New Tapered-Rod Forming Process for Coil Springs

Abstract

A new tapered-rod forming process has been developed and an experimental-scale prototype continuous production system has been set up. In this process, temperature-dependency and strain-rate-dependency of the material's flow stress are utilized as a working principle. That is, a rod with arbitrary taper can be formed by rapid pulling of a bar with precisely controlled longitudinal temperature distribution. This process satisfies some important industrial requirements such as high dimensional accuracy, nearly 100% yield, high production rate (1rod/20-25sec), and low total energy consumption.
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.
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 loadloss resistance.