Coated cutting insert

Abstract

The invention relates to a coated cutting insert, in particular for heavy-duty machining, having a main body and a coating, wherein the coating comprises at least one coating layer made of α-AI2O3, which is deposited using a CVD method and which results in an X-ray diffractogram measured with Cu-Ka radiation and with a theta-2theta scan, wherein texture coefficients (TC) are calculated according to the Harris formula (I), wherein I(hkl) stands for a measured intensity of a (hkl) reflection, l0(hkl) stands for a standard diffraction intensity for a plane (hkl) according to the JCPDS card no. 00-042-1212, n stands for a number of reflections used in the calculation. In order to be able to provide cutting inserts with long service lives under different operating conditions, according to the invention n = 8 and the reflections (012), (104), (110), (006), (113), (116), (214) and (300) are used for the calculation, wherein TC (006) ≤ 5.75 and the sum of TC (104) and TC (110) > 0.50.

Description

[0001] Coated cutting insert

[0002] The invention relates to a coated cutting insert, in particular for heavy machining, with a base body and a coating, wherein the coating comprises at least one coating layer of a-ALOs, which is deposited using a CVD process and which produces an X-ray diffractogram measured with Cu-Ka radiation and with a theta-2theta scan, wherein texture coefficients (TC) according to the Harris formula be calculated, where

[0003] I (hkl) stands for a measured intensity of a (hkl) reflection, lo(hkl) stands for a standard diffraction intensity for a plane (hkl) according to JCPDS card no. 00-042-1212, n stands for a number of reflections used in the calculation.

[0004] Coatings made of aluminum oxide (Al2O3) in various modifications and deposited via chemical vapor deposition (CVD) have proven highly effective for cutting inserts. In particular, α-aluminum oxide is used to produce coating layers intended to provide long service life for cutting tools.

[0005] Aluminum oxide coating layers have been investigated in a wide variety of fields. In particular, with a-aluminum oxide, a key focus is on producing coating layers of a-aluminum oxide with a specific preferred orientation. It has been found that various preferred orientations lead to improved service life for tools or tool inserts used in cutting operations.

[0006] Although numerous studies and experiments have been conducted in this area, leading to steady improvements in tool life, there is still interest in further developing corresponding coating systems to achieve even longer tool life. Even small improvements in the single-digit percentage range can represent a significant improvement, as a tool often uses a large number of identical cutting inserts, and in the interests of high productivity, it is often desirable to utilize the cutting tools as fully as possible with minimal downtime. Longer tool life not only means less wear per unit time and thus a longer service life and, across the number of cutting inserts and their service life, significantly less material consumption, but also less tool downtime for cutting insert changes.

[0007] In the field of heavy-duty machining, too, the goal is to be able to work with cutting inserts for as long as possible. Heavy-duty machining, typically involving milling or turning, involves machining large components, for example, in wheel set machining or roller machining, as well as in the machining of pipe ends or steel bars. This process involves extremely high loads during both smooth and interrupted cuts. The parts to be machined are often large, such as ship crankshafts, are regularly made of very hard materials, and are machined with the desired high productivity. All of this leads to an extremely high load profile, particularly for cutting inserts used in milling.

[0008] This is where the invention comes in. The object of the invention is to further develop a cutting insert of the type mentioned above in such a way that it has a long service life under various operating conditions.

[0009] This task is solved if, for a cutting insert of the type mentioned above, where n = 8 and the reflections (012), (104), (110), (006), (113), (116), (214) and (300) are used for the calculation, where TC(006) < 5.75 and a sum of TC(104) and TC(110) > 0.50.

[0010] The texture coefficients refer to JCPDS card no. 00-042-1212 of the International Centre for Diffraction Data. The advantage of a cutting insert according to the invention is that it achieves a long tool life under various conditions, particularly during heavy-duty machining, for example wheelset machining or crankshaft machining. The coating layer made of a-aluminum oxide has a preferred orientation, with TC(006) having a value of < 5.75 and with the sum of TC(104) and TC(110) being > 0.50. In comparison with other coating layers made of a-aluminum oxide and a preferred orientation for TC(006), attempts are often made to maximize TC(006). However, according to the invention, a preferred orientation of the plane (006) is provided, but with a specifically selected upper threshold value. At the same time, the sum of TC(104) and TC(110) exceeds the value of 0.50.

[0011] A moderate preferential orientation for the plane (006) and at the same time a predetermined minimum for the orientations of the planes (104) and (110) thus lead to a development of the coating layer of a-aluminum oxide, which is not maximized with respect to a preferential orientation of a single plane, but results in a balanced mixture of the orientations of individual planes for heavy-duty machining under different conditions.

[0012] The cutting insert can be a cutting plate attached to a larger tool, such as a milling cutter with a milling head. However, the cutting insert can also be a tool in itself. In this respect, the cutting insert can either be part of a larger tool or represent the tool itself.

[0013] It is particularly preferred that 3.0 < TC(006) < 5.5, preferably 3.5 < TC(006) < 5.5, especially 4.0 < TC(006) < 5.5. A range for TC(006) of 3.0 to 5.5, preferably 3.5 to 5.5, and especially 4.0 to 5.5, proves suitable with regard to a desired long service life.

[0014] The sum of TC(104) and TC(110) is advantageously > 0.60, preferably > 0.70, in particular > 0.80, for example > 0.90 or > 1.00. Within the scope of the invention, TC(012) and / or TC(300) can be > 0.40, preferably > 0.55, in particular > 0.80. In addition to a moderately pronounced preferred orientation for the (006) plane, the (104), (110) and (300) and / or (012) planes are thus also formed with a stronger preferred orientation compared to the other planes of the eight peaks used. In particular, it can also be provided that a sum of TC(104), TC(110), and TC(300), or a sum of TC(104), TC(110), and TC(012) is > 1.00, preferably > 1.50, in particular > 2.00. For example, TC(300) can be < 0.10 and balanced by higher preferred orientations of the other two planes. The same applies to TC(012) for the sum formed with TC(012), so that TC(012) can be < 0.10.On the other hand, a sum of TC(113), TC(116) and TC(214) is advantageously < 0.60, preferably < 0.50, in particular < 0.45, for example < 0.45 or < 0.30.

[0015] Typically, the coating has a bonding layer of titanium nitride deposited on the base body. This allows for good bonding of the entire coating, including the coating layers following the bonding layer, particularly in the case of a cemented carbide base body. The titanium nitride coating layer can have a thickness of up to 1.5 μm. Typically, the thickness of this titanium nitride coating layer is in the range of 0.5 μm to 1.2 μm.

[0016] For wear resistance, the coating may include one or more coating layers of titanium carbon nitride. The coating layer of titanium carbon nitride may, in particular, be a coating layer of titanium carbon nitride formed with elongated crystallites. Typically, these are structures of titanium carbon nitride deposited at medium temperatures of approximately 850°C to 900°C. Such coating layers are also referred to as MT-TiCN (medium-temperature titanium carbon nitride). These coating layers are characterized by their high wear resistance and therefore represent a suitable base for a coating layer of α-aluminum oxide.The corresponding coating layers also typically exhibit a preferred orientation in the sense that the elongated crystals extend perpendicular to a plane onto which an MT-TiCN coating layer is deposited. Typically, the corresponding crystallites are arranged perpendicular to the corresponding plane with a maximum deflection angle to a vertical line to the deposition plane of, on average, ± 30°.

[0017] Within the scope of the invention, it can also be provided, in particular, that a further coating layer of titanium carbon nitride is deposited on this MT-TiCN coating layer, but at a higher temperature than the first coating layer of titanium carbon nitride. This is usually so-called HT-TiCN (high-temperature titanium carbon nitride), which is deposited at temperatures of approximately 950°C to 1020°C.

[0018] Additionally or alternatively, a coating layer made of titanium carbon nitride can also be provided, which comprises crystallites with an inhomogeneous distribution of the elements carbon and nitrogen in the nanometer range. Such coating layers are known from WO 2007 / 056785 A1 and comprise crystallites with a core-shell structure, in which the core has a different chemical composition than the surrounding shell. Such special coating layers made of titanium carbon nitride serve not only as working layers, but also, in particular, as good bonding layers, because during deposition in a CVD process, a branched structure with individual tips forms on the surface, ensuring excellent anchoring of subsequently deposited, additional coating layers.

[0019] For the deposition of the coating layer made of a-aluminum oxide, it can be provided that, specifically following a coating layer made of titanium carbonitride or generally, a coating layer made of titanium oxynitride that is doped with aluminum is provided. This can be followed by a further coating layer made of titanium oxycarbonitride that is doped with aluminum. These corresponding coating layers are advantageously provided in order to achieve deposition of a coating layer made of a-aluminum oxide with the desired texture. In particular, the last coating layer deposited before the coating layer made of a-aluminum oxide serves to form nuclei for the formation of the coating layer made of a-aluminum oxide. It is particularly preferred that the at least one coating layer made of a-aluminum oxide is deposited on a coating layer made of titanium oxynitride that is doped with aluminum.Alternatively, bonding layers of CVD-deposited AlxTh-xN with x > 0.80 directly beneath the a-aluminum oxide coating layer can also be used. Such coating layers also allow for very good bonding of the a-aluminum oxide. In addition, coating layers with Al can be used. x Tii-xN with x > 0.80 must also be deposited externally over the coating layer of a-aluminum oxide in order to optimize the cutting performance.

[0020] Additional coating layers can be deposited on the at least one coating layer of a-aluminum oxide. For example, it is possible for a coating layer of titanium carbon nitride to be deposited on the coating layer of a-aluminum oxide. Although the coating layer of a-aluminum oxide, together with the underlying coating layers, is fundamentally crucial for service life, the property profile of the coating can be further adjusted and optimized by depositing additional coating layers on the coating layer of a-aluminum oxide.

[0021] In principle, it is possible for individual coating layers to be deposited using different processes, for example, physical vapor deposition (PVD). However, it is more efficient if all coating layers are deposited using a single CVD process.

[0022] The base body is usually made of a hard metal, but can also be made of a cermet, a ceramic or a high-speed steel.

[0023] Further features, advantages, and effects of the invention will become apparent from the exemplary embodiment presented below. In the drawing, to which reference is made, Fig. 1 shows a schematic representation of a base body with a coating comprising several coating layers applied to the base body.

[0024] Fig. 1 shows a highly schematic section of a base body with a coating applied to it. The base body is made of a hard metal. The hard metal can typically contain 80 to 95 weight percent tungsten carbide, with the remainder being a binder metal made of cobalt, nickel, and / or iron. The hard metal base body can also have a more complex structure, for example, by including titanium carbide, tantalum carbide, and / or niobium carbide as the hard material in addition to tungsten carbide.

[0025] A multilayer coating is deposited on the base body, consisting of the individual coating layers as shown in Fig. 1. The individual coating layers are all deposited sequentially using a CVD process, which can be used in a commercially available Bernex 530 L CVD reactor from the IHI Group. Table 1 below shows typical reaction parameters for the supply of individual reactive gases. Aluminum trichloride is obtained from solid aluminum by reaction with HCl, for which aluminum pellets can be used, for example. Titanium tetrachloride (TiCl) and acetonitrile (CH3CN) are obtained by evaporating the corresponding liquid phases, which also applies to hydrogen sulfide (H2S).For the corresponding liquids, the gas conversions are given in mL per minute due to the small quantities, whereas the flows for the components present in gaseous form at room temperature are given in L per minute.

[0026] Table 1: Reaction parameters

[0027] The coating thus created was examined with an X-ray diffractometer in a theta-2 theta scan with Cu-Ka radiation with regard to texturing of the coating layer of a-alumina, resulting in texture coefficients according to Table 2 below.

[0028] Table 2: Texture coefficients of a coating layer made of a-alumina (prepared according to Table 1)

[0029] Corresponding coating layers were applied to hard metal cutting inserts. The inserts were then tested in various cutting operations.

[0030] First, inserts with a coating according to Table 1 were used in a rotary peeling operation on steel bars and compared with previously used inserts with a coating according to WO 2007 / 056785 A1, using the same chip former geometry. The cutting data were as follows:

[0031] Speed ​​n [mim 1 ]: 1850

[0032] Cutting speed vo [m / min]: 98

[0033] Cutting depth a p [mm]: 0.35

[0034] Feed rate f [m / min]: 8.5

[0035] feed f n [mm / ll]: 15.6

[0036] Raw diameter [mm]: 17.7

[0037] Finished diameter [mm]: 17

[0038] Length [mm]: 7070

[0039] A wavy surface was defined as the criterion for the end of tool life. It was found that an insert coated according to the invention showed hardly any wear after 142 machined bars and achieved a 10% increase in tool life compared to a comparable insert. Furthermore, significantly lower skiving noise and a smoother, more evenly machined surface were observed. In a further test, inserts coated according to the invention were tested in an interrupted-cut turning operation. Inserts with the same chip-forming geometry, but coated with a K-aluminum oxide working layer, served as the comparison. The cutting data were as follows:

[0040] Speed ​​n [min -1 ]: 250

[0041] Cutting depth a p [mm]: 1.50

[0042] Feed f [m / min]: 0.30 K: 95°

[0043] Cooling: no

[0044] The tool life criteria were visually detectable plastic deformation, fracture, and maximum wear mark width. It was found that the inserts coated according to the invention achieved at least the same tool life as the comparison inserts, while providing better chip formation and significantly lower machining noise.

[0045] In another experiment, cutting inserts coated according to the invention were used to machine steel shafts. Cutting inserts from the market leader served as comparison inserts. The cutting data were as follows:

[0046] Cutting speed v c [m / min]: 150

[0047] Cutting depth a p [mm]: 2.0

[0048] Feed rate f [m / min]: 0.35

[0049] Cooling: no

[0050] With significantly lower machining noise, tool life improvements of up to 20% were observed with inserts coated according to the invention when machining shafts in a smooth cut relative to the comparison inserts.

[0051] In yet another experiment, inserts coated according to the invention were used in a milling operation for steel components. Inserts of the same geometry, but with a PVD aluminum titanium nitride coating, served as comparison inserts. The cutting data were as follows: v c [m / min]: 180 n [rpm]: 909 a p [mm]: 42 a e [mm]: 2 f z [mm / Z]: 0.25 Vf [mm / min]: 227 K: 95°

[0052] Cooling: no D: 63

[0053] Z: 1

[0054] The test criterion was the maximum wear width mark of 0.15 mm at 500 cm 3Compared to the reference inserts, the tool life was increased by no less than 100%.

[0055] Cutting inserts according to the invention thus exhibit a highly balanced property profile, allowing for long-lasting use under a wide range of conditions. The texturing of the a-aluminum oxide coating layer does not maximize the preferred orientation, but allows for efficient use of the coating under a wide range of conditions. Furthermore, machining noise is significantly reduced when using cutting inserts coated according to the invention, which represents an advantage in terms of working conditions.

Claims

Patent claims 1 . Coated cutting insert, in particular for heavy machining, with a base body and a coating, wherein the coating comprises at least one coating layer of aA^Os, which is deposited by a CVD process and which produces an X-ray diffractogram measured with Cu-Ka radiation and with a theta-2theta scan, wherein texture coefficients (TC) according to the Harris formula where l(hkl) stands for a measured intensity of a (hkl) reflection, lo(hkl) for a standard diffraction intensity for a plane (hkl) according to the JCPDS Card No. 00-046-1212, n stands for a number of reflections used in the calculation, where n = 8 and the reflections (012), (104), (110), (006), (113), (116), (214) and (300) are used for the calculation, where TC(006) < 5.75 and a sum of TC(104) and TC(110) > 0.

50.

2. Cutting insert according to claim 1, wherein 3.0 < TC(006) < 5.5, preferably 3.5 < TC(006) < 5.5, in particular 4.0 < TC(006) < 5.

5.

3. Cutting insert according to claim 1 or 2, wherein the sum of TC(104) and TC(110) is > 0.60, preferably > 0.70, in particular > 0.

80.

4. Cutting insert according to one of claims 1 to 3, wherein TC(012) and / or TC(300) is > 0.40, preferably > 0.55, in particular > 0.

80.

5. Cutting insert according to one of claims 1 to 4, wherein a sum of TC(113), TC(116) and TC(214) is < 0.80, preferably < 0.60, in particular < 0.55, for example < 0.45 or < 0.

30.

6. Cutting insert according to one of claims 1 to 5, wherein the coating comprises a bonding layer of titanium nitride deposited on the base body.

7. Cutting insert according to one of claims 1 to 6, wherein the coating comprises one or more coating layers of titanium carbonitride.

8. Cutting insert according to claim 7, wherein a first coating layer is formed of titanium carbonitride with elongated crystallites.

9. Cutting insert according to claim 8, wherein a second coating layer of titanium carbonitride is deposited on the first coating layer of titanium carbonitride, wherein the second coating layer of titanium carbonitride is deposited at a higher temperature than the first coating layer of titanium carbonitride.

10. Cutting insert according to claim 7, wherein a coating layer of titanium carbonitride is provided which has crystallites with inhomogeneous element distribution of the elements carbon and nitrogen in the nanometer range.

11. Cutting insert according to one of claims 1 to 10, wherein the coating comprises at least one coating layer of titanium oxynitride doped with aluminum.

12. Cutting insert according to one of claims 1 to 11, wherein the coating comprises at least one coating layer of titanium oxycarbonitride doped with aluminum.

13. Cutting insert according to one of claims 1 to 12, wherein the at least one coating layer of a-Al2O3 is deposited on a coating layer of titanium oxynitride doped with aluminum.

14. Cutting insert according to one of claims 1 to 13, wherein a coating layer of titanium carbonitride is deposited on the at least one coating layer of aAlOs.

15. Cutting insert according to one of claims 1 to 14, wherein all coating layers are deposited using a CVD process.

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