Shot Peening: Ensuring high spring quality

Categories: Company News, News, Springtelligence|646 words|3.2 min read|By |Published On: March 23rd, 2021|

In this series of blog posts, we will look at how to reduce the net stress on springs through quality manufacturing. In this post, we delve into how shot peening achieves this.

This process traces back to its use in the automobile industry in the late 1920s. It is still widely used today in aerospace and automotive high performance component production.

What is Shot Peening?

Shot peening is the cold working process of firing spherical pellets at the surface of a spring material at high speed, to induce plastic deformation. This modifies the mechanical characteristics of the metal’s surface, through inducing residual compressive stresses and work-hardening the spring surface.

Plastic deformation is the ‘permanent deformation or change in shape of a solid body without fracture under the action of a sustained force’.


The number, size and composition of the shots, as well as the size of the exposure area, impact the coverage of shot peening. The coverage is the indented surface area percentage due to the process. This coverage (sometimes referred to as intensity) of shot peening is measured using Almen strips – made from SAE 1070 steel – and Almen Testing.

The Almen test often occurs prior to the process. This involves a thin, test strip of the material undergoing the intended conditions. The strip bends due to residual compressive stress (RCS) causing deflection. The largest amount of Almen strip deflection is the value of the arc height.

How Does Shot Peening Act as Stress Relief?

The most important benefit of shot peening springs is the production of residual compressive stresses (RCS). Net stress on a spring surface is the applied stress minus residual compressive stresses; therefore, the process is stress relieving due to the reduced net stress.

The second benefit is work hardening the surface, which increases the time before fatigue cracks onset. This has the potential to increase a spring’s lifespan by millions of cycles. Though this is significantly less important than the gaining of RCS.

As an example, compression springs made from carbon steel (EN10270-1 DH) operating between corrected stresses of 104 and 727 MPa would be at risk of fatigue failure soon after 100,000 cycles. However, after shot peening the springs the predicted life would be more than 10 million cycles.

The Institute of Spring Technology’s (IST) Goodman Diagrams below illustrate the predicted performance of a compression spring with and without shot peening:

The predicted performance of a compression spring with and without shot peening

In summary, shot peening spring materials creates compressive residual stress. This, in turn, defers the occurrence of cracking, due to fatigue, within the spring surface.

To discover more about shot peening, visit Spring Expert, Mark Hayes’ in-depth article. For best spring practices, browse our blogs and webpages, including others in this series:

Ensuring High Spring Quality Through Best Manufacturing Practices: Prestressing

Ensuring High Spring Quality Through Best Manufacturing Practices: Heat Treatment

Alternatively, to request a quote or advice about a specific spring query, please complete the enquiry form on our Contact Page.