WO2007048154A1 - Hard metal for cutting plates of crankshaft millers - Google Patents

Abstract

The invention relates to a hard metal comprising several hard material phases and a binder phase, a cutting element made of such a hard metal, and a crankshaft miller encompassing such a cutting element. In order to reduce the formation of undesired comb-type fractures in cutting plates, a hard metal is used for producing said cutting plates, more than 70 percent by weight of said hard metal being composed a hard material phase made of tungsten carbide having a mean grain size of less than 1.5?m while the hard metal contains at least 2.5 percent by weight of another hard material phase made of a tantalum carbide or a tantalum niobium carbide, a titanium carbide fraction amounting to less than 5.0 percent by weight.

Description

Carbide for cutting inserts of crankshaft cutters

The invention relates to a hard metal having a plurality of hard material phases and a binder phase.

Next, the invention has a cutting element of such a hard metal to the object.

Finally, the invention relates to a crankshaft milling cutter with an insert, which consists of a hard metal with a plurality of hard material phases and a binder phase.

Carbides are composites that consist of metallic hard materials and a binder phase. As metallic hard materials are intermetallic phases such as hexagonal crystallizing carbides, for example Mo ₂ C, Nb ₂ C, TaC, WC and W ₂ C, cubic crystallizing carbides such as NbC, TiC, VC or ZrC, and nitrides such as TiN, borides, eg LaB ₆ or TiB ₂ and silicides, for example WSi ₂ used. The binder phase is primarily cobalt, iron and nickel and their alloys use, which are connected to the hard materials together by sintering at high temperatures, for example at 1450 ⁰ C, connected.

Hard metals are characterized by a very large proportion of hard materials in the composite by very high hardness, which makes them particularly attractive for the production of highly wear-resistant tools for metal, plastic or wood processing. In particular, in machining technology, where tools can be exposed to high temperature peaks in use and at the same time withstand a variety of Verscheißarten as long as possible, an economic work without the use of carbide tools or parts made of carbide is not feasible in many areas.

According to the prior art, hard metals are also used for the production of coated inserts for crankshaft milling cutters, for example those known from AT 406 028 B. These inserts are particularly resistant to wear due to their construction of a highly durable material. Of course, they are still subject, as usual with cutting tools, different types of wear and ultimately have a finite life. In general, with a longer service life or duration of use of inserts especially scoring wear, flank wear and / or comb cracks can be observed in the region of the cutting edge as signs of wear. In this case, the occurrence of a wear phenomenon beyond a critical value may already be sufficient to make a cutting insert unusable for further use.

In the case of cutting inserts of crankshaft cutters, comb cracks often limit a maximum service life, which is particularly troublesome. Namely, while a flank wear and a Kolkverschleiß usually start at a cutting edge and continue to progress in the course of their use until the insert is simply no longer used and replaced in case of excessive wear, a formation of comb cracks occurs spontaneously and a cutting edge in more Episode suddenly break out. As a result, not only is the insert useless, but it also suffers damage to the machined workpiece. It is therefore desirable to increase resistance to comb cracking on cutting inserts of crankshaft cutters such that well controllable flank wear becomes the dominant mode of wear.

As a result, the invention has the object to provide a hard metal, with which cutting plates with less tendency to form cracks can be prepared.

A further object of the invention is to provide a cutting element, in particular a cutting insert for crankshaft milling cutters, which in use has a low tendency to form comb cracks.

Finally, it is an object of the invention to provide a crankshaft cutter of the type mentioned, with a harmless machining of workpieces is possible even with progressive wear of inserts.

The object according to the invention is achieved by a hard metal having the features according to claim 1.

With the invention, a hard metal is provided, from which or with which highly wear-resistant cutting plates can be produced, their tendency to form Comb cracks when used appropriately is particularly low. For this purpose, an application of several measures is required at the same time. Firstly, it is necessary to keep a content of tungsten carbide (WC) more than 70% by weight, with an average grain size not larger than 2.5 μm. On the other hand, tantalum carbide or tantalum niobium carbide must be provided to a minimum extent of 2.5% by weight in order to achieve a high resistance to comb cracks. In combination with these measures, a content of titanium carbide is also to be kept below 5.0 percent by weight, if back cracks are to be kept for cutting inserts.

The material-chemical relationships of interactions of the individual components in a hard metal according to the invention are not yet understood exactly. It was found, however, that the individual components work together in combination. For example, higher titanium carbide contents than 5.0 percent by weight lead to comb breaks in the case of cutting inserts, even if the other conditions according to the invention are fulfilled and even if titanium carbide in hard metals is fundamentally attributed positive effects. Likewise, an average WC grain size of, for example, 2.5 μm or more does not lead to the goal achieved according to the invention.

Tantalum carbide and tantalum niobium carbide may be used in commercially available form in terms of average grain size, with a tantalum niobium carbide having an atomic ratio of Tantak Niob in tantalum niobium carbide being preferably 1.0 or greater.

The already excellent properties of a hard metal according to the invention can be further increased if the binder phase consists essentially of cobalt and a relative magnetic saturation polarization 4IIσ is less than 88 percent, preferably less than 85 percent:

As is known to those skilled in a saturation polarization of cobalt in

WC / cobalt-based cemented carbides of a carbon content or an addition of carbon during the production or mixing of a powder for the hard metal. Typically, carbon black is added to a powder to be sintered to compensate for loss of carbon during sintering due to reaction of carbide carbon with oxygen of the oxide skin of WC particles to volatile carbon dioxide or carbon monoxide. A lot of added Carbon or soot is adjusted to maintain an atomic ratio of tungsten to carbon at 1: 1; at these values there is also a maximum saturation polarization 4IIσm _a x of the cobalt. If too much carbon is added, unwanted graphite precipitates during sintering. If too little carbon is added, then tungsten is in excess of stoichiometric amounts with respect to carbon and dissolves in the cobalt, and if a certain tungsten excess is reached, precipitation of likewise undesired η phase occurs. As the content of dissolved tungsten increases, a saturation polarization of the cobalt decreases from 1.0 to 0.75 relative to the maximum saturation polarization, whereupon η-phase is finally precipitated.

As mentioned, within the scope of the invention, an additional increase in comb crack resistance can be achieved if a relative magnetic saturation polarization is less than 88 percent, preferably less than 85 percent, realized by a correspondingly limited addition of carbon to the sinter powder. This measure is based on the not yet scientifically confirmed assumption that, in particular for cutting inserts of crankshaft cutters, which contact the workpiece relatively briefly in use and heat up to high temperatures and then cool again for a relatively long time, comb cracks due to different thermal expansion coefficient of hard material and binder phase arise and that this difference in the expansion coefficient can be reduced when tungsten is dissolved in the binding metal cobalt.

In connection with this, it is advantageous if an undesirable η-phase should be avoided so that a relative magnetic saturation polarization 4IIσ is more than 75 percent.

In order to bring full advantage of positive properties of a hard metal according to the invention, it may be provided that this contains 75 to 90 weight percent tungsten carbide. It is also preferable that an average grain size of the tungsten carbide is less than 1.5 μm, preferably less than 1.2 μm, in particular 0.4 μm to 1.0 μm. In this particle size range, a good cohesion between binder metal and WC particles is given. In addition, a content of tantalum carbide or tantalum niobium carbide in the hard metal is preferably limited to 15% by weight at the top, since at higher contents, a slight wetting by the binder metal may be present.

Although tantalum carbide or tantalum niobium carbide generally has a favorable effect with respect to comb cracking already from 2.5% by weight, it has been found that there is an optimum between 3.0% and 7.0% by weight tantalum carbide or tantalum niobium carbide in this respect.

Since it was further recognized that titanium carbide in a hard metal according to the invention can not develop the basically attributed positive effects, but rather noticeably adverse effect, it is advantageous if the carbide contains less than 1.0 weight percent titanium carbide, preferably substantially free of titanium carbide ,

A proportion of binder phase is not critical per se and may conveniently be 8 to 14 weight percent.

The further object of the invention to provide a cutting element, in particular a cutting insert for crankshaft milling cutters, which in use has a low tendency to form comb cracks, is achieved by a cutting element according to claim 11.

Advantages of a cutting element according to the invention are in particular the fact that in this case a formation of comb cracks is at least greatly reduced in use, so that wear of the cutting element is determined primarily by free surface and / or Kolkverschleiß. These types of wear develop continuously in use, progress steadily and are therefore easy to control. Spontaneous and surprising cutting edge breakouts as a result of comb cracking are obstructed or at least reduced, so that an associated risk of damage to the machined workpiece is also reduced.

The abovementioned advantages are particularly evident in the case of cutting plates for crankshaft milling cutters, which are arranged substantially along a circumferential circular path, for example on a disk, and are set in rotation about an axis of the crankshaft milling cutter during milling. When cutting come the Cutting plates only for a short time in contact with a workpiece, are thereby heated strongly and then cool down again quickly before a next cutting engagement takes place on the workpiece. As a result of these temperature changes is a tendency to crack formation and thus a cutting edge breakout and damage to the machined workpiece particularly large. Now, with a cutting plate according to the invention a high resistance of cutting plates against Kammrissbildung is given, so that there is no great risk of damage to the workpiece with Kurbelwellenfräsem even with long-term use of inserts.

Accordingly, the object to provide a crankshaft cutter of the type mentioned, with a harmless machining of workpieces is possible even with progressive wear of inserts, achieved by a Kurbelwellenfräser according to claim 12.

Further advantages and positive effects of the invention will become apparent from the context of the description and the embodiments.

In the following, the invention is explained in more detail on the basis of test data and exemplary embodiments.

It shows

FIG. 1: Resistance to comb crack formation of inserts with cyclic heating / cooling over 15,000 cycles.

In a first test, cutting plates with compositions according to Table 1 were heated or allowed to cool with a laser in a constant area of their surface in repeating cycles. In each cycle, heating was performed by laser light for 10 milliseconds; Thereafter, the so heated panel was allowed to cool for 990 milliseconds before the next heating took place. Temperature measurements showed that heating up in the area of the laser spot reached temperatures of around 800 ^° C. Cyclic heating / cooling as well as the maximum temperatures achieved thereby simulate conditions that exist when using inserts in the crankshaft milling for carbide. For each insert, the heating / cooling cycle was repeated 15,000 times. Table 1: Carbide compositions (% by weight, unless otherwise stated).

* Tantalum niobium carbide with a tantalum / niobium weight ratio of 90 to 10 ** Average grain sizes were determined on linear-cut sections by measuring grain sizes along three lines and forming three arithmetic mean values; From the three mean values thus obtained, an arithmetic mean was again formed, which corresponds to the specified average grain size

FIG. 1 graphically summarizes the results of the testing, wherein a material failure corresponds to an occurrence or presence of comb cracks at the temperature-treated locations of the cutting inserts. As can be seen, with inserts of known hard metals 1 to 7 at the latest 5000 cycles

Comb cracks observable, which in use can lead to a cutting edge breakout and damage to the surface of a machined crankshaft. In comparison, cutting inserts made of a hard metal according to the invention can be loaded at least up to 10,000 times without having any comb cracks. Particularly excellent results are also obtained, as can be seen, for carbide inserts A and B which have a relative saturation polarization 4Ilσ of 0.85 and 0.84, respectively (carbide C inserts had a relative saturation polarization of 0.83). In a second series of tests, cutting inserts based on carbide 1, 2 and 3, as well as A, B and C, were produced by sintering and these inserts were used after coating in a conventional crankshaft milling cutter. Analogous to the results shown in FIG. 1, it has been found that cutting inserts made of hard metals 1, 2 and 3 often form comb cracks, which can also lead to cutting edge breakouts. In the case of inserts according to the invention made from the hard metals A and B, on the other hand, crack cracking did not occur at all or was so far reduced in their intensity (hard metal C) that a service life was determined by flank wear and / or crater wear.

It is understood by those skilled in the art that a carbide or cutting inserts made of such a hard metal depending on the application can be coated with one or more layers, for example of alumina, Al ₂ O ₃ , a titanium nitride, carbide or carbonitride, or Aluminiumtitannitrid ,

Claims

claims 1. carbide with a plurality of hard phases and a binder phase, wherein the hard metal consists of more than 70 weight percent of a hard material phase of tungsten carbide having an average grain size of less than 2.5 microns and at least 2.5 weight percent of another hard material phase of a tantalum carbide or a tantalum carbide and a proportion titanium carbide is less than 5.0% by weight. A cemented carbide according to claim 1, wherein the binder phase consists essentially of cobalt and a relative magnetic saturation polarization 4IIσ is less than 88 percent, preferably less than 85 percent. A cemented carbide according to claim 2, wherein a relative magnetic saturation polarization 4IIσ is more than 75 percent. 4. A cemented carbide according to any one of claims 1 to 3, which contains 75 to 90 weight percent tungsten carbide. 5. The cemented carbide according to claim 1, wherein an average grain size of the tungsten carbide is less than 1.5 μm, preferably less than 1.2 μm, in particular 0.4 μm to 1.0 μm. 6. A cemented carbide according to any one of claims 1 to 5, wherein a maximum of 15 weight percent tantalum carbide or Tantalniobarbid present. 7. A cemented carbide according to any one of claims 1 to 6, which contains 3.0 to 7.0 weight percent tantalum carbide or tantalum niobium carbide. 8. Hard metal according to one of claims 1 to 7, which is less than 1.0 Contains percent by weight of titanium carbide, preferably substantially free of titanium carbide present. 9. The cemented carbide according to any one of claims 1 to 8, wherein a content of binder phase is 8 to 14 weight percent. 10. Use of a cemented carbide according to one of claims 1 to 9 in a cutting element, in particular an insert for crankshaft milling cutters. 11. Cutting element, in particular cutting plate for crankshaft milling cutter, consisting of a hard metal according to one of claims 1 to 9. 12. crankshaft cutter with an insert consisting of a cemented carbide according to one of claims 1 to 9.