Surface treatment / Fatigue strength improvement
Shot peening
Shot peening is a process that blasts small hard balls (shot) at high speed onto the surface of metal parts, introducing compressive residual stress that raises fatigue strength. It is used to extend fatigue life and suppress stress corrosion cracking in parts under cyclic load, such as springs, gears and shafts.
How it works
"Why it works"As countless shots strike the surface, the surface layer deforms plastically and tries to expand, but it is restrained by the material beneath, so compressive residual stress remains in the surface layer.
Most fatigue cracks start and grow from tensile stress at the surface. Compressive residual stress at the surface suppresses crack initiation and growth, extending fatigue life.
Quality is controlled by peening intensity, measured as the arc height of an Almen strip, and by coverage, the extent to which the surface is covered by impact dents.
Fine particle peening (such as WPC treatment) is a derivative technique that uses smaller media to modify the near-surface region.
Main effects
- Higher fatigue strength and longer fatigue life
- Suppression of stress corrosion cracking and corrosion fatigue
- Work hardening of the surface
- Better sliding properties with fine particle peening
Definitions
- Arc height (Almen intensity)
- The curvature of a standard steel strip (Almen strip) peened on one side. Used as the measure of peening intensity.
- Coverage
- The percentage of the treated surface covered by impact dents. 100% means the entire surface is covered.
- Shot blasting
- A process that uses media to remove rust and scale and to clean and roughen a surface. The equipment is similar to peening, but the purpose and control measures differ.
Applications
"Where it is used"| Field | Examples |
|---|---|
| Automotive | Coil springs, leaf springs, gears, drive shafts |
| Aerospace | Fatigue protection for engine and structural parts |
| Industrial machinery | Molds and dies; fatigue and stress corrosion cracking protection for welds |
Typical process conditions
"Under what conditions"These are general guides. Actual conditions are set by the supplier for each part, material and specification.
| Item | Typical |
|---|---|
| Media | Steel shot, cut wire, glass beads, ceramics, etc. |
| Intensity | Specified as Almen strip arc height |
| Coverage | 100% or more is commonly specified |
| Affected depth | Generally about 0.1 to several tenths of a mm from the surface |
| Surface roughness | Larger media produce a rougher surface |
| Related standards | SAE J442 (Almen strips), AMS 2430, etc. |
FAQ
"Direct answers"What is the difference between shot peening and shot blasting?
Shot blasting removes rust and dirt and prepares the surface. Shot peening introduces compressive residual stress to raise fatigue strength, and its quality is controlled by intensity and coverage.
How is the effect verified?
Intensity is checked by Almen strip arc height, and the effect by residual stress measurement (such as X-ray diffraction) or fatigue testing.
How does it differ from fine particle peening?
Fine particle peening uses media of about 200 μm or smaller. Its affected layer is shallower, but it excels at modifying the near-surface region and forming fine surface texture.
Can I order small lots or a single piece?
It depends on the supplier. See the minimum lot column in the comparison table below for each company's published information.
Which companies in Japan offer Shot peening?
Among the companies listed on FactoryMatch, Fuji WPC Co., Ltd. offer Shot peening (based on each company's published information). See the supplier comparison table for minimum lots and overseas support.
Suppliers
"Who to ask"Based on the listed companies' published information.
| Company | Location | Relevant technology | Minimum lot | Overseas support |
|---|---|---|---|---|
| Fuji WPC Co., Ltd. | Sagamihara, Kanagawa | WPC Treatment®, Hyper Mori Shot®, Molybdenum disulfide shot | From 1 pc | English inquiry OK, 2005: established the US subsidiary WPC Treatment Co., Inc in Los Angeles |