WO2014051327A1

WO2014051327A1 - Blank insert, cutting insert using the same and cutter including cutting insert

Info

Publication number: WO2014051327A1
Application number: PCT/KR2013/008572
Authority: WO
Inventors: Sang Kil SO
Original assignee: Taegutec Ltd.
Priority date: 2012-09-27
Filing date: 2013-09-25
Publication date: 2014-04-03
Also published as: KR20140041169A; KR101471252B1

Abstract

A cutting insert is made using a blank insert having a rotationally symmetrical recess portion. The cutting insert has upper and lower surfaces, side surfaces extending between the upper and lower surfaces, and a through hole extending through the upper and lower surfaces. Each of the upper and lower surfaces has a recess portion centrally located, four flat corner surfaces, four concave surfaces, and four cutting edges. The concave surface is located between adjacent corner surfaces. The cutting edge is formed at the intersection between the concave surface and the side surface. The recess portion is rotationally symmetrical when rotating the cutting insert by 90 or 180 degrees around a central axis of the through hole. The cutting edges in each of the upper and lower surfaces have at least one or more curvatures according to the rotational symmetry of the recess portion.

Description

BLANK INSERT, CUTTING INSERT USING THE SAME AND CUTTER INCLUDING CUTTING INSERT

The present invention relates to a blank insert having a particularly-shaped recess portion in its opposing surfaces. Further, the present invention relates to a cutting insert made using such a blank insert and a cutter in which such a cutting insert is mounted.

Cutters for machining a workpiece such as a rail are designed to correspond to the shape of the rail. A plurality of cutting inserts are mounted to such a cutter in a particular array.

FIG. 1 shows a conventional cutter for machining a particular part of a rail. A plurality of cutting inserts 20, each of which has concave cutting edges for machining a convex part of the rail 1, are mounted to the cutter 10 shown in FIG. 1. Such a cutting insert 20 is generally made by grinding a top surface of a blank insert 30 having a rectangular parallelepiped shape shown in FIG. 2. The cutting insert 20, which is made by grinding the top surface of the blank insert 30, has only two cutting edges 22. Thus, the cutting insert 20 has a shortcoming of short-term service life since the number of its available cutting edges is insufficient.

Korean Laid-Open Patent Publication No. 10-2010-0055246 discloses a blank insert and a cutting insert made using the same, which address the aforementioned shortcoming. As shown in FIG. 3, the blank insert disclosed in the aforementioned document has two raised portions 42 and a notch 44 extending therebetween in each of its upper and lower surfaces. A cutting insert 50 made by grinding the blank insert 40 has two cutting edges 52 at each of its upper and lower surfaces.

A conventional cutting insert, which is made using the blank insert having the two raised portions and the notch in each of the upper and lower surfaces, includes two cutting edges at the respective upper and lower surfaces. Since the two raised portions and the notch therebetween extend throughout the entire length of the upper surface and the lower surface in the conventional cutting insert, the conventional cutting insert does not have the cutting edges at all the edges of the upper and lower surfaces. Although the conventional cutting insert is a double-sided insert, it has a small number of cutting edges and thus has a short-term service life.

Further, in the conventional cutting insert, the two cutting edges provided in the respective upper and lower surfaces are opposed to each other. Said two cutting edges are formed concurrently through a grinding operation such that they have the same curvature. As a result, the conventional cutting insert does not have the cutting edges having different curvatures in the respective upper and lower surfaces.

The present invention is directed to solving the aforementioned problems of the prior art. The present invention provides a blank insert having a particularly-shaped recess portion in opposing two surfaces. Further, the present invention provides a cutting insert, which is made using such a blank insert and has four concave cutting edges at each of the opposing two surfaces, wherein the cutting edges have at least one or more curvatures. Furthermore, the present invention provides a cutter to which such a cutting insert is securely mountable.

One aspect of the present invention provides a blank insert. In an exemplary embodiment, the blank insert comprises an upper surface, a lower surface, a plurality of side surfaces extending between the upper surface and the lower surface, and a through hole extending through the upper surface and the lower surface. Each of the upper surface and the lower surface includes a recess portion that is located centrally. The recess portion has a rotationally symmetrical shape that is rotationally symmetrical when rotating the blank insert by 90 or 180 degrees around a central axis of the through hole.

In one embodiment, the recess portion is surrounded by a side wall in each of the upper surface and the lower surface. Further, the upper and lower surfaces of the blank insert have a square shape.

A further aspect of the present invention provides a cutting insert made using the blank insert. In an exemplary embodiment, the cutting insert comprises an upper surface, a lower surface, a plurality of side surfaces extending between the upper surface and the lower surface, and a through hole extending through the upper surface and the lower surface. Each of the upper surface and the lower surface includes: a recess portion located centrally; four flat corner surfaces, each located at a corner; four concave surfaces, each located between the adjacent corner surfaces; and four cutting edges at intersections between the concave surfaces and the side surfaces. The recess portion has a rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 90 or 180 degrees around a central axis of the through hole. The cutting edges in each of the upper surface and the lower surface have at least one or more curvatures according to the rotationally symmetrical shape of the recess portion.

In one embodiment, the cutting edges comprise first to fourth cutting edges along an edge of the upper surface and fifth to eighth cutting edges along an edge of the lower surface. The first to eighth cutting edges have an identical curvature when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 90 degrees.

In one embodiment, the cutting edges comprise first to fourth cutting edges along an edge of the upper surface. The first and third cutting edges are opposed to each other, while the second and fourth cutting edges are opposed to each other. The first and third cutting edges have a curvature different from a curvature of the second and fourth cutting edges when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 180 degrees. Further, the cutting edges comprise fifth to eighth cutting edges along an edge of the lower surface. The fifth and seventh cutting edges are opposed to each other, while the sixth and eighth cutting edges are opposed to each other. The fifth and seventh cutting edges have a curvature different from a curvature of the sixth and eighth cutting edges when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 180 degrees. Further, the curvature of the first and third cutting edges, the curvature of the second and fourth cutting edges, the curvature of the fifth and seventh cutting edges and the curvature of the sixth and eighth cutting edges may be different from one another.

In one embodiment, the recess portion is surrounded by a side wall in each of the upper surface and the lower surface.

In one embodiment, the upper surface and the lower surface have one of a square shape, a square shape with corners cut out linearly and a square shape with corners cut out curvilinearly.

In one embodiment, a surface area of the corner surface of the cutting insert becomes smaller as a concavity degree of the concave surface becomes greater.

A still further aspect of the present invention provides a cutter to which the cutting insert according to an embodiment is mountable. In an exemplary embodiment, the cutter includes a plurality of insert pockets. The insert pocket includes: two side walls supporting adjacent two side surfaces of the cutting insert, respectively; and a base wall supporting the upper or lower surface of the cutting insert. The base wall includes: a boss portion having a shape corresponding to a shape of the recess portion of the upper or lower surface of the cutting insert; and a seat portion receiving the upper or lower surface of the cutting insert except the recess portion.

In one embodiment, the seat portion supports the corner surfaces of the upper or lower surface of the cutting insert. The boss portion has a protrusion height equal to or different from a maximum recessed depth of the recess portion. When the protrusion height of the boss portion is equal to the maximum recessed depth of the recess portion, the cutting insert is supported with the recess portion in contact with the boss portion and with the corner surfaces in contact with the seat portion. When the protrusion height of the boss portion is greater than the maximum recessed depth of the recess portion, the cutting insert is supported with the recess portion in contact with the boss portion. When the protrusion height of the boss portion is less than the maximum recessed depth of the recess portion, the cutting insert is supported with the corner surfaces in contact with the seat portion.

The blank insert according to an embodiment has the particularly-shaped recess portion in each of opposing upper and lower surfaces. The recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the upper surface or the lower surface by 90 or 180 degrees. The cutting insert, which is made using the blank insert, includes such a particularly-shaped recess portion of the blank insert in its upper and lower surfaces as the recess portion is intact. Thus, the cutting insert can be securely mounted in the insert pocket of the cutter.

Further, the cutting insert according to an embodiment has four concave cutting edges at each of the upper surface and the lower surface. Thus, the cutting insert has an enhanced service life due to increase in the number of available cutting edges. Additionally, as to the four cutting edges provided at each of the upper surface and the lower surface, the pair of opposing cutting edges may have a curvature different from a curvature of another cutting edge adjacent thereto or another pair of opposing cutting edges adjacent thereto, according to the rotationally symmetrical shape of the recess portion. This can accomplish a cutting insert wherein certain cutting edges have an identical curvature, while the rest of the cutting edges have a different curvature. The cutting insert can be mounted to only the insert pocket having the boss portion corresponding to the recess portion of the cutting insert. This prevents the cutting inserts from being erroneously mounted to the cutter wherein a plurality of the cutting inserts must be arranged in a particular array.

Further, the cutter according to an embodiment has the insert pocket including the boss portion, which corresponds to the recess portion provided in each of the upper and the lower surfaces of the cutting insert. Thus, the cutting insert can be securely mounted to the cutter.

FIG. 1 is a perspective view showing a conventional cutter for machining a particular part of a rail.

FIG. 2 is a perspective view showing a conventional blank insert and a conventional cutting insert made by grinding the blank insert.

FIG. 3 is a perspective view showing another conventional blank insert and another conventional cutting insert made by grinding the blank insert.

FIG. 4 is a perspective view showing a blank insert according to an embodiment of the present invention.

FIG. 5 is a plan view showing a lower surface of the blank insert shown in FIG. 4.

FIGS. 6 to 13 are plan views showing various examples of a recess portion, which are employed in the blank insert according to an embodiment of the present invention.

FIGS. 14 to 17 are plan views showing various examples of a recess portion, which are employed in the blank insert according to another embodiment of the present invention.

FIG. 18 is a perspective view showing a cutting insert according to an embodiment of the present invention.

FIG. 19 is a plan view showing a lower surface of the cutting insert shown in FIG. 18.

FIG. 20 is a perspective views showing a cutting insert according to another embodiment of the present invention.

FIG. 21 is a perspective views showing a cutting insert according to yet another embodiment of the present invention.

FIG. 22 is a perspective view showing a cutter according to an embodiment of the present invention.

FIG. 23 is a perspective view showing an insert pocket, which is employed in a cutter according to an embodiment of the present invention.

FIG. 24 is a perspective view showing an insert pocket, which is employed in a cutter according to another embodiment of the present invention.

Embodiments of a blank insert, embodiments of a cutting insert made using the blank insert and embodiments of a cutter to which such a cutting insert is mountable will now be described with reference to the accompanying drawings. Like reference numerals in the drawings refer to like elements or parts.

A blank insert 100 shown in FIGS. 4 to 17 according to an embodiment of the present invention is a semi-manufactured product for use in manufacturing a cutting insert with cutting edges having various concavity degrees. Such a blank insert 100 is typically made by a pressure molding method.

Referring to FIGS. 4 and 5, the blank insert 100 includes an upper surface 110, a lower surface 120, a plurality of side surfaces 130 extending between the upper surface 110 and the lower surface, and a through hole 140 extending through the upper surface 110 and the lower surface 120. The upper surface 110 and the lower surface are opposed to each other and are parallel to each other. The lower surface 120 has the same shape and configuration as the upper surface 110. The blank insert 100 is a rectangular parallelepiped, wherein the upper and

lower surfaces

110, 120 have a square shape and four side surfaces 130 extend between the upper surface 110 and the lower surface 120.

Further, the blank insert 100 includes a pair of recess portions 150, one of which is located in the upper surface 110, and the other of which is located in the lower surface 120. The recess portion 150 is stepwise recessed at the central region of each of the upper and

lower surfaces

110 and 120, thus having a bottom wall 151a and a side wall 152a located between the bottom wall 151a and the upper surface 110 or between the bottom wall 151a and the lower surface 120. The bottom wall 151a of the recess portion 150a is parallel to the upper surface 110 or the lower surface 120. Since the upper surface 110 and the lower surface 120 are parallel to each other, the bottom walls of a pair of the recess portions 150 are parallel to each other. The bottom wall 151a of the recess portion 150 comprises a flat surface and is formed by stepwise recessing the central region of the upper surface 110 or the lower surface 120. Thus, the recess portion 150a has a uniform recessed depth H₁ with respect to the upper surface 110 or the lower surface 120. Herein, the uniform recessed depth H₁ of the recess portion 120 means that the perpendicular distances between the bottom wall 151a of the recess portion 150a and a plane of the upper surface 110 or the lower surface 120 are uniform at every location. In other embodiment, the bottom wall 151a of the recess portion 150a may comprise an inclined surface that upwardly or downward inclined toward the center of the blank insert 100.

The recess portion 150a is surrounded by the side wall 152a and is connected to the upper surface 110 or the lower surface 120 through the side wall 152a. The side wall 152a is located between the upper surface 110 and the bottom wall 151a of the recess portion 150a or between the lower surface 120 and the bottom wall 151a of the recess portion 150a. The side wall 152a may be inclined or vertical with respect to the upper surface 110 or the lower surface 120. Further, a portion of the side wall 152 in a vertical direction may be inclined, while the rest may be vertical.

The blank insert 100 according to an embodiment is configured such that the recess portion 150a becomes rotationally symmetrical when the blank insert 100 is rotated by every predetermined angle (e.g. 90 degrees or 180 degrees). That is, the blank insert 100 includes, at the upper surface 110 and the lower surface 120, one of the recess portions having the shape that is rotationally symmetrical when the blank insert 100 is rotated by said predetermined angle. FIGS. 6 to 17 illustrates various recess portions 150b to 150m having the rotationally symmetrical shape. Similar to the recess portion 150a shown in FIGS. 4 and 5, the recess portions 150b to 150m shown in FIGS. 6 to 17 have a bottom wall and a side wall. FIGS. 6 to 17 show the recess portion formed in the upper surface 110 of the blank insert 100. The lower surface 120 of the blank insert 100 is formed with the recess portion having the same shape as the recess portion formed in the upper surface 110.

The recess portions 150a to 150i, which are shaped to be rotationally symmetrical when rotating the blank insert 100 by every 90 degrees, are described with reference to FIGS. 4 to 13. The recess portion 150a of the blank insert 100 shown in FIGS. 4 and 5 has an approximately square shape with roundly enlarged corners when the blank insert 100 is viewed from top. The recess portion 150b of the blank insert 100 shown in FIG. 6 has a square shape when the blank insert 100 is viewed from top. The recess portion 150c of the blank insert 100 shown in FIG. 7 has an approximately square shape with corners cut out linearly, when the blank insert 100 is viewed from top. The recess portion 150d of the blank insert 100 shown in FIG. 8 has an approximately square shape with corners cut out curvilinearly, when the blank insert 100 is viewed from top. The recess portion 150e of the blank insert 100 shown in FIG. 9 has an approximately square shape with round corners and sides curvilinearly convex toward the central axis C of the through hole 140, when the blank insert 100 is viewed from top. The recess portion 150f of the blank insert 100 shown in FIG. 10 and the recess portion 150g of the blank insert 100 shown in FIG. 11 have an approximately square shape with round corners and wavy sides, when the blank insert 100 is viewed from top. The recess portion 150h of the blank insert 100 shown in FIG. 12 has a circular shape, when the blank insert 100 is viewed from top. The recess portion 150i of the blank insert 100 shown in FIG. 13 has a square shape, when the blank insert 100 is viewed from top. The recess portion 150i shown in FIG. 13 is formed in the blank insert 100 such that its diagonal is rotated relative to the diagonal of the upper surface 110 at a predetermined angle. Further, the above-described

recess portions

150a, 150c, 150d, 150e, 150f and 150g may be formed in the blank insert 100 such that their diagonals are rotated relative to the diagonal of the upper surface 110 at a predetermined angle.

In the above-described recess portions 150a to 150i, portions opposed relative to the central axis C are symmetrical when viewing the blank insert 100 from top (or from below). The recess portions 150a to 150i have the rotationally symmetrical shape wherein the shape before rotation and the shape after rotation coincide with each other when rotating the blank insert 100 around the central axis C by every 90 degrees. Thus, all the cutting edges of the cutting insert, which is made from the blank insert 100 with the above-described recess portion 150a to 150i, may be used for cutting operation. This is because the cutting insert may be mounted in the cutter while being rotated by every 90 degrees or in such a manner that it is reversed and then is rotated by every 90 degrees. Further, the cutting insert, which is made from the blank insert with one of the above-described recess portions 150a to 150i, may be formed such that its cutting edges have at least one or more curvatures. The 90 degrees rotationally symmetrical shape of the recess portion formed in the blank insert 100 is not limited to the examples shown in FIGS. 5 to 13. The 90 degrees-rotationally symmetrical recess portion of the blank insert 100 may have various shapes which satisfy the condition where the cutting insert made from the blank insert 100 may be mounted in the cutter through every 90 degrees rotation, i.e., the condition of the 90 degrees rotational symmetry.

The recess portions 150j to 150m, which are rotationally symmetrical when rotating the blank insert 100 by every 180 degrees, are described with reference to FIGS. 14 to 17. The blank insert 100 includes one of the recess portions 150j to 150m at the upper surface 110 and the lower surface 120. The recess portions 150j to 150m have a rotationally symmetrical shape that is rotationally symmetrical when rotating the blank insert 100 around the central axis C of the through hole 140 by 180 degrees.

The recess portion 150j of the blank insert 100 shown in FIG. 14 has a diamond shape when the blank insert 100 is viewed from top. The recess portion 150k of the blank insert 100 shown in FIG. 15 has an approximately diamond shape with two corners in a short diagonal protruding. The recess portion 150l of the blank insert 100 shown in FIG. 16 has an elliptical shape when the blank insert 100 is viewed from top. The recess portion 150m of the blank insert 100 shown in FIG. 17 has an approximately elliptical shape with two opposing sides in an elliptical major axis protruding, when the blank insert 100 is viewed from top. In the recess portions 150j to 150m, two half sections divided by the diagonal of the upper surface 110 or the lower surface 120 are symmetrical. Accordingly, the cutting insert, which is made from the blank insert with one of the above-described recess portions 150j to 150m, may be formed such that its cutting edges have at least one or more curvatures. Further, such a cutting insert may be mounted in the cutter in such a manner that it is rotated by every 180 degrees, or that it is reversed and then rotated by every 180 degrees. Further, such a cutting insert may be mounted in the cutter in the position different from its initial position, so that another cutting edge having a curvature different from that of the initially-used cutting edge can cut another convex portion of a workpiece. In such a case, the cutting insert may be mounted in the cutter as rotated by 90 degrees from its initial position, so that the cutting edge having another curvature can be directed to the workpiece. The 180 degrees-rotationally symmetrical shape of the recess portion formed in the blank insert 100 is not limited to the examples shown in FIGS. 14 to 17. The 180 degrees-rotationally symmetrical recess portion of the blank insert 100 may have various shapes which satisfy the condition where the cutting insert made from the blank insert 100 may be mounted in the cutter through every 180 degrees rotation, i.e., the condition of the 180 degrees rotational symmetry.

The cutting insert 200 according to an embodiment of the present invention is made by grinding the above-described blank insert 100. Specifically, the cutting insert 200 is made by grinding the upper surface 110 and the lower surface 120 of the blank insert 100 except the recess portion 150a to 150m. Thus, the cutting insert 200 has a shape approximately identical to the shape of the blank insert 100 except upper and lower surfaces of the cutting insert.

Referring to FIGS. 18 and 19, the cutting insert 200 includes an upper surface 210, a lower surface 220, four side surfaces 230 extending between the upper surface 210 and the lower surface 220, a through hole 240 extending through the upper surface 210 and the lower surface, and a recess portion 250 stepwise recessed at the central region of each of the upper surface 210 and the lower surface 220.

The recess portion 250 of the cutting insert 200 has a bottom wall 251 and a side wall 252. The bottom wall 251 of the recess portion 250 comprises a flat surface and is parallel to the upper surface 210 or the lower surface 220. The recess portion 250 is surrounded by the side wall 252 and is connected to the upper surface 210 or the lower surface 220 through the side wall 252. The side wall 252 is concave due to grinding for the upper surface 110 and the lower surface 120 of the blank insert 100. Further, the recess portion 250 has the rotationally symmetrical shape that is rotationally symmetrical such that the shape before rotation and the shape after rotation coincide with each other when rotating the cutting insert 200 around the central axis C by every 90 degrees or 180 degrees. The recess portion 150a to 150m, which is provided in the blank insert 100, remains intact without grinding and therefore becomes the recess portion 250 of the cutting insert 200. Such a recess portion 250 functions as a positioning part for use in mounting the cutting insert 200 in the insert pocket of the cutter. Since the recess portion 250 has the shape of the recess portion 150a to 150m shown in FIGS. 5 to 17, the cutting insert 200 may be stably and firmly mounted in the cutter by virtue of the particular shape feature of the recess portion 250. Further, since the recess portion 250 of the cutting insert 200 has the rotationally symmetrical shape, the cutting insert 200 may be mounted in the cutter such that all the cutting edges located in the upper surface 210 and the lower surface 220 can be used for cutting operation.

The cutting insert 200 includes four flat corner surfaces 260 and four concave surfaces 270 in each of the upper surface 210 and the lower surface 220. Four corner surfaces 260 are located at four corners of the upper surface 210 or the lower surface 220, respectively. Each concave surface 270 is located between two adjacent corner surfaces 260 along the edge of the upper surface 210 or the lower surface 220. The corner surface 260 functions as an abutment surface for stably mounting the cutting insert 200 in the insert pocket of the cutter. The concave surface 270 is a surface grinded concavely for forming a cutting edge 281 to 288. The concave surface 270 has various concavity degrees corresponding to the convexity degrees of a convex shape of a workpiece.

The corner surface 260 of the cutting insert 200 is formed by flat grinding each corner portion of the upper surface 110 or the lower surface 120 of the blank insert 100. Further, the edge portion except the corner portion in each of the upper surface 110 and the lower surface 120 of the blank insert 100 is grinded concavely in a thickness direction of the blank insert 100 (in the direction of the central axis C), thus forming the concave surface 270 of the cutting insert 200. As a result, in the recess portion 250 of the cutting insert 200, a recessed depth H₂ at the corner surface 260 is different from a recessed depth H₃ at the concave surface 270. At the recessed depth H₂, the height of the side wall 253 is maximum from the bottom wall 251 of the recess portion 250. The recessed depth H₃ decreases from the corner surface 260 toward the middle of the concave surface 270 in conformity with the concavity degree of the concave surface 270. The recessed depth H₃ is small by a grinding depth, when compared with the recessed depth H₁ of the recess portion 150a of the blank insert 100.

The four concave surfaces 270 of the upper surface 210 or the lower surface 220 adjoin the four side surfaces 230. Accordingly, the cutting insert 200 has four cutting edges 281 to 284, which are located between the side surfaces 230 and the concave surfaces 270 of the upper surface 210, and four cutting edges 285 to 288, which are located between the side surfaces 230 and the concave surfaces 270 of the lower surface 220. As shown in FIG. 19, the lower surface 220 of the cutting insert 200 has the same shape and configuration as the upper surface 210. Thus, the cutting insert 200 has eight cutting edges 281 to 288 in total (four cutting edges at the upper surface 210 and four cutting edges at the lower surface 220).

The cutting edges 281 to 288 of the cutting insert 200 may have various curvatures. For various curvatures of the cutting edges, the blank insert 100 may be grinded such that the concavity degree of the concave surface 270 may vary. The concavity degree of the concave surface 270 may vary depending on the shape of a workpiece. As the grinding depth for the blank insert 100 increases, the concavity degree of the concave surface 270 becomes larger. Further, as the grinding depth for the blank insert 100 increases, the surface area of the corner surface 260 decreases and the cutting edge 281 to 288 located between adjacent corner surfaces 260 becomes longer.

When the concavity degree of the concave surface 270 exceeds the height of the side wall 152a in the blank insert 100 during machining the cutting insert 200 by grinding the blank insert 100, the blank insert 100 may be grinded up to the bottom wall 151a of the recess portion 150a. In order that the recess portion 150a of the blank insert 100 can remain intact in the cutting insert 200, the blank insert 100 is grinded such that the concave surface 270 has various curvatures within the recessed depth H₁ of the recess portion 150a in the blank insert 100.

The upper surface 210 and the lower surface 220 of the cutting insert 200 have a square shape. FIGS. 20 and 21 show cutting inserts according to another embodiment. FIG. 20 shows the cutting insert 200a wherein corner portions between the side surfaces 230 are chamfered in the shape of a flat surface. The cutting insert 200a has a flat corner side surface 231 between the adjacent side surfaces 230. Thus, the upper surface 210a and the lower surface 220a of the cutting insert 200a has an approximately square shape with corners cut out linearly. FIG. 21 shows the cutting insert 200b wherein corners portions between the side surfaces 230 are chamfered in the shape of a curved surface. The cutting insert 200b has a curved corner side surface 232 between the adjacent side surfaces 230. Thus, the upper surface 210b and the lower surface 220b of the cutting insert 200b has an approximately square shape with corners cut out curvilinearly.

The cutting edges 281 to 288 of the cutting

insert

200, 200a, 200b may have at least one or more curvatures according to the rotationally symmetrical shape of the recess portion 250. Henceforth, four cutting edges located along the edge of the upper surface 210 (see FIG. 18) are referred to as first to fourth cutting edges 281 to 284 respectively, and four cutting edges located along the edge of the lower surface 220 (see FIG. 19) are referred to as fifth to eighth cutting edges 285 to 288 respectively. In the upper surface 210, the first cutting edge 281 and the third cutting edge 283 are opposed relative to the central axis C, and the second cutting edge 282 and the fourth cutting edge 284 are opposed relative to the central axis C. In the lower surface 220, the fifth cutting edge 285 and the seventh cutting edge 287 are opposed relative to the central axis C, and the sixth cutting edge 282 and the eighth cutting edge 288 are opposed relative to the central axis C. When manufacturing the cutting insert 200 from the blank insert 100, the opposed cutting edges in the upper and

lower surfaces

210, 220 may be formed through grinding in one direction. Thus, the opposed cutting edges in each of the upper surface 210 and the lower surface 220 may have the same curvature.

In case the recess portion 250 has the rotationally symmetrical shape that is rotationally symmetrical when the cutting insert 200 is rotated around the central axis C of the through hole 240 by every 90 degrees (i.e., in case the cutting insert 200 is manufactured from the blank insert 100 having one of the recess portions 150a to 150i shown in FIGS. 5 to 12), the first to eight cutting edges 281 to 288 of the cutting insert 200 may be formed to have the same curvature. When one of the cutting edges of such a cutting insert 200 is worn out or damaged and the cutting insert 200 needs to be replaced, the cutting insert 200 may be mounted in the insert pocket of the cutter again such that one of the rest seven cutting edges can be used for cutting operation.

In another example, in the upper surface 210, the pair of the first and

third cutting edges

281 and 283 may be formed to have the same curvature, and the pair of the second and

fourth cutting edges

282 and 284 may be formed to have the same curvature. Further, the pair of the first and

third cutting edges

281 and 283 may be formed to have a curvature different form that of the pair of the second and

fourth cutting edges

282 and 284. Similarly, in the lower surface 220, the pair of the fifth and

seventh cutting edges

285 and 287 may be formed to have the same curvature, and the pair of the sixth and

eighth cutting edges

286 and 288 may be formed to have the same curvature. Further, the pair of the fifth and

seventh cutting edges

285 and 287 may be formed to have a curvature different form that of the pair of the sixth and eight

cutting edges

282 and 284. Further, the pair of the first and

third cutting edges

281 and 283, the pair of the second and

fourth cutting edges

282 and 284, the pair of the fifth and

seventh cutting edges

285 and 287 and the pair of the sixth and

eighth cutting edges

286 and 288 may be formed to have different curvatures. In this case, the cutting insert 200 may have four different curvatures.

In another embodiment, the recess portion 250 has the rotationally symmetrical shape that is rotationally symmetrical when the cutting insert 200 is rotated around the central axis C of the through hole 240 by every 180 degrees. That is, the cutting insert 200 is manufactured from the blank insert 100 having one of the recess portions 150j to 150m shown in FIGS. 14 to 17. In this example, in the upper surface 210 of the cutting insert 200, the pair of the first and

third cutting edges

281 and 283 may be formed to have a curvature different from that of the pair of the second and

fourth cutting edges

282 and 284. Further, in the lower surface 220, the pair of the fifth and

seventh cutting edges

285 and 287 may be formed to have a curvature different from that of the pair of the sixth and

eighth cutting edges

286 and 288. Further, the pair of the first and

third cutting edges

281 and 283, the pair of the second and

fourth cutting edges

282 and 284, the pair of the fifth and

seventh cutting edges

285 and 287 and the pair of the sixth and

eighth cutting edges

When the above-described cutting insert 200 is mounted in the cutter in a particular array corresponding to the convex part of the workpiece such as a rail, the cutting insert may be mounted in the cutter at different locations depending on the curvatures of the cutting edges. One cutting insert includes the cutting edges having different curvatures, thus reducing the number of the types of the cutting inserts to be mounted in the cutter.

FIG. 22 shows the cutter 300 according to an embodiment of the present invention. As shown in FIG. 22, the plurality of the above-described cutting inserts 200 may be mounted in the cutter in a particular array. The cutter 200 includes a plurality of

insert pockets

310a, 310b shown in FIG. 23 or FIG. 24. The cutting insert 200 with the cutting edges 281 to 288 having various concavity degrees (curvatures) is mounted in the

insert pocket

310a, 310b. FIG. 22 shows that the cutting insert 200 provided with the recess portion 250 is mounted in the cutter 300. The recess portion 250 of the cutting insert 200 shown in FIG. 22 has the rotationally symmetrical shape that is rotationally symmetrical when the cutting insert 200 is rotated around the central axis C of the through hole 240 by every 90 degrees. In another embodiment, the cutting insert 200 with the recess portion 250, which has the shape rotationally symmetrical by 180 degrees around the central axis C of the through hole 240, is mounted in the cutter 300.

Referring to FIGS. 23 and 24, the

insert pocket

310a, 310b of the cutter 300 includes a

base wall

320a, 320b and two side walls 330. The

base wall

320a, 320b supports the upper surface 210 or the lower surface 220 of the cutting insert 200. The side walls 330 supports the adjacent side surfaces 230 of the cutting insert 200. Further, the

base wall

320a, 320b of the

insert pocket

310a, 310b includes a boss portion 322 and a

seat portion

324a, 324b surrounding the boss portion 322. The boss portion 322 protrudes from the

seat portion

324a, 324b and has the shape corresponding to the shape of the recess portion 250 provided in the upper surface 210 or the lower surface 220 of the cutting insert 200. A portion of the upper surface 210 or the lower surface 220, which excludes the recess portion 250, (i.e., the corner surfaces 260 formed in the upper surface 210 or the lower surface 220) is seated on the

seat portion

324a, 324b. A threaded hole 340 is formed in the central region of the boss portion 322. The through hole 240 of the cutting insert 200 is aligned with the threaded hole 340 and a fastening screw is fastened to the threaded hole 340. FIGS. 23 and 24 show that the boss portion 322 is shaped to be fittable to the recess portion 250 having the 90 degrees rotational symmetry. It is a matter of course that the boss portion 322 may be shaped to be fittable to the recess portion having the 180 degrees rotational symmetry.

The insert pocket 310a shown in FIG. 23 and the insert pocket 310b shown in FIG. 24 have a difference in shape due to a machining method. As for the insert pocket 310a shown in FIG. 23, a relief groove 328a is machined through drilling. Thus, a drilled hole 326 deeper than the seat portion 334a exists at the relief groove 328a located between the side walls 330 and the relief groove 328a located at the end of the side wall 330. As for the insert pocket 320a shown in FIG. 24, a relief groove 328b is machined by an end mill and therefore the seat portion 324b is formed to be flat up to its corner adjoining the relief groove 328b. The

insert pocket

310a, 310b may be formed such that the inclined angle of the side wall 330 relative to the

seat portion

324a, 324b is equal to the inclined angle of the side surface 230 of the cutting insert 200 relative to the upper surface 210 or the lower surface 220. Thus, the cutting insert 200 may be mounted in the

insert pocket

310a, 310b of the cutter 300 without interference and be prevented from being damaged. When the cutting insert 200 is mounted in the

insert pocket

310a, 310b of the cutter 300, the boss portion 322 of the

base wall

320a, 320b is fitted to the recess portion 250 provided in the upper surface 210 or the lower surface 220 of the cutting insert 200, thus providing a radial support force.

The boss portion 322 has a protrusion height H₄ which is equal to or different from the maximum recessed depth of the recess portion 250, i.e., the recessed depth H₂ of the recess portion 250 relative to the corner surface 260 of the cutting insert 200. If the maximum recessed depth H₂ of the recess portion 250 is equal to the protrusion height H₄ of the boss portion 322, the cutting insert 200 is supported by the

insert pocket

310a, 310b as the recess portion 250 and the boss portion 322 are in contact with each other and the corner surface 260 and the seat portion 334a, 334b are in contact with each other. If the maximum recessed depth H₂ of the recess portion 250 is less than the protrusion height H₄ of the boss portion 322, the cutting insert 200 is supported by the

insert pocket

310a, 310b as the corner surface 260 and the seat portion 334a, 334b are spaced from each other and the recess portion 250 and the boss portion 322 are in contact with each other. If the maximum recessed depth H₂ of the recess portion 250 is greater than the protrusion height H₄ of the boss portion 322, the cutting insert 200 is supported by the

insert pocket

310a, 310b as the boss portion 322 is fitted to the recess portion 250 without contact between opposing surfaces of the boss portion 322 and the recess portion 250 and the corner surface 260 and the seat portion 334a, 334b are in contact with each other. When the bottom wall 251 of the recess portion 250 includes a flat surface, the surface of the boss portion 322, which is opposed to the recess portion 250, may include a flat surface so that it can come into surface contact with the recess portion 250.

As shown in FIG. 24, when the entirety of the seat portion 334b is flat, all of the four corner surfaces 260 of the cutting insert 200 can come into surface contact with the seat portion 334a. When the drilled holes 32 exist in the seat portion 334a as shown in FIG. 23, two corner surfaces except the corner surfaces to be positioned at the drilled holes 326 can come into surface contact with the seat portion 334a.

The side surfaces 230, which are adjacent in the cutting insert 200, are supported by two side walls 330a of the

insert pocket

310a, 310b, irrespective of the contact between the corner surfaces 260 of the cutting insert 200 and the seat portion 334a, 334b of the

insert pocket

310a, 310b. The concave surface 270 between the corner surfaces 260 does not contact the seat portion 334a, 334b. Thus, although the cutting edges of the concave surfaces 270 have various concavity degrees, the cutting insert 200 may be stably mounted in the cutter 200 without regard to the shapes of the cutting edges.

The cutting

insert

200, 200a, 200b, wherein the recess portion 250 is rotationally symmetrical when rotating the cutting insert by 180 degrees around the central axis C of the through hole 240, cannot be mounted in the

insert pocket

310a, 310b having the boss portion, which corresponds to the recess portion 250 having the 90 degrees rotational symmetry. This is because the shape of the recess portion 250 does not fit to the shape of the boss portion 322 when the cutting

insert

200, 200a, 200b having the 180 degrees rotational symmetry is rotated by 90 degrees. That is, the cutting

insert

200, 200a, 200b having the 180 degrees rotational symmetry is capable of being mounted in the

insert pocket

310a, 310b only when such a cutting insert is rotated by 180 degrees. This can readily prevent the

cutting insert

200, 200a, 200b from being erroneously mounted in the insert pocket mismatched thereto.

While the present invention has been described hereinbefore with reference to the foregoing embodiments depicted in the accompanying drawings, the present invention should not be limited thereto and various substitutions, alternations or modifications may be made without departing from the scope of the present invention. By way of example, cutting inserts with cutting edges having various convexity degrees may be formed by grinding the corners of the upper and lower surfaces of the above-described blank insert. As such, it will be apparent to those of ordinary skill in the art that various substitutions, alternations or modifications may be made without departing from the scope of the present invention.

Claims

A cutting insert, comprising:

an upper surface;

a lower surface;

a plurality of side surfaces extending between the upper surface and the lower surface; and

a through hole extending through the upper surface and the lower surface,

wherein each of the upper surface and the lower surface comprises:

a recess portion located centrally;

four flat corner surfaces each located at a corner;

four concave surfaces each located between the adjacent corner surfaces; and

four cutting edges at intersections between the concave surfaces and the side surfaces,

wherein the recess portion has a rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 90 or 180 degrees around a central axis of the through hole, and

wherein the cutting edges in each of the upper surface and the lower surface have at least one or more curvatures according to the rotationally symmetrical shape of the recess portion.
The cutting insert of Claim 1, wherein the cutting edges comprise first to fourth cutting edges along an edge of the upper surface and fifth to eighth cutting edges along an edge of the lower surface, and

wherein the first to the eighth cutting edges have an identical curvature when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 90 degrees.
The cutting insert of Claim 1, wherein the cutting edges comprise first to fourth cutting edges along an edge of the upper surface, the first and third cutting edges being opposed to each other, the second and fourth cutting edges being opposed to each other, and

wherein the first and third cutting edges have a curvature different from a curvature of the second and fourth cutting edges when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 180 degrees.
The cutting insert of Claim 3, wherein the cutting edges comprise fifth to eighth cutting edges along an edge of the lower surface, the fifth and seventh cutting edges being opposed to each other, and the sixth and eighth cutting edges being opposed to each other, and

wherein the fifth and seventh cutting edges have a curvature different from a curvature of the sixth and eighth cutting edges when the recess portion has the rotationally symmetrical shape that is rotationally symmetrical when rotating the cutting insert by 180 degrees.
The cutting insert of Claim 4, wherein the curvature of the first and third cutting edges, the curvature of the second and fourth cutting edges, the curvature of the fifth and seventh cutting edges and the curvature of the sixth and eighth cutting edges are different from one another.
The cutting insert of Claim 1, wherein the recess portion is surrounded by a side wall in each of the upper surface and the lower surface.
The cutting insert of Claim 1, wherein the upper surface and the lower surface have one of a square shape, a square shape with corners cut out linearly and a square shape with corners cut out curvilinearly.
The cutting insert of Claim 1, wherein a surface area of the corner surface becomes smaller as a concavity degree of the concave surface becomes greater.
A cutter, comprising:

the cutting insert of any one of Claims 1 to 8; and

an insert pocket in which the cutting insert is mounted,

wherein the insert pocket includes:

two side walls supporting adjacent two side surfaces of the cutting insert respectively; and

a base wall supporting the upper or lower surface of the cutting insert,

wherein the base wall comprises:

a boss portion having a shape corresponding to a shape of the recess portion of the upper or lower surface of the cutting insert; and

a seat portion receiving the upper or lower surface of the cutting insert except the recess portion.
The cutter of Claim 9, wherein the seat portion supports the corner surfaces of the upper or lower surface of the cutting insert.
The cutter of Claim 10, wherein the boss portion has a protrusion height equal to or different from a maximum recessed depth of the recess portion,

wherein when the protrusion height of the boss portion is equal to the maximum recessed depth of the recess portion, the cutting insert is supported with the recess portion in contact with the boss portion and with the corner surfaces in contact with the seat portion,

wherein when the protrusion height of the boss portion is greater than the maximum recessed depth of the recess portion, the cutting insert is supported with the recess portion in contact with the boss portion, and

wherein when the protrusion height of the boss portion is less than the maximum recessed depth of the recess portion, the cutting insert is supported with the corner surfaces in contact with the seat portion.
A blank insert, comprising:

an upper surface;

a lower surface;

a plurality of side surfaces extending between the upper surface and the lower surface; and

a through hole extending through the upper surface and the lower surface,

wherein each of the upper surface and the lower surface comprise a recess portion located centrally,

wherein the recess portion has a rotationally symmetrical shape that is rotationally symmetrical when rotating the blank insert by 90 or 180 degrees around a central axis of the through hole.
The blank insert of Claim 12, wherein the recess portion is surrounded by a side wall in each of the upper surface and the lower surface.
The blank insert of Claim 12, wherein the upper surface and the lower surface have a square shape.