JP4120185B2 - 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、切刃の外周端側には凸曲線状切刃部を形成することにより、切刃の外周端におけるドリル本体強度を確保してチッピングや欠けの発生を防止することができるとともに、この凸曲線状切刃部に滑らかに連なる凹曲線状切刃部を内周側に形成することにより、切屑全体を内周側に巻き込むようにしてカールさせることができ、その効率的な処理を図ることができる。従って、乾式でしかも高速切削となるような過酷な加工条件においても、ドリルの寿命の延長を図って円滑かつ安定した穴明け加工を行うことができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態を示す軸線Ｏ方向先端視の正面図である。
【図２】 図１に示す実施形態の軸線Ｏに直交する断面図である。
【図３】 図１に示す実施形態のシンニング部１８を示すドリル本体１先端部の斜視図である。
【図４】 第１、第２凹曲面部８，１２間に接続面２３を形成した場合を示す断面図である。
【図５】 （イ）は本発明の実施形態によるドリルによって生成された切屑を示す図であり、（ロ）は実施形態とは第１、第２凹曲面部８，１２の半径Ｒ２，Ｒ４の大小が反対とされた比較ドリル３による切屑を示す図である。
【符号の説明】
１ ドリル本体
２ 先端逃げ面
３ 切屑排出溝
４，９ 切屑排出溝３の内壁面
５ 切刃
７ 第１凸曲面部
８ 第１凹曲面部
１１ 第２凸曲面部
１２ 第２凹曲面部
１３ 内壁面４の外周端
１５ 切刃５の外周端
１６ 凸曲線状切刃部
１７ 凹曲線状切刃部
１８ シンニング部
１９ シンニング切刃部
２０ 第１シンニング部
２１ 第１シンニング部２０の谷底部
２２ 第２シンニング部
２３ 接続面
Ｏ ドリル本体１の軸線
Ｔ ドリル回転方向
Ｒ１〜Ｒ４ 第１、第２凸凹曲面部７，８，１１，１２が軸線Ｏに直交する断面においてなす曲線の曲率半径
Ｓ１，Ｓ２ 第１、第２仮想直線
Ｌ１，Ｌ２ 第１、第２凹曲面部８，１２の凹み量
ｄ ドリル本体１の芯厚
α 切刃５の外周端１５側における径方向すくい角[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drill capable of a smooth and stable drilling process even under severe processing conditions such as high-speed dry cutting.
[0002]
[Prior art]
As a drill intended to cope with such severe processing conditions that use only a dry or trace amount of cutting fluid, a drill described in, for example, Japanese Patent Application Laid-Open No. 2000-198011 has been proposed. That is, in the drill described in this publication, on the outer peripheral side of the cutting blade formed at the tip of the drill body, an outer corner cutting blade is formed that recedes in the drill rotation direction at an angle from the middle portion of the cutting blade, Since the crossing angle between the outer corner cutting edge and the margin of the outer periphery of the drill body can be made obtuse, it is possible to prevent the outer edge of the cutting edge from being chipped even under the above processing conditions. Become. Moreover, as a drill which bent the outer peripheral edge side of the cutting blade in the drill rotation direction rear side in this way, for example, as described in Japanese Patent Publication No. 4-46690, the first and second of the cutting blade outer peripheral side A straight ridge having a substantially V-shaped convex shape has been proposed, and in the drill described in this publication, the inner peripheral side of the secondary straight ridge is further formed into a concave shape with roundness. Further, as such a drill having a concave cutting edge, for example, in Japanese Examined Patent Publication No. 61-58246, a concave curve is used so that the rake angle in the radial direction of the cutting edge portion on the outer peripheral side becomes 0 ° to positive. A tied one has also been proposed.
[0003]
[Problems to be solved by the invention]
Of these, as described in Japanese Examined Patent Publication No. 61-58246, when the outer peripheral cutting edge portion has a concave curve, the processing by chip curling can be performed smoothly and stably under normal processing conditions. However, since the crossing angle with the margin part on the outer peripheral edge side of the cutting edge becomes an acute angle and the strength is insufficient, chipping and chipping immediately occur on the outer peripheral edge side of this cutting edge under severe conditions such as high-speed dry cutting. Will occur and the tool life will be very short. On the other hand, as described in Japanese Patent Application Laid-Open No. 2000-198011 and Japanese Patent Publication No. 4-46690, the outer peripheral end side of the cutting blade is bent in an angle toward the rear side in the drill rotation direction with a V-shaped convex shape. Although the crossing angle with the margin can be made obtuse and the occurrence of chipping and chipping can be suppressed, the chips generated by the cutting edge are divided at this bending point. Chips are entangled with each other and clogging the chips, and especially the chips generated on the outer peripheral edge side of the bending point tend to flow out to the outer peripheral side, resulting in poor curling and increased resistance to the drill body, which promotes wear. There is a risk of increasing the drill rotation driving force during machining.
[0004]
The present invention has been made under such a background, and prevents the shortening of the tool life even under severe processing conditions such as high-speed dry cutting and provides excellent chip disposal and enables smooth and stable drilling. The purpose is to provide a simple drill.
[0005]
[Means for Solving the Problems]
In order to solve the above problems and achieve such an object, according to the present invention, a chip discharge groove extending toward the rear end side is formed on the outer periphery of the distal end portion of the drill body rotated about the axis, and the chip is In a drill in which a cutting edge is formed at an intersecting ridge line portion between the inner wall surface of the discharge groove facing the drill rotation direction and the tip flank of the drill body, the outer peripheral end side of the cutting blade protrudes in the drill rotation direction. A convex curvilinear cutting edge portion is formed, and on the inner peripheral side of the convex curvilinear cutting blade portion, a convex curvilinear cutting edge is formed on the rear side in the drill rotation direction. A concave curved cutting edge portion that is smoothly connected to the blade portion is formed, and a smooth curved shape is formed from the concave curved cutting edge portion to the outer peripheral edge of the cutting blade from the convex curved cutting blade portion. On the other hand, on the inner wall surface facing the rear side in the drill rotation direction of the chip discharge groove, a convex curve is located on the outer peripheral side and reaches the heel portion, and the cross section perpendicular to the axis is convex rearward in the drill rotation direction. Forming the second convex curved surface part It is characterized by that. Therefore, in the drill configured in this way, since the convex curved cutting edge portion that is convex in the drill rotation direction is formed on the outer peripheral end side of the cutting blade, the outer peripheral side of the convex curved cutting blade portion, That is, at the intersection with the margin portion on the outer periphery of the drill body, the intersection angle can be increased to ensure sufficient strength, and the occurrence of chipping and chipping can be prevented even under the above processing conditions. And the concave curved cutting edge part which becomes a concave in the drill rotation direction back side is continued on the inner peripheral side of this convex curved cutting edge part, and the convex curved cutting edge part from this concave curved cutting edge part As a result, the cutting edge up to the outer peripheral edge is formed in a smooth curved shape, so that the chip is not divided at the inner and outer circumferences, and the chip is wound around the inner peripheral side by the concave curved cutting edge portion. In this way, it is possible to sufficiently curl and process smoothly.
[0006]
Here, in order to ensure the strength at the intersecting portion more reliably, it is desirable to set the radial rake angle on the outer peripheral end side of the cutting edge to the negative angle side. Further, a thinning portion connected to the inner peripheral end side of the cutting blade is formed on the distal end side of the inner wall surface of the chip discharge groove, and a concave curved valley is formed in the thinning portion, and the valley bottom portion is the inner wall surface. On the other hand, a first thinning portion extending toward the inner peripheral end of the cutting blade while retracting toward the inner peripheral side of the drill body is provided, so that the inner peripheral end side portion of the chip is formed by the first thinning portion. By guiding the curved surface, the entire chip can be more reliably wound and curled on the inner peripheral side. Further, the thinning portion includes a second thinning portion that is formed on the distal end side of the first thinning portion and reaches the inner peripheral end of the cutting blade while further retreating to the inner peripheral side with respect to the valley bottom portion. Thus, the width of the chisel at the tip of the drill body can be reduced by this second thinning portion, and the biting property to the workpiece can be improved. In order to ensure sufficient rigidity of the drill body while promoting smooth discharge of the curled chips, the core thickness of the drill body is set to 0 with respect to the outer diameter D of the cutting blade. It is desirable to set in the range of 15 × D to 0.3 × D.
[0007]
On the other hand, when the above-mentioned cutting edge shape is formed on the intersecting ridge line portion between the inner wall surface facing the drill rotation direction of the chip discharge groove and the tip clearance surface of the drill body, the inner portion of the chip discharge groove facing the drill rotation direction is formed. On the wall surface, a convex curved surface portion continuous with the convex curved cutting edge portion and a first concave curved surface portion continuous with the concave curved cutting edge portion are formed, and the concave curved cutting edge portion is formed as described above. Thus, the chips generated so as to be wound on the inner peripheral side can be brought into sliding contact with the first concave curved surface portion and further curled. In addition, a second concave curved surface portion having a curved shape that is concave in the drill rotating direction is formed on the inner wall surface facing the rear side in the drill rotating direction of the chip discharge groove so as to be smoothly connected to the first concave curved surface portion. For example, smooth discharge can be promoted without inhibiting the flow of chips curled by the first concave curved surface portion.
[0008]
However, in this case, if the dent on the rear side in the drill rotation direction of the first concave curved surface portion is too small, there is a possibility that sufficient curling due to the sliding contact of chips may not be achieved, but conversely if the dent is too large. Further, the braking action due to the sliding contact of the chips becomes too strong, and the chips may be crushed and the discharge performance may be impaired, or the drill driving force may be increased. Moreover, also about the said 2nd concave curved surface part, when the dent to a drill rotation direction is too small, the chip | tip which flowed from the 1st concave curved surface part may be strongly pressed against this 2nd concave curved surface part, and a big braking action may arise. On the other hand, if the dent is too large, the chips are curled only by sliding contact with the first concave curved surface portion, and may not be sufficiently curled. For this reason, in the above case, in the cross section orthogonal to the axis, the dent amount L1 of the first concave curved surface portion from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction. Is set in a range of −0.06 × D to 0 with respect to the outer diameter D of the cutting edge, and the second concave curved surface portion from the second imaginary straight line that intersects the first imaginary straight line at the axis. It is desirable to set the dent amount L2 in the range of −0.06 × D to 0.06 × D.
[0009]
Further, the convex curved surface portion and the first concave curved surface portion are formed on the inner wall surface facing the drill rotation direction of the chip discharge groove in this manner, and the first concave curved surface portion is formed on the inner wall surface facing the rear side of the chip discharge groove in the drill rotation direction. When the second concave curved surface portion that is smoothly connected is formed, the radius of curvature of the concave curve formed by the second concave curved surface portion is larger than the radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section orthogonal to the axis. By enlarging, the first concave curved surface portion having a small radius of curvature can curl the chip with sufficient curl, and the curled chip has the curvature radius of the second concave curved surface portion set to the first concave surface. By making it larger than the curved surface portion, the second concave curved surface portion can be discharged more smoothly without being pressed too strongly. At this time, the radii of curvature of the first and second concave curved surface portions may be constant in each case, that is, the first and second concave curved surface portions in the cross section are in smooth contact with each other at one contact point with arcs having different radii. In addition, various shapes such as an ellipse, a trochoid, a cycloid, an involute, etc. in the cross section are used so that the radius of curvature gradually increases from the first concave curved surface portion side to the second concave curved surface portion side. It may be configured to exhibit a curved shape.
[0010]
Furthermore, in the case where the first concave curved surface portion and the second concave curved surface portion are smoothly connected in this way, the first and second concave curved surface portions are provided with a first cross section perpendicular to the axis. A tangential connection surface is formed in contact with both the concave curve formed by the concave curved surface portion and the concave curve formed by the second concave curved surface portion, and the first and second concave curved surface portions are connected via this connection surface. May be. In this case, the groove width of the chip discharge groove can be secured without being limited by the radius of curvature of the concave curve formed by the first and second concave curved surface portions, and the curling property and discharge performance of the chip can be ensured. At the same time, it is possible to improve the distance between the first concave curved surface portion and the second concave curved surface portion by the connecting surface, so that the chips curled by the first concave curved surface portion are second concave. It is possible to more surely prevent the surface from being pressed against the curved surface portion, to achieve smooth discharge, and to promote reduction of the drill rotation driving force. Such a connection surface may be formed between the convex curved surface portion and the first concave curved surface portion, or on the outer peripheral side of the convex curved surface portion or the second concave curved surface portion. Further, a linear cutting blade portion may be interposed between the uneven curved cutting blade portions so that the curved cutting blade portions are smoothly connected.
[0011]
When the convex curved surface portion and the first and second concave curved surface portions that are smoothly connected to the inner wall surface of the chip discharge groove are formed in this way, the curvature radius of the convex curve formed by the convex curved surface portion first in the cross section orthogonal to the axis. However, if this is too large, the width of the concave curved cutting edge portion of the cutting edge may be relatively small and curling of the chips may be insufficient. May be reduced, and sufficient strength may not be ensured at the intersection with the margin portion. Therefore, the outer diameter D of the cutting blade is set in a range of 0.1 × D to 0.8 × D. Is desirable. In addition, as for the radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section perpendicular to the axis, there is a possibility that it cannot be sufficiently curled by sliding the chips if it is too large. If it is too small, the chips are abruptly curled and the braking action may become too large. Therefore, the cutting edge is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting edge. Is desirable. Furthermore, if the radius of curvature of the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis is too large, the chips do not slide on the second concave curved surface portion and are curled only by the first concave curved surface portion. On the other hand, if it is too small, the sliding contact of the chips with the second concave curved surface portion becomes too strong and a large braking action is generated. It is desirable to set in the range of 0.2 × D to 0.5 × D. Furthermore, if the surface of at least the tip of the drill body is coated with a hard coating such as TiN, TiCN, TiAlN, etc., the wear resistance of the tip of the drill body can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 to 3 show an embodiment of the present invention. In the present embodiment, the drill body 1 is formed in a substantially cylindrical shape centering on the axis O by a hard material such as a cemented carbide, and is constant at the tip portion from the tip flank 2 toward the rear end side. A pair of chip discharge grooves 3, 3 that are twisted to the rear side in the drill rotation direction T at a twist angle of? Are formed symmetrically with respect to the axis O, and the drill rotation direction T side of these chip discharge grooves 3, 3 is Cutting blades 5 and 5 are formed at the intersecting ridges between the facing inner wall surfaces 4 and 4 and the tip flank 2, respectively. The tip of the drill body 1 is coated with a hard coating such as TiN, TiCN, TiAlN on the outer peripheral surface, the tip flank 2 and the chip discharge groove 3.
[0013]
Here, the inner wall surface 4 is located on the outer peripheral side of the inner wall surface 4 and intersects the margin portion 6, and forms a convex curve that is convex in the drill rotation direction T as shown in FIG. 2 in a cross section orthogonal to the axis O. The convex curved surface portion 7 and the first concave curved surface portion 8 which is located on the inner peripheral side of the first convex curved surface portion 7 and has a concave curved shape recessed in the rear side in the drill rotation direction T in the cross section. The concave and convex curves formed by the cross sections of the first concave and convex curved surface portions 7 and 8 are connected so as to smoothly contact at the contact point P1. Moreover, in this embodiment, the inner wall surface 9 facing the drill rotation direction T rear side of the chip discharge groove 3 is also located on the outer peripheral side and reaches the heel portion 10, and the above-mentioned cross section is convex toward the drill rotation direction T rear side. A second convex curved surface portion 11 having a convex curve, and a second concave curved surface portion 12 having a concave curved shape which is located on the inner peripheral side of the second convex curved surface portion 11 and whose cross section is recessed toward the drill rotation direction T side. The concave and convex curves formed by the second concave and convex curved surface portions 11 and 12 are connected so as to smoothly contact at the contact point P2, and the first and second concave curved surface portions 8 and 12 of the inner wall surfaces 4 and 9 are connected to each other. However, the concave curve formed by the cross section of the contact point P3 smoothly contacts and continues. The outer peripheral surface of the land portion extending from the margin portion 6 to the heel portion 10 on the rear side in the drill rotation direction T is formed in a cylindrical surface receding from the margin portion 6 to the inner peripheral side in one step.
[0014]
Furthermore, in the present embodiment, in the cross section, the uneven curves formed by the first and second uneven curved surface portions 7, 8, 11, and 12 are arcs having radii R1 to R4 with the points C1 to C4 as the centers. The center C1 of the convex arc formed by the first convex curved surface portion 7 is the intersection of the first convex curved surface portion 7 and the margin portion 6, that is, the margin portion 6 at the outer peripheral end 13 of the inner wall surface 4. The center C3 of the circular arc formed by the second convex curved surface portion 11 is positioned on the inner peripheral side with respect to the straight line Q1 in contact with the circular arc formed by the second convex curved surface portion 11 and the circle formed by the outer peripheral end 13 around the axis O. At the intersection 14 with the extended line, the line is positioned further to the inner peripheral side than the straight line Q2 in contact with the circle. Accordingly, the first convex curved surface portion 7 is convex toward the drill rotation direction T side with respect to the first virtual straight line S1 connecting the axis O and the outer peripheral end 13 of the inner wall surface 4, and the first convex at the outer peripheral end 13. The tangent line of the curved surface portion 7 is inclined with respect to the first imaginary straight line S1 so as to extend rearward in the drill rotation direction T toward the outer peripheral side, and is obtuse with the straight line Q1 orthogonal to the first imaginary straight line S1. Can be crossed. Further, the second convex curved surface portion 11 is also convex toward the rear side in the drill rotation direction T from the straight line connecting the intersection with the heel portion 10 and the axis O. On the other hand, since the arc centers C2 and C4 formed by the first and second concave curved surface portions 8 and 12 are in contact with each other at the contact P3, both of them are on the straight line extending from the axis O through the contact P3. Will be located. Furthermore, since this contact P3 becomes the groove bottom of the chip discharge groove 3, in this embodiment, a circle passing through this contact P3 with the axis O as the center becomes the core thickness circle of the drill body 1, and the diameter of this core thickness circle, that is, The core thickness d of the drill body 1 is in the range of 0.15 × D to 0.3 × D with respect to the diameter of the circle formed by the outer peripheral edge 15 of the cutting blade 5 around the axis O, that is, the outer diameter D of the cutting blade 5. Is set to
[0015]
The contact point P1 of the uneven curve formed by the first uneven surface portions 7 and 8 is positioned on the outer peripheral side with respect to the circle having the diameter of 2/3 of the outer diameter D of the cutting blade 5 with the axis O as the center. More preferably, it is positioned on the outer peripheral side of a circle having a diameter of 5/6 of the outer diameter D around the axis O. In addition, the size of the recess of the first concave curved surface portion 8 toward the rear side in the drill rotation direction T is such that the recess amount L1 from the first imaginary straight line S1 is −0.06 × with respect to the outer diameter D of the cutting blade 5. The second imaginary straight line S2 is set in the range of D to 0, and the size of the dent of the second concave curved surface portion 12 toward the drill rotation direction T is perpendicular to the first imaginary straight line S1 by the axis O in the cross section. Is set to be in a range of −0.06 × D to 0.06 × D. However, these dent amounts L1 and L2 are parallel to the first and second imaginary straight lines S1 and S2 in the cross section, respectively, and the first and second straight lines in contact with the concave curves formed by the first and second concave curved surface portions 8 and 12 respectively. The distance between the second virtual straight line S1 and S2, and as shown in FIG. 2, with respect to the amount of recess L1 of the first concave curved surface portion 8, the drill rotation direction T side is positive from the first virtual straight line S1. The rear side is negative, and conversely, with respect to the dent amount L2 of the second concave curved surface portion 12, the drill rotation direction T side from the second virtual straight line S2 is negative and the rear side is positive. Therefore, in the present embodiment, the entire first concave curved surface portion 8 is not positioned on the drill rotation direction T side with respect to the first virtual straight line S1.
[0016]
Further, in the cross section, the radii R1 to R4 of the arc formed by the first and second uneven curved surface portions 7, 8, 11, and 12 have a radius R 1 of the first convex curved surface portion 7 with respect to the outer diameter D of the cutting edge 5. In the range of 0.1 to 0.8 × D, the radius R2 of the first concave curved surface portion 8 is in the range of 0.18 to 0.35 × D, and the radius R3 of the second convex curved surface portion 11 is 0.1 to 0.1 × D. In the range of 0.8 × D, the radius R4 of the second concave curved surface portion 12 is set in the range of 0.2 to 0.5 × D. And in this embodiment, radius R4 of the 2nd concave curved surface part 12 is made larger than radius R2 of the 1st concave curved surface part 8 among these. In addition, the groove width ratio of the chip discharge groove 3 formed in this way is set to a range of 0.8 to 1.2: 1 in the present embodiment.
[0017]
In the cutting edge 5 formed at the intersecting ridge line portion between the inner wall surface 4 and the tip flank 2 of the chip discharge groove 3, the inner wall surface 4 is formed by the first uneven curved surface portions 7 and 8. As a result, a convex curvilinear cutting edge portion 16 having a curved shape convex in the drill rotation direction T is formed on the outer peripheral end 15 side, and the first convex curved surface portion 7 is connected to the rear end side, On the inner peripheral side of the convex curvilinear cutting edge portion 16, a concave curvilinear cutting edge portion 17 that forms a concave curvilinear shape on the rear side in the drill rotation direction T and that is in smooth contact with the convex curvilinear cutting blade portion 16 is connected. Is formed, and the first concave curved surface portion 8 is connected to the rear end side thereof, and the cutting blade 5 is curved between the convex and concave curved cutting blade portions 16 and 17 so as to be gently curved toward the front end in the direction of the axis O. Will exhibit a shape. However, the cutting edge 5 is provided with a tip angle by being inclined toward the rear end side of the drill body 1 as the tip flank 2 moves from the inner peripheral side to the outer peripheral side, and chip discharge is performed. Since the groove 3 is twisted in a spiral shape, the S-shaped uneven curve formed by the uneven curved cutting edge portions 16 and 17 of the cutting edge 5 when viewed from the front in the axis O direction is the first curve of the inner wall surface 4. The uneven curve formed in the cross section where the uneven curved surface portions 7 and 8 are orthogonal to the axis O will have a shape that gradually shifts toward the drill rotation direction T side toward the inner peripheral side. Therefore, the convex curved cutting edge portion 16 has a tangent line at the outer peripheral end 15 that is larger in inclination than the tangent line at the outer peripheral end 13 of the convex curve formed by the first convex curved surface portion 7 in the cross section. As it goes to the outer peripheral side, it extends to the rear side in the drill rotation direction T, and the crossing angle with the margin portion 6 is also made larger than the obtuse angle formed by the first convex curved surface portion 7, whereby the cutting edge 5 is The rake angle α in the radial direction at 15 is set to the negative angle side.
[0018]
On the other hand, the tip flank 2 from the inner peripheral side of the first concave curved surface portion 8 to the second concave curved surface portion 12 and the second convex curved surface portion 11 is formed on the distal end side of the inner wall surfaces 4 and 9 of the chip discharge groove 3. A thinning portion 18 that reaches the heel portion 10 is formed so as to cut out the crossed ridge line portion toward the inside of the chip discharge groove 3 toward the rear end side of the drill body 1. The inner peripheral end side is formed at the intersecting ridge line portion between the thinning portion 18 and the tip flank 2 and is directed from the inner peripheral end of the concave curved cutting blade portion 17 toward the axis O at the center of the tip flank 2. A thinning cutting edge portion 19 extending in the direction is provided. The portion of the cutting blade 5 where the thinning cutting edge portion 19 and the concave curved cutting edge portion 17 intersect is smoothly connected by a curve or straight line that is convex in the drill rotation direction T when viewed from the front end of the axis O direction. ing.
[0019]
Here, a portion of the thinning portion 18 that extends to the front end side intersecting the inner wall surfaces 4 and 9 of the chip discharge groove 3 is a first thinning portion 20, and this first thinning portion 20 is rotated by a drill. The portion extending to the heel portion 10 side intersecting the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the direction T is formed in a flat shape, while the inner wall surface 4 facing the inner wall surface 9 and the drill rotation direction T side. 3, that is, a portion extending from the contact P3 portion of the first and second concave curved surface portions 8 and 12 toward the center of the tip flank 2 as shown in FIG. It is formed so as to form a concave curved valley when viewed from the direction toward the center, and the concave valley bottom 21 is on the inner peripheral side of the drill body 1 with respect to the inner wall surfaces 4, 9. The inner peripheral end of the cutting edge 5, that is, the thin It is formed to extend distally toward the inner peripheral end of the ring cutting edge 19. Note that the radius of curvature of the concave curve formed in the cross section of the concave bottom portion 21 of the first thinning portion 20 is set in the range of 0.1 to 0.5 mm. In addition, the curvature radius of the concave curve which the cross section of this valley bottom part 21 makes may be made large as it goes to a rear-end side.
[0020]
Further, in the portion where the foremost valley bottom portion 21 of the first thinning portion 20 is about to reach the inner peripheral end of the cutting edge 5, the first thinning portion 20 further recedes toward the inner peripheral side of the drill body 1 with respect to the valley bottom portion 21. A valley-shaped second thinning portion 22 extending toward the inner peripheral end side of the cutting blade 5 while being inclined one step is formed, and in the vicinity of the axis O at the center of the tip flank 2, the second thinning portion 22 is formed. Intersects the tip flank 2 and the inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion. Here, the curvature radius of the valley bottom of the second thinning portion 22 is smaller than the curvature radius of the valley bottom 21 of the first thinning portion 20 and is less than 0.1 mm. That is, the bottom of the valley may be formed in a V-shaped valley that is not concavely curved, and is further increased in size toward the rear end side of the drill body 1 in the same manner as the valley bottom 21 of the first thinning portion 20. Also good. Further, the tip end of the drill body 1 is formed by forming the inner peripheral end of the cutting edge 5 at the intersecting ridge line portion between the second thinning portion 22 and the tip flank 2 which are inclined further by one step than the first thinning portion 20 in this way. The width of the chisel defined between the pair of cutting edges 5 and 5, that is, the center of the tip flank 2 is such that the first thinning portion 20 intersects the tip flank 2 as it is and the inner peripheral edge of the cutting blade 5 The chisel width is in the range of 0 to 0.2 mm in this embodiment, that is, the inner peripheral ends of the cutting blades 5 and 5 coincide on the axis O. May be.
[0021]
In the drill constructed in this way, first, a convex curved cutting edge portion 16 that is convex in the drill rotation direction T is formed on the outer peripheral end 15 side of the cutting edge 5, and accordingly, the front end of the axis O direction is viewed. The intersection angle between the convex curved cutting edge portion 16 and the margin portion 6 at the outer peripheral end 15 can be set to a large angle as described above, and more than the intersection angle with the first convex curved surface portion 7. The strength of the drill body 1 in the vicinity of the outer peripheral end 15 can be sufficiently ensured. For this reason, since it is located on the outer periphery of the drill body 1, the cutting speed is the highest, and the amount of chips generated is the largest, so that an excessive load is likely to be generated, so that the outer peripheral edge 15 of the cutting blade 5 is chipped or chipped. The tool life can be extended even under severe processing conditions such as high-speed dry cutting. Moreover, in this embodiment, the convex curved cutting edge portion 16 is formed so as to protrude in the drill rotation direction T from the straight line connecting the outer peripheral end 15 of the cutting edge 5 and the axis O when viewed from the front in the axis O direction. Thus, as described above, since the radial rake angle α is a negative angle, the crossing angle with the margin portion 6 becomes an obtuse angle, and the strength of the drill body 1 around the outer peripheral end 15 is more reliably determined. Can be secured.
[0022]
The convex curved cutting edge portion 16 has a curved shape that is convex in the drill rotation direction T as described above, and the bending point at which the cutting blade 5 is bent into a V shape with an angle as in the conventional case. In addition, a concave curved cutting edge portion 17 that is concave on the rear side in the drill rotation direction T is formed on the inner peripheral side so as to be smoothly connected to the convex curved cutting edge portion 16. Therefore, the chips generated by the cutting blade 5 are not divided at the bending points as described above, and the portion generated by the concave curved cutting blade portion 17 flows out toward the inner peripheral side. Then, it is smoothly curled so that it is entirely wound on the inner peripheral side. For this reason, the divided chips are not entangled with each other and the chips are not clogged, and the chips on the outer peripheral end 15 side flow out to the outer peripheral side to increase the resistance and accelerate the wear of the drill body 1. Therefore, smooth and stable processing of chips can be promoted to reduce the drill rotational driving force at the time of drilling, and the tool life can be further extended by suppressing wear. Further, the tip of the drill body 1 including the cutting edge 5 is coated with a hard film such as TiN, TiCN, TiAlN, etc., so that the wear resistance of the drill body 1 can be further improved. .
[0023]
Furthermore, in this embodiment, the thinning part 18 is formed in the front end side of the chip discharge groove | channel 3, Thereby, the inner peripheral end side of the cutting blade 5 is made into the thinning cutting edge part 19 which goes to the center of the front end flank 2. A portion where the thinning cutting edge portion 19 and the concave curved cutting edge portion 17 intersect with each other is formed into a convex curve shape or a straight line smoothly connected to the both cutting edge portions 17 and 19, and the thinning cutting edge portion. Since the first thinning portion 20 connected to 19 has a valley shape in which the valley bottom portion 21 is bent, the bending point as described above is not formed over the entire length of the cutting edge 5. The inner peripheral side portion of the chips generated by the thinning cutting edge portion 19 is also formed on the inner peripheral side along the concave curve formed by the cross section of the valley bottom portion 21 of the first thinning portion 20 as shown by the black arrow in FIG. It can be curled like a roll. For this reason, coupled with the fact that chips are wound on the inner peripheral side by the concave curved cutting edge portion 17, it is possible to further improve the chip disposability, particularly in the processing of difficult-to-cut materials. is there. In the present embodiment, the radius of curvature of the concave curve formed by the valley bottom portion 21 of the first thinning portion 20 is set to 0.1 to 0.5 mm. If this radius of curvature is larger than this, This is because there is a possibility that the inner peripheral side portion cannot be sufficiently curled up and curled. On the other hand, if the inner peripheral side portion is smaller than this, the inner peripheral side portion of the chips may be clogged in the thinning portion 18.
[0024]
Further, a second thinning portion 22 is formed at the distal end of the thinning portion 18 so as to be inclined one step further from the valley bottom portion 21 of the first thinning portion 20 and reach the distal end flank 2, and the second thinning portion 22. The inner peripheral end of the cutting edge 5 is formed on the intersecting ridge line portion between the tip flank 2 and the curvature radius of the groove bottom of the second thinning portion 22 is less than 0.1 mm, which is greater than the valley bottom portion 21. Since it is made small, the inner peripheral end of the cutting blade 5 is arranged on the inner peripheral side, and the width of the chisel is set to an extremely short width of 0 to 0.2 mm. For this reason, it is possible to improve the biting property and the straight running stability when the drill bites the workpiece, and to perform further stable and highly accurate machining, and the thrust acting on the drill body 1 in the axial direction thereof The force can be suppressed, and further reduction of the drill driving force can be promoted. Moreover, the thinning portion 18 is formed by the first and second plurality of thinning portions 20 and 22 that increase in inclination toward the inner peripheral end of the cutting blade 5 in this manner, so that the second thinning portion 22 at the distal end is formed. The angle of the tip of the drill body 1 in the cross section along the groove bottom is larger than that when the groove bottom of a single thinning portion is inclined so as to have the same chisel width. It is possible to provide a drill that sufficiently secures the strength around the center of rotation of the tip of the drill body 1 and that is not damaged even by an impact load at the time of biting. However, the second thinning portion 22 may not be provided as long as the biting property, straight running stability, and strength of the drill body 1 can be secured by the first thinning portion 20 alone.
[0025]
On the other hand, in order to form the cutting blade 5 provided with such concave and convex curved cutting edge portions 16 and 17, in this embodiment, the concave and convex curved shape is formed on the inner wall surface 4 facing the drill rotation direction T of the chip discharge groove 3. The first uneven curved surface portions 7 and 8 that are continuous with the cutting edge portions 16 and 17 are formed. Therefore, the chips generated continuously in the width direction without being divided by the cutting blade 5 are entirely inside. It is curled further by being wound around the circumferential side and pressed while being in sliding contact with the first concave curved surface portion 8, and is pushed out and discharged to the rear end side as the drill body 1 rotates. Further, on the inner peripheral side of the first concave curved surface portion 7, a second concave curved surface portion 12 of the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the drill rotation direction T is smooth with the first concave curved surface portion 7. The second concave curved surface portion 12 is formed so as to be recessed in the drill rotation direction T, contrary to the first concave curved surface portion 8, so that the first concave curved surface portion 8 makes the second concave curved surface portion smaller. The curled chips are smoothly discharged as described above without hindering the flow of the chips. In addition, in the present embodiment, the second convex curved surface portion 11 is formed so as to be smoothly connected to the outer peripheral side of the second concave curved surface portion 12, so that the flow of chips may be inhibited on the heel portion 10 side. In addition, the strength of the drill body 1 in the heel portion 10 can be ensured.
[0026]
In the present embodiment, the dent amounts L1 and L2 of the first and second concave curved surface portions 8 and 12 are connected to each other, and the first concave curved surface portion 8 is connected to the axis O and the outer peripheral end 13 of the inner wall surface 4. The range of −0.06 × D to 0 with respect to the outer diameter D of the cutting edge 5 from the imaginary straight line S1 (however, the rear side of the drill rotation direction T is negative). The axis O is set to be in the range of −0.06 × D to 0.06 × D from the second virtual line S2 orthogonal to the first virtual line S1 (however, the drill rotation direction T side is negative). Thus, the chips can be brought into sliding contact with the first and second concave curved surface portions 8 and 12 without being too strong and not too weak, and an appropriate braking action can be given. For this reason, the chips can be reliably curled and processed without damaging the smooth evacuation due to excessive braking action and without causing an increase in the drill rotation driving force. In order to achieve such an effect more reliably, the curvature radius R2 of the concave curve (concave arc) formed by the first concave curved surface portion 8 in the cross section orthogonal to the axis O as in the present embodiment is cut. The outer radius D of the blade 5 is set in a range of 0.18 to 0.35 × D, and the radius of curvature R4 of the second concave curved surface portion 12 is set in a range of 0.2 to 0.5 × D. Is desirable.
[0027]
In the present embodiment, the radius of curvature of the concave curve formed by the second concave curved surface portion 12 in the cross section orthogonal to the axis O, that is, the radius R4 is also between the first and second concave curved surface portions 8 and 12. The radius of curvature of the concave curve formed by one concave curved surface portion 8, that is, larger than the radius R 2, and therefore, the chips generated by the cutting blade 5 are first converted into the first concave curved surface portion 8 having a relatively small radius R 2. The curled chips are curled with a sufficient curl, and the curled chips are caused to flow out toward the second concave curved surface portion 12 having a relatively large radius R4. In the curved surface portion 12, chips are not pressed too strongly, facilitating smoother discharge and further reducing the drill rotation driving force. In addition, the concave curve formed by the first and second concave curved surface portions 8 and 12 is configured to draw a continuous concave curve in contact with the contact point P3 of 1 in the present embodiment. It is possible to make the flow of chips from the first to the second concave curved surface portion 12 smoother, and to promote smoother chip discharge.
[0028]
However, instead of forming the first and second concave curved surface portions 8 and 12 so that the concave curve formed by the cross section thereof is in contact with the first contact point P3 and smoothly connected, for example, as shown in FIG. Between the first and second concave curved surface portions 8 and 12, a contact point P4 is connected to both the concave curve formed by the first concave curved surface portion 8 and the concave curve formed by the second concave curved surface portion 12 in a cross section orthogonal to the axis O. , P5 may be formed so as to form a tangential connection surface 23, and the two concave curved surface portions 8 and 12 may be smoothly connected via the connection surface 23. Also in this case, the chips with the curl formed by the first concave curved surface portion 8 are not pressed against the connection surface 23 without impairing the flow, and the drill rotational driving force is not increased. The second concave curved surface portion 12 can be sent out and discharged smoothly. On the other hand, when such a connection surface 23 is interposed between the first and second concave curved surface portions 8 and 12, the curvature radii R2, R2 of the first and second concave curved surface portions 8 and 12 are provided. Since the groove width of the chip discharge groove 3 can be set without being limited to R4, for example, contrary to the above, the second concave curved surface portion 12 is also slidably contacted with the chip according to the material of the workpiece. Even when the radius of curvature R4 is reduced when curling must be performed, the groove width can be secured sufficiently large to maintain smooth discharge performance.
[0029]
Further, in the present embodiment, the curvature radii R1 and R3 of the convex curves (convex arcs) formed by the first and second convex curved surface portions 7 and 11 in the cross section are 0 with respect to the outer diameter D of the cutting blade 5, respectively. .1 to 0.8 × D, so that the strength around the margin portion 6 and the strength around the heel portion 10 at the outer peripheral ends 13 and 15 of the inner wall surface 4 and the cutting edge 5 of the drill body 1 are set. While ensuring sufficient, it can prevent that the radial direction width | variety of the 1st, 2nd concave curved surface part 8 and 12 becomes small too much, and can aim at the reliable improvement of chip disposal property. In addition, in order to achieve both the securing of the strength of the drill body 1 and the improvement of the chip disposal in this way even under conditions such as high-speed dry cutting, the first uneven surface in the cross section as in the present embodiment. The contact point P1 of the uneven curve formed by the portions 7 and 8 is located on the outer peripheral side from the circle O having a diameter of 2/3 of the outer diameter D of the cutting blade 5 from the axis O, and more preferably a circle having a diameter of 5/6 of the outer diameter D. It is desirable that the groove width ratio of the chip discharge groove 3 is in the range of 0.8 to 1.2: 1.
[0030]
Furthermore, in this embodiment, as the chip disposability is improved and the drill rotational driving force is reduced in this way, the load that the drill body 1 itself receives during processing becomes smaller, and thereby the core thickness is reduced. d can also be set to a relatively small range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting edge 5. For this reason, especially the thrust force is reduced among the loads received by the drill body 1 and the cross-sectional area of the chip discharge groove 3 is increased to facilitate smooth chip discharge, thereby further increasing the power during drilling. Mitigation can be achieved. On the other hand, the cross-sectional area of the drill body 1 is large on the outer peripheral side by setting the curvature radii R1 to R4 in an appropriate range as described above, and in particular by the first and second convex curved surface portions 7 and 11. Therefore, the necessary and sufficient amount can be secured, and therefore the rigidity of the drill body 1 can be maintained, so that the machining power can be further reduced as described above. It is possible to prevent a situation in which breakage or the like sometimes occurs and the drill life is consumed.
[0031]
Here, the following table 1 shows the drill of the embodiment shown in FIGS. 1 to 3, the size of the radius R1 of the first convex curved surface portion 7, the size of the first and second concave curved surface portions 8, 12, and The comparison drills 1 to 5 are the same as in this embodiment except that the size of the core thickness d is different, and show the results when the cutting speed was changed and the drilling test was performed dry. The processing conditions and evaluation are as shown below the table.
[0032]
[Table 1]

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

Claims (12)

A chip discharge groove extending toward the rear end is formed on the outer periphery of the tip end of the drill body rotated around the axis, and the inner wall surface of the chip discharge groove facing the drill rotation direction intersects the tip flank of the drill body. A drill in which a cutting edge is formed in a ridge line portion, and a convex curvilinear cutting edge portion forming a curved shape convex in the drill rotation direction is formed on the outer peripheral end side of the cutting blade. On the inner peripheral side of the convex curved cutting edge portion, a concave curved cutting edge portion is formed which forms a concave curved shape on the rear side in the drill rotation direction and smoothly continues to the convex curved cutting edge portion. The inner wall surface facing the rear side in the drill rotation direction of the chip discharge groove is formed in a smooth curved shape from the concave curved cutting edge part to the outer peripheral end of the cutting edge from the convex curved cutting edge part Is located on the outer peripheral side, reaches the heel part, and is perpendicular to the axis. There drill, wherein a second convex surface portions forming a convex curve that is convex in the drill rotation direction rear side. 2. The drill according to claim 1, wherein a rake angle in the radial direction on the outer peripheral end side of the cutting blade is set to a negative angle side. A thinning portion connected to the inner peripheral end side of the cutting blade is formed on the tip side of the inner wall surface of the chip discharge groove, and the thinning portion has a concave curved valley shape, and the bottom portion of the valley is the above The first thinning portion that extends toward the inner peripheral end of the cutting blade while retracting toward the inner peripheral side of the drill body with respect to the inner wall surface is provided. Drill. The said thinning part is provided in the front end side of the said 1st thinning part, and is equipped with the 2nd thinning part which reaches | attains the inner peripheral end of the said cutting blade, retreating further to the inner peripheral side with respect to the said valley bottom part The drill according to claim 3. The core thickness of the drill body is set in a range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting blade. The drill of crab. On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. On the inner wall surface facing the drill rotation direction rear side of the chip discharge groove, a second concave curved surface portion that is smoothly connected to the first concave curved surface portion and has a concave shape in the drill rotation direction is formed, In the cross section orthogonal to the axis, the dent amount L1 of the first concave curved surface portion from the first imaginary straight line connecting the axis and the outer peripheral end of the inner wall surface facing the drill rotation direction is the outer diameter D of the cutting blade. Is set in a range of −0.06 × D to 0, and a dent amount L2 of the second concave curved surface portion from the second virtual straight line intersecting the first virtual straight line at the axis is −0. It is set in the range of 06 × D to 0.06 × D Drill according to any one of 1 to claim 5. On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. On the inner wall surface facing the drill rotation direction rear side of the chip discharge groove, a second concave curved surface portion that is smoothly connected to the first concave curved surface portion and has a concave shape in the drill rotation direction is formed, 2. The curvature radius of the concave curve formed by the second concave curved surface portion is set to be larger than the curvature radius of the concave curve formed by the first concave curved surface portion in a cross section orthogonal to the axis. The drill according to any one of claims 6 to 6. On the inner wall surface facing the drill rotation direction of the chip discharge groove, a convex curved surface portion connected to the convex curved cutting blade portion and a first concave curved surface portion continuous to the concave curved cutting blade portion are formed. A second concave curved surface portion having a concave shape in the drill rotating direction is formed on the inner wall surface facing the rear side in the drill rotating direction of the chip discharge groove, and between the first and second concave curved surface portions. Is formed with a tangential connection surface that contacts both the concave curve formed by the first concave curved surface portion and the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis. The drill according to any one of claims 1 to 7, wherein the first concave curved surface portion and the second concave curved surface portion are smoothly connected. The radius of curvature of the convex curve formed by the convex curved surface portion in the cross section orthogonal to the axis is set in a range of 0.1 × D to 0.8 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 8, wherein the drill is characterized. The radius of curvature of the concave curve formed by the first concave curved surface portion in the cross section perpendicular to the axis is set in a range of 0.18 × D to 0.35 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 9, wherein the drill is characterized. The radius of curvature of the concave curve formed by the second concave curved surface portion in the cross section orthogonal to the axis is set in the range of 0.2 × D to 0.5 × D with respect to the outer diameter D of the cutting blade. The drill according to any one of claims 6 to 10, wherein: The drill according to any one of claims 1 to 11, wherein a hard film is coated on a surface of at least a tip portion of the drill body.

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