Lubricating Cap for Interference Fastener Hole Insertion
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Solution Overview
Problem
The existing methods for installing interference fasteners in aircraft structures face challenges such as increased insertion forces due to geometric step effects when transitioning between layers of different materials, leading to potential fastener breakage and coating deterioration, especially in thick assemblies with varying material rigidities and coaxiality defects.
Innovation Solution
A cap is positioned on the fastener to lubricate the inner wall of the perforation, distributing lubricant as the fastener is inserted, reducing friction and wear across material layers, and the cap can be reused after reconditioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If interference fasteners are installed in multi-layer aircraft structures with varying material rigidities, then structural resistance to cyclical loads is improved, but geometric step effects between layers cause increased insertion forces that may lead to fastener breakage
Solution Approach 1:
A lubricating cap is introduced as an intermediary component between the fastener and the multi-layer structure. The cap contains a lubricant reservoir that releases lubricant during insertion, creating a lubricated interface that reduces friction and insertion forces when the fastener passes through layers with varying material rigidities, thereby preventing fastener breakage while maintaining the interference fit's structural benefits
Solution Approach 2:
The lubricant is pre-loaded into the cap's reservoir before installation. This preliminary action ensures that lubricant is available at the exact moment and location where friction forces are highest during insertion, allowing the fastener to smoothly transition between layers with different material properties without experiencing excessive insertion forces
2Productivity
If high insertion forces are applied to install interference fasteners in thick assemblies, then fasteners can be installed through multi-layer structures, but coating deterioration and fastener breakage occur
Solution Approach 1:
The lubricating cap acts as a protective intermediary that reduces direct contact friction between the fastener shaft and the structure's perforation walls. By maintaining continuous lubrication during insertion, the cap prevents coating deterioration on the fastener surface and eliminates the risk of fastener breakage that would occur with high-force insertion methods
Solution Approach 2:
The lubricant reservoir in the cap provides beforehand cushioning by pre-positioning the lubricant that will cushion the fastener during insertion. This prevents direct metal-to-metal or coated-surface contact that would cause coating deterioration and potential fastener failure under high insertion forces
3Force
If lubricant is applied to the fastener surface, then friction during insertion is reduced, but lubricant distribution becomes uneven due to geometric step effects between layers
Solution Approach 1:
The cap serves as a controlled intermediary lubricant delivery system. Instead of relying on free application of lubricant to the fastener surface, the cap's reservoir and internal geometry control the lubricant's release, ensuring uniform distribution along the fastener shaft as it passes through the perforation, even when encountering geometric step effects between layers
Solution Approach 2:
The cap provides localized lubricant delivery at different positions along the fastener shaft. The internal structure of the cap ensures that lubricant is distributed uniformly across the contact surface between the fastener and the structure, compensating for the non-uniform geometric step effects created by multi-layer assemblies with varying material rigidities
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
The cap significantly reduces installation forces, prevents fastener breakage, and maintains continuous lubrication, enabling easier insertion in multi-layer structures with varying materials like titanium and steel, even in thick assemblies.
Implementation Method 1
A cap to lubricate an inner wall of a perforation... distributing lubricant as the fastener is inserted, reducing friction and wear across material layers
Data Source
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AI summary
The object of the invention is a cap to lubricate an inner wall of a perforation going through at least two elements of the structure. The cap comprises a tubular body and at least one lubricant reserve, and before installation in the structure said cap has a largest external diameter larger than an internal diameter (DS) of the perforation, and the cap lubricates the internal surface of the perforation when its largest external diameter is radially compressed by a wall of the perforation. The invention also concerns a fastener comprising this type of cap, and an interference assembly process for the fastener equipped with the cap. The invention is applicable to the assembly of aircraft structures.