PURPOSE: To improve the forming accuracy by reducing gradually the pressing force of a rolling reduction roll corresponding to the expansion of a product diameter at forming time of an annular blank and setting the pressing force slightly enabling the elongation forming just before the completion of forming.
CONSTITUTION: The driving roll 10 borne by a stationary bearing 5 and mobile bearing 6 is provided on the device main body 4 and the rolling reduction roll 20 vertically moving by a rolling reduction cylinder 22 and borne by bearings 24, 26 is arranged as well. An annular product outer diameter detecting device 30 is arranged at the lower pat of the device 4. In this mechanism, the pressing force of the rolling reduction roll 20 is set in plural stages and the forming is performed with confirming the outer diameter on each set pressure at the respective stage. At the stage just before the forming completion the roll 20 is controlled with the pressure of overcoming the deformation resistance of the blank. Since the effect of the variance in the hardness of the blank material is removed by this method, the forming accuracy of the product is improved.
YAMAMOTO HAKOBU
SUGIYAMA KEIICHI
SAKUMA YASUO
NIIGATA NIKKEI KOEI KK
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