| 摘要 |
PURPOSE:To form a long crank arm by obtaining an intermediate formed part by forming an arm part, etc. having a suitable excess thickness from a billet in a metallic die, and subsequently, cogging the arm part to a prescribed size, through a holding plate. CONSTITUTION:A billet is inserted into a space of a metallic die constituted of an outer die and a lower die, a journal peripheral part is formed by pressure of a plunger punch, and also a crank pin and its peripheral part are formed through a holding plate. In this case, a thickness t1 of an arm part of an obtained intermediate formed part has a suitable excess thickness against the final shape size, and also its width is formed so as to be smaller by a suitable quantity than the final size. Subsequently, a tool 23 having a prescribed thickness t2 is inserted between the arms of the intermediate formed part 22, it is cogged to a prescribed size through a limit base 30 between upper and lower anvils 26, 24, and a formed part of the final forged shape is obtained. According to this method, the capacity shortage of a forming machine is dissolved, and a long crank arm can be formed.
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