Definition - What does Peening mean?

Peening is the process of working a metal's surface to improve its material properties, usually by mechanical means such as:

  • Hammering
  • Blasting with shot (shot peening)
  • Blasting with light beams (laser peening)

Peening is employed during the welding of cast iron and, in certain cases, where post-weld heat treatment is not possible. It can also be used to flatten sheet metal and is specifically used as a primary technique to flatten steel belts used in industrial conveying and pressing operations.

Corrosionpedia explains Peening

Peening is a cold-working process in which the surface of the component is deliberately deformed, in the basic method, by hammering. It expands the surface of the cold metal, thereby inducing compressive stresses or relieving tensile stresses already present. Peening can also encourage strain hardening of the surface metal.

During peening, the surface layer attempts to expand laterally but is prevented from doing so by the elastic nature of the sub-surface, bulk material. This results in the development of beneficial, compressive residual stresses in the surface layer, which are balanced by tensile residual stresses elsewhere. The layer of compressed surface material produced by peening resists the development and propagation of cracks and increases resistance to fatigue failure, corrosion fatigue, stress corrosion and cavitation erosion.

The most common peening techniques are:

  • Shot peening - Involves bombardment of the metal surface by spherical shot. The shot consists of rounded particles of cast iron, cast steel or stainless steel in various mesh sizes. Both mechanized and manual systems are used, depending on the particular component and area to be treated.
  • Roto (flail) peening - The surfaces are impacted by two or more shot-coated flaps which extend radially from a spindle. Each flap consists of shot (cast steel or tungsten carbide) embedded into a wire mesh or fiber.
  • Needle peening - Uses a de-scaling gun but with needles having radiussed ends. The cluster of metal needles is usually made from hardened tool steel.
  • Hammer peening - Similar to needle peening except that a single metal rod, rather than a cluster of needles, is used and applied in a similar way.
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