Differential-Hardness Threaded Fastener for Break-Resistant Flexing
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Solution Overview
Problem
Conventional threaded fasteners used in vehicle beds often break under various directional forces, which is undesirable.
Innovation Solution
A threaded fastener design featuring a head and shaft with distinct threaded portions, where the tip portion has a higher hardness than the middle portion, achieved through heat treatment and case hardening, and optionally plated with zinc, to enhance strength and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the entire fastener is made with high hardness material, then strength increases, but brittleness increases and flexibility decreases
Solution Approach 1:
The fastener applies different hardness levels to different portions: the tip portion (first threaded portion) is hardened to high hardness (58-65 HRC) for strength and thread engagement, while the shaft portion (second threaded portion) maintains lower hardness (25-35 HRC) for flexibility and shock absorption. This local differentiation resolves the contradiction by providing high strength where needed while preserving overall flexibility.
Solution Approach 2:
The fastener is divided into distinct portions with different material properties: a tip portion subjected to heat treatment and case hardening for high hardness, and a shaft portion subjected only to heat treatment for moderate hardness. This segmentation allows each portion to have optimized properties for its specific function, resolving the strength-flexibility contradiction.
2Ease of manufacture
If the fastener uses uniform hardness throughout, then manufacturing is simpler, but the fastener breaks under directional forces
Solution Approach 1:
The patent applies different heat treatment processes to different portions of the fastener: the tip portion receives both heat treatment and case hardening, while the shaft portion receives only heat treatment. This local quality differentiation improves reliability under directional forces while maintaining reasonable manufacturing complexity through selective process application.
Solution Approach 2:
The patent changes the material hardness parameter across different portions of the fastener by applying different heat treatment processes. The tip portion achieves 58-65 HRC hardness while the shaft portion achieves 25-35 HRC, creating a gradient that improves reliability without requiring complete redesign of the manufacturing system.
3Reliability
If the tip portion is made harder than the shaft portion, then resistance to breaking increases, but manufacturing complexity increases
Solution Approach 1:
The manufacturing process is segmented into two stages: first, heat treatment of the entire fastener to achieve base hardness; second, selective case hardening of only the tip portion to achieve higher hardness. This segmentation of the manufacturing process achieves the reliability benefit while controlling complexity through process sequencing rather than requiring entirely different manufacturing approaches.
Solution Approach 2:
The fastener undergoes heat treatment as a preliminary action before case hardening. This preliminary heat treatment establishes a base hardness and prepares the material structure for subsequent case hardening, allowing the tip portion to be selectively hardened while the shaft portion retains the base hardness, thus managing manufacturing complexity.
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 fastener exhibits increased strength and resistance to breaking, allowing it to withstand forces that typically cause conventional fasteners to fail, while maintaining sufficient pliability to bend up to 30 degrees without breaking.
Implementation Method 1
The first portion and the second portion may be treated in a first hardening process, and only the first portion may be treated in a second hardening process. The first hardening process may be a heat treatment.
Implementation Method 2
The second hardness may be provided by a case hardening. Both the first portion and the second portion may be treated with the heat treatment, and only the first portion may be treated with the case hardening.
Implementation Method 3
The fastener may be plated with, for example, zinc.
Data Source
AI summary
A fastener having a head and a shaft extending from a first end at the head to a second end forming a tip. The shaft has a first threaded portion and a second threaded portion. The first threaded portion is disposed at the tip. A hardness of the first portion is higher than a hardness of the second threaded portion.