| 摘要 |
PURPOSE:To improve a yield of a raw material and to reduce machinings by forming an outside surface of an annular die groove to be vertical and forming an inner diameter of a lower end side larger than that of an upper end side at an inside surface, further by forming the center relief of upper die to be a reversely tapered cavity. CONSTITUTION:The upper die 40 is formed conically of its bottom surface 41 and in its center, the reversely tapered cavity 42 of expanded inner space is provided. An annular sintered alloy body 50 is inserted into the annular die groove 10 to ascend the die 20 and the lower die 30 and a projection 34 of the lower die is inserted into the hollow 42 of the upper die. The upper die 40 is rotated swingingly and at its lower surface 41, the upper surface of the alloy 50 is locally pressed uniformly to the cold forged. After the forge is finished, the die 20 and the lower die 30 are lowered to detach the alloy body 50 from the upper die 40, then the lower die 30 is ascended to pull out the alloy body 50 from the die 20. As the surface of outer periphery is released, so the alloy body 50 is slightly expanded by its spring back and its outside diameter becomes larger than the inside diameter of the die 20. In this way, the alloy body 50 is forged to form equal to a finished product or nearly equal to it, and to eliminate the machining after the forging.
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