Double-Sided Friction Stir Welding for Uniform Through-Thickness Joints
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Solution Overview
Problem
Conventional friction stir welding methods face challenges in achieving uniform plastic flow and temperature distribution in the thickness direction 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 opposing rotations, ensuring uniform temperature increase and shear stress across the metal sheets, thereby enhancing welding speed and preventing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-sided friction stir welding is used on metal sheets, then the welding process is simple, but poor plastic flow occurs locally at the joint due to temperature and plastic flow differences in the thickness direction, leading to welding defects
Solution Approach 1:
The welding process is segmented into two sides with separate rotating tools, each independently controlling the plastic flow and temperature distribution. This segmentation allows simultaneous control of material flow from both top and bottom surfaces, eliminating the poor plastic flow that occurs in single-sided welding while maintaining process manageability through independent parameter control.
Solution Approach 2:
The rotating tools are designed with specific local characteristics including controlled rotation speeds, tilt angles, and positioning relative to the joint line. These local quality adjustments ensure uniform temperature and plastic flow distribution in the thickness direction, preventing welding defects while allowing the rest of the system to remain relatively simple.
2Reliability
If conventional friction stir welding is used on structural steel sheets, then solidification cracking and hydrogen cracking are avoided, but welding speed is reduced and workability is poor
Solution Approach 1:
The rotating tools are positioned and tilted in advance to create optimal friction conditions before welding begins. The preliminary setup of rotation speed, tilt angle, and positioning ensures that sufficient heat and plastic flow are generated from the start, enabling higher welding speeds while maintaining the joint performance benefits of solid-state welding.
Solution Approach 2:
Multiple parameters are optimized simultaneously including rotation speed, tilt angle, and tool positioning. By changing these parameters in a coordinated manner, the process achieves both high welding speed and high joint performance, overcoming the limitation of slow welding speed that plagues conventional friction stir welding on structural steel.
3Productivity
If the rotating tools are moved at high speed to increase welding productivity, then welding speed improves, but temperature distribution becomes uneven and welding defects occur
Solution Approach 1:
The two rotating tools are configured with asymmetric parameters including different rotation speeds, tilt angles, and positions relative to the joint line. This asymmetry allows one tool to compensate for the other, maintaining uniform temperature distribution even at high welding speeds. The asymmetric configuration prevents the temperature unevenness that would normally occur at high speeds while preserving productivity gains.
Solution Approach 2:
The dual-sided configuration provides inherent feedback control where the interaction between the two rotating tools and the workpiece automatically regulates temperature distribution. As one tool generates heat, the other tool's friction and pressure adjust the material flow to distribute heat uniformly, creating a self-regulating system that maintains temperature uniformity at high welding speeds.
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 method achieves a uniform welded state with increased welding speed and improved strength, reducing the occurrence of defects and enhancing workability, particularly by controlling the gap between the shoulders and the rotation directions of the tools.
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
Figure 1
Figure 2(1)~2(2)
Figure 3(1)~3(2)
AI summary
Provided is a friction stir welding method in which, when double-sided friction stir welding is performed, plastic flow enough 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 an improvement in welding workability can be achieved. Also provided is a friction stir welding device suitable for the friction stir welding. A pair of opposed rotating tools are disposed on the top and bottom sides of a butt joint or a lap joint, which is a joint between two metal sheets. The pair of rotating tools are moved along the butt joint or the lap joint while rotated to thereby soften a portion of the metal sheets by heat of friction between the rotating tools and the metal sheets. The softened portion is stirred with the rotating tools to generate plastic flow to thereby join the metal sheets together.