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Designated Contracting States: |
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AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR |
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Designated Extension States: |
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AL LT LV MK |
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Priority: |
25.04.2002 US 131137
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(71) |
Applicant: GENERAL ELECTRIC COMPANY |
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Schenectady, NY 12345 (US) |
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(72) |
Inventors: |
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- Devine, Robert H.
Houston,
Texas 77346 (US)
- Placko, James M.
Schenectady,
New York 12345 (US)
- Downs, Justin W.
Schenectady,
New York 12345 (US)
- Schaeffer, Jon C.
Schenectady,
New York 12345 (US)
- Peterson, Lance G.
Schenectady,
New York 12345 (US)
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(74) |
Representative: Pedder, James Cuthbert |
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GE London Patent Operation,
Essex House,
12/13 Essex Street London WC2R 3AA London WC2R 3AA (GB) |
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[0001] The invention relates to a new way to manufacture inserts for steam cooled hot gas
path components.
[0002] Inserts are required in air and steam cooled nozzles to provide impingement cooling
to airfoil walls and ribs. The prior art methods of production of inserts use sheet
metal forming operations, including welding and brazing, and electro discharge machining
of the holes. The problem with the prior art methods is that the large complicated
inserts combined with strict dimensional tolerances result in 3D structures that have
a very low yield relative to design specifications.
[0003] The inventive process casts the inserts to tight tolerance using any ceramic core
casting process such as, for example, pressure casting, centrifugal casting, squeeze
casting or vacuum casting (also known as counter gravity casting). Counter gravity
casting as employed by Hitchiner Manufacturing Co., Inc. of Milford, New Hampshire
uses metal dies with a vacuum pour to help fill thin sections of the casting and eliminate
porosity. After casting has been completed, the core material is then used as a backer
during subsequent drilling operations. Finally, the core is removed by acid leaching
and the cast parts are machined, if necessary, to finish specifications.
[0004] With the inventive manufacturing method certain commercial and performance needs
are met. For example, the inventive method facilitates the production of complicated
3D insert geometrics in a Ni-base superalloy with thin walls and tight tolerances.
The inventive method also provides for accurate and precise drilling of the cast inserts
with improved processing times and fixtures.
[0005] The inventive method also solves the problems in the prior art by using the ceramic
core in the insert casting process to act as a backer for laser drilling. The laser
holes then facilitate the use of leachant to quickly remove the core, speeding the
manufacturing process.
[0006] The invention will now be described in greater detail, by way of example, with reference
to the drawings, in which:-
Figure 1 show a cast insert prior to laser drilling of the insert holes;
Figure 2 shows the case insert of Figure 1 after laser drilling of the insert holes
but with the ceramic core still in place; and
Figure 3 shows the cast and drilled insert immersed in an acid bath for removal of
the ceramic core.
[0007] The inventive method uses, for example, Hitchiner's thin wall casting process to
produce the insert geometry from a wax model. The Hitchiner process substitutes counter
gravity casting for more conventional casting by, for example, gravity pouring.
[0008] In the basic investment casting process, wax replicas of the desired castings are
produced by injection molding. Depending on the size of the castings, multiple wax
replicas may be attached to a central waxed stick, termed a sprue, to thereby form
a casting assembly. Thereafter, a ceramic shell is formed around the casting or the
casting assembly made up of the multiple wax replicas of the desired castings. Next,
the ceramic is dried and the wax is melted out creating a negative impression of the
casting assembly within the ceramic shell.
[0009] If using the basic casting process, the casting shell is filled with molten metal
by gravity pouring. Conversely, in the Hitchiner counter gravity process the ceramic
casting shell is placed within a vacuum and dipped into a hot metal melt which is
then siphoned up around and into the ceramic casting assembly. After the metal is
allowed to solidify on the ceramic casting the vacuum is released and residual metal
flows back in to the melt. Figure 1 schematically shows a cast insert 10 with ceramic
core 12 shown in place by dotted lines. Also shown is laser drilling apparatus 14
prior to the drilling process.
[0010] Preferably, the cast inserts are made from IN625 (Ni-base superalloy). After the
insert are cast into the desired geometry, the ceramic core is not immediately leached
out. Instead the casting is put in a fixture for laser drilling holes with the ceramic
core still in place. The casting tolerances are such that a fixture can handle a production
run without a lot of rework.
[0011] The insert is then laser drilled with the ceramic core as a backer. The backer stops
backwall strikes and will act as a breakthrough detector. Figure 2 schematically shows
insert 10 after holes 16 have been drilled by laser drilling apparatus 14.
[0012] After the large number of holes (∼300 holes/insert) are drilled with laser precision,
the ceramic core is leached out with suitable caustics. Figure 3 schematically shows
ceramic 12 being removed by immersing cast insert 10 in acid bath 18.
[0013] Another advantage of the inventive method is the reduction in the number of heat
treatments that the part goes through relative to current state of the art processing.
Reducing heat treatments reduces the amount of distortion caused by residual stresses
and results in higher quality. The invention will produce inserts and baffles for
hot gas path hardware at a greater level of performance and yield.
[0014] While the invention has been described in connection with what is presently considered
to be the most practical and preferred embodiment, it is to be understood that the
invention is not to be limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
1. A method of forming inserts (10) for steam cooled hot gas path components in a turbine,
said method comprising:
casting the geometrical configuration of the insert(10); and
laser drilling impingement holes (16) in the cast insert (10) without removing a ceramic
casting core (12) of the cast insert (10).
2. A method as claimed in claim 1, wherein the ceramic casting core (12) is removed by
leachant.
3. A method as claimed in claim 1 or 2, wherein said casting (12) comprises pressure
casting.
4. A method as claimed in claim 1 or 2, wherein said casting (12) comprises centrifugal
casting.
5. A method as claimed in claim 1 or 2, wherein said casting (12) comprises squeeze casting.
6. A method as claimed in claim 1 or 2, wherein said casting (12) comprises counter gravity
casting.
7. A method as claimed in any preceding claim 1 or 2, wherein the inserts (10) are made
of a Ni-base superalloy.