| 摘要 |
PROBLEM TO BE SOLVED: To apply a drill for drilling a metal for a titanium alloy being low in thermal conduction, prevent the generation of a plastic fluidized bed and a white layer by which reduction of a material life is caused, and a tool life is also increased. SOLUTION: A tip part blade 2 of a drill body 1 is formed to keep a slight gap 4 between a drill diameter and a tip blade size, and margin parts 3 making contact with a drill diameter at a P point are formed on both sides. The margin part 3 is formed such that a width L of a conventional step-form margin part is notched at an angle (θ=1-2 degree) by a taper-form notch part 5. A role of the margin part is (1) a guide of a tool and (2) burnishing of a machined surface. In (2), a friction heat is generated and an internal part is filled with heat, a plastic fluidized bed layer and a white layer are generated at a machined surface, and a material life is decreased. Since a width L of a conventional margin part is removed, the influence of friction is eliminated, and a tool life is increased.
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