| 摘要 |
A manufacturing method of a yoke for a universal joint by using first and second molds, a central mold, and divided molds is provided to be able to improve reliability of a product while reducing the machining speed of a workpiece. A manufacturing method of a yoke for a universal joint comprises a cold forging step of forming a circular rod-shaped part workpiece into a forged workpiece through cold forging, and a detailed machining step of forming the forged workpiece into a yoke for a universal joint as a final finished product through cutting and heat treatment. The cold forging step includes a first process of cold forging a first end portion to form a preformed workpiece on one end of the part workpiece, and a second process of cold forging a second end portion to form the forged workpiece on the other end of the preformed workpiece. The second process is performed by pressing the respective molds in a state that the preformed workpiece is positioned between a pair of first and second molds(30,40) having forming spaces(30a,40a) in which shapes of the first and second end portion sides of the forged workpiece are engraved. The second mold includes at least two divided molds(43,46) which can be dividingly operated with each other in the radius direction such that the second end portion is capable of being withdrawn from the forming space of the second mold in a state that the second end portion is formed. The second mold includes a central mold(41) and the divided molds such that the second forming space is formed between the central mold and the divided molds. |
