Turning tool and cutting insert therefor

Abstract

The present invention relates to a cutting insert (1, 40, 90) for a turning tool, the cutting insert having a first side (2) and a second side (3) disposed opposite each other and facing in opposite directions, the first and second sides extending generally in respective first and second planes (P1, P2) parallel to each other, the first side (2) having a first rake face (11). A central axis (L) of the cutting insert extends from the first side (2) to the second side (3) in a direction perpendicular to the first and second planes (P1, P2). The cutting insert has a peripheral surface (4) connecting the first side (2) and the second side (3), the peripheral surface (4) including a first flank surface (7) extending parallel or substantially parallel to the central axis. The first cutting edge (5) is disposed at the intersection between the first flank face (7) and the first rake face (11), and the first cutting edge (5) comprises a first nose cutting edge (51). The cutting insert has a maximum thickness (t) measured from the first side (2) to the second side (3) in a direction parallel to the central axis (L), and the first flank face (7) adjacent to the first nose cutting edge (51) has an extension length (h) in a direction parallel to the central axis (L) that is less than 75% of the maximum thickness (t) of the cutting insert (1). The present invention also relates to a turning tool (10) comprising such a cutting insert.

Description

[Technical Field]

[0001] The present invention relates to metal cutting, and in particular to turning operations in which a turning tool is used to machine a rotating workpiece. [Background technology]

[0002] In the field of metal cutting, turning tools may be used to machine the surface of a rotating workpiece, for example the inside of a hole in the workpiece. This is referred to as internal turning or boring. In such machining operations, the tool may extend along a central axis that is parallel to the axis of rotation of the workpiece.

[0003] Turning tools typically include cutting inserts made of a wear-resistant material, such as cemented carbide, that are positioned to engage with the workpiece surface. For external turning operations, cutting inserts with a negative base shape, i.e., cutting inserts without an inherent clearance angle, are commonly used. Negative cutting inserts have the advantage of high cutting edge strength and are suitable for severe cutting conditions. However, for internal turning operations, positive cutting inserts, i.e., cutting inserts with an inherent clearance angle, are typically used to ensure clearance from the workpiece surface.

[0004] EP 3456442 discloses a turning tool for internal turning with a cutting insert having a negative base shape. The required clearance is achieved by proper placement and orientation of the cutting insert within the tool body. However, excessive inclination of the cutting insert can result in less favorable cutting conditions, for example, with regard to chip breaking.

[0005] Therefore, there is a need for improved turning tools for internal turning operations. Summary of the Invention

[0006] It is an object of the present invention to alleviate the drawbacks of the prior art and to provide an improved cutting insert having good accessibility and high strength, and a turning tool to be used therewith for internal turning operations.

[0007] According to a first aspect, the present invention relates to a cutting insert for a turning tool, the cutting insert comprising a first side and a second side disposed opposite each other and facing in opposite directions, the first and second sides generally extending in respective first and second planes parallel to each other, the first side comprising a first rake face. A central axis extends from the first side to the second side in a direction perpendicular to the first and second planes. The cutting insert further comprises a peripheral surface connecting the first and second sides, the peripheral surface including a first flank face extending parallel or substantially parallel to the central axis. A first cutting edge is disposed at the intersection between the first flank face and the first rake face, the cutting edge including a first nose edge. The cutting insert has a maximum thickness measured from the first side to the second side in a direction parallel to the central axis. The first flank surface adjacent the first nose cutting edge has an extension length in a direction parallel to the central axis that is less than 75% of the maximum thickness of the cutting insert.

[0008] This provides increased clearance to the machined surface in internal turning operations without compromising the strength of the cutting insert.

[0009] The first flank is parallel to the central axis of the cutting insert, meaning that the cutting insert has a negative base shape. To enhance stability, it may be preferable for the turning tool used for internal turning, and the cutting insert placed therein, to be as large as permitted by the diameter of the hole being machined. The inventors have found that shortening the length of the flank, i.e., the portion of the peripheral surface closest to the inner wall of the machined hole, still maintains sufficient strength of the cutting insert, provided in part by the thickness of the cutting insert. This allows for a larger clearance from the machining surface. This is particularly useful when machining small holes, where the size of the cutting tool and cutting insert is significantly limited by the available space in the hole.

[0010] Therefore, the design according to the invention allows a relatively thick cutting insert with a negative base shape to be used for internal turning with reduced risk of friction between the flank and the machined surface.

[0011] Some prior art cutting inserts may have a slight axially raised surface relative to the trailing edge of the cutting edge and / or flank, but such raised surface is smaller than that proposed in the present invention and is primarily an effect of the manufacturing process and / or to facilitate secure mounting of the cutting insert within the insert seat, rather than being used to improve clearance.

[0012] The first flank surface adjacent to the first nose cutting edge may have an extension length parallel to the central axis that varies slightly along the nose cutting edge, i.e., the nose cutting edge may be curved in side view. However, according to the present disclosure, the extension length of the first flank surface is less than 75% of the maximum thickness of the cutting insert at all positions along the nose cutting edge, and particularly at the position of the nose cutting edge where such extension length is greatest.

[0013] A "turning tool" should be understood as a cutting tool used to machine a rotating workpiece. Such a tool is sometimes referred to as a boring bar in the context of machining the interior of a hole in a rotating workpiece. The central axis of such a turning tool is parallel to, but typically not coaxial with, the axis of rotation of the workpiece, and the turning tool can be moved radially within the hole to engage the surface of the workpiece. This allows various interior profiles of the hole to be machined by varying the radial displacement between the turning tool and the axis of rotation of the workpiece.

[0014] As used herein, the term "cutting edge," unless otherwise specified, should be understood as a combination of cutting edge segments that together form a complete cutting edge, potentially including multiple cutting edge segments such as a nose edge, a major cutting edge, and a minor cutting edge. Thus, according to the present disclosure, each cutting edge of a cutting insert can include not only a nose edge, but also a major cutting edge and, in some cases, a minor cutting edge, where the major cutting edge can extend from one end of the nose edge and the minor cutting edge can extend from the other end of the nose edge. Thus, a cutting insert according to the present invention can include a first cutting edge that includes a first major cutting edge, a first minor cutting edge, and a first nose edge.

[0015] Each of the major and minor cutting edges may be straight in plan view of the first or second side. The nose edge may be convexly curved in plan view, i.e., preferably arc-shaped. In this regard, the nose edge may be formed, for example, by a single radius connecting the major cutting edge to the minor cutting edge, or may include multiple curved segments of different radii.

[0016] The first and second sides generally extend in respective first and second planes that are parallel to one another. This means that at least a substantial portion of the first and second sides extend in such planes. While at least some portions of the first and second sides may be flat surfaces, at least some of which extend in the respective first and second planes, the first and second sides may also include various geometric formations, including, for example, recesses or protrusions to vary the cutting geometry and improve chip breakage, and may include regions with flat or curved surfaces that extend obliquely or perpendicular to the first and second planes.

[0017] The central axis of the cutting insert extends from the first side to the second side through the geometric center of the cutting insert, perpendicular to the first and second planes in which the respective first and second sides generally extend. The cutting insert may include through holes opening into the first and second sides and usable for fastening the cutting insert into an insert seat in the tool body using a fastening element such as a screw. The through hole may extend along the central axis of the cutting insert and may be circular in a cross section perpendicular to the central axis.

[0018] The cutting insert according to the invention is primarily intended for and adapted to longitudinal turning, i.e. turning in which the feed direction is parallel to the axis of rotation of the workpiece, in which the main cutting edge may be arranged to function as a turning working edge and the nose cutting edge is arranged to produce a surface that is cylindrical or concentric with the axis of rotation of the metalwork.

[0019] According to some embodiments, the first flank surface adjacent to the first nose cutting edge has an extension length in a direction parallel to the central axis that is greater than 30% of the maximum thickness of the cutting insert, and may be, for example, 40% to 70% of the maximum thickness of the cutting insert.

[0020] By having the flank extension length be at least 30%, for example 40% to 70% of the maximum thickness, an optimum trade-off between available clearance and strength of the cutting insert can be achieved.

[0021] According to some embodiments, the cutting insert has a maximum thickness of 3 mm to 6 mm and an extension length of the flank face of 1 mm to 4.5 mm. As an example, for a cutting insert having a maximum thickness of 3 mm, the flank face may have an extension length of 1 mm to 2.25 mm, e.g., about 2 mm, and for a cutting insert having a maximum thickness of 6 mm, the flank face may have an extension length of 2 mm to 4.5 mm, e.g., about 4 mm.

[0022] The second side of the cutting insert may include a contact surface arranged to abut against a support surface of the insert seat of the turning tool. Such contact surface may be at least partially formed by a flat surface portion of the second side extending in the second plane, which may be located in a region of the second side around the central axis of the cutting insert, for example, adjacent to the opening of a through hole extending through the cutting insert along the central axis. The second side may include a transition region extending from such contact surface to the first flank. The transition region may include an inclined surface portion that is oblique to the central axis. In other words, the transition between the shortened flank and the contact surface of the cutting insert preferably includes at least some sections that are inclined with respect to the second plane and the central axis, rather than simply being formed by one or more 90° steps (i.e., one section extending parallel to the second plane from the flank and another section extending parallel to the central axis toward the contact surface). This may be preferable in terms of manufacturing the cutting insert, as such a transition from the flank face to the contact face is also less likely to break and the strength of the cutting insert is essentially maintained.

[0023] According to some embodiments, the transition region extends from the point of intersection between the first flank surface and the transition region in a direction along a radial line toward the central axis of the cutting insert a distance that is at least 10% of the total distance along such radial line from that point to the central axis. The transition region thereby provides significant setback of the flank surface, thus ensuring sufficient clearance with respect to the machined surface. The extension of the transition region may be greatest at the intersection between the transition region and the first flank surface adjacent to the first nose cutting edge. As an example, the transition region may extend a distance of at least 0.5 mm from the point of intersection between the first flank surface and the transition region in a direction along a radial line toward the central axis of the cutting insert.

[0024] The first cutting edge may include a first main cutting edge connected to the first nose cutting edge and extending therefrom along the intersection between the first flank face and the first rake face. According to some embodiments, the distance from such first main cutting edge to the second side decreases with increasing distance from the first nose cutting edge. Thus, according to such embodiments, in a side view of the cutting insert, the main cutting edge does not extend parallel to the first and second side edges, but is angled away from the nose cutting edge. In other embodiments, at least a portion of the first main cutting edge may extend parallel to the first and second side edges.

[0025] The cutting insert may include a plurality of flanks, rake faces, and corresponding cutting edges formed at the intersections therebetween. In other words, the cutting insert may be indexable so that different cutting edges can be positioned in operative positions for machining a workpiece depending on the orientation of the cutting insert mounted in the insert seat of the turning tool body. The flanks of all the cutting edges extend parallel to each other and parallel or substantially parallel to the central axis.

[0026] Thus, according to some embodiments, the peripheral surface comprises a second flank, the first side or the second side comprises a second rake face, the second cutting edge is disposed at the intersection between the second flank and the second rake face, the second cutting edge comprises a second nose cutting edge, and the second flank adjacent to the second nose cutting edge has an extension length in a direction parallel to the central axis that is less than 75% of the maximum thickness of the cutting insert.

[0027] Thus, both the first and second flank surfaces of such an indexable cutting insert have an extension length in a direction parallel to the central axis that is less than 75% of the maximum thickness of the cutting insert.

[0028] Thus, according to some embodiments, the peripheral surface includes first and second flank surfaces, the first side includes a first rake surface, the second side includes a second rake surface, a first cutting edge including a first nose edge is disposed at an intersection between the first flank surface and the first rake surface, a second cutting edge including a second nose edge is disposed at an intersection between the second flank surface and the second rake surface, and each of the first and second flank surfaces adjacent to the first and second nose edges, respectively, has an extension length in a direction parallel to the central axis of the cutting insert that is less than 75% of the maximum thickness of the cutting insert. The first and second flank surfaces may be disposed on opposite or substantially opposite sides of the peripheral surface.

[0029] According to another embodiment, the second side may include a first opposing rake face opposite the first rake face, and the first opposing cutting edge is located at the intersection between the first opposing rake face and the first flank face. The first opposing cutting edge preferably has a design similar to the first cutting edge and thus includes a first opposing nose cutting edge. Therefore, the cutting insert may be double-sided, i.e., have cutting edges located at both ends of the first flank face, so that the cutting insert can be indexed by simply flipping the cutting insert in the insert seat. The first flank face serves as a flank face for both the first cutting edge and the first opposing nose cutting edge. Therefore, the first flank face adjacent to the first opposing nose cutting edge has an extension length in a direction parallel to the central axis that is less than 75% of the maximum thickness of the cutting insert.

[0030] In such an embodiment, at least a portion of the transition region on the second side is defined by the first opposing rake face.

[0031] The cutting insert may also have a second flank surface, a second rake surface disposed on the first side, and a second opposing rake surface disposed on the second side, such that the cutting insert has first and second cutting edges disposed at respective intersections between the first side and the first and second flank surfaces, and first and second opposing cutting edges disposed at respective intersections between the second side and the first and second flank surfaces. In other words, the cutting insert may be four-indexable.

[0032] According to some embodiments, the cutting insert has a rhomboid or substantially rhomboid basic shape in plan view of the first or second side, however, the cutting insert may have other shapes suitable for turning.

[0033] According to another aspect, the present invention relates to a turning tool comprising a tool body including an insert seat in which a cutting insert according to any of the embodiments described herein is mounted.

[0034] The turning tool may be configured to machine a metal workpiece and may include a front end to which a cutting insert is attached and a rear end adapted to be clamped directly or indirectly to a machine interface of a machine tool such as a computer numerically controlled (CNC) lathe.

[0035] The solution will now be explained in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a perspective view of a cutting insert according to a first embodiment. [Figure 2] FIG. 2 is a top view of the cutting insert according to the first embodiment. [Figure 3] 3 is a side view of the cutting insert according to the first embodiment as viewed from a direction III shown in FIG. 2. FIG. [Figure 4] 4 is a side view of the cutting insert according to the first embodiment as viewed from a direction IV shown in FIG. 2. FIG. [Figure 5] 3 is a side view of the cutting insert according to the first embodiment as viewed from a V direction shown in FIG. 2. FIG. [Figure 6] 6 illustrates a turning tool according to an embodiment of the present invention during an internal turning operation on a workpiece, the turning tool comprising the cutting insert shown in FIGS. 1-5. [Figure 7] 7 is a view showing a turning tool and a workpiece taken along a cross section VII-VII shown in FIG. 6. FIG. [Figure 8] 8 is an enlarged view of a portion of the turning tool and workpiece shown in FIG. 7. [Figure 9] FIG. 10 is a perspective view of a cutting insert according to a second embodiment. [Figure 10] FIG. 4 is a top view of a cutting insert according to a second embodiment. [Figure 11] FIG. 4 is a side view of a cutting insert according to a second embodiment. [Figure 12]FIG. 10 is a perspective view of a cutting insert according to a third embodiment. [Figure 13] FIG. 10 is a top view of a cutting insert according to a third embodiment. [Figure 14] FIG. 10 is a side view of a cutting insert according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0037] All figures are schematic and not necessarily to scale, generally showing only parts necessary to explain the respective embodiments, other parts may be omitted or merely suggested. Unless otherwise indicated, like reference symbols refer to like parts in different figures.

[0038] Next, a cutting insert 1 according to one embodiment of the present invention will be described with reference to FIGS.

[0039] The cutting insert 1 has a first side 2, a second side 3, and a peripheral surface 4 connecting the first and second sides 2, 3. The first and second sides 2, 3 face in opposite directions and extend in respective first and second planes P1, P2 (shown in FIG. 5) that are generally parallel to each other. A central axis L (also shown in FIG. 5) extends from the first side 2 to the second side 3 and is perpendicular to the parallel planes P1, P2. The central axis L passes through a geometric center GC of the cutting insert. A through hole 13 extends along the central axis L.

[0040] The peripheral surface 4 includes a first flank 7 and a second flank 8. The first side portion 2 includes a first rake face 11, and the second side portion 3 includes a second rake face 12. A first cutting edge 5 is formed at the boundary between the first flank 7 and the first rake face 11. A second cutting edge 6 is formed at the boundary between the second flank 8 and the second rake face 12.

[0041] The first cutting edge 5 has a first nose cutting edge 51, a first major cutting edge 52, and a first minor cutting edge 53. Thus, the first flank 7 also includes a first nose flank 71, a first major flank 72, and a first minor flank 73 (shown in FIG. 4 ).

[0042] In a corresponding manner, the second cutting edge 6 includes a second nose cutting edge 61, a second major cutting edge 62, and a second minor cutting edge 63, and the second flank 8 includes a second nose flank 81, a second major flank 82, and a second minor flank 83 (shown in FIG. 3).

[0043] The flanks 7 and 8 are parallel to the central axis L.

[0044] As best seen in FIG. 5 , the first side portion 2 includes a first planar contact surface 34 extending in a first plane P1 and a first transition region 35 extending from the second flank surface 8 to the first contact surface 34. A majority of the surface of the first transition region 35 is disposed obliquely relative to the central axis L and therefore extends at an angle relative to the central axis L and the first plane P1. The second side portion 3 includes a second planar contact surface 36 extending in a second plane P2 and a second transition region 37 extending from the first flank surface 7 to the second contact surface 36. The second transition region 37 is disposed corresponding to the first transition region 35.

[0045] Each of the first and second nose cutting edges 51 and 61 is convexly curved in plan view, as best seen in Figure 2, and the first and second major and minor cutting edges 52, 53, 62, 63 are straight in such view. Thus, the first and second major and minor flanks 72, 73, 82, 83 are flat surfaces, and the nose flanks 71, 81 are convex surfaces, each defined by a single radius connecting the respective major and minor flanks. In side view, the first and second major and minor cutting edges 52, 53, 62, 63 are angled away from the first and second nose cutting edges 51, 61, respectively.

[0046] 3-5, the distance from the first major cutting edge 52 to the second side portion 3 decreases with increasing distance from the first nose cutting edge 51, and the distance from the second major cutting edge 62 to the first side portion 2 decreases with increasing distance from the second nose cutting edge 61. Correspondingly, the distance from the first minor cutting edge 53 to the second side portion 3 decreases with increasing distance from the first nose cutting edge 51, and the distance from the second minor cutting edge 63 to the first side portion 2 decreases with increasing distance from the second nose cutting edge 61.

[0047] The first major clearance surface 72 and the second major clearance surface 82 are adjacent to each other and lie on the same planar sub-surface of the peripheral surface 4, as best seen in FIG.

[0048] As best seen in FIG. 5 , the extension length h of each of the first and second flank faces 7, 8 adjacent the respective first and second nose cutting edges 51, 61 in a direction parallel to the central axis L is much less than the total thickness t of the cutting insert 1. In this first embodiment, the extension length h is approximately 70% of the total thickness t. The flank faces 7, 8 have their maximum extension length in a direction parallel to the central axis L at a point along the nose cutting edges 51, 61. Thus, in this embodiment, the maximum extension length of each of the first and second flank faces 7, 8 in a direction parallel to the central axis L is approximately 70% of the total thickness t of the cutting insert 1.

[0049] 6-8 illustrate a turning tool 10 including a tool body 20 according to one embodiment of the present invention engaged in an internal turning operation to machine a workpiece 31 along a feed direction F, with the workpiece 31 rotating in a rotational direction R about a spindle axis W. The tool body 20 has a leading end 21, a trailing end 22, and a tool body central axis C extending longitudinally through the tool body from the leading end 21 to the trailing end 22. Although not shown in FIG. 6, the workpiece 31 and turning tool 10 are positioned within a machine tool, such as a computer numerically controlled (CNC) lathe.

[0050] The tool body peripheral surface 23 connects the front end 21 and the rear end 22. The tool body peripheral surface 23 has flutes 26 formed therein for discharging chips. The tool body 20 further includes a first insert seat and a second insert seat formed at the interface between the front end 21 and the tool body peripheral surface 23. The first and second insert seats are located on opposite sides of the tool body central axis C.

[0051] A threaded hole is located in each of the insert seats. The cutting insert 1 according to FIGS. 1-5 is attached to the first insert seat using a screw extending through the through hole 13 of the cutting insert 1 and into the threaded hole of the first insert seat. The second cutting insert 30 is similarly attached to the second insert seat. The second cutting insert 30 is different from the first cutting insert 1 and is used in a different machining operation. For example, the turning tool 10 may be controlled so that the second cutting insert 30 first engages the surface of the rotating workpiece 31 as it machines forward, e.g., into a hole in the workpiece, and the turning tool 10 may thereafter be controlled so that the first cutting insert 1 engages the workpiece 31 as it machines backward, e.g., out of the hole.

[0052] As can be seen in FIGS. 7-8 , the cutting insert 1 is responsible for machining the interior 32 of a hole in a workpiece 31. For an efficient machining process, it is important that there is sufficient clearance between the flank 7 and the machined surface 32. In the illustrated embodiment, sufficient clearance is achieved by having a short flank 7, as described above with reference to FIG. 5 . As shown by the dotted line in FIG. 8 , if the extension of the flank 7 is too large, the flank 7 will interfere with the machined surface 32, causing rubbing between the workpiece and the cutting insert, which will have a negative impact on tool life and the quality of the machined surface.

[0053] The strength of the cutting insert 1 is not significantly affected by the shortened flank 7, since the majority of the cutting insert 1 still has a thickness that corresponds to the maximum thickness t of the cutting insert.

[0054] 9-11 are schematic diagrams of a cutting insert 40 according to a second embodiment. The cutting insert 40 differs from the cutting insert 1 of the first embodiment in that it has a different shape, i.e., a substantially diamond shape, in top view, as best seen in FIG. 10, and in that the second rake face 12 is disposed on the first side 2, i.e., the first and second cutting edges 5, 6 are formed at the intersections between the first side 2 and the first and second flank faces 7, 8, respectively. As in the first embodiment, the second side 3 of the cutting insert includes a flat contact surface 36 and a transition region 37 extending between the contact surface 36 and the respective first and second flank faces 7, 8. In this second embodiment, the maximum extension length h of each of the first and second flank faces 7, 8 adjacent to the nose edges of the respective first and second cutting edges 5, 6 in a direction parallel to the central axis L is approximately 60% of the total thickness t of the cutting insert 40.

[0055] 12-14 are schematic diagrams of a cutting insert 90 according to a third embodiment. The cutting insert 90 differs from the cutting insert 40 in the second embodiment in that it is double-sided, i.e., includes first and second opposing rake faces 91, 92 disposed on the second side 3 and corresponding first and second opposing cutting edges 93, 94 formed at the intersections between the first and second flank faces 7, 8 and the first and second opposing rake faces 91, 92, respectively. In such an embodiment, a first transition region 35 of the first side 2 extending between the first contact surface 34 and the first and second flank surfaces 7, 8 is at least partially formed by the first and second rake surfaces 11, 12, and a second transition region 37 of the second side 3 extending between the second contact surface 36 and the first and second flank surfaces 7, 8 is at least partially formed by the first and second opposing rake surfaces 91, 92. In this third embodiment, the maximum extension length h of each of the first and second flank surfaces 7, 8 adjacent the nose edges of the first and second cutting edges 5, 6, respectively, in a direction parallel to the central axis L is about 50% of the total thickness t of the cutting insert 90.

[0056] While the above description contains a number of specificities, these should not be construed as limiting the scope of the concepts described herein, but rather as merely providing illustrations of a number of exemplary embodiments of the concepts described herein. It will be understood that the scope of the concepts described herein fully encompasses other embodiments that may become apparent to one of ordinary skill in the art, and thus the scope of the concepts described herein should not be limited.

Claims

1. A cutting insert (1, 40, 90) for a turning tool, said cutting insert comprising: a first side (2) and a second side (3) disposed opposite each other and facing in opposite directions, said first and second sides generally extending in respective first and second planes (P1, P2) that are parallel to each other, said first side comprising a first rake face (11); a central axis (L) extending from the first side portion (2) to the second side portion (3) in a direction perpendicular to the first and second planes (P1, P2); a peripheral surface (4) connecting the first side portion (2) and the second side portion (3), the peripheral surface (4) including a first flank surface (7) extending parallel or substantially parallel to the central axis (L); a first cutting edge (5) disposed at an intersection between the first flank surface (7) and the first rake face (11), the first cutting edge comprising a first nose cutting edge (51); the cutting insert has a maximum thickness (t) measured in a direction parallel to the central axis (L) from the first side (2) to the second side (3), and the first flank surface (7) adjacent to the first nose cutting edge (51) has an extension length (h) in a direction parallel to the central axis (L) that is less than 75% of the maximum thickness (t) of the cutting insert.

2. 2. The cutting insert according to claim 1, wherein the first flank surface adjacent the first nose cutting edge has an extending length (h) in a direction parallel to the central axis that is greater than 30% of the maximum thickness (t) of the cutting insert.

3. 3. The cutting insert according to claim 1, wherein the first flank surface adjacent to the first nose cutting edge has an extension length (h) in a direction parallel to the central axis that is 40% to 70% of the maximum thickness (t) of the cutting insert.

4. The cutting insert according to any one of claims 1 to 3, wherein the second side comprises a contact surface (36) arranged to abut against a support surface of an insert seat of a turning tool.

5. The cutting insert according to claim 4, wherein the second side comprises a transition area (37) extending from the contact surface (36) to the first flank surface (7).

6. The cutting insert according to claim 5, wherein the transition region (37) includes an inclined surface portion that is oblique to the central axis (L).

7. 7. The cutting insert according to claim 5 or 6, wherein, from a point of intersection between the first flank surface (7) and the transition region (37), in a direction along a radial line towards the central axis (L), the transition region (37) extends a distance that is at least 10% of the total distance along such radial line from said point to the central axis (L).

8. 8. The cutting insert according to claim 1, wherein the first cutting edge (5) comprises a first main cutting edge (52) connected to the first nose cutting edge (51) and extending therefrom along the intersection between the first flank surface (7) and the first rake face (11).

9. The cutting insert according to claim 8, wherein the distance from the first main cutting edge (52) to the second side portion (3) decreases with increasing distance from the first nose cutting edge (51).

10. 10. The cutting insert according to claim 1, wherein the peripheral surface comprises a second flank surface (8), the first side portion (2) or the second side portion (3) comprises a second rake face (12), a second cutting edge (6) is disposed at the intersection between the second flank surface (8) and the second rake face (12), the second cutting edge (6) comprises a second nose edge (61), and the second flank surface (8) adjacent to the second nose edge (61) has an extension length (h) in a direction parallel to the central axis (L) that is less than 75% of the maximum thickness (t) of the cutting insert.

11. The cutting insert (90) according to any one of claims 1 to 10, wherein the second side (3) comprises a first opposing rake face (91) opposite the first rake face (11), and a first opposing cutting edge (93) is disposed at the intersection between the first opposing rake face (91) and the first flank face (7).

12. The cutting insert (40, 90) according to any one of claims 1 to 11, wherein the cutting insert has a rhomboidal or substantially rhomboidal basic shape in plan view of the first or second side.

13. A turning tool (10) comprising a tool body (20) including an insert seat in which a cutting insert (1, 40, 90) according to any one of claims 1 to 12 is mounted.

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