Compression Spring End Contouring for Stress Reduction
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Solution Overview
Problem
Conventional compression springs experience stress concentration and potential failure due to rounded inner surfaces contacting adjacent coils under load, leading to adverse stress/strain distribution and reduced operational life.
Innovation Solution
Compression springs with selectively contoured inner contact surfaces, such as grooved or concave surfaces, are machined to reduce contact stress, where the end portions have a thickness less than the wire diameter, allowing the adjacent coil to be received in a groove or channel, thereby minimizing rocker points and stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the inner surfaces of end portions are left round or non-machined, then the manufacturing process is simpler, but stress concentration occurs and the spring may fail under load
Solution Approach 1:
The patent applies local quality by machining only the inner surfaces of the end portions while leaving the outer surfaces and body coils unchanged. This creates a localized contoured surface (grooved, concave, or flattened) at the critical contact area where the adjacent coil engages, reducing stress concentration specifically at this location without requiring complete spring remanufacturing
2Ease of operation
If the end surfaces are ground or machined to be planar, then the spring can be seated against planar surfaces, but the inner facing surfaces remain round and continue to cause stress concentration
Solution Approach 1:
The patent extends the local quality approach by specifically targeting the inner facing surfaces of the end portions for machining. This distinguishes the invention from conventional practice by applying selective machining to the previously neglected inner surfaces, creating a dual-function end portion with both planar outer surfaces for seating and contoured inner surfaces for stress reduction
3Shape
If the thickness of the end portion is reduced below the wire diameter, then the contoured surface can be formed, but the end portion becomes thinner and potentially weaker
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the end portion to be between 0.5 and 1.5 times the wire diameter, with the contoured surface depth limited to 0.1 to 0.5 times the wire diameter. These specific parameter ranges ensure that the contoured surface geometry is sufficient to reduce stress concentration while maintaining adequate material thickness to preserve end portion strength
Data Source
AI summary
Compression springs, such as helical compression springs, include end portions with selectively contoured inner contact surfaces. The selective contours of the inner contact surfaces may take the form of planar, grooved, concave, or other shaped, non-circular surfaces. In addition, enough of the inner contact surface is contoured to reduce the contact stress and/or stress concentration effects on the adjacent coils when the compression spring is placed under load and the adjacent coil engages or contacts the respective end portion. The selective contouring of the end portions may be accomplished by holding the spring in a holder and moving a cutter relative to the end portion of the spring to remove the desired amount of material from the end portion.