Shot peening is a method to improve the operating life of your spring by creating beneficial compressive residual stress. We are able to shot peen a spring with wire diameters ranging from 0.010 inches up to 3.5 inches. Shot peening can increase the operating life by 5 to 10 times more when compared to un-peened spring.
How it works:
Shot peening is a cold working process in which small spheres called shot to bombard the surface of your spring at high velocity under controlled conditions. This creates compressive residual stress which delays the initiation of fatigue cracking and strengthens your spring thus improving the fatigue life of your spring.
Benefits of Shot Peening:
- Increases fatigue strength and fatigue life
- Delays fatigue crack initiation at the wire surface
- Reduces susceptibility to stress corrosion cracking
- Reduces susceptibility to hydrogen-assisted cracking
Shot peening is not a corrosion barrier. Where the spring is exposed to moisture, salt, or chemicals, specify a protective finish such as powder coating or a phosphate conversion coating alongside peening.
Contact us for more information on shot peening and prices.
Spring Shot Peening Services FAQs
What is shot peening and what does it do to a spring?
Shot peening is a cold working process in which small spheres called shot bombard the surface of your spring at high velocity under controlled conditions. Each impact plastically deforms a small volume of the surface, and the surrounding material holds that volume in compression once the shot has moved on. The result is a compressive residual stress layer that delays the initiation of fatigue cracking and strengthens the spring. Nothing is added to the part and no material is removed. The entire improvement comes from the stress state left behind in the surface layer.
How much fatigue life does shot peening add?
Shot peening can increase operating life by 5 to 10 times compared with an un-peened spring. The mechanism explains the size of that gain. Fatigue cracks in springs start at the surface, where torsional stress is highest, and a crack cannot open under a compressive field. Peening does not raise the tensile strength of the material. It changes the stress a crack initiation site actually experiences, subtracting the compressive residual stress from the applied tensile stress. The benefit is therefore largest on parts cycling at high stress and smallest on springs that sit essentially static.
What wire sizes can Coiling Technologies shot peen?
Wire diameters from 0.010 inches up to 3.5 inches. The upper end covers the heavy-duty and large compression spring work where peening pays off most, since a large suspension or die spring runs at high stress and is expensive to replace once installed. The lower end means small precision springs are not excluded from the process. That range also reaches above the 2.5 inch material diameter limit for cold coiling, so peening is not the constraint on large spring work. Give the wire diameter with your cycle life requirement when you request a quote.
What parameters control shot peening quality?
Two, and both belong on the drawing if peening matters to your design. Intensity is the energy delivered to the surface, measured with Almen strips: a standard steel coupon peened alongside the part arcs by an amount that correlates with the depth and magnitude of the compressive layer. Coverage is the percentage of surface actually impacted, and under-coverage leaves unprotected initiation sites behind. Shot size, hardness and condition matter as well, since broken shot cuts the surface rather than deforming it. If your specification names an intensity and coverage, state them at the quote stage.
Why is peening standard practice on suspension and high cycle springs?
Suspension springs cycle continuously at high stress for the life of the vehicle, so their duty is fatigue limited rather than load limited. Designing without peening means either accepting shorter life or moving to heavier wire and a larger envelope to bring stress down, which adds weight and cost. Peening buys the fatigue margin instead. The same logic applies to valve springs, die springs and any part carrying a high cycle count in the specification. Coiling Technologies works extensively in vehicle suspensions and military suspension springs, where peened compression springs are the normal expectation.
When is shot peening not the right answer?
Peening addresses fatigue crack initiation at the surface. It will not rescue a spring that is overstressed at solid height, one designed with too few active coils, or one that takes a permanent set the first time it is compressed. Those are design problems, and no surface treatment covers them. Peening is also not a corrosion barrier the way a coating is, though the compressive layer does reduce susceptibility to stress corrosion cracking and hydrogen-assisted cracking, both of which need surface tension to propagate. A spring facing genuine corrosive exposure needs peening and a coating, in that order.
