Double-Side Friction Stir Welding for Uniform Through-Thickness Flow
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Solution Overview
Problem
The friction stir welding method faces challenges in achieving a homogeneous plastic flow and sufficient joint strength when applied to structural steel sheets or plates due to temperature and plastic flow differences in the thickness direction, leading to welding defects and limited welding speed.
Innovation Solution
The double-side friction stir welding method involves controlling the gap and inclination angle between the shoulder parts of rotating tools, adjusting their diameters and the thickness of the metal sheets or plates, and ensuring opposite rotation directions to achieve a homogeneous temperature increase and shear stress, thereby promoting a uniform plastic flow and strengthening the welded joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-side friction stir welding is used, then the welding process is simple, but localized improper plastic flow occurs due to temperature and plastic flow differences in thickness direction
Solution Approach 1:
The welding process is segmented into two independent welding operations performed from opposite sides of the workpiece. Two rotating tools simultaneously or sequentially weld from the top and bottom surfaces, dividing the single complex welding task into two simpler, more controllable welding actions that together achieve uniform plastic flow throughout the thickness direction.
Solution Approach 2:
The welding approach transitions from a single-sided two-dimensional process to a dual-sided three-dimensional process. By introducing welding from the opposite side (another dimension), the system achieves uniform heat distribution and plastic flow control throughout the entire thickness of the workpiece, eliminating localized improper plastic flow.
2Productivity
If welding speed is increased, then productivity improves, but welding defects occur due to insufficient temperature and plastic flow
Solution Approach 1:
The heating and plastic flow generation processes are segmented between two rotating tools working simultaneously from opposite sides. This division allows each tool to contribute to the overall temperature rise and plastic flow, enabling higher welding speeds while maintaining sufficient thermal input and material softening for defect-free welds.
Solution Approach 2:
The thermal effects and plastic flow generation from two separate welding operations are merged into a unified welding process. The combined heat input and shear stress from both rotating tools create uniform temperature distribution and adequate plastic flow throughout the workpiece thickness, ensuring high welding quality even at increased welding speeds.
3Productivity
If tool diameter is increased, then welding speed can be increased, but excessive load is applied to the tools
Solution Approach 1:
The total welding load and tool diameter requirements are segmented between two rotating tools. Each tool can use a smaller diameter than a single tool would require, reducing the load on each individual tool while collectively achieving the necessary welding speed and productivity through simultaneous operation.
Solution Approach 2:
The welding capabilities of two tools are merged to achieve the overall welding effect. By combining the contributions of two smaller-diameter tools, the system attains the equivalent productivity of a larger tool while distributing the mechanical load across both tools, preventing excessive load on any 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 enhances welding speed, suppresses defects, and ensures a strong, homogeneous welded state with improved workability, particularly by maintaining a gap and diameter ratio that prevents concave-shaped surfaces and excessive load on the tools.
Implementation Method 1
while the metal sheets or the metal plates are softened by frictional heat generated between the rotating tools and the metal sheets or the metal plates
Implementation Method 2
softened parts are stirred by the rotating tools. As a result, a plastic flow is caused to occur at the welded joint
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-side friction stir welding is performed, it becomes possible to realize a plastic flow sufficient for attaining a homogeneous welded state with respect to a thickness direction of metal sheets or metal plates, to increase the welding speed while suppressing defects at the time of welding from occurring, to ensure a sufficient strength, and to improve welding workability. Also provided is a friction stir welding device suitable for performing the friction stir welding. According to the present invention, a pair of rotating tools facing each other is respectively arranged on a top-surface side and a bottom-surface side of a butted portion or an overlapping portion, which comprises a joint portion of two metal sheets or two metal plates, the pair of rotating tools is moved in a welding direction while being rotated at the butted portion or the overlapping portion, and while the metal sheets or the metal plates are softened by frictional heat generated between the rotating tools and the metal sheets or the metal plates, softened parts are stirred by the rotating tools to produce a plastic flow to join the metal sheets or the metal plates to each other.