The present invention relates to a coated cemented carbide cutting tool particularly for turning applications with high toughness demands, of stainless steels of different compositions and microstructures, and of low and medium alloyed non-stainless steels. The cemented carbide is wc-Co based with a composition of 9-12 wt % Co, 0.2-2.0 wt % cubic carbides from elements from group IVa, Va or VIa of the periodic table and balance wc with a grain size of 1.5-2 μm. The binder phase is W-alloyed with a CW-ratio in the range of 0.77-0.95. The coating includes a multilayered structure of the composition (TixAl1−x,)N in which x varies repeatedly between the two ranges 0.45<x<0.55 and 0.70<x<0.80, adding up to a total thickness of 2-9 μm.
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1. A coated cemented carbide cutting tool comprising:
a WC—Co based cemented carbide body comprising a composition of 9-12 wt % Co, 0.2-2.0 wt % cubic carbides from elements from group IVa, Va or VIa of the periodic table and balance wc with an average grain size of the wc of 1.5-2 μm and a W-alloyed binder phase with a CW-ratio in the range of 0.77-0.95; and
a hard and wear resistant coating deposited on the WC—Co cemented carbide body comprising:
a first innermost bonding layer of tin;
a second layer comprising a multilayered structure of 0.05-0.2 μm thick sublayers of the composition (TixAl1−x)N in which x varies repeatedly between the two ranges 0.45<x<0.55 and 0.70<x<0.80, the first sublayer of (TixAl1−x)N adjacent to the tin bonding layer having an x-value in the range 0.45<x<0.55, the second sublayer of (TixAl1−x)N having an x-value in the range 0.70<x<0.80 and the third sublayer having an x value in the range 0.45<x<0.55 and so forth repeated until 8-30 sublayers are built up;
a third at least 0.2 μm thick layer of (TixAl1−x)N, where x is in the range 0.45<x<0.55;
a fourth outermost layer of tin;
wherein the total coating thickness is in the range of 2-9 μm and the thickness of the second layer constitutes 75-95% of the total coating thickness.
9. A method of making a cutting tool, the method comprising:
forming a powder mixture containing wc, Co and cubic carbides;
mixing said powders with pressing agent and W metal such that the desired CW-ratio is obtained;
milling and spray drying the mixture to a powder material with the desired properties;
pressing and sintering the powder material at a temperature of 1300-1500° C., in a controlled atmosphere of about 50-mbar followed by cooling to form a substrate; and
applying a hard, wear resistant coating by PVD techniques comprising:
depositing a first innermost bonding layer of tin;
depositing a second layer comprising a 0.05-0.2 μm thick multilayered structure of sublayers of the composition (TixAl1−x)N in which x varies repeatedly between the two ranges 0.45<x<0.55 and 0.70<x<0.80, the first sublayer of (TixAl1−x)N adjacent to the tin bonding layer having an x-value in the range 0.45<x<0.55, the second sublayer of (TixAl1−x)N having an x-value in the range 0.70<x<0.80 and the third sublayer having an x value in the range 0.45<x<0.55, and so forth repeated until 8-30 sublayers are built up;
depositing a third at least 0.2 μm thick layer of (TixAl1−x)N, where x is in the range 0.45<x<0.55;
depositing a fourth outermost layer of tin;
wherein the total coating thickness is in the range of 2-9 μm and the thickness of the second layer constitutes 75-95 % of the tool coating thickness.
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The hard and wear resistant refractory coating deposited on the above described cemented carbide substrate according to the present invention comprises a first (innermost) thin 0.1-0.5 μm bonding layer of TiN, a second layer comprising a multilayered structure of sublayers of the composition (TixAl1−x)N in which x varies repeatedly between the two ranges 0.45<x<0.55 and 0.70<x<0.80, a third thin, at least 0.2 μm, preferably 0.4-0.8 μm, layer of (TixAl1−x)N having an x-value in the range 0.45<x<0.55 and a fourth outermost thin 0.1-0.2 μm layer of TiN.
The first sublayer of (TixAl1−x)N adjacent to the TiN bonding layer has an x-value in the range 0.45<x<0.55, the second sublayer of (TixAl1−x)N has an x-value in the range 0.70<x<0.80 and the third sublayer has x in the range 0.45<x<0.55 and so forth repeated until 8-30 sublayers, preferably 22-24 sublayers, are formed. The thickness of this second layer comprising a multilayered structure of sublayers constitutes 75-95% of the total coating thickness. The individual sublayers of (TixAl1−x)N are essentially of the same thickness but their thickness may also vary in a regular or irregular way and said sublayer thickness is found in the range of 0.05-0.2 μm.
The total thickness of the coating deposited on the cemented carbide substrate according to the present invention may vary in the range of 2-9 μm, preferably 3.5-7 μm. The layer thickness, the sublayer thickness and the coating thickness quoted above refers to measurements made close to the cutting edge, i.e. the functional part of the cutting tool.
A. A cemented carbide turning insert according to the invention with the composition 10.5 wt % Co, 1.16 wt % Ta, 0.28 wt % Nb and balance made up by WC and with an average WC grain size of 1.7 μm, with a binder phase alloyed with W corresponding to a CW-ratio of 0.90, were coated with a total coating thickness of 4.5 μm by applying conventional PVD cathodic arc technique. The coating comprised a first (innermost) 0.2 μm layer of TiN followed by a 3.7 μm thick second layer comprising 23 alternating sublayers of (TixAl1−x)N, where x alternatively varied between 0.5 and 0.75, and a third 0.4 μm (TixAl1−x)N layer, where x=0.5, and, finally, an outermost 0.2 μm layer of TiN.
B. A commercial cemented carbide turning insert with the composition 8.0 wt % Co, and balance made up by WC with an average WC grain size of 3.0 μm, with a binder phase low alloyed with W corresponding to a CW-ratio of 0.94, were coated with a 2.8 μm thick conventional multilayered CVD-coating according to the sequence TiN/TiCN/TiCN/TiN. The sublayers have approximately the same thickness.
Operation:
Alternating axial and facial turning of an
80 mm diameter bar
Work-piece material:
Austenitic stainless steel (AISI316L)
Cutting speed:
160 m/min
Feed rate:
0.4 mm/rev
Depth of cut:
2 mm
Insert-style:
CNMG120408-MM
Results:
Tool life (cycles):
Inserts A:
5
Inserts B:
2
Comment. The main wear mechanism was plastic deformation of the cutting edge line resulting in a flank wear. Tool life criterion was flank wear>0.3 mm.
Inserts as in A and B from Example 1 were tested in a turning operation.
Operation:
Facing of a 130 mm bar with two flat sides
Work-piece material:
Austenitic stainless steel (SS2343)
Cutting speed:
190 m/min
Feed rate:
0.3 mm
Depth of cut:
2 mm
Insert-style:
CNMG120408-MM
Results:
Tool-life (cycles)
Inserts A:
14
Inserts B:
6
Comment: The performance criterion was bad cutting action. The insert B shows more chipping along the cutting edge caused by more adhesion to the chips during the operation.
Inserts as in A and B from Example 1 were tested in a turning operation.
Operation:
External turning of a ring with 18 mm thickness
Work-piece material:
Austenitic stainless steel (AISI316L)
Cutting speed:
140 m/min
Feed rate:
0.35 mm
Depth of cut:
4 mm
Insert-style:
CNMG190616-MR
Results:
Tool-life (cycles)
Inserts A:
40
Inserts B:
29
Comment: The tool-life criterion was spalling on the work piece caused by edge chipping due to lack of edge toughness.
Inserts as in A and B from Example 1 were tested in a turning operation.
Operation:
Longitudinal turning with interrupted cuts
Work-piece material:
Steel (SS1312)
Cutting speed:
80 m/min
Feed rate:
0.4 mm
Depth of cut:
2 mm
Insert style:
CNMG120408-MM
Results:
Tool-life (minutes)
Inserts A:
10
Inserts B:
5
Comment: The tool-life criterion was edge breakage. Insert A ran a full cycle. Since the difference is very big you can consider insert A to have a better toughness behaviour.
Inserts as in A and B from Example 1 were tested in a turning operation.
Operation:
Alternating facing and turning of a bar
70 mm in diameter
Work-piece material:
Ferriteaustenitic steel (SAF2205)
Cutting speed:
100 m/min
Feed rate:
0.3 mm
Depth of cut:
2 mm
Insert-style:
CNMG120408-MM
Results:
Tool-life (cycles)
Inserts A:
11
Inserts B:
4
Comment: The tool-life criterion was bad cutting action due to edge frittering, which is due to lack of edge toughness.
Inserts as in A and B from Example 1 were tested in a turning operation.
Operation:
External turning of a bar 120 mm in diameter
Work-piece material:
Steel (SS2541)
Cutting speed:
110 m/min
Feed rate:
0.6 mm
Depth of cut:
2 mm
Insert-style:
CNMG120408-MM
Results:
Edge depression (mm)
Inserts A:
0.035
Inserts B:
0.085
Comment: Tool-life criterion was predetermined time in cut (0.5 min). The depression in the cutting edge was caused by lack of resistance to plastic deformation.
The present invention also relates to a method of making the above mentioned coated cutting tool insert comprising a WC-Co based cemented carbide body including an amount lower than 2.0 wt % of cubic carbides and with a composition of WC/Co in the range of 9-12 wt % Co, preferably 10-11 wt % Co and most preferably 10.2-10.8 wt % Co, and an amount of cubic carbides in the range of 0.2-2.0 wt %, and the balance is made up by WC. The average WC grain size is found in the range of 1.5-2.0 μm, preferably 1.6-1.8 μm.
The hard and wear resistant refractory coating is deposited onto the cemented carbide substrate by conventional PVD (Physical Vapor Deposition) methods. According to the present invention, a first (innermost) thin 0.1-0.5 μm bonding layer of TiN is deposited, a second layer comprising a multilayered structure of sublayers of the composition (TixAl1−x)N in which x varies repeatedly between the two ranges 0.45<x<0.55 and 0.70<x<0.80is then deposited, a third thin, at least 0.2 μm, preferably 0.4-0.8 μm, layer of (TixAl1−x)N having an x-value in the range 0.45<x<0.55 is deposited, and a fourth (outermost) thin 0.1-0.2 μm layer of TiN is finally deposited. Additionally, the first sublayer of (TixAl1−x)N adjacent to the TiN bonding layer has an x-value in the range 0.45<x<0.55, the second sublayer of (TixAl1−x)N has an x-value in the range 0.70<x<0.80 and the third sublayer has x in the range 0.45<x<0.55 and so forth repeated until 8-30 sublayers, preferably 22-24 sublayers, are formed. The thickness of this second layer comprising a multilayered structure of sublayers constitutes 75-95% of the total coating thickness. The individual sublayers of (TixAl1−x)N are essentially of the same thickness but their thickness may also vary in a regular or irregular way and said sublayer thickness is found in the range of 0.05-0.2 μm.
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.
Lenander, Anders, Lindholm, Mikael, Lindskog, Per
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