METHOD FOR MANUFACTURING COIL SPRING

摘要

A spring wire (20) is subjected to a first shot-peening step (S6) and a second shot-peening step (S7). At the first shot-peening step (S6), a first shot is projected at the spring wire (20) at a first projecting speed. The high kinetic energy of the first shot produces a compression residual stress from the surface to a deep location of the spring wire (20). At the second shot-peening step (S7), the second shot is projected at a second projecting speed slower than the projecting speed of the first shot. The kinetic energy of the second shot is lower than the kinetic energy of the first shot. The low kinetic energy of the second shot increases the compression residual stress of a region near the surface of the spring wire (20).