JP2002254216A - Throwaway tip and cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a throwaway tip which has little cutting resistance and can obtain, a stable transformational effect for tips. SOLUTION: At almost the center of an edge 15a of a front cutting edge 15, a recessed circular arc 25 is formed so as to lower a cutting face 16, and a recessed spherical surface 26 is formed at the cutting face 16. In the case of parting cutting, tips, copying the front cutting edge 15, are narrowly transformed into circular arcs which have cross sectional shapes protruded to a lower side, and discharged backwardly along the recessed spherical surface 26, but since the transformation is not caused by been pressed against a protruded part formed on conventional cutting faces, small cutting resistance is achieved, and the tip is deformed irrespective of vertical feeding speeds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a throw-away insert (insert for a cutting tool) used for parting off or grooving in turning and a cutting tool using the same.

[0002]

2. Description of the Related Art A tip 101 as shown in FIG. 13 is known as a throw-away tip (hereinafter also simply referred to as a tip) used for parting or grooving (hereinafter also simply referred to as parting). This chip 101
On the left and right sides of the rake face 16 near the front cutting edge 15, a pair of raised convex portions (inclined walls) 20 are provided. In this method, the chip K is forcibly pressed against the convex portions 20 on both right and left sides thereof, and the cross section is deformed from a flat form to a concave or V-shaped form and discharged. is there.

The chip K formed by such a chip 101 has such a deformed cross section that its rigidity is higher and its width is narrower than that of a chip having a flat cross section. Therefore, even if the chips are discharged in the form of a spiral, they are easily cut at an appropriate length, so that they are not entangled with a cutting tool, a work material (also referred to as a work) or a chuck, and are excellent in chip processing. ing.

[0004]

When cutting off or grooving with the above-mentioned conventional tip 101, chips K are forcibly applied to the projections 20 on both sides near the cutting edge 15 in the discharging process. To deform its cross-sectional shape. Therefore, the resistance to the chip or the work is greater than that of the part without the convex part 20 for the deformation, and the wear of the cutting edge becomes faster and the service life is shortened when it comes to the chip. There was a problem.

[0005] In addition, due to the large cutting resistance, there is the following problem in the case of parting off. Immediately before the front cutting edge 15 is cut off with a slight lead angle like the tip 101 shown in FIG. 13, the cut-off width portion V is, as shown in FIG.
The end face T side (right side in the figure) of the work to be cut off has a thin tapered shape, and the front cutting edge 15 is further fed vertically and cut off. In this parting-off, the width portion V cut by the front cutting edge 15 gradually becomes smaller in diameter, and the work (right side in the figure) is cut off at last, but slightly before the cutting edge 15 reaches the center of the end face T of the work. The cutting is performed by the lateral force of the vertical feeding force so as to be folded without depending on the cutting. Therefore, a boss-shaped burr (hereinafter, also referred to as a center boss) remains protrudingly at the center of the end face (right side in the figure) of the cut and cut-off work.

However, in the case of the above-mentioned conventional insert, the central boss tends to be large because the cutting resistance near the cut surface (end surface) of the work is large due to the convex portions on both sides of the front cutting edge. Was. Therefore, in the case of a precision shaft component that requires high machining accuracy on the end face, it has been necessary to separately cut off the center boss in a subsequent process (secondary machining). Incidentally, the end face of the remaining part (left side in the figure) gripped by the chuck is vertically fed to a position where the front cutting edge exceeds the center of the end face, thereby preventing the generation of the center boss.

For the same reason, when a pipe (pipe) -shaped part is cut off, the center of the pipe (inner diameter side) is attached to the inner diameter end of the end face of the cut off and cut off work.
Burrs (hereinafter, also referred to as inner diameter burrs) protrude toward the surface. Therefore, in this case as well, parts that require high processing accuracy on the end face must be similarly separately cut in a subsequent step.

Further, in the above-mentioned conventional chip, since the convex portion for deforming the chip cross section is provided at a position slightly away from the cutting edge, the deformation effect differs depending on the cutting feed speed and the cutting feed speed is also different. When is small, the deformation effect may not be expected in some cases. For example, when the cutting feed rate is as low as 0.05 mm / rev or less, the chips are thin and cannot be pressed against the convex portions (do not collide),
In some cases, the deformation is very small or no deformation effect can be expected, and even if a collision occurs, the chip may only act as a breaker due to a decrease in chip temperature. Therefore, the chips to be discharged have a flat cross section and low rigidity, the winding is rough even in a spiral shape, or there is a strong tendency to be continuously discharged for a long time, and the discharge direction tends to be unstable, There is a problem that the work is easily entangled.

On the other hand, for example, the cutting feed rate is 0.1 mm /
With rev, the chip section can be deformed somehow, but the deformation effect is not sufficient. For this reason, there is a problem similar to that described above. Further, for example, when the cutting feed rate is as large as 0.2 mm / rev or more, the chips are thick, the pressing force on the convex portions is increased, and the deformation effect is large. Therefore, stable chip processing can be obtained,
On the other hand, the pressing force increases the cutting resistance, that is, the resistance given to the cutting edge, and the cutting life of the chip is shortened due to the generation of excessive cutting heat. That is, in the above-mentioned conventional chip, there is a problem that the region of the speed at which the chip deformation effect can be exhibited stably is narrow, and the life is shortened when stable chip processing is obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional cut-away insert for cutting off, and has a small cutting resistance and a stable chip deformation effect. Its purpose is to provide chips.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention according to claim 1 is a throw-away insert used for parting off or grooving, wherein a cutting edge of a front cutting edge is provided. In addition, an arc-shaped recess is provided so as to lower the rake face, and a spherical recess connected to the arc-shaped recess is provided on the rake face. The present invention according to claim 2 is a throwaway tip used for parting or grooving, wherein a spherical concave portion is provided on a rake face, and the spherical concave portion is provided on a cutting edge ridge of a front cutting edge. It is characterized by forming an arcuate concave portion. In the present specification, the spherical concave portion refers to a concave portion formed of a spherical surface or a substantially spherical surface, and the substantially spherical surface includes a curved surface having a dome shape such as a curved surface (peripheral surface) of a substantially spheroid and a curved surface of an oval body. Further, the arc-shaped concave portion refers to a concave portion having an arc shape or a substantially arc shape.

In the above-mentioned means, for example, when a round bar is cut off, the chips are deformed by being squeezed into a shape having a downwardly convex cross-sectional shape following the arc-shaped concave portion of the front cutting edge. Is discharged backward from the front cutting edge along the spherical concave portion. That is, the chips become highly rigid due to the squeezing deformation in the width direction, and are discharged to the rear, which is the direction opposite to the cut-off (longitudinal) feed direction (the direction away from the front cutting edge). The deformation is given not by being pressed against the projection provided on the rake face behind the front cutting edge, but by the arcuate concave shape of the front cutting edge itself and the spherical concave portion of the rake face connected thereto. . Therefore, since the cutting resistance is small and the chips are deformed regardless of the vertical feed speed of the chip, the deformation effect can be obtained stably.

Further, since there is no convex portion which deforms the chips, the cutting resistance is small, so that the center boss and the inner diameter burr generated on the end face of the work cut off at the time of parting can be reduced. In addition, as the cutting resistance is reduced, the wear of the cutting edge is reduced, so that the life of the parting-off or grooving is expected to be prolonged.

In the above means, the arc-shaped concave portion is substantially at the center of the cutting edge ridge of the front cutting edge, but the chip discharging direction is stabilized rearward. Is preferred. Further, in each of the means, the maximum depth of the arc-shaped concave portion is set to Da.
In this case, it is preferable that Da be in the range of 0.05 to 0.25 mm. If the maximum depth of the arc-shaped recess is less than 0.05 mm, the chip deformation effect is small,
If the maximum depth of the arc-shaped concave portion exceeds 0.25 mm, the chip deformation effect is large, but the tool life is shortened. Furthermore, assuming that the maximum depth of the arc-shaped concave portion is Da, the value of Da is 0.05 to 0.05.
More preferably, it is in the range of 0.2 mm.
This is because by setting Da to 0.2 mm or less, it is possible to more stably discharge chips.

In each of the above means, when the width of the front cutting edge is W and the width of the arc-shaped concave portion of the front cutting edge is Wa, W and Wa are as follows. W
It is preferable to satisfy the dimensional relationship of / 2 ≦ Wa ≦ 2W / 3. If Wa is smaller than W / 2, the deformation effect is small, and if Wa is larger than 2W / 3, the strength at both ends of the cutting edge is reduced. Furthermore, in each of the means, assuming that the maximum depth of the arc-shaped concave portion is Da and the maximum depth of the spherical concave portion is Db, Da and Db satisfy Da <D. It is preferable to have a dimensional relationship of Db. With such a configuration, cutting resistance can be further reduced, and generation of burrs can be more effectively suppressed. In addition, in each of the means, when the width of the arc-shaped concave portion of the front cutting edge is Wa and the maximum width of the spherical concave portion is Wb, Wa and Wb are defined as Wa and Wb. It is preferable to have a dimensional relationship of <Wb. By adopting such a configuration, the cutting resistance can be further reduced, and the chip discharge performance can be further stabilized. Any of the throw-away tips of the present invention is used by being fixed (clamped) to a holder. According to a ninth aspect of the present invention, there is provided a cutting tool comprising the indexable insert according to any one of the first to eighth aspects and a holder.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a perspective view of a throw-away tip according to a first embodiment of the present invention and an enlarged view of a main part thereof, FIG. 2 is a plan view of a main part of FIG. 1 (view from the rake face side), and FIG. FIG. 4 is an enlarged view of a main part of the throw-away tip of FIG. 1 as viewed from the front flank side, FIG. 4 is a sectional view taken along line AA of FIG. 2, and FIG. The indexable insert 1 of the present embodiment is made of a sintered body such as cemented carbide, cermet, or ceramic, and has a parallelogram block shape in a side view. Since it is a two-corner type having 15 corners, only one corner will be described.
In the present embodiment, the triangular portion 13 including the acute angle portion 12 is made thin, and the remaining thick base portion 14 is provided at the center of the clamp hole 1.
It is configured to be fixed to a holder (not shown) via 4a.

In this embodiment, the front cutting edge 15 forming one corner is formed by a rake face 16 and a front flank face 17, and the rake face 16 is viewed from above (in plan view). It extends linearly with two receding angles from each end toward the rear, and is formed so as to become narrower toward the rear. The rake face 16 is inclined downward at a positive angle of 6 degrees from the cutting edge ridge 15a of the front cutting edge 15,
A breaker wall 18 having an arc surface is provided at the rear. The front flank 17 is provided with a bevel before 6 degrees, and the side flank 19 is provided with a side bevel of 3 degrees. In addition,
The front cutting edge 15 has a lead angle θ of 5 degrees in a plan view.

The rake face 16 has a spherical recess 2.
6, and the spherical concave portion 26 is formed so as to cut downward in the center of the cutting edge ridge (the intersection ridge line between the rake face 16 and the front flank face 17) 15a of the linear front cutting edge 15. Are formed. In the present embodiment, the spherical concave portion 26 is a spheroid having a major axis at the center in the width direction of the rake face 16 rearward from the arcuate concave portion 25 of the front cutting edge 15 when viewed from the rake face 16 side. It has a curved surface. And this spherical concave portion 2
The rear end portion 6 has a shape cut from the breaker wall 18 to the clamping pressing surface 29 of the chip 1.

In this embodiment, the width W of the front cutting edge 15 is
Is, for example, about 1.8 mm, and the arc-shaped recess 25 formed therein has a width Wa of about 0.9 mm, and when viewed from the front flank 17 side, the arc-shaped recess 25 in the front cutting edge 15. Has a radius R of 1.5 mm. Also, the maximum width Wb of the spherical concave portion 26 parallel to the front cutting edge 15
Is 1.2 mm, which is set to be larger than the width Wa of the arc-shaped concave portion 25. As a result, the cutting resistance can be further reduced, and the chip discharge performance can be further stabilized. In this embodiment, the arc-shaped concave portion 25 is used.
Has a maximum depth Da of 0.15 mm. However,
Maximum depth Db at the rake face 16 of the spherical concave portion 26
Is about 0.25 mm, and is configured to be deeper behind the arcuate concave portion 25 of the front cutting edge 15. By setting Da <Db, the cutting resistance can be further reduced, and the occurrence of burrs can be suppressed more effectively. The arc-shaped concave portion 25 and the spherical concave portion 26 of the front cutting edge 15 may be formed integrally in the process of molding the sintered body of the throw-away tip 1, but the arc-shaped concave portion 25 and the spherical concave portion After sintering and forming as a throw-away tip without 26, it can also be formed by grinding (polishing) with a diamond grindstone having an outer peripheral surface shape corresponding to the arc-shaped concave portion 25 and the spherical concave portion 26.

When the shaft part is cut off by the indexable insert 1 of the present embodiment configured as described above, the following is performed. That is, the indexable insert 1 is fixed (clamped) to a holder (not shown) to form a cutting tool, and is used for machining. In the parting-off process, the chips are squeezed and deformed into an arc shape having a downwardly convex cross-sectional shape following the front cutting edge 15, and the inside of the spherical concave portion 26 of the rake face 16 is deformed from the front cutting edge 15. It flows backward and is discharged. In other words, the chips become highly rigid due to the narrowing deformation in the width direction and are discharged backward,
The deformation is not caused by being pressed against the convex portion provided on the rake face behind the front cutting edge as in the related art, but the arc shape of the arc-shaped concave portion 25 of the front cutting edge 15 itself and the rake connected thereto. Deformation is provided by the spherical recess 26 in the surface 16.

Therefore, the cutting resistance is small and the chips are deformed irrespective of the vertical feed speed of the chip, so that a stable chip deformation effect can be obtained. That is, the chip is deformed in the maximum temperature range of the chip by the front cutting edge 15, so that the resistance at the time of deformation can be reduced. In addition, since there is no convex part that deforms the chips, the cutting resistance is small, so the center boss generated on the end face of the work can be reduced when cutting off the shaft member, and when cutting through the pipe member, the inner diameter burrs are reduced. Can be smaller.

Next, in the throwaway tip 1 of the above-described embodiment, the spherical radius of the spherical concave portion 26 is the same, and the maximum depth Da of the arc-shaped concave portion 25 in the front cutting edge 15 is 0 to 0.
Samples having different dimensions in the range of 0.30 mm were prepared, the shaft parts were cut off, and the diameter of the center boss and the protrusion amount (height) on the cut surface of the cut-off work were compared. However, the radius of the arc-shaped concave portion 25 as viewed from the front flank 17 side of the arc is constant at about 1.5 mm, and the width W of the front cutting edge 15 of the tip 1 is 1.8 mm. The cutting conditions were as follows: spindle speed = 2000 rpm, f (feed) = 0.03 mm / rev, dry cutting. Work material is S
US303, its outer diameter is 12mm. The results are as shown in Table 1. However, the numerical values in the table are average values obtained by cutting off 10 times (the same applies hereinafter). The indexable insert (sample No. 1) of the comparative example (comparative example) had a straight front cutting edge and no arc-shaped concave portion and spherical concave portion, and was located near the front cutting edge on the rake face. The projections are provided at the portions near both ends.

[0023]

[Table 1]

As shown in Table 1, in the case of the parting-off with the product of the present invention, the diameter of the center boss and the projecting amount were almost small as compared with the comparative example (sample No. 1). This means that the cutting (cut off) proceeded to a position closer to the center of the end face in the case of the example product as compared with the case of the comparative example, which demonstrates that the cutting resistance is small. It is. Also, it can be seen that if the maximum depth of the arc-shaped concave portion is 0.05 mm, the chip deformation action is good. In the case of the comparative example, the tool life was long and good, but on the other hand, no chip deformation effect was observed. This is probably because the feed speed is low. Further, regarding the tool life, the maximum depth of the arc-shaped concave portion of the front cutting edge was reduced at 0.3 mm.
For this reason, it is appropriate to form a spherical concave portion on the rake surface such that the maximum depth of the arc-shaped concave portion of the front cutting edge is in the range of 0.05 to 0.25 mm. Further, by setting the maximum depth of the arc-shaped concave portion to 0.2 mm or less, it becomes possible to more stably discharge the chips. This is considered to be due to the fact that when the maximum depth of the arc-shaped concave portion exceeds 0.2 mm, the resistance to chip deformation increases. Therefore, it is more preferable that the maximum depth of the arc-shaped concave portion of the front cutting edge be in the range of 0.05 to 0.2 mm.

Next, the sample No. A cut-off test was performed by changing only the point that the work was a tube member having an outer diameter of 12 mm and an inner diameter of 8 mm with the chips of 1 to 3, and the thickness and the protrusion amount of the inner diameter burr on the cut surface of the cut-off work were similarly compared. I tried to. The results are as shown in Table 2.

[0026]

[Table 2]

As shown in Table 2, the thickness of the inner diameter burr and the protrusion amount were smaller in the case of the example product than in the comparative example. This is considered to be because the cutting resistance is smaller in the case of the example product than in the case of the comparative example.

Next, the maximum depth Da of the arcuate recess at the front cutting edge is made constant (0.15 mm), and the width Wa of the arcuate recess is 0.3 to 1.5 mm. A sample with a varied arc radius was prepared, and a cut-off test of the shaft member was performed to confirm the chip deformation action and tool life (strength at both ends of the cutting edge). However, the width W of the front cutting edge is constant at 1.8 mm. The results are as shown in Table 3.

[0029]

[Table 3]

As shown in Table 3, the sample No. When the width Wa of the arc-shaped concave portion is smaller than W / 2 as in the cases of 1 and 2, the groove width of the front cutting edge is reduced, so that the deformation effect of the chips is reduced. Sample No. Wa is 2W / like 5
If it is larger than 3, the deformation effect of the chips was good,
The life of the cutting edge has been shortened. Thus, the relationship between the width W of the front cutting edge 15 and the width Wa of the arc-shaped recess 25 is W / 2 ≦ Wa.
It is understood that it is appropriate to set ≦ 2W / 3.

Second Embodiment Next, a second embodiment will be described with reference to FIGS. However, this chip 21 has an arc-shaped concave portion 25 of the front cutting edge 15 and a spherical concave portion 26 provided on the rake face 16 and forming the arc-shaped concave portion 25 as a true spherical shape.
The only difference from the above-described embodiment is that the front side of the breaker wall 18 on the rake face, that is, the rear end of the spherical concave portion 26 exists on the rake face.
That is, since the present embodiment is different from the above-described embodiment only in that the spherical concave portion 26 is not cut into the clamping pressing surface 29 of the chip 1, the same portions are given the same reference numerals, and detailed description will be given. Is omitted. Note that the chip 2 of the present embodiment example
Chips generated when cutting off at 1 are not shown,
Since the distance from the arc-shaped concave portion 25 of the front cutting edge 15 to the rear end of the spherical concave portion 26 is small, chips are less likely to flow backward.
Suitable for processing when the cutting amount is small,
The cross-sectional shape of the generated chips is deformed into a shape following the arc-shaped concave portion 25 of the front cutting edge 15 and discharged in the same manner as in the above embodiment.

Third Embodiment Next, a third embodiment will be described with reference to FIGS. However, according to the first embodiment, the maximum depth Da of the arc-shaped concave portion 25 of the front cutting edge 15 is larger than that of the first embodiment.
Although the maximum depth Db of the spherical concave portion 26 is made deeper, only the following point is different. That is, in the chip 31 of the third embodiment, the depth to the bottom surface of the spherical concave portion 26 provided on the rake face 16 gradually becomes shallower than the depth of the circular concave portion 25 from the circular concave portion 25 toward the rear. The only difference is in the way they are made. Therefore, the same portions are denoted by the same reference numerals.

The throw-away tip according to the present invention is not limited to the above-described embodiments, and the design can be changed as appropriate without departing from the gist thereof. For example, in the third embodiment, the spherical concave portion 26 is used.
The rear end portion is provided so as to cut into the breaker wall 18. However, as in the third embodiment, the depth to the bottom surface of the spherical concave portion 26 provided on the rake face 16 gradually becomes shallower than the depth of the circular concave portion 25 toward the rear from the circular concave portion 25. 11 and FIG.
Like the tip 41 shown in FIG. 2, the rear end of the spherical concave portion 26 may be rounded up on the rake face 16. The spherical recess according to the invention can be embodied with or without a breaker wall behind the rake face. The spherical concave portion may be designed into a concave dome shape, such as a curved surface of a spheroid or a part of a spherical surface, according to the size of the rake face (such as the width of a cutting edge) and cutting conditions.

In the above-described embodiment, the parallelogram (diamond) type throwaway insert of the two corners (having two cutting edges) has been described. The present invention can be applied to various types of throwaway tips used for cutting off, such as a three-corner throwaway tip having three cutting edges. Further, the indexable insert of the present invention can be used for grooving.

[0035]

As is apparent from the above description, when the parting-off process is performed by the indexable insert of the present invention, the chips become concave due to the drawing deformation in the width direction, become high in rigidity, and become rearward. Discharged, but the deformation is given by the arcuate recess shape of the front cutting edge itself and the spherical recess behind. Therefore, the deformation is not due to the fact that it is pressed against the convex portion provided on the rake face behind the front cutting edge as in the past, so the cutting resistance is small, and it is deformed into chips regardless of the vertical feed speed of the chip , The deformation effect is stably obtained.
In addition, since a stable curl shape is obtained for the chip, the chip discharge property is good, and the processing surface is effectively prevented from being scratched, so that the processing surface roughness is improved.

Further, since there is no convex portion which deforms the chips, the cutting resistance is small, so that the center boss and the inner diameter burr generated on the end face of the work cut off at the time of cut-off can be reduced. In addition, since the cutting resistance is small, the wear of the cutting edge is reduced, so that the life of the cutting off or grooving is expected to be prolonged.

[Brief description of the drawings]

FIG. 1 is a perspective view of a throw-away tip according to a first embodiment of the present invention and an enlarged view of a main part thereof.

FIG. 2 is a plan view of a main part of FIG. 1 (view from the rake face side).

FIG. 3 is an enlarged view of a main part of the throw away tip of FIG. 1 as viewed from a front flank side.

FIG. 4 is a sectional view taken along line aa of FIG. 2 (a sectional view of a spherical concave portion).

FIG. 5 is an enlarged side view of a main part of the throw-away tip of FIG. 1;

FIG. 6 is an essential part perspective view of a throw-away tip according to a second embodiment of the present invention.

FIG. 7 is a view of the chip of FIG. 6 as viewed from the front flank side.

FIG. 8 is an enlarged side view of a main part of the chip of FIG. 6;

FIG. 9 is a perspective view of a main part of a throw-away tip according to a third embodiment of the present invention.

FIG. 10 is an enlarged side view of a main part of the chip of FIG. 9;

FIG. 11 is a perspective view of a main part of a throw-away tip according to another embodiment of the present invention.

FIG. 12 is an enlarged side view of a main part of the chip of FIG. 11;

FIG. 13 is an enlarged plan view of a main part of a conventional indexable insert for cut-off.

[Explanation of symbols]

 1, 21, 31, 41 throw-away insert 15 front cutting edge 15a cutting edge ridge 16 rake face 25 arc-shaped recess 26 spherical recess Da maximum depth of arc-shaped recess Db maximum depth of spherical recess W W front cutting edge Width Wa Width of arc-shaped recess

Claims (9)

[Claims] 1. A throw-away insert used for parting or grooving, wherein an arc-shaped concave portion is provided on a cutting edge of a front cutting edge so as to lower a rake surface, and the arc-shaped concave portion is provided on the rake surface. A throw-away tip characterized by providing a spherical concave portion connected to the concave portion. 2. A throw-away insert used for parting or grooving, wherein a spherical concave portion is provided on a rake face, and the spherical concave portion forms an arc-shaped concave portion on a cutting edge ridge of a front cutting edge. A throwaway tip characterized by becoming. 3. The indexable insert according to claim 1, wherein the arc-shaped concave portion is located substantially at the center of the cutting edge of the front cutting edge. 4. The indexable insert according to claim 1, wherein Da is in a range of 0.05 to 0.25 mm, where Da is a maximum depth of the arc-shaped concave portion. 5. The indexable insert according to claim 1, wherein Da is in a range of 0.05 to 0.2 mm, where Da is a maximum depth of the arc-shaped concave portion. 6. When the width of the front cutting edge is W and the width of the arc-shaped concave portion of the front cutting edge is Wa, W and Wa are W
The throw-away tip according to any one of claims 1 to 5, wherein a dimensional relationship of / 2≤Wa≤2W / 3 is satisfied. 7. The dimensional relationship according to claim 1, wherein Da and Db have a dimensional relationship of Da <Db, where Da is a maximum depth of said arcuate concave portion and Db is a maximum depth of said spherical concave portion. A throwaway tip according to any of the above. 8. The width of the arcuate recess of the front cutting edge is Wa,
When the maximum width of the spherical concave portion is Wb, Wa and Wb
Are in a dimensional relation of Wa <Wb. 9. A cutting tool comprising the indexable insert according to claim 1 and a holder.