| 摘要 |
PURPOSE:To produce a leg member with a decreased welding part by a method wherein, after a square steel lump is placed in a container having a part corresponding to a cord, expanded in a semicircle, a mandrel bar is buried in the central part of the steel lump to bore a hole. CONSTITUTION:A steel lump 20, heated to about 1,000-1,100 deg.C, is contained in a container 21. A mandrel bar is buried in the steel lump 20 to bore a hole, and simultaneously, expansion is effected. The steel lump 20 is expanded to a semicircular non-constraint part 24 of a part 23 corresponding to a cord part to form it into a coarse shaped-material. After the material is heated to about 1,000-1,100 deg.C to extrusion-mold it, hardening and tempering are effected. Further, the material is fused to form a rack tooth profile in a rack part. |
