Rotary cutting tools

Abstract

The rotary cutting tool disclosed in the present invention can rotate around an axis and has a rake face and a flank face. The flank face is connected to the rake face. The ridges of the rake face and the flank face constitute a cutting edge. In a cross section perpendicular to the axis, the rake face is composed of a plurality of straight line portions.

Description

Technical Field

[0001] The present disclosure relates to rotary cutting tools. Background Art

[0002] Japanese Patent Application Laid-Open No. 2017-159380 (Patent Document 1) describes an end mill having a plurality of grooves (concave portions) formed on a rake face.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-159380 Summary of the invention

[0006] The rotary cutting tool disclosed in the present invention is rotatable about an axis and has a rake face and a flank face. The flank face is connected to the rake face. The ridges of the rake face and the flank face constitute a cutting edge. In a cross section perpendicular to the axis, the rake face is composed of a plurality of straight line portions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic perspective view showing the structure of the rotary cutting tool according to the present embodiment.

[0008] Figure 2 It is a side schematic diagram showing the structure of the rotary cutting tool involved in this embodiment.

[0009] Figure 3 is along Figure 2 Schematic cross-sectional view taken along line III-III.

[0010] Figure 4 yes Figure 3 An enlarged schematic diagram of region IV.

[0011] Figure 5 yes Figure 3 An enlarged schematic diagram of region V.

[0012] Figure 6 This is a diagram showing the relationship between the angle formed by two adjacent straight line portions and the position in the chip removal groove.

[0013] Figure 7 It is a schematic cross-sectional view showing a state in which cutting processing is being performed using the rotary cutting tool involved in this embodiment. DETAILED DESCRIPTION

[0014] [Problems to be Solved by the Present Disclosure]

[0015] When a workpiece is cut using a rotating cutting tool, it is difficult to effectively deliver the coolant to the vicinity of the cutting point while retaining the coolant near the cutting point due to the centrifugal force acting on the coolant. In the end mill described in Japanese Patent Publication No. 2017-159380, the lubricity is improved by retaining the coolant in the valley portion of the concave portion provided on the rake face. However, in this end mill, when a large cutting resistance is applied to the cutting edge, there is a case where stress is concentrated in the concave portion and the cutting edge is damaged.

[0016] [Effects of the present disclosure]

[0017] According to the present disclosure, it is possible to provide a rotary cutting tool that can suppress breakage of a cutting edge.

[0018] [Overview of Embodiments of the Present Disclosure]

[0019] First, an overview of the embodiments of the present disclosure will be described.

[0020] (1) The rotary cutting tool 100 according to the present disclosure is rotatable about the axis A and includes a rake face 10 and a flank face 31. The flank face 31 is connected to the rake face 10. The ridges of the rake face 10 and the flank face 31 constitute the cutting edge 20. In a cross section perpendicular to the axis A, the rake face 10 is composed of a plurality of straight line portions.

[0021] (2) In the rotary cutting tool 100 according to (1) above, the difference between the maximum value of the angle formed by two adjacent straight line portions and the minimum value of the angle formed by two adjacent straight line portions among the plurality of straight line portions may be greater than 8°.

[0022] (3) In the rotary cutting tool 100 according to (1) or (2), the plurality of straight line portions may include: a first straight line portion 11 connected to the flank surface 31; a second straight line portion 12 inclined relative to the first straight line portion 11 and connected to the first straight line portion 11; a third straight line portion 13 inclined relative to the second straight line portion 12 and connected to the second straight line portion 12; and a fourth straight line portion 14 inclined relative to the third straight line portion 13 and connected to the third straight line portion 13. A first angle θ1 formed by the first straight line portion 11 and the second straight line portion 12 may be greater than a second angle θ2 formed by the second straight line portion 12 and the third straight line portion 13. The second angle θ2 may be greater than a third angle θ3 formed by the third straight line portion 13 and the fourth straight line portion 14.

[0023] [Details of the embodiments of the present disclosure]

[0024] Hereinafter, the details of the embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described based on the drawings. It should be noted that in the following drawings, the same or corresponding parts are marked with the same reference numerals, and their description will not be repeated.

[0025] Figure 1 It is a perspective schematic diagram showing the structure of the rotary cutting tool 100 according to the present embodiment. Figure 2 1 is a side view schematically showing the structure of the rotary cutting tool 100 according to the present embodiment. Figure 1 as well as Figure 2 As shown, the rotary cutting tool 100 involved in this embodiment is, for example, an end mill, and is composed of a blade 90, a joint 8, and a shank 3. The blade 90 has a first rake face 10, a first relief face 31, a second rake face 15, a second relief face 33, an outer peripheral cutting edge 20, a bottom cutting edge 21, and a front end 58. The shank 3 has a rear end 59. The blade 90 is fixed to the shank 3 by the joint 8. The joint 8 is a solder. The joint 8 is located between the blade 90 and the shank 3.

[0026] The rotary cutting tool 100 is configured to be rotatable around an axis A. From another perspective, the axis A is the rotation axis of the rotary cutting tool 100. The material constituting the blade 90 includes, for example, a cubic boron nitride (cBN) sintered body. The material constituting the blade 90 may include diamond. Diamond may be single crystal diamond or polycrystalline diamond. The shank 3 includes, for example, cemented carbide. Cemented carbide is, for example, tungsten carbide (WC)-based cemented carbide, cemented carbide containing Co on the basis of WC, cemented carbide formed by adding carbonitride compounds such as Cr, Ti, Ta, Nb, etc. to WC, etc.

[0027] The front end 58 of the rotary cutting tool 100 is a portion opposite to the workpiece. The rear end 59 of the rotary cutting tool 100 is a portion opposite to the tool that rotates the rotary cutting tool 100. The shank 3 is a portion mounted on the tool that rotates the rotary cutting tool 100. The direction along the axis A is the axial direction. The direction perpendicular to the axial direction is the radial direction. In this specification, the direction from the front end 58 toward the rear end 59 is referred to as the axial rear. Conversely, the direction from the rear end 59 toward the front end 58 is referred to as the axial front.

[0028] like Figure 1 as well as Figure 2As shown, the first rake face 31 is connected to the first front cutting face 10. The ridge line between the first rake face 10 and the first rake face 31 constitutes the peripheral cutting edge 20. The second rake face 33 is connected to the second rake face 15. The ridge line between the second rake face 15 and the second rake face 33 constitutes the bottom cutting edge 21. The first rake face 10 is connected to the second rake face 15. The first rake face 10 is located axially rearward relative to the second rake face 15. The first rake face 31 is connected to the second rake face 33. The first rake face 31 is located axially rearward relative to the second rake face 33.

[0029] A first chip groove 1 and a second chip groove 2 are formed on the blade portion 90 of the rotary cutting tool 100. The first chip groove 1 is composed of a first rake face 10 and a first chip face 40. The second chip groove 2 is composed of a second rake face 15 and a second chip face 45. The second chip face 45 is connected to the first chip face 40. The first chip groove 1 is arranged in a spiral shape around the axis A. The second chip groove 2 is connected to the first chip groove 1. In the direction along the axis A, the length of the first chip groove 1 is longer than the length of the second chip groove 2.

[0030] The rotary cutting tool 100 involved in this embodiment is, for example, a multi-edge tool. Specifically, the number of the peripheral cutting edges 20 is, for example, 2 or more. The lower limit of the number of the peripheral cutting edges 20 is not particularly limited, and for example, it can be 4 or more, or 8 or more. The upper limit of the number of the peripheral cutting edges 20 is not particularly limited, and for example, it can be 20 or less, or 16 or less. Figure 1 In the illustrated rotary cutting tool 100 , the number of the peripheral cutting edges 20 is five. The number of the bottom cutting edges 21 may be the same as the number of the peripheral cutting edges 20 .

[0031] Figure 3 is along Figure 2 The cross-sectional view of the structure is shown along the line III-III. This cross section is perpendicular to the axis. Figure 3 As shown, a plurality of first chip grooves 1 are arranged along the circumferential direction (rotation direction R). Similarly, a plurality of first flank faces 31 are arranged along the circumferential direction. Similarly, a plurality of peripheral cutting edges 20 are arranged along the circumferential direction. That is, when the combination of the first flank face 31, the first chip groove 1 and the peripheral cutting edge 20 is set as a cutting component, a plurality of cutting components are arranged along the circumferential direction. In this cutting component, the first chip groove 1 is located in front of the first flank face 31 in the rotation direction. In this cutting component, the first front cutting face 10 is located in front of the peripheral cutting edge 20 in the rotation direction. In this cutting component, the first chip surface 40 is located in front of the first front cutting face 10 in the rotation direction.

[0032] like Figure 3As shown, in the rotation direction R, the first flank surface 31 and the first chip removal groove 1 are alternately arranged. One end of the first flank surface 31 constitutes the peripheral cutting edge 20. The other end of the first flank surface 31 constitutes the tail portion 5. The first flank surface 31 is connected to the first rake surface 10 at the peripheral cutting edge 20. The first flank surface 31 is connected to the first chip removal surface 40 at the tail portion 5. In the radial direction, the length from the axis A to the peripheral cutting edge 20 (first length L1) is longer than the length from the axis A to the tail portion 5 (second length L2).

[0033] Figure 4 yes Figure 3 An enlarged schematic diagram of region IV. Figure 4 As shown, in a cross section perpendicular to the axis A, the first front cutting edge 10 is composed of a plurality of straight portions. The plurality of straight portions include, for example, a first straight portion 11, a second straight portion 12, a third straight portion 13, and a fourth straight portion 14. The first straight portion 11 is connected to the first back cutting edge 31. The first straight portion 11 is inclined relative to the first back cutting edge 31. The boundary between the first straight portion 11 and the first back cutting edge 31 is the peripheral cutting edge 20. The second straight portion 12 is inclined relative to the first straight portion 11. The second straight portion 12 is connected to the first straight portion 11. The second straight portion 12 is located on the opposite side of the first back cutting edge 31 relative to the first straight portion 11. From another perspective, the first straight portion 11 is located between the second straight portion 12 and the first back cutting edge 31.

[0034] The third straight portion 13 is inclined relative to the second straight portion 12. The third straight portion 13 is connected to the second straight portion 12. The third straight portion 13 is located on the side opposite to the first straight portion 11 relative to the second straight portion 12. From another perspective, the second straight portion 12 is located between the third straight portion 13 and the first straight portion 11. The fourth straight portion 14 is inclined relative to the third straight portion 13. The fourth straight portion 14 is connected to the third straight portion 13. The fourth straight portion 14 is located on the side opposite to the second straight portion 12 relative to the third straight portion 13. From another perspective, the third straight portion 13 is located between the fourth straight portion 14 and the second straight portion 12.

[0035] Among the plurality of straight line portions, the angle formed by two adjacent straight line portions may become smaller as they move away from the first back cutting edge 31. Specifically, the first angle θ1 formed by the first straight line portion 11 and the second straight line portion 12 may be greater than the second angle θ2 formed by the second straight line portion 12 and the third straight line portion 13. The second angle θ2 formed by the second straight line portion 12 and the third straight line portion 13 may be greater than the third angle θ3 formed by the third straight line portion 13 and the fourth straight line portion 14. The first angle θ1 is, for example, greater than 140° and less than 180°. The lower limit of the first angle θ1 is not particularly limited, and for example, it may be greater than 150°, or greater than 160°. The upper limit of the first angle θ1 is not particularly limited, and for example, it may be less than 178°, or less than 175°.

[0036] The boundary between the first straight portion 11 and the second straight portion 12 is the first position X1. The boundary between the second straight portion 12 and the third straight portion 13 is the second position X2. The boundary between the third straight portion 13 and the fourth straight portion 14 is the third position X3. The length of the first straight portion 11 (the straight distance between the peripheral cutting edge 20 and the first position X1) may be greater than the length of the second straight portion 12 (the straight distance between the first position X1 and the second position X2). The length of the second straight portion 12 (the straight distance between the first position X1 and the second position X2) may be greater than the length of the third straight portion 13 (the straight distance between the second position X2 and the third position X3).

[0037] In the rotational direction, the distance between the peripheral cutting edge 20 and the first position X1 (first distance a1) may be the same as the distance between the first position X1 and the second position X2 (second distance a2). In the radial direction, the distance between the first position X1 and the second position X2 (second distance a2) may be the same as the distance between the second position X2 and the third position X3 (third distance a3).

[0038] Figure 5 yes Figure 3 An enlarged schematic diagram of area V. In a cross section perpendicular to the axis A, the first chip discharge surface 40 may be composed of a plurality of straight portions, for example. The first chip discharge surface 40 has, for example, a fifth straight portion 41, a sixth straight portion 42, a seventh straight portion 43 and an eighth straight portion 44. The fifth straight portion 41 is inclined relative to the first back tool surface 31. The fifth straight portion 41 is connected to the tail portion 5. The sixth straight portion 42 is inclined relative to the fifth straight portion 41. The sixth straight portion 42 is connected to the fifth straight portion 41. The sixth straight portion 42 is located on the opposite side of the tail portion 5 relative to the fifth straight portion 41. From another perspective, the fifth straight portion 41 is located between the sixth straight portion 42 and the tail portion 5.

[0039] The seventh straight portion 43 is inclined relative to the sixth straight portion 42. The seventh straight portion 43 is connected to the sixth straight portion 42. The seventh straight portion 43 is located on the side opposite to the fifth straight portion 41 relative to the sixth straight portion 42. From another perspective, the sixth straight portion 42 is located between the seventh straight portion 43 and the fifth straight portion 41. The eighth straight portion 44 is inclined relative to the seventh straight portion 43. The eighth straight portion 44 is connected to the seventh straight portion 43. The eighth straight portion 44 is located on the side opposite to the sixth straight portion 42 relative to the seventh straight portion 43. From another perspective, the seventh straight portion 43 is located between the eighth straight portion 44 and the sixth straight portion 42.

[0040] A fourth angle θ formed by the fifth straight line portion 41 and the sixth straight line portion 42 n-1 may be greater than a fifth angle θ formed by the sixth straight line portion 42 and the seventh straight line portion 43. n-2 A fifth angle θ formed by the sixth straight line portion 42 and the seventh straight line portion 43 is n-2 may be greater than a sixth angle θ formed by the seventh straight line portion 43 and the eighth straight line portion 44. n-3 .

[0041] The boundary between the fifth straight line portion 41 and the sixth straight line portion 42 is the fourth position X n-1 The boundary between the sixth straight line portion 42 and the seventh straight line portion 43 is the fifth position X n-2 The boundary between the seventh straight line portion 43 and the eighth straight line portion 44 is the sixth position X n-3 The length of the fifth straight line portion 41 (the length between the tail 5 and the fourth position X n-1 The straight line distance between the fourth position X n-1 and the fifth position X n-2 The length of the sixth straight line portion 42 (the fourth position X n-1 and the fifth position X n-2 The straight line distance between the fifth position X n-2 and the sixth position X n-3 straight-line distance between them).

[0042] In the rotation direction, the tail 5 and the fourth position X n-1 The distance between the fourth position X and the fourth position X (the fourth distance b1) can be n-1 and the fifth position X n-2 The distance between the fourth position X and the fifth position B2 is the same. n-1 and the fifth position X n-2 The distance between the fifth position X and the fifth position X (fifth distance b2) can be n-2 and the sixth position X n-3 The distance between them (sixth distance b3) is the same.

[0043] Figure 6 : is a diagram showing the relationship between the angle formed by two adjacent straight line portions and the position in the first chip removal groove. Figure 6 As shown, in the first rake face 10, the angle formed by two adjacent straight portions can decrease monotonically as it moves from the peripheral cutting edge 20 toward the first chip removal face 40. In a section perpendicular to the axis A, the rake face 10 can, for example, be composed of more than 5 straight portions. Similarly, in the first chip removal face 40, the angle formed by two adjacent straight portions can decrease monotonically as it moves from the tail portion 5 toward the first rake face 10. In a section perpendicular to the axis A, the first chip removal face 40 can, for example, be composed of more than 5 straight portions. In a section perpendicular to the axis A, the surface of the first chip removal groove 1 can be composed of multiple straight portions.

[0044] The lower limit of the number of straight line portions is not particularly limited, and may be, for example, 10 or more, or 20 or more. The upper limit of the number of straight line portions is not particularly limited, and may be, for example, 50 or less, or 40 or less.

[0045] like Figure 6 As shown, in the rake face 10, the difference between the maximum value of the angle formed by two adjacent straight line portions and the minimum value of the angle formed by two adjacent straight line portions (angle difference B) is, for example, 8° or more. The lower limit of the angle difference B is not particularly limited, for example, it can be 10° or more, or 12° or more. The upper limit of the angle difference B is not particularly limited, for example, it can also be 30° or less.

[0046] The rotary cutting tool 100 is, for example, an end mill, but is not limited to an end mill. The rotary cutting tool 100 can be, for example, a reamer, a drill, or a tap.

[0047] Next, the effects of the rotary cutting tool 100 according to the present embodiment will be described.

[0048] Figure 7 1 is a cross-sectional schematic diagram showing a state in which a cutting process is being performed using the rotary cutting tool 100 according to the present embodiment. Figure 7 As shown, the chips 61 of the workpiece 60 cut by the cutting edge 20 of the rotating cutting tool 100 are discharged while contacting the rake face 10. When the friction between the chips 61 and the rake face 10 is high, the chips 61 may be welded to the rake face 10. There is a case where the cutting edge 20 is broken due to the welding of the chips 61.

[0049] According to the rotary cutting tool 100 involved in the present disclosure, in a cross section perpendicular to the axis A, the rake face 10 is composed of a plurality of straight portions. Specifically, in a cross section perpendicular to the axis A, the rake face 10 has a first straight portion 11, a second straight portion 12 inclined relative to the first straight portion 11 and connected to the first straight portion 11, and a third straight portion 13 inclined relative to the second straight portion 12 and connected to the second straight portion 12. When the chip 61 moves on the rake face 10, the chip 61 is curled with a certain curvature. Therefore, a gap 9 is formed between the curled chip 61 and the boundary between the first straight portion 11 and the second straight portion 12. Similarly, a gap 9 is formed between the curled chip 61 and the boundary between the second straight portion 12 and the third straight portion 13. When the workpiece 60 is cut, the coolant is introduced into the above-mentioned gap 9 by capillary action. As a result, the coolant can be effectively transported to the vicinity of the cutting point and maintained. As a result, the friction force between the chips 61 and the rake face 10 can be reduced. Therefore, the cutting edge 20 can be prevented from being broken.

[0050] Example

[0051] (Prepare samples)

[0052] First, prepare the rotary cutting tools 100 of samples 1 to 8. The rotary cutting tools 100 of samples 1 to 7 are end mills involved in the embodiments. The rotary cutting tool 100 of sample 8 is an end mill involved in the comparative example. A cBN sintered body is brazed to the front end of the shank made of cemented carbide. In the rotary cutting tools 100 of samples 1 to 7, a plurality of straight portions are formed on the surface of the chip groove spirally provided on the cBN sintered body. The plurality of straight portions are formed by finishing the surface (front cutting edge) of the chip groove using a grinding wheel provided with the straight portions. The processing is performed multiple times while changing the angle of the grinding wheel. In the rotary cutting tool 100 of sample 8, the surface (front cutting edge) of the chip groove is curved.

[0053] In the rotary cutting tool of sample 1, the number of straight line portions constituting the first chip removal groove 1 is set to 5. The maximum value of the angle formed by two adjacent straight line portions is set to 178°. The minimum value of the angle formed by two adjacent straight line portions is set to 151°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 27°.

[0054] In the rotary cutting tool of sample 2, the number of straight line portions constituting the first chip removal groove 1 is set to 10. The maximum value of the angle formed by two adjacent straight line portions is set to 178°. The minimum value of the angle formed by two adjacent straight line portions is set to 155°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 23°.

[0055] In the rotary cutting tool of sample 3, the number of straight line portions constituting the first chip removal groove 1 is set to 20. The maximum value of the angle formed by two adjacent straight line portions is set to 178°. The minimum value of the angle formed by two adjacent straight line portions is set to 162°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 16°.

[0056] In the rotary cutting tool of sample 4, the number of straight line portions constituting the first chip removal groove 1 is set to 30. The maximum value of the angle formed by two adjacent straight line portions is set to 178°. The minimum value of the angle formed by two adjacent straight line portions is set to 168°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 10°.

[0057] In the rotary cutting tool of sample 5, the number of straight line portions constituting the first chip removal groove 1 is set to 10. The maximum value of the angle formed by two adjacent straight line portions is set to 175°. The minimum value of the angle formed by two adjacent straight line portions is set to 163°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 12°.

[0058] In the rotary cutting tool of sample 6, the number of straight line portions constituting the first chip removal groove 1 is set to 10. The maximum value of the angle formed by two adjacent straight line portions is set to 175°. The minimum value of the angle formed by two adjacent straight line portions is set to 167°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 8°.

[0059] In the rotary cutting tool of sample 7, the number of straight line portions constituting the first chip removal groove 1 is set to 40. The maximum value of the angle formed by two adjacent straight line portions is set to 176°. The minimum value of the angle formed by two adjacent straight line portions is set to 171°. The difference between the maximum value of the above angle and the minimum value of the above angle is set to 5°.

[0060] (Evaluation method)

[0061] Next, the workpiece 60 was machined using the rotary cutting tools 100 of samples 1 to 8 (see Figure 7 ). The workpiece 60 is Ti-6Al-4V. The cutting speed (Vc) is 300 m / min. The feed rate (f) is 0.01 mm / blade. The lateral cutting depth (Ae) is 0.1 mm. The axial cutting depth (Ap) is 0.5 mm. The coolant is an emulsion diluted 20 times.

[0062] (Evaluation results)

[0063] [Table 1]

[0064] Test material Number of straight lines <![CDATA[θ max ]]> <![CDATA[θ min ]]> <![CDATA[θ max -θ min ]]> Tool life Sample 1 5 178 151 27 38 minutes Sample 2 10 178 155 23 41 minutes Sample 3 20 178 162 16 43 minutes Sample 4 30 178 168 10 50 minutes Sample 5 10 175 163 12 45 minutes Sample 6 10 175 167 8 46 minutes Sample 7 40 176 171 5 20 minutes Sample 8 0 - - - 10 minutes

[0065] Table 1 shows the tool life when the cut material 60 is processed using the rotary cutting tool 100 of samples 1 to 8. The tool life is the time from the start of processing to the chipping of the cutting edge. As shown in Table 1, the tool life when the cut material 60 is processed using the rotary cutting tool 100 of samples 1 to 7 is more than 20 minutes and less than 50 minutes. On the other hand, the tool life when the cut material 60 is processed using the rotary cutting tool 100 of sample 8 is 10 minutes. Based on the above results, it is confirmed that in a cross-section perpendicular to the axis A, the front cutting face 10 is formed by a plurality of straight line portions, thereby suppressing the chipping of the cutting edge. In addition, it is confirmed that by setting the difference between the maximum and minimum values ​​of the angle formed by two adjacent straight line portions to more than 8°, the chipping of the cutting edge can be further suppressed.

[0066] The embodiments and examples disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0067] Description of Reference Numerals

[0068] 1: First chip flute; 2: Second chip flute; 3: Shank; 5: Tail; 8: Joint; 9: Gap; 10: First rake face (rake face); 11: First straight line; 12: Second straight line; 13: Third straight line; 14: Fourth straight line; 15: Second rake face; 20: Cutting edge (peripheral cutting edge); 21: Bottom cutting edge; 31: First flank face (flank face); 33: Second flank face; 40: First chip flute surface; 41: fifth straight line portion; 42: sixth straight line portion; 43: seventh straight line portion; 44: eighth straight line portion; 45: second chip removal surface; 58: front end; 59: rear end; 60: workpiece; 61: chips; 90: blade; 100: rotating cutting tool; A: axis; B: angle difference; L1: first length; L2: second length; R: rotation direction; X1: first position; X2: second position; X3: third position; X n-1 : Fourth position; X n-2 : Fifth position; X n-3 : sixth position; a1: first distance; a2: second distance; a3: third distance; b1: fourth distance; b2: fifth distance; b3: sixth distance; θ1: first angle; θ2: second angle; θ3: third angle; θ n-1 : The fourth angle; θ n-2 : The fifth angle; θ n-3 : The sixth angle.

Claims

1. A rotary cutting tool capable of rotating about an axis, wherein: The rotary cutting tool comprises: Rake face; and a back cutting edge connected to the front cutting edge, The ridges of the rake face and the flank face constitute a cutting edge, In a cross section perpendicular to the axis, the rake face is composed of a plurality of straight line portions. The rotary cutting tool is provided with a chip removal groove, The chip removal groove is arranged in a spiral shape around the axis, A portion of the chip removal groove is formed by the rake face, The plurality of straight line portions include: a first straight line portion connected to the back cutting surface; a second straight line portion inclined relative to the first straight line portion and connected to the first straight line portion, A first angle formed by the first straight line portion and the second straight line portion is greater than or equal to 160°.

2. The rotary cutting tool according to claim 1, wherein: In the plurality of straight line portions, a difference between a maximum value of an angle formed by two adjacent straight line portions and a minimum value of an angle formed by two adjacent straight line portions is 8° or more.

3. The rotary cutting tool according to claim 1 or 2, wherein: The plurality of straight line portions include: a third straight line portion that is inclined relative to the second straight line portion and connected to the second straight line portion; and a fourth straight line portion that is inclined relative to the third straight line portion and connected to the third straight line portion, The first angle is greater than a second angle formed by the second straight portion and the third straight portion, and The second angle is greater than a third angle formed by the third straight line portion and the fourth straight line portion.

4. The rotary cutting tool according to claim 3, wherein: The length of the first straight line portion is greater than the length of the second straight line portion.

5. The rotary cutting tool according to claim 3, wherein: The length of the second straight line portion is greater than the length of the third straight line portion.

6. The rotary cutting tool according to claim 1 or 2, wherein: The number of the cutting edges is 2 or more.

7. The rotary cutting tool according to claim 1 or 2, wherein: The number of the cutting edges is 20 or less.

8. The rotary cutting tool according to claim 1 or 2, wherein: The first angle is less than 178°.

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