Patent Application
20070292672
It has now surprisingly been found that improved properties of milling cutting tool inserts can be obtained with respect to the different wear types prevailing at the above mentioned cutting operations if the inserts comprise: a cemented carbide body with a W-alloyed binder phase and with a well balanced chemical composition and a certain grain size of the WC, a columnar TiCxNy -layer and a post treated α-Al2O3 top layer.
According to the present invention, coated cutting tool inserts are provided comprising a cemented carbide body with a composition of from about 7.3 to about 7.9 wt-% Co, preferably from about 7.5 to about 7.7 wt-% Co, from about 1.0 to about 2.0 wt-%, preferably from about 1.3 to about 1.7 wt-%, cubic carbides of the metals Ta, Nb and Ti and balance WC, preferably 90.6-91.2 wt-% WC. The Ti-content is preferably on the level of technical impurity or less, down to 0. The coercivity, Hc, should have a value in the range from about 13.8 to about 15.7 kA/m, preferably within from about 14.2 to about 15.2 kA/m.
The cobalt binder phase is alloyed with W. The content of W in the binder phase is expressed as the
CW-ratio=magnetic-% Co/wt-% Co
where magnetic-% Co is the weight percentage of magnetic Co and wt-% Co is the weight percentage of Co in the cemented carbide.
The CW-value is a function of the W content in the Co binder phase. A CW-value of from about 0.75 to about 0.8 corresponds to a very high W-content in the binder phase whereas a CW-ratio of 1 corresponds in principle to no W-alloying.
According to the present invention improved cutting performance is achieved if:
A) the cemented carbide body has a cobalt binder alloyed with W corresponding to a CW-ratio of from about 0.85 to about 0.94, preferably of from about 0.88 to about 0.92 and
B) the inserts have an from about 25 to about 50 μm edge rounding before coating.
C) the coating comprises
a first, innermost layer of TiCxNyOz with x+y+z=1, y>x and z less than about 0.2, preferably y more than about 0.8 and z=0 and a thickness of from about 0.1 to about 1.5 μm, preferably more than about 0.4 μm.
a second layer of TiCxNy with x+y=1, x more than about 0.3 and y more than about 0.3, with a thickness of from about 4.5 to about 9.5 μm, preferably from about 5 to about 7.5 μm, with columnar grains.
a third layer of TiCxNyOz with x+y+z=1, x more than about 0.3 and z more than about 0.3, y equal to or greater than 0 and less than about 0.2, with a thickness of from about 0.3 to about 1.5 μm.
a fourth layer of a smooth α-Al2O3 with a thickness of from about 9 to about 15 μm, preferably from about 10 to about 12 μm and a surface roughness in the cutting area zone of Ra<0.4 μm over a length of 10 μm.
The ratio of layer thicknesses of the fourth layer Al2O3 and the second layer of TiCxNy is preferably from about 1.3 to about 2.4.
a from about 0.1 to about 2 μm thick colored top layer, preferably TiN or ZrN, on the clearance side.
The present invention also relates to a method of making coated cutting tool inserts consisting of a cemented carbide body with a composition of from about 7.3 to about 7.9 wt-% Co, preferably from about 7.5 to about 7.7 wt-% Co, from about 1.0 to about 2.0 wt-%, preferably from about 1.3 to about 1.7 wt-%, cubic carbides of the metals Ta, Nb and Ti and balance WC, preferably from about 90.6 to about 91.2 wt-% WC. The Ti-content is preferably on the level of technical impurity or less, down to 0. The manufacturing conditions are chosen to obtain an as sintered structure with the coercivity, Hc, of from about 13.8 to about 15.7 kA/m, preferably from about 14.2 to about 15.2 kA/m and a cobalt binder phase alloyed with W corresponding to a CW-ratio of from about 0.85 to about 0.94, preferably from about 0.88 to about 0.92 defined as above. After wet blasting the inserts to from about 25 to about 50 μm edge rounding, a coating comprising the following layers is deposited:
a first, innermost layer of TiCxNyOz with x+y+z=1, y more than about x and z less than about 0.2, preferably y more than about 0.8 and z=0 and a total thickness from about 0.1 to about 1.5 μm, preferably more than about 0.4 μm, using known CVD-methods,
a second layer of TiCxNy with x+y=1, x more than about 0.3 and y more than about 0.3, preferably x more than about 0.5, with a thickness of from about 4.5 to about 9.5 μm, preferably from about 5 to about 7.5 μm, with columnar grains using the MTCVD-technique with acetonitrile as the carbon and nitrogen source for forming the layer in the temperature range of from about 700 to about 900° C. The exact conditions, however, depend to a certain extent on the design of the equipment used,
a third layer of TiCxNyOz with x+y+z=1, x more than about 0.3 and z more than about 0.3, y is equal to or greater than zero and less than about 0.2, with a thickness of from about 0.3 to about 1.5 μm, produced by CVD using the reaction mixtures TiCl4, CO, H2 or TiCl4, CO, H2, N2,
a fourth layer of a smooth α-Al2O3, with a thickness of from about 9 to about 15 μm, preferably from about 10 to about 12 μm using known CVD-methods.
The ratio of layer thicknesses of the fourth layer Al2O3 and the second layer of TiCxNy is preferably from about 1.3 to about 2.4.
a from about 0.1 to about 2 μm thick colored top layer, preferably TiN or ZrN, using CVD or PVD-technique.
Finally, the Al2O3-layer on the rake face and along the cutting edge line is subjected to an intense wet blasting operation to obtain a smooth surface finish, preferably with a surface roughness in the cutting area zone of Ra<0.4 μm over a length of 10 μm using a slurry comprising Al2O3 grits and water. Alternatively, this wet-blasting step may be performed prior to the deposition of the colored top layer on the clearance faces.
The invention also relates to the use of a cutting tool insert as described above for the dry milling of cast irons such as grey cast iron, highly alloyed grey cast iron or compacted graphite iron at a cutting speed of from about 150 to about 375 m/min and a feed of from about 0.1 to about 0.35 mm/tooth depending on cutting speed and insert geometry.
The invention is additionally illustrated in connection with the following examples, which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the examples.
Cemented carbide milling blanks were pressed in styles R245-12T3M-KM, R290-12T308M-KM and SPKN1204 EDR from powder with the composition 7.6 wt-% Co, 1.25 wt-% TaC, 0.30 wt-% NbC and balance WC and sintered with normal technique at 1410° C. giving as-sintered inserts with an Hc value of 14.7 kA/m and a magnetic Co-content of 6.85 wt-% corresponding to a CW-ratio of 0.90. The inserts were edge rounded using a wet blasting method to a radius of 35 μm and then coated with a first 0.5 μm thick TiCxNy-layer with a high nitrogen content corresponding to a y-value of about 0.95, followed by a second 6 μm thick TiCxNy-layer, with an x-value of about 0.55 and with a columnar grain structure using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle, a third 1 μm thick Ti(C,O)-layer was deposited followed by a fourth 11 μm thick layer of α-Al2O3 and a 1 μm thick top layer of TiN.
The inserts were wet blasted on the rake face with alumina grit in order to remove the top TiN-layer and to produce a smooth surface finish of the exposed Al2O3-layer of Ra=0.2 μm over a length of 10 μm.
Cemented carbide milling inserts according to table 1 with the same insert styles as in Example 1 were produced according to known technique.
Inserts from Example 1 according to the present invention were tested in a face milling of cylinder heads in highly alloyed grey cast iron.
Tool: R245-12T3M-KM
Number of inserts in the cutter: 24 pcs
Criterion: Surface finish and work piece frittering.
Reference: R245-12T3M-KM, prior art Ref A from Example 2
Cutting data
Cutting speed: Vc=350 m/min
Feed rate: Fz=0.15 mm per tooth
Depth of cut: Ap=0.5 mm
Dry conditions
The tool life of Ref A was 174 cylinder heads and 215 cylinder heads for inserts according to the invention was measured.
Results: Increased tool life by 23% and improved surface finish with the inserts according to the invention.
Inserts from Example 1 according to the invention were tested in a face milling of a central block in highly alloyed grey cast iron.
Tool: R245-12T3M-KM
Number of inserts in the cutter: 10 pcs
Criteria: Surface finish and work piece frittering.
Reference R245-12T3M-KM, prior art Ref A from Example 2.
Cutting data
Cutting speed: Vc=251 m/min
Feed rate: Fz=0.24 mm per tooth
Depth of cut: Ap=2-3 mm
Dry conditions
The tool life as an average of two tests was 50 minutes for Ref A and 80 minutes for inserts according to the invention.
Inserts from Example 1 according to the present invention were tested in face milling of a Hub swivel for a generator engine made of grey cast iron
Tool: SPKN1204 EDR
Number of inserts in the cutter: 8 pcs
Criteria: Surface finish and work piece frittering.
Reference SPKN1204 EDR, prior art Ref B from Example 2.
Cutting data
Cutting speed: Vc=350 m/min
Feed rate: Fz=0.19 mm per tooth
Depth of cut: Ap=3-4 mm
Dry conditions
The tool life of Ref B and of inserts according to the invention was 38 and 56 minutes, respectively.
Inserts from Example 1 according to the present invention were tested in a face milling of cylinder heads in compacted graphite iron (CGI).
Tool: R290-12T308M-KM
Number of inserts in the cutter: 6 pcs
Criterion: Surface finish and work piece frittering.
Reference: R290-12T308M-KM, prior art Ref A from Example 2.
Cutting data
Cutting speed: Vc=300 m/min
Feed rate: Fz=0.15 mm per tooth
Depth of cut: Ap=3.0 mm
Dry conditions
The tool life of Ref A and the inserts according to the invention was 60 cylinder heads and 85 cylinder heads, respectively.
From Examples 3-6 it is evident that the insert according to the invention shows much better cutting performance than inserts according to prior art. The main advantage is a slower growth of the flank and crater wear, due to a well balanced composition of the cemented carbide body together with a very big total coating thickness.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0601313-0 | Jun 2006 | SE | national |
