Explain the role of stress relieving in the manufacturing of multi-turn wave springs.

After the coiling process, multi-turn wave springs contain significant residual stresses from the cold-forming of the waves and the helix. Stress relieving, typically performed at temperatures between $315^\circ C$ and $480^\circ C$ for stainless steels, allows for the redistribution of these internal stresses. This stabilization prevents 'growth' or 'shrinkage' of the spring dimensions during service and improves fatigue life by reducing the peak internal tension. For precision medical implants, vacuum stress relieving is used to ensure no oxidation layer forms on the surface.