An innovative tapered-rod forming process with high dimensional accuracy, nearly 100% yield, and a high production rate (1rod/20-25sec) has been developed. Temperature-dependancy 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 axial temperature distribution. An experimental-scale prototype continuous production system has been set up. Tapered rods manufactured by the system have been tested with regard to properties of a processed segment itself, and to properties of a tapered-rod coil spring as a final product.
Results are;
1. Tensile properties and fatigue strength after heat treatment are not altered by processing (i.e., heating followed by tensile deformation).
2. Coil springs made from tapered rods manufactured by the new process and by the conventional turning method have the same spring properties, fatigue properties, and load-loss resistance.
