| 摘要 |
PURPOSE:To reduce the forging cost by executing a closed preforging by spare upper and lower dies, and subsequently, executing a bulge forging by the lower die having the first and the second flange part cavities, and the upper die provided with the corresponding first and second pressure part. CONSTITUTION:An axial part cavity 10 and a flange part cavity 11 having a narrow flange width are provided on a spare lower die 1 and a closed preforging is executed between said lower die and a spare upper die 2. Subsequently, a bulge forging is executed to a preforged part by a forging lower die 4 having the first flange part cavity 41 being thinner than thickness of a non-circular flange and the second flange part cavity 42 which has bulged to its upper part, and a forging upper die 5 provided with corresponding pressure parts 50, 51. According to this method, generation of a burr on a spotting surface can be suppressed, therefore, the yield of a material is improved. Accordingly, the forging cost can be reduced.
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