Double-sided negative cutting insert and milling tool

Abstract

To provide a double-sided negative cutting insert that has a novel and favorable design.SOLUTION: A double-sided negative cutting insert for use in milling with eight machining positions. A peripheral surface extends around the cutting insert (1) and has four main side faces including first and second main side faces (11a, 11b) arranged opposite to each other on opposite sides of the cutting insert and third and fourth main side faces (11c, 11d) arranged opposite to each other on two other opposite sides of the cutting insert. The cutting insert has eight sets of cutting edges, each of which includes a main cutting edge, a corner cutting edge and a minor cutting edge. Two flat side surfaces (14a, 14b) that are inclined towards each other are provided on each one of the first and second main side faces. The main cutting edges (21a and others) are arranged along the respective side surfaces on the first and second main side faces and all minor cutting edges (22a and others) are arranged along the third and fourth main side faces.SELECTED DRAWING: Figure 1a

Description

[Technical Field]

[0001] The present invention relates to a double-sided negative cutting insert for milling according to the preamble of claim 1. The present invention also relates to a milling tool comprising such a double-sided negative cutting insert. [Background technology]

[0002] A milling tool is a rotary cutting tool and can include one or more cutting inserts removably mounted in respective insert seats in the tool body of the milling tool. One type of cutting insert that can be used in a milling tool is a double-sided negative cutting insert with eight different cutting positions. This type of cutting insert is previously known from U.S. Pat. No. 9,623,495 and is rotatable to eight different cutting positions, with four cutting positions provided by four different sets of cutting edges formed on the contact surface between the peripheral surface and the first major surface of the cutting insert, and four additional cutting positions provided by four other different sets of cutting edges formed on the contact surface between the peripheral surface and the second major surface of the cutting insert. When a cutting edge in one such set of cutting edges wears, the cutting insert can be repositioned within its seat and installed in a new cutting position with another of a different set of cutting edges in the active cutting position. All cutting edges of the cutting insert disclosed in U.S. Pat. No. 9,623,495 are designed as right-hand cutting edges, meaning that the cutting insert can only be installed in right-hand insert seats.

[0003] In this description, an insert seat designed to receive a cutting insert having a set of right-side cutting edges of the cutting insert in the active cutting position is referred to as a right-side insert seat, and an insert seat designed to receive a cutting insert having a set of left-side cutting edges of the cutting insert in the active cutting position is referred to as a left-side insert seat.

[0004] In some types of milling operations, for example, when a half-side and front disc milling cutter of the type shown in FIG. 4a with a right-side insert seat and a half-side and front disc milling cutter of the type shown in FIG. 6a with a left-side insert seat are combined with each other and mounted on the same arbor, as shown schematically in FIG. 5, it is necessary to use both right-side and left-side cutting edges. This also applies when using a double half-side and front disc milling cutter of the type shown in FIG. 7a, in which a right-side cutting edge is used on the cutting insert mounted in the right-side insert seat on the front side of the milling tool and a left-side cutting edge is used on the cutting insert mounted in the left-side insert seat on the rear side of the milling tool. If the cutting insert is incorrectly mounted with the right-side cutting edge pair in the active cutting position of the left-side insert seat, or vice versa, harmful tool failure will occur.

[0005] Double-sided negative cutting inserts of the type described above offer numerous different machining positions and can be manufactured in a relatively simple and cost-effective manner. Because the cutting insert has a negative geometry, it must be given a negative axial inclination angle and a negative radial inclination angle when installed in an insert seat within the tool body of a milling tool, meaning that the cutting insert must be tilted axially forward and radially outward within the tool body to obtain clearance. The negative axial inclination angle is necessary to create a clearance angle behind the active main cutting edge, and the negative radial inclination angle is necessary to create a clearance angle behind the active main cutting edge. As a result of the negative axial inclination angle, the cutting process is more difficult because the cutting insert is more difficult to cut compared to a corresponding cutting process performed with a cutting insert having a positive axial inclination angle. To counteract the adverse effects of the axial inclination angle, each main cutting edge may be given a downward inclination away from the adjacent corner cutting edge.

[0006] Object of the invention SUMMARY OF THE INVENTION It is an object of the present invention to provide a double-sided negative cutting insert of the type described above having a new and preferred design. Summary of the Invention

[0007] According to the present invention, the above-mentioned object is achieved by a double-sided negative cutting insert having the features defined in claim 1.

[0008] The double-sided negative cutting insert according to the present invention can be rotated to eight different machining positions, a first major surface and a second major surface disposed opposite each other on opposite sides of the cutting insert, the first and second major surfaces functioning one at a time as rake surfaces and configured to define a front surface and a rear surface of the cutting insert when mounted in an insert seat of the tool body, as viewed in an intended direction of rotation of the tool body, the cutting insert having a through hole extending through a center of the cutting insert between the first and second major surfaces and a first central surface extending midway between the first and second major surfaces perpendicular to a central axis of the through hole; extending around the cutting insert between the first and second major surfaces; a first major side surface and a second major side surface disposed opposite each other on opposite sides of the cutting insert, the cutting insert extending midway between the first major side surface and the second major side surface and including a central axis of the through hole; a third major side surface and a fourth major side surface disposed opposite each other on two opposite sides of the cutting insert, the cutting insert having a third central plane extending midway between the third major side surface and the fourth major side surface and including a central axis of the through hole; a first corner side disposed between the first major side and the fourth major side; a second corner side disposed between the first major side and the third major side; a third corner side disposed between the second major side and the third major side; a peripheral surface including a fourth corner side disposed between the second major side and the fourth major side; a curved first corner cutting edge formed at an intersection between the first corner side and the first main surface; a curved second corner cutting edge formed at an intersection between the second corner side and the first main surface; a curved third corner cutting edge formed at an intersection between the third corner side and the first main surface; a curved fourth corner cutting edge formed at an intersection between the fourth corner side and the first main surface; a curved fifth corner cutting edge formed at an intersection between the first corner side and the second major surface; a curved sixth corner cutting edge formed at an intersection between the second corner side and the second main surface; a curved seventh cutting edge formed at an intersection between the third cutting edge and the second main surface; and a curved eighth corner cutting edge formed at the intersection between the fourth corner side and the second major surface.

[0009] The first major side comprises a first side and a second side located on either side of the third central plane, the first side extending between the first and second major faces and adjacent to the first corner side, and the second side extending between the first and second major faces and adjacent to the second corner side. Similarly, the second major side comprises a third side and a fourth side located on either side of the third central plane, the third side extending between the first and second major faces and adjacent to the third corner side, and the fourth side extending between the first and second major faces and adjacent to the fourth corner side.

[0010] The third major side includes a fifth side and a sixth side located on either side of the second central plane, the fifth side extending between the first and second major faces and adjacent to the second corner side, and the sixth side extending between the first and second major faces and adjacent to the third corner side. Similarly, the fourth major side includes a seventh side and an eighth side located on either side of the second central plane, the seventh side extending between the first and second major faces and adjacent to the fourth corner side, and the eighth side extending between the first and second major faces and adjacent to the first corner side.

[0011] Due to the fact that the cutting insert is a negative cutting insert, the peripheral surface extends between the first and second main surfaces perpendicular to the above-mentioned first central plane, which means that each of the above-mentioned first, second, third, fourth, fifth, sixth, seventh and eighth side surfaces included in the peripheral surface are perpendicular to the first central plane.

[0012] The cutting insert according to the present invention comprises: a first major cutting edge formed at an intersection between the first side surface and the first major surface and a first minor cutting edge formed at an intersection between the eighth side surface and the first major surface, the first minor cutting edge, the first angular cutting edge, and the first major cutting edge forming a first cutting edge set and positioned in series with one another with the first angular cutting edge positioned between the first major cutting edge and the first minor cutting edge; a second major cutting edge formed at an intersection between the second side surface and the first major surface, and a second minor cutting edge formed at an intersection between the fifth side surface and the first major surface, wherein the second minor cutting edge, the second angular cutting edge, and the second major cutting edge form a second cutting edge set and are positioned in series with one another with the second angular cutting edge positioned between the second major cutting edge and the second minor cutting edge; a third major cutting edge formed at an intersection between the third side surface and the first major surface and a third minor cutting edge formed at an intersection between the sixth side surface and the first major surface, wherein the third minor cutting edge, the third angular cutting edge, and the third major cutting edge form a third cutting edge set and are positioned in series with one another with the third angular cutting edge positioned between the third major cutting edge and the third minor cutting edge; a fourth major cutting edge formed at an intersection between the fourth side surface and the first major surface and a fourth minor cutting edge formed at an intersection between the seventh side surface and the first major surface, wherein the fourth minor cutting edge, the fourth angular cutting edge, and the fourth major cutting edge form a fourth cutting edge set and are positioned in series with one another with the fourth angular cutting edge positioned between the fourth major cutting edge and the fourth minor cutting edge; a fifth major cutting edge formed at an intersection between the first side surface and the second major surface and a fifth minor cutting edge formed at an intersection between the eighth side surface and the second major surface, wherein the fifth minor cutting edge, the fifth angular cutting edge, and the fifth major cutting edge form a fifth cutting edge set and are positioned in series with one another with the fifth angular cutting edge positioned between the fifth major cutting edge and the fifth minor cutting edge; a sixth major cutting edge formed at an intersection between the second side surface and the second major surface and a sixth minor cutting edge formed at an intersection between the fifth side surface and the second major surface, wherein the sixth minor cutting edge, the sixth angular cutting edge, and the sixth major cutting edge form a sixth cutting edge set and are positioned in series with one another with the sixth angular cutting edge positioned between the sixth major cutting edge and the sixth minor cutting edge; a seventh major cutting edge formed at an intersection between the third side surface and the second major surface and a seventh minor cutting edge formed at an intersection between the sixth side surface and the second major surface, wherein the seventh minor cutting edge, the seventh angular cutting edge, and the seventh major cutting edge form a seventh cutting edge set and are positioned in series with each other with the seventh angular cutting edge positioned between the seventh major cutting edge and the seventh minor cutting edge; and an eighth major cutting edge formed at the intersection of the fourth side surface and the second major surface and an eighth minor cutting edge formed at the intersection between the seventh side surface and the second major surface, wherein the eighth minor cutting edge, the eighth angular cutting edge, and the eighth major cutting edge form an eighth cutting edge set and are positioned in series with one another with the eighth angular cutting edge positioned between the eighth major cutting edge and the eighth minor cutting edge.

[0013] Each of the major cutting edges has a first end facing the adjacent angular cutting edge and an opposite second end facing the third central plane, and each of the major cutting edges is inclined relative to the first central plane such that its first end is located farther from the first central plane than its second end. Thus, the major cutting edges in each set of edges have a downward inclination away from the adjacent angular cutting edge in the same set of edges, which counteracts the adverse effects of the axial inclination angle required for double-sided negative cutting inserts.

[0014] The first side surface is substantially planar and extends in a first plane, the second side surface is substantially planar and extends in a second plane, and the first and second side surfaces are inclined toward each other at the same angle relative to the second central plane, such that the first and second sides form an angle with each other that is greater than or equal to 90° and less than 180°. Similarly, the third side surface is substantially planar and extends in a third plane, and the fourth side surface is substantially planar and extends in a fourth plane, and the third and fourth side surfaces are inclined toward each other at the same angle relative to the second central plane, such that the third and fourth sides form an angle with each other that is equal to the angle formed with each other by the first and second sides.

[0015] The double-sided negative cutting insert of the present invention provides a large number of different machining positions and can be manufactured in a relatively simple and cost-effective manner. By appropriately inclining the first, second, third, and fourth flanks, taking into account the above-mentioned downward inclination of the main cutting edge, it is possible to achieve an incidence angle of 90°, or at least very close to 90°, at each machining position of the cutting insert.

[0016] When a double-sided negative cutting insert is installed in a seat with one of the major cutting edges in the active cutting position, the minor cutting edges in the same set of cutting edges are intended to be in the active surface-wiping position. Thus, the minor cutting edges are intended to function as surface-wiping edges in each of the cutting insert's eight machining positions. By having all eight major cutting edges located along the opposing first and second major faces and all eight minor cutting edges located along the opposing third and fourth major faces, the cutting edges in four of the available sets of eight cutting edges constitute right-hand cutting edges, and the cutting edges in the other four sets of cutting edges constitute left-hand cutting edges, with the different sets of cutting edges positioned on the cutting insert such that the one of the four sets of cutting edges with the right-hand cutting edges is always in the active cutting position when the cutting insert is installed in the right-hand insert seat, and the one with the left-hand cutting edges is always in the active cutting position when the cutting insert is installed in the left-hand insert seat. Thus, with this cutting insert, there is no risk of incorrectly installing the cutting insert in a left-hand seat with a set of right-hand cutting edges in the active cutting position, or in a right-hand seat with a set of left-hand cutting edges in the active cutting position. The cutting insert of the present invention is therefore suitable for use in milling tools for straddle milling of the type shown in Figure 5, and in both half side and face disc milling cutters of the type shown in Figure 7a.

[0017] The through hole extending between the first and second major surfaces is configured to receive a fastening element, for example in the form of a screw, by which the cutting insert can be removably secured to an insert seat in a tool body of a milling tool. At each machining position of the cutting insert, at least one surface of one of the first and second major surfaces serves as a tangential abutment surface of the cutting insert and is configured to abut a corresponding tangential support surface of the insert seat in the tool body, at least one surface of one of the first and second major side surfaces serves as a radial abutment surface of the cutting insert and is configured to abut a corresponding radial support surface of the insert seat, and at least one surface of one of the third and fourth major side surfaces serves as an axial abutment surface of the cutting insert and is configured to abut a corresponding axial support surface of the insert seat. The first and second angled side surfaces on the first major side surface are preferably configured to collectively function as radial abutment surfaces for the cutting insert in four of the eight possible machining positions of the cutting insert, and the third and fourth angled side surfaces on the second major side surface are configured to collectively function as radial abutment surfaces for the cutting insert in the other four machining positions of the cutting insert, although the first, second, third, and fourth side surfaces may alternatively be configured to function as radial abutment surfaces for the cutting insert one at a time in different machining positions of the cutting insert.

[0018] According to one embodiment of the present invention, each of the aforementioned major cutting edges has an inclination relative to the first central plane such that an imaginary straight reference line extending between a first end point of the major cutting edge at its first end and a second end point of the major cutting edge at its second end forms an angle of 1 to 30°, preferably 5 to 15°, with the first central plane. The angle must be at least 1° to have a positive inclination. Angles greater than 30° are less suitable and may attract axial cutting forces. However, the angle may be greater than 30° if necessary. The angle is preferably 5 to 15°. The effect is more pronounced when the angle is greater than 5°. Angles greater than 15° may result in significant shape errors during sintering of the cutting insert.

[0019] Another embodiment of the present invention is the first and second major cutting edges are mirror images of each other with respect to the third central plane; the third and fourth major cutting edges are mirror images of each other with respect to the third central plane; the fifth and sixth major cutting edges are mirror images of each other with respect to the third central plane; The seventh and eighth major cutting edges are characterized by being mirror images of each other with respect to the third central plane.

[0020] According to another embodiment of the present invention, the angle formed by the first and second planes with respect to each other is greater than or equal to 140° and less than 180°, preferably greater than or equal to 160° and less than 180°. When this angle is at least 140°, the cutting insert may be given a slim design. When this angle is at least 160°, the risk of chip wear on the inactive main cutting edge located above the active main cutting edge in the general machining position of the cutting insert is reduced.

[0021] Another embodiment of the present invention is each of said fifth, sixth, seventh, and eighth sides being substantially flat or convexly curved when viewed in any plane parallel to the first central plane and extending across the side under discussion; the fifth side surface has a first lateral edge adjacent to the second corner side surface and extending linearly from the first main surface to the second main surface parallel to the central axis of the through hole, and an opposite second lateral edge parallel to the first lateral edge and extending linearly from the first main surface to the second main surface; the sixth side surface is adjacent to the third corner side surface and has a first lateral edge extending linearly from the first main surface to the second main surface parallel to the central axis of the through hole, and an opposite second lateral edge parallel to the first lateral edge and extending linearly from the first main surface to the second main surface; the seventh side surface is adjacent to the fourth corner side surface and has a first lateral edge extending linearly from the first main surface to the second main surface parallel to the central axis of the through hole, and an opposite second lateral edge parallel to the first lateral edge and extending linearly from the first main surface to the second main surface; The eighth side surface is characterized in that the eighth side surface is adjacent to the first corner side surface and has a first lateral edge portion extending linearly from the first main surface to the second main surface parallel to the central axis of the through hole, and an opposite second lateral edge portion parallel to the first lateral edge portion and extending linearly from the first main surface to the second main surface.

[0022] Each of the fifth and sixth side surfaces may be adjacent, via its second lateral edge, to a respective adjacent surface on the third major side surface, which is convexly curved when viewed in any plane parallel to the first central plane. Similarly, each of the seventh and eighth side surfaces may be adjacent, via its second lateral edge, to a respective adjacent surface on the fourth major side surface, which is convexly curved when viewed in any plane parallel to the first central plane. Each of the aforementioned convexly curved surfaces on the third and fourth major sides preferably has a radius of curvature of 10 mm or less when viewed in a plane parallel to the first central plane. The appropriate radius of curvature of these convexly curved surfaces on the third and fourth major sides may additionally or alternatively be defined in relation to the radius of curvature of the corner side. In the latter case, each convexly curved surface adjacent to one of the fifth, sixth, seventh, and eighth side surfaces through the second lateral edge of the side under consideration preferably has a radius of curvature smaller than the radius of curvature of the adjacent corner side surface to which the side under consideration is adjacent through its first lateral edge. In this way, it is possible to provide an appropriate length for each of the minor cutting edges, and an appropriate radius of curvature for each of the angular cutting edges.

[0023] When the fifth, sixth, seventh, and eighth side surfaces are convexly curved, each of these side surfaces is preferably convexly curved with a radius of curvature of 30 to 1000 mm when viewed in any plane parallel to the first central plane and extending across the side surface under consideration. This allows for a good surface finish of the milled workpiece to be achieved. If the radius of curvature is less than 30 mm, the surface finish may be poor. If the radius of curvature is greater than 1000 mm, the large manufacturing tolerances of the insert seat and cutting insert may result in a poor surface finish of the milled workpiece. Preferably, the radius of curvature is 50 to 500 mm, more preferably 50 to 300 mm, when viewed in any plane parallel to the first central plane and extending across the side surface under consideration. Even with sintering errors, a more improved surface finish is achieved when the radius of curvature is 50 to 500 mm. When the radius of curvature is 50 to 300 mm, good performance is observed, and the milling tool is less prone to vibration.

[0024] Another embodiment of the present invention is The second side surface has an inclination relative to the fifth side surface such that the second plane forms an angle of 87 to 93 degrees with a fifth plane including the first and second lateral edges of the fifth side surface; the third side has an inclination relative to the sixth side such that said third plane includes the first and second lateral edges of the sixth side and forms an angle with said sixth plane equal to the angle said second plane forms with said fifth plane; the fourth side has an inclination relative to the seventh side such that said fourth plane includes the first and second lateral edges of the seventh side and forms an angle with said seventh plane equal to the angle said second plane forms with said fifth plane; The first side is characterized by an inclination relative to the eighth side such that said first plane includes first and second lateral edges of the eighth side and forms an angle with the eighth plane equal to the angle said second plane forms with said fifth plane.

[0025] When the aforementioned angle is 87 to 93 degrees, the insert seat can have a more advantageous inclination angle that can achieve an incident angle of 90 degrees or close to 90 degrees and at the same time obtain good cutting characteristics.

[0026] According to another embodiment of the present invention, the fifth and sixth side surfaces are inclined away from each other at the same angle relative to the third central plane, and the fifth and sixth planes form an angle with each other that is less than 180°. The seventh and eighth side surfaces are inclined away from each other at the same angle relative to the third central plane, and the seventh and eighth planes form an angle with each other that is equal to the angle formed by the fifth and sixth planes. When the cutting insert is positioned in a machining position within an insert seat in the tool body with one of the minor cutting edges in the active surface wiping position, the inactive minor cutting edge, adjacent to the active minor cutting edge and on the same major surface as the active minor cutting edge, moves closely above the machined workpiece surface leveled by the active minor cutting edge. To prevent small pieces of workpiece material from getting stuck between the inactive minor cutting edge and the workpiece surface, thereby exposing the inactive minor cutting edge to minor damage, there must be an appropriate clearance between the inactive minor cutting edge and the workpiece surface. This clearance is improved by the aforementioned mutual inclination between the fifth and sixth sides and between the seventh and eighth sides, respectively, which reduces the risk of damage to the aforementioned inactive secondary cutting edges.

[0027] Preferably, the first and second major side surfaces have 180° rotational symmetry about a first imaginary reference axis extending along the line of intersection between the first central surface and the third central surface. In this context, each of the first and second major side surfaces is considered to have 180° rotational symmetry about the first imaginary reference axis even if one or more small markings, for example in the form of recesses, are provided on either of these major side surfaces that lack 180° rotational symmetry about the first imaginary reference axis, provided that the small markings are not related to the function of the cutting insert.

[0028] Preferably, each of the third and fourth major side surfaces has 180° rotational symmetry about a second imaginary reference axis extending along the intersection line between the first and second central surfaces. In this context, each of the third and fourth major side surfaces is considered to have 180° rotational symmetry about the second imaginary reference axis even if one or more small markings, for example in the form of recesses, are provided on either of these major side surfaces that lack 180° rotational symmetry about the second imaginary reference axis, provided that the small markings are not related to the function of the cutting insert.

[0029] Preferably, each of the first and second major surfaces has 180° rotational symmetry about the central axis of the through hole. In this context, each of the first and second major surfaces is considered to have 180° rotational symmetry about the central axis of the through hole even if one or more small markings, for example in the form of recesses, are provided on either of these major surfaces that lack 180° rotational symmetry about the central axis of the through hole, provided that the small markings are not related to the function of the cutting insert.

[0030] Preferably, the first and second major surfaces are mirror images of each other with respect to the first central plane. In this context, the first and second major surfaces are considered to be mirror images of each other with respect to the first central plane, even if one or more small markings, for example in the form of recesses, are present on either of these major surfaces that are not mirror images of the first central plane, provided that the small markings are not related to the function of the cutting insert.

[0031] Another embodiment of the present invention is the first major surface comprises a substantially flat first tangential abutment surface, and the first, second, third, and fourth angular cutting edges are all located farther from the first central surface than the first tangential abutment surface; The second major surface has a substantially flat second tangential abutment surface, and the fifth, sixth, seventh, and eighth angular cutting edges are all located farther from the first central surface than the second tangential abutment surface.

[0032] The first tangential abutment surface on the first main surface serves as the tangential abutment surface of the cutting insert and is configured to abut against corresponding tangential support surfaces of the insert seat in the tool body in four of the eight possible machining positions of the cutting insert, and the second tangential abutment surface on the second main surface serves as the tangential abutment surface of the cutting insert and is configured to abut against corresponding tangential support surfaces of the insert seat in the tool body in the other four machining positions of the cutting insert.

[0033] Another embodiment of the present invention is the first, second, third, and fourth major cutting edges and the first, second, third, and fourth minor cutting edges are all located farther from the first central plane than the first tangential abutment surface; The fifth, sixth, seventh, and eighth major cutting edges and the fifth, sixth, seventh, and eighth minor cutting edges are also all characterized by being located farther from the first central plane than the second tangential abutment surface.

[0034] Another embodiment of the present invention is The fifth and sixth sides are separated from each other by a first groove provided in the third major side surface between the fifth and sixth sides, this first groove extending from the first major surface to the second major surface, and the seventh and eighth sides are separated from each other by a second groove provided in the fourth major side surface between the seventh and eighth sides, this second groove extending from the first major surface to the second major surface.

[0035] Therefore, the first groove forms a gap between the fifth and sixth sides on the third major side surface, thereby forming a gap between the second and third minor cutting edges and between the sixth and seventh minor cutting edges, while the second groove forms a gap between the seventh and eighth sides on the fourth major side surface, thereby forming a gap between the fourth and first minor cutting edges and between the eighth and fifth minor cutting edges. This allows the minor cutting edges to be given a length that is optimal for the application.

[0036] According to another embodiment of the present invention, each of the first and second grooves has a substantially flat bottom surface parallel to the third central plane and configured to function as an axial abutment surface for the cutting insert in four of the aforementioned eight possible machining positions of the cutting insert and to abut against a corresponding axial support surface of the insert seat in the tool body when the cutting insert is mounted in the seat in any of these four machining positions. Thus, the bottom surface of the first groove functions as an axial abutment surface for the cutting insert and is configured to abut against a corresponding axial support surface in the insert seat in the tool body in four of the eight possible machining positions of the cutting insert, and the bottom surface of the second groove functions as an axial abutment surface for the cutting insert and is configured to abut against a corresponding axial support surface of the insert seat in the tool body in the other four machining positions of the cutting insert.

[0037] Another embodiment of the present invention is the first and second sides are separated from one another by a first transition region on the first major side, the first transition region extending between the first major surface and the second major surface; The third side and the fourth side are separated from one another by a second transition region on the second major side, the second transition region extending between the first major surface and the second major surface.

[0038] Thus, the first transition region forms a space between the first and second side faces on the first major side face, thereby forming a space between the first and second major cutting edges and between the fifth and sixth major cutting edges, while the second transition region forms a space between the third and fourth side faces on the second major side face, thereby forming a space between the third and fourth major cutting edges and between the seventh and eighth major cutting edges. This makes the cutting insert stronger because the presence of the first and second transition regions reduces stresses generated during use of the cutting insert. Each of the first and second transition regions is preferably concavely curved when viewed in any plane parallel to the first central plane and extending across the transition region under discussion.

[0039] Further advantageous features of the double-sided negative cutting insert according to the present invention will become apparent from the following description.

[0040] The invention also relates to a milling tool comprising at least one double-sided negative cutting insert of the type described above, the milling tool preferably being a half-side and back disc milling cutter, a half-side and front disc milling cutter or a double half-side and front disc milling cutter.

[0041] Further advantageous features of the milling tool according to the invention will become apparent from the following description.

[0042] Embodiments of the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0043] [Figure 1a] 1A-1C are perspective views of a double-sided negative cutting insert according to an embodiment of the present invention, from different directions. [Figure 1b] 1A-1C are perspective views of a double-sided negative cutting insert according to an embodiment of the present invention, from different directions. [Figure 1c] FIG. 2 is a plan view from above of the cutting insert of FIGS. 1a and 1b. [Figure 1d] FIG. 2 is a plan view from below of the cutting insert of FIGS. 1a and 1b. [Figure 1e] FIG. 2 is a side view of the cutting insert of FIGS. 1a and 1b, viewed from a first side. [Figure 1f] 1a and 1b, viewed from a second, opposite side; FIG. [Figure 1g] FIG. 2 is a front view of the cutting insert of FIGS. 1a and 1b. [Figure 1h] FIG. 2 is a rear view of the cutting insert of FIGS. 1a and 1b. [Figure 2] FIG. 10 is a perspective view of a double-sided negative cutting insert according to an alternative embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view of a double-sided negative cutting insert according to another alternative embodiment of the present invention. [Figure 4a] 1a to 1h show different perspective views of a milling tool in the form of a half side and front disc milling cutter with a right-hand insert seat and cutting insert according to the embodiment shown in FIGS. 1a to 1h. [Figure 4b] 1a to 1h show different perspective views of a milling tool in the form of a half side and front disc milling cutter with a right-hand insert seat and cutting insert according to the embodiment shown in FIGS. 1a to 1h. [Figure 4c] FIG. 4c is a side view of the milling tool of FIGS. 4a and 4b. [Figure 4d] FIG. 4c is a plan view of the milling tool of FIGS. 4a and 4b. [Figure 4e] 4e is an enlarged detail view of rectangle IVe of FIG. 4b, in which the cutting insert is seen removed from its insert seat in the tool body of the milling tool. [Figure 4f] FIG. 4c is a detailed enlargement of rectangle IVf. [Figure 5] 6a-6e are schematic side views of a half side and front disc milling cutter of the type shown in FIGS. 4a-4f and a half side and front disc milling cutter of the type shown in FIGS. 6a-6e mounted on the same arbor; [Figure 6a] 1a to 1h show different perspective views of a milling tool in the form of a half side and front disc milling cutter with a left-hand insert seat and cutting insert according to the embodiment shown in FIGS. 1a to 1h. [Figure 6b] 1a to 1h show different perspective views of a milling tool in the form of a half side and front disc milling cutter with a left-hand insert seat and cutting insert according to the embodiment shown in FIGS. 1a to 1h. [Figure 6c] FIG. 6c is a side view of the milling tool of FIGS. 6a and 6b. [Figure 6d] 6b , showing the cutting insert removed from its seat in the tool body of the milling tool; FIG. [Figure 6e] FIG. 6c is a detailed enlargement of rectangle VIe. [Figure 7a] 1a to 1h show different perspective views of a milling tool in the form of a double half side and face disc milling cutter provided with cutting inserts according to the embodiment shown in FIGS. 1a to 1h; [Figure 7b] 1a to 1h show different perspective views of a milling tool in the form of a double half side and front disc milling cutter provided with cutting inserts according to the embodiment shown in FIGS. 1a to 1h; [Figure 7c] FIG. 7c is an enlarged detail view of rectangle VIIc of FIG. 7a, in which the cutting insert is seen removed from its insert seat in the tool body of the milling tool. [Figure 7d] FIG. 7b is an enlarged detail view of rectangle VIId in FIG. 7b, in which the cutting insert is seen removed from its insert seat in the tool body of the milling tool. DETAILED DESCRIPTION OF THE INVENTION

[0044] An embodiment of a double-sided negative cutting insert 1 according to the present invention is shown in Figures 1a-1h. The cutting insert 1 is configured for use in milling and is adapted for use in a milling tool, for example a milling tool of any of the types shown in Figures 4a-4f, 6a-6e, and 7a-7d.

[0045] The cutting insert 1 has an essentially rectangular basic shape and is rotatable into eight different machining positions. The cutting insert 1 comprises a first major surface 2 and a second major surface 3 arranged opposite each other on either side of the cutting insert. The two major surfaces 2, 3 are configured to function as rake surfaces, one at a time, and are configured to constitute the front and rear surfaces of the cutting insert when the cutting insert 1 is mounted in its insert seat 34, 34' in the tool body 31, as viewed in the intended direction of rotation R of the tool body. Thus, the cutting insert 1 is configured to be mounted in its insert seat 34, 34' in the tool body 31 with one of the two major surfaces 2, 3 facing forward in the intended direction of rotation R of the tool body and functioning as a rake surface, and the other major surface facing rearward in the intended direction of rotation R of the tool body.

[0046] The cutting insert 1 is provided with a through hole 5 extending centrally through the cutting insert between the first and second major surfaces 2 and 3, i.e., from the first to the second major surface 3. The through hole 5 is configured to receive a fastening element 6, for example in the form of a screw, by which the cutting insert can be removably fixed to an insert seat 34, 34' of a milling tool. The through hole 5 has a central axis C that coincides with the central axis of the cutting insert 1. A first central plane MP1 (FIGS. 1e-1h) constituting an imaginary plane extends perpendicular to the central axis C of the through hole 5 partway between the first and second major surfaces 2 and 3.

[0047] The peripheral surface 10 extends around the cutting insert 1 between the first main surface 2 and the second main surface 3, perpendicular to the first central plane MP1. The peripheral surface 10 includes four major side surfaces 11a-11d and four corner side surfaces 12a-12d, with each corner side surface 12a-12d located between two adjacent major side surfaces 11a-11d. The major side surfaces include a first major side surface 11a and a second major side surface 11b, which are disposed opposite each other on two opposing sides of the cutting insert 1. The major side surfaces further include a third major side surface 11c and a fourth major side surface 11d, which are disposed opposite each other on two other opposing sides of the cutting insert. Thus, the first and second major side surfaces 11a, 11b are located opposite each other on both sides of the through hole 5. Similarly, the third and fourth major side surfaces 11c, 11d are located opposite each other on both sides of the through hole 5. In the illustrated embodiment, the first and second major sides 11a, 11b are identical to one another within manufacturing tolerances. In the illustrated embodiment, the third and fourth major sides 11c, 11d are identical to one another within manufacturing tolerances.

[0048] The second mid-plane MP2, which constitutes an imaginary plane, extends partway between the first major side surface 11a and the second major side surface 11b and includes the central axis C of the through hole 5. The third mid-plane MP3, which also constitutes an imaginary plane, extends partway between the third major side surface 11c and the fourth major side surface 11d and includes the central axis C of the through hole 5. The second and third mid-planes MP2 and MP3 extend perpendicular to each other and intersect each other along the central axis C of the through hole 5. Each of the first and second major side surfaces 11a, 11b has 180° rotational symmetry about a first imaginary reference axis A1 (see Figures 1e and 1f) extending along the line of intersection between the first and third central planes MP1, MP3, and each of the third and fourth major side surfaces 11c, 11d has 180° rotational symmetry about a second imaginary reference axis A2 (see Figures 1g and 1h) extending along the line of intersection between the first and second central planes MP1, MP2.

[0049] The corner side is a first corner side 12a disposed between the first major side 11a and the fourth major side 11d; a second corner side surface 12b disposed between the first major side surface 11a and the third major side surface 11c; a third corner side surface 12c disposed between the second major side surface 11b and the third major side surface 11c; and a fourth corner side surface 12d disposed between the second major side surface 11b and the fourth major side surface 11d.

[0050] Each of the corner sides 12a-12d is convexly curved as seen in a cross section of the cutting insert 1 along the first central plane MP1 and as seen in any plane parallel to the first central plane MP1 and extending across the corner side under discussion.

[0051] The first major side surface 11a includes a first side surface 14a and a second side surface 14b located on either side of a third central plane MP3, with the first side surface 14a extending from the first major surface 2 to the second major surface 3 and adjacent to the first corner side surface 12a, and the second side surface 14b extending from the first major surface 2 to the second major surface 3 and adjacent to the second corner side surface 12b. Similarly, the second major side surface 11b includes a third side surface 14c and a fourth side surface 14d located on either side of the third central plane MP3, with the third side surface 14c extending from the first major surface 2 to the second major surface 3 and adjacent to the third corner side surface 12c, and the fourth side surface 14d extending from the first major surface 2 to the second major surface 3 and adjacent to the fourth corner side surface 12d. In the illustrated embodiment, the first and second side surfaces 14a, 14b are separated from one another by a first transition region 15a on the first major side surface 11a, and the third and fourth side surfaces 14c, 14d are separated from one another by a second transition region 15b on the second major side surface 11b, with each of the first and second transition regions 15a, 15b extending from the first major surface 2 to the second major surface 3. Each of the first and second transition regions 15a, 15b is preferably convex when viewed in a cross-section of the cutting insert 1 along the first mid-plane MP1 and when viewed in any plane parallel to the first mid-plane MP1 and extending across the transition regions 15a, 15b. Each of the first, second, third and fourth side surfaces 14a to 14d has a first lateral edge 16a adjacent to the adjacent corner side surface 12a to 12d and extending linearly from the first main surface 2 to the second main surface 3 parallel to the central axis C of the through hole 5, and an opposite second lateral edge 16b adjacent to the adjacent transition region 15a, 15b and extending linearly from the first main surface 2 to the second main surface 3 parallel to the aforementioned first lateral edge 16a.

[0052] The first side surface 14a is substantially flat and extends within a first plane P1 (see FIG. 1c), the second side surface 14b is substantially flat and extends within a second plane P2, the third side surface 14c is substantially flat and extends within a third plane P3, and the fourth side surface 14d is substantially flat and extends within a fourth plane P4. The first and second side surfaces 14a, 14b are inclined toward each other at the same angle relative to the second central plane MP2, meaning that the angle formed between the first plane P1 and the second central plane MP2 is equal to the angle formed between the second plane P2 and the second central plane MP2. Furthermore, the first and second side surfaces 14a, 14b are inclined toward each other such that the first and second planes P1, P2 form an angle γ between each other that is greater than or equal to 90° and less than 180° (i.e., 90°≦γ<180°). The third and fourth side surfaces 14c, 14d are inclined toward each other at the same angle relative to the second central plane MP2, meaning that the angle formed between the third plane P3 and the second central plane MP2 is equal to the angle formed between the fourth plane P4 and the second central plane MP2. Furthermore, the third and fourth side surfaces 14c, 14d are inclined toward each other such that the third and fourth planes P3, P4 form an angle γ with each other that is equal to the angle γ formed by the first and second planes P1, P2 with each other. Therefore, the first lateral edge 16a of each of the first, second, third, and fourth side surfaces 14a-14d is located farther from the second central plane MP2 than the second lateral edge 16b of the same side surface. This means that the perpendicular distance between the second central plane MP2 and the second lateral edge 16b of any of the first, second, third, and fourth side surfaces 14a-14d is shorter than the perpendicular distance between the second central plane MP2 and the first lateral edge 16a of the same side surface. The angle γ formed by the first and second planes P1 and P2 is advantageously greater than or equal to 140° and less than 180° (i.e., 140°≦γ<180°), and preferably greater than or equal to 160° and less than 180° (i.e., 160°≦γ<180°). In the illustrated embodiment, the angle γ is 175.4°.

[0053] The first and second side surfaces 14a, 14b are preferably configured to jointly function as radial abutment surfaces for the cutting insert 1 in four of the eight possible machining positions of the cutting insert 1, and the third and fourth side surfaces 14c, 14d are configured to jointly function as radial abutment surfaces for the cutting insert in the other four machining positions of the cutting insert 1. However, the first, second, third and fourth side surfaces 14a-14d may alternatively be configured to function as radial abutment surfaces for the cutting insert 1 in different machining positions of the cutting insert 1, one at a time.

[0054] The third major side surface 11c has a fifth side surface 14e and a sixth side surface 14f located on either side of the second central plane MP2, the fifth side surface extending from the first major surface 2 to the second major surface 3 and adjacent to the second corner side surface 12b, and the sixth side surface 14f extending from the first major surface 2 to the second major surface 3 and adjacent to the third corner side surface 12c. Similarly, the fourth major side surface 11d has a seventh side surface 14g and an eighth side surface 14h located on either side of the second central plane MP2, the seventh side surface 14g extending from the first major surface 2 to the second major surface 3 and adjacent to the fourth corner side surface 12d, and the eighth side surface 14h extending from the first major surface 2 to the second major surface 3 and adjacent to the first corner side surface 12a. In the illustrated embodiment, the fifth and sixth sides 14e, 14f are separated from each other by a first groove 17a provided in the third major side 11c between the fifth side 14e and the sixth side 14f, the seventh and eighth sides 14g, 14h are separated from each other by a second groove 17b provided in the fourth major side 11d between the seventh side 14g and the eighth side 14h, and each of the first and second grooves 17a, 17b extends from the first major surface 2 to the second major surface 3.

[0055] In the illustrated embodiment, each of the first and second grooves 17a, 17b is parallel to the third central plane MP3 and has a substantially flat bottom surface 18 configured to serve as an axial abutment surface for the cutting insert 1 in four of the aforementioned eight machining positions of the cutting insert 1 and to abut against a corresponding axial support surface 38 of the insert seat 34, 34′ of the tool body 31 when the cutting insert 1 is mounted in the insert seat in any of these four machining positions. Thus, the bottom surface 18 of the first groove 17a is configured to serve as an axial abutment surface for the cutting insert 1 in four of the eight possible machining positions of the cutting insert 1, and the bottom surface 18 of the second groove 17b is configured to serve as an axial abutment surface for the cutting insert 1 in the other four machining positions of the cutting insert 1.

[0056] Each of the fifth, sixth, seventh and eighth side surfaces 14e-14h is preferably substantially flat. However, each of the fifth, sixth, seventh and eighth side surfaces 14e-14h may alternatively be convexly curved with a radius of curvature of 30-1000 mm, preferably 50-500 mm, more preferably 50-300 mm, as viewed in a cross-section of the cutting insert 1 along the first mid-plane MP1 and in any plane parallel to the first mid-plane MP1 and extending across the side surface under discussion. Each of the fifth, sixth, seventh and eighth side surfaces 14e to 14h is adjacent to the adjacent corner side surfaces 12a to 12d and has a first lateral edge 19a extending linearly from the first main surface 2 to the second main surface 3 parallel to the central axis C of the through hole 5, and an opposite second lateral edge 19b extending linearly from the first main surface 2 to the second main surface 3 parallel to the aforementioned first lateral edge 19a. In the illustrated embodiment, each of the fifth and sixth side surfaces 14e, 14f adjoins, via its second lateral edge 19b, an adjacent surface 20 on the convexly curved third major side surface 11c, as viewed in any plane parallel to the first central plane MP1, and each of the seventh and eighth side surfaces 14g, 14h adjoins, via its second lateral edge 19b, an adjacent surface 20 on the convexly curved fourth major side surface 11d, as viewed in any plane parallel to the first central plane MP1. Each of these convexly curved surfaces 20 on the third and fourth major side surfaces 11c, 11d preferably has a radius of curvature of 10 mm or less, as viewed in any plane parallel to the first central plane MP1. The appropriate radius of curvature of these convexly curved surfaces 20 on the third and fourth major side surfaces 11c, 11d may alternatively be defined in terms of the radii of curvature of the corner sides 12a-12d. In the latter case, each of the convexly curved surfaces 20 adjacent to one of the fifth, sixth, seventh and eighth side surfaces via the second lateral edge 19b of the side surface under consideration preferably has a radius of curvature smaller than the radius of curvature of the adjacent corner side surface 12a-12d to which the side surface under consideration is adjacent via its first lateral edge 19a.

[0057] The second side surface 14b preferably has an inclination relative to the fifth side surface 14e such that the aforementioned second plane P2 forms an angle α of 87 to 93° with a fifth plane P5 (see FIG. 1c) that includes the first and second lateral edges 19a, 19b of the fifth side surface 14e; the third side surface 14c has an inclination relative to the sixth side surface 14f such that said third plane P3 includes the first and second lateral edges 19a, 19b of the sixth side surface 14f and forms an angle α with the sixth plane P6 that is equal to the angle α that the second plane P2 forms with the fifth plane P5; the fourth side surface 14d has an inclination relative to the seventh side surface 14g such that said fourth plane P4 includes the first and second lateral edges 19a, 19b of the seventh side surface 14g and forms an angle α with the seventh plane P7 that is equal to the angle α that the second plane P2 forms with the fifth plane P5; The first side 14a has an inclination relative to the eighth side 14h such that the aforementioned first plane P1 includes the first and second lateral edges 19a, 19b of the eighth side 14h and forms an angle α with the eighth plane P8 that is equal to the angle α that the second plane P2 forms with the fifth plane P5.

[0058] In the illustrated embodiment, the aforementioned angle α is 90.7°.

[0059] The fifth and sixth side surfaces 14e, 14f are preferably inclined outwardly relative to the third central plane MP3 such that the fifth and sixth planes P5, P6 form an angle β of less than 180° with respect to the third central plane MP3. The seventh and eighth side surfaces 14g, 14h are also inclined outwardly relative to the third central plane MP3 such that the seventh and eighth planes P7, P8 form an angle β equal to the angle β formed by the fifth and sixth planes P5, P6. Therefore, the angle formed between the fifth plane P5 and the third central plane MP3 is equal to the angle formed between the sixth plane P6 and the third central plane MP3, and the angle formed between the seventh plane P7 and the third central plane MP3 is equal to the angle formed between the eighth plane P8 and the third central plane MP3. In the illustrated embodiment, the angle β is 174°.

[0060] The cutting insert 1 is a first main cutting edge 21a formed at the intersection between the first side surface 14a and the first main surface 2; a second main cutting edge 21b formed at the intersection between the second side surface 14b and the first main surface 2; a third main cutting edge 21c formed at an intersection between the third side surface 14c and the first main surface 2; a fourth main cutting edge 21d formed at an intersection between the fourth side surface 14d and the first main surface 2; a fifth main cutting edge 21e formed at the intersection between the first side surface 14a and the second main surface 3; a sixth main cutting edge 21f formed at an intersection between the second side surface 14b and the second main surface 3; a seventh main cutting edge 21g formed at an intersection between the third side surface 14c and the second main surface 3; an eighth main cutting edge 21h formed at an intersection between the fourth side surface 14d and the second main surface 3; a first minor cutting edge 22a formed at an intersection between the eighth side surface 14h and the first main surface 2; a second minor cutting edge 22b formed at an intersection between the fifth side surface 14e and the first main surface 2; a third minor cutting edge 22c formed at an intersection between the sixth side surface 14f and the first main surface 2; a fourth minor cutting edge 22d formed at an intersection between the seventh side surface 14g and the first main surface 2; a fifth minor cutting edge 22e formed at an intersection between the eighth side surface 14h and the second main surface 3; a sixth minor cutting edge 22f formed at an intersection between the fifth side surface 14e and the second main surface 3; a seventh minor cutting edge 22g formed at an intersection between the sixth side surface 14f and the second main surface 3; an eighth minor cutting edge 22h formed at an intersection between the seventh side surface 14g and the second main surface 3; a curved first corner cutting edge 23a formed at the intersection between the first corner side surface 12a and the first main surface 2; a curved second corner cutting edge 23b formed at the intersection between the second corner side surface 12b and the first main surface 2; a curved third corner cutting edge 23c formed at the intersection between the third corner side surface 12c and the first main surface 2; a curved fourth corner cutting edge 23d formed at the intersection between the fourth corner side surface 12d and the first main surface 2; a curved fifth corner cutting edge 23e formed at the intersection between the first corner side surface 12a and the second main surface 3; a curved sixth corner cutting edge 23f formed at the intersection between the second corner side surface 12b and the second main surface 3; a curved seventh corner cutting edge 23g formed at the intersection between the third corner side surface 12c and the second main surface 3; The cutting edge has a curved eighth corner edge 23h formed at the intersection between the fourth corner side surface 12d and the second main surface 3.

[0061] Each of the major cutting edges 21a-21h preferably extends entirely along the lateral surface 14a-14d associated with the major cutting edge under consideration.

[0062] The first major cutting edge 21a, the first angular cutting edge 23a, and the first minor cutting edge 22a form a first set of cutting edges, and are arranged in series with one another, with the first angular cutting edge 23a located between the first major cutting edge 21a and the first minor cutting edge 22a. The second major cutting edge 21b, the second angular cutting edge 23b, and the second minor cutting edge 22b form a second set of cutting edges, and are arranged in series with the second angular cutting edge 23b located between the second major cutting edge 21b and the second minor cutting edge 22b. The third major cutting edge 21c, the third angular cutting edge 23c, and the third minor cutting edge 22c form a third set of cutting edges, and are arranged in series with the third angular cutting edge 23c located between the third major cutting edge 21c and the third minor cutting edge 22c. The fourth major cutting edge 21d, the fourth angular cutting edge 23d, and the fourth minor cutting edge 22d form a fourth set of cutting edges, and are arranged in series with the fourth angular cutting edge 23d located between the fourth major cutting edge 21d and the fourth minor cutting edge 22d. The fifth major cutting edge 21e, the fifth angular cutting edge 23e, and the fifth minor cutting edge 22e form a fifth set of cutting edges, and are arranged in series with the fifth angular cutting edge 23e located between the fifth major cutting edge 21e and the fifth minor cutting edge 22e. The sixth major cutting edge 21f, the sixth angular cutting edge 23f, and the sixth minor cutting edge 22f form a sixth set of cutting edges, and are arranged in series with the sixth angular cutting edge 23f located between the sixth major cutting edge 21f and the sixth minor cutting edge 22f. The seventh major cutting edge 21g, the seventh angular cutting edge 23a, and the seventh minor cutting edge 22g form a seventh set of cutting edges, which are arranged in series with one another, with the seventh angular cutting edge 23g located between the seventh major cutting edge 21g and the seventh minor cutting edge 22g. The eighth major cutting edge 21h, the eighth angular cutting edge 23h, and the eighth minor cutting edge 22h form an eighth set of cutting edges, which are arranged in series with the eighth angular cutting edge 23h located between the eighth major cutting edge 21h and the eighth minor cutting edge 22h. The first, second, third, fourth, fifth, sixth, seventh, and eighth sets of cutting edges are configured to be in active cutting positions at each of the eight machining positions of the cutting insert 1.In the illustrated embodiment, cutting edges 21a, 22a, 23a, 21c, 22c, 23c, 21f, 22f, 23f, 21h, 22h, 23h in the first, third, sixth, and eighth sets of cutting edges constitute right-side cutting edges, meaning that any one of the cutting edges in these four sets of cutting edges is in an active cutting position when the cutting insert 1 is installed in the right-side insert seat. Furthermore, in the illustrated embodiment, cutting edges 21b, 22b, 23b, 21d, 22d, 23d, 21e, 22e, 23e, 21g, 22g, 23g in the second, fourth, fifth, and seventh sets of cutting edges constitute left-side cutting edges, meaning that any one of the cutting edges in these four sets of cutting edges is in an active cutting position when the cutting insert 1 is installed in the left-side insert seat.

[0063] Each of the major cutting edges 21a-21h has a first end 25a facing the adjacent cutting edge 23a-23h and an opposite second end 25b facing the third central plane MP3, and each of the major cutting edges 21a-21h is inclined with respect to the first central plane MP1 so that its first end 25a is located farther from the first central plane MP1 than its second end 25b. Therefore, the vertical distance between the first central plane MP1 and the second end 25b of each of the major cutting edges 21a-21h is shorter than the vertical distance between the first central plane MP1 and the first end 25a of the same major cutting edge. Each of the major cutting edges 21a-21h suitably has an inclination relative to the first central plane MP1 such that an imaginary straight reference line RL (see FIG. 1e) extending between a first endpoint EP1 of the major cutting edge at its first end 25a and a second endpoint EP2 of the major cutting edge at its second end 25b forms an angle λ of 1 to 30°, preferably 5 to 15°, with the first central plane MP1. In the illustrated embodiment, said angle λ is 8°.

[0064] The first main surface 2 comprises a first tangential abutment surface 7a configured to serve as a tangential abutment surface for the cutting insert 1 in four of the eight machining positions of the cutting insert 1 and to abut against a corresponding tangential support surface 36 in the insert seat 34, 34' of the tool body 31 of the milling tool when the cutting insert 1 is mounted in the insert seat in one of these four machining positions. The second main surface 3 comprises a second tangential abutment surface 7b configured to serve as a tangential abutment surface for the cutting insert 1 in the other four machining positions of the cutting insert 1 and to abut against a corresponding tangential support surface 36 in the insert seat 34, 34' of the tool body 31 of the milling tool when the cutting insert 1 is mounted in the insert seat in one of these four machining positions. In the illustrated embodiment, the first tangential abutment surface 7a is flat or at least substantially flat and extends in a plane PL1 (see FIG. 1g) parallel to the first central plane MP1, and the second tangential abutment surface 7b is also flat or at least substantially flat and extends in another plane PL2 parallel to the first central plane MP1. In the illustrated embodiment, cutting edges 21a-21d, 22a-22d, 23a-23d included in the above-mentioned first, second, third, and fourth sets of cutting edges are all located farther from the first central plane MP1 than the first tangential abutment surface 7a, and as a result, when the cutting insert 1 is positioned with the first main surface 2 facing upward, they are located at a higher height than the first tangential abutment surface 7a, and cutting edges 21e-21h, 22e-22h, 23e-23h included in the above-mentioned fifth, sixth, seventh, and eighth sets of cutting edges are all located farther from the first central plane MP1 than the second tangential abutment surface 7b, and as a result, when the cutting insert 1 is positioned with the second main surface 3 facing upward, they are located at a higher height than the second tangential abutment surface 7b.

[0065] The cutting insert 1 according to the present invention can be designed with corner side surfaces 12a-12d having various radii of curvature. As shown in FIG. 2, the cutting insert 1 can have corner side surfaces 12a-12d with a smaller radius of curvature than the corner side surfaces 12a-12d of the cutting insert shown in FIGS. 1a-1h. As shown in FIG. 3, the cutting insert 1 can have corner side surfaces 12a-12d with a larger radius of curvature than the corner side surfaces 12a-12d of the cutting insert shown in FIGS. 1a-1h. In the rest, the cutting insert 1 shown in FIGS. 2 and 3 has a design corresponding to the cutting insert 1 described above with reference to FIGS. 1a-1h.

[0066] In the illustrated embodiment, the first major surface 2 is provided with markings in the form of the numerals 1 and 2, and the second major surface 3 is provided with markings in the form of the numerals 3 and 4. The markings facilitate identification of eight different machining positions of the cutting insert 1. Except for the markings, the first and second major surfaces 2, 3 are identical to one another within manufacturing tolerances. Furthermore, excluding the markings, each of the first and second major surfaces 2, 3 has 180° rotational symmetry about the central axis C of the through hole 5. Furthermore, in the illustrated embodiment, the first and second major surfaces 2, 3 are mirror images of one another with respect to the first central plane MP1, excluding the markings.

[0067] Preferably, the cutting insert 1 is mirror symmetrical with respect to at least one of the first, second, and third central planes MP1, MP2, MP3, excluding the above-mentioned markings. More preferably, the cutting insert 1 is mirror symmetrical with respect to any two of the first, second, and third central planes MP1, MP2, MP3, excluding the above-mentioned markings. Most preferably, the cutting insert 1 is mirror symmetrical with respect to all three central planes MP1, MP2, MP3, excluding the above-mentioned markings, as shown in Figures 1a to 1h, 2, and 3.

[0068] Figures 4a to 4f show a milling tool 30 in the form of a half side and front disc milling cutter having a right-hand insert seat 34, Figures 6a to 6e show a milling tool 30' in the form of a half side and front disc milling cutter having a left-hand insert seat 34', and Figures 7a to 7d show a milling tool 30" in the form of both a half side and front disc milling cutter having a right-hand insert seat 34 and a left-hand insert seat 34'. Each milling tool 30, 30', 30" comprises a tool body 31 and is arranged to rotate about an axis of rotation 32. The tool body 31 has a rear end 31a and an opposite front end 31b. The tool body 31 has a central axis 33 extending between a rear end 31a and a front end 31b of the tool body, the central axis 33 coinciding with the rotation axis 32 of the milling tool 30, 30', 30". The front end 31b is provided with a front face 31c of the tool body 31. The tool body 31 also has a peripheral surface 31d. The tool body 31 is mounted, for example via a tool holder, to a rotating spindle of a milling machine or the like. The tool body 31 has an insert 1 configured to receive the cutting insert 1. Each insert seat 34, 34' is provided in the tool body 31. A chip pocket 39 is provided in the tool body 31 forward of each insert seat 34, 34', as viewed in the intended direction of rotation R of the tool body 31. The insert seats 34, 34' may be formed directly in the tool body 31, as shown in Figures 4a-4f, 6a-6e and 7a-7d. However, each insert seat may alternatively be formed in a separate cassette, which cassette is removably attached to the tool body.

[0069] 4a to 4f and 6a to 6e, the tool body 31 is provided with ten insert seats 34, 34' evenly distributed around the longitudinal axis 33 of the tool body and configured to receive respective cutting inserts 1. However, the tool body 31 may alternatively be provided with any other suitable number of insert seats 34, 34', in particular depending on the diameter of the tool body. Each insert seat 34, 34' of the milling tools 30, 30' shown in Figures 4a to 4f and 6a to 6e is located at the transition between the front surface 31c and the peripheral surface 31d of the tool body 31, and the insert seat 34, 34' is open toward the front surface 31c of the tool body 31 to allow the cutting insert 1 attached to the insert seat 34, 34' to protrude in the axial direction of the tool body 31 beyond the front surface 31c of the tool body 31, and also is open toward the peripheral surface 31d of the tool body 31 to allow the cutting insert 1 attached to the insert seat 34, 34' to protrude in the radial direction of the tool body 31 beyond the peripheral surface 31d of the tool body 31.

[0070] The milling tool 30″ shown in FIGS. 7a to 7d includes a first row of forward-facing right-side insert seats 34, each located at the transition between the front surface 31c and the peripheral surface 31d of the tool body 31, and each of these insert seats 34 is open toward the front surface 31c of the tool body 31 to allow the cutting insert 1 attached to the insert seat 34 to protrude in the axial direction of the tool body 31 beyond the front surface 31c of the tool body 31, and is also open toward the peripheral surface 31d of the tool body 31 to allow the cutting insert 1 attached to the insert seat 34 to protrude in the radial direction of the tool body 31 beyond the peripheral surface 31d of the tool body 31. The milling tool 30″ shown in FIG. 1D includes a second row of rearward-facing left-hand insert seats 34′ each located at the transition between the rear surface 31e of the tool body 31 and the peripheral surface 31d of the tool body 31, each of the insert seats 34′ open toward the rear surface 31e of the tool body 31 to allow the cutting insert 1 mounted in the insert seat 34′ to protrude in the axial direction of the tool body 31 beyond the rear surface 31e of the tool body 31, and also open toward the peripheral surface 31d of the tool body 31 to allow the cutting insert 1 mounted in the insert seat 34′ to protrude in the radial direction of the tool body 31 beyond the peripheral surface 31d of the tool body 31.

[0071] The cutting inserts 1 are mounted in respective insert seats 34, 34' in the tool body 31. In the embodiment shown in Figures 4a-4f, 6a-6e and 7a-7d, the milling tool 30, 30', 30" is provided with cutting inserts 1 of the type shown in Figures 1a-1h. Each cutting insert 1 is configured to be removably mounted in its associated insert seat 34, 34'. In the illustrated embodiment, each cutting insert 1 is threaded through a through hole 5 in the cutting insert 1 and threaded through a threaded hole 35 in a tangential support surface 36 of the insert seat (Figures 4e, 6d, 7c and 7d). The cutting insert 1 is fixed to the associated seat 34, 34' by a fastening element 6 in the form of a screw engaging with a cutting insert 12 (see ). The seat 34, 34' also comprises two radial support surfaces 37a, 37b and an axial support surface 38. Since each cutting insert 1 has a negative shape, each seat 34, 34' is designed in such a way that it is given a negative axial inclination angle and a negative radial inclination angle when the cutting insert 1 is mounted in the seat 34, 34' in any of its machining positions.

[0072] Each cutting insert 1 can be mounted in four different machining positions in one of the right-side insert seats 34 of the milling tools 30, 30" shown in Figures 4a-4f and 7a-7d, and in four other different machining positions in one of the left-side insert seats 34' of the milling tools 30', 30" shown in Figures 6a-6e and 7a-7d. In each of the different machining positions of the cutting insert 1, the tangential abutment surfaces 7a, 7b on the main surfaces 2, 3 which now constitute the rear surfaces of the cutting insert 1 are adapted to abut against the tangential support surfaces 36 of the associated insert seats 34, 34'; a bottom surface 18 of the groove 17a, 17b in one of the third and fourth major side surfaces 11c, 11d serves as an axial abutment surface of the cutting insert 1 and is configured to abut against an axial support surface 38 of the associated insert seat 34, 34′; Two side surfaces (14a and 14b, or 14c and 14d) of one of the first and second major side surfaces 11a, 11b jointly function as radial abutment surfaces of the cutting insert 1 and are configured to abut against the radial support surfaces 37a, 37b, respectively, of the associated insert seats 34, 34'.

[0073] 4f shows a cutting insert 1 of the type shown in FIGS. 1a-1h mounted in the insert seat 34 of the milling tool 30 in one of the eight machining positions, i.e., the right-hand insert seat. FIG. 6e shows a cutting insert 1 of the type shown in FIGS. 1a-1h mounted in the insert seat 34' of the milling tool 30 in one of the eight machining positions, i.e., the left-hand insert seat. For the cutting insert 1 of the type shown in FIGS. 1a-1h, the angle of incidence K r It can be seen in Figures 4f and 6e that is very close to 90°.

[0074] A half side and front disc milling cutter 30 of the type shown in Figures 4a to 4h having a right-hand insert seat 34 and a half side and front disc milling cutter 30' of the type shown in Figures 6a to 6e having a left-hand insert seat 34' may be combined with each other and mounted on the same arbor 40 to perform straddle milling, as shown schematically in Figure 5.

[0075] The cutting insert 1 is made of a hard, wear-resistant material, preferably cemented carbide, and the tool body 31 is preferably made of steel.

[0076] Of course, the present invention is in no way limited to the above-described embodiments, but on the contrary, many possibilities for modification thereof will be apparent to those skilled in the art without departing from the basic concept of the invention as defined in the appended claims.

Claims

1. A double-sided negative cutting insert for use in milling, said cutting insert (1) being rotatable into eight different machining positions; a first main surface (2) and a second main surface (3) disposed opposite each other on either side of the cutting insert (1), the first and second main surfaces (2, 3) functioning as rake surfaces one at a time and configured to constitute a front and a rear surface of the cutting insert (1) when mounted in an insert seat (34, 34') of a tool body (31) in an intended direction of rotation (R) of the tool body (31), the cutting insert (1) having a through hole (5) extending centrally through the cutting insert (1) between the first and second main surfaces (2, 3) and a first central plane (MP1) extending perpendicular to a central axis (C) of the through hole (5) midway between the first and second main surfaces (2, 3); extending around the cutting insert (1) between the first and second major surfaces (2, 3); a first major side surface (11a) and a second major side surface (11b) arranged opposite each other on either side of the cutting insert (1), the cutting insert (1) having a second central plane (MP2) extending midway between the first and second major side surfaces (11a, 11b) and including the central axis (C) of the through hole (5); a third major side surface (11c) and a fourth major side surface (11d) arranged opposite each other on the other two sides of the cutting insert (1), the cutting insert (1) having a third central plane (MP3) extending midway between the third and fourth major side surfaces (11c, 11d) and including the central axis (C) of the through hole (5); a first corner side (12a) disposed between the first and fourth major sides (11a, 11d); a second corner side (12b) disposed between the first and third major sides (11a, 11c); a third corner side (12c) disposed between the second and third major sides (11b, 11c); a peripheral surface (10) having a fourth corner side (12d) disposed between the second and fourth major side surfaces (11b, 11d); a curved first corner cutting edge (23a) formed at the intersection between the first corner side surface (12a) and the first main surface (2); a curved second corner cutting edge (23b) formed at the intersection between the second corner side surface (12b) and the first main surface (2); a curved third corner cutting edge (23c) formed at the intersection between the third corner side surface (12c) and the first main surface (2); a curved fourth corner cutting edge (23d) formed at an intersection between the fourth corner side surface (12d) and the first main surface (2); a curved fifth corner cutting edge (23e) formed at the intersection between the first corner side surface (12a) and the second main surface (3); a curved sixth corner cutting edge (23f) formed at the intersection between the second corner side surface (12b) and the second main surface (3); a curved seventh corner cutting edge (23g) formed at the intersection between the third corner side surface (12c) and the second main surface (3); a curved eighth corner cutting edge (23h) formed at the intersection between the fourth corner side surface (12d) and the second main surface (3); The first major side surface (11a) has a first side surface (14a) and a second side surface (14b) located on either side of the third central plane (MP3), the first side surface (14a) extending between the first and second major surfaces (2, 3) and adjacent to the first corner side surface (12a), and the second side surface (14b) extending between the first and second major surfaces (2, 3) and adjacent to the second corner side surface (12b); The second major side surface (11b) has a third side surface (14c) and a fourth side surface (14d) located on either side of the third central plane (MP3), the third side surface (14c) extending between the first and second major surfaces (2, 3) and adjacent to the third corner side surface (12c), and the fourth side surface (14d) extending between the first and second major surfaces (2, 3) and adjacent to the fourth corner side surface (12d); The third major side surface (11c) has a fifth side surface (14e) and a sixth side surface (14f) located on either side of the second central plane (MP2), the fifth side surface (14e) extending between the first and second major surfaces (2, 3) and adjacent to the second corner side surface (12b), and the sixth side surface (14f) extending between the first and second major surfaces (2, 3) and adjacent to the third corner side surface (12c); The fourth major side surface (11c) has a seventh side surface (14g) and an eighth side surface (14h) located on both sides of the second central plane (MP2), the seventh side surface (14g) extending between the first and second major surfaces (2, 3) and adjacent to the fourth corner side surface (12d), and the eighth side surface (14h) extending between the first and second major surfaces (2, 3) and adjacent to the first corner side surface (12a); A first major cutting edge (21a) is formed at the intersection of the first side surface (14a) and the first main surface (2), a second major cutting edge (21b) is formed at the intersection between the second side surface (14b) and the first main surface (2), a third major cutting edge (21c) is formed at the intersection between the third side surface (14c) and the first main surface (2), a fourth major cutting edge (21d) is formed at the intersection between the fourth side surface (14d) and the first main surface (2), a fifth major cutting edge (21e) formed at the intersection between the first side surface (14a) and the second main surface (3); a sixth major cutting edge (21f) formed at the intersection between the second side surface (14b) and the second main surface (3); a seventh major cutting edge (21g) formed at the intersection between the third side surface (14c) and the second main surface (3); and an eighth major cutting edge (21h) formed at the intersection between the fourth side surface (14d) and the second main surface (3); a first minor cutting edge (22a) is formed at the intersection between the eighth side surface (14h) and the first main surface (2), and the first minor cutting edge (22a), the first angular cutting edge (23a), and the first major cutting edge (21a) are arranged in series with one another, with the first angular cutting edge (23a) located between the first major cutting edge (21a) and the first minor cutting edge (22a); a second minor cutting edge (22b) is formed at the intersection between the fifth side surface (14e) and the first major surface (2), and the second minor cutting edge (22b), the second angular cutting edge (23b), and the second major cutting edge (21b) are arranged in series with one another with the second angular cutting edge (23b) located between the second major cutting edge (21b) and the second minor cutting edge (22b); a third minor cutting edge (22c) is formed at the intersection between the sixth side surface (14f) and the first major surface (2), and the third minor cutting edge (22c), the third angular cutting edge (23c), and the third major cutting edge (21c) are arranged in series with one another, with the third angular cutting edge (23c) located between the third major cutting edge (21c) and the third minor cutting edge (22c); a fourth minor cutting edge (22d) is formed at the intersection between the seventh side surface (14g) and the first major surface (2), and the fourth minor cutting edge (22d), the fourth angular cutting edge (23d), and the fourth major cutting edge (21d) are arranged in series with one another, with the fourth angular cutting edge (23d) located between the fourth major cutting edge (21d) and the fourth minor cutting edge (22d); a fifth minor cutting edge (22e) is formed at the intersection between the eighth side surface (14h) and the second main surface (3), and the fifth minor cutting edge (22e), the fifth angular cutting edge (23e), and the fifth major cutting edge (21e) are arranged in series with one another, with the fifth angular cutting edge (23e) located between the fifth major cutting edge (21e) and the fifth minor cutting edge (22e); a sixth minor cutting edge (22f) is formed at the intersection between the fifth side surface (14f) and the second main surface (3), and the sixth minor cutting edge (22f), the sixth angular cutting edge (23f), and the sixth major cutting edge (21f) are arranged in series with one another, with the sixth angular cutting edge (23f) located between the sixth major cutting edge (21f) and the sixth minor cutting edge (22f); a seventh minor cutting edge (22g) is formed at the intersection between the sixth side surface (14f) and the second main surface (3), and the seventh minor cutting edge (22g), the seventh angular cutting edge (23g), and the seventh major cutting edge (21g) are arranged in series with one another, with the seventh angular cutting edge (23g) located between the seventh major cutting edge (21g) and the seventh minor cutting edge (22g); an eighth minor cutting edge (22h) is formed at the intersection between the seventh side surface (14g) and the second main surface (3), and the eighth minor cutting edge (22h), the eighth angular cutting edge (23h), and the eighth major cutting edge (21h) are arranged in series with one another, with the eighth angular cutting edge (23h) located between the eighth major cutting edge (21h) and the eighth minor cutting edge (22h); each of the major cutting edges (21a-21h) has a first end (25a) facing the adjacent angular cutting edge (23a-23h) and an opposite second end (25b) facing the third central plane (MP3), and each of the major cutting edges (21a-21h) is inclined with respect to the first central plane (MP1) such that its first end (25a) is located further away from the first central plane (MP1) than its second end (25b); the first side surface (14a) is substantially flat and extends in a first plane (P1), the second side surface (14b) is substantially flat and extends in a second plane (P2), the first and second side surfaces (14a, 14b) are inclined towards each other at the same angle relative to the second central plane (MP2), and the first and second planes (P1, P2) form an angle (γ) with each other that is greater than or equal to 90° and less than 180°; a second central plane (MP2) extending in a direction perpendicular to the first plane (MP2) from the first plane (MP2) to the second plane (MP2), and a third side surface (14c) extending in a direction perpendicular to the first plane (MP2) from the second plane (MP2) to the second plane (MP2), and a fourth side surface (14d) extending in a direction perpendicular to the first plane (MP2) from the second plane (MP2) to the second plane (MP2), and a fourth ... second plane (MP2) from the second plane (MP2) to the second plane (MP2),

2. 2. The double-sided negative cutting insert according to claim 1, wherein each of the first, second, third, fourth, fifth, sixth, seventh, and eighth major cutting edges (21 a-21 h) has an inclination relative to the first central plane (MP1) such that an imaginary straight reference line (RL) extending between a first end point (EP1) of the major cutting edge at the first end (25 a) and a second end point (EP2) of the major cutting edge at the second end (25 b) forms an angle (λ) of 1 to 30°, preferably 5 to 15° with the first central plane (MP1).

3. the first and second main cutting edges (21a, 21b) are mirror symmetrical to each other with respect to the third central plane (MP3); the third and fourth main cutting edges (21c, 21d) are mirror symmetrical to each other with respect to the third central plane (MP3); the fifth and sixth main cutting edges (21e, 21f) are mirror images of each other with respect to the third central plane (MP3); The seventh and eighth main cutting edges (21g, 21h) are mirror images of each other with respect to the third central plane (MP3). The double-sided negative cutting insert according to claim 1 , characterized in that:

4. 2. The double-sided negative cutting insert according to claim 1, characterized in that the angle (γ) formed by the first and second planes (P1, P2) with each other is ≧140° and less than 180°, preferably ≧160° and less than 180°.

5. each of said fifth, sixth, seventh, and eighth sides (14e-14h) is parallel to said first central plane (MP1) and is substantially flat or convexly curved when viewed in any plane extending across said side under discussion; the fifth side surface (14e) is adjacent to the second corner side surface (12b), and has a first lateral edge (19a) extending linearly from the first main surface (2) to the second main surface (3) parallel to the central axis (C) of the through hole (5), and an opposite second lateral edge (19b) parallel to the first lateral edge (19a) and extending linearly from the first main surface (2) to the second main surface (3); The sixth side surface (14f) is adjacent to the third corner side surface (12c), and has a first lateral edge (19a) extending linearly from the first main surface (2) to the second main surface (3) parallel to the central axis (C) of the through hole (5), and an opposite second lateral edge (19b) parallel to the first lateral edge (19a) and extending linearly from the first main surface (2) to the second main surface (3), the seventh side surface (14g) is adjacent to the fourth corner side surface (12d), and has a first lateral edge (19a) extending linearly from the first main surface (2) to the second main surface (3) parallel to the central axis (C) of the through hole (5), and an opposite second lateral edge (19b) parallel to the first lateral edge (19a) and extending linearly from the first main surface (2) to the second main surface (3); The eighth side surface (14h) is adjacent to the first corner side surface (12a) and has a first lateral edge (19a) extending linearly from the first main surface (2) to the second main surface (3) parallel to the central axis (C) of the through hole (5), and an opposite second lateral edge (19b) parallel to the first lateral edge (19a) and extending linearly from the first main surface (2) to the second main surface (3). The double-sided negative cutting insert according to claim 1 , characterized in that:

6. 6. The double-sided negative cutting insert according to claim 5, characterized in that each of the fifth, sixth, seventh and eighth side surfaces (14e-14h) is parallel to the first central plane (MP1) and convexly curved with a radius of curvature of 30-1000 mm, preferably 50-500 mm, more preferably 50-300 mm, as viewed in any plane extending across the side surface under discussion.

7. the second side surface (14b) has an inclination relative to the fifth side surface (14e) such that the second plane (P2) forms an angle (α) of 87 to 93° with a fifth plane (P5) containing the first and second lateral edges (19a, 19b) of the fifth side surface (14e); the third side surface (14c) has an inclination relative to the sixth side surface (14f) such that the third plane (P3) includes the first and second lateral edges (19a, 19b) of the sixth side surface (14f) and forms an angle (α) with the sixth plane (P6) that is equal to the angle (α) that the second plane (P2) forms with the fifth plane (P5); the fourth side surface (14d) has an inclination relative to the seventh side surface (14g) such that the fourth plane (P4) includes the first and second lateral edges (19a, 19b) of the seventh side surface (14g) and forms an angle (α) with the seventh plane (P7) that is equal to the angle (α) that the second plane (P2) forms with the fifth plane (P5); The first side surface (14a) has an inclination with respect to the eighth side surface (14h) such that the first plane (P1) includes the first and second lateral edges (19a, 19b) of the eighth side surface (14h) and forms an angle (α) with the eighth plane (P8) that is equal to the angle α that the second plane (P2) forms with the fifth plane (P5). The double-sided negative cutting insert according to claim 5, characterized in that it is

8. the fifth and sixth side surfaces (14e, 14f) are inclined outwardly from one another at the same angle relative to the third central plane (MP3) and such that the fifth and sixth planes (P5, P6) form an angle (β) with one another that is less than 180°; The seventh and eighth side surfaces (14g, 14h) are inclined outwardly from each other at the same angle relative to the third central plane (MP3), and the seventh and eighth planes (P7, P8) form an angle (β) with each other that is equal to the angle (β) formed by the fifth and sixth planes (P5, P6) with each other. The double-sided negative cutting insert according to claim 7, characterized in that it is

9. 2. The double-sided cutting insert according to claim 1, characterized in that each of the first and second major side surfaces (11a, 11b) has a rotational symmetry of 180° about a first imaginary reference axis (A1) extending along an intersection line between the first mid-plane (MP1) and the third mid-plane (MP3).

10. 2. The double-sided cutting insert according to claim 1, characterized in that each of the third and fourth major side surfaces (11c, 11d) has a rotational symmetry of 180° about a second imaginary reference axis (A2) extending along an intersection line between the first mid-plane (MP1) and the second mid-plane (MP2).

11. 2. The double-sided cutting insert according to claim 1, characterized in that each of the first and second main surfaces (2, 3) has a rotational symmetry of 180° around the central axis (C) of the through hole (5).

12. 2. Double-sided cutting insert according to claim 1, characterized in that the first and second main faces (2, 3) are mirror images of each other with respect to the first central plane (MP1).

13. the first main surface (2) comprises a substantially flat first tangential abutment surface (7a), and the first, second, third and fourth angular cutting edges (23a-23d) are all located farther from the first central plane (MP1) than the first tangential abutment surface (7a); The second main surface (3) has a substantially flat second tangential abutment surface (7b), and the fifth, sixth, seventh, and eighth angular cutting edges (23e-23h) are all located farther from the first central plane (MP1) than the second tangential abutment surface (7b). The double-sided cutting insert according to claim 1 , characterized in that:

14. In addition, the first, second, third, and fourth major cutting edges (21a to 21d) and the first, second, third, and fourth minor cutting edges (22a to 22d) are all located farther from the first central plane (MP1) than the first tangential abutment surface (7a), In addition, the fifth, sixth, seventh, and eighth major cutting edges (21e to 21h) and the fifth, sixth, seventh, and eighth minor cutting edges (22e to 22h) are all located farther from the first central plane (MP1) than the second tangential abutment surface (7b). The double-sided cutting insert according to claim 13, characterized in that

15. the fifth and sixth sides (14e, 14f) are separated from each other by a first groove (17a) provided in the third major side (11c) between the fifth side (14e) and the sixth side (14f), the first groove (17a) extending from the first major surface (2) to the second major surface (3); The seventh and eighth sides (14g, 14h) are separated from each other by a second groove (17b) provided in the fourth major side (11d) between the seventh side (14g) and the eighth side (14h), and this second groove (17b) extends from the first major surface (2) to the second major surface (3). The double-sided cutting insert according to claim 1 , characterized in that:

16. 16. The double-sided negative cutting insert according to claim 15, characterized in that each of the first and second grooves (17a, 17b) has a substantially flat bottom surface (18) that is parallel to the third central plane (MP3), serves as an axial abutment surface of the cutting insert (1) in four of the eight machining positions of the cutting insert (1), and is configured to abut a corresponding axial support surface (38) of the insert seat (34, 34') of the tool body (31) when the cutting insert (1) is mounted in the insert seat in any of these four machining positions.

17. the first and second sides (14a, 14b) are separated from one another by a first transition region (15a) on the first major side (11a), the first transition region (15a) extending between the first and second major faces (2, 3); The third and fourth sides (14c, 14d) are separated from each other by a second transition region (15b) on the second major side (11b), the second transition region (15b) extending between the first and second major faces (2, 3). The double-sided cutting insert according to claim 1 , characterized in that:

18. A milling tool comprising at least one double-sided negative cutting insert (1) according to any one of claims 1 to 17.

19. 19. The milling tool of claim 18, wherein the milling tool (30, 30', 30") is a half side and back disc milling cutter, a half side and front disc milling cutter, or a double half side and front disc milling cutter.

Images