Shot peening is a cold working process in which the surface of a spring is bombarded with small spherical media called steel shot. Each piece of shot striking the surface creates a small indentation or dimple. Overlapping dimples develop an even layer of metal in residual compressive stress. Fatigue cracks will not start or propagate in a compressively stressed zone. When a residual compressive stress is produced in the surface, the tensile stress created by the applied load must first overcome the residual compressive stress before the resultant surface stress becomes tensile.

Use of Peening

Shot peening has many uses in industry, particularly in the manufacture of parts as different as gears, springs, welded joints, aircraft parts, transmission shafts, torsion bars, etc. Experience has shown that shot peening could increase the endurance limit of lifting hooks up to 50%. For this to be done the necessary equipment must be obtained. Best of blasting gives useful information and guidelines for the purchasing of shot peening equipment. Other experienced shot peening equipment users can respond to your queries on the best of blasting forums.

Peening is now frequently used as an alternative to polishing where directional scratches can propagate minute cracks. It is ideal for the treatment of fillets, grooves or unsupported edges or anywhere where sudden changes in form occur.