JP4120186B2 - Drill - Google Patents

Description

【００３３】
この表１の結果より、まず第１凸曲面部７の半径Ｒ１が切刃５の外径Ｄに対して０．１×Ｄを下回る比較ドリル１では、この第１凸曲面部７の幅が小さくなるのに伴い先端の凸曲線状切刃部１６の幅も小さくなって、この凸曲線状切刃部１６ごと切刃５の肩すなわち上記外周端１５部分にチッピングが生じ、またこれとは逆に半径Ｒ１が０．８×Ｄを上回る比較ドリル２では、これら第１凸曲面部７および凸曲線状切刃部１６が幅広となって、相対的に第１凹曲面部８および凹曲線状切刃部１７が幅狭となり、これにより切屑のカーリング性が損なわれて切屑排出溝３の内壁面４，９に切屑が強く押し付けられ、大きな摩耗を生じる結果となった。また、上記実施形態とは逆に第１凹曲面部８の半径Ｒ２を第２凹曲面部１２の半径Ｒ４よりも大きくした比較ドリル３では、切屑が第２凹曲面部１２に強く押し付けられることによって図５（ロ）に示すように潰れを生じ、またこの第２凹曲面部１２の摩耗も著しかった。さらに、芯厚ｄを０．３×Ｄよりも大きくした比較ドリル４では、切屑排出溝３の断面積が小さくなってやはり切屑の擦過による摩耗が大きく、しかもスラスト力が増大してドリル駆動力も大きくなったのに対し、逆に芯厚ｄを０．１５×Ｄより小さくした比較ドリル５では、スラスト力は小さくなったものの、剛性不足によって折損が生じてしまった。
【００３４】
これらの比較ドリル１〜５に対して、上記実施形態のドリル１〜３では、いずれも排出された切屑が図５（イ）に示すように潰れを生じたりすることなく小さくカールさせられていて、切屑排出溝３の内壁面４，９等における工具摩耗も正常なものであり、特に芯厚ｄを０．２３×Ｄとした実施形態ドリル２ではスラスト力、水平分力とも小さく、より安定した穴明け加工を行うことが可能であった。なお、これに対して芯厚ｄを０．２０×Ｄとやや小さめにした実施形態ドリル３では、その分剛性も小さくなったため水平分力が大きくなる傾向となったが、比較ドリル５のように折損に至るようなことはなく、実用上十分な寿命を得ることができた。
【００３５】
【発明の効果】
以上説明したように、本発明によれば、切屑排出溝のドリル回転方向を向く壁面の外周端側に凸曲面部を形成することにより、この切屑排出溝の外周端におけるドリル本体強度を確保してチッピングや欠けの発生を防止することができる。そして、この凸曲面部の内周側に滑らかに連なる第１凹曲面部を形成することにより、切屑全体を内周側に巻き込むようにして巻き癖をつけてカールさせ、効率的な処理を図ることができるとともに、ドリル回転方向後方側を向く壁面には第２凹曲面部を形成してこれら第１、第２凹曲面部を接続面によって滑らかに接続することにより、カールされた切屑がこの第２凹曲面部や接続面に強く押し付けられすぎるのを防いで、ドリル本体の摩耗やドリル回転駆動力の低減を図ることができる。また、この接続面の幅を適宜設定することにより、第１、第２凹曲面部の曲率半径に関わらず、ドリル本体の剛性や切屑排出溝の断面積を確保することもできる。従って、乾式でしかも高速切削となるような過酷な加工条件においても、ドリルの寿命の延長を図って円滑かつ安定した穴明け加工を行うことができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態を示す軸線Ｏ方向先端視の正面図である。
【図２】 図１に示す実施形態の軸線Ｏに直交する部分断面図である。
【図３】 図１に示す実施形態のシンニング部１９を示すドリル本体１先端部の斜視図である。
【図４】 （イ）は本発明の実施形態によるドリルによって生成された切屑を示す図であり、（ロ）は実施形態とは第１、第２凹曲面部８，１２の半径Ｒ３，Ｒ４の大小が反対とされた比較ドリル３による切屑を示す図である。
【符号の説明】
１ ドリル本体
２ 先端逃げ面
３ 切屑排出溝
４，９ 切屑排出溝３の内壁面
５ 切刃
７ 第１凸曲面部
８ 第１凹曲面部
１１ 第２凸曲面部
１２ 第２凹曲面部
１３ 接続面
１４ 内壁面４の外周端
１６ 切刃５の外周端
１７ 凸曲線状切刃部
１８ 凹曲線状切刃部
１９ シンニング部
２０ シンニング切刃部
２１ 第１シンニング部
２２ 第１シンニング部２１の谷底部
２３ 第２シンニング部
Ｏ ドリル本体１の軸線
Ｔ ドリル回転方向
Ｒ１〜Ｒ４ 第１、第２凸凹曲面部７，８，１１，１２が軸線Ｏに直交する断面においてなす曲線の曲率半径
Ｓ１，Ｓ２ 第１、第２仮想直線
Ｌ１，Ｌ２ 第１、第２凹曲面部８，１２の凹み量
ｄ ドリル本体１の芯厚[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drill capable of a smooth and stable drilling process even under severe processing conditions such as high-speed dry cutting.
[0002]
[Prior art]
As a drill intended to cope with such severe processing conditions that use only a dry or trace amount of cutting fluid, a drill described in, for example, Japanese Patent Application Laid-Open No. 2000-198011 has been proposed. That is, in the drill described in this publication, on the outer peripheral side of the cutting blade formed at the tip of the drill body, an outer corner cutting blade that is angled from the middle portion of the cutting blade and recedes in the drill rotation direction is formed, The leading edge formed from the chip discharge groove and the margin portion is provided with a chamfered portion having a linear shape or a curved shape following the corner cutting edge, and the crossing angle between the outer corner cutting edge and the chamfered portion and the margin portion is determined. Since the obtuse angle can be obtained, it is possible to prevent the chip or the chip discharge groove from being chipped even under the above processing conditions. Moreover, as a drill which bent the outer peripheral end side of the cutting blade or the chip discharge groove to the rear side in the drill rotation direction as described above, for example, as described in Japanese Patent Publication No. 4-46690, the first on the outer peripheral side of the cutting blade is used. A secondary straight ridge having a substantially V-shaped convex shape has also been proposed. In the drill described in this publication, the inner peripheral side of the secondary straight ridge has a rounded concave shape. Further, as such a drill having a concave cutting edge, for example, in Japanese Examined Patent Publication No. 61-58246, a concave curve is used so that the rake angle in the radial direction of the cutting edge portion on the outer peripheral side becomes 0 ° to positive. A tied one has also been proposed.
[0003]
[Problems to be solved by the invention]
Of these, as described in Japanese Examined Patent Publication No. 61-58246, when the outer peripheral cutting edge portion has a concave curve, the processing by chip curling can be performed smoothly and stably under normal processing conditions. However, since the crossing angle with the margin part of the inner wall facing the drill rotation direction of the chip discharge groove becomes an acute angle and the strength of the drill body is insufficient, this inner wall surface is immediately exposed under severe conditions such as high-speed dry cutting. Chipping and chipping occur on the outer peripheral end side, and the tool life is consumed in a very short time. On the other hand, as described in Japanese Patent Application Laid-Open No. 2000-198011 and Japanese Patent Publication No. 4-46690, a chamfered portion is provided on the outer peripheral end side of the inner wall surface of the chip discharge groove, or the outer peripheral end side of the cutting blade is In the case where the outer peripheral end of the chip discharge groove has a V-shaped cross section along with the V-shaped convex shape, the crossing angle with the margin part of the chip discharge groove can be made an obtuse angle. Although chipping is suppressed, the chips generated by the cutting blade are likely to flow out to the outer peripheral side from the chamfered portion of the inner surface of the chip discharge groove and the outer peripheral side of the convex V shape. The curling property as a whole deteriorates, and thus the chips that are not sufficiently curled are strongly pressed against the inner wall surface of the chip discharge groove facing the rear side of the drill rotation direction, which gives a great resistance to the drill body. Worn there is a risk of or cause an increase in drill rotation driving force at the time of processing or promoted.
[0004]
The present invention has been made under such a background, and prevents the shortening of the tool life even under severe processing conditions such as high-speed dry cutting and provides excellent chip disposal and enables smooth and stable drilling. The purpose is to provide a simple drill.
[0005]
[Means for Solving the Problems]
In order to solve the above problems and achieve such an object, according to the present invention, a chip discharge groove extending toward the rear end side is formed on the outer periphery of the distal end portion of the drill body rotated about the axis, and the chip is A drill in which a cutting edge is formed at an intersecting ridge line portion between the inner wall surface of the discharge groove facing the drill rotation direction and the tip flank of the drill body, and the inner wall surface of the chip discharge groove facing the drill rotation direction A convex curved surface portion that is located on the outer peripheral end side, intersects the margin portion, and forms a convex curved surface that is convex in the drill rotation direction, and is formed on the inner peripheral side of the convex curved surface portion. Forming a first concave curved surface portion that forms a curved surface that is smoothly connected to the rear side of the drill rotation direction and has a concave shape in the drill rotation direction on the inner wall surface facing the rear side of the drill discharge groove in the drill rotation direction. A second concave curved surface portion having a curved surface shape is formed. Between the first and second concave curved surface portions, a connecting surface that forms a tangential line that touches both the concave curve formed by the first concave curved surface portion and the concave curve formed by the second concave curved surface portion in a cross section orthogonal to the axis. And the first concave curved surface portion and the second concave curved surface portion are smoothly connected via the connection surface. In the cross section orthogonal to the axis, the radius of curvature of the concave curve formed by the second concave curved surface portion is made larger than the radius of curvature of the concave curve formed by the first concave curved surface portion, so that the first concave curved surface portion is The radius of curvature of the concave curve formed is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting edge, and the radius of curvature of the concave curve formed by the second concave curved surface portion is set. The outer diameter D of the cutting blade is set in a range of 0.2 × D to 0.5 × D. It is characterized by that.
[0006]
Therefore, in the drill configured in this way, a convex curved surface portion that is convex in the drill rotation direction is formed on the outer peripheral end side of the chip discharge groove, so the outer peripheral side of this convex curved surface portion, that is, the outer periphery of the drill body At the intersection with the margin portion, the intersection angle can be increased to ensure a sufficient strength, and chipping and chipping can be prevented even under the above processing conditions. And the 1st concave curved surface part which becomes a concave in the drill rotation direction back side is formed in the inner peripheral side of this convex curve surface part smoothly, and a chip is slidably contacted to this 1st concave curved surface part. As a result, it is possible to curl the entire chip on the outer peripheral side that has flowed out to the convex curved surface part so as to be wound on the inner peripheral side, and to rotate the drill on the inner wall surface facing the rear side in the drill rotation direction of the chip discharge groove A second concave curved surface portion that is concave in the direction is formed, and a connecting surface that smoothly touches both concave curved surface portions is formed between the first and second concave curved surface portions. It is possible to smoothly flow out the chips without pressing strongly against the inner wall surface facing the rear side of the drill rotation direction of the chip discharge groove, reducing resistance to the drill body during processing, reducing wear and driving the drill To reduce power Door can be. In addition, by forming the connection surface between the first and second concave curved surface portions in this way, the groove width of the chip discharge groove is ensured without being limited by the curvature radius of the first and second concave curved surface portions. Therefore, it is possible to simultaneously improve the curling property and discharging property of the chips as described above. However, in the present invention, in the cross section perpendicular to the axis, the radius of curvature of the concave curve formed by the second concave curved surface portion is made larger than the radius of curvature of the concave curve formed by the first concave curved surface portion. The first concave curved surface portion can curl the chip with sufficient curl, and the radius of curvature of the second concave curved surface portion is made larger than that of the first concave curved surface portion. By interposing the connection surface between the first and second concave curved surface portions, it is possible to further suppress chip pressing to the second concave curved surface portion and to further smooth chip discharge. In addition, as for the radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section perpendicular to the axis, there is a possibility that it cannot be sufficiently curled by sliding the chips if it is too large. If it is too small, the chips are abruptly curled and the braking action may become too large, so the range is set in the range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting edge. Furthermore, if the radius of curvature of the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis is too large, the chips do not slide on the second concave curved surface portion and are curled only by the first concave curved surface portion. On the other hand, if it is too small, the sliding contact of the chips with the second concave curved surface portion becomes too strong and a large braking action is generated. It is set in the range of 0.2 × D to 0.5 × D. Such a connection surface may be formed between the convex curved surface portion and the first concave curved surface portion, or on the outer peripheral side of the convex curved surface portion or the second concave curved surface portion.
[0007]
However, in this case, if the dent on the rear side in the drill rotation direction of the first concave curved surface portion is too small, there is a possibility that sufficient curling due to the sliding contact of chips may not be achieved, but conversely if the dent is too large. Further, the braking action due to the sliding contact of the chips becomes too strong, and the chips may be crushed and the discharge performance may be impaired, or the drill driving force may be increased. Also, with respect to the second concave curved surface portion, depending on the width of the connection surface, if the recess in the drill rotation direction is too small, chips flowing from the first concave curved surface portion are strongly pressed against the second concave curved surface portion. On the other hand, if this dent is too large, the chips may be curled only by sliding contact with the first concave curved surface portion, and may not be sufficiently curled. There is. For this reason, the dents of the first and second concave curved surface portions are the first imaginary line from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction in a cross section orthogonal to the axis. From the second imaginary straight line that intersects the first imaginary straight line at the axis line while setting the dent amount L1 of the concave curved surface part to a range of −0.06 × D to 0 with respect to the outer diameter D of the cutting edge. It is desirable to set the dent amount L2 of the second concave curved surface portion in the range of −0.06 × D to 0.06 × D.
[0008]
The radii of curvature of the first and second concave curved surface portions may be constant in each case, that is, the first and second concave curved surface portions in the cross section are smoothly in contact with each other at one contact point with arcs having different radii. The shape may be a shape, and the radius of curvature gradually increases from the first concave curved surface portion side to the second concave curved surface portion side through the connection surface having a tangential cross section, for example, an elliptical shape or a trochoid in the cross section, Various curvilinear shapes such as a cycloid and an involute may be exhibited.
[0009]
Further, when the convex curved surface portion and the first and second concave curved surface portions that are smoothly connected to the inner wall surface of the chip discharge groove are formed in this way, the curvature radius of the convex curve formed by the convex curved surface portion first in the cross section orthogonal to the axis line. On the other hand, if this is too large, the curling of chips may be insufficient. On the other hand, if it is too small, sufficient strength cannot be secured at the intersection with the margin portion. In contrast, it is desirable to set a range of 0.1 × D to 0.8 × D. Furthermore, in order to sufficiently ensure the rigidity of the drill body while facilitating smooth discharge of the chips curled as described above, the core thickness of the drill body is set to the outer diameter D of the cutting blade. It is desirable to set it in the range of 0.15 × D to 0.3 × D. Furthermore, if the surface of at least the tip of the drill body is coated with a hard coating such as TiN, TiCN, TiAlN, etc., the wear resistance of the tip of the drill body can be improved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
1 to 3 show an embodiment of the present invention. In the present embodiment, the drill body 1 is formed in a substantially cylindrical shape centering on the axis O by a hard material such as a cemented carbide, and is constant at the tip portion from the tip flank 2 toward the rear end side. A pair of chip discharge grooves 3, 3 that are twisted to the rear side in the drill rotation direction T at a twist angle of? Are formed symmetrically with respect to the axis O, and the drill rotation direction T side of these chip discharge grooves 3, 3 is Cutting blades 5 and 5 are formed at the intersecting ridges between the facing inner wall surfaces 4 and 4 and the tip flank 2, respectively. The tip of the drill body 1 is coated with a hard coating such as TiN, TiCN, TiAlN on the outer peripheral surface, the tip flank 2 and the chip discharge groove 3.
[0011]
Here, the inner wall surface 4 is located on the outer peripheral side thereof, intersects the margin portion 6, and forms a convex curve that is convex in the drill rotation direction T as shown in FIG. 2 in a cross section orthogonal to the axis O. 1 convex curved surface part 7 and the 1st concave curved surface part 8 which makes the concave curve shape which is located in the inner peripheral side of this 1st convex curved surface part 7, and dents in the back side of the drill rotation direction T in the said cross section are formed. The uneven curves formed by the cross sections of the first uneven surface portions 7 and 8 are connected so as to smoothly contact at the contact point P1. Further, in the present embodiment, the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the drill rotation direction T is also located on the outer peripheral side and reaches the heel portion 10, and the above-mentioned cross section protrudes toward the rear side in the drill rotation direction T. A second convex curved surface portion 11 that forms a convex curve, and a second concave curved surface portion 12 that is located on the inner peripheral side of the second convex curved surface portion 11 and has a concave curved shape whose cross section is recessed toward the drill rotation direction T. Are formed so that the uneven curves formed by the second uneven curved surface portions 11 and 12 are also smoothly contacted at the contact point P2. Between the first and second concave curved surface portions 8 and 12, both the concave curve formed by the first concave curved surface portion 8 and the concave curve formed by the second concave curved surface portion 12 in a cross section orthogonal to the axis O. A connecting surface 13 is formed in a tangential shape that contacts the contacts P3 and P4, and the both concave curved surface portions 8 and 12 are smoothly connected via the connecting surface 13. In addition, by forming the chip discharge groove 3 in a twisted groove shape, the connection surface 13 is a twisted surface that is twisted in the same manner as the chip discharge groove 3 toward the rear end side of the drill body 1. Further, the outer peripheral surface of the land portion extending from the margin portion 6 to the heel portion 10 in the drill rotation direction T rear side is formed in a cylindrical surface shape that recedes from the margin portion 6 to the inner peripheral side in one step.
[0012]
Furthermore, in the present embodiment, in the cross section, the uneven curves formed by the first and second uneven curved surface portions 7, 8, 11, and 12 are arcs having radii R1 to R4 with the points C1 to C4 as the centers. The center C1 of the convex arc formed by the first convex curved surface portion 7 is the intersection of the first convex curved surface portion 7 and the margin portion 6, that is, the margin portion 6 at the outer peripheral end 14 of the inner wall surface 4. The center C3 of the circular arc formed by the second convex curved surface portion 11 is positioned on the inner peripheral side with respect to the straight line Q1 in contact with the circular arc formed by the second convex curved surface portion 11 and the circle formed by the outer peripheral end 14 around the axis O. At the intersection 15 with the extended line, the straight line Q2 that is in contact with the circle is also located on the inner peripheral side. Accordingly, the first convex curved surface portion 7 is convex toward the drill rotation direction T side with respect to the first virtual straight line S1 connecting the axis O and the outer peripheral end 14 of the inner wall surface 4, and the first convex at the outer peripheral end 14. The tangent line of the curved surface portion 7 is inclined with respect to the first imaginary straight line S1 so as to extend rearward in the drill rotation direction T toward the outer peripheral side, and is obtuse with the straight line Q1 orthogonal to the first imaginary straight line S1. Can be crossed. Further, the second convex curved surface portion 11 is also convex toward the rear side in the drill rotation direction T from the straight line connecting the intersection with the heel portion 10 and the axis O.
[0013]
On the other hand, since the arc centers C2 and C4 formed by the first and second concave curved surface portions 8 and 12 are in contact with the tangent line formed by the connection surface 13 at the contact points P3 and P4, the contact point P3 , P4, respectively, are located on a pair of parallel lines orthogonal to each other. Furthermore, in this embodiment, this connection surface 13 is the groove bottom that is recessed most on the inner peripheral side of the drill body 1 in the chip discharge groove 3, and therefore the core thickness of the drill body 1 that is in contact with this connection surface 13 about the axis O. Yen. The diameter of the core thickness circle, that is, the core thickness d of the drill body 1 is 0.15 × with respect to the diameter of the circle formed by the outer peripheral end 16 of the cutting blade 5 around the axis O, that is, the outer diameter D of the cutting blade 5. It is set in the range of D to 0.3 × D.
[0014]
The contact point P1 of the uneven curve formed by the first uneven surface portions 7 and 8 is positioned on the outer peripheral side with respect to the circle having the diameter of 2/3 of the outer diameter D of the cutting blade 5 with the axis O as the center. More preferably, it is positioned on the outer peripheral side of a circle having a diameter of 5/6 of the outer diameter D around the axis O. In addition, the size of the recess of the first concave curved surface portion 8 toward the rear side in the drill rotation direction T is such that the recess amount L1 from the first imaginary straight line S1 is −0.06 × with respect to the outer diameter D of the cutting blade 5. The second imaginary straight line S2 is set in the range of D to 0, and the size of the dent of the second concave curved surface portion 12 toward the drill rotation direction T is perpendicular to the first imaginary straight line S1 by the axis O in the cross section. Is set to be in a range of −0.06 × D to 0.06 × D. However, these dent amounts L1 and L2 are parallel to the first and second imaginary straight lines S1 and S2 in the cross section, respectively, and the first and second straight lines in contact with the concave curves formed by the first and second concave curved surface portions 8 and 12 respectively. The distance between the second virtual straight line S1 and S2, and as shown in FIG. 2, with respect to the amount of recess L1 of the first concave curved surface portion 8, the drill rotation direction T side is positive from the first virtual straight line S1. The rear side is negative, and conversely, with respect to the dent amount L2 of the second concave curved surface portion 12, the drill rotation direction T side from the second virtual straight line S2 is negative and the rear side is positive. Therefore, in the present embodiment, the entire first concave curved surface portion 8 is not positioned on the drill rotation direction T side with respect to the first virtual straight line S1.
[0015]
Further, in the cross section, the radii R1 to R4 of the arc formed by the first and second uneven curved surface portions 7, 8, 11, and 12 have a radius R 1 of the first convex curved surface portion 7 with respect to the outer diameter D of the cutting edge 5. In the range of 0.1 to 0.8 × D, the radius R2 of the first concave curved surface portion 8 is in the range of 0.18 to 0.35 × D, and the radius R3 of the second convex curved surface portion 11 is 0.1 to 0.1 × D. In the range of 0.8 × D, the radius R4 of the second concave curved surface portion 12 is set in the range of 0.2 to 0.5 × D. And in this embodiment, radius R4 of the 2nd concave curved surface part 12 is made larger than radius R2 of the 1st concave curved surface part 8 among these. In addition, the groove width ratio of the chip discharge groove 3 formed in this way is set to a range of 0.8 to 1.2: 1 in the present embodiment.
[0016]
In the cutting edge 5 formed at the intersecting ridge line portion between the inner wall surface 4 and the tip flank 2 of the chip discharge groove 3, the inner wall surface 4 is formed by the first uneven curved surface portions 7 and 8. Accordingly, as shown in FIG. 1, a convex curved cutting edge portion 17 having a curved shape convex in the drill rotation direction T is formed on the outer peripheral end 16 side, and the first convex curved surface is formed on the rear end side. The portion 7 is continuous, and on the inner peripheral side of the convex curved cutting edge portion 17, a curved shape that is concave on the rear side in the drill rotation direction T is formed so as to be in smooth contact with the convex curved cutting blade portion 17. A concave curved cutting edge portion 18 is formed, and the first concave curved surface portion 8 is connected to the rear end side thereof, and the cutting blade 5 is located between the convex and concave curved cutting blade portions 17 and 18 in the front view in the direction of the axis O. It will exhibit an S-shape that gently curves. However, the cutting edge 5 is provided with a tip angle by being inclined toward the rear end side of the drill body 1 as the tip flank 2 moves from the inner peripheral side to the outer peripheral side, and chip discharge is performed. Since the groove 3 is twisted in a spiral shape, the S-shaped uneven curve formed by the uneven curved cutting edge portions 17 and 18 of the cutting edge 5 when viewed from the front in the direction of the axis O is the first curve of the inner wall surface 4. The uneven curve formed in the cross section where the uneven curved surface portions 7 and 8 are orthogonal to the axis O will have a shape that gradually shifts toward the drill rotation direction T side toward the inner peripheral side. Therefore, the convex curve-shaped cutting edge portion 17 has a tangent at the outer peripheral end 16 that is larger in inclination than the tangent at the outer peripheral end 14 of the convex curve formed by the first convex curved surface portion 7 in the cross section when viewed from the front in the axis O direction. As it goes to the outer peripheral side, it extends to the rear side in the drill rotation direction T, and the crossing angle with the margin portion 6 is also made larger than the obtuse angle formed by the first convex curved surface portion 7, whereby the cutting edge 5 is 16 is set to the negative angle side.
[0017]
On the other hand, the tip flank 2 from the inner peripheral side of the first concave curved surface portion 8 to the second concave curved surface portion 12 and the second convex curved surface portion 11 is formed on the distal end side of the inner wall surfaces 4 and 9 of the chip discharge groove 3. A thinning portion 19 reaching the heel portion 10 is formed so as to cut out the crossed ridge line portion toward the rear end side of the drill body 1 toward the inside of the chip discharge groove 3. The inner peripheral end side is formed at the intersecting ridge line portion between the thinning portion 19 and the tip flank 2 and is directed from the inner peripheral end of the concave curved cutting edge portion 18 toward the axis O at the center of the tip flank 2. The thinning cutting edge portion 20 extends. Note that a portion of the cutting blade 5 where the thinning cutting blade portion 20 and the concave curved cutting blade portion 18 intersect is smoothly connected by a curve or straight line that is convex in the drill rotation direction T when viewed from the front in the axis O direction. ing.
[0018]
Here, a portion of the thinning portion 19 that intersects the inner wall surfaces 4 and 9 of the chip discharge groove 3 and extends to the front end side is a first thinning portion 21, and this first thinning portion 21 is rotated by a drill. The portion extending to the heel portion 10 side intersecting the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the direction T is formed in a flat shape, while the inner wall surface 4 facing the inner wall surface 9 and the drill rotation direction T side. 3, that is, a portion extending from the contact P3 portion of the first and second concave curved surface portions 8 and 12 toward the center of the tip flank 2 as shown in FIG. It is formed so as to form a concave curved valley when viewed from the direction toward the center, and the concavely curved valley bottom 22 is located on the inner peripheral side of the drill body 1 with respect to the inner wall surfaces 4, 9. The inner peripheral end of the cutting edge 5, that is, the thin It is formed to extend distally toward the inner peripheral end of the ring cutting edge 20. In addition, the curvature radius of the concave curve which the trough bottom part 22 which the concave part of this 1st thinning part 21 makes in the cross section is set to the range of 0.1-0.5 mm. Further, the radius of curvature of the concave curve formed by the cross section of the valley bottom 22 may be increased toward the rear end side.
[0019]
Further, in the portion where the foremost valley bottom portion 22 of the first thinning portion 21 is about to reach the inner peripheral end of the cutting edge 5, the first thinning portion 21 is further retracted toward the inner peripheral side of the drill body 1 with respect to the valley bottom portion 22. A valley-shaped second thinning portion 23 extending toward the inner peripheral end side of the cutting blade 5 while being inclined one step is formed, and in the vicinity of the axis O at the center of the tip flank 2, the second thinning portion 23 is formed. Intersects the tip flank 2 and the inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion. Here, the curvature radius of the valley bottom portion of the second thinning portion 23 is smaller than the curvature radius of the valley bottom portion 22 of the first thinning portion 21 and is less than 0.1 mm. That is, the bottom of the valley may be formed in a V-shaped valley that is not concavely curved, and is further increased in size toward the rear end side of the drill body 1 in the same manner as the valley bottom 22 of the first thinning portion 21. Also good. In addition, the tip end of the drill body 1 is formed by forming the inner peripheral end of the cutting edge 5 at the intersecting ridge line portion between the second thinning portion 23 and the tip flank 2 which are inclined further by one step than the first thinning portion 21 in this way. The distance between the pair of cutting edges 5, 5, that is, the width of the chisel defined at the center of the tip flank 2 is such that the first thinning portion 21 intersects the tip flank 2 as it is and the inner peripheral edge of the cutting blade 5. The width of the chisel is in the range of 0 to 0.2 mm in this embodiment. Accordingly, the inner peripheral ends of the cutting blades 5 and 5 may be aligned on the axis O.
[0020]
In the drill configured in this way, first, the first convex curved surface portion 7 is formed on the outer peripheral end 14 side of the inner wall surface 4 facing the drill rotation direction T of the chip discharge groove 3. Since the crossing angle between the inner wall surface 4 and the margin portion 6 of the chip discharge groove 3 can be increased, and the strength of the drill body 1 around the outer peripheral end 14 can be ensured. Even under severe processing conditions, it is possible to prevent a situation in which chipping or chipping occurs around the outer peripheral end 14 to shorten the tool life. Further, a first concave curved surface portion 8 is formed on the inner peripheral side of the first convex curved surface portion 7 so as to be smoothly connected to the first convex curved surface portion 7, and flows on the first convex curved surface portion 7. Even if the outer peripheral side portion of the chip is about to flow out to the outer peripheral side, the chip inner peripheral side portion flowing on the first concave curved surface portion 8 is pressed while being in sliding contact with the first concave curved surface portion 8, thereby It can be curled small by attaching a curl so that it is entirely wound on the inner peripheral side.
[0021]
Further, in the drill having the above-described configuration, the first concave curved surface portion 8 is provided on the inner peripheral side of the inner wall surface 9 of the chip discharge groove 3 facing the rear side of the drill rotation direction T opposite to the first concave curved surface portion 8. On the contrary, a second concave curved surface portion 12 that is concave in the drill rotation direction T is formed, and the first and second concave curved surface portions 8 and 12 are smoothly connected to the both concave curved surface portions 8 and 12. Since it is connected by the surface 13, the chips curled small by the first concave curved surface portion 8 as described above are pressed more strongly against the second concave curved surface portion 12 and the connecting surface 13 and are crushed. It is possible to discharge smoothly without obstructing the flow of chips. Further, since the chips are not strongly pressed against the second concave curved surface portion 12 and the connecting surface 13 in this way, the abrasion of the inner wall surface 9 of the chip discharge groove 3 is promoted by the scraping of the chips, or the drill rotational driving force is increased. Is not invited. In addition, in the present embodiment, the second convex curved surface portion 11 is formed so as to be smoothly connected to the outer peripheral side of the second concave curved surface portion 12, so that the flow of chips may be inhibited on the heel portion 10 side. In addition, the strength of the drill body 1 in the heel portion 10 can be ensured. Further, since the tip of the drill body 1 including the cutting edge 5 is coated with a hard film such as TiN, TiCN, or TiAlN, the wear resistance of the drill body 1 can be further improved. .
[0022]
Further, when the connection surface 13 is interposed between the first and second concave curved surface portions 8 and 12 in this way, the radius of curvature R2 and R4 of the first and second concave curved surface portions 8 and 12 is limited. The groove width of the chip discharge groove 3 can be set without any change. Therefore, for example, when the chip tends to curl due to the material of the workpiece, the radii R2 and R4 of the first and second concave curved surface portions 8 and 12 are increased in order to prevent the chip from being curled too small, and as a result If the cross-sectional area of the drill body 1 is reduced as the groove width of the chip discharge groove 3 is increased and the rigidity may be impaired, the width of the connection surface 13 is reduced to reduce the chip discharge groove 3. Accordingly, the cross-sectional area of the drill body 1 can be ensured to maintain the rigidity. On the other hand, for example, when it is difficult for the chip to curl, the radius R2 of the first concave curved surface portion 8 is decreased to try to strongly curl the chip, or the radius of the second concave curved surface portion 12 is set. When R4 is made small to try to press the chip against the second concave curved surface portion 12 to some extent, the cross-sectional area of the chip discharge groove 3 may be reduced and chip clogging may occur. In this case, by increasing the groove width of the connection surface 13, a sufficient cross-sectional area is secured in the chip discharge groove 3 regardless of the radii R2 and R4 of the first and second concave curved surface portions 8 and 12. Smooth chip discharge performance can be maintained.
[0023]
Further, in the present embodiment, the first and second concave curved surface portions 8 and 12 are connected to the concave amounts L1 and L2, and the first concave curved surface portion 8 is connected to the axis O and the outer peripheral end 14 of the inner wall surface 4 with respect to the first concave curved surface portion 8. The range from −0.06 × D to 0 with respect to the outer diameter D of the cutting edge 5 from the imaginary straight line S1 (however, the rear side of the drill rotation direction T is negative). O is set to be in the range of −0.06 × D to 0.06 × D from the second virtual line S2 orthogonal to the first virtual line S1 (however, the drill rotation direction T side is negative). As a result, the chip can be brought into sliding contact with the first and second concave curved surface portions 8 and 12 without being too strong and not too weak, and an appropriate braking action can be given. For this reason, the chips can be reliably curled and processed without damaging the smooth evacuation due to excessive braking action and without causing an increase in the drill rotation driving force. In order to achieve such an effect more reliably, the curvature radius R2 of the concave curve (concave arc) formed by the first concave curved surface portion 8 in the cross section orthogonal to the axis O as in the present embodiment is cut. The outer radius D of the blade 5 is set in a range of 0.18 to 0.35 × D, and the radius of curvature R4 of the second concave curved surface portion 12 is set in a range of 0.2 to 0.5 × D. Is desirable.
[0024]
In the present embodiment, the radius of curvature of the concave curve formed by the second concave curved surface portion 12 in the cross section perpendicular to the axis O between the first and second concave curved surface portions 8 and 12, that is, the radius R4 is the first. The radius of curvature of the concave curve formed by the concave curved surface portion 8, that is, the radius R2 is made larger. For this reason, the chip generated by the cutting blade 5 is first slidably brought into contact with the first concave curved surface portion 8 having a relatively small radius R2, so that the chip is curled with a sufficient curl and thus curled. By flowing out the chips to the second concave curved surface portion 12 side having a relatively large radius R4 via the connection surface 13, it is possible to further suppress the strong pressing of the chips on the second concave curved surface portion 12 and the connection surface 13. Therefore, it is possible to promote smoother chip discharge and further reduce the drill rotation driving force.
[0025]
Further, in the present embodiment, the curvature radii R1 and R3 of the convex curves (convex arcs) formed by the first and second convex curved surface portions 7 and 11 in the cross section are 0 with respect to the outer diameter D of the cutting blade 5, respectively. .1 to 0.8 × D, so that the strength around the margin portion 6 and the strength around the heel portion 10 at the outer peripheral end 14 of the inner wall surface 4 of the drill body 1 are sufficiently secured. The width of the first and second concave curved surface portions 8 and 12 in the radial direction can be prevented from becoming too small, and reliable chip disposal can be improved. In addition, in order to achieve both the securing of the strength of the drill body 1 and the improvement of the chip disposal in this way even under conditions such as high-speed dry cutting, the first uneven surface in the cross section as in the present embodiment. The contact point P1 of the uneven curve formed by the portions 7 and 8 is located on the outer peripheral side from the circle O having a diameter of 2/3 of the outer diameter D of the cutting blade 5 from the axis O, and more preferably a circle having a diameter of 5/6 of the outer diameter D. It is desirable that the groove width ratio of the chip discharge groove 3 is in the range of 0.8 to 1.2: 1.
[0026]
Furthermore, in this embodiment, as the chip disposability is improved and the drill rotational driving force is reduced in this way, the load that the drill body 1 itself receives during processing becomes smaller, and thereby the core thickness is reduced. d can also be set to a relatively small range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting edge 5. For this reason, especially the thrust force is reduced among the loads received by the drill body 1 and the cross-sectional area of the chip discharge groove 3 is increased to facilitate smooth chip discharge, thereby further increasing the power during drilling. Mitigation can be achieved. On the other hand, the cross-sectional area of the drill body 1 is large on the outer peripheral side by setting the curvature radii R1 to R4 in an appropriate range as described above, and in particular by the first and second convex curved surface portions 7 and 11. Therefore, the necessary and sufficient amount can be secured, and therefore the rigidity of the drill body 1 can be maintained, so that the machining power can be further reduced as described above. It is possible to prevent a situation in which breakage or the like sometimes occurs and the drill life is consumed.
[0027]
On the other hand, in the drill of this embodiment in which the first uneven curved surface portions 7 and 8 are formed on the inner wall surface 4 facing the drill rotation direction T of the chip discharge groove 3 in this way, the drill is formed at the intersecting ridge line portion with the tip flank 2. On the outer peripheral end 16 side of the cutting edge 5 to be formed, a convex curved cutting edge portion 17 that is convex in the drill rotation direction T is formed. And the margin portion 6 can be set to a large angle as described above, and larger than the cross angle with the first convex curved surface portion 7, and the drill body in the vicinity of the outer peripheral end 16 of the cutting edge 5. The strength of 1 can be sufficiently secured. For this reason, since it is located on the outer periphery of the drill body 1, the cutting speed is the highest, and the amount of chips generated is the largest, so that an excessive load is likely to occur, and the outer peripheral edge 16 of the cutting blade 5 is easily chipped or chipped. Therefore, the tool life can be further extended under processing conditions such as high-speed dry cutting. Moreover, in the present embodiment, the convex curved cutting edge portion 17 is formed so as to protrude in the drill rotation direction T from the straight line connecting the outer peripheral end 16 of the cutting edge 5 and the axis O when viewed from the front of the axis O direction. Thus, as described above, since the radial rake angle α is a negative angle, the crossing angle with the margin portion 6 becomes an obtuse angle, and the strength of the drill body 1 around the outer peripheral end 16 is more reliably determined. Can be secured.
[0028]
Further, the convex curved cutting edge portion 17 has a curved shape that is convex in the drill rotation direction T in this way, and the cutting edge is bent into a convex V shape with an angle as in the conventional drill described above. Therefore, a bending point is not formed on the cutting edge, and a concave curved cutting edge portion 18 which is concave on the rear side in the drill rotation direction T is formed on the inner circumferential side of the cutting edge. Therefore, the chip generated by the cutting blade 5 is not divided at the bending point, and the portion generated by the concave curved cutting blade portion 18 is the inner circumference. As it flows out toward the side, it is slidably brought into contact with the second concave curved surface portion 8 while being generated so as to be entirely wound on the inner peripheral side, and is smoothly curled. For this reason, in the present embodiment, there is no fear that chips will be clogged by being divided and entangled at the bending point on the cutting edge as in the prior art, and also divided on the outer peripheral side of the bending point. Drill rotation drive during drilling by promoting smoother and more stable processing of chips without increasing the resistance and accelerating the wear of the drill body. In addition to reducing the force, it is possible to suppress wear and extend the tool life.
[0029]
Furthermore, in this embodiment, the thinning part 19 is formed in the front end side of the chip discharge groove | channel 3, By this, the inner peripheral end side of the cutting blade 5 is made into the thinning cutting edge part 20 which goes to the center of the front-end | tip flank 2. A portion where the thinning cutting edge portion 20 and the concave curved cutting edge portion 18 intersect with each other is formed into a convex curve shape or a straight line smoothly connected to both the cutting edge portions 18 and 20, and the thinning cutting edge portion. Since the first thinning portion 21 connected to 20 has a valley shape in which the valley bottom portion 22 is bent, the bending point as described above is not formed even over the entire length of the cutting edge 5. The inner peripheral side portion of the chips generated by the thinning cutting edge portion 20 is also on the inner peripheral side along the concave curve formed by the cross section of the valley bottom portion 22 of the first thinning portion 21 as shown by the black arrow in FIG. Can be curled so that For this reason, coupled with the fact that chips are wound on the inner peripheral side by the concave curvilinear cutting edge portion 18, it is possible to further improve the chip disposability, especially in the processing of difficult-to-cut materials. is there. In this embodiment, the radius of curvature of the concave curve formed by the valley bottom portion 22 of the first thinning portion 21 is set to 0.1 to 0.5 mm. If this radius of curvature is larger than this, This is because the inner peripheral side portion may not be sufficiently wound and curled, and conversely, if it is smaller than this, the inner peripheral side portion of the chips may be clogged in the thinning portion 19.
[0030]
Further, a second thinning portion 23 is formed at the tip of the thinning portion 19 so as to be inclined one step further from the valley bottom portion 22 of the first thinning portion 21 and reach the tip flank 2. The inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion between the tip flank 2 and the radius of curvature of the groove bottom of the second thinning portion 23 is less than 0.1 mm, which is higher than that of the valley bottom portion 22. Since it is made small, the inner peripheral end of the cutting blade 5 is arranged on the inner peripheral side, and the width of the chisel is set to an extremely short width of 0 to 0.2 mm. For this reason, it is possible to improve the biting property and the straight running stability when the drill bites the workpiece, and to perform further stable and highly accurate machining, and the thrust acting on the drill body 1 in the axial direction thereof The force can be suppressed, and further reduction of the drill driving force can be promoted. In addition, the thinning portion 19 is formed by the first and second thinning portions 21 and 23 whose inclination increases toward the inner peripheral end of the cutting blade 5 in this way, so that the second thinning portion 23 at the tip end is formed. The angle of the tip of the drill body 1 in the cross section along the groove bottom is larger than that when the groove bottom of a single thinning portion is inclined so as to have the same chisel width. It is possible to provide a drill that sufficiently secures the strength around the center of rotation of the tip of the drill body 1 and that is not damaged even by an impact load at the time of biting. However, the second thinning portion 23 may not be provided as long as the biting property, straight running stability, and strength of the drill main body 1 can be secured only by the first thinning portion 21.
[0031]
Here, the following table 1 shows the drill of the embodiment shown in FIGS. 1 to 3, the size of the radius R1 of the first convex curved surface portion 7, the size of the first and second concave curved surface portions 8, 12, and The comparison drills 1 to 5 are the same as in this embodiment except that the size of the core thickness d is different, and show the results when the cutting speed was changed and the drilling test was performed dry. The processing conditions and evaluation are as shown below the table.
[0032]
[Table 1]

[0033]
From the results of Table 1, first, in the comparative drill 1 in which the radius R1 of the first convex curved surface portion 7 is less than 0.1 × D with respect to the outer diameter D of the cutting blade 5, the width of the first convex curved surface portion 7 is As it becomes smaller, the width of the convex curvilinear cutting edge portion 16 at the tip also becomes smaller, and the shoulder of the cutting blade 5 together with the convex curvilinear cutting edge portion 16, that is, the outer peripheral end 15 portion is chipped. On the contrary, in the comparative drill 2 in which the radius R1 exceeds 0.8 × D, the first convex curved surface portion 7 and the convex curved cutting edge portion 16 are wide, and the first concave curved surface portion 8 and the concave curved curve are relatively formed. As a result, the curled portion of the chip was damaged, and the chip was strongly pressed against the inner wall surfaces 4 and 9 of the chip discharge groove 3, resulting in large wear. In contrast to the above embodiment, in the comparative drill 3 in which the radius R2 of the first concave curved surface portion 8 is larger than the radius R4 of the second concave curved surface portion 12, chips are strongly pressed against the second concave curved surface portion 12. As shown in FIG. 5 (b), crushing occurred, and the wear of the second concave curved surface portion 12 was remarkable. Further, in the comparative drill 4 in which the core thickness d is larger than 0.3 × D, the cross-sectional area of the chip discharge groove 3 is reduced, so that wear due to chip abrasion is also large, and the thrust force is increased and the drill driving force is also increased. On the contrary, in the comparative drill 5 in which the core thickness d was smaller than 0.15 × D, the thrust force was reduced, but breakage occurred due to insufficient rigidity.
[0034]
With respect to these comparative drills 1 to 5, in the drills 1 to 3 of the above embodiment, the discharged chips are curled small without causing crushing as shown in FIG. The tool wear on the inner wall surfaces 4 and 9 of the chip discharge groove 3 is also normal. In particular, in the embodiment drill 2 in which the core thickness d is 0.23 × D, both the thrust force and the horizontal component force are small and more stable. Drilling was possible. On the other hand, in the embodiment drill 3 in which the core thickness d is slightly reduced to 0.20 × D, since the rigidity is reduced accordingly, the horizontal component force tends to increase. However, there was no breakage and a practically sufficient life could be obtained.
[0035]
【The invention's effect】
As described above, according to the present invention, the convex body is formed on the outer peripheral end of the wall surface facing the drill rotation direction of the chip discharge groove, thereby ensuring the strength of the drill body at the outer peripheral end of the chip discharge groove. Occurrence of chipping and chipping can be prevented. Then, by forming the first concave curved surface portion that is smoothly connected to the inner peripheral side of the convex curved surface portion, curling is performed by curling the curl so that the entire chip is wound on the inner peripheral side, thereby achieving efficient processing. In addition, the second concave curved surface portion is formed on the wall surface facing the rear side in the drill rotation direction, and the first and second concave curved surface portions are smoothly connected by the connection surface, so that the curled chips can be removed. It is possible to prevent excessive pressing against the second concave curved surface portion and the connection surface, and to reduce wear of the drill body and drill rotation driving force. In addition, by appropriately setting the width of the connection surface, the rigidity of the drill body and the cross-sectional area of the chip discharge groove can be ensured regardless of the radii of curvature of the first and second concave curved surface portions. Therefore, even under severe conditions such as dry and high-speed cutting, the drill life can be extended and smooth and stable drilling can be performed.
[Brief description of the drawings]
FIG. 1 is a front view of an embodiment of the present invention as viewed from the front in the direction of an axis O. FIG.
FIG. 2 is a partial cross-sectional view orthogonal to the axis O of the embodiment shown in FIG.
3 is a perspective view of the distal end portion of a drill body 1 showing a thinning portion 19 of the embodiment shown in FIG. 1. FIG.
4A is a view showing chips generated by the drill according to the embodiment of the present invention, and FIG. 4B is a view showing the radii R3 and R4 of the first and second concave curved surface portions 8 and 12 in the embodiment. It is a figure which shows the chip | tip with the comparative drill 3 by which the magnitude | size of was reversed.
[Explanation of symbols]
1 Drill body
2 Tip flank
3 Chip discharge groove
4,9 Inner wall surface of chip discharge groove 3
5 Cutting blade
7 First convex curved surface
8 first concave curved surface
11 Second convex curved surface
12 Second concave curved surface
13 Connection surface
14 Outer peripheral edge of inner wall surface 4
16 Outer edge of cutting edge 5
17 Convex curve cutting edge
18 Concave curved cutting edge
19 Thinning club
20 Thinning cutting edge
21 First thinning section
22 Valley bottom of the first thinning part 21
23 Second thinning section
O Axis of drill body 1
T Drill rotation direction
R1 to R4 Curvature radii of curves formed by the first and second uneven curved surface portions 7, 8, 11, and 12 in a cross section orthogonal to the axis O
S1, S2 first and second virtual straight lines
L1, L2 Depression amount of the first and second concave curved surface portions 8, 12
d Core thickness of drill body 1

Claims (5)

A chip discharge groove extending toward the rear end is formed on the outer periphery of the tip end of the drill body rotated about the axis, and the inner wall surface of the chip discharge groove facing the drill rotation direction intersects the tip flank of the drill body. A drill in which a cutting edge is formed in a ridge line portion, and the inner wall surface facing the drill rotation direction of the chip discharge groove is located on the outer peripheral end side, intersects the margin portion, and protrudes in the drill rotation direction. A convex curved surface portion having a convex curved surface shape is formed, and a first curved surface shape that is smoothly connected to the convex curved surface portion and concave on the rear side in the drill rotation direction is formed on the inner peripheral side of the convex curved surface portion. A concave curved surface portion is formed, and a second concave curved surface portion having a curved shape that is concave in the drill rotating direction is formed on the inner wall surface facing the rear side in the drill rotating direction of the chip discharge groove. Between the second concave curved surface portions, there is a break perpendicular to the axis. A tangential connection surface is formed in contact with both the concave curve formed by the first concave curved surface portion and the concave curve formed by the second concave curved surface portion, and the first concave curved surface portion and the first concave curved surface portion are formed through this connection surface. The second concave curved surface portion is smoothly connected, and in the cross section orthogonal to the axis, the radius of curvature of the concave curve formed by the second concave curved surface portion is the radius of curvature of the concave curve formed by the first concave curved surface portion. And the radius of curvature of the concave curve formed by the first concave curved surface portion is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting edge. The radius of curvature of the concave curve formed by the second concave curved surface portion is set in a range of 0.2 × D to 0.5 × D with respect to the outer diameter D of the cutting blade. .   In the cross section orthogonal to the axis, the dent amount L1 of the first concave curved surface portion from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction is the outer diameter D of the cutting blade. Is set in a range of −0.06 × D to 0, and a dent amount L2 of the second concave curved surface portion from the second virtual straight line intersecting the first virtual straight line at the axis is −0. The drill according to claim 1, wherein the drill is set in a range of 06 × D to 0.06 × D. The radius of curvature of the convex curve formed by the convex curved surface portion in the cross section orthogonal to the axis is set in a range of 0.1 × D to 0.8 × D with respect to the outer diameter D of the cutting blade. The drill according to claim 1 or 2 , wherein the drill is characterized. Core thickness of the drill main body, any claims 1, characterized in that set in the range 0.15 × D~0.3 × D with respect to outer diameter D of the cutting edge of claims 3 The drill described in crab. The drill according to any one of claims 1 to 4 , wherein a hard film is coated on a surface of at least a tip portion of the drill body.

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