| 摘要 |
PROBLEM TO BE SOLVED: To show high toughness up to torque of a fixed limit not nearly twisting and to impart a twisting characteristic easily twisting beyond the limit by using a metal drawn wire having round cross section and forming a prescribed diameter only with cold forging. SOLUTION: When producing an energy absorption shaft for a retractor of a sheet belt, a wire rod of JIS-SWCH8R, in which a large diameter stock is made to wire diameter of 9.2 mm by several cold drawings, is used for a stock. The stock is cut to a prescribed length, subjecting to five-time forging by a multiple forging machine, enlarging a diameter D2 of a shaft part g1 to 9.5 mm, forming engaging parts g2, g3 of hexagon at both ends and a small diameter shaft part g4 extending from the engaging part g3. By this method, a high hardness layer having hardness higher than the inside and a prescribed thickness is formed on a shaft part g1 surface, twisting is hardly generated to the shaft part g1 up to torque of 5.8 kgf-mm, when exceeding, the twisting of a whole shaft is made easy with breaking the surface high hardness layer. |
