Coil Spring Hardness Zoning for Corrosion Fatigue Resistance
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Solution Overview
Problem
Existing coil springs for vehicle suspension face challenges in balancing settling resistance and corrosion fatigue resistance, with increased hardness leading to rapid crack propagation and decreased resistance when corrosion occurs.
Innovation Solution
A coil spring design featuring a helically wound wire with a first area and a second area softer than the first area, where the second area is wider in circumference, formed through localized softening using high-frequency alternating currents, ensuring the second area is primarily on the inner diameter side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hardness of the wire is increased to improve settling resistance, then settling resistance is improved, but corrosion fatigue resistance deteriorates because cracks progress quickly when corrosion pits are generated
Solution Approach 1:
The wire is designed with non-uniform hardness distribution: the inner diameter side (first region) maintains high hardness for settling resistance, while the outer diameter side (second region) has reduced hardness to prevent crack propagation from corrosion pits. This local differentiation resolves the contradiction by optimizing each region's hardness for its specific functional requirement.
Solution Approach 2:
The wire cross-section is segmented into two distinct hardness zones: a first region on the inner diameter side with higher hardness and a second region on the outer diameter side with lower hardness. This segmentation allows independent optimization of corrosion resistance in the outer region while maintaining settling resistance in the inner region.
2Reliability
If the hardness of the wire is decreased to improve corrosion fatigue resistance, then corrosion fatigue resistance is improved, but settling resistance deteriorates
Solution Approach 1:
Different regions of the wire are assigned different hardness qualities appropriate to their functional needs: the inner diameter region maintains high hardness for settling resistance while the outer diameter region has reduced hardness for corrosion fatigue resistance, eliminating the need to compromise overall performance.
Solution Approach 2:
The wire is segmented into functional zones where the first region (inner diameter side) preserves high hardness for mechanical strength and the second region (outer diameter side) has reduced hardness for corrosion resistance, allowing both requirements to be satisfied simultaneously.
3Reliability
If the second softer area is formed over a wider circumferential range, then corrosion fatigue resistance is improved, but the area available for maintaining structural integrity is reduced
Solution Approach 1:
The softer second area is strategically positioned on the outer diameter side where corrosion exposure is highest, while the harder first region on the inner diameter side maintains structural integrity. This localized quality distribution optimizes corrosion protection without compromising overall strength.
Solution Approach 2:
The hardness distribution is made asymmetric across the wire cross-section, with the softer region concentrated on the outer diameter side exposed to corrosion and the harder region on the inner diameter side providing structural support, rather than applying uniform hardness throughout.
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
Enhances corrosion fatigue resistance by preventing crack development from corrosion pits while maintaining settling resistance, particularly in the end turn portions, without affecting the overall spring performance.
Implementation Method 1
applying an alternating current of 1 kHz or more between the pair of electrodes to heat a portion of the end turn portion and form a first area and a second area softer than the first area on a surface of the wire in the end turn portion
Data Source
AI summary
According to an embodiment, a coil spring is formed of a wire wound in a helical shape, and includes an end turn portion and an effective portion. A surface of the wire in the end turn portion has a first area and a second area softer than the first area. Further, in a circumferential direction around an axis of the wire, the second area is formed over a range wider than that of the first area.