Blind Fastener Break-Off Structure for Flush Torque-Controlled Joints
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Solution Overview
Problem
Existing blind fasteners face challenges in controlling the rotation of the bolt and nut during installation, 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, including frangible portions and tool engagement features, along with a specialized tool that inhibits nut rotation during installation, allowing for controlled torque and flush installation without post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the core bolt is rotated to provide preload, then the joint strength is improved, but the break-off point cannot be controlled and post-installation grinding is required
Solution Approach 1:
The patent incorporates a controlled break-off feature directly into the core bolt design, where a predetermined portion of the bolt is designed to fracture at a specific location after providing the necessary preload. This preliminary design ensures that the break-off occurs at the intended position, eliminating the need for post-installation grinding and achieving both joint strength and manufacturing precision.
2Manufacturing precision
If rotation of both bolt and nut is controlled, then installation precision is improved, but installation complexity and time increase
Solution Approach 1:
The patent extracts the rotation control requirement from the installation process by designing the core bolt with an asymmetric cross-section that naturally prevents rotation once inserted. The bolt's geometry itself provides the control mechanism, eliminating the need for complex rotational control procedures or additional control devices, thus maintaining installation precision while reducing complexity.
3Adaptability or versatility
If grip length variations are accommodated, then adaptability is improved, but fastener strength may be compromised
Solution Approach 1:
The patent employs a sleeve with a frangible portion that can deform and adapt to varying grip lengths. The sleeve's design allows it to flex and conform to different panel thicknesses while maintaining clamping force. This dynamic adaptability ensures the fastener remains effective across a range of grip lengths without compromising joint strength, as the sleeve continuously adjusts to the specific installation conditions.
4Productivity
If excessive torque is applied, then installation speed is improved, but the sleeve flares out forming a defective tulip configuration
Solution Approach 1:
The patent incorporates a frangible portion in the sleeve that is designed to fracture at a predetermined torque level. This feature acts as a built-in torque limiter that prevents excessive torque from being applied during installation. By designing this protective feature in advance, the patent ensures that even if high torque is attempted, the frangible portion will break before the sleeve can deform into a defective tulip configuration, thus protecting installation quality while allowing for rapid installation.
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
Enables efficient, cost-effective installation of blind fasteners that are flush with the panels, adaptable to varying grip lengths, and resistant to torque-induced defects, ensuring a strong and aesthetically pleasing joint.
Implementation Method 1
The first frangible portion is configured to break off from the bolt head such that an end surface of the bolt head is flush with or recessed from a front surface of the plurality of workpieces, and the second frangible portion is configured to break off from the nut head such that an end surface of the nut head is flush with or recessed from the front surface
Data Source
Figure 1~2
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AI summary
A blind fastener (10) for connecting workpieces (26,30) includes a bolt (14) and nut (18). The bolt includes a shaft (110), bolt head (114), and lug (118). The bolt head is between the shaft and lug and extends radially outward from the shaft. The shaft defines external threads (126)opposite the bolt head. The lug includes a first tool engagement portion (1509 and a first frangible portion (174) that frangibly couples the lug to the bolt head. The nut includes a sleeve (210), nut head (214), and handling member (218). The shaft is threadably received in the sleeve. The nut head extends radially outward from the sleeve and defines a recess (242) that receives the bolt head. The handling member surrounds at least a portion of the lug. The handling member includes a second frangible (270) portion and a second tool engagement portion (266). The second frangible portion frangibly couples the second tool engagement portion to the nut head.