Embodiments described herein generally relate to methods for making a turbine blade. More particularly, embodiments described herein generally relate to methods for making a turbine blade using investment casting to make a net shape, complex internal skeleton, followed by the application of an outer wall to create a near wall circuit and complete the turbine blade.
Cast turbine airfoils for advanced gas turbine engines have internal features that can challenge the capability of current casting technologies. The castings require complex ceramic cores to form the internal features and those cores are fragile during the casting process. The result is that casting yields of 50 percent to 70 percent are not uncommon. The 30 percent to 50 percent casting scrap factors into the cost of the useable castings. The issue is compounded by exotic alloys, such as single crystal materials, that can drive up the cost to cast a part, and thus drive up the cost caused by scrapping hardware.
Investment casting results in a blade having internal and external portions fabricated from the same materials. Similarly, because diffusion processes are used to apply environmental coatings to the blade, it is common for internal and external portions of the blade to comprise the same coatings. Such processes do not allow for the manufacturing or coating of internal portion of the blade independently of the external portion.
Accordingly, there remains a need for improved methods for making turbine blades having complex and efficient cooling schemes that can avoid the previously discussed issues.
Embodiments herein generally relate to methods for making a turbine blade comprising: casting an internal skeleton comprising a plurality of internal ribs which form a plurality of open cooling channels; applying a filler material to the open cooling channels; and applying an outer wall about the internal skeleton having the filler material applied to the open cooling channels.
Embodiments herein also generally relate to methods for making a turbine blade comprising: casting an internal skeleton comprising a superalloy and including: more than one closed cooling channel; and a plurality of internal ribs which form a plurality of open cooling channels; drilling cross-over holes between the open cooling channels and closed cooling channels; applying a filler material to the open cooling channels; and applying an outer wall about the internal skeleton having the filler material applied to the open cooling channels.
Embodiments herein also generally relate to methods for making a turbine blade comprising: casting an internal skeleton comprising a superalloy and including: more than one closed cooling channel; and a plurality of internal ribs which form a plurality of open cooling channels; drilling cross-over holes between the open cooling channels and closed cooling channels; applying an internal environmental coating to the internal skeleton; applying a filler material to the open cooling channels; applying an outer wall about the internal skeleton having the filler material applied to the open cooling channels; and removing the filler material to produce a finished turbine blade.
These and other features, aspects and advantages will become evident to those skilled in the art from the following disclosure.
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.
Embodiments described herein generally relate to methods for making turbine blades. More particularly, embodiments described herein generally relate to methods for making a turbine blade using investment casting to make a net shape, complex internal skeleton, followed by the application of an outer wall to create a near wall circuit and complete the turbine blade.
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
First and second sidewalls 44 and 46, respectively, extend longitudinally or radially outward to span from a blade root 52 positioned adjacent to dovetail 43 to a top plate 54, which defines a radially outer boundary of a cooling circuit 56. Cooling circuit 56 is defined within airfoil 42 between sidewalls 44 and 46, and is known in the art. In the exemplary embodiment, cooling circuit 56 includes a serpentine passage 58, as shown in
In the embodiments herein, investment casting can be used to make a net shape, complex internal skeleton defining open cooling channels, and optionally additional closed cooling channels. The open cooling channels may then be filled with a filler material and an outer wall applied to close the open cooling channels, as set forth below.
Initially, an internal skeleton 60 as shown in
Optionally, following investment casting of internal ribs 64 of internal skeleton 60, a plurality of cross-over holes 70 between open cooling channels 62 and closed cooling channels 68, can be drilled using conventional drilling methods if desired, as shown in
Internal skeleton 60 can then be optionally coated using any suitable environmental coating material to produce an internal environmental coating 72 on skeleton 60 prior to further processing. An example of a suitable internal environmental coating acceptable for use herein can include, but should not be limited to, diffusion aluminide. The application of internal environmental coating 72 at this point in the process can allow the internal coating to be tailored for optimum blade performance and not limited to the same coating applied to the exterior of the finished blade, as is done currently.
Open cooling channels 62 can be filled with a filler material 74 in preparation of applying the outer wall, as shown in
With the cooling channels filled with filler material 74, outer wall 76 can be applied about internal skeleton 60, including open cooling channels 62 having filler material 74, as shown in
Outer wall 76 can comprise any of a number of materials suitable for use in turbine blade construction, such as the previously set forth nickel-based superalloys. Such materials can be selected to help optimize blade design. For example, in one embodiment, outer wall 76 may comprise a material such as Rene 195, which can provide environmental resistance to the blade. This could allow for a higher strength, lower environmentally resistant material to be used to fabricate the internal skeleton to allow the skeleton to carry the blade loads, but prevent the cost associated with having to apply a separate exterior environmental coating to the finished blade. In another embodiment, outer wall 76 may comprise a material having a lower coefficient of thermal expansion than the material used to make internal skeleton 60 in order to reduce thermal stresses due to through thickness temperature gradients. Outer wall 76 may comprise the same, or different, material from that used to fabricate internal skeleton 60.
After outer wall is applied, filler material can be removed using any suitable technique as described previously, leaving finished blade 130 having a near wall circuit 66 comprising the formerly open cooling channels 62 and optional closed cooling channels 68, as shown in
The methods described herein can offer advantages in turbine blade manufacturing. Using the presently described process can allow for two different cooling circuits; the inner cooling circuit, and the near wall circuit defined by the cooling channels and the outer wall. Additionally, the present embodiments can eliminate the use of complex cores in making the near wall circuit, which can result in higher casting yields due to lower core related defects, such as core slip. Moreover, by applying the outer wall as a separate component in the blade fabrication process, it can allow the cooling channels of the near wall circuit to have features as fine as those allowed by conventional investment casting processes (but without the use of cores), as well as a greater degree of freedom in placement. Cross-over holes between the cooling channels and the inner cooling circuit can be drilled that are not possible with conventional casting practices. Such cross-over holes can allow for complex impingement cooling in the near wall circuit, thus further increasing cooling efficiency. Materials used to fabricate the internal skeleton can be selected independently of the materials used to fabricate the outer wall, as can internal environmental coatings be selected independently of external environmental coatings, thereby allowing tailoring of the materials and coatings to optimize blade performance.
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.
This application claims priority to U.S. Provisional Application Ser. No. 61/287,870, filed Dec. 18, 2009, which is herein incorporated by reference in its entirety.
Number | Date | Country | |
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61287870 | Dec 2009 | US |