Flush-Break Blind Fastener for Recess-Free Surface Finishing
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Solution Overview
Problem
Traditional blind fasteners often result in a protruding tip or recesses after installation, requiring additional processes to achieve a flush surface, which is time-consuming, labor-intensive, and can compromise the integrity and aerodynamics of workpieces like aircraft.
Innovation Solution
A recess-free blind fastener design featuring a bolt with a non-threaded portion and an annular break groove, allowing the bolt to break off flush with the workpiece during installation, eliminating the need for secondary shaving or grinding operations and incorporating a drive nut with a knurled surface to prevent rotation and ensure a flush finish.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional blind fasteners are installed, then the fastening function is achieved, but protruding tips or recesses are created on the workpiece surface requiring additional shaving operations
Solution Approach 1:
The bolt is segmented into distinct portions: a first threaded portion for engagement with the nut, a non-threaded portion for breaking off, and a second threaded portion for final engagement. This segmentation allows the non-threaded portion to break cleanly at the workpiece surface, eliminating protrusions and recesses that would require additional machining operations.
Solution Approach 2:
The break groove is pre-formed in the non-threaded portion of the bolt before installation. This preliminary action ensures that when the bolt is driven home, it will break at the predetermined location, creating a flush surface without requiring subsequent shaving or grinding operations.
2Manufacturing precision
If additional shaving operations are performed to achieve flush surface, then surface quality is improved, but installation time and labor cost increase
Solution Approach 1:
The fastener system is self-finishing: the bolt automatically breaks off at the workpiece surface during the fastening operation itself, creating a flush surface without requiring separate shaving or grinding operations. The break groove ensures clean breaking at the precise location, making the fastener its own finishing tool.
Solution Approach 2:
The fastening function and surface finishing function are merged into a single operation. The bolt breaking off at the workpiece surface simultaneously achieves both the mechanical fastening and the flush surface condition, eliminating the need for separate shaving operations and improving overall productivity.
3Manufacturing precision
If repetitive shaving operations are performed on multiple fasteners, then surface quality is maintained, but operator fatigue and safety risks increase
Solution Approach 1:
The fastener performs its own finishing operation by breaking off at the predetermined location, eliminating the need for operators to perform repetitive shaving operations. This self-service mechanism removes the operator from the potentially hazardous repetitive task, improving safety while maintaining consistent surface quality across all fasteners.
4Strength
If conventional blind fastener design is used, then fastening function is achieved, but secondary operations are required to remove protruding portions
Solution Approach 1:
The bolt is divided into functional segments with the non-threaded portion specifically designed for breaking off. This segmentation allows the fastening function to be achieved while the excess portion automatically separates, eliminating the need for secondary removal operations and reducing overall process complexity.
Solution Approach 2:
The break groove is created in advance during manufacturing, so that during installation the bolt will naturally break at the correct location without requiring any additional operations. This preliminary preparation simplifies the installation process by built-in the finishing operation into the fastening process itself.
Data Source
AI summary
The fastener includes a bolt, a nut, a sleeve, and a drive nut. The drive nut interfaces with the nut. The bolt is disposed through the nut, sleeve, and drive nut. The bolt comprises one or more threaded portions and a non-threaded portion. The fastener breaks-off at the non-threaded portion during installation. The installed fastener comprises a recess-free, flush surface with a workpiece.