Lockbolt Single Pull Groove Design for Debris Resistance
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Solution Overview
Problem
Existing lockbolt fasteners face issues with alignment sensitivity, debris clogging, manufacturing complexity, and potential for tampering or injury due to multiple pull grooves and fine pitch collet teeth, leading to increased costs and risks in installation and use.
Innovation Solution
A lockbolt design featuring a single large pull groove with a retaining feature, annular locking grooves, and a simpler installation tool with a hydraulic piston and collet, reducing alignment requirements, minimizing debris accumulation, and preventing unscrewing, while ensuring safety and ease of use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple pull grooves are provided on the pin, then the fastener can be engaged by multiple collet teeth, but the crests of the teeth may not engage sufficiently with the shallow grooves, causing increased loads and slippage
Solution Approach 1:
The single pull groove is segmented into multiple zones including a first tapered section, a second tapered section, and a shoulder, creating distinct engagement regions that distribute and control the interaction with collet teeth
Solution Approach 2:
The pull groove geometry is optimized with specific taper angles and depth parameters to ensure adequate engagement depth while maintaining sufficient crest width, changing the dimensional parameters from shallow multiple grooves to a deeper single groove with controlled geometry
2Reliability
If multiple pull grooves and fine pitch collet teeth are used, then the fastener can be securely engaged, but the grooves and teeth can easily become clogged with debris in dirty working environments
Solution Approach 1:
The design extracts the engagement function from multiple shallow grooves to a single deeper groove, reducing the number of crevices where debris can accumulate while maintaining secure engagement capability
Solution Approach 2:
The groove geometry is changed from multiple shallow grooves to a single deeper groove with optimized depth and width parameters, creating a smoother profile that is less susceptible to debris accumulation
3Reliability
If multiple pull grooves are provided on the pin, then the fastener can be engaged by collet teeth, but the narrow shallow grooves are vulnerable to damage by sand and small stones
Solution Approach 1:
The single pull groove is segmented into multiple functional zones including tapered sections and a shoulder, creating a robust structure that distributes stress and resists damage from external factors
Solution Approach 2:
The groove depth and width parameters are optimized to create a more robust structure that can withstand external forces and environmental damage, changing from shallow narrow grooves to a deeper, wider single groove
4Reliability
If multiple collet teeth with fine pitch are used, then the fastener can be securely engaged, but the teeth require small radii which increases stresses and leads to premature cracking
Solution Approach 1:
Instead of using multiple fine pitch teeth, the design inverts the approach by using a single larger engagement feature with optimized geometry, reversing the conventional multiple-teeth approach
5Reliability
If multiple pull grooves are provided on the pin, then the fastener can be engaged by collet teeth, but misalignment or pitch error may result in uneven distribution of pulling load and higher localised stresses
Solution Approach 1:
The single pull groove is segmented into multiple zones that work together to distribute the pulling load evenly, eliminating the alignment and pitch error issues associated with multiple grooves
Solution Approach 2:
Multiple pull grooves are merged into a single pull groove with optimized geometry, combining the engagement function into one feature that is inherently more tolerant to manufacturing variations
6Ease of operation
If a single large pull groove is used, then alignment requirements are reduced and debris accumulation is minimized, but the groove must be deeper and larger in size
Solution Approach 1:
The groove dimensions are optimized with specific depth, width, and taper angle parameters to achieve the desired alignment ease while controlling the overall size and material displacement
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 enhances installation productivity, reduces manufacturing costs, minimizes the risk of premature failure, and ensures secure locking without the risk of tampering or injury, while maintaining tool safety and durability in harsh environments.
Implementation Method 1
actuating the tool thereby applying a pulling force to the collet, such that the anvil section of the nosepiece causes the collet to close and therefore engage the contact surface of the pull groove, thereby applying a pulling force to the pin tail via the pull groove
Implementation Method 2
causing the tool anvil section of the nosepiece to apply a force to the collar, thereby to gradually swage the collar into the locking grooves of the pin tail
Data Source
Figure 1
Figure 2~2a
Figure 3a~3b
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, 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 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.