Coated milling insert has a WC—Co cemented carbide with a low content of cubic carbides and a highly w-alloyed binder phase and a coating including an inner layer of ticxNy with columnar grains followed by a layer of κ-Al2O3 and a top layer of tin. The coated milling insert is particularly useful for milling of grey cast iron with or without cast skin under wet conditions at low and moderate cutting speeds and milling of nodular cast iron and compacted graphite iron with or without cast skin under wet conditions at moderate cutting speeds.
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6. A method of wet milling comprising the steps of:
providing a cutting tool insert comprising a cemented carbide body comprising WC, 7.3-7.9 wt. % Co, 1.0-1.8 wt. % cubic carbides of Ta and nb, and a highly w-alloyed binder phase with a CW-ratio of 0.86-0.94, a coating comprising a first, innermost layer of ticxNyOz with x+y+z=1, y>x and z<0.2 having an equiaxed grain structure with a size <0.5 μm and a total thickness of 0.1-1.5 μm, a layer of ticxNy with x+y=1, x>0.3 and y>0.3 with a thickness of 1-4 μm having a columnar grain structure with an average diameter of <5 μm, a layer of a smooth, fine-grained, 0.5-2 μm κ-Al2O3 with a thickness of 1-2.5 μm, and an outer layer of tin with a thickness of 0.5-1.0 μm;
operating the cutting tool insert at a speed of 70-180 m/min; and
feeding at a rate of 0.1-0.4 μm/tooth, wherein the wet milling is wet milling a cast iron, a compacted graphite iron or a nodular iron.
1. A method of making a milling insert comprising a cemented carbide body and a coating wherein the WC-Co-based cemented carbide body comprises WC, 7.3-7.9 wt. % Co and 1.0-1.8 wt. % cubic carbides of Ta and nb and a highly w-alloyed binder phase with a CW-ratio of 0.86-0.94, the method comprising the steps of:
depositing by a CVD-method a first, innermost layer of ticxNyOz with x+y+z=1, y>x and z<0.2 having an equiaxed grain structure with a size <0.5 μm and a total thickness of 0.1-1.5 μm;
depositing by a MTCVD-technique a layer of ticxNy with x+y=1, x>0.3 and y>0.3 with a thickness of 1-4 μm having a columnar grain structure with an average diameter of <5 μm, wherein the MTCVD-technique uses acetonitrile as a source of carbon and nitrogen for forming a layer in a temperature range of 700-900° C.;
depositing a layer of a smooth κ-Al2O3 with a thickness of 1-2.5 μm; and
depositing an outer layer of tin with a thickness of 0.5-1.0 μm.
2. The method according to the
3. The method according to
4. The method of making a milling insert of
0. 8. The method according to
0. 9. The method according to
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0. 11. The method according to
0. 12. The method according to
0. 13. The method according to
0. 14. The method according to
0. 15. The method according to
0. 16. The method of
0. 17. The method of
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It has now been found according to the present invention that improved cutting performance is achieved if the cemented carbide body has a CW-ratio of 0.86-0.94. The cemented carbide may contain small amounts, <3 vol. %, of η-phase (M6C), without any detrimental effect.
The coating comprises
The present invention also relates to a method of making coated cutting tool inserts consisting of a cemented carbide body with a composition of 7.3-7.9 wt. % Co, preferably 7.6 wt. % Co, 1.0-1.8 wt. % cubic carbides, preferably 1.4-1.7 wt. % cubic carbides of the metals Ta and Nb and balance WC. The average grain size of the WC is in the range of about 1.5-2.5 μm, preferably about 1.8 μm. Onto the cemented carbide body is deposited.
The smooth coating surface is obtained by a gentle wet-blasting the coating surface with fine grained (400-150 mesh) alumina powder or by brushing the edges with brushes based on e.g. SiC as disclosed e.g. in U.S. Pat. No. 5,861,210. The TiN-layer is preferably removed along the cutting edge and the underlying alumina layer may be partly or completely removed along the cutting edge.
The invention also relates to the use of cutting tool inserts according to above for wet milling using fluid coolant of cast irons such as grey cast iron, compacted graphite iron and nodular iron particularly grey cast iron at a cutting speed of 70-180 m/min and a feed of 0.1-0.4 μm/tooth depending on cutting speed and insert geometry.
A. Cemented carbide milling inserts in accordance with the invention with the composition 7.6 wt. % Co, 1.25 wt. % TaC, 0.30 wt. % NbC and balance WC with average grain size of 1.8 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.87 were coated with a 0.5 μm equiaxed TiC0.05N0.95-layer (with a high nitrogen content corresponding to an estimated C/N-ratio of 0.05) followed by a 2.6 μm thick TiC0.54N0.46-layer, with columnar grains by using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle, a 1.3 μm thick layer of Al2O3 was deposited using a temperature 970° C. and a concentration of H2S dopant of 0.4% as disclosed in U.S. Pat. No. 5,674,564. A thin (0.5 μm) layer of TiN was deposited on top according to known CVD-technique. XRD-measurement showed that the Al2O3-layer consisted of 100% κ-phase.
The coated inserts were brushed using a nylon straw brush containing SiC grains. Examination of the brushed inserts in a light optical microscope revealed that the outermost, thin TiN-layer and some of the Al2O3-layer had been brushed away along the very cutting edge, leaving there a smooth Al2O3-surface. Coating thickness measurements on cross sectioned, brushed inserts showed that the outermost TiN-layer and roughly half the Al2O3-layer had been removed along the edge line.
B. Commercial cemented carbide milling inserts with the composition 9 wt. % Co, 1.23 wt. % TaC, 0.30 wt. % NbC and balance WC with a WC grain size in average of 1.7 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.92 were coated with an innermost 0.5 μm equiaxed TiN-layer followed by a 5.5 μm thick Ti(C,N)-layer, with columnar grains by using MTCVD-technique and outermost a 4 μm thick layer of Al2O3. XRD-measurement showed that the Al2O3-layer consisted of 100% α-phase.
C. Cemented carbide milling inserts with the composition 6 wt. % Co and balance WC with average grain size 1.8 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.90 were coated with a 2 μm thick TiC-layer using known CVD-technique. In subsequent steps during the same coating cycle, a 1 μm thick layer of Al2O3 was deposited.
Inserts from A, B and C were tested in face milling of grey cast iron cylinder heads.
Operation:
Face milling - roughing
Work-piece:
Cylinder head
Material:
Peailitic grey cast iron, alloyed,
Cutting speed:
116 in/min
Feed rate/tooth:
0.32 μm/rev.
Depth of cut:
2 μm
Insert-style:
TNEF 1204AN-CA
Note:
Wet, single tooth milling
Results:
Tool-life, number of passes per edge
Grade A: (invention)
99
Grade B: (prior art)
60
Grade C: (prior art)
49
Tool-life criterion was chippings and fractures of the edges.
D. Cemented carbide milling inserts in accordance with the invention with the composition 7.6 wt. % Co, 1.25 wt. % TaC, 0.30 wt. % NbC and balance WC with an average grain size of 1.75 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.88 were coated with a 0.5 μm equiaxed TiC0.05N0.095-layer (with a high nitrogen content corresponding to an estimated C/N-ratio of 0.05) followed by a 2.0 μm thick TiC0.54N46-layer, with columnar grains by using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle, a 1.4 μm thick layer of Al2O3 was deposited using a temperature 970° C. and a concentration of H2S dopant of 0.4% as disclosed in U.S. Pat. No. 5,674,564. A thin (0.5 μm) layer of TiN was deposited on top according to known CVD-technique. XRD-measurement showed that the Al2O3-layer consisted of 100% κ-phase.
The coated inserts were brushed using a nylon straw brush containing SiC grains. Examination of the brushed inserts in a light optical microscope showed that the outermost, thin TiN-layer and some of the Al2O3-layer had been brushed away along the very cutting edge, leaving there a smooth Al2O3-surface. Coating thickness measurements on cross sectioned, brushed inserts showed that the outermost TiN-layer and roughly half the Al2O3-layer had been removed along the edge line.
Inserts from D and C were tested in face milling of grey cast iron cylinder heads.
Operation:
Face milling - roughing
Work-piece:
Cylinder head
Material:
Pearlitic grey cast iron, alloyed,
Cutting speed:
116 m/min
Feed rate/tooth:
0.32 μm/rev.
Depth of cut:
1.5-2 μm
Insert-style:
TNEF 1204AN-CA
Note:
Wet, 13 teeth, unstable tendencies
Results:
Tool-life, number of component per edge set
Grade D: (invention)
685
Grade C: (prior art)
475
Tool-life criterion was edge break-out on the work pieee due to chipping and high flank wear of the edges.
E. Cemented carbide milling inserts in accordance with the invention, identical to the inserts described in D (Example 2), except for that the coating not was brushed.
Inserts from D and E were tested in face milling of grey cast iron cylinder heads.
Operation:
Face milling - roughing
Work-piece:
Cylinder head
Material:
Pearlitic grey cast iron, alloyed,
cutting speed:
116 m/min
Feed rate/tooth:
0.32 μm/rev.
Depth of cut:
1.5-2 μm
Insert-style:
TNEF 1204AN-CA
Note:
Wet, 13 teeth, unstable tendencies
Results:
Tool-life, number of component per edge
set
Grade D: (invention)
685
Grade E: (outside invention)
570
Tool-life criterion was edge break-out on the work piece due to chipping and high flank wear of the edge.
F. Cemented carbide milling inserts in accordance with the invention with the composition 7.6 wt. % Co, 1.25 wt. % TaC, 0.30 wt. % NbC and balance WC with a grain size in average of 1.79 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.86 were coated with a 0.5 μm equiaxed TiC0.05N0.95-layer (with a high nitrogen content corresponding to an estimated C/N-ratio of 0.05) followed by a 2.7 μm thick TiC0.54N0.46-layer, with columnar grains by using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle, a 1.2 μm thick layer of Al2O3 was deposited using a temperature 970° C. and a concentration of H2S dopant of 0.4% as disclosed in U.S. Pat. No. 5,674,564. A thin (0.8 μm) layer of TiN was deposited on top according to known CVD-technique. XRD-measurement showed that the Al2O3-layer consisted of 100% κ-phase.
The coated inserts were brushed using a nylon straw brush containing SiC grains. Examination of the brushed inserts in a light optical microscope showed that the outermost, thin TiN-layer and some of the Al2O3-layer had been brushed away along the very cutting edge, leaving there a smooth Al2O3-surface. Coating thickness measurements on cross sectioned, brushed inserts showed that the outermost TiN-layer and roughly half the Al2O3-layer had been removed along the edge line.
G. Commercial cemented carbide milling inserts with the composition of 8 wt-% Co, 0.1 wt-% TiC, 1.7 wt-% TaC, 0.1 wt-% NbC, and balance WC and CW-ratio of 0.86. The WC-grain size was 1.74 μm. The inserts were coated with a 0.5 μm TiN-layer followed by a 1.5 μm thick TiC-layer and finally followed by a 0.5 μm TiN-layer.
H. Commercial cemented carbide cutting inserts with the composition of 8 wt. % Co, 0.1 wt. % TiC, 1.8 wt. % TaC, 0.1 wt. % NbC and balance WC, CW-ratio of 0.86 and WC-grain size 1.71 μm were coated with a 5 μm TiAlN-layer deposited by PVD-technique.
Inserts from F, G and H were tested in face milling of an alloyed pearlitic grey cast iron cylinder head.
Operation:
Face milling - roughing
Work-piece:
Cylinder head
Material:
Pearlitic grey cast iron, alloyed,
Cutting speed:
116 m/min
Feed rate/tooth:
0.32 μm/rev.
Depth of cut:
2 μm
Insert-style:
TNEF 1204AN
Note:
Wet, single tooth milling
Results:
Tool-life number of passes per edge
Grade F: (invention)
78
Grade G: (prior art)
60
Grade H: (prior art)
58
Tool-life criterion was chipping and edge fractures of the edges.
I. Cemented carbide milling inserts in accordance with the invention with the composition 7.6 wt. % Co, 1.25 wt. % TaC, 0.30 wt. % NbC and balance WC with a grain size in average of 1.75 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.90 were coated with a 0.5 μm equiaxed TiC0.05N0.95-layer (with a high nitrogen content corresponding to an estimated C/N-ratio of 0.05) followed by a 2.7 μm thick TiC0.54N0.46-layer, with columnar grains by using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle, a 1.7 μm thick layer of Al2O3 was deposited using a temperature 970° C. and a concentration of H2S dopant of 0.4% as disclosed in U.S. Pat. No. 5,674,564. A thin (0.7 μm) layer of TiN was deposited on top according to known CVD-technique. XRD-measurement showed that the Al2O3-layer consisted of 100% κ-phase.
The coated inserts were brushed using a nylon straw brush containing SiC grains. Examination of the brushed inserts in a light optical microscope showed that the outermost, thin TiN-layer and some of the Al2O3-layer had been brushed away along the very cutting edge, leaving there a smooth Al203-surface. Coating thickness measurements on cross sectioned, brushed inserts showed that the outermost TiN-layer and roughly half the Al2O3-layer had been removed along the edge line.
Inserts from I and G were tested in face milling of pearlitic grey cast iron engine blocks.
Operation:
Face milling - roughing
Work-piece:
Engine block
Material:
Pearlitic gray cast iron, un-alloyed
Cutting speed:
106 m/min
Feed rate/tooth:
0.20 μm/rev
Depth of cut:
3 μm
Insert-style:
TNEF 1204AN
Note:
Wet milling, 56 teeth per set
Results:
Tool-life, number of components per set
Grade I: (invention)
975
Grade G: (prior art)
700
Tool-life criterion was edge break-out on the work piece due to chipping and high flank wear of the edges.
Inserts from I and B were tested in face milling of pearlitic nodular cast iron gearbox housing.
Operation:
Face milling - roughing
Work-piece:
Gear box housing.
Material:
Pearlitic nodular cast iron, alloyed
Cutting speed:
137 m/min
Feed rate/tooth:
0.15 μm/rev.
Depth of cut:
5 μm
Insert-style:
TNEF 1204AN-CA
Note:
Wet milling, 20 teeth, unstable tendencies
Results:
Tool-life, minutes of tool life per edge set
Grade I: (invention)
105
Grade B: (prior art)
60
Tool-life criterion was crack formation and chipping of the edges.
Inserts from I and C were tested in face milling of nodular cast iron engine block component
Operation:
Face milling - roughing
Work-piece:
Engine block, bearing part
Material:
Nodular cast iron
Cutting speed:
93 m/min
Feed rate/tooth:
0.25 μm/rev
Insert-style:
TNEF 1204AN-CA
Note:
Wet milling, 26 teeth
Results:
Tool-life, number of components per edge set
Grade I: (invention)
38000
Grade C: (prior art)
20000
Tool-life criterion was burr and spalling on the work piece.
Hessman, Ingemar, Mikus, Marian, Nordgren, Anders
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