Patent Application
20130047692
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 U.S. Pat. No. 0,416,9366 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.
U.S. Pat. No. 0,477,3251 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 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.
With the present invention 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 sever 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.
The invention is characterized by the features as defined in the enclosed independent claim 1.
Advantageous embodiments of the invention are further defined in the dependent claims 2-7
The invention will be further described in the following by way of example and with reference to the drawings, where:
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
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 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 5%)
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.
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 γ′ in the case of Nickel-based Superalloys and carbides in the case of 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(Al,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 (γ′). 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.
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.
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:
indicates data missing or illegible when filed
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:
indicates data missing or illegible when filed
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 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
where:
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 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 the Manson-Coffin relation to discuss the fatigue properties of the die material and to benchmark different die solutions.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20100218 | Feb 2010 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO2011/000050 | 2/9/2011 | WO | 00 | 10/1/2012 |
