Abstract:
A casting includes a wall thickness check feature for measuring thickness of a wall second aside an in-wall cooling passageway. The thickness is determined by observing the existence and/or size of an opening formed by the feature. The casting is cast from a pattern including portions forming the feature. To manufacture the pattern, a pattern-forming die is assembled with a ceramic feedcore and a refractory metal core (RMC). The assembling leaves an inlet portion of the RMC engaged to the ceramic feedcore and leaves an outlet portion of the RMC engaged to the die. A pattern-forming material is molded in the die at least partially over the ceramic feedcore and RMC. The die is disengaged from the pattern-forming material. The assembling engages a stepped projection of the RMC with a mating surface of the die.

Description:
BACKGROUND 
       [0001]    The disclosure relates to gas turbine engines. More particularly, the disclosure relates to casting of cooled airfoils for gas turbine engine blades and vanes. 
         [0002]    Investment casting is a commonly used technique for forming metallic components having complex geometries, especially hollow components, and is used in the fabrication of superalloy gas turbine engine components. The invention is described in respect to the production of particular superalloy castings, however it is understood that the invention is not so limited. 
         [0003]    Gas turbine engines are widely used in aircraft propulsion, electric power generation, and ship propulsion. In gas turbine engine applications, efficiency is a prime objective. Improved gas turbine engine efficiency can be obtained by operating at higher temperatures, however current operating temperatures in the turbine section exceed the melting points of the superalloy materials used in turbine components. Consequently, it is a general practice to provide air cooling. Cooling is provided by flowing relatively cool air from the compressor section of the engine through passages in the turbine components to be cooled. Such cooling comes with an associated cost in engine efficiency. Consequently, there is a strong desire to provide enhanced specific cooling, maximizing the amount of cooling benefit obtained from a given amount of cooling air. This may be obtained by the use of fine, precisely located, cooling passageway sections. 
         [0004]    The cooling passageway sections may be cast over casting cores. Ceramic casting cores may be formed by molding a mixture of ceramic powder and binder material by injecting the mixture into hardened steel dies. After removal from the dies, the green cores are thermally post-processed to remove the binder and fired to sinter the ceramic powder together. The trend toward finer cooling features has taxed core manufacturing techniques. The fine features may be difficult to manufacture and/or, once manufactured, may prove fragile. Commonly-assigned U.S. Pat. No. 6,637,500 of Shah et al., U.S. Pat. No. 6,929,054 of Beals et al., U.S. Pat. No. 7,014,424 of Cunha et al., U.S. Pat. No. 7,134,475 of Snyder et al., U.S. Pat. No. 7,216,689 of Verner et al., and U.S. Patent Publication Nos. 20060239819 of Albert et al. and 20070044934 of Santeler et al. (the disclosures of which are incorporated by reference herein as if set forth at length) disclose use of ceramic and refractory metal core combinations. 
       SUMMARY 
       [0005]    One aspect of the disclosure involves a method for inspecting a part having an in-wall cooling passageway. The in-wall cooling passageway separates an interior wall section from an exterior wall section. A reference location along the in-wall cooling passageway is observed. A size of an aperture at the reference location is determined. Based upon the determined size, a condition of the associated wall section is determined. 
         [0006]    The method may be performed sequentially on a plurality of said parts. The parts may be a plurality of cooled airfoils, each having a pressure side and a suction side. The method may be performed for both the wall sections on each part. The method may be performed for a plurality of the in-wall passageways on each part. The method may be performed for multiple walls on each part. 
         [0007]    Another aspect of the disclosure involves a method for manufacturing a casting pattern. A pattern-forming die is assembled with a ceramic feedcore and a refractory metal core (RMC). The assembling leaves an inlet portion of the RMC engaged to the ceramic feedcore and leaves an outlet portion of the RMC engaged to the die. A pattern-forming material is molded in the die at least partially over the ceramic feedcore and RMC. The die is disengaged from the pattern-forming material. The assembling engages a stepped projection of the RMC with a mating surface of the die. The stepped projection may be intermediate the inlet and outlet portions. 
         [0008]    Another aspect of the disclosure involves a casting pattern. The pattern includes a ceramic feedcore, a refractory metal core (RMC) mated to the ceramic feedcore, and a sacrificial pattern material is molded at least partially over the ceramic feedcore and RMC. The sacrificial pattern material defines a pressure side and a suction side. The RMC has an inlet portion mated to the ceramic feedcore and an outlet portion protruding from the sacrificial pattern material. A stepped intermediate portion protrudes from the main body portion. 
         [0009]    Another aspect of the disclosure involves a casting core assembly comprising a ceramic feedcore and a refractory metal core (RMC). The RMC is mated to the ceramic feedcore and comprises means for providing a wall thickness check feature in a casting cast over the core. 
         [0010]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a view of a gas turbine engine blade. 
           [0012]      FIG. 2  is a cross-sectional view of the blade of  FIG. 1 , taken along line  2 - 2 . 
           [0013]      FIG. 3  is an enlarged view of the blade of  FIG. 2 . 
           [0014]      FIG. 4  is a view of a refractory metal core for casting a passageway of the blade of  FIG. 1 . 
           [0015]      FIG. 5  is a sectional view of a pattern in a pattern forming die. 
           [0016]      FIG. 6  is a sectional view of a shell formed from the pattern of  FIG. 5 . 
           [0017]      FIG. 7  is a sectional view of a first worn or defective airfoil. 
           [0018]      FIG. 8  is a sectional view of a second defective airfoil. 
           [0019]      FIG. 9  is a view of a third defective airfoil. 
           [0020]      FIG. 10  is a sectional view of a fourth defective airfoil. 
           [0021]      FIG. 11  is a sectional view of an alternate refractory metal core. 
       
    
    
       [0022]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows a gas turbine engine blade  20  having an airfoil  22 , an attachment root  24 , and a platform  26 . The exemplary airfoil, root, and platform may be formed as a unitary casting (e.g., of a nickel- or cobalt-based superalloy). The exemplary root  24  extends from an inboard end  28  to an outboard end  30  at an underside  32  of the platform  26 . The root  24  has a convoluted so-called fir tree profile for attaching to a complementary slot (not shown) in a disk. 
         [0024]    The airfoil  22  extends from an inboard end  34  at an outboard surface  36  of the platform to an outboard end  38 . The exemplary outboard end  38  is a free distal tip. Alternative blades may have outboard shrouds. Alternative airfoils may be implemented in fixed vanes. 
         [0025]    The airfoil  22  has an exterior/external aerodynamic surface extending from a leading edge  40  to a trailing edge  42 . The airfoil has a pressure side (surface)  44  and a suction side (surface)  46 . 
         [0026]    The airfoil  22  is cooled via a cooling passageway system  50 . The passageway system  50  includes one or more trunks  52  extending from one or more inlets  54  in the root  24 . The exemplary network  50  includes a plurality of span-wise passageway legs (e.g., feed passageways)  60 A-G ( FIG. 2 ). The exemplary passageway legs leave a pressure side wall  62  and a suction side wall  64 . The pressure side wall  62  and suction side wall  64  may be connected by a number of dividing walls  66  which separate adjacent pairs of the feed passageway legs. The feed passageway legs may be, in one or more combinations, separate passageways or legs of one or more common passageways connected by turns or other means. 
         [0027]    One or both of the pressure side wall  62  and the suction side wall  64  may be cooled via one or more wall cooling passageways (in-wall passageways)  70 . The exemplary wall cooling passageways include inlets (ports)  72  at one or more of the feed passageway legs, a slot-like main section  74  extending in the span-wise and stream-wise directions, and outlets (ports)  76  to the associated pressure side  44  or suction side  46 . Respective inlet and outlet terminal portions  78  and  79  extend between the inlets and outlets on the one hand and the main section  74  on the other hand. 
         [0028]    Such wall cooling passageways  70  may be cast using refractory metal cores (RMCs) as are known or may be developed. Each of the wall cooling passageways  70  separates an interior section/portion  80  of its associated pressure side wall  62  or suction side wall  64  from an exterior section/portion  82  of that wall. With the interior section  80  typically exposed directly to the cool cooling air flowing through the passageway legs, the section  80  is typically designated the “cooled wall”. The exterior section  82  is typically exposed to hot gas of the engine core flowpath and is typically designated the “hot wall”. An overall wall thickness is shown as T W . T W  ( FIG. 3 ) is equal to the sum of the cooled wall thickness T C , the wall cooling passageway thickness T P , and the hot wall thickness T H . T W , T C , T P , and T H  may vary in relative or absolute terms with the particular location along the airfoil. 
         [0029]    It is desired to visually determine wall condition (e.g., of the pressure side wall and/or suction side wall). More particularly it is desired to verify that the wall thicknesses T C  and T H  are within specified limits. For example, erosion during use may reduce the thickness T H  below an acceptable minimum value. Additionally, or alternatively, as-manufactured (e.g., as-cast) thickness may be verified for T C , T H , or both. 
         [0030]    Exemplary means for providing the thickness check include an extension (e.g., a branch or alcove)  90  of the wall cooling passageway into the interior wall section and another extension  92  into the exterior wall section. Exemplary extensions are from the main section  74  of the wall cooling passageway. 
         [0031]    Some implementations may not include both extensions  90  and  92 . 
         [0032]    Exemplary extensions  90  and  92  are nominally through-extensions, penetrating through the associated wall section  62  or  64 . The term “nominally” contemplates the possibility that they may be through-extensions only in a normal situation (e.g., when the thickness is not excessive). In such a situation, the absence of penetration would indicate an excessive wall thickness. The exemplary extensions have stepped cross-section (e.g., a proximal portion  94  of the extension has a larger cross-section in at least one dimension than does a distal portion  96 ). Normally, the distal portion  96  will be open to the associated surface (i.e., exterior surface (pressure side  44  or suction side  46 ) or an interior surface  100 ). Thus, normally, observation of that surface (at a reference location where the extension is) will yield a view of an aperture characterized by the cross-section of the distal portion  96 . If the distal portion  96  is effectively worn away or if a manufacturing defect similarly reduces the thickness of the wall section, the inspection will show in the cross-section of the proximal portion and will, thereby, indicate an insufficient thickness thereby causing part rejection (e.g., leading to disposal or restoration). 
         [0033]    The extensions  90  and  92  may be cast by associated projections  120  and  122  ( FIGS. 4 and 5 ) from the refractory metal core (RMC)  124 . An exemplary casting process is an investment casting process wherein the RMCs are assembled to a feedcore (e.g., a ceramic feedcore) in a pattern-forming die. A sacrificial pattern material (e.g., a wax) is molded in the die at least partially over the feedcore and RMCs to define a pressure side and a suction side of the pattern. The die elements are separated and the pattern removed from the die. The pattern may be shelled (e.g., via a multi-stage stuccoing process). The sacrificial pattern material may be removed (e.g., in a dewaxing) to leave a void for casting the blade or vane. Molten metal is introduced to the void and cooled to solidify. The shell may be removed (e.g., via mechanical means). The core may be removed (e.g., via chemical means) to leave a raw casting. The casting may be machined, treated, and/or coated. 
         [0034]    An exemplary RMC  124  for forming the wall cooling passageways has a main body portion  126  which may be flat or off-flat to conform to the shape of the associated side wall. An inlet end portion  128  ( FIG. 4 ) may project transverse to the main body portion  126 . A distal end  130  of the inlet end portion may mate with an associated leg  132  of the feedcore  136 . A proximal portion  140  of the inlet end portion casts inlet apertures/ports  72  to the wall cooling passageway. Similarly, an outlet end portion  144  may project transverse to the main body portion opposite the inlet end portion (e.g., at a downstream end of the main body portion). A distal end  146  of the outlet end portion may be positioned to be received by a die element  150  of the pattern-forming die to project from the sacrificial pattern material  152  and, in turn, become embedded in the shell  154  ( FIG. 6 ). A proximal portion  156  ( FIG. 6 ) of the outlet end portion casts outlet holes/ports  76  to the associated pressure side or suction side. 
         [0035]    Exemplary extensions  90  and  92  are formed as streamwise intermediate portions of the RMC (i.e., intermediate the inlet and outlet ends of the main section  74 ). 
         [0036]    The exemplary RMC is formed from sheetstock (e.g., by cutting and shaping followed by coating). A first face of the sheet forms an outboard face of the main body portion  126  and the second face of the sheet forms the inboard face of the main body portion  126 . 
         [0037]    An exemplary manufacturing process involves separately forming the projections  120  and  122  and then attaching them to the remainder of the RMC. This, for example, may allow greater choice of cross-sectional shape for the projections. For example, the projections may be formed as stepped right circular cylinders. A large diameter/cross-section base portion  200  of the projection could be secured at the RMC main body portion such as by a mechanical interfit (e.g., a depending projection  202  of the cylinder interfitting with an aperture  204  of the main body portion) and/or a metallurgical attachment (e.g., weld, braze, and the like). After the attachment, the RMC may be coated (if at all). 
         [0038]    In the exemplary stepped right circular cylindrical projections, the base portion  200  casts the extension proximal portion  94 . A projection intermediate portion  210  casts the distal portion  96 . A shoulder  212  separates the intermediate portion  210  from the base portion  200 . The intermediate portion  210  has a distal end  214 . The exemplary distal end  214  is a shoulder separating the intermediate portion  210  from a distal portion  216 . The distal portion  216  extends to an end  218 . 
         [0039]    The projections mate with associated compartments  220  and  222  respectively in the feedcore  136  and die element  150 . In the exemplary implementation, these compartments  220  and  222  are stepped with a base portion capturing the projection distal portion  216  and an outer portion capturing an end of the projection intermediate portion  210 . For the outer/exterior projection  122 , the distal portion  216  and the end of the intermediate portion  210  which were received in the die compartment  222  protrude from the sacrificial pattern material after molding and become embedded in a corresponding compartment  228  formed in the shell  154 . 
         [0040]      FIG. 7  shows a first situation wherein the hot wall  82  is excessively thin while the cooled wall  80  is of acceptable (e.g., nominal/normal) thickness. For example, the hot wall  82  may have been cast with insufficient thickness. Alternatively, the hot wall may have eroded along the exterior surface (e.g., the suction side  46  in  FIG. 7 ) sufficiently to get down below the distal portion  96 . In such a situation, the larger size of the proximal portion  94  will be visible from external inspection. Accordingly, the proximal portion may be formed with a height H P  that represents the minimum tolerable thickness (T C  or T H ) of the corresponding section  80  or  82 . Although shown of equal size, H P  and other dimensions may differ between the two projections. 
         [0041]      FIG. 8  shows a situation in which the hot wall  82  is excessively thick. An end portion  260  of the associated extension  92  has been cast by the projection distal portion  216 , leaving a particularly small cross-section opening/aperture which may be distinguished from the cross-section of the normal extension distal portion  96 . The projection intermediate portion  210  may have a thickness such that the overall projection height at the intermediate portion distal end  214  corresponds to the maximum acceptable associated wall thickness T H  or T C . 
         [0042]      FIG. 9  shows a situation where the cooled wall  80  is excessively thin. This may be observed via use of an endoscope  300  (e.g., inserted through an inlet  54  and associated feed passageway). 
         [0043]      FIG. 10  shows a situation wherein the cooled wall  80  is excessively thick. 
         [0044]    In situations where the extensions are provided along both the interior wall section and the exterior wall section, the extensions may be distributed so as to eliminate or limit the chances for leakage flow (e.g., a leakage flow from a feed passageway through the interior wall extension and out the exterior wall extension). In one example, there are multiple wall cooling passageways. One or more of the wall cooling passageways have only the interior wall extension  90  while one or more others of the wall cooling passageways have only the exterior wall extension  92 . In situations where a given wall cooling passageway has both one or more interior wall extensions  90  and one or more exterior wall extensions  92 , the respective extensions may be offset from each other in span-wise and/or stream-wise directions to limit leakage flow. 
         [0045]    In an alternative method of manufacture, the projections may be formed in the same process from the same sheet. For example, the projections  400  and  402  ( FIG. 11 ) may be cut (e.g., laser cut) to have a stepped cross-section (stepped in only one direction) while the sheet is flat. The projections may then be bent out of local coplanarity to the main body portion. In the  FIG. 11  example, the projections  400  and  402  are formed along an aperture  404  with the RMC main body portion. This allows the projections to be unitarily formed with the adjacent portions of the RMC (e.g., unitarily formed with a by-mass majority portion of the RMC or essentially a remainder of the RMC). 
         [0046]    The foregoing principles may be applied in the reengineering of an existing core/process/part configuration. For example, the projections could be added to an existing core configuration for making a drop-in replacement for an existing airfoil. However, the principles may be applied in a clean sheet engineering or a more comprehensive reengineering. 
         [0047]    One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when implemented in a reengineering of a given part configuration, details of the existing configuration and/or details of existing manufacturing equipment may influence details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.