| 摘要 |
PURPOSE:To form a groove having closed both ends on inner peripheral face of a cylindrical material by inserting a mandrel to which a die piece for forming groove is fitted detachably and after reducing the cylindrical material, pulling out only the mandrel. CONSTITUTION:The die piece 4 for forming groove is fitted in the groove of the mandrel 3 detachably, and the mandrel is inserted into the cylindrical blank 6 having slightly larger inner diameter. After positioning the die piece 4 for forming groove, the cylindrical blank 6 is passed through a die 7, moved in axial direction and reduced and pressed by drawing. By this way, inner peripheral face of the cylindrical blank 6 is pressed to outer peripheral face of the mandrel 3, and groove forming member 4B of the die piece 4 is pressed in the inner peripheral face of the cylindrical blank 6 to form a groove 2 having closed both ends. When the mandrel 3 is pulled out, the die piece 4 remains fitting to the formed groove 2 having closed both ends. After pulling out the mandrel 3, the die piece 4 is taken out from inner peripheral face of the cylindrical blank 6. Thus, forming of a groove 2 having closed both ends is completed.
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