Answer
Wave springs are typically manufactured by coiling edge-wound flat wire. The grain structure of the cold-rolled strip is oriented along the length of the wire. When the spring is compressed, the maximum tensile stresses are perpendicular to the grain flow. If the material has significant non-metallic inclusions or 'stringers' oriented along the grain, these can act as nucleation sites for fatigue cracks. Using 'Smarter' or 'Vacuum Melted' steels (like VIM-VAR) ensures a cleaner microstructure with fewer inclusions. Additionally, the edge-winding process ensures that the 'rolled' edges are on the OD and ID, which are the neutral axes in the primary bending mode, thereby reducing the risk of edge-initiated failure compared to stamped wave washers.
