Patent ID: 9623475
Date: 2017-04-18
CPC Classifications: B21D,B21F,C21D,F27D,H05B,Y10T

Claim:
1. A method of producing a coil spring, the method comprising: a forming step of forming a spring steel material into a shape of a coil spring; a first clamping step of clamping one end of the spring steel material formed into the shape of the coil spring by a first electrode; a second clamping step of clamping the other end of the spring steel material formed into the shape of the coil spring by a second electrode; and a heat treatment step of eliminating a machining strain generated in the spring steel material by the forming step by electrically heating the spring steel material by applying a current from the first electrode to the second electrode via the spring steel material, and allowing the first electrode to move in an axial direction of the shape of the coil spring and to rotate around an axis of the shape of the coil spring with respect to the second electrode clamping the other end of the spring steel material during the heat treatment step to thereby eliminate the machining strain; wherein the heat treatment step comprises a first step of heating the spring steel material to a predetermined set temperature, and a second step of keeping the spring steel material at the set temperature for a predetermined set time period subsequent to the first step, the set temperature is set to be higher than 430° C. but not higher than 500° C.