JPWO2020039981A1 - Cutting inserts and replaceable cutting edge ball end mills - Google Patents

Abstract

A cutting insert (1) that is attached to the insert mounting seat of a ball end mill with interchangeable blades, and has a rake face (2) that faces the direction of rotation of the end mill and a seating surface (3) that faces the opposite side of the rake face (2). A rake face (2) and a flank surface (4) extending around the rake face (2) and the seating surface (3) are provided. ) Is connected to the tip of the arcuate cutting edge portion (5a) extending in a convex arc shape in the plan view and the arcuate cutting edge portion (5a) in the plan view. A cutting edge (5) having an inner peripheral cutting edge portion (5c) extending in a direction intersecting with the inner peripheral cutting edge portion (5c) is formed, and the inner peripheral cutting edge portion (5c) is a relief connected to the inner peripheral cutting edge portion (5c). When viewed from the side facing the surface (4), it is formed in a concave shape that extends toward the seating surface (3) as it moves away from the tip of the arcuate cutting edge portion (5a) and then separates from the seating surface (3). NS.

Description

The present invention is a cutting insert that is detachably attached to an insert mounting seat formed at the tip of the end mill body of a ball end mill with a replaceable cutting edge that is rotated around an axis, and the cutting insert is an insert mounting seat at the tip of the end mill body. Regarding a ball end mill with a replaceable cutting edge that is detachably attached to.
The present application claims priority based on Japanese Patent Application No. 2018-155368 filed in Japan on August 22, 2018, the contents of which are incorporated herein by reference.

As such a cutting insert, for example, in Patent Document 1, one end of the arcuate cutting edge portion of the cutting edge of the insert body extends on a virtual plane in which the arcuate cutting edge portion is located and has an blunt angle to the arcuate cutting edge portion. The one in which a short inner peripheral cutting edge portion (small cutting edge) intersecting with the above is described. Further, in Patent Document 2, a cutting insert in which an inner peripheral cutting edge portion (small cutting edge) is formed at one end of such an arcuate cutting edge portion is provided, and the inner peripheral cutting edge portion is used as the rotation axis of the end mill body. Blade tip replaceable ball end mills mounted so as to intersect are described.

In such a cutting insert and a ball end mill with a replaceable cutting edge, an arcuate cutting edge is applied to a portion of the cutting edge where a large cutting load is applied because the rotation speed is close to 0 and is located near the rotation axis of the end mill body. Since the inner peripheral cutting edge portion that intersects at an obtuse angle is formed in the portion, the cutting edge strength can be ensured. Therefore, it is possible to prevent the insert body from being damaged such as a chip due to such a large cutting load.

Japanese Unexamined Patent Publication No. 7-276128 Japanese Unexamined Patent Publication No. 11-197933

By the way, when such an inner peripheral cutting edge portion is formed in a direction that intersects the arcuate cutting edge portion at an blunt angle, a virtual cutting edge portion is formed like the cutting insert described in Patent Document 1. If the inner peripheral cutting edge portion is located on a flat surface, that is, if the inner peripheral cutting edge portion is linear, chips are generated so as to be involved, and the outflow direction is not controlled and the inner circumference of the end mill body is not controlled. There is a risk of it leaking to the side. When the chips flow out to the inner peripheral side of the end mill body in this way, chip clogging occurs, or the chips that flow out to the inner peripheral side flow out to the inner peripheral side as the end mill body rotates, and the arcuate cutting edge portion and the machined surface of the work material are processed. There is a risk that it will be bitten between the and the machined surface and the roughness of the machined surface will deteriorate.

The present invention is made under such a background, and an inner peripheral cutting edge portion extending in a direction that intersects the arcuate cutting edge portion at an blunt angle is provided at one end (tip) of the arc-shaped cutting edge portion of the cutting edge. When formed, it is possible to prevent chips generated by the inner peripheral cutting edge portion from flowing out to the inner peripheral side of the end mill body, and to prevent chip clogging and deterioration of machined surface roughness. It is an object of the present invention to provide an insert and a ball end mill with a replaceable cutting edge to which such a cutting insert is detachably attached.

In order to solve the above problems and achieve such an object, the cutting insert of the present invention is attached to and detached from the insert mounting seat formed at the tip of the end mill body of the blade tip exchange type ball end mill rotated around the axis. A cutting insert that can be mounted, a rake surface that is oriented in the direction of rotation of the end mill body, a seating surface that faces the opposite side of the rake surface and is seated on the bottom surface of the insert mounting seat, and these rake surfaces. An arc-shaped cutting extending in a convex arc shape in a plan view from a direction facing the rake surface is provided at the intersection ridge of the rake surface and the escape surface. A cutting edge including a blade portion and an inner peripheral cutting edge portion that is connected to the tip of the arc-shaped cutting edge portion and extends in a direction that intersects the arc-shaped cutting edge portion at an blunt angle in the plan view is formed. The peripheral cutting edge portion extends toward the seating surface side as the distance from the tip of the arcuate cutting edge portion increases in a side view seen from a direction facing the flank surface connected to the inner peripheral cutting edge portion, and then the seating surface. It is characterized in that it is formed in a concave shape away from.

Further, the blade tip exchange type ball end mill of the present invention is a blade edge exchange type ball end mill in which such a cutting insert is detachably attached to an insert mounting seat formed at the tip of an end mill body that is rotated around an axis. Therefore, the arcuate cutting edge portion of the cutting edge is arranged on a spherical surface whose rotation locus around the axis line has a center on the axis line, and the inner peripheral cutting edge portion of the cutting edge is the rake surface. In a plan view viewed from the direction facing the end mill, the end mill extends from the tip of the arcuate cutting edge toward the inner peripheral side of the end mill body so as to extend beyond the axis toward the rear end and from the tip side in the axis direction. When viewed from the front, it is characterized in that it is located on the end mill rotation direction side with respect to the straight line connecting the axis and the tip of the arcuate cutting edge 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 side surface of the inner peripheral cutting edge portion as viewed from the direction facing the flank surface connected to the inner peripheral cutting edge portion. In view, since it is formed in a concave shape that extends toward the seating surface side of the insert body as it moves away from the tip of the arcuate cutting edge portion and then separates from the seating surface, the chips generated by this inner peripheral cutting edge portion also have a cross section. Will be generated so as to have a concave shape, and it will be difficult to get caught.

The chips generated in this way are substantially orthogonal to the inner peripheral cutting edge portion in a plan view from the direction facing the rake face of the insert body, that is, the rear end of the end mill body in the blade tip exchange type ball end mill. It flows out and is discharged in the direction toward the outer peripheral side as it goes toward the side. For this reason, chips may flow out to the inner peripheral side of the end mill body to cause chip clogging, or the chips flowing out to the inner peripheral side may be caught between the arcuate cutting edge and the machined surface as the end mill body rotates. This can prevent deterioration of the machined surface roughness.

Further, in the ball end mill with replaceable cutting edge having the above configuration, the inner peripheral cutting edge portion of the cutting edge is located from the tip of the arcuate cutting edge portion to the inner peripheral side of the end mill body when viewed from the direction facing the rake face. It extends beyond the above axis toward the rear end side as it goes toward it, and is located on the end mill rotation direction side of the straight line connecting the axis and the tip of the arcuate cutting edge when viewed from the tip side in the axis direction. ing. Therefore, the inner peripheral cutting edge portion is parallel to the straight line connecting the tip of the arc-shaped cutting edge portion and the rear end of the inner peripheral cutting edge portion on the side opposite to the tip of the arc-shaped cutting edge portion in the above front view. It is located on the side opposite to the seating surface with respect to the straight line passing through the axis line, and is arranged so-called centered up. Then, the chips generated by the inner peripheral cutting edge portion are generated so that the cross section has a concave shape, and the chips are formed into a vine-wound shape and are difficult to be caught.

Therefore, by feeding the end mill body in the direction perpendicular to the axis, the arcuate cutting edge can form a machined surface having a concave arc shape in the work material, and the end mill body can be moved toward the tip side in the axis direction. When performing thrusting to cut the work material by giving a feed, the inner peripheral cutting edge of the part that reaches the axis of the end mill body from the tip of the arcuate cutting edge in a plan view from the direction facing the rake face. As a result, it is possible to cut the rotation center portion, which is the portion around the axis line at the tip end portion of the end mill body.

Here, the inner peripheral cutting edge portion of the cutting insert is formed in a concave curved shape recessed toward the seating surface side when viewed from the side facing the flank surface connected to the inner peripheral cutting edge portion. Is desirable. If the inner peripheral cutting edge portion is, for example, V-shaped 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 and the rear end of the inner peripheral cutting edge portion on the opposite side of the tip of the arc-shaped cutting edge portion are Of the cross sections orthogonal to the straight line to be connected, the blade angle of the inner peripheral cutting edge portion in the cross section at the position where the inner peripheral cutting edge portion is most recessed toward the seating surface in the side view viewed from the direction facing the flank surface. Is preferably in the range of 80 ° to 95 °. If the cutting edge angle in the cross section at the position where the inner peripheral cutting edge is most recessed is less than 80 °, it becomes impossible to secure sufficient cutting edge strength for the inner peripheral cutting edge, and the fracture resistance may be impaired. There is. On the other hand, if the cutting tool angle exceeds 95 °, the cutting resistance may increase. The blade angle of the inner peripheral cutting edge portion is more preferably in the range of 82 ° to 93 °, and further preferably in the range of 83 ° to 92 °.

Further, it is desirable that the clearance angle of the inner peripheral cutting edge portion is within the range of 14 ° to 30 °. If the clearance angle of the inner peripheral cutting edge is less than 14 °, the clearance surface may come into contact with the machined surface of the work material, causing an increase in cutting resistance and deterioration of 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 becomes the axis when viewed from the tip side in the axial direction of the end mill body like the blade tip exchange type ball end mill having the above configuration. If the end mill is located closer to the rotation direction of the end mill than the straight line connecting the tip of the arc-shaped cutting edge, the machined surface accuracy may decrease when the arc-shaped cutting edge forms a machined surface with a concave arc shape. 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 portion that intersects the inner peripheral cutting edge portion in a plan view seen from a direction facing the rake face in the vicinity of the inner peripheral cutting edge portion, and the valley bottom portion has a valley bottom portion. It is desirable that it is formed in a valley shape that is recessed toward the seating surface side. As a result, the chips generated by the inner peripheral cutting edge portion can be guided along the valley-shaped valley bottom formed by the rake face, and can be more reliably discharged to the outer peripheral side of the end mill body.

Further, the rake face may be inclined so as to be parallel to the seating surface or toward the seating surface side as the distance from the arc-shaped cutting edge portion increases, at least around the arc-shaped cutting edge portion. As a result, the sharpness of the arcuate cutting edge portion can be sharpened and the cutting resistance can be reduced.

On the other hand, on the contrary, the rake face may be inclined toward the side opposite to the seating surface as the distance from the arc-shaped cutting edge portion increases, at least around the arc-shaped cutting edge portion. .. As a result, the cutting edge angle of the arcuate cutting edge portion can be increased to improve the fracture resistance.

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

As a result, for example, as in the blade tip exchange type ball end mill described in Patent Documents 1 and 2, the inner peripheral cutting edge portion is on the opposite side of the first cutting insert attached so as to intersect the rotation axis of the end mill body. , When a second cutting insert whose arc-shaped cutting edge portion is arranged at a position away from the rotation axis is attached, the axis line between the tips of the arc-shaped cutting edge portions of these first and second cutting inserts. The step in the direction can be reduced to reduce the thickness of the chips. Therefore, the load on the cutting edge can be reduced and the fracture resistance can be improved.

In this case, when the arcuate cutting edge portion is viewed from the side facing the flank surface connected to the arcuate cutting edge portion, the arcuate cutting edge portion is viewed from the seating surface toward the inner peripheral cutting edge portion side. When it is formed in a convex curve shape toward the seating surface side after being separated and has the most protruding maximum convex point with respect to the seating surface, the inner peripheral cutting edge portion side of the most convex point is closer to the seating surface. It is desirable that the second cutting edge portion is formed therein. As a result, the thickness of the chips can be further reduced, so that the fracture resistance at the tip of the cutting edge can be remarkably improved even under unstable machining conditions such as intermittent cutting with large chatter vibration.

Further, the first cutting edge portion and the second cutting edge portion may be formed so as to intersect at an obtuse angle, but the curvature from the first cutting edge portion toward the second cutting edge portion. It is desirable that the radius becomes large and the first cutting edge portion and the second cutting edge portion are connected via a convex curved connecting portion in contact with the second cutting edge portion. This makes it possible to finish the machined surface of the work material smoothly. In this way, the first cutting edge portion and the second cutting edge portion are connected via a convex curved connecting portion in which the radius of curvature increases from the first cutting edge portion to the second cutting edge portion. Alternatively, for example, the arcuate cutting edge portion may be formed in an elliptical arc shape in which the radius of curvature gradually increases from the second cutting edge portion toward the first cutting edge portion.

On the other hand, in the blade tip exchange type ball end mill having the above configuration, the tip of the arcuate cutting edge portion and the tip of the arcuate cutting edge portion are opposite to the tip of the arcuate cutting edge portion in a plan view from the direction facing the rake face. The straight line connecting the rear end of the inner peripheral cutting edge portion moves toward the rear end side toward the inner peripheral side of the end mill body at an inclination angle within the range of 30 ° to 70 ° with respect to the plane perpendicular to the axis. It is desirable that it extends toward you.

That is, if this inclination angle is less than 30 °, flank contact occurs, which causes an increase in cutting resistance and deterioration of the machined surface roughness, and there is a possibility that the cutting resistance also increases in the above-mentioned thrusting. .. On the other hand, when this inclination angle exceeds 70 °, the intersection angle between the inner peripheral cutting edge portion and the arc-shaped cutting edge portion intersecting the tip of the arc-shaped cutting edge portion at the tip end portion of the cutting edge becomes small, and the strength decreases. However, 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 viewed from a direction facing the rake face, the axis is perpendicular to the axis of the rear end of the inner peripheral cutting edge portion opposite to the tip of the arcuate cutting edge portion. 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. As a result, the above-mentioned thrusting process can be reliably performed, and the inner peripheral cutting edge portion between the tip of the arc-shaped cutting edge portion and the axis line is prevented from becoming too long, and the arc-shaped cutting edge portion is prevented from becoming too long. It is possible to secure the accuracy of the machined surface having a concave arc shape in cross section.

Specifically, in a plan view viewed from the direction facing the rake face, the axis is perpendicular to the axis and the rear end of the inner peripheral cutting edge portion opposite to the tip of the arcuate cutting edge portion. The distance between the tip of the arcuate cutting edge and the axis in the direction perpendicular to the axis is larger than 0.0 mm and is 0, while the distance in the above direction is 0.23 mm or more and within the range of 1.25 mm or less. It is desirable that it is within the range of .80 mm or less.

If the distance between the axis of the end mill body and the rear end of the inner peripheral cutting edge on the opposite side of the tip of the arcuate cutting edge is less than 0.23 mm in the direction perpendicular to the axis, the end mill body will be thrust during thrusting. If the amount of feed to the tip side in the axial direction is large, the tip of the end mill body may come into contact with the work material. Further, if the distance between the axis of the end mill body and the rear end of the inner peripheral cutting edge portion is so large that it exceeds 1.25 mm, an insert mounting seat that greatly protrudes to the side beyond the axis of the end mill body must be formed. However, there is a risk that the wall thickness of the tip of the end mill body will decrease on the side beyond this axis, leading to a decrease in strength. The distance between the axis of the end mill body and the rear end of the inner peripheral cutting edge opposite to the tip of the arcuate cutting edge in the direction perpendicular to the axis is in the range of 0.24 mm or more and 1.20 mm or less. It is more desirable that it is within the range of 0.25 mm or more and 1.15 mm or less.

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, so that the tip of the arcuate cutting edge is arranged on the axis or is located beyond the axis. The inner peripheral cutting edge portion does not act as a cutting edge at the time of thrusting, and there is a possibility that a flank contact may occur. Further, if the distance between the tip of the arc-shaped cutting edge and the axis of the end mill body is larger than 0.80 mm, the portion where the arc-shaped cutting edge is not formed becomes large at the tip of the end mill body, and the cross section is concave. There is a risk that the machined surface accuracy when forming the machined surface will decrease. The distance between the tip of the arcuate cutting edge and the axis in the direction perpendicular to the axis is more preferably greater than 0.0 mm and within the range of 0.70 mm or less, and more than 0.0 mm. It is more desirable that it is largely within the range of 0.60 mm or less.

As described above, according to the present invention, the concave inner peripheral cutting edge portion can generate a concave cross section in which chips are less likely to be caught, and the outflow direction of the chips thus generated can be set to the end mill main body. It can be controlled in the direction toward the outer peripheral side toward the rear end side. For this reason, chips may flow out to the inner peripheral side of the end mill body to cause chip clogging, or the chips flowing out to the inner peripheral side may be caught between the arcuate cutting edge portion and the machined surface to make the machined surface roughness. It is possible to prevent the deterioration of the. Further, by using this inner peripheral cutting edge portion, it is possible to perform a thrusting process in which the end mill main body is fed to the tip side in the axial direction.

It is a perspective view which shows the 1st Embodiment of the cutting insert of this invention. FIG. 5 is a plan view of the cutting insert shown in FIG. 1 as viewed from a direction facing the rake face. FIG. 5 is a bottom view of the cutting insert shown in FIG. 1 as viewed from a direction facing the seating surface on the side opposite to the rake surface. It is a side view of the arrow line V direction view in FIG. It is a side view of the arrow line W direction view in FIG. It is a side view of the arrow X direction view in FIG. It is a side view of the arrow line Y direction view in FIG. It is an enlarged plan view of the part A in FIG. It is an enlarged side view of the part B in FIG. FIG. 2 is a cross-sectional view taken along the line ZZ in FIG. It is a perspective view of the tip end part of the end mill main body which shows 1st Embodiment of the cutting edge exchange type ball end mill of this invention. It is a front view which saw the cutting edge exchange type ball end mill shown in FIG. 11 from the tip side in the axial direction. It is a top view of the arrow line V direction view in FIG. It is a side view of the arrow line W direction view in FIG. It is a bottom view of the arrow X direction view in FIG. It is a side view of the arrow line Y direction view in FIG. FIG. 14 is a cross-sectional view taken along the line ZZ in FIG. It is an enlarged plan view of the part A in FIG. It is an enlarged front view of the part B in FIG. FIG. 13 is a cross-sectional view taken along the line ZZ in FIG. It is a perspective view which shows the 2nd Embodiment of the cutting insert of this invention. FIG. 21 is a perspective view of the cutting insert shown in FIG. 21 as viewed from the rake face side. FIG. 21 is a perspective view of the cutting insert shown in FIG. 21 as viewed from the seating surface side. FIG. 21 is a plan view of the cutting insert shown in FIG. 21 as viewed from a direction facing the rake face. It is a side view of the arrow line W direction view in FIG. 24. It is a side view of the arrow line X direction view in FIG. 24. It is a side view of the arrow line Y direction view in FIG. 24. It is an enlarged side view around the inner peripheral cutting edge portion of the cutting insert shown in FIG. 21 corresponding to the B portion in FIG. It is a ZZ cross-sectional view in FIG. 24. The arrow in FIG. 12 of the tip of the end mill body showing the third embodiment of the cutting insert of the present invention and the second embodiment of the cutting edge replaceable ball end mill of the present invention to which the cutting insert of the third embodiment is attached. It is a figure corresponding to the plan view of the line V direction view.

1 to 10 show the cutting insert 1 of the first embodiment of the present invention. Further, FIGS. 11 to 20 show the first one of the ball end mill with replaceable cutting edge of the present invention, in which the cutting insert 1 of this embodiment is detachably attached to the insert mounting seat 12 formed at the tip of the end mill main body 11. It shows the tip part of the embodiment.

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

The intersecting ridges of the rake face 2 and the flank 4 are formed by arcuate cutting edge portions 5a and 6a extending in an arc shape as shown in FIG. 2 in the above plan view seen from the direction facing the rake face 2. Two cutting blades having linear cutting edge portions 5b and 6b extending so as to be in contact with the arc-shaped cutting edge portions 5a and 6a are the arc-shaped cutting edge portions 5a and 6a and the linear cutting edge portions 5b and 6b, respectively. Are alternately positioned in the circumferential direction of the rake face 2. One of these two cutting blades is the main cutting blade 5, and the other cutting blade is the secondary cutting blade 6.

Further, the flank surface 4 is inclined so as to be directed toward the inner peripheral side of the cutting insert 1 from the rake surface 2 toward the seating surface 3, and the cutting insert 1 of the present embodiment is a positive type cutting insert. There is. Further, a mounting hole 7 having a circular cross section formed around the insert center line L is opened in the central portion of the rake face 2 and the seating surface 3 so as to penetrate the cutting insert 1. The portion of the mounting hole 7 on the rake face 2 side is formed so that the diameter decreases toward the seating surface 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 above plan view, the arcuate cutting edge portion 5a of the main cutting edge 5 has a substantially 1/4 arcuate shape. On the other hand, the arcuate cutting edge portion 6a of the sub cutting edge 6 has the same radius as the arcuate cutting edge portion 5a of the main cutting edge 5, but the length in the circumferential direction is the arcuate cutting edge of the main cutting edge 5. It is shorter than the portion 5a, that is, it is formed in an arc shape shorter than the 1/4 arc. Along with this, the linear cutting edge portion 5b of the main cutting edge 5 is conversely shorter than the linear cutting edge portion 6b of the sub cutting edge 6. That is, the cutting insert 1 of the present embodiment is not formed 180 ° rotationally symmetrically around the insert center line L, and is asymmetrical.

Further, the linear cutting edge portions 5b and 6b of the main cutting edge 5 and the sub cutting edge 6 are the linear cutting edge portions 6b of the arcuate cutting edge portion 5a of the main cutting edge 5 and the sub cutting edge 6 in the above plan view. From the first corner portion 2a of the rake face 2 where It extends toward the corner portion 2b so as to approach each other. Further, these first and second corner portions 2a and 2b are chamfered so as to intersect the arcuate cutting edge portions 5a and 6a of the main cutting edge 5 and the sub cutting edge 6 and the linear cutting edge portions 5b and 6b at an obtuse angle. It is formed in a shape. Further, the first corner portion 2a is arranged closer to the seating surface 3 than the second corner portion 2b.

Furthermore, the arcuate cutting edge portions 5a and 6a of the main cutting edge 5 and the sub cutting edge 6 are separated from the seating surface 3 side as they are separated from the linear cutting edge portions 5b and 6b, respectively, and then the seating surface 3 side. It is formed in a convex curve shape that approaches, and the convex curve formed by the arcuate cutting edge portion 5a of the main cutting edge 5 is the most distant and convex point with respect to the seating surface 3 (most protruding from the seating surface 3). The 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 the most distant and convex with respect to the seating surface 3. (The point most protruding from the seating surface 3) is the most convex point S6 of the arcuate cutting edge portion 6a of the secondary cutting edge 6. The linear cutting edges 5b and 6b of the main cutting edge 5 and the secondary cutting edge 6 are arcuate cutting edges as shown in FIGS. 5 and 7 even when viewed from the side facing the flank surface 4. It is in contact with the convex curve formed by the portions 5a and 6a, and extends in a substantially straight line approaching the seating surface 3 side as the distance from the arcuate cutting edge portions 5a and 6a increases.

Further, around the opening of the mounting hole 7 in the central portion of the rake face 2, a substantially elliptical shape is formed in the plan view in which the main cutting blade 5 and the sub cutting blade 6 project in a direction away from the seating surface 3. 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 to the upper end surface of the protrusion 2c. Further, the outer peripheral surface of the protrusion 2c is inclined toward the inside of the rake surface 2 toward the upper end surface side.

Furthermore, the rake face 2 extends toward the seating surface 3 as it moves away from the main cutting edge 5 and the secondary cutting edge 6 toward the inside of the rake face 2, and then forms a concave curved surface to form the outer peripheral surface of the protrusion 2c. It is connected to. Further, on the rake face 2 between the arcuate cutting edge portions 5a and 6a of the main cutting edge 5 and the sub cutting edge 6 and the protrusion 2c, the arcuate cutting edge portions 5a and 6a are viewed in a plan view. In the above, a plurality of concave grooves 2d extending shortly in the radial direction of the arcuate cutting edge portions 5a and 6a are formed at intervals in the circumferential direction of the arcuate cutting edge portions 5a and 6a.

Further, the flanks 4 connected to the linear cutting edges 5b and 6b of the main cutting edge 5 and the secondary cutting edge 6 are moved toward the inner peripheral side of the cutting insert 1 from the rake surface 2 toward the seating surface 3 as described above. It is formed in a plane that slopes toward it. On the other hand, the flank 4 connected to the arcuate cutting edge portions 5a and 6a of the main cutting edge 5 and the sub cutting edge 6 is in the circumferential direction of the cutting insert 1 along the arcuate cutting edge portions 5a and 6a on the rake face 2 side. However, as described above, the seating surface 3 side is a flat surface cut out in a plane shape while being inclined toward the inner peripheral side of the cutting insert 1 from the rake surface 2 toward the seating surface 3 side. It has a part 4a.

Furthermore, of the first and second corner portions 2a and 2b of the rake face 2, chamfering that intersects the arcuate cutting edge portion 5a of the main cutting edge 5 and the linear cutting edge portion 6b of the secondary cutting edge 6. 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 blade 5 and extends in a direction that intersects the arc-shaped cutting edge portion 5a at an blunt angle in the plan view. An inner peripheral cutting edge portion (small cutting edge) 5c is formed. The inner peripheral cutting edge portion 5c is viewed from the tip C1 of the arcuate cutting edge portion 5a as shown in FIG. 9 when viewed from the side facing the flank 4 connected to the inner peripheral cutting edge portion 5c. It is formed in a concave shape that extends toward the seating surface 3 as the distance increases and then separates from the seating surface 3.

Here, the inner peripheral cutting edge portion 5c is formed in a concave curved shape recessed 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. Further, the inner peripheral cutting edge portion 5c also intersects the linear cutting edge portion 6b of the auxiliary cutting edge 6 intersecting the first corner portion 2a at an obtuse angle in the above plan view. Of the first and second corner portions 2a and 2b of the rake face 2, the second corner portion 2b is the linear cutting edge portion 5b of the main cutting edge 5 and the secondary cutting edge in the above plan view as described above. Although it intersects the arcuate cutting edge portion 6a of No. 6 at an obtuse angle, the inner peripheral cutting edge portion is not formed in the second corner portion 2b.

Further, in the above plan view, the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 and the rear end (secondary cutting) of the inner peripheral cutting edge portion 5c on the side opposite to the tip end C1 of the arcuate cutting edge portion 5a. Of the cross section orthogonal to the straight line M shown in FIG. 8 connecting C2 with the tip of the linear cutting edge portion 6b of the blade 6, in the side view seen from the direction facing the flank 4 connected to the inner peripheral cutting edge portion 5c. The blade angle γ of the inner peripheral cutting edge portion 5c in the cross section (cross section shown in FIG. 10) at the position where the inner peripheral cutting edge portion 5c is most recessed toward the seating surface 3 is in the range of 80 ° to 95 °. ..

Further, the clearance angle β of the inner peripheral cutting edge portion 5c also shown in FIG. 10 is within the range of 14 ° to 30 °. The clearance angle β is defined with respect to a straight line in which the clearance surface 4 is parallel to the insert center line L in the cross section at the position where the inner peripheral cutting edge portion 5c is most recessed toward the seating surface 3 in the cross section orthogonal to the straight line M. It is a cross section. Therefore, by giving the clearance angle β to the clearance surface 4 in this way, the inner peripheral cutting edge portion 5c extends inward of the rake face 2 as it is separated from the tip C1 of the arcuate cutting edge portion 5a even in the above plan view. After that, it is formed in a concave shape toward the outside.

As described above, the rake face 2 extends toward the seating surface 3 as it moves away from the main cutting edge 5 and the secondary cutting edge 6 toward the inside of the rake face 2, and then forms a concave curved surface to form an outer peripheral surface of the protrusion 2c. The rake face 2 intersects the inner peripheral cutting edge portion 5c with the concave curved surface in the plan view around the inner peripheral cutting edge portion 5c excluding the protruding portion 2c. It has a valley bottom portion to be formed, and is formed in a valley shape recessed toward the seating surface 3 side toward the valley bottom portion. 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 the chamfered flank surface 4 connected to the inner peripheral cutting edge portion 5c. ..

Further, as shown in FIG. 3, a groove 8 is formed on the seating surface 3. Here, in the present embodiment, as shown in FIG. 3, the first and second groove portions 8A and 8B are viewed from the bottom surface viewed from a direction perpendicularly opposed to the seating surface 3 along the insert center line L. However, the seating surface 3 is formed on opposite sides to each other with a space between the opening and the opening of the mounting hole 7. The first groove 8A is formed on the first corner 2a side of the rake face 2 with respect to the opening of the mounting hole 7, and the second groove 8B is formed on the second corner 2b side of the rake face 2. Has been done.

These groove portions 8 have a cross section orthogonal to the extending direction of the groove portion 8 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 extend from each other. It includes two facing first and second wall surfaces 8a and 8b, and a bottom surface 8c parallel to a seating surface 3 extending between these first and second wall surfaces 8a and 8b. The first wall surface 8a of each groove portion 8 faces the first corner portion 2a side of the rake face 2, and the second wall surface 8b faces the second corner portion 2b side of the rake face 2. The intersecting ridges of the first and second wall surfaces 8a and 8b and the seating surface 3 are chamfered by a convex curved surface, and the corners where the first and second wall surfaces 8a and 8b and the bottom surface 8c intersect are concave. It is formed in a curved shape.

Further, the first groove portion 8A opens in the flank 4 connected to the linear cutting edge portion 6b of the secondary cutting edge 6 and also opens in the flank 4 connected to the arcuate cutting edge portion 5a of the main cutting blade 5. It is formed in the shape of a blind groove. The end of the main cutting edge 5 on the arcuate cutting edge portion 5a side of the first groove portion 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 in the bottom view, that is, the groove width of the first groove portion 8A is constant. Further, the end portion of the main cutting edge 5 on the arc-shaped cutting edge portion 5a side of the first groove portion 8A has a concave arc shape extending along the arc-shaped cutting edge portion 5a in the bottom view facing the seating surface 3. It is formed.

On the other hand, in the present embodiment, the second groove 8B is provided on both the flank 4 connected to the linear cutting edge 5b of the main cutting edge 5 and the flank 4 connected to the arcuate cutting edge 6a of the sub cutting edge 6. It is formed in the shape of a through groove that opens. Further, in the present embodiment, the second groove portion 8B has a narrow portion 9 in which the groove width becomes narrower from one end side to the other end side in the direction in which the second groove portion 8B extends. Here, in the present embodiment, the flank 4 side connected to the linear cutting edge portion 5b of the main cutting edge 5 is set to one end side of the second groove portion 8B, and the arcuate cutting edge portion 6a of the sub cutting edge 6 is formed. The side of the connecting flanks 4 is the other end side, and as shown in FIG. 3, the entire second groove 8B is the narrow portion 9.

Further, in the narrow portion 9, in the present embodiment, the ratio of narrowing 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 first grooves 8B of the second groove portion 8B. The wall surfaces 8a and 8b of No. 2 are formed so as to form a straight line and approach each other from one end side to the other end side in the bottom view. Further, the opening of the second groove 8B to the flank 4 connected to the arcuate cutting edge portion 6a of the secondary cutting edge 6 has a convex curved shape in the side view. 6a is located closer to the linear cutting edge portion 6b of the secondary cutting edge 6 than the most convex point S6 at which the 6a is most convex with respect to the seating surface 3.

Here, the cutting insert 1 formed of such a hard material such as cemented carbide is manufactured according to the basic process of powder metallurgy technology. That is, when the cutting insert 1 is made of cemented carbide, a mold is used by using a granular granulated powder containing tungsten carbide powder and cobalt powder as main components and chromium, tantalum and the like as subcomponents as necessary. Perform powder press molding using. The press-molded body thus obtained can be sintered for a predetermined time in a sintering furnace controlled to an appropriate atmosphere and temperature to produce a sintered body to be the cutting insert 1. The basic shape of the cutting insert 1 is reflected by the above-mentioned mold design, and the detailed shape of the cutting insert 1 is obtained by mold molding. Further, in order to improve the accuracy of the cutting edge shape of the cutting insert 1, grinding processing using a grinding wheel may be performed as necessary.

The cutting insert 1 having such a configuration is detachably attached to the insert mounting seat 12 formed at the tip of the end mill body 11 as described above, and the cutting edge replaceable ball of the present invention shown in FIGS. 11 to 20 is attached. It constitutes the first embodiment of the end mill. The end mill main body 11 is formed of a metal material such as a steel material, and the rear end portion is a columnar shank portion centered on the axis O, and the tip portion is a convex hemisphere having a center on the axis line O. There is. In the ball end mill with replaceable cutting edge of the present embodiment, the end mill main body 11 is rotated around the axis O in the end mill rotation direction T, and is normally sent out in a direction intersecting the axis O to the insert mounting seat 12. The work material is cut by the attached cutting insert 1.

In the present embodiment, of the directions in which the axis O extends, 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 tip side, and the insert is inserted. The direction from the mounting seat 12 toward the shank portion (direction toward the right side in FIGS. 13 to 16) is referred to as a rear end side. Further, the direction orthogonal to the axis O is referred to as a radial direction, the direction of the radial direction approaching the axis O is referred to as the inner peripheral side, and the direction away from the axis O is referred to as the outer peripheral side.

Here, in the present embodiment, two tip pockets 13 are formed so as to cut out the outer periphery of the tip portion of the end mill main body 11, and inserts are attached to the bottom surfaces of these tip pockets 13 facing the end mill rotation direction T, respectively. The seats 12 are formed on opposite sides of each other at intervals in the circumferential direction. A coolant hole 11a is formed in the end mill main body 11 along the axis O from the shank portion as shown in FIG. 17, and the coolant hole 11a branches at the tip end portion of the end mill main body 11 to form the above 2 Each of the three chip pockets 13 is open. Then, two first and second cutting inserts 1A and 1B of the same shape and the same size based on the cutting insert 1 of the above embodiment are attached to the two insert mounting seats 12, respectively.

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

Further, between these wall surfaces 12b and 12c, a recessed recess 12d is formed in order to avoid contact with the curved flank surface 4 of the cutting insert 1. Further, the bottom surface 12a is formed with a screw hole 12e into which a clamp screw (not shown) inserted into the mounting hole 7 of the cutting insert 1 is screwed. The center line of the screw hole 12e is connected to the linear cutting edge portions 5b and 6b of the main cutting edge 5 and the sub cutting edge 6 by seating the seating surface 3 of the cutting insert 1 on the bottom surface 12a as described above. With the flat surface portion 4a on the seating surface 3 side of the flank surface 4 connected to the flat flank surface 4 and the arcuate cutting edge portions 5a and 6a in contact with the wall surfaces 12b and 12c, the mounting hole 7 of the cutting insert 1 It is designed to be slightly eccentric to the recess 12d side of the center line.

Of these two insert mounting seats 12, the first insert mounting seat 12A is formed so as to cut out the tip end portion of the end mill main body 11 on the tip end side to a range including the axis O as shown in FIGS. 11 to 14. ing. In the first insert mounting seat 12A, the first cutting insert 1A is located on a convex hemisphere having an arcuate cutting edge portion 5a of the main cutting edge 5 extending from the vicinity of the axis O and having a center on the axis O. At the same time, the linear cutting edge portion 5b of the main cutting edge 5 is attached so as to be positioned on a cylindrical surface centered on the axis O in contact with the convex hemisphere.

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

Further, on the bottom surface 12a of the first insert mounting seat 12A, a first convex portion 14A to which the wall surface of the groove portion 8 formed on the seating surface 3 of the first cutting insert 1A can come into contact is provided with a screw hole 12e. It is formed so as to project between the wall surface 12c and the wall surface 12c and extend from the outer peripheral surface of the tip end portion of the end mill main body 11 toward the recess 12d to the front of the recess 12d at a distance from the recess 12d. Therefore, the second groove 8B of the groove 8 formed on the seating surface 3 of the first cutting insert 1A comes into contact with the first convex portion 14A, and the first insert mounting seat 12A is in contact with the second groove 8B. The convex portion with which the first groove portion 8A abuts is not formed.

Here, the first convex portion 14A has a substantially rectangular shape in which the cross section orthogonal to the extending direction of the first convex portion 14A is flattened in the end mill rotation direction T, and the whole is a narrow portion 9. The width of the second groove 8B becomes wider as a whole from the other end side in the extending direction toward the one end side (from the inner peripheral side to the outer peripheral side of the end mill main body 11). Is formed in. However, the width of the first convex portion 14A (the width in the direction orthogonal to the extending direction of the first convex portion 14A) is at a position where the second convex portion 8B abuts on the first convex portion 14A in the extending direction. The width of the first convex portion 14A is slightly smaller than the width of the first convex portion 14A (the width in the direction orthogonal to the extending direction of the second groove portion 8B), and the protruding height of the first convex portion 14A from the bottom surface 12a is also the seating surface 3 of the first cutting insert 1A. It is made slightly smaller than the depth of the second groove 8B from.

On the other hand, of the two insert mounting seats 12, the second insert mounting seat 12B is formed from a position slightly distant from the axis O on the distal end side of the end mill main body 11 as shown in FIGS. 15 and 16. There is. The second cutting insert 1B is attached to the second insert mounting seat 12B, and the arcuate cutting edge portion 6a of the secondary cutting edge 6 is placed on the main cutting edge 5 of the first cutting insert 1A from a position away from the axis O. The arcuate cutting edge portion 5a is positioned on the convex hemisphere where the arcuate cutting edge portion 5a is located, and the linear cutting edge portion 6b of the sub cutting edge 6 is formed by the linear cutting edge portion 5b of the main cutting edge 5 of the first cutting insert 1A. It is attached so as to be positioned on the above-mentioned cylindrical surface in which it is located.

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

A second convex portion 14B is formed on the bottom surface 12a of the second insert mounting seat 12B on the tip side of the screw hole 12e, and a third convex portion is formed 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 tip 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 up to the front of the wall surface 12b of the second insert mounting seat 12B, and the third convex portion 14C is the concave portion 12d of the second insert mounting seat 12B. It is formed at a distance from the recess 12d up to the front of the recess. Therefore, the second groove 8B of the second cutting insert 1B abuts on the second convex portion 14B, and the first groove 8A of the second cutting insert 1B abuts on the third convex portion 14C.

Further, these second and third convex portions 14B and 14C also have a substantially rectangular shape in which the cross section orthogonal to the extending direction of the second and third convex portions 14B and 14C is flattened in the end mill rotation direction T. Of these, the second convex portion 14B has a narrow portion 9 as a whole of the second groove portion 8B of the second cutting insert 1B that comes into contact with the second convex portion 14B. On the other hand, the second groove 8B is formed so as to become wider as a whole from the other end side in the extending direction toward the one end side (from the outer peripheral side to the inner peripheral side of the end mill main body 11). .. The width of the third convex portion 14C is constant along the direction in which the third convex portion 14C extends.

Further, the widths of the second and third convex portions 14B and 14C (widths in the direction orthogonal to the extending direction of the second and third convex portions 14B and 14C) are also the widths of the second and first groove portions 8B and 8A. Is slightly smaller than the width at the position where the second and third convex portions 14B and 14C abut in the extending direction (the width in the direction orthogonal to the extending direction of the second and first groove portions 8B and 8A). ing. Further, the protruding heights of the second and third convex portions 14B and 14C from the bottom surface 12a of the second insert mounting seat 12B are also the second and first groove portions 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 truncated cone-shaped head is provided. When the screw hole 12e is inserted through the mounting hole 7 and screwed into the screw hole 12e, the center line of the screw hole 12e is slightly eccentric to the recess 12d side of 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 plane of the flank 4 connected to the linear cutting edge portion 6b of the sub cutting edge 6 of the first cutting insert 1A and the flank surface 4 connected to the arcuate cutting edge portion 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 connected to the linear cutting edge portion 5b of the main cutting edge 5 of the second cutting insert 1B is pressed against 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 4 connected to the blade portion 5a is pressed against the wall surface 12c.

At the same time, in the first insert mounting seat 12A, the second groove portion 8B of the first cutting insert 1A comes into contact with the first convex portion 14A from the tip end side of the end mill main body 11. Therefore, the second wall surface 8b of the second groove portion 8B of the first cutting insert 1A abuts on the side surface of the end mill main body 11 facing the tip end side of the first convex portion 14A, and the second groove portion 8B There will be a slight gap between the first wall surface 8a and the first convex portion 14A.

Further, in the second insert mounting seat 12B, the second and first groove portions 8B and 8A of the second cutting insert 1B are similarly connected to the second and third convex portions 14B and 14C from the tip end side of the end mill main body 11. Contact. Therefore, the first wall surfaces 8a of the second and first groove portions 8B and 8A abut on the side surfaces of the end mill main body 11 facing the tip end side of the second and third convex portions 14B and 14C, respectively, and the second , There is a slight gap between the second wall surface 8b of the first groove portions 8B and 8A and the second and third convex portions 14B and 14C. In this way, by bringing the first and second groove portions 8A and 8B into contact with the first to third convex portions 14A to 14C, it is possible to prevent the cutting insert 1 from shifting due to a load during cutting. ..

Then, in such a blade tip 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 the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A is As shown in FIG. 18 in a plan view seen from the direction facing the rake face 2, the rear end side crosses the axis O from the tip C1 of the arcuate cutting edge portion 5a toward the inner peripheral side of the end mill main body 11. It extends toward. Further, the inner peripheral cutting edge portion 5c is a straight line N connecting the axis line O and the tip end C1 of the arcuate cutting edge portion 5a as shown in FIG. 19 when viewed from the front end side in the axis O direction of the end mill main body 11. It is located on the T side of the end mill rotation direction.

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

Further, in the blade tip exchange type ball end mill of the present embodiment, as shown in FIG. 18 in a plan view of the first cutting insert 1A when viewed from the direction facing the rake surface 2, the axis O and the main cutting edge 5 are circular. The main cutting edge 5 of the first cutting insert 1A is larger than the distance A in the direction perpendicular to the axis O between the inner peripheral cutting edge portion 5c and the rear end C2 on the side opposite to the tip end C1 of the arc-shaped cutting edge portion 5a. 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 viewed from the direction facing the rake face 2, the inside of the axis O and the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A are opposite to each other. The distance A in the direction perpendicular to the axis O between the peripheral cutting edge portion 5c and the rear end C2 is 0.23 mm or more and 1.25 mm or less. Similarly, in a plan view viewed from the direction facing the rake face 2, it is perpendicular to the axis O between the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the axis O. The distance B in the above direction is larger than 0.0 mm and within the range of 0.80 mm or less, and the relationship of A> B is set.

In the cutting insert 1 and the blade tip exchange type ball end mill configured in this way, the inner peripheral cutting edge portion 5c that intersects the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A at an blunt angle. In the plan view facing the rake face 2, the tip C1 extends toward the inner peripheral side of the end mill main body 11 beyond the axis O and toward the rear end side, and the front view seen from the tip side in the O direction of the axis. Then, 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 arcuate cutting edge portion 5a. Therefore, even when the end mill main body 11 is fed to the tip end side in the axis O direction to thrust the work material, the inner peripheral cutting edge portion 5c is a portion around the axis line O at the tip end portion of the end mill main body 11. The center of rotation can be cut.

Then, when such a thrusting process is performed, or when the end mill main body 11 is sent out only in the direction intersecting the axis O, the cross section of the work material is formed by the arcuate cutting edge portions 5a and 6a of the main cutting edge 5 and the sub cutting edge 6. Even when machining a concave arc-shaped wall surface, in the cutting insert 1 and the blade tip exchange type ball end mill having the above configuration, the inner peripheral cutting edge portion 5c of the main cutting edge 5 is connected to the inner peripheral cutting edge portion 5c. When viewed from the side facing the surface 4, the cutting insert 1 has a concave shape that 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 5a of the main cutting edge 5. Since it is formed, the chips generated by the inner peripheral cutting edge portion 5c are also generated so that the cross section has a concave shape.

Therefore, the chips generated in the concave cross section are less likely to be caught in the chip, and the direction substantially orthogonal to the inner peripheral cutting edge portion 5c in the plan view from the direction facing the rake face 2, that is, the cutting edge replaceable ball end mill. The outflow direction is controlled and discharged in the direction toward the outer peripheral side toward the rear end side of the end mill main body 11. For this reason, the chips generated so as to be caught flow out to the inner peripheral side of the end mill main body 11 to cause chip clogging, and the chips flowed out to the inner peripheral side in this way flow out to the inner peripheral side as the end mill main body 11 rotates and the main cutting edge 5 It is possible to prevent deterioration of the machined surface roughness due to being bitten between the arcuate cutting edge portion 5a and the machined surface of the work material.

Further, in the present embodiment, the inner peripheral cutting edge portion 5c is formed in a concave curved shape recessed 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. Therefore, when chips having a concave cross section are generated as described above, it is possible to suppress the concentration of stress due to the cutting load on the inner peripheral cutting edge portion 5c. Therefore, it is possible to prevent a situation in which the cutting insert 1 is damaged due to cracks generated from the inner peripheral cutting edge portion 5c due to such concentration of stress.

Further, in the present embodiment, the tip of the arcuate cutting edge 5a (the tip of the inner peripheral cutting edge 5c) of the main cutting edge 5 of the first cutting insert 1A in a plan view viewed from the direction facing the rake face 2. ) Of the cross section orthogonal to the straight line M connecting C1 and the rear end C2 of the inner peripheral cutting edge portion 5c opposite to the tip end C1 of the arcuate cutting edge portion 5a, as shown in FIGS. 10 and 20. 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 in the side view viewed from the direction facing the flank surface 4 is 80 ° to 95 °. It is said to be within the range of.

Therefore, it is possible to secure the cutting edge strength of the inner peripheral cutting edge portion 5c to prevent chipping and the like, and to suppress an increase in cutting resistance. That is, if the blade angle γ at the position where the inner peripheral cutting edge portion 5c is recessed most toward the seating surface 3 side is less than 80 °, it becomes impossible to secure sufficient cutting edge strength for the inner peripheral cutting edge portion 5c. Fracture resistance may be impaired. On the other hand, when the blade angle γ exceeds 95 °, it is a rake to secure the clearance angle of the inner peripheral cutting edge portion 5c in the main cutting edge 5 of the first cutting insert 1A in the state of being attached to the end mill main body 11. The angle must be increased to the negative angle side, which may lead to an increase in 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 °.

Further, in the present embodiment, the clearance angle β of the inner peripheral cutting edge portion 5c is set in the range of 14 ° to 30 °, which also makes it possible to reduce the cutting resistance and the arc-shaped cutting edge. It is possible to improve the accuracy of the machined surface when the machined surface having a concave arc shape in 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 clearance surface 4 comes into contact with the machined surface of the work material, causing an increase in cutting resistance and a roughening of the machined surface. It may cause deterioration. On the other hand, if the clearance angle β of the inner peripheral cutting edge portion 5c exceeds 30 °, the machining surface accuracy when the arc-shaped cutting edge portion 5a of the main cutting edge 5 forms a machined surface having a concave arc-shaped cross section may decrease. There is. The clearance angle β of the inner peripheral cutting edge portion 5c is more preferably in the range of 18 ° to 26 °, and further preferably in the range of 20 ° to 24 °.

Further, in the cutting insert 1 of the present embodiment, the rake face 2 has a valley bottom portion that intersects the inner peripheral cutting edge portion 5c in the plan view around the inner peripheral cutting edge portion 5c, and faces the valley bottom portion. Since it is formed in a valley shape recessed on the seating surface side, the chips generated by the inner peripheral cutting edge portion 5c can be guided along the valley bottom portion of the valley shape formed by the rake face 2. Therefore, the chips can be more reliably discharged to the outer peripheral side of the end mill main body 11, and the chip clogging and the biting of the chips can be more effectively prevented.

On the other hand, in the blade tip exchange type ball end mill of the present embodiment, as shown in FIG. 18, the tip c1 of the arcuate cutting edge portion 5a and the arcuate cutting edge are viewed in a plan view from the direction facing the rake face 2. The straight line M connecting the rear end C2 of the inner peripheral cutting edge portion 5c opposite to the tip C1 of the portion 5a has an inclination angle α within a range of 30 ° to 70 ° with respect to the plane P perpendicular to the axis O. The cutting insert 1 having the above 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 main body 11. Therefore, it is possible to prevent an increase in cutting resistance and deterioration of the machined surface roughness while maintaining the strength of the main cutting edge 5.

That is, if the inclination angle α is less than 30 °, flank contact may occur, leading to an increase in cutting resistance and deterioration of the machined surface roughness. In addition, the cutting resistance may increase even in the above-mentioned thrusting process. On the other hand, when the inclination angle α exceeds 70 °, the intersection angle between the inner peripheral cutting edge portion 5c and the arc-shaped cutting edge portion 5a at the tip C1 of the arc-shaped cutting edge portion 5a, which is the tip end portion of the main cutting edge 5, becomes large. It becomes smaller and the strength decreases, and there is a possibility that chipping may occur at the tip C1. 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 plan view facing the rake face 2, the inner peripheral cutting on the side opposite to the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the axis O and the first cutting insert 1A. The distance A in the direction perpendicular to the axis O with the rear end C2 of the blade 5c is closer to the axis O between the tip C1 of the arcuate cutting edge 5a of the main cutting edge 5 of the first cutting insert 1A and the axis O. The interval B in the vertical direction is reduced.

Therefore, the inner peripheral cutting edge portion 5c extending from the tip end C1 of the arcuate cutting edge portion 5a to the opposite side beyond the axis O allows the rotation center portion at the tip end portion of the end mill main body 11 during the above-mentioned thrusting. It is possible to reliably cut a portion around a certain axis O. Further, when the arc-shaped cutting edge portion 5a forms a machined surface having a concave arc-shaped cross section, it is possible to prevent the machined surface accuracy from being impaired due to the arc-shaped cutting edge portion 5a becoming too short.

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

That is, when the distance A between the axis O and the rear end C2 of the inner peripheral cutting edge portion 5c of the first cutting insert 1A in the direction perpendicular to the axis O is less than 0.23 mm, the axis O of the tip end portion of the end mill body 11 At the center of rotation above, the length of the inner peripheral cutting edge portion 5c extending beyond the axis O in the above plan view from the tip C1 of the arcuate cutting edge portion 5a becomes shorter, and the tip side in the axis O direction during thrusting is shortened. If the feed amount to the end mill body 11 is large, the tip end portion of the end mill main body 11 may come into contact with the work material. Further, when this interval A is large enough to exceed 1.25 mm, the first insert mounting seat 12A must be formed so as to greatly protrude to the side beyond the axis O of the end mill main body 11, and the axis O must be exceeded. On the other side, the wall thickness of the tip of the end mill body 11 may decrease, resulting in a decrease in strength. The distance A between the axis O and the rear end C2 of the inner peripheral cutting edge portion 5c of the first cutting insert 1A in the direction perpendicular to the axis O is within the range of 0.24 mm or more and 1.20 mm or less. It is more desirable that it is 0.25 mm or more and 1.15 mm or less.

Further, the fact that the distance B between the tip C1 of the arcuate cutting edge portion 5a and the axis O of the end mill body 11 is 0.0 mm or less means that the arcuate cutting edge portion 5a faces the rake surface 2 in the plan view. The tip C1 is on the axis O or is arranged at a position beyond the axis O, and the inner peripheral cutting edge portion 5c does not act as a cutting edge at the time of thrusting, and there is a possibility that a flank contact may occur. There is. Furthermore, when the distance B between the tip C1 of the arcuate cutting edge portion 5a and the axis O of the end mill body 11 is larger than 0.80 mm, the arcuate cutting edge portion 5a is located at the center of rotation at the tip end portion of the end mill body 11. The portion where is not formed becomes large, and there is a possibility that the machined surface accuracy when forming the machined surface having a concave arc shape in cross section is lowered. The distance B between the tip C1 of the arcuate cutting edge portion 5a and the axis O of the end mill main body 11 is more preferably larger than 0.0 mm and within the range of 0.70 mm or less, and more than 0.0 mm. It is more desirable that it is largely within the range of 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 portion 8B of the groove portions 8 of the cutting insert 1 is moved from one end side to the other end side in the direction in which the second groove portion 8B extends. Since the narrow portion 9 is provided so that the groove width is narrowed toward the end, a large wall thickness of the cutting insert 1 is secured on the other end side of the second groove portion 8B where the groove width of the narrow portion 9 is reduced. The strength can be improved. Therefore, even if an excessive load acts on the cutting insert 1 during cutting, it is possible to prevent the cutting insert 1 from being damaged from the second groove 8B.

Further, since the groove width of the narrow portion 9 is conversely widened on one end side in the direction in which the second groove portion 8B extends, the narrow portion of the second groove portion 8B is used in the end mill body 11 of the ball end mill with a replaceable cutting edge. The first and second convex portions 14A and 14B at the portion where the 9 abuts can be formed wide. Therefore, it is possible to increase the mounting rigidity of the cutting insert 1 with respect to the load during the cutting process, and it is possible to more reliably prevent the displacement movement of the cutting insert 1 and perform the cutting process with high accuracy.

Further, in the cutting insert 1 of the first embodiment, the rake face 2 is formed so as to extend toward the seating surface 3 toward the inside of the rake face 2 away from the main cutting edge 5 and the sub cutting edge 6. As a result, the sharpness of the main cutting edge 5 and the secondary 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 surface 3 in a cross section perpendicular to the main cutting edge 5 and the sub cutting edge 6 in the above plan view, for example.

On the other hand, contrary to these, as in the cutting insert 21 of the second embodiment of the present invention shown in FIGS. 21 to 29, the rake face 2 is formed at least around the arcuate cutting edge portions 5a and 6a. As the distance from the arcuate cutting edge portions 5a and 6a increases, the cutting edge portions 5a and 6a may be inclined so as to face the side opposite to the seating surface 3. In the cutting inserts 21 of the second embodiment shown in FIGS. 21 to 29, the same reference numerals are assigned to the parts common to the cutting inserts 1 of the first embodiment shown in FIGS. 1 to 10. It is done.

Here, in the cutting insert 21 of the second embodiment, as shown in FIG. 24, the most convex point of the arcuate cutting edge portion 5a of the main cutting edge 5 in the plan view seen from the direction facing the rake face 2. The arc-shaped cutting edge portion passes through the center of the hemisphere formed by the rotation locus of the arc-shaped cutting edge portion 5a when the cutting insert 21 is attached to the first insert mounting seat of the end mill main body of the blade tip exchange type ball end mill. Approximately located on a straight line (a straight line showing a ZZ cross section in FIG. 24) forming an angle of 45 ° from the contact point between the 5a and the linear cutting edge portion 5b of the main cutting edge 5 toward the tip C1 side of the arcuate cutting edge portion 5a. It is arranged like this.

Then, in the second embodiment, as shown in FIG. 29 in a cross section parallel to the insert center line L through the most convex point S5, an arc shape which is an intersection angle formed by the rake face 2 and the flank surface 4. The rake face 2 is inclined toward the side opposite to the seating surface 3 as it is separated from the arcuate cutting edge portion 5a so that the blade angle δ of the cutting edge portion 5a is an obtuse angle of 92 °. The sub cutting edge 6 has the same configuration. Further, in this second embodiment, the concave groove 2d is not formed on the rake face 2.

According to the cutting insert 21 of the second embodiment configured in this way, the cutting edge strength of the arc-shaped cutting edge portion 5a is improved by increasing the cutting edge angle δ of the arc-shaped cutting edge portion 5a in this way. Therefore, the fracture resistance of the arcuate cutting edge portion 5a can be improved. Inside the rake face 2 away from the arcuate cutting edge portion 5a, the rake face 2 inclines toward the seating surface 3 side as the distance from the arcuate cutting edge portion 5a increases, as in the first embodiment. You may be. Further, in the second embodiment, the rake face 2 of the linear cutting edge portion 5b is also inclined toward the side opposite to the seating surface 3 as the distance from the linear cutting edge portion 5b increases. On the contrary, 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 arcuate cutting edge portion 5a of the main cutting edge 5 is formed so as to draw a single arc in the plan view. Like the cutting insert 31 of the third embodiment of the present invention and the blade tip exchange type ball end mill of the second embodiment shown in FIG. 30, the arcuate cutting edge portion 5a of the main cutting edge 5 has the above-mentioned inner peripheral cutting. The first cutting edge portion 5A is formed on the side opposite to the blade portion 5C, the second cutting edge portion 5B is formed on the inner peripheral cutting edge portion 5C side, and the second cutting edge portion 5B is formed. The radius of curvature RB may be larger than the radius of curvature RA of the first cutting edge portion 5A, and may be recessed from the extension line of the first cutting edge portion 5A toward the inner peripheral cutting edge portion 5c. .. Also in FIG. 30, the same reference numerals are given to the parts common to the cutting insert 1 and the cutting edge replaceable ball end mill of the first embodiment shown in FIGS. 1 to 20.

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

In the cutting insert 31 of the third embodiment and the blade tip exchange type ball end mill of the second embodiment configured in this way, the circle in the main cutting edge 5 of the first cutting insert 31A indicated by reference numeral Q1 in FIG. 30 The position of the tip C1 of the arc-shaped cutting edge portion 5a extends the first cutting edge portion 5A of the arc-shaped cutting edge portion 5a indicated by reference numeral Q2 in FIG. 30 to the inner peripheral side of the tip of the end mill main body 11 with the same radius RA. It recedes toward the rear end side in the O-direction of the axis line from the position of the tip end at the time, but is more than the position of the tip end C3 of the arcuate cutting edge portion 6a in the auxiliary cutting edge 6 of the second cutting insert 31B shown by reference numeral Q3 in FIG. It will be located on the tip side in the O direction of the axis line.

Therefore, in the cutting insert 31 of the third embodiment and the cutting edge replaceable ball end mill of the second embodiment, the tips of the arcuate cutting edge portions 5a and 6a of the first and second cutting inserts 31A and 31B are used. The thickness of the chips can be reduced by reducing the step in the axis O direction between C1 and C3. Moreover, the second cutting edge portion 5B of the arc-shaped cutting edge portion 5a of the first cutting insert 31A has a radius RB larger than the radius RA of the first cutting edge portion 5A and is an extension of the second cutting edge portion 5A. Since it is retracted from the line, for example, when the end mill main body 11 is sent out in the direction perpendicular to the axis O, the thickness of the chips becomes even 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 5a of the first cutting insert 31A is viewed from the side facing the flank 4 connected to the arcuate cutting edge portion 5a. It is formed in a convex curve shape toward the seating surface 3 side after being separated from the seating surface 3 toward the 5c side, and has the most protruding most convex point S5 with respect to the seating surface 3. The cutting edge portion 5B is formed on the inner peripheral cutting edge portion 5c side of the most convex point S5. Therefore, since the thickness of the chips can be further reduced, the fracture resistance at the tip of the arcuate cutting edge portion 5a is remarkably improved even under unstable machining conditions such as intermittent cutting with large chatter vibration. be able to.

The first cutting edge portion 5A and the second cutting edge portion 5B may intersect at an obtuse angle as shown in FIG. 30, but the first cutting edge portion 5A to the second cutting edge portion 5A It is desirable that the radius increases toward 5B and 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. As a result, the machined 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 arcuate cutting edge portion 5a is directed from the first cutting edge portion 5A to 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 increases toward the tip C1 of the arcuate cutting edge portion 5a.

Furthermore, it is desirable that the circumferential length of the second cutting edge portion 5B in the plan view is shorter than the circumferential length of the first cutting edge portion 5A. Further, the center of the second cutting edge portion 5B may be located on the axis O in the plan view with the first cutting insert 31A attached to the end mill main body 11, and may be separated from the axis O. It may be in the same position.

According to the present invention, the concave inner peripheral cutting edge portion can generate a concave cross-section that makes it difficult for chips to be caught, and the outflow direction of the chips thus generated is directed toward the rear end side of the end mill body. Therefore, it can be controlled in the direction toward the outer peripheral side. For this reason, the chips flow out to the inner peripheral side of the end mill body to cause chip clogging, and the chips that flow out to the inner peripheral side are bitten between the arcuate cutting edge portion and the machined surface to make the machined surface roughness. In addition to being able to prevent deterioration of the end mill, it is also possible to use this inner peripheral cutting edge portion to perform a thrusting process in which the end mill body is fed to the tip side in the axial direction.

1 (1A, 1B), 21, 31A, 31B Cutting insert 2 Scoop surface 2a First corner part of rake surface 2 2b Second corner part of rake surface 2 3 Seating surface 4 Escape surface 5 Main cutting edge (cutting edge) )
5a Arc-shaped cutting edge of main cutting edge 5 5b Linear cutting edge of main cutting edge 5 5c Inner peripheral cutting edge 5A First cutting edge 5B Second cutting edge 6 Secondary cutting edge (cutting edge)
6a Arc-shaped cutting edge of the secondary cutting edge 6 6b Linear cutting edge of the secondary cutting edge 6 7 Mounting hole 8 (8A, 8B) Groove 9 Narrow section 11 End mill body 12 (12A, 12B) Insert mounting seat 14A ~ 14C Convex L Insert center line S5, S6 Most convex point O Axis 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 of inner peripheral cutting edge 5c C3 Sub-cutting The tip 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 from the direction facing the rake face 2. B Spacing in the direction perpendicular to the axis O of B When viewed in a plan view from the direction facing the rake face 2, the tip C1 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A and the axis O Spacing in the direction perpendicular to the axis O between them M In a plan view from the direction facing the rake face 2, the tip C1 and the inner peripheral cutting of the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A A straight line connecting the rear end C2 of the blade portion 5c When viewed from the front end side in the axis O direction of the N end mill main body 11, the axis O and the arcuate cutting edge portion 5a of the main cutting edge 5 of the first cutting insert 1A Straight line connecting the tip C1 In a plan view from the direction facing the rake face 2, the tip C1 of the arcuate cutting edge 5a and the inner peripheral cutting edge 5c of the main cutting edge 5 of the first cutting insert 1A. Inclined angle β formed by a straight line M connecting the rear end C2 with respect to a plane P perpendicular to the axis O.
γ Blade angle of inner peripheral cutting edge 5c δ Blade angle of arcuate cutting edge 5a RA Radius of the first cutting edge 5A Radius of RB Second cutting edge 5B

Claims (14)

A cutting insert that can be detachably attached to the insert mounting seat formed at the tip of the end mill body of a ball end mill with a replaceable cutting edge that rotates around the axis.
A rake surface facing the rotation direction of the end mill body, a seating surface that faces the opposite side of the rake surface and is seated on the bottom surface of the insert mounting seat, and a flank extending around these rake surfaces and the seating surface. With and
The intersecting ridgeline portion between the rake face and the flank surface is connected to an arcuate cutting edge portion extending in a convex arc shape in a plan view from a direction facing the rake face and the tip of the arcuate cutting edge portion. A cutting edge having an arcuate cutting edge portion and an inner peripheral cutting edge portion extending in a direction intersecting an obtuse angle is formed in the plan view.
The inner peripheral cutting edge portion extends toward the seating surface side as the distance from the tip of the arc-shaped cutting edge portion increases in a side view seen from a direction facing the flank surface connected to the inner peripheral cutting edge portion. A cutting insert characterized by being formed in a concave shape away from the seating surface. The inner peripheral cutting edge portion is formed in a concave curved shape recessed toward the seating surface side when viewed from a side view from a direction facing the flank surface connected to the inner peripheral cutting edge portion. Item 1. The cutting insert according to item 1. A straight line connecting the tip of the arcuate cutting edge and the rear end of the inner peripheral cutting edge opposite to the tip of the arcuate cutting edge in a plan view seen from the direction facing the rake face. Of the cross sections orthogonal to the above, the blade angle of the inner peripheral cutting edge portion in the cross section at the position where the inner peripheral cutting edge portion is most recessed toward the seating surface in the side view viewed from the direction facing the flank surface is 80. The cutting insert according to claim 1 or 2, wherein the cutting insert is in the range of ° to 95 °. The cutting insert according to any one of claims 1 to 3, wherein the clearance angle of the inner peripheral cutting edge portion is in the range of 14 ° to 30 °. The rake face has a valley bottom portion that intersects the inner peripheral cutting edge portion in a plan view seen from a direction facing the rake face in the vicinity of the inner peripheral cutting edge portion, and the valley bottom portion is directed toward the valley bottom portion. 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. The rake face is characterized in that, at least around the arcuate cutting edge portion, the rake face is inclined so as to be parallel to the seating surface or toward the seating surface side as the distance from the arcuate cutting edge portion increases. The cutting insert according to any one of claims 1 to 5. The rake face is claimed according to claim 1, wherein at least around the arcuate cutting edge portion, the rake face is inclined so as to move toward the opposite side to the seating surface as the distance from the arcuate cutting edge portion increases. Item 5. The cutting insert according to any one of Item 5. In a plan view seen from the direction facing the rake face, the arcuate cutting edge portion is formed with a first cutting edge portion on the side opposite to the inner peripheral cutting edge portion, and the inner peripheral cutting edge portion is formed. A second cutting edge portion is formed on the blade portion side, and the second cutting edge portion has a larger radius of curvature than the first cutting edge portion, and the inside 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 the extension line to the peripheral cutting edge side. The arcuate cutting edge portion is viewed from a side view from a direction facing the flank surface connected to the arcuate cutting edge portion, and the seating surface is separated from the seating surface toward the inner peripheral cutting edge portion side. It is formed in a convex curve toward the side, and has the most protruding most convex point with respect to the seating surface.
The cutting insert according to claim 8, wherein the second cutting edge portion is formed on the inner peripheral cutting edge portion side of the most convex point. The first cutting edge portion and the second cutting edge portion have a radius of curvature that increases from the first cutting edge portion to the second cutting edge portion, and the first cutting edge portion and the second cutting edge portion are formed. The cutting insert according to claim 8 or 9, wherein the cutting insert is connected via a convex curved connecting portion in contact with the cutting edge portion of the above. A ball end mill with a replaceable cutting edge, to which the cutting insert according to any one of claims 1 to 10 is detachably attached to an insert mounting seat formed at the tip of an end mill body that is rotated around an axis. And
The arcuate cutting edge portion of the cutting edge is arranged on a spherical surface in which a rotation locus around the axis is centered on the axis.
The inner peripheral cutting edge portion of the cutting edge crosses the axis line from the tip end of the arc-shaped cutting edge portion toward the inner peripheral side of the end mill body in a plan view viewed from the direction facing the rake face. It is characterized in that it extends toward the side and is located on the end mill rotation direction side of the straight line connecting the axis and the tip of the arcuate cutting edge portion when viewed from the front end side in the axial direction. Ball end mill with replaceable cutting edge. A straight line connecting the tip of the arcuate cutting edge portion and the rear end of the inner peripheral cutting edge portion on the side opposite to the tip end of the arcuate cutting edge portion in a plan view viewed from the direction facing the rake face. However, the claim is characterized in that it extends toward the rear end side toward the inner peripheral side of the end mill main body at an inclination angle within the range of 30 ° to 70 ° with respect to a plane perpendicular to the axis. Item 2. The blade tip exchange type ball end mill according to Item 11. From the distance between the axis and the rear end of the inner peripheral cutting edge on the opposite side of the tip of the arcuate cutting edge in the direction perpendicular to the axis in a plan view from the direction facing the rake face. The blade tip exchange type ball end mill according to claim 11 or 12, wherein the distance between the tip of the arcuate cutting edge portion and the axis in the direction perpendicular to the axis is small. In a plan view from the direction facing the rake face, the distance between the axis and the rear end of the inner peripheral cutting edge portion opposite to the tip of the arcuate cutting edge portion in the direction perpendicular to the axis is The range is 0.23 mm or more and 1.25 mm or less, and the distance between the tip of the arcuate cutting edge and the axis in the direction perpendicular to the axis is larger than 0.0 mm and 0.80 mm or less. The blade end exchange type ball end mill according to claim 13, wherein the inside is inside.

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