DE102012007991A1 - Mixed ceramic cutting tool and blended ceramic granules therefor and method of manufacturing the cutting tool - Google Patents

Abstract

Disclosed is a Mischkeramisches cutting tool, in particular an insert or an indexable insert, which has at least two ceramic hard materials. A first of the hard materials has an oxide of zirconium or molybdenum or niobium, and the second of the hard materials has a carbide or a nitride of a compound of at least two of tantalum, tungsten, hafnium or rhenium.

Description

The invention relates to a mixed-ceramic cutting tool according to the preamble of patent claim 1, a mixture of ceramic granules for sintering of such a cutting tool according to the preamble of patent claim 5 and a method for manufacturing a mixed-ceramic cutting tool according to the preamble of patent claim 7.

Known ceramic cutting tools, for example made of cubic crystalline boron nitride (CBN) or of an oxide ceramic, for example Al ₂ O ₃ , have a high hardness, temperature resistance, thermal and wear resistance and chemical resistance. With them high cutting and processing speeds can be realized in machining production. In addition, they can be used with a lubrication / coolantless dry machining, since a reduction in the temperature load of a cutting edge in engagement because of their high heat resistance is not necessary.

However, these favorable properties of the mentioned ceramics are disadvantageous compared with their brittle-hard material behavior. Due to a lack of toughness and flexural strength, ceramic cutting materials are still insufficient today in the area of high feed speeds or in the case of interrupted cuts, as occurs, for example, during milling.

Although available high speed tool steels (HSS) desirably have high toughness and flexural strength values, they do not achieve the hardness and hot strength of the ceramic cutting or hard materials.

The use of mixtures of ceramics, in particular based on oxide and nitride ceramics such as Al ₂ O ₃ and Si ₃ N ₄ , results in cutting materials of high hardness with higher toughness. A disadvantage of these mixtures, however, is that the range of application of the cutting material is thereby shifted relatively little in the range of higher feeds or the interrupted section, as these mixed ceramics still have a relatively low toughness. In addition, there is a loss of hardness compared to the hardest oxide ceramics or the CBN.

Mixed ceramics based on aluminum oxide (Al ₂ O ₃ ), titanium carbide (TiC) and titanium nitride (TiN) are also known. However, these also have only a limited field of application for hard finishing in smooth cutting or for the finishing of cast iron in smooth or interrupted cut.

In contrast, the invention is based on the object to provide a universal usable mixed ceramic cutting tool and to provide a mixture of ceramic granules and a manufacturing process for it.

This object is achieved by a cutting tool having the features of patent claim 1, a mixture of ceramic granules having the features of patent claim 5 and a manufacturing method having the features of patent claim 7.

Advantageous developments of the invention are described in the claims 2 to 4, 6 and 8 to 10.

A mixed-ceramic cutting tool, in particular an insert or an indexable insert, has at least two ceramic hard materials.

According to the invention, a first ceramic hard material of these comprises an oxide of zirconium or molybdenum or niobium and a second ceramic hard material comprises a carbide or a nitride formed by a compound comprising at least two of the following: tantalum, tungsten, hafnium , Rhenium. The oxide of zirconium or molybdenum or niobium has a dispersive effect on the mixture of the ceramic hard materials and gives the cutting tool a high toughness. The first ceramic hard material preferably comprises ZrO or ZrO ₂ or MoO ₂ or NbO ₂ . The carbide or the nitride with the at least two substances gives the cutting tool its high hardness. The use of two different substances in the carbide or in the nitride contributes to bridge formation with the oxide of the first ceramic hard material and additionally increases the hardness of the cutting tool compared to conventional cutting tools. The second hard material preferably has tantalum with tungsten or with hafnium or with rhenium or tungsten with hafnium or with rhenium or hafnium with rhenium. Particularly preferred is tantalum hafnium carbide (Ta ₄ HfC ₅ ), tantalum rhenium carbide, tungsten tantalum carbide or tungsten niobium carbide. Due to the increased hardness and increased toughness due to the selected hard material mixture according to the invention, the cutting tool can be used more flexibly and universally. This makes it particularly suitable for drilling, turning or milling. The field of application covers a field of materials with different material and cutting properties such as ferritic materials, free-cutting steels, structural steels, case-hardening steels, superalloys, cast iron and ADI casting. Furthermore, the range of processing types such as fine machining, center machining, hard machining and finishing and Scrubbing possible. It is a hard machining with geometrically defined cutting edge for all cutting processes, even with interrupted cutting and workpieces with different hardness zones, possible. Compared to conventional. mixed-ceramic cutting tools increases the service life of the cutting tool due to the very wear-resistant hard materials to about twice and a life cycle to about 5 times. Another advantage is the increased process reliability, since tool breakage occurs less frequently or is less likely. Thus, also rejects and machine damage are reduced. The cutting tool according to the invention also allows compared to conventional mixed-ceramic cutting tools about 2.5 times the cutting speed. A particular advantage of the universal cutting tool is that it can substitute several special tools, which can reduce logistics, investment and operating costs in machining production.

In a preferred embodiment of the cutting tool, this additionally has a third ceramic hard material which has a carbide deviating from the second hard ceramic or different nitride, which is formed by one of the above-described compounds, which has at least two of the substances tantalum, tungsten, hafnium, rhenium , By suitable choice of the third ceramic hard material while the field of application of the ceramic cutting tool can be focused on narrower fields of application or even further expandable.

A preferred development of the cutting tool has a fourth ceramic hard material, which has a deviating from the first ceramic hard oxide zirconium or molybdenum or niobium according to the foregoing description.

An increase in the toughness and hardness of the cutting tool over conventional cutting tools results when a mass fraction of the first or the first and fourth ceramic hard material about 20-40% and a mass fraction of the second or the second and third ceramic hard material about 80-60% of a mass of the cutting tool is. Thus, the second or the second and third ceramic hard materials (carbide / nitride) preferably act as a ceramic matrix, in which the first ceramic hard material or the first and the second ceramic hard material (oxide) is or are embedded.

As a precursor for sintering a mixed ceramic cutting tool according to the preceding description, a mixture of ceramic granules according to the invention is preferred which has a granulate of the first ceramic hard material and at least one granulate of the second ceramic hard material. In a preferred development of the mixture, this mixture additionally comprises granules of a third or of a third and fourth ceramic hard material according to the preceding description.

If the melting temperatures of the ceramic hard material differ, it proves to be advantageous for a subsequent sintering if a particle size of the granules of that hard material with the lower temperature is about two to ten times, more preferably three to five times larger than a particle size of the granules of that Hard material with the higher melting temperature. In this way, sintering can be facilitated. The grain size of the granules having the higher melting temperature is preferably in the range of 1/100 mm. This applies in particular to mixtures in which tantalum hafnium carbide Ta ₄ HfC ₅ , which at 4215 ° C. has one of the highest known melting temperatures, is involved as the second hard material.

A method according to the invention for the production of the above-described cutting tool has at least one step "approximation of melting temperatures of the hard materials of the ceramic mixture". This approach in particular allows sintering of the above-described advantageous cutting tool. The approach preferably takes place via an adjustment of different pressures for the different hard materials.

In a preferred development of the method, a step "connection of granules of the hard substances of the mixture, in particular by paraffin" is carried out before the step "approach of the melting temperatures".

In a further preferred embodiment of the method, a step "hot pressing the mixture of granules and paraffin" is performed after the step "compound of the granules" and before a step "sintering".

In a further preferred embodiment of the method, the step "sintering" of the mixture of the ceramic hard materials takes place in the connection or during the step "approximation of the melting temperatures" of the ceramic hard materials.

Embodiments of inventive mixtures of hard materials for a cutting tool with reference to a table and an embodiment of the cutting tool according to the invention are explained in more detail below with reference to two schematic figures. Show it:

1 a table with embodiments of hard material mixtures for a cutting tool;

2 an embodiment of the cutting tool in a plan view; and

3 the embodiment according to 2 in a cross section.

1 shows possible mixtures of hard materials for the production or sintering of a cutting tool according to the invention. In 1 On the left, in the table of the first hard material, those hard materials are listed which are intended for the intended increase in the toughness of the mixed ceramic. These are zirconia (ZrO ₂ ), molybdenum dioxide (MoO ₂ ) and niobium dioxide (NbO ₂ ).

The right table in 1 lists possible second hard materials that can be formed from the combination of two substances from the group of tantalum, hafnium, tungsten, rhenium in conjunction with either carbon (carbide) or nitrogen (nitride). This results in a potential amount of at least six times two combinations, that is 12 different second hard materials.

Considered alone, that is without the presence of the first hard material, the cutting tool would be very hard and brittle from the carbides shown. Their hardness would be on the Mohs scale> 5, the hardness of Tantalhafniumcarbids is for example 9 to 10. The distinguishing material properties of carbides and nitrides are thus their high hardness and heat resistance, and their temperature resistance.

The proposed mixtures of first and second hard material result from a first hard material, for example zirconium dioxide, over a dashed line symbolizing the mixture 20 to the selected second hard material, for example tantalum hafnium carbide. The chemical compound of tantalum and hafnium with carbon to tantalum hafnium carbide is according to 1 over the solid line 22 symbolizes. Tantalum carbide is an extremely hard, non-oxide ceramic with one of the highest known melting points at 4215 ° C. In the exemplary embodiment of the mixture of hard materials with tantalum hafnium carbide and zirconium dioxide, the tantalum hafnium carbide thus brings about the extreme hardness, heat resistance and temperature resistance, so that the cutting tool formed therefrom can be used in particular for high cutting speeds and hard materials. About the first hard material, or mixing partner of Tantalhafniumcarbids, the zirconia, the proposed hard material mixture is toughened. The zirconia shows a dispersive behavior in the mixture, which favors this toughness. In particular, the hafnium contained in tantalum hafnium contributes to bridging between the tantalum hafnium carbide and the zirconia. The toughness introduced by the first hard material zirconium dioxide into the hard material mixture makes it possible to use the cutting tool at high feed, and in particular during interrupted cutting, as is the case for milling, for example.

Further particularly preferred embodiments, as in accordance with 1 are molybdenum dioxide in combination with tungsten niobium carbide, niobium dioxide in combination with tantalum tungsten carbide or mixtures which are carried out with tantalum ruthenium carbide, of which the greatest hardness is to be expected. As an alternative to niobium dioxide, compounds with Nb ₂ O ₅ are also possible.

When using a deviating from the second hard material third hard material as described above, this is about the combinations, as described 1 are possible for the second hard material, representable. Similarly, when using a deviating from the first hard material fourth hard material according to the preceding description, this on combinations, as in accordance with 1 are possible for the first hard material, representable.

An embodiment of a running as a cutting plate mixed ceramic cutting tool 1 with a chip breaker for optimized chip removal is in the 2 and 3 shown. The insert is designed in S-shape (square). Their first hard material is tough ZrO ₂ and their second hard material is hard and temperature-stable tantalum hafnium carbide Ta ₄ HfC ₅ . The hard materials are located in the cutting tool 1 in a mass ratio of 40% and 60%. The embodiment has a high hardness and toughness, so that it is suitable for universal machining. The area of application is extended to turning, milling, drilling, finishing, roughing and tapping. Machinable steels, structural steels, case-hardened steels, cast iron and superalloys are possible as workable materials. The scope extends far beyond the classes DIN ISO 513 ,

A diameter 2 the cutting plate is 15 mm in this first embodiment. corners 4 of the insert are rounded with a corner radius R ₀ of 1.6 mm. The rounded corners 4 each pointing in a plane that the viewer of 2 facing, a circumferential cutting edge 6 on. To illustrate the relevant Geometries on the insert 1 follows the description of 3 ,

3 represents the first embodiment according to 2 along the section AA (cf. 2 ). The insert has a tool reference plane 8th which is defined to be perpendicular to an assumed cutting direction 10 (according to DIN 6851 ) of the cutting plate is arranged. Furthermore, a cutting point (not shown) of the cutting edge 6 in the tool reference plane 8th arranged. The cutting plate has a support surface 11 for resting on a tool carrier (not shown). The bearing surface 11 is parallel to the tool reference plane 8th ,

In a normal operation of the cutting plate, the workpiece moves parallel to and against the cutting direction 10 on the cutting plate 1 past. The cutting plate is engaged with the workpiece with a certain engagement depth over which the chip thickness is fixed in engagement.

The cutting plate is designed such that an open space 12 parallel to an assumed working plane of the insert. It follows that a clearance angle α between the assumed working plane and the free surface 12 has the value 0 °. Furthermore, the cutting plate is designed such that a wedge angle β between the free surface 12 and a rake surface 14 has the value 90 °. This is accompanied by the fact that one between the chip surface 14 and the tool reference plane 8th spanned rake angle γ has the value 0 °. The open space 12 is against the rake surface 14 over the cutting edge 6 demarcated. The cutting edge 6 has a radius R ₁ of 0.3 mm. Due to the above-described mixture of hard materials and the right angle wedge angle β is the edge of the cutting edge 6 protected against breakage, in particular during hard machining and / or an interrupted cut.

In the direction of chip removal, according to 2 from left to right along the left rake surface 14 takes place, adjacent to the chip surface 14 a transitional area 16 with a transition radius R ₂ of 0.5 mm. This transitional area 16 is a section of a chip guide 18 extending from the rake face 14 along its chip removal depth B extends. The chip guiding surface 18 is with a chip angle δ of -37 ° against the tool reference plane 8th hired. In this case, the chip breaker angle according to the preceding description, starting from the tool reference plane 8th Are defined.

This division of Spanleitfläche 18 against the rake surface 14 and the tool reference plane 8th results in improved chip formation during the machining of the workpiece. It comes increasingly to favorable cylindrical or spiral filaments. Also shavings are increasingly observed. The formation of ribbon and / or random chips is reduced compared to conventional geometries of cutting inserts, in particular in the form of T-bevel cutting inserts.

Disclosed is a Mischkeramisches cutting tool, in particular an insert or an indexable insert, which has at least two ceramic hard materials. A first of the hard materials has an oxide of zirconium or molybdenum or niobium, and the second of the hard materials has a carbide or a nitride of a compound of at least two of tantalum, tungsten, hafnium or rhenium.

LIST OF REFERENCE NUMBERS

1

Mixed ceramic cutting tool

2

diameter

4

corner

6

cutting edge

8th

Tool reference plane

10

cutting direction

11

bearing surface

12

open space

14

clamping surface

16

Transition surface

18

chip guide

20

L

Clamping surface depth

B

Spanleitflächentiefe

α

clearance angle

β

wedge angle

γ

rake angle

δ; δ '

Spanleitwinkel

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• DIN ISO 513 [0031]
• DIN 6851 [0033]

Claims (10)

Mixture ceramic cutting tool with at least two ceramic hard materials, characterized in that a first of the ceramic hard materials has an oxide of zirconium or molybdenum or niobium, and that a second of the ceramic hard materials, a carbide or a nitride of a compound of at least two of tantalum, tungsten, hafnium , Rhenium. A cutting tool according to claim 1, comprising a third ceramic hard material which has a carbide other than the second hard ceramic or a different nitride of a compound of at least two of tantalum, tungsten, hafnium, rhenium. Cutting tool according to claim 1 or 2 with a fourth ceramic hard material, one of the first. ceramic hard material deviating oxide of zirconium or molybdenum or niobium. A cutting tool according to any one of claims 1 to 3, wherein a mass fraction of the first or first and fourth hard ceramic material is about 20-40% and a mass fraction of the second or second and third hard ceramic is about 80-60% of a mass of the cutting tool ( 1 ) is. Mixture of ceramic granules for sintering a cutting tool ( 1 ), characterized in that it comprises at least a first and a second ceramic hard material according to one of the preceding claims. Mixture according to claim 5, wherein a grain size of a granulate of the hard material, which has a lower melting temperature, about 2 to 10 times greater than a grain size of a granulate of the hard material having the higher melting temperature. Process for the production, in particular sintering, of a mixed-ceramic cutting tool ( 1 ) formed according to any one of claims 1 to 4 and accordingly comprising at least a first and a second hard material, characterized by a step: - "approximation of the melting temperatures of the hard materials". Method according to claim 7, wherein the step "approximation of the melting temperatures" by a step "setting different pressures for the different hard materials" takes place. Method according to claim 7 or 8, wherein before the step "approach of the melting temperatures", a step "compound of granules of hard materials", in particular with a paraffin, takes place. Method according to claim 9, wherein after the step "compound of the granules" a step "hot pressing of the mixture of granules and paraffin" and a step "sintering" take place.

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