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Shot peening has existed since 1929.

Shot Peening was discovered by Jo Almen, a General Motors engineer. By chance, he found an increase in the life of the leaf spring following a sandblasting operation. Subsequently he “understood” the phenomenon (setting compression), and went on to developing and characterizing the process still valid today.

Shot peening has grown considerably  in the following sectors :

  • Automotive : gearboxes gears, springs, …
  • Aeronautics : landing gear, wheels, screws, springs, …
  • Energy : drilling heads, gas plants, lids, …


The process offers several alternatives:

  • The Peen forming : Process for deforming parts (like airplane wings)
  • The Texturing : optimizes the hydrodynamic performance (bearings)
  • Aesthetics : gives a matt (wheels, blasting)
  • The resistance to stress corrosion (chemical tanks)
  • The holding of welded assemblies (the problem of HAZ)

The process

Shot peening involves bombarding a metal part with a media (steel, ceramics, glass, others…) in a controled way

Usually, this repetitve operation is performed by automated or robotic machines, ensuring the media’s speed, the media itself (particle size and sphericity), the angle of attack, the distance between nozzles and part, and the flow and air pressure.

These are all measures applied in order to guarantee making intensity (energy transfer from media to part) and covering (blasted surface of the part and covering rate) as uniform as possible.

Shot Peening is a process that involves “matifying” a stainless steel part with glass beads (for esthetic reasons or texturing).

This is not to be confused with traditional blasting done in an uncontroled way in order to “clean up” a part (rust for example) and/or to prepare a painting operation

What is it for ?

Shot peening’s key benefits :

  • allows lesser weight and/or smaller size for the same performances (automotive)
  • creates greater safety margin against component breakages (aeronautics)
  • increase the lifetime of components (heavy transports, machinery, railways)

But also…

  • reduces attrition caused by vibration (typing oxidation and fretting corrosion)
  • increases attrition resistance
  • increases corrosion resistance

Surface modification also allows :

  • facilitating grip coatings (paint…)
  • increase of friction coefficient
  • improving lubrication

Source CETIM

How does it work ?

Shot peening is characterized by three phenomena :

  • a compression of the part’s outer surface
  • a phenomenon of outer surface hardening
  • a degradation of the surface condition

Setting into compression is a result of the extension of the surface material grain and a natural response of the material to fill the void generated by media’s impact.

According there phenomena and to the following principles of mechanical physics :

  • A part ALWAYS breaks in traction
  • We can ADD two stress fields

The part being “artificially” into compression, when it is subjected to fatigue cycles (tension, compression), it is “alleviated” if it is in tension.

That’s why a blasted part has an increased lifetime (enhanced endurance phenomenon) since 90% of the parts breackages have their origin in its surface.

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