Cutting insert and shoulder millng tool

A cutting insert for a shoulder milling tool has a trigonal shape and includes a first surface, a second surface, and a circumferential surface extending between the first surface and the second surface. The circumferential surface includes a countersunk circumferential waist portion. The circumferential surface has a first and a second clearance surface extending along a first and a second main cutting edge. Each of the first and second clearance surfaces forma a negative nominal clearance angle. Each of the first and second main cutting edges is arranged inside the countersunk circumferential waist portion, as seen in the view towards the first and second surfaces, respectively.

RELATED APPLICATION DATA

This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2017/078860 filed Nov. 10, 2017 with priority to EP 16206443.0, filed Dec. 22, 2016.

TECHNICAL FIELD AND BACKGROUND

The present invention relates to a cutting insert for a shoulder milling tool. The present invention further relates to a shoulder milling tool.

One or more cutting inserts are secured to a shoulder milling tool. In a shoulder milling operation, the shoulder milling tool is rotated and fed into a workpiece, wherein a cutting edge of each of the one or more cutting inserts enters into cutting engagement with the workpiece for milling a shoulder therein.

Cutting inserts are available in various different shapes, some of which are indexable, i.e. they comprise more than one useable cutting edge and may be secured in different index positions to the shoulder milling tool. The indexable cutting insert may also be double-sided, i.e. they comprise indexable cutting edges on a first or upper surface as well as a second or lower surface to provide even further useable cutting edges. A cutting insert having a generally hexagonal shape comprising three 90 degree corners is referred to as a trigonally shaped cutting insert.

WO 2015/174200 discloses a trigonally shaped and double-sided cutting insert comprising: a first surface and a second surface which each have a hexagonal shape and which are disposed back-to-back, lateral surfaces that run to the first surface and the second surface, and cutting edges that are respectively formed by a ridgeline at a position where the first surface and the lateral surfaces intersect, and by a ridgeline at a position where the second surface and the lateral surfaces intersect. Seat surfaces are disposed parallel and are respectively formed at the insert center side of the first surface and of the second surface; and depressions for separating the lateral surface that runs to the first surface and the lateral surface that runs to the second surface. The cutting edges are formed of a first cutting edge and a second cutting edge. The first cutting edge is longer than the second cutting edge. An end of the first cutting edge is in a position that is higher than the seat surface.

SUMMARY

It is an object of the present invention to provide a cutting insert for shoulder milling having an improved resistance against the formation of cracks and/or the fracture of the cutting insert.

According to an aspect of the invention, the object is achieved by a cutting insert for a shoulder milling tool. The cutting insert has a trigonal shape and a median plane extending through the cutting insert. The cutting insert comprises a first surface, a second surface, and a circumferential surface extending between the first surface and the second surface, the first and second surfaces, extending on opposite sides of the median plane. The cutting insert comprises a first cutting edge extending along an intersection between the first surface and the circumferential surface, and a second cutting edge extending along an intersection between the second surface and the circumferential surface, the first and second cutting edges, as seen in a view towards the first and second surfaces, respectively, extending along a corner of the cutting insert. The first cutting edge comprises a first main cutting edge, a first corner cutting edge, and a first surface-wiping secondary cutting edge, wherein the first main cutting edge adjoins to the first corner cutting edge, and the first corner cutting edge adjoins to the first surface-wiping secondary cutting edge. The second cutting edge comprises a second main cutting edge, a second corner cutting edge, and a second surface-wiping secondary cutting edge, wherein the second main cutting edge adjoins to the second corner cutting edge, and the second corner cutting edge adjoins to the second surface-wiping secondary cutting edge. The circumferential surface comprises a countersunk circumferential waist portion situated at the median plane. The first main cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second surface-wiping secondary cutting edge, and the first surface-wiping secondary cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second main cutting edge. The circumferential surface comprises a first clearance surface extending along the first main cutting edge, the first clearance surface extending at an acute angle to the median plane along the first main cutting edge, such that the first clearance surface is forming a negative nominal clearance angle. The circumferential surface comprises a second clearance surface extending along the second main cutting edge, the second clearance surface extending at an acute angle to the median plane along the second main cutting edge, such that the second clearance surface is forming a negative nominal clearance angle. The first main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the first surface, and the second main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the second surface.

The main cutting edge being arranged inside the countersunk circumferential waist portion, as seen in the view towards the first or second surface, means that the relevant main cutting edge is arranged closer to a centre of the cutting insert than the countersunk circumferential waist portion. An improved resistance against the formation of cracks and fracturing the whole cutting insert is hereby achieved by the first main cutting edge being arranged inside the countersunk circumferential waist portion. More precisely, the countersunk circumferential waist portion of the cutting insert provides a supporting amount of material (the cutting insert body) extending outside and underneath the first main cutting edge, which not only improves the resistance against crack formation in the first main cutting edge (making it stronger), but also the resistance against cracks propagating past the countersunk circumferential waist portion to the second surface (bottom) of the cutting insert. In other words, the cracks that may nevertheless arise if the first main cutting edge is subjected to excessive wear and/or large cutting forces in a shoulder milling operation are prevented from causing a failure/fracture of the whole cutting insert. Consequently, the second surface-wiping secondary cutting edge on the bottom side of the cutting insert opposite to the first main cutting edge will also remain intact even if the first main cutting edge would exhibit cracks. Moreover, a corresponding amount of material is also provided on the outside and above the second main cutting edge. This also provides an improved resistance against crack propagation through the countersunk circumferential waist portion. In other words, the second main cutting edge, which is also arranged inside the countersunk circumferential waist portion provide an improved resistance against the cracks that may arise in the first surface-wiping secondary edge by preventing them from reaching the bottom side of the cutting insert and thereby cause a similar failure/fracture of the whole cutting insert. The cutting insert hereby exhibits an improved resistance against cracks that may arise in for instance a ramping or plunge milling operation when the first surface-wiping secondary cutting edge is subjected to excessive wear and/or relatively large cutting forces. Consequently, the second main cutting edge on the bottom side opposite to the first surface-wiping secondary cutting edge will also remain intact during such cutting conditions. Accordingly, the cutting insert remains intact and the above mentioned object is not just achieved in conventional shoulder milling, but also in milling operations involving ramping and plunge milling.

Hence, the cutting insert is configured to be fixed in a seat of a shoulder milling tool for cutting a 90° shoulder in a workpiece, but a shoulder milling tool can also be used for ramping and plunge milling including a feed in an axial direction of the shoulder milling tool into the workpiece. The median plane is an imaginary plane extending centrally in between the first and second surfaces and intersects with the circumferential surface. The main cutting edge is extending in the axial direction of the shoulder milling tool and configured for cutting the 90° shoulder or wall in the workpiece, in relation to the surface-wiping secondary cutting edge, which is extending in the radial direction of the shoulder milling tool and configured for surface-wiping the workpiece surface extending perpendicularly to the axial direction of the shoulder milling tool. The trigonal shape of the cutting insert for the shoulder milling tool may hereby provide three indexable (and identical) cutting edges extending along the intersection between the first surface and the circumferential surface, each of the three indexable cutting edges extending along a (90 degree) corner of the cutting insert, wherein three further indexable cutting edges may also extend along an intersection between the second surface and the circumferential surface. In other words, a double-sided and indexable trigonally shaped cutting insert can advantageously provide a total of six indexable cutting edges to be used for shoulder milling (including ramping/plunge milling).

According to an embodiment, the first clearance surface along the first main cutting edge extends at an acute angle within a range of 83-87 degrees to the median plane, and the second clearance surface along the second main cutting edge extends at an acute angle within a range of 83-87 degrees to the median plane. In this manner, a negative nominal clearance angle within a range of 3-7 degrees is provided for each of the first and second clearance surface. This provides a suitable range for arranging the main cutting edges inside the countersunk circumferential waist portion in order to achieve the above mentioned object, while the cutting insert can be mounted at a reasonable radial rake angle for achieving a functional clearance in the shoulder milling tool during milling (further described below).

According to an embodiment, a first flat waist portion of the countersunk circumferential waist portion extends in a plane perpendicularly to the median plane at the first surface-wiping secondary cutting edge and the second main cutting edge, and a second flat waist portion of the countersunk circumferential waist portion extends in a plane perpendicular to the median plane at the second surface-wiping secondary cutting edge and the first main cutting edge. In this manner, the first and second flat waist portions in the countersunk circumferential waist portion provide suitable first and second side abutment surfaces for supporting the cutting insert, in particular a double-sided indexable cutting insert, in the seat of the shoulder milling tool. Hence, it provides well defined (flat) and protected (countersunk) first and second side abutment surfaces for supporting the cutting insert in the seat of the shoulder milling tool.

According to an embodiment, the first surface-wiping secondary cutting edge extends at an angle to the first flat waist portion, as seen in a view towards the first surface, and the second surface-wiping secondary cutting edge extends at an angle to the second flat waist portion, as seen in a view towards the second surface, in such a way that the first and second flat waist portions in relation to the first and second surface-wiping secondary edges become more countersunk toward the corner of the cutting insert. In other words, the first surface-wiping secondary cutting edge is arranged at an angular relation to the first flat waist portion and the second surface-wiping secondary cutting edge is arranged at an angular relation to the second flat waist portion to provide relatively deeper portions of the countersunk circumferential waist portion. In this manner, the first and second flat waist portions are well protected from detrimental wear during milling in an area close to the corner cutting edges where the first and second abutment surfaces for the cutting insert are suitably located as the first and second flat waist portions are more countersunk towards the corner cutting edges and grow more shallow farther away from the corner cutting edges.

According to an embodiment, the first main cutting edge extends at an angle to the second flat waist portion, as seen in a view towards the first surface, and the second main cutting edge extends at an angle to the first flat waist portion, as seen in a view towards the second surface, in such a way that the first main cutting edge is arranged at an increasing distance inside the second flat waist portion in a direction towards the first corner cutting edge, and the second main cutting edge is arranged at an increasing distance inside the first flat waist portion in a direction towards the second corner cutting edge. Thus, the first main cutting edge is extending inwards in relation the second flat waist portion as it extends towards the first corner cutting edge whereby the cutting forces are supported by a successively increasing body of the cutting insert lying underneath the first main cutting edge to enhance the protection against cracks and fracture of the first main cutting edge in proximity to the first corner cutting edge. Furthermore, in ramping or plunge milling with the first surface-wiping secondary cutting edge being subjected to relatively large cutting forces that may cause cracks in the first surface-wiping secondary cutting edge, the angle on the second main cutting edge in relation to the first flat waist portion provides an enhanced protection against cracks reaching the opposite (lower) second main cutting edge and thereby causing a fracturing of the entire cutting insert.

According to an embodiment, the cutting insert comprises in total three cutting edges of the same kind as the first cutting edge extending along the intersection between the first surface and the circumferential surface, and three cutting edges of the same kind as the second cutting edge extending along an intersection between the second surface and the circumferential surface. In this manner a double-sided and six times indexable cutting insert is provided. Since the main cutting edge of each of the six cutting edges is arrange inside the relevant countersunk circumferential waist portion, wherein the relevant waist portion for each of the six cutting edges provides improved resistance against the propagation of cracks.

According to a further embodiment, the first flat waist portion comprises a first flat abutment surface configured for abutment against an axial and/or radial support surface of the shoulder milling tool, and the second flat waist portion comprises a second flat abutment surface configured for abutment against an axial and/or radial support surface of the shoulder milling tool. In this manner, the double-sided cutting insert is configured to be axially and/or radially supported in a stable and precise manner in the insert seat of the shoulder at milling tool, and the first and second flat abutment surfaces remain intact in the countersunk circumferential waist portion in relation to the clearance surfaces, since the first and second abutment surfaces are protected from wear during milling.

It is a further object of the present invention to provide a shoulder milling tool, which utilises the cutting insert comprising cutting edges on opposite sides of the cutting insert providing improved resistance against formation of cracks and fracture of the cutting insert. Hence, according to a further aspect of the invention, this object is achieved by a shoulder milling tool comprising a tool body being provided with an insert seat for receiving a cutting insert, wherein the shoulder milling tool comprises the cutting insert according to any one of aspects and/or embodiments discussed herein arranged in the insert seat.

As discussed above, when in cutting engagement with a workpiece, the main cutting edges arranged inside the countersunk circumferential waist portion improves the resistance against cracks from forming and propagating through an adjacent countersunk circumferential waist portion, and when the surface wiping secondary cutting edges are worn down or in high cutting load engagement with a workpiece, cracks will not propagate through the countersunk circumferential waist portion to the underlying inactive main cutting edge arranged inside the countersunk circumferential waist portion. Thus, improved resistance against cracks and fracture of the cutting insert is also achieved in the shoulder milling tool. The cutting insert is hereby more reliable/safer in operation by the reduced risk of cutting insert failure/fracture for safer milling and the cutting insert can be indexed when an active cutting edge is worn out, whereby a previously inactive new cutting edge is positioned for cutting engagement with the workpiece.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

DETAILED DESCRIPTION

Aspects of the present invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

FIGS. 1a-1eillustrate various views of a cutting insert2according to an embodiment. The cutting insert2is configured for use in a shoulder milling tool. However, the cutting insert2may also be used for ramping or plunge milling. The cutting insert2is double-sided and six times indexable, i.e. the cutting insert2comprises six identical cutting edges in total, such that the cutting insert2can be mounted in six different index positions in an insert seat of the shoulder milling tool, to provide one active cutting edge at a time for milling a workpiece. The cutting insert2comprises a through hole3for screw mounting the cutting insert to the shoulder milling tool, the through hole3extending centrally through the cutting insert2.

The cutting insert2is preferably manufactured from a cemented carbide material, but it may be manufactured from a material comprising e.g. one or more of ceramics, cubic boron nitride, polycrystalline diamond, and/or cermet. The cutting insert2is also preferably coated with surface coatings such as e.g. titanium nitride, titanium carbonitride, and/or aluminium oxide.

The cutting insert2has a trigonal shape and an imaginary median plane4extends through the cutting insert2. The median plane4extends perpendicularly to a centre axis5of the through hole3or cutting insert2.FIG. 1eshows a cross section through the insert2, along the median plane4. Seen in a view towards the median plane4, the trigonal shape has three 90 degree angled corners6and three 150 degree angled corners8in between the 90 degree angled corners6. A 60 degree angle10is formed between sides12of two different 90 degree angled corners6.

The actual angles of a cutting insert may vary due to manufacturing tolerances. The surfaces are formed in pressing and sintering operations in the manufacturing of the cutting insert, wherein some surface are ground after the sintering operation. Thus, angles between surface, edges, and/or planes may have different manufacturing tolerances.

The various angles given herein may be approximately a number of degrees. In practice, the number of degrees on the actual cutting insert may depend on manufacturing tolerances, a particular chosen layout of the cutting insert and shoulder milling tool, and/or a specific part of the cutting insert requiring stricter manufacturing tolerances involving relatively small angles. Hence, in some cases, the approximate angle may vary a few degrees from the number given, such as +/−3 degrees. The advantages of different aspects and/or embodiments of the invention are present within such angular ranges. Accordingly, the above mentioned 90 degree corner, may be considered as an approximately 90 degree angled corner encompassing corner angles within a range of 87-93 degrees, and the (approximately) 150 degree angled corners may encompass corner angles within a range of 147-153 degrees, and the (approximately) 60 degree angles may encompass angles within a range of 57-63 degrees.

The insert2comprises a first surface14, and a second surface16opposite to the first surface14, and a circumferential surface18extending between the first surface14and the second surface16. The first and second surfaces14,16extend on opposite sides of the median plane4. The median plane4extends centrally in between the first and second surfaces14,16and intersects with the circumferential surface18. Put differently, the median plane4extends in the middle of the insert2with one half of the insert2on each side of the median plane4.

The through hole3extends through the insert from the first surface14to the second surface16. Each of the first and second surfaces14,16as a trigonal shape corresponding to the trigonal shape of the median plane4discussed above with reference toFIG. 1e. Corners of the median plane4and the first and second surfaces14,16are substantially aligned.

A cutting edge20extends along an intersection between the first surface14and the circumferential surface18. A second cutting edge20′″ extends along an intersection between the second surface16and the circumferential surface18. The first cutting edge20, as seen in a view towards the first surface14, seeFIG. 1b, extends along a corner22of the insert2. The second cutting edge20′″, as seen in a view towards the second surfaces16, seeFIG. 1c, also extends along the corner22of the insert2. The corner22of the insert2is a 90 degree corner and is arranged at one of the 90 degree corners6of the median plane4shown inFIG. 1e.

The first cutting edge20comprises three portions; a first main cutting edge24, a first corner cutting edge26, and a first surface-wiping secondary cutting edge28. The first main cutting edge24adjoins to the first corner cutting edge26, and the first corner cutting edge26adjoins to the first surface-wiping secondary cutting edge28. The second cutting edge20′″ comprises three portions, a second main cutting edge24′, a second corner cutting edge26′, and a second surface-wiping secondary cutting edge28′, wherein the second main cutting edge24′ adjoins to the second corner cutting edge26′, and the second corner cutting edge26′ adjoins to the second surface-wiping secondary cutting edge28′. Each of the first and second corner cutting edges26,26′ may have a cutting insert corner radius for forming a standard corner radius in a workpiece, such as a radius of e.g. 0.8 mm, 1.2 mm, or 1.6 mm.

The circumferential surface18comprises a countersunk circumferential waist portion92situated at the median plane4. The first main cutting edge24is arranged on an opposite side of the countersunk circumferential waist portion92to the second surface-wiping secondary cutting edge28′, wherein the first surface-wiping secondary cutting edge28is arranged on an opposite side of the countersunk circumferential waist portion92to the second main cutting edge24′, see e.g.FIGS. 1a, 1dand3b.

When the cutting insert2is arranged in a shoulder milling tool with the first cutting edge20arranged for cutting, the first main cutting edge24is extending in an axial direction of the shoulder milling tool and arranged for cutting into the workpiece, in a radial feed direction of the shoulder milling tool. The first surface-wiping secondary cutting edge28is extending in a radial direction of the shoulder milling tool and configured for surface-wiping the workpiece, or cutting in an axial feed direction of the shoulder milling tool. A 90° shoulder is milled in a workpiece during shoulder milling in the radial feed direction, wherein ramping or plunge milling also involves cutting in the axial feed direction of the shoulder milling tool into the workpiece. In a shoulder milling operation, the first main cutting edge24usually performs the major cut into the workpiece, while the first surface-wiping secondary cutting edge28only performs a shallow surface smoothing of the machined surface. However, during ramping or plunge milling (involving an axial feed), the first surface-wiping secondary cutting edge28performs a substantially deeper cut into the workpiece, in the axial direction of the shoulder milling tool, than during the shoulder milling operation. Obviously, in ramping or plunge milling, the first main cutting edge24may also cut into the workpiece.

When the cutting insert2is arranged in the shoulder milling tool with the first cutting edge20being active or mounted for cutting action, the second cutting edge20′″ faces rearwardly in a rotational direction of the shoulder milling tool. Hence, the second cutting edge20′″ is inactive and does not engage with the workpiece. In order to cut with the second cutting edge20′″, the cutting insert2has to be removed from the shoulder milling tool and indexed such that the second cutting edge20′″ becomes active and faces forwardly in the rotational direction of the shoulder milling tool.

Referring toFIGS. 1a-1c, each of the first and second surfaces14,16comprises a flat centre surface44. At least a portion of the flat centre surface44forms an abutment surface when the first or second surface14,16face the insert seat of the shoulder milling tool. Accordingly, when the flat centre surface44abuts against a support surface in an insert seat of a shoulder milling tool, seeFIG. 5. Suitably, a radially outer portion of the flat centre surface44forms an abutment surface against a bottom support surface in the insert seat of the shoulder milling tool.

FIG. 2aillustrates a partial top view of the cutting insert2ofFIGS. 1a-1e.FIGS. 2band 2cillustrate partial cross sections through the cutting insert2along lines IIb-IIb, and IIc-IIc inFIG. 2a. The circumferential surface18comprises a first clearance surface50extending along the first main cutting edge24. The first clearance surface50extends at an acute angle c to the median plane4along the first main cutting edge24, such that the first clearance surface50along the first main cutting edge24is forming a negative nominal clearance angle α. The circumferential surface18comprises a second clearance surface50′ extending along the second main cutting edge24′. The second clearance surface50′ extends at an acute angle c to the median plane4along the second main cutting edge24′, such that the second clearance surface50′ is forming a negative nominal clearance angle α.

The nominal clearance angle α is the clearance angle of the relevant clearance surface50,50′ measured on the cutting insert2as such, in relation to a normal of the median plane4. A functional clearance angle is formed when the cutting insert2is secured to a shoulder milling tool, seeFIGS. 4aand 4b. The functional clearance angle is always positive and constitutes the clearance angle between the clearance surface of the cutting insert and the machined workpiece surface during operation of the shoulder milling tool.

The first main cutting edge24is arranged inside the countersunk circumferential waist portion92, as seen in the view towards the first surface14, seeFIG. 1b. Specifically, in the highlighted portionFIG. 1b′ the countersunk circumferential waist portion92is indicated with a broken line in relation to the first main cutting edge24. Namely, in the view towards the first surface14, the first clearance surface50conceals the countersunk circumferential waist portion92. The second main cutting edge24′ is arranged inside the countersunk circumferential waist portion92, as seen in the view towards the second surface16, seeFIG. 1c. Specifically, in the highlighted portionFIG. 1c′ the countersunk circumferential waist portion92is indicated with a broken line in relation to the second main cutting edge24′. Namely, in the view towards the second surface16, the second clearance surface50′ conceals the countersunk circumferential waist portion92.

In this manner, the cutting insert2is wider at the median plane4than at the first and second main cutting edges24,24′. Accordingly, if cracks should form in the first main cutting edge24during cutting with the first cutting edge20, such cracks or fracture of the first main cutting edge24will be prevented by the countersunk circumferential waist portion92and will not tend to propagate past the countersunk circumferential waist portion92to the second surface-wiping secondary cutting edge28′. Also, if cracks should form in the first surface-wiping secondary cutting edge28during cutting with the first cutting edge20, such cracks or fracture of the first surface-wiping secondary cutting edge28will be prevented by the countersunk circumferential waist portion92and will not tend to propagate past the countersunk circumferential waist portion92to the second main cutting edge24′. Thus, as previously described, the second surface-wiping secondary edge28′ and the second cutting edge20′″ remain intact on the cutting insert during cutting with the first cutting edge20. Hence, the second cutting edge20′″ at the second side surface16of the cutting insert can be used when the cutting insert2is indexed, such that the second cutting edge20′″ becomes active for cutting engagement with the workpiece. Accordingly, a safe and durable indexable cutting insert2is provided wherein an inactive cutting edge20-20Vadjacent to an active cutting edge20-20Vis protected on the cutting insert2.

Referring toFIGS. 2a-2c, in the shown embodiment, the first clearance surface50along the first main cutting edge24extends at an acute angle c within a range of 83-87 degrees to the median plane4. The second clearance surface50′ along the second main cutting edge24extends at an acute angle c within a range of 83-87 degrees to the median plane4. In this manner, a negative nominal clearance angle α within a range of 3-7 degrees is provided for each of the first and second main cutting edges24,24′. More precisely, according to the embodiment, the negative nominal clearance angle α along each of the first and second main cutting edges24,24′ is 5 degrees, i.e. the acute angle c is approximately 85 degrees along the entire first and second main cutting edges24,24′.

During manufacturing of the cutting insert2, the first and second clearance surfaces50,50′ as well as the clearance surfaces at the first and second surface-wiping cutting edges28,28′ may be formed in respective grinding operations. Also, the countersunk circumferential waist portion92may be formed in a grinding operation. According to these embodiments, the height of the countersunk circumferential waist portion92, i.e. the length in parallel with the centre axis5of the cutting insert2, is greater than a maximum height of each of the first and second clearance surfaces50,50′, as well as greater than a maximum height of each of the clearance surfaces at the first and second surface-wiping cutting edges28,28′. Accordingly, the same grinding wheel can be used in each of the grinding operations.

FIGS. 3aand 3billustrate two different side views of the cutting insert ofFIGS. 1a-1e. In particular, the first and second cutting edges20,20′″ are shown along the median plane4from two different sides of the cutting insert2.

A first flat waist portion100of the countersunk circumferential waist portion92extends in a plane perpendicularly to the median plane4at the first surface-wiping secondary cutting edge28and the second main cutting edge24′, see also e.g.FIG. 1a. A second flat waist portion100′ of the countersunk circumferential waist portion92extends in a plane at the second surface-wiping secondary cutting edge28′ and the first main cutting edge24. InFIGS. 3aand 3bthe flat first and second waist portions100,100′ are indicated with hatched areas.

Referring toFIGS. 1a-1e, the first and second main and surface-wiping secondary cutting edges24,24′,28,28′ extend along straight lines, seen in the view towards the first and second surfaces14,16, respectively. According to the shown embodiment, the first surface-wiping secondary cutting edge28extends at an angle d to the first flat waist portion100, as seen in a view towards the first surface14, see the highlighted portionFIG. 1b″. The second surface-wiping secondary cutting edge28′ extends at an angle d to the second flat waist portion100′, as seen in a view towards the second surface16, see the highlighted portionFIG. 1c″. More precisely, the first and second flat waist portions100,100′ are extending in relation to the first and second surface-wiping secondary edges28,28′ to become more countersunk toward the corner22of the cutting insert2. The first surface-wiping secondary cutting edge28is arranged outside the countersunk circumferential waist portion92and the first flat waist portion100, as seen in the view towards the first surface14, seeFIG. 1b. Specifically, in the highlighted portionFIG. 1b″ the countersunk circumferential waist portion92is indicated with a broken line in relation to the first surface-wiping secondary cutting edge28. Namely, in the view towards the first surface14, the first surface-wiping secondary cutting edge28conceals the countersunk circumferential waist portion92and the first waist portion100. The second surface-wiping secondary cutting edge28′ is arranged outside the countersunk circumferential waist portion92and the second waist portion100′, as seen in the view towards the second surface16, seeFIG. 1c. Specifically, in the highlighted portionFIG. 1c″ the countersunk circumferential waist portion92is indicated with a broken line in relation to the second surface-wiping secondary cutting edge28′. Namely, in the view towards the second surface16, the second surface-wiping secondary cutting edge28′ conceals the countersunk circumferential waist portion92and the second waist portion100′.

According to the shown embodiments, the angle d may be 0.9 degrees. According to alternative embodiments, the angle d may be within a range of 0.5-1.5 degrees. As discussed above, when the first surface-wiping secondary cutting edge28is positioned for cutting engagement with a workpiece, the second main cutting edge24′, positioned behind the first surface-wiping secondary cutting edge28, is arranged inside the countersunk circumferential waist portion92and accordingly, protected behind the countersunk circumferential waist portion92in case of cracks or fractures of the surface-wiping secondary cutting edge28,28′.

According to an embodiment, the first main cutting edge24extends at an angle e to the second flat waist portion100′, as seen in a view towards the first surface14, see the highlighted portionFIG. 1b′. The second main cutting edge24′ extends at an angle e to the first flat waist portion100, as seen in a view towards the second surface16, see the highlighted portionFIG. 1c′. In this manner, the first main cutting edge24is arranged at a successively greater distance inside the countersunk circumferential waist portion92and the first flat waist portion10in the direction towards the first corner cutting edge26. Thus, during cutting with the first cutting edge20, the first main cutting edge24is more supported by a body of the cutting insert2towards the first corner cutting edge26, where cutting forces on the first main cutting edge24and more likely to cause a fracture of the cutting insert. Moreover, the second main cutting edge24′ is arranged at a successively greater distance inside the countersunk circumferential waist portion92and the first flat waist portion10in a direction towards the second corner cutting edge26′. Thus, during cutting with the first cutting edge20, the second main cutting edge24′ is more protected being the countersunk waist portion92towards the second corner cutting edge26′, where cutting forces on the first surface-wiping secondary cutting edge28are more likely to cause a fracture of the cutting insert, than at a distance from the second corner cutting edge26′.

According to the shown embodiment, the angle e may be 0.8 degrees. According to alternative embodiments, the angle e may be within a range of 0.5-1.5 degrees.

The cutting insert2is a double-sided and six times indexable cutting insert. Accordingly, the cutting insert2comprises in total three cutting edges20,20′,20″ of the same kind as the first cutting edge20extending along the intersection between the first surface14and the circumferential surface18. Also, three cutting edges20′″,20″″,20Vof the same kind as the second cutting edge20′″ extend along an intersection between the second surface16and the circumferential surface18. Since the main cutting edge of each of the six cutting edges20-20Vis arranged inside the relevant countersunk circumferential waist portion92, each of the six cutting edges20-20Vis useable even if the cutting edge on the opposite side of the cutting edge should wear down and crack.

Referring toFIGS. 3aand 3b, according to the shown embodiment, the first flat waist portion100comprises or forms a first abutment surface90configured for abutment against an axial and/or radial support surface of the shoulder milling tool. The second flat waist portion100′ also comprises or forms a second abutment surface90′ configured for abutment against an axial and/or radial support surface of the shoulder milling tool. Thus, the cutting insert2is configured to be axially and/or radially supported in the insert seat of the shoulder milling tool by the axial and/or radial support surfaces thereof abutting against the first and/or second flat abutment surfaces90,90′ of the first and second flat waist portions100,100′, when the indexable cutting edges20′,20″,20″″,20Vare arranged to be active in the insert seat for cutting engagement with the workpiece. See also below with reference toFIGS. 4a, 4b, andFIG. 5.

The first and second flat waist portions100,100′ extend at a 90 degree angle to each other at the first cutting edge20. Thus, also the first and second flat abutment surfaces90,90′ extend at a 90 degree angle to each other.

The first and second flat abutment surfaces90,90′ are well protected at the first and second flat waist portions100,100′, i.e. within the countersunk circumferential waist portion92, during cutting with the cutting insert2in the shoulder milling tool. InFIGS. 3aand 3ban example of the first and second flat abutment surfaces90,90′ are indicated with cross-hatchings. The first and second abutment surfaces90,90′ form part of the first and second flat waist portions100,100′ and in practice, the first and second flat abutment surfaces90,90′ may not be distinguishable from a remainder of the first and second flat waist portions100.100′. The first and second flat waist portions100,100′ form recesses in the insert2at the median plane4. In other words, the first and second flat abutment surfaces90,90′ along the first main cutting edge24and the second surface-wiping secondary cutting edge28′, and along the second main cutting edge24′ and the first surface-wiping secondary cutting edge28are countersunk in relation to the first and the second clearance surfaces50,50′.

FIGS. 4aand 4billustrate a shoulder milling tool60according to an embodiment. The shoulder milling tool60comprises a tool body62being provided with an insert seat64for receiving the cutting insert2described above. The shoulder milling tool60comprises the cutting insert2arranged in the insert seat64. The cutting insert2is secured to the tool body62in the insert seat64by means of a screw66extending through the through hole3of the cutting insert2. The screw66engages with internal threads67in the tool body62. Other means of securing the cutting insert2to shoulder milling tool60may be used.

The shoulder milling tool60is typically provided with more than one cutting insert2. In this embodiment, the shoulder milling tool60comprises six cutting inserts2arranged in six insert seats64of the tool body62. The shoulder milling tool60is rotatable about a central rotation axis68in a direction indicated by the arrow70, wherein the cutting insert2is mounted for cutting into a workpiece with the main cutting edge extending in the axial direction and the surface-wiping secondary cutting edge extending in the radial direction of the shoulder milling tool. The shoulder milling tool60can also be used for plunge milling, i.e. milling in the axial direction of the shoulder milling tool60. Mentioned purely as an example, the shoulder milling tool60may have a diameter within a range of 32-250 mm. Obviously, the number of insert seats and cutting inserts2may vary depending on for instance the diameter of the shoulder milling tool and/or the operating conditions, such as e.g. operational stability, power consumption and workpiece material.

According to the shown embodiment, the insert seat64is configured to provide a negative axial rake angle γp for the median plane4of the cutting insert2arranged in the insert seat64. The insert seat64is hereby configured to provide a negative axial rake angle γp within a range of 1-11 degrees, more precisely 4-8 degrees, or of approximately 6 degrees. The negative axial rake angle γp is measured between the median plane4of the cutting insert2and a line72extending in parallel with the rotation axis68(the axial direction of the shoulder milling tool) and provides an axial clearance between the clearance surface of the surface-wiping secondary cutting edge and the workpiece during milling.

According to the embodiment, the insert seat64is also configured to provide a negative radial rake angle γf for the median plane4of the cutting insert2arranged in the insert seat64. The insert seat64is configured to provide a negative radial rake angle γf within a range of 8-20 degrees, more precisely 11-17 degrees, or of approximately 14 degrees. The negative radial rake angle γf is measured between the median plane4of the cutting insert2and a radially extending line74from the rotation axis68(the radial direction of the shoulder milling tool). In combination with the nominal negative clearance angle α of the main cutting edge24, discussed above with reference toFIGS. 2band 2c, a functional positive clearance angle of the main cutting edge is formed by the radial rake angle γf. For instance, the exemplified negative clearance angle α of approximately 5 degrees and the negative radial rake angle γf of approximately 14 degrees provides a functional clearance angle of the main cutting edge of approximately 9 degrees.

FIG. 5aillustrates an insert seat64of the shoulder milling tool60ofFIGS. 4aand 4b. The insert seat64is provided with a bottom support surface76, a first side support surface78, a second side support surface80, and a third side support surface82. The first and second side support surfaces78,82are also shown inFIG. 4a. The bottom support surface76is shown as a cross-hatched surface inFIG. 5. As can be seen, the bottom support surface76provides a raised peripheral portion at a bottom of the insert seat64for stably supporting at the periphery of the flat centre surface44of the cutting insert2, seeFIGS. 1a-1c. The insert seat64obviously comprises a radial opening84for exposing the active main cutting edge of the cutting insert, when secured in the insert seat64, and an axial opening86for exposing the active surface-wiping secondary cutting edge of the cutting insert.

The first support surface78, the second support surface80, and the third support surface82are arranged at a 90 degree angle to the bottom support surface76. The first and second support surfaces78,80are arranged at a 90 degree angle to each other at an end of the insert seat64opposite to the axial opening86, and the third support surface82is arranged at an end of the insert seat64close to the axial opening86. The first support surface78faces towards the radial opening84. The second support surface80faces away from the radial opening84. The third support surface82faces towards the radial opening84.

The cutting insert2is arranged with at least part of the even abutment surface44, seeFIG. 1c, abutting against the bottom support surface76of the insert seat64. Respective first and second abutment surfaces90,90′ of the cutting insert2, seeFIGS. 3aand 3b, at the inactive cutting edges20′,20″ abut against the first support surface78, the second support surface80, and the third support surface82.

During use of the shoulder milling tool60, the first and second side support surfaces78,80form axial support surfaces for the cutting insert, the first and third side support surfaces78,82form radial support surfaces for the cutting insert, and the bottom support surface76forms a tangential support surface for the cutting insert.

Referring toFIGS. 4a-5d, of the six cutting edges of the cutting insert2only one is active or arranged for cutting engagement with the workpiece. Hence, the first cutting edge20is arranged for such cutting engagement and is therefore referred to as the active cutting edge. Accordingly, the radial opening84exposes the active first main cutting edge24and the axial opening86exposes the active first surface-wiping secondary cutting edge28. Naturally, the active first corner cutting edge26is also exposed for cutting action with the workpiece. The other two cutting edges20′,20″, at the first surface14are arranged in inactive positions. Some of the first and second abutment surfaces90,90′ at the other two cutting edges20′,20″ abut against the first, second, and third side support surfaces78,80,82. Specifically, the second abutment surface90′ at the first main cutting edge of the inactive cutting edge20′ abuts against the first side support surface78, seeFIG. 5c, and the first abutment surface90at the surface-wiping secondary cutting edge of the inactive cutting edge20′ abuts against the second side support surface80. The first abutment surface90at the surface-wiping secondary cutting edge of the inactive cutting edge20″ abuts against the third side support surface82, seeFIG. 5d.

As discussed above, the main cutting edges24of the six cutting edges20-20Vare arranged inside the countersunk circumferential waist portion92such that cracks in the main cutting edge24of a cutting edge arranged in cutting engagement with a workpiece do not propagate past the countersunk circumferential waist portion92to the underlying cutting edge, and such that cracks in the corresponding surface wiping secondary cutting edge of the cutting edge arranged in cutting engagement with the workpiece do not propagate past the countersunk circumferential waist portion92to the main cutting edge of the underlying cutting edge.

Since the first and second abutment surfaces90,90′ at the respective cutting edges20-20Vare arranged at the countersunk circumferential waist portion, the first and second abutment surfaces90,90′ are comparatively well protected in case of wear down of the cutting edges20-20V. Thus, the first and second abutment surfaces90,90′ may serve as abutment surfaces in the insert seat64, even if an adjacent cutting edge20should have been worn down or ruptured during prior use in an active position in the insert seat64.

It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended claims.