End mill

Abstract

To provide an end mill enabling safe cutting even when a radial depth of cut is increased.SOLUTION: An end mill comprises a body extending along a central axis, a plurality of bottom blades located at a tip of the body, and a plurality of outer peripheral blades located on an outer peripheral surface of the body and spirally twisting around the central axis. At least one or more chip breakers which break chips into pieces are provided on each outer peripheral blade. The chip breaker has a rotation locus when rotating the end mill around the central axis, whose shape is a laterally symmetrical recessed shape and a composite R shape in which a plurality of circular arcs different in curvature radius is smoothly connected to each other. The length in the central axis direction of the rotation locus of the chip breakers is 1.5 mm or more and 2.0 mm or less. In the rotation locus of the chip breakers, the curvature radius of a valley part radially recessed inward is 0.6 mm or more and 2.5 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an end mill. [Background technology]

[0002] BACKGROUND ART Conventionally, an end mill is known that has a chip breaker on its peripheral cutting edge that breaks up chips for chip disposal during deep cutting (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2012-518550 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for even higher efficiency in end mills. One method of achieving this is to increase the radial depth of cut (ae). For example, in trochoidal cutting, the radial depth of cut is usually set to a value not exceeding 20% ​​of the tool diameter D (0.2 x D). However, by using an end mill capable of high depth of cut cutting exceeding 0.2 x D, machining efficiency can be significantly improved.

[0005] An object of the present invention is to provide an end mill that is capable of stable cutting even when the radial depth of cut is large. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an end mill that rotates around a central axis, the end mill comprising a body extending along the central axis, a plurality of end cutting edges located at the tip of the body, and a plurality of peripheral cutting edges located on the outer periphery of the body and twisted spirally around the central axis. Each of the peripheral cutting edges is provided with at least one chip breaker that breaks chips. The distance between adjacent chip breakers in one peripheral cutting edge in the axial direction is in the range of Lc+2 [mm] or more and Lc+20 [mm] or less, where Lc [mm] is the length of the chip breaker in the axial direction.The chip breaker has a rotation locus when the end mill is rotated around the central axis, symmetrical about a radial line The chip breaker has a concave shape and a compound R shape formed by smoothly connecting multiple arcs having different radii of curvature. The length of the rotational locus of the chip breaker in the central axis direction is 1.5 mm or more and 2.0 mm or less. The radius of curvature of the valley portion recessed radially inward in the rotational locus of the chip breaker is 0.6 mm or more and 2.5 mm or less.

[0007] With this configuration, the chip breaker that separates the peripheral cutting edge is formed with an appropriate shape and size, so even if the radial depth of cut is increased, the chip breaker can effectively remove chips while minimizing damage to the tool. With an end mill with the above configuration, highly efficient cutting is possible.

[0008] The radius of curvature of a peak portion projecting radially outward in a rotational locus of the chip breaker may be 0.2 mm or more and 0.7 mm or less.

[0009] The depth of the valley in the rotational locus of the chip breaker may be 0.15 mm or more and 0.5 mm or less.

[0010] Each of the peripheral cutting edges is provided with a plurality of chip breakers. , complex The chip breakers are arranged spirally around the central axis on the outer periphery of the body, and the spiral arrangement of the chip breakers extends in the direction opposite to the rotation direction of the end mill as it approaches the tip of the body, and the body may be configured to have two or three spiral arrangements of the chip breakers. [Effects of the Invention]

[0011] According to one aspect of the present invention, an end mill is provided that is capable of stable cutting even when the radial depth of cut is increased. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is a perspective view showing an end mill according to an embodiment. [Figure 2] FIG. 2 is a side view of the end mill according to the embodiment. [Figure 3] FIG. 3 is a view of the end mill according to the embodiment as seen from the tip side. [Figure 4] FIG. 4 is a schematic view showing the rotation locus of the outer peripheral edge and the rotation locus of the chip breaker when the end mill is rotated around the central axis. [Figure 5] FIG. 5 is a view schematically showing a developed view of the entire body of the embodiment. [Figure 6] FIG. 6 is an example of a developed view of a body having three spiral arrays of chip breakers.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] FIG. 1 is a perspective view showing the end mill according to the embodiment. FIG. 2 is a side view of the end mill according to the embodiment. FIG. 3 is a view of the end mill according to the embodiment as seen from the tip side. The end mill 10 of the present embodiment shown in FIG. 1 is substantially cylindrical about the central axis O. In the case of the present embodiment, the end mill 10 is rotated about the central axis O. Therefore, the central axis O is the rotation axis of the end mill 10. In this specification, the direction extending along the central axis O may be referred to as the "axial direction", the direction orthogonal to the central axis O may be referred to as the "radial direction", and the direction around the axis of the central axis O may be referred to as the "circumferential direction".

[0014] The end mill 10 is made of a hard material such as cemented carbide, for example. The end mill 10 has a shank 2 and a body 3. The shank 2 is located on the rear end side (upper side in FIG. 2) of the end mill 10, and the body 3 is located on the tip side (lower side in FIG. 2) of the end mill 10. The shank 2 is cylindrical in the case of the present embodiment. The body 3 extends from the tip of the shank 2 toward the tip side along the central axis O. The body 3 has a plurality of chip discharge grooves 4 and a plurality of outer peripheral relief surfaces 11. An outer peripheral edge 7 is formed at the intersection ridge line portion on the front side in the end mill rotation direction T of the chip discharge groove 4 and the outer peripheral relief surface 11.

[0015] The end mill 10 has a shank 2 held by the spindle of a machine tool and rotated in an end mill rotation direction T around a central axis O. The end mill 10 is fed, for example, in a direction perpendicular to the central axis O, and performs cutting on a workpiece with the cutting edge (peripheral cutting edge 7) of the body 3.

[0016] The chip discharge grooves 4 extend on the outer periphery of the body 3, twisting around the central axis O in the opposite direction to the end mill rotation direction T, from the axial front end to the rear end of the body 3. In this embodiment, five chip discharge grooves 4 are formed on the outer periphery of the body 3 at intervals in the circumferential direction.

[0017] The peripheral cutting edges 7 are formed on the ridgeline at the front side in the rotation direction between the rake face 12, which is the wall surface of the chip discharge groove 4 facing forward in the end mill rotation direction T, and the peripheral flank 11, which is the outer peripheral surface of the body 3 adjacent to the rake face 12. In this embodiment, the body 3 has five peripheral cutting edges 7. The body 3 also has multiple chip breakers 8 that divide the peripheral cutting edges 7 into multiple cutting edges. In this embodiment, the chip breakers 8 consist of notches formed by partially cutting out the peripheral cutting edges 7.

[0018] At the tip of the chip discharge groove 4, a concave groove-shaped gash 5 is formed along the wall surface facing forward in the end mill rotation direction T of the chip discharge groove 4. At the tip edge of the wall surface of each gash 5 facing the end mill rotation direction T, a plurality of bottom cutting edges 6, each with the wall surface as a rake face, extend inward from the tip of the peripheral cutting edge 7.

[0019] The end mill 10 of this embodiment is a square end mill in which the bottom cutting edges 6 and the peripheral cutting edges 7 intersect at a predetermined angle at the outer peripheral end of the body 3. The end mill 10 of this embodiment can also be configured as a radius end mill or a ball end mill. The end mill 10 of this embodiment is an unequal-split end mill in which the division angles of the five bottom cutting edges 6 are not equal. The end mill 10 of this embodiment may also be an equal-split end mill.

[0020] As shown in FIG. 3, the five end cutting edges 6 are composed of one long end cutting edge 6a and five short end cutting edges 6b. The long end cutting edge 6a is a cutting edge that is longer than the other four short end cutting edges 6b. The long end cutting edge 6a extends radially from the outer circumferential edge of the tip flank face of the end mill 10 to near the central axis O. The other short end cutting edges 6b extend from the outer circumferential edge of the tip flank face of the end mill 10 to a position that is spaced further from the central axis O than the long end cutting edge 6a. On the tip flank face of the end mill 10, multiple gashes 5 are connected to each other through a region that is inside the inner circumferential edge of the short end cutting edges 6b.

[0021] In this embodiment, each peripheral cutting edge 7 extends spirally from the leading edge to the trailing edge in the axial direction at a constant twist angle. In this embodiment, the twist angles of all five peripheral cutting edges 7 are equal to each other. An end mill with an unequal lead, in which the twist angles of multiple peripheral cutting edges 7 are different for each cutting edge, may also be used.

[0022] The chip breaker 8 is a notch that discontinuities the peripheral cutting edge 7. The chip breaker 8 cuts the peripheral flank 11 circumferentially and crosses it to connect two circumferentially adjacent chip discharge flutes 4. The chip breaker 8 is a groove that is recessed radially inward from the peripheral flank 11 and extends circumferentially. In other words, the chip breaker 8 is a groove that connects two circumferentially adjacent chip discharge flutes 4 circumferentially. The end of the chip breaker 8 on the side of the end mill rotation direction T opens onto the rake face 12 of the peripheral cutting edge 7. The end of the chip breaker 8 on the rear side of the end mill rotation direction T opens onto the wall of the chip discharge flute 4 located on the rear side of the peripheral flank 11 in the end mill rotation direction T. Each chip breaker 8 extends approximately parallel to the end mill rotation direction T. When the end mill 10 is rotated around the central axis O, each chip breaker 8 has the same rotational trajectory.

[0023] FIG. 4 is a schematic diagram showing a rotational trajectory 70 of the peripheral cutting edge 7 and a rotational trajectory 80 of the chip breaker 8 when the end mill 10 is rotated around the central axis O. 4, the rotation locus 70 of the peripheral cutting edge 7 is a straight line extending along the central axis O. When the end mill 10 of the chip breaker 8 is rotated around the central axis O, the rotation locus 80 is a bilaterally symmetrical concave shape and a compound R shape formed by smoothly connecting multiple arcs having different radii of curvature. That is, the rotation locus 80 of the chip breaker 8 is made up of two peaks 81a, 81b located at both ends of the chip breaker 8 in the axial direction, and a valley 82 sandwiched between the two peaks 81a, 81b.

[0024] The peaks 81a and 81b are portions that protrude radially outward from the rotation trajectory 80 of the chip breaker 8. In this embodiment, the peaks 81a and 81b are arc-shaped with the same radius of curvature R1. At both axial ends of the chip breaker 8, the peaks 81a and 81b smoothly connect to the rotation trajectory 70 of the peripheral cutting edge 7.

[0025] The valley portion 82 is a portion that is recessed radially inward in the rotation trajectory 80 of the chip breaker 8. The valley portion 82 is arc-shaped with a radius of curvature R2. An end on one axial side (the left side in the figure) of the valley portion 82 is smoothly connected to one end (the end on the right side in the figure) of the peak portion 81a. An end on the other axial side (the right side in the figure) of the valley portion 82 is smoothly connected to one end (the end on the left side in the figure) of the peak portion 81b.

[0026] In this embodiment, the length Lc in the axial direction of the rotational locus 80 of the chip breaker 8 is 1.5 mm or more and 2.0 mm or less. If the length Lc in the axial direction is less than 1.5 mm, the chip breaker 8 will not be able to break the chips sufficiently. Chip clogging will be more likely to occur, making the tool more susceptible to breakage. If the length Lc in the axial direction exceeds 2.0 mm, the cutting edge that acts in machining will become shorter, the load on the peripheral cutting edge 7 will increase, and sufficient tool life will not be achieved.

[0027] In this embodiment, the radius of curvature R2 of the valleys 82 recessed radially inward along the rotation trajectory 80 of the chip breaker 8 is 0.6 mm or more and 2.5 mm or less. If the radius of curvature R2 of the valleys 82 is less than 0.6 mm, the stress acting on the valleys 82 during cutting becomes excessively large, making tool breakage likely to occur starting from the chip breaker 8. If the radius of curvature R2 of the valleys 82 exceeds 2.5 mm, the recessed shape of the chip breaker 8 becomes a gently sloping, horizontally elongated shape. Therefore, if the depth of the chip breaker 8 is set large enough to adequately break chips, the length Lc of the chip breaker 8 in the central axial direction becomes large. This shortens the cutting edge that is effective in machining, increasing the load on the peripheral cutting edge 7 and preventing sufficient tool life.

[0028] The radius of curvature R1 of the peaks 81a, 81b that protrude radially outward in the rotation trajectory 80 of the chip breaker 8 is preferably 0.2 mm or more and 0.7 mm or less. By setting the radius of curvature R1 of the peaks 81a, 81b within the above range, it becomes easier to obtain an end mill 10 that can perform stable cutting even when the radial depth of cut is large.

[0029] In this embodiment, the depth d of the valleys 82 in the rotational trajectory 80 of the chip breaker 8 is preferably 0.15 mm or more and 0.5 mm or less. The depth d of the valleys 82 is the radial length from the rotational trajectory 70 of the peripheral cutting edge 7 to the bottom of the valleys 82, as shown in Fig. 4. By setting the depth d of the valleys 82 within the above range, it becomes easier to obtain an end mill 10 that can perform stable cutting even when the radial depth of cut is large.

[0030] In the end mill 10 of this embodiment, the chip breaker 8 is configured such that when the end mill 10 is rotated around its central axis, the rotation locus 80 has a bilaterally symmetrical concave shape and a compound R shape formed by smoothly connecting multiple arcs having different radii of curvature, the length of the rotation locus 80 of the chip breaker 8 in the central axis direction is 1.5 mm to 2.0 mm, and the radius of curvature of the valley portion of the rotation locus 80 of the chip breaker 8 that is concave radially inward is 0.6 mm to 2.5 mm. This enables good chip disposal by the chip breaker 8 while suppressing damage to the tool, even when the radial depth of cut is large. The end mill 10 of this embodiment enables highly efficient cutting.

[0031] Next, Figure 5 is a schematic development view of the entire body 3 of this embodiment. In Figure 5, all peripheral cutting edges 7 (peripheral flanks 11) are shown as a single straight line to make the arrangement of the peripheral cutting edges 7 and chip breakers 8 easier to see. The lower side of Figure 5 is the front end side of the body 3, and the upper side of Figure 5 is the rear end side (shank side) of the body 3. In this embodiment, the body 3 has five peripheral cutting edges 7, and each peripheral cutting edge 7 is provided with two or three chip breakers 8.

[0032] In this embodiment, the body 3 has thirteen chip breakers 8. Two peripheral cutting edges 7 each have two chip breakers 8, and three peripheral cutting edges 7 each have three chip breakers 8. Furthermore, as shown in FIG. 5, the chip breakers 8 are arranged in a spiral around the central axis on the outer periphery of the body 3. The spiral arrangement of the chip breakers 8 extends in the direction opposite to the end mill rotation direction T as it approaches the tip of the body 3. In other words, while the peripheral cutting edges 7 are in a right-twist spiral, the arrangement of the chip breakers 8 is in a left-twist spiral.

[0033] By arranging the chip breakers 8 in a left-twist spiral, when the end mill 10 rotates forward (right), the position of the chip breaker 8 that comes into contact with the workpiece gradually moves toward the tip of the body 3, so the cutting resistance of the cutting edge at the tip of the body 3 gradually decreases as the end mill 10 rotates. This makes it less likely for the body 3 to bend during cutting, resulting in an end mill 10 that allows for stable cutting.

[0034] In this embodiment, the body 3 has two spiral arrangements of chip breakers 8. The body 3 in this embodiment is provided with spiral arrangements A1 and A2 of chip breakers 8. The arrangement direction of the chip breakers 8 is along a line connecting the chip breakers that are closest to each other in the circumferential direction. Alternatively, as shown in FIG. 6, the body 3 may have three spiral arrangements of chip breakers 8, A1, A2, and A3.

[0035] When the spiral arrangement of the chip breakers 8 is single-thread, the cutting edges separated by the chip breakers 8 become longer, resulting in longer chips. If the spacing P between the chip breakers 8 of one peripheral cutting edge 7 is reduced to shorten the chips, the chip breakers 8 of circumferentially adjacent peripheral cutting edges 7 tend to overlap in the axial direction. When the chip breakers 8 of circumferentially adjacent peripheral cutting edges 7 overlap in the axial direction, the thickness of the chip cut by the cutting edge next to the two edges where the chip breakers 8 overlap increases. When the chip thickness increases, the load on the cutting edge increases, making chipping and abnormal damage more likely to occur. Furthermore, if the spiral arrangement of the chip breakers 8 is four or more, the number of chip breakers 8 in the body 3 becomes too large, and the cutting edge acting in the cutting process becomes too short, which increases the load on the cutting edge and leads to a shortened tool life.

[0036] In other words, by having two or three spiral rows of the chip breaker 8, chips of appropriate thickness and length can be produced, the load on the peripheral cutting edge 7 during cutting is not excessive, and the tool life is less likely to be reduced.

[0037] In this embodiment, the distance P between adjacent chip breakers 8 in the axial direction on each peripheral cutting edge 7 is approximately constant throughout the body 3. Specifically, the distance P in the axial direction (in the direction of the central axis) between adjacent chip breakers 8 on one peripheral cutting edge 7 is in the range of Lc+2 [mm] or more and Lc+20 [mm] or less, where Lc [mm] is the length in the direction of the central axis of the chip breaker 8. In this embodiment, the length Lc of the chip breaker 8 in the direction of the central axis is 1.5 mm or more and 2.0 mm or less, so the lower limit of the distance P is in the range of 3.5 mm or more and 4 mm or less, and the upper limit of the distance P is in the range of 21.5 mm or more and 22 mm or less.

[0038] If the spacing P between the chip breakers 8 is below the above-mentioned lower limit, the cutting edges separated by the chip breakers 8 become excessively short, increasing the load on the cutting edges and making chipping or abnormal damage more likely to occur. If the spacing P between the chip breakers 8 exceeds the above-mentioned upper limit, the chips become long and chip disposal becomes difficult.

[0039] In this embodiment, the spacing P between the chip breakers 8 is approximately constant throughout the body 3, but this is not limited to this configuration. For example, if the end mill 10 is an end mill with unequal divisions or unequal leads, the circumferential spacing between the peripheral cutting edges 7 will not be constant. In this case, it is advisable to adjust the spacing P between the chip breakers 8 on each peripheral cutting edge 7 so that the multiple chip breakers 8 are arranged in a left-twisted spiral.

[0040] In this embodiment, the chip breaker 8 is configured as a recessed groove that extends across the outer circumferential flank 11 in the circumferential direction, but the chip breaker 8 can be modified in various ways as long as the rotation trajectory shape shown in Fig. 4 is obtained. For example, the chip breaker 8 may not cross the entire outer circumferential flank 11, and the rear end of the chip breaker 8 may be located on the outer circumferential flank 11.

[0041] According to the above embodiment, the following aspects can also be understood. (1) An end mill that rotates around a central axis, The cutting tool comprises a body extending along a central axis, a plurality of end cutting edges located at the tip of the body, and a plurality of peripheral cutting edges located on the outer circumferential surface of the body and twisted spirally around the central axis, Each of the peripheral cutting edges is provided with a plurality of chip breakers that break chips, the distance between adjacent chip breakers in one peripheral cutting edge in the central axis direction is in the range of Lc+2 [mm] or more and Lc+20 [mm] or less, where Lc [mm] is the length of the chip breaker in the central axis direction; The plurality of chip breakers are arranged in a spiral shape around a central axis on the outer periphery of the body, The spiral arrangement of the chip breakers extends in a direction opposite to the rotation direction of the end mill toward the tip of the body, The body has two or three spiral arrangements of the chip breakers. End mill.

[0042] According to the above aspect, it is possible to prevent the body from tipping during machining, enabling stable cutting, and also to prevent shortening of the tool life due to wear through good chip disposal. [Example]

[0043] The present invention will be described in more detail below with reference to examples.

[0044] (First Example) The inventors have verified the effectiveness of the chip breaker of the above embodiment through cutting tests using a number of end mills.

[0045] In this example, 24 end mill samples were produced, two for each of 12 conditions in which the length and depth of the chip breaker were varied. The basic structure of each end mill sample was the same as the square end mill shown in Figures 1 to 4. The tool diameter D of the end mill was 12 mm. The pitch of the chip breaker in the central axis direction was a fixed 12 mm. The chip breaker was arranged in a two-thread left-handed spiral pattern.

[0046] Cutting tests were performed using trochoidal cutting with each end mill manufactured. Specifically, trochoidal cutting was performed multiple times while increasing the radial depth of cut ae by 0.6 mm, and the maximum depth of cut ae at which stable cutting was possible was evaluated. The maximum depth of cut ae for each end mill is listed as the "feed limit" in Table 2. "N1" and "N2" in Table 2 correspond to the first and second samples, respectively, under the same conditions.

[0047] [Table 1]

[0048] [Table 2]

[0049] As shown in Table 2, the end mills Nos. 1 to 6, in which the length of the chip breaker's rotation path in the central axis direction was 1.5 mm to 2.0 mm and the radius of curvature of the valley portion recessed radially inward in the chip breaker's rotation path was 0.6 mm to 2.5 mm, had feed limits N1 and N2 of 3 mm or more. Normally, the feed limit in trochoidal machining is 20% or less of the tool diameter D, and in this example, it was 2.4 mm (12 mm x 0.2) or less. With the end mills Nos. 1 to 6, trochoidal machining could be performed with a larger radial depth of cut than conventional methods, enabling highly efficient machining. Furthermore, the most efficient machining was possible with the No. 1 and No. 2 end mills, which had a curvature radius of the root of the chip breaker of 1 mm or more and 1.5 mm or less.

[0050] On the other hand, for end mills Nos. 7 to 12, where the length of the chip breaker's rotational trajectory in the central axis direction is outside the range of 1.5 mm or more and 2.0 mm or the radius of curvature of the valley portion of the chip breaker's rotational trajectory that is recessed radially inward is outside the range of 0.6 mm or more and 2.5 mm or less, at least one of the feed limits N1 and N2 is 2.4 mm or less, and trochoidal machining could only be performed with the same radial depth of cut as before.

[0051] (Second Example) In this example, three end mill samples A, B, and C were produced, each with a different number of grooves on the chip breaker. The basic configuration of each end mill sample is the same as the square end mill shown in Figures 1 to 4. The tool diameter D of the end mill was 12 mm. The pitch of the chip breaker in the central axis direction was a fixed pitch of 12 mm. The chip breaker had one to three grooves arranged in a left-handed spiral pattern.

[0052] Cutting tests were carried out by groove machining using each end mill manufactured. Groove machining is more prone to chip clogging than trochoidal machining. A groove 24 mm deep and 150 mm long was machined into the workpiece with a radial depth of cut ae of 12 mm. Qualitative evaluations were made of the amount of chip jamming during machining, the volume of machining noise, and the wall surface properties of the machined groove.

[0053] [Table 3]

[0054] [Table 4]

[0055] When machining using the end mill of sample A, which has a single-thread chip breaker, more chip jamming occurred than when machining using the end mill of sample B, which has a two-thread chip breaker, or the end mill of sample C, which has a three-thread chip breaker.The end mill of sample A also produced the loudest machining noise.

[0056] In this example, the wall surface of the workpiece located on the right side of the tool travel direction is the down-cut surface, while the wall surface of the workpiece located on the left side of the tool travel direction is the up-cut surface. All end mills, Samples A to C, produced good down-cut surfaces. On the other hand, there were differences in the quality of the up-cut surfaces between Samples A to C. As shown in Table 4, the end mill, Sample A, which has a single-thread chip breaker, produced numerous scratches on the machined surface due to chip intrusion. In contrast, the end mill, Sample B, which has a two-thread chip breaker, and the end mill, Sample C, which has a three-thread chip breaker, produced significantly fewer scratches on the machined surface due to chip intrusion. It was confirmed that using a two- or three-thread chip breaker effectively suppresses chip intrusion and results in good machined surface quality. [Explanation of symbols]

[0057] 2...Shank 3. Body 4...Chip discharge groove 5...Gash 6…Bottom blade 6a…Long bottom blade 6b…Short bottom blade 7…Peripheral blade 8...Chip breaker 10...End mill 11...Outer flank 12...Scooping surface 70,80...Rotation trajectory 81a, 81b...Yamabe 82... Valley A1, A2, A3...spiral arrangement D…Tool diameter d...depth Lc: length along the central axis O…Central axis P: Distance between chip breakers in the axial direction R1,R2…curvature radius T...End mill rotation direction

Claims

1. An end mill that rotates around a central axis, The cutting tool comprises a body extending along a central axis, a plurality of end cutting edges located at the tip of the body, and a plurality of peripheral cutting edges located on the outer circumferential surface of the body and twisted spirally around the central axis, Each of the peripheral cutting edges is provided with at least one chip breaker that breaks chips, a distance between adjacent chip breakers in one peripheral cutting edge in the central axis direction is in the range of Lc+2 [mm] or more and Lc+20 [mm] or less, where Lc [mm] is the length of the chip breaker in the central axis direction; the chip breaker has a rotation locus when the end mill is rotated around a central axis that is a concave shape symmetrical with respect to a radial line and has a compound R shape in which a plurality of arcs having different radii of curvature are smoothly connected, The length of the rotation locus of the chip breaker in the central axial direction is 1.5 mm or more and 2.0 mm or less, a radius of curvature of a valley portion recessed radially inward in a rotation locus of the chip breaker is 0.6 mm or more and 2.5 mm or less; End mill.

2. The radius of curvature of the ridge portion protruding radially outward in the rotation trajectory of the chip breaker is 0.2 mm or more and 0.7 mm or less. The end mill according to claim 1 .

3. The depth of the valley in the rotation trajectory of the chip breaker is 0.15 mm or more and 0.5 mm or less. The end mill according to claim 1 or 2.

4. Each of the peripheral cutting edges is provided with a plurality of the chip breakers, The plurality of chip breakers are arranged in a spiral shape around a central axis on the outer periphery of the body, The spiral arrangement of the chip breakers extends in a direction opposite to the rotation direction of the end mill toward the tip of the body, The body has two or three spiral arrangements of the chip breakers. The end mill according to any one of claims 1 to 3.

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