| 摘要 |
PURPOSE:To improve drilling performance by giving more bending strength and more rigidity to a cemented carbide material while making the best use of the materials's advantages. CONSTITUTION:The drill 5 made of cemented carbide is given a web thickness corresponding to 25-35% of the drill diameter to improve its ridigity for wretching, as well as to facilitate discharge of chips. The groove width ratio is designed to be in a range of 0.4-0.8: 1 so as to improve curling or cutting of the chips. The shape of the lip end view is formed by straight or curve lines so as to make the radial rake angle by -5- positive degrees in its outer peripheral region including at least 2/3 of the drill diameter. Thus, the cutting resistance l2 between the lip 1 and the opposite groove wall is redued so that the chips can be discharged only by the groove holes. |
