Patent Grant
7531213
The present invention relates to a coated cutting tool, suitable for chip forming machining of metals, and a method for producing the same. According to the present invention, there is provided a reliable method for removing coating layers on selected faces of a cutting insert during coating post-treatment.
Modem high productivity chip forming machining of metals requires reliable tools with excellent wear properties. This is achieved by employing a cemented carbide tool body coated with a wear resistant coating, of single layer or multilayer type, most commonly comprising wear layers of TiC, TiN, TiCN and Al2O3. For depositing the different layers onto the cemented carbide body, CVD, PVD, or similar coating techniques are used.
EP-A-693574 describes how different parts of a tool are subject to different types of wear during a machining operation. Since the various coating layers have different abilities to withstand the different types of wear, it is suggested to have an outermost Al2O3layer on the rake face, because of its ability to withstand diffusion type wear, and on the clearance side it is suggested to have an outermost MeCxNyOz type layer, where Me is a metal selected from groups IVB, VB, VIB of the periodic table, because of its high resistance to flank wear. A top layer of TiCxNyOz or, in particular, a goldish TiN, ZrN or HfN top layer also makes it easy to differentiate between a used and an unused cutting edge by the naked eye. Hence, the TiCxNyOz layer is mechanically removed from either only the edge line or from both the rake face and the edge line to expose the Al2O3layer. Normally this is done by a post-treatment such as blasting or brushing of the coated inserts.
During the post-treatment, it is important not to reduce the Al2O3 layer thickness along the edge line. The method must therefore be so gentle that only the top TiCxNyOz layer is removed, leaving the Al2O3at the edge line as untouched as possible. However, the described post-treatment method is unreliable as residues of TiCxNyOz occasionally appear on the Al2O3surface after blasting process. TiCxNyOz residues on the Al2O3surface reduce the flaking resistance, due to welding of TiCxNyOz to the work piece at the cutting edge resulting in coating withdrawal and a lower lifetime of the insert. A second effect of these residues after blasting is the discoloration, visible to the naked eye, of the Al2O3surface. In production, blasting is usually repeated or modified in order to remove residual TiCxNyOz, but this often results in damage, such as flaking of the coating at the cutting edge line. It is therefore important to find a solution to this problem, especially for thin Al2O3 coatings, where usually lower blasting pressures are used in order not to damage the coating at the cutting edge, thus being subject to a higher risk of having TiCxNyOz residues after the blasting process.
In U.S. Pat. No. 6,426,137, a titanium oxide layer is utilized in order to reduce smearing onto the cutting edge. In this case the titanium oxide layer is fully covering the Al2O3 surface, acting as the top layer with a thickness of 0.1-3 μm. In another embodiment the titanium oxide layer is coated with a TiN layer.
It is an object of the present invention to solve the problem of residual TiCxNyOz on the post-treated edge line and rake face.
In accordance with the invention there is provided a method for making a coated cutting tool insert having an upper face (rake face), an opposite face and at least one clearance face intersecting said upper and opposite faces to define cutting edges comprising depositing by CVD, onto a cemented carbide, titanium based or ceramic substrate
by a post-treatment removing at least said outermost layer on the edge-line and on the rake face.
A—TiN residues, and
B—Al2O3.
A—Ti2O3 residues, and
B—Al2O3.
A—TiN residues, and
B—Al2O3.
According to the present invention, there is now provided a method of making a coated cutting tool insert, having an upper face (rake face), an opposite face and at least one clearance face intersecting said upper and opposite faces to define cutting edges, comprising depositing onto a cemented carbide, titanium based or ceramic substrate, using known CVD methods
followed by a post-treatment, preferably blasting or brushing, removing at least said outermost layer on the edge-line and on the rake face. To ensure the performance of the insert and the absence of any discoloration due to TiN residues, it is preferred that said post-treatment also removes at least 50% of the TiOx layer, in terms of surface coverage, i.e., preferably at least 50% of the outer layer surface of said hard layer system is exposed.
Using TiOx, which has a hardness of about 20% of that of Al2O3 with the proposed thickness, the TiCxNyOz layer is thus lifted up above the rough Al2O3 surface, so that it can be fully removed by the blasting media. TiOx is furthermore a transparent oxide, which means that any residues left on the Al2O3surface are not visible to the naked eye, as is the case with, e.g., TiN.
The present invention also relates to a coated cutting tool insert having an upper face (rake face), an opposite face and at least one clearance face intersecting said upper and opposite faces to define cutting edges made of cemented carbide, titanium based carbonitride or ceramics. The insert is coated with a hard layer system, having a total thickness of from about 2 to about 50 μm, comprising at least one layer selected from titanium carbide, titanium nitride, titanium carbonitride, titanium carboxide and aluminum oxide, and an outer, from about 1 to about 15 μm thick, aluminum oxide, preferably fine grained of a grain size of from about 0.50 to about 3 μm, α-Al2O3, layer or (Al2O3+ZrO2)*N multilayer, said hard layer system is provided with a TiOx layer, where x ranges from about 1 to about 2, preferably from about 1.3 to about 1.9, with a thickness of preferably from about 0.05 to about 3 μm, most preferably 0.1-1.0 μm, said TiOx layer being the outermost layer on the cutting edge line and rake face, and said TiOx layer is on the clearance side provided with an outermost, 0.3-2 μm thick, TiCxNyOz layer, where x+y+z=1, x≧0, y’preferably a single layer or multilayer of TiN, TiC or TiCxNy, where x+y=1, x≧0 and y≧0.
The grain size of the Al2O3 layer is determined from a SEM top view micrograph at 5,000 X magnification of the as deposited Al2O3 layer surface. Drawing three straight lines in random directions, the average distances between grain boundaries along the lines, are taken as a measure of the grain size.
In a preferred embodiment said TiOx layer on the edge-line and rake face covers less than 50% of the surface of said hard layer system.
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.
A (invention): Cemented carbide cutting inserts CNMG 120408-PM with the composition 5.5 wt-% Co, 8.6 wt-% cubic carbides (TiC+TaC+NbC) and balance WC were coated with CVD-technique according to the following sequence: 0.7 μm TiN, 4.0 μm Ti(CN), 5.0 μm α-Al2O3, 0.7 μm titanium oxide (Ti2O3) and 0.7 μm TiN.
The Ti2O3 layer was deposited by CVD technique, where the substrates to be coated were held at a temperature of 1010° C. and were brought in contact with a hydrogen carrier gas containing TiCl4, CO2 and HCl. The nucleation was started up in a sequence where the reactant gases HCl and CO2 entered the reactor first, in an H2 atmosphere, followed by the TiCl4. The titanium oxide layer was deposited with a CVD process with the following process parameters:
The other layers where deposited by known CVD methods.
The coated inserts were post-treated by blasting at the different blasting pressures 1.8, 2.0 and 2.2 bar, using Al2O3 grits.
B (prior art): Cemented carbide cutting inserts CNMG 120408-PM with the composition 5.5 wt-% Co, 8.6 wt-% cubic carbides (TiC+TaC+NbC) and balance WC were coated with CVD-technique according to the following sequence: 0.7 μm TiN, 4.0 μm Ti(CN), 5.0 μm α-Al2O3 and 0.7 μm TiN by known CVD methods.
The coated inserts were post treated by blasting at 2.4 bar by using Al2O3 grits.
Inserts of type A and B were studied in a light microscope (200×) to detect any TiN residues on the Al2O3 surface and further in a scanning electron microscope (500×) to detect residues of Ti2O3. The amount of residual Ti2O3 was determined using image analysis (Leica Quantimet 500). The results are summarized in the following table.
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 departing from the spirit and scope of the inventions as defined in the appended claims.
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