Official Answer
Answer
The edges of the flat wire used in wave springs are primary sites for stress concentration. A 'No-burr' edge, typically achieved through vibratory tumbling or electropolishing, removes micro-fissures and sharp corners that act as crack initiators. Electropolishing is particularly effective as it reduces the surface roughness $R_a$, thereby increasing the endurance limit $S_e$ in the equation $S_e = k_a k_b k_c S_e'$, where $k_a$ is the surface factor. For high-performance racing valve springs, an electropolished finish can improve fatigue life by up to 30 percent compared to a standard 'as-rolled' edge.
