The impact of strong compression on springs

Permanent deformation of a spring occurs when an external force exceeds the spring+s elastic limit, resulting in a rebound height lower than the original height or a deformation exceeding 0.6 mm. After permanent deformation takes place, the spring’s elastic force and stiffness will also change. Therefore, to obtain springs with qualified performance, designers sometimes specify taller spring dimensions on design drawings. After production, the springs undergo heavy compression treatment to induce controlled permanent deformation and adjust their dimensions to meet the required specifications.

However, improving a spring’s load-bearing capacity via heavy compression (tension, torsion) treatment is subject to prerequisites. During heavy compression, beneficial residual stresses can only form on the spring’s surface material; these residual stresses interact with heavy working loads. Moreover, the residual stresses and substantial plastic deformation generated in spring materials during heavy compression (tension, torsion) can raise the material’s elastic limit. Nevertheless, every material has a finite elastic limit. Once this threshold is surpassed, the material will not only undergo plastic deformation but also full yielding deformation. For most spring materials, full yielding deformation occurs under heavy compression at 0.5σb (tensile strength).

Yield limits vary across different materials, and their values can only be confirmed through strength calculations and testing. Additionally, the effectiveness of heavy compression (tension, torsion) treatment is closely tied to the spring’s geometry, structure, and the specific heavy forming process employed. In terms of spring geometry, springs with a large spring index or a small helix lead angle cannot have their load-bearing capacity enhanced through heavy compression. The target ranges for spring index and helix lead angle that allow effective heavy compression must be determined through dedicated heavy compression design and testing. Simply compressing, stretching or twisting a spring cannot guarantee an immediate increase in its load capacity.

Except for high-stress springs, ordinary compression, tension and torsion springs lack the necessary conditions to benefit from heavy compression (tension, torsion) treatment, though dimensional compliance can still be achieved via the "preliminary oversize forming" process. Taking compression and torsion springs as examples, applying heavy loads to springs with pre-set preliminary overheight and pre-set preliminary overangles serves two purposes: first, to introduce targeted compression and torsional deformation into the springs; second, to adjust the spring’s height or angle after heavy forming to precisely match design requirements.

Our recommendations regarding spring heavy compression treatment are as follows:
1. When considering heavy compression treatment for springs, dedicated heavy compression design shall be carried out first to verify whether the spring is suitable for such treatment.
2. For compression and torsion springs operating under high-stress conditions, heavy compression treatment can significantly enhance their mechanical properties.
3. For tension springs requiring initial tension, heavy tension forming will reduce or even eliminate the initial tension; such springs must not undergo heavy tension treatment. For tension springs without initial tension requirements, it is difficult to boost their load-bearing capacity via heavy tension forming.
4. Springs that operate at high temperatures (above 60°C) or in corrosive environments and receive heavy compression treatment will only achieve dimensional stabilization, with no improvement in load-bearing capacity.
5. Heavy compression treatment shall not be used to increase the load-bearing capacity of springs with various stiffness grades.