| 摘要 |
PURPOSE: To efficiently provide working on projected part in short time by attaching, at the tip end of an air hammer and the like, a tool which is conically reamed at a specific angle in the opening degree, imparting an impact load to the tip end of the necking part and thereby forming a projected burr at the tip end. CONSTITUTION: In that working method of the tip end projected part in the neck which is a preprocess for cold drawing of a tube 1 or a bar, a tool 3 which is conically reamed at an opening degree of 120 deg.±10 deg. is attached to the tip end of an air hammer and the like so as to impart an impact load to the tip end of the neck part 2; and a projected burr 4 is formed at the tip end of the neck part 2. Consequently, without accompanying the extension of cycle time for neck working, the projected burr 4 is formed, of which height is 1mm or more enabling cold drawing, at the tip end of the neck part quickly and surely, thereby improving the yield through the reduction in the neck length in cold drawing. Thus, the tool for imparting an impact load to the tip end of the neck part is selectively used by means of the outer diameter size of the neck, enabling the formation of the projected part.
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