JP2000288803A - Indexable tip - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent the finished surface roughness from becoming rougher than the ideal surface roughness due to an error in the connection point position between the arc-shaped cutting edge and the straight cutting edge, and to improve the surface roughness. . SOLUTION: A negative type rhombus tip 1 having an apex angle of 80 degrees draws a bisector S1 of an apex angle θ1 on a rake face, and bisects a straight line S1 from a center of curvature の of an arc-shaped cutting edge ridge 4a.
Then, a curved concave portion 8 is provided in the cutting edge ridge 4 so that the vicinity of the point P2 where the straight line S2 intersects with the cutting edge ridge 4 is the lowest in the thickness direction. The flat shape of the chip 1 is the same as the conventional one, but when mounted on the holder, the cutting edge ridge 4 corresponding to the curved concave portion 8 is inclined in the clearance angle of the chip seat so that the chip corresponds to the same inclination in plan view. Pull down inside. Accordingly, the radius of curvature of the cutting edge 4 is substantially larger than that of the conventional insert, and the finished surface roughness is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a throw-away insert, and more particularly, to a polygonal plate-like throw-away insert (hereinafter, simply referred to as a chip) used for turning.

[0002]

2. Description of the Related Art The nose of a polygonal plate-shaped throw-away tip conforming to IS @ and JIS standards is designed to be a truly circular arc. The finished surface roughness (surface roughness) H when the outer peripheral surface is turned with such a chip is represented by a well-known formula H = f ² / 8R. Where f is the feed per rotation mm / r
ev and R are nose radii. As is apparent from this equation, theoretically, only the feed amount f and the nose radius R affect the finished surface roughness. Therefore, the nose has a perfect circular arc ISО
When turning a cylinder with different diameters using a standard insertable insert, etc., if the design value radius (R) of the corner of the boundary (end face) between the small diameter portion and the large diameter portion is 1 mm, is this the same? For example, a chip having a nose radius of 0.8 mm or less is used, and cutting conditions for obtaining a desired finished surface roughness are selected.

In such machining, when the surface roughness (design value) of a work is given, the feed amount f
Is determined. On the other hand, if the design surface roughness (accuracy) required for the work is high, the feed amount f must be reduced, and the processing efficiency decreases. Further, since the chips become thinner as the feed amount becomes smaller, there is a problem in the chip processing properties such that the cutting processing of the chips is not performed smoothly. Moreover, the connection point (joint) between the arc-shaped cutting edge ridge of the nose and the straight cutting edge ridge on the side is designed at a straight line drawn from the center of curvature of the arc of the arc-shaped cutting edge due to the chip manufacturing accuracy. Usually 5 to
There is an error of about 15 degrees.

For this reason, as shown in FIG.
Is a diamond-shaped tip 1 having an angle of 80 degrees, and is located at a connection point P1 between the arc-shaped cutting edge 4a of the nose 2 and the straight cutting edge 4b of the side 7 (hereinafter also simply referred to as a connection point) P1. If the straight line drawn from the center of curvature О of the circular arc has an error of, for example, 5 degrees with respect to the design position, the following is performed. That is, in this case, a bisector S1 with respect to the apex angle θ1 is drawn on the rake face 3, and 50 arcs from the center of curvature О of the arc of the arcuate cutting edge 4a of the nose 2 with respect to the bisector S1. Where there should be a connection point between the arc-shaped cutting edge ridge 4a and the straight cutting edge ridge 4b at a position intersecting the straight line drawn in degrees, the connection point P1 is actually at a position intersecting the straight line S2 drawn at 45 degrees. Exists. Therefore, the connection point between the arc-shaped cutting edge ridge 4a and the straight cutting edge ridge 4b is not tangential but forms a gentle angle.

On the other hand, most of the holders 11 on which the diamond-shaped tips 1 are clamped are mounted on the tool rest so that the straight cutting edge ridge 4b and the rotation axis of the work make 5 degrees. Therefore, due to the above error, of the cutting edge ridge,
Connection point P between arc-shaped cutting edge ridge 4a and straight cutting edge ridge 4b
In this case, cutting is performed so that the portion including No. 1 hits the workpiece, and the actual finished surface becomes rougher than the ideal surface roughness.

As a countermeasure, it is conceivable to make the vicinity of the connecting point P1 between the arc-shaped cutting edge ridge 4a of the nose 2 and the linear cutting edge ridge 4b of the side 7 straight so as to be parallel to the rotation axis of the work. Can be This is because, in this case, the surface roughness becomes zero theoretically. However, there is actually an error (tilt) that occurs when the chip is mounted on the holder. Even if such a linear cutting edge (hereinafter also referred to as a flat cutting edge), it must be parallel to the rotation axis. There is no.
Therefore, in this case, the surface roughness actually becomes unstable. In addition, since the flat cutting edge has a longer contact length with the work, the back force is increased, so that chatter is likely to occur and the finished surface accuracy becomes unstable.

Therefore, instead of such a flat cutting edge, an arc-shaped cutting edge ridge 4a of the nose 2 and a straight cutting edge ridge 4
It is conceivable that the vicinity of the connection point P1 of b is intentionally set as a convex R having a large radius when viewed from the rake face 3 side. By doing so, the surface roughness is improved, and the instability and the above-mentioned disadvantages when a flat cutting edge is used can be reduced.

[0008]

However, if a convex radius R having a large radius is intentionally used, the outer peripheral (contour) shape is different from that of the ISО standard product. For this reason, in order to manufacture indexable inserts made of cemented carbide or ceramics, it is necessary to use a press die, an outer peripheral grinding (polishing) machine, or an outer peripheral grinding program that is different in shape from standard chips. Therefore, a chip manufacturer having a facility for manufacturing a standard product increases the manufacturing cost.

Further, when such a shape is formed, the connecting point P1 between the arc-shaped cutting edge ridge 4a of the nose 2 and the straight cutting edge ridge 4b is formed.
The position is farther from the center 2a of the tip of the nose than the original cutting edge ridge (edge) position. For this reason, when the end of cutting becomes a boundary (end face) with the large diameter part in the cylindrical processing of the small diameter part of the different diameter shaft, the corner R of the end of cutting is larger than the turning by the standard insert. Problem. Such a dimensional defect causes a defective fitting when another component is fitted to the small diameter portion and brought into contact with the end face of the cut end portion.

According to the present invention, in the manufacture of a chip, an error occurs at the connection point between the arc-shaped cutting edge of the nose and the straight cutting edge of the side, so that the finished surface roughness H is basically an ideal surface. It is an object of the present invention to provide a polygonal plate-shaped indexable insert capable of improving the finished surface roughness based on the fact that the surface becomes coarser than the roughness and without causing the various problems described above.

[0011]

According to a first aspect of the present invention, in a polygonal plate-like indexable insert, an arc-shaped cutting edge of a nose and a side of the cutting edge are provided. A curved concave portion is formed in the cutting edge ridge such that the vicinity of the connection point of the portion with the straight cutting edge ridge is the lowest (lowest point) in the thickness direction.

According to a second aspect of the present invention, in the polygonal plate-shaped indexable insert, a connecting point between the arc-shaped cutting edge ridge of the nose and the straight cutting edge ridge of the side among the cutting edges. A curved concave portion is formed in the cutting edge ridge so that the center between the arc-shaped cutting edge ridge and the center of the cutting edge is the lowest in the thickness direction. In this case, the lowest position is when the insert is clamped (mounted) on the holder and used for turning.
It is preferable to set so as to be near a point where a straight line parallel to the rotation axis of the work comes into contact or near a point where a straight line perpendicular to the rotation axis comes into contact.

According to the above-mentioned means, since the curved concave portion has a substantially arc shape when viewed from the flank surface side, the cutting edge ridge of the portion corresponding to the curved concave portion when viewed from the rake surface side in the case of the positive type tip has such a shape. It retreats to the inside of the chip (inside the rake face) as compared with a conventional chip having no curved concave portion. Accordingly, the projected radius of curvature (apparent radius of curvature) of the cutting edge ridge at a portion corresponding to the curved concave portion in plan view (apparent radius of curvature) is substantially larger than the designed value of the standard product because the cutting edge ridge is thus retreated. growing. However, when such a chip is mounted on a holder so as to be turned at a portion of a cutting edge ridge having a large apparent radius of curvature R and used for turning, the finished surface roughness is expressed by the formula H = Since R at f ² / 8R means that R becomes larger than that of the conventional chip having no curved concave portion, the finished surface roughness (H) is improved. In a positive tip, the larger the positive angle is, the larger the apparent radius of curvature R is, and the greater the effect is.

On the other hand, in the case of a negative type chip, the chip is inclined and clamped on the chip seat of the holder so that a clearance angle exists in the flank. Therefore, when viewed from a direction along a vertical line (vertical line) with respect to the holder reference plane (upper and lower surfaces), the cutting edge ridge corresponding to the curved concave portion has such a clearance angle (slope) because of the clearance angle (inclination). Retreat inside the chip compared to the case without. Therefore, the projected radius of curvature of the cutting edge ridge in plan view is substantially larger than the design value of the standard product, and the finished surface roughness (H) can be similarly improved with this product.

In addition, in the insert having such a shape, since the cutting edge to be subjected to turning is not a flat cutting edge but R,
There is no such disadvantage as in the case of a flat cutting edge. Further, since there is no need to make the outer peripheral shape different from the ISО standard product, the cost does not increase.
That is, according to the insert according to the present invention, it is possible to improve the finished surface roughness in turning as compared with the conventional standard product chip, and conversely, if the finished surface roughness is equivalent to that of the standard product, Since the feed (f) can be increased, the processing time can be reduced. In addition, when the feed is increased in this way, the chip thickness can be increased accordingly,
Chips are easily separated, and scratches on the finished surface can be reduced.

Although the present invention can be embodied in various polygonal plate-shaped throw-away tips, in the case of a polygonal plate-shaped throw-away tip having an apex angle of approximately 80 degrees or 75 degrees, the above-mentioned top surface is formed on the rake face. Draw a bisector to the corner,
A straight line is drawn at 45 degrees to the bisector from the center of curvature of the arc of the nose arc-shaped cutting edge, so that the vicinity of the point where the straight line intersects the cutting edge is the lowest in the thickness direction. It is preferable to form a curved concave portion on the cutting edge. Polygonal plate-like indexable inserts having such apical angles represented by diamond-shaped inserts are drawn at 45 degrees with respect to the above bisector because of the holder structure (standard) on which they are clamped. This is because the vicinity of the point where the straight line intersects the cutting edge ridge is used for turning in a form in contact with a straight line parallel to the rotation axis of the work or a straight line perpendicular thereto.

On the other hand, in the case of a throw-away insert having a triangular plate shape having an apex angle of approximately 60 degrees, a bisector is drawn on the rake face with respect to the apex angle, and the arc is cut from the center of curvature of the arc of the nose arc-shaped cutting edge. A straight line may be drawn at 30 degrees with respect to the bisector, and a curved concave portion may be formed in the cutting edge so that the vicinity of the point where the straight line intersects the cutting edge is the lowest in the thickness direction. In such a chip, the straight cutting edge is often mounted on the holder in such a manner as to be inclined at, for example, 30 degrees with respect to the rotation axis of the work. The reason is that a straight line drawn at 30 degrees from the center of curvature of the arc of the arc-shaped cutting edge of the nose with respect to the bisector is cut centering on a point intersecting the cutting edge.

In the present invention, it is preferable to form curved concave portions on both sides of the apex angle of the cutting edge ridge of each nose, but it is also possible to form only one side. However, it is preferable that the cutting edge ridge forms a waveform curve continuously from the curved concave portion when viewed from the flank side. If you do this,
This is because, since the cutting edge ridge is corrugated, in addition to the above-described effect of improving the finished surface roughness, the chip cross section can be curved, and the chip disposability can be enhanced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a throw-away tip according to the present invention will be described in detail with reference to FIGS. In the drawing, reference numeral 1 denotes a diamond-shaped negative chip (IS チ ッ プ standard: CNMG120408) having a plate-like shape with a constant thickness, which is formed using a cemented carbide or cermet as a material. The apex angle θ1 of the nose 2 of the tip 1 of this embodiment is 8
At 0 degree, the nose radius R is, for example, 0.8 mm. A chip breaker groove 5 is formed on the rake face 3 along the cutting edge ridge 4 including the arc-shaped cutting edge ridge 4a and the linear cutting edge ridge 4b. In addition, both rake faces 3 are relatively protruded from the chip breaker groove 5 at a position closer to the center (FIG. 3).
), And a mounting hole 6 for clamping is provided at the center.

As shown in FIGS. 2 to 4, in the arc-shaped cutting edge ridge 4 a of the nose 2, in the thickness direction of the chip 1 at a position near the connecting point P 1 with the linear cutting edge ridge 4 b of the side 7. A curved recess 8 is formed in the cutting edge ridge 4 so as to be at the lowest position. The curved concave portion 8 straddles the arc-shaped cutting edge ridge 4a and the straight cutting edge ridge 4b. As shown in FIG. 2, when viewed from the flank 9 side, the chip breaker groove 5 on the rake face 3 side is formed. It has a concave arc shape, and its arc radius R
V is 0.8 mm, and the depth D of the arc is 0.2 mm. In this embodiment, however, as shown in FIG. 1, a bisector S1 is drawn on the rake face 3 with respect to the apex angle θ1, and the center of curvature О of the arc of the arc-shaped cutting edge 4a of the nose 2 is drawn. The cutting edge ridge is curved so that a point P2 at which the straight line S2 drawn at 45 degrees with respect to the equal line S1 intersects the cutting edge ridge is the lowest. The same applies to the other nose 2.

Then, as shown in FIGS. 1 and 5, this chip 1 is placed on a predetermined holder 11 by a straight cutting edge 4a.
b and a straight line S3 parallel to the rotation axis of the work (not shown) are 5
When a cylinder is machined by clamping so as to have a side clearance angle and a front clearance angle of, for example, 6 degrees, it is as follows. That is, the tip 1 has the same planar shape as the conventional tip, but because of the inclination when the tip 1 is mounted on the tip seat of the holder 11, the curved concave portion 8 of the arc-shaped cutting edge 4 a of the nose 2, In the plan view (when viewed along a straight line perpendicular to the reference plane 12 of the holder 11) in a plan view (corresponds to the clearance angle) (downwardly) corresponding to the clearance angle. Becomes

Therefore, for example, when the connection point P1 of the arc-shaped cutting edge 4a and the straight cutting edge 4b of the side 7 has an error of 5 degrees, it is actually located at the point P2 in FIG. Is as follows. In this case, when the curved concave portion 8 is not provided, the cutting is performed such that the connection point P2 between the arc-shaped cutting edge ridge 4a and the straight cutting edge ridge 4b becomes a contact point, so that the finished surface is rougher than the ideal surface roughness. On the other hand, in this embodiment, since the cutting edge ridge 4 is provided with the curved concave portion 8, the cutting edge ridge 4 is located at a position retracted on a plane projection from the cutting edge ridge in the conventional chip. Therefore, it is processed with a substantially large radius.

That is, when turning is performed at the cutting edge 4 having such a nose 2, the surface roughness is expressed by the formula H = f ² /
Since R is large in 8R, when the feed amount f is constant, H becomes small, so that the finished surface roughness is improved. Conversely, if the same surface roughness H is sufficient, the feed rate can be increased and the machining efficiency can be increased, and if the feed rate is increased in this way, the chip thickness can be increased by that amount, and the chips can be easily separated, Scratch on the finished surface can also be reduced.
As shown in FIG. 4, the cutting edge 4 is formed so as to form a waveform curve continuously from the curved concave portion 8 when viewed from the flank 9 side, and the chip breaker groove is also formed so as to form a waveform curve. You may. With this configuration, the chip cross section also becomes corrugated, so that the rigidity of the chip is increased, and the chip is easily divided, so that the chip disposability can be further improved.

Moreover, the chip 1 of the present embodiment does not have a flat cutting edge at the connection point, and therefore does not have a drawback such as an unstable surface roughness. Further, since it is not necessary to make the outer peripheral shape different from that of the ISО standard product, and it is possible to form the same standard product by grinding the curved concave portion 8, the cost is slightly increased. Although not shown, if the embodiment is embodied as a configuration in which a land is provided along the cutting edge ridge, the cutting edge ridge (edge) accuracy is improved, and the processing accuracy is further improved.

FIGS. 6 to 9 show a chip (CNMT09T308) 21 according to another embodiment of the present invention.
Except for the positive type, there is no essential difference from the rhombic plate-shaped chip of the above-mentioned form, so that the same portions are given the same reference numerals and only the differences will be described. That is, in this example, the center of the arc-shaped cutting edge 4a is located closer to the connecting point P1 between the arc-shaped cutting edge 4a and the straight cutting edge 4b in the cutting edge of the conventional tip shown by the broken line in FIGS. Since the curved concave portion 8 is provided so that the portion closer to 2a is at the lowest position, the cutting edge ridge 4 corresponding to the curved concave portion 8 is located at a position retracted from the cutting edge ridge of the conventional chip in plan view (FIG. 6). (See enlarged view in FIG. 7 and FIG. 7). Therefore, even when the holder is horizontally mounted on the reference surface of the holder, the radius of the arc-shaped cutting edge ridge 4a becomes substantially large, and the same effect as in the above embodiment can be obtained.

Another embodiment of the indexable insert 31 according to the present invention will be described in detail with reference to FIGS. However, this is a triangular negative type chip (TNMG160412) 31 having an apex angle θ1 of 6
The only difference from the negative type diamond-shaped chip 1 is that it is embodied as 0 degrees, so only the differences will be described. That is, this is a triangular plate-shaped throw-away tip, which has an arc-shaped cutting edge ridge 4a and a side portion 7 of a nose.
The curved concave portion 8 is formed so that the distance between the connection point P1 of the straight cutting edge 4b and the center 2a of the arc-shaped cutting edge 4a is the lowest in the thickness direction. However, the curved recess 8
Is as follows. That is, a bisector S1 with respect to the apex angle θ1 is drawn on the rake face 3, and the bisector S1 is drawn from the center of curvature О of the arc of the arc-shaped cutting edge 4a of the nose 2.
The curved concave portion 8 is formed such that the straight line S2 is drawn at an angle of 30 degrees to the cutting edge ridge 4 and the point P3 where the straight line S2 intersects with the cutting edge ridge 4 is the lowest in the thickness direction.

In this case, for example, the straight cutting edge ridge 4b of the tip 31 is moved 29 degrees with respect to the rotation axis of the work (not shown).
When it is clamped so as to have a clearance angle of 6 degrees and used for outer diameter processing, the apparent R at the cutting edge ridge corresponding to the curved concave portion 8 is large as in the case of the above-mentioned negative type diamond insert. Therefore, the finished surface roughness is improved as compared with the conventional triangular tip having no curved concave portion 8.

In each of the above embodiments, a rhombus having an apex angle of 80 degrees or a triangular tip having an apex angle of 60 degrees is embodied. It can be embodied in an away chip. However, a tip such as a tip having an apex angle of 80 degrees (or 75 degrees) which is used by being clamped to a standard product holder and having a fixed angle of the straight cutting edge with respect to the rotation axis of the workpiece (CNMG) , ENMG, WNMG, etc.), the effect is particularly large.

The shape and depth of the curved concave portion and the length along the cutting edge are set so that the radius R of the cutting edge of the nose is smooth and the radius R is effectively increased. If the depth of the curved concave portion is too small, the effect of increasing the apparent radius is small, and if the depth is too large, on the contrary, the wave shape of the chip cross section becomes too large and hinders the smooth discharge of the chip. I do. Considering these, the depth of the curved concave portion is 0.05
It is appropriate to set the length along the cutting edge ridge (width of the curved concave portion) to 0.3 to 1.0 mm.

Next, a cutting test (processing) was performed to confirm the finished surface roughness Rz (H). However, the sample is sample No. 1,
2 is the product of the present invention, and samples Nos. 3 and 4 are comparative examples.
In sample No. 1, the depth of the curved concave portion was 0.15 mm and the width was 0.1 mm.
Sample No. 2 has a depth of 0.08 mm and a width of 0.4 mm in Sample No. 2. Sample No. 3 is a conventional standard product, and sample No. 4 is 0.5 mm at the connection point between the arcuate cutting edge and the straight cutting edge of the conventional standard product of sample No. 3.
Are provided with flat cutting edges.

The results are as shown in Table 1. However, the conditions are as follows. Tip: Shape ISО CNMG
120408, material ISО HT-P10 (cermet), holder 11: shape ISО PCLNR252
5. Work: Material JIS SCM415 (HB16
0), shape φ50 mm × length 200 mm, cutting conditions: dry cutting of outer diameter, cutting speed 200 mm / min, depth of cut 0.
5mm, feed variable.

[0032]

[Table 1]

From Table 1, it can be seen that Samples No. 1 and No.
In the case of the chip No. 2, the feed amount f is within an appropriate range (0.1 to 0.3).
mm / rev), the finished surface roughness was improved as compared with the comparative example (sample No. 3). Comparative Example (Sample No. 4)
When the feed amount f was 0.1, chatter became large and cutting could not be performed. In the comparative example (sample No. 4), when the feed amount f was 0.2 or 0.3, the surface roughness was unstable and the desired gloss could not be obtained.

[0034]

As is apparent from the above description, according to the indexable insert of the present invention, there is an error in the position of the connecting point between the arcuate cutting edge and the straight cutting edge of the nose in the manufacture thereof. Also, it is possible to prevent the finished surface roughness from being reduced as in the case of the conventional chip, and to improve the finished surface roughness. The tip having such a shape does not have a flat cutting edge but a convex R at the connection point, and therefore does not have the above-mentioned disadvantages caused by the flat cutting edge. In addition, if the finished surface roughness of the conventional chip is sufficient, the feed (f) can be increased, so that the processing time can be reduced. Furthermore, when the feed is increased in this manner, the thickness of the chips can be increased by that amount, so that the chips can be easily separated and the scratch on the finished surface can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment embodying a throw-away tip of the present invention and an enlarged view of a main part thereof.

FIG. 2 is a partially omitted intermediate view seen from an arrow A (flank side) in the enlarged view of FIG. 1;

FIG. 3 is an enlarged perspective view of the throw-away tip shown in FIG. 1;

FIG. 4 is a partially omitted intermediate view of the throw away tip of FIG. 1 as viewed from a flank side.

FIG. 5 is a view of the indexable insert of FIG. 1 attached to a holder as viewed from a flank side.

FIG. 6 is a plan view and a main part enlarged view of another embodiment of the present invention.

FIG. 7 is an enlarged view of a portion K in FIG. 6;

FIG. 8 is a view seen from an arrow B (flank side) in FIG. 6;

FIG. 9 is an enlarged perspective view of a nose of the throw-away tip of FIG. 6;

FIG. 10 is a plan view of another embodiment of the present invention and an enlarged view of a main part thereof.

11 is an arrow C (flank side) in the enlarged view of FIG. 11;
The figure seen from.

FIG. 12 is a plan view of a conventional diamond-shaped throw-away tip and an enlarged view of a main part thereof.

[Explanation of symbols]

1, 21, 31 throw-away tip 2 nose 3 rake face 4 cutting edge ridge 4a arc-shaped cutting edge ridge 4b linear cutting edge ridge 7 side 8 curved concave 9 flank θ1 apex angle S1 bisector line to apex angle S2 Straight line drawn at 45 or 30 degrees to the bisector (S1) О Center of curvature of the arc of the arc-shaped cutting edge P1 Connection point P2 Straight line drawn at 45 degrees to S1 intersects the cutting edge The point where the straight line drawn at 30 degrees to P3 S1 intersects the cutting edge

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Inayama 14-18 Takatsuji-cho, Mizuho-ku, Nagoya F-term in Japan Special Ceramics Co., Ltd. 3C022 LL02 3C046 CC01 JJ04

Claims (6)

[Claims] 1. In a polygonal plate-shaped indexable insert, the vicinity of a connection point between an arc-shaped cutting edge of a nose and a straight cutting edge of a side of a cutting edge is lowest in a thickness direction. A throw-away tip, wherein a curved concave portion is formed in the cutting edge ridge so that 2. In a polygonal plate-shaped indexable insert, a connecting point between an arc-shaped cutting edge of a nose and a straight cutting edge of a side of a cutting edge, and a center of the arc-shaped cutting edge. Characterized in that a curved concave portion is formed in the cutting edge so that a space between the cutting edge and the cutting edge is the lowest in the thickness direction. 3. A polygonal plate-like indexable insert having an apex angle of approximately 80 degrees, a bisector of the apex angle is drawn on a rake face, and the center of curvature of the arc of the nose arc-shaped cutting edge ridge is formed. Draw a straight line at 45 degrees to the bisector from
A throwaway tip, wherein a curved concave portion is formed in the cutting edge so that the vicinity of the point where the straight line intersects the cutting edge is the lowest in the thickness direction. 4. A polygonal plate-like indexable insert having an apex angle of approximately 75 degrees, a bisector of the apex angle is drawn on a rake face, and the center of curvature of the arc of the nose arc-shaped cutting edge ridge is formed. Draw a straight line at 45 degrees to the bisector from
A throwaway tip, wherein a curved concave portion is formed in the cutting edge so that the vicinity of the point where the straight line intersects the cutting edge is the lowest in the thickness direction. 5. A triangular plate-shaped insert having an apex angle of approximately 60 degrees, a bisector is drawn on the rake face with respect to the apex angle, and the bisector of the nose is cut from the center of curvature of the arc of the arc-shaped cutting edge. A straight line is drawn at 30 degrees with respect to the bisector, and a curved concave portion is formed in the cutting edge ridge so that the vicinity of a point where the straight line intersects the cutting edge is the lowest in the thickness direction. And throw away tip. 6. The cutting edge according to claim 1, wherein said cutting edge has a waveform curve which is continuous with said curved concave portion when viewed from the flank side.
The throw-away tip according to 3, 4 or 5.