Method of manufacturing a suspension coil spring

A method of manufacturing a suspension coil spring, the suspension coil spring including a lower end turn portion which is less than one turn from a lower end of a wire formed into a helical shape, and an upper end turn portion which is less than one turn from an upper end of the wire, the method comprising:

• a primary shot peening step comprising forming first shot peening indentations on a surface of the wire by projecting first shots toward the wire and forming a compressive residual stress portion to which a compressive residual stress is imparted from the surface of the wire to a first depth;
• and
• an ultrasonic shot peening step performed after the primary shot peening step, the ultrasonic shot peening step comprising:
• projecting ball shots as second shots toward the lower end turn portion by an ultrasonic apparatus, wherein a size of each of the ball shots is larger than a size of each of the first shots, and
• forming, by the projection of the ball shots, second shot peening indentations on a surface of the lower end turn portion, and a deep residual stress portion in the lower end turn portion, a compressive residual stress of the deep residual stress portion being imparted from the surface of the wire to a second depth that is deeper than the first depth.