Manufacturing Method for Coil Spring

Author:  NHK Spring Co., Ltd.
Source:  US Patent 8,607,605
Doc ID:  2013048
Year of Publication:  2013
Abstract:  
A spring wire is subjected to a first shot peening process and a second shot peening process. In the first shot peening process, a first shot is projected on the spring wire at a first projectile speed. High kinetic energy of the first shot produces compressive residual stress in a region ranging from the surface of the spring wire to a deep position. In the second spring wire process, a second shot is projected at a second projectile speed lower than the speed of the first shot . The kinetic energy of the second shot is lower than that of the first shot. The low kinetic energy of the second shot increases the compressive residual stress in a region near the surface of the spring wire.