| 摘要 |
PURPOSE:To improve the accuracy of a fine hole diameter by roughening the roll surface of multi-stages roller dies to specified roughness and drawing a metallic pipe under the specified back tension exerted thereto. CONSTITUTION:A drawing drum 6 is disposed before the multi-stages roller dies 5 and the metallic pipe 1 is drawn by the drum 6. The outside peripheral surfaces (roll surfaces) of the rollers of the dies 5 are roughened by using diamond wheels and back tension of the specified magnitude is exerted to the pipe 1 prior to entry to the dies 5 by a pinioning device 3. The pipe 1 is surely gripped by the above-mentioned method and therefore the decrease in the wall thickness (t) of a part 18 to be deformed by the roller tops is decreased. The mis-alignment of the pipe 1 is further prevented by the back tension and therefore the formation of the hole having the extremely small diameter is made possible with high accuracy.
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