Self-locking Fastener with Angled Crests
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Solution Overview
Problem
Existing self-locking fastener systems face issues with transitional radial elastic yielding, tool 'cam-off' during installation, and unreliable locking mechanisms, particularly when used with synthetic composite materials and liquid seals, leading to sporadic failures and increased costs in aircraft manufacturing.
Innovation Solution
A self-locking fastener system featuring a free-running collar with deformable duplex barrel portions, a pin with a helical locking trough, and a reconfigured pentagon recess in the pintail face, utilizing spring-loaded twin sockets to apply torque in tandem, ensuring sequential tightening and locking operations without overburdening the restraining key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a free-running collar is used to eliminate frictional drag, then the collar can rotate smoothly onto the pin threads, but the collar may not come to a full stop and overstrains the hex key causing sporadic failure
Solution Approach 1:
The collar is pre-formed with axial crests that are machined at specific angles (20 or 15 degrees opening rearward) to control the material flow and deformation characteristics during installation, ensuring the collar comes to a controlled stop without overstraining the hex key
Solution Approach 2:
The collar crests are machined at specific angles (20 or 15 degrees) rather than being parallel to the axis, changing the geometric parameters to control the elastic yielding behavior and material flow during the tightening operation, preventing collar grab and hex key failure
2Ease of operation
If liquid seal coating is applied to reduce friction in composite material joints, then the coating acts as a lubricant, but friction is reduced beyond the counter-torque capacity of the hex key
Solution Approach 1:
The pin trough and collar crests are pre-formed with specific geometric characteristics that will interact to create mechanical locking independent of friction, ensuring reliable locking even when lubrication reduces friction below the hex key's counter-torque capacity
Solution Approach 2:
The collar crests are designed to flow and deform under load, with the material itself creating the locking action through its deformation characteristics rather than relying on friction alone, making the system self-locking regardless of surface lubrication
3Device complexity
If a single socket tool is used to tighten and lock the collar, then the installation process is simplified, but the socket cam-offs from the collar without fulfilling the task
Solution Approach 1:
The collar is divided into distinct functional zones with axial crests that create discrete engagement points for the socket tool, allowing the socket to maintain engagement throughout the installation process without camming off, while still using a single tool for the operation
Solution Approach 2:
The collar crests are spaced axially to create periodic engagement points with the socket tool during rotation, ensuring continuous mechanical connection and torque transmission throughout the tightening and locking sequence
4Productivity
If collar ribs are designed to drive rotation and then collapse axially into pin flutes, then the collar can be tightened and locked, but the transitional elastic yielding causes collar grab and pin overstrain
Solution Approach 1:
The collar crests are machined at specific angles (20 or 15 degrees) rather than parallel to the axis, changing the deformation characteristics to control material flow and reduce sudden elastic yielding that causes collar grab and pin overstrain
Solution Approach 2:
The transitional phase of elastic yielding is rushed through by controlling the material flow with angled crests, minimizing the time and magnitude of the transition period where collar grab could occur, thereby reducing stress on the pin and key
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 system effectively prevents collar over-strain, maintains hoop form integrity, and ensures reliable locking, reducing the risk of improper installations and costly rework in aircraft assembly, while allowing for adjustments in material grade variations and preserving protective coatings.
Implementation Method 1
spring-loaded twin sockets to apply torque in tandem
Implementation Method 2
utilizing spring-loaded twin sockets to apply torque in tandem
Implementation Method 3
Latent friction between the head of a standard pin and a workpiece is sufficient to arrest the pin
Data Source
AI summary
A threaded fastener, inserted into a hole in materials to be joined, receives a free-running collar (nut) with out-of-round duplex barrels. Spring-loaded twin sockets cradle the barrels and a restraining polygon key extends through the sockets and into a recess in the small face on the pin tail. Installation advances in tandem sequence; tightening before swaging. A machined groove with flat bottom and side rising at about 20 degrees from axial forms a boundary and partly reshapes crests from parallel to angular. Such inclination keeps the collar connected to the cavity of the larger of twin sockets throughout tangential tightening, rise of torque, displacement of crest material, recoil of the smaller socket on the end barrel, cessation of collar rotation and plunging torque. When recoil ends, radial torque on the smaller socket crushes and locks barrel material into underlying left hand helical troughs that interrupt the last few pin threads.