Material requirements for canted coil springs

A canted coil spring is a mechanical part that works by elasticity: it deforms under load and returns to its original shape when the load is removed. Canted coil springs come in several forms, including helical, spiral, plate and special-shaped versions, and are generally made from spring steel. The choice of material decides how well the spring resists fatigue, stress relaxation and forming defects.

High strength

To resist fatigue damage and stress relaxation, the spring material should have a high yield strength and a high elastic limit, and in particular a high yield ratio. Because the elastic limit of a material is roughly proportional to its yield strength, designers and manufacturers aim for a material with the highest practical yield strength.

Good plasticity and toughness

The material is deformed during forming, so it must have enough plasticity to be worked. Complex tension and torsion springs form hook loops and torsion arms at small bend radii; during winding or stamping-and-bending the material must not crack or show other defects.

Where the spring is subject to shock or variable loading, the material must also be tough, which directly improves the service life of the part.

Surface quality and fatigue performance

Fatigue damage normally starts at the surface of the wire, where service stresses are highest. Canted coil springs for demanding applications such as valve and suspension springs must survive millions or tens of millions of cycles, placing a high demand on fatigue performance. Fatigue is influenced by chemical composition, hardness, steel purity, surface quality and metallographic structure, and surface quality is especially important.

Dimensional accuracy

Many springs must hold tight load tolerances. The load deviation of a valve spring, for example, must not exceed 5-6% of the specified load. For a round-wire tension or compression spring, a 1% deviation in wire diameter produces roughly a 4% deviation in load, so strict dimensional control is essential to spring quality.

Material uniformity

Spring wire must be uniform and stable in chemical composition, mechanical properties and dimensional deviation. Inconsistent material makes the spring difficult to produce to specification and causes scatter in product geometry, hardness and load, in severe cases producing scrap.