Blind Fastener Assembly With Flush Break-Off and Torque Control
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Solution Overview
Problem
Existing blind fasteners face challenges in controlling the rotation of both the bolt and nut, achieving a flush finish, adapting to variations in grip length, and preventing defective installations due to excessive torque, which affects the strength and aesthetics of the joint.
Innovation Solution
A blind fastener design featuring a bolt with a shaft, bolt head, and lug, and a nut with a sleeve and handling member, incorporating frangible portions and dimples to control rotation and ensure a flush installation, along with a ductile zone in the sleeve for adaptability and torque management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the core bolt break-off point is located outside the countersunk head of the sleeve, then the fastener can be installed, but post-installation grinding is required to make it flush with the panels
Solution Approach 1:
The patent incorporates frangible portions that are pre-configured to break off at specific locations during installation. The first frangible portion on the bolt is positioned to break at the end of the bolt head, and the second frangible portion on the nut is positioned to break at the end of the nut head, ensuring flush surfaces are created automatically during the installation process itself, eliminating the need for post-installation grinding
Solution Approach 2:
The fastener system performs its own finishing operation through the controlled breakage of frangible portions. The breakage occurs automatically during installation when the bolt and nut are tightened, creating flush surfaces without requiring external intervention or additional machining operations
2Manufacturing precision
If rotation of the bolt and nut is controlled to ensure flush finish, then aesthetic quality is improved, but installation complexity increases
Solution Approach 1:
The patent separates the rotation control function into a dedicated friction control element that is extracted as a distinct component. This element provides controlled friction between the bolt and nut during installation to prevent premature rotation, while the actual tightening rotation is then controlled by the standard thread engagement mechanism
Solution Approach 2:
The friction control element acts as an intermediary between the bolt and nut, mediating their relative rotation during installation. It provides the necessary friction to control rotation until the frangible portions break, at which point the mediation is no longer needed
3Adaptability or versatility
If the sleeve is made ductile to adapt to variations in grip length, then adaptability is improved, but the sleeve may flare out under excessive torque
Solution Approach 1:
The patent applies different material properties to different regions of the fastener components. The sleeve is made ductile in specific zones to accommodate grip length variations, while other regions maintain higher strength to prevent flaring. Similarly, the bolt and nut have frangible portions with controlled material properties that break at specific locations under excessive torque
4Reliability
If a torque control feature is added to prevent excessive torque, then installation reliability is improved, but device complexity increases
Solution Approach 1:
The patent uses frangible portions that are designed to break off after serving their temporary purpose of controlling installation. These portions are disposable elements that provide torque control during installation by breaking when excessive torque is applied, then are discarded as part of the installation process, leaving a simple permanent structure
Data Source
AI summary
A blind fastener for connecting panels includes a bolt and nut. The bolt includes a shaft, bolt head, and lug. The bolt head is between the shaft and lug. The shaft defines external threads opposite the bolt head. The lug includes a first tool engagement portion and first frangible portion that connects the lug and bolt head. The nut includes a sleeve, nut head, and handling member. A central bore of the sleeve receives the shaft and defines internal threads mated with the external threads. The nut head is between the handling member and sleeve. The nut head extends radially from the sleeve and defines a recess that receives the bolt head. The handling member surrounds a portion of the lug. The handling member includes a second frangible portion and a second tool engagement portion. The second frangible portion couples the second tool engagement portion to the nut head.