Patent Application
20100025001
Embodiments herein generally relate to methods for fabricating components using disposable dies. More specifically, embodiments herein generally relate to methods for fabricating gas turbine components, such as blades, nozzles, and shrouds, using integrated disposable core and shell dies having through-rods disposed therein.
Investment casting or the lost-wax process is used for forming complex three dimensional, or 3D, components of a suitable material such as metal.
A turbine blade includes an airfoil integrally joined at its root with a blade platform below which is integrally joined a multilobed supporting dovetail. The airfoil is hollow and includes one or more radial channels extending along the span thereof that commence inside the blade dovetail, which has one or more inlets for receiving pressurized cooling air during operation in the engine.
The airfoil may have various forms of intricate cooling circuits therein for tailoring cooling of the different portions of the opposite pressure and suction sides of the airfoil between the leading and trailing edges thereof and from the root at the platform to the radially outer tip.
In current airfoil designs, complex cooling circuits can include a dedicated channel inside the airfoil along the leading edge for providing internal impingement cooling thereof. A dedicated channel along the thin trailing edge of the airfoil provides dedicated cooling thereof. And, a multi-pass serpentine channel may be disposed in the middle of the airfoil between the leading and trailing edges. The three cooling circuits of the airfoil have corresponding inlets extending through the blade dovetail for separately receiving pressurized cooling air.
The cooling channels inside the airfoil may include local features such as short turbulator ribs or pins for increasing the heat transfer between the heated sidewalls of the airfoil and the internal cooling air. The partitions or bridges which separate the radial channels of the airfoil may include small bypass holes therethrough such as the typical impingement cooling holes extending through the forward bridge of the airfoil for impingement cooling the inside of the leading edge during operation.
Such turbine blades are typically manufactured from high strength, superalloy metal materials in conventional casting processes. In the common investment casting or lost-wax casting process, a precision ceramic core is first manufactured to conform with the intricate cooling passages desired inside the turbine blade. A precision die or mold is also created which defines the precise 3-D external surface of the turbine blade including its airfoil, platform, and integral dovetail.
The ceramic core is assembled inside two die halves, which form a space or void therebetween that defines the resulting metal portions of the blade. Wax is injected into the assembled dies to fill the void and surround the ceramic core encapsulated therein. The two die halves are split apart and removed from the molded wax. The molded wax has the precise configuration of the desired blade and is then coated with a ceramic material to form a surrounding ceramic shell.
The wax is melted and removed from the shell leaving a corresponding void or space between the ceramic shell and the internal ceramic core. Molten metal is then poured into the shell to fill the void therein and again encapsulate the ceramic core contained in the shell.
The molten metal is cooled and solidified, and then the external shell and internal core are suitably removed leaving behind the desired metallic turbine blade in which the internal cooling passages are found.
The cast turbine blade may then undergo subsequent manufacturing processes such as the drilling of suitable rows of film cooling holes through the sidewalls of the airfoil as desired for providing outlets for the internally channeled cooling air which then forms a protective cooling air film or blanket over the external surface of the airfoil during operation in the gas turbine engine.
Gas turbine engine efficiency is increased typically by increasing the temperature of the hot combustion gases generated during operation from which energy is extracted by the turbine blades. The turbine blades are formed of superalloy metals, such as nickel based superalloys, for their enhanced strength at high temperature to increase the durability and useful life of the turbine blades.
The intricate cooling circuits provided inside the airfoils are instrumental in protecting the blades from the hot combustion gases for the desired long life of the blades in an operating turbine engine.
The cooling circuits inside turbine blades are becoming more and more complex and intricate for tailoring the use of the limited pressurized cooling air and maximizing the cooling effectiveness thereof. Any such cooling air bled from the compressor during operation for cooling the turbine blades is not used in the combustion process and correspondingly decreases the overall efficiency of the engine.
Recent developments in improving turbine airfoil cooling include the introduction of double walls therein for enhancing local cooling of the airfoil where desired. The typical airfoil includes main channels such as the dedicated leading edge and trailing edge channels and the multi-pass serpentine channels that provide the primary cooling of the airfoil. These channels are typically defined between the thin pressure and suction sidewalls of the airfoil which may be about 40 to 50 mils (about 1.2 mm) thick.
In introducing double wall construction of the airfoil, a thin internal wall is provided between the main sidewalls of the airfoil and the main channels therein to define auxiliary or secondary channels which are relatively narrow. The secondary wall may include impingement holes therethrough for channeling from the main flow channels impingement cooling air against the inner surface of the main sidewalls.
The introduction of the double wall construction and the narrow secondary flow channels adds to the complexity of the already complex ceramic cores used in typical investment casting of turbine blades. See for example U.S. Pat. Nos. 5,484,258; 5,660,524; 6,126,396; and 6,174,133. Since the ceramic core identically matches the various internal voids in the airfoil which represent the various cooling channels and features thereof, it becomes correspondingly more complex as the cooling circuit increases in complexity.
Each radial channel of the airfoil requires a corresponding radial leg in the ceramic core, and the legs must be suitably interconnected or otherwise supported inside the two dies during the casting process. As the ceramic core legs become thinner, such as for the secondary channels, their strength correspondingly decreases which leads to a reduction in useful yield during the manufacture of the cores that are subject to brittle failure during handling.
Since the ceramic cores are separately manufactured and then assembled inside the two die halves, the relative positioning thereof is subject to corresponding assembly tolerances. The walls of the airfoil are relatively thin to begin with, and the features of the ceramic core are also small and precise. Therefore, the relative position of the ceramic core inside the die halves is subject to assembly tolerances which affect the final dimensions and relative position of the intricate cooling circuit inside the thin walls of the resulting airfoil.
Additionally, current methods for fabricating turbine components typically address only the steps required to make the internal core. See for example U.S. Patent Application 2005/0006047. Such methods still require the use of wax dies, wax injection and/or external ceramic shell coating to form a casting mold for final casting of the component.
Accordingly, there remains a need for simplified methods for fabricating gas turbine components, and in particular airfoils, having complex internal designs.
Embodiments described herein generally relate to methods involving providing an integrated disposable core and shell die of an authentic gas turbine component, inserting at least one through-rod through the integrated disposable core and shell die, casting an integrated core and shell mold inside of the integrated disposable core and shell die, removing the integrated disposable core and shell die to obtain the integrated core and shell casting mold having the at least one through-rod disposed therein, casting an authentic gas turbine component replica using the integrated core and shell casting mold, and removing the integrated core and shell casting mold and the at least one through-rod to obtain the authentic gas turbine component replica.
Embodiments herein also generally relate to methods involving generating a numeric model of an authentic gas turbine component, the numeric model having an outer shell die disposed thereabout, fabricating an integrated disposable core and shell die of the authentic gas turbine component, inserting at least one through-rod through the integrated disposable core and shell die, casting an integrated core and shell mold inside of the integrated disposable core and shell die, removing the integrated disposable core and shell die to obtain the integrated core and shell casting mold having the at least one through-rod disposed therein, casting an authentic gas turbine component replica using the integrated core and shell casting mold, and removing the integrated core and shell casting mold and the at least one through-rod to obtain the authentic gas turbine component replica.
Embodiments herein also generally relate to methods involving providing a numeric model of an authentic airfoil having a plurality of internal channels, the numeric model generated using computer aided design and having an outer shell disposed thereabout, fabricating an integrated disposable core and shell die of the numeric model of the authentic airfoil using an additive layer manufacturing process selected from the group consisting of micro-pen deposition, selective laser sintering, laser wire deposition, fused deposition, ink jet deposition, electron beam melting, laser engineered net shaping, direct metal laser sintering, direct metal deposition and combinations thereof, inserting a plurality of through-rods through the integrated disposable core and shell die, casting an integrated core and shell mold comprising a ceramic slurry inside of the integrated disposable core and shell die, curing the ceramic slurry to produce an integrated core and shell casting mold comprising a solidified ceramic, removing the integrated disposable core and shell die to obtain the integrated core and shell casting mold having the plurality of through-rods disposed therein, casting an authentic airfoil replica using the integrated core and shell casting mold, and removing the integrated core and shell casting mold and the plurality of through-rods to obtain the authentic airfoil replica.
While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the embodiments set forth herein will be better understood from the following description in conjunction with the accompanying figures, in which like reference numerals identify like elements, whether being described in reference to authentic components or models thereof, as set forth herein below.
Embodiments herein generally relate to methods for fabricating gas turbine components using an integrated disposable core and shell die. More particularly, embodiments herein generally relate to methods involving providing an integrated disposable core and shell die of an authentic gas turbine component, inserting at least one through-rod through the integrated disposable core and shell die, casting an integrated core and shell mold inside of the integrated disposable core and shell die having the at least one through-rod therein, removing the integrated disposable core and shell die to obtain the integrated core and shell casting mold, casting an authentic gas turbine component replica using the integrated core and shell casting mold, and removing the integrated core and shell casting mold and the at least one through-rod to obtain the authentic gas turbine component replica.
While embodiments herein may generally describe the fabrication of turbine blades, it will be understood by those skilled in the art that the description should not be limited to such. The present embodiments are applicable to the fabrication of any component having a core, such as but not limited to, turbine blades and portions thereof, turbine nozzles, including vanes and bands, and shrouds.
Turning to the figures,
Blade 10 can be single-walled or multi-walled and have a complex three dimensional, or 3D, configuration as required for its proper use in a gas turbine engine. As mentioned, the airfoil portion of blade 10 may include a substantially hollow interior 21 (indicated in
Turning to
Returning to
As an example, in the embodiment illustrated in
Any suitable SLA material 40, such as a liquid resin, may be contained in a pool, and a laser beam 42 emitted from laser 36 can be used to locally cure material 40 thereby producing a solidified SLA material 41 and creating disposable die 34. Disposable die 34 can be supported on any suitable fixture in the pool and can be built layer by layer as laser beam 42 is precisely guided over the full configuration of die 34 following the dimensions of numeric model 28 stored in computer 26.
If desired, a support material (not shown) comprising a wax or thermoplastic for example, may be deposited concurrently or alternately with the SLA material to provide support to the disposable die during fabrication. Once construction of the disposable die is complete, the supporting material may be removed by melting or dissolution, for example.
Numeric model 28 of blade 10 can be used to create disposable die 34 using SLA machine 32 such that disposable die 34 and authentic blade 10 are virtually identical with the exception of material composition. Blade 10 can be formed from any suitable alloy or superalloy metal as is typical for most gas turbine engine applications while disposable die 34 can be fabricated, for example, from any suitable SLA material 40 capable of being cured by laser 36 to produce solidified SLA material 41. Those skilled in the art will appreciate that the materials used to make disposable die 34 can vary depending on the method of fabrication.
Integrated disposable die 34 can be defined by solidified SLA material 41, for example, and can include a precise external configuration and surfaces for the entire blade as well as the precise internal cooling circuit therein, including any channels and openings desired. As used herein throughout, “integrated” means that the core and shell are coupled together as a unitary structure rather than being independent pieces.
A cross-section of one embodiment of the resulting disposable core and shell die 34 made from solidified SLA material 41 is shown in
Additionally, at least one through-rod 43, and as shown in
The diameter of through-rods 43 can also vary. However, in one embodiment, through-rods 43 can have a diameter ranging from about 0.025 inches to about 0.065 inches (about 0.064 cm to about 0.17 cm), and in one embodiment from about 0.040 inches to about 0.060 inches (about 0.10 cm to about 0.15 cm). Moreover, all through-rods 43 can have the same diameter, different diameters, or each through-rod can have a varying diameter along its length.
Through-rods 43 can be inserted into disposable die 34 by, for example, pushing the through-rods through holes 47 and/or openings 39. As previously mentioned, openings 39 can be included in the disposable die to support airflow in the authentic blade replica. Holes 47 can be drilled into the disposable die post-fabrication using any conventional drilling tool or alternately, holes 47 can be included in the disposable die during fabrication, similar to openings 39. As shown in
As shown in
Disposable core and shell die 34 may then be removed, leaving integrated core and shell casting mold 44 having through-rods 43 disposed therein, as shown in
Accordingly, an authentic gas turbine component replica, which in one embodiment comprises a blade replica, may then be cast within the integrated core and shell mold using conventional investment casting processes. As used herein, “replica” refers to a substantially identical copy of the authentic component made using the methods described herein. Like the authentic component, the replica is capable of installation and use in a gas turbine engine. During casting, molten metal may be poured into integrated mold 44 to fill by gravity the void 45 (shown in
Integrated mold 44 may then be suitably removed from authentic blade replica 48 by breaking or dissolving the generally brittle material of construction. Alternately, if integrated mold 44 is constructed from ceramic, it may be suitably removed from blade replica 48 by chemical leaching. More specifically, in one embodiment, core portion 49, shell portion 50 and through-rods 43 can be removed simultaneously, leaving the authentic blade replica 48, as shown in
In an alternate embodiment, mold shell portion 50 may be removed first, along with any segments of through-rods 43 extending therethrough. Mold shell portion 50 may be removed by any acceptable means, such as mechanical devices. For example, in one embodiment, a hammer may be used to break apart shell portion 50, along with the segments of through-rods 43 contained therein. Once shell portion 50 and through-rod segments 43 contained therein have been removed from authentic blade replica 48 as shown in
The resulting blade replica 48 may then undergo typical post-casting processes, such as drilling rows of cooling holes through the sidewalls thereof, or patching any unneeded holes remaining after removal of the through-rods. The end result is the production of an authentic gas turbine component replica 46, such as authentic blade replica 48 shown in
The previously described methods can reduce the use of a wax die, as well as the corresponding waxing and de-waxing process. This can save both time and expense. Additionally, and as previously mentioned, the integrated core and shell mold can be used to fabricate any number of component designs, including single-wall and multi-wall airfoils, which can often times be too complex for current casting methods. Moreover, the integrated core and shell mold provides the manufacturer with more control in wall thickness which results in the production of more accurately fabricated components. Also, the use of through rods allows a single rod to control multiple wall thicknesses simultaneously. Other benefits will be apparent to those skilled in the art from the previous detailed description.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
