New Tapered-Rod Forming Process for Coil Springs

An innovative tapered-rod forming process with high dimensional accuracy, nearly 100 % yield, and a high production rate (1 rod/20 sec) has been developed. Temperature-dependency of the material’s flow stress is utilized as a working principle; a rod with arbitrary taper can be formed by rapid pulling of a bar with precisely controlled longitudinal temperature distribution. Tapered rods manufactured by the new process and by the turning method have been confirmed to have the same spring properties, fatigue properties, and load-loss resistance as tapered-rod coil springs.