Friction Stir Welding Pass Sequence for Exit Hole Re-Welding
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Solution Overview
Problem
Friction-stir welding (FSW) is limited by the need for large forces, restricted weld speeds, and the creation of exit holes, which can compromise the quality and homogeneity of welds, especially in dissimilar workpiece thicknesses and non-linear welds.
Innovation Solution
A method involving two passes with tools rotating in opposite directions, where the second pass incorporates the first exit hole into the weld region, reducing the size of exit holes and enhancing weld homogeneity by re-welding partially unwelded areas, allowing for more controlled and effective friction-stir welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single pass of friction-stir welding is performed, then the welding process is simple and fast, but exit holes are created that compromise weld quality and homogeneity
Solution Approach 1:
The welding process is divided into multiple passes (first pass, second pass, and optional third pass) instead of performing a single continuous weld. Each pass serves a specific function: the first pass creates initial weld material, the second pass fills exit holes and reinforces the joint, and the third pass (if needed) provides final homogenization. This segmentation resolves the contradiction by sacrificing some welding speed to achieve superior weld quality and eliminate exit holes.
2Strength
If large mechanical forces are applied during friction-stir welding, then the welding process can join workpieces effectively, but the process becomes less suitable for dissimilar workpiece thicknesses and complex geometries
Solution Approach 1:
The welding process parameters (force, speed, tool position) are dynamically adjusted between passes and during each pass to adapt to varying workpiece conditions. The multi-pass approach allows optimization of forces for each specific welding stage and workpiece configuration, enabling effective welding of dissimilar thicknesses and complex geometries while maintaining adequate weld strength.
3Ease of operation
If the probe is fully withdrawn after the first pass, then the tool can be removed from the workpiece, but exit holes remain that reduce weld quality
Solution Approach 1:
The second pass is specifically designed to perform preliminary action of filling the exit holes created during the first pass. By inserting the tool again at the exit hole location and performing a controlled welding pass, the holes are filled with fresh weld material before final tool removal, eliminating the defect while maintaining operational simplicity.
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 minimizes the deleterious effects of exit holes and improves the mechanical properties of friction-stir welds, achieving more homogeneous and effective joints, particularly in complex geometries and dissimilar materials.
Implementation Method 1
Heat is thus generated by friction between the rotating tool and the workpiece(s), resulting in a softened region of material of the workpiece(s) proximal the rotating tool.
Data Source
Figure 1~2
Figure 3~4(g)
Figure 5A
AI summary
A method of friction-stir welding, FSW, a joint J, for example a T joint and/or a lap joint, between a first workpiece W1 and a second workpiece W2, is described. The method comprises: performing a first pass P1 of FSW of the joint J by moving therealong a first tool (10), comprising a first probe (100) rotating in a first rotational direction RD1, in a first movement direction MD1 defining a first line L1, on a first side S1 of the joint J, comprising: inserting the first probe (100) to a first depth D1, thereby providing a first welded region WR1; withdrawing at least partially the first probe (100), thereby providing a first partially welded and/or unwelded region PWUR1; and fully withdrawing the first probe (100), thereby resulting in a first exit hole EXH1; performing a second pass P2 of FSW of the joint J by moving therealong a second tool (20), comprising a second probe (200) rotating in a second rotational direction RD2, in a second movement direction MD2 defining a second line L2, on the first side S1 of the joint J, comprising: inserting the second probe (200) to a second depth D2, thereby providing a second welded region WR2; optionally withdrawing at least partially the second probe (200); and fully withdrawing the second probe 200, thereby resulting in a second exit hole EXH2; wherein the second welded region WR2 includes the first exit hole EXH1; and wherein the second exit hole EXH2 is included in the first welded region WR1.