| 摘要 |
PROBLEM TO BE SOLVED: To provide a cemented carbide twist drill capable of drilling a hole having a small diameter ofϕ0.5-3.5 mm and a depth 5-10 times the diameter in a steel product having shock-resistant tough structure inside and a high carbon layer having high hardness and applied with carburizing and quenching to a surface and preventing its chipping and chipping of a cutting edge in a short time even when the drill enters the shock-resistant tough structure inside while maintaining wear resistance to the high carbon layer having high hardness. SOLUTION: A twist angleγof the drill is set to a small angle of 13°-17°to maintain its strength, and web thickness W of a groove part is set to a small thickness being 0.30-0.37 times the diameter of the drill to reduce resistance in cutting, discharge chips smoothly, and prevent weld-deposition. An angleθof a second cutting edge formed by the second cutting edge to a first cutting edge being a main cutting edge is set to 143-148°to prevent chipping of the cutting edge in the high carbon layer having high hardness on the surface of the steel product and prevent weld-deposition of chips in the shock-resistant tough structure inside. In addition, web taper WT is set to -0.05 to -0.40 mm/100 to discharge chips smoothly and satisfactorily. COPYRIGHT: (C)2008,JPO&INPIT
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