Peening

Shot peening is used to increase the service life of components from fatigue failure, stress corrosion cracking and fretting fatigue.  ‘Hammering’ the component surface using a spherical shot or bead – from cast shot, ceramic or glass bead to condition-cut wire pellets in carbon steel or stainless steel – induces a compressive stress that helps prevent crack initiation caused by tensile stresses due to repetitive mechanical movement.  

Shot peening is widely used in the aerospace, offshore and automotive industries to increase the lifespan of a wide range of components, including gears, cams, shafts, springs, landing gear, turbine blades and rollers.  Some manufacturing processes, such as welding, plating, EDM spark erosion and grinding, can also cause tensile stresses in the surface layers of metals and these can be stress-relieved by a peening process.  The hardness of the media will have an effect on the amount of compressive stress relief created by the peening action – it normally needs to be as hard as or harder than the component being processed.  If the peening intensity is not measured and set correctly, this can cause distortion in thin sub structures and these will tend to bend towards the blast/peening stream. 

To ensure the correct intensity is used, sample peening is conducted against test strips, called Alment Test Strips.  These are based on a given thickness and hardness, and generate documents that define a known control base line against which exposure to certain peening intensities can be assessed.  The deflection of the test strip caused by the peening processes is measured against a gauge – normally an Alment Gauge.  The peening intensity can be altered by increasing or decreasing either the media size or the media flow velocity. 

Shot peening is used to increase the service life of components from fatigue failure, stress corrosion cracking and fretting fatigue.  ‘Hammering’ the component surface using a spherical shot or bead – from cast shot, ceramic or glass bead to condition-cut wire pellets in carbon steel or stainless steel – induces a compressive stress that helps prevent crack initiation caused by tensile stresses due to repetitive mechanical movement. 

Shot peening is widely used in the aerospace, offshore and automotive industries to increase the lifespan of a wide range of components, including gears, cams, shafts, springs, landing gear, turbine blades and rollers.  Some manufacturing processes, such as welding, plating, EDM spark erosion and grinding, can also cause tensile stresses in the surface layers of metals and these can be stress-relieved by a peening process.  The hardness of the media will have an effect on the amount of compressive stress relief created by the peening action – it normally needs to be as hard as or harder than the component being processed.  If the peening intensity is not measured and set correctly, this can cause distortion in thin sub structures and these will tend to bend towards the blast/peening stream.   

To ensure the correct intensity is used, sample peening is conducted against test strips, called Alment Test Strips.  These are based on a given thickness and hardness, and generate documents that define a known control base line against which exposure to certain peening intensities can be assessed.  The deflection of the test strip caused by the peening processes is measured against a gauge – normally an Alment Gauge.  The peening intensity can be altered by increasing or decreasing either the media size or the media flow velocity.