Friction Stir Welding Stiffener Flange Microcavity Elimination
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Solution Overview
Problem
Friction stir welding techniques face challenges in achieving effective sealing between stiffeners and aircraft panels, leading to corrosion risks due to microcavities formed during the welding process, especially when the panel width exceeds the rotary pin's diameter, necessitating the use of a sealant that can mix with the materials and compromise structural integrity.
Innovation Solution
A method of linear friction stir welding by transparency, where a weld bead is produced along the flange of the stiffener, extending from one lateral edge to the opposite edge, avoiding microcavities and eliminating the need for a sealant, by using a welding system with multiple rotating pins and counter-bearing units to ensure optimal cohesion and structural homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If friction stir welding is used to attach stiffeners to aircraft panels, then assembly speed and cost are improved, but sealing quality deteriorates due to microcavity formation
Solution Approach 1:
The welding process is divided into multiple passes or stages, allowing the weld bead to be formed systematically across the entire stiffener flange width. This segmentation enables complete material mixing and elimination of microcavities while maintaining assembly speed through optimized process sequencing.
Solution Approach 2:
The welding approach transitions from a single-point linear weld to a multi-dimensional solution where the weld bead extends across the entire width of the stiffener flange. This dimensional expansion ensures complete coverage and eliminates microcavities by addressing the sealing issue in the width dimension rather than relying solely on length-based welding.
2Reliability
If sealant is used to prevent microcavity corrosion, then sealing quality is improved, but structural integrity deteriorates due to material mixing
Solution Approach 1:
The friction stir welding process, which initially creates microcavities that require sealant (potentially compromising strength), is optimized to eliminate these microcavities through complete material mixing. The same friction and material softening that could create defects are converted into benefits by ensuring thorough mixing that prevents cavity formation, thereby eliminating the need for sealant and preserving structural integrity.
Solution Approach 2:
Process parameters such as welding speed, pin rotation speed, and plunge depth are optimized to achieve complete material mixing without creating microcavities. By changing these parameters, the welding process transitions from one that creates defects requiring sealant to one that produces homogeneous welds with inherent sealing capability, maintaining both reliability and strength.
3Adaptability or versatility
If the stiffener flange width is greater than the rotating pin diameter, then adaptability to different panel sizes is improved, but welding quality deteriorates due to incomplete material mixing
Solution Approach 1:
The welding of wide stiffener flanges is achieved through segmented passes or multiple welding heads that work in sequence or parallel. This segmentation allows each pin to maintain optimal material mixing within its zone while collectively covering the entire flange width, thus preserving welding quality across various panel sizes.
Solution Approach 2:
The friction stir welding system is designed with multi-functionality to handle various stiffener flange widths.通过使用多个焊头或多次焊接，系统既能适应不同尺寸的面板，又能保证每个焊接区域的材料充分混合，从而在不同应用场景下都保持高质量的焊接效果。
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 prevents microcavity formation, reduces corrosion risks, maintains optimal structural properties, and eliminates the material mixing issues associated with sealants, while maintaining the speed and cost advantages of friction stir welding.
Implementation Method 1
a local softening of the material forming the panel and of the material forming the stiffener base, caused by the heat induced by the friction of said rotating pins
Implementation Method 2
The rotation of the rotating pin 12, as well as, where applicable, that of the shoulder 14, causes a mixing of the material in the pasty state
Implementation Method 3
The extrusion induced by the rotating pin 12 and the forging provided by the shoulder 14 thus result in the formation of a weld bead progressively
Implementation Method 4
This weld bead takes the form of a new metallurgical structure common to both materials, formed through restoration-recrystallization phenomena
Data Source
Figure 1~2
Figure 3~3b
Figure 4
AI summary
The process comprises forming a weld bead along a flange of a stiffener by a rotating pin of a head of a welding system. A width of the flange of the stiffener is greater than double a maximum diameter of the rotating pin. The weld bead extends in cross section from a first lateral edge to a second lateral edge of the stiffener flange. The welding heads include a shoulder, which extends at a base of the rotating pin, and a counter-bearing unit, which has a support surface. The process comprises forming a weld bead along a flange of a stiffener by a rotating pin of a head of a welding system. A width of the flange of the stiffener is greater than double a maximum diameter of the rotating pin. The weld bead extends in cross section from a first lateral edge to a second lateral edge of the stiffener flange. The welding heads include a shoulder, which extends at a base of the rotating pin, and a counter-bearing unit, which has a support surface. The process further comprises inserting the respective rotating pins of the welding heads into a panel and into the stiffener flange, then moving the welding heads along the stiffener flange in a direction of welding, and pressing a support surface of the counter-bearing unit onto the flange of the stiffener to counteract the pressure exerted by the rotating pins. The rotating pins of the welding heads are mutually offset in a transverse direction, which is orthogonal to the direction of welding and to respective axes of rotation of each of the rotating pins. A footprint formed by all rotating pins of the welding heads extends in cross section from the first lateral edge to a second lateral edge of the stiffener flange. The welding heads are arranged according to a triangular configuration. The moving step is carried out by local softening of the material forming the panel and of the material forming the stiffener flange caused by the heat produced by the friction of the rotating pins. The welding heads include two lateral welding heads centered in relation to a given plane orthogonal to the direction of welding and a central welding head offset in the direction of welding in relation to each of the lateral welding heads. A first welding head is positioned on a web (30) of the stiffener while other two welding heads are offset in relation to the web of the stiffener, and a penetration depth of the rotating pin of the first welding head into the flange of the stiffener is less than a penetration depth of the respective rotating pins of the other two welding heads into the flange of the stiffener. The welding heads move in a direction such that the central welding head is arranged to the rear of the lateral welding heads. The support surface is formed jointly by two rollers, which are carried by the counter-bearing unit and move by rolling against the flange of the stiffener. An independent claim is included for a welding system.