Self-Drilling Fastener Geometry for Faster Drilling and Pullout
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Solution Overview
Problem
Current self-drilling self-tapping fasteners face challenges in improving drilling time, pullout force, ductility, tapping torque, torsional strength, and tensile strength without compromising other performance categories.
Innovation Solution
A self-drilling self-tapping fastener design featuring a head, shank, and helical thread formation with a drill tip and chip breakers, where the second shank portion includes longitudinally extending flutes and chip breakers, and a drill tip with tapered cutting edges, optimized through milling or forging, to enhance drilling efficiency and pullout force without sacrificing ductility or strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional self-drilling self-tapping fastener design is used, then basic fastening function is achieved, but drilling time is excessive and pullout force is insufficient
Solution Approach 1:
The shank is divided into two distinct portions: a first shank portion with a drill tip for drilling, and a second shank portion with thread formation for fastening. This segmentation allows each portion to be optimized for its specific function, with the drill tip geometry optimized for rapid material removal and the thread formation optimized for high pullout force, thereby resolving the contradiction between drilling speed and fastening strength
Solution Approach 2:
Different geometries and properties are applied to different locations along the shank. The drill tip features specific helix angles and cutting edge geometries optimized for drilling efficiency, while the thread formation features optimized pitch, depth, and profile for maximum pullout force. This local optimization of properties at different locations enables simultaneous improvement of both drilling time and pullout force
2Productivity
If drilling efficiency is improved, then drilling time decreases, but pullout force may be compromised
Solution Approach 1:
The separation of drilling function (first shank portion with drill tip) and fastening function (second shank portion with threads) allows independent optimization. The drill tip can be designed with aggressive geometry for high productivity without compromising the thread formation's ability to generate pullout force, as each segment operates independently with its own optimized characteristics
3Strength
If pullout force is increased, then fastening strength is improved, but drilling time may increase
Solution Approach 1:
By dividing the shank into specialized segments, the thread formation can be optimized for maximum pullout force with deeper threads and optimized pitch, while the drill tip segment maintains aggressive geometry for rapid drilling. This segmentation eliminates the trade-off that would exist in a unified shank design, allowing both high pullout force and short drilling time to be achieved simultaneously
4Strength
If fastener strength is enhanced, then pullout force and torsional strength improve, but ductility may decrease
Solution Approach 1:
The fastener exhibits local quality variations along its length, with the drill tip and thread formation portions having optimized geometries that enhance strength locally where needed for cutting and fastening, while the overall material composition and heat treatment maintain adequate ductility throughout. This localized optimization of strength properties without compromising overall material integrity resolves the contradiction between high torsional strength and sufficient ductility
Data Source
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Figure 2
Figure 2A
AI summary
A self-drilling self-tapping fastener that provides improved performance in both drilling time and pullout force without decreasing performance in any of ductility, tapping torque, torsional strength, and tension strength.