COMPRESSION COIL SPRING, AND COIL SPRING MANUFACTURING DEVICE AND MANUFACTURING METHOD

摘要

By winding a material for a coil spring around a cored bar at a temperature at which springback occurs, bending deformation exceeding yield stress is applied thereto. Simultaneously with the application of the bending deformation, coiling is performed, and a load is removed after the coiling. The spring comprises an outside surface region (W3) having compressive residual stress and a compressive stress decrease region (W4) in which the compressive residual stress decreases from the outside surface region (W3) toward the center of the material. A stress change portion (P1) in which a change from the compressive residual stress to tensile residual stress occurs is present between the outside surface region (W3) and the center of the material. The spring includes a tensile stress peak portion (P2), a tensile stress decrease region (W5), and an inside surface region (W6). The inside surface region (W6) has the tensile residual stress or compressive residual stress having an absolute value smaller than that of the outside surface region (W3).