Abstract:
An article includes a blade casting core combination. The combination includes a ceramic feedcore and a metallic core. The ceramic feedcore has: a root end; a tip end; a leading end; a trailing end; a first side; a second side; and a plurality of legs extending between the root and tip ends and arrayed between the leading and trailing ends. The metallic core has: a first face; a second face; a first portion extending from the feedcore trailing end; and a second portion extending from the tip end. The article may be a pattern where the core is embedded in a wax or may be a shell formed from such a pattern. The article may be used in a method for forming the resultant blade.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to gas turbine engines. More particularly, the invention relates to the casting of gas turbine engine blades. 
     Heat management is an important consideration in the engineering and manufacture of turbine engine blades. Blades are commonly formed with a cooling passageway network. A typical network receives cooling air through the blade platform. The cooling air is passed through convoluted paths through the airfoil, with at least a portion exiting the blade through apertures in the airfoil. These apertures may include holes (e.g., “film holes”) distributed along the pressure and suction side surfaces of the airfoil and holes at junctions of those surfaces at leading and trailing edges. Additional apertures may be located at the blade tip. In common manufacturing techniques, a principal portion of the blade is formed by a casting and machining process. During the casting process a sacrificial core is utilized to form at least main portions of the cooling passageway network. 
     In turbine engine blades (especially high pressure turbine (HPT) section blades), thermal fatigue of tip region of a blade airfoil is one area of particular concern. U.S. Pat. No. 6,824,359 discloses cooling air outlet passageways fanned along a trailing tip region of the airfoil. U.S. Pat. No. 7,059,834 discloses direction of air through a relief in a wall of a tip pocket to cool a trailing tip portion. U.S. patent application Ser. No. 11/317,394 discloses use of a tip flag passageway to deliver a high volume of cooling air to a trailing tip portion. 
     SUMMARY OF THE INVENTION 
     The article may be a pattern where the core is embedded in a wax or may be a shell formed from such a pattern. The pattern may comprise a wax body over portions of the metallic core and feedcore and may include portions corresponding to the ultimate casting (e.g., a platform portion; an airfoil portion having leading and trailing edges, pressure and suction sides, a tip and a proximal end at the platform; and a root portion depending from the platform portion opposite the airfoil portion). The metallic core first portion may include a main portion embedded in the wax body and a perimeter portion protruding from the wax body at the airfoil trailing edge. The metallic core second portion may include a main portion embedded in the wax body and a perimeter portion protruding from the wax body at the airfoil tip. The shell may be over portions of the metallic core and feedcore and may have a cavity generally corresponding to the shape of the article to be cast (e.g., a platform portion; an airfoil portion having leading and trailing edges, pressure and suction sides, a tip and a proximal end at the platform; and a root portion depending from the platform portion opposite the airfoil portion). The metallic core first portion may include a main portion exposed within the cavity and a perimeter portion embedded in the shell at the airfoil trailing edge. The metallic core second portion may include a main portion exposed within the cavity and a perimeter portion embedded in the shell at the airfoil tip. The article may be used in a method for forming the resultant blade. In the method, the ceramic feedcore may be molded. A metallic sheet may be cut to form the RMC. The RMC may be secured to the feedcore. The sacrificial pattern material (wax) may be molded at least partially over the assembled feedcore and RMC to form the pattern. The pattern may be shelled to form a shell. The wax may be removed from the shell. Metal may be cast in the shell. The shell and assembled feedcore and RMC may be removed from the cast metal. The removal of the metallic core may leave a trailing edge outlet passageway and a tip outlet passageway. The securing may embed a portion of the RMC in slots in trailing and tip portions of the feedcore. The shelling may embed portions of the RMC in the slots and the trailing tip portions of the shell. The removing may leave a plurality of posts in the trailing edge outlet passageway and the tip outlet passageway. 
     The article may be a pattern where the core is embedded in a wax or may be a shell formed from such a pattern. The article may be used in a method for forming the resultant blade. 
     Another aspect of the disclosure involves a blade which may be cast from the article. The blade has: a platform; an airfoil; and a root. The airfoil has: a leading edge; trailing edge; a pressure side; a suction side; a tip; and a proximal end at the platform. The root depends from the platform opposite the airfoil. The blade has a plurality of feed passageways. An outlet slot extends from the feed passageways to the trailing edge and tip. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a gas turbine engine blade. 
         FIG. 2  is a first side view of a core assembly according to principles of the invention. 
         FIG. 3  is a first side view of a refractory metal core (RMC) of the assembly of  FIG. 2 . 
         FIG. 4  is a partial sectional view of the assembly of  FIG. 2  taken along line  4 - 4 . 
         FIG. 5  is a partial sectional view of the blade of  FIG. 1  taken along line  5 - 5 . 
         FIG. 6  is a slot-wise sectional view of an outlet slot of the blade of  FIG. 1  along the trailing edge. 
         FIG. 7  is a partial sectional view of the blade of  FIG. 1  taken along line  7 - 7 . 
         FIG. 8  is a slot-wise sectional view of the outlet slot of the blade of  FIG. 1  along the tip. 
         FIG. 9  is a view of a pattern. 
         FIG. 10  is a view of a shell. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a blade  20  (e.g., an HPT blade) having an airfoil  22  extending along a span from an inboard end  24  to an outboard tip  26 . The blade has leading and trailing edges  30  and  32  and pressure and suction sides  34  and  36 . 
     A platform  40  is formed at the inboard end  24  of the airfoil and locally forms an inboard extreme of a core flowpath through the engine. A convoluted so-called “fir tree” attachment root  42  depends from the underside of the platform  40  for attaching the blade to a separate disk. One or more ports  44  may be formed in an inboard end of the root  42  for admitting cooling air to the blade. The cooling air may pass through a passageway system  46  and exit through a number of outlets (described below) along the airfoil. As so far described, the blade  40  may be representative of many existing or yet-developed blade configurations. Additionally, the principles discussed below may be applied to other blade configurations. 
       FIG. 2  shows an exemplary core assembly  50  for forming the passageway system. The assembly includes a feedcore  52  used to cast major portions of the passageway system. The assembly further includes a refractory metal core (RMC)  54  (e.g., comprising a substrate comprising at least 50% by weight of one or more refractory metals). The feedcore  52  may be formed of one or more molded ceramic pieces assembled to each other or to additional components such as refractory metal cores. For ease of reference, core directions are identified relative to associated directions of the resulting blade cast using the core. Similarly, core portions may be identified with names corresponding to associated passageway portions formed when those core portions are removed from a casting. Additional passageway portions may be drilled or otherwise machined. 
     The feedcore  50  extends from an inboard end  60  to an outboard/tip end  62 . A base  64  is formed at the inboard end, with a port/plenum section  65  outboard thereof. From upstream to downstream, six trunks  66 ,  67 ,  68 ,  69 ,  70 , and  71  extend tipward from the port/plenum section  65 . The feedcore  50  also has a leading end or edge  74 , a trailing end or edge  75 , a suction side  76  ( FIG. 4 ), and a pressure side  77  ( FIG. 4 ). The trunks extend within the root  42  of the resulting blade  20  and form associated passageway trunks. The base  64  typically becomes embedded in a casting shell and falls outside the root  42 . 
     In the exemplary feedcore  50 , the leading trunk  66  joins a first spanwise feed passageway portion (leg)  80  extending to a tip/distal/outboard end  82 . The exemplary feed passageway portion  80  is connected to a leading edge impingement chamber/cavity portion  84 . The exemplary portion  84  is segmented. The cavity cast by the portion  84  may be impingement fed by airflow from the feed passageway cast by the leg  80 , the air passing through a series of apertures cast by connecting posts  86 . The airflow may cool a leading edge portion of the airfoil via exiting the impingement cavity through drilled or cast outlet holes. 
     The second trunk  67  joins a spanwise feed passageway portion (leg)  88  having a tip/distal/outboard end  90  joined to the first leg tip end  82  by a streamwise extending portion  92 . In a similar fashion, the third and fourth trunks  68  and  69  respectively join spanwise feed passageway portions (legs)  94  and  96  having tip ends  98  and  100  joined by a streamwise extending portion  102 . In similar fashion, the fifth and sixth trunks  70  and  71  respectively join spanwise feed passageway portions (legs)  104  and  106  having tip ends  108  and  110  joined by a streamwise extending portion  112 . 
     Various adjacent spanwise legs may be joined at one or more intermediate locations by connectors  120 . The connectors  120  may enhance core rigidity and may cast corresponding holes through walls between adjacent passageway legs of the casting. 
     The RMC  54  is generally L-shaped in planform having a leg portion  130  extending from an inboard first end  132  to a junction  134  with an outboard foot portion  136 . The foot portion  136  extends to a leading end  140 . The leg portion has a leading edge  142  extending outboard from the end  132  to an edge region  144  along the junction  134  and merging with an inboard edge  146  of the foot. The leg portion has a trailing edge  148  extending to the junction  134  where it joins an outboard edge  150  of the foot portion which forms an outboard end of the RMC  54 . 
     A slot  160  ( FIG. 4 ) is formed in the leg  106  along the trailing edge  75  of the feedcore and along the feedcore tip end  62  across the spanwise portions  92 ,  102 , and  112 . The slot  160  receives an adjacent portion  164  of the RMC (a leading portion along the edge  142  and an inboard portion along the edge  146 ).  FIG. 4  shows the RMC as having first and second faces  170  and  172  received abutting associated slot faces  174  and  176 , with a slot base  178  abutting the adjacent RMC edge  142 ,  140 ,  146 .  FIG. 4  further shows the RMC  54  as having an essentially constant thickness T between the faces  170  and  172 . The slot height between the faces  174  and  176  may be the same or slightly greater and may accommodate an adhesive and/or other gap filler (e.g., a ceramic adhesive). 
     The RMC leg and foot portions cast respective trailing edge and tip portions of an outlet slot  180  ( FIG. 5 ) for discharging cooling air delivered through the feed passageways cast by the feedcore. The slot  180  has an upstream inlet  182  at a trailing feed passageway leg  184  cast by the feedcore leg  106 . The slot  180  extends downstream to an outlet  186  at the blade trailing edge. The slot has opposite side surfaces  188  and  190  separated by a height H. Exemplary H is essentially the same as the RMC thickness T. Along the RMC leg and foot portions, the RMC has a plurality of through-apertures for casting walls or posts in the slot. The exemplary RMC apertures include a leading group of apertures  200  ( FIG. 3 ). The apertures  200  arrayed parallel to the edge portions  142 ,  144 ,  146 . The apertures  200  are elongate in the direction of their array and are spaced relatively closely so as to cast a segmented wall  202  ( FIGS. 5 and 6 ) with gaps  204  for metering an outlet flow. The apertures also include an array of streamwise elongate and tapering apertures  206  near the trailing edge  148  to define outlet walls  208 . Intermediate groups of apertures  210  may cast posts  212 . 
     Adjacent the outboard edge  150 , the exemplary RMC includes the apertures  200  and  206 , but not the intermediate apertures  210 . However, other configurations are possible.  FIG. 7  shows the walls or posts  202  and  208  cast by these apertures along the tip portion of the slot. The RMC apertures and resulting walls and posts may form a continuous array across the leg and foot portions of the RMC and associated trailing edge and tip portions of the slot. In particular, the orientation of the apertures  206  and posts/walls  208  may continuously fan across the transition at the trailing tip corner.  FIG. 7  shows the wall  202  and post/walls  208  along the tip. Along the tip portion of the slot, the slot inlet  182  is at an exemplary feed passageway turn  220  cast by one of the feedcore spanwise portions  92 ,  102 ,  112 . 
     The RMC apertures and associated slot walls and posts may be engineered by conventional techniques of computer modeling or iterative prototyping. In an exemplary reengineering situation, the resulting slot may offer reduced heat loading associated with blade tip vortices than in the baseline airfoil (e.g., having a conventional tip flag arrangement). 
       FIG. 9  shows a pattern formed over such a core assembly.  FIG. 10  shows a shell formed by shelling such a pattern and removing the pattern wax in a dewax process. 
     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the invention may be implemented in the context of various existing or yet-developed casting technologies and core manufacturing technologies. The principles may be implemented in the manufacturing of a variety of blades including reengineerings of existing blade configurations. In such situations, details of the technologies, applications, and configurations may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.