved. There is also provided a friction stir welding device suitable for the friction stir welding.