Hollow Spring Compression Processing for Inner-Surface Fatigue Life
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Solution Overview
Problem
Existing methods for manufacturing hollow springs face challenges in applying compressive residual stress to the inner surface, leading to potential breakage and reduced fatigue life, especially when dealing with complex shapes or smaller diameters, and require additional equipment components.
Innovation Solution
A method involving compression processing using a die to apply compressive residual stress to the inner surface of a steel tube by pressing from the circumferential direction, which can be applied to both straight and bending portions of the tube without complex equipment, ensuring the stress is imparted uniformly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is applied to the outer surface to impart compressive residual stress, then the stress on the outer surface is relieved, but the stress difference between outer and inner surfaces is reduced, leading to breakage from the inner surface
Solution Approach 1:
Instead of applying compressive residual stress to the outer surface through shot peening, the invention inverts the approach by applying compressive residual stress to the inner surface through compression processing. This reverses the location of stress relief from outer to inner surface, preventing breakage initiation at the inner surface while maintaining outer surface strength.
Solution Approach 2:
The invention segments the stress treatment approach by applying different stress conditions to different surfaces: the outer surface maintains its original stress state while the inner surface receives compressive residual stress through compression processing. This segmented approach allows independent optimization of each surface's stress state.
2Weight of moving object
If the thickness of the hollow spring is reduced to reduce weight, then weight reduction is achieved, but the stress difference between outer and inner surfaces becomes more remarkable, increasing breakage risk
Solution Approach 1:
The invention applies preliminary anti-action by introducing compressive residual stress to the inner surface before the hollow spring is subjected to service loads. This pre-applied compressive stress counteracts the tensile stress that would otherwise concentrate at the inner surface, particularly in thin-walled structures where the stress difference is more remarkable.
3Reliability
If reflection members and guide members are used to apply compressive residual stress to the inner surface, then fatigue life is prolonged, but the equipment complexity increases and the inner surface of bending portions may be scratched
Solution Approach 1:
The invention extracts and removes the complex equipment components (reflection members, guide members, wires, dust collectors) from the stress application system. Instead of using these elaborate mechanisms to direct shots to the inner surface, the invention directly applies compression processing to the entire hollow spring, eliminating the need for these auxiliary components.
Solution Approach 2:
The hollow spring serves itself in the compression processing method. The entire hollow spring is placed in the compression processing device and subjected to uniform compressive force, allowing the structure to receive stress treatment without requiring external guide members or reflection members to direct the processing force to specific areas.
4Reliability
If reflection members are moved along the hole by wire in bending portions, then compressive residual stress can be applied, but the guide member slides along the inner surface causing scratches
Solution Approach 1:
The invention removes the guide member that slides along the inner surface, eliminating the source of scratches. By applying compression processing to the entire hollow spring simultaneously, there is no need for a guide member to traverse the inner surface, thus preventing mechanical damage while still achieving compressive residual stress.
5Reliability
If reflection members are arranged to the hole of the pipe, then inner surface stress can be relieved, but the method cannot cope with pipes with more complicated shapes or smaller diameters
Solution Approach 1:
The compression processing method is universal and can be applied to hollow springs of any shape or size. The compression processing device applies force to the outer surface of the entire hollow spring regardless of its geometry, making the method adaptable to complicated shapes and small diameters without requiring adjustment of reflection members or guide members.
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 method effectively prolongs the fatigue life of hollow springs by reducing tensile stress and enhancing compressive residual stress on the inner surface, particularly at high-stress areas like bending portions, without the need for additional components.
Implementation Method 1
compression processing to a steel tube by pressing a die
Implementation Method 2
impart the compressive residual stress to an inner surface
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3~5
AI summary
A method includes, providing a tubular member (10) used for a hollow spring, and applying the compressive residual stress to at least a portion of an inner surface of the steel tube by applying the compressive force to at least a portion of an outer surface of the tubular member (10) from a circumferential direction, and a fatigue life of the tubular member (10) is prolonged by applying the compressive residual stress to the inner surface of the tubular member (10). Applying the force to the outer surface of the tubular member (10) includes pressing the tubular member (10) with a die (1). The die (1) has a pressing surface (1a) shaped such that the compressive force can be applied to at least the portion of the outer surface of the tubular member (10) from the circumferential direction.