Blind Fastener Hole Edge Machining for Lower Composite Stress
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Solution Overview
Problem
Blind fasteners face challenges in securing composite structures due to high stress areas created during installation, particularly when accessing the blind side of workpieces is difficult or impossible.
Innovation Solution
A method involving a machining tool with a cutting tip is used to form a surface modification at the edge of a workpiece, allowing for the installation of a fastener that engages the modified surface, reducing stress and improving fatigue resistance by forming a bulb that counters fatigue cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blind fastener is installed directly into a hole in a composite workpiece, then the fastener can secure the workpiece, but high stress areas are created during installation that reduce reliability
Solution Approach 1:
The patent applies preliminary action by forming a surface modification (such as a countersink or rounded edge) at the hole edge before installing the blind fastener. This pre-modification of the hole edge geometry reduces stress concentrations that would otherwise be created during fastener installation, thereby improving reliability while allowing direct fastener installation without requiring complex stress-mitigation structures
2Manufacturing precision
If the cutting tip is extended during insertion, then the machining tool can form the surface modification, but the tool cannot be inserted through the hole
Solution Approach 1:
The patent applies dynamics by making the cutting tip extendable and retractable relative to the machining tool body. The cutting tip can be retracted during hole insertion to allow the tool to pass through, then extended at the target location to perform the surface modification. This dynamic configuration enables both tool insertion and precise surface modification without requiring the cutting tip to be permanently extended
Solution Approach 2:
The patent applies the nesting principle by placing the cutting tip inside the machining tool body when retracted. The cutting tip can be stored within the tool housing and only extended when needed for machining operations. This nested configuration allows the tool to maintain a compact insertion length while still providing the full cutting tip length when performing surface modifications
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 method effectively secures workpieces by reducing stress concentrations and enhancing fatigue resistance through the formation of a bulb that compressively counters fatigue initiation, improving the reliability of blind fastener installations in composite structures.
Implementation Method 1
the cutting tip includes a cutting portion... forming a surface modification at the edge of the hole with the cutting tip
Implementation Method 2
forming a bulb that compressively counters fatigue cracks... Installation of fasteners tend to create high stress areas
Data Source
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AI summary
A method includes inserting a machining tool through a hole of at least one workpiece that includes a first surface and a second surface opposite the first surface and extends from the first surface to the second surface. The hole forms an inner wall. The machining tool includes a shaft and a cutting tip proximate to one end of the shaft. The cutting tip includes a cutting portion. The method includes positioning the cutting portion of the cutting tip to abut an edge of the hole. The edge is located at a junction of the second surface of the one of the at least one workpiece and the inner wall. The method includes forming a surface modification at the edge with the cutting tip. The method includes removing the machining tool from the hole. The method includes installing a fastener within the hole. The fastener engages the surface modification.