End mill

Abstract

To provide an end mill excellent in chip discharging performance and vibration damping properties.SOLUTION: An end mill comprises a body extending along a central axis, a plurality of bottom blades, and a plurality of outer peripheral blades. The plurality of bottom blades is arranged at dividing angles different from each other. An angle difference of the respective dividing angles is 0.5° or more. A maximum value of the angle difference is an angle of 90° / N or less relative to the number N of bottom blades. The dividing angle of a long bottom blade with the longest edge length is the largest among the dividing angles of the bottom blades. An outer peripheral flank of an outer peripheral blade has a first flank adjacent to the outer peripheral blade and a second flank adjacent backward in an end mill rotational direction of the first flank. The clearance angle of the first flank is 2° or more and 4° or less. The clearance width of the first flank is 0.04 mm or more and 0.2 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, in end mills equipped with multiple end cutting edges and multiple peripheral cutting edges, a configuration has been known in which the peripheral cutting edges are arranged at unequal dividing angles to suppress chatter vibration, as disclosed in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-091306 Summary of the Invention [Problem to be solved by the invention]

[0004] When an end mill is divided into unequal parts, the width of the chip discharge flute and gash varies depending on the division angle, which can affect chip discharge performance. In particular, on the end cutting edge, the gash can become too narrow, reducing chip discharge performance. [Means for solving the problem]

[0005] 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 in a spiral shape around the central axis. The plurality of end cutting edges are arranged at different parting angles. The division angle is the angle between a straight line radially connecting the outer peripheral end of the bottom cutting edge to the central axis and a straight line radially connecting the outer peripheral end of another bottom cutting edge adjacent to the bottom cutting edge forward in the end mill rotation direction T to the central axis.The angular difference between each of the division angles is 0.5° or more. The maximum value of the angle difference is an angle of 90° / N or less, where N is the number of teeth of the end cutting edge. The division angle of the long bottom cutting edge having the longest cutting edge length among the plurality of end cutting edges is the largest among the division angles of the end cutting edges. The peripheral flank of the peripheral cutting edge has a first flank adjacent to the peripheral cutting edge and a second flank adjacent to the rear of the first flank in the end mill rotation direction. The flank angle of the first flank is 2° or more and 4° or less. The flank width of the first flank is 0.04 mm or more and 0.2 mm or less.

[0006] According to the above configuration, by setting the difference in the division angles of the multiple cutting edges to a range of 0.5° or more and 90° / N or less, vibration damping performance due to unequal division can be further improved. Furthermore, by forming the outer circumferential flank into a two-stage flank and providing a first flank with a clearance angle of 2° to 4° and a clearance width of 0.04 mm to 0.2 mm, vibration damping performance can be further improved by the damping effect. Furthermore, by setting the division angle of the long bottom cutting edge to the largest among the division angles of the multiple end cutting edges, chip discharge performance from the long bottom cutting edge, which discharges a large amount of chips, can be improved. As described above, according to the above aspect, an end mill having excellent chip discharge properties and vibration damping properties can be obtained.

[0007] The angle difference between the division angles of the plurality of end cutting edges may be 1° or more, or 2° or more.The angle difference between the division angles of the plurality of end cutting edges may be 80° / N or less. The clearance angle of the first flank may be 2.5° or more, or 3.5° or less. The clearance width of the first flank may be 0.07 mm or more, or 0.15 mm or less.

[0008] The helix angles of all the peripheral cutting edges are equal to each other, The dividing angle of the peripheral cutting edge may be configured to differ depending on the cutting length of the end cutting edge connected to the peripheral cutting edge.

[0009] The multiple bottom blades may include a first short bottom blade located immediately behind the long bottom blade in the end mill rotation direction, and a first chamfer surface facing radially inward may be provided at the radially inner end of the first short bottom blade.

[0010] The end mill may be configured to have five or more bottom blades and peripheral blades, and the multiple bottom blades may include a second short bottom blade located immediately after the first short bottom blade in the direction of end mill rotation, and a second chamfer surface facing radially inward may be provided at the radially inner end of the second short bottom blade.

[0011] A groove is formed on the tip surface of the end mill on which the multiple bottom blades are arranged, and the multiple bottom blades have a third short bottom blade whose angular difference around the central axis relative to the long bottom blade is 165° or more and 195° or less, and when the tip surface of the end mill is viewed in the central axis direction, the angle between the direction in which the groove extends and the direction in which the third short bottom blade extends is 5° or less.

[0012] The plurality of end cutting edges include a first short cutting edge positioned immediately behind the long cutting edge in the end mill rotation direction, and a plurality of gashes are provided on the tip surface of the end mill on which the plurality of end cutting edges are arranged, and a first short cutting edge is provided adjacent to the front side of the first short cutting edge in the end mill rotation direction. A ridge line portion where the gash and the flank of the long bottom cutting edge intersect An arc-shaped R-shaped portion is formed when viewed from the central axis direction, and the radius of curvature of the R-shaped portion is 0.04 × D or more and 0.15 × D or less where D is the tool diameter, and in a plane defined by the valley line of the deepest part of the gash and the central axis, the inclination angle of the valley line of the deepest part of the gash with respect to a reference line that is a straight line perpendicular to the central axis is defined as a gash notch angle of the plurality of gashes, the gash notch angle of the plurality of gashes is 20° or more and 45° or less, and the gash rake angle of the plurality of gashes is 0° or more and 10° or less.

[0013] The radius of curvature of the R-shaped portion may be 0.06×D or more, or 0.08×D or more, where D is the tool diameter. The radius of curvature of the R-shaped portion may be 0.13×D or less, or 0.11×D or less, where D is the tool diameter. The gash notch angle may be 25° or more, or 30° or more. The gash notch angle may be 40° or less, or 35° or less. The gash rake angle may be set to 2° or more, or 4° or more. The gash rake angle may be set to 8° or less, or 6° or less. [Effects of the Invention]

[0014] According to one aspect of the present invention, an end mill having excellent chip removal properties and vibration damping properties is provided. [Brief explanation of the drawings]

[0015] [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 of the embodiment as seen from the tip side. [Figure 4] FIG. 4 is an enlarged cross-sectional view perpendicular to the central axis showing the periphery of the peripheral cutting edge of the end mill according to the embodiment. [Figure 5] FIG. 5 is an enlarged view of the center portion of the tip face of the end mill of FIG. [Figure 6] FIG. 6 is a side view of the periphery of the bottom cutting edge, shown for explaining the gash notch angle. [Figure 7] FIG. 7 is a side view of the periphery of the bottom cutting edge shown for explaining the gash rake angle. DETAILED DESCRIPTION OF THE INVENTION

[0016] Fig. 1 is a perspective view showing an end mill of an embodiment, Fig. 2 is a side view of the end mill of an embodiment, and Fig. 3 is a view of the end mill of an embodiment as seen from the tip side. The end mill 10 of this embodiment shown in FIG. 1 has a substantially cylindrical shape centered on a central axis O. In this embodiment, the end mill 10 rotates about the central axis O. Therefore, the central axis O is the axis of rotation 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 perpendicular to the central axis O as the "radial direction," and the direction around the central axis O as the "circumferential direction."

[0017] The end mill 10 is made of a hard material such as cemented carbide. The end mill 10 has a shank 2 and a body 3. The shank 2 is located at the rear end of the end mill 10 (upper side in FIG. 2), and the body 3 is located at the tip end of the end mill 10 (lower side in FIG. 2). In this embodiment, the shank 2 is cylindrical. The body 3 extends from the tip of the shank 2 toward the tip end along the central axis O. The body 3 has multiple chip discharge flutes 4 and multiple outer peripheral flanks 11. A peripheral cutting edge 7 is formed at the intersection ridgeline between the chip discharge flutes 4 and the outer peripheral flanks 11 on the forward side in the end mill rotation direction T.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] At the tip of the chip discharge groove 4, a concave groove-shaped gash 5 is formed along the wall surface of the chip discharge groove 4 facing forward in the end mill rotation direction T. 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 surface, extend from the tip of the peripheral cutting edge 7 toward the inner periphery (radially inward).

[0022] The end mill 10 of this embodiment is a square end mill in which the bottom cutting edge 6 and the peripheral cutting edge 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 division end mill in which the division angles of the five bottom cutting edges 6 are not equal. In this embodiment, each peripheral cutting edge 7 extends spirally from the axial tip to the rear end at a constant twist angle. In this embodiment, the twist angles of all five peripheral cutting edges 7 are equal to each other.

[0023] 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. The end mill 10 of this embodiment may also be configured without the chip breaker 8.

[0024] As shown in FIG. 3, the five bottom cutting edges 6 are composed of one long bottom cutting edge 60 and a first short bottom cutting edge 61, a second short bottom cutting edge 62, a third short bottom cutting edge 63, and a fourth short bottom cutting edge 64. The long bottom cutting edge 60 is a cutting edge that is longer than the other four first short bottom cutting edges 61 to 64. The long bottom cutting edge 60 extends radially from the outer circumferential edge of the end mill tip surface 10A to a position that reaches the central axis O. The other four first short bottom cutting edges 61 to 64 also extend radially inward from the outer circumferential edge of the end mill tip surface 10A, similar to the long bottom cutting edge 60. The radially inner ends of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 do not reach the central axis O. In the end mill tip surface 10A, the region inside the radially inner ends of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 forms a chip discharge groove in which multiple gashes 5 and recessed grooves 50 are connected in the circumferential direction.

[0025] In this embodiment, the division angle (cutting distance) of a certain bottom cutting edge 6 means the angle between a straight line radially connecting the outer peripheral end of that bottom cutting edge 6 to the center axis O and a straight line radially connecting the outer peripheral end of another bottom cutting edge 6 adjacent to that bottom cutting edge 6 forward in the end mill rotation direction T to the center axis O.

[0026] In FIG. 3, the division angle θ of the long bottom cutting edge 60 is a central angle formed by two radii connecting the outer peripheral edge of the fourth short bottom cutting edge 64 and the outer peripheral edge of the long bottom cutting edge 60 with the central axis O. The division angle θ1 of the first short bottom cutting edge 61 is a central angle formed by two radii connecting the outer circumferential edge of the long bottom cutting edge 60 and the outer circumferential edge of the first short bottom cutting edge 61 with the central axis O. The division angle θ2 of the second short bottom cutting edge 62 is a central angle formed by two radii connecting the outer circumferential ends of the first short bottom cutting edge 61 and the second short bottom cutting edge 62 with the central axis O. The division angle θ3 of the third short bottom cutting edge 63 is a central angle formed by two radii connecting the outer circumferential ends of the second short bottom cutting edge 62 and the third short bottom cutting edge 63 with the central axis O. The division angle θ4 of the fourth short bottom cutting edge 64 is a central angle formed by two radii connecting the outer circumferential ends of the third short bottom cutting edge 63 and the fourth short bottom cutting edge 64 with the central axis O.

[0027] 3, in this embodiment, the division angles θ, θ1 to θ4 of all the bottom cutting edges 6 arranged on the end mill tip face 10A are different from each other. This allows the division angle of the peripheral cutting edge 7 connected to the bottom cutting edge 6 to be different from the division angles of the other peripheral cutting edges 7, thereby suppressing the occurrence of chatter vibrations.

[0028] Furthermore, in this embodiment, the division angle θ of the long bottom cutting edge 60 is the largest division angle among the bottom cutting edges 6. In other words, the division angle θ is larger than the other division angles θ1 to θ4. The long bottom cutting edge 60, which has a long cutting edge length, generates more chips than the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64. By making the division angle θ of the long bottom cutting edge 60 the largest division angle among the bottom cutting edges 6, chip clogging on the end mill tip surface 10A can be suppressed. Tool breakage or chipping caused by chip clogging can be suppressed.

[0029] In this embodiment, the division angle θ of the long bottom cutting edge 60 and the division angles θ1 to θ4 of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 increase in the order θ2<θ3<θ1<θ4<θ. More specifically, θ: 80°, θ1: 72°, θ2: 64°, θ3: 68°, and θ5: 76°. The angle difference between the division angles of the bottom cutting edges 6 is in the range of 2° to 16°.

[0030] The angle difference between the division angles of the bottom cutting edge 6 is at least 0.5° or more. By making the angle difference 0.5° or more, it is possible to obtain a vibration-damping effect due to unequal division. The angle difference between the division angles of the bottom cutting edge 6 is preferably 1° or more, and more preferably 2° or more. By increasing the angle difference between the division angles of the bottom cutting edge 6, a higher vibration-damping effect can be obtained.

[0031] On the other hand, if the difference in angle between the division angles of the end cutting edges 6 is too large, the end cutting edges 6 will have extremely small division angles. A bottom cutting edge 6 with a division angle that is too small is prone to chip clogging, which may lead to early tool breakage. Therefore, the difference in angle between the division angles of the end cutting edges 6 is set to 90° / N or less, where N is the number of teeth of the bottom cutting edges 6. In this embodiment, since N=5, the difference in angle between the division angles of the end cutting edges 6 is 18° or less. Furthermore, by setting the difference in angle to 16° or less, i.e., 80° / N or less, it becomes easier to ensure that all end cutting edges 6 have division angles of an appropriate size. This further reduces chip clogging.

[0032] In this embodiment, the cutting lengths of the four first short bottom cutting edges 61 to 64 are approximately the same. In this embodiment, the cutting lengths of the first short bottom cutting edges 61 to 64 are approximately 50 to 60% of the radius of the end mill tip surface 10A, and grooves of sufficient size are formed on the inner peripheral sides of the first short bottom cutting edges 61 to 64, thereby achieving good chip discharge performance.

[0033] In this embodiment, the division angle θ of the long bottom cutting edge 60 and the division angles θ1 to θ4 of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 may be set to lengths corresponding to the blade lengths of the long bottom cutting edge 60 and the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64. That is, the division angle of the bottom cutting edge 6 may be increased as the cutting edge length of the bottom cutting edge 6 increases. Since the amount of chips generated from the bottom cutting edge 6 increases with increasing cutting edge length, increasing the division angle of the bottom cutting edge 6 with a longer cutting edge length facilitates good chip discharge performance for all bottom cutting edges 6. For example, if the cutting edges of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 are relatively long, the space on the inner periphery of the first short bottom cutting edge 61 to the fourth short bottom cutting edge 64 becomes narrow, making chip clogging more likely to occur. However, by increasing the division angle according to cutting edge length, chip clogging can be more easily suppressed.

[0034] FIG. 4 is an enlarged cross-sectional view perpendicular to the central axis O showing the periphery of the peripheral cutting edge 7 of the end mill 10 of this embodiment. As shown in Figure 4, the peripheral flank 11 forming the peripheral cutting edge 7 has a first flank 11a adjacent to the peripheral cutting edge 7 and a second flank 11b adjacent to the first flank 11a on the rear side in the end mill rotation direction T. The first flank 11a is formed with a first clearance angle α1. The second flank 11b is formed with a second clearance angle α2.

[0035] In this embodiment, the first clearance angle α1 of the first clearance face 11a is equal to or greater than 2° and equal to or less than 4°. The first clearance angle α1 is the angle between a tangent to the first clearance face 11a at the position of the peripheral cutting edge 7 and a reference line C1 shown in FIG. 4. The reference line C1 is a line that is perpendicular to a line that passes through the central axis O and the peripheral cutting edge 7 and passes through the peripheral cutting edge 7. The clearance width 31a of the first clearance face 11a is equal to or greater than 0.04 mm and equal to or less than 0.2 mm.

[0036] By setting both the first clearance angle α1 and clearance width 31a of the first clearance face 11a within the above ranges, vibration-damping properties can be improved by the damping effect during machining. That is, by setting the first clearance angle α1 to a small value, the first clearance face 11a can be more easily brought into contact with the workpiece surface during machining, and chatter vibrations can be suppressed by contact with the workpiece. Furthermore, by reducing the clearance width 31a, vibration-damping effects can be obtained while suppressing flank wear. In this embodiment, the first clearance angle α1 may be 2.5° or more. The first clearance angle α1 may be 3.5° or less. Furthermore, the clearance width 31a may be 0.07 mm or more. The clearance width 31a may be 0.15 mm or less.

[0037] The second clearance angle α2 of the second clearance surface 11b is the angle between the reference line C1 and a tangent to the second clearance surface 11b at the boundary position 11c between the first clearance surface 11a and the second clearance surface 11b. The second clearance angle α2 is larger than the first clearance angle α1. The second clearance angle α2 is, for example, 10° or greater and 16° or less. The second clearance angle α2 may be 12° or greater. The second clearance angle α2 may be 14° or less.

[0038] FIG. 5 is an enlarged view of the center portion of the tip surface 10A of the end mill shown in FIG. As shown in FIGS. 3 and 5, in the end mill 10 of this embodiment, a groove 50 extending along the long bottom cutting edge 60 is formed in the center of the end mill tip surface 10A. The groove 50 is located on the rear side of the long bottom cutting edge 60 in the end mill rotation direction T. The direction 53 in which the groove 50 extends is from the gash 5 adjacent to the front of the first short bottom cutting edge 61 toward the gash 5 adjacent to the front of the third short bottom cutting edge 63. The groove 50 may have a concave curved inner wall surface made up of a curved surface, or may be a square groove whose inner wall surface is made up of multiple flat surfaces. Alternatively, the groove 50 may have an inner wall surface that includes both curved and flat surfaces.

[0039] The groove 50 is cut out at the radially inner end of the first short bottom cutting edge 61 and the radially inner end of the second short bottom cutting edge 62. As a result, part of the inner wall surface of the groove 50 forms a first chamfered surface 51 located at the radially inner end of the first short bottom cutting edge 61 and a second chamfered surface 52 located at the radially inner end of the second short bottom cutting edge 62. Both the first chamfered surface 51 and the second chamfered surface 52 face radially inward.

[0040] The first chamfer surface 51 and the second chamfer surface 52 are arranged apart from each other in the circumferential direction. Between the first chamfer surface 51 and the second chamfer surface 52, a gash 5 that forms a second short bottom cutting edge 62 opens.

[0041] By forming the first chamfer surface 51, the thin portion on the radially inner side of the first short bottom cutting edge 61 can be eliminated. Furthermore, by forming the second chamfer surface 52, the thin portion on the radially inner side of the second short bottom cutting edge 62 can be eliminated. The cutting edge at the center of the tool is prone to fracture because a force that crushes the workpiece is applied during ramping and plunge cutting. According to the configuration of this embodiment, by forming the first chamfer surface 51 and the second chamfer surface 52, the portions on the inner periphery of the first short bottom cutting edge 61 and the second short bottom cutting edge 62 that are prone to fracture are removed, thereby preventing fracture of the first short bottom cutting edge 61 and the second short bottom cutting edge 62.

[0042] In this embodiment, the end mill tip surface 10A is configured to have two surfaces, a first chamfer surface 51 and a second chamfer surface 52, but it may also be configured to have only the first chamfer surface 51. For example, if the end mill 10 of this embodiment is a four-blade end mill, the spacing between the end cutting edges 6 can be made wider, so a chamfer surface may be provided only on the inner peripheral portion of the first short bottom cutting edge 61, where the spacing is likely to become narrow. In the case of an end mill with five or more blades, it is preferable to provide the second chamfer surface 52 on the inner peripheral portion of the second short bottom cutting edge 62, as the spacing between the long bottom cutting edge 60 and the second short bottom cutting edge 62 is likely to become narrow.

[0043] When the third short bottom cutting edge 63 is located opposite the long bottom cutting edge 60 across the central axis O, it is preferable that the extension direction 53 of the recessed groove 50 is approximately parallel to the extension direction of the third short bottom cutting edge 63. When the third short bottom cutting edge 63 is located opposite the long bottom cutting edge 60 across the central axis O, this means that the angular difference between the long bottom cutting edge 60 and the third short bottom cutting edge 63 around the central axis O is 165° or more and 195° or less. Furthermore, when the end mill tip surface 10A is viewed in the direction of the central axis O, the extension direction 53 of the recessed groove 50 and the extension direction of the third short bottom cutting edge 63 are approximately parallel to each other, which means that the angle between the extension direction 53 of the recessed groove 50 and the extension direction of the third short bottom cutting edge 63 is 5° or less.

[0044] By making the extension direction 53 of the groove 50 and the extension direction of the third short bottom cutting edge 63 approximately parallel, it is possible to form a chamfer on the short bottom cutting edge while ensuring back metal on the inner peripheral portion of the long bottom cutting edge 60. If the groove 50 is tilted clockwise from the position shown in Figure 5, the back metal on the portion of the long bottom cutting edge 60 closer to the center axis O tends to be smaller. If the back metal is insufficient, chipping is more likely to occur in the central portion of the long bottom cutting edge 60. On the other hand, if the groove 50 is tilted counterclockwise from the position shown in Figure 5, the cutting length of the second short bottom cutting edge 62 tends to be shorter. If the second short bottom cutting edge 62 becomes too short, the life of the end mill 10 will be shortened.

[0045] As shown in Figure 5, in the end mill 10 of this embodiment, an arc-shaped R-shaped portion 5a is formed at the end of the gash 5 on the long bottom cutting edge 60 side, adjacent to the forward side of the first short bottom cutting edge 61 in the end mill rotation direction T, when viewed from the direction of the central axis O. By providing an R-shape to the radially inner end of the gash 5, the edge of the gash 5 has a smooth curved shape. The bottom surface of the gash 5 also has a concave curved shape. Chips are less likely to get caught on the wall surface of the gash 5, and stress concentration on the wall surface of the gash 5 is less likely to occur. This improves the chipping resistance and breakage resistance at the tip of the end mill 10. In this embodiment, the radially inner end of the gash 5 immediately after the long bottom cutting edge 60, where the gash 5 is likely to be shallow due to the back metal of the long bottom cutting edge 60, is made R-shaped. In other words, the R-shaped portion 5a of the gash 5 is formed when the gash 5 extends toward the straight cutting edge.

[0046] The radius of curvature of the R-shaped portion 5a is preferably 0.04 × D or more and 0.15 × D or less where D is the tool diameter. If the radius of curvature of the R-shaped portion 5a is too small, chip removal performance is reduced and chipping is more likely to occur. If the radius of curvature of the R-shaped portion 5a is too large, the back metal of the long bottom cutting edge 60 is insufficient, reducing the strength of the long bottom cutting edge 60. The radius of curvature of the R-shaped portion 5a may be 0.06×D or more, or 0.08×D or more, where D is the tool diameter. The radius of curvature of the R-shaped portion 5a may be 0.13×D or less, or 0.11×D or less, where D is the tool diameter.

[0047] FIG. 6 is a side view of the periphery of the bottom cutting edge, shown for explaining the gash notch angle. In the end mill 10 of this embodiment, the gash notch angle of the multiple gashes 5 is preferably 20° or more and 45° or less. As shown in Fig. 6, the gash notch angle β is the inclination angle of the deepest valley line 5b of the gash 5 with respect to the reference line C2. The reference line C2 is a straight line that is perpendicular to the central axis O in the plane defined by the valley line 5b and the central axis O.

[0048] If the gash notch angle β is less than 20°, the gash 5 becomes too shallow, resulting in poor chip discharge. On the other hand, if the gash notch angle β exceeds 45°, breakage is likely to occur due to insufficient cutting edge strength. The gash notch angle β may be set to 25° or more, or 30° or more. The gash notch angle β may be set to 40° or less, or 35° or less.

[0049] FIG. 7 is a side view of the periphery of the bottom cutting edge shown for explaining the gash rake angle. In the end mill 10 of this embodiment, the gash rake angle γ of the multiple gashes 5 is preferably between 0° and 10°. The gash rake angle γ is the angle between the rake face 15 that forms the end cutting edge 6 and the reference line C3. The reference line C3 is a straight line parallel to the central axis O that passes through the end cutting edge 6 in a cross section perpendicular to the end cutting edge 6. The gash rake angle γ is the angle between the tangent to the rake face 15 at the position of the end cutting edge 6 and the reference line C3 in the above cross section.

[0050] If the gash rake angle γ is less than 0°, chip removal performance is reduced. If the gash rake angle γ is more than 10°, the end cutting edge 6 is more likely to break due to insufficient cutting edge strength. The gash rake angle γ may be set to 2° or more, or 4° or more. The gash rake angle γ may be set to 8° or less, or 6° or less.

[0051] In the end mill 10 of this embodiment, by providing an R-shaped portion 5a to a portion of the gash 5, and configuring the gash notch angle β to be 20° or more and 45° or less, and the gash rake angle γ to be 0° or more and 10° or less, it is possible to improve chip discharge performance while maintaining the cutting edge strength of the end cutting edge 6. This allows the end mill 10 to perform stable cutting.

[0052] 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, The plurality of end cutting edges include a long bottom cutting edge having the longest cutting edge length and a first short bottom cutting edge positioned immediately behind the long bottom cutting edge in the end mill rotation direction, A plurality of gashes are provided on the tip surface of the end mill on which the plurality of bottom cutting edges are arranged, An arc-shaped R-shaped portion is formed at the end of the long bottom blade side of the gash adjacent to the front side of the first short bottom blade in the end mill rotation direction, when viewed from the central axis direction, The radius of curvature of the R-shaped portion is equal to or greater than 0.04 × D and equal to or less than 0.15 × D, where D is the tool diameter, The gash notch angles of the plurality of gashes are equal to or greater than 20° and equal to or less than 45°, The gash rake angles of the plurality of gashes are greater than or equal to 0° and less than or equal to 10°. End mill.

[0053] According to the above aspect, an end mill can be obtained that can improve chip removal performance while maintaining the strength of the cutting edge. With this end mill, stable cutting processing is possible. [Explanation of symbols]

[0054] 2...Shank 3. Body 4...Chip discharge groove 5...Gash 5a...R shape part 5b…Tani line 6…Bottom blade 7…Peripheral blade 8...Chip breaker 10...End mill 10A...End mill tip surface 11...Outer flank 11a...First relief face 11b...Second flank 11c…Boundary position 12,15...Scooping surface 31a…width 50...Groove 51...First chamfer surface 52...Second chamfer surface 53... Groove extension direction 60...Long-bottomed blade 61...First short bottom blade 62...Second short bottom blade 63...Third short bottom blade 64...4th short bottom blade C1,C2,C3…Reference line D…Tool diameter N…Number of blades O…Central axis T...End mill rotation direction α1...First relief angle α2...Second relief angle β…Gash notch angle γ…Gash rake angle θ, θ1, θ2, θ3, θ4…Division angle

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, The plurality of end cutting edges are arranged at different parting angles, The division angle is an angle formed by a line radially connecting the outer peripheral end of the end cutting edge and the central axis and a line radially connecting the outer peripheral end of another end cutting edge adjacent to the end cutting edge and the central axis in the forward direction of the end mill rotation T, the angular difference between the respective division angles is 0.5° or more, the maximum value of the angle difference is an angle of 90° / N or less, where N is the number of teeth of the end cutting edges; the division angle of the long bottom cutting edge having the longest cutting edge length among the plurality of bottom cutting edges is the largest among the division angles of the bottom cutting edges, The peripheral flank of the peripheral cutting edge has a first flank adjacent to the peripheral cutting edge and a second flank adjacent to the rear of the first flank in the rotation direction of the end mill, a clearance angle of the first clearance surface is equal to or greater than 2° and equal to or less than 4°; The relief width of the first relief surface is 0.04 mm or more and 0.2 mm or less. End mill.

2. The helix angles of all the peripheral cutting edges are equal to each other, The dividing angle of the peripheral cutting edge varies depending on the cutting length of the end cutting edge connected to the peripheral cutting edge. The end mill according to claim 1 .

3. The plurality of end cutting edges include a first short bottom cutting edge positioned immediately behind the long bottom cutting edge in the end mill rotation direction, A first chamfer surface facing inward in the radial direction is provided at an end portion on the radially inner side of the first short bottom cutting edge. The end mill according to claim 1 or 2.

4. five or more of the end cutting edges and the peripheral cutting edges; The plurality of end cutting edges include a second short bottom cutting edge positioned immediately behind the first short bottom cutting edge in the end mill rotation direction, A second chamfer surface facing radially inward is provided at a radially inner end of the second short bottom cutting edge. The end mill according to claim 3 .

5. A recessed groove is formed on the tip surface of the end mill on which the plurality of bottom cutting edges are arranged, the recessed groove including both the first chamfer surface of the first short bottom cutting edge and the second chamfer surface of the second short bottom cutting edge as part of the inner wall surface, the plurality of end blades include a third short end blade whose angular difference about the central axis with respect to the long end blade is 165° or more and 195° or less; When the tip surface of the end mill is viewed in the central axis direction, the angle formed between the direction in which the recessed groove extends and the direction in which the third short bottom cutting edge extends is 5° or less. The end mill according to claim 4.

6. The plurality of end cutting edges include a first short bottom cutting edge positioned immediately behind the long bottom cutting edge in the end mill rotation direction, A plurality of gashes are provided on the tip surface of the end mill on which the plurality of bottom cutting edges are arranged, An arc-shaped R-shaped portion is formed on a ridge line portion where the gash adjacent to the front side of the first short bottom cutting edge in the end mill rotation direction and the flank of the long bottom cutting edge intersect, when viewed from the central axis direction, the radius of curvature of the R-shaped portion is equal to or greater than 0.04 × D and equal to or less than 0.15 × D where D is the tool diameter, In a plane defined by the valley line of the deepest part of the gash and the central axis, the inclination angle of the valley line of the deepest part of the gash with respect to a reference line that is a straight line perpendicular to the central axis is defined as the gash notch angle of the plurality of gashes, The gash notch angles of the plurality of gashes are equal to or greater than 20° and equal to or less than 45°, The gash rake angles of the plurality of gashes are greater than or equal to 0° and less than or equal to 10°. The end mill according to any one of claims 1 to 5.

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