JP7806573B2 - End mill - Google Patents

Description

The present invention relates to an end mill.

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 angular intervals to suppress chatter vibration, as disclosed in Patent Document 1, for example.

JP 2012-091306 A

When an end mill is divided unequally, the width of the chip discharge groove and gash varies depending on the division angle, which can affect chip discharge performance depending on the division angle. In particular, with the end cutting edge, the gash can become too narrow, reducing chip discharge performance.

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, multiple end cutting edges located at the tip of the body, and multiple peripheral cutting edges located on the outer periphery of the body and twisting in a spiral shape around the central axis. The multiple end cutting edges are arranged at different division angles. The division angle is the angle between a line radially connecting the outer periphery of a particular end cutting edge to the central axis and a line radially connecting the outer periphery of the end cutting edge to the central axis of another adjacent end cutting edge forward in the direction of end mill rotation T. The angular difference between 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 edges. The division angle of the long bottom cutting edge with the longest cutting edge length among the multiple 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 first flank rearward in the direction of end mill rotation. The first flank has a clearance angle of 2° to 4°, and a clearance width of 0.04 mm to 0.2 mm.

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 providing a first flank with a two-stage flank on the outer circumferential flank and a flank angle of 2° to 4° and a flank 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.

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. The clearance angle of the first flank may be 3.5° or less.
The clearance width of the first flank may be 0.07 mm or more. The clearance width of the first flank may be 0.15 mm or less.

The twist angles of all the peripheral cutting edges may be equal to one another, and the division angles of the peripheral cutting edges may differ depending on the cutting length of the end cutting edges connected to the peripheral cutting edges.

The multiple end cutting edges may include a first short end cutting edge positioned immediately behind the long end cutting edge in the end mill rotation direction, and a first chamfered surface facing radially inward may be provided at the radially inner end of the first short end cutting edge.

The end mill may have five or more end cutting edges and peripheral cutting edges, and the end cutting edges may include a second short bottom cutting edge positioned immediately behind the first short bottom cutting edge in the direction of end mill rotation, and a second chamfered surface facing radially inward may be provided at the radially inner end of the second short bottom cutting edge.

A recessed groove is formed on the tip surface of the end mill on which the multiple bottom blades are arranged, and the recessed groove includes both the first chamfered surface of the first short bottom blade and the second chamfered surface of the second short bottom blade as part of the inner wall surface. The multiple bottom blades have a third short bottom blade whose angle difference around the central axis with respect to the long bottom blade is 165° or more and 195° or less. When the tip surface of the end mill is viewed in the direction of the central axis, the angle between the extension direction of the recessed groove and the extension direction of the third short bottom blade may be 5° or less.

The plurality of bottom blades include a first short bottom blade located immediately behind the long bottom blade 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 bottom blades are arranged, and an arc-shaped R-shaped portion is formed at the ridge where the gash adjacent to the front side of the first short bottom blade in the end mill rotation direction intersects with the flank surface of the long bottom blade , when viewed from the central axis direction, and the radius of curvature of the R-shaped portion is 0.04 x D or more and 0.15 x D or less relative to the tool diameter D, 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 which is a straight line perpendicular to the central axis is defined as the gash notch angle of the plurality of gashes, and 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.

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.

One aspect of the present invention provides an end mill with excellent chip removal and vibration damping properties.

FIG. 1 is a perspective view showing an end mill according to an embodiment. FIG. 2 is a side view of the end mill according to the embodiment. FIG. 3 is a view of the end mill of the embodiment as seen from the tip side. 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. FIG. 5 is an enlarged view of the center portion of the tip surface of the end mill shown in FIG. FIG. 6 is a side view of the periphery of the bottom cutting edge, shown for explaining the gash notch angle. FIG. 7 is a side view of the periphery of the bottom cutting edge shown for explaining the gash rake angle.

1 is a perspective view of an end mill according to an embodiment, FIG. 2 is a side view of the end mill according to an embodiment, and FIG. 3 is a view of the end mill according to an embodiment as viewed from the tip side.
The end mill 10 of this embodiment shown in Figure 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."

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 Figure 2), and the body 3 is located at the tip end of the end mill 10 (lower side in Figure 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 peripheral flanks 11. The peripheral cutting edge 7 is formed at the intersection ridge between the chip discharge flutes 4 and the peripheral flanks 11 on the forward side in the direction of end mill rotation T.

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

On the outer periphery of the body 3, the chip discharge grooves 4 extend twistedly around the central axis O in the opposite direction to the end mill rotation direction T as they move from the axial tip 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, spaced apart from one another in the circumferential direction.

The peripheral cutting edges 7 are formed on the ridgeline at the front of the rotational direction, where the rake face 12, which is the wall surface of the chip discharge groove 4 facing forward in the end mill rotation direction T, intersects with the peripheral relief face 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 that partially cut out the peripheral cutting edges 7.

At the tip of each chip discharge groove 4, a concave 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 leading edge of the wall surface of each gash 5 facing the end mill rotation direction T, multiple bottom cutting edges 6, each with the wall surface as its rake surface, extend from the tip of the peripheral cutting edge 7 toward the inner periphery (radially inward).

The end mill 10 of this embodiment is a square end mill in which the bottom cutting edges 6 and 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. 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.

The chip breaker 8 is a notch that discontinuities the peripheral cutting edge 7. The chip breaker 8 cuts the peripheral flank 11 circumferentially across the flank 11 to connect two circumferentially adjacent chip discharge grooves 4. The chip breaker 8 is a groove that recesses 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 grooves 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 groove 4 located on the rear side of the peripheral flank 11 in the end mill rotation direction T. Each chip breaker 8 extends roughly 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 can also be configured without the chip breaker 8.

As shown in FIG. 3, the five end cutting edges 6 consist 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 peripheral 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, like the long bottom cutting edge 60, also extend radially inward from the outer peripheral edge of the end mill tip surface 10A. 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. On the end mill tip surface 10A, the area 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 circumferentially.

In this embodiment, the division angle (cutting distance) of a certain bottom cutting edge 6 refers to the angle between a line radially connecting the outer circumferential edge of that bottom cutting edge 6 to the central axis O and a line radially connecting the outer circumferential edge of another bottom cutting edge 6 adjacent to that bottom cutting edge 6 forward in the end mill rotation direction T to the central axis O.

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 circumferential edge of the fourth short bottom cutting edge 64 and the outer circumferential 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.

As shown in Figure 3, in this embodiment, the division angles θ, θ1 to θ4, of all 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.

In addition, 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 at the end mill tip surface 10A can be suppressed. Tool breakage or chipping caused by chip clogging can be suppressed.

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 angular difference between the division angles of the bottom cutting edges 6 is in the range of 2° to 16°.

The angular difference between the division angles of the end cutting edges 6 is at least 0.5° or more. By making the angle difference 0.5° or more, a vibration-damping effect can be achieved through unequal division. The angular difference between the division angles of the end cutting edges 6 is preferably 1° or more, and more preferably 2° or more. By increasing the angle difference between the division angles of the end cutting edges 6, a greater vibration-damping effect can be achieved.

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. End cutting edges 6 with division angles that are too small are 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 on the end 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 appropriate division angles. This further helps to prevent chip clogging.

In this embodiment, the cutting lengths of the four first to fourth short bottom cutting edges 61 to 64 are approximately the same. In this embodiment, the cutting lengths of the first to fourth short bottom cutting edges 61 to 64 are approximately 50 to 60% of the radius of the end mill tip surface 10A, and since grooves of sufficient size are formed on the inner periphery of the first to fourth short bottom cutting edges 61 to 64, good chip removal performance can be achieved.

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. In other words, the division angle of a bottom cutting edge 6 may be increased as the cutting edge length of the bottom cutting edge 6 increases. The amount of chips generated by a bottom cutting edge 6 increases with increasing cutting edge length. Therefore, by increasing the division angle of the bottom cutting edge 6 with a longer cutting edge length, good chip discharge performance can be achieved 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.

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.

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

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 set to 2.5° or more. The first clearance angle α1 may be set to 3.5° or less. Furthermore, the clearance width 31a may be set to 0.07 mm or more. The clearance width 31a may be set to 0.15 mm or less.

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, greater than or equal to 10° and less than or equal to 16°. The second clearance angle α2 may also be greater than or equal to 12°. The second clearance angle α2 may also be less than or equal to 14°.

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 Figures 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.

The groove 50 has a notch 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 chamfer surface 51 located at the radially inner end of the first short bottom cutting edge 61 and a second chamfer surface 52 located at the radially inner end of the second short bottom cutting edge 62. Both the first chamfer surface 51 and the second chamfer surface 52 face radially inward.

The first chamfer surface 51 and the second chamfer surface 52 are spaced apart in the circumferential direction. Between the first chamfer surface 51 and the second chamfer surface 52, a gash 5 that forms the second short bottom cutting edge 62 opens.

By forming the first chamfer surface 51, the thin portion on the radially inner side of the first short bottom cutting edge 61 is 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 is eliminated. The cutting edge at the center of the tool is prone to fracture due to the force that crushes the workpiece 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.

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 tends to become narrow. In the case of an end mill with five or more blades, it is preferable to provide a 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 tends to become narrow.

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 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" 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, "the extension direction 53 of the groove 50 and the extension direction of the third short bottom cutting edge 63 being approximately parallel" means that the angle between the extension direction 53 of the groove 50 and the extension direction of the third short bottom cutting edge 63 is 5° or less when the end mill tip surface 10A is viewed in the direction of the central axis O.

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 backmetal 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 backmetal on the portion of the long bottom cutting edge 60 closer to the center axis O tends to be smaller. If there is insufficient backmetal, 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.

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 front 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 also 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 cutting edge 60, where the gash 5 tends to be shallow due to the back metal of the long cutting edge 60, is R-shaped. That is, the R-shaped portion 5a of the gash 5 is formed when the gash 5 extends toward the straight cutting edge.

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 5 a 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 5 a may be 0.13×D or less, or 0.11×D or less, where D is the tool diameter.

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 plurality of 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 a plane defined by the valley line 5b and the central axis O.

If the gash notch angle β is less than 20°, the gash 5 becomes too shallow, resulting in poor chip discharge performance. On the other hand, if the gash notch angle β is more than 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.

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 0° or greater and 10° or less. The gash rake angle γ is the angle between the rake face 15 that forms the bottom 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 bottom cutting edge 6 in a cross section perpendicular to the bottom cutting edge 6. The gash rake angle γ is the angle between the tangent to the rake face 15 at the position of the bottom cutting edge 6 and the reference line C3 in the above cross section.

If the gash rake angle γ is less than 0°, chip discharge 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.

In the end mill 10 of this embodiment, by providing an R-shaped portion 5a on some of the gashes 5, with a gash notch angle β of 20° to 45° and a gash rake angle γ of 0° to 10°, it is possible to improve chip removal performance while maintaining the cutting edge strength of the bottom cutting edge 6. This allows for an end mill 10 that is capable of stable cutting.

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 gash on the long bottom blade side 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.

The above aspect provides an end mill that can improve chip removal while maintaining the strength of the cutting edge. This end mill enables stable cutting.

2...Shank 3...Body 4...Chip discharge groove 5...Gash 5a...R-shaped portion 5b...Groove line 6...Bottom cutting edge 7...Peripheral cutting edge 8...Chip breaker 10...End mill 10A...End mill tip face 11...Peripheral flank face 11a...First flank face 11b...Second flank face 11c...Boundary position 12, 15...Rake face 31a...Width 50...Groove 51...First chamfered face 52...Second chamfered face 53...Groove extension direction 60...Long bottom cutting edge 61...First short bottom cutting edge 62...Second short bottom cutting edge 63...Third short bottom cutting edge 64...Fourth short bottom cutting edge C1, C2, C3...Reference line D...Tool diameter N...Number of teeth 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...Partition angle

Claims (6)

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. 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 . 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. 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 . 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. 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.