Patent Publication Number: US-11642727-B2

Title: Turning insert

Description:
RELATED APPLICATION DATA 
     This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2019/059722 filed Apr. 16, 2019 claiming priority to EP 18169560.2 filed Apr. 26, 2018. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention belongs to the technical field of metal cutting. More specifically the present invention belongs to the field of turning inserts used for metal cutting in machines such as CNC-machines. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention refers to a turning insert according to the preamble of claim  1 . In other words, the present invention refers to a turning insert comprising a top surface, an opposite bottom surface, wherein a reference plane located parallel to and between the top surface and the bottom surface, wherein a center axis extends perpendicular to the reference plane, a side surface connecting the top surface and the bottom surface, a nose portion comprising a convex nose cutting edge, a first cutting edge and a second cutting edge, wherein the nose cutting edge connects the first and second cutting edges, in that in a top view the first and second cutting edges forms a nose angle of 71-85° relative to each other, wherein a bisector extends equidistantly from the first and second cutting edges, in that the nose portion comprises a third convex cutting edge adjacent to the first cutting edge and a fourth cutting edge adjacent to the third convex cutting edge, in that in a top view the fourth cutting edge forms an angle of 10-30° relative to the bisector, in that the bisector intersect the nose cutting edge at a nose cutting edge center point, in that the third convex cutting edge and the fourth cutting edge is connected by a first transition point, in that the first cutting edge and third convex cutting edge is connected by a second transition point, in that the top surface comprises a first protrusion, in that the first protrusion comprises a first chip breaker wall facing the fourth cutting edge, and in that the first chip breaker wall is arranged between an upper border line and a lower border line. 
     Such a turning insert is disclosed in EP3153261A1. In turning of a metal work piece, the metal work piece rotates around a center axis. The metal work piece is clamped at one end by a chuck or jaws or by other means, which means rotates. The end of the work piece which is clamped can be called a clamping end or a driving end. For stable clamping, the clamping end or the driving end of the metal work piece has a larger diameter than the opposite end of the metal work piece and/or has a larger diameter of a portion of the metal work piece located between the clamping end and the opposite end. Alternatively, the metal work piece has a constant diameter before a machining, i.e. metal cutting, operation. The turning insert is moved in relation to the metal work piece. This relative movement is called feed. The movement of the turning insert can be in a direction parallel to the center axis of the metal work piece, this is commonly called longitudinal feed or axial feed. The movement of turning insert can furthermore be in a direction perpendicular to the center axis of the metal work piece, this is commonly called radial feed or facing. Other angles of movement are also possible. Such turning is commonly known as copying or copy-turning. During the relative movement of the turning insert, material from the metal work piece is removed in the form of chips. The chips are preferably short and/or have a shape or direction of movement which prevents chip jamming and/or do not give a poor surface finish of the machined surface. 
     The turning insert in EP3153261A1 is intended to overcome drawbacks in machining an external 90° corner in a metal work piece. Said turning insert can be used in axial turning (longitudinal turning), i.e. where the movement of the turning insert is in a direction parallel to the center axis of the metal work piece. Said turning insert give good tool life. 
     SUMMARY OF THE INVENTION 
     The inventors have found that under certain cutting conditions the chip control and/or chip breaking can be further improved in longitudinal turning. 
     Especially, there is a need to improve chip control and/or chip breaking in longitudinal turning at low (&lt;45°) entering angles and at low cutting depth, and/or in low feed rates. Said need is especially present when the chip-breaking properties of the work piece material is low, such as when the work piece material is e.g. a low carbon (maximum 0.20 wt. % Carbon content) steel (such as S355J2 according to EN 10025-2:2004). 
     An object of the present invention is to provide an improvement in at least some of the above described aspects. This is achieved by a the above described turning insert where a distance from at least a portion of the fourth cutting edge to the reference plane is increasing at increasing distance from the nose cutting edge, in that a second protrusion is arranged between the nose cutting edge and the first protrusion, in that the second protrusion intersects the bisector, in that the second protrusion comprises a second chip breaker wall, and in that a distance from the second chip breaker wall to the reference plane is shorter than a distance from the upper border line of the first chip breaker wall to the reference plane. 
     By such an insert, the inventors have found that the insert wear is low because the turning insert can be used at low (&lt;45°) entering angles in longitudinal turning. The relatively large nose angle gives reduced insert wear at the nose cutting edge. The nose angle is sufficiently small, less or equal than 85°, so that a 90° corner can be machined. 
     The inventors have found that by using the above described turning insert under such conditions, chip breaking is surprisingly significantly improved, especially at cutting depths of up to 1.0 mm and/or at feed rates of 0.4-0.7 mm/rev, and/or especially when the work piece is a steel having a Carbon content of maximum 0.20 wt. % and/or where the fourth cutting edge is active at an entering angle of 15-35°, preferably 20-30°. 
     By such an insert, the inventors have found that the insert wear is low because the turning insert can be used at low (&lt;45°) entering angles in longitudinal turning. The relatively large nose angle gives reduced insert wear at the nose cutting edge. The nose angle is sufficiently small, less or equal than 85°, so that a 90° corner can be machined. 
     The top surface comprises a rake face. The bottom surface comprises a seating surface. In other words, at least a portion of the bottom surface is arranged to be in contact with a seating surface of a tool body or a shim located in a seat of a tool body. The reference plane is mid-way between the top and bottom surfaces in such a way that the distance from the reference plane to the top surface and bottom surface is equal or substantially equal. 
     The top and bottom surfaces may be identical or shaped in a corresponding manner. In other words, the turning insert may be symmetrical in relation to the reference plane. By such turning insert, the use of the turning insert may be increased. 
     Preferably, the bottom surface area is smaller than the top surface area, where said areas are projected onto the reference plane. By such turning insert, which is a positive turning insert, the accessibility is improved and the cutting forces may be reduced. 
     The bottom surface may be flat and parallel to the reference plane. The bottom surface may comprise one or more insert locking means, e.g. in the form of one or more grooves or ridges. 
     The center axis passes through a geometrical center of the insert. Preferably the center axis coincides with a center axis of a through hole having openings in the top and bottom surfaces. The reference plane is perpendicular to said center axis. The nose cutting edge form the most distal portions of the turning insert, in other words, the nose cutting edge is the part of the cutting insert which are located at the greatest distance from the center axis. A nose portion is a peripheral portion of the cutting insert where a rake face is formed on the top surface between the first, second and nose cutting edges. The nose cutting edge has the shape of an circular arc or a portion of a circle having its center between the first and second cutting edge, wherein the circle preferably has a radius of 0.2-2.0 mm. In other words, the nose cutting edge is preferably a convex cutting edge having a radius of curvature of 0.2-2.0 mm. The nose angel of 71-85° give the advantage that a 90° corner, i.e. two wall surfaces being perpendicular to each other, can be machined with one nose portion of the turning insert, without any reorientation of the turning insert. Alternatively, a nose angle of 71-85° is equal to a nose cutting edge having the shape of a circular arc of an angle of 71-85°. The nose cutting edge may have a shape that deviates slightly from a perfect circular arc. 
     In a top view, the radius of curvature of the third cutting edge is preferably greater than the radius of curvature of the nose cutting edge. 
     A top view is a view in which the top surface is facing the viewer and the bottom surface is facing away from the viewer. The first and second cutting edges are preferably straight in a top view. If the first and second cutting edges are not straight, e.g. slightly convex, slightly concave or saw-tooth shaped, the angles are measured using straight lines between the end points of the first and second cutting edges respectively. 
     By such a turning insert, the cutting force direction and/or chip flow direction will be less dependent of the cutting depth, i.e. depth of cut. 
     In this context, a concave or convex radius of curvature greater than 200 mm is considered straight or linear. If any of the first, second and fourth cutting edges have a radius of curvature greater than 200 mm, this radius of curvature is substantially greater, or more than 10 times greater, than the radius of curvature of the third cutting edge. 
     The fourth cutting edge preferably has a length in a top view which is 4-25 mm, even more preferably 6-10 mm. The length of the fourth cutting edge in a top view is greater, preferably 3-7 times greater, even more preferably 4-5 times greater, than the length of the first cutting edge. 
     The fourth cutting edge is preferably straight or linear in a top view. In a top view, the turning insert, measured along a line perpendicular to the bisector and intersecting the center axis, has a width of 8-20 mm, more preferably 9-13 mm. 
     The first and second cutting edges preferably have a length of 0.5-20.0 mm, even more preferably 1.0-3.0 mm. At least a portion of, preferably more than 50%, even more preferably more than 90% of the fourth cutting edge is sloping away from the bottom surface and the reference plane away from the nose cutting edge in a side view. The fourth cutting edge preferably forms an angle in relation to the reference plane which is in the range of 1-5°. 
     The nose portion is preferably symmetrical or substantially symmetrical in relation to the bisector. 
     The first protrusion extends further away from the reference plane than surrounding portions of the top surface. The first protrusion preferably has an extension along the bisector. The first protrusion is spaced apart from the nose cutting edge, the first cutting edge, the second cutting edge, the third cutting edge and the fourth cutting edge. 
     The second protrusion protrudes away from the reference plane. The second protrusion may be spaced apart from or connected to the first protrusion. The second protrusion is spaced apart from the nose cutting edge. 
     The second protrusion is preferably arranged symmetrical in relation to the bisector. 
     The second protrusion comprises a second chip breaker wall, which is inclined in relation to the reference plane. 
     The second protrusion is preferably oval or substantially oval in a top view. 
     Preferably, in a top view a distance along the bisector from a nose cutting edge center point to highest point of the second protrusion along the bisector is 0.8-1.3 mm, even more preferably 0.9-1.2 mm. 
     Preferably, the turning insert comprises a second nose portion comprising a further nose cutting edge. In such case, all nose cutting edges are preferably located in a common plane parallel to the reference plane. 
     Preferably, each nose portion comprises exactly one second protrusion. 
     Preferably, no protrusion is located between the first protrusion and the third and forth cutting edges, respectively. 
     A cutting edge is an edge of the turning insert which borders to a rake face and a clearance surface. 
     The turning insert is for metal cutting and is made from or comprises a wear resistant material such as preferably cemented carbide. Alternatively, the turning insert may comprise a wear resistant material such as cermet, cubic Boron Nitride (CBN), polycrystalline diamond (PCD). 
     According to an embodiment, an angle which the first chip breaker wall forms in relation to the reference plane is increasing away from the bisector. 
     By such a turning insert, chip breaking is improved, especially at cutting depth up to 1.0 mm. 
     Preferably, said angle is gradually increasing away from the bisector. 
     According to an embodiment, in a side view a distance from the nose cutting edge center point to the first chip breaker wall is greater than a distance from the second transition point to the first chip breaker wall, in that said first mentioned distance is measured along a first line parallel to the reference plane and intersecting the nose cutting edge center point and in a top view is perpendicular to the cutting edge tangent at the nose cutting edge center point, in that said first mentioned distance is 1.3-2.3 mm, 
     in that said second mentioned distance is measured along a second line parallel to the reference plane and intersecting the second transition point and in a top view perpendicular to the cutting edge tangent at the second transition point, and in that said second mentioned distance is 0.7-1.3 mm. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, an angle which the first chip breaker wall forms in relation to the reference plane at the first line is 15-25°. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, in a side view a distance from the second transition point to the first chip breaker wall is greater than a distance from the first transition point to the first chip breaker wall, in that said first mentioned distance is measured along a second line parallel to the reference plane and intersecting the second transition point and in a top view is perpendicular to the cutting edge tangent at the second transition point, in that said second mentioned distance is measured along a third line parallel to the reference plane and intersecting the first transition point and in a top view perpendicular to the cutting edge tangent at the first transition point, and in that said second mentioned distance is. 
     According to an embodiment, an angle which the first chip breaker wall forms in relation to the reference plane at the second line is 23-35°. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, an angle which the first chip breaker wall forms in relation to the reference plane at the third line is 30-40°. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, in a side view a distance from the nose cutting edge center point to the second chip breaker wall is shorter than a distance from the first transition point to the first chip breaker wall, in that said first mentioned distance is measured along a first line parallel to the reference plane and intersecting the second transition point and in a top view is perpendicular to the cutting edge tangent at the second transition point, and in that said second mentioned distance is measured along a third line parallel to the reference plane and intersecting the first transition point and in a top view perpendicular to the cutting edge tangent at the first transition point. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, the second protrusion in a top view is elongated in a direction perpendicular to or substantially perpendicular to the bisector. 
     By such a turning insert, chip breaking is further improved. 
     According to an embodiment, the top surface comprises a land surface extending between an inner border line thereof and the cutting edge portions, in that the land surface forms a constant or substantially constant positive rake angle which is 6-16°. 
     By such a turning insert, chip breaking is further improved. By such a turning insert, cutting forces are decreased. 
     In other words, the turning insert comprises a positive rake angle, which preferably is within the range of 6-16°. In other words, preferably the top surface is sloping downwards, i.e. towards the reference plane, from the cutting edges towards the lower border line. 
     Preferably in a top view a width of the land surface is smaller along the nose cutting edge than along the third convex cutting edge, where said widths of the land surface is measured from the inner border line thereof to and perpendicular to the respective cutting edge. 
     Preferably, along the bisector the second protrusion protrudes away from the reference plane between the inner border line of the land surface and the lower border line of the first chip breaker wall. 
     According to an embodiment, the distance from at least a portion of the third convex cutting edge to the reference plane is decreasing at increasing distance from the nose cutting edge, in that in a side view, the lowest point of the third and fourth cutting edges is the first transition point, or a point within 1.00 mm from the first transition point, in that a distance between the upper and lower border lines is decreasing away from the nose cutting edge, in that said distance is measured in a top view perpendicular to the fourth cutting edge, in that the distance from the first cutting edge to the reference plane is decreasing at increasing distance from the nose cutting edge. 
     By such a turning insert, the chip breaking is further improved, especially at cutting depths of up to 0.7 mm. 
     Preferably, the third cutting edge forms an angle of 1-6° relative to the reference plane. 
     Preferably, a distance from the reference plane to lowest point of the third and fourth cutting edges is shorter than, preferably 0.1-0.2 mm shorter than a distance from the reference plane to the nose cutting edge. In other words, in a side view each of the third and fourth cutting edges slope upwards from the transition point, or from a point in the vicinity of, i.e. within 1.00 mm from the transition point. 
     The distance from the first cutting edge to the reference plane is decreasing at increasing distance from the nose cutting edge, i.e. the distance from different points of the first cutting edge to the reference plane varies in such a way that that this distance is decreasing at increasing distance from the nose cutting edge. In other words, the first cutting edge slopes towards the reference plane in a side view. In other words, the nose cutting edge is located at a greater distance from the reference plane than at least a majority of the first cutting edge. 
     Preferably, the first cutting edge forms an angle of 1-6° relative to the reference plane. 
     According to an embodiment, the turning insert comprises a second nose portion, and in that in a top view the turning insert is 120° or 180° symmetrical or substantially 120° or 180° symmetrical, and in that the nose portion is symmetrical or substantially symmetrical in relation to the bisector. 
     The turning insert is 120° or 180° symmetrical, in other words, if the turning insert is rotated 120° or 180° around the center axis A 1 , the turning insert is identical. In other words, the at least two opposite nose portions are identical. 
     Each nose portion is thus symmetrical in relation to the bisector, i.e. each nose portion has a shape which is mirrored in a plane perpendicular to the reference plane and comprising the bisector. In other words, the half of the nose portion which is located on one side of the bisector is a mirror shape of the other half of the nose portion located on the opposite side of the bisector. The symmetry in this meaning is the shape and extension of the cutting edges and topography, e.g. chip breaker formation, of the top surface. 
     According to an embodiment, a turning tool comprises a turning insert and a tool body, wherein the tool body comprising a front end, an opposite rear end, a main extension along a longitudinal axis extending from the front end to the rear end, an insert seat formed in the front end in which the turning insert is mountable such that in a top view the distance from the forth cutting edge of an active nose portion to the longitudinal axis of the tool body is shorter than the distance from the second cutting edge of an active nose portion to the longitudinal axis of the tool body, in that the bisector of the active nose portion forms an angle 40-50° relative to the longitudinal axis A 2 . 
     By such a turning tool, the performance is further improved when the turning tool is moving in a direction perpendicular to the longitudinal axis of the tool body and parallel to the rotational axis of the metal work. If the entering angle is less than 10°, the width of the chips would be too wide resulting in poor chip control, and the risk of vibration would increase. Also, less depth of cut is possible. If the entering angle is over 45°, the insert wear would increase. 
     The active nose portion, i.e. the nose portion which is in an active position, is the nose portion which in a mounted state comprises the nose cutting edge which in a top view is the part of the turning insert which is most distal in relation to the rear end of the tool body and in relation to the longitudinal axis of the tool body. The angle which the first cutting edge of the active nose portion forms in relation to the longitudinal axis of the tool body is greater than the angle which the second cutting edge of the active nose portion forms in relation to the longitudinal axis of the tool body. The angle which the fourth cutting edge of the active nose portion forms in relation to the longitudinal axis of the tool body is greater than the angle which the second cutting edge of the active nose portion forms in relation to the longitudinal axis of the tool body. The center axis of the turning insert in a mounted state is perpendicular or substantially perpendicular, or within +/−20° from being perpendicular, in relation to the longitudinal axis of the tool body. The insert seat of the tool body is open cavity or a cut-out in which a turning insert is mountable. Example of means for mounting the insert includes a screw and a top-clamp. The rear end of the tool body is the part of the tool body that is located at a greatest distance from the active nose cutting edge. The rear end of the tool body is mounted to or connected to a machine tool, such as a turning lathe, preferably a computer numerical control (CNC) lathe. 
     According to an embodiment, a method to generate a cylindrical surface on a metal work piece comprises the steps of: providing a turning tool, rotating the metal work piece around a rotational axis, positioning the first cutting edge of an active nose portion such that the first cutting edge forms a smaller angle relative to the rotational axis of the metal work piece than the angle formed by the second cutting edge relative to the rotational axis of the metal work piece, positioning the longitudinal axis of the tool body perpendicular to the rotational axis of the metal work piece, and moving the turning insert in a direction parallel to the rotational axis such that the first cutting edge is active and is ahead of the surface generating nose cutting edge in the direction of movement of the turning insert, such that the fourth cutting edge is active at a entering angle of 10-45°, such that the lowest point of the third and fourth cutting edges is active, and such that a cylindrical surface is formed. 
     By such a method, a prior or subsequent machining step can be in the form of out-facing, such that the second cutting edge is active. 
     In other words, the forth cutting edge forms an entering angle of 10-45°, even more preferably 20-30°, when the turning tool is moving in a direction perpendicular to the longitudinal axis A 2  of the tool body. 
     A cylindrical surface is a surface which has an extension along the rotational axis of the metal work piece and is located at a constant distance from the rotational axis of the metal work piece. Constant distance means a wavy surface where the wave height is less than 0.10 mm. An active nose portion is the nose portion which is positioned such that during cutting, the nose portion comprises at least one cutting edge which cuts chips from the metal work piece. The active nose portion is positioned closer to the rotational axis of the metal work piece and closer to the first end of the metal work piece than any other nose portion, in the case the turning insert comprises more than one nose portion. The fourth cutting edge is active means that the fourth cutting edge cuts chips from the metal work piece. The first cutting edge is active. Further, a portion of the nose cutting edge adjacent to the active first cutting edge is active. The second cutting edge, formed on the same nose portion as the first cutting edge, is inactive simultaneously as the first cutting edge is active. The moving of the turning insert is commonly known as feeding, in this case axial feed. The axial feed is preferably in a direction away from an end of the work piece which is clamped by clamping means, such as e.g. a chuck or jaws. 
     The method preferably further comprises the step of setting the cutting speed to within the range of 30-1000 m/min, preferably within the range of 40-800 m/min. 
     Preferably, the method comprises the further step of arranging the first cutting edge such that it forms an entering angle of 2.5-7.5°, even more preferably 4-6°. 
     Preferably, the method comprises the further step of setting the radial distance between the cylindrical surface and the transition point is within the range of 0.4-2.0 mm, even more preferably 0.4-1.0 mm. 
     Preferably, the method comprises the further step of positioning the nose cutting edge a greater distance from the longitudinal axis of the tool body than all other parts of the turning tool. 
     According to an embodiment, the method comprises the further steps of selecting the work piece material ( 50 ) to be a steel having a Carbon content of maximum 0.20 wt. %, and selecting cutting data such that a feed rate is 0.4-0.7 mm/rev and/or a cutting depth is less than or equal to 1.0 mm. 
     By such a method, the improvement in chip breaking is especially significant. 
     Preferably, a feed rate is 0.4-0.7 mm/rev and a cutting depth is less than or equal to 0.1-0.8 mm. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will now be explained in more detail by a description of embodiments of the invention and by reference to the accompanying drawings. 
         FIG.  1    is a perspective view showing a turning insert according to a first embodiment. 
         FIG.  2    is a second perspective view showing the turning insert in  FIG.  1   . 
         FIG.  3    is a top view of the turning insert in  FIG.  1   . 
         FIG.  4    is a side view of the turning insert in  FIG.  1   , taken in the direction indicated by arrow A in  FIG.  3   . 
         FIG.  5    is a top view of the turning insert in  FIG.  1   . 
         FIG.  6    is a partially enlarged view of a cross section taken along the line B-B in  FIG.  5   . 
         FIG.  7    is a partially enlarged view of a cross section taken along the line D-D in  FIG.  5   . 
         FIG.  8    is a partially enlarged view of a cross section taken along the line C-C in  FIG.  5   . 
         FIG.  9    is a schematic view showing a turning method using a turning tool comprising the turning insert in  FIG.  1   . 
         FIG.  10    is a chip chart from turning using a known turning insert. 
         FIG.  11    is a chip chart from turning using the turning insert according to the first embodiment. 
     
    
    
     All turning insert figures have been drawn to scale. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Attention is now drawn to  FIGS.  1 - 9   , which show a turning insert  1  according to a first embodiment. The turning insert  1  comprises a top surface  8  and an opposite bottom surface  9 , where a reference plane RP is located parallel to and between the top surface  8  and the bottom surface  9 . The top surface  8  is or comprises a rake face. The bottom surface  9  functioning as a seating surface. 
     A center axis A 1  extends perpendicular to the reference plane RP. A screw hole having openings in the top surface  8  and the bottom surface  9  is concentric with the center axis A 1 . 
     A side surface  13  connects the top surface  8  and the bottom surface  9 . A nose portion  15  comprises a convex nose cutting edge  10 , a first cutting edge  11  and a second cutting edge  12 . The nose cutting edge  10  connects the first  11  and second  12  cutting edges. In a top view, as seen in  FIG.  2   , the first  11  and second  12  cutting edges on the same nose portion  15  forms a nose angle α of 71-85° relative to each other, which nose angle α in  FIG.  2    is 80°. 
     In a top view, the nose cutting edge  10 , which is part of the nose portion, is located at a largest distance from the center axis A 1 , i.e. at a larger distance from the center axis A 1  than all other parts of the turning insert, except for the nose cutting edge which is part of a second nose portion  15 ′. 
     In a top view, imaginary lines coinciding with the first and second cutting edges  11 ,  12 , respectively, converge at a point outside the turning insert  1 . A bisector  7  extends equidistantly from the first  11  and second  12  cutting edges. The bisector  7  intersects the center of the nose cutting edge  10  and the center axis A 1  of the turning insert  1 . 
     The nose portion  15  comprises a third convex cutting edge  60  adjacent to the first cutting edge  11  and a fourth cutting edge  61  adjacent to the third convex cutting edge  60 . In a top view, as in  FIG.  3   , the fourth cutting edge  61  forms an angle β of 10-30° relative to the bisector  7 . The third convex cutting edge  60  and the fourth cutting edge  61  is connected by a first transition point  20 . 
     The turning insert  1  according to the first embodiment is single sided turning insert, or a positive turning insert. The side surface  13  comprises clearance surfaces which are tapered inward from the top surface  8  to the bottom surface  9 . The advantages from the clearance surface arrangement is that out-facing can be performed at small metal work piece diameters, and that larger depth of cut is possible in out-facing. 
     As seen in e.g.  FIG.  4   , a distance from at least a portion of the fourth cutting edge  61  to the reference plane RP is increasing at increasing distance from the nose cutting edge  10 . A distance from at least a portion of the third convex cutting edge  60  to the reference plane RP is decreasing at increasing distance from the nose cutting edge  10 . In a side view as seen in  FIG.  4   , the lowest point of the third and fourth cutting edges  60 ,  61  is the first transition point  20 , or a point within 1.00 mm from the first transition point  20 . The distance from the first cutting edge  11  to the reference plane RP is decreasing at increasing distance from the nose cutting edge  10 . 
     As seen in e.g.  FIG.  3   , the top surface  8  comprises a first protrusion  30 . The first protrusion  30  comprises a first chip breaker wall  34  facing the forth cutting edge  61 . The first chip breaker wall  34  is arranged between an upper border line  21  and a lower border line  22 . 
     The top surface of the first protrusion  30  is flat and parallel to the reference plane RP. The first protrusion  30  is the part of the top surface  8  of the turning insert  1  which are located at the greatest distance from the reference plane RP. 
     As seen in e.g.  FIG.  5   , a distance D 1  between the upper border line  21  and the forth cutting edge  61  is decreasing away from the nose cutting edge  10 , where said distance D 1  is measured in a plane perpendicular to the reference plane RP and perpendicular to the fourth cutting edge  61 . Said upper border line  21  preferably extend in a plane which is parallel to the reference plane. Said distance D 1  decreases from a maximum value of 0.3-0.5 mm to a minimum value of 0.0-0.1 mm. 
     The turning insert  1  comprises a nose portion  15  and an opposite second nose portion  15 ′. In other words, the turning insert comprises two opposite and identical, or substantially identical, nose portions  15 ,  15 ′ formed 180° relative each other around the center axis A 1  of the turning insert  1 . Thus, in a top view as seen in e.g.  FIG.  3   , the turning insert  1  is 180° symmetrical. The first, second and fourth cutting edges  11 ,  12 ,  61  are linear or straight or substantially linear or straight. The nose portion  15  is symmetrical in relation to the bisector  7 . Further, as seen in e.g.  FIG.  3   , the radius of curvature of the third cutting edge  60  is greater than the radius of curvature of the nose cutting edge  10 . 
     In a side view, such as in seen in  FIG.  4   , the fourth cutting edge  61  slopes upwards, such that the fourth cutting edge  61  has the lowest point thereof closer to the nose cutting edge  10 . In other words, the distance from the fourth cutting edge  61  to the reference plane RP varies in such a way that that this distance is increasing at increasing distance from the nose cutting edge  10 . 
     Further, the first, second and third cutting edges  10 ,  11 ,  60  are in a side view sloping downwards, i.e. in an opposite direction compared to the fourth cutting edge  61 , such that in relation to the bottom surface  9 , the nose cutting edge  10  is further away than the first and second cutting edges  11 ,  12 , which in turn are further away than the third cutting edges  60 . In this context, that a cutting edge is further away than another cutting edge refers to the respective mid-points of said cutting edges. 
     Bisectors  7  extend equidistantly from each pair of first  11  and second  12  cutting edges. Each bisector  7  intersects the center axis A 1 , and the bisectors  7  extend in a common direction. 
     As seen in e.g.  FIG.  1   , a second protrusion  44  is arranged between the nose cutting edge  10  and the first protrusion  30 . The second protrusion  44  intersects the bisector  7 . The second protrusion  44  comprises a second chip breaker wall  35 . 
     The second protrusion  44  is in a top view, as seen in e.g.  FIG.  3   , elongated in a direction perpendicular to or substantially perpendicular to the bisector  7  and is oval shaped or substantially oval shaped. 
     As seen in  FIG.  6   , a distance from the second chip breaker wall  44  to the reference plane RP is shorter than a distance from the upper border line  21  of the first chip breaker wall  34  to the reference plane RP. 
     In a top view as seen in e.g.  FIG.  3   , the first, second and fourth cutting edges  11 ,  12 ,  61  are linear or straight or substantially linear or straight, and the radius of curvature of the third cutting edge  60  is greater than the radius of curvature of the nose cutting edge  10 . 
       FIG.  5    show lines B-B, D-D and C-C, which intersects and are tangent to the nose cutting edge center point  52 , the second transition point  53 , and the first transition point  20 , respectively. 
       FIG.  6    show a cross section taken along the line B-B (the bisector  7 ) in  FIG.  5   , where a first line  46  intersect the nose cutting edge center point  52 .  FIG.  7    show a cross section taken along the line D-D in  FIG.  5   , where a second line  47  intersect the second transition point  53 .  FIG.  8    show a cross section taken along the line C-C in  FIG.  5   , where a third line  48  intersect the first transition point  20 . 
     As seen in  FIGS.  6 - 8   , an angle γ, δ, ε which the first chip breaker wall  34  forms in relation to the reference plane RP is increasing in a direction away from the bisector  7 . 
     As seen in  FIGS.  6  and  7   , a distance  40  along the first line  46  from the nose cutting edge center point  52  to the first chip breaker wall  34  is greater than a distance  41  along the second line  47  from the second transition point  53  to the first chip breaker wall  34 . Said first mentioned distance  40  is 1.3-2.3 mm, more precisely 1.8 mm. Said second mentioned distance  41  is 0.7-1.3 mm, more precisely 1.0 mm. 
     As seen in  FIG.  6   , an angle γ which the first chip breaker wall  34  forms in relation to the reference plane RP at the first line  46  is 15-25°, more precisely 30°. 
     The first, second and third lines  46 ,  47 ,  48  in  FIGS.  6 - 8    are each parallel to the reference plane RP. 
     As seen in  FIGS.  7  and  8   , a distance  41  along the second line  47  from the second transition point  53  to the first chip breaker wall  34  is greater than a distance  42  along the third line  48  from the first transition point  20  to the first chip breaker wall  34 . Said second mentioned distance  42  is 0.6-1.2 mm, more precisely 0.9 mm. 
     As seen in  FIG.  7   , an angle δ which the first chip breaker wall  34  forms in relation to the reference plane RP at the second line  47  is 23-35°, more precisely 29°. 
     As seen in  FIG.  8   , an angle ε which the first chip breaker wall  34  forms in relation to the reference plane RP at the third line  48  is 30-40°, more precisely 35°. 
     As seen in  FIGS.  6  and  8   , a distance  43  along the first line  46  from the nose cutting edge center point  52  to the second chip breaker wall  35  is shorter than a distance  42  along the third line  48  from the first transition point  20  to the first chip breaker wall  34 . Said first mentioned distance  43  is 0.5-1.1 mm, more precisely 0.8 mm. 
     As seen in e.g.  FIG.  3   , the top surface  8  comprises a land surface  45  extending between an inner border line  55  thereof and the cutting edge portions  10 ,  11 ,  12 ,  60 ,  61 . As seen in  FIG.  8   , the land surface  45  forms a constant or substantially constant positive rake angle λ which is 6-16°, more precisely 11°. 
     In  FIG.  9   , it is shown a turning tool  3  comprising the turning insert  1  according to the first embodiment and a tool body  2 . The tool body is made from steel. The tool body  2  comprising a front end  44  and an opposite rear end (not shown). A main extension of the tool body  2  is along a longitudinal axis A 2  extending from the front end  44  to the rear end. An insert seat  4  is formed in the front end  44 . The turning insert  1  is mounted or mountable in the insert seat  4  such that in a top view, as shown in  FIG.  9   , the distance from the forth cutting edge  61  of an active nose portion  15  to the longitudinal axis A 2  of the tool body is shorter than the distance from the second cutting edge  12  of an active nose portion  15  to the longitudinal axis A 2  of the tool body. As seen in  FIG.  9   , one nose portion  15 , located closer to the rotational axis A 3  than the opposite inactive nose portion  15 ′, is active. Active means that the nose portion as placed such that it can be used for cutting chips from the metal work piece  50 . 
     The bisector  7  of the active nose portion  15  forms an angle θ in the range of 40-50° relative to the longitudinal axis A 2 . 
     The distance from the forth cutting edge  61  of the active nose portion  15  to the longitudinal axis A 2  of the tool body is shorter than the distance from the second cutting edge  12  of the same active nose portion  15  to the longitudinal axis A 2  of the tool body  2 . 
     The turning insert  1 , seen in top view, is securely and removably clamped in the insert seat  4  or pocket in the tool body  2  by means of a screw (not shown), having a center axis thereof which coincide or substantially coincide with the center axis A 1  of the turning insert  1 . 
     The tool body  2  is may at least partly be in the form of a square shank, which in cross section, in a plane perpendicular to the longitudinal axis A 2 , is square shaped. The sides of the square may have a length of e.g. 25 mm. Alternatively, the tool body may be rectangular in cross section. Alternatively, the tool body may be configured in any other suitable shape where the shape in different cross sections vary. The longitudinal axis A 2  is located at the center of such cross section. The tool body may have a shape comprising e.g. a substantially conical or substantially frustoconical or tapered rear part suitable to be clamped in a tool spindle in a CNC-machine. In such case, the longitudinal axis A 2  is located at the center of such cone. For example, the rear part of the tool body may be shaped in accordance to ISO 26623, or in any other way which is known in the industry under the name of “CAPTO”. 
     In  FIG.  9   , a method to generate a cylindrical surface  53  on a metal work piece  50  is shown, by means of the turning tool  3 . The metal work piece  50  rotates around a rotational axis A 3 . The first cutting edge  11  of the active nose portion  15  is positioned such that the first cutting edge  11  forms a smaller angle relative to the rotational axis A 3  of the metal work piece  50  than the angle formed by the second cutting edge  12  relative to the rotational axis A 3  of the metal work piece  50 . The longitudinal axis A 2  of the tool body  2  is positioned at a constant angle, which is perpendicular to the rotational axis A 3  of the metal work piece  50 . The turning insert  1  is moved in a direction F 1  parallel to the rotational axis A 3  such that the first cutting edge is active and is ahead of the surface generating nose cutting edge  10  in the direction of movement of the turning insert  1 . The fourth cutting edge  61  is active at a entering angle κ 1  of 10-45°, such that the lowest point of the third and fourth cutting edges  60 ,  61  is active, and such that a cylindrical surface  53  is formed. The first transition point  20  is active, as seen in  FIG.  9   . 
     The nose cutting edge  10  is positioned a greater distance from the longitudinal axis A 2  of the tool body  2  than all other parts of the turning tool  3 . By such an arrangement, the turning tool  3  can be used for turning in a further feed direction, which is perpendicular to and away from the rotational axis  3 , without reorientation of the longitudinal axis A 2  in relation to the rotational axis A 3 . 
     The cutting depth is defined by the difference, in distance from the rotational axis A 3 , between the cylindrical surface  53  and the surface  52 . The surface  52  is the surface of the metal work piece  50  which is to be machined by the turning tool  3  in the turning method. The surface  52  may be cylindrical or substantially cylindrical, resulting in a cutting depth which is constant or substantially constant. Alternatively, the surface  52  may have a distance to the rotational axis  52  which varies along the rotational axis, resulting in a cutting depth which varies during the method. 
     The feed direction F 1 , towards the right in  FIG.  9   , is parallel to the rotational axis A 3  and preferably away from an end of the metal work piece  50  which is clamped to the CNC-lathe. The metal work piece  50  is preferably clamped by clamping jaws (not shown, which are pressed against an external surface of the metal work piece  50  at one first end, towards the left-hand side in  FIG.  9   . An opposite second end of the metal work piece  50 , towards the right-hand side in  FIG.  9   , is preferably a free end. 
     In said feed direction, the fourth cutting edge  61  is active at an entering angle κ 1  of 10-45°, preferably 20-40°, which in  FIG.  6    is 25°. The fourth cutting edge  61  is the main cutting edge in said feed direction F 1 , i.e. the majority of the chips are cut by the fourth cutting edge  61 , at least at moderate depth of cut. To a lesser degree, third cutting edge  60 , the first cutting edge  11  and the nose cutting edge  10  are also active. The first cutting edge  11  is ahead of the nose cutting edge  10  in said feed direction F 1 . All parts of the turning insert are ahead of the active nose cutting edge  10  in said feed direction F 1 . The second cutting edge  11 , formed on the active nose portion  15 , is inactive. 
     In the axial turning i.e. the longitudinal turning method shown in  FIG.  9   , chips are curled and/or directed by both the first, and possibly the third and fourth cutting edges  11 ,  60 ,  61 , depending on cutting depth, as well as the nose cutting edge  10 , the first chip breaker wall  34  and the second chip breaker wall  44  and may e.g. be broken by contact with the chip itself. 
     The cylindrical surface  53 , or rational symmetrical surface, generated or formed at least partly by the nose cutting edge in  FIG.  6   , has a wavy shape with small peaks and valleys, and the wavy shape is influenced at least partly by the curvature of the nose radius and the feed rate. The wave height is less than 0.10 mm, preferably less than 0.05 mm. A thread profile is not a cylindrical surface  53  in this sense. 
     The work piece  50  shown in  FIG.  9    is preferably from a steel having a Carbon content of maximum 0.20 wt. %. 
     Attention is now drawn to  FIGS.  10  and  11   , showing photos of chips from turning. The only differences between  FIG.  10    and  FIG.  11    is that the shape of the chips are different, and that  FIG.  10    is a chip chart from the turning insert according to EP3153261A1 ( FIGS.  11   a - e   ), while  FIG.  11    is a chip chart from the turning insert according to the first embodiment as shown in  FIGS.  1 - 9   . Both inserts have a distance in a top view between opposite nose cutting edges which is in the range of 24-26 mm. The chip charts are from turning as shown in  FIG.  9    where the entering angle κ 1  is 25°. The axis in both  FIG.  10    and  FIG.  11    are as follows: the x-axis show feed rates; the photos from left to right 0.3; 0.5; 0.7; 1.0 and 1.2 mm/rev. The y-axis show cutting depth; the photos from bottom to top 0.5; 1.0; 2.0; 3.0 and 4.0 mm. The work piece material is a low-carbon steel designated S355J2 according to the standard EN 10025-2:2004. As can be seen from the chip charts, the chips from the turning insert according to the first embodiment, seen in  FIG.  11   , is an improvement (e.g. shorter chips) over the known turning insert seen in  FIG.  10   , especially at feed rates within the range of 0.4-0.7 mm/rev, and especially at cutting depths within the range of up to 1.0 mm. 
     The turning method shown in  FIG.  9    is preferably performed using a computerized numerical control (CNC) lathe, where the movement of the tool body  2  and the rotation of the metal work piece  50  is controlled by the computerized numerical control (CNC) lathe. The CNC-lathe execute instructions from a computer program. In other words, said computer program has instructions which when executed by a computer numerical control (CNC) lathe cause the computer numerical control (CNC) lathe to perform the method as described above and/or as shown in  FIG.  9   . The computer program may be stored on a computer readable medium. Alternatively, a data stream may be representative of the computer program. 
     Reference is now made to a turning insert according to a second embodiment (not shown). The turning insert according to the second embodiment is double sided, or usable in an upside-down position, in such a way that the top and bottom surface  8 ,  9  are identical. The area of the top and bottom surfaces  8 ,  9  are equal in size. The turning insert is mirror-symmetric in relation to the reference plane. The side surfaces of the turning insert extend along lines parallel to the center axis of the turning insert. In all other aspects, the turning insert according to the second embodiment is identical to, or substantially similar to, the turning insert according to the first embodiment. 
     Reference is now made to a turning insert according to a third embodiment. The turning insert according to the third embodiment comprises three nose portions. Said turning insert is 120° symmetrical. In other words, in a top view, the turning insert is identical or substantially identical if rotated around the center axis by 120° or by 240°. In other aspects, the insert according to the third embodiment is in accordance with the turning insert according to the first embodiment. 
     For all embodiments, the nose angle α, which is the angle between the first and second cutting edges  11 ,  12 , is 75-85°, the angle β is 10-20°, and the radius of curvature in a top view of the nose cutting edge  10  is smaller than the radius of curvature of the third cutting edge. The transitions between all cutting edges are smooth, without sharp corners. By having a relatively large nose angle α, the strength of the nose cutting edge  10  is increased resulting in less wear. By having a relatively large nose angle α, the entering angle for the first cutting edge  11  is relatively small, 2.5-7.5°, which gives reduced wear of the first cutting edge. By having a relatively small radius of curvature of the nose cutting edge  10 , a small radius on the component can be machined, and the turning insert  1  can be used to machine a wider range of shapes. 
     The invention is not limited to the embodiments disclosed, but may be varied and modified within the scope of the following claims. Words such as top, bottom etc. shall be interpreted as understood by the skilled person. The expression top view shall be understood as the view as seen in  FIG.  3   .