Compound-Thread Fasteners for High-Strength Steel Assembly
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Solution Overview
Problem
High strength steels, such as HSLA and AHSS, pose challenges for typical thread forming fasteners due to inadequate ductility, leading to inconsistent performance, loose joints, and damage during assembly.
Innovation Solution
A fastener design featuring a tapered shank with a compound thread form, comprising two stacked thread angles, where the crest angle is greater than the body angle, allowing for effective thread formation in high strength steels without deformation or damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If typical thread forming fasteners are used in high strength steels, then the fasteners can be installed in stronger materials, but the thread formation becomes inconsistent and causes damage due to inadequate ductility
Solution Approach 1:
The patent changes the geometric parameters of the thread form, specifically using a compound thread angle with a crest angle greater than the body angle, and modifies the thread root radius to accommodate the low ductility of high strength steels, enabling consistent thread formation without damage
Solution Approach 2:
The patent applies different thread angle characteristics to different portions of the thread: a larger crest angle at the thread tip for initial penetration and a smaller body angle for thread formation, creating localized geometric properties that address different stages of the threading process
2Force
If typical thread forming fasteners are used in high strength steels, then the fasteners can engage the material, but clamp load is poor and joints become loose
Solution Approach 1:
The modified thread geometry parameters, particularly the compound thread angle and increased root radius, enable proper thread formation that generates consistent clamp load and maintains joint stability in high strength steel applications
3Ease of operation
If typical thread forming fasteners are used in high strength steels, then the fasteners can be installed, but thread deformation and damage occur during assembly
Solution Approach 1:
The patent modifies critical thread geometry parameters including the crest angle, body angle, and root radius to prevent stress concentration and deformation during thread formation, eliminating damage to both the fastener and the high strength steel material
Solution Approach 2:
The increased thread root radius and optimized angle geometry prepare the thread form in advance to distribute stresses evenly during installation, preventing deformation before it can occur
Data Source
AI summary
A fastener has a generally cylindrical shank and a driver at a first end of the shank. The shank has a thread having a first side and a second side opposed to the first side. The first and second sides form a compound angle between the shank and an apex where the first and second sides meet. The compound angle is formed by a body portion extending along the first and second sides from the shank to an intersection, and a crest portion extending along the first and second sides from the intersection to the apex. The first and second sides in the body portion form a body angle with respect to each other, and the first and second sides in the crest portion form a crest angle with respect to each other. The crest angle is greater than the body angle.