Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Modular extrusion die
The present invention relates to an extrusion tool or die for the extrusion of
metallic
material, in particular a material of aluminium or alloys thereof, or other
non-ferrous
metals such as Cu and alloys thereof.
Extrusion is a process used to create solid or hollow objects of a fixed cross
sectional
profile. The material is pushed through the die of the desired cross section.
The two
main advantages of the extrusion process over other manufacturing processes is
its
ability to create very complex cross-sections and finished parts with an
excellent surface
finish.
The dies are, depending of course on the material being extruded and
temperature etc.,
subjected to wear and numerous attempts have been made to improve the life
time of
extrusion dies for example by selecting suitable die materials, heat treatment
and/or
coating of the die with different types of coating such as CVD or nano
particle type
coatings.
From US-04169366 is known an extrusion device for the extrusion of hollow or
semi-
hollow sections of metal, in particular aluminium. The device has at least one
mandrel
support projecting into the die opening where the mandrel head is a special
insert type
which is held in place on a mandrel support by a connecting device.
US-04773251 is related to a 2 part die, whereof one part includes the bearing
and the
other being the support. The specificity of this solution appears to be that
the two die
parts are atomically bonded using powder metallurgy technology. Further, the
"support"
part (the one that does not carry the bearing) is relatively vaguely defined
in terms of
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material selection as a "tough non-ductile heat resistant steel of a
composition
different from the metallic material of the bearing holding part".
JP-06315716 further relates to an extrusion die with a tool comprising a
material
made of a Ni base alloy and having hardness after heat treatment of more than
HRC 33. The purpose of using such alloy is to prevent the penetration of Zn
into the
tool, i.e. preventing Zinc embrittlement.
Still further CN-201287153 shows an aluminium profile extrusion die where the
die
tools, i.e. the parts forming the extrusion profile opening are replaceable
and are
made from a wear resistant material.
According to one aspect of the present invention there is provided an
extrusion die
where the lifetime is quite considerably extended and where the cost of
replacement
and maintenance accordingly is reduced. Tests performed in several aluminium
extrusion plants of the applicant shows that the selection of Ni-base super
alloys as
die material according to the invention reduces severe cracking and improves
the die
lifetime from one/two hundred extruded billets to thousand and more extruded
billets
before replacement of die parts or maintenance is needed.
According to one aspect of the invention, there is provided an extrusion tool
or die for
the extrusion of metallic material, comprising aluminium or alloys thereof, or
other
non-ferrous metals, the die being a modular type comprising die bodie/s with
cavitie/s
provided with insert/s, wherein an area of the die with strong thermo-
mechanical
solicitation comprising the die bodie/s, is made of a nickel, iron or cobalt
based super
alloy, whereas the die in an area with strong tribological solicitation
comprising the
insert/s, is manufactured of a wear resistant material.
The invention will be further described in the following by way of example and
with
reference to the drawings, where:
Fig. 1 shows an example of an extrusion die according to the invention, a)
assembled
in cross section, b) the same in expanded view,
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Fig. 2 shows in larger scale a cross section part of one of the die
cavities shown
in Fig.1 a).
Fig. 3 Shows a Manson-Coffin diagram depicting the linear relationship, on
a log-
log plot, of plastic strain range versus cycles to failure of the most common
tool steels, employed for extrusion dies, with the fatigue properties of a
superalloy according to the invention.
As stated above, extrusion is a process used to create solid or hollow objects
of a fixed
cross sectional profile. The attached figures show an example of an extrusion
tool or die
1 for extruding hollow profiles which will be further explained in the
following. The
extrusion die 1 as shown in Fig. 1 a) and b) includes one bridge die body 2
and one
plate die body 3, each provided with two cavities 4, respectively 5 and each
cavity
further defining openings with inserts 6, 7. The die as shown in Fig. 1
represents what is
defined as being a two cavity die capable of extruding two profiles in
parallel at the
same time. Extrusion dies may however be of one or three or more cavity type
depending on the type, shape (design) and size of the die opening forming the
extruded
product as well as the capacity of the extrusion equipment (ram and block ¨
not shown
in the figures).
Fig. 2 shows in larger scale and in cross section one of the die cavities 4, 5
shown in
Fig.1 a). The two die bodies 2, 3 are, in an assembled condition whereby a
mandrel
part 10 on the bridge die body 2 partly protrudes into the opening of the
cavity 5 in the
die plate 3 such that an opening 11 is formed between the mandrel and cavity
opening
5 in the die 3. The material being extruded is pressed through this opening 11
thereby
forming the shape of the final, extruded hollow product.
With the present invention the mandrel 10 is made of a separate mandrel insert
6
attached to the bridge die body 2 by means of a screw 8.
On the other hand, according to the invention, the opening in the die plate 3
is made of
a separate bearing insert 7, as well being attached to the die plate 3 by
means of
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second screws 9. In stead of being connected by means of screws 9, the bearing
insert
7 may as an alternative be thermally shrunk fit into a recess in the die plate
3 opening 5.
The fundamental idea of the present invention is the selection of different
materials and
the combined utilization of these in the appropriate zones of the extrusion
die, fitting with
the thermo-mechanical solicitations on one side and the tribological
solicitations on the
other side.
In the area of strong thermo-mechanical solicitation (Creep - Low Cycle
Fatigue regime),
the first "modulus" of the die which includes the bridge body 2 and/or die
plate body 3
depending as stated above on whether it is a hollow or solid profile, is made
of a
Superalloy. . In particular the Superalloys are based either on a) Nickel, b)
Cobalt or c)
Iron. The Nickel, Cobalt and Iron based Superalloys ranges may respectively be
defined
as follows:
Nickel based superalloys: Ni (min 39 % max 78 %), Fe (min 0% max 36%), Cr (min
12% max 25%), Al (min 0% max 5%), Co (min 0% max 20%), Mo (min 0% max 10%),
Nb (min 0% max 5%)
Cobalt based superalloys: Co (min 34% max 50%), Ni (min 10 % max 29 %), Fe
(min
3% max 26%), Cr (min 3% max 22%), Al (min 0% max 6%), Nb (min 0% max 3%), W
(min (0% max 15%)
Iron based superalloys: Fe (min 42% max 74%), Ni (min 0 % max 38 %), Cr (min
0%
max 20%), Al (min 0% max 5%), Co (min 0% max 15%), Mo (min 0% max 5%), Nb (min
0% max 5c1/0)
Above defined Superalloys, or high-performance alloy, are alloys that exhibit
excellent
mechanical strength and creep resistance at high temperatures, good surface
stability,
and corrosion and oxidation resistance.
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Superalloys develop high temperature strength through solid solution or
precipitation
strengthening: to a first approximation the elevated temperature strength of a
superalloy
depends upon the amount and distribution of the strengthening intergranular
second
phase, which is y' in the case of Nickel-based Superalloys and carbides in the
case of
5 cobalt-base Superalloys.
Superalloys retains strength over a wide temperature range, attractive for
high
temperature applications where steels would succumb to creep as a result of
thermally-
induced crystal vacancies.
Creep resistance is dependent on reducing the speed of dislocations within the
crystal
structure. The body centred cubic gamma prime phase [Ni3(AI,Ti)], present in
nickel and
nickel-iron Superalloys, presents a barrier to dislocations. Chemical
additions such as
Aluminium and Titanium promote the creation of the gamma prime phase (y'). The
gamma prime phase size can be finally controlled by annealing. Many other
elements,
can be present; Chromium, Molybdenum, Tungsten, Aluminium, Zirconium, Niobium,
Rhenium, Ccarbon or Silicon are a few examples.
Regarding at the Cobalt base Superalloys, considerable amount of refractory
elements
are employed in solution strengthened structure, such as chromium, molybdenum
or
tungsten. These solutes have inhibiting recovery capacity and they obstruct
the
dislocations movement. Carbides, precipitated at grain boundaries, block the
grain
boundaries sliding and produce along high rupture life.
Other crucial material properties are fatigue life, phase stability, as well
as oxidation and
corrosion resistance.
Generally, solid-solution-strengthened alloys are expected to have strong
resistance to
fatigue cracking due to an increased resistance to slip and an enhanced strain
hardening capacity.
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In general, high temperature fatigue may be thought of a cyclic creep rupture
process.
For this reason, the relationships between microstructure, creep deformation
and
fracture, previously described, are applicable.
Focusing on the corrosion and oxidation resistance, the strong resistance
against
environmental effects is provided by the formation of a protective oxide layer
which is
formed, by elements such as aluminium and chromium, when the metal is exposed
to
oxygen and encapsulates the material, and thus protecting the rest of the
component.
Namely, but non-exhausitvely, the alloys hereafter identified in table 1 by
their UNS, ISO
or AFNOR norms are examples falling into the above described families. The
table
contains, for indicative purpose one of the well-established trade-name of the
alloys.
Well-established commercial name Norm (UNS - ISO - AFNOR)
INCONEL@ alloy 600 UNS N06600
INCONEL@ alloy 601 UNS N06601
INCONEL@ alloy 617 UNS NO6617
INCONEL@ alloy 625 UNS N00625
INCONEL@ alloy 625LCF@ UNS N06626
INCONEL@ alloy 706 UNS N09706
INCONEL@ alloy 718 UNS N07718
INCONEL alloy 7I8SPFTM UNS N07719
INCONEL@ alloy X-750 UNS N07750
INCONEL@ alloy MA754 UNS N07754
INCONEL@ alloy 783 UNS R30783
INCONEL@ alloy HX UNS N06002
NIMONICO alloy 75 UNS N06075
NIMONIC@ alloy 80A UNS N07080
NIMONIC@ alloy 90 UNS N07090
NIMONIC@ alloy 105 ISO NW 3021
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NIMONIC alloy 115 AFNOR NCK 15 AID
NIMONIC alloy 263 UNS N0726
NIMONIC alloy 901 UNS N09901
NIMONIC alloy PEI 1 AFNOR Z 8 NCD 38
NIMONIC alloy PE16 AFNOR NW 11 AC
NIMONIC alloy PK33 AFNOR NC 19 KDU
Waspaloy UNS N07001
INCOLOY alloy 903 UNS N19903
INCOLOY alloy 909 UNS N19909
INCOLOY alloy MA956 UNS S67956
INCOLOY alloy A-286 UNS S66286
UDIMET alloy 188 UNS R30188
UDIMET alloy 500 UNS N07500
UDIMET alloy L-605 UNS R30605
UDIMET alloy 700 SAE AMS 5846
UDIMET alloy D-979 UNS N09979
UDIMET alloy R41 UNS N07041
UDIMARO alloy 250 UNS K92890 /UNS K92940
UDIMAR alloy 300 UNS K93120
MP35N UNS R30035
Table 1: primary list of High temperature performance Superalloys covered by
the
present invention.
Additionally to the previous, the following alloys listed in table 2 and
identified by their
commercial names and detailed chemical compositions are also among the
explicitly
covered materials used for the first "modulus", i.e. the high thermo-
mechanical
solicitation area of the die. The materials listed in table 2 are part of the
Ni-base
Superalloys defined above:
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Denomination Ni Fe Cr Al Co Mo Nb Ti W Y203 Ce Si
NIMONIC alloy
86 65 0 25
0 0 10 0 0 0 0 0,03
NIMONICO alloy
101 48 0 24,2 1,4 19,7 1,5 1 3 0 0
0
UDIMETO alloy
520
56 0 19 2 12 6 0 3 1 0 0
UDIMETO alloy 1,2
720 56 0 16 2,5 14,7 3 0 5 5 0
0
Table 2: Ni-base Superalloys of detailed chemical composition and identified
by their
well-established trade-name.
Additionally to the previous, the following alloy identified by its trade-name
and chemical
composition is also among the explicitly covered materials used for the first
"modulus",
i.e. the high thermo-mechanical solicitation area of the die. The material
presented in
table 3 is part of the Ni-base Superalloys defined above:
Denomination Ni Fe Cr Al Co Mo Nb Ti W Y203 Ce Si
AEREX 350 44,5 0 17 1 25 3 1,1 2,2 2
0 0
Table 3: Chemical composition of Ni-base Superalloy AEREX350
On the other hand, in the area of strong tribological solicitation, i.e.
friction and wear due
to passing alloy being formed, the second modulus of the die which is/are the
insert/s,
i.e. the so-called bearings of inserts 6 and 7 (area of the die where the
extruded profile
takes its final shape) is manufactured of a wear resistant material. Such
material could
be any known wear resistant die material such as a high speed tool steel, a
precipitation
hardened steel or a high alloy hot-worked stee and alloys being obtained by a
standard
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forging process, a spray forming technique or by powder metallurgy technology
or any
of such steel or material types provided with surface hardening through
nitriding or
similar process or by a surface coating technology such as chemical vapour
deposition
(CVD), Plasma assisted/Enhanced chemical vapour deposition (PACVD/PECVD),
Physical vapour deposition (PVD) or other spraying processes (Flame Spray,
Cold
spray/high velocity, Plasma spray, high velocity oxyfuel Spray, etc..)
The selection of a material different from a nickel, iron or cobalt-base
Superalloy
belonging the above described groups for the die inserts is a fundamental
requirement
of the concept of the present invention. This particular combination is
crucial for the
overall performance of the concept since 1) the Superalloy in the die body
parts 2 and 3
has superior high temperature mechanical properties but low tribological wear
properties
while 2) the wear resistant materials in the insert bearing areas 6 and 7 have
superior
tribological wear properties but low high temperature mechanical properties.
Consequently, with the present invention is achieved the best possible fit
between local
material selection and local mechanical and tribological solicitations.
Where the stress is high enough to cause plastic deformation, it's preferable
to
characterise Low-cycle fatigue by the Coffin-Manson relation
AC
= (2N)c
2 f
where:
- /1E!) /2 is the plastic strain amplitude at half life;
- Efi is an empirical constant known as the fatigue ductility coefficient,
the failure strain
for a single reversal;
- 2N is the number of reversals to failure (N cycles);
- c is an empirical constant known as the fatigue ductility exponent.
A FEA (Finite Element Analyse) simulations, realized on the area of the die
which is
thermo-mechanical stressed, demonstrated that the transition bridge to mandrel
have
stress concentration beyond yield limit (these zones are called "hot spots"):
this
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indicates plastic deformation of the material which also has been verified
through
inelastic simulations. The cyclic behaviour and the registered lifetimes of
the extrusion
tools show that plastic tensile and compression strains are present during the
extrusion
process. For this reason, relative to the presence of a plastic strain, it is
proper to adopt
5 the Manson-Coffin relation to discuss the fatigue properties of the die
material and to
benchmark different die solutions.
Fig. 3 shows a linear relationship, on a log-log plot, of plastic strain range
versus cycles
to failure. The diagram permits to benchmark the fatigue behaviour of the most
common tool steels, employed for extrusion dies, with the fatigue properties
of a
10 superalloy. It is clear that the superalloy, on equal terms of plastic
strain applied at
elevated temperature, shows a higher fatigue life than a tool steel. The
results highlight
the superior fatigue resistance of the superalloys and confirm the good
adaptability of
these materials for the realisation of the area of the die with a strong
thermo-
mechanical solicitation
The present invention as defined in the claims is not restricted to the above
two cavity
die example for extruding hollow profiles based die inserts 6 and 7, but may
be one or a
three or more cavity type and also single or more cavity die plate for
extruding solid
profiles.
The invention as defined in the claims is further not restricted to the design
as regards
the interconnection of the die parts and inserts by means of screws as shown
in the
figure and described above, but may be secured to one another or
interconnected by
shrink fit or other connecting means.
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