Coil Spring Hardness Profiling for Corrosion Fatigue Resistance
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Solution Overview
Problem
Existing coil spring manufacturing methods fail to effectively address variations in required properties along the circumferential position, leading to uneven compressive residual stress and increased risk of breaking due to corrosion fatigue.
Innovation Solution
A coil spring design with varying hardness distributions in the circumferential direction, achieved by forming layers with different hardness levels and applying alternating current to control current density and heating, combined with shot peening to provide tailored compressive residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shot peening is applied to provide compressive residual stress, then corrosion fatigue resistance is improved, but the compressive residual stress distribution becomes uneven in the circumferential direction
Solution Approach 1:
The patent applies local quality by creating different hardness distributions at different circumferential positions of the wire. The wire is designed with a first hardness distribution at a first circumferential position and a second hardness distribution at a second circumferential position, allowing each location to have optimized properties tailored to its specific functional requirements and stress state.
Solution Approach 2:
The patent utilizes parameter changes through heat treatment processes that modify the hardness and compressive residual stress characteristics of the wire. By controlling heating temperature, heating time, and cooling conditions, the patent achieves different hardness distributions and compressive residual stress profiles at different circumferential positions, resolving the uniformity issue while maintaining corrosion fatigue resistance.
2Ease of manufacture
If uniform hardness is provided throughout the wire, then manufacturing simplicity is maintained, but the coil spring cannot optimize performance for different circumferential positions
Solution Approach 1:
The patent implements local quality by establishing different hardness distributions at different circumferential positions of the wire. This allows the coil spring to have optimized mechanical properties at each location, such as enhanced flexibility at certain positions and increased strength at others, thereby improving overall performance without significantly complicating the manufacturing process through controlled heat treatment.
3Strength
If high hardness is provided throughout the wire, then strength is improved, but settling resistance and corrosion fatigue resistance are compromised
Solution Approach 1:
The patent applies local quality by creating a differentiated hardness distribution where only specific regions of the wire have high hardness, while other regions maintain lower hardness. This ensures that strength is enhanced only where required, while maintaining settling resistance and corrosion fatigue resistance in regions where high hardness would be detrimental.
Solution Approach 2:
The patent utilizes parameter changes through controlled heat treatment processes that selectively modify hardness and compressive residual stress at different locations. By adjusting heating temperature, heating time, and cooling rates, the patent achieves optimal parameter combinations in different wire regions, balancing strength requirements with settling and corrosion fatigue resistance.
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 solution enhances settling resistance and corrosion fatigue resistance while minimizing the risk of breaking, ensuring balanced performance across the coil spring.
Implementation Method 1
forming a hardness distribution varying in the circumferential direction on at least part of the wire by heating the wire by applying alternating current thereto through the first terminal and the second terminal
Implementation Method 2
provides compressive residual stress to the wire formed into the helical shape
Data Source
AI summary
According to an embodiment, a coil spring is formed of a wire wound into a helical shape, and at least part of the wire has a hardness distribution varying in a circumferential direction around an axis of the wire.