Compression Springs and Conical Springs are sometimes preset. Sometimes springs designed to be over-stressed and when deflected, do not return to their original free length. These types of springs are said to have reached a point of deflection beyond their elastic limit. Another term for this is “taking a set”.
Some compression springs are designed to take a set which reduces stress and the chance of breakage. Springs may also be preset to ensure loads are met after the initial deflection.
Highly stressed springs are typically designed to be used in an environment where the spring will travel a short distance. Compressing these types of springs to solid should be avoided as this may cause the spring to not be functional.
It’s more cost-effective for a customer to preset their own springs during assembly whenever possible to avoid additional labor costs incurred by a spring company presetting the springs.