Factors that can impact coverage include the number of impacts (shot flow), exposure time, shot properties (size, chemistry of shot) and the properties of the workpiece itself.

However it is important to optimise the level of coverage to produce the desired surface effect. Using overlapping passes can improve coverage, while a compressively stressed surface can be produced with less than 50% coverage. Because the blast stream is cone shaped, shot hits the material surface at varying angles. This measures the percentage of the surface that has been indented by assessing variations in the angle of the blast stream. The coverage of the process can also be gauged with an Almen round, as developed by R. If the strip is then seen to deform by a further 10% the intensity of the blast stream can be measured. This is done as the strip reaches 10% deformation and is then hit with the same intensity for double the time. The intensity of the blast stream can be measured in the deformation of the almen strip. The surface residual compressive stresses created by shot peening will differ depending on factors including the intensity and coverage of the peening media.Ī method to measure the effect of shot peening was created by John Almen, who devised the ‘Almen Strip’ to measure the compressive stresses that are imparted by the process. However, tensile stresses inside a material are not as problematic, as surface cracks are less likely to start on the inside of a material. Stress corrosion cracking is also mitigated internally as the plastic deformation caused by the various types of shot peening and laser peening aids tensile stressed parts from the inside. The main advantage of shot peening is to extend the service life of a component by creating an induced compressive stress layer to increase resistance to fatigue (including corrosion fatigue, stress corrosion and cavitation erosion) while also helping to resist the development and propagation of cracks.The creation of compression stresses that resist metal fatigue help prevent the propagation of cracks through the material. However, the use of equipment to remove shot fragments during the process can help by cleaning and reconditioning shot and feeders and replacing damaged media. Cut wire can last five times as long as cast shot and is also relatively inexpensive. Cut wire shot is generally preferred since it maintains its spherical shape as it degrades, unlike cast shot, which can break into sharp pieces and damage the workpiece. The peening media that can be used include cast steel shot, ceramic or glass beads and cut wire.

Other shot peening method include ultrasonic peening, wet peening and laser peening, which doesn’t use media. A centrifugal blast wheel uses a high speed paddle wheel which propels the peening media using centrifugal force by adjusting the media entrance location to time the release of the media.

Air blast systems use high pressure air to fire the shots through a nozzle at the workpiece. Shot peening is commonly undertaken using air blast systems or centrifugal blast wheels. When a group of shots impact the surface they generate multiple indentations, resulting in the component being encased by a compressive stressed layer on the metal surface.

Shot peening works by striking a surface with a shot (round metallic, glass or ceramic particle) with enough force to generate plastic deformation. If you have any questions or need help, email us to get expert ContentsĬlick the links below to skip down to a section in the guide: The shot peening process is used to add strength and reduce the stress profile of components. Shot peening is a cold work process used to impart compressive residual stresses on to the surface of a component, which results in modified mechanical properties. National Structural Integrity Research Centre.Structural Integrity Research Foundation.

Bzflag change shot length