Title of Invention

COATING FOR A CUTTING TOOL AND MANUFACTURING METHOD

Abstract The invention relates to a coating (8) for a cutting tool, comprising a wear- protection layer (9) having a metallic -crystalline structure, a top layer (12), and a separating layer (11) applied at least one portion of the wear-protection layer (9) and arranged between the wear -protection layer (9) and the top layer (12), wherein the separating layer (11) has a structure which is not metallic- crystalline and limits the adhesion of the top layer (12) to the wear-protection layer (9), and wherein the separating layer (11) contains or is a chemical compound with a preponderantly covalent bond, or is strongly non- stoichiometrically composed, or is a strongly stressed layer.
Full Text Coating for a Cutting Tool and Manufacturing Method
The invention relates to a coating adapted
particularly for a cutting tool, a cutting tool provided
with such a coating, as well as a manufacturing method
for making the coating.
Cutting tools are regularly provided with coatings
for increasing their chip-removing efficiency, for
extending their service life or for other reasons for
obtaining the desired properties. For example, DE 100 48
899 A1 discloses a cutting tool as a cutting insert which
has a wear-reducing coating which is constituted, for
example, by an Al2O3 layer. The wear-reducing coating
extends over the rake surfaces as well as over the
clearance surfaces of the cutting tool. On the clearance
surfaces an indicator coating is provided, for example,
as a top layer, whose color significantly differs from
the color of the wear-protection layer. The abrasion of
the decorative layer occurring at the clearance surfaces
is thus a reliable indication of a performed use of the
respective adjoining cutting edge. The layers are
produced in a full-surface manner in a CVD process, while
the decorating layer is abraded from the rake surfaces.
This may be effected by a brushing process or the like.
In the mechanical removal of the decorating layer from

the rake surfaces care has to be taken to achieve a good
selectivity. Damages to the wear-protection layer are not
acceptable.
As a rule, cutting inserts made by a PVD process
have a metallic layer of hard material, such as a TiAlN
layer. Such a cutting insert is known, for example, from
DE 199 24 422 C2. Top layers, such as TiB2 layers or the
like applied to the wear-protection layer have, as the
latter, a metallic-crystalline structure. The adhesion
between such top layers and the wear-protection layer is
substantial. The tribological properties of the top
layers have to be therefore taken into consideration if
used as decorative layers. Also, they are not adapted as
wear indicators.
Because of the firm adhesion of the layers to one
another, the top layer has to possess properties
coordinated with the exposure to wear, with its
frictional properties and other properties having an
effect during metal chip forming.
It is therefore the object of the invention to
provide a coating which may be made with a PVD process
and which has a top layer adapted to serve as a wear
indicator.
The coating according to the invention comprises, as
a wear-protection layer, a metallic hard material layer
which is covered at the outside by a top layer. The
latter has a reduced adhesion to the wear-protection
layer or has, by means of a separating layer, a limited
adhesion to the wear-protection layer. The top layer
covers only one part of the surface of the metallic hard

material layer, that is, parts of the latter are exposed.
Between the top layer and the metallic hard material
layer a separating layer is disposed which disrupts or
weakens the metallic-crystalline bond between the top
layer and the wear-protection layer. The separating layer
is thus a layer which interferes with or reduces the
adhesion and disrupts or at least disturbs the metallic-
crystalline structure of the other layers.
The separating layer reduces to a small value the
adhesion of the top layer on the metallic hard material
layer serving as a wear-protection layer. The adhesion is
preferably weak to such an extent that itself or a
superposed layer is abraded as soon as the cutting tool
is used in its intended operation and performs a chip-
forming process. Dependent on the mode of application,
the abrasion may occur over the full surface or may be
localized. In this manner the top layer may be relatively
easily abraded. This permits to design the top layer
purely from an aesthetic point of view as a decorative
layer, and the tribological properties as well as the
wear properties play no role: the top layer will be
abraded as soon as the cutting tool is put into
operation. In this manner the possibility is also
provided to use the top layer as the wear indicating
layer. This applies particularly if the metallic hard
material layer serving as the wear-protection layer and
the top layer significantly differ in color.
Thus, the coating of the cutting tool comprises a
wear-protection layer having a metallic-crystalline
structure, a top layer having a limited adhesion to the
wear-protection layer and/or a separating layer applied
at least to a portion of the wear-protection layer and

disposed between the wear-protection layer and the top
layer for limiting the adhesion of the top layer to the
wear-protection layer. By a layer having a metallic-
crystalline structure there is meant in this context a
layer which has a preponderantly metallic bond. Such is
the case, for example, in TiAlCN layers, AlCrN layers,
TiC layers or the like.
The wear-protection layer is a layer preferably made
in a PVD process; the separating layer and the top layer
too, are produced in the PVD process, making possible the
manufacture of the coating in a single PVD coating step.
The top layer, preferably including the separating layer,
is abraded in a mechanical post-processing step. The
post-processing operation may be performed by brushing,
sandblasting or the like. By virtue of the separating
layer, the abrading periods may last less than a few
seconds. For example, by sandblasting with aluminum oxide
(high-grade corundum) at a pressure of only one bar and
during a blasting period of only two seconds, such a
complete abrading of a TiN top layer of, for example, 0.2
µm is obtained that even at a ten-fold magnification of
the upper surface, no residues of the top layer can be
optically recognized. The wear-protection layer (metallic
hard material layer) is barely affected during such a
short-period strain.
The adhesion of the top layer is nevertheless
sufficient to ensure a safe handling of the cutting tools
without damaging the top layer. A first use of the
cutting tool, however, is immediately recognizable by a
partial abrasion of the top layer. In such a case the top
layer serves as a starting use indicator which responds
to the first use of the cutting tool.

For a top layer, for example, titanium nitride
layers, as well as oxidic (heteropolar) layers, such as
TiO2 are suitable. Likewise, other oxides, carbides or
nitrides of metals of the fourth or fifth side group are
suitable. Top layers having a metallic-crystalline
structure are preferred. In contrast, the separating
layer has, for example, no metallic-crystalline
structure. This may be achieved by using, as the
separating layer, an oxide layer of a side group metal,
preferably of the fourth or fifth side group. Thin layers
of, for example, about 0.1 urn TiO2 layers or other CN
layers which are extremely soft and have low frictional
properties yield good results. Good results are also
obtained with MoS2 layers or extremely non-
stoichiometrical layers. For example, extremely stressed
layers may also limit the adhesion between the top layer
and the wear-protection layer. Stressed TiN layers or
also DLC (diamond-like carbon) layers may be used. The
selection of a suitable separating layer for the
application at hand is dictated by the feasibility of
integrating it, possibly without any additional
expenditure, in the PVD process for making the entire
coating. The separating layer constitutes, to a certain
measure, a "desired location of fracture" for any layer
superposed thereon.
In the simplest case the wear-protection layer
(metallic hard material layer) may have a single-layer
structure. If required, a multi-layer structure may also
be utilized.
The described coating may be manufactured in a PVD
process without substantial expenditure, and the

deposited top layer may be subsequently mechanically
easily removed. In this manner the manufacture of multi-
color cutting tools is feasible simply and rationally. By
cutting tools there are meant in this context complete
cutting tools, such as full hard metal drills, milling
tools and the like, as well as merely cutting inserts,
reversible cutting inserts, cutting bits and the like.
Further advantageous details of additional features
of the invention are contained in the drawing, the
description or the claims. In the drawing, which
illustrates an embodiment of the invention,
Figure 1 is a schematic perspective view of a cutting
tool according to the invention,
Figure 2 is a fragmentary section taken across the
cutting tool according to Figure 1,
Figure 3 is a schematic, cross-sectional, not-on-scale
showing of a cutting tool after a continuous
PVD coating process,
Figure 4 is a schematic cross-sectional view of the
cutting tool according to Figure 3, following a
partial abrading of a top layer and the
underlying separating layer and
Figure 5 is a diagram illustrating an exemplary stress
curve relating to the stresses prevailing in
the various layers.

Figure 1 illustrates a cutting insert 1 as a cutting
tool or at least a substantial portion thereof. The
cutting insert 1 has a top surface which constitutes a
rake surface 2, as well as side surfaces which constitute
clearance surface 3, 4. This designation applies to a
radial installation of the cutting insert 1. In case of a
tangential or a lateral installation, the side surfaces
serve as the rake surfaces, while the top surface serves
as the clearance surface. Between the rake surface 2 and
the clearance surfaces 3, 4 cutting edges 5, 6 are
formed.
The cutting insert 1 is a hard metal cutting insert.
Figure 2 shows a greatly magnified fragmentary cross
section of the cutting insert. As seen, the cutting
insert 1 has a basic body 7, whose upper surface forms a
substrate for a coating 8 provided on the cutting insert
1. The coating 8 is applied in a PVD process. As an inner
layer which directly adjoins the substrate, a wear-
protection layer 9 is provided which is a metallic hard
material layer MH, such as a TiAlN (titanium aluminum
nitride) layer having metallic properties. It adheres
firmly to the basic body 7 which is a hard metal, such as
cobalt-containing tungsten carbide. The thickness of the
TiAlN layer may be set in accordance with the intended
application. In the present embodiment its thickness is
about 4 um. The ratio between titanium and aluminum is
33:67.
To the wear-protection layer 9 a separating layer 11
is applied which interrupts the metallic adhesion bond to
a superposed top layer 12. The top layer 12 too, is
preferably a metallic-crystalline layer, such as a TiN
layer, whose thickness is, for example, 0.2 µm. In such a

case the top layer 12 is a purely decorative layer of
golden color. Such a color is significantly different
from the color of the differently colored wear-protection
layer 9.
The separating layer 11 is, for example, a titanium
dioxide (TiO2) layer which may be selected to be
relatively thin: a thickness of, for example, 0.1 urn
suffices. This oxide layer has no metallic properties and
thus limits the adhesion of the top layer 12 to the wear-
protection layer 9. The described coating 8 may be made
with one continuous process in one and the same reaction
vessel of a PVD coating unit by sequentially depositing
the wear-protection layer 9, the separating layer 11 and
the top layer 12.
As described above, the separating layer 11 and the
top layer 12 may be chemically and/or structurally
different layers. It is, however, also feasible to
combine them into a separating-and-top layer, whose
particular property resides in the limited adhesion to
the wear-protection layer 9. In such a case the
separating layer 11 simultaneously constitutes the top
layer.
The manufacture is as follows:
The basic body 7 is introduced into a suitable PVD
coating unit in which first the wear-protection layer 9,
then the separating layer 11 and thereafter the top layer
12 are precipitated on the basic body 7. The coating 8
obtained in this manner is first produced on all the
exposed surfaces of the basic body 7, that is, at least
on the rake surface 2 and on the clearance surfaces 3, 4.

The cutting insert 1 is removed from the PVD reactor
vessel in this condition.
Frequently two-color cutting inserts are desired
which have on their rake surface 2 a color that is
different from that on the clearance surfaces 3, 4. For
making such a cutting insert, the top layer 12 is removed
from the other surface to be differently colored, in this
instance, from the rake surface 2. This may be done by a
sandblasting jet 14, as indicated in Figure 3. As
sandblasting particles aluminum oxide (320 mesh size
high-grade corundum) may be used. During a short period
of application of, for example, 2 seconds, the top layer
12 as well as the separating layer 11 are removed from
the rake surface 2 without visible residues, as shown in
Figure 4. The earlier-noted TiO2 layer having a thickness
of 0.1 urn, however, has such an adhesion and strength
that the top layer 12 remains undamaged at locations
which are not directly affected by the jet 14.
In further embodiments the cutting insert 1 may have
other wear-protection layers 9 and other top layers 12.
In each instance, however, the wear-protection layer 9 is
a metallic hard material layer produced in the PVD
process. Layers of a hard material without a metal
structure, such as Al2O3, are not included in the metallic
hard material layer of the wear-protection layer 9. As a
top layer, the earlier-noted TiN layer, as well as any
other metallic top layer, such as TiC layers, CrN layers,
HfN layers and the like may find application. As a
separating layer 11 any, preferably non-metallic layer
may be used which limits the adhesion between the top
layer 12 and the wear-protection layer 9. Apart from the
TiO2 layer identified in the previous embodiment, other

oxidic layers may be used which may be precipitated in
the PVD process and which have no metallic bond.
Particularly oxides of metals of the fourth and fifth
side groups may be utilized. Other, preponderantly
covalent bonded layers, such as MCN layers may find
application, where M designates an arbitrary metal,
preferably a metal of the fourth or fifth side group.
Other covalent bonded layers, such as MoS2 layers
(molybdenum sulfide) or carbon layers (DLC) may be used.
It is, however, also contemplated to provide metallically
bonded separating layers, such as TiN layers. For
achieving a limitation of adhesion in the latter, they
may be stressed to an extreme degree. A stressing may be
achieved, for example, by a substantial deviation of the
stoichiometrical relationship. In this connection,Figure
5 illustrates the course of stress in the wear-protection
layer 9, the separating layer 11 and the top layer 12 for
the exemplary case, where a limitation of adhesion is
obtained by an oppositely oriented stressing of the
separating layer 11 with respect to the wear-protection
layer 9 and the top layer 12. The stress prevailing in
the coating is shown as a curve 15. Thus, the stresses in
the wear-protection layer 9, the separating layer 11 and
the top layer 12 are, for example, as follows:
wear-protection layer 9 - up to 2 GPa (Giga pascal =
109 Pascal)pressure stress corresponding to -2 GPa
(Giga pascal = 109 Pascal),
separating layer 11 - approximately 0.8 GPa (Giga
pascal = 109 Pascal) tensile stress corresponding to
0.8 GPa (Giga pascal = 109 Pascal),
top layer 12 - approximately 1 GPa (Giga pascal = 109
Pascal) pressure stress corresponding to -1 GPa
(Giga pascal = 109 Pascal).

A coating, particularly for cutting tools, is
presented which may be manufactured in a single PVD
coating process allowing the making of two-color cutting
tools in a simple manner. Between two metallic hard
material layers of unlike color a separating layer 11 is
provided which, like the other layers, is produced in the
same PVD coating process. The separating layer 11 permits
the abrasion of the top layer by sandblasting, brushing
or the like in very short abrading periods.

We Claim:
1. A coating (8) for a cutting tool, comprising
- a wear-protection layer (9) having a metallic -crystalline structure,
- a top layer (12), and
- a separating layer (11) applied at least one portion of the wear-
protection layer (9) and arranged between the wear -protection
layer (9) and the top layer (12),
wherein the separating layer (11) has a structure which is not metallic-
crystalline and limits the adhesion of the top layer (12) to the wear-
protection layer (9), and
wherein the separating layer (11) contains or is a chemical compound
with a preponderantly covalent bond, or is strongly non-
stoichiometrically composed, or is a strongly stressed layer.
2. The coating as claimed in claim 1, wherein that the top layer (12) has
a color which differs from a color of the wear-protection layer (9).
3. The coating as claimed in claim 1, wherein the top layer (12) is a ZrC,
CrC, ZrN, CrN, TiN, a TiC, a HfC or a HfM layer.
4. The coating as claimed in claim 1, wherein the top layer (12) has a
metallic-crystalline structure.
5. The coating as claimed in claim 1, wherein the separating layer (11) is
an oxide layer containing at least one metal from the IVth or Vth group
of the chemical periodic system of elements.

6. The coating as claimed in claim 1, wherein the metal (M) is an element
of the IVth group,
7. The coating as claimed in claim 5, characterized in that the metal (M)
is an element of the Vth group.
8. The coating as claimed in claim 1, wherein the separating layer (11)
has an inner stress which significantly differs from an inner stress of
the wear -protection layer and the top layer (12).
9. The coating as claimed in claim 1, wherein the separating layer (11) is
a DLC layer.
10. The coating as claimed in claim 1, wherein the separating layer (11) is
an MoS2 layer.
11. The coating as claimed in claim 1, wherein the wear-protection layer
(9) is a TiA1N layer or a CrA1N layer.
12. The coating as claimed in claim 1, wherein the wear-protection layer
(9) has a single-layer structure.
13. The coating as claimed in claim 1, wherein the wear-protection layer
(9) has a multi-layer structure.

14. A method of making a cutting tool, comprising:
first applying in a PVD coating process a coating to a basic body (7) in a
layer sequence including a metallic hard material layer as a wear-protection
layer (9), a separating layer (11) applied at least to one portion of the wear-
protection layer (9), and a top layer (12) on the separating layer (11), and
subsequently removing the top layer (12) from selected upper surface
portions by a mechanical abrading process, wherein the separating layer (11)
has a structure which is not metallic- crystalline, wherein the wear protection
layer (9) has a metallic- crystalline structure, and wherein the separating
layer (11) contains or is a chemical compound with a preponderantly covalent
bond, or is strongly non-stoichiometrically composed, or is a strongly-stressed
layer.
15. The method as claimed in claim 14, wherein the top layer (12) is
removed by a sandblasting process.
16. The method as claimed in claim 14, wherein all the layers of the
coating (8) are applied in a single PVD process.
17. The method as claimed in claim 2, wherein the top layer (12) is a
decorative layer.
18. The method as claimed in claim 8, wherein the metal is titanium or
zirconium.

19. The coating as claimed in claim 1, wherein the wear-protection layer is
predominantly in compression, the separating layer is predominantly in
tension, and the top layer is predominantly in compression.
20. The coating as claimed in claim 1, wherein the separating layer
disrupts or disturbs a metallic-crystalline bond between the top layer
and the wear-protection layer.


The invention relates to a coating (8) for a cutting tool, comprising a wear-
protection layer (9) having a metallic -crystalline structure, a top layer (12), and
a separating layer (11) applied at least one portion of the wear-protection layer
(9) and arranged between the wear -protection layer (9) and the top layer (12),
wherein the separating layer (11) has a structure which is not metallic-
crystalline and limits the adhesion of the top layer (12) to the wear-protection
layer (9), and wherein the separating layer (11) contains or is a chemical
compound with a preponderantly covalent bond, or is strongly non-
stoichiometrically composed, or is a strongly stressed layer.

Documents:

02206-kolnp-2006 abstract.pdf

02206-kolnp-2006 claims.pdf

02206-kolnp-2006 correspondence others.pdf

02206-kolnp-2006 description(complete).pdf

02206-kolnp-2006 drawings.pdf

02206-kolnp-2006 form-1.pdf

02206-kolnp-2006 form-2.pdf

02206-kolnp-2006 form-3.pdf

02206-kolnp-2006 form-5.pdf

02206-kolnp-2006 international publication.pdf

02206-kolnp-2006 international search authority report.pdf

02206-kolnp-2006 pct other document.pdf

02206-kolnp-2006 priority document.pdf

02206-kolnp-2006-correspondence others-1.1.pdf

02206-kolnp-2006-correspondence-1.2.pdf

02206-kolnp-2006-form-26.pdf

02206-kolnp-2006-priority document-1.1.pdf

2206-(05-01-2012)-KOLNP-2006-FORM-27.pdf

2206-KOLNP-2006-(27-12-2012)-FORM-27.pdf

2206-KOLNP-2006-ABSTRACT.pdf

2206-KOLNP-2006-CANCELLED PAGES.pdf

2206-KOLNP-2006-CLAIMS.pdf

2206-kolnp-2006-correspondence.pdf

2206-KOLNP-2006-DESCRIPTION (COMPLETE).pdf

2206-KOLNP-2006-DRAWINGS.pdf

2206-kolnp-2006-examination report.pdf

2206-KOLNP-2006-FORM 1.pdf

2206-kolnp-2006-form 18.pdf

2206-KOLNP-2006-FORM 2.pdf

2206-kolnp-2006-form 26.pdf

2206-kolnp-2006-form 3.1.pdf

2206-KOLNP-2006-FORM 3.pdf

2206-kolnp-2006-form 5.1.pdf

2206-KOLNP-2006-FORM 5.pdf

2206-kolnp-2006-granted-abstract.pdf

2206-kolnp-2006-granted-claims.pdf

2206-kolnp-2006-granted-description (complete).pdf

2206-kolnp-2006-granted-drawings.pdf

2206-kolnp-2006-granted-form 1.pdf

2206-kolnp-2006-granted-form 2.pdf

2206-kolnp-2006-granted-specification.pdf

2206-kolnp-2006-others.pdf

2206-KOLNP-2006-PETITION UNDER RULE 137.pdf

2206-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

2206-kolnp-2006-reply to examination report1.1.pdf

2206-kolnp-2006-translated copy of priority document.pdf

abstract-02206-kolnp-2006.jpg


Patent Number 246720
Indian Patent Application Number 2206/KOLNP/2006
PG Journal Number 11/2011
Publication Date 18-Mar-2011
Grant Date 14-Mar-2011
Date of Filing 04-Aug-2006
Name of Patentee WALTER AG
Applicant Address DERENDINGER STRASSE 53 72072 TUINGEN
Inventors:
# Inventor's Name Inventor's Address
1 SCHIER, VEIT OBERE GARTEN, 70771 LEINFELDEN
PCT International Classification Number C23C 28/00
PCT International Application Number PCT/EP2005/001584
PCT International Filing date 2005-02-17
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10 2004 010 285.6 2004-03-03 Germany