Lockbolt Single Pull Groove Design for Alignment and Strength
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Solution Overview
Problem
Existing lockbolt fasteners face issues with alignment sensitivity, debris clogging, manufacturing complexity, and reduced strength due to multiple shallow grooves, leading to increased loads, slippage, and premature failure.
Innovation Solution
A lockbolt design featuring a single large pull groove with a deep, annular locking portion and a retaining feature, which simplifies alignment, reduces debris accumulation, and enhances strength by increasing the number of interlocked surfaces and ensuring complete groove filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple shallow pull grooves are provided on the pin, then the fastener can be engaged by multiple tool teeth, but the crests of the teeth may not engage sufficiently with the grooves, causing increased loads and slippage
Solution Approach 1:
The patent divides the single large pull groove into multiple segments along the pin tail, with each groove segment capable of engaging a corresponding tool tooth. This segmentation allows multiple engagement points while maintaining sufficient groove depth for reliable tooth engagement, distributing the loading force across multiple points and preventing slippage.
Solution Approach 2:
The pull grooves are designed with varying local characteristics - deeper grooves at critical engagement zones and shallower grooves in other areas. This local quality variation ensures sufficient engagement depth where needed while maintaining overall structural integrity and reducing stress concentration.
2Reliability
If multiple shallow pull grooves are provided on the pin, then the fastener can be engaged by multiple tool teeth, but the narrow, shallow grooves can easily become clogged with debris
Solution Approach 1:
By segmenting the pull groove into multiple smaller groove segments arranged along the pin tail, the design provides multiple discrete engagement points that are less prone to complete clogging. Even if debris blocks one segment, other segments remain functional, maintaining engagement reliability in dirty environments.
Solution Approach 2:
The pull grooves are arranged in a distributed pattern along the length of the pin tail rather than concentrated in a single location. This spatial distribution in another dimension (along the axial direction) reduces the likelihood of complete clogging and improves resistance to debris accumulation.
3Reliability
If multiple collet teeth with small radii are provided on the installation tool, then the teeth can engage the pull grooves, but the small radii increase stresses and lead to premature cracking
Solution Approach 1:
The engagement system is segmented into multiple tooth-groove pairs, distributing the mechanical stress across multiple contact points. This reduces the stress concentration at any single tooth root, preventing premature cracking while maintaining reliable engagement.
Solution Approach 2:
Instead of making the grooves extremely shallow to accommodate multiple teeth, the patent inverts the approach by making the grooves deeper and fewer in number, which allows for larger, stronger tool teeth with larger root radii that are less prone to cracking.
4Reliability
If multiple pull grooves are provided on the pin, then the fastener can be engaged by the tool, but misalignment or pitch error may result in uneven distribution of pulling load
Solution Approach 1:
The segmented groove design provides multiple independent engagement points that are tolerant of minor misalignments. Even if pitch errors or alignment deviations occur during manufacturing or installation, each groove segment can independently engage its corresponding tool tooth, distributing the load evenly and preventing localized overstressing.
5Ease of operation
If a single large pull groove is provided on the pin, then alignment and positioning are less critical, but the groove must be deep to maintain initial position
Solution Approach 1:
The single large pull groove is segmented into multiple smaller groove segments along the pin tail. This segmentation maintains the alignment tolerance benefits of a large groove while distributing the material removal and reducing the complexity of creating a single extremely deep groove. Each segment can be formed independently with standard tooling.
Data Source
AI summary
A lockbolt for installation into apertured workpiece members, comprising a pin having a head and a tail end provided with locking grooves and a single pull groove (20), wherein an installation tool having a collet with a corresponding shape to the pull groove is used to apply an increasing pulling force to the pin tail, thereby to push the collet towards the workpiece, and as the force applied by the hydraulic piston further increases, causing the collar (10) to be swaged into the lock grooves, and halting the force applied by the tool either at a predetermined maximum value or when the pin tail breaks at a breaker groove formed by the single pull groove.