Method for manufacturing rotary tools and machined products

Abstract

This rotary tool has a coolant hole that is opened in a flank face thereof. A cross-section of the coolant hole orthogonal to the rotation axis of the rotary tool has: a first portion which is formed in a protruding curve shape that protrudes toward the front in the rotational direction of the rotary axis and also toward the outer circumferential side; a second portion which is formed in a protruding curve shape that protrudes toward the front in the rotational direction and also toward the central side; and a third portion which is formed in a protruding curve shape that protrudes toward the rear in the rotational direction and also toward the central side.

Description

[Technical field]

[0001] The present disclosure relates to a rotary tool used for cutting a workpiece and a method for manufacturing a machined product. Examples of rotary tools include end mills, drills, and reamers. [Background technology]

[0002] Drills described in Patent Documents 1 and 2 are known as rotary tools used for cutting workpieces such as metals. The drills described in Patent Documents 1 and 2 have coolant holes that extend from the rear end to the tip and open at the tip. During cutting, a coolant is sprayed from the coolant holes to cool the drill and the workpiece. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-020255 A [Patent Document 2] JP 2017-205844 A Summary of the Invention

[0004] A rotating tool according to one embodiment of the present disclosure has a cylindrical body extending along a rotation axis from a first end to a second end, the body having a flank located at the first end, a discharge groove for discharging chips extending from the flank toward the second end, a cutting edge located at an intersection of the flank and the discharge groove, and a coolant hole extending from the second end toward the first end and opening at the flank, the coolant hole having, in a cross section perpendicular to the rotation axis, a first portion of a convex curved shape protruding forward in the rotation direction of the rotation shaft and toward the outer periphery, a second portion of a convex curved shape protruding forward in the rotation direction and toward the center, and a third portion of a convex curved shape protruding rearward in the rotation direction and toward the center. [Brief description of the drawings]

[0005] [Figure 1] 1 is a perspective view of a rotary tool according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an enlarged view of an area A1 shown in FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] 3. FIG. 3 is a cross-sectional view taken along line III-III of FIG. [Figure 6] 3. FIG. 3 is a cross-sectional view taken along line III-III of FIG. 3 to explain the shape of a coolant hole. [Figure 7] 4 is a front view of the rotating tool to explain the flow of coolant ejected from a coolant hole. FIG. [Figure 8] 1 is a schematic diagram showing steps of a method for producing a machined product according to one embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Hereinafter, the rotary tool and the manufacturing method of the machined product according to the embodiment of the present disclosure will be described in detail with reference to the drawings. However, for the convenience of explanation, each of the drawings referred to below shows only the components necessary for explaining the embodiment in a simplified manner. Therefore, the rotary tool may include any components not shown in each of the drawings referred to. Furthermore, the dimensions of the components in each drawing do not faithfully represent the actual dimensions of the components and the dimensional ratios of each component.

[0007] In the present disclosure, the rotation axis refers to the rotation axis center of the rotating tool, and the circumferential direction refers to the direction around the rotation axis. The radial direction refers to a direction perpendicular to the rotation axis and the circumferential direction, the radially inner side refers to a direction or side approaching the rotation axis in the radial direction, and the radially outer side refers to a direction or side away from the rotation axis in the radial direction. In addition, the outer periphery side refers to the outer periphery side of the rotating tool, and the central side refers to the inner periphery side including the center of the rotating tool where the rotation axis is located.

[0008] (1. Rotary tools) <Schematic configuration of rotating tool 1> First, the configuration of a rotating tool 1 according to this embodiment will be described with reference to Figs. 1 to 4. Fig. 1 is a perspective view of the rotating tool 1 according to this embodiment. Fig. 2 is an enlarged view of an area A1 shown in Fig. 1. Fig. 3 is a side view of the rotating tool 1. Fig. 4 is a front view of the rotating tool 1.

[0009] As shown in Fig. 1 and Fig. 3, a drill can be given as an example of the rotating tool 1, and in this embodiment, a drill is given as an example of the rotating tool 1. More specifically, the drill shown in Fig. 1 is called a flat drill with a point angle of 180 degrees. Examples of the rotating tool may include an end mill and a reamer. Of course, the point angle of the drill is not limited to 180 degrees.

[0010] As shown in FIG. 1, the rotary tool 1 in this embodiment has a cylindrical body 3 extending along a rotation axis R1 from a first end 3a to a second end 3b. The first end 3a may be replaced with a front end 3a, and the second end 3b may be replaced with a rear end 3b. The rotary tool 1 has the body 3. The body 3 is rotatable around the axis of the rotation axis R1, and has a cutting part 10 at the first end 3a, which is one end in the axial direction of the rotation axis R1. As shown in FIG. 8, which will be described later, the cutting part 10 comes into contact with a workpiece T to perform cutting processing.

[0011] The main body 3 in the so-called solid type rotary tool 1 may be made of, for example, a hard material. Examples of the hard material include high-speed tool steel, cemented carbide, ceramics, cermet, cBN (Cubic Boron Nitride), and PCD (PolyCrystalline Diamond). In the solid type, at least the cutting part 10 may be made of the above-mentioned hard material, and the cutting part 10 made of the above-mentioned hard material may be brazed to a metal member. The rotary tool may also be composed of a holder and a cutting insert, which are generally called tip-replaceable tools. In this case, the cutting insert that cuts the workpiece T may be made of, for example, the above-mentioned hard material.

[0012] As shown in Figs. 1 and 3, the main body 3 may have a portion called a shank 4 and a portion called a main body 5. The shank 4 is located on the second end 3b side, and the main body 5 is located closer to the first end 3a than the shank 4. The shank 4 is a portion that can be held by a rotatable spindle or the like in a machine tool. The cutting portion 10 is formed on the first end 3a side of the main body 5. A discharge groove 12 extending from the first end 3a is formed in a spiral shape on the outer circumferential surface of the main body 5.

[0013] As will be described in more detail later, the rotating tool 1 has a shank portion 4 held by a machine tool and sent out toward the first end 3a while being rotated in a rotation direction R2 about the axis of a rotation shaft R1, thereby drilling a hole in a workpiece T (see FIG. 8).

[0014] <Cutting part> 2 and 4, the cutting portion 10 located on the first end 3a side has a cutting edge 11, an opening of a discharge groove 12, a clearance face 13, and an opening of a coolant hole 14. The front view of Fig. 4 is a view of the rotating tool 1 as seen from the first end 3a side. Viewing from the first end 3a side is referred to as a front view.

[0015] The flank 13 is located at the first end 3a. As shown in Fig. 4, in this embodiment, the flank 13 is located at the first end 3a and is formed of three flank portions 13A, 13B, and 13C whose flank angles gradually increase toward the rear side in the rotation direction R2. As shown in Fig. 4, in this embodiment, the pair of flanks 13 are formed symmetrically with respect to each other with respect to the rotation axis R1 as viewed from the front. The flank portion 13C in this embodiment is a gash surface.

[0016] The cutting edge 11 is located at the intersection of the flank 13 and the discharge groove 12 located forward of the flank 13 in the rotation direction R2. In detail, the cutting edge 11 is formed at a ridge portion where the first flank portion 13A and the discharge groove 12, particularly the opening of the discharge groove 12, intersect. In the example of FIG. 4, the cutting edge 11 has a thinning edge 11a on the radially inner side. In this embodiment, the pair of cutting edges 11 are formed symmetrically with respect to each other with respect to the rotation axis R1 when viewed from the front.

[0017] The discharge groove 12 opens at the flank 13 at the first end 3a, and extends from the flank 13 toward the second end 3b as shown in Figs. 1 and 3, and has the function of discharging chips generated by cutting with the cutting edge 11. In this embodiment, the pair of discharge grooves 12 are formed symmetrically with respect to each other with respect to the rotation axis R1, extend while twisting as they move from the flank 13 toward the second end 3b, and cut off just before the shank portion 4. From the viewpoint of smoothly discharging the chips to the outside, the discharge groove 12 may have a concave curved shape in a cross section perpendicular to the rotation axis R1.

[0018] The coolant hole 14 extends from the second end 3b toward the first end 3a inside the main body 3 and opens at the flank 13. The coolant hole 14 has the function of spraying a cooling liquid (coolant liquid) supplied from the second end 3b from the opening at the first end 3a to cool the rotating tool 1 and the workpiece T (see FIG. 8). The cooling liquid can also be used to discharge generated chips.

[0019] In this embodiment, as shown in Fig. 4, a pair of coolant holes 14 are provided symmetrically with respect to the rotation axis R1. The pair of coolant holes 14 open to overlap the second flank portion 13B and the first flank portion 13A of the flank 13. The shape and dimensions of these coolant holes 14 in a cross section perpendicular to the rotation axis R1 are constant over the entire length of the main body 3.

[0020] <Coolant hole shape> Next, the shape of the coolant hole 14 will be described in detail with reference to Fig. 5 to Fig. 7. Fig. 5 is a cross-sectional view taken along line III-III in Fig. 3 and a partially enlarged view. Fig. 6 is a diagram for explaining the shape of the coolant hole 14 using a cross-sectional view taken along line III-III in Fig. 3. Fig. 7 is a diagram for explaining the flow of the coolant ejected from the coolant hole 14 using a front view of the rotating tool 1.

[0021] 5, the coolant hole 14 has a first portion 14A, a second portion 14B, and a third portion 14C each having a convex curved shape in a cross section perpendicular to the rotation axis R1. The first portion 14A has a convex curved shape that protrudes forward in the rotation direction R2 and toward the outer periphery. The second portion 14B has a convex curved shape that protrudes forward in the rotation direction R2 and toward the center. The third portion 14C has a convex curved shape that protrudes backward in the rotation direction R2 and toward the center.

[0022] 1) The first portion 14A has a convex curved shape that protrudes forward in the rotation direction and toward the outer periphery. As a result, the coolant spurted out (discharged) from the first portion 14A flows toward the outer periphery portion (radially outer portion) of the cutting edge 11 located forward in the rotation direction R2 with respect to the coolant hole 14, as shown by the arrow Y1 in Fig. 7. During cutting, the rotating tool 1 rotates at high speed in the rotation direction R2, so that centrifugal force acts toward the outer periphery. This centrifugal force allows the coolant to be smoothly discharged toward the outer periphery portion of the cutting edge 11.

[0023] Since the outer peripheral portion of the cutting blade 11 has a large rotational diameter from the rotation axis R1, the amount of chips generated, the cutting load, and the cutting heat generated are all large, and the cutting edge is prone to chipping. However, the first portion 14A supplies a large amount of coolant to the outer peripheral portion of the cutting blade 11 and the cutting portion of the workpiece T (see FIG. 8) cut by the outer peripheral portion, thereby enabling effective cooling.

[0024] 2) The second portion 14B has a convex curved shape that protrudes forward in the direction of rotation and toward the center. As a result, the coolant ejected from the second portion 14B flows toward the portion close to the center where the rotation axis R1 is located, as shown by the arrow Y2 in Fig. 7. The portion close to the center has a slower rotation speed but is prone to heat buildup. This allows a large amount of coolant to be supplied to the portion close to the center and to the portion of the workpiece T (see Fig. 8) located in that portion, enabling effective cooling.

[0025] 3) The third portion 14C has a convex curved shape that protrudes rearward in the rotational direction and toward the center. As a result, the coolant ejected from the third portion 14C flows toward the discharge groove 12 located rearward in the rotational direction R2 with respect to the coolant hole 14, as shown by the arrow Y3 in Fig. 7. The coolant ejected from the rear of the opening of the coolant hole 14 in the rotational direction R2 tends to flow toward the outer periphery due to centrifugal force.

[0026] If the third portion 14C protrudes toward the outer periphery, the coolant is likely to be discharged to the outside of the main body 3 without flowing into the discharge groove 12 located rearward in the rotation direction R2 relative to the coolant hole 14. However, by forming the third portion 14C into a shape that protrudes toward the center, more coolant can be directed toward the discharge groove 12 located rearward in the rotation direction R2 even under conditions in which centrifugal force is applied. This allows more coolant to be supplied toward the discharge groove 12 located rearward in the rotation direction R2 from the third portion 14C, and chips can be discharged well.

[0027] Further, the coolant hole 14 has not only an opening portion on the flank 13 as shown in Fig. 4, but also a first portion 14A to a third portion 14C in a cross section far away from the flank 13 as shown in Fig. 3 and Fig. 5. For example, assume that the coolant hole 14 has the first portion 14A to the third portion 14C only near the opening portion on the flank 13, and the shape of the coolant hole 14 in a cross section far away from the flank 13 is circular. In this case, the flow path loss increases due to deformation of the shape of the coolant hole 14 in the cross section. Therefore, there is a risk that the effect of the first portion 14A to the third portion 14C described above cannot be fully obtained.

[0028] However, when coolant hole 14 has first portion 14A to third portion 14C in a cross section far away from flank 13, it is easy to suppress flow path loss inside coolant hole 14. Therefore, it is easy to obtain the effects of first portion 14A to third portion 14C described above.

[0029] In this way, by making the coolant hole 14 into the above-mentioned shape, it is possible to achieve both cooling of the rotating tool 1 and the workpiece T (see Figure 8) by the coolant sprayed out from the coolant hole 14 and removal of the chips generated by the coolant.

[0030] 5, the coolant hole 14 may further have a fourth portion 14D and a fifth portion 14E, each of which has a concave curved shape, or only one of the fourth portion 14D and the fifth portion 14E, in a cross section perpendicular to the rotation axis R1. The fourth portion 14D is located between the first portion 14A and the second portion 14B, and has a concave curved shape recessed toward the inside of the coolant hole 14. The fifth portion 14E is located between the second portion 14B and the third portion 14C, and has a concave curved shape recessed toward the inside of the coolant hole 14.

[0031] The fourth portion 14D having a concave curved shape narrows the area between the first portion 14A and the second portion 14B having a convex curved shape, thereby narrowing the discharge direction of the cooling liquid supplied from the first portion 14A and the second portion 14B. Furthermore, narrowing the discharge direction can increase the momentum of the cooling liquid. The fifth portion 14E having a concave curved shape narrows the area between the twelfth portion 14B and the third portion 14C having a convex curved shape, thereby narrowing the discharge direction of the cooling liquid supplied from the second portion 14B and the third portion 14C. Furthermore, narrowing the discharge direction can increase the momentum of the cooling liquid.

[0032] 6, an end 14A-1 located in front of the first portion 14A in the rotation direction R2 may be configured to be farther from the rotation axis R1 than an end 14C-1 located in the rear of the third portion 14C in the rotation direction R2. In other words, the end 14A-1 is configured to be located on the outer periphery side (radially outward) farther from the rotation axis R1 than the end 14C-1. In FIG. 6, the end 14A-1 and the end 14C-1 are highlighted by black dots.

[0033] With this configuration, the first portion 14A that supplies cooling liquid toward the outer peripheral portion of the cutting edge 11 is positioned closer to the outer peripheral side, and more cooling liquid can be supplied toward the outer peripheral portion of the cutting edge 11, thereby enabling more effective cooling.

[0034] 6, the first to third regions 14A, 14B, and 14C may all be arc-shaped, with the radius of curvature of each arc being first region 14A>second region 14B>third region 14C. That is, the first region 14A has an arc shape with a first radius of curvature, the second region has an arc shape with a second radius of curvature, and the third region has an arc shape with a third radius of curvature. The first radius of curvature is larger than the second radius of curvature, and the second radius of curvature is larger than the third radius of curvature.

[0035] With this configuration, the direction in which the coolant is ejected from each of the first to third portions 14A, 14B, and 14C corresponds to the cooling or discharge function required for each portion. Therefore, the coolant hole 14 can more effectively achieve both cooling by the coolant and discharge of chips.

[0036] 6, the centers of virtual circles C1 to C3 corresponding to the arc shapes of the first to third portions 14A, 14B, and 14C are defined as centers C1a to C3a, respectively. In this case, the positions of the centers C1a to C3a may be configured such that the distance between the centers C1a and C2a is shorter than the distance between the centers C2a and C3a.

[0037] That is, the virtual circle corresponding to the arc shape in the first portion 14A is the first virtual circle C1, the virtual circle corresponding to the arc shape in the second portion 14B is the second virtual circle C2, and the virtual circle corresponding to the arc shape in the third portion 14C is the third virtual circle C3. The center of the first virtual circle C1 is the first center C1a, the center of the second virtual circle C2 is the second center C2a, and the center of the third virtual circle C3 is the third center C3a. In this case, the distance between the first center C1a and the second center C2a is shorter than the distance between the second center C2a and the third center C3a.

[0038] With this configuration, the first portion 14A and the second portion 14B are close to each other, and the cooling liquid ejected from each of the first portion 14A and the second portion 14B can effectively cool the portion of the cutting edge 11 between the position close to the center and the portion on the outer periphery.

[0039] Furthermore, in this case, as shown in FIG. 6, the first imaginary circle C1 and the second imaginary circle C2 may intersect, and the third imaginary circle C3 may be formed so as to be spaced apart from the first imaginary circle C1 and the second imaginary circle C2.

[0040] With this configuration, the first portion 14A and the second portion 14B are closer to each other, so that the cooling liquid ejected from the first portion 14A and the second portion 14B can more effectively cool the portion of the cutting edge 11 between the position close to the center and the portion on the outer periphery side.

[0041] 6, in a configuration having a fourth portion 14D, the fourth portion 14D may be recessed backward in the rotational direction R2. In a configuration having a fifth portion 14E, the fifth portion 14E may be recessed backward in the rotational direction R2 and toward the outer periphery.

[0042] By recessing the fourth portion 14D toward the rear in the rotation direction R2, the effect of the fourth portion 14D on the flow direction of the coolant supplied from the first portion 14A and the second portion 14B is minimized, and the coolant can easily flow toward the cutting edge 11. In addition, the momentum of the coolant can be increased by narrowing the discharge direction. By recessing the fifth portion 14E toward the rear and outer periphery in the rotation direction R2, the coolant supplied from the second portion 14B can easily flow toward the cutting edge 11, and the coolant supplied from the third portion 14C can easily flow toward the discharge groove 12.

[0043] 6, the fourth portion 14D and the fifth portion 14E may have an arc shape, and the radius of curvature of these arc shapes may be smaller than the radius of curvature of the arc shapes of the first portion 14A to the third portion 14C. In other words, the fourth radius of curvature, which is the radius of curvature of the arc shape of the fourth portion 14D, may be smaller than the first radius of curvature, the second radius of curvature, and the third radius of curvature. Also, the fifth radius of curvature, which is the radius of curvature of the arc shape of the fifth portion 14E, may be smaller than the first radius of curvature, the second radius of curvature, and the third radius of curvature.

[0044] With this configuration, the fourth portion 14D has a compact configuration, and the areas of the first portion 14A and the second portion 14B are easily secured to be wide. This allows the direction of the coolant supplied from the first portion 14A and the second portion 14B to be stably controlled, and allows both cooling by the coolant and discharge of chips to be achieved more effectively. Furthermore, the fifth portion 14E has a compact configuration, and the areas of the second portion 14B and the third portion 14C are easily secured to be wide. This allows the direction of the coolant supplied from the second portion 14B and the third portion 14C to be stably controlled, and allows both cooling by the coolant and discharge of chips to be achieved more effectively.

[0045] 5, the coolant hole 14 may be configured such that in a cross section perpendicular to the rotation axis R1, the distance (spacing) from the coolant hole 14 to the rotation axis R1 is greater than the distance (spacing) from the coolant hole 14 to the outer circumferential surface of the main body 3. In other words, the coolant hole 14 may be formed closer to the outer circumferential side of the main body 3. With this configuration, the core thickness of the rotating tool 1 can be ensured even when the coolant hole 14 is provided.

[0046] 5, in a cross section perpendicular to the rotation axis R1, the distance from the coolant hole 14 to the discharge groove 12 located forward of the coolant hole 14 in the rotation direction R2 may be greater than the distance from the coolant hole 14 to the outer circumferential surface of the main body 3. With this configuration, the coolant hole 14 may be formed closer to the outer circumferential surface of the main body 3 than the cutting edge 11 to be cooled. With this configuration, the core thickness of the rotating tool 1 can be ensured even with the coolant hole 14 provided.

[0047] (2. Manufacturing method of machined products) Next, a method for manufacturing a machined product in one example will be described with reference to Fig. 8. Fig. 8 is a schematic diagram showing steps of the method for manufacturing a machined product in one embodiment. Hereinafter, a method for cutting a workpiece T using a rotating tool 1 to produce a machined product U will be described.

[0048] The manufacturing method of the machined product U in one embodiment may include the following steps: (1) a step of rotating a rotating tool 1; (2) contacting the rotary tool 1 with the workpiece T; (3) a step of separating the rotating tool 1 from the workpiece T; may also include

[0049] More specifically, first, as shown by reference numeral 801 in Fig. 8, a workpiece T is prepared immediately below the rotating tool 1, and the rotating tool 1 attached to a machine tool is rotated about a rotation axis R1. Examples of the workpiece T include aluminum, carbon steel, alloy steel, stainless steel, cast iron, and non-ferrous metals.

[0050] Next, as shown by reference numeral 802 in FIG. 8, the rotating tool 1 and the workpiece T are brought close to each other, and the rotating tool 1 is brought into contact with the workpiece T. As a result, the workpiece T is cut by the cutting blade 11, and a machining hole V is formed. Cutting chips of the cut workpiece T are discharged to the outside through the discharge groove 12. The rotating tool 1 and the workpiece T only need to be relatively close to each other, and the method for doing so is not particularly limited. For example, the rotating tool 1 may be moved toward the fixed workpiece T, or the workpiece T may be moved relative to the fixed rotating tool 1.

[0051] 8, the rotating tool 1 is removed from the workpiece T. As a result, a machined product U, which is the workpiece T with the machined hole V formed therein, is produced.

[0052] The invention according to the present disclosure has been described based on various drawings and examples. However, the invention according to the present disclosure is not limited to the above-mentioned embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0053] 1 Rotary tools 3. Main unit 3a 1st end 3b 2nd end 10 Cutting part 11 Cutting edge 12 Discharge groove 13 Flank 14 Coolant hole 14A 1st part 14A-1 End of the first part 14B 2nd part 14C 3rd part 14C-1 End of the third part 14D 4th part 14E Part 5 C1 First virtual circle C1a 1st center C2 Second virtual circle C2a 2nd center C3 Third imaginary circle C3a 3rd center R1 Rotation axis R2 Rotation direction

Claims

1. A cylindrical body extending along a rotation axis from a first end to a second end, The body includes: a clearance surface located at the first end; a discharge groove extending from the flank surface toward the second end for discharging chips; a cutting edge located at an intersection of the flank and the discharge groove; a coolant hole extending from the second end toward the first end and opening at the relief surface; The coolant hole, in a cross section perpendicular to the rotation axis, a first portion having an arc shape with a first radius of curvature; a second section having an arc shape with a second radius of curvature; a third section having an arc shape having a third radius of curvature; A virtual circle corresponding to the arc shape in the first portion is a first virtual circle. A virtual circle corresponding to the arc shape in the second portion is a second virtual circle. a virtual circle corresponding to the arc shape in the third portion is defined as a third virtual circle; The center of the first virtual circle is called a first center, The center of the second virtual circle is called the second center. If the center of the third virtual circle is defined as the third center, a midpoint of the first portion is located forward of and on an outer circumferential side of the first center in a rotation direction of the rotation shaft, The midpoint of the second portion is located forward and toward the center of the second center in the rotation direction, a midpoint of the third portion is located rearward and toward the center in the rotation direction from the third center, the first radius of curvature is greater than the second radius of curvature; The second radius of curvature is greater than the third radius of curvature.

2. The rotary tool according to claim 1 , wherein an end of the first portion located at a front side in the rotation direction is farther away from the rotation axis than an end of the third portion located at a rear side in the rotation direction.

3. A rotary tool as described in claim 1, wherein the distance between the first center and the second center is shorter than the distance between the second center and the third center.

4. the first virtual circle and the second virtual circle intersect, The rotary tool according to claim 3 , wherein the third imaginary circle is separated from the first imaginary circle and the second imaginary circle.

5. The coolant hole, in a cross section perpendicular to the rotation axis, The rotary tool according to any one of claims 1 to 4, further comprising a fourth portion located between the first portion and the second portion, the fourth portion having a concave curved shape recessed toward an inside of the coolant hole.

6. The fourth portion has an arc shape having a fourth radius of curvature, a virtual circle corresponding to the arc shape in the fourth portion is defined as a fourth virtual circle; If the center of the fourth virtual circle is defined as the fourth center, The rotary tool according to claim 5 , wherein a midpoint of the fourth portion is located rearward of the fourth center in the direction of rotation.

7. A rotary tool as described in claim 6, wherein the fourth radius of curvature is smaller than the first radius of curvature, the second radius of curvature and the third radius of curvature.

8. The coolant hole, in a cross section perpendicular to the rotation axis, The rotary tool according to any one of claims 1 to 4, further comprising a fifth portion located between the second portion and the third portion, the fifth portion having a concave curved shape recessed toward an inside of the coolant hole.

9. The fifth section has an arc shape having a fifth radius of curvature, a virtual circle corresponding to the arc shape in the fifth portion is defined as a fifth virtual circle; If the center of the fifth virtual circle is defined as the fifth center, The rotary tool according to claim 8 , wherein a midpoint of the fifth portion is located rearward and on an outer circumferential side of the fifth center in the rotational direction.

10. A rotary tool as described in claim 9, wherein the fifth radius of curvature is smaller than the first radius of curvature, the second radius of curvature and the third radius of curvature.

11. The rotary tool according to any one of claims 1 to 4, wherein in a cross section perpendicular to the rotation axis, a distance from an end of the coolant hole closest to the rotation axis to the rotation axis is greater than a distance from an end of the coolant hole closest to an outer peripheral surface of the body to the outer peripheral surface.

12. A rotary tool according to any one of claims 1 to 4, wherein in a cross section perpendicular to the rotation axis, a distance from an end of the coolant hole closest to the discharge groove located forward of the coolant hole in the direction of rotation to the discharge groove located forward of the coolant hole in the direction of rotation is greater than a distance from an end of the coolant hole closest to an outer peripheral surface of the body to the outer peripheral surface.

13. A step of rotating the rotary tool according to any one of claims 1 to 4; contacting the rotating rotary tool with a workpiece; and removing the rotating tool from the workpiece.

Images