JP2004090197A

JP2004090197A - Drill and method of manufacture

Info

Publication number: JP2004090197A
Application number: JP2002257598A
Authority: JP
Inventors: Masayuki Mabuchi; 馬渕　雅行
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2002-09-03
Filing date: 2002-09-03
Publication date: 2004-03-25
Anticipated expiration: 2022-09-03
Also published as: JP3979236B2

Abstract

PROBLEM TO BE SOLVED: To further effectively prevent the occurrence of chip clogging by further improving chip discharge performance. SOLUTION: In this drill, a chip discharge groove 15 twisted in a spiral shape to the axis O is formed on the tip part outer periphery of an almost columnar drill body 11 rotated around the axis O, and a cutting edge 16 is formed in a crossing ridgeline part between a wall surface 15A turning in the drill rotating direction of this chip discharge groove 15 and a tip flank 14. A tip side part of the chip discharge groove 15 continuing with the cutting edge 15 is formed as a narrow width part 18 having a twist angle and a groove width set constant to the axis O. A width expanding part 20 having a groove gradually expanding in the drill rotating direction and on the drill rotating directional rear side torward the rear end side to a virtual groove 19 extending the narrow part 18 to the rear end side, is formed in the chip discharge groove 15 on the rear end side from this narrow part 18. COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ドリル本体の先端部外周に螺旋状の切屑排出溝が形成されたドリルおよびその製造方法に関するものである。
【０００２】
【従来の技術】
この種のドリルにおいては、軸線回りに回転される略円柱状のドリル本体の先端部の外周に、該ドリル本体先端の先端逃げ面から後端側に向けて軸線回りにドリル回転方向の後方側に捩れる一対の切屑排出溝が該軸線に対して対称に形成され、これらの切屑排出溝のドリル回転方向側を向く壁面と上記先端逃げ面との交差稜線部に切刃が形成された、いわゆる２枚刃のツイストドリルが一般によく知られている。そして、さらにこのようなツイストドリルにあっては、例えば特許文献１において、図７ないし図９に示すようにドリル本体１の先端部外周に一対の切屑排出溝２，２が形成されてその先端に切刃３が設けられたドリルにおいて、上記切屑排出溝２の溝幅が、ドリル外径をＤとしたときに刃部先端から約２Ｄ離れたＡ点までの間はＷ_１、Ａ点からＢ点にかけてはＷ_１からＷ_２（＞Ｗ_１）に徐々に増え、Ｂ点から刃部後端に至る部分ではＷ_２で一定となるようにし、この後端側での切屑排出性の向上を図って切屑詰まりを防止するようにしたものが提案されている。
【０００３】
【特許文献１】
実開平５−６０７１５号公報
【０００４】
【発明が解決しようとする課題】
ところで、このドリルにおいては、こうして切屑排出溝２の溝幅をＡ点からＢ点に徐々に拡げるに際し、上記図７に示されるように切屑排出溝２のドリル回転方向Ｔ側を向く壁面２Ａは先端側から一定の捩れ角のままに延長するようにしておいて、この壁面２Ａに対向する切屑排出溝のドリル回転方向Ｔの後方側を向く壁面２Ｂ、すなわちヒール側の壁面をドリル回転方向Ｔ側に拡げることにより、溝幅を大きくするようにしている。ところが、このように螺旋状に捩れた切屑排出溝２を通って排出される切屑は、ドリル本体１の回転に伴いこの切屑排出溝２の捩れによってそのドリル回転方向Ｔを向く壁面２Ａに押し付けられるように該壁面２Ａを擦過しながら後端側に送り出されてゆくこととなるため、この壁面２Ａとは反対の壁面２Ｂ側を拡げただけでは、十分な切屑排出性の向上を図ることが困難となるおそれがある。
【０００５】
また、通常このようにドリル本体１の先端部外周に螺旋状に捩れた切屑排出溝２を有するドリルを製造するには、外周部に砥粒層が形成された円板状の砥石をその中心線回りに回転させつつ、この外周部を切屑排出溝２の捩れの方向に沿わせるようにしてドリル本体１の先端部外周に切り込ませ、上記捩れ角に合わせてドリル本体１を上記砥石に対して相対的に軸線Ｏ回りに一定の回転速度で回転させながら該軸線方向に一定の移動速度で移動させる（通常は砥石の中心線を固定しておいて、ドリル本体１を回転させながら軸線Ｏ方向に移動させる）ことにより、上記砥粒層によって上記壁面２Ａ，２Ｂを所定の形状に研削して切屑排出溝２を形成するようにしている。従って、そのような製造方法において、１つの砥石で上述のように切屑排出溝２の溝幅を後端側でドリル回転方向Ｔ側に拡げるには、まず切屑排出溝２の全長に亙ってその捩れ角に合わせ一定の相対回転移動速度でドリル本体１を砥石に対して相対的に回転移動させてドリル回転方向Ｔを向く上記壁面２Ａを研削して形成し、次いで上記Ａ点の位置からこの砥石をドリル回転方向Ｔ側にずらした上で、再び上記捩れ角に合わせて上記と同じ一定の相対回転移動速度でドリル本体１を上記砥石に対して相対的に回転移動させて壁面２Ｂを形成するという、２工程の研削を行うこととなる。
【０００６】
しかしながら、そのような製造方法では、これら２工程の研削の間で図９に破線で示すように初めの工程で研削された壁面２Ａ側と後の工程で研削された壁面２Ｂ側との間に断面山形の突条部Ｒが上記Ａ点から後端側に延びるように残されることとなり、この突条部Ｒは、２工程間で互いに等しい一定の相対回転移動速度でドリル本体１が砥石に対して相対的に回転移動させられることから、少なくとも上記Ｂ点よりも後端側では一定の高さで突出するように形成されることとなる。しかして、このような突条部Ｒが残されると、特に狭い溝幅Ｗ１から広い溝幅Ｗ２に移行して切屑が切屑排出溝２内に広がる上記Ｂ点において、この突条部Ｒに切屑が引っ掛かってその排出性が却って損なわれたりするおそれがある。従って、このような切屑の引っ掛かりを防ぐためには、この突条部Ｒを除去する工程がさらに必要となり、結果的に当該ドリルの製造効率の著しい悪化を招いてしまうことになる。
【０００７】
本発明は、このような背景の下になされたもので、切屑排出性の確実かつ一層の向上を図って切屑詰まりの発生をより効果的に防止することが可能なドリルを提供し、またそのようなドリルを製造効率の悪化を招くことなく製造可能なドリルの製造方法を提供することを目的としている。
【０００８】
【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、本発明のドリルは、軸線回りに回転される略円柱状のドリル本体の先端部外周に上記軸線に対して螺旋状に捩れる切屑排出溝が形成されるとともに、この切屑排出溝のドリル回転方向を向く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であって、上記切刃に連なる上記切屑排出溝の先端側の部分を、上記軸線に対する捩れ角および溝幅が一定とされた幅狭部とするとともに、この幅狭部よりも後端側において該切屑排出溝に、上記幅狭部を後端側に延長した仮想溝に対して溝幅が後端側に向かうに従い上記ドリル回転方向とドリル回転方向後方側とに漸次拡げられる拡幅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よれば、上記拡幅部において切屑排出溝が、先端側の幅狭部に対してドリル回転方向側に拡げられるとともにドリル回転方向後方側にも拡げられるように溝幅が漸次大きくなってゆくので、この切屑排出溝のドリル回転方向後方側に位置してドリル回転方向を向く壁面を押し付けながら擦過する切屑をも、確実に後端側に送り出して排出することが可能となる。
【０００９】
ここで、上記幅狭部と拡幅部との境界は、上記切刃の外周端から上記軸線方向後端側に向けて該切刃の外径Ｄに対し３〜５×Ｄの範囲内に位置しているのが望ましい。すなわち、この境界の位置が上記範囲よりも先端側にあると、これよりも後端側の拡幅部により切屑排出溝において溝幅が漸次大きくなってゆく部分が占める割合が多くなりすぎ、ドリル本体の肉厚が削がれて剛性不足が生じ、穴明け加工時の折損を生じ易くなるおそれがある一方、逆に上記境界の位置が上記範囲よりも後端側にあると、これより先端側の切屑排出溝の幅狭部の長さが長くなってしまい、この幅狭部で切屑詰まりが生じるおそれがある。なお、切屑排出溝の後端側において上記拡幅部によりその溝幅が漸次増大したままであると、例えば上述の２枚刃のツイストドリルにおいて切屑排出溝が形成されるドリル本体先端部の軸線方向の長さが長い場合には、この切屑排出溝の後端部で両切屑排出溝が重なり合ってしまうおそれがあるため、上記拡幅部の後端側では切屑排出溝の溝幅を幅狭部よりも拡幅した大きさで再び一定とするようにしてもよい。また、この拡幅部は、後端側に向けて溝幅が拡がる割合が異なる複数段の拡幅部によって構成されていてもよく、その場合には、上記幅狭部からの切屑の排出性を確保するために、先端側の段の拡幅部が後端側よりも拡幅の割合が大きくなるようにされるのが望ましい。
【００１０】
一方、本発明のドリルの製造方法は、このような構成のドリルを製造するためのものであって、外周部に砥粒層が形成された円板状の砥石を、その中心線回りに回転させつつ上記外周部が上記切屑排出溝の捩れの方向に沿うようにドリル本体の先端部外周に切り込ませ、上記捩れの方向に向けてドリル本体を上記砥石に対して相対的に軸線回りに回転させながら該軸線方向に移動させることにより、上記砥粒層によって上記切屑排出溝を形成するものであり、この切屑排出溝の上記拡幅部となる部分においては、上記幅狭部となる部分におけるドリル本体の砥石に対する相対回転移動速度よりも大きな速度と小さな速度とで、それぞれ上記ドリル本体を砥石に対して相対的に回転させながら移動させることを特徴とする。すなわち、このように拡幅部を形成するに際し、幅狭部を形成する際のドリルと砥石との相対回転移動速度に対して大小の速度で少なくとも２回の研削を行うことにより、相対回転移動速度が大きくされた研削では幅狭部よりも捩れ角の大きな捩れ溝が形成されることとなって、その溝幅が後端側に向かうに従いドリル回転方向の後方側に漸次拡げられることとなり、逆に相対回転移動速度が小さくされた研削では幅狭部よりも捩れ角の緩やかな捩れ溝が形成されて、その溝幅が後端側に向かうに従いドリル回転方向側に漸次拡げられることとなり、これらの捩れ溝が重なり合って幅狭部を延長した上記仮想溝に対して溝幅が後端側に向かうに従い上記ドリル回転方向とその後方側とに漸次拡げられる拡幅部が形成される。そして、こうして形成される拡幅部においては、上記捩れ溝が重なり合うその間に突条部が形成されても、この突条部の高さは先端側に向けて漸次低くなるので、幅狭部から排出される切屑が引っ掛かりを生じるおそれが少なく、またこの突条部を除去する場合でも容易に除去することが可能となる。
【００１１】
【発明の実施の形態】
図１ないし図４は、本発明のドリル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１１は、超硬合金等の硬質材料により形成されて軸線Ｏを中心とした概略円柱状をなし、その後端部（図において右側の端部）はシャンク部１２とされるとともに、先端部はこのシャンク部１２よりも僅かに小径とされた切刃部１３とされている。さらに、この切刃部１３の外周には、ドリル本体１１先端の先端逃げ面１４から後端側に向けて上記シャンク部１２の直前までに、一対の切屑排出溝１５，１５が軸線Ｏに対して互いに対称に、かつ後端側に向かうに従い軸線Ｏを中心として穴明け加工時のドリル回転方向Ｔの後方側に捩れる螺旋状に形成されており、これらの切屑排出溝１５，１５のドリル回転方向Ｔを向く壁面１５Ａの先端側はすくい面とされていて、その上記先端逃げ面１４との交差稜線部に、該先端逃げ面１４の内周側から切刃部１３の外周に達する切刃１６がそれぞれ形成されている。また、ドリル本体１１内には、シャンク部１２の後端から先端側に向けて、切削油剤やエアの供給用の一対の供給孔１７、１７が、上記切屑排出溝１５，１５と同様に軸線Ｏに対して互いに対称に、かつ後端側に向かうに従い軸線Ｏを中心にドリル回転方向Ｔの後方側に捩れるように穿設されており、これらの供給孔１７，１７は切刃部１３においては上記切屑排出溝１５，１５を避けるように延設されて先端逃げ面１４に開口させられている。
【００１２】
そして、このうち上記切刃１６に連なる切屑排出溝１５の先端側の部分は、上記軸線Ｏに対する捩れ角θおよび溝幅Ｗ_１８が一定とされた幅狭部１８とされるとともに、この幅狭部１８よりも後端側において該切屑排出溝１５には、図１および図３に鎖線で示すように上記幅狭部１８を後端側に延長した仮想溝１９に対し、溝幅Ｗ_２０が後端側に向かうに従い図３に示すように上記ドリル回転方向Ｔとドリル回転方向Ｔ後方側とに漸次拡げられるようにされた拡幅部２０が形成されている。また、図４は、上述のように螺旋状に捩れた切屑排出溝１５を軸線Ｏ回りにドリル回転方向Ｔに展開したときの展開図を示すものであるが、この図４に示すように上記拡幅部２０は、後端側に向けて溝幅Ｗ_２０が拡幅する割合が異なる複数段（本実施形態では２段）の拡幅部２０Ａ，２０Ｂにより構成されており、本実施形態では先端側の第１拡幅部２０Ａが後端側の第２拡幅部２０Ｂに対してこの拡幅する割合が大きく、ただし軸線Ｏ方向には短い範囲で形成されている。さらに、上記幅狭部１８と拡幅部２０（第１拡幅部２０Ａ）との境界Ａは、上記切刃１６の外周端から上記軸線Ｏ方向後端側に向けて該切刃１６の外径Ｄに対し３〜５×Ｄの範囲Ｌ内に位置している。なお、図４に符号Ｂで示すのは、第１、第２拡幅部２０Ａ，２０Ｂの境界である。
【００１３】
ここで、本実施形態では、この拡幅部２０における溝幅Ｗ_２０の拡がりは、第１、第２拡幅部２０Ａ，２０Ｂごとに、切屑排出溝１５のドリル回転方向Ｔを向く壁面１５Ａとドリル回転方向Ｔ後方側を向く壁面１５Ｂとの切刃部１３外周面との交差稜線が、それぞれ上記幅狭部１８および仮想溝１９の捩れ角θに対して互いに等しい角度分だけ増減した一定の角度をなして捩れる螺旋状をなすようにされている。従って、第１拡幅部２０Ａの捩れ角θに対する角度の増減分は、第２拡幅部２０Ｂの増減分よりも大きくされている。なお、図１および図４には、第２の拡幅部２０Ｂにおけるこの増減する角度分をγとして示す。また、図３に示すように軸線Ｏに直交する断面において上記壁面１５Ａ，１５Ｂは、上記仮想溝１９に対して互いに等しい幅ｗでドリル回転方向Ｔの後方側とドリル回転方向Ｔ側とに各々拡がるようにされている。なお、切刃部１３の外周面においては、上記ドリル回転方向Ｔを向く壁面１５Ａとの交差稜線に沿って、あるいはこれとドリル回転方向Ｔ後方側を向く壁面１５Ｂとの交差稜線とに沿ってマージン部が形成されていてもよい。
【００１４】
次に、図５および図６は、このようなドリルを製造する際の本発明の製造方法の一実施形態を示すものであって、両図の（イ）は螺旋状に捩れた切屑排出溝１５をその溝幅Ｗ_１８，Ｗ_２０の中心線がドリル本体１１の軸線Ｏと一致するように捩れを解いて真っ直ぐ直線状に延ばしたと仮想したときのドリル本体１１の軸線Ｏに対する径方向外周側からの側面図を示すものであるが、本実施形態の製造方法でも、従来と同様これら図５および６に示すように、外周部に砥粒層２１が形成された円板状の砥石２２を、その中心線Ｃ回りに回転させつつ上記外周部が切屑排出溝１５の捩れの方向（ただし、図５および図６の（イ）では軸線Ｏに沿うように示されている。）に沿うようにドリル本体１１の先端部外周の切刃部１３に切り込ませ、上記捩れの方向に向けてドリル本体１１を砥石２２に対して相対的に軸線Ｏ回りに回転させながら該軸線Ｏ方向に移動させることにより、上記砥粒層２１によって切屑排出溝１５の両壁面１５Ａ，１５Ｂを研削して該切屑排出溝１５を形成する。なお、図５および図６の（イ）では砥石２２を移動するように示してあるが、通常は砥石２２を固定してドリル本体１１を回転移動させる。また、同じく図５および図６の（イ）では上述のように切屑排出溝１５が直線状に延ばされているので、ドリル本体１１と砥石２２とは相対回転しないように示されている。
【００１５】
しかして、本実施形態の製造方法では、上記切屑排出溝１５の幅狭部１８を形成するときには、該幅狭部１８が一定の捩れ角θおよび一定の溝幅Ｗ１８となるようにドリル本体１１を砥石２２に対して一定の回転速度および移動速度で相対的に回転移動させるのに対し、拡幅部２０となる部分においては、この幅狭部１８となる部分におけるドリル本体１１の砥石２２に対する相対回転移動速度よりも大きな速度と小さな速度とで、それぞれドリル本体１１を砥石２２に対して相対的に回転させながら移動させることにより、その溝幅Ｗ_２０が上記仮想溝１９に対して後端側に向かうに従いドリル回転方向Ｔとその後方側とに漸次拡げられるようにしている。
【００１６】
すなわち、本実施形態ではまず図５に示すように、ドリル本体１１の先端逃げ面１４から後端側に向けて上記境界Ａまでの幅狭部１８となる部分では、ドリル本体１１と砥石２２との相対回転移動の速度を、該相対回転移動によって砥石２２がドリル本体１１の外周に描く螺旋の捩れ角が上記捩れ角θと等しくなるように一定の速度とする一方、これよりも後端側の拡幅部２０となる部分では、この相対回転移動速度を、砥石２２がドリル本体１１の後端側に移動するとした場合において上記幅狭部１８における一定の速度よりも大きくすることにより、ドリル本体１１と砥石２２との相対回転移動速度をそのまま一定とした場合の上記仮想溝１９の捩れ角θよりも大きな捩れ角の捩れ溝を形成し、これによって図５の（ロ）〜（ホ）に示すようにこの仮想溝１９のドリル回転方向Ｔを向く壁面１９Ａよりもドリル回転方向Ｔの後方側に後退した壁面１５Ａを形成する。なお、このとき、この相対回転移動速度を上記一定の速度よりも大きな範囲で段階的に変化させれば、拡幅部２０を拡幅の割合が段階的に変化する複数段に構成することができ、例えば拡幅部２０の先端側でこの速度を大きくし、上記境界Ｂよりも後端側では小さく（ただし、上記一定速度よりは大きく）すれば、上記実施形態のような２段の第１、第２拡幅部２０Ａ，２０Ｂの壁面１５Ａを形成することができる。
【００１７】
次いで、本実施形態では上記砥石２２と同じ砥石２２を用いて図６に示すように、上記境界Ａよりも後端側の拡幅部２０となる部分で、やはり砥石２２がドリル本体１１の後端側に移動するとした場合における上記相対回転移動速度を、幅狭部１８における一定の速度よりも図５の場合とは逆に小さくすることにより、上記捩れ角θよりも小さな捩れ角の捩れ溝を形成するようにして、この図６の（ロ）〜（ホ）に示すように上記仮想溝１９のドリル回転方向Ｔ後方側を向く壁面１９Ｂよりもドリル回転方向Ｔ側に後退した壁面１５Ｂを形成する。なお、このとき、やはり上記とは逆に拡幅部２０の先端側でこの相対回転移動速度をより小さくし、上記境界Ｂよりも後端側では大きく（ただし、上記一定速度よりは小さく）すれば、上記実施形態のような２段の第１、第２拡幅部２０Ａ，２０Ｂの壁面１５Ｂを形成することができる。従って、この壁面１５Ｂと上記壁面１５Ａと合わせて、溝幅Ｗ_２０が幅狭部１８を延長した仮想溝１９に対して後端側に向かうに従いドリル回転方向Ｔとその後方側とに漸次拡げられる拡幅部２０を形成することができる。
【００１８】
しかして、このような製造方法により製造される上記構成のドリルにおいては、上記拡幅部２０における切屑排出溝１５の溝幅Ｗ_２０が、幅狭部１８およびこれを延長した仮想溝１９に対してドリル回転方向Ｔ側に拡げられるとともに、これに対向するドリル回転方向Ｔの後方側にも拡げられているため、溝幅Ｗ_２０が溝幅Ｗ_１８よりも大きくされることで切屑排出溝１５の断面積が大きくなることにより切屑詰まりが防止されるのは勿論、穴明け加工時のドリル本体１１の回転に伴いこのドリル回転方向Ｔの後方側の壁面１５Ａに押し付けられるように該壁面１５Ａを擦過して後方側に送り出される切屑をより円滑に排出することが可能となり、これによっても切刃部１３の後端側における切屑の詰まりを確実に防止することができる。すなわち、このようにして切屑が切屑排出溝１５の壁面１５Ａを押し付けながら擦過するのに対し、この壁面１５Ａが拡幅部２０においてドリル回転方向Ｔの後方側に後退させられていることにより、この拡幅部２０では切屑排出溝１５内を通る切屑が壁面１５Ａ側に押し付けられる押圧力が緩和され、この押圧力によって切屑同士が圧縮されたり絡まり合ったりして切屑詰まりが発生するような事態を防ぐことができ、拡幅部２０で断面積が大きくされた切屑排出溝１５内の空間を有効に利用して切屑排出性の一層の向上を図ることができるのである。
【００１９】
しかも、この幅狭部２０の溝幅Ｗ_２０が幅狭部１８との境界Ａから後端側に向けて漸次広くなってゆくように形成されており、切屑排出溝１５の溝幅が幅狭部１８から急激に大きくなるようなことがないので、特に上記壁面１５Ａを擦過する切屑の排出を一層円滑にすることができる。また、本実施形態では、この拡幅部２０と幅狭部１８との境界Ａが、切刃１６の外周端から軸線Ｏ方向後端側に向けて切刃１６の外径Ｄに対し３〜５×Ｄの範囲内に位置しているので、拡幅部２０によってドリル本体１１に剛性不足を生じ、特に切刃部１３の長さが切刃１６の外径Ｄに対して極めて長い場合などに折損が生じたりするのを避けることができる一方で、逆に先端側の幅狭部１８が長くなりすぎて拡幅部２０に到達する前にこの幅狭部１８内において切屑詰まりが生じてしまったりするのも防ぐことができる。
【００２０】
さらに、本実施形態のドリルでは、この拡幅部２０が第１、第２の２段の拡幅部２０Ａ，２０Ｂによって構成されており、先端側の第１拡幅部２０Ａが後端側の第２拡幅部２０Ｂよりも溝幅Ｗ_２０の拡幅する割合が大きく、かつ軸線Ｏ方向に短い範囲で形成されているので、幅狭部１８から送り出された切屑をより円滑に拡幅部２０に導いて排出することができる一方、切刃部１３の後端側において溝幅Ｗ_２０が大きくなりすぎて、例えば切刃部１３の長さが長い場合などに切刃部１３の後端側においてドリル本体１１の肉厚が大きく削がれて剛性不足を生じたり、一対の切屑排出溝１５，１５同士の間で該切屑排出溝１５が重なり合ってしまったりするような事態を防止することができる。なお、このような事態をより確実に防止するには、上記拡幅部２０の後端側にさらに切屑排出溝１５の溝幅が幅狭部１８よりも拡幅された状態で一定とされる幅広部を形成するようにしてもよい。
【００２１】
一方、本実施形態のドリルの製造方法では、このような拡幅部２０を形成するのに、上記図６ないし図８に示した従来のドリルを製造する場合と同様に２工程の研削を行うようにしているが、その際に、一定の捩れ角θの上記幅狭部１８を形成するときのドリル本体１１と砥石２２との一定の相対回転移動速度に対し、これよりも大きい相対回転移動速度と小さい相対回転移動速度とでこの２工程の研削を行うようにしている。しかして、このような切屑排出溝１５の壁面１５Ａ，１５Ｂの研削は、上述したように通常はその中心線Ｃ回りに回転する砥石２２の位置を固定しておいて、ドリル本体１１を軸線Ｏ回りに回転させながら該軸線Ｏ方向に移動させて研削を行うので、このように相対回転移動速度を変化させるにしても、このドリル本体１１の軸線Ｏ回りの回転速度と軸線Ｏ方向の移動速度との少なくとも一方を幅狭部１８の研削時の速度に対して大小に調節すればよく、従って一般的なドリル研削盤の制御によって比較的容易に上述のような優れた効果を奏するドリルを製造することが可能となる。
【００２２】
そして、さらにこのような製造方法によれば、こうして拡幅部２０においてドリル本体１１と砥石２２との相対回転移動速度を大小に変化させることにより、上述のように上記仮想溝１９のドリル回転方向Ｔ側とその後方側とに上記捩れ角θよりも大きな捩れ角の捩れ溝と小さな捩れ角の捩れ溝とを形成し、これによって溝幅Ｗ_２０を幅狭部１８の溝幅Ｗ_１８に対して後端側に向かうに従いドリル回転方向Ｔ側とその後方側とに漸次拡幅させることとなり、従ってこれらの捩れ溝同士が重なり合う間の部分には従来と同様に図３に示すように突条部Ｒが形成されることとなるが、この捩れ溝同士が重なり合う部分は、互いの捩れ角が上記捩れ角θに対して大小とされているために図５（ハ）〜（ホ）に示すように拡幅部２０の後端側で小さく、先端側に向かうに従い漸次大きくなり、これとは逆に上記突条部Ｒの突出高さは同図５（ハ）〜（ホ）に示すように拡幅部２０の後端側で大きく、先端側に向かうに従い漸次小さくなるように形成されることとなる。このため、上記幅狭部１８から拡幅部２０に排出された切屑が、従来のようにこのような突条部Ｒに引っ掛かって詰まりを生じたりするなど、却って切屑排出性が損なわれるような事態を未然に防ぐことができ、またたとえ拡幅部２０の形成後にこのような突条部Ｒを再度研削したりすることによって除去する場合でも、拡幅部２０の後端側の突条部Ｒを除去するだけでよいので作業が容易である。
【００２３】
なお、本実施形態の製造方法においては、このようにドリル本体１１と砥石２２との相対回転移動速度を拡幅部２０において幅狭部１８に対し大小に変化させる２工程の研削加工を行うことにより、上記実施形態のドリルを製造するようにしているが、本発明のドリル自体はこのような製造方法に限らず、例えば砥石２２の中心線Ｃに直交する平面がドリル本体１１の軸線Ｏに対してなす角度すなわち砥石２２の振り角を、拡幅部２０において後端側に向かうに従い漸次大きくしながら研削したりすることによっても製造することができ、この場合には１工程で拡幅部２０を形成することができるとともに突条部Ｒが形成されることもない。また、このように砥石の振り角を変えないにしても、例えば拡幅部で幅狭部よりも砥石のドリル本体内周側への切り込み量を漸次大きくしてその両壁面を拡げ、溝幅を大きくすることも可能ではあるが、この場合には拡幅部の後端側に向かうに従いドリル本体の心厚が漸次小さくなり、切屑排出性は向上するものの折損が生じ易くなるため、好ましくはない。むしろ、この拡幅部２０の後端側すなわち切刃部１３の後端側では、切屑排出性は溝幅Ｗ_２０が漸次大きくなることによって確保されるため、ドリル本体１１の心厚は上記とは逆に後端側に向かうに従い漸次大きくなるの望ましい。
【００２４】
【発明の効果】
以上説明したように、本発明のドリルによれば、切屑排出溝先端側の幅狭部に対してその溝幅が後端側に向かうに従いドリル回転方向とその後方側とに拡がる拡幅部を形成することにより、特にドリル回転方向後方側に位置してドリル回転方向を向く切屑排出溝壁面を切屑が押し付ける押圧力を緩和し、溝幅が広げられることによって断面積が大きくされたこの拡幅部を有効に利用してより確実かつ効率的な切屑排出を図ることができる。また、本発明のドリルの製造方法によれば、切屑排出溝に突条部が形成されたとしても、その突出高さを拡幅部の先端側で小さくして幅狭部から排出された切屑が引っ掛かって切屑詰まりを生じるような事態を未然に防ぐことができ、従って上述のような優れた切屑排出性をより確実に奏功することができるとともに、この突条部を除去する場合でも作業を容易にして当該ドリルの製造効率の悪化を防ぐことができる。
【図面の簡単な説明】
【図１】本発明のドリルの一実施形態を示す側面図である。
【図２】図１におけるＸＸ断面図である。
【図３】図１におけるＹＹ断面図である。
【図４】図１に示すドリルの切屑排出溝１５の展開図である。
【図５】本発明のドリルの製造方法の一実施形態において壁面１５Ａを研削する際の図であって、（イ）は切屑排出溝１５を直線状に延ばしたと仮想したときの側面図、（ロ）〜（ホ）は（イ）におけるＥＥ〜ＨＨ断面図である。
【図６】本発明のドリルの製造方法の一実施形態において壁面１５Ｂを研削する際の図であって、（イ）は切屑排出溝１５を直線状に延ばしたと仮想したときの側面図、（ロ）〜（ホ）は（イ）におけるＥＥ〜ＨＨ断面図である。
【図７】従来のドリルの側面図である。
【図８】図７におけるＸＸ断面図である。
【図９】図７におけるＹＹ断面図である。
【符号の説明】
１１　ドリル本体
１４　先端逃げ面
１５　切屑排出溝
１５Ａ，１５Ｂ　切屑排出溝１５の壁面
１６　切刃
１８　幅狭部
１９　幅狭部１８を延長した仮想溝
２０　拡幅部
２０Ａ　第１拡幅部
２０Ｂ　第２拡幅部
２１　砥粒層
２２　砥石
Ｏ　ドリル本体１１の軸線
Ｃ　砥石２２の中心線
Ｔ　ドリル回転方向
Ｄ　切刃１６の外径
Ｗ_１８　幅狭部１８における溝幅
Ｗ_２０　拡幅部２０における溝幅
Ａ　幅狭部１８と拡幅部２０（第１拡幅部２０Ａ）との境界
Ｂ　第１、第２拡幅部２０Ａ，２０Ｂの境界
θ　切屑排出溝１５の幅狭部１８における捩れ角
γ　拡幅部２０（第２拡幅部２０Ｂ）における壁面１５Ａ，１５Ｂの捩れ角の幅狭部１８に対する増減分[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a drill in which a spiral chip discharge groove is formed on the outer periphery of the tip of a drill body, and a method for manufacturing the same.
[0002]
[Prior art]
In this type of drill, the outer periphery of the distal end portion of a substantially cylindrical drill body that is rotated around an axis is disposed on the rear side in the drill rotation direction around the axis from the distal flank of the distal end of the drill body toward the rear end side. A pair of chip discharge grooves that are twisted into are formed symmetrically with respect to the axis, and a cutting edge is formed at an intersection ridge line portion between the wall surface of the chip discharge groove facing the drill rotation direction side and the tip flank surface, So-called two-flute twist drills are generally well known. Further, in such a twist drill, for example, in Patent Document 1, as shown in FIGS. In the drill provided with the cutting edge 3, the width of the chip discharge groove 2 is W until the point A which is about 2D away from the tip of the blade when the outer diameter of the drill is D. ₁ , From point A to point B ₁ To W ₂ (> W ₁ ) And gradually increases from point B to the rear end of the blade. ₂ In order to prevent chip clogging by improving the chip discharge property at the rear end side, it has been proposed.
[0003]
[Patent Document 1]
Japanese Utility Model Application Laid-Open No. 5-60715
[0004]
[Problems to be solved by the invention]
By the way, in this drill, when gradually increasing the groove width of the chip discharge groove 2 from the point A to the point B, the wall surface 2A of the chip discharge groove 2 facing the drill rotation direction T side as shown in FIG. The wall surface 2B facing the rear side of the chip discharge groove facing the wall surface 2A in the drill rotation direction T, that is, the wall surface on the heel side is extended in the drill rotation direction T from the tip side while maintaining a constant twist angle. The width of the groove is increased by expanding the groove to the side. However, the chips discharged through the spirally twisted chip discharge groove 2 are pressed against the wall surface 2A facing the drill rotation direction T by the twist of the chip discharge groove 2 as the drill body 1 rotates. As a result, the wall 2A is sent to the rear end side while being rubbed, so it is difficult to sufficiently improve the chip discharge performance only by expanding the wall 2B opposite to the wall 2A. May be caused.
[0005]
Usually, in order to manufacture a drill having a chip discharge groove 2 twisted helically on the outer periphery of the distal end portion of the drill body 1 as described above, a disc-shaped grindstone having an abrasive layer formed on the outer periphery is used as the center. While rotating around the line, the outer periphery is cut into the outer periphery of the tip of the drill body 1 along the direction of twist of the chip discharge groove 2, and the drill body 1 is attached to the grindstone according to the torsion angle. On the other hand, while rotating at a constant rotational speed relatively around the axis O, it is moved at a constant moving speed in the axial direction (normally, the center line of the grindstone is fixed, and the axis of the drill is rotated while rotating the drill body 1). By moving in the O direction), the wall surfaces 2A and 2B are ground into a predetermined shape by the abrasive layer to form the chip discharge grooves 2. Therefore, in such a manufacturing method, in order to widen the groove width of the chip discharge groove 2 in the drill rotation direction T side at the rear end side with one grindstone as described above, first, the chip discharge groove 2 is extended over the entire length of the chip discharge groove 2. The drill body 1 is rotated relative to the grindstone at a constant relative rotational movement speed in accordance with the torsion angle, and the wall surface 2A facing the drill rotation direction T is formed by grinding. Then, from the position of the point A, After displacing the grindstone in the drill rotation direction T, the drill body 1 is rotationally moved relative to the grindstone again at the same constant relative rotational movement speed as described above in accordance with the torsion angle, and the wall surface 2B is moved. That is, two steps of grinding for forming are performed.
[0006]
However, in such a manufacturing method, as shown by a broken line in FIG. 9, between the grinding in the two steps, the wall 2A side ground in the first step and the wall 2B ground in the subsequent step. The projecting ridge R having a mountain-shaped cross section is left so as to extend from the point A to the rear end side. Since it is relatively rotated and moved relative to the point B, it is formed so as to protrude at a constant height at least on the rear end side of the point B. When such a ridge R is left, the chip moves to the wide groove width W2 from the narrow groove width W1 and the chip spreads into the chip discharge groove 2 at the point B. May be caught and its dischargeability may be impaired. Therefore, in order to prevent such chips from being caught, a step of removing the ridge portion R is further required, and as a result, the production efficiency of the drill is remarkably deteriorated.
[0007]
The present invention has been made under such a background, and provides a drill capable of more effectively preventing chip clogging by reliably and further improving the chip discharge property. It is an object of the present invention to provide a method of manufacturing a drill capable of manufacturing such a drill without deteriorating the manufacturing efficiency.
[0008]
[Means for Solving the Problems]
In order to solve the above problems and achieve such an object, a drill according to the present invention is twisted helically with respect to the axis on the outer periphery of the distal end of a substantially cylindrical drill body that is rotated around the axis. A chip having a chip discharge groove formed therein, wherein a cutting edge is formed at an intersection ridge portion between a wall surface of the chip discharge groove facing the drill rotation direction and a flank of a tip flank of the drill body. The leading end portion of the continuous chip discharge groove is a narrow portion having a constant twist angle with respect to the axis and the groove width, and the chip discharge groove is provided with the width at the rear end side of the narrow portion. With respect to the virtual groove whose narrow portion is extended to the rear end side, a widened portion is formed which gradually widens in the drill rotation direction and the drill rotation direction rear side as the groove width goes to the rear end side. Therefore, according to the drill configured as described above, the chip discharge groove in the widened portion is expanded in the drill rotation direction side with respect to the narrow portion on the distal end side and also expanded in the drill rotation direction rear side. Since the groove width gradually increases, chips that are located behind this chip discharge groove in the drill rotation direction and that rub against the wall while pressing against the wall in the drill rotation direction must also be reliably sent to the rear end and discharged. Becomes possible.
[0009]
Here, the boundary between the narrow portion and the widened portion is located within a range of 3 to 5 × D with respect to the outer diameter D of the cutting blade from the outer peripheral end of the cutting blade toward the rear end side in the axial direction. It is desirable to have. That is, if the position of this boundary is on the front end side of the above range, the ratio of the portion where the groove width gradually increases in the chip discharge groove due to the widened portion on the rear end side becomes too large, and the drill body becomes too large. The thickness of the edge is shaved and the rigidity is insufficient, which may cause breakage during drilling. On the other hand, if the boundary is located on the rear end side of the above range, the front end side is The length of the narrow portion of the chip discharge groove becomes longer, and there is a possibility that chip clogging may occur in the narrow portion. If the width of the groove is gradually increased at the rear end side of the chip discharge groove by the widening portion, for example, the axial direction of the tip end portion of the drill body where the chip discharge groove is formed in the above-mentioned two-flute twist drill If the length of the chip discharge groove is long, the chip discharge grooves may overlap at the rear end of the chip discharge groove. May also be made constant again with the widened size. Further, the widened portion may be constituted by a plurality of widened portions having different ratios of the width of the groove expanding toward the rear end side. In this case, the dischargeability of the chips from the narrow portion is ensured. In order to do so, it is desirable that the widened portion of the step on the front end side has a larger rate of widening than the rear end side.
[0010]
On the other hand, the drill manufacturing method of the present invention is for manufacturing a drill having such a configuration, and rotates a disc-shaped grindstone having an abrasive layer formed on an outer peripheral portion around a center line thereof. The outer peripheral portion is cut into the outer periphery of the distal end portion of the drill body so as to be along the direction of twist of the chip discharge groove, and the drill body is rotated around the axis relative to the grinding stone in the direction of the twist. By moving in the axial direction while rotating, the chip discharge groove is formed by the abrasive grain layer, and in the portion serving as the widened portion of the chip discharge groove, in the portion serving as the narrow portion The method is characterized in that the drill body is moved while rotating relative to the grindstone at a speed greater than and smaller than the relative rotational movement speed of the drill body relative to the grindstone. In other words, when forming the widened portion in this way, by performing at least two times of grinding at a speed larger or smaller than the relative rotational speed of the drill and the grindstone when forming the narrow portion, the relative rotational speed is increased. In the grinding where the diameter is increased, a twist groove having a larger twist angle than the narrow part is formed, and the groove width gradually increases toward the rear end side in the drill rotation direction as going toward the rear end side, and conversely. In the grinding in which the relative rotational movement speed was reduced, a twist groove having a gentler twist angle than the narrow portion was formed, and the groove width gradually increased in the drill rotation direction side toward the rear end side. With respect to the imaginary groove in which the torsional grooves overlap each other to extend the narrow portion, a widened portion is formed which gradually widens in the drill rotation direction and the rear side as the groove width moves toward the rear end side. In the wide portion thus formed, even if a ridge portion is formed between the overlapping portions of the twisted grooves, the height of the ridge portion gradually decreases toward the distal end, so that the discharge from the narrow portion is performed. There is little possibility that the chips to be caught will be caught, and even when this ridge is removed, it can be easily removed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 4 show an embodiment of the drill of the present invention. In this embodiment, the drill body 11 is formed of a hard material such as a cemented carbide and has a substantially columnar shape centered on the axis O, and a rear end (right end in the figure) is a shank portion 12. At the same time, the tip portion is a cutting blade portion 13 slightly smaller in diameter than the shank portion 12. Further, on the outer periphery of the cutting edge portion 13, a pair of chip discharge grooves 15, 15 are formed on the axis O from the tip flank 14 at the tip of the drill body 11 to the rear end side and immediately before the shank portion 12. Are formed in a helical shape that is symmetrical to each other and twists rearward in the drill rotation direction T at the time of drilling with the axis O as the center toward the rear end side. The tip side of the wall surface 15A facing the rotation direction T is a rake face, and a cut reaching from the inner peripheral side of the tip flank 14 to the outer periphery of the cutting edge 13 at the intersection ridge line with the tip flank 14. Each of the blades 16 is formed. Further, in the drill body 11, a pair of supply holes 17 for supplying cutting oil and air is formed from the rear end of the shank portion 12 toward the front end side. The supply holes 17, 17 are formed symmetrically with respect to O and twisted rearward in the drill rotation direction T about the axis O toward the rear end side. Are extended so as to avoid the chip discharge grooves 15 and 15 and are opened to the tip flank 14.
[0012]
The tip of the chip discharge groove 15 connected to the cutting edge 16 has a twist angle θ with respect to the axis O and a groove width W. ₁₈ Is narrowed, and the chip discharge groove 15 at the rear end side of the narrow portion 18 is provided with the narrow portion 18 as shown by a chain line in FIGS. For the virtual groove 19 extended to the rear end side, the groove width W ₂₀ As shown in FIG. 3, a widened portion 20 is formed so as to be gradually expanded in the drill rotation direction T and the rear side in the drill rotation direction T as shown in FIG. FIG. 4 is a development view when the chip discharge groove 15 twisted helically as described above is developed in the drill rotation direction T around the axis O. As shown in FIG. The widened portion 20 has a groove width W toward the rear end side. ₂₀ Is constituted by a plurality of (two in this embodiment) widening portions 20A and 20B having different widening ratios. In the present embodiment, the first widening portion 20A on the front end side is the second widening portion 20B on the rear end side. However, the width is increased in a large range, but is formed in a short range in the direction of the axis O. Further, a boundary A between the narrow portion 18 and the widened portion 20 (the first widened portion 20A) is defined by an outer diameter D of the cutting blade 16 from the outer peripheral end of the cutting blade 16 toward the rear end side in the axis O direction. Is located within a range L of 3 to 5 × D. In addition, what is indicated by reference numeral B in FIG. 4 is a boundary between the first and second widened portions 20A and 20B.
[0013]
Here, in the present embodiment, the groove width W in the widened portion 20 is set. ₂₀ The first and second widened portions 20A and 20B have an outer peripheral surface of a cutting edge portion 13 of a wall surface 15A of the chip discharge groove 15 facing the drill rotation direction T and a wall surface 15B of the chip discharging groove 15 facing the rear side of the drill rotation direction T. Are formed so as to form a helical shape which is twisted at a fixed angle which is increased or decreased by an angle equal to the twist angle θ of the narrow portion 18 and the virtual groove 19 respectively. Therefore, the increase or decrease of the angle of the first widened portion 20A with respect to the twist angle θ is set to be larger than the increase or decrease of the second widened portion 20B. In FIGS. 1 and 4, the increasing / decreasing angle of the second widened portion 20 B is indicated as γ. As shown in FIG. 3, in the cross section orthogonal to the axis O, the wall surfaces 15 A and 15 B have the same width w with respect to the virtual groove 19 and are located on the rear side in the drill rotation direction T and on the drill rotation direction T side. It is made to spread. In addition, on the outer peripheral surface of the cutting edge portion 13, along the intersection ridge line with the wall surface 15A facing the drill rotation direction T, or along the intersection ridge line with the wall surface 15B facing the drill rotation direction T rear side. A margin portion may be formed.
[0014]
Next, FIGS. 5 and 6 show one embodiment of the manufacturing method of the present invention when manufacturing such a drill. In both figures, (A) shows a helically twisted chip discharge groove. 15 is the groove width W ₁₈ , W ₂₀ 3 shows a side view from the radially outer side with respect to the axis O of the drill body 11 when it is assumed that the center line of the drill body is untwisted and extends straight and straight so as to coincide with the axis O of the drill body 11. Also in the manufacturing method of the present embodiment, as shown in FIGS. 5 and 6, the disc-shaped grindstone 22 having the abrasive layer 21 formed on the outer periphery is rotated around the center line C as in the conventional method. The outer peripheral portion is cut along the torsion direction of the chip discharge groove 15 (however, it is shown along the axis O in FIGS. 5 and 6A). By making a cut in the blade part 13 and moving the drill body 11 in the direction of the axis O while rotating the drill body 11 around the axis O relative to the grindstone 22 in the direction of the twist, the abrasive layer 21 Both wall surfaces 15 of the chip discharge groove 15 , By grinding and 15B to form The sections flutes 15. 5 and FIG. 6A, the grindstone 22 is shown to be moved, but usually, the grindstone 22 is fixed and the drill body 11 is rotated. Also, in FIG. 5 and FIG. 6A, since the chip discharge groove 15 is linearly extended as described above, the drill main body 11 and the grindstone 22 are shown not to rotate relative to each other.
[0015]
However, in the manufacturing method according to the present embodiment, when the narrow portion 18 of the chip discharge groove 15 is formed, the drill body 11 is formed so that the narrow portion 18 has a constant twist angle θ and a constant groove width W18. Is relatively rotated with respect to the grindstone 22 at a constant rotation speed and moving speed, whereas in the portion to be the widened portion 20, the relative position of the drill body 11 to the grindstone 22 at the portion to be the narrow portion 18 By moving the drill body 11 while rotating relative to the grindstone 22 at a speed higher and lower than the rotational movement speed, the groove width W is increased. ₂₀ Are gradually expanded in the drill rotation direction T and the rear side thereof toward the rear end side with respect to the virtual groove 19.
[0016]
That is, in the present embodiment, first, as shown in FIG. 5, in the portion that becomes the narrow portion 18 from the front flank 14 of the drill body 11 to the rear end side toward the boundary A, the drill body 11 and the grindstone 22 Is set to a constant speed such that the torsion angle of the spiral drawn by the grindstone 22 on the outer periphery of the drill body 11 by the relative rotation is equal to the above-mentioned torsion angle θ. In the portion that becomes the widened portion 20, the relative rotational movement speed is set to be larger than the constant speed in the narrow portion 18 when the grindstone 22 moves to the rear end side of the drill body 11, so that the drill body A torsion groove having a torsion angle larger than the torsion angle θ of the imaginary groove 19 when the relative rotational movement speed of the wheel 11 and the grindstone 22 is kept constant is formed, and thereby, (b) to (e) of FIG. I'll show you As described above, a wall surface 15A which is set back on the rear side in the drill rotation direction T from the wall surface 19A of the virtual groove 19 facing the drill rotation direction T is formed. At this time, if the relative rotational movement speed is changed stepwise in a range larger than the fixed speed, the widening portion 20 can be configured in a plurality of stages in which the ratio of widening changes stepwise. For example, if this speed is increased on the leading end side of the widening portion 20 and is decreased on the trailing end side of the boundary B (however, it is larger than the constant speed), the first and second steps of the two-stage as in the above embodiment are performed. The wall surfaces 15A of the two widened portions 20A and 20B can be formed.
[0017]
Next, in the present embodiment, as shown in FIG. 6, the same grindstone 22 as the grindstone 22 is used, and as shown in FIG. 5 is made smaller than the fixed speed in the narrow portion 18 in the opposite direction to that in FIG. 5 so that the twist groove having a twist angle smaller than the twist angle θ is formed. As shown in FIGS. 6B to 6E, the wall surface 15B which is set back in the drill rotation direction T side from the wall surface 19B of the virtual groove 19 facing the drill rotation direction T rear side is formed as shown in FIGS. I do. Note that, at this time, the relative rotational movement speed may be made smaller on the leading end side of the widening portion 20 and larger on the trailing end side of the boundary B (but smaller than the constant speed). The wall surfaces 15B of the first and second widened portions 20A and 20B in two steps as in the above embodiment can be formed. Therefore, the groove width W is combined with the wall surface 15B and the wall surface 15A. ₂₀ A widened portion 20 can be formed which gradually widens in the drill rotation direction T and the rear side thereof toward the rear end side with respect to the virtual groove 19 extending the narrow portion 18.
[0018]
Thus, in the drill having the above configuration manufactured by such a manufacturing method, the groove width W of the chip discharge groove 15 in the widened portion 20 is used. ₂₀ Is widened in the drill rotation direction T with respect to the narrow portion 18 and the virtual groove 19 extended from the narrow portion 18 and is also expanded in the rear side in the drill rotation direction T opposite to the narrow portion 18 and the groove width W. ₂₀ Is the groove width W ₁₈ By increasing the diameter, the cross-sectional area of the chip discharge groove 15 is increased so that chip clogging is prevented, and of course, the rotation of the drill body 11 at the time of drilling makes it possible to prevent the chip from being clogged. It is possible to more smoothly discharge the chips sent to the rear side by rubbing the wall surface 15A so as to be pressed against the wall surface 15A, thereby also reliably preventing the clogging of the chip at the rear end side of the cutting blade portion 13. can do. That is, while the chips are rubbed while pressing the wall surface 15A of the chip discharge groove 15 in this manner, the wall surface 15A is retracted to the rear side in the drill rotation direction T in the widening portion 20, so that the width is increased. In the part 20, the pressing force with which the chips passing through the chip discharge groove 15 are pressed against the wall surface 15A is reduced, and this pressing force prevents the chips from being compressed or entangled with each other to cause the chip to be clogged. Thus, the space in the chip discharge groove 15 whose cross-sectional area has been increased by the widening portion 20 can be effectively used to further improve the chip discharge performance.
[0019]
Moreover, the groove width W of the narrow portion 20 ₂₀ Is formed so as to gradually increase from the boundary A with the narrow portion 18 toward the rear end side, and the groove width of the chip discharge groove 15 does not suddenly increase from the narrow portion 18. Therefore, the discharge of the chips scraping the wall surface 15A can be further smoothed. Further, in the present embodiment, the boundary A between the widened portion 20 and the narrow portion 18 is 3 to 5 with respect to the outer diameter D of the cutting blade 16 from the outer peripheral end of the cutting blade 16 toward the rear end side in the axis O direction. Since it is located within the range of × D, the rigidity of the drill body 11 is insufficient due to the widened portion 20, and the breakage occurs particularly when the length of the cutting edge portion 13 is extremely long with respect to the outer diameter D of the cutting edge 16. However, on the other hand, the narrow portion 18 on the distal end side becomes too long, and chip clogging occurs in the narrow portion 18 before the narrow portion 18 reaches the widened portion 20. Can also be prevented.
[0020]
Further, in the drill according to the present embodiment, the widened portion 20 is constituted by first and second two-stage widened portions 20A and 20B, and the first widened portion 20A on the front end side is the second widened portion on the rear end side. Groove width W than section 20B ₂₀ Is formed in a range in which the width of the sheet is widened and is short in the direction of the axis O, so that the chips sent out from the narrow portion 18 can be more smoothly guided to the widened portion 20 and discharged, while the cutting edge portion 13 at the rear end side ₂₀ Becomes too large, for example, when the length of the cutting edge portion 13 is long, etc., the thickness of the drill body 11 is largely cut off at the rear end side of the cutting edge portion 13 to cause insufficient rigidity, or a pair of chips is discharged. It is possible to prevent the chip discharge grooves 15 from overlapping each other between the grooves 15. In order to more reliably prevent such a situation, a wide portion in which the chip width of the chip discharge groove 15 is further fixed to the rear end side of the wide portion 20 in a state where the groove width is wider than the narrow portion 18. May be formed.
[0021]
On the other hand, in the drill manufacturing method of the present embodiment, two steps of grinding are performed to form such a widened portion 20 in the same manner as in the case of manufacturing the conventional drill shown in FIGS. At this time, the relative rotation speed of the drill body 11 and the grindstone 22 at the time of forming the narrow portion 18 having the constant twist angle θ is larger than the relative rotation speed of the drill body 11 and the grindstone 22. This two-step grinding is performed at a low relative rotational movement speed. In the grinding of the wall surfaces 15A and 15B of the chip discharge groove 15, the position of the grindstone 22 which normally rotates around the center line C is fixed, and the drill body 11 is fixed to the axis O as described above. Since the grinding is performed by moving the drill body 11 in the direction of the axis O while rotating it around, even if the relative rotation speed is changed in this way, the rotation speed of the drill body 11 around the axis O and the movement speed in the axis O direction It is only necessary to adjust at least one of the above and the speed at the time of grinding the narrow portion 18, and therefore, it is relatively easy to manufacture a drill having the above-described advantageous effects relatively easily by controlling a general drill grinder. It is possible to do.
[0022]
Further, according to such a manufacturing method, by changing the relative rotational movement speed of the drill body 11 and the grindstone 22 in the widened portion 20 as described above, the drill rotational direction T of the virtual groove 19 is changed as described above. And at the rear side thereof, a twist groove having a twist angle larger than the above-mentioned twist angle θ and a twist groove having a small twist angle are formed. ₂₀ Is the groove width W of the narrow portion 18 ₁₈ In contrast to this, the width gradually increases in the drill rotation direction T and the rear side toward the rear end side, so that the portion where these twisted grooves overlap each other as shown in FIG. Although the ridge portion R is formed, the portions where the twist grooves overlap each other are shown in FIGS. 5 (c) to 5 (e) because the mutual twist angle is larger or smaller than the above twist angle θ. As shown in the figure, the width is small on the rear end side of the widened portion 20 and gradually increases toward the front end side. On the contrary, the protruding height of the ridge R is as shown in FIGS. The widened portion 20 is formed so as to be large on the rear end side and gradually decrease toward the front end side. For this reason, chips discharged from the narrow portion 18 to the widened portion 20 may be clogged by being caught by such ridges R as in the related art, and the chip discharge performance may be impaired. Even if such a ridge R is removed by grinding again after the widened portion 20 is formed, the ridge R on the rear end side of the widened portion 20 is removed. The work is easy because it only needs to be done.
[0023]
Note that, in the manufacturing method of the present embodiment, by performing the two-step grinding process in which the relative rotational movement speed of the drill body 11 and the grindstone 22 is changed to be larger or smaller than the narrow portion 18 in the widened portion 20 as described above. Although the drill of the above embodiment is manufactured, the drill itself of the present invention is not limited to such a manufacturing method. For example, a plane orthogonal to the center line C of the grindstone 22 is aligned with the axis O of the drill body 11. It can also be manufactured by grinding while increasing the angle formed, that is, the swing angle of the grindstone 22, in the widened portion 20 while gradually increasing toward the rear end side. In this case, the widened portion 20 is formed in one step. And the ridge R is not formed. Even if the swing angle of the grindstone is not changed in this way, for example, the amount of cutting of the grindstone into the inner peripheral side of the drill body is gradually increased at the widened portion compared with the narrow portion, and both wall surfaces thereof are enlarged to increase the groove width. Although it is possible to increase the diameter, it is not preferable in this case, since the core thickness of the drill body gradually decreases toward the rear end side of the widened portion and the chip discharge property is improved, but breakage is likely to occur. Rather, on the rear end side of the widened portion 20, that is, on the rear end side of the cutting edge portion 13, the chip discharge property is determined by the groove width W. ₂₀ Is ensured by gradually increasing the diameter of the drill body 11, so that the thickness of the core of the drill body 11 preferably gradually increases toward the rear end side, contrary to the above.
[0024]
【The invention's effect】
As described above, according to the drill of the present invention, a widened portion that expands in the drill rotation direction and the rear side as the groove width approaches the rear end side with respect to the narrow portion on the tip side of the chip discharge groove is formed. By relieving the pressing force against which the chips press the chip discharge groove wall surface located in the drill rotation direction rearward and facing the drill rotation direction, the width of the groove is increased, so that the widened portion whose cross-sectional area is enlarged is increased. More effective and efficient chip discharge can be achieved. Further, according to the drill manufacturing method of the present invention, even if a ridge portion is formed in the chip discharge groove, the protrusion height is reduced at the tip side of the widened portion so that chips discharged from the narrow portion are reduced. It is possible to prevent a situation in which the chips are clogged due to being caught, so that the above-described excellent chip discharge performance can be more reliably achieved, and the work can be easily performed even when removing the ridge portion. In this way, it is possible to prevent the manufacturing efficiency of the drill from deteriorating.
[Brief description of the drawings]
FIG. 1 is a side view showing an embodiment of a drill of the present invention.
FIG. 2 is a sectional view taken along line XX in FIG.
FIG. 3 is a sectional view taken along line YY in FIG.
4 is a development view of a chip discharge groove 15 of the drill shown in FIG.
FIG. 5 is a view when grinding the wall surface 15A in one embodiment of the drill manufacturing method of the present invention, and FIG. 5A is a side view when it is assumed that the chip discharge groove 15 is linearly extended; (B) to (e) are EE to HH sectional views in (a).
FIG. 6 is a view when grinding the wall surface 15B in one embodiment of the drill manufacturing method of the present invention, and FIG. 6 (a) is a side view when the chip discharge groove 15 is assumed to be linearly extended; (B) to (e) are EE to HH sectional views in (a).
FIG. 7 is a side view of a conventional drill.
8 is a sectional view taken along the line XX in FIG.
FIG. 9 is a sectional view taken along the line YY in FIG. 7;
[Explanation of symbols]
11 drill body
14 Tip flank
15 Chip discharge groove
15A, 15B Wall surface of chip discharge groove 15
16 cutting blade
18 Narrow part
19 Virtual groove extending the narrow part 18
20 Widening section
20A First widening section
20B 2nd widening section
21 Abrasive layer
22 Whetstone
O Axis of drill body 11
C Center line of whetstone 22
T drill rotation direction
D Outer diameter of cutting blade 16
W ₁₈ Groove width at narrow portion 18
W ₂₀ Groove width in widening section 20
A Boundary between narrow portion 18 and widened portion 20 (first widened portion 20A)
B Boundary of first and second widened portions 20A, 20B
θ Twist angle at the narrow portion 18 of the chip discharge groove 15
γ Increase / decrease of the twist angles of the wall surfaces 15A and 15B in the widened portion 20 (second widened portion 20B) with respect to the narrowed portion 18

Claims

A chip discharge groove spirally twisted with respect to the axis is formed on the outer periphery of the distal end portion of the substantially cylindrical drill body rotated about the axis, and a wall surface of the chip discharge groove facing the drill rotation direction and the drill are formed. A drill in which a cutting edge is formed at an intersection ridge line portion with a tip flank of a main body, wherein a tip side portion of the chip discharge groove connected to the cutting edge has a constant twist angle and groove width with respect to the axis. In the chip discharge groove at the rear end side of the narrow portion, the groove width is set to the rear end side with respect to the virtual groove extending the narrow portion to the rear end side. A drill, characterized in that a widened portion that is gradually widened is formed in the drill rotation direction and the drill rotation direction rear side as it goes.

The boundary between the narrow portion and the widened portion is located within a range of 3 to 5 × D with respect to the outer diameter D of the cutting blade from the outer peripheral end of the cutting blade toward the rear end in the axial direction. The drill according to claim 1, wherein:

While rotating the disc-shaped grindstone with the abrasive layer formed on the outer periphery, around the center line, cut into the outer periphery of the tip of the drill body so that the outer periphery follows the twist direction of the chip discharge groove. The chip discharge groove is formed by the abrasive grain layer by moving the drill body in the axial direction while rotating the drill body relative to the grinding wheel around the axis in the direction of the twist. Alternatively, in the method for manufacturing a drill according to claim 2, in a portion to be a widened portion of the chip discharge groove, a speed larger than a relative rotational movement speed of the drill body with respect to the grindstone in the portion to be the narrow portion. A method of manufacturing a drill, wherein the drill body is moved while rotating the drill body relative to a grindstone at a small speed.