How does the process of 'Presetting' (or 'Scragging') improve wave spring performance?

Presetting involves compressing the wave spring to its solid height during manufacturing. This process induces beneficial residual compressive stresses on the inner surfaces of the waves where the highest tensile stresses occur during operation. This shifts the mean stress downward on the Goodman diagram, significantly improving fatigue life. Mathematically, it allows the spring to operate at higher nominal loads because the initial 'set' is taken in a controlled environment, ensuring the spring height $H$ remains stable during its service life in the field.