Cutting inserts and indexable cutting tools

Abstract

This cutting insert (1) has two cutting blades (5, 6) that are formed at a cross-ridge line part between a rake face (2) and a flank face (4), and that each comprise: a circular arc-like cutting-blade portion (5a, 6a) that extends in a circular arc-like shape in a planar view; and a linear cutting-blade portion (5b, 6b). The cutting blades (5, 6) each have a protruding curved portion (17) that comes close to a seating face (3) after having moved away from the seating face (3) in association with at least the corresponding circular arc-like cutting-blade portion (5a, 6a) moving away from the linear cutting-blade portion (5b, 6b). In a side view, the circular arc-like cutting-blade portions (5a, 6a) each have a curvature changing point (Q1, Q2) located between the most protruding point (S1, S2) located farthest away from the seating face (3) and a cutting-edge tip (2a, 2b) of the corresponding circular arc-like cutting-blade portion.

Description

[Technical field]

[0001] The present invention relates to a cutting insert and an indexable cutting tool. This application claims priority based on Japanese Patent Application No. 2021-030531, filed on February 26, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] For example, Patent Document 1 discloses a cutting insert that is attached to an indexable cutting tool, which includes a rake face facing the rotation direction of the tool body, a seating face facing the opposite side of the rake face and seated on the bottom surface of the insert mounting seat, and a flank extending around the rake face and the seating face. At the intersection ridge between the rake face and the flank face, two cutting edges are formed, each of which includes an arc-shaped cutting edge portion that extends in an arc shape in a plan view from the direction facing the rake face, and a linear cutting edge portion that extends so as to be in contact with the arc-shaped cutting edge portion, with the arc-shaped cutting edge portion and the linear cutting edge portion being alternately positioned in the circumferential direction of the rake face. Furthermore, the arc-shaped cutting edge portion of the main cutting edge and the arc-shaped cutting edge portion of the auxiliary cutting edge are formed in a convex curve shape that moves away from the seating surface side and then approaches the seating surface side again as it moves away from the linear cutting edge portion. As a result, the arc-shaped cutting edge portion gradually bites into the workpiece from the most convex point, which is the furthest convex from the seating surface during cutting, and cuts into the workpiece, thereby reducing cutting resistance, as described in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6540928 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the cutting insert described in Patent Document 1 is used for cutting with a depth of cut that does not match the design position of the most convex point, there is a problem that the cutting insert is likely to have a short life due to insufficient strength of the cutting edge. Patent Document 1 describes that the position of the most convex point can be set in a wide range on the arc-shaped cutting edge by using the first intersecting angle and the second intersecting angle, but in reality, it is necessary to select whether the most convex point should be set at a position corresponding to machining with a large cutting depth or a position corresponding to machining with a small cutting depth.

[0005] For example, if the most convex point is provided at a position corresponding to machining with a large cutting depth, when that cutting insert is used for machining with a small cutting depth, damage will occur at the tip of the cutting insert due to stress concentration, resulting in a short lifespan. On the other hand, if the most convex point is located at a position corresponding to machining of high-hardness materials or difficult-to-cut materials with a small cutting depth, the cutting insert will suffer damage (cracks) due to stress concentration even when machining with a cutting depth exceeding the most convex point in machining where the cutting depth varies, resulting in a short service life.

[0006] For example, when a ball end mill is used to machine a complex mold shape, the cutting depth varies for each machining location. It is not realistic to use a cutting tool that is appropriate for the cutting depth only in certain areas. The cutting depth also varies when machining overlay welded materials, but even in that case, it is not realistic to change tools depending on the cutting depth. Overlay welded materials are used for the purpose of repairing dies and ensuring partial strength, and unevenness occurs on the machined surface at each machining location as described above, so the cutting depth often varies due to these unevenness.

[0007] The present invention has been made against this background, and aims to provide a cutting insert and an indexable cutting tool that can suppress the occurrence of cracks in the cutting edge by dispersing stress during cutting and increasing the strength of the tip of the cutting edge over a wider range of cutting depths than conventional techniques. [Means for solving the problem]

[0008] A cutting insert according to one aspect of the present invention is a cutting insert that is detachably attached to an insert mounting seat formed at the tip of a tool body of an indexable cutting tool that rotates about an axis, and includes a rake face facing the rotation direction of the tool body, a seating surface facing the opposite side to the rake face and seated on the bottom surface of the insert mounting seat, and a flank surface extending around the rake face and the seating surface. At an intersection ridge between the rake face and the flank surface, two cutting edges are formed, each of which includes an arc-shaped cutting edge portion that extends in an arc shape in a plan view from a direction facing the rake face, and a linear cutting edge portion that extends so as to be tangent to the arc-shaped cutting edge portion, with the arc-shaped cutting edge portion and the linear cutting edge portion alternately positioned in the circumferential direction of the rake face. The cutting edge has at least a convex curved portion which moves away from the seating surface and then approaches the seating surface as the arc-shaped cutting edge portion moves away from the linear cutting edge portion, and when viewed from a side from a direction opposite to the flank surface, the arc-shaped cutting edge portion has a curvature change point between the most convex point and the tip of the cutting edge of the arc-shaped cutting edge portion, where the most convex point is the point on the convex curved portion farthest from the seating surface.

[0009] According to this configuration, in a side view from the direction facing the flank of the cutting edge, the arcuate cutting edge portion has a curvature change point between the most convex point on the convex curve portion that is the farthest from the seating surface and the cutting edge tip of the arcuate cutting edge portion, so that the curvature changes at the curvature change point, and the stress during cutting is distributed over a wide range of the arcuate cutting edge portion during cutting with a wider cutting depth than in the past. This avoids the occurrence of chipping or damage (cracks) of the cutting insert, increases the strength of the entire arcuate cutting edge portion, and suppresses the occurrence of cracks in the cutting edge portion. Furthermore, by providing a curvature change point between the most convex point and the cutting edge tip, the cutting edge shape becomes smooth at the initial stage when the cutting insert bites into the workpiece, and the twist of the chip shape is also reduced. Therefore, it is possible to prevent the twisted chip from applying irregular force to the cutting insert or the workpiece.

[0010] In one aspect of the present invention, in a side view seen from the normal direction with respect to the tangent line of the arc-shaped cutting edge portion passing through the most convex point, the cutting edge includes arcs having at least two different curvatures. When the arc radius on the cutting edge tip side is R1 and the arc radius on the most convex point side is R2, the relationship R1 < R2 may be satisfied.

[0011] According to this configuration, among the arc radii R1 and R2 of two different curvatures that form part of the cutting edge, the arc radius R1 on the cutting edge tip side is smaller than the arc radius R2 on the most convex point side, and the curve of the arc on the cutting edge tip side is shaped steeply. Therefore, the cutting edge comes into smooth contact with the workpiece, the impact acting on the cutting edge is reduced, the stress is dispersed, and the effect of reducing the cutting resistance can be obtained.

[0012] Note that according to this configuration, it is only necessary to include arcs of two different curvatures from the cutting edge tip side to the cutting edge on the most convex point side. For example, the space between the arcs of two different curvatures or the space between the arc on the most convex point side and the most convex point may be connected by a curve or a straight line. Also, among the arcs of two different curvatures, the space between the arc on the most convex point side and the most convex point may be connected by a curve or a straight line. In such a case, the straight line may or may not be a tangent line of the arc. On the other hand, in the present invention, since the arc-shaped cutting edge portion gradually contacts the workpiece during cutting to relieve the impact acting on the cutting edge during processing, the straight line is formed parallel to the seating surface or away from the seating surface as it goes from the cutting edge tip toward the most convex point. Similarly, the curve is also formed to always move away from the seating surface as it goes from the cutting edge tip toward the most convex point.

[0013] In one aspect of the present invention, the arc radius R1 may be configured to be 1 / 2 or less of the arc radius R2, preferably 1 / 3 or less, and more preferably 1 / 4 or less.

[0014] According to this configuration, the arc radius R1 is formed to be at least 1 / 2 the arc radius R2 or less, so that the arc cutting edge on the tip side of the cutting edge forms a sharp curve, and the impact on the cutting edge can be sufficiently reduced. Furthermore, by forming the arc radius R1 to be 1 / 3 or 1 / 4 or less of the arc radius R2, the curve becomes even sharper, and the impact on the tip of the cutting edge is mitigated. There is no lower limit for R1 / R2, but in reality it is about 1 / 100.

[0015] In one embodiment of the cutting insert of the present invention, when viewed from the side, the cutting edge may comprise a first cutting edge that is curved and convex upward relative to the seating surface on the tip side of the cutting edge and a second cutting edge that is convex upward relative to the seating surface on the most convex point side, the second cutting edge being formed of a curved or straight second cutting edge with a smaller curvature than the first cutting edge, and the intersection of the first cutting edge and the second cutting edge being the curvature change point.

[0016] According to this configuration, the first cutting edge located on the tip side of the cutting edge has a steeper curve shape than the second cutting edge located on the most convex point side, across the curvature change point where two first cutting edges and second cutting edges with different curvatures intersect.This allows the cutting edges to come into smooth contact with the workpiece, reduces the impact acting on the cutting edge, distributes stress, and reduces cutting resistance.

[0017] The curvature of the straight line is 0. Therefore, even when the second cutting edge is a straight line, the curvature of the second cutting edge is smaller than the curvature of the first cutting edge, and therefore the same effect can be obtained as when the second cutting edge is formed as a curve with a smaller curvature than the first cutting edge.

[0018] In one embodiment of the cutting insert of the present invention, the curvature of the first cutting edge may be at least twice as large as the curvature of the second cutting edge, preferably at least three times, and more preferably at least four times.

[0019] According to this configuration, when the curvature of the second cutting edge is at least twice as large as the curvature of the first cutting edge, the impact acting on the cutting edge becomes sufficiently small. On the other hand, when the curvature of the second cutting edge is less than twice as large as the curvature of the first cutting edge, the curvature of the first cutting edge cannot be said to be sufficiently large, and stress is likely to concentrate on the cutting edge during cutting.

[0020] In one embodiment of the cutting insert of the present invention, the second cutting edge may be a portion of the arc-shaped cutting edge portion in side view, where the ratio of the height from the tip of the cutting edge to an arbitrary cutting edge ridge line to the height from the tip of the cutting edge to the most convex point in a direction perpendicular to the seating surface is 90% or more.

[0021] According to this configuration, in the direction perpendicular to the seating surface, the height from the tip of the cutting edge to the curvature change point is 90% or more of the height from the curvature change point to the most convex point, and the curve shape is steeper on the tip side of the cutting edge than on the most convex point side across the curvature change point, so that the cutting edge comes into smooth contact with the workpiece, and the impact acting on the cutting edge can be reduced. Although there is no upper limit on the height from the tip of the cutting edge to the curvature change point relative to the height from the curvature change point to the most convex point, in reality it is about 98%.

[0022] In one embodiment of the cutting insert of the present invention, a groove portion having a wall surface capable of abutting a convex portion protruding from the bottom surface of the insert mounting seat is formed, and two groove portions are formed on either side of a mounting hole for mounting the cutting insert, and the curvature change point may be formed closer to the tip of the cutting edge than one of the two groove portions which is closer to the arc-shaped cutting edge portion.

[0023] According to this configuration, the curvature change point is formed closer to the tip of the cutting edge than one of the groove portions which is closer to the arc-shaped cutting edge portion, thereby ensuring the thickness at the curvature change point and increasing the strength of the cutting edge.

[0024] In one embodiment of the cutting insert of the present invention, the arc-shaped cutting edge portion is composed of at least two or more arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N is an integer of 2 or more) having different arc radii, sequentially from a position corresponding to the tool tip side, and the first cutting edge on the tip side has a smaller arc radius than the other second cutting edges to Nth cutting edges, and the first cutting edge may have a cutting edge angle, which is the angle between the clearance face and the cutting face, gradually decreasing from the second cutting edge side toward the tool tip side.

[0025] According to this configuration, by gradually reducing the cutting edge angle of the first cutting edge of the arc-shaped cutting edge portion from the rear end to the tip, the clearance angle of the cutting edge can be increased when cutting with the tip of the cutting edge, and the progression of clearance wear at the tip of the cutting edge can be suppressed.

[0026] In general, in this type of tool, the tip of the arc-shaped cutting edge is likely to be chipped because it is subjected to a thrust force from the Z-axis direction during cutting. In general, the larger the cutting edge angle of the cutting edge, the thicker the cutting edge becomes and the stronger the cutting edge becomes. However, when cutting a workpiece such as high-hardness steel, if the clearance angle is small, the life of the cutting edge may vary even if the thickness is large. In contrast, in the above-mentioned embodiment, the clearance angle of the cutting edge tip is gradually increased from the rear end side to the front end side of the first cutting edge, and the clearance angle at the tip of the arc-shaped cutting edge is secured to a certain extent during cutting, thereby stabilizing the life of the tip of the arc-shaped cutting edge.

[0027] In one embodiment of the indexable cutting tool of the present invention, when the center point of the arc-shaped cutting edge portion located on the axis is defined as P, the angle between the axis and a line connecting the center point and the most convex point is defined as θ1, and the angle between the axis and a line connecting the center point and the curvature change point is defined as θ2, the angle may be such that θ2<θ1, 30°≦θ1≦50°, 15°≦θ2≦40°, and preferably is in the range of 40°≦θ1≦50°, 17°≦θ2≦37°.

[0028] According to this configuration, the curvature change point is formed on the tip side of the cutting edge rather than the most convex point, and the cutting stress can be dispersed over a wide area of ​​the cutting edge, making it possible to prevent chipping or damage (cracks) caused by stress concentration. This increases the strength of the tip side of the cutting edge, and suppresses the occurrence of cracks in the cutting edge. Furthermore, it also has the effect of reducing resistance during cutting.

[0029] In one embodiment of the indexable cutting tool of the present invention, the distance from the tip of the cutting edge of the cutting insert to the point where the curvature changes in the direction along the axis is H, and the diameter of the tool body is D, may be configured to satisfy the relationship D / 30≦H≦D / 10.

[0030] According to this configuration, it is possible to obtain the effect of preventing stress concentration on the cutting edge and mitigating the impact on the tip of the cutting edge during cutting, regardless of the cutting depth which changes according to the tool diameter.

[0031] In one embodiment of the indexable cutting tool of the present invention, the arc-shaped cutting edge portion is composed of at least two or more arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N is an integer of 2 or more) having different arc radii, sequentially from a position corresponding to the tool tip side, and the first cutting edge on the tip side has a smaller arc radius than the other second cutting edges to Nth cutting edges, and the clearance angle formed by the clearance face of the cutting insert and the workpiece surface of the first cutting edge gradually increases from the second cutting edge side toward the tool tip side.

[0032] According to this configuration, the clearance angle of the cutting insert gradually increases from the second cutting edge side toward the tool tip side of the first cutting edge of the arc-shaped cutting edge portion, so that the clearance angle of the cutting edge can be made relatively large during cutting by the cutting edge tip, and the progression of clearance wear of the cutting edge tip can be suppressed.

[0033] In addition, since the clearance angle of the first cutting edge of the cutting insert gradually increases from the second cutting edge side toward the tool tip side, a certain degree of clearance angle can be secured during cutting processing, and the life of the tip of the arc-shaped cutting edge portion can be stabilized.

[0034] In one embodiment of the indexable cutting tool of the present invention, when multiple cutting inserts are attached to the tool body, when the difference between the lowest point of any one of the cutting inserts and the lowest point of the other cutting inserts is H, the relationship with the tool body diameter D may be H / D of 0.025 or less.

[0035] In this configuration, by setting H / D to 0.025 or less, the cutting insert cutting edge step relative to the tool diameter D can be sufficiently reduced. As a result, the area where cutting is performed only by the cutting insert with the lowest point (cutting insert 1A in the embodiment described later, i.e., parent edge) is reduced, and wear at the tip of the cutting insert with the lowest point (parent edge) is suppressed, thereby extending the life of the cutting insert. H / D is preferably 0.020 or less, and more preferably 0.017 or less. There is no lower limit for H / D, but in reality it is about 0.010.

[0036] In one embodiment of the indexable cutting tool of the present invention, two insert mounting seats are formed at positions spaced 180° from each other at the tip of the tool body, and any of the cutting inserts described above may be removably attached to each of the two insert mounting seats. However, in the present invention, three insert mounting seats may be formed at the tip of the tool body spaced 120° from each other, or similarly, four or more insert mounting seats may be formed at equal intervals in the circumferential direction. Effect of the Invention

[0037] According to the present invention, it is possible to provide a cutting insert and an indexable cutting tool that can suppress the occurrence of cracks in the cutting edge portion by dispersing the stress generated in the arc-shaped cutting edge portion. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a diagram showing the tip side of one embodiment of an indexable ball end mill of the present invention (as viewed in the direction of arrow I in FIG. 9), and shows a configuration in which multiple cutting inserts of one embodiment of the present invention are removably attached to a tool body. [Diagram 2] FIG. 2 is a front view showing the configuration of the cutting insert according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a rear view showing the configuration of the cutting insert according to one embodiment of the present invention. [Figure 4] FIG. 4 is a side view seen from the direction of arrow IV in FIG. [Diagram 5] FIG. 5 is a side view seen from the direction of arrow V in FIG. [Figure 6] FIG. 6 is a side view seen from the direction of arrow VI in FIG. [Figure 7] FIG. 7 is a side view seen from the direction of arrow VII in FIG. [Figure 8] FIG. 8 is a perspective view showing a cutting insert according to one embodiment of the present invention. [Figure 9] FIG. 9 is a front view of the indexable ball end mill according to one embodiment of the present invention. [Figure 10] Figure 10 is a plan view of two cutting inserts arranged in the positional relationship when attached to the tool body, viewed from a direction facing the cutting face of the first cutting insert (the cutting insert on the right in Figure 10) whose main cutting edge is used for cutting. [Figure 11A] FIG. 11A is a graph showing the relationship between the distance from cutting edge tip 2b and the height at any position on arcuate cutting edge portion 5a. [Figure 11B] FIG. 11B is a graph showing the relationship between the ratio of the distance from the tip of the cutting edge 2b to the most convex point in a direction parallel to the seating surface at an arbitrary position on the arc-shaped cutting edge portion 5a and the ratio of the height of an arbitrary point on the arc-shaped cutting edge portion to the height from the tip of the cutting edge to the most convex point in a direction perpendicular to the seating surface. [Figure 12A] FIG. 12A is a diagram showing the shape of a chip and the maximum principal stress acting on the cutting insert and the chip, obtained by simulation analysis during cutting using a conventional cutting insert in which the angle from the axis to the most convex point is 16.5°. [Figure 12B] FIG. 12B is a diagram showing the maximum principal stress acting on a cutting insert by simulation analysis during cutting using a conventional cutting insert in which the angle from the axis to the most convex point is 16.5°. [Figure 13A] FIG. 13A is a diagram showing the shape of a chip and the maximum principal stress acting on the cutting insert and the chip, obtained by simulation analysis during cutting using a conventional cutting insert in which the angle from the axis to the most convex point is 22.5°. [Figure 13B] FIG. 13B is a diagram showing the maximum principal stress acting on a cutting insert by simulation analysis during cutting using a conventional cutting insert in which the angle from the axis to the most convex point is 22.5°. [Figure 14A] FIG. 14A is a diagram showing a chip shape and maximum principal stress acting on the cutting insert and the chip, obtained by simulation analysis during cutting using a cutting insert 1 of one embodiment of the present invention, in which the angle from the axis O to the most convex point S1 is 45° and the angle from the axis to the curvature change point is 22.5°. [Figure 14B] FIG. 14B is a diagram showing the maximum principal stress acting on a cutting insert according to one embodiment of the present invention, in which the angle from the axis to the most convex point is 45° and the angle from the axis to the curvature change point is 22.5°, based on a simulation analysis of the maximum principal stress acting on the cutting insert during cutting. [Figure 15] FIG. 15 is a diagram showing the maximum principal stress acting on a cutting insert by simulation analysis during cutting with a conventional cutting insert in which the angle θ1 from the axis to the most convex point is 16.5°. [Figure 16] FIG. 16 is a diagram showing the maximum principal stress acting on a cutting insert according to one embodiment of the present invention, in which the angle θ1 from the axis to the most convex point is 45° and the angle θ2 from the axis to the cutting edge change point is 22.5°, based on a simulation analysis of the maximum principal stress acting on the cutting insert during cutting. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, the configuration of a cutting insert and an indexable cutting tool according to one embodiment of the present invention will be described with reference to Figs. 1 to 11B. Fig. 1 is a diagram showing the tip side of one embodiment of an indexable ball end mill of the present invention (as viewed in the direction of arrow I in Fig. 9), and is a diagram showing a configuration in which a plurality of cutting inserts 1 of one embodiment of the present invention (two in this embodiment) are detachably attached to a tool body 11. Fig. 9 is a front view of the indexable ball end mill of one embodiment of the present invention.

[0040] <Indexable cutting tools> 1 and 9, an indexable ball end mill (indexable cutting tool) 100 according to an embodiment of the present invention includes a plurality of cutting inserts 1 and a tool body 11 that holds the plurality of cutting inserts 1. The tool body 11 is rotated around an axis O.

[0041] The cutting inserts 1 are detachably attached to the insert mounting seats 12 (two in this embodiment) formed on the tip side of the tool body 11. In this embodiment, two cutting inserts 1 (1A, 1B) are attached to two insert mounting seats 12 (12A, 12B) provided on the end mill body. These two cutting inserts 1 (1A, 1B) have the same shape and size. In the present invention, the number of cutting inserts 1 and insert mounting seats 12 is not limited to two, and three or more insert mounting seats 12 may be provided at equal intervals in the circumferential direction around the axis O. In this embodiment, the cutting insert 1A is located lower than the cutting insert 1B, and in this case, the cutting insert 1A is called the parent blade and the cutting insert 1B is called the child blade.

[0042] (End mill body) The tool body 11 is formed from a metal material such as steel, and its rear end is a cylindrical chunk portion centered on the axis O, while its tip end is a convex hemispherical shape centered on the axis O.

[0043] In the indexable ball end mill 100 of this embodiment, the tool body 11 is rotated around the axis O in the rotational direction of the tool body 11 while being fed in a direction intersecting the axis O, so that the cutting insert 1 attached to the insert mounting seat 12 performs cutting on the workpiece.

[0044] In this embodiment, among the directions in which the axis O extends, the direction from the shank portion of the tool body 11 toward the insert mounting seat 12 is referred to as the tip side (lower end side in FIG. 1), and the direction from the insert mounting seat 12 toward the shank portion is referred to as the rear end side (upper end side in FIG. 1). The direction perpendicular to the axis O is referred to as the radial direction. Among the radial directions, the direction approaching the axis O is referred to as the inner circumferential side, and the direction moving away from the axis O is referred to as the outer circumferential side.

[0045] In this embodiment, two chip pockets 13 are formed by cutting out the outer periphery of the tip of the tool body 11, and insert mounting seats 12 are formed on the bottom surfaces 12a of these two chip pockets 13 facing the end mill rotation direction T, respectively, on opposite sides spaced apart circumferentially.

[0046] In this embodiment, two cutting inserts 1 (1A, 1B) of one type and the same shape and size are detachably attached to two insert mounting seats 12 (12A, 12B) of the tool body 11. By attaching the two cutting inserts 1 (1A, 1B) of one type to the tool body 11, cutting can be performed from near the axis O of the tip of the tool body 11 to the outer periphery, and cutting can be performed from a position away from the axis O to the outer periphery. This makes it easier to manage the cutting inserts 1, and only one type of mold is required to manufacture the cutting inserts 1 (1A, 1B).

[0047] The cutting insert 1 (1A, 1B) has a major cutting edge 5 and a minor cutting edge 6, each of which has an arc-shaped cutting edge portion and a linear cutting edge portion. In the positional relationship when the cutting inserts 1 (1A, 1B) are attached to the tool body 11, as shown in FIG. 10, there is a step H3 in the axial direction between the tip of the major cutting edge 5 of one cutting insert 1A and the tip of the minor cutting edge 6 of the other cutting insert 1B. Specifically, as shown in FIG. 10, the cutting edge tip 2b of one cutting insert 1A is located forward of the cutting edge tip 2a of the other cutting insert 1B. In addition, the major cutting edge 5 of one cutting insert 1A and the minor cutting edge 6 of the other cutting insert 1B are attached so that their rotation trajectories during cutting overlap, except for the region corresponding to the step H3.

[0048] When the cutting insert 1 (1A, 1B) is attached to the insert mounting seat 12 (12A, 12B), the first cutting insert 1A is arranged so that the arcuate cutting edge portion 5a of the major cutting edge 5 extends from the vicinity of the axis O on the tip side of the tool body 11 to the rear end side. Meanwhile, the second cutting insert 1B is arranged so that the arcuate cutting edge portion 6a of the minor cutting edge 6 extends from a position away from the axis O on the tip side of the tool body 11 toward the outer periphery to the rear end side.

[0049] Accordingly, in the indexable ball end mill 100 of this embodiment shown in Figure 1, the first insert mounting seat 12A is formed by cutting out the tip side of the tool body 11 up to a range including the axis O at the tip side, while the second insert mounting seat 12B is formed from a position slightly away from the axis O toward the outer periphery.

[0050] These two cutting inserts 1 (1A, 1B) are positioned on the same convex hemispherical surface at the tip end side of the tool body 11.

[0051] If the main cutting edge 5 of the first cutting insert 1A and the minor cutting edge 6 of the second cutting insert 1B become worn due to cutting, these cutting inserts 1 can be reattached to the insert mounting seat 12 on the opposite side, so that the first cutting insert 1A can be reused as the second cutting insert 1B and the second cutting insert 1B can be reused as the first cutting insert 1A, which is economical.

[0052] (Cutting insert) Next, the configuration of the cutting insert 1 according to one embodiment of the present invention will be described in detail. FIG. 2 is a front view showing the configuration of the cutting insert 1 according to one embodiment of the present invention. FIG. 3 is a rear view showing the configuration of the cutting insert 1 according to one embodiment of the present invention. FIG. 4 is a side view seen from the direction of the arrow IV in FIG. 2. FIG. 5 is a side view seen from the direction of the arrow V in FIG. 2. FIG. 6 is a side view seen from the direction of the arrow VI in FIG. 2. FIG. 7 is a side view seen from the direction of the arrow VII in FIG. 2. FIG. 8 is a perspective view showing the configuration of the cutting insert 1 according to one embodiment of the present invention. FIG. 10 is a plan view of two cutting inserts 1 (1A, 1B) arranged in a positional relationship when attached to a tool body 11, seen from a direction facing the rake face of the first cutting insert 1A (the cutting insert on the right side in FIG. 10) used for cutting, with the main cutting edge 5.

[0053] As shown in Figures 2 to 8, a cutting insert 1 (1A, 1B) of one embodiment of the present invention is attached to the tool body 11 shown in Figure 1 to constitute one embodiment of the indexable ball end mill 100 of the present invention described above.

[0054] As shown in Figure 2, the cutting insert 1 (1A, 1B) in this embodiment has a cutting face 2 facing the rotational direction T of the tool body 11 shown in Figure 1, a seating surface 3 facing the opposite side to the cutting face 2 and seated on the bottom surface 12a of the insert mounting seat 12, and a clearance surface 4 extending around the cutting face 2 and the seating surface 3. At the position where the rake face 2 and the flank face 4 intersect, a ridgeline formed by them (hereinafter referred to as an intersecting ridgeline portion) has two main cutting edges (cutting edges) 5 and a minor cutting edge (cutting edge) 6 formed thereon.

[0055] 2, the main cutting edge 5 and the minor cutting edge 6 each include an arc-shaped cutting edge portion 5a, 6a extending in an arc shape and a linear cutting edge portion 5b, 6b extending tangent to each of the arc-shaped cutting edge portions 5a, 6a in a front view of the cutting insert 1 seen from the axial direction facing the rake face 2. These two main cutting edges 5 and minor cutting edges 6 are formed by positioning the arc-shaped cutting edge portions 5a, 6a and the linear cutting edge portions 5b, 6b alternately in the circumferential direction of the rake face 2.

[0056] 4, 5, and 6, in the main cutting edge 5 and the minor cutting edge 6 of this embodiment, at least the arcuate cutting edge portions 5a, 6a have convex curved portions 17 that move away from the seating surface 3 and then approach the seating surface 3 as they move away from the linear cutting edge portions 5b, 6b. The points at which the convex curved portions 17 formed by the arcuate cutting edge portions 5a, 6a are furthest from the seating surface 3 and become convex (the most convex points that protrude most from the seating surface 3) are the most convex point S1 of the main cutting edge and the most convex point S2 of the minor cutting edge, respectively.

[0057] 4 and 5, in a side view from a direction facing the flank 4, the arcuate cutting edge portion 5a has a curvature change point Q1 between the most convex point S1 of the main cutting edge that is the most distant from the seating surface 3 on the convex curved portion 17 and the cutting edge tip 2b of the arcuate cutting edge portion 5a. Also, as shown in Fig. 6, the arcuate cutting edge portion 6a of the minor cutting edge 6 has a curvature change point Q2 between the most convex point S2 of the minor cutting edge that is the most distant from the seating surface 3 on the convex curved portion 17 and the cutting edge tip 2a of the arcuate cutting edge portion 6a.

[0058] When the arc-shaped cutting edge portion 5a (6a) from the cutting edge tip 2b (2a) to the main cutting edge most convex point S1 (minor cutting edge most convex point S2) is composed of arcs or curves with two different curvatures, the curvature change point Q1 (Q2) can be identified as a point where the curvatures of the two arcs or curves are different from each other. Also, when there is a straight line or curve between two different arcs, the curvature change point Q1 (Q2) can be identified as an end point on the cutting edge tip 2b (2a) side of the arc closest to the most convex point S1 (S2). Furthermore, when the cutting edge tip 2b (2a) side is composed of a curve and the most convex point S1 (S2) side is composed of a straight line, it can be identified as a point where the curve and the straight line intersect. It is also preferable that the curvature on the most convex point S1 (S2) side be at least twice as large as the curvature on the cutting edge tip 2b (2a) side from the curvature change point Q1 (Q2). In other words, it is possible to identify the curvature change point Q1 (Q2) by measuring the curvature from the cutting edge tip 2b (2a) to the most convex point S1 (S2).

[0059] In a side view (FIG. 7) seen from a direction facing the flank 4, that is, a normal direction (arrow VII direction in FIG. 2) to the tangent N1 of the arc-shaped cutting edge portion 5a passing through the main cutting edge most convex point S1, the arc-shaped cutting edge portion 5a includes at least two arcs with different curvatures. Specifically, the arc-shaped cutting edge portion 5a is formed by a curved first cutting edge 51 located on the cutting edge tip 2b side, and a curved (or linear) second cutting edge 52 located on the main cutting edge most convex point S1 side and having a smaller curvature than the first cutting edge 51, with the main cutting edge curvature change point Q1 as a boundary. In this way, the arc-shaped cutting edge portion 5a in this embodiment is composed of a first cutting edge 51 curved on the cutting edge tip 2b side convex upward with respect to the seating surface 3, and a second cutting edge 52 on the main cutting edge most convex point S1 side convex upward with respect to the seating surface 3, with the main cutting edge curvature change point Q1 as a boundary. The intersection point between the first cutting edge 51 and the second cutting edge 52 is a main cutting edge curvature changing point Q1.

[0060] Also, in the arcuate cutting edge portion 6a, when viewed in a side view from the normal direction with respect to the tangent line N2 of the arcuate cutting edge portion 6a passing through the flank most convex point S2, that is, in the direction facing the flank 4, the arcuate cutting edge portion 6a includes at least two arcs with different curvatures. Specifically, the arcuate cutting edge portion 6a is formed by a curved first cutting edge 61 located on the cutting edge tip 2a side with the flank curvature change point Q2 as a boundary, and a curved (or linear) second cutting edge 62 located on the flank most convex point S2 side and having a smaller curvature than the first cutting edge 61. Thus, the arcuate cutting edge portion 6a in this embodiment consists of a curved first cutting edge 61 with the cutting edge tip 2a side protruding upward with respect to the seating surface 3 and a second cutting edge 62 with the flank most convex point S2 side convex upward with respect to the seating surface 3, with the intersection of the first cutting edge 61 and the second cutting edge 62 being the flank curvature change point Q2.

[0061] The arcuate cutting edge portion 5a is formed by a first cutting edge 51 and a second cutting edge 52 that form arcs with the above-described two different curvatures. Among the arcuate cutting edge portion 5a, if the radius of the arc of the first cutting edge 51 on the cutting edge tip 2b side is the arc radius R1 and the radius of the arc of the second cutting edge 52 on the major cutting edge most convex point S1 side is the arc radius R2, then R1 < R2, and the arc radius R1 is formed to be 1 / 2 or less of the arc radius R2. In this embodiment, specifically, the magnitudes of these two arc radii R1 and R2 are R1 = 6.8 mm and R2 = 56.4 mm, satisfying the relationship that the arc radius R2 is twice or more the arc radius R2.

[0062] Also, the arcuate cutting edge portion 6a may also be formed by a first cutting edge 61 and a second cutting edge 62 that form arcs with the above-described two different curvatures. In that case, the arc radius R2 of the second cutting edge 62 is larger than the arc radius R1 of the first cutting edge 61. That is, also in the arcuate cutting edge portion 6a, R1 < R2, and the arc radius R1 is formed to be 1 / 2 or less of the arc radius R2. In this embodiment, specifically, the magnitudes of these two arc radii R1 and R2 are R1 = 2.7 mm and R2 = 56.4 mm, satisfying the relationship that the arc radius R2 is twice or more the arc radius R2.

[0063] [Table 1]

[0064] Table 1 shows the cutting edge profile in the side view (FIG. 7) of this embodiment as seen from the normal direction (arrow VII direction in FIG. 2) to the tangent N1 of the arc-shaped cutting edge portion 5a passing through the main cutting edge most convex point S1. When the cutting edge position is measured in 1 mm increments in a direction parallel to the seating surface 3 toward the main cutting edge most convex point S1, with the cutting edge tip 2b as the origin, the "height [mm] from the seating surface 3 in a direction perpendicular to the seating surface 3" changes as shown in (1), and the "height [mm] from the cutting edge tip 2b in a direction perpendicular to the seating surface 3" changes as shown in (2). In addition, the "percentage [%] (of the height of the cutting edge at each measurement point) when the height from the cutting edge tip 2b to the main cutting edge most convex point S1 in a direction perpendicular to the seating surface 3 is taken as 100%" is (3).

[0065] 11A is a graph showing the relationship between the distance from the cutting edge tip 2b in a direction parallel to the seating surface 3 at any position on the arc-shaped cutting edge portion 5a and the height from the seating surface 3 in a direction perpendicular to the seating surface 3, by taking the "distance [mm] from the cutting edge tip 2b in a direction parallel to the seating surface 3" in Table 1 on the horizontal axis and the above (1) on the vertical axis. Here, the height from the seating surface 3 to the arc-shaped cutting edge portion 5a means the so-called "wall thickness." In the side view shown in Figure 7 from the normal direction to the tangent N1 of the arc-shaped cutting edge portion 5a, for example, as shown in Figure 13A, the height from the seating surface 3 to the cutting edge tip 2b is 4.571 mm, the height from the seating surface 3 to the main cutting edge curvature change point Q1 is 7.250 mm, and the height from the seating surface 3 to the main cutting edge most convex point S1 is 7.498 mm.

[0066] In this embodiment, in the side view shown in Figure 7, seen from the normal direction to the tangent N1 of the arc-shaped cutting edge portion 5a, the height T1 from the cutting edge tip 2b to the main cutting edge curvature change point Q1 from the seating surface 3 is more than 10 times the height T2 from the main cutting edge curvature change point Q1 to the main cutting edge most convex point S1 from the seating surface 3.

[0067] As a specific example, the height T1 from the seating surface 3 from the cutting edge tip 2b to the main cutting edge curvature change point Q1 is 2.679 mm, and the height T2 from the seating surface 3 from the main cutting edge curvature change point Q1 to the main cutting edge most convex point S1 is 0.248 mm, and the height T1 is more than 10 times the height T2.

[0068] FIG. 11B is a graph showing the “distance [mm] from the cutting edge tip 2b in the direction parallel to the seating surface 3” from Table 1 on the horizontal axis and the “percentage [%] when the distance from the cutting edge tip 2b to the most convex point S1 is taken as 100%” on the vertical axis. As shown in FIG. 11B, when the height from the cutting edge tip 2b to the main cutting edge most convex point S1 is taken as the standard (100%), the height from the cutting edge tip 2b to the main cutting edge curvature change point Q1 is about 92% of the standard. In this embodiment, the height at any multiple points from the main cutting edge curvature change point Q1 to the main cutting edge most convex point S1 meets 90% or more of the standard, and the height difference from the main cutting edge curvature change point Q1 to the main cutting edge most convex point S1 is small. On the other hand, the height at any multiple points from the main cutting edge curvature change point Q1 to the cutting edge tip 2b ranges from 90% to 0% of the standard, and the height changes greatly between adjacent points. Therefore, the height difference is larger on the cutting edge tip 2b side than on the main cutting edge most convex point S1 side at the main cutting edge curvature change point Q1, and the curve shape is abruptly approaching the seating surface 3 from the cutting edge tip 2b to the main cutting edge curvature change point Q1.

[0069] In this embodiment, among the arc-shaped cutting edge portion 5a including the first cutting edge 51 and the second cutting edge R52, the first cutting edge 51 located on the cutting edge tip 2b side has a steeper arc curve than the second cutting edge 52 located on the main cutting edge most convex point S1 side. The same can be said about the arc-shaped cutting edge portion 6a.

[0070] In this embodiment, durability can be ensured by ensuring that the thickness of the arc-shaped cutting edge portions 5a, 6a on the main cutting edge most convex point S1 side, which includes the main cutting edge curvature change point Q1, is 90% or more of the main cutting edge most convex point S1. Also, by making the arc curve on the cutting edge tips 2b, 2a side steeper than the main cutting edge curvature change point Q1, the arc-shaped cutting edge portions 5a, 6a come into contact with the workpiece smoothly, reducing the impact acting on the cutting edge and the cutting resistance.

[0071] 2 and 8, in the cutting face 2 of this embodiment, breakers 21 are formed in the shape of convex curves in the direction away from the seating surface 3 near each intersecting ridgeline portion (arcuate cutting edge portions 5a, 6a). In a cross section perpendicular to the main cutting edge 5 and the minor cutting edge 6, the apex (ridgeline) 21a of each breaker 21 is at a greater distance (height) from the seating surface 3 than the arcuate cutting edge portions 5a, 6a. The breakers 21 are preferably formed within a range of 0°<θ3<50° from the axis O, centered on the center point P of the arcuate cutting edge portions 5a, 6a located on the axis O.

[0072] As shown in Fig. 3, a groove 8 is formed on the seating surface 3 side of the cutting insert 1, which can be engaged with a protrusion protruding from the bottom surface 12a of the first insert mounting seat 12A. Two grooves 8 are formed on both radial sides of the mounting hole 7 for mounting the cutting insert 1. The major cutting edge curvature change point Q1 is formed on the cutting edge tip 2b side of one of the two grooves 8A, 8B, which is closer to the arc-shaped cutting edge portion 5a, the groove 8B. The minor cutting edge curvature change point Q2 is formed on the cutting edge tip 2a side of the other groove 8A which is closer to the arc-shaped cutting edge portion 6a.

[0073] The groove 8B on the side closer to the cutting edge tip 2b is a groove with one end in the length direction opening to the side surface on the minor cutting edge 6 side and the other end opening to the side surface on the main cutting edge 5 side, and the width on the minor cutting edge 6 side is narrower than the width on the main cutting edge 5 side. The minor cutting edge most convex point S2 and the minor cutting edge curvature change point Q2 on the minor cutting edge 6 are formed in positions that are not affected by the reduction in thickness due to the groove 8B, and the thickness at the minor cutting edge most convex point S2 and the minor cutting edge curvature change point Q2 is sufficiently secured. Therefore, the strength of the cutting insert 1 can be improved, and damage to the cutting insert 1 due to the load during cutting can be prevented.

[0074] On the other hand, the groove portion 8A on the side closer to the cutting edge tip 2a has a blind groove shape in which one end in the length direction opens to the side surface on the minor cutting edge 6 side, but the other end does not open to the side surface on the main cutting edge 5 side. Therefore, the main cutting edge most convex point S1 and the main cutting edge curvature change point Q1 on the main cutting edge 5 are formed in positions that are not affected by the reduction in thickness due to the groove portion 8A, and the thickness at the main cutting edge most convex point S1 and the main cutting edge curvature change point Q1 is sufficiently secured. Therefore, the strength of the arc-shaped cutting edge portion 5a of the main cutting edge 5 can also be improved to prevent damage.

[0075] Furthermore, as shown in Figure 10, when the cutting insert 1 is attached to the tool body 11, if the center point of the hemispherical surface of the tool body 11 (cutting insert 1) on the axis O is defined as P, the angle between the axis O and a line L1 connecting the center point P and the most convex point S1 of the main cutting edge is defined as θ1, and the angle between the axis O and a line L2 connecting the center point P and the curvature change point Q1 of the main cutting edge is defined as θ2, the angle θ2 is smaller than the angle θ1 (θ2<θ1).

[0076] Here, the angle θ1 between the axis O and a line L1 connecting the center point P and the most convex point S1 of the main cutting edge is within a range of 30°≦θ1≦50°, and more preferably within a range of 40°≦θ1≦50°. In this embodiment, the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 45°.

[0077] If the most convex point S1 of the main cutting edge is located at an angle position where the angle θ1 is less than 30°, there is a problem that when the cutting depth is increased in a rough machining process, etc., a portion where tensile stress is concentrated occurs in the cutting insert, while if the most convex point S1 of the main cutting edge is located at an angle position where the angle θ1 exceeds 50°, the most convex point S1 of the main cutting edge is located away from the contact point between the workpiece and the cutting insert toward the rear end of the tool, and the effect of dispersing stress concentration is reduced. Therefore, it is preferable to set the angle θ1 from the axis O to the most convex point S1 of the main cutting edge within the above range.

[0078] The angle θ2 between the axis O and the line L2 connecting the center point P and the curvature change point Q1 of the main cutting edge is in the range of 15°≦θ2≦40°, and more preferably in the range of 17°≦θ2≦37°. In this embodiment, the angle θ2 from the axis O to the curvature change point is 22.5°.

[0079] If the curvature change point Q1 of the main cutting edge is located at an angle position where the angle θ2 is less than 15°, stress concentration occurs at the boundary between the main cutting edge 5 and the workpiece when the cutting depth is greater than that of the curvature change point Q1, resulting in early wear and tear. On the other hand, if the curvature change point Q1 of the main cutting edge is located at an angle position where the angle θ2 is more than 40°, a problem occurs in that a portion where stress is concentrated is generated at the tip of the arc-shaped cutting edge portion 5a. Therefore, it is preferable to set the angle θ2 from the axis O to the curvature change point Q1 of the main cutting edge within the above range.

[0080] 12A to 16 show the results of a simulation analysis of when a workpiece is cut by a conventional cutting insert or a cutting insert of the present invention. The conditions for the simulation analysis in FIG. 12A to FIG. 14B are the spindle rotation speed n=2122 [min -1 ], feed rate per tooth fz = 0.4 [mm / tооth], cutting depth ap × cutting width ae = 3 × 3 [mm], tool diameter 30 [mm], workpiece material SKD61 (44HRC), and maximum principal stress were used for evaluation. On the other hand, the conditions for the simulation analysis in Figs. 15 and 16 are spindle speed n = 2122 [min -1], feed rate per tooth fz = 0.4 [mm / tооth], cutting depth ap × cutting width ae = 3 × 3 [mm], tool diameter 30 [mm], workpiece material SKD61 (44HRC), and minimum principal stress were used for evaluation.

[0081] Fig. 12A is a diagram showing cutting stresses by simulation analysis during cutting with a conventional cutting insert 90 in which the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 16.5°, and shows the maximum principal stresses acting on the cutting insert 90 and the workpiece 91 (including chips 91a) by cutting. Fig. 12B is a diagram showing the maximum principal stresses acting on the cutting insert 90 in simulation analysis during cutting with a conventional cutting insert 90 in which the angle from the axis O to the most convex point S1 of the main cutting edge is 16.5°.

[0082] Fig. 13A is a diagram showing cutting stresses by simulation analysis during cutting using a conventional cutting insert 92 in which the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 22.5°, and shows the maximum principal stresses acting on the cutting insert 92 and the workpiece 91 (including chips 91a) by cutting. Fig. 13B is a diagram showing the maximum principal stresses acting on the cutting insert 92 by simulation analysis during cutting using a conventional cutting insert 92 in which the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 22.5°. Fig. 13B is a diagram showing only the cutting insert 92 from Fig. 13A.

[0083] Fig. 14A is a diagram showing cutting stress by simulation analysis during cutting with a cutting insert 1 of one embodiment of the present invention, in which the angle θ1 from the axis O to the main cutting edge most convex point S1 is 45° and the angle θ2 from the axis O to the main cutting edge curvature change point Q1 is 22.5°, and shows the maximum principal stress applied to the cutting insert 1 and the workpiece 91 (including chips 91a) by cutting. Fig. 14B is a diagram showing the maximum principal stress applied to the cutting insert 1 by simulation analysis during cutting with a cutting insert 1 of one embodiment of the present invention, in which the angle θ1 from the axis O to the main cutting edge most convex point S1 is 45° and the angle θ2 from the axis O to the main cutting edge curvature change point Q1 is 22.5°. Fig. 14B is a diagram showing only the cutting insert 1 from Fig. 14A.

[0084] FIG. 15 is a diagram showing cutting stresses based on a simulation analysis during cutting using a conventional cutting insert 94 in which the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 16.5, and shows the minimum principal stress acting on the cutting insert 94 during cutting.

[0085] Figure 16 is a diagram showing cutting stresses based on a simulation analysis during cutting using a cutting insert 1 of one embodiment of the present invention, in which the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 45° and the angle θ2 from the axis O to the curvature change point Q1 of the main cutting edge is 22.5°, and shows the minimum principal stress applied to the cutting insert 1 due to cutting.

[0086] From Fig. 12B, it can be seen that when the most convex point S1 of the main cutting edge is located at an angle θ1 of 16.5° from the axis O, the maximum principal stress, i.e., tensile stress, is concentrated near the most convex point S1 of the main cutting edge during cutting. Furthermore, from Fig. 15, it can be seen that when the most convex point S1 of the main cutting edge is located at the same position as Fig. 12B, there is a portion where the minimum principal stress, i.e., compressive stress, is concentrated before and after the most convex point S1 of the main cutting edge. From Fig. 12B and Fig. 15, in the conventional arc-shaped cutting edge shape, both tensile stress concentration portions and compressive stress concentration portions are generated in the arc-shaped cutting edge portion 5a during cutting, which makes it easy for chipping or breakage (cracks) of the cutting insert to occur.

[0087] Furthermore, even when the most convex point S1 is provided at the same position as the curvature change point Q1 in this embodiment (the angle θ1 from the axis O is 16.5°) and the cutting edge shape is such that the main cutting edge curvature change point Q1 does not exist between the main cutting edge most convex point S1 and the cutting edge tip 2b, it can be seen that a tensile stress concentration area occurs near the main cutting edge most convex point S1 during cutting, as shown in Figures 13A and 13B.

[0088] In contrast, in the case of the cutting edge shape of the main cutting edge 5 of this embodiment, in which the main cutting edge most convex point S1 is at a position of 45° from the axis O and the main cutting edge curvature change point Q1 exists between the main cutting edge most convex point S1 and the cutting edge tip 2b (at a position where the angle θ2 from the axis O is 22.5°), the stress during cutting is distributed over a wide area of ​​the arc-shaped cutting edge portion 5a as shown in FIG. 14B. Similarly, the compressive stress is also distributed over a wide area of ​​the arc-shaped cutting edge portion 5a as shown in FIG. 16. In other words, the workpiece is gradually cut from the main cutting edge most convex point S1 side to the main cutting edge curvature change point Q1, so that stress concentration can be avoided and the strength of the main cutting edge 5 can be improved.

[0089] 12A and 13A show that the chip 91a is significantly twisted. On the other hand, in FIG. 14A showing the present embodiment, the chip 91a is shown to have a smaller twist than that of the conventional example. The chip 91a is formed along the arc-shaped cutting edge portion 5a. That is, by providing the main cutting edge curvature change point Q1 between the main cutting edge most convex point S1 and the cutting edge tip 2b, it is possible to form the chip 91a with a smaller twist.

[0090] When the cutting inserts 1 (1A, 1B) of this embodiment are attached to the insert mounting seats 12 (12A, 12B) formed at the tip of the tool body 11 shown in Fig. 1, the angle θ1 from the axis O to the most convex point S1 of the major cutting edge of the first cutting insert 1A and the angle θ3 from the axis O to the most convex point S2 of the minor cutting edge of the second cutting insert 1B are equal to each other, as shown in Fig. 10. Therefore, in this embodiment, the angle θ3 is set to 45°, similar to the angle θ1.

[0091] In the cutting insert 1 (1A, 1B) of this embodiment, the major cutting edge 5 and the minor cutting edge 6 have an asymmetric shape, and accordingly, of the two insert mounting seats 12A, 12B, the first insert mounting seat 12A is formed so as to cut out the tip portion of the tool body 11 up to a range including the axis line O on the tip side. On the other hand, the second insert mounting seat 12B is formed from a position slightly away from the axis line O on the tip side of the tool body 11 toward the outer periphery as shown in FIG.

[0092] As shown in FIG. 1, the first cutting insert 1A and the second cutting insert 1B are respectively attached to the first insert mounting seat 12A or the second insert mounting seat 12B by clamp screws 9 inserted through the respective mounting holes 7 (FIG. 10).

[0093] The first cutting insert 1A is attached to the first insert mounting seat 12A such that the arcuate cutting edge portion 5a of the main cutting edge 5 is positioned on a convex hemisphere extending from near the axis O and having its center on the axis O. The first cutting insert 1A is also attached such that the linear cutting edge portion 5b of the main cutting edge 5 is positioned on a cylindrical surface tangent to the convex hemisphere and centered on the axis O.

[0094] The second cutting insert 1B is attached to the second insert mounting seat 12B such that the arcuate cutting edge portion 6a of the minor cutting edge 6 is positioned on the convex hemisphere where the arcuate cutting edge portion 5a of the major cutting edge 5 of the first cutting insert 1A is positioned from a position away from the axis O. The second cutting insert 1B is attached such that the linear cutting edge portion 6b of the minor cutting edge 6 is positioned on the cylindrical surface where the linear cutting edge portion 5b of the major cutting edge 5 of the first cutting insert 1A is positioned.

[0095] When the first cutting insert 1A and the second cutting insert 1B are attached to the tool body 11 in this manner, as shown in Figure 10, if the diameter of the tool body 11 is D and the distance in the direction along the axis O from the cutting edge tip 2b of the main cutting edge 5 to the main cutting edge curvature change point Q1 is H, the relationship D / 30≦H≦D / 10 is satisfied, and it is preferable that, for example, H≧D / 20.

[0096] In the direction along the axis O, the lower limit position of the curvature change point Q1 of the main cutting edge and the upper limit position of the most convex point S1 of the main cutting edge are related to the maximum cutting depth (maximum cutting amount). In addition, the maximum cutting depth generally increases as the tool diameter D increases. For example, when the tool diameter D is 30 mm, even if there are multiple arcs with different curvatures between the curvature change point Q1 of the main cutting edge and the cutting edge tip 2b, the portion with the maximum cutting depth of 1.0 mm or less does not become the curvature change point Q1 of the main cutting edge in this embodiment. That is, in the direction along the axis O, the distance H from the cutting edge tip 2b to the curvature change point Q1 of the main cutting edge (the lower limit position of the curvature change point Q1 of the main cutting edge) is preferably 1.0 mm or more when the tool diameter D is 30 mm.

[0097] For example, when the tool diameter D is 30 mm, the distance H from the cutting edge tip 2b to the main cutting edge curvature change point Q1 is smaller than the maximum cutting depth of 3.0 mm. Specifically, in this embodiment, the distance H from the cutting edge tip 2b to the main cutting edge curvature change point Q1 is approximately 1.4 mm.

[0098] In addition, it is preferable that the upper limit position of the most convex point S1 of the main cutting edge is equal to or greater than the maximum cutting depth in the direction along the axis O. When the tool diameter D is 30 mm, the distance H1 from the cutting edge tip 2b to the most convex point S1 of the main cutting edge is greater than the maximum cutting depth of 3.0 mm. Specifically, in this embodiment, the distance H1 from the cutting edge tip 2b to the most convex point S1 of the main cutting edge is approximately 4.6 mm.

[0099] By forming the arc-shaped cutting edge portion 5a of the main cutting edge 5 in a shape such that the distance H1 from the cutting edge tip 2b to the main cutting edge's most convex point S1 is greater than the maximum cutting depth, the workpiece is gradually cut from the main cutting edge's most convex point S1 side to the main cutting edge's curvature change point Q1, thereby avoiding stress concentration and reducing cutting resistance, thereby improving the strength of the main cutting edge 5. If the distance H1 from the cutting edge tip 2b to the main cutting edge most convex point S1 is smaller than the maximum cutting depth, the workpiece is first cut from the main cutting edge most convex point S1, so cutting stress tends to concentrate at the main cutting edge most convex point S1 and cracks tend to occur on the tool rear end side rather than the main cutting edge most convex point S1. Therefore, it is preferable to use a shape in which the distance H1 from the cutting edge tip 2b to the main cutting edge most convex point S1 is greater than the maximum cutting depth.

[0100] As described above, in this embodiment, the arcuate cutting edge portion 5a of the main cutting edge 5 and the arcuate cutting edge portion 6a of the auxiliary cutting edge 6 are formed in a convex curve shape that moves away from the seating surface 3 side and then approaches the seating surface 3 side again as it moves away from the linear cutting edge portions 5b, 6b, and the curvature change points Q1, Q2 are provided between the most convex points S1, S2 of the arcuate cutting edges 5a, 6a that are the most convex with respect to the seating surface 3 and the cutting edge tips 2b, 2a. By providing the curvature change points Q1, Q2 in addition to the most convex points S1, S2, the arcuate cutting edges 5a, 6a gradually bite into and cut into the workpiece from the most convex points S1, S2 side that are the most convex with respect to the seating surface 3 to the curvature change points Q1, Q2 during cutting, so that the stress during cutting can be distributed over a wide range including the range from the most convex points S1, S2 to the curvature change points Q1, Q2. In this way, by providing the most convex points S1, S2, the thickness of the cutting insert 1 is ensured and its strength is improved, and by providing the curvature change points Q1, Q2 between the most convex points S1, S2 and the cutting edge tips 2b, 2a, the cutting resistance can be reduced, thereby preventing damage to the cutting insert 1 due to the load during cutting processing.

[0101] In addition, chips are generated during cutting, but in the case of a conventional shape in which there is no curvature change point Q between the most convex point S and the cutting edge tip 2b of the arc-shaped cutting edge portion 5a, the chips are bent and pulled.

[0102] In contrast, in this embodiment, the curvature change point Q exists between the most convex point S and the cutting edge tip 2b, so that the chips generated by cutting are less likely to bend, and the stress during cutting is dispersed. This improves the discharge of the chips, and prevents the arc-shaped cutting edge portion 5a from being chipped or damaged (cracked). As a result, the life of the cutting insert 1 can be extended.

[0103] Furthermore, as shown in Figure 3, the most convex points S1, S2 and the curvature change points Q1, Q2 are positioned so as not to overlap with the opening of the groove portion 8 to the clearance face 4. This ensures a sufficient thickness from the seating surface 3 to the most convex points S1, S2 and the curvature change points Q1, Q2, preventing damage to the main cutting edge 5 and the minor cutting edge 6 even if a large cutting force is applied to the cutting insert 1.

[0104] In this manner, the cutting insert 1 of the present embodiment can suppress the occurrence of cracks in the cutting edge portion by dispersing the stress during cutting and increasing the strength of the cutting edge tip side over a wider cutting depth than conventional cutting inserts.

[0105] Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. A person skilled in the art may conceive of various modified or revised examples within the scope of the technical ideas described in the claims. These also fall within the technical scope of the present invention. The configurations of the above-described embodiments may be appropriately combined.

[0106] In addition, the cutting insert according to the present invention is preferably manufactured from a cemented carbide based on tungsten carbide-cobalt (WC-Co) as the main raw material. However, in addition to the tungsten carbide-cobalt base, cemented carbide containing carbonitride-based cermets, high speed steel, titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, ceramics consisting of mixtures of these, cubic boron nitride sintered bodies, diamond sintered bodies, polycrystalline diamond or ultra-high pressure sintered bodies in which a hard phase consisting of cubic boron nitride and a bonding phase such as ceramics or iron group metals are sintered under ultra-high pressure, etc. can also be used.

[0107] In the cutting insert of the above embodiment, the arc-shaped cutting edge portion (5a, 6a) may be composed of at least two or more arc-shaped first cutting edges (51, 61), second cutting edges (52, 62) to Nth cutting edges (N is an integer of 2 or more, N=2 in the above embodiment) having different arc radii, in order from a position corresponding to the tool tip side. The first cutting edge (51, 61) on the tip side may have a smaller arc radius than the other second cutting edges (52, 62) to Nth cutting edges, and the first cutting edge (51, 61) may have a cutting edge angle, which is an angle between the flank face (4) and the rake face (2), gradually decreasing from the second cutting edge (52, 62) side toward the tool tip side.

[0108] In this case, by gradually decreasing the cutting edge angle of the first cutting edge (51, 61) of the arc-shaped cutting edge portion (5a, 6a) from the second cutting edge (52, 62) side toward the tip, the clearance angle of the cutting edge can be increased when cutting with the tip of the cutting edge, and the progression of clearance wear at the tip of the cutting edge can be suppressed. Generally, the tip of the arc-shaped cutting edge is likely to be chipped due to the force of being thrust up from the Z-axis direction during cutting. Generally, the larger the blade angle, the thicker the blade and the stronger the cutting edge. However, when cutting a workpiece such as high-hardness steel, if the clearance angle is small, the life may vary even if the thickness is large. In contrast, in the above configuration, the clearance angle of the tip of the cutting edge is gradually reduced from the rear end side to the front end side of the first cutting edge (51, 61) to ensure a certain degree of clearance angle at the tip of the arc-shaped cutting edge during cutting, thereby stabilizing the life of the tip of the arc-shaped cutting edge. It is preferable that the clearance angle of the first cutting edge (51, 61) is about 10 to 25° on the tool tip side and about 5 to 20° on the second cutting edge (52, 62) side, with the difference between the two being about 5 to 15°. More preferably, the cutting edge angle of the first cutting edge (51, 61) is about 15 to 25° on the tool tip side and about 8 to 18° on the second cutting edge (52, 62) side, with the difference between the two being about 10 to 15°.

[0109] In the above embodiment, the difference H3 between the lowest point of the cutting insert 1A and the lowest point of the other cutting insert 1B may be 0.025 or less, in relation to the diameter D of the tool body 11. In this case, by making H3 / D 0.025 or less, the cutting insert cutting edge step with respect to the tool diameter D can be sufficiently reduced. As a result, the range where cutting is performed only by the cutting insert 1A with the lower lowest point (i.e., the parent cutting edge) is reduced, and wear at the tip of the cutting insert 1A with the lower lowest point is suppressed, thereby extending the life of the cutting insert 1A. H3 / D is preferably 0.020 or less, more preferably 0.017 or less. The lower limit of H3 / D is not limited, but in reality it is about 0.010. [Industrial Applicability]

[0110] According to the cutting insert and indexable cutting tool of the present invention, the stress generated in the arc-shaped cutting edge portion can be dispersed, thereby suppressing the occurrence of cracks in the cutting edge portion, and therefore the present invention is industrially applicable. [Explanation of symbols]

[0111] 1...Cutting insert 2…Scooping surface 2a, 2b...Tip of cutting edge 3…Seating surface 4…Flank 5...Main cutting edge (cutting edge) 5a, 6a...Arc-shaped cutting edge 5b,6b…Straight cutting edge part 6…Sub-cutting edge (cutting edge) 7…Mounting hole 8(8A,8B)…Groove 11...Tool body 12, 12A…Insert mounting seat 12a…Bottom surface 17...Convex curved part 21...Breaker 21a…Vertex (ridge) 51,61…First cutting edge 52,62…Second cutting edge 100...Replaceable ball end mill (replaceable cutting tool) H,H1,H3…distance L1,L2…line N1,N2…tangent O…Axis line P...center point Q(Q1,Q2)…Curvature change point R1, R2...Arc radius S(S1,S2)…Most convex point T…Rotation direction of the end mill body T1: Height from the seating surface to the tip of the cutting edge to the point where the curvature changes (thickness) T2: Height from the seating surface from the curvature change point to the most convex point (wall thickness) θ1, θ2, θ3...Angles

Claims

1. A cutting insert that is removably attached to an insert mounting seat formed at a tip of a tool body of an indexable cutting tool that is rotated about an axis, a cutting face oriented in a rotational direction of the tool body; a seating surface facing away from the rake surface and seated on a bottom surface of the insert mounting seat; a clearance surface extending around the rake surface and the seating surface; At an intersection ridge portion between the rake face and the flank face, two cutting edges each having an arc-shaped cutting edge portion extending in an arc shape in a plan view seen from a direction facing the rake face and a linear cutting edge portion extending so as to be tangent to the arc-shaped cutting edge portion are formed by positioning the arc-shaped cutting edge portion and the linear cutting edge portion alternately in the circumferential direction of the rake face, A cutting insert in which each cutting edge at least forms a convex curved portion that moves away from the seating surface and then approaches the seating surface as the arc-shaped cutting edge portion moves away from the linear cutting edge portion, and when viewed from a side from a direction facing the escape surface, the arc-shaped cutting edge portion has a curvature change point between the most convex point and the cutting edge tip of the arc-shaped cutting edge portion, when the most convex point is the point on the convex curved portion that is farthest from the seating surface.

2. In the side view seen from a normal direction to a tangent line of the arcuate cutting edge portion passing through the most convex point, each cutting edge includes at least two arcs of different curvature; The cutting insert according to claim 1 , wherein a relationship of R1<R2 is satisfied, where R1 is a circular arc radius on the cutting edge tip side and R2 is a circular arc radius on the most convex point side.

3. The cutting insert according to claim 2 , wherein the arc radius R1 is equal to or smaller than ½ of the arc radius R2.

4. In the side view, The cutting edge includes a first cutting edge having a curved shape convex upward with respect to the seating surface on the cutting edge tip side and a second cutting edge having a curved shape convex upward with respect to the seating surface on the most convex point side, the first cutting edge being curved upward with respect to the seating surface on the curvature change point side, The second cutting edge is formed in a curved or linear shape having a smaller curvature than the first cutting edge, The cutting insert according to claim 1 or 2, wherein an intersection point between the first cutting edge and the second cutting edge is the curvature change point.

5. The cutting insert according to claim 4 , wherein the curvature of the first cutting edge is at least twice as large as the curvature of the second cutting edge.

6. In the arcuate cutting edge portion as viewed from the side, The cutting insert according to claim 5, wherein the second cutting edge is a portion where a ratio of a height from the tip of the cutting edge to an arbitrary cutting edge ridgeline to a height from the tip of the cutting edge to the most convex point in a direction perpendicular to the seating surface is 90% or more.

7. the cutting insert is formed with a groove having a wall surface capable of contacting a protrusion protruding from the bottom surface of the insert mounting seat, The groove portion is formed in two portions on either side of a mounting hole for mounting the cutting insert, The cutting insert according to claim 1 or 2, wherein the curvature change point is formed closer to the cutting edge tip side than one of the two groove portions that is closer to the arc-shaped cutting edge portion.

8. The arc-shaped cutting edge portion is composed of at least two or more arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N is an integer of 2 or more) having different arc radii from one another, in order from a position corresponding to a tip side of the tool, The first cutting edge on the tip side has a smaller arc radius than the other second cutting edges to the Nth cutting edges, The cutting insert according to claim 1 or 2, wherein a tool angle, which is an angle between the flank face and the rake face, of the first cutting edge gradually decreases from the second cutting edge side toward the tool tip side.

9. The cutting insert according to claim 1 or 2, and a tool body to which a plurality of the cutting inserts can be attached, When the center point of the arcuate cutting edge portion located on the axis of the tool body is defined as P, The angle between the line connecting the center point P and the most convex point and the axis is θ1, an indexable cutting tool, wherein an angle formed by a line connecting the center point and the curvature change point and the axis line is θ2, and θ2<θ1, 30°≦θ1≦50°, and 15°≦θ2≦40°.

10. 10. The indexable cutting tool according to claim 9, wherein, in a direction along the axis, a distance from a tip of the cutting edge of the cutting insert to a curvature change point is defined as H, and a diameter of the tool body is defined as D, satisfying a relationship of D / 30≦H≦D / 10.

11. In a state where the cutting insert is attached to the tool body, The arc-shaped cutting edge portion is composed of at least two or more arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N is an integer of 2 or more) having different arc radii from one another, in order from a position corresponding to a tip side of the tool, The first cutting edge on the tip side has a smaller arc radius than the other second cutting edges to the Nth cutting edges, 10. The indexable cutting tool according to claim 9, wherein a clearance angle, which is an angle between the clearance face of the cutting insert and a surface of a workpiece, gradually increases from the second cutting edge side toward the tool tip side in the first cutting edge.

12. In a state where a plurality of the cutting inserts are attached to the tool body, 10. The indexable cutting tool according to claim 9, wherein when a difference between a lowest point of any one of the cutting inserts and a lowest point of the other cutting insert is H, the relationship between H and a diameter D of the tool body is H / D which is 0.025 or less.

13. The tip of the tool body is provided with two insert mounting seats spaced 180° apart from each other. The indexable cutting tool according to claim 9 , wherein the cutting insert is removably attached to each of the two insert mounting seats.

Images