SK287369B6 - Tool having a protective layer system - Google Patents

Abstract

There is proposed a tool with a tool body and a wear resistant layer system, which layer system comprises at least one layer of MeX. Me comprises titanium and aluminium and X is a nitrogen or carbon. Thereby, in the MeX layer the quotient QI as defined by the ratio of the diffraction intensity I(200) to I(111) assigned respectively to the (200) and (111) plains in the X ray diffraction of the material using the THETA - THETA 2 method is selected to be. QI has a value QI <= 2. A tool is a solid carbide end mill or a solid carbide ball nose mill or a cemented carbide gear cutting tool. Further, the I(111) is at least twenty times larger than the intensity average noise value, both measured with a well-defined equipment and setting thereof.

Description

The invention relates to a tool having a tool body and a wear-resistant coating system, the coating system comprising at least one MeX layer.

The invention also relates to a method of manufacturing a tool comprising a tool body and a wear resistant coating system comprising at least one layer of hard material.

BACKGROUND OF THE INVENTION

It is generally known in the art for tool protection to employ wear resistant coating systems comprising at least one layer of hard material defined as MeX.

It is an object of the present invention to achieve a significant improvement in the life of such tools.

SUMMARY OF THE INVENTION

This is solved by selecting for at least one layer the value of Q _b to which it applies

Qi <2, wherein the tool is a solid carbide end mill or cylindrical milling cutter or solid carbide ball milling cutter, or a cutting tool for machining sintered carbide gears.

In addition, the value of 1 (111) is a factor of at least 20 greater than the average noise level measured in accordance with the MS.

The term Qj is defined as the ratio of the bending intensity I (200) to the bending intensity 1 (111), converted respectively to the X-ray diffraction planes (200) and (111) in the material using method θ - 20. Thus, Qj = 1 (200) / 1 (111).

The intensity values were measured using the following equipment and with the following adjustment or adjustment:

Diffractometer Siemens D500

Input:

Hole aperture:

Detector diaphragm:

Time constant:

θ angular velocity: Radiation:

Operating voltage: 30 kV Operating current: 25 mA Aperture I position: 1 °

Aperture II position: 0.1 ° Soller slit p

0.05 ° / min.

Cu-Koc (0.15406 nm)

If it is referred to as "measured in accordance with MS", it is referred to this equipment and to this setting or adjustment.

Thus, all quantitative results for Q1 and I in the specification of this application were measured using MS.

The term "tool body" means an uncoated tool.

The term 'hard material' means the material to which tools subjected to high mechanical and thermal loads during operation are coated for wear resistance. Preferred examples of such materials are listed below as MeX materials.

Thus, in accordance with the present invention, a tool has been developed with a tool body and a wear resistant coating system, the coating system comprising at least one MeX layer, wherein

Me contains titanium and aluminum,

X is at least one of nitrogen and carbon, the layer having a value of Qi defined as the ratio of bending intensity I (200) to bending intensity I (111) converted into X-ray bending planes (200) and (111) respectively , using method 0-20, then the intensity values are measured using the following equipment and settings:

Diffractometer Siemens D500

Hole aperture:

Detector diaphragm:

Time constant:

θ angular velocity: Radiation:

where Q] has a value

Operating voltage: 30 kV Operating current: 25 mA Aperture I position: 1 ° Aperture II position: 0.1 ° Soller slit with

0.05 ° / min.

Cu-Ka (0.15406 nm)

And wherein the tool is one of the following group of tools a solid carbide end milling cutter, a solid carbide milling cutter, a sintered carbide cutting tool, wherein the value of I (111) is at least 20 times the average noise intensity value. In a preferred embodiment of the tool according to the invention for Qi:

preferably thereafter Qj <L, Q, <0.5, and particularly preferably Qi á 0,2, and particularly preferably Qi <0, l.

The MeX material is preferably one of titanium and aluminum nitride, titanium, aluminum and carbon nitride, titanium, aluminum and boron nitride, and preferably one of titanium and aluminum nitride and titanium, aluminum and carbon nitride.

Me preferably further comprises at least one other element selected from the group consisting of boron, zirconium, hafnium, yttrium, silicon, tungsten, chromium, preferably at least one of yttrium and silicon and boron.

Preferably, a further element containing i is contained in Me

0,05 at. % <i <60 at. %, the Ti content being taken as 100 at. %.

The tool according to the invention preferably further comprises a further layer of titanium nitride between the at least one layer and the tool body, the further layer having a thickness d for which it applies

0.05 pm <d <5.0 pm.

The layer system is preferably comprised of at least one layer and another layer.

In a preferred embodiment, the stress σ in the at least one layer is

GPa <σ <8 GPa, preferably thereafter

GPa <σ <6 GPa.

The titanium x content in Me is primarily:

at. %> x> 40 at. %, preferably at. %> x> 55 at. %.

The aluminum content y in Me is primarily:

% <y <60 at. %, at.

preferably at. % <y <45 at. %.

In accordance with another aspect of the present invention, a method for manufacturing a tool comprising a tool body and a wear resistant coating system comprising at least one layer of hard material, the method comprising the steps of: reactive PVD applying at least one MeX layer to the body wherein Me contains titanium and aluminum, and x is at least one of nitrogen and carbon, a choice of predetermined process parameter values for PVD deposition, and in addition at least one of two parameters relating to the reactive gas partial pressure in the vacuum chamber and bias tool body relative to a predetermined reference potential, adjusting at least a partial pressure and / or bias to realize a layer having a desired value of Q _{I (} which may have a value greater than or less than a unit) and realize the size of at least one of I (200) and I (111) such that it is at least d n-times greater than the average noise intensity value, and taking advantage of the fact that the value of Qj as a function of partial pressure and bias decreases with decreasing partial pressure and increasing prestressing, wherein Q is defined as the ratio of bending intensity I (200) to the bending intensity I (111), converted to X-ray diffraction planes (200) and (111) respectively in the material, using the 0-2 Θ method, after which the intensity values are measured using the following equipment and setting:

Diffractometer Siemens D500

Input:

Hole aperture:

Detector diaphragm:

Time constant:

3 angular velocity: Radiation:

Operating voltage: 30 kV Operating current: 25 mA Aperture I position: 1 ° Aperture II position: 0.1 ° Soller slit with

0.05 ° / min.

Cu-Ka (0.15406 nm).

Preferably, the method of the invention further comprises the step of performing reactive PVD deposition by reactive cathodic arc evaporation.

Preferably, the method of the invention further comprises the step of magnetic arc evaporation control.

The method of the invention preferably further comprises the step of depositing a MeX layer on the tool body, wherein Me comprises titanium and aluminum, and X is at least one of nitrogen and carbon, which is fed to the PVD deposition via a reactive gas.

The tool is preferably one of the following group: solid carbide end milling cutter, solid carbide milling cutter, sintered carbide cutting tool, then the value Qj is selected such that

Qi <2 by adjusting at least one of the reactive pressure and bias for reactive PVD deposition. In a preferred embodiment, the value is then selected such that it is preferably then or even true

Qi <1,

Qi <0.5,

Qi <0.2.

Preferably, the value of Qj is then chosen to be valid

Q, < 0.1.

In accordance with the present invention, it has been found that the specified Qi values result in a significantly high improvement in wear resistance and hence tool life as long as the tool is of the type indicated.

Until now, the application of wear-resistant coating systems of hard MeX material has been carried out independently of the interaction between the tool body material and the mechanical and thermal loads to which the tool is subjected during operation.

The object of the present invention is thus based on the fact that it has been found that an excellent improvement in wear resistance is achieved when a selectively specific value of Q 1 is combined. with a specific type of instruments, resulting in a value of 1 (111) higher by a factor of at least 20, such as the average sound level, both measured in accordance with the MS.

The improvement achieved by the invention is even increased when the value of Q i is selected to be at most 1, and further improvement can be achieved if the value of Q i is at most 0.5 or even at most 0.2. The greatest improvements are achieved when the value of Q i is at most 0.1.

It should be emphasized that the value of Qi may drop to zero if the sheet material is made with a uniform crystalline orientation in accordance with the zero bending intensity I (200). Therefore, no lower limit is set for the value of Q _b, which is only set from a practical point of view.

As is well known to one skilled in the art, there is a correlation between the hardness of the layer and the stress or strain in the layer. The higher the stress or stress, the higher the hardness.

However, with increasing tension, the adhesion to the tool body tends to decrease. High hardness is more important for the tool according to the invention than the highest possible adhesion. Therefore, the stress in the MeX layer is preferably chosen at the upper end of the following stress range.

In practice, these circumstances limit the usable value of Q _b

In a preferred embodiment of the tool of the present invention, the MeX tool material is titanium and aluminum nitride, titanium, aluminum and carbon nitride, or titanium, aluminum and boron nitride, the first two of which are currently preferred over titanium, aluminum and boron nitride.

In another embodiment of the tool of the invention, the Me metal in the MeX sheet material may further comprise at least one of boron, zirconium, hafnium, yttrium, silicon, tungsten and chromium, of which preference is given to the use of yttrium and / or silicon , and / or boron.

Said additional elements to titanium and aluminum are introduced into the layer material, preferably in the content i, to which it applies

0.05 at.% <I <60 at.%, With Me taken as 100 at.%.

Yet another improvement in all different embodiments of the at least one MeX layer is achieved by inserting an additional titanium nitride layer between the MeX layer and the d-body of the tool to which it applies

0.05 pm <d <5 pm.

In view of the general object of the present invention, which is to propose a new tool that can be manufactured at the lowest possible cost and thus as cost-effective as possible, it has further been suggested that this tool be colored with only one layer of MeX material and an additional layer that is located between the MeX layer and the tool body.

In addition, the stress σ in the MeX material is selected so that its magnitude is within the range

GPa <σ <8 GPa, and more preferably in the range

GPa <σ <6 GPa.

The x content of the titanium in the metal component Me of the MeX layer is preferably selected such that at%> x> 40 at% is true, so that in a further preferred embodiment the range at%> x> 55 at% applies.

On the other hand, the aluminum content y in the metal component Me of the MeX material is preferably selected such that at% < y < 60 at% applies, and in another preferred embodiment at% < y < 45 at%.

In yet another preferred embodiment, both these ranges, i.e. the titanium-related range and the aluminum-related range, are met.

The deposition of the MeX layer in particular can be carried out by any known vacuum deposition technique, in particular by a reactive PVD coating technique, such as reactive cathode arc evaporation or reactive sputtering. By suitably controlling the process parameters that affect the coating increase, advantageous use of the Q 1 range is achieved.

In order to achieve excellent and repeatable adhesion of the layers to the tool body, an argon plasma-based plasma etching technology as described in US-A-5 709 784 is used as a preparatory step and is incorporated herein by reference. , in terms of such etching and subsequent coating. This document is in accordance with U.S. Pat. 08/710 095 by the same inventor (two inventors) and the applicant as the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail below with reference to the accompanying drawings, in which: FIG. 1 is a graph showing the amount of partial pressure of nitrogen as a function of the bias of the tool body; Fig. 2 is a graph of typical intensity versus angle 2Θ for a titanium-aluminum nitride hard material layer;

Fig. 3 shows an analogous graph to that of FIG. 2, however, where titanium and aluminum nitride deposition was controlled by biasing and partial nitrogen pressure to achieve a Qi <1 result;

Fig. 4 is a graph analogous to FIG. 2 and FIG. 3, and which applies to the operating point P of FIG. First

DETAILED DESCRIPTION OF THE INVENTION

Example 1

An arc ion plating apparatus using magnetically controlled arc sources, as described in US-A-5,709,784, was used under the operating conditions shown in Table 1 to apply a MeX layer as also shown in the Table. 1, for solid carbide end mills with a diameter of 10 mm, z = 6. The thickness of the applied MeX layer was always 3 µm. So for samples no. 1 to 5, the Q i values determined according to the invention were used, whereas for comparison no. 6 to 10, this condition is met.

The value of 1 (111) was always significantly greater than twenty times the average noise value measured in accordance with the MS. The coated end mills were used for milling under the following conditions to determine the milling distance achievable up to the average blade width of 0.20 mm. The resulting milling distance corresponding to the life of such tools is also shown in Table 1.

Test cutting conditions:

- Tool: Solid carbide end mill with a diameter of 10 mm, z = 6 - Material to be machined: - Cutting conditions: AISID2 (DIN 1.2379) at _c = 20 m / min. f _t = 0.031 mm and _p = 15 mm and _e = 1 mm consecutive dry milling

From the data contained in Table 1, it can be clearly seen that end mills coated in accordance with the present invention are much more protected against chipping and wear than end mills coated under comparative conditions.

Example 2

The apparatus which was used for coating in accordance with Example 1 was also used for coating samples no. 11 to 20 according to Table 2.

The coated tools and test test conditions were the same as in Example 1. The layer thickness is shown in Table 2.

It can be seen that in addition to the coating in accordance with Example 1, a titanium nitride interlayer was applied between the MeX layer and the tool body, and an outer layer of the respective material as shown in Table 2. I (111) and average noise levels, measured in accordance with MS, were sufficiently met.

It should be noted that the application of an intermediate layer between the MeX layer and the tool body already results in further improvement.

An additional improvement is achieved by applying an outer layer of one of the materials, such as titanium nitride and carbon, titanium oxinitride and aluminum, and in particular an outer layer of aluminum oxide. Again, it can be seen that the application of the determined values of Q! according to the invention in comparison with the comparative samples no. 16 to 20 leads to a significant improvement.

The outer layer of 0.3 µm aluminum oxide was formed by plasma CVD.

As already mentioned, coated end mills were tested under the same cutting conditions as those in Example 1, with a Q value ₍ measured according to MS.

Example 3

Solid carbide end mills were re-coated with the apparatus of Example 1 with a MeX layer as shown in Table 3, which still fulfills the conditions Q _b determined in accordance with the present invention, and conditions 1 (111) regarding the average noise level, measured according to MS. Thus, one of the elements of the group consisting of zirconium, hafnium, yttrium, silicon and chromium has been included in the metal layer Me in the indicated amount.

The coated end mills were placed in an air furnace at 750 ° C for thirty minutes for oxidation. The resulting oxide layer thickness was then measured. These results are also shown in Table 3. For comparison purposes, liners coated in accordance with the present invention with MeX material having different Me compositions were tested in the same manner. Obviously, by adding any of the elements in accordance with samples 23 to 32 to Me, the thickness of the resulting oxide coating is greatly reduced. In terms of oxidation, the best results were achieved by the addition of silicon or yttrium.

It should be emphasized here that it is well known to the person skilled in the art that the material of the wear-resistant MeX layers is: the better the oxidation resistance, which makes the resulting oxidation coating thinner, the better the cutting properties .

Example 4

Again, a coating device and coating method were used, which were also applied to the samples of Example 1.

The 10 mm six-tooth solid carbide end mills were coated with a 3.0 µm MeX layer, with an intermediate layer of titanium nitride TiN having a thickness of 0.08 µm arranged between the MeX layer and the tool body. The end mill test conditions were as follows:

tool:

material:

Cutting parameters:

Solid carbide end mill with 6 mm diameter, z = 6

AISID2 (DIN 1.2379)

60HRC at _c = 20m / min.

f _t = 0.031 mm and _p = 15 mm and _e = 1 mm consecutive dry milling

Solid carbide end mills were used until the average blade back wear width was 0.20 mm. The results are shown in Table 4. Again, the value 1 (111) of the noise conditions, measured in accordance with MS, was quite clearly met for Sample no. 35, wherein for sample no. 34, the noise value of I (200) was satisfied.

Example 5

Again, the apparatus and coating method of Example 1 was used.

Solid carbide ball end mills were coated with a 3.1 µm MeX layer of titanium nitride TiN with a thickness of 0.07 µηι. The coated tools were tested by milling hardened wrought steel.

The test conditions were as follows:

Tool: solid carbide ball end milling cutter

J97 (Jabro) R4 (0 8 x 65mm)

Material: Wrought steel H 11 (DIN 1.2343)

HRC 49.5

Cutting parameters: v _c = 22 0 m / min.

and _p = 0.5 mm without coolant

Tool life was evaluated in minutes.

In FIG. 1 is a graph showing the magnitude of the partial pressure of nitrogen as a function of the bias of the tool body, which is applied to the reactive cathode arc evaporation in the reactive PVD plating method used to carry out the examples.

All process parameters of the cathode arc evaporation process, in particular

- arc current,

- operating temperature,

- plating intensity,

- vaporized material,

- force and arrange the magnetic field near the arc source,

- the geometry and dimensions of the process chamber and the metallized tool were kept constant.

The remaining process parameters, in particular the reactive gas partial pressure (or total pressure) and the tool body bias to be metallized as a workpiece, as well as the predetermined electrical reference potential, such as the chamber wall ground potential, have been changed.

Under these conditions, titanium and aluminum nitride were deposited. With regard to the partial pressure of the reactive gas and to the bias of the tool body, different operating points have been established, and the resulting Qi values for the layers of deposited hard material were measured in accordance with MS.

It should be pointed out here that in the graph of FIG. 1, there is an area P that extends in a first approximation linearly from at least an adjacent origin of the graph coordinates, the resulting layer resulting in very low values of I (200) and I (111) of the XRD intensity.

It is quite clear that a large number of measurements are required to accurately determine the limits of area P. Thus, none of the intensity values I (200) and I (111) are as great as twenty times the average noise level measured in accordance with the MS.

On one side of said region P, as shown in FIG. 1, is greater than 1, while in the second region it is less than 1, in terms of region P.

In both of these areas, at least one of I (200) and I (111) is greater than twenty times the average noise level measured in accordance with the MS.

As shown by the arrows in FIG. 1, and decreasing the reactive gas partial pressure (or total pressure if practically equal to said partial pressure) and / or increasing the bias of the metal-plated tool body leads to a decrease in Qp.

Thus, a method of manufacturing a tool comprising a tool body and a wear resistant coating system according to the present invention, wherein the coating system comprises at least one hard material layer, comprises the steps of reactive PVD storing at least one hard material layer in a vacuum chamber, then preselecting values. process parameters for the PVD storage process step in addition to one or both of the two process parameters, in particular the reactive gas partial pressure and the tool body bias.

It is one of these two parameters, or both, which are then set to achieve the desired Q _I values _; thus, according to the present invention, the bias is reduced and / or the reactive gas partial pressure is increased in order to achieve Q _b values which, as mentioned, have a value of at most 2, preferably at most 1 or even at most 0.5 or even at most 0 '2. Most preferred is value

Qi <0.1.

In addition to the Q _b value used in the present invention, in the "right" region with respect to P, the value of 1 (111) is greater, and usually much greater than twenty times the average noise intensity level measured in accordance with the MS.

In FIG. 2 is a graph of typical intensity versus angle 2 &apos; for a hard material layer of titanium nitride and aluminum deposited in the region Qi &gt; 1 according to the present invention and FIG. 1, resulting in a value of 5.4. The average N * noise level is much less than I (200) / 20. Measurements were made in accordance with MS.

In FIG. 3 is an analogous graph to that of FIG. 2, however, where titanium and aluminum nitride deposition was controlled by biasing and partial nitrogen pressure to achieve a Qi <1 result. has a size of 0.03. The t 1 value (111) is greater than twenty times the average noise intensity level measured in accordance with the MS.

It should be noted that in FIG. 1, the respective values in the respective areas are indicated at each working point, measured in accordance with the MS.

In FIG. 4 is a graph analogous to FIG. 2 and FIG. 3, and which applies to the operating point Pi of FIG. It can be seen that the intensities I (200) and I (111) are significantly reduced compared to the intensities in the outside area P. None of the I (200) and I (111) values are twenty times the average N * noise level.

Thus simply adjusting at least one of the two parameter Q _p controlling reactive PVD process, in particular partial pressure of a reactive gas and biasing the workpiece is controlled by the used value of Qj of the invention.

In FIG. 1 is generically shown for the setting direction for decreasing Q _b for 5QI < 0 while it is evident that increasing the Q _b in the opposite direction of setting the two parameters for controlling the process

Claims (17)

A tool having a tool body and a wear-resistant coating system, the coating system comprising at least one MeX layer, characterized in that: Me contains titanium and aluminum, X is at least one of nitrogen and carbon elements, the layer having a value of Q _b defined as the ratio of the bending intensity I (200) to the bending intensity 1 (111), converted to X-ray diffraction planes (200) and (111) respectively of material, using method θ - 20, the intensity values are then measured using the following equipment and setting: Diffractometer Siemens D500 Input: Operating current; Detector diaphragm: Time constant: 2 θ angular velocity: radiation: Operating voltage: 30 kV 25 mA Aperture diaphragm: Aperture I position: 1 ° Aperture II position: 0.1 ° Sollerova slit 4 p 0.05 ° / min. Cu-Koc (0.15406 nm) wherein Q 1 has a value And wherein the tool is one of the following group of tools a solid carbide end milling cutter, a solid carbide milling cutter, a sintered carbide cutting tool, wherein the value of I (111) is at least 20 times the average noise intensity value. Tool according to claim 1, characterized in that for Q ₍ holds: Q 1 < 1, preferably thereafter Q 1 < 0.5 and particularly preferably Q 1 < 0.2, and particularly preferably Q, < 0.1. Tool according to either of Claims 1 and 2, characterized in that the MeX material is one of the group consisting of titanium and aluminum nitride, titanium, aluminum and carbon nitride, titanium, aluminum and boron nitride, and preferably one of the group consisting of: containing titanium and aluminum nitride and titanium, aluminum and carbon nitride. Tool according to one of claims 1 to 3, characterized in that Me further comprises at least one further element selected from the group consisting of boron, zirconium, hafnium, yttrium, silicon, tungsten, chromium, preferably at least one of the group consisting of: containing yttrium and silicon and boron, Tool according to claim 4, characterized in that a further element containing i is contained in the Me 0,05 at. % <i <60 at. %, the Ti content being taken as 100 at. %. Tool according to one of Claims 1 to 5, characterized in that it further comprises a further layer of titanium nitride between the at least one layer and the tool body, the further layer having a thickness d to which it applies 0.05 µm <d <5.0 µm. Tool according to claim 6, characterized in that the layer system comprises at least one layer and another layer. Tool according to one of Claims 1 to 7, characterized in that the stress σ in the at least one layer is 2 GPa <σ <8 GPa, preferably thereafter 4 GPa <σ <6 GPa. Tool according to one of claims 1 to 8, characterized in that the x content of titanium in Me is: 70 at. %> x> 40 at. %, preferably thereafter 65 at. %> x> 55 at. %. Tool according to one of claims 1 to 9, characterized in that the aluminum content y in said Me is: 30 at. I <y <60 at. %, preferably thereafter 35 at. % <y <45 at. %. A method of manufacturing a tool comprising a tool body and a wear resistant coating system comprising at least one hard material layer, comprising the steps of: reactive PVD deposition of at least one MeX layer on the body, wherein Me contains titanium and aluminum, and x is at least one of nitrogen and carbon, the choice of predetermined process parameter values for PVD deposition, and in addition at least one of two parameters related to PVD deposition the reactive gas partial pressure in the vacuum chamber and the tool body bias with respect to a predetermined reference potential, adjusting at least the partial pressure and / or bias to realize a layer with a desired Q _b value which may be greater than or less than the unit; from the values of I (200) and I (111) to be at least twenty times greater than the average value of noise intensity, and taking advantage of the fact that the value of Q [as a function of partial pressure and preload decreases with decreasing partial pressure and increasing with bias, wherein the value of Q i is defined as the bending ratio i the stresses I (200) to the bending intensity I (111), converted into X-ray diffraction planes (200) and (111) respectively in the material, using the method 20 - 20, then the intensity values are measured using the following equipment and adjustment: Diffractometer Siemens D500 Hole aperture: Detector diaphragm: Time constant: 2 θ angular velocity: Radiation: Operating voltage: 30 kV Operating current: 25 mA Aperture I position: 1 ° Aperture II position: 0,1 ° Soller slit 4 p 0.05 ° / min. Cu-Ka (0.15406 nm). The method of claim 11, further comprising the step of performing reactive PVD deposition by reactive cathodic arc evaporation. The method of claim 12, comprising the step of magnetic arc evaporation control. The method according to any one of claims 11 to 13, further comprising the step of depositing a MeX layer on the tool body, wherein Me comprises titanium and aluminum, and X is at least one of nitrogen and carbon elements that is fed to the PVD deposition via a reactive gas. Method according to one of Claims 11 to 14, characterized in that the tool is one of the following group: solid carbide end milling cutter, solid carbide end milling cutter, cutting tool for sintered carbide gears, then a value of Q is selected ; so that they pay Qi <2 by adjusting at least one of the reactive pressure and bias for reactive PVD deposition. Method according to claim 15, characterized in that the value of Q 1 is then selected such that Q 1 <1, preferably then or even Qi <0.5 Qi <0.2. Method according to claim 16, characterized in that the value of Qi is then chosen to be valid