Answer
Standard coiled compression springs use round wire, whereas premium wave springs utilize flat wire rolled precisely from high-quality round wire.
Engineering Merits of Flat Wire Rolling:
1. Uniform Cross-Section: Precision rolling mills control the width-to-thickness ratio with tolerances tighter than $\pm 0.005\text{ mm}$. Any variation in material thickness ($t$) has a cubic effect ($t^3$) on the spring rate ($k$);
$$\Delta k \approx 3 \cdot \frac{\Delta t}{t}$$
Therefore, absolute thickness consistency is paramount.
2. Grain Orientation: Rolling aligns the metal grain structure along the longitudinal axis of the flat wire, maximizing the active tensile and compressive stresses the wire can handle when coiled into waves.
3. No Dynamic Twist: The rectangular cross-section prevents the wire from twisting out-of-plane during coiling, ensuring the wave crests remain perfectly parallel to the mating surfaces, maintaining uniform axial loading.
