U.S. patent application number 12/000503 was filed with the patent office on 2008-07-10 for coated cemented carbide endmill.
This patent application is currently assigned to SANDVIK INTELLECTUAL PROPERTY AB. Invention is credited to Mats Ahlgren, Anders Jonsson, Susanne Norgren, Torbjorn Selinder, Ragnar Sjostrom.
Application Number | 20080166580 12/000503 |
Document ID | / |
Family ID | 39226632 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080166580 |
Kind Code |
A1 |
Selinder; Torbjorn ; et
al. |
July 10, 2008 |
Coated cemented carbide endmill
Abstract
The present invention relates to a cemented carbide endmilling
tool particularly useful for semifinishing and finishing machining
of hardened steels of HRC above 46, comprising a substrate and a
wear resistant coating. The substrate, a, comprises from about 90
to about 94 wt % WC in a binder phase of Co also containing Cr in
such an amount that the Cr/Co weight ratio is from about 0.05 to
about 0.18. The wear resistant coating, b, is from about 1.8 to
about 9.5 .mu.m thick, and comprises a first layer, c, of a hard
and wear resistant refractory PVD AlMe nitride or carbonitride
where Me is Zr, V, Nb, Cr or Ti having a thickness of from about
1.0 to about 4.5 .mu.m and an atomic fraction of Al to Me of from
about 1.20 to about 1.50, a second layer, d, of hard and wear
resistant refractory PVD AlMe nitride or carbonitride where Me is
Zr, V, Nb, Cr or Ti, having a thickness of from about 0.5 to about
4.5 .mu.m, and an atomic fraction of Al to Me of 1.30-1.70, and in
between the first layer (c) and the second layer (d), a from about
0.05 to about 1.0 .mu.m thick low-Al layer, e, the thickness being
less than about 0.95 times the thickness of thinnest of the first
and the second layer, of an AlMe nitride or carbonitride where Me
is Zr, V, Nb, Cr or Ti and an atomic fraction of Al to Me of from
about 0 to about 0.3.
Inventors: |
Selinder; Torbjorn;
(Stockholm, SE) ; Norgren; Susanne; (Huddinge,
SE) ; Ahlgren; Mats; (Taby, SE) ; Sjostrom;
Ragnar; (Johanneshov, SE) ; Jonsson; Anders;
(Gavle, SE) |
Correspondence
Address: |
DRINKER BIDDLE & REATH (DC)
1500 K STREET, N.W., SUITE 1100
WASHINGTON
DC
20005-1209
US
|
Assignee: |
SANDVIK INTELLECTUAL PROPERTY
AB
|
Family ID: |
39226632 |
Appl. No.: |
12/000503 |
Filed: |
December 13, 2007 |
Current U.S.
Class: |
428/548 ;
419/7 |
Current CPC
Class: |
C23C 14/0021 20130101;
Y10T 428/265 20150115; B22F 2005/001 20130101; C23C 30/005
20130101; Y10T 428/12028 20150115; Y10T 428/24975 20150115; C23C
14/0641 20130101 |
Class at
Publication: |
428/548 ;
419/7 |
International
Class: |
B32B 15/01 20060101
B32B015/01; B32B 33/00 20060101 B32B033/00; B22F 3/12 20060101
B22F003/12; B22F 9/04 20060101 B22F009/04; B22F 7/02 20060101
B22F007/02; C23C 14/16 20060101 C23C014/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2006 |
SE |
0602747-8 |
Mar 28, 2007 |
SE |
0700800-6 |
Claims
1. Cemented carbide endmilling tool comprising a substrate and a
wear resistant coating wherein: the substrate (a) comprises from
about 90 to about 94 wt % WC in a binder phase of Co also
containing Cr in such an amount that the Cr/Co weight ratio is
0.05-0.18, and the wear resistant coating (b) is from about 1.8 to
about 9.5 .mu.m thick comprising: a first layer (c) of a hard and
wear resistant refractory PVD AlMe nitride or carbonitride where Me
is Zr, V, Nb, Cr or Ti having a thickness of from about 1.0 to
about 4.5 .mu.m and an atomic fraction of Al to Me of from about
1.20 to about 1.50, a second layer (d) of hard and wear resistant
refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb,
Cr or Ti having a thickness of from about 0.5 to about 4.5 .mu.m,
and an atomic fraction of Al to Me of from about 1.30 to about
1.70, and in between the first and the second layer, a from about
0.05 to about 1.0 .mu.m thick low-Al layer (e), the thickness of
layer (e) being less than about 0.95 times the thickness of
thinnest of the first layer (c) and the second layer (d), of an
AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti and an
atomic fraction of Al to Me of from about 0 to about 0.3.
2. Cemented carbide endmilling tool of claim 1, wherein the Cr/Co
ratio of the binder phase is from about 0.06 to about 0.16.
3. Cemented carbide endmilling tool of claim 1, wherein the first
layer and the second layer both have crystallites of the cubic rock
salt structure with a grain size less than about 50 nm.
4. Cemented carbide endmilling tool of claim 1, wherein the low-Al
layer (e) has a crystallite grain size larger than about 40 nm
perpendicular to the growth direction and larger than about 100 nm
parallel to the growth direction.
5. Cemented carbide endmilling tool of claim 1, wherein the first
layer (c) has a residual compressive stress more than about 1000
MPa and that the second layer (d) has a residual compressive stress
more than about 1000 MPa.
6. Cemented carbide endmilling tool of claim 1, wherein the low-Al
layer (e) has a residual stress of an absolute value less than 600
MPa, being compressive or tensile.
7. Cemented carbide endmilling tool of claim 1, wherein the
substrate comprises from about 91 to about 93 wt-% WC and the Cr/Co
weight ratio of the substrate is from about 0.06 to about 0.16, the
wear resistant coating is from about 2.5 to about 6.0 .mu.m thick,
the Me of the said first layer (c) is Ti, said first layer (c)
having a thickness of from about 2 to about 3 .mu.m and an atomic
fraction of Al to Me of from about 1.30 to about 1.40.
8. Cemented carbide endmilling tool of claim 7, wherein in said
second layer (d), Me is Ti and said second layer (d) has a
thickness of from about 1.0 to about 2.0 .mu.m and an atomic
fraction of Al to Me is from about 1.50 to about 1.6.
9. Cemented carbide endmilling tool of claim 8, wherein the
thickness of said low-Al layer (e) is from about 0.1 to about 0.7
.mu.m, the thickness being less than about 0.8 times the thickness
of the thinnest of the first layer (c) and second layer (d), Me of
said low-Al layer (e) is Ti and the atomic fraction of Al to Me is
from zero to about 0.05.
10. Cemented carbide endmilling tool of claim 7, wherein the Cr/Co
ratio of the substrate is from about 0.07 to about 0.14, the
thickness of the low-Al layer (e) is less than about 0.5 times the
thickness of the thinnest of the first layer (c) and second layer
(d).
11. Cemented carbide endmilling tool of claim 1, wherein the low-Al
layer (e) is MeN.
12. Cemented carbide endmilling tool of claim 3, wherein the grain
size of said crystallite of said first layer (c) and second layer
(d) is less than about 40 .mu.m.
13. Cemented carbide endmilling tool of claim 4, wherein the grain
size of said crystallite of said low-Al layer (e) is less than
about 50 nm.
14. Cemented carbide endmilling tool of claim 5, wherein the first
layer (c) and second layer (d) each have a residual compressive
stress from about 1800 to about 3500 MPa.
15. Cemented carbide endmilling tool of claim 6, wherein the low-Al
layer (e) has a residual stress of an absolute value less than
about 300 MPa.
16. Cemented carbide endmilling tool of claim 15, wherein the
low-Al layer (e) has a residual stress of an absolute value less
than about 80 MPa.
17. Method of making a cemented carbide endmilling comprising the
following steps: providing a cemented carbide endmill blank with a
composition comprising from about 90 to about 94 wt % WC in a
binder phase of Co also containing Cr in such an amount that the
Cr/Co weight ratio is from about 0.05 to about 0.18, wet milling
submicron powders of tungsten carbide cobalt, at least one of
Cr.sub.3C.sub.2, Cr.sub.23C.sub.6 and Cr.sub.7C.sub.3 to obtain a
slurry, drying the slurry to obtain a powder, pressing the powder
into rods, sintering the rods in vacuum or in nitrogen, and
optionally performing an isostatic gas pressure step during
sintering temperature or at the final stage of sintering, grinding
the rods cylindrical to h6 tolerance, grinding flutes using diamond
wheels with emulsion cutting fluid, depositing whilst maintaining a
partial pressure of nitrogen in the recipient, and using the
appropriate selection of active evaporation sources and rates, a
wear resistant coating (b) from about 1.8 to about 9.5 .mu.m thick,
comprising: a first layer (c) of a hard and wear resistant
refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb,
Cr or Ti having a thickness of from about 1.0 to about 4.5 .mu.m
and an atomic fraction of Al to Me of from about 1.20 to about 1.50
with process parameters: arc current from about 50 to about 200 A
in the equipment, N.sub.2-pressure from about 5 to about 50 .mu.bar
and deposition temperature from about 400 to about 700.degree. C.
and a substrate bias of from about -150 to about -300V, a second
layer (d) of hard and wear resistant refractory PVD AlMe nitride or
carbonitride where Me is Zr, V, Nb, Cr or Ti, having a thickness of
from about 0.5 to about 4.5 .mu.m and an atomic fraction of Al to
Me of from about 1.30 to about 1.70 with process parameters: arc
current from about 50 to about 200 A in the equipment,
N.sub.2-pressure from about 5 to about 50 .mu.bar, and deposition
temperature from about 400 to about 700.degree. C. and a substrate
bias of about -50 to about -140 V, and in between the first and the
second layers, a from about 0.05 to about 1.0 .mu.m thick low-Al
layer (e) at a temperature from about 400 to about 700.degree. C.,
the substrate bias from about -30 to about 150 V and the arc
current from about 80 to about 210 A.
18. Method of making a cemented carbide endmilling tool of claim
17, further comprising: the substrate comprises from about 91 to
about 93 wt-% WC and the Cr/Co weight ratio of the substrate is
from about 0.06 to about 0.16, the wear resistant coating is from
about 2.5 to about 6.0 .mu.m thick, the Me of the said first layer
(c) is Ti, said first layer (c) having a thickness of from about 2
to about 3 .mu.m and an atomic fraction of Al to Me of from about
1.30 to about 1.40; in said second layer (d), Me is Ti and said
second layer (d) has a thickness of from about 1.0 to about 2.0
.mu.m and an atomic fraction of Al to Me is from about 1.50 to
about 1.6, and the thickness of said low-Al layer (e) is from about
0.1 to about 0.7 .mu.m, the thickness being less than about 0.8
times the thickness of the thinnest of the first layer (c) and
second layer (d), Me of said low-Al layer (e) is Ti and the atomic
fraction of Al to Me is from zero to about 0.5.
19. Method of making a cemented carbide endmilling tool of claim
17, further comprising the Cr/Co ratio of the substrate is from
about 0.07 to about 0.14, the thickness of the low-Al layer (e) is
less than about 0.5 times the thickness of the thinnest of the
first layer (c) and second layer (d).
20. Method of making a cemented carbide endmilling tool of claim
17, further comprising the low-Al layer (e) is MeN.
21. Method of making a cemented carbide endmilling tool of claim
17, wherein the process parameters for depositing said first layer
(c) are arc current from about 120 to about 160 A, N.sub.z-pressure
7 to about 20 .mu.bar, deposition temperature of from about 550 to
about 650.degree. C. and a substrate bias of from about -170 to
about -230 V.
22. Method of making a cemented carbide endmilling tool of claim
17, wherein the process parameters for depositing said second layer
(d) are arc current from about 120 to about 160 A, N.sub.z-pressure
7 to about 20 .mu.bar, deposition temperature of from about 550 to
about 650.degree. C. and a substrate bias of from about -80 to
about -120 V.
23. Method of making a cemented carbide endmilling tool of claim
17, wherein the process parameters for depositing said low-Al layer
(e) are arc current from about 140 to about 190 A, N.sub.z-pressure
7 to about 20 .mu.bar, deposition temperature of from about 550 to
about 650.degree. C. and a substrate bias of from about -70 to
about -120 V.
Description
RELATED APPLICATION DATA
[0001] This application claims priority under 35 U.S.C. .sctn.119
and/or .sctn.365 to Swedish Application No. 0602747-8, filed Dec.
15, 2006, and also to Swedish Application No. 0700800-6, filed Mar.
28, 2007; the entire contents of each are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a metal cutting tool. More
specifically the invention relates to a PVD coated cemented carbide
endmill suitable particularly for semifinishing to finishing
machining of hardened steels.
[0003] In chip forming machining of steel the requirements of high
productivity, i.e., higher cutting speeds and feeds combined with
increased tool lifetime, put severe demands on tool properties.
When hardened, work piece steels normally have a hardness of
between HRC 46 and 55, but may have hardness values of up to HRC 63
or even higher. For semifinishing and finishing operations of
hardened steel so-called solid carbide tools are used. Such tools
are produced, e.g., by grinding a cylindrical cemented carbide
blank into a substrate of desired shape or providing a blank of
desired shape by extrusion, which is subsequently coated by, e.g.,
physical vapor deposition (PVD). One very common application of
solid carbide tools is endmilling of components, dies and molds,
but it is usually not possible to cover the whole hardness range
with one single tool grade.
[0004] Endmilling of hardened steels generates large amounts of
heat, which causes high temperatures at the cutting edge. Very
often, the shape of the machined component is such that shank
overhangs are large. Both of these factors make necessary the use
of hard cemented carbide grades that do not soften appreciably at
the elevated temperatures at hand and that are rigid so that tool
bending is negligible. The need for a harder grade has, however, to
be balanced against the lowered bulk toughness that follows. For
general machining, the typical substrate hardness is below about
1600 HV3, whereas in hard part machining typical HV3 values range
from about 1700 up to in excess of about 1800. A severe problem
here is that substrate brittleness causes chipping problems of the
sharply ground cutting edge, which is not easily remedied by
standard PVD coatings. Any cracks that occur in the coating due to
the machining tend to propagate through the entire coating
thickness. At the interface to the substrate, these cracks may
serve as crack initiation points for substrate bulk fracture.
[0005] Cemented carbide grades for endmilling applications
generally contain fine grain WC, .gamma.-phase which is a solid
solution of generally TiC, NbC, TaC and WC, and binder phase,
generally Co or Ni. Cemented carbides having a fine grain size less
than about 1 .mu.m are produced through the incorporation of grain
growth inhibitors such as V, Cr, Ti, Ta and combinations thereof in
the initial powder blend. Typical inhibitor additions are from
about 0.5 to about 5 wt-% of the binder phase. In addition the
sintering temperature must be low, from about .about.1350 to about
1390.degree. C., in order to further restrict grain coarsening. To
generate a sintered substrate with a grain size of about 0.6 .mu.m,
in general, the WC powder is essentially finer, typically from
about 0.2 to about 0.3 .mu.m.
[0006] PVD coatings for endmills are, for instance, (Ti,Al)N single
layers, with high hardness and wear resistance. By the use of
intense ion bombardment of the coating during its growth, PVD
layers have high residual stress levels, of the order of at least
about 2000 MPa compressive, and usually higher than about 3000 MPa
compressive. A compressive stress is in general considered an
advantage because considerable mechanical load on the tool is
needed to initiate a crack in the coating. At the same time,
however, a maximum coating thickness of around 3 .mu.m is imposed
due to the high stress and limited coating adhesion.
[0007] Improved tool toughness may be achieved with coating design,
e.g., with non-periodic TiN+(Ti,Al)N multilayers such as disclosed
in EP 983 393. In these, the average Al contents are lower than in
the case of single layer coatings which compromises the wear
resistance.
OBJECTS AND SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a coated
cemented carbide endmill with improved wear resistance without
sacrificing toughness and edge security particularly useful for
semifinishing and finishing in steels with hardnesses of HRC 46-63,
and above.
[0009] In one embodiment of the invention, there is provided a
cemented carbide endmilling tool comprising a substrate and a wear
resistant coating wherein the substrate (a) comprises from about 90
to about 94 wt % WC in a binder phase of Co also containing Cr in
such an amount that the Cr/Co weight ratio is 0.05-0.18, and the
wear resistant coating (b) is from about 1.8 to about 9.5 .mu.m
thick comprising a first layer (c) of a hard and wear resistant
refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb,
Cr or Ti having a thickness of from about 1.0 to about 4.5 .mu.m
and an atomic fraction of Al to Me of from about 1.20 to about
1.50, a second layer (d) of hard and wear resistant refractory PVD
AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having
a thickness of from about 0.5 to about 4.5 .mu.m, and an atomic
fraction of Al to Me of from about 1.30 to about 1.70, and in
between the first and the second layer, a from about 0.05 to about
1.0 .mu.m thick low-Al layer (e), the thickness of layer (e) being
less than about 0.95 times the thickness of thinnest of the first
layer (c) and the second layer (d), of an AlMe nitride or
carbonitride where Me is Zr, V, Nb, Cr or Ti and having an atomic
fraction of Al to Me of from about 0 to about 0.3.
[0010] In still another embodiment of the invention, there is
provided a method of making a cemented carbide endmilling tool for
semifinishing and finishing machining comprising the following
steps: providing a cemented carbide endmill blank with a
composition comprising from about 90 to about 94 wt % WC in a
binder phase of Co also containing Cr in such an amount that the
Cr/Co weight ratio is from about 0.05 to about 0.18, wet milling
submicron powders of tungsten carbide cobalt, at least one of
Cr.sub.3C.sub.2, Cr.sub.23C.sub.6 and Cr.sub.7C.sub.3 to obtain a
slurry, drying the slurry to obtain a powder, pressing the powder
into rods, sintering the rods in vacuum or in nitrogen, and
optionally performing an isostatic gas pressure step during
sintering temperature or at the final stage of sintering, grinding
the rods cylindrical to h6 tolerance, grinding flutes using diamond
wheels with emulsion cutting fluid, depositing whilst maintaining a
partial pressure of nitrogen in the recipient using the appropriate
selection of active evaporation sources and rates, a wear resistant
coating (b) from about 1.8 to about 9.5 .mu.m thick, comprising a
first layer (c) of a hard and wear resistant refractory PVD AlMe
nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having a
thickness of from about 1.0 to about 4.5 .mu.m and an atomic
fraction of Al to Me of from about 1.20 to about 1.50 with process
parameters: arc current from about 50 to about 200 A in the
equipment, N.sub.2-pressure from about 5 to about 50 .mu.bar and
deposition temperature from about 400 to about 700.degree. C. and a
substrate bias of from about -150 to about -300V, a second layer
(d) of hard and wear resistant refractory PVD AlMe nitride or
carbonitride where Me is Zr, V, Nb, Cr or Ti, having a thickness of
from about 0.5 to about 4.5 .mu.m and an atomic fraction of Al to
Me of from about 1.30 to about 1.70 with process parameters: arc
current from about 50 to about 200 A in the equipment,
N.sub.2-pressure from about 5 to about 50 .mu.bar, and deposition
temperature from about 400 to about 700.degree. C. and a substrate
bias of about -50 to about -140 V, and in between the first and the
second layers, a from about 0.05 to about 1.0 .mu.m thick low-Al
layer (e) at a temperature from about 400 to about 700.degree. C.,
the substrate bias from about -30 to about -150 V and the arc
current from about 80 to about 210 A.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a Scanning Electron Microscope (SEM) micrograph
of a fracture section of an exemplary end mill according to the
invention in which
[0012] a--substrate
[0013] b--coating
[0014] c--first layer
[0015] d--second layer
[0016] e--low Al-layer.
[0017] FIG. 2 shows a SEM micrograph of an exemplary substrate
according to the invention.
[0018] FIG. 3 shows a light optical micrograph of a cross section
micrograph of an exemplary endmill according to the invention.
[0019] FIG. 4 shows a SEM micrograph of a worn edge of an exemplary
endmill according to the invention.
[0020] FIG. 5 shows a SEM micrograph of a worn edge of an end mill
according to prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] It has surprisingly been found that by sandwiching a low-Al
containing (Ti,Al)N layer, having the unexpected property of being
essentially stressless, between two high-Al containing (Ti,Al)N
layers having high compressive residual stresses edge chipping is
suppressed. Thus, the use of harder substrate grades as well as
thicker coatings, and thanks to that, more wear resistant coatings
are enabled.
[0022] According to the present invention, there is provided a
coated solid carbide endmill particularly useful for semifinishing
and finishing machining of hardened steels of HRC from about 46 to
about 63, and above, comprising a cemented carbide substrate and a
wear resistant coating, wherein [0023] the substrate, (a),
comprises from about 90 to about 94 wt %, preferably from about 91
to about 93 wt %, WC in a binder phase of Co also containing Cr in
such an amount that the Cr/Co weight ratio is from about 0.05 to
about 0.18, preferably from about 0.06 to about 0.16, more
preferably from about 0.07 to about 0.14, most preferably from
about 0.075 to about 0.13, and with a coercivity of more than about
22 kA/m, preferably from about 25 to about 30 kA/m, and [0024] the
wear resistant coating, (b), is from about 1.8 to about 9.5 .mu.m,
preferably from about 2.5 to about 6.0 .mu.m thick, comprising
[0025] a first layer, (c), of a hard and wear resistant refractory
PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti,
preferably Ti having a thickness of from about 1.0 to about 4.5
.mu.m, preferably from about 2.0 to about 3.0 .mu.m, and an atomic
fraction of Al to Me of from about 1.20 to about 1.50, preferably
from about 1.30 to about 1.40, [0026] a second layer, (d), of hard
and wear resistant refractory PVD AlMe nitride or carbonitride
where Me is Zr, V, Nb, Cr or Ti, preferably Ti having a thickness
of from about 0.5 to about 4.5 .mu.m, preferably from about 1.0 to
about 2.0 .mu.m, and an atomic fraction of Al to Me of from about
1.30 to about 1.70, preferably from about 1.50 to about 1.60, and
[0027] in between the first and the second layer, a from about 0.05
to about 1.0 .mu.m, preferably from about 0.1 to about 0.7 .mu.m,
thick low-Al layer, (e), the thickness being less than about 0.95
times, preferably less than about 0.8 times, most preferably less
than about 0.5 times, the thickness of thinnest of the first layer
(c) and the second layer (d), of an AlMe nitride or carbonitride
where Me is Zr, V, Nb, Cr or Ti, preferably Ti, and an atomic
fraction of Al to Me of from about 0 to about 0.3, preferably from
about 0 to about 0.05, most preferably MeN.
[0028] The atomic fraction of Al to Me in the layers is measured by
averaging at least four point analyses in cross section
transmission electron microscopy (TEM).
[0029] In a preferred embodiment, the first layer and the second
layer both have crystallites of the cubic rock salt structure with
a grain size less than about 50 nm, preferably less than about 40
nm. The sandwiched low-Al layer has a crystallite grain size larger
than about 40 nm, preferably larger than about 50 nm perpendicular
to the growth direction and larger than about 100 nm parallel to
the growth direction, i.e., having columnar growth, and most
preferably extending in the growth direction throughout its
thickness.
[0030] X-ray diffraction techniques, more specifically the
sin.sup.2.psi. method (I. C. Noyan, J. B. Cohen, Residual Stress
Measurement by Diffraction and Interpretation, Springer-Verlag, New
York, 1987, pp 117-130), is used for determining the residual
stress.
[0031] In a further preferred embodiment, the first layer has a
residual compressive stress more than about 1000 MPa, preferably
from about 1800 to about 3500 MPa, the second layer has a residual
compressive stress more than about 1000 MPa, preferably from about
1800 to about 3500 MPa and the low-Al layer has a residual stress
of an absolute value less than about 600 MPa (i.e., being
compressive or tensile), preferably less than about 300 MPa, more
preferably less than about 80 MPa.
[0032] Optionally applied onto the second layer are further layers
which may be used for further improving wear resistance, cosmetic
appearance or for wear detection purposes as known to the skilled
artisan.
[0033] The present invention further relates to a method of making
a cemented carbide endmill with a composition according to above
including the following steps: [0034] wet milling submicron powders
of tungsten carbide cobalt, at least one of Cr.sub.3C.sub.2,
Cr.sub.23C.sub.6 and Cr.sub.7C.sub.3 to obtain a slurry, [0035]
drying the slurry to obtain a powder, [0036] pressing the powder
into rods, [0037] sintering the rods in vacuum or in nitrogen as
described in EP-A-1 500 713 (also published U.S. 2006/029511),
hereby incorporated by reference in its entirety, and [0038]
possibly performing an isostatic gas pressure step during sintering
temperature or at the final stage of sintering.
[0039] The so obtained cemented carbide rods are centerless ground
cylindrical to h6 tolerance. Flutes are ground using diamond wheels
with emulsion cutting fluid.
[0040] The as-ground solid carbide endmill substrates are wet
cleaned. The substrates are subjected to a PVD coating process in a
coater using reactive arc evaporation type PVD equipment containing
metal evaporation MeAl-sources with suitable composition to obtain
the desired Al/Me atomic ratios, arranged such to coat the full
charge homogeneously. The MeAl-sources can, e.g., be three single
targets arranged so that each target coats the full charge
homogeneously or, as an alternative, six MeAl-sources can be
arranged pairwise so that each pair coats the full charge
homogeneously. However, other number of targets and arrangements
are within the scope of the invention. The coater is evacuated,
followed by the steps of heating and plasma etching in order to
further clean the tools, and to condition their surfaces by
removing excess binder phase from the WC surface. By metal
evaporation whilst maintaining a partial pressure of nitrogen in
the recipient, i.e., the coating furnace or vacuum vessel in which
the deposition process takes place, and using the appropriate
selection of active evaporation sources and rates, the following
layers are deposited: [0041] a wear resistant coating, (b), is from
about 1.8 to about 9.5 .mu.m, preferably from about 2.5 to about
6.0 .mu.m thick, comprising [0042] a first layer, (c), of a hard
and wear resistant refractory PVD AlMe nitride or carbonitride
where Me is Zr, V, Nb, Cr or Ti, preferably Ti having a thickness
of from about 1.0 to about 4.5 .mu.m, preferably from about 2.0 to
about 3.0 .mu.m, and an atomic fraction of Al to Me of from about
1.20 to about 1.50, preferably from about 1.30 to about 1.40, with
process parameters: arc current from about 50 to about 200 A,
preferably from about 120 to about 160 A in the equipment,
N.sub.2-pressure from about 5 to about 50 .mu.bar, preferably from
about 7 to about 20 .mu.bar, and deposition temperature from about
400 to about 700.degree. C., preferably from about 550 to about
650.degree. C., and a substrate bias of from about -150 to about
-300 V, preferably from about -170 to about -230 V, [0043] a second
layer, (d), of hard and wear resistant refractory PVD AlMe nitride
or carbonitride where Me is Zr, V, Nb, Cr or Ti, preferably Ti
having a thickness of from about 0.5 to about 4.5 .mu.m, preferably
from about 1.0 to about 2.0 .mu.m, and an atomic fraction of Al to
Me of from about 1.30 to about 1.70, preferably from about 1.50 to
about 1.60, with process parameters: arc current from about 50 to
about 200 A preferably from about 120 to about 160 A in the
equipment, N.sub.2-pressure from about 5 to about 50 .mu.bar,
preferably from about 7 to about 20 .mu.bar, and deposition
temperature from about 400 to about 700.degree. C., preferably from
about 550 to about 650.degree. C., and a substrate bias of from
about -50 to about -140 V, preferably from about -80 to about -120
V. [0044] in between the first and the second layer, a from about
0.05 to about 1.0 .mu.m, preferably from about 0.1 to about 0.7
.mu.m, thick low-Al layer, (e), the thickness being less than about
0.95 times, preferably less than about 0.8 times, most preferably
less than about 0.5 times, the thickness of thinnest of the first
layer (c) and the second layer (d), of an AlMe nitride or
carbonitride where Me is Zr, V, Nb, Cr or Ti, preferably Ti, and an
atomic fraction of Al to Me of from about 0 to about 0.3,
preferably from about 0 to about 0.05, most preferably MeN, with
temperature from about 400 to about 700.degree. C., preferably from
about 550 to about 650.degree. C., N.sub.2-pressure from about 5 to
about 50 .mu.bar, preferably from about 7 to about 20 .mu.bar the
substrate bias from about -30 to about -150 V preferably from about
-70 to about -120 V and the arc current from about 80 to about 210
A, preferably from about 140 to about 190 A.
[0045] The coating can also be deposited by other PVD technologies,
such as, magnetron sputtering, dual magnetron sputtering or arc
technology.
[0046] The invention is additionally illustrated in connection with
the following examples, which are to be considered as illustrative
of the present invention. It should be understood, however, that
the invention is not limited to the specific details of the
examples.
Example 1
[0047] Tungsten carbide powder with an FSSS grain size of 0.9
.mu.m, 7 wt % very fine grained cobalt powder and 0.7 wt-% Cr added
as H. C. Starck fine grained Cr.sub.3C.sub.2-powder, were wet
milled together with conventional pressing agents. After milling
and spray drying the powder was pressed into 6 mm diameter rods and
sintered at 1410.degree. C. and 40 bar Ar gas pressure. The
sintered material had a coercivity of 28 kA/m.
[0048] The so obtained cemented carbide rods were centerless ground
cylindrical to h6 tolerance. Flutes were ground using diamond
wheels with emulsion cutting fluid.
[0049] The as-ground solid carbide endmill substrates were wet
cleaned and subjected to a PVD coating process according to the
following. The substrates were loaded into a reactive arc
evaporation type PVD equipment chamber containing six metal
evaporation sources, arranged pairwise so that each pair would coat
the full charge homogeneously. One pair of evaporators had Ti metal
targets and the other two pairs had AlTi alloy targets having a
composition ratio Al/Ti of 2. The chamber was evacuated, followed
by the steps of heating and plasma etching in order to further
clean the tools, and to condition their surfaces by removing excess
binder phase from the WC surface. By metal evaporation whilst
maintaining a partial pressure of nitrogen in the recipient, and
using the appropriate selection of active evaporation sources and
-rates TiN and (Ti,Al)N alloy layers were deposited at a
temperature of 600.degree. C. The process conditions during the
deposition steps were as below:
TABLE-US-00001 TABLE 1 Arc Time current Bias Pressure N.sub.2 Ar
Layer Target [min] [A] [V] [.mu.bar] [sccm] [sccm] C 4xAlTi 130 140
-200 10 N.sub.2 E 2xTi 25 170 -100 800 400 D 4xAlTi 65 140 -100 10
N.sub.2
[0050] The so manufactured and coated solid carbide endmills were
analysed metallographically. Cross sections were prepared by
cutting the endmill 10 mm from the tip, followed by mechanical
grinding and polishing by diamond grit. A typical section of
coating and substrate is shown in the optical micrograph in FIG. 3.
The coating thicknesses indicated in Table 1 were measured on the
cylindrical land, i.e., clearance side, more than 0.2 mm away, and
less than 1.0 mm, from the cutting edge.
[0051] X-ray diffraction techniques, more specifically the
sin.sup.2.psi. method, (I. C. Noyan, J. B. Cohen, Residual Stress
Measurement by Diffraction and Interpretation, Springer-Verlag, New
York, 1987 (pp 117-130)), was used for determining the residual
stress in the three layers. The results are reported in Table
2.
[0052] Thin film transmission electron microscopy equipped with an
EDS spectrometer was used to determine the Al/Ti atomic ratio as an
average of four point analyses and grain size in the three layers,
see Table 2.
TABLE-US-00002 TABLE 2 Coating Thickness Al/Ti atomic Grain size
Residual Layer type [.mu.m] ratio [nm] stress [MPa] C (Ti, Al)N 2.4
1.34 35 -2400* E TiN 0.2 0 columnar -80 75 .times. 150 D (Ti, Al)N
1.6 1.56 30 -2300 *Estimated
Example 2
[0053] Endmills from Example 1 were tested and compared with
endmills of a commercially available grade for the intended
application area. Wear resistance test in very hard steel; a wear
resistant and toughness demanding semifinishing test with 30%
stepover. The test represents the upper range in terms of work
piece hardness.
TABLE-US-00003 Type of test Cavity milling, size 48 .times. 48 mm,
using diameter 1 mm BNE Tool life criterion Max flank wear 0.20 mm
Work piece Uddeholm Vanadis 10, HRC 62 Cutting speed, V.sub.c
(m/min) 60 Tooth feed, f.sub.z (mm/edge) 0.11 Engagement,
a.sub.p/a.sub.e (mm) 0.3/0.3 Cooling Dry Machine Modig MD 7200
Result: Tool life in minutes Invention (from Example 1) 29
Commercial grade 22
[0054] There is a significant improvement in comparison to the
commercial grade which is optimised for this range of work piece
hardness. This clearly expresses the superior wear resistance of
the invented tool.
Example 3
[0055] Endmills from Example 1 were tested and compared with
endmills of a commercially available grade for the intended
application area. This is a toughness demanding sidemilling test in
hardened die steel. The machining situation was a very typical
application. It represents, in terms of work piece hardness, the
lower end of the application area for endmilling in hardened
steels.
TABLE-US-00004 Type of test Sidemilling with a six-fluted, diameter
10 mm corner endmill Tool life criterion v.sub.b max 0.20 mm Work
piece Uddeholm Orvar Supreme HRC 48 Cutting speed, V.sub.c (m/min)
375 Tooth feed, f.sub.z (mm/edge) 0.10 Engagement, a.sub.p/a.sub.e
(mm) 10/0.5 Cooling Compressed air Machine Modig MD 7200 Result:
Tool life in milled distance Invention (from Example 1) 750 m
Commercial grade 500 m
[0056] The improvement compared to the commercial grade, which is
designed for hard part machining, shows the excellent width of the
application area for the invented endmill.
Example 4
[0057] Endmills from Example 1 were tested and compared with
endmills of a commercially available grade for the intended
application area. Machining of two identical tools for die and mold
applications. In this application, edge security and toughness is
essential. It represents a vital customer value to be able to
machine a complete part without tool change.
TABLE-US-00005 Type of test Finishing of mold using diameter 6 mm
ball nosed endmill Tool demand >296 min life time, completion of
one part Work piece Uddeholm Orvar Supreme, HRC 51 Cutting speed,
rpm 12468 rpm Tooth feed, f.sub.z mm/edge 0.08 mm Engagement,
a.sub.p/a.sub.e mm 0.07/0.1 mm Cooling dry Result: Invention (from
Example 1) see FIG. 4 Commercial grade see FIG. 5
[0058] The result of this test was that the commercial grade tool
failed to meet the demanded tool life, whereas the invented tool
finished the operation with very little wear. The result clearly
shows a superior wear resistance of the invention and ability to
sustain an integer cutting edge compared to the commercial grade
tool.
Example 5
[0059] Field test at customer, manufacturing of hot forge dies in
hardened tools steel HRC 53. The machining was done using three
different steps using ball nosed endmills (BNE) of diameters 10, 6,
and 2 mm.
TABLE-US-00006 Type of test Tool life test using diameter 10, 6,
and 2 mm BNE Tool life criterion Stopped cutting Work piece
Uddeholm Orvar Supreme HRC 53 Cutting speed, V.sub.c (m/min) 110,
110, and 107 respectively Spindle speed, (rpm) 35000, 12500, and
6300 respectively Tooth feed, f.sub.z (mm/edge) 0.05, 0.11, and
0.70 respectively Engagement, a.sub.p/a.sub.e (mm) 0.07/0.05,
0.35/1.20, and 0.8/2.20 respectively Cooling Oil Mist Machine Modig
MD 7200
TABLE-US-00007 TABLE 3 Result: Tool life in minutes Layer BNE 10 mm
BNE 6 mm BNE 2 mm Invention (from 374 428 1202 Example 1)
Commercial grade 130 330 660
[0060] The results indicated a significant improvement in tool live
for the endmill according to the invention.
[0061] Although the present invention has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions, deletions,
modifications, and substitutions not specifically described may be
made without department from the spirit and scope of the invention
as defined in the appended claims.
* * * * *