There are innumerable contexts in which the process of improving metal strength is useful. Some of those contexts are architecture and construction, aircraft repairs, automotive spring manufacturing, surface finishing and other manufacturing contexts.
Peening is performed after products have already been manufactured and put to use. Descaling, decoring, sand removal and other structural improvements are often made to gear parts, clutch springs, camshafts, gearwheels, connecting rods, turbine blades and many other kinds of machinery through the process of shot peening.
Other processes that use non-metal peening media like glass or ceramics are still referred to as peening, though their applications are generally limited to softer surfaces that could be damaged by heavy, angular or bead-shaped blast media.
Peening as a metallurgical treatment dates back many years. It was originally performed with a peening hammer, the contact surface of which was usually curved. High-impact peening shot provides for the same effect but over a much wider area in much less time. Peening works by imparting residual compressive stress in a surface through the repeated collision of the surface and blunt instruments.
This stress translates, in terms of the properties the treated metal assumes after its treatment, into resistance to metal fatigue. Fatigue-resistant metals boast obvious advantages over untreated metal parts in applications where extended performance under demanding conditions is expected of the material. Aside from the potential for changing mechanical and performance properties of metals, shot peening can also be used as a cosmetic surface treatment.
Because the particulate size of steel shot and other metal shot materials is so large, it imparts much more visible impact artifacts than smaller media like silica or crushed walnut shells. Shot peening is often used to treat surfaces where an irregular decorative finish is desired. The way light is reflected by overlapping dimples caused by some varieties of shot peening treatment is one of the desirable features of shot peened surfaces.