US 12,135,068 B2
Hollow spring and method of manufacturing the same
Hironobu Sayama, Ichihara (JP); and Toru Hirokane, Ichihara (JP)
Assigned to MITSUBISHI STEEL MFG. CO., LTD., Tokyo (JP)
Appl. No. 17/618,160
Filed by MITSUBISHI STEEL MFG. CO., LTD., Tokyo (JP)
PCT Filed May 15, 2020, PCT No. PCT/JP2020/019498
§ 371(c)(1), (2) Date Dec. 10, 2021,
PCT Pub. No. WO2021/229808, PCT Pub. Date Nov. 18, 2021.
Prior Publication US 2022/0170524 A1, Jun. 2, 2022
Int. Cl. F16F 1/14 (2006.01); B60G 21/055 (2006.01); C21D 9/02 (2006.01); F16F 1/02 (2006.01); C21D 9/08 (2006.01)
CPC F16F 1/14 (2013.01) [B60G 21/055 (2013.01); C21D 9/02 (2013.01); F16F 1/025 (2013.01); F16F 1/145 (2013.01); B60G 2202/135 (2013.01); B60G 2206/012 (2013.01); B60G 2206/427 (2013.01); B60G 2206/724 (2013.01); B60G 2206/81 (2013.01); C21D 9/08 (2013.01); F16F 2224/0208 (2013.01); F16F 2226/04 (2013.01); F16F 2228/08 (2013.01); F16F 2238/024 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A method of manufacturing a hollow spring, comprising:
providing a steel tube processed by bending to a predetermined shape used for the hollow spring; and
applying compressive force to at least a portion of an outer surface of the steel tube, including a portion processed by bending, from a circumferential direction to apply compressive residual stress to at least a portion of an inner surface of the steel tube; wherein
applying the compressive force to the outer surface of the steel tube comprises pressing the steel tube with a die,
the die comprises a pressing surface shaped such that the compressive force can be applied to the at least the portion of the outer surface of the steel tube, including the portion processed by bending, from the circumferential direction,
the pressing surface extends in the circumferential direction along the outer surface of the steel tube,
the pressing surface extends in the circumferential direction of the steel tube over a half of a circumference, and
a fatigue life of the steel tube is prolonged by applying the compressive residual stress to the inner surface of the steel tube.