Blades, casting cores, and methods

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.

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.

DETAILED DESCRIPTION

FIG. 1shows a blade20(e.g., an HPT blade) having an airfoil22extending along a span from an inboard end24to an outboard tip26. The blade has leading and trailing edges30and32and pressure and suction sides34and36.

A platform40is formed at the inboard end24of the airfoil and locally forms an inboard extreme of a core flowpath through the engine. A convoluted so-called “fir tree” attachment root42depends from the underside of the platform40for attaching the blade to a separate disk. One or more ports44may be formed in an inboard end of the root42for admitting cooling air to the blade. The cooling air may pass through a passageway system46and exit through a number of outlets (described below) along the airfoil. As so far described, the blade40may be representative of many existing or yet-developed blade configurations. Additionally, the principles discussed below may be applied to other blade configurations.

FIG. 2shows an exemplary core assembly50for forming the passageway system. The assembly includes a feedcore52used 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 feedcore52may 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 feedcore50extends from an inboard end60to an outboard/tip end62. A base64is formed at the inboard end, with a port/plenum section65outboard thereof. From upstream to downstream, six trunks66,67,68,69,70, and71extend tipward from the port/plenum section65. The feedcore50also has a leading end or edge74, a trailing end or edge75, a suction side76(FIG. 4), and a pressure side77(FIG. 4). The trunks extend within the root42of the resulting blade20and form associated passageway trunks. The base64typically becomes embedded in a casting shell and falls outside the root42.

In the exemplary feedcore50, the leading trunk66joins a first spanwise feed passageway portion (leg)80extending to a tip/distal/outboard end82. The exemplary feed passageway portion80is connected to a leading edge impingement chamber/cavity portion84. The exemplary portion84is segmented. The cavity cast by the portion84may be impingement fed by airflow from the feed passageway cast by the leg80, the air passing through a series of apertures cast by connecting posts86. The airflow may cool a leading edge portion of the airfoil via exiting the impingement cavity through drilled or cast outlet holes.

The second trunk67joins a spanwise feed passageway portion (leg)88having a tip/distal/outboard end90joined to the first leg tip end82by a streamwise extending portion92. In a similar fashion, the third and fourth trunks68and69respectively join spanwise feed passageway portions (legs)94and96having tip ends98and100joined by a streamwise extending portion102. In similar fashion, the fifth and sixth trunks70and71respectively join spanwise feed passageway portions (legs)104and106having tip ends108and110joined by a streamwise extending portion112.

Various adjacent spanwise legs may be joined at one or more intermediate locations by connectors120. The connectors120may enhance core rigidity and may cast corresponding holes through walls between adjacent passageway legs of the casting.

The RMC54is generally L-shaped in planform having a leg portion130extending from an inboard first end132to a junction134with an outboard foot portion136. The foot portion136extends to a leading end140. The leg portion has a leading edge142extending outboard from the end132to an edge region144along the junction134and merging with an inboard edge146of the foot. The leg portion has a trailing edge148extending to the junction134where it joins an outboard edge150of the foot portion which forms an outboard end of the RMC54.

A slot160(FIG. 4) is formed in the leg106along the trailing edge75of the feedcore and along the feedcore tip end62across the spanwise portions92,102, and112. The slot160receives an adjacent portion164of the RMC (a leading portion along the edge142and an inboard portion along the edge146).FIG. 4shows the RMC as having first and second faces170and172received abutting associated slot faces174and176, with a slot base178abutting the adjacent RMC edge142,140,146.FIG. 4further shows the RMC54as having an essentially constant thickness T between the faces170and172. The slot height between the faces174and176may 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 slot180(FIG. 5) for discharging cooling air delivered through the feed passageways cast by the feedcore. The slot180has an upstream inlet182at a trailing feed passageway leg184cast by the feedcore leg106. The slot180extends downstream to an outlet186at the blade trailing edge. The slot has opposite side surfaces188and190separated 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 apertures200(FIG. 3). The apertures200arrayed parallel to the edge portions142,144,146. The apertures200are elongate in the direction of their array and are spaced relatively closely so as to cast a segmented wall202(FIGS. 5 and 6) with gaps204for metering an outlet flow. The apertures also include an array of streamwise elongate and tapering apertures206near the trailing edge148to define outlet walls208. Intermediate groups of apertures210may cast posts212.

Adjacent the outboard edge150, the exemplary RMC includes the apertures200and206, but not the intermediate apertures210. However, other configurations are possible.FIG. 7shows the walls or posts202and208cast 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 apertures206and posts/walls208may continuously fan across the transition at the trailing tip corner.FIG. 7shows the wall202and post/walls208along the tip. Along the tip portion of the slot, the slot inlet182is at an exemplary feed passageway turn220cast by one of the feedcore spanwise portions92,102,112.

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. 9shows a pattern formed over such a core assembly.FIG. 10shows 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.