JP4120185B2

JP4120185B2 - Drill

Info

Publication number: JP4120185B2
Application number: JP2001209585A
Authority: JP
Inventors: 一也柳田; 武井上
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2001-07-10
Filing date: 2001-07-10
Publication date: 2008-07-16
Anticipated expiration: 2021-07-10
Also published as: JP2003025125A

Description

【０００１】
【発明の属する技術分野】
本発明は、特に高速乾式切削のような過酷な加工条件下でも円滑かつ安定した穴明け加工が可能なドリルに関するものである。
【０００２】
【従来の技術】
このような乾式あるいは微量の切削油剤しか用いない過酷な加工条件に対応することを目的としたドリルとしては、例えば特開２０００−１９８０１１号公報に記載されたようなものが提案されている。すなわち、この公報記載のドリルでは、ドリル本体先端に形成される切刃の外周側に、この切刃の中間部から角度をつけてドリル回転方向に後退する外側コーナー切刃が形成されており、この外側コーナ切刃とドリル本体外周のマージン部との交差角を鈍角にすることができるため、上述のような加工条件でも切刃の外周端に欠けが生じたりするのを防ぐことが可能となる。また、このように切刃の外周端側をドリル回転方向後方側に折曲させたドリルとしては、例えば特公平４−４６６９０号公報に記載のように切刃外周側の第１、第２次直線稜を略Ｖ字状の凸形状としたものも提案されており、この公報記載のドリルではさらにこの第２次直線稜の内周側を丸味を伴った凹形状としている。さらに、このように切刃を凹形状としたドリルとしては、例えば特公昭６１−５８２４６号公報などに、外周側の切刃部分の径方向すくい角が０°〜正になるように凹曲線で結んだものも提案されている。
【０００３】
【発明が解決しようとする課題】
このうち、特公昭６１−５８２４６号公報に記載のように外周側の切刃部分を凹曲線としたものは、通常の加工条件では切屑のカーリングによる処理も円滑で安定した穴明けが可能であるものの、切刃の外周端側におけるマージン部との交差角が鋭角となって強度が不足するため、高速乾式切削のような過酷な条件下では直ぐにこの切刃の外周端側に欠けやチッピングが発生してしまい、工具寿命が極めて短期で費えてしまう。一方、特開２０００−１９８０１１号公報や特公平４−４６６９０号公報に記載のように切刃の外周端側をＶ字状の凸形状としてドリル回転方向後方側に角度をもって折曲したものでは、マージン部との交差角を鈍角にすることができて欠けやチッピングの発生は抑えられるものの、切刃によって生成される切屑がこの折曲点において分断されてしまうため、高速切削ではこれら分断された切屑が絡み合って切屑詰まりを起こすとともに、特に折曲点の外周端側で生成された切屑は外周側に流出しようとするのでカーリング性が悪く、ドリル本体にも大きな抵抗を与えるので摩耗が促進されたり加工時のドリル回転駆動力の増大を招いたりするおそれがある。
【０００４】
本発明は、このような背景の下になされたもので、高速乾式切削等の過酷な加工条件でも工具寿命の短縮を防ぐとともに優れた切屑処理性を奏して円滑かつ安定した穴明け加工が可能なドリルを提供することを目的としている。
【０００５】
【課題を解決するための手段】
上記課題を解決して、このような目的を達成するために、本発明は、軸線回りに回転されるドリル本体の先端部外周に後端側に向けて延びる切屑排出溝が形成され、この切屑排出溝のドリル回転方向を向く内壁面と上記ドリル本体の先端逃げ面との交差稜線部に切刃が形成されてなるドリルにおいて、上記切刃の外周端側に、上記ドリル回転方向に凸となる曲線状をなす凸曲線状切刃部を形成するとともに、この凸曲線状切刃部の内周側には、ドリル回転方向の後方側に凹となる曲線状をなして上記凸曲線状切刃部に滑らかに連なる凹曲線状切刃部を形成して、この凹曲線状切刃部から上記凸曲線状切刃部にかけての上記切刃の外周端までを滑らかな曲線状に形成する一方、上記切屑排出溝のドリル回転方向後方側を向く内壁面には、その外周側に位置してヒール部に達し、上記軸線に直交する断面がドリル回転方向後方側に凸となる凸曲線をなす第２凸曲面部を形成したことを特徴とする。従って、このように構成されたドリルにおいては、切刃の外周端側にドリル回転方向に凸となる凸曲線状切刃部が形成されているため、この凸曲線状切刃部の外周側、すなわちドリル本体外周のマージン部との交差部ではその交差角を大きくして十分な強度を確保することができ、上述のような加工条件でも欠けやチッピングの発生を防止することができる。そして、この凸曲線状切刃部の内周側にはドリル回転方向後方側に凹となる凹曲線状切刃部が連ねられていて、この凹曲線状切刃部から凸曲線状切刃部にかけての切刃の外周端までが滑らかな曲線状に形成されることとなるので、内外周で切屑が分断されるようなことがなく、凹曲線状切刃部によって切屑を内周側に巻き込むようにして十分にカールさせ、円滑に処理することが可能となる。
【０００６】
ここで、上記交差部における強度をより確実に確保するには、上記切刃の外周端側における径方向すくい角を負角側に設定するのが望ましい。また、上記切屑排出溝の内壁面の先端側に、切刃の内周端側に連なるシンニング部を形成し、このシンニング部に、凹曲面状の谷形をなし、その谷底部が上記内壁面に対して上記ドリル本体の内周側に後退しつつ上記切刃の内周端に向けて延びる第１シンニング部を備えることにより、切屑の内周端側部分をこの第１シンニング部がなす凹曲面に案内することによって切屑全体をさらに確実に内周側に巻き込んでカールさせることが可能となる。さらに、このシンニング部に、上記第１シンニング部の先端側に形成されて、上記谷底部に対してさらに内周側に後退しつつ上記切刃の内周端に達する第２シンニング部を備えることにより、この第２のシンニング部によってドリル本体先端のチゼルの幅を小さくして加工物への食い付き性を向上させることができる。また、このようにカールさせられた切屑の円滑な排出を促しつつも、ドリル本体の剛性を十分に確保するには、このドリル本体の芯厚を、上記切刃の外径Ｄに対して０．１５×Ｄ〜０．３×Ｄの範囲に設定するのが望ましい。
【０００７】
一方、上述のような切刃形状を、切屑排出溝のドリル回転方向を向く内壁面とドリル本体の先端逃げ面との交差稜線部に形成する場合、この切屑排出溝のドリル回転方向を向く内壁面には、上記凸曲線状切刃部に連なる凸曲面部と、上記凹曲線状切刃部に連なる第１凹曲面部とが形成されることとなり、上述のように凹曲線状切刃部によって内周側に巻き込むように生成した切屑をこの第１凹曲面部に摺接させてさらに確実にカールさせることができる。また、切屑排出溝のドリル回転方向後方側を向く内壁面には、ドリル回転方向に凹となる曲面状をなす第２の凹曲面部を上記第１凹曲面部に滑らかに連なるように形成すれば、この第１凹曲面部によってカールされた切屑の流れを阻害することなく円滑な排出を促すことができる。
【０００８】
ただし、この場合、上記第１凹曲面部のドリル回転方向後方側への凹みが小さすぎると、切屑の摺接による十分なカーリングが図られなくなるおそれがある一方、逆にこの凹みが大きすぎると、切屑の摺接によるブレーキング作用が強くなりすぎ、切屑が潰れて排出性が損なわれたりドリル駆動力の増大を招いたりするおそれがある。また、上記第２凹曲面部についても、ドリル回転方向への凹みが小さすぎると、第１凹曲面部から流れた切屑がこの第２凹曲面部に強く押し付けられて大きなブレーキング作用が生じるおそれがある一方、逆にこの凹みが大きすぎると、切屑が第１凹曲面部との摺接だけによってカーリングさせられることになって、十分にカールさせられなくなるおそれがある。このため、上記の場合には、上記軸線に直交する断面において、該軸線と上記ドリル回転方向を向く内壁面の外周端とを結ぶ第１仮想直線からの上記第１凹曲面部の凹み量Ｌ１を、上記切刃の外径Ｄに対して−０．０６×Ｄ〜０の範囲に設定するとともに、上記第１仮想直線に上記軸線において交差する第２仮想直線からの上記第２凹曲面部の凹み量Ｌ２を−０．０６×Ｄ〜０．０６×Ｄの範囲に設定するのが望ましい。
【０００９】
また、このように切屑排出溝のドリル回転方向を向く内壁面に凸曲面部と第１凹曲面部とを、切屑排出溝のドリル回転方向後方側を向く内壁面には第１凹曲面部に滑らかに連なる第２凹曲面部を形成した場合、上記軸線に直交する断面において、この第２凹曲面部がなす凹曲線の曲率半径を、第１凹曲面部がなす凹曲線の曲率半径よりも大きくすることにより、曲率半径の小さな第１凹曲面部によって切屑に十分な巻き癖をつけてカールさせることができるとともに、こうしてカールされた切屑を、第２凹曲面部の曲率半径を第１凹曲面部より大きくすることでこの第２凹曲面部にはあまり強く押し付けずに、より円滑に排出することが可能となる。なお、このときこれら第１、第２凹曲面部の曲率半径はそれぞれにおいて一定でもよく、すなわち上記断面において第１、第２凹曲面部が半径の異なる円弧を１の接点で互いに滑らかに接するようにした形状であってもよく、また第１凹曲面部側から第２凹曲面部側に向けて曲率半径が漸次大きくなるように、例えば上記断面において楕円状やトロコイド、サイクロイド、インボリュート等の各種曲線状を呈するようにされていてもよい。
【００１０】
さらにまた、このように第１凹曲面部と第２凹曲面部とを滑らかに連ねる場合にあっては、これら第１、第２凹曲面部の間に、上記軸線に直交する断面において第１凹曲面部がなす凹曲線と第２凹曲面部がなす凹曲線との双方に接する接線状をなす接続面を形成して、この接続面を介して上記第１、第２凹曲面部を接続してもよい。この場合には、これら第１、第２凹曲面部がなす凹曲線の曲率半径に制限されることなく、切屑排出溝の溝幅を確保することができて切屑のカーリング性と排出性とを同時に向上させることが可能となるとともに、第１凹曲面部から第２凹曲面部の間に上記接続面によって間隔をあけることができるので、第１凹曲面部でカールされた切屑が第２凹曲面部に押し付けられるのをより確実に防止して円滑な排出を図るとともにドリル回転駆動力の低減を促すことが可能となる。なお、このような接続面は凸曲面部と第１凹曲面部の間や凸曲面部、第２凹曲面部の外周側に形成されていてもよい。また、上記凸凹曲線状切刃部間に直線状の切刃部を介在させてこれらの曲線状切刃部を滑らかに連ねるようにしてもよい。
【００１１】
なお、こうして切屑排出溝の内壁面に滑らかに連なる凸曲面部と第１，第２凹曲面部とを形成した場合、上記軸線に直交する断面においてまず上記凸曲面部がなす凸曲線の曲率半径は、これが大きすぎると相対的に切刃の凹曲線状切刃部の幅が小さくなって切屑のカーリングが不十分となるおそれがある一方、逆に小さすぎると凸曲線状切刃部の幅が小さくなってマージン部との交差部における十分な強度確保が図られなくなるおそれが生じるので、上記切刃の外径Ｄに対して０．１×Ｄ〜０．８×Ｄの範囲に設定されるのが望ましい。また、上記軸線に直交する断面において第１凹曲面部がなす凹曲線の曲率半径については、これが大きすぎると切屑を摺接させることによって十分にカールさせることができなくなるおそれがある一方、逆に小さすぎると切屑が急激にカールさせられてブレーキング作用が大きくなりすぎるおそれが生じるので、切刃の外径Ｄに対して０．１８×Ｄ〜０．３５×Ｄの範囲に設定されるのが望ましい。さらに、軸線に直交する断面において第２凹曲面部がなす凹曲線の曲率半径についても、これが大きすぎると切屑はこの第２凹曲面部には摺接しなくなって第１凹曲面部によってのみカールさせられるようなこととなる一方、逆に小さすぎると切屑の第２凹曲面部への摺接が強くなりすぎてやはり大きなブレーキング作用が生じることとなるので、切刃の外径Ｄに対して０．２×Ｄ〜０．５×Ｄの範囲に設定されるのが望ましい。さらにまた、ドリル本体の少なくとも先端部の表面に、ＴｉＮ、ＴｉＣＮ、ＴｉＡｌＮ等の硬質皮膜を被覆すれば、このドリル本体先端部の耐摩耗性の向上を図ることができる。
【００１２】
【発明の実施の形態】
図１ないし図３は、本発明の一実施形態を示すものである。本実施形態においてドリル本体１は、超硬合金等の硬質材料により軸線Ｏを中心とした略円柱状に形成されており、その先端部には、先端逃げ面２から後端側に向かうに従い一定の捩れ角でドリル回転方向Ｔの後方側に捩れる一対の切屑排出溝３，３が軸線Ｏに対して対称に形成されていて、これらの切屑排出溝３，３のドリル回転方向Ｔ側を向く内壁面４，４と上記先端逃げ面２との交差稜線部にそれぞれ切刃５，５が形成されている。なお、このドリル本体１先端部には、その外周面や先端逃げ面２、切屑排出溝３に、ＴｉＮ、ＴｉＣＮ、ＴｉＡｌＮ等の硬質皮膜が被覆されている。
【００１３】
ここで、上記内壁面４は、その外周側に位置してマージン部６に交差し、軸線Ｏに直交する断面において図２に示すようにドリル回転方向Ｔに凸となる凸曲線をなす第１の凸曲面部７と、この第１凸曲面部７の内周側に位置して、上記断面においてドリル回転方向Ｔの後方側に凹む凹曲線状をなす第１凹曲面部８とから構成されており、これら第１の凸凹曲面部７，８の断面がなす上記凸凹曲線は接点Ｐ１において滑らかに接するように連ねられている。また、本実施形態では切屑排出溝３のドリル回転方向Ｔ後方側を向く内壁面９も、その外周側に位置してヒール部１０に達し、上記断面がドリル回転方向Ｔ後方側に凸となる凸曲線をなす第２凸曲面部１１と、この第２凸曲面部１１の内周側に位置してその断面がドリル回転方向Ｔ側に凹む凹曲線状をなす第２凹曲面部１２とから構成され、これら第２の凸凹曲面部１１，１２がなす上記凸凹曲線も接点Ｐ２において滑らかに接するように連ねられるとともに、両内壁面４，９の第１、第２凹曲面部８，１２同士も、その断面がなす凹曲線が接点Ｐ３において滑らかに接して連なるようにされている。なお、上記マージン部６からドリル回転方向Ｔ後方側に上記ヒール部１０に至るランド部の外周面は、マージン部６から一段内周側に後退した円筒面状に形成されている。
【００１４】
さらに、本実施形態では、上記断面において、第１、第２の凸凹曲面部７，８，１１，１２がなす凸凹曲線がそれぞれ点Ｃ１〜Ｃ４を中心とした半径Ｒ１〜Ｒ４の円弧となるようにされており、このうち第１凸曲面部７がなす凸円弧の中心Ｃ１は、この第１凸曲面部７とマージン部６との交点すなわち上記内壁面４の外周端１３において該マージン部６に接する直線Ｑ１よりも内周側に位置させられるとともに、第２凸曲面部１１がなす円弧の中心Ｃ３は、上記外周端１３が軸線Ｏ回りになす円と第２凸曲面部１１がなす円弧の延長線との交点１４において上記円に接する直線Ｑ２よりもやはり内周側に位置させられている。従って、上記第１凸曲面部７は、軸線Ｏと内壁面４の外周端１３とを結ぶ第１仮想直線Ｓ１よりもドリル回転方向Ｔ側に凸となって、この外周端１３における第１凸曲面部７の接線は、外周側に向かうに従いドリル回転方向Ｔ後方側に延びるように第１仮想直線Ｓ１に対して傾斜させられるとともに、この第１仮想直線Ｓ１と直交する上記直線Ｑ１とは鈍角をなして交差させられる。また、第２凸曲面部１１も、ヒール部１０との交点と軸線Ｏとを結ぶ直線よりもドリル回転方向Ｔ後方側に凸となるようにされている。一方、第１、第２凹曲面部８，１２がなす円弧の中心Ｃ２，Ｃ４は、これらの円弧が接点Ｐ３で接していることから、両者とも軸線Ｏからこの接点Ｐ３を通る直線の延長線上に位置することとなる。さらに、この接点Ｐ３が切屑排出溝３の溝底となることから、本実施形態では軸線Ｏを中心としてこの接点Ｐ３を通る円がドリル本体１の芯厚円となり、この芯厚円の直径すなわちドリル本体１の芯厚ｄは、上記切刃５の外周端１５が軸線Ｏ回りになす円の直径すなわち切刃５の外径Ｄに対し、０．１５×Ｄ〜０．３×Ｄの範囲に設定されている。
【００１５】
なお、第１凸凹曲面部７，８がなす凸凹曲線の接点Ｐ１は、軸線Ｏを中心として上記切刃５の外径Ｄの２／３の直径を有する円よりも外周側に位置させられており、より望ましくは軸線Ｏを中心として外径Ｄの５／６の直径を有する円よりも外周側に位置させられる。また、第１凹曲面部８のドリル回転方向Ｔ後方側への凹みの大きさは、上記第１仮想直線Ｓ１からの凹み量Ｌ１が切刃５の外径Ｄに対して−０．０６×Ｄ〜０の範囲に設定されるとともに、第２凹曲面部１２のドリル回転方向Ｔ側への凹みの大きさは、上記断面において第１仮想直線Ｓ１に軸線Ｏで直交する第２仮想直線Ｓ２からの凹み量Ｌ２が−０．０６×Ｄ〜０．０６×Ｄの範囲となるように設定されている。ただし、これらの凹み量Ｌ１，Ｌ２は、それぞれ上記断面において第１、第２仮想直線Ｓ１，Ｓ２に平行で第１、第２凹曲面部８，１２がなす凹曲線に接する直線と第１、第２仮想直線Ｓ１，Ｓ２との間の距離とされており、かつ図２に示すように、第１凹曲面部８の凹み量Ｌ１については第１仮想直線Ｓ１からドリル回転方向Ｔ側を正、後方側を負とし、逆に第２凹曲面部１２の凹み量Ｌ２については第２仮想直線Ｓ２からドリル回転方向Ｔ側を負、後方側を正としている。従って、本実施形態においては、第１凹曲面部８の全体が上記第１仮想直線Ｓ１よりもドリル回転方向Ｔ側に位置することはない。
【００１６】
さらに、上記断面において第１、第２凸凹曲面部７，８，１１，１２がなす円弧の半径Ｒ１〜Ｒ４は、切刃５の外径Ｄに対し、第１凸曲面部７の半径Ｒ１が０．１〜０．８×Ｄの範囲に、第１凹曲面部８の半径Ｒ２が０．１８〜０．３５×Ｄの範囲に、第２凸曲面部１１の半径Ｒ３が０．１〜０．８×Ｄの範囲に、第２凹曲面部１２の半径Ｒ４が０．２〜０．５×Ｄの範囲に、それぞれ設定されている。そして、本実施形態では、このうち第２凹曲面部１２の半径Ｒ４が、第１凹曲面部８の半径Ｒ２よりも大きくされている。なお、こうして形成された切屑排出溝３の溝幅比は、本実施形態では０．８〜１．２：１の範囲とされている。
【００１７】
このような切屑排出溝３の上記内壁面４と先端逃げ面２との交差稜線部に形成される切刃５においては、この内壁面４が上記第１凸凹曲面部７，８によって形成されることにより、その外周端１５側には、ドリル回転方向Ｔに凸となる曲線状をなす凸曲線状切刃部１６が形成されてその後端側に上記第１凸曲面部７が連なるとともに、この凸曲線状切刃部１６の内周側には、ドリル回転方向Ｔの後方側に凹となる曲線状をなして凸曲線状切刃部１６に滑らかに接して連なる凹曲線状切刃部１７が形成され、その後端側に上記第１凹曲面部８が連なることになって、これら凸凹曲線状切刃部１６，１７間で切刃５は軸線Ｏ方向先端視に緩やかに湾曲するＳ字状を呈することとなる。ただし、この切刃５には、先端逃げ面２が内周側から外周側に向かうに従いドリル本体１の後端側に向けて傾斜させられることにより先端角が付されており、これと切屑排出溝３が螺旋状に捩れていることとから、この切刃５の凸凹曲線状切刃部１６，１７が軸線Ｏ方向先端視においてなす上記Ｓ字状の凸凹曲線は、内壁面４の第１凸凹曲面部７，８が軸線Ｏに直交する断面においてなす凸凹曲線が、内周側に向かうに従いドリル回転方向Ｔ側に漸次ずれたような形状をなすこととなる。従って、この軸線Ｏ方向先端視において上記凸曲線状切刃部１６は、その外周端１５における接線が、上記断面において第１凸曲面部７がなす凸曲線の外周端１３における接線よりも大きな傾斜で外周側に向かうに従いドリル回転方向Ｔ後方側に延びるようにされるとともに、マージン部６との交差角も第１凸曲面部７がなす鈍角より大きくされ、これにより切刃５が上記外周端１５においてなす径方向すくい角αは負角側に設定される。
【００１８】
一方、切屑排出溝３の内壁面４，９の先端側には、上記第１凹曲面部８の内周側から第２凹曲面部１２および第２凸曲面部１１までの先端逃げ面２との交差稜線部分を、ドリル本体１の後端側に向かうに従い切屑排出溝３の内側に向けて切り欠くようにして、ヒール部１０に達するシンニング部１８が形成されており、従って切刃５の内周端側は、このシンニング部１８と先端逃げ面２との交差稜線部に形成されて、上記凹曲面状切刃部１７の内周端から先端逃げ面２の中心の上記軸線Ｏに向けて延びるシンニング切刃部１９とされている。なお、切刃５においてこのシンニング切刃部１９と上記凹曲線状切刃部１７とが交差する部分は、軸線Ｏ方向先端視にドリル回転方向Ｔに凸となる曲線または直線によって滑らかに接続されている。
【００１９】
ここで、このシンニング部１８のうち、切屑排出溝３の内壁面４，９に交差して先端側に延びる部分は第１シンニング部２０とされており、この第１シンニング部２０は、ドリル回転方向Ｔ後方側を向く切屑排出溝３の内壁面９と交差してヒール部１０側に延びる部分においては平面状に形成される一方、この内壁面９とドリル回転方向Ｔ側を向く内壁面４とが交差する部分、すなわち上記第１、第２凹曲面部８，１２の接点Ｐ３部分から、先端逃げ面２の中心に向けて延びる部分は、図３に示すようにこの先端逃げ面２の中心に向かう方向から見た場合に凹曲面状の谷形をなすように形成されており、その凹曲する谷底部２１は、上記内壁面４，９に対してドリル本体１の内周側に後退するように傾斜しつつ、切刃５の内周端すなわちシンニング切刃部１９の内周端に向けて先端側に延びるように形成されている。なお、この第１シンニング部２０の凹曲する谷底部２１がその断面においてなす凹曲線の曲率半径は、０．１〜０．５mmの範囲に設定されている。なお、この谷底部２１の断面がなす凹曲線の曲率半径は、後端側に向かうに従い大きくなるようにされていてもよい。
【００２０】
さらに、この第１シンニング部２０の最先端の上記谷底部２１が切刃５の内周端に達しようとする部分には、この谷底部２１に対してさらにドリル本体１の内周側に後退するように一段傾斜しつつ切刃５内周端側に向けて延びる谷形の第２シンニング部２２が形成されており、先端逃げ面２の中心の軸線Ｏ近傍においてはこの第２シンニング部２２が先端逃げ面２に交差してその交差稜線部上に切刃５の内周端が形成される。ここで、この第２シンニング部２２の谷底部の曲率半径は、第１シンニング部２０の谷底部２１の曲率半径よりも小さく、０．１mm未満とされており、場合によっては曲率半径が０、すなわちこの谷底部が凹湾曲しないＶ字谷状に形成されていてもよく、さらに第１シンニング部２０の谷底部２１と同様にドリル本体１の後端側に向かうに従い大きくなるようにされていてもよい。また、このように第１シンニング部２０よりもさらに一段傾斜する第２シンニング部２２と先端逃げ面２との交差稜線部に切刃５の内周端が形成されることにより、ドリル本体１先端の一対の切刃５，５間の間隔すなわち先端逃げ面２の中心に画成されるチゼルの幅は、第１シンニング部２０をそのまま先端逃げ面２に交差させて切刃５の内周端を形成するのに比べて狭くなり、このチゼル幅は本実施形態では０〜０．２mmの範囲とされていて、すなわちこれら切刃５，５の内周端が軸線Ｏ上で一致するようにされていてもよい。
【００２１】
このように構成されたドリルにおいては、まず、この切刃５の外周端１５側にドリル回転方向Ｔに凸となる凸曲線状切刃部１６が形成されており、従って軸線Ｏ方向先端視の外周端１５における凸曲線状切刃部１６とマージン部６との交差角を上述のように大きな角度に、しかも第１凸曲面部７との交差角よりも大きな角度にすることができ、この外周端１５近傍におけるドリル本体１の強度を十分に確保することができる。このため、ドリル本体１外周に位置するために切削速度が最も高く、しかも切屑生成量も最も多くなるために過大な負荷が生じやすいこの切刃５の外周端１５に欠けやチッピングなどが発生するのを防止することができ、たとえ高速乾式切削となるような過酷な加工条件下においても工具寿命の延長を図ることができる。しかも、本実施形態ではこの凸曲線状切刃部１６が軸線Ｏ方向先端視に切刃５の外周端１５と軸線Ｏとを結ぶ直線よりもドリル回転方向Ｔに凸となるように形成されていて、これにより上述のようにその径方向すくい角αが負角とされているので、マージン部６との上記交差角は鈍角になり、より確実にこの外周端１５周辺におけるドリル本体１の強度を確保することが可能となる。
【００２２】
そして、この凸曲線状切刃部１６は、このようにドリル回転方向Ｔに凸となる曲線状をなしていて、従来のように切刃５が角度をもってＶ字状に折れ曲がるような折曲点が形成されることがなく、しかもその内周側にはドリル回転方向Ｔ後方側に凹となる凹曲線状切刃部１７が該凸曲線状切刃部１６に滑らかに連なるように形成されており、従って切刃５により生成される切屑は、上述のような曲折点で分断されたりすることなく、凹曲線状切刃部１７によって生成された部分が内周側に向けて流れ出るのに伴い、全体的に内周側に巻き込まれるようにして円滑にカールさせられる。このため、分断された切屑が絡まり合って切屑詰まりを生じたりするようなこともなく、また外周端１５側の切屑が外周側に流れ出て抵抗を増大させたりドリル本体１の摩耗を速めたりするようなこともなく、切屑の円滑かつ安定した処理を促して穴明け加工時のドリル回転駆動力の低減を図るとともに、摩耗を抑えて工具寿命を一層延長させることが可能となる。また、この切刃５を含めたドリル本体１の先端部には、ＴｉＮ、ＴｉＣＮ、ＴｉＡｌＮ等の硬質皮膜が被覆されているので、ドリル本体１の耐摩耗性の一層の向上を図ることができる。
【００２３】
さらに、本実施形態では、切屑排出溝３の先端側にシンニング部１８が形成されていて、これにより切刃５の内周端側は先端逃げ面２の中心に向かうシンニング切刃部１９とされており、このシンニング切刃部１９と上記凹曲線状切刃部１７とが交差する部分が両切刃部１７，１９に滑らかに連なる凸曲線状または直線状とされるとともに、シンニング切刃部１９に連なる第１シンニング部２０は谷底部２１が凹曲した谷形とされているので、切刃５の全長に亙って上述のような折曲点が形成されることはなく、しかもこのシンニング切刃部１９によって生成された切屑の内周側部分をも、図３に黒塗り矢線で示すように第１シンニング部２０の谷底部２１断面がなす凹曲線に沿って内周側に巻き込むようにカールさせることができる。このため、上記凹曲線状切刃部１７によって切屑が内周側に巻き込まれるのと相俟って、一層の切屑処理性の向上を図ることができ、特に難削材の加工において効果的である。なお、本実施形態ではこの第１シンニング部２０の谷底部２１がなす凹曲線の曲率半径を０．１〜０．５mmとしているが、これは、この曲率半径がこれよりも大きいと上記切屑の内周側部分を十分に巻き込んでカールさせることができなくなるおそれがある一方、逆にこれよりも小さいとこの切屑の内周側部分がシンニング部１８内において詰まりを生じるおそれがあるからである。
【００２４】
また、このシンニング部１８の先端には、第１シンニング部２０の上記谷底部２１からさらに一段傾斜して先端逃げ面２に達する第２シンニング部２２が形成されていて、この第２シンニング部２２と先端逃げ面２との交差稜線部上に切刃５の内周端が形成されており、しかもこの第２シンニング部２２の溝底の曲率半径が０．１mm未満と上記谷底部２１よりも小さくされていることから、この切刃５の内周端はより内周側に配置されることとなり、これによってチゼルの幅が０〜０．２mmと極短い幅とされている。このため、当該ドリルが加工物に食い付く際の食い付き性や直進安定性の向上を図ってさらに安定かつ高精度の加工を行うことができるとともに、ドリル本体１にその軸線方向に作用するスラスト力を抑えることことができて、ドリル駆動力の一層の軽減を促すことも可能となる。しかも、このようにシンニング部１８が切刃５の内周端に向けて傾斜の大きくなる第１、第２の複数のシンニング部２０，２２によって形成されることにより、先端の第２シンニング部２２の溝底に沿った断面におけるドリル本体１の先端角度は、単一のシンニング部の溝底を同じチゼル幅となるように傾斜させた場合に比べて大きくなるので、本実施形態によればこのドリル本体１先端の回転中心周辺における強度も十分に確保して、食い付き時の衝撃的負荷などによっても損傷の生じることのないドリルを提供することができる。ただし、第１シンニング部２０だけでドリル本体１の食い付き性や直進安定性と強度とが確保できるのであれば、第２シンニング部２２はなくてもよい。
【００２５】
一方、このような凸凹曲線状切刃部１６，１７を備えた切刃５を形成するのに、本実施形態では、切屑排出溝３のドリル回転方向Ｔを向く内壁面４にこれら凸凹曲線状切刃部１６，１７にそれぞれ連なる第１凸凹曲面部７，８を形成しており、従ってこの切刃５によって分断されることなく幅方向に連続して生成された切屑は、全体的に内周側に巻き込まれて第１凹曲面部８に摺接しつつ押し付けられることによりさらに小さくカールさせられ、ドリル本体１の回転に伴い後端側に押し出されて排出される。さらに、この第１凹曲面部７の内周側には、ドリル回転方向Ｔ後方側を向く切屑排出溝３の内壁面９の第２凹曲面部１２が、この第１凹曲面部７と滑らかに連なるように形成されており、この第２凹曲面部１２は第１凹曲面部８とは逆にドリル回転方向Ｔに凹むように形成されているので、第１凹曲面部８によってさらに小さくカールされた切屑の流れを阻害することなく、上述のようにして円滑に排出される。しかも、本実施形態ではこの第２凹曲面部１２の外周側にやはり滑らかに連なるように第２凸曲面部１１が形成されており、従って切屑の流れがヒール部１０側で阻害されることもなく、またこのヒール部１０におけるドリル本体１の強度も確保することができる。
【００２６】
そして、さらに本実施形態では、これら第１、第２凹曲面部８，１２の凹み量Ｌ１，Ｌ２を、第１凹曲面部８については軸線Ｏと内壁面４の外周端１３とを結ぶ第１仮想直線Ｓ１から切刃５の外径Ｄに対して−０．０６×Ｄ〜０の範囲となるように（ただし、ドリル回転方向Ｔ後方側が負）、また第２凹曲面部１２については軸線Ｏにおいて上記第１仮想直線Ｓ１と直交する第２仮想直線Ｓ２から−０．０６×Ｄ〜０．０６×Ｄの範囲となるように（ただし、ドリル回転方向Ｔ側が負）それぞれ設定されており、これにより切屑を強すぎず弱すぎずに第１、第２凹曲面部８，１２に摺接させて、適度なブレーキング作用を与えることができる。このため、過大なブレーキング作用によって切屑が潰れて円滑な排出性が損なわれたりドリル回転駆動力の増大を招いたりすることなく、しかしながら確実に切屑をカールさせて処理することができる。なお、このような作用効果をより確実に奏功せしめるには、本実施形態のように軸線Ｏに直交する断面において、第１凹曲面部８がなす凹曲線（凹円弧）の曲率半径Ｒ２は切刃５の外径Ｄに対して０．１８〜０．３５×Ｄの範囲に、また第２凹曲面部１２の曲率半径Ｒ４は０．２〜０．５×Ｄの範囲に、それぞれ設定されるのが望ましい。
【００２７】
また、本実施形態では、これら第１、第２凹曲面部８，１２間においても、軸線Ｏに直交する断面において第２凹曲面部１２がなす凹曲線の曲率半径すなわち上記半径Ｒ４が、第１凹曲面部８がなす凹曲線の曲率半径すなわち上記半径Ｒ２よりも大きくなるようにされており、従って切刃５によって生成された切屑を、まず比較的小さな半径Ｒ２の第１凹曲面部８に摺接させることにより、この切屑に十分な巻き癖をつけてカールさせるとともに、こうしてカールされた切屑を比較的大きな半径Ｒ４の第２凹曲面部１２側に流出させることにより、この第２凹曲面部１２においては切屑があまり強く押し付けられることがなくなり、より円滑な排出を促すとともにドリル回転駆動力の一層の軽減を図ることができる。しかも、これら第１、第２凹曲面部８，１２がなす凹曲線が、本実施形態では１の上記接点Ｐ３で接して連続する凹曲線を描くようにされており、第１凹曲面部８から第２凹曲面部１２への切屑の流れをよりスムーズにして、一層円滑な切屑排出を促すことが可能となる。
【００２８】
ただし、このように第１、第２凹曲面部８，１２を、その断面がなす凹曲線が１の接点Ｐ３で接して滑らかに連なるように形成する代わりに、例えば図４に示すように、これら第１、第２凹曲面部８，１２の間に、軸線Ｏに直交する断面において第１凹曲面部８がなす凹曲線と第２凹曲面部１２がなす凹曲線との双方に接点Ｐ４，Ｐ５で接する接線状をなす接続面２３を形成して、この接続面２３を介して両凹曲面部８，１２が滑らかに連なるようにしてもよい。この場合にも、第１凹曲面部８によって巻き癖がつけられた切屑を、その流れを損なうことなく、しかもこの接続面２３に強く押し付けてドリル回転駆動力の増大を招いたりすることもなく、第２凹曲面部１２側に送り出して円滑に排出することが可能となる。また、その一方で、このような接続面２３を第１、第２凹曲面部８，１２間に介在させた場合には、これら第１、第２凹曲面部８，１２の曲率半径Ｒ２，Ｒ４に制限されることなく切屑排出溝３の溝幅を設定することができるので、例えば上記とは逆に加工物の材質などに応じて第２凹曲面部１２にも切屑を十分に摺接させてカールさせなければならない場合にその曲率半径Ｒ４を小さくしたとしても、溝幅は十分大きく確保して円滑な排出性を維持することも可能となる。
【００２９】
さらに、本実施形態では、上記第１、第２凸曲面部７，１１が上記断面においてなす凸曲線（凸円弧）の曲率半径Ｒ１，Ｒ３が、切刃５の外径Ｄに対してそれぞれ０．１〜０．８×Ｄの範囲に設定されており、これにより、ドリル本体１の内壁面４や切刃５の外周端１３，１５におけるマージン部６周辺の強度やヒール部１０周辺における強度を十分に確保しつつ、第１、第２凹曲面部８，１２の径方向の幅が小さくなりすぎるのを防いで、確実な切屑処理性の向上を図ることができる。なお、高速乾式切削のような条件下でも、このようにドリル本体１の強度確保と切屑処理性の向上とをより確実に両立させるには、本実施形態のように上記断面において第１凸凹曲面部７，８がなす凸凹曲線の接点Ｐ１を、軸線Ｏから切刃５の外径Ｄの２／３の直径の円より外周側に、より望ましくは外径Ｄの５／６の直径の円よりも外周側に位置させ、また切屑排出溝３の溝幅比を０．８〜１．２：１の範囲とするのが望ましい。
【００３０】
さらにまた、本実施形態ではこのように切屑処理性の向上が図られてドリル回転駆動力の低減が図られるのに伴い、加工時にドリル本体１自体が受ける負荷も小さくなり、これによってその芯厚ｄも切刃５の外径Ｄに対して０．１５×Ｄ〜０．３×Ｄと比較的小さな範囲に設定することができる。このため、上記ドリル本体１が受ける負荷のうち特にスラスト力を軽減させるとともに、切屑排出溝３の断面積を大きくしてさらに円滑な切屑排出を促し、これらによって穴明け加工時の動力の一層の軽減を図ることができる。その一方で、ドリル本体１の断面積は、上記曲率半径Ｒ１〜Ｒ４が上述のように適当な範囲に設定されることと、特に第１、第２凸曲面部７，１１によって外周側で大きくなることとにより、必要かつ十分に確保することができ、従ってドリル本体１の剛性も維持することができるので、上述のように加工動力の一層の軽減が図られることとも相俟って、加工時に折損等が生じてドリル寿命が費えてしまうような事態をも防止することが可能となる。
【００３１】
ここで、次表１は、図１〜図３に示した実施形態のドリルと、それぞれ第１凸曲面部７の半径Ｒ１の大きさと第１、第２凹曲面部８，１２の大小、および芯厚ｄの大きさが異なる以外はこの実施形態と同様とされた比較ドリル１〜５とで、切削速度を変化させ、かつ乾式で穴明け加工試験を行ったときの結果を示すものであり、加工条件や評価は表下に示した通りである。
【００３２】
【表１】

【００３３】
この表１の結果より、まず第１凸曲面部７の半径Ｒ１が切刃５の外径Ｄに対して０．１×Ｄを下回る比較ドリル１では、この第１凸曲面部７の幅が小さくなるのに伴い先端の凸曲線状切刃部１６の幅も小さくなって、この凸曲線状切刃部１６ごと切刃５の肩すなわち上記外周端１５部分にチッピングが生じ、またこれとは逆に半径Ｒ１が０．８×Ｄを上回る比較ドリル２では、これら第１凸曲面部７および凸曲線状切刃部１６が幅広となって、相対的に第１凹曲面部８および凹曲線状切刃部１７が幅狭となり、これにより切屑のカーリング性が損なわれて切屑排出溝３の内壁面４，９に切屑が強く押し付けられ、大きな摩耗を生じる結果となった。また、上記実施形態とは逆に第１凹曲面部８の半径Ｒ２を第２凹曲面部１２の半径Ｒ４よりも大きくした比較ドリル３では、切屑が第２凹曲面部１２に強く押し付けられることによって図５（ロ）に示すように潰れを生じ、またこの第２凹曲面部１２の摩耗も著しかった。さらに、芯厚ｄを０．３×Ｄよりも大きくした比較ドリル４では、切屑排出溝３の断面積が小さくなってやはり切屑の擦過による摩耗が大きく、しかもスラスト力が増大してドリル駆動力も大きくなったのに対し、逆に芯厚ｄを０．１５×Ｄより小さくした比較ドリル５では、スラスト力は小さくなったものの、剛性不足によって折損が生じてしまった。
【００３４】
これらの比較ドリル１〜５に対して、上記実施形態のドリル１〜３では、いずれも排出された切屑が図５（イ）に示すように潰れを生じたりすることなく小さくカールさせられていて、切屑排出溝３の内壁面４，９等における工具摩耗も正常なものであり、特に芯厚ｄを０．２３×Ｄとした実施形態ドリル２ではスラスト力、水平分力とも小さく、より安定した穴明け加工を行うことが可能であった。なお、これに対して芯厚ｄを０．２０×Ｄとやや小さめにした実施形態ドリル３では、その分剛性も小さくなったため水平分力が大きくなる傾向となったが、比較ドリル５のように折損に至るようなことはなく、実用上十分な寿命を得ることができた。
【００３５】
【発明の効果】
以上説明したように、本発明によれば、切刃の外周端側には凸曲線状切刃部を形成することにより、切刃の外周端におけるドリル本体強度を確保してチッピングや欠けの発生を防止することができるとともに、この凸曲線状切刃部に滑らかに連なる凹曲線状切刃部を内周側に形成することにより、切屑全体を内周側に巻き込むようにしてカールさせることができ、その効率的な処理を図ることができる。従って、乾式でしかも高速切削となるような過酷な加工条件においても、ドリルの寿命の延長を図って円滑かつ安定した穴明け加工を行うことができる。
【図面の簡単な説明】
【図１】本発明の一実施形態を示す軸線Ｏ方向先端視の正面図である。
【図２】図１に示す実施形態の軸線Ｏに直交する断面図である。
【図３】図１に示す実施形態のシンニング部１８を示すドリル本体１先端部の斜視図である。
【図４】第１、第２凹曲面部８，１２間に接続面２３を形成した場合を示す断面図である。
【図５】（イ）は本発明の実施形態によるドリルによって生成された切屑を示す図であり、（ロ）は実施形態とは第１、第２凹曲面部８，１２の半径Ｒ２，Ｒ４の大小が反対とされた比較ドリル３による切屑を示す図である。
【符号の説明】
１ドリル本体
２先端逃げ面
３切屑排出溝
４，９切屑排出溝３の内壁面
５切刃
７第１凸曲面部
８第１凹曲面部
１１第２凸曲面部
１２第２凹曲面部
１３内壁面４の外周端
１５切刃５の外周端
１６凸曲線状切刃部
１７凹曲線状切刃部
１８シンニング部
１９シンニング切刃部
２０第１シンニング部
２１第１シンニング部２０の谷底部
２２第２シンニング部
２３接続面
Ｏドリル本体１の軸線
Ｔドリル回転方向
Ｒ１〜Ｒ４第１、第２凸凹曲面部７，８，１１，１２が軸線Ｏに直交する断面においてなす曲線の曲率半径
Ｓ１，Ｓ２第１、第２仮想直線
Ｌ１，Ｌ２第１、第２凹曲面部８，１２の凹み量
ｄドリル本体１の芯厚
α 切刃５の外周端１５側における径方向すくい角[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drill capable of a smooth and stable drilling process even under severe processing conditions such as high-speed dry cutting.
[0002]
[Prior art]
As a drill intended to cope with such severe processing conditions that use only a dry or trace amount of cutting fluid, a drill described in, for example, Japanese Patent Application Laid-Open No. 2000-198011 has been proposed. That is, in the drill described in this publication, on the outer peripheral side of the cutting blade formed at the tip of the drill body, an outer corner cutting blade is formed that recedes in the drill rotation direction at an angle from the middle portion of the cutting blade, Since the crossing angle between the outer corner cutting edge and the margin of the outer periphery of the drill body can be made obtuse, it is possible to prevent the outer edge of the cutting edge from being chipped even under the above processing conditions. Become. Moreover, as a drill which bent the outer peripheral edge side of the cutting blade in the drill rotation direction rear side in this way, for example, as described in Japanese Patent Publication No. 4-46690, the first and second of the cutting blade outer peripheral side A straight ridge having a substantially V-shaped convex shape has been proposed, and in the drill described in this publication, the inner peripheral side of the secondary straight ridge is further formed into a concave shape with roundness. Further, as such a drill having a concave cutting edge, for example, in Japanese Examined Patent Publication No. 61-58246, a concave curve is used so that the rake angle in the radial direction of the cutting edge portion on the outer peripheral side becomes 0 ° to positive. A tied one has also been proposed.
[0003]
[Problems to be solved by the invention]
Of these, as described in Japanese Examined Patent Publication No. 61-58246, when the outer peripheral cutting edge portion has a concave curve, the processing by chip curling can be performed smoothly and stably under normal processing conditions. However, since the crossing angle with the margin part on the outer peripheral edge side of the cutting edge becomes an acute angle and the strength is insufficient, chipping and chipping immediately occur on the outer peripheral edge side of this cutting edge under severe conditions such as high-speed dry cutting. Will occur and the tool life will be very short. On the other hand, as described in Japanese Patent Application Laid-Open No. 2000-198011 and Japanese Patent Publication No. 4-46690, the outer peripheral end side of the cutting blade is bent in an angle toward the rear side in the drill rotation direction with a V-shaped convex shape. Although the crossing angle with the margin can be made obtuse and the occurrence of chipping and chipping can be suppressed, the chips generated by the cutting edge are divided at this bending point. Chips are entangled with each other and clogging the chips, and especially the chips generated on the outer peripheral edge side of the bending point tend to flow out to the outer peripheral side, resulting in poor curling and increased resistance to the drill body, which promotes wear. There is a risk of increasing the drill rotation driving force during machining.
[0004]
The present invention has been made under such a background, and prevents the shortening of the tool life even under severe processing conditions such as high-speed dry cutting and provides excellent chip disposal and enables smooth and stable drilling. The purpose is to provide a simple drill.
[0005]
[Means for Solving the Problems]
In order to solve the above problems and achieve such an object, according to the present invention, a chip discharge groove extending toward the rear end side is formed on the outer periphery of the distal end portion of the drill body rotated about the axis, and the chip is In a drill in which a cutting edge is formed at an intersecting ridge line portion between the inner wall surface of the discharge groove facing the drill rotation direction and the tip flank of the drill body, the outer peripheral end side of the cutting blade protrudes in the drill rotation direction. A convex curvilinear cutting edge portion is formed, and on the inner peripheral side of the convex curvilinear cutting blade portion, a convex curvilinear cutting edge is formed on the rear side in the drill rotation direction. A concave curved cutting edge portion that is smoothly connected to the blade portion is formed, and a smooth curved shape is formed from the concave curved cutting edge portion to the outer peripheral edge of the cutting blade from the convex curved cutting blade portion. On the other hand, on the inner wall surface facing the rear side in the drill rotation direction of the chip discharge groove, a convex curve is located on the outer peripheral side and reaches the heel portion, and the cross section perpendicular to the axis is convex rearward in the drill rotation direction. Forming the second convex curved surface part It is characterized by that. Therefore, in the drill configured in this way, since the convex curved cutting edge portion that is convex in the drill rotation direction is formed on the outer peripheral end side of the cutting blade, the outer peripheral side of the convex curved cutting blade portion, That is, at the intersection with the margin portion on the outer periphery of the drill body, the intersection angle can be increased to ensure sufficient strength, and the occurrence of chipping and chipping can be prevented even under the above processing conditions. And the concave curved cutting edge part which becomes a concave in the drill rotation direction back side is continued on the inner peripheral side of this convex curved cutting edge part, and the convex curved cutting edge part from this concave curved cutting edge part As a result, the cutting edge up to the outer peripheral edge is formed in a smooth curved shape, so that the chip is not divided at the inner and outer circumferences, and the chip is wound around the inner peripheral side by the concave curved cutting edge portion. In this way, it is possible to sufficiently curl and process smoothly.
[0006]
Here, in order to ensure the strength at the intersecting portion more reliably, it is desirable to set the radial rake angle on the outer peripheral end side of the cutting edge to the negative angle side. Further, a thinning portion connected to the inner peripheral end side of the cutting blade is formed on the distal end side of the inner wall surface of the chip discharge groove, and a concave curved valley is formed in the thinning portion, and the valley bottom portion is the inner wall surface. On the other hand, a first thinning portion extending toward the inner peripheral end of the cutting blade while retracting toward the inner peripheral side of the drill body is provided, so that the inner peripheral end side portion of the chip is formed by the first thinning portion. By guiding the curved surface, the entire chip can be more reliably wound and curled on the inner peripheral side. Further, the thinning portion includes a second thinning portion that is formed on the distal end side of the first thinning portion and reaches the inner peripheral end of the cutting blade while further retreating to the inner peripheral side with respect to the valley bottom portion. Thus, the width of the chisel at the tip of the drill body can be reduced by this second thinning portion, and the biting property to the workpiece can be improved. In order to ensure sufficient rigidity of the drill body while promoting smooth discharge of the curled chips, the core thickness of the drill body is set to 0 with respect to the outer diameter D of the cutting blade. It is desirable to set in the range of 15 × D to 0.3 × D.
[0007]
On the other hand, when the above-mentioned cutting edge shape is formed on the intersecting ridge line portion between the inner wall surface facing the drill rotation direction of the chip discharge groove and the tip clearance surface of the drill body, the inner portion of the chip discharge groove facing the drill rotation direction is formed. On the wall surface, a convex curved surface portion continuous with the convex curved cutting edge portion and a first concave curved surface portion continuous with the concave curved cutting edge portion are formed, and the concave curved cutting edge portion is formed as described above. Thus, the chips generated so as to be wound on the inner peripheral side can be brought into sliding contact with the first concave curved surface portion and further curled. In addition, a second concave curved surface portion having a curved shape that is concave in the drill rotating direction is formed on the inner wall surface facing the rear side in the drill rotating direction of the chip discharge groove so as to be smoothly connected to the first concave curved surface portion. For example, smooth discharge can be promoted without inhibiting the flow of chips curled by the first concave curved surface portion.
[0008]
However, in this case, if the dent on the rear side in the drill rotation direction of the first concave curved surface portion is too small, there is a possibility that sufficient curling due to the sliding contact of chips may not be achieved, but conversely if the dent is too large. Further, the braking action due to the sliding contact of the chips becomes too strong, and the chips may be crushed and the discharge performance may be impaired, or the drill driving force may be increased. Moreover, also about the said 2nd concave curved surface part, when the dent to a drill rotation direction is too small, the chip | tip which flowed from the 1st concave curved surface part may be strongly pressed against this 2nd concave curved surface part, and a big braking action may arise. On the other hand, if the dent is too large, the chips are curled only by sliding contact with the first concave curved surface portion, and may not be sufficiently curled. For this reason, in the above case, in the cross section orthogonal to the axis, the dent amount L1 of the first concave curved surface portion from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction. Is set in a range of −0.06 × D to 0 with respect to the outer diameter D of the cutting edge, and the second concave curved surface portion from the second imaginary straight line that intersects the first imaginary straight line at the axis. It is desirable to set the dent amount L2 in the range of −0.06 × D to 0.06 × D.
[0009]
Further, the convex curved surface portion and the first concave curved surface portion are formed on the inner wall surface facing the drill rotation direction of the chip discharge groove in this manner, and the first concave curved surface portion is formed on the inner wall surface facing the rear side of the chip discharge groove in the drill rotation direction. When the second concave curved surface portion that is smoothly connected is formed, the radius of curvature of the concave curve formed by the second concave curved surface portion is larger than the radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section orthogonal to the axis. By enlarging, the first concave curved surface portion having a small radius of curvature can curl the chip with sufficient curl, and the curled chip has the curvature radius of the second concave curved surface portion set to the first concave surface. By making it larger than the curved surface portion, the second concave curved surface portion can be discharged more smoothly without being pressed too strongly. At this time, the radii of curvature of the first and second concave curved surface portions may be constant in each case, that is, the first and second concave curved surface portions in the cross section are in smooth contact with each other at one contact point with arcs having different radii. In addition, various shapes such as an ellipse, a trochoid, a cycloid, an involute, etc. in the cross section are used so that the radius of curvature gradually increases from the first concave curved surface portion side to the second concave curved surface portion side. It may be configured to exhibit a curved shape.
[0010]
Furthermore, in the case where the first concave curved surface portion and the second concave curved surface portion are smoothly connected in this way, the first and second concave curved surface portions are provided with a first cross section perpendicular to the axis. A tangential connection surface is formed in contact with both the concave curve formed by the concave curved surface portion and the concave curve formed by the second concave curved surface portion, and the first and second concave curved surface portions are connected via this connection surface. May be. In this case, the groove width of the chip discharge groove can be secured without being limited by the radius of curvature of the concave curve formed by the first and second concave curved surface portions, and the curling property and discharge performance of the chip can be ensured. At the same time, it is possible to improve the distance between the first concave curved surface portion and the second concave curved surface portion by the connecting surface, so that the chips curled by the first concave curved surface portion are second concave. It is possible to more surely prevent the surface from being pressed against the curved surface portion, to achieve smooth discharge, and to promote reduction of the drill rotation driving force. Such a connection surface may be formed between the convex curved surface portion and the first concave curved surface portion, or on the outer peripheral side of the convex curved surface portion or the second concave curved surface portion. Further, a linear cutting blade portion may be interposed between the uneven curved cutting blade portions so that the curved cutting blade portions are smoothly connected.
[0011]
When the convex curved surface portion and the first and second concave curved surface portions that are smoothly connected to the inner wall surface of the chip discharge groove are formed in this way, the curvature radius of the convex curve formed by the convex curved surface portion first in the cross section orthogonal to the axis. However, if this is too large, the width of the concave curved cutting edge portion of the cutting edge may be relatively small and curling of the chips may be insufficient. May be reduced, and sufficient strength may not be ensured at the intersection with the margin portion. Therefore, the outer diameter D of the cutting blade is set in a range of 0.1 × D to 0.8 × D. Is desirable. In addition, as for the radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section perpendicular to the axis, there is a possibility that it cannot be sufficiently curled by sliding the chips if it is too large. If it is too small, the chips are abruptly curled and the braking action may become too large. Therefore, the cutting edge is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting edge. Is desirable. Furthermore, if the radius of curvature of the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis is too large, the chips do not slide on the second concave curved surface portion and are curled only by the first concave curved surface portion. On the other hand, if it is too small, the sliding contact of the chips with the second concave curved surface portion becomes too strong and a large braking action is generated. It is desirable to set in the range of 0.2 × D to 0.5 × D. Furthermore, if the surface of at least the tip of the drill body is coated with a hard coating such as TiN, TiCN, TiAlN, etc., the wear resistance of the tip of the drill body can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 to 3 show an embodiment of the present invention. In the present embodiment, the drill body 1 is formed in a substantially cylindrical shape centering on the axis O by a hard material such as a cemented carbide, and is constant at the tip portion from the tip flank 2 toward the rear end side. A pair of

chip discharge grooves

3, 3 that are twisted to the rear side in the drill rotation direction T at a twist angle of? Are formed symmetrically with respect to the axis O, and the drill rotation direction T side of these

chip discharge grooves

3, 3 is Cutting

blades

5 and 5 are formed at the intersecting ridges between the facing inner wall surfaces 4 and 4 and the tip flank 2, respectively. The tip of the drill body 1 is coated with a hard coating such as TiN, TiCN, TiAlN on the outer peripheral surface, the tip flank 2 and the chip discharge groove 3.
[0013]
Here, the inner wall surface 4 is located on the outer peripheral side of the inner wall surface 4 and intersects the margin portion 6, and forms a convex curve that is convex in the drill rotation direction T as shown in FIG. 2 in a cross section orthogonal to the axis O. The convex curved surface portion 7 and the first concave curved surface portion 8 which is located on the inner peripheral side of the first convex curved surface portion 7 and has a concave curved shape recessed in the rear side in the drill rotation direction T in the cross section. The concave and convex curves formed by the cross sections of the first concave and convex

curved surface portions

7 and 8 are connected so as to smoothly contact at the contact point P1. Moreover, in this embodiment, the inner wall surface 9 facing the drill rotation direction T rear side of the chip discharge groove 3 is also located on the outer peripheral side and reaches the heel portion 10, and the above-mentioned cross section is convex toward the drill rotation direction T rear side. A second convex curved surface portion 11 having a convex curve, and a second concave curved surface portion 12 having a concave curved shape which is located on the inner peripheral side of the second convex curved surface portion 11 and whose cross section is recessed toward the drill rotation direction T side. The concave and convex curves formed by the second concave and convex curved surface portions 11 and 12 are connected so as to smoothly contact at the contact point P2, and the first and second concave

curved surface portions

8 and 12 of the inner wall surfaces 4 and 9 are connected to each other. However, the concave curve formed by the cross section of the contact point P3 smoothly contacts and continues. The outer peripheral surface of the land portion extending from the margin portion 6 to the heel portion 10 on the rear side in the drill rotation direction T is formed in a cylindrical surface receding from the margin portion 6 to the inner peripheral side in one step.
[0014]
Furthermore, in the present embodiment, in the cross section, the uneven curves formed by the first and second uneven

curved surface portions

7, 8, 11, and 12 are arcs having radii R1 to R4 with the points C1 to C4 as the centers. The center C1 of the convex arc formed by the first convex curved surface portion 7 is the intersection of the first convex curved surface portion 7 and the margin portion 6, that is, the margin portion 6 at the outer peripheral end 13 of the inner wall surface 4. The center C3 of the circular arc formed by the second convex curved surface portion 11 is positioned on the inner peripheral side with respect to the straight line Q1 in contact with the circular arc formed by the second convex curved surface portion 11 and the circle formed by the outer peripheral end 13 around the axis O. At the intersection 14 with the extended line, the line is positioned further to the inner peripheral side than the straight line Q2 in contact with the circle. Accordingly, the first convex curved surface portion 7 is convex toward the drill rotation direction T side with respect to the first virtual straight line S1 connecting the axis O and the outer peripheral end 13 of the inner wall surface 4, and the first convex at the outer peripheral end 13. The tangent line of the curved surface portion 7 is inclined with respect to the first imaginary straight line S1 so as to extend rearward in the drill rotation direction T toward the outer peripheral side, and is obtuse with the straight line Q1 orthogonal to the first imaginary straight line S1. Can be crossed. Further, the second convex curved surface portion 11 is also convex toward the rear side in the drill rotation direction T from the straight line connecting the intersection with the heel portion 10 and the axis O. On the other hand, since the arc centers C2 and C4 formed by the first and second concave

curved surface portions

8 and 12 are in contact with each other at the contact P3, both of them are on the straight line extending from the axis O through the contact P3. Will be located. Furthermore, since this contact P3 becomes the groove bottom of the chip discharge groove 3, in this embodiment, a circle passing through this contact P3 with the axis O as the center becomes the core thickness circle of the drill body 1, and the diameter of this core thickness circle, that is, The core thickness d of the drill body 1 is in the range of 0.15 × D to 0.3 × D with respect to the diameter of the circle formed by the outer peripheral edge 15 of the cutting blade 5 around the axis O, that is, the outer diameter D of the cutting blade 5. Is set to
[0015]
The contact point P1 of the uneven curve formed by the first

uneven surface portions

7 and 8 is positioned on the outer peripheral side with respect to the circle having the diameter of 2/3 of the outer diameter D of the cutting blade 5 with the axis O as the center. More preferably, it is positioned on the outer peripheral side of a circle having a diameter of 5/6 of the outer diameter D around the axis O. In addition, the size of the recess of the first concave curved surface portion 8 toward the rear side in the drill rotation direction T is such that the recess amount L1 from the first imaginary straight line S1 is −0.06 × with respect to the outer diameter D of the cutting blade 5. The second imaginary straight line S2 is set in the range of D to 0, and the size of the dent of the second concave curved surface portion 12 toward the drill rotation direction T is perpendicular to the first imaginary straight line S1 by the axis O in the cross section. Is set to be in a range of −0.06 × D to 0.06 × D. However, these dent amounts L1 and L2 are parallel to the first and second imaginary straight lines S1 and S2 in the cross section, respectively, and the first and second straight lines in contact with the concave curves formed by the first and second concave

curved surface portions

8 and 12 respectively. The distance between the second virtual straight line S1 and S2, and as shown in FIG. 2, with respect to the amount of recess L1 of the first concave curved surface portion 8, the drill rotation direction T side is positive from the first virtual straight line S1. The rear side is negative, and conversely, with respect to the dent amount L2 of the second concave curved surface portion 12, the drill rotation direction T side from the second virtual straight line S2 is negative and the rear side is positive. Therefore, in the present embodiment, the entire first concave curved surface portion 8 is not positioned on the drill rotation direction T side with respect to the first virtual straight line S1.
[0016]
Further, in the cross section, the radii R1 to R4 of the arc formed by the first and second uneven

curved surface portions

7, 8, 11, and 12 have a radius R 1 of the first convex curved surface portion 7 with respect to the outer diameter D of the cutting edge 5. In the range of 0.1 to 0.8 × D, the radius R2 of the first concave curved surface portion 8 is in the range of 0.18 to 0.35 × D, and the radius R3 of the second convex curved surface portion 11 is 0.1 to 0.1 × D. In the range of 0.8 × D, the radius R4 of the second concave curved surface portion 12 is set in the range of 0.2 to 0.5 × D. And in this embodiment, radius R4 of the 2nd concave curved surface part 12 is made larger than radius R2 of the 1st concave curved surface part 8 among these. In addition, the groove width ratio of the chip discharge groove 3 formed in this way is set to a range of 0.8 to 1.2: 1 in the present embodiment.
[0017]
In the cutting edge 5 formed at the intersecting ridge line portion between the inner wall surface 4 and the tip flank 2 of the chip discharge groove 3, the inner wall surface 4 is formed by the first uneven

curved surface portions

7 and 8. As a result, a convex curvilinear cutting edge portion 16 having a curved shape convex in the drill rotation direction T is formed on the outer peripheral end 15 side, and the first convex curved surface portion 7 is connected to the rear end side, On the inner peripheral side of the convex curvilinear cutting edge portion 16, a concave curvilinear cutting edge portion 17 that forms a concave curvilinear shape on the rear side in the drill rotation direction T and that is in smooth contact with the convex curvilinear cutting blade portion 16 is connected. Is formed, and the first concave curved surface portion 8 is connected to the rear end side thereof, and the cutting blade 5 is curved between the convex and concave curved

cutting blade portions

16 and 17 so as to be gently curved toward the front end in the direction of the axis O. Will exhibit a shape. However, the cutting edge 5 is provided with a tip angle by being inclined toward the rear end side of the drill body 1 as the tip flank 2 moves from the inner peripheral side to the outer peripheral side, and chip discharge is performed. Since the groove 3 is twisted in a spiral shape, the S-shaped uneven curve formed by the uneven curved

cutting edge portions

16 and 17 of the cutting edge 5 when viewed from the front in the axis O direction is the first curve of the inner wall surface 4. The uneven curve formed in the cross section where the uneven

curved surface portions

7 and 8 are orthogonal to the axis O will have a shape that gradually shifts toward the drill rotation direction T side toward the inner peripheral side. Therefore, the convex curved cutting edge portion 16 has a tangent line at the outer peripheral end 15 that is larger in inclination than the tangent line at the outer peripheral end 13 of the convex curve formed by the first convex curved surface portion 7 in the cross section. As it goes to the outer peripheral side, it extends to the rear side in the drill rotation direction T, and the crossing angle with the margin portion 6 is also made larger than the obtuse angle formed by the first convex curved surface portion 7, whereby the cutting edge 5 is The rake angle α in the radial direction at 15 is set to the negative angle side.
[0018]
On the other hand, the tip flank 2 from the inner peripheral side of the first concave curved surface portion 8 to the second concave curved surface portion 12 and the second convex curved surface portion 11 is formed on the distal end side of the inner wall surfaces 4 and 9 of the chip discharge groove 3. A thinning portion 18 that reaches the heel portion 10 is formed so as to cut out the crossed ridge line portion toward the inside of the chip discharge groove 3 toward the rear end side of the drill body 1. The inner peripheral end side is formed at the intersecting ridge line portion between the thinning portion 18 and the tip flank 2 and is directed from the inner peripheral end of the concave curved cutting blade portion 17 toward the axis O at the center of the tip flank 2. A thinning cutting edge portion 19 extending in the direction is provided. The portion of the cutting blade 5 where the thinning cutting edge portion 19 and the concave curved cutting edge portion 17 intersect is smoothly connected by a curve or straight line that is convex in the drill rotation direction T when viewed from the front end of the axis O direction. ing.
[0019]
Here, a portion of the thinning portion 18 that extends to the front end side intersecting the inner wall surfaces 4 and 9 of the chip discharge groove 3 is a first thinning portion 20, and this first thinning portion 20 is rotated by a drill. The portion extending to the heel portion 10 side intersecting the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the direction T is formed in a flat shape, while the inner wall surface 4 facing the inner wall surface 9 and the drill rotation direction T side. 3, that is, a portion extending from the contact P3 portion of the first and second concave

curved surface portions

8 and 12 toward the center of the tip flank 2 as shown in FIG. It is formed so as to form a concave curved valley when viewed from the direction toward the center, and the concave valley bottom 21 is on the inner peripheral side of the drill body 1 with respect to the inner wall surfaces 4, 9. The inner peripheral end of the cutting edge 5, that is, the thin It is formed to extend distally toward the inner peripheral end of the ring cutting edge 19. Note that the radius of curvature of the concave curve formed in the cross section of the concave bottom portion 21 of the first thinning portion 20 is set in the range of 0.1 to 0.5 mm. In addition, the curvature radius of the concave curve which the cross section of this valley bottom part 21 makes may be made large as it goes to a rear-end side.
[0020]
Further, in the portion where the foremost valley bottom portion 21 of the first thinning portion 20 is about to reach the inner peripheral end of the cutting edge 5, the first thinning portion 20 further recedes toward the inner peripheral side of the drill body 1 with respect to the valley bottom portion 21. A valley-shaped second thinning portion 22 extending toward the inner peripheral end side of the cutting blade 5 while being inclined one step is formed, and in the vicinity of the axis O at the center of the tip flank 2, the second thinning portion 22 is formed. Intersects the tip flank 2 and the inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion. Here, the curvature radius of the valley bottom of the second thinning portion 22 is smaller than the curvature radius of the valley bottom 21 of the first thinning portion 20 and is less than 0.1 mm. That is, the bottom of the valley may be formed in a V-shaped valley that is not concavely curved, and is further increased in size toward the rear end side of the drill body 1 in the same manner as the valley bottom 21 of the first thinning portion 20. Also good. Further, the tip end of the drill body 1 is formed by forming the inner peripheral end of the cutting edge 5 at the intersecting ridge line portion between the second thinning portion 22 and the tip flank 2 which are inclined further by one step than the first thinning portion 20 in this way. The width of the chisel defined between the pair of cutting

edges

5 and 5, that is, the center of the tip flank 2 is such that the first thinning portion 20 intersects the tip flank 2 as it is and the inner peripheral edge of the cutting blade 5 The chisel width is in the range of 0 to 0.2 mm in this embodiment, that is, the inner peripheral ends of the

cutting blades

5 and 5 coincide on the axis O. May be.
[0021]
In the drill constructed in this way, first, a convex curved cutting edge portion 16 that is convex in the drill rotation direction T is formed on the outer peripheral end 15 side of the cutting edge 5, and accordingly, the front end of the axis O direction is viewed. The intersection angle between the convex curved cutting edge portion 16 and the margin portion 6 at the outer peripheral end 15 can be set to a large angle as described above, and more than the intersection angle with the first convex curved surface portion 7. The strength of the drill body 1 in the vicinity of the outer peripheral end 15 can be sufficiently ensured. For this reason, since it is located on the outer periphery of the drill body 1, the cutting speed is the highest, and the amount of chips generated is the largest, so that an excessive load is likely to be generated, so that the outer peripheral edge 15 of the cutting blade 5 is chipped or chipped. The tool life can be extended even under severe processing conditions such as high-speed dry cutting. Moreover, in this embodiment, the convex curved cutting edge portion 16 is formed so as to protrude in the drill rotation direction T from the straight line connecting the outer peripheral end 15 of the cutting edge 5 and the axis O when viewed from the front in the axis O direction. Thus, as described above, since the radial rake angle α is a negative angle, the crossing angle with the margin portion 6 becomes an obtuse angle, and the strength of the drill body 1 around the outer peripheral end 15 is more reliably determined. Can be secured.
[0022]
The convex curved cutting edge portion 16 has a curved shape that is convex in the drill rotation direction T as described above, and the bending point at which the cutting blade 5 is bent into a V shape with an angle as in the conventional case. In addition, a concave curved cutting edge portion 17 that is concave on the rear side in the drill rotation direction T is formed on the inner peripheral side so as to be smoothly connected to the convex curved cutting edge portion 16. Therefore, the chips generated by the cutting blade 5 are not divided at the bending points as described above, and the portion generated by the concave curved cutting blade portion 17 flows out toward the inner peripheral side. Then, it is smoothly curled so that it is entirely wound on the inner peripheral side. For this reason, the divided chips are not entangled with each other and the chips are not clogged, and the chips on the outer peripheral end 15 side flow out to the outer peripheral side to increase the resistance and accelerate the wear of the drill body 1. Therefore, smooth and stable processing of chips can be promoted to reduce the drill rotational driving force at the time of drilling, and the tool life can be further extended by suppressing wear. Further, the tip of the drill body 1 including the cutting edge 5 is coated with a hard film such as TiN, TiCN, TiAlN, etc., so that the wear resistance of the drill body 1 can be further improved. .
[0023]
Furthermore, in this embodiment, the thinning part 18 is formed in the front end side of the chip discharge groove | channel 3, Thereby, the inner peripheral end side of the cutting blade 5 is made into the thinning cutting edge part 19 which goes to the center of the front end flank 2. A portion where the thinning cutting edge portion 19 and the concave curved cutting edge portion 17 intersect with each other is formed into a convex curve shape or a straight line smoothly connected to the both cutting

edge portions

17 and 19, and the thinning cutting edge portion. Since the first thinning portion 20 connected to 19 has a valley shape in which the valley bottom portion 21 is bent, the bending point as described above is not formed over the entire length of the cutting edge 5. The inner peripheral side portion of the chips generated by the thinning cutting edge portion 19 is also formed on the inner peripheral side along the concave curve formed by the cross section of the valley bottom portion 21 of the first thinning portion 20 as shown by the black arrow in FIG. It can be curled like a roll. For this reason, coupled with the fact that chips are wound on the inner peripheral side by the concave curved cutting edge portion 17, it is possible to further improve the chip disposability, particularly in the processing of difficult-to-cut materials. is there. In the present embodiment, the radius of curvature of the concave curve formed by the valley bottom portion 21 of the first thinning portion 20 is set to 0.1 to 0.5 mm. If this radius of curvature is larger than this, This is because there is a possibility that the inner peripheral side portion cannot be sufficiently curled up and curled. On the other hand, if the inner peripheral side portion is smaller than this, the inner peripheral side portion of the chips may be clogged in the thinning portion 18.
[0024]
Further, a second thinning portion 22 is formed at the distal end of the thinning portion 18 so as to be inclined one step further from the valley bottom portion 21 of the first thinning portion 20 and reach the distal end flank 2, and the second thinning portion 22. The inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion between the tip flank 2 and the curvature radius of the groove bottom of the second thinning portion 22 is less than 0.1 mm, which is greater than the valley bottom portion 21. Since it is made small, the inner peripheral end of the cutting blade 5 is arranged on the inner peripheral side, and the width of the chisel is set to an extremely short width of 0 to 0.2 mm. For this reason, it is possible to improve the biting property and the straight running stability when the drill bites the workpiece, and to perform further stable and highly accurate machining, and the thrust acting on the drill body 1 in the axial direction thereof The force can be suppressed, and further reduction of the drill driving force can be promoted. Moreover, the thinning portion 18 is formed by the first and second plurality of thinning

portions

20 and 22 that increase in inclination toward the inner peripheral end of the cutting blade 5 in this manner, so that the second thinning portion 22 at the distal end is formed. The angle of the tip of the drill body 1 in the cross section along the groove bottom is larger than that when the groove bottom of a single thinning portion is inclined so as to have the same chisel width. It is possible to provide a drill that sufficiently secures the strength around the center of rotation of the tip of the drill body 1 and that is not damaged even by an impact load at the time of biting. However, the second thinning portion 22 may not be provided as long as the biting property, straight running stability, and strength of the drill body 1 can be secured by the first thinning portion 20 alone.
[0025]
On the other hand, in order to form the cutting blade 5 provided with such concave and convex curved

cutting edge portions

16 and 17, in this embodiment, the concave and convex curved shape is formed on the inner wall surface 4 facing the drill rotation direction T of the chip discharge groove 3. The first uneven

curved surface portions

7 and 8 that are continuous with the

cutting edge portions

16 and 17 are formed. Therefore, the chips generated continuously in the width direction without being divided by the cutting blade 5 are entirely inside. It is curled further by being wound around the circumferential side and pressed while being in sliding contact with the first concave curved surface portion 8, and is pushed out and discharged to the rear end side as the drill body 1 rotates. Further, on the inner peripheral side of the first concave curved surface portion 7, a second concave curved surface portion 12 of the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the drill rotation direction T is smooth with the first concave curved surface portion 7. The second concave curved surface portion 12 is formed so as to be recessed in the drill rotation direction T, contrary to the first concave curved surface portion 8, so that the first concave curved surface portion 8 makes the second concave curved surface portion smaller. The curled chips are smoothly discharged as described above without hindering the flow of the chips. In addition, in the present embodiment, the second convex curved surface portion 11 is formed so as to be smoothly connected to the outer peripheral side of the second concave curved surface portion 12, so that the flow of chips may be inhibited on the heel portion 10 side. In addition, the strength of the drill body 1 in the heel portion 10 can be ensured.
[0026]
In the present embodiment, the dent amounts L1 and L2 of the first and second concave

curved surface portions

8 and 12 are connected to each other, and the first concave curved surface portion 8 is connected to the axis O and the outer peripheral end 13 of the inner wall surface 4. The range of −0.06 × D to 0 with respect to the outer diameter D of the cutting edge 5 from the imaginary straight line S1 (however, the rear side of the drill rotation direction T is negative). The axis O is set to be in the range of −0.06 × D to 0.06 × D from the second virtual line S2 orthogonal to the first virtual line S1 (however, the drill rotation direction T side is negative). Thus, the chips can be brought into sliding contact with the first and second concave

curved surface portions

8 and 12 without being too strong and not too weak, and an appropriate braking action can be given. For this reason, the chips can be reliably curled and processed without damaging the smooth evacuation due to excessive braking action and without causing an increase in the drill rotation driving force. In order to achieve such an effect more reliably, the curvature radius R2 of the concave curve (concave arc) formed by the first concave curved surface portion 8 in the cross section orthogonal to the axis O as in the present embodiment is cut. The outer radius D of the blade 5 is set in a range of 0.18 to 0.35 × D, and the radius of curvature R4 of the second concave curved surface portion 12 is set in a range of 0.2 to 0.5 × D. Is desirable.
[0027]
In the present embodiment, the radius of curvature of the concave curve formed by the second concave curved surface portion 12 in the cross section orthogonal to the axis O, that is, the radius R4 is also between the first and second concave

curved surface portions

8 and 12. The radius of curvature of the concave curve formed by one concave curved surface portion 8, that is, larger than the radius R 2, and therefore, the chips generated by the cutting blade 5 are first converted into the first concave curved surface portion 8 having a relatively small radius R 2. The curled chips are curled with a sufficient curl, and the curled chips are caused to flow out toward the second concave curved surface portion 12 having a relatively large radius R4. In the curved surface portion 12, chips are not pressed too strongly, facilitating smoother discharge and further reducing the drill rotation driving force. In addition, the concave curve formed by the first and second concave

curved surface portions

8 and 12 is configured to draw a continuous concave curve in contact with the contact point P3 of 1 in the present embodiment. It is possible to make the flow of chips from the first to the second concave curved surface portion 12 smoother, and to promote smoother chip discharge.
[0028]
However, instead of forming the first and second concave

curved surface portions

8 and 12 so that the concave curve formed by the cross section thereof is in contact with the first contact point P3 and smoothly connected, for example, as shown in FIG. Between the first and second concave

curved surface portions

8 and 12, a contact point P4 is connected to both the concave curve formed by the first concave curved surface portion 8 and the concave curve formed by the second concave curved surface portion 12 in a cross section orthogonal to the axis O. , P5 may be formed so as to form a tangential connection surface 23, and the two concave

curved surface portions

8 and 12 may be smoothly connected via the connection surface 23. Also in this case, the chips with the curl formed by the first concave curved surface portion 8 are not pressed against the connection surface 23 without impairing the flow, and the drill rotational driving force is not increased. The second concave curved surface portion 12 can be sent out and discharged smoothly. On the other hand, when such a connection surface 23 is interposed between the first and second concave

curved surface portions

8 and 12, the curvature radii R2, R2 of the first and second concave

curved surface portions

8 and 12 are provided. Since the groove width of the chip discharge groove 3 can be set without being limited to R4, for example, contrary to the above, the second concave curved surface portion 12 is also slidably contacted with the chip according to the material of the workpiece. Even when the radius of curvature R4 is reduced when curling must be performed, the groove width can be secured sufficiently large to maintain smooth discharge performance.
[0029]
Further, in the present embodiment, the curvature radii R1 and R3 of the convex curves (convex arcs) formed by the first and second convex curved surface portions 7 and 11 in the cross section are 0 with respect to the outer diameter D of the cutting blade 5, respectively. .1 to 0.8 × D, so that the strength around the margin portion 6 and the strength around the heel portion 10 at the outer peripheral ends 13 and 15 of the inner wall surface 4 and the cutting edge 5 of the drill body 1 are set. While ensuring sufficient, it can prevent that the radial direction width | variety of the 1st, 2nd concave

curved surface part

8 and 12 becomes small too much, and can aim at the reliable improvement of chip disposal property. In addition, in order to achieve both the securing of the strength of the drill body 1 and the improvement of the chip disposal in this way even under conditions such as high-speed dry cutting, the first uneven surface in the cross section as in the present embodiment. The contact point P1 of the uneven curve formed by the

portions

7 and 8 is located on the outer peripheral side from the circle O having a diameter of 2/3 of the outer diameter D of the cutting blade 5 from the axis O, and more preferably a circle having a diameter of 5/6 of the outer diameter D. It is desirable that the groove width ratio of the chip discharge groove 3 is in the range of 0.8 to 1.2: 1.
[0030]
Furthermore, in this embodiment, as the chip disposability is improved and the drill rotational driving force is reduced in this way, the load that the drill body 1 itself receives during processing becomes smaller, and thereby the core thickness is reduced. d can also be set to a relatively small range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting edge 5. For this reason, especially the thrust force is reduced among the loads received by the drill body 1 and the cross-sectional area of the chip discharge groove 3 is increased to facilitate smooth chip discharge, thereby further increasing the power during drilling. Mitigation can be achieved. On the other hand, the cross-sectional area of the drill body 1 is large on the outer peripheral side by setting the curvature radii R1 to R4 in an appropriate range as described above, and in particular by the first and second convex curved surface portions 7 and 11. Therefore, the necessary and sufficient amount can be secured, and therefore the rigidity of the drill body 1 can be maintained, so that the machining power can be further reduced as described above. It is possible to prevent a situation in which breakage or the like sometimes occurs and the drill life is consumed.
[0031]
Here, the following table 1 shows the drill of the embodiment shown in FIGS. 1 to 3, the size of the radius R1 of the first convex curved surface portion 7, the size of the first and second concave

curved surface portions

8, 12, and The comparison drills 1 to 5 are the same as in this embodiment except that the size of the core thickness d is different, and show the results when the cutting speed was changed and the drilling test was performed dry. The processing conditions and evaluation are as shown below the table.
[0032]
[Table 1]

[0033]
From the results of Table 1, first, in the comparative drill 1 in which the radius R1 of the first convex curved surface portion 7 is less than 0.1 × D with respect to the outer diameter D of the cutting blade 5, the width of the first convex curved surface portion 7 is As it becomes smaller, the width of the convex curvilinear cutting edge portion 16 at the tip also becomes smaller, and the shoulder of the cutting blade 5 together with the convex curvilinear cutting edge portion 16, that is, the outer peripheral end 15 portion is chipped. On the contrary, in the comparative drill 2 in which the radius R1 exceeds 0.8 × D, the first convex curved surface portion 7 and the convex curved cutting edge portion 16 are wide, and the first concave curved surface portion 8 and the concave curved curve are relatively formed. As a result, the curled portion of the chip was damaged, and the chip was strongly pressed against the inner wall surfaces 4 and 9 of the chip discharge groove 3, resulting in large wear. In contrast to the above embodiment, in the comparative drill 3 in which the radius R2 of the first concave curved surface portion 8 is larger than the radius R4 of the second concave curved surface portion 12, chips are strongly pressed against the second concave curved surface portion 12. As shown in FIG. 5 (b), crushing occurred, and the wear of the second concave curved surface portion 12 was remarkable. Further, in the comparative drill 4 in which the core thickness d is larger than 0.3 × D, the cross-sectional area of the chip discharge groove 3 is reduced, so that wear due to chip abrasion is also large, and the thrust force is increased and the drill driving force is also increased. On the contrary, in the comparative drill 5 in which the core thickness d was smaller than 0.15 × D, the thrust force was reduced, but breakage occurred due to insufficient rigidity.
[0034]
With respect to these comparative drills 1 to 5, in the drills 1 to 3 of the above embodiment, the discharged chips are curled small without causing crushing as shown in FIG. The tool wear on the inner wall surfaces 4 and 9 of the chip discharge groove 3 is also normal. In particular, in the embodiment drill 2 in which the core thickness d is 0.23 × D, both the thrust force and the horizontal component force are small and more stable. Drilling was possible. On the other hand, in the embodiment drill 3 in which the core thickness d is slightly reduced to 0.20 × D, since the rigidity is reduced accordingly, the horizontal component force tends to increase. However, there was no breakage and a practically sufficient life could be obtained.
[0035]
【The invention's effect】
As described above, according to the present invention, by forming a convex curvilinear cutting edge on the outer peripheral end side of the cutting edge, the strength of the drill body at the outer peripheral end of the cutting edge is secured, and chipping and chipping occur. By forming a concave curved cutting edge portion smoothly connected to the convex curved cutting edge portion on the inner peripheral side, the entire chip can be curled so as to be wound on the inner peripheral side. And efficient processing can be achieved. Therefore, even under severe conditions such as dry and high-speed cutting, the drill life can be extended and smooth and stable drilling can be performed.
[Brief description of the drawings]
FIG. 1 is a front view of an embodiment of the present invention as viewed from the front in the direction of an axis O. FIG.
FIG. 2 is a cross-sectional view orthogonal to an axis O of the embodiment shown in FIG.
3 is a perspective view of the distal end portion of a drill body 1 showing a thinning portion 18 of the embodiment shown in FIG. 1. FIG.
4 is a cross-sectional view showing a case where a connection surface 23 is formed between first and second concave

curved surface portions

8 and 12. FIG.
5A is a view showing chips generated by a drill according to an embodiment of the present invention, and FIG. 5B is a view showing radii R2 and R4 of first and second concave

curved surface portions

8 and 12 according to the embodiment. It is a figure which shows the chip | tip with the comparative drill 3 by which the magnitude | size of was reversed.
[Explanation of symbols]
1 Drill body
2 Tip flank
3 Chip discharge groove
4,9 Inner wall surface of chip discharge groove 3
5 Cutting blade
7 First convex curved surface
8 first concave curved surface
11 Second convex curved surface
12 Second concave curved surface
13 Outer peripheral edge of inner wall surface 4
15 Outer edge of cutting edge 5
16 Convex curved cutting edge
17 Concave curved cutting edge
18 Thinning part
19 Thinning cutting edge
20 First thinning section
21 Valley bottom of first thinning section 20
22 Second thinning section
23 Connection surface
O Axis of drill body 1
T Drill rotation direction
R1 to R4 Curvature radii of curves formed by the first and second uneven

curved surface portions

7, 8, 11, and 12 in a cross section orthogonal to the axis O
S1, S2 first and second virtual straight lines
L1, L2 Depression amount of the first and second concave

curved surface portions

8, 12
d Core thickness of drill body 1
α Radial rake angle on the outer peripheral edge 15 side of the cutting edge 5

Claims

A chip discharge groove extending toward the rear end is formed on the outer periphery of the tip end of the drill body rotated around the axis, and the inner wall surface of the chip discharge groove facing the drill rotation direction intersects the tip flank of the drill body. A drill in which a cutting edge is formed in a ridge line portion, and a convex curvilinear cutting edge portion forming a curved shape convex in the drill rotation direction is formed on the outer peripheral end side of the cutting blade. On the inner peripheral side of the convex curved cutting edge portion, a concave curved cutting edge portion is formed which forms a concave curved shape on the rear side in the drill rotation direction and smoothly continues to the convex curved cutting edge portion. The inner wall surface facing the rear side in the drill rotation direction of the chip discharge groove is formed in a smooth curved shape from the concave curved cutting edge part to the outer peripheral end of the cutting edge from the convex curved cutting edge part Is located on the outer peripheral side, reaches the heel part, and is perpendicular to the axis. There drill, wherein a second convex surface portions forming a convex curve that is convex in the drill rotation direction rear side.

2. The drill according to claim 1, wherein a rake angle in the radial direction on the outer peripheral end side of the cutting blade is set to a negative angle side.

A thinning portion connected to the inner peripheral end side of the cutting blade is formed on the tip side of the inner wall surface of the chip discharge groove, and the thinning portion has a concave curved valley shape, and the bottom portion of the valley is the above The first thinning portion that extends toward the inner peripheral end of the cutting blade while retracting toward the inner peripheral side of the drill body with respect to the inner wall surface is provided. Drill.

The said thinning part is provided in the front end side of the said 1st thinning part, and is equipped with the 2nd thinning part which reaches | attains the inner peripheral end of the said cutting blade, retreating further to the inner peripheral side with respect to the said valley bottom part The drill according to claim 3.

The core thickness of the drill body is set in a range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting blade. The drill of crab.

On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. On the inner wall surface facing the drill rotation direction rear side of the chip discharge groove, a second concave curved surface portion that is smoothly connected to the first concave curved surface portion and has a concave shape in the drill rotation direction is formed, In the cross section orthogonal to the axis, the dent amount L1 of the first concave curved surface portion from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction is the outer diameter D of the cutting blade. Is set in a range of −0.06 × D to 0, and a dent amount L2 of the second concave curved surface portion from the second virtual straight line intersecting the first virtual straight line at the axis is −0. It is set in the range of 06 × D to 0.06 × D Drill according to any one of 1 to claim 5.

On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. On the inner wall surface facing the drill rotation direction rear side of the chip discharge groove, a second concave curved surface portion that is smoothly connected to the first concave curved surface portion and has a concave shape in the drill rotation direction is formed, 2. The curvature radius of the concave curve formed by the second concave curved surface portion is set to be larger than the curvature radius of the concave curve formed by the first concave curved surface portion in a cross section orthogonal to the axis. The drill according to any one of claims 6 to 6.

On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. A second concave curved surface portion having a concave shape in the drill rotating direction is formed on the inner wall surface facing the rear side in the drill rotating direction of the chip discharge groove, and between the first and second concave curved surface portions. Is formed with a tangential connection surface that contacts both the concave curve formed by the first concave curved surface portion and the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis. The drill according to any one of claims 1 to 7, wherein the first concave curved surface portion and the second concave curved surface portion are smoothly connected.

The radius of curvature of the convex curve formed by the convex curved surface portion in the cross section orthogonal to the axis is set in a range of 0.1 × D to 0.8 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 8, wherein the drill is characterized.

The radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section perpendicular to the axis is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 9, wherein the drill is characterized.

The radius of curvature of the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis is set in the range of 0.2 × D to 0.5 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 10, wherein:

The drill according to any one of claims 1 to 11, wherein a hard film is coated on a surface of at least a tip portion of the drill body.