|By Prof S S Chauhan, IEC College of Engineering & Technology, Greater Noida|
Design of Helical Springs
A helical spring is a spiral wound wire with a constant coil diameter and uniform pitch. The most common form of helical spring is the compression spring but tension springs are also widely used. Helical springs are generally made from round wire. It is comparatively rare for springs to be made from square or rectangular sections. The strength of the steel used is one of the most important criteria to consider in designing springs. Most helical springs are mass produced by specialist’s organizations. It is not recommended that springs are made specifically for applications if off-the-shelf springs can be obtained to the job.
The design of a new spring involves the following considerations:
Space into which the spring must fit and operate.
Values of working forces and deflections
Accuracy and reliability needed.
Tolerances and permissible variations in specifications.
Environmental conditions such as temperature, presence of a corrosive atmosphere.
Cost and qualities needed.
The designers use these factors to select a material and specify suitable values for the wire size, the number of turns, the coil diameter and the free length, type of ends and the spring rate needed to satisfy working force deflection requirements. The primary design constraints are that the wire size should be commercially available and that the stress at the solid length be no longer greater than the tensional yield strength. Further functioning of the spring should be stable.