Controlled Shot Peening

Shot peening is a controlled process used to increase the fatigue life of components and fabrications.

Shot peening is the process of impacting materials with spherical media to impart energy to the surface of a component. The amount of stress imparted to the material is proportional to the amount of energy applied; this energy introduces a surface and sub surface compressive layer. The introduction of this compressive layer reduces the effect that any applied tensile stresses may have on the material.

Theoretically the greater the compressive stress achieved the greater the increase in component performance, but, there are many overriding factors which offset this advantage; not least is how compressive stress is imparted and the resultant effect on the material surface.
Each media type and media size has a limit as to how much energy it can impart, and although one can effectively ‘supercharge’ the media this is neither beneficial to the component nor the media.
It is therefore important to understand the process limitations and how best to integrate the combined process tools to achieve the best results.

The application of shot peening is down to the science of the component and the environment in which it is designed to exist.
That is where our expert knowledge and experience is invaluable.
Engineers at Sandwell enjoy the challenges that new applications and designs can bring, if you are at design stage, have a problem component or product then talk to us. An initial discussion costs nothing but may significantly improve component performance or product life.

Information for designers and engineers can be found in Design Notes

Typical compressive stress profiles for single and duplex peened components.

Specification
There are many shot peening specifications available.

The principle specification is AMS 2430 and its generic range, this specification provides the requirements for control of process and media.

Whilst there are many criteria to consider when specifying shot peening, the variables that provide significant effect are;
Shot Size
Shot Intensity
The combination of these two elements dictates the amount of energy imparted to the component.

Shot size is quoted as its diameter in either metric or imperial sizes;

Typically        S110 shot ~ 0.011’’ ~ 0.28mm
                     S230 shot ~ 0.023” ~ 0.58mm
                     S550 shot ~ 0.055” ~ 1.40 mm

Shot Intensity is quoted by its Almen number which can also be quoted in imperial or metric. The number relates to the amount of curvature of a regulated test strip which is peened on one side only. There are 3 thicknesses of test strip N, A & C.

Type N - 0.80mm thick, used in the range 0.10mm (0.004”) to 0.40mm (0.016’’)
Used for measuring low range intensities

Type A - 1.3mm thick, used in the range 0.10mm (0.004’’) to 0.61 (0.024”)
Used for most Steels, Titanium.
Approximate conversion from an A strip to N strip is x3 so an intensity of 0.004” A is equivalent to 0.012” N

Type C - 2.4mm thick and is used for high range intensities.

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