Double-sided cutting inserts and helical milling cutters

Abstract

A double-sided cutting insert (1) for use in a helical milling cutter having a rectangular basic shape and four different working positions. The peripheral surface (10) extends around the cutting insert between two main surfaces (2, 3) and has two longer main surfaces (11, 12) and two shorter main surfaces (13, 14). Main cutting edges (31-34) are formed at the intersections between each longer main surface (11, 12) and each main surface (2, 3). Inclined chip guide surfaces (41-44) extend between each shorter main surface (13, 14) and each main surface (2, 3). Each chip guide surface intersects with the contact surfaces (5a, 5b) of adjacent main surfaces on both sides of the longitudinal center surface of the cutting insert. The present invention also relates to a helical milling cutter comprising a plurality of such cutting inserts.

Description

Technical Field

[0003] , ,

[0001] The present invention relates to a double-sided cutting insert as described in the preamble of claim 1 for use in a helical milling cutter. The present invention also relates to a helical milling cutter comprising a plurality of such double-sided cutting inserts.

[0002] A helical milling cutter is a rotary cutting tool that can comprise one or more cutting inserts removably mounted in respective insert seats within the tool body of the helical milling cutter. One previously known type of helical milling cutter comprises two or more chip flutes formed in the peripheral surface of the tool body and extending side by side in respective helically curved paths, each chip flute having a leading face and an opposite trailing face in a state where the leading face is positioned in front of the trailing face when viewed in the intended direction of rotation of the tool body, and each chip flute being provided with an array of insert seats located continuously along the trailing face of the chip flute, whereby the insert seats within the same array of insert seats are spaced apart from one another in a stepped manner in the circumferential direction of the tool body.

[0003] The type of helical milling cutter described above is disclosed, for example, in U.S. Patent No. 5,913,644. In the helical milling cutter according to U.S. Patent No. 5,913,644, the insert seats in each separate array of insert seats are positioned relative to each other such that the rear-facing end section of a cutting insert mounted on an insert seat located axially forward of an adjacent insert seat within the same array of insert seats partially overlaps the front-facing end section of a cutting insert mounted on that adjacent insert seat. In this case, the cutting edges on the cutting inserts within the exact same array of insert seats are arranged to jointly form a long row of cutting edges in a stepped configuration. The problem with this arrangement of cutting inserts is that the free space between the overlapping rear-facing end sections of a first cutting insert and the overlapping front-facing end sections of an adjacent second cutting insert within the same array of insert seats is severely limited, which can impair chip formation and chip evacuation.

[0004] Object of the invention The object of the present invention is to provide a double-sided cutting insert having a novel and advantageous design and suitable for use in the above-described type of helical milling cutter. [Overview of the project]

[0005] According to the present invention, the problem is solved by a double-sided negative cutting insert having the features defined in claim 1.

[0006] The double-sided cutting insert according to the present invention can be changed to four different working positions. -The cutting insert has a first principal surface and a second principal surface, which are positioned on both sides of the cutting insert and function as the top and bottom surfaces of the cutting insert, i.e., function as rake surfaces with rake faces, wherein the cutting insert has a central axis extending between the first principal surface and the second principal surface, and a median surface extending perpendicular to the central axis and midway between the first principal surface and the second principal surface, wherein the cutting insert has a basic rectangular shape when viewed in the direction along the central axis, and each of the first principal surface and the second principal surface includes a contact surface, which functions as a tangential contact surface of the cutting insert in two of the working positions of the cutting insert, and is configured to contact the corresponding tangential support surface of the insert seat of the tool body of the helical milling cutter when the cutting insert is mounted on the insert seat in either of the two working positions, -A peripheral surface extending around the cutting insert between the first main surface and the second main surface, • A first main surface and a second main surface are arranged opposite to each other on the two opposing long sides of the cutting insert, • A third and fourth main surface are positioned opposite each other on two opposing short sides of the cutting insert, • A first corner side positioned between the first main side and the fourth main side, • A second corner side positioned between the first main side and the third main side, • A third corner side positioned between the second main side and the third main side, • A perimeter surface including a fourth corner side positioned between the second and fourth main sides, -A curved first corner cutting edge formed at the intersection between the first corner side surface and the first main surface, -A curved second corner cutting edge formed at the intersection between the second corner side surface and the first main surface, -A curved third corner cutting edge formed at the intersection between the third corner side surface and the first main surface, -A curved fourth corner cutting edge formed at the intersection between the fourth corner side surface and the first main surface, -A curved fifth corner cutting edge formed at the intersection between the second corner side surface and the second main surface, -A curved sixth corner cutting edge formed at the intersection between the first corner side surface and the second main surface, -A curved seventh corner cutting edge formed at the intersection between the fourth corner side surface and the second main surface, -A curved eighth corner cutting edge formed at the intersection between the third corner side and the second main surface, -A first main cutting edge formed at the intersection between the first main surface and the first main side surface, the first main cutting edge extends between the first corner cutting edge and the second corner cutting edge, -A second main cutting edge formed at the intersection between the first main surface and the second main side surface, the second main cutting edge extends between the third corner cutting edge and the fourth corner cutting edge, -A third main cutting edge formed at the intersection between the second main surface and the first main side surface, the third main cutting edge extends between the fifth corner cutting edge and the sixth corner cutting edge, -A fourth main cutting edge formed at the intersection between the second main surface and the second main side surface, the fourth main cutting edge extends between the seventh corner cutting edge and the eighth corner cutting edge, - An inclined first chip guide surface extending between a first main surface and a third main side surface, and located between a second corner side surface and a third corner side surface, wherein the first chip guide surface has a first edge forming a boundary between the first chip guide surface and the first main surface, and a second edge forming a boundary between the first chip guide surface and the third main side surface, the first chip guide surface being bounded by these first and second edges, the first edge intersecting the second edge at the first end of the first chip guide surface facing the second corner cutting edge, and at the second end of the first chip guide surface facing the third corner cutting edge, - An inclined second chip guide surface extending between the first main surface and the fourth main side surface, and located between the first corner side surface and the fourth corner side surface, the second chip guide surface having a first edge forming a boundary between the second chip guide surface and the first main surface, and a second edge forming a boundary between the second chip guide surface and the fourth main side surface, the second chip guide surface being bounded by these first and second edges, the first edge intersecting the second edge at the first end of the second chip guide surface facing the fourth corner cutting edge, and at the second end of the second chip guide surface facing the first corner cutting edge, - An inclined third chip guide surface extending between the second main surface and the fourth main side surface, and located between the first corner side surface and the fourth corner side surface, wherein the third chip guide surface has a first edge forming a boundary between the third chip guide surface and the second main surface, and a second edge forming a boundary between the third chip guide surface and the fourth main side surface, the third chip guide surface is bounded by these first and second edges, and the first edge intersects with the second edge at the first end of the third chip guide surface facing the sixth corner cutting edge, and at the second end of the third chip guide surface facing the seventh corner cutting edge, - An inclined fourth chip guide surface extending between a second main surface and a third main side surface, and located between a second corner side surface and a third corner side surface, the fourth chip guide surface having a first edge forming a boundary between the fourth chip guide surface and the second main surface, and a second edge forming a boundary between the fourth chip guide surface and the third main side surface, the fourth chip guide surface being bounded by these first and second edges, the first edge intersecting with the second edge at a first end of the fourth chip guide surface facing an eighth corner cutting edge, and at a second end of the fourth chip guide surface facing a fifth corner cutting edge, the fourth chip guide surface comprising

[0007] Each of the first and second chip guide surfaces is a longitudinal surface of the cutting insert, extending perpendicular to the median plane and midway between the first and second main surfaces, and intersects with the contact surface of the first main surface on both sides of the longitudinal surface of the cutting insert that includes the central axis. Correspondingly, each of the third and fourth chip guide surfaces intersects with the contact surface of the second main surface on both sides of its longitudinal surface.

[0008] Furthermore, the cutting insert has a cross-section which extends midway between the third and fourth main surfaces, perpendicular to the median plane and perpendicular to the longitudinal plane, and includes a central axis, and each of the first, second, third, and fourth chip guide surfaces has an inclination with respect to the cross-section such that, when viewed in the longitudinal plane and in any plane extending across the chip guide surface and parallel to the longitudinal plane, the first edge of the chip guide surface is located closer to the cross-section than the second edge of the same chip guide surface.

[0009] In each working position of the double-sided cutting insert, when properly mounted in the insert seat of the helical milling cutter, the rearward end section of the cutting insert has two chip guide surfaces, one of which faces the leading surface of the associated chip flute, and the other of which faces away from the leading surface of the associated chip flute.

[0010] When two double-sided cutting inserts having such chip guide surfaces are arranged adjacent to each other in the same array of one insert seat of a helical milling cutter, as described above with reference to U.S. Patent No. 5,913,644, one of the two chip guide surfaces of the rearward end section of the cutting insert located axially forward of the other cutting insert provides increased free space between the overlapping ends of the two cutting inserts, thereby facilitating chip formation and chip evacuation during machining. One of the two chip guide surfaces is the surface facing away from the leading surface of the chip flute. It has been observed that guiding the chip by the chip guide surface of the cutting insert during chip generation results in reduced damage to the inactive corner cutting edge and main cutting edge of the cutting insert, and also results in reduced erosion of the active main surface, i.e., one of the first and second main surfaces that function as the active rake face. Furthermore, the other chip guide surface of the rearward end section of each cutting insert provides increased free space between the rearward end section of the cutting insert and the leading surface of the associated chip flute, which facilitates the removal of chips from the top surface of the cutting insert during machining, thereby reducing the risk of chip clogging that could damage the inactive main cutting edge on the top surface of the cutting insert.

[0011] The aforementioned central axis of the cutting insert extends between the center point of the first main surface and the center point of the second main surface. The center point refers to the centroid or geometric center. The cutting insert may be provided with a through hole that extends through the center of the cutting insert between the first and second main surfaces, and the central axis of the through hole coincides with the central axis of the cutting insert.

[0012] According to one embodiment of the present invention, each of the third and fourth principal surfaces has 180° rotational symmetry about a first virtual reference axis extending along the intersection line between the median plane and the longitudinal plane. In this regard, each of the third and fourth principal surfaces is considered to have 180° rotational symmetry about the first virtual reference axis, even if one or more small markings, for example in the form of a recess, are provided on either of these principal surfaces, provided that these one or more markings are not related to the function of the cutting insert.

[0013] According to another embodiment of the present invention, each of the first and second principal surfaces has 180° rotational symmetry about a second virtual reference axis extending along the line of intersection between the median plane and the cross-section. In this regard, each of the first and second principal surfaces is considered to have 180° rotational symmetry about the second virtual reference axis, even if one or more small markings, for example in the form of a recess, are provided on either of these principal surfaces, provided that these one or more markings are not related to the function of the cutting insert.

[0014] According to another embodiment of the present invention, each of the first principal surface and the second principal surface has 180° rotational symmetry about a central axis. In this regard, each of the first principal surface and the second principal surface is considered to have 180° rotational symmetry about a central axis, even if one or more small markings, for example in the form of recesses, are provided on either of these principal surfaces and these one or more markings do not relate to the function of the cutting insert.

[0015] Another embodiment of the present invention is, -The aforementioned contact surface of the first main surface is flat, that is, flat within manufacturing tolerances, and extends in a first plane parallel to the median plane. - The above-mentioned abutting surface of the second main surface is flat, that is, flat within manufacturing tolerances, and extends in a second plane parallel to the median plane.

[0016] In this case, the first edge of the first chip guiding surface and the first edge of the second chip guiding surface are substantially located in the first plane, and the first edge of the third chip guiding surface and the first edge of the fourth chip guiding surface are substantially located in the second plane.

[0017] Another embodiment of the present invention is - The first edge of each chip guiding surface includes a substantially straight central edge portion, and the substantially straight central edge portion is located on the opposite side of the substantially straight central edge portion of the second edge of the same chip guiding surface, and preferably extends parallel to it. - Each chip guiding surface has a central region formed by a portion of the chip guiding surface located between the central edge portion of the first edge of the chip guiding surface and the central edge portion of the second edge of the chip guiding surface. This central region consists of one or more sub-surfaces, and each sub-surface is convex or planar when viewed in any plane extending across the sub-surface parallel to the longitudinal plane.

[0018] Another embodiment of the present invention is - At least the main part of the central region of each chip guiding surface consists of a flat main sub-surface. - The main sub-surfaces of each of the first chip guiding surface and the second chip guiding surface form an angle of 20 to 45°, preferably 35 to 45°, with the abutting surface of the first main surface. - The main sub-surfaces of each of the third chip guiding surface and the fourth chip guiding surface form an angle of 20 to 45°, preferably 35 to 45°, with the abutting surface of the second main surface.

[0019] When the angle is less than 20°, in order to create sufficient free space between the overlapping end regions of the two cutting inserts, the chip guiding surface must occupy most of the adjacent abutting surface, which reduces the stability of the cutting insert. When the angle is greater than 45°, the inclination of the chip guiding surface becomes too steep and chip formation is impaired. The best performance was observed when the angle was 35 - 45°.

[0020] As an alternative, the central region of each chip guiding surface may be completely convex when viewed in any plane extending across the central region parallel to the longitudinal plane. The convex shape reduces the contact area between the chip and the chip guiding surface and facilitates chip formation.

[0021] According to another embodiment of the present invention, the longitudinal plane extends across the flat main and secondary surfaces of each chip guiding surface.

[0022] Another embodiment of the present invention is - the second edge of the first chip guiding surface and the second edge of the fourth chip guiding surface are located on both sides of the median plane, - characterized in that the second edge of the second chip guiding surface and the second edge of the third chip guiding surface are located on both sides of the median plane.

[0023] Another embodiment of the present invention is - the second corner cutting edge is connected to the first chip guiding surface at the first end of the first chip guiding surface, - the fourth corner cutting edge is connected to the second chip guiding surface at the first end of the second chip guiding surface, - the sixth corner cutting edge is connected to the third chip guiding surface at the first end of the third chip guiding surface, - characterized in that the eighth corner cutting edge is connected to the fourth chip guiding surface at the first end of the fourth chip guiding surface.

[0024] Another embodiment of the present invention is - The first main cutting edge is inclined with respect to the median plane such that the first end of the first main cutting edge facing the first corner cutting edge is located further away from the median plane than the second end of the first main cutting edge facing the second corner cutting edge. - The second main cutting edge is inclined with respect to the median plane such that the first end of the second main cutting edge facing the third corner cutting edge is located further away from the median plane than the second end of the second main cutting edge on the opposite side facing the fourth corner cutting edge. - The third main cutting edge is inclined with respect to the median plane such that the first end of the third main cutting edge facing the fifth corner cutting edge is located further away from the median plane than the second end of the third main cutting edge on the opposite side facing the sixth corner cutting edge. - The fourth main cutting edge is characterized by being inclined with respect to the median plane such that the first end of the fourth main cutting edge facing the seventh corner cutting edge is located further away from the median plane than the second end of the fourth main cutting edge on the opposite side facing the eighth corner cutting edge.

[0025] In this case, each main cutting edge preferably has an inclination with respect to the midline plane such that it forms an angle of less than 6° with the midline plane.

[0026] The angle of the main cutting edge is preferable in terms of chip evacuation from the top surface of the cutting insert during machining, providing good cutting characteristics. If the angle of inclination is greater than 6°, it will result in thread-shaped chips that spread too much in the axial direction, hindering the cutting process of the helical milling cutter.

[0027] Further advantageous features of the double-sided cutting insert according to the present invention will become apparent from the following description.

[0028] The present invention also relates to a helical milling cutter comprising a plurality of double-sided cutting inserts of the type described above.

[0029] One embodiment of the present invention is - The helical milling cutter comprises an elongated tool body having a rear end and an opposite front end, the central longitudinal axis of the tool body extending between the rear and front ends of the tool body, • The rear end, located at the rear of the tool body, is configured to be attached to the machine. • The front end of the tool body, - Two or more chip flutes formed on the circumferential surface of the tool body, extending side by side along a portion of the tool body from the front to the rear, wherein the chip flutes are separated from each other in the circumferential direction of the tool body, and each of the two or more chip flutes extends in a spirally curved path along the relevant portion of the tool body, having a front face and an opposite rear face, and each of the two or more chip flutes is provided with an array of two or more insert seats continuously located along the rear face of the chip flute, wherein the insert seats within the same array of insert seats are spaced apart from each other in a stepped manner in the circumferential direction of the tool body, comprising two or more chip flutes, - The above type of double-sided cutting insert is detachably mounted to one of each insert seat in an array of insert seats, and each cutting insert is mounted to the associated insert seat with the contact surface on one of the first and second main faces of the cutting insert functioning as an effective tangential contact surface and in contact with the tangential support surface of the insert seat, one of the main cutting edges on the other of the first and second main faces of the cutting insert functioning as an effective main cutting edge and extending along a portion of the periphery of the tool body, one of the third and fourth main faces of the cutting insert is included in the forward end section of the cutting insert facing the front end of the tool body, and the other of the third and fourth main faces of the cutting insert is included in the rear end section of the cutting insert facing the rear end of the tool body. - The insert seats within the array of insert seats are positioned relative to each other such that the rear-facing end section of a cutting insert mounted on an insert seat located axially forward of an adjacent insert seat within the same array of insert seats and the front-facing end section of a cutting insert mounted on this adjacent insert seat overlap each other at least partially.

[0030] The leading edge of the chip flute refers to the surface of the chip flute provided on the tool body that is in front of the opposing surface of the same chip flute when viewed in the intended direction of rotation of the tool body, that is, in front of the opposing surface of the same chip flute in the direction of rotation when viewed in the intended direction of rotation of the tool body. Correspondingly, the rear edge of the chip flute refers to the surface of the chip flute provided on the tool body that is behind the opposing surface of the same chip flute when viewed in the intended direction of rotation of the tool body, that is, behind the opposing leading edge of the same chip flute in the direction of rotation when viewed in the intended direction of rotation of the tool body.

[0031] According to another embodiment of the present invention, each of the two or more chip flutes is arranged in the tool body at a positive helix angle, and the insert seats in the array of insert seats are positioned relative to each other such that an insert seat located axially forward of an adjacent insert seat in the same array of insert seats is also located rotationally forward of that adjacent insert seat when viewed in the intended rotational direction of the tool body. In this case, at least a portion of the rearward end section of a cutting insert mounted on an insert seat located axially forward of an adjacent insert seat in the same array of insert seats protrudes axially from the tool body over at least a portion of the forward end section of a cutting insert mounted on that adjacent insert seat, thereby overlapping with that at least portion.

[0032] According to another embodiment of the present invention, at least one of the two or more chip flutes, preferably the leading edge of each of the two or more chip flutes, is provided with at least one recess located opposite an array of insert seats provided on the rear surface of the same chip flute. This at least one recess provides increased free space between at least one cutting insert in the chip flute and the leading edge of the chip flute, which facilitates the removal of chips from the top surface of one or more cutting inserts during machining, thereby reducing the risk of chip clogging without weakening the tool. The axial length of the recess, i.e., the length of the recess in the axial direction of the tool body, is preferably greater than 50% of the length of the main cutting edge of the cutting insert, and more preferably greater than the length of the main cutting edge of the cutting insert.

[0033] Further advantageous features of the helical milling cutter according to the present invention will become apparent from the following description.

[0034] The embodiments of the present invention will be described in detail below with reference to the attached drawings. The drawings are as follows. [Brief explanation of the drawing]

[0035] [Figure 1a] This is a perspective view of a double-sided cutting insert according to one embodiment of the present invention from different directions. [Figure 1b] This is a perspective view of a double-sided cutting insert according to one embodiment of the present invention from different directions. [Figure 1c] Figures 1a and 1b are top views of the cutting insert. [Figure 1d] Figures 1a and 1b are plan views of the cutting insert from below. [Figure 1e] This is a cross-sectional view along the Ie-Ie line in Figure 1c. [Figure 1f] These are side views of the cutting inserts shown in Figures 1a and 1b, viewed from the first side. [Figure 1g] These are side views of the cutting insert shown in Figures 1a and 1b, viewed from the second side on the opposite side. [Figure 1h] Figures 1a and 1b are front views of the cutting insert. [Figure 1i] Figures 1a and 1b show the rear view of the cutting insert. [Figure 2a] This is a perspective view of a double-sided cutting insert according to an alternative embodiment of the present invention. [Figure 2b] Figure 2a is a top view of the cutting insert. [Figure 2c] This is a cross-sectional view along the line IIc-IIc in Figure 2b. [Figure 3] Figures 1a to 1i show a perspective view of a helical milling cutter equipped with a cutting insert according to the embodiment shown. [Figure 4] Figure 3 is a perspective view of the helical milling cutter from a different direction. [Figure 5] Figure 3 is a side view of the helical milling cutter. [Figure 6] Figure 3 is a front view of the helical milling cutter. [Figure 7] Figure 3 is a side view of the tool body included in the helical milling cutter. [Figure 8] Figure 7 is a perspective view of the tool body, showing the cutting inserts attached to some of the insert seats on the tool body. [Figure 9] Figure 3 is a detailed enlarged view of a part of the helical milling cutter. [Figure 10] Figure 3 is another detailed enlarged view of a part of the helical milling cutter. [Figure 11] This is a cross-sectional view along the line XI-XI in Figure 10. [Figure 12] Figure 3 is a perspective view of a helical milling cutter, schematically showing the chips formed by two of the cutting inserts of the helical milling cutter. [Figure 13] This is a detailed enlarged view corresponding to Figure 10, schematically showing the chip formed by one of the cutting inserts. [Modes for carrying out the invention]

[0036] Two different embodiments of the double-sided cutting insert 1 according to the present invention are shown in Figures 1a to 1i and Figures 2a to 2c. The cutting insert 1 is configured for use in a helical milling cutter, for example, a helical milling cutter 50 of the type shown in Figures 3 to 13.

[0037] The cutting insert 1 can be changed to four different working positions. The cutting insert 1 comprises a first main surface 2 and a second main surface 3, which are located on both sides of the cutting insert and function as the top and bottom surfaces of the cutting insert. The first main surface 2 and the second main surface 3 constitute the rake face of the cutting insert 1 and provide a rake face. The first main surface 2 and the second main surface 3 have a basically rectangular shape, as seen in the plan view of the cutting insert 1. The cutting insert has a central axis C extending between the first main surface 2 and the second main surface 3. The median plane MP, which constitutes a virtual plane, extends midway between the first main surface 2 and the second main surface 3, perpendicular to the central axis C, as shown in Figures 1e to 1i. In the illustrated embodiment, the first main surface 2 is provided with a marking 4a in the form of a circular recess, and the second main surface 3 is provided with a marking 4b in the form of two circular recesses. The markings 4a and 4b facilitate the identification of the four different working positions of the cutting insert 1. Except for markings 4a and 4b, the first main surface 2 and the second main surface 3 are identical to each other within the manufacturing tolerance. Furthermore, except for markings 4a and 4b, each of the first main surface 2 and the second main surface 3 has 180° rotational symmetry about the central axis C.

[0038] Each of the first main surface 2 and the second main surface 3 includes contact surfaces 5a and 5b, which function as tangential contact surfaces of the cutting insert 1 in two of the working positions of the cutting insert, and are configured to contact the corresponding tangential support surfaces 63 of the insert seat 60 of the tool body 51 of the helical milling cutter 50 (see Figures 7, 8 and 11) when the cutting insert 1 is mounted on the insert seat in either of these two working positions. Thus, the contact surface 5a on the first main surface 2 is configured to function as a tangential contact surface of the cutting insert 1 in two of the working positions of the cutting insert, and the contact surface 5b on the second main surface 3 is configured to function as a tangential contact surface of the cutting insert 1 in the other two working positions of the cutting insert. In the illustrated embodiment, the contact surface 5a of the first main surface 2 is flat or at least fundamentally flat and extends into a first plane P1 (see Figure 1h) parallel to the median plane MP, and the contact surface 5b of the second main surface 3 is also flat or at least fundamentally flat and extends into a second plane P2 parallel to the first plane P1 and the median plane MP.

[0039] In the illustrated embodiment, the cutting insert 1 includes a through hole 6 extending through the center of the cutting insert between a first main surface 2 and a second main surface 3. The through hole 6 is configured to receive a fastening element 7, for example, in the form of a screw, by which the cutting insert can be releasably secured to the insert seat 60 of the helical milling cutter 50. The central axis C of the cutting insert 1 coincides with the central axis of the through hole 6. Alternatively, the cutting insert 1 may lack the through hole 6, and the cutting insert may be configured to be releasably secured to the insert seat of the helical milling cutter by appropriate clamping means.

[0040] The peripheral surface 10 extends around the cutting insert 1 between the first main surface 2 and the second main surface 3. The peripheral surface 10 is - The first main surface 11 and the second main surface 12 are arranged opposite to each other on the two opposing long sides of the cutting insert 1, - The third main surface 13 and the fourth main surface 14 are arranged opposite to each other on the two opposing short sides of the cutting insert 1, -A first corner side surface 15a positioned between the first main side surface 11 and the fourth main side surface 14, -A second corner side surface 15b positioned between the first main side surface 11 and the third main side surface 13, -A third corner side 15c positioned between the second main side 12 and the third main side 13, -A fourth corner side surface 15d is positioned between the second main side surface 12 and the fourth main side surface 14.

[0041] Therefore, the first main surface 11 and the second main surface 12 are positioned opposite each other on mutually opposing sides of the central axis C of the cutting insert 1. Correspondingly, the third main surface 13 and the fourth main surface 14 are positioned opposite each other on mutually opposing sides of the central axis C of the cutting insert 1.

[0042] The longitudinal plane LP, which constitutes the virtual plane, extends midway between the first main surface 11 and the second main surface 12, perpendicular to the median plane MP, and includes the central axis C of the cutting insert 1. The transverse plane TP, which also constitutes the virtual plane, extends midway between the third main surface 13 and the fourth main surface 14, perpendicular to the median plane MP, and includes the central axis C of the cutting insert 1. The longitudinal plane LP and the transverse plane TP extend perpendicularly to each other and intersect each other along the central axis C of the cutting insert 1. Each of the third main surface 13 and the fourth main surface 14 has 180° rotational symmetry about a first virtual reference axis A1 (see Figures 1h and 1i) extending along the line of intersection between the median plane MP and the longitudinal plane LP, and each of the first main surface 11 and the second main surface 12 has 180° rotational symmetry about a second virtual reference axis A2 (see Figures 1f and 1g) extending along the line of intersection between the median plane MP and the transverse plane TP.

[0043] Cutting insert 1 has the following cutting edge, namely, -A curved first corner cutting edge 21 formed at the intersection between the first corner side surface 15a and the first main surface 2, -A curved second corner cutting edge 22 is formed at the intersection between the second corner side surface 15b and the first main surface 2, -A curved third corner cutting edge 23 formed at the intersection between the third corner side surface 15c and the first main surface 2, -A curved fourth corner cutting edge 24 formed at the intersection between the fourth corner side surface 15d and the first main surface 2, -A curved fifth corner cutting edge 25 formed at the intersection of the second corner side surface 15b and the second main surface 3, -A curved sixth corner cutting edge 26 formed at the intersection of the first corner side surface 15a and the second main surface 3, -A curved seventh corner cutting edge 27 formed at the intersection of the fourth corner side surface 15d and the second main surface 3, -A curved eighth corner cutting edge 28 formed at the intersection of the third corner side surface 15c and the second main surface 3, -A first main cutting edge 31 formed at the intersection between the first main surface 2 and the first main side surface 11, wherein the first main cutting edge 31 extends between the first corner cutting edge 21 and the second corner cutting edge 22 and has a first end 31a connected to the first corner cutting edge 21 and a second end 31b on the opposite side connected to the second corner cutting edge 22, -A second main cutting edge 32 formed at the intersection between the first main surface 2 and the second main side surface 12, the second main cutting edge 32 extending between the third corner cutting edge 23 and the fourth corner cutting edge 24, having a first end 32a connected to the third corner cutting edge 23 and a second end 32b on the opposite side connected to the fourth corner cutting edge 24, -A third main cutting edge 33 formed at the intersection between the second main surface 3 and the first main surface 11, the third main cutting edge 33 extending between the fifth corner cutting edge 25 and the sixth corner cutting edge 26, having a first end 33a connected to the fifth corner cutting edge 25 and a second end 33b on the opposite side connected to the sixth corner cutting edge 26, - A fourth main cutting edge 34 formed at the intersection between the second main surface 3 and the second main side surface 12, the fourth main cutting edge 34 extending between the seventh corner cutting edge 27 and the eighth corner cutting edge 28, having a first end 34a connected to the seventh corner cutting edge 27 and a second end 34b on the opposite side connected to the eighth corner cutting edge 28.

[0044] Cutting edges 21, 31, 22, 23, 32, 24 located along the periphery of the first main surface 2 form two distinct sets of cutting edges, the first set of which comprises first and second corner cutting edges 21, 22 and an intermediate first main cutting edge 31, and the other set of which comprises third and fourth corner cutting edges 23, 24 and an intermediate second main cutting edge 32. In a corresponding manner, cutting edges 25, 33, 26, 27, 34, 28 located along the periphery of the second main surface 3 form two other sets of cutting edges, the first set of which comprises fifth and sixth corner cutting edges 25, 26 and an intermediate third main cutting edge 33, and the other set of which comprises seventh and eighth corner cutting edges 27, 28 and an intermediate fourth main cutting edge 34. In each of the four different working positions of the cutting insert 1, one of the four different sets of cutting edges described above constitutes the effective cutting edge of the cutting insert.

[0045] The aforementioned 180° rotational symmetry of the first principal surface 2 with respect to the central axis C is, - The first and second main cutting edges 31 and 32 are identical to each other within the manufacturing tolerance. - The first and third corner cutting edges 21 and 23 are identical to each other within the manufacturing tolerance. - This means that the second and fourth corner cutting edges 22 and 24 are identical to each other within the manufacturing tolerance.

[0046] Correspondingly, the aforementioned 180° rotational symmetry of the second principal surface 3 about the central axis C is, -The third and fourth main cutting edges 33 and 34 are identical to each other within the manufacturing tolerance range. -The fifth and seventh corner cutting edges 25 and 27 are identical to each other within the manufacturing tolerance. - This means that the sixth and eighth corner cutting edges 26 and 28 are identical to each other within the manufacturing tolerance.

[0047] In the illustrated embodiment, each main cutting edge 31-34 is inclined with respect to the median plane MP. - The first main cutting edge 31 is inclined with respect to the median plane MP such that the first end 31a of the first main cutting edge is located further away from the median plane MP than the second end 31b of the first main cutting edge. - The second main cutting edge 32 is inclined with respect to the median plane MP such that the first end 32a of the second main cutting edge is located further away from the median plane MP than the second end 32b of the second main cutting edge. - The third main cutting edge 33 is inclined with respect to the median plane MP such that the first end 33a of the third main cutting edge is located further away from the median plane MP than the second end 33b of the third main cutting edge. - The fourth main cutting edge 34 is inclined with respect to the median plane MP such that the first end 34a of the fourth main cutting edge is located further away from the median plane MP than the second end 34b of the fourth main cutting edge.

[0048] It is advantageous that the inclination of the main cutting edges 31-34 is such that each main cutting edge 31-34 forms an angle β (see Figure 1f) with respect to the median plane MP that is less than 6°, preferably greater than 1°.

[0049] In the illustrated embodiment, both the first and second main cutting edges 31 and 32 are positioned at a greater distance from the median plane MP compared to the contact surface 5a of the first main surface 2, and as a result, when the cutting insert 1 is positioned with the first main surface 2 facing upward, they are positioned at a higher level than the contact surface 5a. Correspondingly, both the third and fourth main cutting edges 33 and 34 are positioned at a greater distance from the median plane MP compared to the contact surface 5b of the second main surface 3, and as a result, when the cutting insert 1 is positioned with the second main surface 3 facing upward, they are positioned at a higher level than the contact surface 5b.

[0050] Cutting insert 1 is - An inclined first chip guide surface 41 extending between the first main surface 2 and the third main surface 13, and located between the second corner surface 15b and the third corner surface 15c, - An inclined second chip guide surface 42 extending between the first main surface 2 and the fourth main surface 14, and located between the first corner surface 15a and the fourth corner surface 15d, - An inclined third chip guide surface 43 extending between the second main surface 3 and the fourth main surface 14, and located between the first corner surface 15a and the fourth corner surface 15d, - Further comprising an inclined fourth chip guide surface 44 that extends between the second main surface 3 and the third main surface 13 and is located between the second corner surface 15b and the third corner surface 15c.

[0051] The first chip guide surface 41 has a first edge 41a that forms the boundary between the first chip guide surface and the first main surface 2, and a second edge 41b that forms the boundary between the first chip guide surface and the third main surface 13. The first chip guide surface 41 is completely bounded by these first and second edges 41a and 41b. The first edge 41a intersects with the second edge 41b at the first end 41c of the first chip guide surface facing the second corner cutting edge 22, and at the second end 41d of the first chip guide surface facing the third corner cutting edge 23.

[0052] The second chip guide surface 42 has a first edge 42a that forms a boundary between the second chip guide surface and the first main surface 2, and a second edge 42b that forms a boundary between the second chip guide surface and the fourth main surface 14. The second chip guide surface 42 is completely bounded by these first and second edges 42a and 42b. The first edge 42a intersects with the second edge 42b at the first end 42c of the second chip guide surface facing the fourth corner cutting edge 24, and at the second end 42d of the second chip guide surface facing the first corner cutting edge 21.

[0053] The third chip guide surface 43 has a first edge 43a that forms a boundary between the third chip guide surface and the second main surface 3, and a second edge 43b that forms a boundary between the third chip guide surface and the fourth main surface 14. The third chip guide surface 43 is completely bounded by these first and second edges 43a and 43b. The first edge 43a intersects with the second edge 43b at the first end 43c of the third chip guide surface facing the sixth corner cutting edge 26, and at the second end 43d of the third chip guide surface facing the seventh corner cutting edge 27.

[0054] The fourth chip guide surface 44 has a first edge 44a that forms a boundary between the fourth chip guide surface and the second main surface 3, and a second edge 44b that forms a boundary between the fourth chip guide surface and the third main surface 13. The fourth chip guide surface 44 is completely bounded by these first and second edges 44a and 44b. The first edge 44a intersects with the second edge 44b at the first end 44c of the fourth chip guide surface facing the eighth corner cutting edge 28, and also at the second end 44d of the fourth chip guide surface facing the fifth corner cutting edge 25.

[0055] Each of the first chip guide surface 41 and the second chip guide surface 42 intersects with the aforementioned contact surface 5a of the first main surface 2 on both sides of the longitudinal surface LP. Correspondingly, each of the third chip guide surface 43 and the fourth chip guide surface 44 intersects with the aforementioned contact surface 5b of the second main surface 3 on both sides of the longitudinal surface LP. Furthermore, each of the chip guide surfaces 41, 42, 43, and 44 has an inclination with respect to the cross section TP such that the first edges 41a, 42a, 43a, and 44a of the chip guide surface are located closer to the cross section TP than the second edges 41b, 42b, 43b, and 44b of the same chip guide surface, as can be seen in the longitudinal surface LP and in any plane that extends across the chip guide surface and is parallel to the longitudinal surface LP. Therefore, each of the chip guide surfaces 41, 42, 43, and 44 is inclined outward away from the cross section TP, as seen in the longitudinal plane LP and in any plane extending across the chip guide surface and parallel to the longitudinal plane LP, in the direction from its first edges 41a, 42a, 43a, and 44a to its second edges 41b, 42b, 43b, and 44b.

[0056] None of the chip guide surfaces 41 to 44 intersect with the median plane MP. Therefore, the second edge 41b of the first chip guide surface 41 extends along the third main surface 13 on the first side of the median plane MP, and the second edge 44b of the fourth chip guide surface 44 extends along the third main surface 13 on the second side opposite to the median plane MP. Correspondingly, the second edge 42b of the second chip guide surface 42 extends along the fourth main surface 14 on the first side of the median plane MP, and the second edge 43b of the third chip guide surface 43 extends along the fourth main surface 14 on the second side opposite to the median plane MP.

[0057] In the illustrated embodiment, - The second corner cutting edge 22 is connected to the first chip guide surface 41 at the first end 41c of the first chip guide surface, while the third corner cutting edge 23 is spaced apart from the second end 41d of the first chip guide surface. - The fourth corner cutting edge 24 is connected to the second chip guide surface 42 at the first end 42c of the second chip guide surface, while the first corner cutting edge 21 is spaced apart from the second end 42d of the second chip guide surface. - The sixth corner cutting edge 26 is connected to the third chip guide surface 43 at the first end 43c of the third chip guide surface, while the seventh corner cutting edge 27 is spaced apart from the second end 43d of the third chip guide surface. - The eighth corner cutting edge 28 is connected to the fourth chip guide surface 44 at the first end 44c of the fourth chip guide surface, while the fifth corner cutting edge 25 is spaced apart from the second end 44d of the fourth chip guide surface.

[0058] In the illustrated embodiment, both the first edge 41a of the first chip guide surface 41 and the first edge 42a of the second chip guide surface 42 are located within the first plane P1 described above. Correspondingly, both the first edge 43a of the third chip guide surface 43 and the first edge 44a of the fourth chip guide surface 44 are located within the second plane P2 described above.

[0059] In the illustrated embodiment, the first edges 41a, 42a, 43a, 44a of each chip guide surface 41, 42, 43, 44 include a basically straight central edge portion 45a located opposite to the basically straight central edge portion 45b of the second edges 41b, 42b, 43b, 44b of the same chip guide surface, and the central edge portion 45a of the first edge of each chip guide surface preferably extends basically parallel to the central edge portion 45b of the second edge of the same chip guide surface. In this case, each chip guide surface 41, 42, 43, 44 has a central region 46 formed by a portion of the chip guide surface located between the central edge portion 45a of the first edge of the chip guide surface and the central edge portion 45b of the second edge of the chip guide surface, and this central region 46 consists of one or more sub-surfaces 46a, 46a', 46b, each of which is convex or flat as seen in any plane extending across the sub-surface parallel to the longitudinal plane LP.

[0060] In the embodiments shown in Figures 1a to 1i, the main portion of the central region 46 of each chip guide surface 41 to 44 consists of a flat main sub-surface 46a, which is adjacent to a convex sub-surface 46b located between the main sub-surface 46a and the central edge portion 45a of the first edges 41a, 42a, 43a, and 44a of the chip guide surface. The main sub-surfaces 46a of the first chip guide surface 41 and the second chip guide surface 42 form an angle α of 20 to 45°, preferably 35 to 45° (see Figure 1e) with the aforementioned contact surface 5a of the first main surface 2. Correspondingly, the main sub-surfaces 46a of the third chip guide surface 43 and the fourth chip guide surface 44 form an angle α of 20 to 45°, preferably 35 to 45°, with the aforementioned contact surface 5b of the second main surface 3. The longitudinal surface LP extends across the main and secondary surfaces 46a of each chip guide surface 41-44.

[0061] In the embodiments shown in Figures 2a to 2c, the main portion of the central region 46 of each chip guide surface 41 to 44 consists of a convex main sub-surface 46a', and this convex main sub-surface 46a' is adjacent to a convex sub-surface 46b located between the main sub-surface 46a' and the central edge portion 45a of the first edge portions 41a, 42a, 43a, and 44a of the chip guide surface.

[0062] Figures 3 to 6 show a milling tool in the form of a helical milling cutter 50. This is a right-hand milling tool. The helical milling cutter 50 comprises an elongated tool body 51 and is configured to rotate around a rotation axis 52. The tool body 51 has a rear end 51b and an opposite front end 51a. The longitudinal axis 53 of the tool body 51 extends between the rear end 51b and the front end 51a of the tool body, and this longitudinal axis 53 coincides with the rotation axis 52 of the helical milling cutter 50. At the rear end 51b, the tool body 51 has a rear section 54, through which the tool body 51 can be attached to a machine, such as the rotating spindle of a milling machine, either directly or via an intermediate tool holder. At the front end 51a, the tool body 51 has a front section 55. The tool body 51 has a circumferential surface 56 having a substantially cylindrical basic shape.

[0063] The chip flutes 57 are formed on the circumferential surface 56 of the tool body 51, extending side by side along a portion of the tool body 51 from the front 55 to the rear 54, and the chip flutes 57 are separated from each other in the circumferential direction of the tool body 51. In the illustrated example, the tool body 51 is provided with five chip flutes 57 evenly distributed around the longitudinal axis 53 of the tool body. However, the tool body 51 may, alternatively, be provided with any other suitable number of chip flutes 57, in particular depending on the diameter of the tool body. A tool body with a smaller diameter may be provided with, for example, two chip flutes 57, and a tool body with a larger diameter may be provided with more than five chip flutes 57. Each chip flute 57 extends along the relevant portion of the tool body 51 in a spirally curved path and has, as shown in Figures 7 and 8, preferably a leading surface 57a intersecting with the front surface 55 of the tool body and an opposing rear surface 57b.

[0064] Each chip flute 57 is provided with a first insert seat 58 that constitutes the axially foremost insert seat of the chip flute and is located in the transition area between the front surface 55 and the circumferential surface 56 of the tool body 51. This first insert seat 58 is open toward the front surface 55 of the tool body 51 to allow a cutting insert 59 mounted on the first insert seat 58 to protrude axially beyond its front end 51a of the tool body 51, and is also open toward the circumferential surface 56 of the tool body 51 to allow a cutting insert 59 mounted on the first insert seat 58 to protrude radially beyond its circumferential surface 56 of the tool body 51.

[0065] Each chip flute 57 is also provided with an array of two or more insert seats 60 located front to back along the rear surface 57b of the chip flute 57, and the insert seats 60 within the same array of insert seats are spaced apart from each other in a stepped manner in the circumferential direction of the tool body 51. Each insert seat 60 in the array of insert seats has an end wall 61 at a first end facing the front end 51a of the tool body 51 and an open second end on the opposite side facing the rear end 51b of the tool body 51. Each insert seat 60 in the array of insert seats is also open toward the circumferential surface 56 of the tool body 51 to allow the cutting insert 1 mounted on the insert seat 60 to project radially beyond the circumferential surface 56 of the tool body 51. A double-sided cutting insert 1 is mounted on each of the arrayed insert seats 60. In the illustrated embodiment, the helical milling cutter 50 is provided with a double-sided cutting insert 1 of the type shown in Figures 1a to 1i. Each cutting insert 1 is configured to be removably mounted to an associated insert seat 60. In the illustrated embodiment, each cutting insert 1 is secured to the associated insert seat 60 by a fastening element 7 in the form of a thread, the fastening element 7 extending through a through hole 6 of the cutting insert 1 and engaging with a threaded hole 62 (see Figures 7 and 8) in the tangential support surface 63 of the insert seat. The insert seat 60 is also provided with a radial support surface 64. Each cutting insert 1 is mounted to the associated insert seat 60, - One of the contact surfaces 5a and 5b of the first main surface 2 and the second main surface 3 of the cutting insert functions as an effective tangential contact surface and contacts the tangential support surface 63 of the insert seat. - One of the main cutting edges 31-34 on the other of the first main surface 2 and the second main surface 3 of the cutting insert functions as the effective main cutting edge and extends along a portion of the peripheral surface 56 of the tool body 51. - One of the first main surface 11 and the second main surface 12 of the cutting insert functions as an effective radial contact surface and contacts the radial support surface 64 of the insert seat. - One of the third main surface 13 and the fourth main surface 14 of the cutting insert is included in the forward end section 8a of the cutting insert that faces the front end 51a of the tool body 51, - The third main surface 13 and the other of the fourth main surface 14 of the cutting insert are included in the rear-facing end section 8b of the cutting insert, which faces the rear end 51b of the tool body 51.

[0066] The insert seats 60 within the array of insert seats are positioned such that the rear-facing end section 8b of a cutting insert 1 mounted on an insert seat 60 located axially forward of an adjacent insert seat 60 within the same array of insert seats, and the forward-facing end section 8a of a cutting insert 1 mounted on this adjacent insert seat 60, overlap each other at least partially when viewed in the axial direction of the tool body 51, thereby enabling the active cutting edges of the cutting inserts 1 within one of the same arrays of insert seats 60 to jointly form a stepped, elongated cutting edge.

[0067] In the illustrated embodiment, the chip flutes 57 are positioned on the tool body 51 at a positive helix angle. In this case, the insert seats 60 in the array of insert seats are positioned relative to each other such that an insert seat 60 located axially forward of an adjacent insert seat 60 in the same array of insert seats is also located axially forward of that adjacent insert seat 60 when viewed in the intended rotational direction R of the tool body 51. This arrangement of the insert seats 60 means that, as shown in Figures 9 to 11, a portion of the rearward end section 8b of a cutting insert 1 mounted on an insert seat 60 located axially forward of an adjacent insert seat 60 in the same array of insert seats protrudes over a portion of the forward end section 8a of the cutting insert 1 mounted on that adjacent insert seat, thereby overlapping the tool body 51 axially.

[0068] The chip flutes 57 may, alternatively, be positioned on the tool body 51 at a negative helix angle. In this case, the insert seats 60 in the array of insert seats are positioned relative to each other such that an insert seat 60 located axially forward of an adjacent insert seat 60 in the same array of insert seats is also located axially rearward of that adjacent insert seat 60 when viewed in the intended rotational direction R of the tool body 51. This arrangement of the insert seats 60 means that a portion of the forward end section 8a of a cutting insert 1 mounted on an insert seat 60 located axially rearward of an adjacent insert seat 60 in the same array of insert seats protrudes over a portion of the rearward end section 8b of a cutting insert 1 mounted on that adjacent insert seat, thereby overlapping axially with the tool body 51.

[0069] In the illustrated example, each cutting insert 1 is positioned on the associated insert seat 60 such that the contact surface 5b of the second main surface 3 functions as an effective tangential contact surface and contacts the tangential support surface 63 of the insert seat, and the first main cutting edge 31 functions as an effective main cutting edge. In this case, the fourth chip guide surface 44 of the cutting insert 1 mounted on the insert seat 60 located axially forward of an adjacent insert seat 60 in the same array of insert seats overlaps with and faces the forward end section 8a of the cutting insert 1 mounted on this adjacent insert seat, thereby guiding the chip 9 formed by the effective main cutting edge of the cutting insert described last. Each cutting insert 1 may, of course, be mounted on the associated insert seat 60 in any other position among its four working positions.

[0070] In the illustrated example, the array of insert seats within each chip flute 57 is provided with four consecutive insert seats 60 configured to receive each cutting insert 1. However, the array of insert seats within the chip flute 57 may, alternatively, comprise any other suitable number of insert seats 60.

[0071] In the illustrated embodiment, the leading edge 57a of each chip flute is provided with a recess 66 located opposite an array of insert seats 60 provided on the rear edge 57b of the same chip flute. In the illustrated example, the threaded holes 62 provided in the insert seats 60 of the chip flutes 57 are formed as through holes and terminate at the leading edge 57a of the adjacent chip flutes 57, and the recess 66 is formed by the widened ends of these through holes. Preferably, at least one such recess 66 has an axial length greater than 50%, more preferably greater than 100%, of the length of one of the main cutting edges 31-34 of the cutting insert 1, i.e., a length measured in the axial direction of the tool body 51. In the illustrated embodiment, the axially rearmost recess 66 on the leading edge 57a of each chip flute has such an axial length.

[0072] The illustrated embodiments of the double-sided cutting inserts are right-side modifications, i.e., they are arranged to be used with the right-side tools illustrated in Figures 3 to 13. Viewed along the central axis C toward the first main surface 2, the circumferential surfaces 10 are arranged, when viewed clockwise, such that the first main surface 11 is followed by the first corner surface 15a, the fourth main surface 14, the fourth corner surface 15d, the second main surface 12, the third corner surface 15c, the third main surface 13, the second corner surface 15b, and the first main surface 11.

[0073] Looking toward the first main surface 2 along the central axis C, as can be seen in Figure 1c, and moving clockwise starting from the fourth corner cutting edge 24, the fourth corner cutting edge 24 is followed by the second main cutting edge 32, the third corner cutting edge 23, the inclined first chip guide surface 41, the second corner cutting edge 22, the first main cutting edge 31, the first corner cutting edge 21, the inclined second chip guide surface 42, and finally the fourth corner cutting edge 24. Looking toward the second main surface 3 along the central axis C, as seen in Figure 1d, and moving clockwise starting from the sixth corner cutting edge 26, the sixth corner cutting edge 26 is followed by the third main cutting edge 33, the fifth corner cutting edge 25, the inclined fourth chip guide surface 44, the curved eighth corner cutting edge 28, the fourth main cutting edge 34, the seventh corner cutting edge 27, the inclined third chip guide surface 43, and the sixth corner cutting edge 26. The illustrated right-hand embodiment of the double-sided cutting insert is configured such that when the insert is mounted on the right-hand cutting tool body, the first end of the effective main cutting edge is positioned closer to the front end 51a of the tool body than the second end of the effective main cutting edge.

[0074] A left-side variant of the double-sided milling insert (not shown) is arranged similarly to the right-side variant of the insert, the only difference being the relative order of the sides. In the left-side variant, the circumferential surface 10 is arranged such that, when viewed along the central axis C toward the first main surface 2 and in a clockwise direction, the first main surface 11 is followed by the second corner surface 15b, the third main surface 13, the third corner surface 15c, the second main surface 12, the fourth corner surface 15d, the fourth main surface 14, the first corner surface 15a, and the first main surface 11. When this left-side variant of the double-sided milling insert is mounted on a left-side milling tool body (not shown), the first end of the effective main cutting edge is positioned closer to the front end of the tool body than the second end of the effective main cutting edge.

[0075] The present invention is, of course, not limited to the embodiments described above. Rather, many possibilities for modifications will be apparent to those skilled in the art, without departing from the fundamental concepts of the invention as defined in the appended claims.

Claims

1. A double-sided cutting insert for use in a helical milling cutter, wherein the cutting insert (1) can be changed to four different working positions. The cutting insert (1) has a first main surface and a second main surface (2, 3) positioned on both sides of the cutting insert (1) and functioning as the top and bottom surfaces of the cutting insert, wherein the cutting insert (1) has a central axis (C) extending between the first main surface and the second main surface (2, 3), and a median surface (MP) perpendicular to the central axis (C) and extending midway between the first main surface and the second main surface (2, 3), and the cutting insert (1) has a basic rectangular shape when viewed in the direction along the central axis (C), and the first main surface and the front Each of the second main surfaces (2, 3) includes a contact surface (5a, 5b), which functions as a tangential contact surface of the cutting insert (1) in two of the working positions of the cutting insert, and is configured to contact the corresponding tangential support surface (63) of the insert seat (60) of the tool body (51) of the helical milling cutter when the cutting insert (1) is mounted on the insert seat in either of these two working positions, the first main surface and the second main surfaces (2, 3), A peripheral surface (10) extending around the cutting insert (1) between the first main surface and the second main surfaces (2, 3), The cutting insert (1) has two opposing long sides, on which are the first main surface and the second main surface (11, 12), which are arranged opposite to each other. The cutting insert (1) has two opposing short sides, on which are a third main surface and a fourth main surface (13, 14) arranged opposite to each other, A first corner side surface (15a) is positioned between the first main side surface and the fourth main side surfaces (11, 14), A second corner side surface (15b) is positioned between the first main side surface and the third main side surfaces (11, 13), A third corner side surface (15c) is positioned between the second main side surface and the third main side surfaces (12, 13), A circumferential surface (10) including a fourth corner surface (15d) positioned between the second main surface and the fourth main surface (12, 14), A curved first corner cutting edge (21) is formed at the intersection between the first corner side surface (15a) and the first main surface (2), A curved second corner cutting edge (22) is formed at the intersection between the second corner side surface (15b) and the first main surface (2), A curved third corner cutting edge (23) is formed at the intersection between the third corner side surface (15c) and the first main surface (2), A curved fourth corner cutting edge (24) is formed at the intersection between the fourth corner side surface (15d) and the first main surface (2), A curved fifth corner cutting edge (25) is formed at the intersection between the second corner side surface (15b) and the second main surface (3), A curved sixth corner cutting edge (26) is formed at the intersection between the first corner side surface (15a) and the second main surface (3), A curved seventh corner cutting edge (27) is formed at the intersection between the fourth corner side surface (15d) and the second main surface (3), A curved eighth corner cutting edge (28) is formed at the intersection between the third corner side surface (15c) and the second main surface (3), A first main cutting edge (31) is formed at the intersection between the first main surface (2) and the first main side surface (11), wherein the first main cutting edge (31) extends between the first corner cutting edge (21) and the second corner cutting edge (22), A second main cutting edge (32) is formed at the intersection between the first main surface (2) and the second main side surface (12), wherein the second main cutting edge (32) extends between the third corner cutting edge (23) and the fourth corner cutting edge (24), A third main cutting edge (33) is formed at the intersection between the second main surface (3) and the first main surface (11), wherein the third main cutting edge (33) extends between the fifth corner cutting edge (25) and the sixth corner cutting edge (26), A fourth main cutting edge (34) is formed at the intersection between the second main surface (3) and the second main side surface (12), wherein the fourth main cutting edge (34) includes a fourth main cutting edge (34) that extends between the seventh corner cutting edge (27) and the eighth corner cutting edge (28), The cutting insert (1) is An inclined first chip guide surface (41) extending between the first main surface (2) and the third main surface (13) and located between the second corner surface (15b) and the third corner surface (15c), wherein the first chip guide surface (41) has a first edge (41a) forming a boundary between the first chip guide surface and the first main surface (2), and a second edge (41b) forming a boundary between the first chip guide surface and the third main surface (13). The first chip guide surface (41) is bounded by these first and second edges (41a, 41b), and the first edge (41a) intersects with the second edge (41b) at the first end (41c) of the first chip guide surface facing the second corner cutting edge (22), and at the second end (41d) of the first chip guide surface facing the third corner cutting edge (23), the first chip guide surface (41) and the second edge (41b). An inclined second chip guide surface (42) extending between the first main surface (2) and the fourth main surface (14) and located between the first corner surface (15a) and the fourth corner surface (15d), wherein the second chip guide surface (42) has a first edge (42a) forming a boundary between the second chip guide surface and the first main surface (2), and a second edge (42b) forming a boundary between the second chip guide surface and the fourth main surface (14). The second chip guide surface (42) is bounded by these first and second edges (42a, 42b), and the first edge (42a) intersects with the second edge (42b) at the first end (42c) of the second chip guide surface facing the fourth corner cutting edge (24), and at the second end (42d) of the second chip guide surface facing the first corner cutting edge (21), the second chip guide surface (42) and the second chip guide surface (42). An inclined third chip guide surface (43) extending between the second main surface (3) and the fourth main surface (14) and located between the first corner surface (15a) and the fourth corner surface (15d), wherein the third chip guide surface (43) has a first edge (43a) forming a boundary between the third chip guide surface and the second main surface (3), and a second edge (43b) forming a boundary between the third chip guide surface and the fourth main surface (14). The third chip guide surface (43) is bounded by these first and second edges (43a, 43b), and the first edge (43a) intersects with the second edge (43b) at the first end (43c) of the third chip guide surface facing the sixth corner cutting edge (26), and at the second end (43d) of the third chip guide surface facing the seventh corner cutting edge (27), the third chip guide surface (43) and An inclined fourth chip guide surface (44) extending between the second main surface (3) and the third main surface (13) and located between the second corner surface (15b) and the third corner surface (15c), wherein the fourth chip guide surface (44) includes a first edge (44a) forming a boundary between the fourth chip guide surface and the second main surface (3), and a second edge (44b) forming a boundary between the fourth chip guide surface and the third main surface (13), The fourth chip guide surface (44) is bounded by these first and second edges (44a, 44b), and the first edge (44a) intersects with the second edge (44b) at the first end (44c) of the fourth chip guide surface facing the eighth corner cutting edge (28), and at the second end (44d) of the fourth chip guide surface facing the fifth corner cutting edge (25), the fourth chip guide surface (44) is provided with Each of the first chip guide surface and the second chip guide surface (41, 42) is a longitudinal surface (LP) of the cutting insert (1), which is perpendicular to the median plane (MP) and extends midway between the first main surface and the second main surface (11, 12), and intersects with the contact surface (5a) of the first main surface (2) on both sides of the longitudinal surface (LP) which includes the central axis (C), Each of the third chip guide surface and the fourth chip guide surface (43, 44) intersects with the contact surface (5b) of the second main surface (3) on both sides of the longitudinal surface (LP), The cutting insert (1) has a cross-section (TP), which extends perpendicular to the median plane (MP) and perpendicular to the longitudinal plane (LP) between the third main surface and the fourth main surface (13, 14), and includes the central axis (C), and the chip guide surfaces of the first chip guide surface, the second chip guide surface, the third chip guide surface, and the fourth chip guide surface (41, 42, 43, 44) are, A double-sided cutting insert characterized in that, when viewed in the longitudinal direction (LP) and in any plane extending across the chip guide surface and parallel to the longitudinal direction (LP), the first edges (41a, 42a, 43a, 44a) of the chip guide surface are located closer to the cross-section (TP) than the second edges (41b, 42b, 43b, 44b) of the same chip guide surface, with respect to the cross-section (TP).

2. The double-sided cutting insert according to claim 1, characterized in that each of the third and fourth main surfaces (13, 14) has 180° rotational symmetry about a first virtual reference axis (A1) extending along the intersection line between the median plane (MP) and the longitudinal plane (LP).

3. The double-sided cutting insert according to claim 1 or 2, characterized in that each of the first main surface and the second main surface (11, 12) has 180° rotational symmetry about a second virtual reference axis (A2) extending along the intersection line between the median plane (MP) and the cross-section (TP).

4. The double-sided cutting insert according to any one of claims 1 to 3, characterized in that each of the first main surface and the second main surfaces (2, 3) has 180° rotational symmetry about the central axis (C).

5. The contact surface (5a) of the first main surface (2) is flat and extends in a first plane (P1) parallel to the median plane (MP), The abutment surface (5b) of the second main surface (3) is flat and extends in a second plane (P2) parallel to the median plane (MP). A double-sided cutting insert according to any one of claims 1 to 4, characterized in that

6. The first edge (41a) of the first chip guide surface (41) and the first edge (42a) of the second chip guide surface (42) are located in the first plane (P1), The first edge (43a) of the third chip guide surface (43) and the first edge (44a) of the fourth chip guide surface (44) are located on the second plane (P2). The double-sided cutting insert according to claim 5, characterized in that

7. The first edge portions (41a, 42a, 43a, 44a) of each of the first chip guide surfaces (41, 42, 43, 44) include a basically straight central edge portion (45a), and the basically straight central edge portion (45a) is located on the opposite side of the basically straight central edge portion (45b) of the second edge portions (41b, 42b, 43b, 44b) of the same chip guide surface. Each of the first, second, third, and fourth chip guide surfaces (41, 42, 43, 44) has a central region (46) formed by the portion of the chip guide surface located between the central edge portion (45a) of the first edge of the chip guide surface and the central edge portion (45b) of the second edge of the chip guide surface, the central region (46) consists of one or more sub-surfaces (46a, 46a', 46b), and each of the sub-surfaces is convex or flat when viewed in any plane extending across the sub-surface parallel to the longitudinal surface (LP). A double-sided cutting insert according to any one of claims 1 to 6, characterized in that

8. At least the main portion of the central region (46) of each of the first, second, third, and fourth chip guide surfaces (41, 42, 43, 44) consists of a flat main sub-surface (46a). The main sub-surface (46a) of each of the first chip guide surface and the second chip guide surface (41, 42) forms an angle (α) of 20 to 45°, preferably 35 to 45°, with respect to the contact surface (5a) of the first main surface (2). The main and secondary surfaces (46a) of the third and fourth chip guide surfaces (43, 44) each form an angle (α) of 20 to 45°, preferably 35 to 45°, with the contact surface (5b) of the second main surface (3). A double-sided cutting insert according to claim 7, combined with claim 5, characterized in that

9. The double-sided cutting insert according to claim 8, characterized in that the longitudinal surface (LP) extends across the main sub-surface (46a) of each of the first chip guide surface, the second chip guide surface, the third chip guide surface, and the fourth chip guide surface (41, 42, 43, 44).

10. A double-sided cutting insert according to any one of claims 7 to 9, characterized in that the central edge portion (45a) of the first edge of each of the first chip guide surfaces (41, 42, 43, 44) extends basically parallel to the central edge portion (45b) of the second edge of the same chip guide surface.

11. The second edge (41b) of the first chip guide surface (41) and the second edge (44b) of the fourth chip guide surface (44) are located on both sides of the median plane (MP), The second edge (42b) of the second chip guide surface (42) and the second edge (43b) of the third chip guide surface (43) are located on both sides of the median plane (MP). A double-sided cutting insert according to any one of claims 1 to 10, characterized in that

12. The second corner cutting edge (22) is connected to the first chip guide surface (41) at the first end (41c) of the first chip guide surface, The fourth corner cutting edge (24) is connected to the second chip guide surface (42) at the first end (42c) of the second chip guide surface, The sixth corner cutting edge (26) is connected to the third chip guide surface (43) at the first end (43c) of the third chip guide surface. The eighth corner cutting edge (28) is connected to the fourth chip guide surface (44) at the first end (44c) of the fourth chip guide surface. A double-sided cutting insert according to any one of claims 1 to 11, characterized in that

13. The double-sided cutting insert according to any one of claims 1 to 12, characterized in that the cutting insert (1) is provided with a through hole (6) that extends through the center of the cutting insert between the first main surface and the second main surfaces (2, 3), and the central axis of the through hole (6) coincides with the central axis (C) of the cutting insert (1).

14. The first main cutting edge (31) is inclined with respect to the median plane (MP) such that the first end (31a) of the first main cutting edge facing the first corner cutting edge (21) is located further away from the median plane (MP) than the second end (31b) of the first main cutting edge facing the second corner cutting edge (22), The second main cutting edge (32) is inclined with respect to the median plane (MP) such that the first end (32a) of the second main cutting edge facing the third corner cutting edge (23) is located further away from the median plane (MP) than the second end (32b) of the second main cutting edge facing the fourth corner cutting edge (24), The third main cutting edge (33) is inclined with respect to the median plane (MP) such that the first end (33a) of the third main cutting edge facing the fifth corner cutting edge (25) is located further away from the median plane (MP) than the second end (33b) of the third main cutting edge facing the sixth corner cutting edge (26), The fourth main cutting edge (34) is inclined with respect to the median plane (MP) such that the first end (34a) of the fourth main cutting edge facing the seventh corner cutting edge (27) is located further away from the median plane (MP) than the second end (34b) of the fourth main cutting edge facing the eighth corner cutting edge (28). A double-sided cutting insert according to any one of claims 1 to 13, characterized in that

15. The double-sided cutting insert according to claim 14, characterized in that each of the first, second, third, and fourth main cutting edges (31, 32, 33, 34) forms an angle (β) smaller than 6° with the median plane (MP).

16. A helical milling cutter comprising a plurality of double-sided cutting inserts (1) according to any one of claims 1 to 15.

17. The helical milling cutter comprises an elongated tool body (51) having a rear end (51b) and an opposite front end (51a), the central longitudinal axis (53) of the tool body (51) extending between the rear end (51b) and the front end (51a) of the tool body, and the tool body (51) is The rear part (54) is located at the rear end (51b) of the tool body (51) and is configured to be attached to a machine, The front surface (55) located at the front end (51a) of the tool body (51), Two or more chip flutes (57) are formed on the circumferential surface (56) of the tool body (51) and extend side by side along a portion of the tool body (51) from the front surface (55) toward the rear surface (54), wherein the chip flutes (57) are separated from each other in the circumferential direction of the tool body (51), and each of the two or more chip flutes (57) extends in a spirally curved path along the relevant portion of the tool body and has a front surface (57a) and an opposite rear surface (57b), and each of the two or more chip flutes (57) is provided with an array of two or more insert seats (60) that are continuously located along the rear surface (57b) of the chip flute (57), wherein the insert seats (60) within the same array of insert seats are spaced apart from each other in a stepped manner in the circumferential direction of the tool body (51), Equipped with, A double-sided cutting insert (1) according to any one of claims 1 to 15 is detachably mounted to one of the insert seats (60) in the array of insert seats, and each cutting insert (1) is mounted to the associated insert seat (60) such that the contact surfaces (5a, 5b) on one of the first main surface and the second main surface (2, 3) of the cutting insert function as effective tangential contact surfaces and are in contact with the tangential support surface (63) of the insert seat. One of the main cutting edges (31, 32, 33, 34) on the other of the first main surface and the second main surface (2, 3) of the cutting insert functions as an effective main cutting edge and extends along a portion of the peripheral surface (56) of the tool body (51), and one of the third main surface (13) and the fourth main surface (14) of the cutting insert is included in the forward end section (8a) of the cutting insert facing the front end (51a) of the tool body (51), and the other of the third main surface (13) and the fourth main surface (14) of the cutting insert is included in the rear end section (8b) of the cutting insert facing the rear end (51b) of the tool body (51), The helical milling cutter according to claim 16, characterized in that the insert seats (60) in the array of insert seats are positioned relative to each other such that the rear-facing end section (8b) of a cutting insert mounted on an insert seat (60) located axially forward of an adjacent insert seat (60) in the same array of insert seats and the forward-facing end section (8a) of a cutting insert (1) mounted on the adjacent insert seat (60) overlap each other at least partially.

18. The helical milling cutter according to claim 17, characterized in that each chip flute (57) of the two or more chip flutes is positioned within the tool body (51) at a positive helix angle, and the insert seats (60) in the array of insert seats are positioned relative to each other such that an insert seat (60) located axially forward of an adjacent insert seat (60) in the same array of insert seats is also located axially forward of this adjacent insert seat (60) when viewed in the intended rotational direction (R) of the tool body (51).

19. The helical milling cutter according to claim 17 or 18, wherein at least one of the two or more chip flutes (57) has a leading surface (57a) with at least one recess (66) positioned opposite to the array of insert seats (60) provided on the rear surface (57b) of the same chip flute (57), and the axial length of this at least one recess (66) is preferably greater than 50% of the length of one of the first, second, third, and fourth main cutting edges (31-34) of the cutting insert (1), and more preferably greater than this length.

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