End mill

Abstract

To provide an end mill whose tip is less likely to be damaged. [Solution] The end mill includes a main body 1 having a rotation axis AX and a tapered portion 2 provided in a region including the tip 1a of the main body 1. The tapered portion 2 includes grooves 31a and 31b and cutting edges 33a and 33b formed on the outer peripheral surface of the main body 1. The width W1 of the tapered portion 2, which is the maximum length of the tapered portion 2 in a direction passing through the rotation axis AX and perpendicular to the extension direction of the rotation axis AX, decreases toward the tip 1a of the main body 1 along the extension direction of the rotation axis AX. The angle θ1 formed by the outermost peripheral surface of the part of the tapered portion 2 closest to the tip 1a of the main body 1 is between 40 degrees and 70 degrees. The ratio of the core thickness W2 to the maximum width WM of the tapered portion 2 at a first position P1, which is a position along the extension direction of the rotation axis AX where the ratio of the width W1 of the tapered portion 2 to the maximum width WM of the tapered portion 2 is 10%, is between 5.14% and 7.40%.

Description

[Technical Field]

[0001] The present invention relates to an end mill, and more particularly to an end mill whose tip is resistant to damage. [Background technology]

[0002] An end mill is a cutting tool used in milling. It is a cylindrical cutting tool with cutting edges on the end and side faces. A tapered end mill, which is a type of end mill, has a tapered tip (gradually becoming thinner towards the tip). Tapered end mills are suitable for forming tapered grooves and for finishing processes.

[0003] Conventional tapered end mills are disclosed, for example, in Patent Document 1. Patent Document 1 discloses a tapered end mill in which the second relief angle of the second relief face of each peripheral cutting edge is smaller on the rear side than on the tip side of the tool body, and the third relief angle of the third relief face is larger on the rear side than on the tip side of the tool body, and the ratio of core thickness to cutting diameter dimension in the tool body on which each peripheral cutting edge is formed is smaller on the rear side than on the tip side of the tool body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7360506 Summary of the Invention [Problem to be solved by the invention]

[0005] FIG. 11 is a diagram showing the relationship between the tapered groove TG formed on the surface of the workpiece RK and the point angle θ1 of the end mill 1010 used to form the tapered groove TG.

[0006] Referring to Figure 11, a tapered groove TG is formed on the surface of the workpiece RK. The cross section of the workpiece RK in Figure 11 is a cross section perpendicular to the direction of relative movement of the end mill 1010 with respect to the workpiece RK when forming the tapered groove TG (the direction indicated by the arrow in Figure 11). A tapered groove is a groove whose width narrows toward the tip when viewed in the cross section of Figure 11.

[0007] Conventionally, there has been a growing need to form tapered grooves with steep wall surfaces. A tapered groove with steep wall surfaces refers to a tapered groove TG in which, when viewed in the cross section of FIG. 11 , the angle θ101 formed by the straight lines constituting each of the two side wall surfaces constituting the groove is small. Generally, the angle θ101 of the tapered groove TG is the same as the point angle θ1 of the end mill 1010. Therefore, in order to form a tapered groove with steep wall surfaces, it is necessary to set the point angle θ1 of the end mill 1010 used for formation to be small (in other words, to make the tip of the end mill 1010 sharp). However, with conventional end mills 1010, when attempting to set the point angle θ1 of the end mill 1010 to be small so that the point angle θ1 is 70 degrees or less, the mechanical strength of the tip of the end mill 1010 is reduced, resulting in a problem in that the tip of the end mill 1010 is easily damaged.

[0008] The present invention has been made to solve the above problems, and its object is to provide an end mill whose tip is less likely to be damaged. [Means for solving the problem]

[0009] An end mill according to one aspect of the present invention comprises a body having a rotation axis and a tapered portion provided in an area including the tip of the body, the tapered portion including a groove and a cutting edge formed on the outer peripheral surface of the body, the width W1 of the tapered portion, which is the maximum length of the tapered portion in a direction passing through the rotation axis and perpendicular to the extension direction of the rotation axis, decreases along the extension direction of the rotation axis toward the tip of the body, when viewed in a cross section including the extension direction of the rotation axis, the angle formed by the outermost peripheral surface of the part of the tapered portion closest to the tip of the body is 40 degrees or more and 70 degrees or less, and the ratio of the core thickness W2 at a first position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 10%, to the maximum width WM of the tapered portion is 5.14% or more and 7.40% or less.

[0010] In the above-mentioned end mill, preferably, the ratio of the core thickness W2 at a second position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 20%, to the maximum width WM of the tapered portion is 9.75% or more and 14.38% or less.

[0011] In the above-mentioned end mill, preferably, the ratio of the core thickness W2 at a third position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 30%, to the maximum width WM of the tapered portion is 14.41% or more and 20.93% or less.

[0012] In the above end mill, preferably, the core thickness W2 of the tapered portion increases from the first position toward the third position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 30%.

[0013] In the above-mentioned end mill, preferably, the ratio of the core thickness W2 to the width W1 of the tapered portion in a cross section including the extension direction of the rotation axis is constant or decreases from a first position to a second position, which is a position along the extension direction of the rotation axis at which the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 20%.

[0014] In the above-mentioned end mill, preferably, the ratio of the core thickness W2 to the width W1 of the tapered portion in a cross section including the extension direction of the rotation axis is constant or decreases from the first position to a third position, which is a position along the extension direction of the rotation axis at which the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 30%.

[0015] In the end mill, preferably, the angle formed by the outermost peripheral surface of the tapered portion closest to the tip of the body is equal to or greater than 40 degrees and equal to or less than 60 degrees. [Effects of the Invention]

[0016] According to the present invention, an end mill whose tip is less likely to be damaged can be provided. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a first perspective view showing a configuration of an end mill 10 as viewed from a tip 1a side of a main body 1 in an embodiment of the present invention. [Figure 2] 2 is a second perspective view showing the configuration of the end mill 10 as viewed from the tip 1a side of the main body 1 in the embodiment of the present invention. FIG. [Figure 3] 1 is a plan view showing the configuration of an end mill 10 when viewed from the tip 1a side of a main body 1. FIG. [Figure 4] 2 is a plan view showing the configuration of the vicinity of the tapered portion 2 of the end mill 10 when viewed from the side of the main body 1. FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] 10 is a diagram showing the relationship between the width W1 of the tapered portion 2 and the maximum value WM of the width W1 of the tapered portion 2 in a cross section including the direction in which the rotation axis AX extends. [Figure 7] 7 is a cross-sectional view taken along line VII-VII in FIG. 6, and is a cross-sectional view at a first position P1. [Figure 8] 8 is a cross-sectional view taken along line VIII-VIII in FIG. 6, and is a cross-sectional view at a second position P2. [Figure 9]FIG. 7 is a cross-sectional view taken along line IX-IX in FIG. 6, and is a cross-sectional view at a third position P3. [Figure 10] 1 is a table showing various dimensions and strength of the tip of an end mill for invention examples A to E and comparative example F in one embodiment of the present invention. [Figure 11] 10 is a diagram showing the relationship between a tapered groove TG formed on the surface of a workpiece RK and a point angle θ1 of an end mill 1010 used to form the tapered groove TG. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] [Outline of end mill structure]

[0020] First, the schematic configuration of the end mill 10 in this embodiment will be described.

[0021] 1 to 4 are diagrams schematically illustrating the configuration of an end mill 10 according to one embodiment of the present invention. FIGS. 1 and 2 are perspective views illustrating the configuration of the end mill 10 as viewed from the tip 1a side of the main body 1. FIG. 3 is a plan view illustrating the configuration of the end mill 10 as viewed from the tip 1a side of the main body 1. FIG. 4 is a plan view illustrating the configuration of the end mill 10 near the tapered portion 2 as viewed from the side of the main body 1.

[0022] 1 to 4, an end mill 10 (an example of an end mill) in this embodiment is a tapered end mill used for forming tapered grooves, etc. The end mill 10 is attached to a chuck of a cutting device (not shown) at a portion near the rear end 1b of the main body 1, and is rotated about a rotation axis AX in a predetermined rotation direction D to cut a workpiece (an object to be cut).

[0023] The end mill 10 includes a main body 1 (an example of a main body), two grooves 31a and 31b (an example of a groove), two flanks 32a and 32b, two cutting edges (cutting edges) 33a and 33b (an example of a cutting edge), and a tip plane 34. The main body 1 has a rotation axis AX and a tip end 1a and a rear end 1b that extend along the direction of the rotation axis AX. The two grooves 31a and 31b, the two flanks 32a and 32b, and the two cutting edges 33a and 33b are each provided on the outer circumferential surface of the main body 1 in a region that includes the tip end 1a of the main body 1, and extend from the tip end 1a toward the rear end 1b.

[0024] Grooves 31a and 31b are grooves for discharging chips generated from the workpiece during cutting to the outside of end mill 10. Grooves 31a and 31b each have the same shape and are formed spirally about the direction of extension of rotation axis AX. Grooves 31a and 31b are point-symmetric with each other with respect to rotation axis AX. A rake face 311 is provided on the inner peripheral surface of each of grooves 31a and 31b facing downstream in rotation direction D. Rake face 311 is the surface that acts on the workpiece.

[0025] Each of the flanks 32a and 32b is a portion for reducing cutting resistance and preventing wear of the end mill 10. The flank 32a is provided on the upstream side of the groove 31a in the rotation direction D. The flank 32b is provided on the upstream side of the groove 31b in the rotation direction D. Each of the flanks 32a and 32b has the same shape and is formed in a spiral shape centered on the extension direction of the rotation axis AX. Each of the flanks 32a and 32b is a surface that corresponds to the back surface of the portion where each of the cutting edges 33a and 33b comes into contact with the workpiece. Each of the flanks 32a and 32b is recessed toward the inner diameter side relative to each of the cutting edges 33a and 33b.

[0026] Each of the flanks 32a and 32b includes a second flank 321, a third flank 322, a fourth flank 323, a fifth flank 324, and a sixth flank 325. The second flank 321, the third flank 322, the fourth flank 323, the fifth flank 324, and the sixth flank 325 are arranged in this order from the downstream side to the upstream side in the direction of rotation D. The second flank 321, the third flank 322, the fourth flank 323, the fifth flank 324, and the sixth flank 325 are different surfaces and have different clearance angles. The second flank 321, the third flank 322, the fourth flank 323, the fifth flank 324, and the sixth flank 325 are each formed of a flat surface or a concave curved surface.

[0027] Each of the cutting edges 33a and 33b is a portion that mainly cuts the workpiece. The cutting edge 33a extends from the tip plane 34 toward the rear end 1b of the body 1 at the boundary between the groove 31a and the flank 32a. The cutting edge 33b extends from the tip plane 34 toward the rear end 1b of the body 1 at the boundary between the groove 31b and the flank 32b. Each of the cutting edges 33a and 33b has the same shape and is a helical blade formed in a spiral shape centered on the extension direction of the rotation axis AX. Each of the cutting edges 33a and 33b may be a straight blade that extends linearly along the extension direction of the rotation axis AX. Each of the cutting edges 33a and 33b is provided at the outer diameter side end of the rake face 311 of each of the grooves 31a and 31b.

[0028] The tip plane 34 is provided at the tip 1a of the main body 1 and is configured as a plane perpendicular to the rotation axis AX. The tip plane 34 may be formed into a shape other than the above-mentioned plane.

[0029] Fig. 5 is a cross-sectional view taken along line VV in Fig. 4. Fig. 6 is a diagram showing the relationship between the width W1 of the tapered portion 2 and the maximum value WM of the width W1 of the tapered portion 2 in a cross section including the extension direction of the rotation axis AX. Fig. 5 corresponds to a cross-sectional view taken in a direction perpendicular to the extension direction of the rotation axis AX. Fig. 6 shows the width W1 at a certain position along the rotation axis AX.

[0030] 1 to 6, the end mill 10 further includes a tapered portion 2 (one example of a tapered portion). The tapered portion 2 is provided in a region including the tip 1a of the main body 1. At least a portion of each of the two grooves 31a and 31b, the two flanks 32a and 32b, and the two cutting edges 33a and 33b is provided in the tapered portion 2.

[0031] The maximum length of the end mill 10 in a direction passing through the rotation axis AX and perpendicular to the direction of extension of the rotation axis AX is defined as the width W1 of the end mill 10. The tapered portion 2 is a portion in which the width W1 decreases toward the tip 1a of the main body 1 along the direction of extension of the rotation axis AX. Therefore, the width W1 of the tapered portion 2 along the direction of extension of the rotation axis AX reaches a maximum value WM at a position closest to the rear end 1b of the main body 1 along the direction of extension of the rotation axis AX. In this embodiment, the width W1 of the tapered portion 2 corresponds to the distance between the cutting edges 33a and 33b in a direction passing through the rotation axis AX and perpendicular to the direction of extension of the rotation axis AX.

[0032] On the other hand, the portion of the main body 1 other than the tapered portion 2 has a generally cylindrical shape and a constant width W1 along the direction of extension of the rotation axis AX. The width W1 of the portion of the main body 1 other than the tapered portion 2 is equal to the maximum value WM of the width W1 of the tapered portion 2.

[0033] The core thickness W2 is the minimum value of the length of the end mill 10 in a direction passing through the rotation axis AX and perpendicular to the extension direction of the rotation axis AX. The core thickness W2 of the tapered portion 2 of the end mill 10 decreases as it approaches the tip 1a.

[0034] Referring particularly to FIG. 6, the tip angle θ1 of the end mill 10 is between 40 degrees and 70 degrees, and preferably between 40 degrees and 60 degrees. The tip angle θ1 is the angle formed by the outermost peripheral surface of the portion of the tapered portion 2 closest to the tip 1a of the main body 1 when viewed in a cross section including the extension direction of the rotation axis AX. In this embodiment, the outermost peripheral surface of the tapered portion 2 is formed by each of the cutting edges 33a and 33b, and extends linearly. Therefore, the tip angle θ1 corresponds to the angle formed by each of the cutting edges 33a and 33b.

[0035] Referring particularly to FIG. 5, the rake angle θ2 (the angle between the rake face 311 and the line connecting the cutting edge 33a or 33a to the rotation axis AX) near the front end 1a of the main body 1 is preferably negative (the rake face 311 protrudes downstream in the direction of rotation D from the line connecting the cutting edge 33a or 33a to the rotation axis AX, resulting in a negative rake angle θ2), and the absolute value of the rake angle θ2 preferably decreases from the front end 1a toward the rear end 1b of the main body 1. This ensures the strength of the front end 1a of the main body 1 while improving the cutting performance toward the rear end. Alternatively, the rake angle θ2 may change from a negative shape to a positive shape from the front end 1a toward the rear end 1b of the main body 1 (the rake face 311 recesses upstream in the direction of rotation D from the line connecting the cutting edge 33a or 33a to the rotation axis AX, resulting in a positive rake angle θ2).

[0036] [End mill core thickness]

[0037] 6, the position along the extension direction of the rotation axis AX where the ratio of the width W1 of the tapered portion 2 to the maximum width WM of the tapered portion 2 is 10% is defined as the first position P1. The position along the extension direction of the rotation axis AX where the ratio of the width W1 of the tapered portion 2 to the maximum width WM of the tapered portion 2 is 20% is defined as the second position P2. The position along the extension direction of the rotation axis AX where the ratio of the width W1 of the tapered portion 2 to the maximum width WM of the tapered portion 2 is 30% is defined as the third position P3.

[0038] Fig. 7 is a cross-sectional view taken along line VII-VII in Fig. 6, and is a cross-sectional view at a first position P1. Fig. 8 is a cross-sectional view taken along line VIII-VIII in Fig. 6, and is a cross-sectional view at a second position P2. Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 6, and is a cross-sectional view at a third position P3. Each of Figs. 7 to 9 corresponds to a cross-sectional view taken in a direction perpendicular to the extension direction of the rotation axis AX.

[0039] 6 to 9, the ratio of the core thickness W2 at the first position P1 to the maximum width WM of the tapered portion 2 is equal to or greater than 5.14% and is equal to or less than 7.40%.

[0040] Furthermore, the ratio of the core thickness W2 at the second position P2 to the maximum width WM of the tapered portion 2 is preferably 9.75% or more and 14.38% or less, which can prevent damage to the end mill 10 at the second position P2.

[0041] Furthermore, the ratio of the core thickness W2 at the third position P3 to the maximum width WM of the tapered portion 2 is 14.41% or more and 20.93% or less. This makes it possible to prevent damage to the end mill 10 at the third position P3.

[0042] Furthermore, it is preferable that the core thickness W2 of the tapered portion increases from the first position P1 toward the third position P3.

[0043] On the other hand, the ratio of the core thickness W2 to the width W1 of the tapered portion in a cross section including the extension direction of the rotation axis AX (cross section in FIG. 6) is preferably constant or decreases from the first position P1 to the second position P2. It is more preferable that the ratio of the core thickness W2 to the width W1 of the tapered portion is constant or decreases from the first position P1 to the third position P3. As a result, the ratio of the grooves 31a and 31b in the cross section of the tapered portion 2 increases from the first position P1 to the rear end 1b of the main body 1, allowing for efficient removal of chips.

[0044] [Effects of the embodiment]

[0045] According to the above-described embodiment, the ratio of the core thickness W2 at the first position P1 to the maximum width WM of the tapered portion 2 is 5.14% or more, which is large. This improves the mechanical strength of the vicinity of the tip 1a of the body 1. As a result, damage to the tip of the end mill 10 can be suppressed. Meanwhile, the ratio of the core thickness W2 at the first position P1 to the maximum width WM of the tapered portion 2 is 7.40% or less. This ensures a sufficient volume for the grooves 31a and 31b near the tip 1a of the body 1, allowing for efficient removal of chips. As a result, damage to the tip of the end mill 10 due to increased cutting resistance can be suppressed. As a result, damage to the tip of the end mill 10 can be suppressed even when the point angle θ1 of the end mill 10 is set to 70 degrees or less. According to the above-described embodiment, even when the point angle θ1 of the end mill 10 is reduced to 40 degrees, the effect of suppressing damage to the tip of the end mill 10 can be obtained.

[0046] [Example]

[0047] Next, an embodiment of the present invention will be described.

[0048] The inventors of the present application created six types of end mills, Invention Examples A to E and Comparative Example F, in a simulation by setting various parameters for the machining conditions of the end mills, and measured various dimensions of each end mill. The inventors also performed a simulation in which a predetermined load was applied to the tip of the end mill, and evaluated the effect of preventing breakage of the tip of each of the end mills, Invention Examples A to E and Comparative Example F.

[0049] FIG. 10 is a table showing various dimensions and strength of the tip of the end mill for invention examples A to E and comparative example F in one embodiment of the present invention.

[0050] 10, each of Inventive Example A and Comparative Example F was a straight blade, and each of Inventive Examples B to E was a spiral blade. The tip angle θ1 of each of Inventive Examples A to D and Comparative Example F was 60 degrees, and the tip angle θ1 of Inventive Example E was 40 degrees.

[0051] The maximum value WM of the width W1 of the tapered portion 2 of each of invention examples A, C, E, and comparison example F (in other words, the outer diameter of the end mill) was 6 mm, the maximum value WM of the width W1 of the tapered portion 2 of invention example B was 3 mm, and the maximum value WM of the width W1 of the tapered portion 2 of invention example D was 12 mm.

[0052] The ratio (W2 / WM) of the core thickness W2 at the first position P1 to the maximum width W1 WM was 5.14% or more and 7.40% or less for each of Invention Examples A to E. On the other hand, the ratio (W2 / WM) of the core thickness W2 at the first position P1 to the maximum width W1 WM for Comparative Example F was 1.67%.

[0053] The ratio (W2 / WM) of the core thickness W2 at the second position P2 to the maximum value WM of the width W1 was 9.75% or more and 14.38% or less for each of Invention Examples A to E. On the other hand, the ratio (W2 / WM) of the core thickness W2 at the second position P2 to the maximum value WM of the width W1 for Comparative Example F was 1.83%.

[0054] The ratio (W2 / WM) of the core thickness W2 at the third position P3 to the maximum width W1 WM was 14.41% or more and 20.93% for each of Invention Examples A to E. Meanwhile, the ratio (W2 / WM) of the core thickness W2 at the third position P3 to the maximum width W1 WM for Comparative Example F was 4.78%.

[0055] The core thickness ratio based on the maximum width (in other words, the ratio of core thickness W2 to the maximum width WM) (W2 / WM) increased from the first position P1 to the second position P2 in all of invention examples A to E and comparison example F, and also increased from the second position P2 to the third position P3.

[0056] The width-based core thickness ratio (W2 / W1) (in other words, the ratio of core thickness W2 to width W1 at a certain position) decreased from the first position P1 to the second position P2 and also decreased from the second position P2 to the third position P3 in each of Invention Examples A to E. In Comparative Example F, the core thickness ratio decreased from the first position P1 to the second position P2 and increased from the second position P2 to the third position P3.

[0057] In each of invention examples A to E, the tip of the end mill did not break when a load was applied to the tip of the end mill, and breakage of the tip of the end mill was prevented. On the other hand, in comparative example F, the tip of the end mill broke when a load was applied to the tip of the end mill, and breakage of the tip of the end mill was not prevented.

[0058] [others]

[0059] The number and shape of each of the grooves, flanks, and cutting edges are arbitrary, and may be spirally shaped about the rotation axis AX as described above, or may extend linearly along the direction of extension of the rotation axis AX. When there are multiple grooves, flanks, and cutting edges, they may be arranged at equal intervals around the rotation axis AX, or may be arranged at unequal intervals around the rotation axis AX. Each of the multiple grooves, each of the multiple flanks, and each of the multiple cutting edges may have a different shape. The end mill may be provided with a land portion.

[0060] The outermost surface of the tapered portion may be composed of a plurality of outermost surfaces that form a plurality of angles with respect to the rotation axis (i.e., the cutting edge may have multiple stages). In this case, the angle formed by the outermost surface of the tapered portion closest to the tip of the main body 1 among the plurality of outermost surfaces corresponds to the tip angle of the end mill.

[0061] The above-described embodiments and examples should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0062] 1 Main body (example of the main body) 1a Tip of the main body 1b Rear end of the body 2 Tapered section (example of tapered section) 10,1010 End mill (an example of an end mill) 31a, 31b Groove (an example of a groove) 32a, 32b flank 33a, 33b Cutting edge (an example of a cutting edge) 34 Tip plane 311 Rake face 321 Second relief face 322 Third relief face 323 Fourth relief face 324 No. 5 relief face 325 No. 6 relief face 1010 end mill AX Rotation Axis D Rotation direction P1 First position P2 Second position P3 Third position RK Workpiece TG tapered groove W1 Width of tapered part W2 Core thickness WM Maximum value at the tip of the tapered section θ1 Tip angle

Claims

1. a main body having a rotation axis; a tapered portion provided in a region including the tip of the main body, the tapered portion includes a groove and a cutting edge formed on the outer circumferential surface of the body; a width W1 of the tapered portion, which is the maximum value of the length of the tapered portion in a direction passing through the rotation axis and perpendicular to the extension direction of the rotation axis, decreases toward the tip of the main body along the extension direction of the rotation axis; When viewed in a cross section including the extending direction of the rotary shaft, the angle formed by the outermost peripheral surface of the tapered portion closest to the tip of the main body is 40 degrees or more and 70 degrees or less, This end mill has a core thickness W2 at a first position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 10%, and the ratio of the core thickness W2 to the maximum width WM of the tapered portion is 5.14% or more and 7.40% or less.

2. The end mill of claim 1, wherein the ratio of the core thickness W2 at a second position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum value WM of the width of the tapered portion is 20%, to the maximum value WM of the width of the tapered portion is 9.75% or more and 14.38% or less.

3. The end mill of claim 2, wherein the ratio of the core thickness W2 at a third position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 30%, to the maximum width WM of the tapered portion is 14.41% or more and 20.93% or less.

4. 2. The end mill according to claim 1, wherein the core thickness W2 of the tapered portion increases from the first position toward a third position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum width WM of the tapered portion is 30%.

5. 2. The end mill according to claim 1, wherein the ratio of the core thickness W2 to the width W1 of the tapered portion in a cross section including the extension direction of the rotation axis is constant or decreases from a first position to a second position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum value WM of the width of the tapered portion is 20%.

6. 6. The end mill according to claim 5, wherein the ratio of the core thickness W2 to the width W1 of the tapered portion in a cross section including the extension direction of the rotation axis is constant or decreases from the first position to a third position, which is a position along the extension direction of the rotation axis where the ratio of the width W1 of the tapered portion to the maximum value WM of the width of the tapered portion is 30%.

7. 2. The end mill according to claim 1, wherein the angle formed by the outermost peripheral surface of the tapered portion closest to the tip of the body is between 40 degrees and 60 degrees.

Images