Hollow Spring Inner Surface Polishing via Viscoelastic Abrasive Medium
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Solution Overview
Problem
Hollow springs with reduced wall thickness for weight reduction face challenges in evenly polishing the inner surface to reduce surface roughness and apply compressive residual stress, especially in complex shapes or thinner diameters, which affects their fatigue life.
Innovation Solution
A method involving a viscoelastic abrasive medium flowing alternately through a steel tube to polish and apply compressive residual stress to the inner surface, ensuring even surface roughness reduction and stress distribution across the inner surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the wall thickness of the hollow spring is reduced for weight reduction, then the weight is reduced, but the stress difference between outer and inner surfaces is reduced and breakage originating from the inner surface occurs
Solution Approach 1:
The patent applies different surface treatments to different locations of the hollow spring. Shot peening is applied to the outer surface to create compressive residual stress, while inner surface polishing is applied to the inner surface to reduce roughness. This local differentiation of surface quality allows the thin-walled structure to maintain high fatigue resistance at both surfaces despite reduced wall thickness.
2Strength
If shot peening is performed for the outer surface to give compressive residual stress, then the stress at the outer surface is reduced, but the difference in stress between outer and inner surfaces is reduced
Solution Approach 1:
The patent combines two complementary surface treatment methods: shot peening for the outer surface and inner surface polishing for the inner surface. This combination allows both surfaces to be optimized simultaneously - the outer surface gains compressive residual stress while the inner surface gains reduced roughness - thereby maintaining a favorable stress distribution throughout the wall thickness.
3Manufacturing precision
If the inner surface of the hollow spring is subjected to blasting with an abrasive, then the surface roughness is reduced, but it is difficult to polish the inner surface evenly in complex shapes
Solution Approach 1:
The patent uses a slurry jet polishing method that employs high-velocity fluid streams to transport abrasive particles. This pneumatic/hydraulic approach allows the abrasive slurry to flow through the complex internal geometry of the hollow spring, reaching all surfaces including bent portions and areas with varying cross-sections, thereby achieving uniform polishing regardless of shape complexity.
4Reliability
If shot peening is performed while a reflection member is moving, then the inner surface is given compressive residual stress, but the process becomes complicated and cannot deal with pipe materials of more complex shapes
Solution Approach 1:
The patent replaces the complex mechanical shot peening system with a slurry jet system that uses fluid dynamics to deliver abrasive particles. The high-velocity slurry jet can navigate complex geometries without requiring moving reflection members or complex positioning systems, simplifying the overall process while maintaining the ability to impart compressive residual stress on the inner surface.
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 improves the fatigue life of hollow springs by evenly polishing and applying compressive residual stress to the inner surface, enhancing durability and resistance to bending cycles.
Implementation Method 1
When the inner surface of such a hollow spring is subjected to blasting with an abrasive, the abrasive tends to hit some areas harder than other areas
Implementation Method 2
another technique is provided which performs shot peening for the inner surface of a pipe material to give compressive residual stress to the inner surface
Data Source
Figure 1
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Figure 3(a)~4(c)
AI summary
A hollow spring includes a steel tube in which the average of surface roughness is smaller than 10 µm across the entire inner surface of the steel tube and/or compressive residual stress is given to the entire inner surface of the steel tube. The hollow spring may be manufactured by a step of polishing the inner surface of the steel tube by flowing a viscoelastic abrasive medium (200) within the tubular member (10), between a first opening (11) and a second opening (12) of the tubular member (10). The abrasive medium (200) may include a viscoelastic base material and a granular abrasive. The inner surface of the steel tube is polished evenly to reduce the surface roughness and/or is given compressive residual stress to increase the fatigue life of the hollow spring.