Friction Stir Welding with Overlapping Stir Zones in Thick Plates
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Solution Overview
Problem
Friction stir welding apparatuses face challenges with thicker metal plates, as increased thickness leads to potential welding defects like kissing bonds and increased load on tools, particularly in materials with poor flow characteristics, such as 2000 and 7000 series aluminum alloys, and requires longer probes, which can result in tool damage and increased apparatus size.
Innovation Solution
A method involving a first and second friction stir welding process where the first stirring region and second stirring region overlap in the thickness direction, eliminating the need for a predetermined gap between tools and allowing the process to adapt to varying plate thickness without changing tool lengths, using reaction force tools to maintain positional stability and heat input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a predetermined gap is provided between the front ends of the probes of the upper and lower rotary tools, then the apparatus can accommodate varying plate thickness, but welding defects such as kissing bonds occur especially in thicker plates and materials with poor flow characteristics
Solution Approach 1:
Instead of maintaining a gap between probe ends, the invention inverts the approach by making the probes extend beyond the plate thickness so that their stirring regions overlap within the plate. This ensures complete weld penetration and eliminates kissing bonds while still accommodating varying plate thickness through adjustable probe extension lengths.
Solution Approach 2:
The invention transitions from considering only the gap distance between probe ends (one-dimensional approach) to considering the three-dimensional overlap of stirring regions within the plate thickness. By defining the stirring region depth and ensuring overlap, the method guarantees complete weld penetration regardless of plate thickness variations.
2Adaptability or versatility
If the length of the probes is increased to weld thicker metal plates, then the welding capability for thicker plates is improved, but the bending moment applied to the probes increases leading to higher load on the tools and increased possibility of damage
Solution Approach 1:
The invention makes the probe extension length a dynamic parameter that can be adjusted according to plate thickness. Rather than using fixed long probes for all thicknesses, the system optimizes probe extension to provide sufficient overlap for the specific plate being welded, thereby minimizing unnecessary probe length and reducing bending moments and tool load.
Solution Approach 2:
The invention changes the parameter of probe extension length to optimize the balance between welding capability and tool strength. By adjusting this parameter based on plate thickness, the system achieves adequate stirring region overlap for thick plates while avoiding excessive probe length that would increase bending moments and risk of tool damage.
3Strength
If the diameter of the probes is increased to withstand the load applied to the tools, then the tool strength is improved, but the rotary tools become larger requiring increased apparatus configuration such as shaft or motor
Solution Approach 1:
The invention dynamically adjusts probe diameter based on the specific welding requirements and plate thickness. Rather than using uniformly large-diameter probes to handle maximum possible loads, the system selects probe diameters optimized for each application, thereby avoiding unnecessary increases in tool size and associated apparatus complexity.
4Manufacturing precision
If the probes are provided across the thickness direction of the metal plate, then the welding can be performed through the entire thickness, but when the thickness increases it is necessary to lengthen the probes which increases the bending moment and load on the tools
Solution Approach 1:
Instead of making probes just reach across the plate thickness, the invention inverts the approach by extending probes beyond the plate so that their stirring regions overlap within the plate. This ensures complete penetration and weld quality while allowing the use of shorter probes compared to traditional methods, thereby reducing bending moments and tool load.
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 effectively suppresses welding defects and reduces the load on rotary tools, enabling reliable friction stir welding across the entire thickness of the metal plate without the need for tool length adjustments, even as the plate thickness changes.
Implementation Method 1
a friction stir welding apparatus which upper and lower rotary tools inserted from a front surface side and a back surface side of a welding part of a metal plate are used to weld the metal plate by friction stirring with the upper and lower rotary tools
Data Source
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AI summary
A friction stir welding method comprises a first friction stir welding process of forming a first stirring region in a welded part of a metallic material, and a second friction stir welding process of forming a second stirring region in the welded part. The first and second stirring regions respectively reach an interior of the welded part from the one or the other side of the welded part in the thickness direction and they overlap each other inside the welded part. The second friction stir welding process is performed after the first friction stir welding process. In the first and second friction stir welding processes respective reaction force rotary tools are used which each have a tool body, an insertion hole, and a probe pin. In the first friction stir welding process, the first rotary tool and the first reaction force rotary tool are disposed such that the first rotary axis and the second rotary axis are coaxial with each other, the first probe pin and the second probe pin are opposed to each other with a predetermined gap therebetween, and a protruding length of the first probe pin is set to be longer than the length of the second probe pin. The method includes, after performing the first friction stir welding process, a replacing process of setting the first rotary tool as the second reaction force rotary tool and setting the first reaction force rotary tool as the second rotary tool, by displacing the protruding length of the first probe pin of the first rotary tool and the protruding length of the second probe pin of the first reaction force rotary tool to set the protruding length of the second probe pin to be longer than the first probe pin.