Mechanically Locked Blind Bolt Fastener Flush Surface
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Solution Overview
Problem
Existing blind fasteners face issues with protrusion beyond the flush surface, reduced strength, and inability to maintain high residual clamp loads, especially in aerodynamic applications and aircraft structures, where they fail to provide a smooth aerodynamic surface and sufficient structural strength.
Innovation Solution
A mechanically locked blind bolt fastener with a core bolt and deformable sleeve, featuring buttress threads and mechanical locks to prevent unthreading and maintain high clamp loads, ensuring a flush surface and enhanced structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the break groove is positioned to break flush with the fastener body head, then a smooth aerodynamic surface is achieved, but variations in panel thickness cause the core bolt to protrude beyond the flush position requiring additional grinding operations
Solution Approach 1:
The core bolt is designed with a predetermined break point (notch or groove) that is positioned and dimensioned to ensure the break occurs at or below the flush position regardless of panel thickness variations. This preliminary design feature prevents protrusion before installation, eliminating the need for post-installation grinding operations.
Solution Approach 2:
The break groove geometry and positioning parameters are optimized to control the break location. By adjusting the depth, width, and position of the break groove relative to the fastener body head, the design ensures consistent break location at or below the flush position, accommodating panel thickness variations without requiring additional operations.
2Reliability
If conventional non-blind threaded fasteners are mechanically locked to prevent unthreading, then reliability is improved, but device complexity increases due to additional locking components
Solution Approach 1:
The mechanical locking feature is integrated directly into the core bolt structure as an inherent part of the fastener assembly. The core bolt includes a protrusion that engages with a corresponding groove in the nut body, creating a mechanical lock that prevents unthreading without requiring separate locking rings or lock-wires. This merging of functions reduces component count while maintaining reliability.
3Manufacturing precision
If the core bolt is designed to break at a predetermined torque, then manufacturing precision is improved, but the fastener may not maintain high residual clamp loads
Solution Approach 1:
The break groove dimensions, depth, and position are carefully controlled to ensure the core bolt breaks at the predetermined torque while maintaining adequate residual clamp load. The groove geometry is optimized to create a stress concentration that initiates controlled breaking at the desired location without compromising the clamping force generated by the threaded engagement before breakage.
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 solution prevents core bolt protrusion, maintains high residual clamp loads, and enhances structural strength, reducing the need for additional operations and components, while ensuring a smooth aerodynamic surface and improved joint shear strength.
Implementation Method 1
The core bolt has a groove for receiving a nose portion of the body to mechanically lock the core bolt to the body. The sleeve has a protrusion (or nose region) for engaging a groove in the body to mechanically lock the sleeve to the body.
Implementation Method 2
The core bolt is threadingly engaged with the sleeve. Upon insertion of the fastener into the aligned apertures of a pair of workpieces and upon turning motion of the core bolt relative to the nut body, the core bolt is moved in an axially outward direction through the nut body.
Implementation Method 3
This axially outward movement typically causes a deformable sleeve around the core bolt and intermediate the nut body to deform around the tapered nose of the nut body. The deformable sleeve forms a bulb-like shape to provide a blind side head against the inner surface of the inner work piece.
Data Source
AI summary
The present invention provides a blind bolt fastener having a core bolt. The core bolt has a threaded portion and a non-threaded portion engaging a deformable sleeve and a body. A protrusion extends from the sleeve or the body to engage a groove in the core bolt to prevent axial movement of the core bolt with respect to the body and the sleeve. An optional drive nut is positioned between a head of the body and wrenching flats of the core bolt. The drive nut has protrusions engaging mating members in the head of the body.