A Study on the Free State of Contact-Type Spiral Springs

Abstract

There are two types of contact-type spiral springs: a spring without a primary winding in which the free state has a spiral shape and an S-shaped spring in which the free state has an S-shape. In order to accurately predict the torque characteristics of these springs, it is essential to estimate the free state by highly accurate elastic-plastic analysis. However, it is difficult to create a highly accurate material model because the amount of change in strain varies from the inner end to the outer end of the spring. It is also necessary to consider the effects of the primary winding process and the heat treatment process. In this paper, we first clarify the elastic-plastic deformation behavior of contact-type spiral springs during winding. For contact-type spiral springs with various dimensions or different primary windings, the deformation during winding was collected as the curvature during winding and the curvature in the free state after winding. These data are converted from curvature to surface strain to make non-dimensional parameter, and then organized considering the initial curvature derived from the primary winding of S-shaped spring. As a result, it was found that the elastic-plastic deformation in winding can be comprehensively expressed without depending on the type of spring.