TECHNICAL FIELD
[0001] This invention relates to components for use in casting of engine parts. More particularly,
though not exclusively, it relates to components for use in investment casting of
engine parts such as turbine blades.
BACKGROUND OF THE INVENTION AND PRIOR ART
[0002] Investment casting processes are widely used to create hollow, near net-shape metal
components, e.g. turbine blades, by pouring molten metal into a ceramic mould of the
desired final shape and subsequently removing the ceramic. The process is an evolution
of the lost-wax process, wherein a component of the size and shape required in metal
is manufactured in wax using wax injection moulding, which pattern is then dipped
in ceramic slurry to create a shell; the wax is then removed and the shell fired in
order to harden it. The resulting shell thus has one or more open cavities therewithin
for receiving molten metal when poured inside, the cavities being of the size and
shape required for the final component, e.g. a turbine blade.
[0003] Often engine parts are required to have complex internal cavities for the purpose
of acting as internal cooling channels. To form such internal cavities, at least one,
and often several, ceramic core(s) is/are required in order to define and form the
internal channels during the casting process. The cores are manufactured separately
and placed inside the wax pattern die prior to wax injection. After casting the alloy
the cores are leached out with alkaline solution to leave the hollow metal component.
[0004] During the various stages of the metal casting process, these cores must be located
within the wax injection die and held in clearly defined, stable relative positions
until the metal solidifies around them. This accurate positioning is required
inter alia for producing cast wall sections of accurate thicknesses and with optimum stress
resistance properties. However, the ability to maintain such cores accurately in desired
positions during the casting process is difficult and presents several practical problems.
[0005] Historically one well-used technique for maintaining cores in desired positions during
the casting process has involved the use of platinum pins, e.g. of the order of 1
- 2 mm in diameter, which are passed transversely through the wax pattern prior to
the application of the ceramic shell and thus hold the core in position relative to
one or more neighbouring cores or other components within the die until the metal
is cast. The platinum pins simply dissolve in the cast metal once it is poured and
solidifies, which for many metal alloys destined for turbine blades and other engine
parts is acceptable and does not adversely affect the properties of the resultant
casting.
[0006] Other known proposals for tackling the same problem have included:
- using platinum chaplets to support the core walls, as disclosed for example in GB2281238A;
- forming ceramic "bumpers" on the core which locally touch one or more neighbouring
cores or other components within the die and allow the desired wall section to be
maintained during the casting process, as disclosed for example in US5296308; and
- using a platinum wire woven between and around multiple core passages to maintain
the desired cast wall thickness, as disclosed for example in US4487246.
[0007] However none of these known proposals is wholly satisfactory and they all present
additional problems. For instance:
- the cost of platinum is high, so the use of platinum pins, chaplets and wires, which
all use relatively large amounts of the metal, is generally undesirable;
- the use of chaplets makes locating them accurately in the core body practically difficult;
- it is practically difficult to securely and accurately support a core in a given position
relative to a neighbouring core or other component when the core wall is not generally
parallel to the neighbouring core wall or component surface, as is the case with many
turbine blade geometries, and so the above known techniques at best only have limited
efficacy in ameliorating this particular problem;
- with the use of bumpers, in a single crystal metal casting (as is desirably the case
with high-performance turbine blades) re-crystallisation near the site of the bumpers
can cause problems with localised weaknesses, leading to deleterious lifing issues
with the associated thin bumper wall;
- with the use of a woven platinum wire to hold core sections in place, the physical
process of weaving the wire into the correct holding position is fiddly, difficult
and time-consuming. It also tends not to produce a wall section with enough of a controlled
thickness, since the wire can at best only define the relative positions of the cores
approximately, and the arrangement of the woven wire itself is prone to bending, leading
to positional inaccuracies.
SUMMARY OF THE INVENTION
[0008] It is thus a primary object of the present invention to ameliorate or at least partially
solve at least some of the shortcomings of the above prior art techniques and to provide
a system for the accurate positioning of cores within a die in an investment casting
process which leads to greater accuracy and stability of the cores' positioning and
thus can lead to cast metal walls having improved characteristics.
[0009] Aspects of the present invention relate to a process for investment casting of an
engine part, a support element for use in the casting process, an engine part produced
by the casting process, and an engine including a part made by the process.
[0010] In a first aspect of the present invention there is provided a process for investment
casting of an engine part having at least one internal cavity, substantially as described
in claim 1.
[0011] The support element may comprise a shaped wire, this allows the support element to
be of a different material to the cast component. This is a particular advantage when
the component comprises a superalloy. As it is desirable to match the material of
the element with the casting, there is a significant cost advantage in a wire. Work
hardening in the wire drawing process provides improved strength and permits cheaper
materials to be used for the support elements in alternative to the cast component
material.
[0012] The investment casting process of the invention may be used to cast a wide variety
of engine parts, but it is especially applicable to the casting of high-performance
engine parts such as turbine blades, such as for use in a gas turbine engines e.g.
for aircraft. Such parts, which are often formed from high-performance metal alloys
and required to have a single-crystal metal structure, are desirably formed with metal
walls defining various, often complex, internal cavities for the passage of cooling
air therethrough which have accurately controlled wall thicknesses and geometries.
Thus the invention is especially applicable to the casting of such turbine blades
and other high-performance engine parts.
[0013] In embodiments of the process of the invention the one or more cores whose spatial
positioning is to be maintained in a controlled manner may be selected from any number
and/or shape and/or geometry of one or more cores as may be necessary or desired for
the casting of any given engine part.
[0014] In embodiments the at least one other component of or within the die may be one or
more other cores also being positioned within an overall die within which the part
is to be cast. Alternatively or additionally the at least one other component may
be an element of the die itself, e.g. an internal surface of a die outer shell or
wall. Indeed, in embodiments of the subject process the at least one support element
which characterises the present invention may be utilised to control the relative
spatial positioning of any two or more neighbouring or adjacent walls, surfaces or
elements of or within a die during an investment casting procedure.
[0015] In embodiments of the invention any number of the said support elements may be used
to control the spatial positioning of any number of core members, depending for example
on their physical geometries, the number and geometries of any neighbouring or adjacent
cores or other component(s) of or within the die, and generally the degree to which
appropriate supporting of the relevant core members(s) may be necessary or desirable
for optimum stability and accuracy of positioning during the relevant part(s) of the
investment casting procedure.
[0016] In some embodiments of the invention the at least one support element may preferably
comprise an elongate member configured to include therein at least one loop with opposed
sides.
[0017] In some embodiments the elongate member forming the or the respective support element
may be configured into a looped member comprising a plurality of turns with opposed
sides.
[0018] In some embodiments the elongate member may be configured so as to include a coil,
e.g. a coil having any number of windings, such as from 2 up to about 5 or about 10
(or perhaps even up to about 15 or more) windings. The number of windings may be selected
for example to give the support element any particular desired overall size and/or
strength.
[0019] In some embodiments the coil or other looped member forming the or each support element
may include at least one, optionally a pair of, free end portions, which may usefully
be employed, in addition to the coiled or other looped or turn-containing portion
thereof, for further supporting and/or positioning the respective core in its desired
position relative to the one or more other components. For example one or both of
the free end portions of the support element may be used to grip or attach itself
to a or a respective part of the respective core to be positioned and/or of the respective
other component.
[0020] In some embodiments of the invention the support element comprising the said coil-,
or loop(s)-, or turn(s)-containing elongate member may be oriented, relative to a
wall or surface of the core whose spatial position is to be maintained, with its coil,
loop(s) or turn(s) bearing against the said core wall or surface with its axis of
highest spring constant (i.e. maximum stiffness) generally substantially normal to
the said core wall or surface (at least at or in the vicinity or region of its bearing
thereagainst). Thus, in the case of a supporting element comprising a coil, it may
preferably be oriented with its longitudinal winding axis generally substantially
parallel to the said core wall or surface (at least at or in the vicinity or region
of its bearing thereagainst).
[0021] However, in certain other embodiments the orientation of the coil-, or loop(s)-,
or turn(s)-containing elongate member may be perpendicular to that defined above,
so that its longitudinal winding axis is generally substantially normal to the said
core wall or surface (at least at or in the vicinity or region of its bearing thereagainst),
whereby the support elongate element may act more as a true spring, taking advantage
of its lower spring constant along its longitudinal winding axis.
[0022] In some embodiments the elongate member forming the or the respective support element
may be formed from a length of wire. To form the said coil- or loop- or other turn-containing
support element the wire may be formed into the required shape by any suitable means.
For example it may be wound around a mandrel so as to adopt its desired shape and
configuration. However, other winding apparatuses and techniques may alternatively
so be used.
[0023] In many embodiments the or each elongate member forming the or the respective support
element may usefully be formed of a material, especially a metal, whose residual presence
in the cast engine part is tolerable or does not adversely affect the desired properties
of the cast engine part. Thus, in practical embodiments of the process of the invention
the one or more support elements may remain within the metal of the cast engine part,
preferably by virtue of being dissolved or dispersed therein during the metal pouring
and solidifying step, without any significant deleterious implications therefor.
[0024] Suitably the material used to form the or each support element in embodiments of
the invention may be selected from a metal or metal alloy which is readily deformable
(by virtue of its malleability) but preferably also of medium or low resilience, whereby
it can be configured readily into the requisite form and shape by straightforward
mechanical means, e.g. by manual or mechanical winding. Suitably the material used
to form the support element in embodiments of the invention may be selected from one
or more of: platinum, an alloy of platinum with one or more other metals, a platinum-nickel
alloy, nickel, nickel coated with one or more other metals, and other metals, alloys
or materials currently used for core-positioning components in known investment casting
processes. A particularly preferred material may be platinum metal, e.g. in the form
of platinum wire, such as with a diameter in the range of from about 0.1 to about
1 or 1.5 mm, preferably from about 0.25 to about 1 mm. Examples of suitable platinum
wires are widely commercially available.
[0025] In some embodiments of the process of this first aspect of the invention, at least
one of the respective core member and/or respective other component whose relative
spatial positioning is to be controlled by the turn-containing elongate support element
may include at least one surface formation for location therein of at least part of
the or each said support element, whereby its positioning relative to the said respective
core member and/or respective other component may be facilitated and/or more accurately
assured.
[0026] Such one or more surface formations may take the form, for example, of one or more
recesses, wells, channels or passages formed a short distance (e.g. to a depth of
from about 0.1 or 0.2 or 0.3 up to about 0.5 or 1.0 or 1.5 mm, or perhaps even up
to about 2 or 3 or even 5 mm for larger scaled engine parts) into the outer surface
or wall of the respective core or other component. Although the use of such recessed
or other surface formations may typically result in some small localised increases
in the resulting cast wall thickness at the sites of the surface formations on the
relevant core members, this may generally be acceptable in practice, because such
resultant features in the cast metal wall may be expected not to deleteriously affect
the wall material's resulting physical properties, unlike small localised decreases
in wall thicknesses, which may have the opposite effect.
[0027] In some embodiments such one or more said surface formations may be provided in one
only of the said respective core or other component, preferably at the or each location
or region at which the or respective support element(s) is/are to bear thereagainst
to fulfil its/their supporting function. However, in other embodiments such one or
more said surface formations may be provided in both of the said respective core and
other component, at mutually generally opposite locations or regions thereon at which
the or respective support element(s) is/are to bear thereagainst to fulfil its/their
supporting function.
[0028] The provision and use of the above-defined one or more surface formations may be
useful in certain embodiments not only for assisting optimum positioning of the or
each relevant support element in its respective position on or against the relevant
wall or outer surface of the relevant core to be supported, but also for the purpose
of directing placement of particular ones of a plurality of support elements at correct
ones of different sites or locations around any arrangement of one or more cores.
This may be useful for example where a plurality of differently-configured support
elements are provided each for placement at a specific or unique site or location
on or between given core(s), and so may aid and speed up the task of assembling a
particular overall core assembly within a die ready for investment casting. Colour-coding
of specific support elements and their matching appropriate sites or locations on
the relevant core(s) may further assist this task.
[0029] Embodiments of the invention may be applied to the positioning of one or more cores
with respect to one or more other components of or within the die during any stage
of an overall investment casting operation. For example embodiments of the invention
may be applied in particular to the step of locating and positioning one or more ceramic
cores within a die prior to the pouring of molten metal therein for the actual casting
of the final metal part. Alternatively they may be applied to any earlier stage in
an overall investment casting operation, such as the production of the initial wax
pattern itself, where corresponding usefulness in being able to stably and accurately
position one or more core members relative to one or more other components may also
present itself. In a second aspect of the present invention there is provided a support
element for use in a process according to the first aspect of the invention or any
embodiment thereof.
[0030] Thus in embodiments of this second aspect of the invention there may be provided
a support element for maintaining at least one core member in a desired spatial position
relative to at least one other component of or within a die during at least part of
a process for investment casting of an engine part having at least one internal cavity,
in which the at least one core member defines the or a respective cavity,
[0031] wherein the support element comprises a drawn elongate member configured to include
therein at least one turn with opposed sides, the drawn elongate member being positionable
between the respective core member and respective other component with the opposed
sides of its at least one turn in space-maintaining relationship between the respective
core member and respective other component.
[0032] Optional or preferred features of the support element of embodiments of this second
aspect of the invention may correspond to any of the optional or preferred features
of any embodiment support element defined herein in the context of the first, process,
aspect of the invention.
[0033] In a third aspect of the present invention there is provided an engine part produced
by a process according to the first aspect of the invention or any embodiment thereof.
[0034] In a fourth aspect of the present invention there is provided an engine, such as
a gas turbine engine, including at least one part made by a process according to the
first aspect of the invention or any embodiment thereof.
[0035] Particular or various embodiments of the invention may lead to one or more of any
of the following advantages:
- (i) Known core-supporting elements for use in existing investment casting processes
typically do not lend themselves to maintaining and producing internal cast wall geometries
and thicknesses at optimum required accuracies without compromising the designed wall
geometry or requiring costly additional specialist platinum consumable items, as described
above. Embodiments of the invention address and seek to at least partially ameliorate
at least some such shortcomings. For example:
- (ii) Embodiments of the invention may do away with the need for expensive, specialist-manufactured
items such as platinum chaplets, e.g. as proposed in GB2281238A. This can also lead to reductions in amounts of platinum metal (an expensive precious
metal) used, and in embodiments using platinum wire for making the subject support
element(s), may utilise a commodity which may already be readily available by virtue
of being in use on-site in other contexts in the gas turbine engine industry.
- (iii) Embodiments of the invention may do away with the currently preferred use of
through-going pins (e.g. of platinum) which pass from one side of the pattern to be
cast and keep the core element(s) in their desired spatial position(s). Generally
this known technique only works if the pattern passage to be cast can be accessed
from both sides thereof. This is frequently not the case with complex internal-cavitied
engine parts like high-performance turbine blades, to which embodiments of the invention
may be especially directed.
- (iv) Embodiments of the invention may do away with the need for ceramic "bumpers"
on the core(s), which are designed to locally touch neighbouring core(s) or other
component(s) in order to maintain particular core spatial positioning(s) for creating
particular desired cast wall geometries. However, since by their very nature such
"bumpers" reduce the wall thickness in localised sections, they can lead to undesirable
casting re-crystallisation, and can also act as a localised stress-raiser within the
final cast part, both of which phenomena are undesirable in the production of modern
high-performance engine parts like turbine blades.
- (v) Embodiments of the invention may do away with the need for woven wires around
and between plural core passages, e.g. as proposed in US4487246, for controlling particular cast wall geometries. Such woven wires do not provide
accurate lateral positioning for cores in a linear bundle, as one proposal in US4487246 teaches. Thus embodiments of the present invention may be particularly useful in
areas where enhanced precision of cast wall geometries is required. Moreover the use
of woven wires as taught in US4487246 does not lend itself to the controlled positioning of pluralities of cores in the
casting of engine parts with especially complex arrangements of plural internal cavities,
as is often the case with modern high-performance turbine blades.
[0036] Within the scope of this application it is expressly envisaged that the various aspects,
embodiments, examples and alternatives, and in particular the individual features
thereof, set out in the preceding paragraphs, in the claims and/or in the following
description and drawings, may be taken independently or in any combination. For example
features described in connection with one embodiment are applicable to all embodiments,
unless such features are incompatible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Embodiments of the invention will now be described, by way of example only, with
reference to the accompanying drawings, in which:
Figure 1 is a cross-sectional view of a modern high-performance turbine blade for
use in an aircraft gas turbine engine, showing an arrangement of internal cavities
to be formed by respective ceramic core members during the casting of the blade in
an investment casting process;
Figure 2 is a cross-sectional view of the corresponding arrangement of core members
for use in casting the blade of Figure 1, showing some (though not all, for clarity)
of the core members being held in their desired relative spatial positions using some
examples of specially formed and variously configured support elements in accordance
with certain embodiments of the invention;
Figures 3(a) and (b) are side views of two further examples of specially formed and
configured support elements suitable for use in embodiments of the invention;
Figure 4 is a cross-sectional view, corresponding to that of Figure 2 but omitting
the support elements, of an arrangement of modified core members for use in alternative
embodiments of the invention, in which the core members are provided with surface
formations for assisting, and optionally also directing, placement of the various
support elements in their correct positions and/or locations; and
Figure 5 is a cross-sectional view, corresponding to that of Figure 4, showing some
(though not all, for clarity) of the variously configured support elements in position
at their respective locations.
DETAILED DESCRIPTION OF EMBODIMENTS
[0038] Referring firstly to Figure 1, here there is shown by way of example an arrangement
of complex-shaped internal cavities C within the body of a high-performance turbine
blade B, such as of a gas turbine engine for use in aircraft. The various cavities
C are defined by, and separated by, a network of walls M of cast metal, e.g. of a
high-performance alloy grown as a single crystal during pouring thereof during an
investment casting process. The general principles and stepwise procedures of such
a casting process are well-known and widely commercially used, so need not be described
in detail here. Figure 2 shows the corresponding arrangement of ceramic internal cores
10 which are contained within an outer ceramic shell 2 in a die or mould (not shown)
and ready for a metal-pouring stage of the investment casting procedure, which after
completion of the pouring of the metal and its subsequent solidification results,
after leaching out of the ceramic of the cores 10, the arrangement of cavities of
the blade shown in Figure 1. The various cores 10 may themselves be made, and their
particular general shapes designed and selected, in accordance with known investment
casting principles and techniques, examples of which are already well-known and widely
practised in the art.
[0039] As an important step in the preparation of the arrangement of cores 10 shown in Figure
2 in readiness for the metal-pouring stage, it is important that the various cores
10 are spatially positioned as accurately as possible - both relative to each other
and to the outer shell 2 - and as stably as possible, especially during the metal-pouring
and any subsequent steps. This is so that the resulting metal-cast wall sections defining
the various internal cavities within the blade have defined thicknesses and the cavities
themselves defined geometries which are as accurate and consistent as possible, and
within as narrow ranges of tolerances as possible.
[0040] To achieve and control this desired accurate spatial relative positioning of the
various cores 10, a collection of support elements 20, such as 20a, 20b, 20c, etc,
are employed to define predetermined spacings between particular portions of or sites
on certain of the cores 10 and corresponding portions of or sites on neighbouring
or adjacent cores 10.
[0041] It is to be understood that any number of support elements 20a, 20b, 20c, etc may
be employed, depending for example on the number and arrangement of cores 10 and the
precise portions thereof or sites thereon which need purposive separating and maintaining
at carefully defined distances in order to maintain those cores in the desired mutually
accurately defined spatial positional relationship. However, in Figure 2 only three
such support elements 20a, 20b and 20c are shown for clarity.
[0042] Each support element 20a, 20b, 20c is configured as a looped or coiled length of
wire, e.g. platinum wire (although certain other metal or metal alloy wires may be
suitable instead). The wire may be of any suitable diameter, e.g. in the range of
from about 0.25 to about 1 mm. Such wires are readily commercially available, and
may even already be in use in other contexts in a given industrial site in the field
of aircraft engine manufacture. However it will generally be preferred that the metal
(or metal alloy) of the wire should be one that is compatible with - and not deleteriously
affect the resultant physical properties of - the metal once it has been poured and
solidified to form the required blade walls, since the metal wire support elements
20a, 20b, 20c will ultimately remain in the poured metal and be dissolved thereinto,
as is currently the case with known platinum pins.
[0043] Each support element 20a, 20b, 20c is configured into its required shape for example
by being wound manually or mechanically on an appropriately sized and shaped mandrel.
Other known techniques for forming wound metal coils may alternatively be used.
[0044] Each support element 20a, 20b, 20c is shown here by way of example with a different
shape and configuration, but it is to be understood that any desired shape and configuration
of support elements may be employed, depending for example on the size and shape of
the gap or spacing to be defined thereby and whether the support elements may for
instance be designed to support just two adjacent or neighbouring cores 10, or perhaps
even three (or possibly even more than three) adjacent or neighbouring cores 10, e.g.
at a three-way junction thereof. An example of the latter is the support element 20c
as shown in Figure 2.
[0045] For better clarity, two further examples 20d, 20e of support elements suitable for
use as support elements in accordance with embodiments of the invention are shown
in Figures 3(a) and (b). Here each support element 20d, 20e is configured such that
it comprises a central portion in the form of a coil 22, 24 with an appropriately
selected number of turns or windings. These turns or windings collectively present
two opposed sides 30, 32 of the relevant support element 20d, 20e, which in many preferred
embodiments are those sides of the support element 20d, 20e which serve the primary
locating and spatial positioning function. This primary functionality is shown by
all three support elements 20a, 20b, 20c in Figure 2, where they can been seen to
be supporting and maintaining in a defined spatial relationship the respective cores
10 upon or against which they are mounted or bear to fulfil their supporting and spacing
function.
[0046] However, in the case of the example support element 20e of Figure 3(b), it is configured
to additionally comprise a pair of terminal end portions 40, 42, one or both of which
may serve a secondary locating and spatial positioning function, by virtue of being
configurable so as to grip, grasp or otherwise engage or attach themselves to part
of the relevant core 10. This same secondary functionality is also shown by the terminal
end portions of the support elements 20a and 20b in Figure 2.
[0047] It is to be understood that many other examples of variously shaped and configured
looped or coiled support elements 20 may be designed and utilised within embodiments
of the invention, with those shown in Figures 2 and 3 being just a few illustrative
examples.
[0048] As illustrated in Figure 2, each support element 20a, 20b, 20c is oriented at its
respective location with its longitudinal coil axis generally parallel to the plane
of the respective core outer walls against which it bears at the site of its placement
thereagainst. This means that the maximum spring constant of the coil, which is directed
along any transverse axis perpendicular to the coil's longitudinal winding axis, is
exhibited by the support element in a direction generally substantially normal to
the opposed core walls whose spacing is to be defined and maintained by the respective
support element 20a, 20b, 20c. This therefore makes each coiled support element 20a,
20b, 20c appear relatively "stiff" in the direction in which it is intended to exert
maximum spacing-maintaining force between the relevant cores 10.
[0049] Of course, however, in certain other alternative arrangements any one or more of
the coiled support elements may be oriented oppositely, i.e. with its/their longitudinal
winding axis(es) substantially normal to the relevant core walls. In this manner a
less stiff spacing force may be able to be applied between adjacent cores, which may
for example be useful if the invention is being applied for example to the spatial
positioning of cores against portions of a wax pattern e.g. earlier in an overall
investment casting process.
[0050] Turning to Figures 4 and 5 (in which features which correspond to those of the embodiments
of Figure 2 are indicated with the same reference numerals but incremented by 100),
here there is shown a modified embodiment in which some 110a of the cores 110 of any
adjacent or neighbouring pair whose relative spatial positioning is to be controlled
by the relevant coiled support elements 120f, 120g, 120h each has formed in its outer
wall or surface a respective well, recess, channel or passage 180 for seating and
location therein of the respective support element 120f, 120g, 120h, or at least a
portion thereof, e.g. the central coiled portion thereof only, or possibly one of
the terminal end portions thereof only. As shown in Figure 4, it may be desirable
or appropriate that the wells, recesses, channels or passages 180 are formed in the
walls of only some 110a (and not all) of the cores 100, for example in only those
cores 110a which are intended to have a relevant support element 120f, 120g, 120h
applied thereto.
[0051] Each respective well, recess, channel or passage 180 may be dimensioned appropriately
to accommodate and securely seat and/or retain therein the relevant portion of the
respective support element 120f, 120g, 120h, for example by having a depth in the
range of about 0.1, 0.2 or 0.3 up to about 0.5, 1.0, 1.5, or even up to about 2 or
3 mm. The wells, recesses, channels or passages 180 may be formed by appropriate provision
of correspondingly shaped and positioned surface formations in or on the original
patterns from which the relevant cores 110a were formed in an earlier stage of the
overall investment casting operation.
[0052] Where such wells, recesses, channels or passages 180 are provided in two facing walls
of adjacent or neighbouring cores 110a, if desired or necessary their relative lateral
positioning with respect to each other in the general planes of the respective core
walls may be tailored to take account of any laterally offset relative positioning
of the relevant portions of the respective support elements 120f, 120g, 120h which
are to be accommodated in them.
[0053] Although the use of such wells, recesses, channels or passages 180 may typically
result in some small localised increases in the resulting cast wall thickness at the
sites thereof, in general this can be expected not to be a problem in practical terms,
because such resultant features in the resulting cast metal wall may be expected not
to deleteriously affect the wall material's resulting physical properties, unlike
small localised decreases in wall thicknesses, which may have the opposite effect.
[0054] The provision of the various wells, recesses, channels or passages 180 in the walls
of the cores 110a may be particularly useful not only for assisting optimum positioning
of each of the support elements 120f, 120g, 120h in its respective position on or
against the relevant core 110a, but also for the purpose of directing placement of
particular ones of the support elements 120f, 120g, 120h at the correct sites at which
they are designed to fit and be mounted. Colour-coding of respective support elements
relative to their respective intended core well, recess, channel or passage can usefully
assist this task. This may be particularly useful in cases where a potentially large
number of differently sized, shaped and configured support elements 120 may be provided
for assembling into a required die of a complex arrangement of, and/or a large number
of, core members 110, and differently-configured support elements need to be placed
at predetermined unique locations on the various cores.
[0055] Embodiments of the invention may be put into practice in the positioning of one or
more cores with respect to one or more other components of or within a die during
any stage of an overall investment casting operation. Many embodiments, such as those
described above in conjunction with the accompanying drawings, may be applied in particular
to the step of locating and positioning one or more ceramic cores within a die prior
to the pouring of molten metal therein for the actual casting of a final metal part.
Alternatively certain other embodiments may be applied to any earlier stage in an
overall investment casting operation, such as the production of the initial wax pattern
itself, where corresponding usefulness in being able to stably and accurately position
one or more core members relative to one or more other components may also present
itself. In such a case, the subject looped or coiled support elements could be used
to replace plastic chaplets in the wax, which may then remove the need to use P-pins,
as currently, to locate the cores in the relevant die. In this case the orientation
of the looped or coiled support elements between the adjacent or neighbouring cores
with their longitudinal winding axis normal to the core wall, i.e. so that the support
elements are used more like a conventional spring by loading the coil through the
axis of lowest spring constant, may be more appropriate. Other possibilities for implementation
of embodiments of the invention may also be envisaged in various other stages of an
overall investment casting procedure.
[0056] It is to be understood that the above description of embodiments and aspects of the
invention has been by way of non-limiting examples only, and various modifications
may be made from what has been specifically described and illustrated whilst remaining
within the scope of the invention as defined in the appended claims.
[0057] Throughout the description and claims of this specification, the words "comprise"
and "contain" and variations of the words, for example "comprising" and "comprises",
mean "including but not limited to", and are not intended to (and do not) exclude
other moieties, additives, components, integers or steps.
[0058] Throughout the description and claims of this specification, the singular encompasses
the plural unless the context otherwise requires. In particular, where the indefinite
article is used, the specification is to be understood as contemplating plurality
as well as singularity, unless the context requires otherwise.
[0059] Furthermore, features, integers, components, elements, characteristics or properties
described in conjunction with a particular aspect, embodiment or example of the invention
are to be understood to be applicable to any other aspect, embodiment or example described
herein, unless incompatible therewith.
1. A process for investment casting of an engine part (B) having at least one internal
cavity (C), in which at least one core member (10) defining the or a respective cavity
(C) is maintained in a desired spatial position relative to at least one other component
(10, 2) of or within a die during at least part of the casting procedure, the at least
one core member (10) being maintained in the desired spatial position by at least
one support element (20) which comprises a different material to that from which the
engine part (B) is to be cast,
characterised in that the or each support element (20) comprises a drawn elongate member configured to
include therein at least one turn (22, 24) with opposed sides (30, 32), the elongate
member being positioned between the respective core member (10) and respective other
component (10, 2) with the opposed sides of its at least one turn (22, 24) in space-maintaining
relationship between the respective core member (10) and respective other component
(10, 2).
2. A process as claimed in claim 1 wherein the support element comprises a wire.
3. A process according to claim 1 or claim 2 wherein the support element (20) is oriented,
relative to a wall or surface of the core (10) whose spatial position is to be maintained,
with its at least one turn (22, 24) bearing against the said core wall or surface
either:
(i) with its axis of highest spring constant generally substantially normal to the
said core wall or surface, at least at or in the vicinity or region of its bearing
thereagainst; or
(ii) perpendicular to that defined in (i) above, whereby its longitudinal winding
axis is generally substantially normal to the said core wall or surface, at least
at or in the vicinity or region of its bearing thereagainst.
4. A process according to any of Claims 1 to 3, wherein the engine part (B) is a turbine
blade for a gas turbine engine.
5. A process according any of Claims 1 to 4, wherein the at least one other component
(10, 2) of or within the die (2) is selected from:
(i) one or more other cores (10) also being positioned within an overall die within
which the part (B) is to be cast; and/or
(ii) an element (2) of the die itself.
6. A process according to any preceding Claim, wherein the drawn elongate member is configured
so as to include a coil (22, 24) having a plurality of windings.
7. A process according to any preceding Claim, wherein the drawn elongate member forming
the support element (20) includes at least one free end portion (40, 42) for further
supporting and/or positioning the respective core (10) in its desired position relative
to the one or more other components (10, 2).
8. A process according to any preceding claim, wherein the or each drawn elongate member
forming the or the respective support element (20) is formed of a material whose residual
presence in the cast engine part (B) is tolerable or does not adversely affect the
desired properties of the cast engine part (B), and
the material used to form the support element (20) is selected from one or more of:
platinum, an alloy of platinum with one or more other metals, a platinum-nickel alloy,
nickel, nickel coated with one or more other metals.
9. A process according to any preceding Claim, wherein at least one of the respective
core member (10) and/or respective other component (10, 2) whose relative spatial
positioning is to be controlled by the turn-containing elongate support element (20)
includes at least one surface formation (180) for location therein of at least part
of the or each said support element (20), whereby its positioning relative to the
said respective core member (10) and/or respective other component (10, 2) may be
facilitated and/or more accurately assured.
10. A process according to Claim 9, wherein:
(i) the said one or more said surface formations (180) is/are provided in one only
of the said respective core (10) or other component (10, 2), at the or each location
or region at which the or respective support element(s) (10) is/are to bear thereagainst
to fulfil its/their supporting function; or
(ii) the said one or more said surface formations (180) is/are provided in both of
the said respective core (10) and other component (10, 2), at mutually opposite locations
or regions thereon at which the or respective support element(s) (20) is/are to bear
thereagainst to fulfil its/their supporting function.
1. Verfahren zum Feingießen eines Triebwerksteils (B), das mindestens einen inneren Hohlraum
(C) aufweist, bei dem mindestens ein Kernelement (10), das den oder einen jeweiligen
Hohlraum (C) definiert, in einer gewünschten räumlichen Position relativ zu mindestens
einer anderen Komponente (10, 2) von oder innerhalb einer Matrize während mindestens
eines Teils des Gießvorgangs gehalten wird, wobei das mindestens eine Kernelement
(10) in der gewünschten räumlichen Position durch mindestens ein Stützelement (20)
gehalten wird, das ein anderes Material umfasst als das, aus dem das Triebwerksteil
(B) gegossen werden soll,
dadurch gekennzeichnet, dass das oder jedes Stützelement (20) ein gezogenes längliches Element umfasst, das konfiguriert
ist, um darin mindestens eine Windung (22, 24) mit gegenüberliegenden Seiten (30,
32) zu umfassen, wobei das längliche Element zwischen dem jeweiligen Kernelement (10)
und der jeweiligen anderen Komponente (10, 2) mit den gegenüberliegenden Seiten seiner
mindestens einen Windung (22, 24) in raumerhaltender Beziehung zwischen dem jeweiligen
Kernelement (10) und der jeweiligen anderen Komponente (10, 2) positioniert ist.
2. Verfahren nach Anspruch 1, wobei das Stützelement einen Draht umfasst.
3. Verfahren nach Anspruch 1 oder Anspruch 2, wobei das Stützelement (20) relativ zu
einer Wand oder Oberfläche des Kerns (10), dessen räumliche Position gehalten werden
soll, mit seiner mindestens einen Windung (22, 24) an der Kernwand oder -oberfläche
anliegend ausgerichtet ist entweder:
(i) mit seiner Achse der höchsten Federkonstante im Allgemeinen im Wesentlichen normal
zur Kernwand oder -oberfläche zumindest an oder in der Nähe oder im Bereich seiner
Anlage an dieser; oder
(ii) senkrecht zu der in (i) oben definierten, wobei seine Längswindungsachse im Allgemeinen
im Wesentlichen normal zu der Kernwand oder -oberfläche zumindest an oder in der Nähe
oder im Bereich seiner Anlage an dieser ist.
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei das Triebwerksteil (B) eine Turbinenschaufel
für ein Gasturbinentriebwerk ist.
5. Verfahren nach einem der Ansprüche 1 bis 4, wobei die mindestens eine andere Komponente
(10, 2) von oder innerhalb der Matrize (2) ausgewählt ist aus:
(i) einem oder mehreren anderen Kernen (10), die ebenfalls innerhalb einer Gesamtmatrize
positioniert sind, innerhalb welcher das Teil (B) gegossen werden soll; und/oder
(ii) einem Element (2) der Matrize selbst.
6. Verfahren nach einem der vorhergehenden Ansprüche, wobei das gezogene längliche Element
konfiguriert ist, um eine Spule (22, 24) zu umfassen, die mehrere Windungen aufweist.
7. Verfahren nach einem der vorhergehenden Ansprüche, wobei das gezogene längliche Element,
das das Stützelement (20) bildet, mindestens einen freien Endabschnitt (40, 42) zum
weiteren Stützen und/oder Positionieren des jeweiligen Kerns (10) in seiner gewünschten
Position relativ zu der einen oder den mehreren anderen Komponenten (10, 2) umfasst.
8. Verfahren nach einem der vorhergehenden Ansprüche, wobei das oder jedes gezogene längliche
Element, das das oder das jeweilige Stützelement (20) bildet, aus einem Material gebildet
ist, dessen verbleibendes Vorhandensein im gegossenen Triebwerksteil (B) tolerierbar
ist oder die gewünschten Eigenschaften des gegossenen Triebwerksteils (B) nicht nachteilig
beeinflusst, und
das zum Bilden des Stützelements (20) verwendete Material ausgewählt ist aus einem
oder mehreren von: Platin, einer Platinlegierung mit einem oder mehreren anderen Metallen,
einer Platin-Nickel-Legierung, Nickel, Nickel, das mit einem oder mehreren anderen
Metallen beschichtet ist.
9. Verfahren nach einem der vorhergehenden Ansprüche, wobei mindestens eines von dem
jeweiligen Kernelement (10) und/oder der jeweiligen anderen Komponente (10, 2), dessen
relative räumliche Positionierung durch das windungshaltige längliche Stützelement
(20) gesteuert werden soll, mindestens eine Oberflächengestaltung (180) zur Anordnung
darin von mindestens einem Teil des oder jedes der Stützelemente (20) umfasst, wobei
seine Positionierung relativ zu dem jeweiligen Kernelement (10) und/oder der jeweiligen
anderen Komponente (10, 2) erleichtert und/oder genauer sichergestellt werden kann.
10. Verfahren nach Anspruch 9, wobei:
(i) die eine oder die mehreren Oberflächengestaltungen (180) in nur einem von dem
jeweiligen Kern (10) oder der anderen Komponente (10, 2) an der oder jeder Stelle
oder dem oder jedem Bereich bereitgestellt ist/sind, an der oder dem das oder jeweilige
Stützelement(e) (10) anliegen soll(en), um seine/ihre unterstützende Funktion zu erfüllen;
oder
(ii) die eine oder mehreren Oberflächengestaltungen (180) sowohl in dem jeweiligen
Kern (10) als auch in der anderen Komponente (10, 2) aneinander gegenüberliegenden
Stellen oder Bereichen darauf bereitgestellt ist/sind, an denen das oder jeweilige
Stützelement(e) (20) anliegen soll(en), um seine/ihre unterstützende Funktion zu erfüllen.
1. Procédé permettant la coulée à modèle perdu d'une pièce de moteur (B) possédant au
moins une cavité interne (C), dans lequel au moins un élément de noyau (10) définissant
la ou une cavité respective (C) est maintenu dans une position spatiale souhaitée
par rapport à au moins un autre composant (10, 2) d'une matrice ou à l'intérieur de
celle-ci durant au moins une partie de la procédure de coulée, l'au moins un élément
de noyau (10) étant maintenu dans la position spatiale souhaitée par au moins un élément
de support (20) qui comprend un matériau différent de celui à partir duquel la pièce
de moteur (B) doit être coulée,
caractérisé en ce que le ou chaque élément de support (20) comprend un élément allongé étiré configuré
pour comprendre dans celui-ci au moins une spire (22, 24) avec des côtés opposés (30,
32), l'élément allongé étant positionné entre l'élément de noyau respectif (10) et
l'autre composant respectif (10, 2) avec les côtés opposés de sa au moins une spire
(22, 24) dans une relation de maintien d'espace entre l'élément de noyau respectif
(10) et l'autre composant respectif (10, 2).
2. Procédé selon la revendication 1, ledit élément de support comprenant un fil métallique.
3. Procédé selon la revendication 1 ou 2, ledit élément de support (20) étant orienté,
par rapport à une paroi ou une surface du noyau (10) dont la position spatiale doit
être maintenue, avec sa au moins une spire (22, 24) en appui contre ladite paroi ou
surface de noyau soit :
(i) avec son axe de constante d'élasticité la plus élevée généralement sensiblement
normal à ladite paroi ou surface de noyau, au moins au niveau de son appui contre
celle-ci ou au voisinage ou dans la région de celle-ci ; soit
(ii) perpendiculaire à celle définie en (i) ci-dessus, grâce à quoi son axe d'enroulement
longitudinal est généralement sensiblement normal à ladite paroi ou surface de noyau,
au moins au niveau ou au voisinage ou dans la région de son appui contre celle-ci.
4. Procédé selon l'une quelconque des revendications 1 à 3, ladite pièce de moteur (B)
étant une aube de turbine pour un moteur à turbine à gaz.
5. Procédé selon l'une quelconque des revendications 1 à 4, ledit au moins un autre composant
(10, 2) de la matrice (2) ou à l'intérieur de celle-ci étant choisi parmi :
(i) un ou plusieurs autres noyaux (10) également positionnés à l'intérieur d'une matrice
globale à l'intérieur de laquelle la pièce (B) doit être coulée ; et/ou
(ii) un élément (2) de la matrice elle-même.
6. Procédé selon l'une quelconque des revendications précédentes, ledit élément allongé
étiré étant conçu de façon à comprendre une bobine (22, 24) possédant une pluralité
d'enroulements.
7. Procédé selon l'une quelconque des revendications précédentes, ledit élément allongé
étiré formant l'élément de support (20) comprenant au moins une partie d'extrémité
libre (40, 42) pour supporter et/ou positionner davantage le noyau respectif (10)
dans sa position souhaitée par rapport à l'autre ou aux autres composants (10, 2).
8. Procédé selon l'une quelconque des revendications précédentes, ledit ou chaque élément
allongé étiré formant le ou l'élément de support respectif (20) étant formé d'un matériau
dont la présence résiduelle dans la pièce de moteur coulée (B) est tolérable ou n'affecte
pas négativement les propriétés souhaitées de la pièce de moteur coulée (B), et
ledit matériau utilisé pour former l'élément de support (20) étant choisi parmi un
ou plusieurs parmi : le platine, un alliage de platine avec un ou plusieurs autres
métaux, un alliage platine-nickel, le nickel, le nickel revêtu d'un ou plusieurs autres
métaux.
9. Procédé selon l'une quelconque des revendications précédentes, au moins l'un de l'élément
de noyau respectif (10) et/ou de l'autre composant respectif (10, 2) dont le positionnement
spatial relatif doit être commandé par l'élément de support allongé contenant la spire
(20) comprenant au moins une formation de surface (180) pour le placement dans celle-ci
d'au moins une partie dudit ou de chaque élément de support (20), grâce à quoi son
positionnement par rapport audit élément de noyau respectif (10) et/ou à l'autre composant
respectif (10, 2) peut être facilité et/ou plus précisément assuré.
10. Procédé selon la revendication 9,
(i) ladite ou lesdites formations de surface (180) étant disposée(s) dans un seul
dudit noyaux respectif (10) ou dudit autre composant (10, 2), au niveau du ou de chaque
emplacement ou région au niveau duquel le ou les élément(s) de support respectif(s)
(10) doit/doivent s'appuyer contre celles-ci pour remplir sa/leur fonction de support
; ou
(ii) ladite ou lesdites formations de surface (180) étant disposée(s) à la fois dans
ledit noyau respectif (10) et dans ledit autre composant (10, 2), au niveau des emplacements
ou régions mutuellement opposés sur celui-ci au niveau desquels le ou les élément(s)
de support respectif(s) (20) doit/doivent s'appuyer contre celles-ci pour remplir
sa/leur fonction de support.