JP2004034202A

JP2004034202A - Drill for machining deep hole

Info

Publication number: JP2004034202A
Application number: JP2002192830A
Authority: JP
Inventors: Makoto Hiranaka; 平中　誠
Original assignee: Toshiba Tungaloy Co Ltd
Current assignee: Tungaloy Corp
Priority date: 2002-07-02
Filing date: 2002-07-02
Publication date: 2004-02-05

Abstract

<P>PROBLEM TO BE SOLVED: To provide such a combination of the form of a flank at the tip of a main cutting edge of a drill with a thinning form as to improve chip discharging performance, cutting resistance, breakage resistance of a tool, and cutting performance in machining a deep hole. <P>SOLUTION: Thinning is applied to eliminate part of a chisel edge of a drill ground to have so-called spiral points, so that cutting edges around a center formed by thinning are smoothly arc-shaped with no inflection points as seen from the tip in an axial line direction for the whole range. Parts of the cutting edge around the center where they cross the main cutting edge are continuously formed with no inflection points, while leaving the length of the chisel edge by 3% or more of a drill diameter. Chip discharging performance and biting performance of the drill are improved, cutting resistance is reduced, and especially, cutting performance in deep hole machining can be improved. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
この発明は、深穴を高能率、高精度に加工するのに適したドリル形状に関するものである。
【０００２】
【従来の技術】
ドリルの先端逃げ面の研削に関して、従来からいくつかの刃研形状のドリルが知られており、その主なものを以下に列挙する。
（ａ）１つめは２段平面研削とシンニングを組み合わせた刃研形状であり、スリーレーキ刃研形状と呼ばれるものであり、超硬合金製ドリル等の刃研形状としてよく知られている。図３にスリーレーキ刃研形状のドリルの先端視形状を示す。また、図４の（ａ）、（ｂ）、（ｃ）、（ｄ）にスリーレーキ刃研方法の模式図を示す。
【０００３】
ドリルの主切れ刃稜線につらなる先端逃げ面、いわゆる２番を研削するとき、前記ドリルの中心軸線は、図４（ｃ）に示すよう砥石外周面に対して先端角θの１／２の角度傾けられる。そして、前記ドリルの回転方向の位置は、図４（ａ）に示すように、主切れ刃の外周部Ａ点と内周部Ｂ点を結んだ直線が前記砥石外周面と係合するように水平に位置決めされ、さらに、図４（ｂ）に示すように、前記２番の逃げ角（２番角）は、前記ドリルの中心軸線が前記砥石の中心軸線に対しＨ寸法の芯上がりにセットされ、前記芯上がり位置における前記砥石の接線角度によって付与される。
前記２番から連なり、前記ドリル回転方向に対し後ろ側に形成される先端逃げ面、いわゆる３番の研削方法は、前記２番の研削方法とほぼ同様であるが、回転方向の位置が図４（ａ）に示すように外周部Ａ´点と内周部Ｂ´を結んだ直線が前記砥石外周面と係合するように水平に位置決めされる。また、図４（ｂ）に示された前記ドリル軸線と砥石軸線の高さの差Ｈは、前記２番を研削するときより大きく設定されることによって、大きな逃げ角が付与される。その後、シンニング加工によって中心部付近に切れ刃が形成される。
【０００４】
この刃研方法は、被削材の材質や切削条件に応じて前記先端逃げ角や前記先端角などの基本形状を容易に変更できる利点がある。例えば、アルミニウム合金を加工する場合には、刃先へ凝着することを防止するため先端逃げ角を大きくし、硬度の高い被削材を加工する場合には、切れ刃強度を高めるため逃げ角を小さくするということが容易にできる。
【０００５】
（ｂ）２つめは円錐刃研形状である。図５にこの刃研形状のドリルの先端視形状を示す。また、図６にこの刃研方法の模式図を示す。この刃研方法は、主切れ刃先端逃げ面が円錐面の一部分となるように研削する方法であり、図６に示すように前記ドリルの中心軸線が砥石外周面に対して先端角θの１／２の角度に傾けられ、ＸＸ線回りに前記ドリルを回転させることによって前記主切れ刃先端逃げ面が研削される方法である。前記主切れ刃先端逃げ面は、頂角２βの円錐面で形成され、先端逃げ角は、前記円錐の軸線ＸＸと前記ドリルの中心軸線軸線とをＫだけずらすことにより与えられる。
この刃研形状のドリルでは、前記主切れ刃先端逃げ面の逃げ角は、主切れ刃中心部付近が外周部付近より大きくできるという特徴を有している。ドリルの切削機構上、前記主切れ刃中心部付近の先端逃げ角は前記外周部付近の先端逃げ角よりも大きくする必要があり、その点で、この刃研形状のドリルは合理的な先端逃げ角を得ることができる。したがって、ドリルの刃研方法として最も多く用いられてきた刃研方法である。
【０００６】
（ｃ）３つめは円筒刃研形状である。図７にこの刃研形状のドリルの先端視形状を示す。また、図８にこの刃研方法の模式図を示す。この刃研方法は主切れ刃先端逃げ面が円筒面の一部分となるように研削する方法であり、図８に示すように、前記ドリルの中心軸線が砥石外周面に対して先端角θの１／２の角度に傾けられ、ＸＸ線回りに前記ドリルを回転させることによって前記主切れ刃先端逃げ面が研削される刃研方法である。前記主切れ刃先端逃げ面の逃げ角は、前記円筒の軸線ＸＸと前記ドリルの中心軸線とをＫだけずらすことにより与えられる。その後、シンニング加工によって中心部付近に切れ刃が形成される。この刃研方法は段取り回数と研削除去量が少ないという点で優れている。
【０００７】
（ｃ）４つめはスパイラルポイント刃研形状である。図９にこの刃研形状のドリルの先端視形状を示す。また、図１０にこの刃研方法の一例を模式図で示す。
図１０に示すように、主切れ刃及びチゼルエッジの先端側逃げ面の研削方法は、砥石を中心軸線から離間し平行な軸線回りに自転させ、さらにドリル中心軸線回りに公転させることによって前記ドリル中心軸線回りに遊星運動させ、さらに前記砥石による研削加工位置が前記主切れ刃から前記ドリルの反回転方向に向かって離間するにしたがい前記ドリル中心軸線方向に平行且つ後端方向へ送ることによって前記先端逃げ面が略ねじれ面で形成される刃研方法である。この刃研方法によるドリルは、切れ刃の外周部付近の先端逃げ角を小さくしたまま中心部付近の先端逃げ角を大きくすることができる。また、該刃研形状のドリルは、他の刃研形状のドリルにくらべると、チゼルエッジのすくい角が大きくなり、軸線方向先端視においてチゼルエッジの形状が丸くＳ字型になり、チゼルエッジの方向からみたドリル中心部の先端角が鋭利になるため、シンニング加工を行わなくても、上述した他の刃研形状のドリルにくらべ加工時の喰い付き性、求心性といった切削性に優れている。
【０００８】
その他に考案された刃研形状のドリルとして、実開平６−２４８１０に開示されたドリルがある。これは（ｄ）項で記述したスパイラルポイント刃研形状のドリルに類似したものである。該ドリルの軸線方向先端視を図１１に示す。図１２は図１１において矢印Ｙの方向からみた側面図である。主切れ刃が砥石表面によってほぼ研削されるドリルの回転位置を研削開始の回転位置ψ＝０゜、前記研削開始の回転位置から９０゜回転した位置を研削完了の回転位置ψ＝９０゜とすれば、図１３と図１４は、それぞれ前記研削開始の位置と研削完了の位置におけるドリルと砥石と係合状態を示す図である。また、図１５乃至図１９は、図番の順番に、前記ドリルの回転位置ψが−３０゜、０゜、３０゜、６０゜、９０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示す図である。
【０００９】
実開平６−２４８１０に開示された考案の記載によれば、該ドリルは、ドリル直径の２５乃至４０％の心厚を有しドリルポイントグラインディングによって研削された主逃げ面を備えた特に超硬のツイストドリルにおいて、
（イ）研削開始時に、砥石の表面に対するツイストドリルの回転位置を０゜と
し、この回転位置でほぼ主切れ刃を研削し、その際主逃げ面を形成すべき砥石表面の外周輪郭をドリル軸線を超えて突出させ、この超えた距離を超過量と呼べばこの超過量がドリル直径の３乃至１５％であり、
（ロ）引き続く研削時に砥石を半径方向で前記超過位置から半径方向の送りに
よって、主逃げ面の研削完了時に砥石の外周輪郭がドリル軸線を超えない手前の位置にあるように引き戻し、ドリル軸線を超えない手前の位置とドリル軸線との間隔を不足量と呼べば、この不足量がドリル直径の７乃至１４％であり、
（ハ）主切れ刃の研削から出発して全研削範囲にわたり、主切れ刃からの距離
の増大に伴なって先端逃げ角を増大するように、母線の軸方向送りをドリル軸方向で累進的に増大させて成るツイストドリルである。
この発明のドリルによれば、チゼルエッジがほぼ連続的に両方の主切れ刃に移行するように研削が行われており、切りくずに衝突するエッジが形成されない。という効果が得られる。
【００１０】
【発明が解決しようとする課題】
しかしながら、上述の従来刃研形状のドリルには、以下に列挙するような問題点がある。
（ａ）まず、スリーレーキ刃研のドリルに関して、シンニング前の、すなわち２段平面刃研を施されただけのドリル形状は、チゼルエッジの軸線方向先端視における形状が直線となり、すくい角も大きな負角であるため、切削抵抗が高く、喰い付き性に劣るという問題がある。そのようなことからスリーレーキ刃研では、シンニングを追加することによりチゼルエッジのすくい角を大きくする必要があった。そのためスリーレーキ刃研では段取り回数と研削除去量が多くなってしまい、多くの手間と時間がかかり、砥石の寿命も短いという問題がある。
【００１１】
（ｂ）次に、円錐刃研のドリルは、チゼルエッジが大きな負のすくい角となり、軸線方向先端視において直線に近い切れ刃形状となるため、切削抵抗が高く、切りくずの排出性が良くないという問題がある。
【００１２】
（ｃ）円筒刃研のドリルは、前述した２段平面研削と同様な問題を有している。さらに、刃研方法の性質上、ドリルの外周から中心部へ向かうにしたがって逃げ角が小さくなる。そのため、一般的に高い送り量で加工されるアルミニウム合金等の被削材においては、最も逃げ角の小さくなるドリル中心部付近の切れ刃に被削材の凝着が発生してしまう。これを避けるため、中心部付近の切れ刃先端逃げ角を大きくしようとすると、外周部の逃げ角が必要以上に大きくなってしまうことから、主切れ刃の強度低下をきたしてしまい、ドリルの切れ刃欠損や破損が生じ易くなってしまう。
【００１３】
（ｄ）スパイラルポイント刃研したドリル及び実開平６−２４８１０に開示された考案のドリルは、他の刃研形状のドリルにくらべるとチゼルエッジのすくい角が大きいため、シンニングがなくても切削性に優れたドリルであるが、延性が高い被削材や凝着しやすい被削材を加工する場合、チゼルエッジの切りくずポケット容量が不十分なため、切りくずがうまく排出されないという問題がある。
上述した従来ドリルは、特に深穴加工において、切削抵抗、切りくず処理性、耐凝着性といった性能が不十分なため、加工条件的な制約を受けたり、加工した穴の精度が悪かったり、場合によっては加工不可能な状況となってしまうことがある。
【００１４】
本発明は、以上のような課題に鑑みなされたもので、ドリルの喰い付き性、耐破損性、および切りくず排出性を改善し、深穴を高能率、高精度に行うのに適したドリルを提供することを目的とする。
【００１５】
【課題を解決するための手段】
本発明の第１発明のドリルは、中心軸線周りに回転させられるドリル本体の外周部に前記中心軸線に沿って延在するフルート溝２を形成するとともに、このフルート溝２の回転方向を向く壁面と先端面との交わる稜線が主切れ刃３をなすツイストドリルにおいて、先端逃げ面をなす前記先端面４が略ねじれ面、または曲面で形成された一種のスパイラルポイント刃研されたドリルであり、Ｘシンニング６によってチゼルエッジ７の一部が除去されるとともに該ドリルの中心近傍に第２切れ刃５が形成されたことを特徴とする。また、前記Ｘシンニングによって形成される前記第２切れ刃が全ての範囲にわたってドリル軸線方向先端視において円弧形状をなし、且つ前記第２切れ刃よりも外周側に形成される前記主切れ刃との交差部がなめらかにつなげられていることを特徴とする。さらに、前記第２切れ刃によって除去された後の前記チゼルエッジの長さが前記ドリル直径の３％以上とされることを特徴とするドリルである。
【００１６】
第２の発明のドリルは、中心軸線周りに回転させられるドリル本体の外周部に前記中心軸線に沿って延在するフルート溝を形成するとともに、このフルート溝の回転方向を向く壁面と先端面との交わる稜線が主切れ刃をなすツイストドリルにおいて、先端逃げ面をなす前記先端面が前記主切れ刃から離間するにしたがって逃げ角を漸次増大するような略ねじれ面、または曲面で形成された一種のスパイラルポイント刃研されたドリルであり、Ｘシンニングによってチゼルエッジの一部が除去され、該ドリルの中心近傍に第２切れ刃が形成されたことを特徴とする。また、前記Ｘシンニングによって形成される前記第２切れ刃が全ての範囲にわたってドリル軸線方向先端視において円弧形状をなし、且つ前記第２切れ刃よりも外周側に形成される前記主切れ刃との交差部がなめらかにつなげられていることを特徴とする。さらに、前記第２切れ刃によって除去された後の前記チゼルエッジの長さが前記ドリル直径の３％以上とされることを特徴とするドリルである。
【００１７】
前述したように、スパイラルポイント刃研形状のドリルは、チゼルエッジの切りくずポケット容積が狭いため、切りくずがつまり易く、切りくず排出性に問題があった。そこで、Ｘシンニングを施すことにより、前記シンニングで形成される切れ刃の切りくずポケットは容積が増すことによって、切りくずづまりの解消、切りくず排出性の改善が図られる。さらに、ドリルの切削抵抗への影響が大きい中心部付近の切れ刃のすくい角が高められることによって、大幅な切削抵抗の低減が図られる。
【００１８】
また、前記Ｘシンニングによって形成される第２切れ刃は、軸線方向先端視において全ての範囲が変曲点のない円弧状をなし、前記第２切れ刃とそれよりも径方向外側に設けられた主切れ刃と交差する部分に変曲点がなく、なめらかにつながれる。これによって、切りくずは急激な変形を生じることなく、体積の小さい排出性の良好な切りくずとなる。また、切りくずの急激な変形に起因する切削抵抗の変動も解消され、切れ刃損傷の改善にもつながる。
【００１９】
スパイラルポイント刃研したドリルでは、チゼルエッジ方向からみたドリル中心部の先端形状が鋭利になるため、Ｘシンニングによってチゼルエッジを完全に除去してしまうと、ドリル中心部の強度低下をきたしてしまうため、この部分がドリル破損の起点となり易くなる。そこで、本発明のドリルは、Ｘシンニング加工後にチゼルエッジを残し、かつ、前記チゼルエッジの長さが前記ドリル直径の３％以上とすることによって、前記ドリル中心部の切れ刃強度が十分確保され破損を阻止することができる。その上、切削抵抗の低減効果、切りくず排出効果をほとんど損なうことがない。
【００２０】
【発明の実施の形態】
次に、この発明の実施形態について、図面を参照しながら説明する。図１は第１の実施形態として、曲線状主切れ刃のツイストドリルの先端部を示したものであり、図２は図１における矢印Ｘの方向からみた側面形状を示した図である。
ドリル本体１には軸線に沿ってねじれを伴なう２条のフルート溝２が形成されている。前記フルート溝２の回転方向に向かう壁と先端面４との交わる稜線が主切れ刃３をなし、先端角θを形成している。前記主切れ刃３は、軸線方向先端視においてドリルの回転方向に向かって凹曲線状をなしている。前記先端面４が前記主切れ刃の先端逃げ面４をなし、前記先端逃げ面４は、ねじれ面または曲面で形成されており、その研削方法はスパイラル刃研方法や実開平６−２４８１０に開示された考案の刃研方法などが挙げられる。前記先端逃げ面の逃げ角は、一定角度に設定されたり、場合によっては被削材の凝着を防止するため、または切削抵抗を下げるために、前記主切れ刃から離間するにしたがって大きくしたりというように状況に応じて適宜設定される。
【００２１】
前記ドリル本体１の中心部に形成されたチゼルエッジの一部を除去するように、Ｘシンニングが設けられ、前記Ｘシンニングによって形成される第２切れ刃は、軸線方向先端視において、全ての範囲で変曲点のない円弧状をなし、前記第２切れ刃と前記主切れ刃との交差する部分も変曲点がなくなめらかに繋がっている。前記第２切れ刃は、もともとのチゼルエッジにくらべ、すくい角が大きくなり、切りくずを排出するための切りくずポケット容積が大きくなるため、ドリルの切削抵抗、喰い付き性、切りくず排出性を改善する効果がある。実際の加工に関しては、穴曲がりや穴精度が向上し、特に深穴加工における切削性が改善される。また、前記チゼルエッジは、前記Ｘシンニングによって完全に除去されてしまうと、切削抵抗の低減効果と切りくず処理性の改善効果は得られるものの、ドリル中心部の強度低下により、切れ刃欠損やドリル破損が生じてしまう。後述の実験結果で述べるように、軸方向先端視において、前記チゼルエッジの長さが前記ドリル直径の３％以上残っていれば、強度低下によるドリル破損が生じなくなり、切削抵抗の低減効果、切りくず処理性の改善効果を損なうこともない。
【００２２】
図２０は第２の実施形態として、直線切れ刃のツイストドリルの軸方向先端視における形状を示したものである。第１の実施形態のドリルに関して主切れ刃を直線としたものである。それ以外の先端逃げ面の研削方法、Ｘシンニングの方法、第２切れ刃の形状については第１の実施形態と同様である。
【００２３】
第１の実施形態、第２の実施形態ともに、発明の構成となるのは、ドリルの先端部の形状であるから、同一構成のドリルであれば、一体型のドリルであっても、あるいは、切れ刃を有する先端部を把持部等で構成された後端部に着脱可能とした分割構造のドリル、いわゆるスローアウェイ式ドリルであっても、同一の作用を有するものである。
【００２４】
以下では、第１の実施形態のドリルを用いて、従来刃研形状のドリルと比較実験を行った結果について詳述する。
切削試験では次の４項目を評価した。
▲１▼ドリルの喰い付き性の評価
▲２▼加工した穴の拡大しろの評価
▲３▼ドリルの耐折損性の評価
▲４▼切りくず形状（切りくず処理性）の評価
【００２５】
それでは、各項目の切削実験について、実験条件と実験結果について述べる。
▲１▼ドリルの喰い付き性の評価（加工可能な穴深さの調査）
この切削実験に用いたドリルの先端部刃研形状は、本発明の第１発明のドリル、そして、従来の刃研形状のドリルであるスパイラルポイント刃研したもの、２段平面刃研にＸシンニングしたもの、および、円筒刃研にＸシンニングしたもの、以上４種類である。
被削材は機械構造用炭素鋼Ｓ５０Ｃを用い、実験条件は、切削速度を６０ｍ／分，回転当り送りを０．３ｍｍ／回転とした。切削油は、水溶性切削油剤を３ＭＰａの油圧で供給した。評価項目は、ドリル直径をＤ、加工する穴深さをＬとして、両者の比Ｌ／Ｄを大きくしていったときの加工限界である。なお、深穴加工時にドリルの喰い付き性を改善するためにセンタ穴をあらかじめ加工したときの加工限界も同時に調査した。
【００２６】
結果は表１に示すように、従来ドリルは、センタ穴があってもＬ／Ｄ＝７までしか加工できなかったが、本発明のドリルは、センタドリルの下穴加工がなくてもＬ／Ｄ＝７まで加工でき、センタ穴があればＬ／Ｄ＝１０の加工が可能であった。本発明のドリルは、Ｘシンニングによって形成された第２切れ刃が切削抵抗と切りくず排出性の改善をもたらし、結果として、加工時のドリル振れまわりが抑えられ、従来ドリルよりも加工可能な穴深さが大幅に向上する。
表１

判定基準：センタ穴の有無による加工の可否
○…センタ穴がなくても加工可能（喰い付き性が良い）
△…センタ穴があれば加工可能
×…センタ穴があっても加工できない（喰い付き性が悪い）
【００２７】
▲４▼切りくず処理性の評価
次に、本発明のドリルにおける切りくず処理性を評価した。実験に用いたドリルは、図２１（ａ）に示した本発明の第１発明のドリルと、Ｘシンニングによって形成される第２切れ刃が図２１（ｂ）に示すように円弧と直線との組み合わせからなり変曲点を有する形状のドリルである。ドリルの直径はφ１６ｍｍ、被削材は機械構造用炭素鋼Ｓ５５Ｃを用い、実験条件は、切削速度を８０ｍ／分，送りを０．３ｍｍ／回転、加工する穴の深さＬは４８ｍｍであり、ドリルの直径Ｄとの比、Ｌ／Ｄは３とした。切削油は、水溶性切削油剤を１ＭＰａの油圧で外部より供給した。評価項目は切りくず形状である。
【００２８】
▲１▼切りくず形状の模式図を図２２に示す。本発明の第１発明のドリルから生じる切りくずは、他方の第２切れ刃に変曲点を有するドリルの切りくずにくらべると、変曲点における急激な変形が生じないことから折れ曲がりがなく、短くカールした容積の小さい切りくずとなる。そのため、切りくずの排出性が良好であり、排出される切りくずによって穴を傷つけることも減少する。また切りくずがスムーズに生成されるため切削力の変動が小さくなる。本発明の請求項３の記載は、上記の実験結果をもとにしたものである。
▲２▼ドリルの喰い付き性の評価（加工した穴の拡大しろ評価）
この切削試験に用いたドリルの先端部刃研形状は、本発明の第１発明のドリル、そして、従来の刃研形状のドリルである円筒刃研にＸシンニングしたもの、２段平面刃研にＸシンニングしたものの３種類である。ドリルの直径は全てφ１６ｍｍである。
被削材は機械構造用炭素鋼Ｓ５５Ｃを用い、試験条件は、切削速度を８０ｍ／分，回転当り送りを０．３ｍｍ／回転，加工する穴の深さＬは４８ｍｍであり、ドリルの直径Ｄとの比、Ｌ／Ｄは３とした。切削油は、水溶性切削油剤を１ＭＰａの油圧で外部より供給した。評価方法は、ドリルの喰い付き時の振れまわりを比較するため、ドリルの直径と加工した穴の直径の差、いわゆる、拡大しろを比較した。
【００２９】
結果を図２３に示す。本発明のドリルは、拡大しろがおよそ０．００５ｍｍから０．０２５ｍｍと従来の刃研形状のドリルよりも明らかに小さくなった。このことは、喰い付き性が良好で、ドリルの振れまわりが小さいことを示しており、特に深穴加工において穴の真円度、真直度といった加工精度が高められる。
【００３０】
▲３▼ドリルの耐破損性の調査
本発明のドリルにおいて、シンニングによって除去された後のチゼルエッジの長さが耐破損性におよぼす影響を調査した。実験に用いたドリルは、本発明の第１発明のドリルであり、Ｘシンニング後のチゼルエッジの長さがドリル直径の３％（０．６６ｍｍ）のドリルと、同１％（０．２２ｍｍ）のドリルである。ともにドリル直径はφ２２ｍｍとした。被削材は機械構造用炭素鋼Ｓ５５Ｃを用い、試験条件は、切削速度を６０ｍ／分、加工する穴の深さＬは６６ｍｍであり、ドリルの直径Ｄとの比、Ｌ／Ｄは３とした。切削油は、水溶性切削油剤を１ＭＰａの油圧で外部より供給した。調査方法は、送りを０．１０ｍｍ／回転から加工を開始し、０．０５ｍｍ／回転きざみに送りを上げていったときにドリルの折損が生じたときの送り値を比較した。なお、送りの上限は０．４０ｍｍ／回転とした。
【００３１】
結果を図２４に示す。チゼルエッジの長さがドリル直径の１％のドリルは、送り０．２０ｍｍ／回転及び０．２５ｍｍ／回転において破損が生じた。これに対し、チゼルエッジの長さがドリル直径の３％の第１発明のドリルは、送り０．４０ｍｍ／回転まで上げても破損を生じることがなく、正常な工具損傷を示しており、高能率な穴加工を可能とする。
【００３２】
【発明の効果】
ドリルの先端逃げ面が略ねじれ面、または曲面で形成される一種のスパイラルポイント刃研形状のドリルであって、Ｘシンニングによってチゼルエッジの一部が除去され、該ドリルの中心近傍に第２切れ刃が形成されたことを特徴とする本発明のドリルは、以下に列挙した効果を有する。
▲１▼主切れ刃の先端逃げ面形状は、他の刃研形状のドリルにくらべ、主切れ刃中央部の先端逃げ角が大きくドリルの切削機構上合理的な逃げ角設定が可能であり、主切れ刃の強度を損なうことなく、優れた耐凝着性をもたらす。
▲２▼Ｘシンニングによって形成される第２切れ刃は、すくい角が大きく、切りくずポケットが大きいことから切削抵抗の低減、喰い付き性向上とともに切りくず排出性の改善をもたらす。
▲３▼前記第２切れ刃は、全ての範囲で変曲点がないように円弧状とされ、且つ前記第２切れ刃とそれより外周側に設けられた主切れ刃との交差する部分は、なめらかにつながれることによって、切りくずの急激な変形及び折れが発生せず、切りくずの体積が小さくなるとともに切削力の変動が抑えられる。
▲４▼前記Ｘシンニングによって除去された後のチゼルエッジが軸線方向先端視において、ドリル直径の３％以上の長さを有することにより、ドリル中心部の強度が保たれ、ドリルの破損が発生しなくなる。しかも、切削低減効果、切りくず排出性を損なうことがない。
以上に列記した効果により、従来ドリルよりも穴深さの加工限界が高くなり、加工した穴の精度が向上し、さらに高い加工条件による高能率加工が可能となる。
【図面の簡単な説明】
【図１】本発明のドリルの軸線方向先端視における形状を示す。
【図２】本発明のドリルの図１における矢印Ｘの方向からみた側面図を示す。
【図３】従来ドリルであるスリーレーキ刃研形状のドリルの軸線方向先端視における形状を示す。
【図４】スリーレーキ刃研方法の模式図を示す。
【図５】従来ドリルである円錐刃研形状ドリルの軸線方向先端視の形状を示す。
【図６】円錐刃研方法の模式図を示す。
【図７】従来ドリルである円筒刃研形状ドリルの軸線方向先端視の形状を示す。
【図８】円筒刃研方法の模式図を示す。
【図９】従来ドリルであるスパイラルポイント刃研形状ドリルの軸線方向先端視の形状を示す。
【図１０】スパイラルポイント刃研方法の模式図を示す。
【図１１】スパイラルポイント刃研に類似した形状のドリルの軸線方向先端視における形状を示す。
【図１２】図１１における矢印Ｙの方向からみた側面図を示す。
【図１３】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝０゜における主切れ刃先端逃げ面と砥石との係合状態を示す。
【図１４】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝９０゜における主切れ刃先端逃げ面と砥石との係合状態を示す。
【図１５】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝−３０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示すドリルの軸線方向先端視の形状を示す。
【図１６】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示すドリルの軸線方向先端視の形状を示す。
【図１７】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝３０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示すドリルの軸線方向先端視の形状を示す。
【図１８】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝６０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示すドリルの軸線方向先端視の形状を示す。
【図１９】図１１，図１２に示したドリルの主切れ刃先端逃げ面を研削するときのドリルの回転方向位置ψ＝９０゜における砥石の外周輪郭、主切れ刃先端逃げ面の母線及びドリルと砥石との接触面を示すドリルの軸線方向先端視の形状を示す。
【図２０】本発明のドリルの第２実施例における軸線方向先端視の形状を示す。
【図２１】本発明のドリルにおいて切りくず形状に及ぼすシンニング切れ刃形状の影響を調査するために実験で使用したドリルの軸方向先端視の形状。
【図２２】本発明のドリルにおけるシンニング切れ刃形状と切りくず形状の関係。
【図２３】本発明のドリルと従来ドリルとの間で加工した穴の拡大しろを比較した結果を示す。
【図２４】本発明のドリルにおけるチゼルエッジの長さとドリル耐破損性の関係。
【符号の説明】
１　ドリル本体
２　フルート溝
３　主切れ刃
４　主切れ刃先端逃げ面
５　Ｘシンニングによって形成される第２切れ刃
６　Ｘシンニング
７　チゼルエッジ
８　マージン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a drill shape suitable for processing a deep hole with high efficiency and high precision.
[0002]
[Prior art]
With respect to the grinding of the flank of the tip of a drill, several edge-shaped drills are conventionally known, and the main ones are listed below.
(A) The first is a sharpened shape obtained by combining two-step surface grinding and thinning, and is called a three-rake sharpened shape, which is well known as a sharpened shape such as a cemented carbide drill. FIG. 3 shows the shape of a drill having a three-rake edge shape as viewed from the tip. 4 (a), 4 (b), 4 (c) and 4 (d) are schematic diagrams of the three lake blade grinding method.
[0003]
When grinding the flank of the tip, which is the so-called flank, which is connected to the ridgeline of the main cutting edge of the drill, the center axis of the drill is an angle of 1/2 of the tip angle θ with respect to the outer peripheral surface of the grindstone as shown in FIG. Can be tilted. Then, as shown in FIG. 4A, the position of the drill in the rotation direction is such that a straight line connecting the outer peripheral point A and the inner peripheral point B of the main cutting edge engages with the outer peripheral surface of the grindstone. Positioned horizontally, and as shown in FIG. 4 (b), the second clearance angle (second angle) is set so that the center axis of the drill is H-centered with respect to the center axis of the whetstone. And the angle is given by the tangent angle of the grinding wheel at the center rising position.
The so-called No. 3 grinding method, which is a tip flank formed from the No. 2 and formed on the rear side with respect to the drill rotation direction, is almost the same as the No. 2 grinding method. As shown in (a), the straight line connecting the point A 'of the outer peripheral portion and the inner peripheral portion B' is positioned horizontally so as to engage with the outer peripheral surface of the grinding wheel. Further, the difference H between the height of the drill axis and the height of the grindstone axis shown in FIG. 4B is set to be larger than when the No. 2 is ground, so that a large clearance angle is provided. Thereafter, a cutting edge is formed near the center by thinning.
[0004]
The edge grinding method has an advantage that the basic shape such as the tip clearance angle or the tip angle can be easily changed according to the material of the work material and the cutting conditions. For example, when machining an aluminum alloy, increase the clearance angle at the tip to prevent adhesion to the cutting edge, and when machining a hard work material, increase the clearance angle to increase the cutting edge strength. It can easily be made smaller.
[0005]
(B) The second has a conical blade shape. FIG. 5 shows the shape of the drill having the sharpened edge as viewed from the front end. FIG. 6 shows a schematic diagram of the edge grinding method. This grinding method is a method of grinding so that the flank of the leading edge of the main cutting edge becomes a part of a conical surface. As shown in FIG. 6, the center axis of the drill has a tip angle .theta. / 2 and the flank of the main cutting edge is ground by rotating the drill around the XX line. The flank of the main cutting edge is formed by a conical surface having a vertex angle of 2β, and the flank of the tip is given by shifting the axis XX of the cone and the axis of the center axis of the drill by K.
This edge-shaped drill is characterized in that the clearance angle of the flank of the tip of the main cutting edge can be larger near the center of the main cutting edge than near the outer periphery. Due to the cutting mechanism of the drill, the tip clearance angle near the center of the main cutting edge needs to be larger than the tip clearance angle near the outer peripheral part. In this regard, this sharpened drill has a reasonable tip clearance. You can get the corner. Therefore, it is the most widely used method for sharpening a drill.
[0006]
(C) The third has a cylindrical blade shape. FIG. 7 shows the shape of the drill having the sharpened edge as viewed from the front end. FIG. 8 is a schematic view of the edge grinding method. This grinding method is a method of grinding so that the flank of the leading edge of the main cutting edge becomes a part of the cylindrical surface. As shown in FIG. 8, the center axis of the drill has a tip angle .theta. / 2 is an angle grinding method, wherein the flank of the main cutting edge is ground by rotating the drill around the XX line. The clearance angle of the flank of the main cutting edge is given by shifting the axis XX of the cylinder and the center axis of the drill by K. Thereafter, a cutting edge is formed near the center by thinning. This blade grinding method is excellent in that the number of setups and the amount of grinding removal are small.
[0007]
(C) The fourth is a spiral point sharpened shape. FIG. 9 shows the shape of the drill having the sharpened edge as viewed from the front end. FIG. 10 is a schematic view showing an example of the blade grinding method.
As shown in FIG. 10, the method of grinding the flank on the tip side of the main cutting edge and the chisel edge is such that the grindstone is rotated about a parallel axis away from the center axis, and further revolves about the center axis of the drill to thereby revolve the center of the drill. The planetary movement around the axis, and further the grinding position by the grindstone is separated from the main cutting edge in the counter-rotating direction of the drill, so that it is parallel to the direction of the axis of the drill and is fed toward the rear end so as to move the tip. This is a blade grinding method in which the flank is formed with a substantially twisted surface. The drill according to the blade grinding method can increase the clearance angle near the center while keeping the clearance angle near the outer periphery of the cutting edge small. In addition, the drill having the sharpened edge has a larger rake angle of the chisel edge than the other sharpened drills, and the chisel edge has a rounded S-shape when viewed from the front in the axial direction, and is viewed from the direction of the chisel edge. Since the tip angle at the center of the drill becomes sharp, it is excellent in cutting performance such as biting property and centripetal property in the processing compared to the above-mentioned other edge-shaped drills without performing the thinning processing.
[0008]
As another invented drill having a sharpened edge, there is a drill disclosed in Japanese Utility Model Laid-Open No. Hei 6-24810. This is similar to the spiral point sharpened drill described in section (d). FIG. 11 shows a front view of the drill in the axial direction. FIG. 12 is a side view as viewed from the direction of arrow Y in FIG. The rotation position of the drill where the main cutting edge is almost ground by the grindstone surface is the rotation position of the grinding start ψ = 0 °, and the position rotated by 90 ° from the rotation position of the grinding start is the rotation position of the grinding completion ψ = 90 °. For example, FIGS. 13 and 14 are diagrams showing the engagement state between the drill and the grindstone at the grinding start position and the grinding completion position, respectively. In addition, FIGS. 15 to 19 show, in the order of the figure numbers, the outer peripheral contour of the grindstone and the flank of the leading edge of the main cutting edge when the rotation position の of the drill is −30 °, 0 °, 30 °, 60 °, 90 °. It is a figure which shows the contact surface of a bus bar, a drill, and a grindstone.
[0009]
According to the description of the invention disclosed in Japanese Utility Model Laid-Open Publication No. Hei 6-24810, the drill has a core thickness of 25 to 40% of the drill diameter and has a main flank surface ground by drill point grinding. In the twist drill of
(A) At the start of grinding, the rotation position of the twist drill with respect to the surface of the grinding wheel is set to 0 °.
In this rotation position, the main cutting edge is almost ground, and at this time, the outer peripheral contour of the grindstone surface on which the main flank is to be formed is projected beyond the drill axis, and the excess distance is called the excess amount. Is 3 to 15% of the drill diameter,
(B) To feed the grinding wheel in the radial direction from the excess position in the radial direction during subsequent grinding
Therefore, when the grinding of the main flank is completed, the grinding wheel is pulled back so that the outer peripheral contour is at a position before the drill axis, and the distance between the position before the drill axis and the drill axis is called an insufficient amount. The shortage is 7-14% of the drill diameter,
(C) The distance from the main cutting edge over the entire grinding range starting from the grinding of the main cutting edge
This is a twist drill in which the axial feed of the generatrix is progressively increased in the axial direction of the drill so as to increase the clearance angle at the tip with an increase in the diameter of the tip.
According to the drill of the present invention, grinding is performed so that the chisel edge shifts to both main cutting edges almost continuously, and an edge that collides with a chip is not formed. The effect is obtained.
[0010]
[Problems to be solved by the invention]
However, the above-mentioned conventional edge-shaped drill has the following problems.
(A) First, with respect to the drill of the three-rake edge grinder, the shape of the drill before thinning, that is, only the two-stage flat edge grinder is performed, has a straight line as viewed from the axial end of the chisel edge, and a large rake angle. Therefore, there is a problem that the cutting resistance is high and the biting property is poor. Therefore, in Three Lake Blade Research, it was necessary to increase the rake angle of the chisel edge by adding thinning. Therefore, the number of setups and the amount of grinding removal in the three rake blade labs are increased, so that much labor and time are required, and the life of the grindstone is short.
[0011]
(B) Next, in the drill of the conical blade, the chisel edge has a large negative rake angle and has a cutting edge shape that is close to a straight line when viewed from the front in the axial direction, so that the cutting resistance is high and the chip discharge property is poor. There is a problem.
[0012]
(C) The cylindrical edge grinding drill has the same problem as the two-stage surface grinding described above. Further, due to the nature of the edge grinding method, the clearance angle becomes smaller from the outer periphery of the drill toward the center. Therefore, in the case of a work material such as an aluminum alloy which is generally processed at a high feed rate, adhesion of the work material occurs on the cutting edge near the center of the drill where the relief angle is the smallest. In order to avoid this, if the clearance angle at the tip of the cutting edge near the center is increased, the clearance angle at the outer periphery becomes unnecessarily large. Blade loss or breakage is likely to occur.
[0013]
(D) The spiral point sharpened drill and the drill of the invention disclosed in Japanese Utility Model Application Laid-Open No. 6-24810 have a larger rake angle of the chisel edge than other sharpened drills, so that the machinability is improved even without thinning. Although it is an excellent drill, when machining a work material having a high ductility or a work material that easily adheres, there is a problem that the chip is not discharged well due to an insufficient chip pocket capacity of the chisel edge.
Conventional drills described above, especially in deep hole drilling, cutting resistance, chip disposal, poor performance such as anti-adhesion, due to restrictions on processing conditions, or the accuracy of the drilled hole is poor, In some cases, processing may be impossible.
[0014]
The present invention has been made in view of the above-described problems, and has improved drill biting, breakage resistance, and chip evacuation, and is suitable for drilling deep holes with high efficiency and high precision. The purpose is to provide.
[0015]
[Means for Solving the Problems]
The drill according to the first aspect of the present invention has a flute groove 2 extending along the central axis formed on an outer peripheral portion of a drill body that is rotated around the central axis, and a wall surface facing the rotational direction of the flute groove 2. In a twist drill in which a ridge line intersecting with a tip surface forms a main cutting edge 3, the tip surface 4 forming a tip flank is a kind of spiral point sharpened drill formed of a substantially twisted surface or a curved surface, A part of the chisel edge 7 is removed by the X thinning 6, and the second cutting edge 5 is formed near the center of the drill. In addition, the second cutting edge formed by the X thinning is formed in an arc shape in the distal end direction in the drill axis direction over the entire range, and the second cutting edge is formed closer to the outer peripheral side than the second cutting edge. It is characterized in that the intersections are smoothly connected. Furthermore, the length of the chisel edge after being removed by the second cutting edge is 3% or more of the drill diameter.
[0016]
A drill according to a second aspect of the present invention forms a flute groove extending along the center axis on an outer peripheral portion of a drill body that is rotated around the center axis, and a wall face and a tip end face facing the rotation direction of the flute groove. In the twist drill in which the ridge line intersecting forms a main cutting edge, a type formed by a substantially twisted surface or a curved surface in which the front end surface forming a front flank gradually increases the clearance angle as the front flank separates from the main cutting edge. Wherein a part of the chisel edge is removed by X thinning and a second cutting edge is formed near the center of the drill. In addition, the second cutting edge formed by the X thinning is formed in an arc shape in the distal end direction in the drill axis direction over the entire range, and the second cutting edge is formed closer to the outer peripheral side than the second cutting edge. It is characterized in that the intersections are smoothly connected. Furthermore, the length of the chisel edge after being removed by the second cutting edge is 3% or more of the drill diameter.
[0017]
As described above, the drill having the spiral point sharpened shape has a small chip pocket volume at the chisel edge, so that the chips are easily clogged, and there is a problem in chip dischargeability. Therefore, by performing the X thinning, the chip pocket of the cutting edge formed by the thinning has an increased volume, thereby eliminating chip jamming and improving chip dischargeability. Further, by increasing the rake angle of the cutting edge near the center, which has a large influence on the cutting resistance of the drill, the cutting resistance can be significantly reduced.
[0018]
In addition, the second cutting edge formed by the X thinning has an arc shape having no inflection point in the entire range when viewed from the front in the axial direction, and is provided radially outward with respect to the second cutting edge. There is no inflection point at the intersection with the main cutting edge, and the connection is smooth. As a result, the chips are small in volume and have good dischargeability without abrupt deformation. Further, the fluctuation of the cutting resistance due to the rapid deformation of the chips is also eliminated, which leads to the improvement of the cutting edge damage.
[0019]
Since the tip of the center of the drill as viewed from the chisel edge direction becomes sharp in a drill with a spiral point blade, if the chisel edge is completely removed by X thinning, the strength of the drill center will decrease. The portion is likely to be a starting point for drill breakage. Therefore, in the drill of the present invention, by leaving the chisel edge after the X-thinning process, and by setting the length of the chisel edge to 3% or more of the drill diameter, the strength of the cutting edge at the center of the drill is sufficiently ensured to prevent breakage. Can be blocked. In addition, the effect of reducing cutting resistance and the effect of chip evacuation are hardly impaired.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a tip portion of a twist drill having a curved main cutting edge as a first embodiment, and FIG. 2 is a diagram showing a side surface shape viewed from the direction of arrow X in FIG.
The drill body 1 is formed with two flute grooves 2 that are twisted along the axis. The ridgeline where the wall facing the rotation direction of the flute groove 2 and the tip surface 4 intersects forms the main cutting edge 3 and forms the tip angle θ. The main cutting edge 3 has a concave curve shape in the rotation direction of the drill when viewed from the front in the axial direction. The tip end face 4 forms a tip flank 4 of the main cutting edge, and the tip flank 4 is formed of a twisted surface or a curved surface, and the grinding method is disclosed in a spiral blade grinding method or Japanese Utility Model Laid-Open No. 6-24810. There is a method of blade polishing of the invented device. The clearance angle of the flank of the tip is set to a fixed angle, or in some cases, increases as the distance from the main cutting edge increases, in order to prevent adhesion of the work material or to reduce cutting resistance. Thus, it is set appropriately according to the situation.
[0021]
X thinning is provided so as to remove a part of the chisel edge formed at the center of the drill main body 1, and the second cutting edge formed by the X thinning has an entire range in the axial front end view. It has an arc shape with no inflection point, and the intersection between the second cutting edge and the main cutting edge is also smoothly connected without any inflection point. Compared to the original chisel edge, the second cutting edge has a larger rake angle and a larger chip pocket volume for discharging chips, thereby improving the cutting resistance, biting property, and chip discharging property of the drill. Has the effect of doing Regarding actual machining, hole bending and hole accuracy are improved, and especially machinability in deep hole machining is improved. When the chisel edge is completely removed by the X thinning, the effect of reducing the cutting resistance and the effect of improving the chip controllability can be obtained. Will occur. As will be described in the experimental results described below, if the length of the chisel edge remains 3% or more of the drill diameter in the axial front view, drill breakage due to a decrease in strength does not occur, the cutting resistance is reduced, and chips are reduced. It does not impair the processability improvement effect.
[0022]
FIG. 20 shows the shape of a twist drill having a straight cutting edge as viewed from the front end in the axial direction, as a second embodiment. The main cutting edge of the drill according to the first embodiment is a straight line. Other methods of grinding the flank of the tip, X thinning, and the shape of the second cutting edge are the same as those in the first embodiment.
[0023]
In both the first embodiment and the second embodiment, the configuration of the invention is the shape of the tip portion of the drill. Therefore, as long as the drill has the same configuration, even if it is an integrated drill, or The same action can be obtained even with a drill having a divided structure in which a front end having a cutting edge can be attached to and detached from a rear end formed by a gripping portion, that is, a so-called throw-away type drill.
[0024]
Hereinafter, a result of a comparative experiment performed with a drill having a conventional edge-sharpening shape using the drill of the first embodiment will be described in detail.
In the cutting test, the following four items were evaluated.
(1) Evaluation of biting property of drill
(2) Evaluation of enlargement of processed hole
(3) Evaluation of breakage resistance of drill
(4) Evaluation of chip shape (chip controllability)
[0025]
Then, about the cutting experiment of each item, an experimental condition and an experimental result are described.
(1) Evaluation of biteability of drill (survey of drillable hole depth)
The tip sharpening shape of the drill used in this cutting experiment is the drill of the first invention of the present invention, and the spiral point sharpening which is a conventional sharpening shape drill, a two-stage flat edge sharpening and X thinning. And the X-thinned version of the cylindrical blade lab.
The work material used was S50C carbon steel for machine structure, and the experimental conditions were a cutting speed of 60 m / min and a feed per rotation of 0.3 mm / rotation. As the cutting oil, a water-soluble cutting oil was supplied at a hydraulic pressure of 3 MPa. The evaluation item is a processing limit when the ratio D / D of the drill diameter is D and the hole depth to be processed is L, and the ratio L / D is increased. In order to improve the biting property of the drill during deep hole drilling, the processing limit when the center hole was drilled in advance was also investigated.
[0026]
The results are shown in Table 1. As shown in Table 1, the conventional drill could only process up to L / D = 7 even with the center hole, but the drill according to the present invention could have L / D even without the center drill. It was possible to machine up to D = 7, and if there was a center hole, machining with L / D = 10 was possible. In the drill of the present invention, the second cutting edge formed by the X thinning provides an improvement in cutting resistance and chip evacuation. The depth is greatly improved.
Table 1

Judgment criteria: Whether or not machining is possible depending on the presence or absence of the center hole
○: Can be machined without center hole (good biting)
△: Processing is possible if there is a center hole
×: Cannot be processed even if there is a center hole (poor biting)
[0027]
(4) Evaluation of chip control
Next, the chip disposability of the drill of the present invention was evaluated. The drill used in the experiment was the drill of the first invention of the present invention shown in FIG. 21 (a), and the second cutting edge formed by X-thinning was an arc and a straight line as shown in FIG. 21 (b). It is a drill made of a combination and having an inflection point. The diameter of the drill is φ16 mm, the work material is carbon steel S55C for machine structure, and the experimental conditions are as follows: cutting speed is 80 m / min, feed is 0.3 mm / rotation, depth L of the hole to be machined is 48 mm, The ratio to the diameter D of the drill, L / D, was 3. As the cutting oil, a water-soluble cutting oil was supplied from the outside at a hydraulic pressure of 1 MPa. The evaluation item is a chip shape.
[0028]
(1) FIG. 22 shows a schematic diagram of the chip shape. Chips generated from the drill of the first invention of the present invention have no bend because there is no sharp deformation at the inflection point when compared with the chips of the drill having the inflection point on the other second cutting edge, and are short. Small chips with curled volume. Therefore, the chip discharge property is good, and the hole is less likely to be damaged by the discharged chip. Further, since the chips are generated smoothly, the fluctuation of the cutting force is reduced. Claim 3 of the present invention is based on the above experimental results.
(2) Evaluation of the biting property of the drill (evaluation of the enlarged margin of the processed hole)
The tip sharpening shape of the drill used in this cutting test is the drill of the first invention of the present invention, and the X-thinning of a cylindrical sharpening which is a conventional sharpening drill is a two-stage flat sharpening. X-thinned three types. All drill diameters are φ16 mm.
The work material was carbon steel S55C for machine structural use. The test conditions were a cutting speed of 80 m / min, a feed per rotation of 0.3 mm / rotation, a depth L of the hole to be machined of 48 mm, and a diameter D of the drill. And L / D was set to 3. As the cutting oil, a water-soluble cutting oil was supplied from the outside at a hydraulic pressure of 1 MPa. In the evaluation method, the difference between the diameter of the drill and the diameter of the processed hole, that is, the so-called enlargement margin, was compared in order to compare the whirling around the bite of the drill.
[0029]
The results are shown in FIG. The drill of the present invention has an enlargement margin of approximately 0.005 mm to 0.025 mm, which is clearly smaller than the conventional edge-shaped drill. This indicates that the biting property is good and the whirling of the drill is small, and particularly in deep hole drilling, the processing accuracy such as the roundness and straightness of the hole is improved.
[0030]
(3) Investigation of breakage resistance of drill
In the drill of the present invention, the effect of the length of the chisel edge after being removed by thinning on the fracture resistance was investigated. The drill used in the experiment is the drill of the first invention of the present invention. The length of the chisel edge after X thinning is 3% (0.66 mm) of the drill diameter, and the length of the chisel edge is 1% (0.22 mm). It is a drill. In both cases, the drill diameter was φ22 mm. The work material used was carbon steel S55C for machine structural use. The test conditions were a cutting speed of 60 m / min, a depth L of the hole to be machined of 66 mm, a ratio to the diameter D of the drill, and L / D of 3. did. As the cutting oil, a water-soluble cutting oil was supplied from the outside at a hydraulic pressure of 1 MPa. In the investigation method, the feed was started from 0.10 mm / rotation, and the feed values when the breakage of the drill occurred when the feed was increased in increments of 0.05 mm / rotation were compared. The upper limit of the feed was 0.40 mm / rotation.
[0031]
The results are shown in FIG. Drills with a chisel edge length of 1% of the drill diameter failed at 0.20 mm / rev and 0.25 mm / rev. On the other hand, the drill of the first invention, in which the chisel edge length is 3% of the drill diameter, does not break even when the feed is increased to 0.40 mm / rotation, shows normal tool damage, and shows high efficiency. Hole drilling is possible.
[0032]
【The invention's effect】
A kind of spiral point sharpened drill in which the flank of the drill is formed with a substantially twisted surface or a curved surface, wherein a part of a chisel edge is removed by X thinning, and a second cutting edge is provided near the center of the drill. The drill according to the present invention, in which is formed, has the effects listed below.
(1) The flank shape of the tip of the main cutting edge is larger than that of other sharpened drills. Provides excellent adhesion resistance without compromising the strength of the main cutting edge.
{Circle around (2)} The second cutting edge formed by X thinning has a large rake angle and a large chip pocket, so that the cutting resistance is reduced, the biting property is improved, and the chip discharging property is improved.
{Circle around (3)} The second cutting edge is formed in an arc shape so that there is no inflection point in all ranges, and the intersection between the second cutting edge and the main cutting edge provided on the outer peripheral side from the second cutting edge is The smooth connection does not cause abrupt deformation and breakage of the chip, thereby reducing the chip volume and suppressing the fluctuation of the cutting force.
{Circle over (4)} The chisel edge after being removed by the X thinning has a length of 3% or more of the drill diameter when viewed from the front in the axial direction, so that the strength of the center of the drill is maintained and the drill does not break. . Moreover, the cutting reduction effect and the chip dischargeability are not impaired.
By the effects listed above, the processing limit of the hole depth is higher than that of the conventional drill, the accuracy of the processed hole is improved, and high-efficiency processing under higher processing conditions becomes possible.
[Brief description of the drawings]
FIG. 1 shows the shape of a drill according to the present invention as viewed from the front in the axial direction.
FIG. 2 shows a side view of the drill according to the invention as seen from the direction of arrow X in FIG.
FIG. 3 shows the shape of a conventional three-rake edged drill, which is a conventional drill, as viewed from the front end in the axial direction.
FIG. 4 shows a schematic view of a three-rake blade grinding method.
FIG. 5 shows a shape of a conventional drill, which is a cone-shaped sharpened drill, as viewed from the front in the axial direction.
FIG. 6 shows a schematic view of a conical blade grinding method.
FIG. 7 shows the shape of a conventional cylindrical drill with a sharp edge in the axial direction as viewed from the front in the axial direction.
FIG. 8 shows a schematic view of a cylindrical blade grinding method.
FIG. 9 shows the shape of a conventional drill, a spiral point sharpening drill, as viewed from the front in the axial direction.
FIG. 10 shows a schematic view of a spiral point blade grinding method.
FIG. 11 shows the shape of a drill having a shape similar to the spiral point edge grinder when viewed from the front end in the axial direction.
12 shows a side view as seen from the direction of arrow Y in FIG.
FIG. 13 shows the engagement state between the flank of the leading edge of the main cutting edge and the grindstone at the rotation direction position ψ = 0 ° of the drill when the flank of the leading edge of the drill shown in FIGS. 11 and 12 is ground. .
FIG. 14 shows an engagement state between the flank of the main cutting edge and the grindstone at a rotational direction position ψ = 90 ° of the drill when the flank of the main cutting edge of the drill shown in FIGS. 11 and 12 is ground. .
FIG. 15 shows an outer peripheral contour of a grindstone at a rotational direction position {= -30} of the drill when grinding the flank of the main cutting edge of the drill shown in FIGS. 3 shows the shape of the drill as viewed from the front in the axial direction, showing the contact surface between the drill and the grindstone.
FIG. 16 shows the outer peripheral contour of the grindstone at the rotational direction position {= 0} of the drill when grinding the flank of the main cutting edge of the drill shown in FIGS. 3 shows the shape of a drill viewed from the front in the axial direction, showing the contact surface between the drill and the grindstone.
FIG. 17 shows the outer peripheral contour of the grindstone, the generatrix of the main flank tip flank and the drill at the rotation direction position ψ = 30 ° of the drill when grinding the flank of the main cutting edge of the drill shown in FIGS. 11 and 12; 3 shows the shape of a drill viewed from the front in the axial direction, showing the contact surface between the drill and the grindstone.
FIG. 18 is a diagram showing the outer peripheral contour of the grindstone, the generatrix of the main flank tip flank, and the drill at the rotation direction position ψ = 60 ° of the drill when grinding the flank of the main cutting edge of the drill shown in FIGS. 11 and 12. 3 shows the shape of a drill viewed from the front in the axial direction, showing the contact surface between the drill and the grindstone.
FIG. 19 shows the outer peripheral contour of the grindstone at the rotational direction position 方向 = 90 ° of the drill when grinding the flank of the main cutting edge of the drill shown in FIGS. 11 and 12, the bus bar of the flank of the main cutting edge, and the drill. 3 shows the shape of a drill viewed from the front in the axial direction, showing the contact surface between the drill and the grindstone.
FIG. 20 shows the shape of the drill according to the second embodiment of the present invention as viewed from the front in the axial direction.
FIG. 21 shows the shape of the drill in the axial front view used in the experiment to investigate the effect of the thinning cutting edge shape on the chip shape in the drill of the present invention.
FIG. 22 shows a relationship between a thinning cutting edge shape and a chip shape in the drill of the present invention.
FIG. 23 shows the result of comparing the enlargement margin of a hole processed between the drill of the present invention and a conventional drill.
FIG. 24 shows the relationship between chisel edge length and drill breakage resistance in the drill of the present invention.
[Explanation of symbols]
1 drill body
2 flute grooves
3 Main cutting edge
4 Main cutting edge tip flank
5 Second cutting edge formed by X thinning
6 X Thinning
7 Chisel edge
8 Margin

Claims

A flute groove extending along the center axis is formed in an outer peripheral portion of the drill body that is rotated around the center axis, and a ridgeline where a wall surface facing the rotation direction of the flute groove and a tip end face forms a main cutting edge. In the drill to be formed, the distal end surface forming the flank of the distal end was formed with a substantially twisted surface or a curved surface, a part of the chisel edge was removed by X thinning, and a second cutting edge was formed near the center of the drill. A drill characterized in that:

A flute groove extending along the center axis is formed in an outer peripheral portion of the drill body that is rotated around the center axis, and a ridgeline where a wall surface facing the rotation direction of the flute groove and a tip end face forms a main cutting edge. In the drill to be formed, the tip flank forming the tip flank is formed as a substantially twisted surface or a curved surface that gradually increases the flank angle as the distance from the main cutting edge increases, and a part of the chisel edge is formed by X thinning. A drill, wherein the second cutting edge has been formed near the center of the drill.

The second cutting edge formed by the X-thinning has an arc shape as viewed from the front in the drill axis direction over the entire range, and intersects with the main cutting edge formed on the outer peripheral side of the second cutting edge. The drill according to claim 1, wherein the drills are smoothly connected.

4. The chisel edge according to claim 1, wherein a part of the chisel edge is removed by the second cutting edge, and a length of the chisel edge after the removal is 3% or more of the drill diameter. 5. Drill.