WO2020039981A1 - Cutting insert and indexable ball end mill - Google Patents

Abstract

A cutting insert (1) to be mounted on an insert mounting seat of an indexable ball end mill comprises a rake face (2) facing in the end mill rotation direction, a seating face (3) facing away from the rake face (2), and a flank face (4) extending around the rake face (2) and the seating face (3), wherein a cutting edge (5) including an arcuate cutting edge portion (5a) extending in a convex arc shape in a plan view as viewed from the direction opposite to the rake face (2), and an inner peripheral cutting edge portion (5c) that is continuous with the tip of the arcuate cutting edge portion (5a) and extends in the direction crossing the arcuate cutting edge portion (5a) at an obtuse angle in a plan view is formed at the intersection ridge line between the rake face (2) and the flank face (4), and the inner peripheral cutting edge portion (5c) is formed in a concave shape away from the seating face (3) after extending to the seating face (3) side following the separation from the tip of the arcuate cutting edge portion (5a) in a side view as viewed from the direction facing the flank face (4) continuous with the inner peripheral cutting edge portion (5c).

Description

Cutting inserts and replaceable ball end mills

The present invention relates to a cutting insert removably mounted on an insert mounting seat formed at a distal end portion of an end mill main body of a cutting edge replaceable ball end mill rotated around an axis, and an insert mounting seat at which the cutting insert is located at a distal end portion of the end mill main body. The present invention relates to a ball end mill having a replaceable cutting edge, which is detachably attached to the end mill.
Priority is claimed on Japanese Patent Application No. 2018-155368 filed on August 22, 2018, the content of which is incorporated herein by reference.

As such a cutting insert, for example, in Patent Literature 1, at one end of an arc-shaped cutting edge portion of a cutting edge of an insert body, an obtuse angle is formed on an imaginary plane where the arc-shaped cutting edge portion is located and extends. A short inner peripheral cutting edge portion (small cutting edge) that intersects with the above is described. Patent Document 2 discloses a cutting insert in which an inner peripheral cutting edge (small cutting edge) is formed at one end of such an arc-shaped cutting edge, and the inner peripheral cutting edge is attached to the rotation axis of the end mill body. An interchangeable cutting edge ball end mill mounted crosswise is described.

In such a cutting insert and a replaceable-type ball end mill, an arc-shaped cutting edge is provided at a portion of the cutting edge, which is located near the rotation axis of the end mill body and has a large cutting load because the rotation speed is close to zero. Since the inner peripheral cutting edge portion that intersects the portion at an obtuse angle is formed, the cutting edge strength can be ensured. Therefore, it is possible to prevent the insert main body from being damaged due to such a large cutting load.

JP-A-7-276128 JP-A-11-197933

By the way, when such an inner peripheral cutting edge portion is formed in a direction intersecting the arcuate cutting edge portion at an obtuse angle, a virtual cutting edge portion formed with an arcuate cutting edge portion like a cutting insert described in Patent Document 1 is disclosed. If the inner peripheral cutting edge is located on a plane, that is, if the inner peripheral cutting edge is linear, chips are generated so as to be entrained, and the outflow direction thereof is not controlled, and the inner peripheral edge of the end mill main body is not controlled. There is a risk of spilling to the side. When the chips flow out to the inner peripheral side of the end mill body in this manner, the chips may be clogged, or the chips flowing out to the inner peripheral side may rotate along with the rotation of the end mill main body and the machining surface of the arc-shaped cutting blade portion and the work material. And the surface roughness may be degraded.

The present invention has been made under such a background, and an inner peripheral cutting edge extending in a direction intersecting the arcuate cutting edge at an obtuse angle is provided at one end (tip) of the arcuate cutting edge of the cutting edge. When formed, it is possible to prevent chips generated by this inner peripheral cutting edge from flowing out to the inner peripheral side of the end mill main body, and to prevent chip clogging and deterioration of the machined surface roughness. It is an object of the present invention to provide an insert and an exchangeable blade end mill having such a cutting insert removably attached thereto.

In order to solve the above problems and achieve such an object, a cutting insert according to the present invention is detachably attached to an insert mounting seat formed at a tip end portion of an end mill body of a tip-changeable ball end mill rotated around an axis. A cutting insert that is mounted so as to be able to be mounted, the rake face being oriented in the rotation direction of the end mill body, a seating face facing the opposite side of the rake face and seated on the bottom surface of the insert mounting seat, and a rake face. And a flank extending around the seating surface, and an arc-shaped notch extending in a convex arc shape in a plan view seen from a direction facing the rake surface at an intersection ridge portion of the rake surface and the flank. A cutting edge comprising an edge portion and an inner peripheral cutting edge portion extending in a direction intersecting with the arcuate cutting edge portion at an obtuse angle in the plan view, which is continuous with the tip of the arcuate cutting edge portion, is formed. The inner peripheral cutting edge portion extends toward the seating surface side as it moves away from the tip of the arcuate cutting edge portion in a side view as viewed from a direction facing the flank surface connected to the inner peripheral cutting edge portion. It is characterized by being formed in a concave shape away from the seating surface.

In addition, the replaceable ball end mill of the present invention is a replaceable ball end mill in which such a cutting insert is detachably mounted on an insert mounting seat formed at the tip of an end mill body that is rotated around an axis. The arc-shaped cutting edge portion of the cutting edge is disposed on a spherical surface having a rotation trajectory around the axis centered on the axis, and the inner peripheral cutting edge portion of the cutting edge includes the rake face. In a plan view viewed from a direction opposite to the front end, the arc-shaped cutting edge portion extends from the tip end of the arc-shaped cutting edge portion toward the inner peripheral side of the end mill body beyond the axis and toward the rear end side, and from the axial direction tip end side. When viewed from the front, it is characterized by being located on the end mill rotation direction side with respect to a straight line connecting the axis and the tip of the arc-shaped cutting blade portion.

In the cutting insert configured as described above, and the cutting edge replaceable ball end mill to which the cutting insert is attached, the inner peripheral cutting edge portion is a side surface viewed from a direction opposite to a flank connected to the inner peripheral cutting edge portion. In view, since it is formed in a concave shape that separates from the seating surface after extending toward the seating surface side of the insert body as it moves away from the tip of the arc-shaped cutting edge, chips generated by the inner peripheral cutting edge also have a cross-section. Is generated so as to have a concave shape, and it is difficult to be caught.

And the chips generated in this manner are substantially perpendicular to the inner peripheral cutting edge portion in plan view as viewed from the direction facing the rake face of the insert main body, that is, the rear end of the end mill main body in the cutting edge replaceable ball end mill. As it goes to the side, it flows out and is discharged in the direction to the outer peripheral side. For this reason, chips flow out to the inner peripheral side of the end mill main body, causing chip clogging, or chips flowing out to the inner peripheral side are caught between the arc-shaped cutting edge portion and the processing surface with rotation of the end mill main body. By doing so, it is possible to prevent the processing surface roughness from deteriorating.

In the blade end replaceable ball end mill having the above-described configuration, the inner peripheral cutting edge portion of the cutting edge is located on the inner peripheral side of the end mill main body from the tip of the arcuate cutting edge portion in plan view when viewed from a direction facing the rake face. As it extends, it extends beyond the axis and toward the rear end, and is located closer to the end mill rotation direction than the straight line connecting the axis and the tip of the arc-shaped cutting edge in a front view as viewed from the front end in the axial direction. ing. Therefore, the inner peripheral cutting edge portion is parallel to a straight line connecting the front end of the arc-shaped cutting edge portion and the rear end of the inner peripheral cutting edge portion opposite to the distal end of the arc-shaped cutting edge portion in the front view. And is located on the opposite side of the seating surface with respect to the straight line passing through the axis, and is disposed so-called upright. Then, the chips generated by the inner peripheral cutting edge portion are generated so that the cross section becomes concave, and the chips are hardly caught in the shape of a vine.

For this reason, by feeding the end mill body in a direction perpendicular to the axis, it is possible to form a machining surface having a concave circular cross section on the work material by the arc-shaped cutting edge portion, and to feed the end mill body to the axial front end side. When performing piercing to cut a work material by giving a feed, the inner peripheral cutting edge part of the part reaching the axis of the end mill main body from the tip of the arcuate cutting edge part in plan view seen from the direction facing the rake face Accordingly, it is possible to cut the rotation center portion, which is the portion around the axis at the end portion of the end mill main body.

Here, the inner peripheral cutting edge portion of the cutting insert is formed in a concave curve shape that is concave toward the seating surface side in a side view as viewed from a direction facing the flank surface connected to the inner peripheral cutting edge portion. It is desirable. If the inner peripheral cutting edge portion has, for example, a V-shape when viewed from the side facing the flank, the stress due to the cutting load may be concentrated on the bottom portion of the V-shape to cause a crack.

Further, in a plan view viewed from a direction facing the rake face, the tip of the arc-shaped cutting edge portion, the rear end of the inner peripheral cutting edge portion on the opposite side to the tip of the arc-shaped cutting edge portion. Of the cross sections orthogonal to the straight line to be connected, the cutting edge angle of the inner peripheral cutting edge portion at a cross section at a position where the inner peripheral cutting edge portion is most recessed toward the seating surface side in a side view viewed from a direction facing the flank surface. Is preferably in the range of 80 ° to 95 °. If the blade angle at the cross section at the position where the inner peripheral cutting edge is most concave is less than 80 °, it is not possible to secure sufficient cutting edge strength at the inner peripheral cutting edge, and the fracture resistance may be impaired. There is. On the other hand, if the blade angle exceeds 95 °, the cutting resistance may be increased. The blade angle of the inner peripheral cutting edge portion is more preferably in the range of 82 ° to 93 °, and even more preferably in the range of 83 ° to 92 °.

Furthermore, it is desirable that the clearance angle of the inner peripheral cutting edge is in the range of 14 ° to 30 °. When the clearance angle of the inner peripheral cutting edge portion is less than 14 °, a flank contact occurs where the flank contacts the machined surface of the work material, which may increase the cutting resistance and deteriorate the machined surface roughness. . On the other hand, when the clearance angle of the inner peripheral cutting edge portion exceeds 30 °, the inner peripheral cutting edge portion is different from the axis in a front view as viewed from the axial front end side of the end mill main body as in the blade end exchangeable ball end mill having the above configuration. When located on the end mill rotation direction side of the straight line connecting the tip of the arcuate cutting edge, the machining surface accuracy may be reduced when the arcuate cutting edge forms a machining surface with a concave arcuate cross section. There is. The clearance angle of the inner peripheral cutting edge portion is more preferably in the range of 18 ° to 26 °, and further preferably in the range of 20 ° to 24 °.

Furthermore, the rake face has a valley bottom that intersects the inner circumference cutting edge in a plan view seen from a direction facing the rake face in the vicinity of the inner circumference cutting edge. It is desirable to be formed in a valley shape that is concave toward the above-mentioned seating surface side. Thereby, it is possible to guide the chips generated by the inner peripheral cutting edge along the valley bottom formed by the rake face and to flow out more reliably to the outer peripheral side of the end mill main body.

Further, the rake face may be inclined parallel to the seating surface at least at the periphery of the arc-shaped cutting edge portion or toward the seating surface side as the distance from the arc-shaped cutting edge portion increases. This makes it possible to sharpen the sharpness of the arcuate cutting edge and reduce cutting resistance.

On the other hand, on the other hand, the rake face may be inclined at least in the vicinity of the arc-shaped cutting edge so as to move away from the arc-shaped cutting edge toward the opposite side to the seating surface. . Thereby, the blade angle of the arcuate cutting edge portion can be increased to improve fracture resistance.

Further, in a plan view seen from a direction facing the rake face, a first cutting edge portion is formed on the arc-shaped cutting edge portion on a side opposite to the inner peripheral cutting edge portion. A second cutting edge portion is formed on the peripheral cutting edge portion side, the second cutting edge portion has a larger radius of curvature than the first cutting edge portion, and the second cutting edge portion has a radius of curvature larger than that of the first cutting edge portion. It may be retracted more than the extension line to the inner peripheral cutting edge part side.

Accordingly, for example, like the blade end exchange type ball end mills described in Patent Documents 1 and 2, the inner peripheral cutting edge portion is on the side opposite to the first cutting insert attached so as to intersect with the rotation axis of the end mill body. When a second cutting insert whose arcuate cutting edge is disposed at a position distant from the rotation axis is attached, the axis between the tips of the arcuate cutting blades of the first and second cutting inserts. By reducing the step in the direction, the thickness of the chips can be reduced. For this reason, the load on the cutting blade can be reduced and the fracture resistance can be improved.

In this case, the arcuate cutting edge portion, from a side view as viewed from a direction facing the flank face connected to the arcuate cutting edge portion, from the seating surface toward the inner peripheral cutting edge portion side. When it is formed in a convex curve shape which goes to the seating surface side after being separated, and has a most protruding point most protruding with respect to the seating surface, the inner peripheral cutting edge portion side than this most protruding point Preferably, the second cutting edge is formed. As a result, the thickness of the chips can be further reduced, so that even under unstable machining conditions such as intermittent cutting with large chatter vibration, the chipping resistance at the tip of the cutting blade can be significantly increased.

Further, the first cutting edge and the second cutting edge may be formed so as to intersect at an obtuse angle, but a curvature is provided from the first cutting edge toward the second cutting edge. It is desirable that the radius is increased and the first cutting edge and the second cutting edge are connected to each other via a convex curved connecting portion that comes into contact with the first cutting edge and the second cutting edge. Thereby, it becomes possible to finish the machined surface of the work material smoothly. The first cutting edge and the second cutting edge are connected to each other through the convex curved connecting portion having a radius of curvature increasing from the first cutting edge toward the second cutting edge. Alternatively, for example, the arc-shaped cutting edge may be formed in an elliptical arc shape in which the radius of curvature gradually increases from the second cutting edge toward the first cutting edge.

On the other hand, in the blade-exchangeable ball end mill having the above-described configuration, in a plan view seen from a direction facing the rake face, the tip of the arc-shaped cutting blade and the tip of the arc-shaped cutting blade opposite to the tip of the arc-shaped cutting blade. A straight line connecting the rear end of the inner peripheral cutting edge portion is inclined toward the inner peripheral side of the end mill body at an inclination angle within a range of 30 ° to 70 ° with respect to a plane perpendicular to the axis. It is desirable to extend toward.

That is, if the angle of inclination is less than 30 °, a flank contact occurs, which increases the cutting resistance and deteriorates the machined surface roughness, and may increase the cutting resistance even in the above-described punching. . On the other hand, when the inclination angle exceeds 70 °, the intersection angle between the inner peripheral cutting edge portion and the arcuate cutting edge portion that intersects the tip of the arcuate cutting edge portion at the tip end portion of the cutting edge decreases, and the strength decreases. And chipping may occur. The inclination angle is more preferably in the range of 40 ° to 60 °, and further preferably in the range of 45 ° to 50 °.

Further, in a plan view as viewed from a direction facing the rake face, in a direction perpendicular to the axis with the rear end of the inner peripheral cutting edge on the opposite side to the tip of the axis and the arc-shaped cutting edge. It is desirable that the distance between the tip of the arcuate cutting edge and the axis in the direction perpendicular to the axis is smaller than the distance. This makes it possible to reliably perform the above-described punching, and to prevent the inner peripheral cutting edge portion between the tip of the arcuate cutting edge portion and the axis from becoming too long. The accuracy of the processing surface having a concave arc shape in cross section can be ensured.

Specifically, in a plan view seen from a direction facing the rake face, the axis is perpendicular to the axis of the rear end of the inner peripheral cutting edge opposite to the tip of the arc-shaped cutting edge. And the distance between the tip of the arcuate cutting edge and the axis in a direction perpendicular to the axis is greater than 0.0 mm and 0 in the range of 0.23 mm or more and 1.25 mm or less. It is desirable that the distance be within a range of .80 mm or less.

If the distance in the direction perpendicular to the axis between the axis of the end mill body and the rear end of the inner peripheral cutting edge opposite to the tip of the arc-shaped cutting edge is less than 0.23 mm, the end mill main body is not pierced during the punching process. If the feed amount to the tip side in the axial direction is large, the tip of the end mill body may come into contact with the workpiece. If the distance between the axis of the end mill main body and the rear end of the inner peripheral cutting edge is larger than 1.25 mm, an insert mounting seat that protrudes greatly beyond the axis of the end mill main body must be formed. However, on the side beyond this axis, the thickness of the end portion of the end mill main body may be reduced, leading to a decrease in strength. The interval in the direction perpendicular to the axis between the axis of the end mill body and the rear end of the inner peripheral cutting edge opposite to the tip of the arc-shaped cutting edge is in the range of 0.24 mm or more and 1.20 mm or less. More preferably, and more preferably within a range from 0.25 mm to 1.15 mm.

Further, the distance between the tip of the arcuate cutting edge and the axis of the end mill body is 0.0 mm or less, which means that the tip of the arcuate cutting edge is disposed on the axis or at a position beyond the axis. At the time of thrusting, the inner peripheral cutting edge portion may not function as a cutting edge, and a flank contact may occur. When the distance between the tip of the arc-shaped cutting edge and the axis of the end mill main body is larger than 0.80 mm, a portion where the arc-shaped cutting edge is not formed at the end of the end mill main body becomes large, and the cross-section has a concave arc shape. There is a possibility that the processing surface accuracy when forming the processing surface is reduced. The distance between the tip of the arcuate cutting edge and the axis in a direction perpendicular to the axis is more preferably greater than 0.0 mm and 0.70 mm or less, and more preferably 0.0 mm or less. It is more desirable that the distance be as large as 0.60 mm or less.

As described above, according to the present invention, it is possible to generate chips in a cross-sectional concave shape in which chips are hardly caught by the concave inner peripheral cutting edge portion, and to control the outflow direction of the chips generated in this way to the end mill body. Can be controlled in the direction toward the outer peripheral side toward the rear end side. For this reason, the chips flow out to the inner peripheral side of the end mill main body, causing chip clogging, and the chips thus flowing out to the inner peripheral side are caught between the arc-shaped cutting edge portion and the processing surface, so that the processing surface roughness is reduced. Can be prevented from deteriorating. In addition, using this inner peripheral cutting edge portion, it is possible to perform a punching process in which the end mill main body is sent to the front end side in the axial direction.

It is a perspective view showing a 1st embodiment of a cutting insert of the present invention. It is the top view which looked at the cutting insert shown in FIG. 1 from the direction facing a rake face. FIG. 2 is a bottom view of the cutting insert shown in FIG. 1 as viewed from a direction facing a seating surface opposite to a rake surface. FIG. 5 is a side view as viewed in the direction of arrow V in FIG. 2. FIG. 3 is a side view as viewed in a direction indicated by an arrow W in FIG. 2. FIG. 3 is a side view as viewed in a direction indicated by an arrow X in FIG. 2. FIG. 3 is a side view as viewed in a direction indicated by an arrow Y in FIG. 2. FIG. 3 is an enlarged plan view of a portion A in FIG. 2. FIG. 6 is an enlarged side view of a portion B in FIG. 5. FIG. 3 is a sectional view taken along the line ZZ in FIG. 2. FIG. 1 is a perspective view of a tip end portion of an end mill main body showing a first embodiment of a replaceable blade end ball end mill of the present invention. It is the front view which looked at the blade edge exchange type ball end mill shown in FIG. 11 from the axial direction front end side. FIG. 13 is a plan view as viewed in the direction of arrow V in FIG. 12. FIG. 13 is a side view as viewed in the direction of arrow W in FIG. 12. FIG. 13 is a bottom view as viewed in the direction of the arrow X in FIG. 12. FIG. 13 is a side view as viewed in a direction indicated by an arrow Y in FIG. 12. It is ZZ sectional drawing in FIG. FIG. 14 is an enlarged plan view of a portion A in FIG. 13. It is an enlarged front view of the B section in FIG. It is ZZ sectional drawing in FIG. It is a perspective view showing a 2nd embodiment of a cutting insert of the present invention. FIG. 22 is a perspective view of the cutting insert shown in FIG. 21 as viewed from a rake face side. FIG. 22 is a perspective view of the cutting insert shown in FIG. 21 as viewed from a seating surface side. FIG. 22 is a plan view of the cutting insert shown in FIG. 21 as viewed from a direction facing a rake face. FIG. 25 is a side view as viewed in the direction of arrow W in FIG. 24. FIG. 25 is a side view as viewed in the direction of the arrow X in FIG. 24. FIG. 25 is a side view as viewed in the direction of the arrow Y in FIG. 24. FIG. 22 is an enlarged side view corresponding to a portion B in FIG. 5 around the inner peripheral cutting edge portion of the cutting insert shown in FIG. 21. FIG. 25 is a sectional view taken along the line ZZ in FIG. 24. Arrow in FIG. 12 of the end portion of the end mill main body showing a third embodiment of the cutting insert of the present invention and a second embodiment of the replaceable blade end mill of the present invention to which the cutting insert of the third embodiment is attached. FIG. 5 is a diagram corresponding to a plan view as viewed in a direction of a line V.

FIGS. 1 to 10 show a cutting insert 1 according to a first embodiment of the present invention. FIGS. 11 to 20 show a first embodiment of a cutting edge replaceable ball end mill according to the present invention in which the cutting insert 1 of this embodiment is detachably mounted on an insert mounting seat 12 formed at the end of the end mill main body 11. It is a figure which shows the front-end | tip part of embodiment.

The cutting insert 1 of the present embodiment is formed of a hard material such as a cemented carbide, and is formed in a leaf-shaped plate shape as shown in FIG. 2 in plan view, and the upper surface thereof has the leaf shape as described above. Rake face 2. The lower surface facing the side opposite to the rake face 2 is slightly smaller than the rake face 2 as shown in FIG. 3, and is formed in a leaf shape that is substantially similar to the rake face 2. The flat seating surface 3 is seated on the bottom surface 12a of the seat 12. Further, a side surface of the cutting insert 1 extending around between the rake face 2 and the seating face 3 is a flank face 4.

At the intersection ridge line between the rake face 2 and the flank face 4, arc-shaped cutting blade portions 5a, 6a extending in an arc shape as shown in FIG. Two cutting blades each having a linear cutting blade portion 5b, 6b extending so as to be in contact with the arc cutting blade portion 5a, 6a are formed by these arc cutting blade portions 5a, 6a and linear cutting blade portions 5b, 6b. Are formed alternately in the circumferential direction of the rake face 2. One of these two cutting edges is a main cutting edge 5, and the other is a sub cutting edge 6.

The flank 4 is inclined so as to go from the rake face 2 toward the seating surface 3 toward the inner peripheral side of the cutting insert 1, and the cutting insert 1 of the present embodiment is a positive type cutting insert. I have. Further, a mounting hole 7 having a circular cross section formed around the center line L of the insert so as to penetrate the cutting insert 1 is opened at the center of the rake face 2 and the seating face 3. The portion of the mounting hole 7 on the rake face 2 side is formed so as to decrease in diameter toward the seating face 3 side. The plan view seen from the direction facing the rake face 2 is a plan view seen along the insert center line L, and the insert center line L extends in a direction perpendicular to the seating surface 3.

Here, in the plan view, the arc-shaped cutting portion 5a of the main cutting edge 5 has a substantially 1/4 arc shape. On the other hand, the arc-shaped cutting edge portion 6a of the sub cutting edge 6 has the same radius as the arc-shaped cutting edge portion 5a of the main cutting edge 5, but the length in the circumferential direction is the arc-shaped cutting edge of the main cutting edge 5. It is shorter than the portion 5a, that is, formed in an arc shape shorter than a quarter arc. Along with this, the straight cutting edge portion 5b of the main cutting edge 5 is shorter than the straight cutting edge portion 6b of the sub cutting edge 6. That is, the cutting insert 1 of the present embodiment is not formed to be 180 ° rotationally symmetric about the insert center line L, but is asymmetric.

Further, the linear cutting edge portions 5b and 6b of the main cutting edge 5 and the sub cutting edge 6 are formed by the arcuate cutting edge portion 5a of the main cutting edge 5 and the linear cutting edge portion 6b of the sub cutting edge 6 in plan view. From the first corner portion 2a of the rake face 2 where the rake face 2 intersects, the second cutting edge 2 of the rake face 2 where the straight cutting edge portion 5b of the main cutting edge 5 and the arc-shaped cutting edge portion 6a of the sub cutting edge 6 intersect. As they approach the corner 2b, they extend closer to each other. The first and second corners 2a, 2b are chamfers which intersect the arc-shaped cutting edges 5a, 6a and the straight cutting edges 5b, 6b of the main cutting edge 5 and the sub cutting edge 6 at an obtuse angle. It is formed in a shape. Further, the first corner 2a is arranged closer to the seating surface 3 than the second corner 2b.

Furthermore, the arc-shaped cutting edges 5a, 6a of the main cutting edge 5 and the sub-cutting edge 6 are separated from the seating surface 3 side after being separated from the respective linear cutting edges 5b, 6b, and then the seating surface 3 side. Are formed in the shape of a convex curve approaching, and the point at which the convex curve formed by the arcuate cutting edge portion 5a of the main cutting edge 5 becomes the most distant and convex with respect to the seating surface 3 (the most protruding from the seating surface 3) Point) is the most convex point S5 of the arcuate cutting edge portion 5a of the main cutting edge 5, and the convex curve formed by the arcuate cutting edge portion 6a of the sub cutting edge 6 is most protruded from the seating surface 3 to be convex. This point (the point most protruding from the seating surface 3) is the most convex point S6 of the arcuate cutting edge portion 6a of the sub cutting edge 6. In addition, the linear cutting edges 5b, 6b of the main cutting edge 5 and the sub cutting edge 6 have arcuate cutting edges as shown in FIG. 5 and FIG. In contact with the convex curve formed by the portions 5a and 6a, the portion 5a extends substantially linearly toward the seating surface 3 as the distance from the arc-shaped cutting edge portions 5a and 6a increases.

Around the opening of the mounting hole 7 at the center of the rake face 2, the main cutting edge 5 and the sub cutting edge 6 protrude further away from the seating surface 3 than the main cutting edge 5 and the sub cutting edge 6, and have a substantially elliptical shape in plan view. A protrusion 2c is formed. The upper end surface of the protrusion 2c is a flat surface parallel to the seating surface 3, and the mounting hole 7 is open at the upper end surface of the protrusion 2c. Further, the outer peripheral surface of the protruding portion 2c is inclined so as to move toward the inside of the rake face 2 toward the upper end surface.

Furthermore, the rake face 2 extends away from the main cutting edge 5 and the sub cutting edge 6 toward the inside of the rake face 2 and toward the seating surface 3 side, and then forms a concave curved surface and forms the outer peripheral surface of the projection 2c. It is connected to. Further, on the rake face 2 between the arc-shaped cutting edge portions 5a, 6a of the main cutting edge 5 and the sub-cutting edge 6 and the projection 2c, the arc-shaped cutting edge portions 5a, 6a are in the above-described plan view. In this embodiment, a plurality of grooves 2d extending short in the radial direction of the arc-shaped cutting blades 5a, 6a are formed at intervals in the circumferential direction of the arc-shaped cutting blades 5a, 6a.

Further, the flank surface 4 connected to the linear cutting edge portions 5b, 6b of the main cutting edge 5 and the sub cutting edge 6 is formed on the inner peripheral side of the cutting insert 1 from the rake face 2 toward the seating face 3 as described above. It is formed in the shape of a plane inclined toward the front. On the other hand, the flank 4 continuous with the arc-shaped cutting edges 5a and 6a of the main cutting edge 5 and the sub-cutting edge 6 has a circumferential direction of the cutting insert 1 along the arc-shaped cutting edges 5a and 6a on the rake face 2 side. However, as described above, the seating surface 3 is notched in a plane while being inclined from the rake face 2 toward the inner peripheral side of the cutting insert 1 as going from the rake face 2 to the seating face 3 side. It has a portion 4a.

Furthermore, of the first and second corner portions 2a and 2b of the rake face 2, a chamfer that intersects the arc-shaped cutting edge portion 5a of the main cutting edge 5 and the linear cutting edge portion 6b of the sub cutting edge 6 is formed. The first corner portion 2a formed in a shape is connected to the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5, and extends in a direction intersecting the arc-shaped cutting edge portion 5a at an obtuse angle in the plan view. An inner peripheral cutting blade portion (small cutting blade) 5c is formed. Then, in a side view as viewed from a direction facing the flank 4 continuous with the inner peripheral cutting edge portion 5c, the inner peripheral cutting edge portion 5c extends from the tip C1 of the arc-shaped cutting edge portion 5a as shown in FIG. It is formed in a concave shape that extends toward the seating surface 3 as it separates and then separates from the seating surface 3.

Here, the inner peripheral cutting edge portion 5c is formed in a concave curve shape that is concave toward the seating surface 3 side when viewed from the side facing the flank surface 4 connected to the inner peripheral cutting edge portion 5c. The inner peripheral cutting edge portion 5c also intersects the straight cutting edge portion 6b of the sub cutting edge 6 intersecting with the first corner portion 2a at an obtuse angle in the plan view. The second corner portion 2b of the first and second corner portions 2a, 2b of the rake face 2 has the straight cutting edge portion 5b of the main cutting edge 5 and the sub cutting edge in the plan view as described above. 6 intersects the arcuate cutting edge 6a at an obtuse angle, but the inner peripheral cutting edge is not formed at the second corner 2b.

Further, in the plan view, the front end C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 and the rear end (the sub-cutting edge) of the inner peripheral cutting edge portion 5c opposite to the front end C1 of the arc-shaped cutting edge portion 5a. In a section orthogonal to the straight line M shown in FIG. 8 connecting the tip 6 of the linear cutting blade 6b of the blade 6 and C2, in a side view as viewed from the direction facing the flank 4 continuing to the inner peripheral cutting blade 5c. The blade angle γ of the inner peripheral cutting edge portion 5c in the cross section at the position where the inner peripheral cutting edge portion 5c is most recessed toward the seating surface 3 (the cross section shown in FIG. 10) is in the range of 80 ° to 95 °. .

Furthermore, the clearance angle β of the inner peripheral cutting edge portion 5c also shown in FIG. 10 is in the range of 14 ° to 30 °. It should be noted that the clearance angle β is set such that the flank 4 is parallel to the insert center line L in the cross section orthogonal to the straight line M at the position where the inner peripheral cutting edge portion 5c is most concave toward the seating surface 3 side. It is an angle to entertain. Therefore, by giving the clearance angle β to the flank surface 4 in this way, the inner peripheral cutting edge portion 5c extends inward of the rake face 2 as the distance from the tip C1 of the arc-shaped cutting blade portion 5a increases even in the plan view. After that, it is formed in a concave shape directed outward.

As described above, the rake face 2 extends away from the main cutting edge 5 and the sub cutting edge 6 toward the inside of the rake face 2 and extends toward the seating face 3 and then forms a concave curved surface and has an outer peripheral surface of the projection 2c. The rake face 2 intersects with the inner peripheral cutting edge portion 5c at the portion having the concave curved surface shape in the plan view around the inner peripheral cutting edge portion 5c except for the protrusion 2c. The valley shape is formed so as to be concave toward the seating surface 3 side toward the valley bottom. In the present embodiment, the concave curved shape formed by the inner peripheral cutting edge portion 5c in the side view is formed by the concave curved surface of the valley bottom intersecting with the chamfered flank surface 4 connected to the inner peripheral cutting edge portion 5c. .

Furthermore, as shown in FIG. 3, a groove 8 is formed in the seating surface 3. Here, in the present embodiment, as shown in FIG. 3, when viewed from a direction perpendicular to the seating surface 3 along the insert center line L, the first and second two groove portions 8A, 8B Are formed at an interval from the opening of the mounting hole 7 in the seating surface 3 and are formed on opposite sides of the opening. The first groove 8A is formed closer to the first corner 2a of the rake face 2 than the opening of the mounting hole 7, and the second groove 8B is formed closer to the second corner 2b of the rake face 2. Have been.

These grooves 8 have a cross section perpendicular to the direction in which the grooves 8 extend, and are formed in a substantially rectangular shape flattened in the direction in which the insert center line L extends, that is, extend in a direction substantially perpendicular to the seating surface 3 and It comprises first and second two opposing wall surfaces 8a and 8b, and a bottom surface 8c extending between the first and second wall surfaces 8a and 8b and parallel to the seating surface 3. The first wall 8a of each groove 8 faces the first corner 2a of the rake face 2, and the second wall 8b faces the second corner 2b of the rake 2. The intersection ridge line between the first and second wall surfaces 8a and 8b and the seating surface 3 is chamfered by a convex curved surface, and the corner where the first and second wall surfaces 8a and 8b intersect with the bottom surface 8c is concave. It is formed in a curved shape.

The first groove 8A is open on the flank 4 connected to the linear cutting edge 6b of the sub-cutting edge 6, and is opened on the flank 4 connected to the arc-shaped cutting edge 5a of the main cutting edge 5. It is formed in a non-stop groove shape. The end of the main cutting edge 5 on the side of the arc-shaped cutting edge 5a in the first groove 8A is connected to the seating surface 3 so as to form a concave curved surface from the bottom surface 8c. Further, in the first groove portion 8A, the first and second wall surfaces 8a and 8b extend parallel to each other when viewed from the bottom, that is, the groove width of the first groove portion 8A is constant. The end of the first cutting edge 8A on the side of the arc-shaped cutting edge 5a of the main cutting edge 5 has a concave arc shape extending along the arc-shaped cutting edge 5a in a bottom view facing the seating surface 3. Is formed.

On the other hand, in the present embodiment, the second groove portion 8B is provided on both the flank surface 4 connected to the linear cutting blade portion 5b of the main cutting blade 5 and the flank surface 4 connected to the arc-shaped cutting blade portion 6a of the sub-cutting blade 6. It is formed in the shape of a through groove that opens. Further, in the present embodiment, the second groove 8B has a narrow portion 9 in which the groove width decreases from one end to the other end in the direction in which the second groove 8B extends. Here, in the present embodiment, the flank 4 side of the main cutting edge 5 continuous with the linear cutting edge portion 5b is set as one end side of the second groove portion 8B, and the arc-shaped cutting edge portion 6a of the sub cutting edge 6 is formed. The continuous flank 4 side is the other end side, and the entire second groove 8B is a narrow portion 9 as shown in FIG.

In this embodiment, the narrowing ratio of the narrow portion 9 is such that the ratio of the narrowing of the groove width is constant from one end side to the other end side of the second groove portion 8B, that is, the first and second portions of the second groove portion 8B. The two wall surfaces 8a and 8b are formed so as to approach each other in a straight line from one end to the other end in the bottom view. Further, the opening of the second groove portion 8B to the flank 4 connected to the arc-shaped cutting edge portion 6a of the sub-cutting edge 6 has an arc-shaped cutting edge portion of the sub-cutting edge 6 which forms a convex curve in a side view. 6a is located closer to the linear cutting edge 6b of the sub cutting edge 6 than the most convex point S6, which is the most convex with respect to the seating surface 3.

Here, the cutting insert 1 formed of such a hard material as a cemented carbide is manufactured according to a basic process of powder metallurgy technology. That is, when the cutting insert 1 is made of a cemented carbide, a mold is formed by using a granulated powder having tungsten carbide powder and cobalt powder as main components and, if necessary, chromium, tantalum, or the like as an auxiliary component. Is performed by powder press molding. The press-formed body thus obtained is sintered for a predetermined time in a sintering furnace controlled to an appropriate atmosphere and temperature, so that a sintered body serving as the cutting insert 1 can be manufactured. The basic shape of the cutting insert 1 is reflected by the design of the mold, and the detailed shape of the cutting insert 1 is obtained by molding. Further, in order to increase the precision of the cutting edge shape of the cutting insert 1, grinding using a grinding wheel may be performed as necessary.

The cutting insert 1 having such a configuration is detachably attached to the insert attachment seat 12 formed at the end of the end mill body 11 as described above, and has a cutting edge replaceable ball of the present invention shown in FIGS. This constitutes a first embodiment of the end mill. The end mill main body 11 is formed of a metal material such as steel, the rear end is a cylindrical shank centered on the axis O, and the front end is a convex hemisphere having a center on the axis O. I have. In the ball end mill of the present embodiment, the end mill body 11 is normally sent out in a direction intersecting the axis O while the end mill body 11 is rotated around the axis O in the end mill rotation direction T, so that the insert mounting seat 12 is provided. The workpiece is cut by the attached cutting insert 1.

In this embodiment, of the extending directions of the axis O, the direction from the shank portion of the end mill main body 11 toward the insert mounting seat 12 (the direction toward the left side in FIGS. 13 to 16) is referred to as the distal end side. A direction from the mounting seat 12 toward the shank portion (a direction toward the right side in FIGS. 13 to 16) is referred to as a rear end side. Further, a direction orthogonal to the axis O is referred to as a radial direction, a direction approaching the axis O in the radial direction is referred to as an inner peripheral side, and a direction away from the axis O is referred to as an outer peripheral side.

Here, in the present embodiment, two tip pockets 13 are formed so as to cut out the outer periphery of the end portion of the end mill main body 11, and insert mounting is performed on the bottom faces of the tip pockets 13 facing the end mill rotation direction T, respectively. The seats 12 are formed on the opposite sides at intervals in the circumferential direction. The end mill body 11 has a coolant hole 11a formed along the axis O from the shank portion as shown in FIG. 17, and the coolant hole 11a branches off at the tip end of the end mill body 11 to form the coolant hole 11a. Each of the chip pockets 13 is open. Then, two first and second cutting inserts 1A and 1B of the same shape and size based on the cutting insert 1 of the embodiment are respectively attached to the two insert mounting seats 12.

These insert mounting seats 12 have a flat bottom surface 12a facing the end mill rotation direction T, a wall surface 12b at the tip inner circumference side extending from the bottom surface 12a in the end mill rotation direction T and facing the outer circumference side of the end mill body 11, and a tip outer circumference side. And a wall surface 12c on the outer peripheral side of the rear end facing the rear surface. The wall surfaces 12b and 12c are formed in a flat shape that is inclined outwardly of the insert mounting seat 12 as the distance from the bottom surface 12a increases, and the main cutting edge 5 and the sub-cutting edge are formed with the seating surface 3 of the cutting insert 1 seated on the bottom surface 12a. The flat flank 4 connected to the linear cutting blades 5b, 6b of the blade 6 and the flat surface 4a on the seating surface 3 side of the flank 4 connected to the arc-shaped cutting blades 5a, 6a can be brought into contact. .

凹 部 A recess 12d is formed between the wall surfaces 12b and 12c to avoid contact with the curved flank 4 of the cutting insert 1. Further, a screw hole 12e into which a not-shown clamp screw inserted into the mounting hole 7 of the cutting insert 1 is formed in the bottom surface 12a. The center line of the screw hole 12e is connected to the straight cutting edge portions 5b, 6b of the main cutting edge 5 and the sub cutting edge 6 with the seating surface 3 of the cutting insert 1 seated on the bottom surface 12a as described above. With the flat surface 4a on the seating surface 3 side of the flank 4 connected to the flat flank 4 and the arc-shaped cutting blades 5a, 6a abutting against the wall surfaces 12b, 12c, the mounting hole 7 of the cutting insert 1 is formed. It is configured to be slightly eccentric to the concave portion 12d side from the center line.

The first insert mounting seat 12A of these two insert mounting seats 12 is formed so as to cut out the distal end of the end mill main body 11 to a range including the axis O on the distal end side as shown in FIGS. ing. In the first insert mounting seat 12A, the first cutting insert 1A extends the arc-shaped cutting edge portion 5a of the main cutting edge 5 from the vicinity of the axis O on a convex hemisphere having a center on the axis O. At the same time, the main cutting edge 5 is attached so that the linear cutting edge portion 5b of the main cutting edge 5 is positioned on a cylindrical surface centered on the axis O contacting the convex hemisphere.

Therefore, the flat flank 4 connected to the linear cutting edge 6b of the sub cutting edge 6 of the first cutting insert 1A is brought into contact with the wall surface 12b of the first insert mounting seat 12A, and the first insert The flat surface 4a of the flank 4 of the arcuate cutting edge 6a of the sub cutting edge 6 of the first cutting insert 1A is brought into contact with the wall surface 12c of the mounting seat 12A.

In addition, a first convex portion 14A to which the wall surface of the groove 8 formed on the seating surface 3 of the first cutting insert 1A can abut is provided on the bottom surface 12a of the first insert mounting seat 12A with a screw hole 12e. And between the inner wall surface and the wall surface 12c, and is formed to extend from the outer peripheral surface of the end portion of the end mill main body 11 toward the concave portion 12d to a position short of the concave portion 12d with an interval from the concave portion 12d. Accordingly, the second groove 8B of the grooves 8 formed on the seating surface 3 of the first cutting insert 1A comes into contact with the first protrusion 14A, and the first protrusion 14A comes into contact with the first insert mounting seat 12A. The convex portion with which the first groove 8A contacts is not formed.

Here, the first convex portion 14A has a substantially rectangular shape in which a cross section orthogonal to a direction in which the first convex portion 14A extends is flat in the end mill rotation direction T, and the whole is the narrow portion 9. With respect to the second groove portion 8B, the overall width becomes wider from the other end side in the direction in which the second groove portion 8B extends to the one end side (from the inner peripheral side to the outer peripheral side of the end mill body 11). Is formed. However, the width of the first convex portion 14A (the width in the direction orthogonal to the direction in which the first convex portion 14A extends) is a position at which the first convex portion 14A comes into contact with the first convex portion 14A in the direction in which the second groove portion 8B extends. (The width in the direction perpendicular to the direction in which the second groove 8B extends), and the height of the first protrusion 14A protruding from the bottom surface 12a is also smaller than the seating surface 3 of the first cutting insert 1A. Is slightly smaller than the depth of the second groove 8B.

On the other hand, the second insert mounting seat 12B of the two insert mounting seats 12 is formed at a position slightly away from the axis O on the distal end side of the end mill main body 11 as shown in FIGS. I have. In the second insert mounting seat 12B, the second cutting insert 1B is provided with the main cutting edge 5 of the first cutting insert 1A from a position away from the axis O of the arcuate cutting edge portion 6a of the sub cutting edge 6. The linear cutting edge portion 5b of the main cutting edge 5 of the first cutting insert 1A is positioned on the convex hemisphere where the arc-shaped cutting edge portion 5a is located. It is attached so as to be located on the cylindrical surface located.

Therefore, the planar flank 4 connected to the linear cutting edge 5b of the main cutting edge 5 of the second cutting insert 1B is brought into contact with the wall surface 12b of the second insert mounting seat 12B, and the second insert 2B is in contact with the second cutting insert 1B. The flat surface 4a of the flank 4 of the arcuate cutting edge 5a of the main cutting edge 5 of the second cutting insert 1B is brought into contact with the wall surface 12c of the mounting seat 12B.

On the bottom surface 12a of the second insert mounting seat 12B, a second convex portion 14B is formed on the tip side from the screw hole 12e, and a third convex portion is provided between the screw hole 12e and the wall surface 12c. 14C is formed. These second and third convex portions 14B and 14C also extend from the outer peripheral surface of the end portion of the end mill main body 11 toward the inner peripheral side. The second convex portion 14B is formed at a distance from the wall surface 12b of the second insert mounting seat 12B before the wall surface 12b, and the third convex portion 14C is a concave portion 12d of the second insert mounting seat 12B. Is formed at a distance from the concave portion 12d up to just before. Therefore, the second groove 8B of the second cutting insert 1B abuts on the second projection 14B, and the first groove 8A of the second cutting insert 1B abuts on the third projection 14C.

The second and third convex portions 14B and 14C also have a substantially rectangular shape whose cross section orthogonal to the direction in which the second and third convex portions 14B and 14C extend is flat in the end mill rotation direction T. In the second protrusion 14B, the entire second groove 8B of the second cutting insert 1B that is in contact with the second protrusion 14B is a narrow portion 9. On the other hand, the second groove 8B is formed such that the overall width becomes wider from the other end in the extending direction to the one end (from the outer peripheral side to the inner peripheral side of the end mill body 11). . The width of the third protrusion 14C is constant over the direction in which the third protrusion 14C extends.

Further, the widths of the second and third convex portions 14B and 14C (the widths in the direction orthogonal to the direction in which the second and third convex portions 14B and 14C extend) are also the same as the second and first groove portions 8B and 8A. Is slightly smaller than the width (the width in the direction orthogonal to the direction in which the second and first groove portions 8B and 8A extend) at the position where it contacts the second and third protrusions 14B and 14C in the extending direction. ing. The height of the second and third protrusions 14B and 14C from the bottom surface 12a of the second insert mounting seat 12B is also different from the height of the second and first grooves 8B from the seating surface 3 of the second cutting insert 1B. It is slightly smaller than the depth of 8A.

The first and second cutting inserts 1A and 1B are seated on the first and second insert mounting seats 12A and 12B as described above, and a clamp screw having an inverted frustoconical head is provided. When the screw is inserted into the mounting hole 7 and screwed into the screw hole 12 e, the center line of the screw hole 12 e is slightly eccentric to the concave portion 12 d side from the center line of the mounting hole 7 of the cutting insert 1. 1 is pressed against the recess 12d side.

At this time, in the first insert mounting seat 12A, the flank 4 continuous with the linear cutting edge 6b of the sub-cutting edge 6 of the first cutting insert 1A and the flank 4 continuous with the arc-shaped cutting edge 6a. The portion 4a is pressed against the wall surfaces 12b and 12c, respectively. Further, in the second insert mounting seat 12B, the flank 4 continuous with the linear cutting edge portion 5b of the main cutting edge 5 of the second cutting insert 1B is pressed by the wall surface 12b, and the arc-shaped cutting of the main cutting edge 5 is performed. The flat surface portion 4a of the flank surface 4 connected to the blade portion 5a is pressed against the wall surface 12c.

And, along with this, in the first insert mounting seat 12A, the second groove 8B of the first cutting insert 1A comes into contact with the first projection 14A from the tip end side of the end mill main body 11. Therefore, the second wall surface 8b of the second groove 8B of the first cutting insert 1A comes into contact with the first convex portion 14A on the side surface facing the distal end side of the end mill main body 11, and the second groove 8B , A slight space is left between the first wall surface 8a and the first convex portion 14A.

In the second insert mounting seat 12B, the second and first groove portions 8B and 8A of the second cutting insert 1B are also provided on the second and third convex portions 14B and 14C from the front end side of the end mill body 11 similarly. Abut Accordingly, the first and second groove portions 8B and 8A abut against the second and third convex portions 14B and 14C, respectively, on the side surfaces of the end mill main body 11 facing the distal end side, and the second and third convex portions 14B and 14C abut on the second wall surfaces. There is a slight space between the second wall surface 8b of the first groove portions 8B and 8A and the second and third convex portions 14B and 14C. As described above, the first and second grooves 8A and 8B abut on the first to third protrusions 14A to 14C, so that the cutting insert 1 can be prevented from shifting due to the load during the cutting. .

And in such a cutting edge exchange type ball end mill to which the cutting insert 1 having the above configuration is attached, the inner peripheral cutting edge portion 5c intersecting with the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A is provided. As seen in a plan view from the direction opposite to the rake face 2, as shown in FIG. 18, the rear end side of the arc-shaped cutting edge portion 5a extends from the front end C1 of the arc-shaped cutting blade portion 5a toward the inner peripheral side of the end mill body 11 beyond the axis O. Extending toward. Further, as shown in FIG. 19, when viewed from the front end side of the end mill main body 11 in the direction of the axis O, the inner peripheral cutting edge 5c has a straight line N connecting the axis O and the tip C1 of the arc-shaped cutting edge 5a. Is located on the end mill rotation direction T side.

In the present embodiment, the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the arc-shaped cutting edge in plan view as viewed from the direction facing the rake face 2. A straight line M connecting the rear end C2 of the inner peripheral cutting edge portion 5c on the opposite side to the front end C1 of the portion 5a has an inclination angle α in a range of 30 ° to 70 ° with respect to a plane P perpendicular to the axis O. And extends toward the rear end side toward the inner peripheral side of the end mill body 11.

In addition, in the blade-end exchangeable ball end mill according to the present embodiment, as shown in FIG. 18, as viewed in a plan view from the direction facing the rake face 2 of the first cutting insert 1 </ b> A, the axis O and the circle of the main cutting edge 5. The main cutting edge 5 of the first cutting insert 1A is larger than the interval A in the direction perpendicular to the axis O between the front end C1 of the arcuate cutting edge 5a and the rear end C2 of the inner peripheral cutting edge 5c on the opposite side. The distance B between the tip C1 of the arcuate cutting edge portion 5a and the axis O in the direction perpendicular to the axis O is small.

Specifically, in a plan view seen from the direction facing the rake face 2, the axis O and the inside of the opposite side to the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A. The interval A between the peripheral cutting edge 5c and the rear end C2 in the direction perpendicular to the axis O is in the range of 0.23 mm or more and 1.25 mm or less. Similarly, in a plan view seen from the direction opposite to the rake face 2, the axis is perpendicular to the axis O between the tip C 1 of the arc-shaped cutting edge portion 5 a of the main cutting edge 5 of the first cutting insert 1 A and the axis O. The interval B in any direction is set to be in a range of more than 0.0 mm and 0.80 mm or less, so that A> B.

In the cutting insert 1 and the cutting edge replaceable ball end mill configured as described above, the inner peripheral cutting edge portion 5c that intersects the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A at an obtuse angle. In the plan view facing the rake face 2, the front end C1 extends beyond the axis O toward the rear end side toward the inner peripheral side of the end mill body 11, and extends from the front end side in the direction of the axis O along the axis O. 19, as shown in FIG. 19, it is located on the end mill rotation direction side with respect to the straight line N connecting the axis O and the tip C1 of the arc-shaped cutting blade portion 5a. For this reason, even when the end mill main body 11 is fed to the front end side in the direction of the axis O to perform a punching process on a workpiece, the inner peripheral cutting edge portion 5c is a portion around the axis O at the front end of the end mill main body 11. The center of rotation can be cut.

In the case of performing such a punching process, or by feeding the end mill main body 11 only in a direction intersecting the axis O, the arc-shaped cutting edge portions 5a and 6a of the main cutting edge 5 and the sub-cutting edge 6 are used to cut the work piece. Even in the case of machining a concave arc-shaped wall surface, in the cutting insert 1 and the cutting edge replaceable ball end mill having the above-described configuration, the inner peripheral cutting edge portion 5c of the main cutting edge 5 is connected to the inner peripheral cutting edge portion 5c. In a side view as viewed from a direction facing the surface 4, the concave shape extends toward the seating surface 3 side of the cutting insert 1 as it moves away from the tip C1 of the arcuate cutting edge portion 5 a of the main cutting edge 5 and then separates from the seating surface 3. Since it is formed, the chips generated by the inner peripheral cutting edge portion 5c are also generated so that the cross section becomes concave.

Accordingly, the chips generated in the concave shape in this manner are difficult to be caught, and are substantially perpendicular to the inner peripheral cutting edge portion 5c in plan view when viewed from the direction facing the rake face 2, that is, the blade end milling type ball end mill. The outflow direction is controlled and discharged in the direction toward the outer peripheral side as going toward the rear end side of the end mill body 11. For this reason, the chips generated so as to be entrained flow out to the inner peripheral side of the end mill main body 11 to cause chip clogging, and the chips thus flown to the inner peripheral side cause the main cutting edge 5 to rotate as the end mill main body 11 rotates. Can be prevented from being degraded by being caught between the arcuate cutting edge portion 5a and the work surface of the work material.

Further, in the present embodiment, the inner peripheral cutting edge portion 5c is formed in a concave curve shape that is concave toward the seating surface 3 in a side view when viewed from a direction opposite to the flank surface 4 connected to the inner peripheral cutting edge portion 5c. Therefore, when chips having a concave cross section are generated as described above, it is possible to suppress concentration of stress due to a cutting load on the inner peripheral cutting edge portion 5c. Accordingly, it is possible to prevent a situation in which the cutting insert 1 is damaged due to the occurrence of cracks from the inner peripheral cutting edge portion 5c due to such concentration of stress.

Furthermore, in the present embodiment, the tip of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A (the tip of the inner peripheral cutting edge portion 5c) in a plan view viewed from the direction facing the rake face 2. FIG. 10 and FIG. 20 show a cross section orthogonal to a straight line M connecting C1 and a rear end C2 of the inner peripheral cutting edge 5c on the opposite side to the tip C1 of the arc-shaped cutting edge 5a. When viewed from the side facing the flank 4, the blade angle γ of the inner peripheral cutting edge 5 c in the cross section at the position where the inner peripheral cutting edge 5 c is most concave toward the seating surface 3 is 80 ° to 95 °. It is within the range.

For this reason, it is possible to prevent the cutting resistance from increasing while securing the cutting edge strength of the inner peripheral cutting edge portion 5c to prevent a loss or the like. That is, if the blade angle γ at the position where the inner peripheral cutting edge portion 5c is most concave to the seating surface 3 side is less than 80 °, it is not possible to secure sufficient cutting edge strength for the inner peripheral cutting edge portion 5c. The fracture resistance may be impaired. On the other hand, when the blade angle γ exceeds 95 °, rake is performed to secure the clearance angle of the inner peripheral cutting edge portion 5c of the main cutting edge 5 of the first cutting insert 1A attached to the end mill main body 11. The angle must be increased to the negative angle side, which may increase the cutting resistance. The blade angle γ of the inner peripheral cutting edge portion 5c is more preferably in the range of 82 ° to 93 °, and further preferably in the range of 83 ° to 92 °.

In the present embodiment, the clearance angle β of the inner peripheral cutting edge portion 5c is set in a range of 14 ° to 30 °, whereby the cutting resistance can be reduced, and the arc-shaped cutting edge can be achieved. It is possible to improve the processing surface accuracy in the case where the processing surface having a concave arcuate cross section is formed by the portion 5a. That is, when the clearance angle β of the inner peripheral cutting edge portion 5c is less than 14 °, the flank surface 4 comes into contact with the flank surface where the flank surface comes into contact with the processing surface of the work material, thereby increasing the cutting resistance and the roughness of the processing surface roughness. Deterioration may be caused. On the other hand, when the clearance angle β of the inner peripheral cutting edge portion 5c exceeds 30 °, the machining surface accuracy when the arcuate cutting edge portion 5a of the main cutting edge 5 forms a concave arc-shaped machining surface may decrease. There is. The clearance angle β of the inner peripheral cutting edge 5c is more preferably in the range of 18 ° to 26 °, and further preferably in the range of 20 ° to 24 °.

Furthermore, in the cutting insert 1 of the present embodiment, the rake face 2 has a valley bottom that intersects the inner peripheral cutting edge 5c in the plan view around the inner peripheral cutting edge 5c, and faces the valley bottom. As a result, the chips generated by the inner peripheral cutting edge portion 5c can be guided along the valley bottom formed by the rake face 2 because of the valley shape recessed toward the seating surface. For this reason, chips can be more reliably discharged to the outer peripheral side of the end mill main body 11, and chip clogging and chip entrapment can be more effectively prevented.

On the other hand, in the blade tip exchange type ball end mill of the present embodiment, as viewed in a plan view from the direction facing the rake face 2, the tip c1 of the arc-shaped cutting edge portion 5a and the arc-shaped cutting edge as shown in FIG. A straight line M connecting the rear end C2 of the inner peripheral cutting edge portion 5c on the opposite side to the front end C1 of the portion 5a forms an inclination angle α within a range of 30 ° to 70 ° with respect to a plane P perpendicular to the axis O. The cutting insert 1 having the above-described configuration is attached as the first cutting insert 1A so as to extend toward the rear end side toward the inner peripheral side of the end mill body 11. For this reason, while maintaining the strength of the main cutting edge 5, it is possible to prevent an increase in the cutting resistance and a deterioration in the machined surface roughness.

That is, if the inclination angle α is less than 30 °, a flank contact may occur, leading to an increase in cutting resistance and deterioration of the machined surface roughness. In addition, there is a possibility that the cutting resistance may increase in the above-described punching. On the other hand, when the inclination angle α exceeds 70 °, the intersection angle between the inner peripheral cutting edge 5c and the arc-shaped cutting edge 5a at the tip C1 of the arc-shaped cutting edge 5a, which is the tip of the main cutting edge 5, becomes larger. There is a possibility that chipping may occur at the tip C1 due to the decrease in strength due to the reduction in size. The inclination angle α is more preferably in the range of 40 ° to 60 °, and further preferably in the range of 45 ° to 50 °.

Further, in the present embodiment, in the above-mentioned plan view facing the rake face 2, the inner circumferential cut on the opposite side to the axis O and the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A. The distance between the front end C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the axis O is larger than the interval A in the direction perpendicular to the axis O with the rear end C2 of the blade portion 5c. The interval B in the vertical direction is reduced.

For this reason, the inner peripheral cutting edge portion 5c extending from the tip C1 of the arc-shaped cutting edge portion 5a to the opposite side beyond the axis O to the rotation center portion at the tip end portion of the end mill body 11 at the time of the above-described punching. Cutting around the axis O can be reliably performed. Further, when forming a processing surface having a concave circular cross section by the circular cutting edge portion 5a, it is possible to prevent the processing surface accuracy from being impaired due to the arc cutting edge portion 5a becoming too short.

In particular, in the present embodiment, the axis O and the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 are opposite to each other in plan view when viewed from the direction facing the rake face 2 of the first cutting insert 1A. The interval A between the inner peripheral cutting edge 5c and the rear end C2 in the direction perpendicular to the axis O is in the range of 0.23 mm or more and 1.25 mm or less, and the tip C1 of the arc-shaped cutting edge 5a Since the distance B between the axis O and the direction perpendicular to the axis O is within a range of more than 0.0 mm and 0.80 mm or less, such an effect can be more reliably achieved.

That is, when the distance A in the direction perpendicular to the axis O between the axis O and the rear end C2 of the inner peripheral cutting edge portion 5c of the first cutting insert 1A is less than 0.23 mm, the axis O of the end of the end mill main body 11 becomes smaller. In the upper rotation center portion, the length of the inner peripheral cutting edge portion 5c extending beyond the axis O in the plan view from the tip end C1 of the arc-shaped cutting edge portion 5a is shortened, and the tip end side in the axis O direction at the time of punching. When the feed amount to the end mill is large, there is a possibility that the tip of the end mill body 11 comes into contact with the work material. If the distance A is larger than 1.25 mm, the first insert mounting seat 12A must be formed so as to protrude largely beyond the axis O of the end mill body 11, and the first insert mounting seat 12A must There is a possibility that the thickness of the end portion of the end mill main body 11 on the side of the end mill decreases, leading to a decrease in strength. The distance A in the direction perpendicular to the axis O between the axis O and the rear end C2 of the inner peripheral cutting edge portion 5c of the first cutting insert 1A is in the range of 0.24 mm or more and 1.20 mm or less. It is more desirable that the distance be in the range of 0.25 mm or more and 1.15 mm or less.

Further, the distance B between the tip C1 of the arc-shaped cutting edge portion 5a and the axis O of the end mill main body 11 is equal to or less than 0.0 mm, which means that the arc-shaped cutting edge portion 5a faces the rake face 2 in plan view. The tip C1 is located on the axis O or located at a position beyond the axis O, and the inner peripheral cutting edge portion 5c does not function as a cutting edge at the time of punching, so that flank contact may occur. There is. Furthermore, if the distance B between the tip C1 of the arc-shaped cutting edge portion 5a and the axis O of the end mill main body 11 is larger than 0.80 mm, the arc-shaped cutting edge portion 5a is provided at the center of rotation at the front end portion of the end mill main body 11. There is a possibility that the portion where no is formed becomes large, and the processing surface accuracy when forming a processing surface having a concave arcuate cross section is reduced. The distance B between the tip C1 of the arc-shaped cutting edge portion 5a and the axis O of the end mill body 11 is more desirably within a range of more than 0.0 mm and 0.70 mm or less, and more preferably less than 0.0 mm. It is more desirable that the distance be as large as 0.60 mm or less.

On the other hand, in the cutting insert 1 and the cutting edge replaceable ball end mill of the present embodiment, the second groove 8B of the groove 8 of the cutting insert 1 is moved from one end to the other end in the direction in which the second groove 8B extends. Since the groove portion has a narrow portion 9 having a narrower width, the other end side of the second groove portion 8B in which the groove width of the narrow portion 9 becomes smaller secures a large thickness of the cutting insert 1. Strength can be improved. For this reason, even if an excessive load acts on the cutting insert 1 at the time of cutting, it is possible to prevent the second groove portion 8B from causing damage to the cutting insert 1.

On the other hand, on the one end side in the direction in which the second groove 8B extends, the narrow portion 9 has a groove width that is conversely wide. Therefore, in the end mill body 11 of the replaceable blade end mill, the narrow portion of the second groove 8B is formed. The first and second projections 14A and 14B in the portion where the projection 9 abuts can be formed wide. For this reason, the mounting rigidity of the cutting insert 1 with respect to the load at the time of cutting can be increased, and the cutting insert 1 can be more reliably prevented from being displaced, thereby performing high-precision cutting.

Furthermore, in the cutting insert 1 of the first embodiment, the rake face 2 is formed so as to extend toward the seating face 3 as the rake face 2 moves away from the main cutting edge 5 and the sub cutting edge 6 toward the inside of the rake face 2. As a result, the sharpness of the main cutting edge 5 and the sub cutting edge 6 can be sharpened, so that the cutting resistance can be reduced. The rake face 2 may be formed so as to extend parallel to the seating face 3 in a cross section perpendicular to the main cutting edge 5 and the sub cutting edge 6 in the plan view, for example.

On the other hand, on the other hand, like the cutting insert 21 of the second embodiment of the present invention shown in FIGS. 21 to 29, the rake face 2 has at least the vicinity of the arc-shaped cutting blades 5a, 6a. It may be inclined so as to move away from the seating surface 3 as it moves away from the arcuate cutting blades 5a, 6a. In the cutting insert 21 according to the second embodiment shown in FIGS. 21 to 29, the same reference numerals are assigned to portions common to the cutting insert 1 according to the first embodiment shown in FIGS. I have.

Here, in the cutting insert 21 according to the second embodiment, as shown in FIG. 24, the most convex point of the arcuate cutting edge portion 5 a of the main cutting edge 5 in a plan view viewed from a direction facing the rake face 2. S5 passes through the center of the hemisphere formed by the rotation trajectory of the arcuate cutting edge portion 5a when the cutting insert 21 is mounted on the first insert mounting seat of the end mill main body of the end-mill type ball end mill, and passes through the arcuate cutting edge portion. It is located substantially on a straight line (a straight line showing a ZZ cross section in FIG. 24) at an angle of 45 ° from the contact point between 5a and the straight cutting edge portion 5b of the main cutting edge 5 to the tip C1 side of the arc cutting edge portion 5a. Are arranged as follows.

In the second embodiment, as shown in FIG. 29, in a cross section passing through the most convex point S5 and parallel to the insert center line L, an arc-shaped crossing angle between the rake face 2 and the flank face 4 is formed. The rake face 2 is inclined so as to face the opposite side to the seating face 3 as the rake face 2 moves away from the arcuate cutting edge 5a so that the blade angle δ of the cutting edge 5a becomes an obtuse angle of 92 °. Note that the sub cutting edge 6 has the same configuration. In the second embodiment, the rake face 2 is not provided with the concave groove 2d.

According to the cutting insert 21 of the second embodiment configured as described above, the blade angle δ of the arc-shaped cutting edge portion 5a is increased, thereby improving the edge strength of the arc-shaped cutting edge portion 5a. Therefore, the fracture resistance of the arcuate cutting edge portion 5a can be improved. Note that, inside the rake face 2 away from the arc-shaped cutting edge 5a, the rake face 2 is inclined so as to move toward the seating surface 3 as the distance from the arc-shaped cutting edge 5a increases, as in the first embodiment. May be. In the second embodiment, the rake face 2 of the linear cutting edge 5b is also inclined toward the side opposite to the seating surface 3 as the distance from the linear cutting edge 5b increases. Conversely, it may be inclined so as to face the seating surface 3 side.

On the other hand, in the cutting inserts 1 and 21 of the first and second embodiments, the arc-shaped cutting edge portion 5a of the main cutting edge 5 is formed so as to draw a single arc in the plan view. As in the cutting insert 31 according to the third embodiment of the present invention shown in FIG. 30 and the ball-end mill of the second embodiment, the inner cutting edge 5a of the main cutting edge 5 is provided. A first cutting edge portion 5A is formed on the opposite side to the blade portion 5C, and a second cutting edge portion 5B is formed on the inner peripheral cutting edge portion 5C side. The radius of curvature RB may be larger than the radius of curvature RA of the first cutting edge 5A, and may be retracted from the extension of the first cutting edge 5A toward the inner peripheral cutting edge 5c. . In FIG. 30, the same reference numerals are assigned to portions common to the cutting insert 1 and the replaceable ball end mill of the first embodiment shown in FIGS. 1 to 20.

Here, in the present embodiment, as shown in FIG. 30, the second cutting edge portion 5B is closer to the inner peripheral cutting edge portion 5c than the most convex point S5 of the arcuate cutting edge portion 5a (in the plan view). It is formed on the tip C1 side of the arc-shaped cutting edge 5a. Further, also in the blade end replaceable ball end mill of the second embodiment, the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 31A in which the main cutting edge 5 is directed to the outer peripheral side of the end of the end mill body 11 is provided. The tip C1 is located on the tip side in the direction of the axis O with respect to the tip C3 of the arc-shaped cutting portion 6a of the second cutting insert 31B in which the sub cutting edge 6 is directed to the tip outer peripheral side of the end mill main body 11. Further, in the cutting insert 31 according to the third embodiment, the rake face 2 is not provided with the concave groove 2d.

In the cutting insert 31 of the third embodiment and the replaceable blade end mill of the second embodiment configured as described above, the circle on the main cutting edge 5 of the first cutting insert 31A indicated by reference numeral Q1 in FIG. The position of the tip C1 of the arc-shaped cutting edge 5a extends the first cutting edge 5A of the arc-shaped cutting edge 5a indicated by reference numeral Q2 in FIG. The position of the distal end C3 of the arc-shaped cutting edge portion 6a of the secondary cutting edge 6a of the second cutting insert 31B of the second cutting insert 31B shown by reference numeral Q3 in FIG. It will be located on the tip side in the direction of the axis O.

For this reason, in the cutting insert 31 of the third embodiment and the replaceable cutting edge ball end mill of the second embodiment, the tip of the arc-shaped cutting edge portion 5a, 6a of the first and second cutting inserts 31A, 31B. The step in the direction of the axis O between C1 and C3 can be reduced to reduce the thickness of the chips. Moreover, the second cutting edge portion 5B of the arcuate cutting edge portion 5a of the first cutting insert 31A has an extension of the second cutting edge portion 5A with a radius RB larger than the radius RA of the first cutting edge portion 5A. Since it is retracted from the line, the thickness of the chip when the end mill main body 11 is sent out in a direction perpendicular to the axis O, for example, becomes thinner. Therefore, according to the present embodiment, it is possible to reduce the load on the arcuate cutting edge portion 5a of the first cutting insert 31A and improve the fracture resistance.

Moreover, in the present embodiment, the inner peripheral cutting edge portion is viewed from the side in which the arcuate cutting edge portion 5a of the first cutting insert 31A is opposed to the flank 4 continuing to the arcuate cutting edge portion 5a. It is formed in the shape of a convex curve that goes away from the seating surface 3 toward the 5c side and then toward the seating surface 3 side, has the most convex point S5 that protrudes the most with respect to the seating surface 3, and has the second shape. The cutting edge portion 5B is formed closer to the inner peripheral cutting edge portion 5c than the most convex point S5. For this reason, since the thickness of the chips can be further reduced, even under unstable machining conditions such as intermittent cutting with large chatter vibration, the chipping resistance at the tip of the arc-shaped cutting edge portion 5a is remarkably enhanced. be able to.

Although the first cutting edge 5A and the second cutting edge 5B may intersect at an obtuse angle as shown in FIG. 30, the first cutting edge 5A and the second cutting edge 5B. It is desirable that the radius increases toward 5B and that the first cutting edge portion 5A and the second cutting edge portion 5B are connected via a convex curved connecting portion in contact with the second cutting edge portion 5B. Thereby, the processed surface of the work material can be finished smoothly.

In addition to connecting the small-diameter portion and the large-diameter portion via such a connecting portion, for example, the radius of curvature of the arc-shaped cutting edge portion 5a may be changed from the first cutting edge portion 5A toward the second cutting edge portion 5B. May be formed in an elliptical arc shape in which is gradually increased. Further, arcs having three or more radii may be connected so that the radius becomes larger toward the tip C1 of the arc-shaped cutting edge portion 5a.

Furthermore, it is desirable that the circumferential length of the second cutting edge portion 5B in the plan view be shorter than the circumferential length of the first cutting edge portion 5A. In addition, the center of the second cutting edge portion 5B may be located on the axis O in the plan view in a state where the first cutting insert 31A is attached to the end mill main body 11, and may be separated from the axis O. Position.

ADVANTAGE OF THE INVENTION According to this invention, a chip | tip can generate | occur | produce a cross-section concave shape which is hard to be caught by a concave inner peripheral cutting edge part, and the outflow direction of the chip | tip generated in this way goes to the rear end side of an end mill main body. In the direction toward the outer peripheral side. For this reason, the chips flow out to the inner peripheral side of the end mill main body, causing chip clogging, and the chips thus flowing out to the inner peripheral side are caught between the arc-shaped cutting edge portion and the processing surface, so that the processing surface roughness is reduced. In addition, it is possible to prevent the deterioration of the end mill, and to perform a punching process of feeding the end mill body toward the front end in the axial direction by using the inner peripheral cutting edge portion.

Reference Signs List 1 (1A, 1B), 21, 31A, 31B Cutting insert 2 Rake surface 2a First corner portion of rake surface 2b Second corner portion of rake surface 2 3 Seating surface 4 Flank 5 Main cutting edge (cutting edge) )
5a Arc-shaped cutting edge portion of main cutting edge 5 5b Linear cutting edge portion of main cutting edge 5 5c Inner peripheral cutting edge portion 5A First cutting edge portion 5B Second cutting edge portion 6 Secondary cutting edge (cutting edge)
6a Arc-shaped cutting edge portion of sub-cutting edge 6 6b Linear cutting edge portion of sub-cutting edge 6 7 Mounting hole 8 (8A, 8B) Groove 9 Narrow portion 11 End mill body 12 (12A, 12B) Insert mounting seat 14A- 14C Convex part L Insert center line S5, S6 Most convex point O Axis line of end mill body 11 T End mill rotation direction C1 Tip of arcuate cutting edge 5a of main cutting edge 5 C2 Rear end C3 of inner peripheral cutting edge 5c Secondary cutting Tip A of the arcuate cutting edge 6a of the blade 6 A Between the axis O and the rear end C2 of the inner peripheral cutting edge 5c of the first cutting insert 1A in a plan view viewed from the direction facing the rake face 2. The distance B in the direction perpendicular to the axis O of the first cutting insert 1A between the tip C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 and the axis O in a plan view seen from the direction facing the rake face 2. Spacing in the direction perpendicular to the axis O between A straight line connecting the front end C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the rear end C2 of the inner peripheral cutting edge portion 5c in a plan view viewed from a direction facing the rake face 2. N When viewed from the front of the end mill main body 11 in the direction of the axis O, a straight line α rake face 2 connecting the axis O and the tip C1 of the arc-shaped cutting edge 5a of the main cutting edge 5 of the first cutting insert 1A is formed. In a plan view as viewed from the opposite direction, a straight line M connecting the front end C1 of the arc-shaped cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the rear end C2 of the inner peripheral cutting edge portion 5c is an axis O. Angle β with respect to a plane P perpendicular to the clearance angle β The clearance angle of the inner peripheral cutting edge 5c
γ Blade angle of the inner peripheral cutting edge 5c δ Blade angle of the arcuate cutting edge 5a RA Radius of the first cutting edge 5A RB Radius of the second cutting edge 5B

Claims (14)

1. A cutting insert removably attached to an insert mounting seat formed at a tip end of an end mill body of a tip-changeable ball end mill rotated around an axis,
   A rake face oriented in the direction of rotation of the end mill body, a seat face facing the opposite side of the rake face and seated on the bottom surface of the insert mounting seat, and a flank extending around the rake face and the seat face. With
   At the intersection ridge line portion of the rake face and the flank face, an arc-shaped cutting edge portion extending in a convex arc shape in a plan view viewed from a direction facing the rake face, and a leading end of the arc-shaped cutting edge portion. A cutting edge provided with the arc-shaped cutting edge portion and an inner peripheral cutting edge portion extending in a direction intersecting at an obtuse angle in the plan view;
   The inner peripheral cutting edge portion, when viewed from the side facing the flank face connected to the inner peripheral cutting edge portion, extends toward the seating surface side as it moves away from the tip of the arc-shaped cutting edge portion, and A cutting insert formed in a concave shape away from a seating surface.
2. The inner peripheral cutting edge portion is formed in a concave curve shape that is concave toward the seating surface side in a side view as viewed from a direction facing the flank surface connected to the inner peripheral cutting edge portion. Item 7. The cutting insert according to Item 1.
3. A straight line connecting the front end of the arc-shaped cutting edge and the rear end of the inner peripheral cutting edge opposite to the front end of the arc-shaped cutting edge in a plan view viewed from a direction facing the rake face. Of the inner peripheral cutting edge portion in a cross section at a position where the inner peripheral cutting edge portion is most concave toward the seating surface side in a side view viewed from the direction facing the flank surface, The cutting insert according to claim 1 or 2, wherein the cutting insert is set in a range of ° to 95 °.
4. The cutting insert according to any one of claims 1 to 3, wherein a clearance angle of the inner peripheral cutting edge portion is in a range of 14 ° to 30 °.
5. The rake face has a valley bottom that intersects the inner circumference cutting edge in a plan view viewed from a direction facing the rake face in the vicinity of the inner circumference cutting edge, and the rake bottom faces toward the valley bottom. The cutting insert according to any one of claims 1 to 4, wherein the cutting insert is formed in a valley shape recessed on the seating surface side.
6. The rake face, at least in the vicinity of the arc-shaped cutting edge portion, is inclined parallel to the seating surface or inclined toward the seating surface side as the distance from the arc-shaped cutting edge portion increases. The cutting insert according to any one of claims 1 to 5.
7. The claim according to claim 1, wherein the rake face is inclined at least around the arc-shaped cutting edge so as to move toward the opposite side to the seating surface as the distance from the arc-shaped cutting edge increases. Item 6. The cutting insert according to any one of Items 5.
8. In a plan view seen from a direction facing the rake face, a first cutting edge portion is formed on the arc-shaped cutting edge portion on a side opposite to the inner peripheral cutting edge portion, and the inner peripheral cutting edge is formed. A second cutting edge portion is formed on the blade portion side, the second cutting edge portion has a larger radius of curvature than the first cutting edge portion, and the inner radius of the first cutting edge portion. The cutting insert according to any one of claims 1 to 7, wherein the cutting insert is retracted from an extension line to the peripheral cutting edge portion side.
9. In a side view seen from a direction facing the flank facing the flank connected to the arc-shaped cutting edge, the arc-shaped cutting edge is separated from the seating surface toward the inner peripheral cutting edge, and the seating surface is separated from the seating surface. It is formed in a convex curve shape toward the side, and has the most protruding point most protruding with respect to the seating surface,
   The cutting insert according to claim 8, wherein the second cutting edge portion is formed closer to the inner peripheral cutting edge portion than the most convex point.
10. The first cutting edge and the second cutting edge have a radius of curvature that increases from the first cutting edge toward the second cutting edge, and the first cutting edge and the second cutting edge. The cutting insert according to claim 8 or 9, wherein the cutting insert is connected via a convex curved connecting portion that is in contact with the cutting edge portion.
11. A cutting edge replaceable ball end mill in which the cutting insert according to any one of claims 1 to 10 is detachably mounted on an insert mounting seat formed at a tip portion of an end mill body that is rotated around an axis. And
    The arc-shaped cutting blade portion of the cutting blade is arranged on a spherical surface having a rotation locus about the axis centered on the axis,
    The inner peripheral cutting edge portion of the cutting edge extends rearward beyond the axis as going from the front end of the arcuate cutting edge portion toward the inner peripheral side of the end mill body in plan view as viewed from a direction facing the rake face. While extending toward the side, and is located on the end mill rotation direction side with respect to a straight line connecting the axis and the tip of the arc-shaped cutting blade portion in a front view as viewed from the tip side in the axial direction. Interchangeable blade end mill.
12. A straight line connecting the front end of the arc-shaped cutting edge and the rear end of the inner peripheral cutting edge opposite to the front end of the arc-shaped cutting edge in a plan view viewed from a direction facing the rake face. Extends at an inclination angle in the range of 30 ° to 70 ° with respect to a plane perpendicular to the axis, toward the inner peripheral side of the end mill body and toward the rear end side. Item 12. An exchangeable ball end mill according to item 11.
13. In a plan view seen from a direction facing the rake face, a distance in a direction perpendicular to the axis with the rear end of the inner peripheral cutting edge opposite to the axis and the tip of the arc-shaped cutting edge. The blade end exchangeable ball end mill according to claim 11 or 12, wherein an interval between a tip of the arcuate cutting edge portion and the axis in a direction perpendicular to the axis is small.
14. In a plan view seen from the direction facing the rake face, the distance in the direction perpendicular to the axis with the rear end of the inner circumferential cutting edge opposite to the axis and the tip of the arcuate cutting edge is A range of not less than 0.23 mm and not more than 1.25 mm, and a distance between a tip of the arcuate cutting edge portion and the axis in a direction perpendicular to the axis is larger than 0.0 mm and not more than 0.80 mm. The ball end mill having a replaceable cutting edge according to claim 13, wherein:

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