Lockbolt Collar Assembly for High Clamp Load and Easy Removal
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Solution Overview
Problem
Conventional lockbolt fasteners require high force for collar removal, leading to plastic deformation and damage, and lack efficient assembly control, especially in high-stress applications like electrical vehicle batteries.
Innovation Solution
A fastener design featuring a stud with a locking portion and a collar having a bore diameter to shaft diameter ratio greater than 1.10:1, allowing for high residual clamp load, thermal management, and easy installation, with a drive portion for tool actuation to unscrew and re-tighten the collar, and materials with differing tensile strengths to facilitate removal and refitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the collar is hardened during installation to provide high tensile strength, then the strength of the fastener is improved, but the force required for collar removal increases leading to plastic deformation and damage
Solution Approach 1:
The collar is divided into two distinct portions: a main portion that is hardened and swaged onto the shaft to provide high tensile strength, and a drive portion that remains softer and more ductile to facilitate easy removal with standard tools. This segmentation allows each portion to have optimized properties for its specific function.
Solution Approach 2:
Different regions of the collar have different material properties: the main portion is hardened for strength while the drive portion is kept softer for ease of removal. This local differentiation of material properties resolves the contradiction between requiring high strength for fastening and ease of operation for removal.
2Ease of repair
If a special removal tool is used to cut the hardened collar, then the collar can be removed, but the device complexity increases and the removal process becomes more difficult
Solution Approach 1:
The drive portion acts as an intermediary element that enables standard removal tools to effectively remove the hardened collar. By providing a softer, more ductile portion that can be engaged by conventional tools, the need for specialized cutting tools is eliminated.
Solution Approach 2:
The collar's drive portion is designed to facilitate its own removal through standard tools without requiring specialized equipment. The softer drive portion essentially serves the function of enabling removal by common tools, making the system self-sufficient.
3Force
If the bore diameter is close to the shaft diameter to reduce installation forces, then the installation force is reduced, but the residual clamp load and resistance to thermal expansion decrease
Solution Approach 1:
The bore diameter is intentionally increased to be 1.05 to 1.20 times the shaft diameter, creating a controlled gap. This parameter change allows the collar to be swaged onto the shaft with reduced installation forces while still achieving sufficient residual clamp load and resistance to thermal expansion and vibration loosening through the swaging process.
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 design achieves high residual clamp load, thermal safety, and easy installation with reduced risk of cross-threading, enabling multiple re-assembly and maintenance without damage, while maintaining structural integrity.
Implementation Method 1
a main portion adapted to be swaged onto the locking portion
Implementation Method 2
materials with differing tensile strengths to facilitate removal and refitting
Data Source
AI summary
A method of installing a fastener to a structure with a first and a second workpiece, fastening assembly and fastener is disclosed herein. Provided is a stud having a head, and a shaft. The head and shaft extend along a longitudinal axis (X) and define a shaft length (Ls), wherein the shaft comprises a locking portion, the locking portion defining a shaft diameter (Ds). A collar is adapted to be fitted over the locking portion of the shaft and includes a first collar end, a second collar end and a central through bore which extends from the first collar end to the second collar end. The central through bore is defines a bore diameter (Db) and a main portion is adapted to be swaged onto the locking portion. A ratio of the bore diameter (Db) to the shaft diameter (Ds) is above 1.10:1.