Reasons for Shot Peening
Fatigue failure is usually related to cyclic loading. Applied tensile stress at the surface is most commonly from bending or torsion. Residual tensile stress induced during manufacturing can also contribute to failure. CWST’s shot peening services process is a cost effective and practical method of improving metal fatigue properties through the use of beneficial compressive stress. This is proven to enhance protection against failures due to:

  • Metal fatigue
  • Stress Corrosion Cracking (SCC)
  • Fretting
  • Contact Fatigue
  • Reduction of fatigue scatter from manufacturing processes

Why is Shot Peening so Important?

Shot peening has become a critical process in many industries due to its ability to improve metal fatigue properties and extend the life of critical components that could potentially fail. Metal fatigue occurs when cyclic loading and the associated tensile stress cause a crack to start in a highly stressed area. Shot peening is able to mitigate this by imparting a high magnitude, residual compressive stress at the surface in the potential failure area.
The shot peening compressive stress is opposite the applied tensile stress that causes a crack to start. Parts that have been shot peened are able to survive 3-10 times longer due to the surface being placed in a residual compressive state.

How Shot Peening is Applied

Controlled shot peening is a cold working process which uses spherical media known as shot. Each piece of shot hits the surface and creates an indentation where the surface yields and is restrained by the substrate material. This creates a beneficial compressive residual stress which makes the surface resistant crack initiation and propagation. Prior manufacturing tensile stresses are converted to residual compressive stress  

Beneficial compressive stress

Shot Peening Residual Stress

The residual stress generated by shot peening is of a compressive nature. This compressive stress offsets or lowers applied tensile stress. Quite simply, less (tensile) stress equates to longer part life. A typical shot peening stress profile is depicted in (FIGURE 1).

Shot Peening Residual Stress

Process Video

Shot peening is a practical method of producing surface residual compressive stresses. For applications that require deeper compressive stresses, CWST’s laser peening process imparts a layer of beneficial compressive stress that is up to ten times deeper than that attainable from conventional shot peening.

Control & Quality Considerations for the Shot Peening Process

Each component’s technical plan is generated prior to processing and takes into account: geometry, manufacturing method, base material and potential for distortion.
CWST facilities are capable of meeting most industry standard shot peening specifications, including:

Stress Corrosion Cracking
  • AMS-S-13165
  • BAC-5730
  • PWA-6
  • RPS-428
  • AMS 2430
  • AMS 2432
  • J2441
  • MIL-S-13165C
  • ABP 1-2028
  • MIL-P 81985(AS)
  • MIL-STD-852
  • P11TF3

Related Articles & Brochures

Additional Applications Using the Controlled Shot Peening Process

Controlled shot peening can also change the shape of a component (i.e. form the curvature in wing skins) and increase resistance to flexural bending fatigue.
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Robotic Peening

Robotic Peening

CWST offers robotic peening to meet the most stringent specifications. Robotic peening offers improved reliability and increased efficiency over previous generations of peening equipment.

C.A.S.E is the combination of shot peening followed by chemically assisted super finishing. Common applications are gears, shafts and air foil geometry. Surfaces are smoothed to a mirror like finish and valleys are left for lubricant retention.
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CWST’s shot peening with different media choices is able to provide a variety of repeatable architectural surface finishes. A Peentex finish creates a visually pleasing long lasting surface.
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