Coated cutting tool and method for manufacturing the same

Abstract

A coated cutting tool includes a substrate having a rake side, a clearance side and a cutting edge and a coating comprising a first layer and a second layer. The second layer has a sandwich structure of an inner layer, an intermediate layer and an outer layer, wherein the inner layer is exposed through an opening in the outer layer, the opening extending over at least a portion of the width of the cutting edge. Thereby, a double layer is provided in critical areas, whereas a single layer is provided in other areas. The double oxide layer is an aluminum oxide layer. A method for manufacturing the coated cutting tool is also provided.

Claims

1. A coated cutting tool comprising: a substrate with a rake side, a clearance side and a cutting edge with an edge rounding described by an inscribed ellipse with a first axis along the rake side of W and a second axis along the clearance side of H at the intersection of the rake side and the clearance side; and a coating with a thickness T, the coating including a first layer and a second layer deposited on the first layer, wherein the second layer comprises a sandwich structure of an inner aluminum oxide layer, an intermediate layer and an outer aluminum oxide layer, wherein the inner aluminum oxide layer is exposed through an opening in the outer aluminum oxide layer and said opening extends over at least a portion of the width of the cutting edge, along at least a portion of the cutting edge in the orthogonal direction, and at least H+T+2 mm into the clearance side from the rake side.

2. The coated cutting tool of claim 1, wherein the opening extends over at least the whole width of the cutting edge.

3. The coated cutting tool of claim 2, wherein the inner aluminum oxide is exposed at least over the whole width of the cutting edge.

4. The coated cutting tool of claim 1, wherein the opening extends into the rake side.

5. The coated cutting tool of claim 1, wherein the opening extends partly into a primary land of the rake side.

6. The coated cutting tool of claim 1, wherein the opening extends at least 50 ?m into the rake side.

7. The coated cutting tool of claim 1, wherein the opening extends at least 100 ?m into the rake side.

8. The coated cutting tool of claim 1, wherein the intermediate layer is exposed through the opening in the outer aluminum oxide layer.

9. The coated cutting tool of claim 1, wherein said aluminum oxide layers are made of ?-Al2O3.

10. The coated cutting tool of claim 1, wherein the thickness of the inner and outer aluminum oxide layers is 2-10 ?m.

11. The coated cutting tool of claim 1, wherein the thickness of the inner aluminum oxide layers is 1-10 ?m.

12. The coated cutting tool of claim 11, wherein the thickness of the inner aluminum oxide layers is 2-5 ?m and the outer aluminum oxide layer is 4-10 ?m.

13. The coated cutting tool of claim 1, wherein the first layer includes one or more layers selected from titanium carbide, titanium nitride, titanium carbonitride, titanium oxycarbide and titanium oxycarbonitride, and has a thickness of 2-15 ?m.

14. A method of manufacturing a substrate having a rake side, a clearance side and a cutting edge at the intersection of the rake side and the clearance side, and a coating including a first layer and a second layer deposited on the first layer, wherein the method comprises the steps of: depositing the first layer on a surface area extending over each of the rake side, the clearance side and the cutting edge; depositing the second layer comprising a sandwich structure of an inner aluminum oxide layer, an intermediate layer and an aluminum oxide outer layer on the surface area covered by the first layer; and selectively removing the outer aluminum oxide layer by lift-off, wherein the sandwich structure is exposed to laser light arranged to irradiate the intermediate layer through the outer aluminum oxide layer and being absorbed by the intermediate layer, thereby exposing the inner aluminum oxide layer through an opening in the outer aluminum oxide layer, wherein said opening extends over at least a portion of the width of the cutting edge, along at least a portion of the cutting edge in the orthogonal direction, and at least H+T+2 mm into the clearance side from the rake side.

15. The method of claim 14, further comprising blasting the coated cutting tool subsequently to the step of removing the outer aluminum oxide layer.

16. The method of claim 15, wherein the blasting removes the exposed intermediate layer, at least on the edge.

17. The method of claim 14, further comprising blasting the coated cutting tool prior to the step of removing the outer layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments of the invention will now be described with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically illustrates a double oxide layer in accordance with the invention,

(3) FIG. 2 schematically illustrates a cutting edge of a cutting tool where the outer oxide layer has been removed from a portion of the rake side, the edge and a portion of the clearance side,

(4) FIG. 3 is a perspective overview image of a cutting edge of a cutting tool in accordance with one embodiment of the invention where laser lift off has removed the outer oxide layer on a portion of the clearance side,

(5) FIG. 4 is a cross-sectional image of a coated cutting tool according to the invention where the inner oxidelayer is exposed in the opening,

(6) FIG. 5 is a cross-sectional image of a coated cutting tool according to the invention where the inner oxide layer and the intermediate layer are exposed in the opening,

(7) FIG. 6 is a cross-sectional image of a coated cutting tool wherein the first layer is exposed in the opening (cutting tool 1b), and

(8) FIG. 7 is a cross-sectional image of a coated cutting tool in accordance to one embodiment of the invention wherein the inner oxide layer is exposed in the opening (cutting tool 2d).

DETAILED DESCRIPTION

Example 1

(9) Coated cutting tools in accordance with one embodiment of the invention were manufactured. First, cemented carbide CNMG120408-PM substrates with a composition of 7.5 wt-% Co and balance WC, a Hc value of 13 kA/m (using a Foerster Koerzimat CS1.096 according to DIN IEC 60404-7) and a hardness of HV3=15 GPa were manufactured by pressing powder and sintering the pressed bodies. Prior to coating deposition the substrates were edge rounded to about 50 ?m by wet blasting.

(10) Referring to FIG. 1, a coating consisting of a first layer and a second layer was deposited by CVD on the substrates. The first layer is a Ti(C,N,O) layer with a total thickness of 10.3 ?m, which consists of the layer sequence 0.4 ?m TiN, 9.1 ?m MTCVD Ti(C,N), 0.2 ?m HTCVD Ti(C,N) and 0.6 ?m Ti(C,O). The second layer is a sandwich structure consisting of an inner 4.5 ?m ?-Al.sub.2O.sub.3 layer, an intermediate 2.5 ?m (Al,Ti)(C,O)/TiN/Ti(C,O) layer and an outer 6.8 ?m ?-Al.sub.2O.sub.3 layer. The coating was deposited in a CVD reactor having radial gas flow using deposition conditions for growth of the MTCVD Ti(C,N) layers and the ?-Al.sub.2O.sub.3 layer. A nucleation step was performed prior to growth of the MTCVD Ti(C,N) layer. Oxidation and nucleation steps were performed prior to growth of the ?-alumina layer.

(11) After deposition the coated cutting tools were subjected to a laser operation and a subsequent wet blasting operation. The laser was a diode-pumped YAG laser (Violine) operated at 10 W, 1064 nm, a pulse length of 6 ns (measured at 10 kHz) and a repetition frequency of 20 kHz. A focal lens with 254 mm focal length was used resulting in a spot size of 100 ?m. The laser beam was directed in an orthogonal direction to the clearance side at the nose of the cutting tool and an area of 6?2 mm was irradiated in a raster scan with scan lines having a width of 0.1 mm in parallel and orthogonally to the cutting edge, as schematically illustrated in FIG. 2. FIG. 2 also schematically illustrates an inscribed ellipse with the 2W axis and the 2H axis. The beam was displaced with a speed of 400 mm/s and three passes were made. The laser operation removed the outer ?-Al.sub.2O.sub.3 layer and exposed the intermediate layer in an opening extending from the clearance side over the cutting edge an into the rake side. FIG. 3 is an image of the coated cutting tool after laser lift-off.

(12) The wet blasting included both top blasting and side blasting, i.e. with the blasting media bombarding the coated cutting tool to the rake side and the clearance side, respectively, using 220 mesh Al.sub.2O.sub.3 particles at a pressure of 1.4-3 bar.

(13) The wet blasting removed the intermediate layer in a surface area extending from the edge into the clearance side, see FIG. 4.

Example 2

(14) Coated cutting tools were manufactured in accordance with Example 1 except for a different wet blasting operation, where only top blasting was applied, see FIG. 5.

Example 3

(15) Cutting tools according to prior art comprising CNMG120408-PM substrates with a composition of 7.5 wt-% Co and balance WC, a Hc value of 13 kA/m (using a Foerster Koerzimat CS1.096 according to DIN IEC 60404-7) and a hardness of HV3=15 GPa and a coating with a 9 ?m first layer of Ti(C,N) and a 4.5 ?m second layer of ?-Al.sub.2O.sub.3 and a Ti(C,N) color layer were manufactured as in Example 2, but without the laser operation. The top blasting operation removed the color layer on the rake side.

Example 4

(16) Cutting tools were manufactured as in Example 2 without removing the second aluminum oxide layer.

Example 5

(17) Cutting tool inserts from Examples 2-4 were tested with respect to flank wear and crater wear by turning in ball bearing steel (Ovako 825B, Tibnor) with depth of cut 2 mm, cutting speed 240 m/min, feed 0.3 mm/rev and using coolant. Tool life criterion for flank wear was for crater wear exceeding 0.2 mm.sup.2 and flank wear exceeding v.sub.B=0.4 mm, as measured by a light optical microscopy on the rake side and the clearance side, respectively. The tool life is presented in Table 1.

(18) TABLE-US-00001 TABLE 1 Tool life (minutes) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Crater wear n.a. >30 15 >30 Flank wear n.a. >30 18 >30

Example 6

(19) Coated cutting tools of Examples 1-4 were tested in facing of nodular cast iron SS0717 including intermittent cutting operations with coolant under the following conditions.

(20) TABLE-US-00002 Cutting speed, V.sub.c 170 m/min Feed, f.sub.n 0.1 mm/rev Depth of cut, a.sub.p 2 mm
Flaking resistance was evaluated based on the percentage of flaking on the edge was observed after machining. The coated cutting tools of Ex. 1 and 4 did not show any flaking at all, whereas the cutting tool of Example 3 for individual inserts showed either no flaking at all or a flaking from 19 up to 45%. The coated cutting tool of Example 2 showed a flaking degree of from 47 up to 85%.

Example 7

(21) Coated cutting tools in accordance with several embodiment of the invention as well as comparative references were manufactured as follows. First, cemented carbide CNMG120408-PM substrates with a composition of 4.1 wt-% Co and balance WC, a Hc value of 16 kA/m (using a Foerster Koerzimat CS1.096 according to DIN IEC 60404-7) and a hardness of HV3=16 GPa were manufactured by pressing powder and sintering the pressed bodies. Prior to coating deposition the substrates were edge rounded to about 45 ?m, as measured as a circle radius (H?W?45 ?m), by brushing, and subsequently blasted with alumina grits in water at low pressure in order to remove any plastic residue from the brushing process. The blasting pressure was 1.8 bar and the alumina grits were F150 mesh (FEPA 42-1:2006).

(22) Said substrates were coated in three different CVD processes in order to define both references as well as embodiments of the invention and they are all described in the following.

(23) Coating 1, consisting of a first layer and a second layer, was deposited by CVD on the substrates. The first layer is a Ti(C,N,O) layer with a total thickness of 11.3 ?m, which consists of the layer sequence 0.4 ?m TiN, 10.1 ?m MTCVD Ti(C,N), 0.2 ?m HTCVD Ti(C,N) and 0.6 ?m Ti(C,O). The second layer is a 11.0 ?m ?-Al.sub.2O.sub.3 layer.

(24) Coating 2, shown schematically in FIG. 1, is a coating consisting of a first layer and a second layer that was deposited by CVD on the substrates. The first layer is a Ti(C,N,O) layer with a total thickness of 11.0 ?m, which consists of the layer sequence 0.4 ?m TiN, 9.8 ?m MTCVD Ti(C,N), 0.2 ?m HTCVD Ti(C,N) and 0.6 ?m Ti(C,O). The second layer is a sandwich structure consisting of an inner 2.9 ?m ?-Al.sub.2O.sub.3 layer, an intermediate 1.2 ?m Ti(C,O)/TiN/Ti(C,O) layer and an outer 6.7 ?m ?-Al.sub.2O.sub.3 layer.

(25) Coating 3, consisting of a first layer and a second layer, was deposited by CVD on the substrates. The first layer is a Ti(C,N,O) layer with a total thickness of 11.7 ?m, which consists of the layer sequence 0.4 ?m TiN, 10.5 ?m MTCVD Ti(C,N), 0.2 ?m HTCVD Ti(C,N) and 0.6 ?m Ti(C,O). The second layer is a 3.0 ?m ?-Al.sub.2O.sub.3 layer.

(26) These three coating variants 1, 2 and 3 were deposited in a CVD reactor having radial gas flow using deposition conditions for growth of the MTCVD Ti(C,N) layers and the ?-Al.sub.2O.sub.3 layer. A nucleation step was performed prior to growth of the MTCVD Ti(C,N) layer. Oxidation and nucleation steps were performed prior to growth of the ?-alumina layer.

(27) After the CVD deposition the coated cutting tools were subjected to posttreatments, where 1b and 2b were subjected to a laser operation on the clearance side, coated cutting tools 2c, 2d where subjected to a first laser treatment on the clearance side and a second laser treatment with a shadow mask present on the rake side, while tools 1a, 2a, 3a were not laser treated.

(28) The laser used was a diode-pumped YAG laser (Violine 3 from Laservall) operated at 10 W, 1064 nm, a pulse length of 6 ns (measured at 10 kHz) and a repetition frequency of 20 kHz. A focal lens with 254 mm focal length was used resulting in a spot size of 100 ?m. The laser beam was directed in an orthogonal direction to the clearance side at the nose of the cutting tool and an area of 6?2 mm was irradiated in a raster scan with scan lines having a width of 0.1 mm in parallel and orthogonally to the cutting edge, as schematically illustrated with arrow in FIG. 2. The beam was displaced with a speed of 750 mm/s and two passes were made. The laser operation removed the outer ?-Al.sub.2O.sub.3 layer and exposed the intermediate layer in an opening extending from the clearance side over the cutting edge an into the rake side. FIG. 2 also schematically illustrates an inscribed ellipse with the 2W axis and the 2H axis and the total coating thickness T. The distance ? is also shown in FIG. 2, defined as a distance ? from the exposed cutting edge to the edge of the remaining outer ?-Al.sub.2O.sub.3 layer as seen from the rake side. The distance ? was measured by light optical microscopy in a direction orthogonal to the rake side when the cutting tool is resting on a flat surface opposite the rake side. The direction R is a direction ortigonal to the width of the cutting edge. The width is measured in the same plane and direction as ?.

(29) The laser lift-off treatment on the clearance side remove the outer ?-Al.sub.2O.sub.3 layer on the whole width of the edge of the coated cutting tools, and into the rake side, to a distance ? of about 50 ?m of tool 1b and about 60 ?m for tool 2b.

(30) As a mean to control the extent of removal of the outer ?-Al.sub.2O.sub.3 layer on the rake side on tools 2c and 2d a cemented carbide shadow mask was used to define the extension of such a removal in a controlled way. The shadow mask protects the layers beneath the mask from being exposed of the laser and thereby the outer ?-Al.sub.2O.sub.3 layer is not being removed from the area beneath the shadow mask. Different shadow masks were used in order to enable different distances ? of the outer ?-Al.sub.2O.sub.3 layer being removed from edge and into the rake side in the laser process on the rake side. The distance ? is measured as the distance from the exposed cutting edge as seen from the rake side as disclosed above, and to the edge of the remaining outer ?-Al.sub.2O.sub.3 layer.

(31) The laser treatment were for all the examples extended in the direction of the cutting edge to a position outside the cutting depth.

(32) Four different exposed distances ? from the edge into the rake side were thus manufactured, about 50 ?m, about 60 ?m, about 130 ?m and about 200 ?m. Tools provided with coating 1 was subjected to a laser operation removing the outer ?-Al.sub.2O.sub.3 layer on the rake side from the edge to a distances ? of about 50 ?m. Tools provided with coating 2 were subjected to a laser operation removing the outer ?-Al.sub.2O.sub.3 layer on the rake side from the edge to a distances ? of about 60 ?m, about 130 ?m and about 200 ?m respectively. The resulting average distance ? for the laser treated tool 1b, 2b, 2c and 2d is shown in Table 2.

(33) TABLE-US-00003 TABLE 2 Tool 1b 2b 2c 2d Average 50 60 130 200 distance ? (?m)

(34) Finally a wet blasting was performed on the rake sides of all the cutting tools, here called a final top blasting. The aim of this treatment was to introduce compressive stresses into the outermost coatings and thereby increase the edge toughness of the tools. The aim was further to smoothen the edge of the remaining outer ?-Al.sub.2O.sub.3 layer and to remove the intermediate layer in the exposed surface area. The blaster slurry consisted of 20 vol-% alumina grits in water and an angle of 90? between the rake side of the cutting insert and the direction of the blaster slurry. The distance between the gun nozzle and the surface of the insert was about 145 mm. The pressure of the slurry to the gun was 1.8 bar for all samples, while the pressure of air to the gun was 2.1 bar for all tools. The alumina grits were F220 mesh (FEPA 42-1:2006). The time for blasting per area unit was about 4 seconds. A summary of the coated cutting tools 1a, 1b, 2a, 2b, 2c, 2d, and 3a manufactured in Example 7 is presented in Table 3.

(35) A cross sectional image of the coated cutting tool 1b is shown in FIG. 6 and a corresponding image of the coated cutting tool 2d is shown in FIG. 7.

(36) TABLE-US-00004 TABLE 3 First Inner Outer Laser Laser layer ?-Al.sub.2O.sub.3 ?-Al.sub.2O.sub.3 treatment treatment Rake TiCN layer layer, Clearance side with Final Tool (?m) (?m) (?m) side shadow mask topblasting 1a 11.3 11.0 No No Yes 1b 11.3 11.0 Yes No, ? = 50 ?m Yes 2a 11.0 2.9 6.7 No No Yes 2b 11.0 2.9 6.7 Yes No, ? = 60 ?m Yes 2c 11.0 2.9 6.7 Yes Yes, ? = 130 ?m Yes 2d 11.0 2.9 6.7 Yes Yes, ? = 200 ?m Yes 3a 11.7 3.0 No No Yes

Example 8Toughness Test

(37) The coated cutting tools 1a, 2a, 2b, 2c, 2d, 3a of Example 7 were tested in a toughness test.

(38) The work piece material consist of two carbon steel bars (Fe 360BFN), mounted parallel to each other with a distance between them. In longitudinal turning of this work piece the cutting tool will be exposed to two interruptions per revolution. In this test the toughness of the cutting tool has shown to be critical for its lifetime. The following cutting data was used;

(39) Cutting speed v.sub.c: 130 m/min

(40) Depth of cut a.sub.p: 1.5 mm

(41) Water miscible metal working fluid was used.

(42) The cutting feed was increased continuously during the test. The start value was 0.15 mm/revolution. After 1 minute of cutting the feed value was 0.20 mm/revolution and after 2 minutes of cutting, the feed value was 0.25 mm/revolution, and after 3 minutes of cutting the feed value was 0.30 mm/revolution.

(43) An equipment for measuring the cutting forces was used. When an insert breakage occurred the cutting force increased clearly and the machine was stopped. 25 cutting edges were evaluated per cutting tool variant. The actual value of the cutting feed at fracture for each one of the 25 cutting edges was registered. The values were sorted from the lowest fracture feed value to the highest, for each cutting tool variant. The wear performance is shown in Table 4, presenting the feed at fracture for edge number 6, the median value of all 25 edges and the value for edge number 20.

(44) TABLE-US-00005 TABLE 4 Coated cutting tool 1a 2a 2b 2c 2d 3a Feed at fracture Rank 6 0.21 0.19 0.21 0.21 0.23 0.28 (mm/revolution) Median 0.23 0.21 0.23 0.22 0.24 0.29 Rank 20 0.25 0.22 0.25 0.24 0.25 0.30

(45) As can be seen in the Table 4 the tool 3a, comprising the relatively thin outer ?-Al.sub.2O.sub.3 layer shows the best performance in this test and the tool 2a comprising a relatively thick outer ?-Al.sub.2O.sub.3 layer shows a shorter time to fracture. The laser treated tool 2d shows a edge toughness performance in between the performance of tool 3a and tool 2a. Thus, the edge line toughness is slightly better for the laser treated tool 2d as compared to the tool 2a with a relatively thick outer ?-Al.sub.2O.sub.3 layer on the edge. Tool 2d performs slightly better than the tools 2b and 1a in this test.

Example 9Crater Wear Test

(46) The coated cutting tools according to table 1 in Example 7, i.e. tools 1a, 1b, 2a, 2b, 2c, 2d, 3a were tested in longitudinal turning in ball bearing steel (100CrMo7-3) using the following cutting data;

(47) Cutting speed v.sub.c: 240 m/min

(48) Cutting feed, f: 0.3 mm/revolution

(49) Depth of cut, a.sub.p: 2 mm

(50) Insert style: CNMG120408-PM

(51) Water miscible metal working fluid was used.

(52) One cutting edge per cutting tool was evaluated.

(53) In analyzing the crater wear, the area of removed material on the rake side (crater wear) was measured, using a light optical microscope. The wear of each cutting tool was evaluated after 2 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 2 minutes run. Beside crater wear, flank wear and build up edge was also observed. The results are shown in Table 5.

(54) TABLE-US-00006 TABLE 5 Coated Crater area Crater area Crater area cutting after 14 after 20 after 24 tool min (mm.sup.2) min (mm.sup.2) min (mm.sup.2) 1a, 2a, 2b, 0 0 0 2c, 2d 1b 0 * * 3a 0.02 0.26 0.43 * The tool 1b with no ?-Al.sub.2O.sub.3 in the edgeline reached its life time due to excessive flank wear after 16 minutes.

(55) As can be seen in Table 5, it was only the cutting tool 3a that showed crater wear. The cutting tool 1b reached its lifetime due to excessive flank wear after 16 minutes cutting. Cutting tool 1b is the only cutting tool in this test that did not comprise an alumina layer as the outermost layer at the cutting edge and clearance side. All the cutting tools with a relatively thick aluminum oxide at the crater area on the rake side showed good resistance against crater wear in this test.

(56) The crater wear area in this test started at a distance of about 300 ?m from the exposed cutting edge, measured by light optical microscope as the shortest distance in the plane of the rake side.

Example 10Flank and Crater Wear Test

(57) The coated cutting tools according to Table 1 in Example 7, i.e. tools 1a, 1b, 2a, 2b, 2c, 2d, 3a were tested in longitudinal turning in ball bearing steel (100CrMo7-3) using the following cutting data;

(58) Cutting speed v.sub.c: 255 m/min

(59) Cutting feed, f: 0.3 mm/revolution

(60) Depth of cut, a.sub.p: 2 mm

(61) Insert style: CNMG120408-PM

(62) Water miscible metal working fluid was used.

(63) One cutting edge per cutting tool was evaluated.

(64) In analyzing the flank wear, the distance from the edge line to the bottom of the flank wear pattern, as seen perpendicular to the clearance side, was measured using a light optical microscope. In analyzing the crater wear, the area of removed material on the rake side (crater wear) was measured, using a light optical microscope. The wear of each cutting tool was evaluated after 4 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 4 minutes run. Beside crater wear, flank wear and build up edge were also observed. The results are shown in Table 6.

(65) TABLE-US-00007 TABLE 6 Coated Flank wear at Flank wear at Time until flank wear cutting main cutting secondary cutting reached or exceeded tool edge (mm) edge (mm) 0.4 mm (min) 1a 0.43 0.36 34 1b 0.40 0.30 12 2a 0.41 0.34 36 2b 0.43 0.48 24 2c 0.43 0.41 28 2d 0.41 0.32 28 3a 0.33* 0.28* 20* *The cutting tool 3a with a relatively thin ?-Al.sub.2O.sub.3 at the whole insert reached life time due to crater wear.

(66) As can be seen in Table 6, the cutting tools 1a and 2a, i.e. the tools with the relatively thickest aluminium oxide over the edge, showed the highest resistance to flank wear. The cutting tools 1b, with no aluminum oxide over the edge, showed the lowest resistance to flank wear. The cutting tools 2b, 2c, 2d showed a higher flank wear resistance as compared to cutting tools 1b. The cutting tool 3a, with a relatively thin aluminum oxide layer covering the whole tool, showed crater wear in this test and the test was stopped before the flank wear criteria 0.4 mm was reached. The cutting tool 2d showed a higher wear resistance compared to 2b.

(67) Also in this test, the crater wear area started at a distance of about 300 ?m from the exposed cutting edge, measured as the shortest distance in the plane of the rake side.

Example 11Flank and Crater Wear Test

(68) The coated cutting tools according to table 1 in Example 7, i.e. samples 1a, 1b, 2a, 2b, 2c, 2d, 3a were tested in longitudinal turning in ball bearing steel (100CrMo7-3) using the following cutting data;

(69) Cutting speed v.sub.c: 270 m/min

(70) Cutting feed, f: 0.3 mm/revolution

(71) Depth of cut, a.sub.p: 2 mm

(72) Insert style: CNMG120408-PM

(73) Water miscible metal working fluid was used.

(74) One cutting edge per cutting tool was evaluated.

(75) In analyzing the flank wear, the distance from the edge line to the bottom of the flank wear pattern, as seen perpendicular to the clearance side, was measured using a light optical microscope. In analyzing the crater wear, the area of removed material on the rake side (crater wear) was measured, using a light optical microscope. The wear of each cutting tool was evaluated after 4 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 4 minutes run. Beside crater wear, flank wear and build up edge was also observed. The results after 22 minutes are shown in Table 7.

(76) TABLE-US-00008 TABLE 7 Coated cutting Flank wear at Flank wear at tool after main cutting secondary cutting Crater wear 22 minutes. edge (mm) edge (mm) (mm.sup.2) 2b 0.34 0.40 0.06 2c 0.32 0.29 0.00 2d 0.30 0.28 0.00 * The cutting tool 3a with thin ?-Al.sub.2O.sub.3 at the whole insert reached its life time due to crater wear.

(77) As shown in Table 7, the flank wear resistance is slightly higher for the cutting tool 2d as compared to the cutting tools 2b and 2c. The reason for this might be that a laser lift off close to the edge effects the shape and micro geometry of the cutting edge.

(78) The crater wear area in this test started at a distance of about 300 ?m from the exposed cutting edge, measured as the shortest distance in the plane of the rake side.

(79) While the invention has been described in connection with various exemplary embodiments, it is to be understood that the invention is not to be limited to the disclosed exemplary embodiments, on the contrary, it is intended to cover various modifications and equivalent arrangements within the appended claims.