Study on Imposing Initial Tension during Coiling Helical Tensile Springs

The tension spring with initial tension is a coil spring with unique properties not found in other springs. It is often used to eliminate backlash, compensate for wear or thermal expansion, and hold parts in contact. While such tension springs have wide industrial applications, the academic literature on their properties and manufacturing is limited. Therefore, this study focuses on the computer numerical control (CNC) coiling machines commonly used to produce coil springs, and explores their process principles and the effects of settings on the geometry and initial tension of the springs through finite element analysis and experimental validation. As a result, the spring diameter can be controlled by adjusting the rake angle of the coiling pin and the distance to the mandrel wire feed opening using an empirical formula derived in this study to determine the parameters associated with a desired diameter. The plane of inclination applied to the mandrel is only used to initially deflect the wire when forming the first spring coil, without significantly affecting the initial stress. On the other hand, the transverse displacement of the mandrel is positively correlated with the pitch of the open compression spring and the initial tension of the tightly wound extension spring.