Method for forming an airfoil with internal cavities

BACKGROUND

0001Illustrative embodiments pertain to the art of turbomachinery, and specifically to airfoils for turbine rotor components.

0002Gas turbine engines are rotary-type combustion turbine engines built around a power core made up of a compressor, combustor and turbine, arranged in flow series with an upstream inlet and downstream exhaust. The compressor compresses air from the inlet, which is mixed with fuel in the combustor and ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas, and drives the compressor via a common shaft. Energy is delivered in the form of rotational energy in the shaft, reactive thrust from the exhaust, or both.

0003The individual compressor and turbine sections in each spool are subdivided into a number of stages, which are formed of alternating rows of rotor blade and stator vane airfoils. The airfoils are shaped to turn, accelerate and compress the working fluid flow, or to generate lift for conversion to rotational energy in the turbine.

0004Airfoils may incorporate various cooling cavities located adjacent external sidewalls and/or internal to the airfoil. Such cooling cavities are subject to both hot material walls (exterior or external) and cold material walls (interior or internal). Further, different cooling schemes may be necessary for blades and vanes due to operational parameters, environment, and/or conditions. Although such cavities are designed for cooling portions of airfoil bodies, improved cooling designs may be desirable.

0005<patcit id="pcit0001" dnum="US2019022743A1"><text>US 2019/022743 A1</text></patcit> discloses a ceramic core used for fabricating a hollow turbine blade using the lost wax casting technique, the blade including calibrated dust-removal holes emanating from a top of at least one cavity and opening out into a bathtub of the blade.

0006<patcit id="pcit0002" dnum="WO0131171A1"><text>WO 01/31171 A1</text></patcit> and <patcit id="pcit0003" dnum="US2008164001A1"><text>US 2008/164001 A1</text></patcit> each disclose further examples of forming airfoils using core assemblies.

BRIEF DESCRIPTION

0007According to the invention, a method for forming an airfoil for a gas turbine engine is provided as described by claim 1.

0008The core assembly may comprise a plurality of core structures including a pressure side core structure and a suction side core structure, wherein the pressure side core structure defines a pressure side cavity in the formed airfoil body and the suction side core structure forms a suction side cavity in the formed airfoil, wherein the purge slot protrusion is on the suction side core structure.

0009The core assembly may further comprise a leading edge core structure and a trailing edge core structure.

0010The method may include forming at least one purge hole connecting the formed pressure side cavity by at least one of a purge hole rod and drilling.

0011The core structure having the purge slot protrusion may have a dimension in a direction from a pressure side to a suction side of the formed airfoil of about 0.075 inches (1.905 mm) or less.

0012The width of the radially extending protrusion may be equal to or greater than 0.014 inches (0.356 mm).

0013The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

0014The following descriptions are provided by way of example only and should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements may be numbered alike and: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a schematic cross-sectional illustration of a gas turbine engine that can incorporate embodiments of the present invention;</li><li><figref idref="f0002">FIG. 2</figref> is a schematic illustration of a portion of a turbine section of a gas turbine engine that can incorporate embodiments of the present invention;</li><li><figref idref="f0003">FIG. 3A</figref> is an isometric elevation schematic illustration of an airfoil in accordance with an embodiment of the present invention;</li><li><figref idref="f0003">FIG. 3B</figref> is a top down plan view illustration of the airfoil of <figref idref="f0003">FIG. 3A</figref>;</li><li><figref idref="f0004">FIG. 4</figref> is a schematic illustration of a core assembly in accordance with an embodiment of the present invention;</li><li><figref idref="f0005">FIG. 5</figref> is a schematic partial cut-away illustration of an airfoil during a part of a manufacturing process thereof in accordance with an embodiment of the present invention;</li><li><figref idref="f0006">FIG. 6A</figref> is a schematic partial cross-sectional illustration of an airfoil during a part of a manufacturing process thereof in accordance with an embodiment of the present invention;</li><li><figref idref="f0006">FIG. 6B</figref> is a schematic partial cross-sectional illustration of the airfoil of <figref idref="f0006">FIG. 6A</figref> during a subsequent part of the manufacturing process thereof;</li><li><figref idref="f0006">FIG. 6C</figref> is a schematic partial cross-sectional illustration of the airfoil of <figref idref="f0006">FIG. 6A</figref> during a subsequent part of the manufacturing process thereof after the part shown in <figref idref="f0006">FIG. 6B</figref>;</li><li><figref idref="f0007">FIG. 7A</figref> is a schematic illustration of a portion of a core structure in accordance with an embodiment of the present invention;</li><li><figref idref="f0007">FIG. 7B</figref> is a schematic illustration of a portion of an airfoil formed using the core structure of <figref idref="f0007">FIG. 7A</figref>;</li><li><figref idref="f0007">FIG. 7C</figref> is a schematic illustration of a part of a machining process being performed on the airfoil of <figref idref="f0007">FIG. 7B</figref>;</li><li><figref idref="f0007">FIG. 7D</figref> is a partial schematic illustration of the formed airfoil of <figref idref="f0007">FIG. 7A</figref> after the machining performed in <figref idref="f0007">FIG. 7C</figref>;</li><li><figref idref="f0008">FIG. 8</figref> is a flow process for manufacturing an airfoil in accordance with an embodiment of the present invention;</li><li><figref idref="f0009">FIG. 9A</figref> is a schematic isometric illustration of a core structure in accordance with an embodiment of the present invention;</li><li><figref idref="f0009">FIG. 9B</figref> is a side elevation illustration of the core structure of <figref idref="f0009">FIG. 9A</figref>;</li><li><figref idref="f0009">FIG. 9C</figref> is a top-down plan view illustration of the core structure of <figref idref="f0009">FIG. 9A</figref>; and</li><li><figref idref="f0009">FIG. 9D</figref> is a partial schematic illustration of a formed airfoil about the core structure of <figref idref="f0009">FIG. 9A</figref>.</li></ul>

DETAILED DESCRIPTION

0015Detailed descriptions of one or more embodiments of the disclosed apparatus and/or methods are presented herein by way of exemplification and not limitation with reference to the Figures.

0016<figref idref="f0001">FIG. 1</figref> schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. The fan section 22 drives air along a bypass flow path B in a bypass duct, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines.

0017The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A_x relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

0018The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 can be connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and high pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. An engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The engine static structure 36 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A_x which is collinear with their longitudinal axes.

0019The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

0020The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five (5:1). Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

0021A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight conditiontypically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption--also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')"--is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. "Low fan pressure ratio" is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane ("FEGV") system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R)/(514.7 °R)]^0.5. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 m/sec).

0022Although the gas turbine engine 20 is depicted as a turbofan, it should be understood that the concepts described herein are not limited to use with the described configuration, as the teachings may be applied to other types of engines such as, but not limited to, turbojets, turboshafts, and turbofans wherein an intermediate spool includes an intermediate pressure compressor ("IPC") between a low pressure compressor ("LPC") and a high pressure compressor ("HPC"), and an intermediate pressure turbine ("IPT") between the high pressure turbine ("HPT") and the low pressure turbine ("LPT").

0023<figref idref="f0002">FIG. 2</figref> is a schematic view of a portion of a turbine section 200 that may employ various embodiments disclosed herein. The turbine section 200 includes a plurality of airfoils, including, for example, one or more blades 201 and vanes 202. The airfoils 201, 202 may be hollow bodies with internal cavities defining a number of channels or cavities, hereinafter airfoil cavities, formed therein and extending from an inner diameter 206 to an outer diameter 208, or vice-versa. The airfoil cavities may be separated by partitions or internal walls or structures within the airfoils 201, 202 that may extend either from the inner diameter 206 or the outer diameter 208 of the airfoil 201, 202, or as partial sections therebetween. The partitions may extend for a portion of the length of the airfoil 201, 202, but may stop or end prior to forming a complete wall within the airfoil 201, 202. Multiple of the airfoil cavities may be fluidly connected and form a fluid path within the respective airfoil 201, 202. The blades 201 and the vanes 202, as shown, are airfoils that extend from platforms 210 located proximal to the inner diameter thereof. Located below the platforms 210 may be airflow ports and/or bleed orifices that enable air to bleed from the internal cavities of the airfoils 201, 202. A root of the airfoil may connect to or be part of the platform 210. Such roots may enable connection to a turbine disc, as will be appreciated by those of skill in the art.

0024The turbine 200 is housed within a case 212, which may have multiple parts (e.g., turbine case, diffuser case, etc.). In various locations, components, such as seals, may be positioned between the airfoils 201, 202 and the case 212. For example, as shown in <figref idref="f0002">FIG. 2</figref>, blade outer air seals 214 (hereafter "BOAS") are located radially outward from the blades 201. As will be appreciated by those of skill in the art, the BOAS 214 can include BOAS supports that are configured to fixedly connect or attach the BOAS 214 to the case 212 (e.g., the BOAS supports can be located between the BOAS and the case). As shown in <figref idref="f0002">FIG. 2</figref>, the case 212 includes a plurality of hooks 218 that engage with the hooks 216 to secure the BOAS 214 between the case 212 and a tip of the blade 201. Similarly, other hooks, as illustratively shown, are arranged to support the vane 202 within the case 212.

0025As shown and labeled in <figref idref="f0002">FIG. 2</figref>, a radial direction R is upward on the page (e.g., radial with respect to an engine axis, such as engine central longitudinal axis A_x shown in <figref idref="f0001">FIG. 1</figref>) and an axial direction A is to the right on the page (e.g., along an engine axis). Thus, radial cooling flows will travel up or down on the page and axial flows will travel left-to-right (or vice versa). A circumferential direction C is a direction into and out of the page about the engine axis.

0026Cooling of the airfoils 201, 202 may be achieved through internal cavities, as will be appreciated by those of skill in the art. Cooling air may be passed into and through the internal cavities, with the cooling air providing heat pick-up to remove heat from the hot material surfaces of the airfoil (e.g., external surfaces exposed to the hot gaspath).

0027During operation, turbine engines ingest dirt, other particulates, debris, and other particles. Such particles may travel through the hot gaspath (i.e., through the compression and combustor systems) and may flow into the internal structures (i.e., cooling cavities) of the blades where the particles (along with the cooling air) is flung or pumped to the outer diameter or tips of the blades. The majority of these particles are extremely fine grain in size and can flow within the cooling air streams that are used to cool the internals of the blades. However, in some cases, the particles may be too large to make abrupt turns inside the turbine blade internal passages, such as through serpentine cooling flows. These larger particles may adhere to the outer most surfaces of the blade internals (i.e., on the internal cavity surfaces at the tip of the blade). This accumulation of dirt can cause various issues, including, but not limited to, premature metallurgical degradation, unwanted insulated areas within the airfoil, and increase the tip pull of the part. Such issues may result in, for example, decreased cooling efficiencies, reduced structural integrity of the blade at the root and disk lugs, reduced part life, and altered structural and vibration responses of the blade.

0028Therefore, it is common practice to have at least one relatively large hole at the tip of the blade which allows entrained larger dirt particles to escape out of the blade into the gas path and out the back of the engine. That is, at one or more locations at the tip of the blade, a hole of sufficient size may be provided to fluidly connect the internal cavities with the external air (i.e., gas path) at the tip, and thus allow the relatively larger particles to exit the internal cavities. These holes are typically cast using alumina or quartz rods, drilled using electrodes or lasers, or are part of the trailing edge exit circuitry.

0029In some configurations, the purge holes may be formed within a pocket or recess formed in the tip of the airfoil (e.g., tip pocket, a squealer pocket, squealer tip pocket, and/or tip shelf). The squealer pocket is configured to allow for air within the airfoil to exit into the gaspath without causing substantial inefficiencies in airflow. That is, air can exit internal cavities of the airfoil into the squealer pocket and align to flow while minimizing flow losses. Further, a portion of the air that exits the internal cavities may enter and remain within the tip pocket, at least for some amount of time, an provide cooling of the walls and base of the tip pocket, which can increase serviceable life of the tip of the airfoil.

0030During manufacture, for example, traditional methods use cast-in rods to create a dirt purge hole at the tip. Such rods may connect a squealer pocket core to an internal cavity core in a core assembly to form the airfoil (although in some configurations the squealer pocket may be machined). The rods require that there be sufficient core material surrounding the rod to ensure that the rod can be held in place during the casting process. The core material is the material that defines the shape, volume, and dimensions of a cavity within a formed airfoil. That is, the core material is the negative of the cooling cavity, with the airfoil body material cast around the core. Because of this, a minimum thickness or dimension must be present in the core to support the rod. For example, in typical casting operations, a minimum thickness of the core must be on the order of about 0.1 inches (about 2.54 mm) plus the diameter of the rod. Typical dirt purge holes may have a diameter of about .015-.035 inches (about .381-.889 mm). As such, a circumferential thickness (i.e., a direction from pressure side to suction side of a formed airfoil), being the typical shortest dimension of a cooling cavity, may be constrained or limited by these requirements associated with rod installation for formation of tip purge holes. That is, a minimum dimension of the cavity core (and thus cavity) may be dictated by the requirements of purging the cavity to prevent particle accumulation.

0031An alternative method of forming such tip purge holes is to form holes into the tip using an electrode (e.g., electrode discharge machining). Such methods require that the core be at least .060 inches (1.524 mm) thick. However, even with this minimum thickness, there may still be a risk of scarfing the internal passages when forming the holes, thus impacting the internal cooling scheme and structural integrity of the formed airfoil. Even in view of the above, there is a desire to form airfoils having cavity geometries with thinner thicknesses (i.e., less than .060 inches (1.524 mm) thick). Embodiments of the present invention are directed to cores, core assemblies, and formed airfoils having cooling cavities with dimensions lower than the prior minimums. Embodiments of the present invention are directed to, in part, airfoil cavity core bodies that include an extension from a tip region to form a purge hole in the tip of a formed airfoil. That is, rather than using a rod or an electrode to form holes, the tip purge holes are formed using an integral structure of the cavity core bodies (e.g., a core extension) that is subsequently machined(e.g.,by electrical discharge machining ("EDM").

0032Tolerances between the tip and any machined tip pocket are such that any protrusion from the core that is of a dirt purge hole diameter (about .015-.035 inches (about .381-.889 mm)) or size would need to be relatively tall (about .070-. 120 inches (about 1.778-3.048 mm)) and thin, which would be relatively delicate and increase scrap rate of components. As such, embodiments of the present invention are directed to core protrusions and geometries thereof that may work with cores that are thinner than that which can accept rods or hole drill and still form a particle tip purge hole.

0033Such thin cores, as provided in accordance with embodiments of the present invention, are formed with a radial protrusion that is the width of the desired purge hole, with such protrusion extending radially from an end of a core (e.g., core to form part of a serpentine cavity). The radial length (or height from the top of a core) of the core protrusion may be sized to take into account desired dimensions (e.g., axial length, circumferential width, etc.) of the purge hole and any core shift and profile tolerances in addition to any machined tip pocket tolerances. During the manufacturing process, a tip-pocket electrode is used to form a tip pocket and intersects with the integrally formed protrusion (defined by the core protrusion).

0034Turning now to <figref idref="f0003">FIGS. 3A-3B</figref>, schematic illustrations of an airfoil 300 in accordance with an embodiment of the present invention is shown. The airfoil 300 includes an airfoil body 302 that extends in a radial direction from a platform 304. An attachment mechanism 306 extends from an opposing side of the platform 304 from the airfoil body 302 and is configured to enable engagement with a disk of a gas turbine engine. The airfoil 300, in this illustrative configuration, is a blade for use with a compressor or turbine section of a gas turbine engine. <figref idref="f0003">FIG. 3A</figref> is an isometric elevation view of the airfoil 300 and <figref idref="f0003">FIG. 3B</figref> is a top down illustration of the airfoil 300.

0035The airfoil body 302 extends between a base 308 at the platform 304 and a tip 310, in a radial direction R. In an axial direction A, the airfoil body 302 extends between a leading edge 312 and a trailing edge 314. In a circumferential direction C, the airfoil body 302 extends between a pressure side 316 and a suction side 318. The directions described herein are relative to an engine axis (e.g., engine central longitudinal axis A_x shown in <figref idref="f0001">FIG. 1</figref>).

0036The airfoil body 302 includes one or more internal cooling cavities, as will be appreciated by those of skill in the art. The cooling cavities can include conventional cavities or hybrid or skin core cavities. Conventional cavities are cavities that are defined between external hot walls of the airfoil, such as from the pressure side 316 to the suction side 318 in the circumference direction C. As such, a conventional cooling cavity provides cooling to two hot walls of the airfoil body. A hybrid or skin core cavity is one that is defined between an external hot wall of the airfoil body and an internal cold wall (a wall that is not exposed to hot external gases). The hybrid or skin core cavities have low height (i.e., circumferential direction C) to width (i.e., axial direction A) aspect ratios, with a flow direction being normal to the height and width (i.e., radial direction R). That is, the hybrid or skin core cavities has thin thicknesses in a direction from the pressure side 316 to the suction side 318 (i.e., less than full thickness of internal size of the airfoil body), whereas a conventional cavity would have a full thickness from the pressure side 316 to the suction side 318 (two hot walls).

0037At the tip 310 of the airfoil 300 is a squealer pocket 320. As discussed above, the squealer pocket 320 can provide a volume for air exiting the internal cavities of the airfoil 300 to align and flow together before entering a hot gaspath, and thus reduce losses associated with such merging of flows. As such, the squealer pocket 320 may include one or more apertures that fluidly connect the squealer pocket 320 to the internal cavities of the airfoil 300.

0038<figref idref="f0003">FIG. 3B</figref> illustrates a top down view of the tip 310 and the squealer pocket 320. The squealer pocket 320 is defined by a pocket base 322 and walls of the airfoil body 302 (leading edge, pressure side, suction side). The pocket base 322 is recessed relative to the tip 310. In this illustrative configuration, the squealer pocket 320 includes two main body cavity purge holes 324. The main body cavity purge holes 324 may fluidly connect to one or more main body cavities within the airfoil body 302. For example, in one non-limiting example, the main body cavity purge holes 324 may be fluidly connected at two distinct locations along a serpentine cavity arranged along the pressure side 316 of the airfoil body 302. The pocket base 322 further includes a cavity purge slot 326 formed within the squealer pocket 320 and extending radially inward from the pocket base 322. The cavity purge slot 326 forms a fluid connection between an internal cavity of the airfoil body 302 and the squealer pocket 320.

0039In this illustrative embodiment, the main body cavity purge holes 324 may be formed by drilling or rods during a casting process. The main body cavity purge holes 324 may be connected to conventional cavities or to skin core cavities. However, as noted above, the core used to form the conventional cavities or skin core cavities must be of sufficient dimensions to accommodate the rods or drilling operation. In contrast, the cavity purge slot 326 is formed to connect to a cavity having dimensions that do not permit the use of rods or drilling. That is, the cavity to which the cavity purge slot 326 connects may have a thickness in a direction between the pressure side 316 and the suction side 318 that does not allow for rods or drilling for forming purge holes. For example, the cavity (and core used to form such cavity) may have a thickness in the direction between the pressure side 316 and the suction side 318 of 0.060 inches (1.524 mm) or less.

0040To form the cavity purge slot 326 in the pocket base 322, an electrical discharge machining ("EDM") process is employed to remove material at the tip 310 and allow for connection with a core extension used to form the cavity purge slot 326. The EDM process is used to cut into a formed airfoil body and thus form the squealer pocket 320 in the tip 310 of the airfoil 300. The removal of material during the EDM process employs an electrode having a desired geometry to form the squealer pocket 320. To achieve this, the internal cavities (and particularly the cavity to have the cavity purge slot 326) are formed with specific geometries and/or features to enable the airfoil 300 to be formed.

0041Turning now to <figref idref="f0004">FIG. 4</figref>, a schematic illustration of a core assembly 450 in accordance with an embodiment of the present invention is shown. The core assembly 450 is used during a manufacturing process for forming an airfoil, such as that shown and described with respect to <figref idref="f0003">FIGS. 3A-3B</figref>. The core assembly 450 comprises a number of different cores that are arranged to define internal cavities within a formed airfoil. Accordingly, the core assembly 450 is formed of a material that may be removed after being cast within material of the airfoil body, as will be appreciated by those of skill in the art.

0042As shown, the core assembly 450 includes a leading edge core structure 452, a pressure side core structure 454, a suction side core structure 456, and a trailing edge core structure 458. The core structures 452, 454, 456, 458 each define separate internal cavities in a formed airfoil and may be fluidly separated or may be fluidly connected. In the core assembly 450, core structures may be connected by rods or other structures to form fluidly connections in a formed airfoil, as will be appreciated by those of skill in the art.

0043In this illustrative embodiment, the leading edge core structure 452 includes a plurality of separate sections and may be arranged to form a plurality of respective impingement cavities along the leading edge of the formed airfoil. The pressure side core structure 454 is arranged as a serpentine cavity that includes one or more purge hole rods 460 that are arranged proximate the tip or top of the pressure side core structure 454. The purge hole rods 460 are configured to be removed during or after manufacture of an airfoil body, and when removed will define or form purge holes located at the tip of the formed airfoil body. The purge hole rods 460 may be used because a thickness of the pressure side core structure 454 permits the use of such purge hole rods 460.

0044In contrast, as shown, the suction side core structure 456 may be relative thin in comparison to the pressure side core structure 454 and may not be able to accommodate the use of purge hole rods. To enable the formation of a purge aperture, the suction side core structure 456 includes a purge slot protrusion 462. The purge slot protrusion 462 is an extension of the material of the suction side core structure 456 and is removed during the manufacturing process of an airfoil body to thus form a radially outward (direction toward the tip of the formed airfoil) extension of a formed cavity on the suction side. This cavity extension enables a cutting or removal process of airfoil material to form a cavity purge slot in a formed airfoil (e.g., cavity purge slot 326 shown in <figref idref="f0003">FIG. 3B</figref>).

0045The purge slot protrusion 462 has a height/length (radial direction R) that is sufficient to ensure that a desired cavity purge slot can be formed after casting of an airfoil body. The length of the purge slot protrusion 462 in the radial direction R may be sized to take into account the desired length of the formed cavity purge slot and accommodate any core shift and/or profile tolerances in addition to any machined tip pocket (i.e., squealer pocket tolerances). The width of the purge slot protrusion 462 in a circumference direction C (i.e., direction from pressure side to suction side) is configured to be a width of the formed cavity purge slot and allows for the formation of a wall to define a portion of a squealer pocket. The purge slot protrusion 462 may have a height in a radial direction R that is sufficient to enable formation of the cavity purge slot while also allowing for formation of a pocket base of a squealer pocket at locations other than the cavity purge slot (and the purge hole rods 460).

0046Turning now to <figref idref="f0005">FIG. 5</figref>, a schematic illustration of an airfoil 500 in accordance with an embodiment of the present invention are shown. <figref idref="f0005">FIG. 5</figref> illustrates an airfoil body 502 after a manufacturing process using a core assembly, such as shown and described with respect to <figref idref="f0004">FIG. 4</figref>, prior to formation of a squealer pocket with a cavity purge slot 526 formed for connecting to the squealer pocket. The airfoil body 502 includes a plurality of internal cavities formed therein, which are formed by removal of core assembly material after casting of the airfoil body 502, as will be appreciated by those of skill in the art.

0047As shown, in this embodiment, the airfoil body 502 includes a leading edge cavity 530, a pressure side cavity 532, a suction side cavity 534, and a trailing edge cavity 536. The pressure side cavity 532 may be a serpentine flow cavity that is fluidly connected to the leading edge cavity 530 through one or more impingement holes, as will be appreciated by those of skill in the art. The suction side cavity 534 may comprise a set of one or more radially extending channels that may be separated by radially extending ribs 538. The radially extending ribs 538 may extend between a core rib 540 that separates the pressure side cavity 532 from the suction side cavity 534 and a suction side 518 of the airfoil body 502.

0048Proximate a tip 510 of the airfoil body 502, the suction side cavity 534 is formed with a cavity purge slot 526 that extends in a radial direction R toward the tip 510. As such, the suction side cavity 534 includes a portion (the cavity purge slot 526) that extends radially closer to the tip 510 than the rest of the suction side cavity 534 (or other internal cavities of the airfoil body 502).

0049After formation of the airfoil body 502 (e.g., using a core assembly as described above), a portion of the airfoil body 502 is further treated or worked to form additional features on the airfoil 500. An EDM process uses an electrode to cut into and remove material of the airfoil body 502 from the tip 510 to form a squealer pocket therein (e.g., as shown in <figref idref="f0003">FIGS. 3A-3B</figref>). As the electrode of the EDM process cuts into the material of the airfoil 500 a portion of the material at the cavity purge slot 526 is exposed, thus forming the cavity purge slot 526 which fluidly connects the suction side cavity 534 with the squealer pocket.

0050Turning now to <figref idref="f0006">FIGS. 6A-6C</figref>, schematic illustrations of part of a manufacturing process for forming an airfoil 600 in accordance with an embodiment of the present invention are shown. The airfoil 600 is similar to that shown and described above, and is formed using a core assembly, as described above. The airfoil 600, as shown, includes a tip 610, a pressure side 616, a suction side 618, an internal pressure side cavity 632, and an internal suction side cavity 634. The pressure side cavity 632 is separated from the suction side cavity 634 by a core rib 640 that extends from a base to a tip of the airfoil 600.

0051<figref idref="f0006">FIG. 6A</figref> illustrates the airfoil 600 prior to formation of a squealer pocket 620 (shown in <figref idref="f0006">FIG. 6C</figref>). In this illustration, the suction side cavity 634 includes a cavity extension 642 that extends closer (radially) to the tip 610 than the rest of the suction side cavity 634 (and closer to the tip 610 than the radial extent of the pressure side cavity 632).

0052<figref idref="f0006">FIG. 6B</figref> illustrates an electrode 670 extending into the material of the airfoil 600 to remove material at the tip 610 to form the squealer pocket 620 (e.g., cutting the material of the airfoil 600). The electrode 670 is sized and shaped to form the squealer pocket 620 having a pocket base 622 extending between the pressure side 616 and the suction side 618 at a depth below the tip 610.

0053When the electrode 670 is removed, the suction side cavity 634 is fluidly connected to the squealer pocket 620 through a cavity purge slot 628 (formerly the cavity extension 642), as shown in <figref idref="f0006">FIG. 6C</figref>. The pressure side cavity 632 may be fluidly connected to the squealer pocket 620 through one or more cavity purge holes formed using rods (not shown), as described above.

0054Turning to <figref idref="f0007">FIGS. 7A-7D</figref>, schematic illustrations of parts of a manufacturing process of an airfoil 780 in accordance with an embodiment of the present invention are shown.

0055In this embodiment, the airfoil 780 is formed using a single core structure 781 having a purge slot protrusion 782 (shown in <figref idref="f0007">FIG. 7A</figref>). The core structure 781 of this embodiment may be arranged to form a conventional internal airfoil cooling cavity 783 (i.e., extending between two hot external walls, i.e., pressure side and suction side). That is, a single, relatively thin airfoil 780 may be formed with the single internal cooling cavity 783 defined therein, based on the core structure 781 shown in <figref idref="f0007">FIG. 7A</figref>. The core structure 781 is used for casting material of the formed airfoil 780, and thus formation of a cavity extension 784 is formed by the purge slot protrusion 782. This configuration may be employed because a width (or other dimensions) of the core structure 781 may be too small to accommodate the use of rods for forming purge holes. As shown in <figref idref="f0007">FIG. 7B</figref>, the airfoil 780 is formed, after casting and removal of the core structure 781, with a tip 785. A squealer pocket 786 (shown in <figref idref="f0007">FIG. 7D</figref>) is formed in order to allow for desired cooling flow exiting from the internal cooling cavity 783 into a hot gas path during operation.

0056To form the squealer pocket 786 within the tip 785, an electrode 787 is used after casting of the airfoil 780. The electrode 787 may be sized and shaped to remove material at the tip 785 of the airfoil 780 such that the squealer pocket 786 is formed in the tip 785 of the airfoil 780. As the electrode 787 cuts into the material of the airfoil 780, a connection with the cavity extension 784 is formed. As such, during formation of the squealer pocket 786, the electrode 787 cuts or removes material of the airfoil to expose the cavity extension 784 to form a cavity purge slot 790 (shown formed in <figref idref="f0007">FIG. 7D</figref>) that provides for fluid communication from the internal cavity 783 and the squealer pocket 786.

0057In accordance with embodiments of the present invention, in view of the teachings herein, those of skill in the art will appreciate that the configurations employing a cavity purge slot (as compared to cavity purge holes) may be used for any cavity of an airfoil, and is not limited to suction side cavities and/or single internal cavities. For example, similar purge slot protrusions may be formed on any given core structure or portion thereof to allow for a cavity purge slot to be formed. Accordingly, in some embodiments, a pressure side cavity may include a purge slot protrusion at a location that may be too thin to accommodate a purge hole rod. Similarly, a leading edge core structure and/or trailing edge core structure may include such protrusions, if a tip purge is desired for such cavities.

0058The electrode used in EDM processes described herein can be made up of multiple pieces or can be a monolithic electrode having the required geometry. Further, the specific location of the core (purge slot) protrusions and cavity extensions may be selected to form a cavity purge slot at a desired location and having desired features (e.g., dimensions, geometry, etc.) to provide appropriate purging capability for a given cavity. As noted above, the core (purge slot) protrusions described herein, used to form cavity purge slots, may be employed on core structures having minimum dimensions that are insufficient to support rods and/or allow for drilling to form purge holes, as typically done for relatively larger core structures and formed cavities. For example, the core protrusions may be used on core structures having a smallest dimension, at the location of the desired purging, of about 0.075 inches (1.905 mm) or less. Typically, such dimension will be in a circumferential direction (i.e., a direction between a pressure side and suction side of a formed airfoil). Further, such core protrusions may be used on hybrid skin cores (i.e., cores used to form skin core cavities having a hot side defined by an external hot wall of an airfoil and an internal cold wall). It will be appreciated that an external hot wall of an airfoil is an external surface that is exposed to a gaspath during operation, and an internal cold wall refers to an internal structure of an airfoil that is not exposed directly to hot gaspath air during operation.

0059Turning now to <figref idref="f0008">FIG. 8</figref>, a flow process 800 for manufacturing an airfoil in accordance with an embodiment of the present invention is shown. The flow process 800 is employed to form an airfoil as shown and described above, or other airfoil configurations that include one or more cores/internal cavities that are too small, narrow, or otherwise dimensioned such that a rod or drilling operation may not be employed to form a cavity purge hole.

0060At block 802, a core assembly is formed with at least one core structure having a purge slot protrusion. The core assembly can include one or more core structures. For example, a single core structure may be employed to form an airfoil having a single internal cooling cavity. However, typically, multiple core structures will be formed and arranged to form multiple different (separate or connected) internal cavities of an airfoil. One or more core structures of a core assembly include such purge slot protrusions. Further, in some embodiments, a single core structure of a core assembly can include multiple purge slot protrusions if desired, and depending on the configuration of the airfoil and internal cooling scheme thereof.

0061At block 804, an airfoil body is formed around the core assembly. The formation of the airfoil body about the core assembly is by casting, as will be appreciated by those of skill in the art.

0062At block 806, the core assembly is removed from the formed airfoil body to form one or more internal cavities. At least one internal cavity will include a cavity extension at the location of the purge slot protrusion. The removal process may be done by known means and mechanisms.

0063At block 808, an operation is performed to form a squealer pocket at the tip of the airfoil body. During such operation, a cut or removal of material at the tip of the firmed airfoil is performed thus exposing the formed cavity extension. Thus, a cavity purge slot is formed that fluidly connects the internal cavity to the squealer pocket at the location of the cavity extension. The process is an electrical discharge machining ("EDM") process.

0064Turning now to <figref idref="f0009">FIGS. 9A-9D</figref>, schematic illustrations of a core structure 990 in accordance with an embodiment of the present invention are shown. <figref idref="f0009">FIG. 9A</figref> is an isometric illustration of the core structure 990 used to form an airfoil body 992 (shown in <figref idref="f0009">FIG. 9D</figref>) and having a purge slot protrusion 994. <figref idref="f0009">FIG. 9B</figref> is a side elevation illustration of the core structure 990. <figref idref="f0009">FIG. 9C</figref> is a top-down plan view illustration of the core structure 990. <figref idref="f0009">FIG. 9D</figref> is a schematic illustration of the core structure 990 within the airfoil body 992 prior to removal of the core structure 990 during a manufacturing process.

0065As shown, the purge slot protrusion 994 that is part of the core structure 990 has a radial length L_R that is defined as height or distance of extension from a top 996 of the core structure 990. In an axial direction, the purge slot protrusion 994 has an axial length or width L_A. Further, the purge slot protrusion 994 has a circumferential length or width L_C (i.e., pressure side to suction side of a formed airfoil, as described above) which is narrower than a circumferential length or width Wc of the core structure 990 (as shown in <figref idref="f0009">FIGS. 9C-9D</figref>).

0066<figref idref="f0009">FIG. 9D</figref> illustrates the core structure 990 as arranged within a formed (e.g., cast) airfoil body 992 around the core structure 990. A shown, the purge slot protrusion 994 extends upward (i.e., the radial direction) beyond the extent of the main body of the core structure 990, and enables formation of a cavity purge slot, as described above.

0067The purge slot protrusion may have specific dimensions to enable formation of the desired purge slot without impacting the manufacturing and/or producibility of parts as discussed herein. For example, without limitation, the purge slot protrusion may have a width (i.e., pressure side to suction side direction) that does not exceed the width of the core from which the purge slot protrusion extends (in the same direction). Stated another way, the width of the purge slot protrusion in the circumferential direction, discussed above, is not larger than the width of the core from which it extends, in the circumferential direction. Further, a cross sectional area of the purge slot protrusion (taken at a radial position; e.g., area defined by dimension in circumferential direction by dimension in axial direction) may define the purge slot size. In one non-limiting example, the circumferential width may be equal to or greater than 0.014 inches (0.356 mm) and the axial length may be equal to or greater than 0.014 inches (0.356 mm). A height (i.e., radial direction; i.e., the length of extension from a core) to circumferential thickness ratio does not to exceed 5:1.

0068Advantageously, embodiments described herein allow for purge mechanisms of internal cavities of airfoils that cannot be formed using traditional mechanisms (e.g., rods, drilling, etc.). According to embodiments described herein, core structures are formed with extensions at a portion of the core structure to enable the formation of a cavity extension within a formed airfoil. The formed cavity extension provides for a thinner material portion at the location thereof, thus enabling cutting or removal of such thinner material and the formation of a purge slot, as shown and described above.

0069As used herein, the term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, "about" may include a range of ± 8%, or 5%, or 2% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

0070The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "radial," "axial," "circumferential," and the like are with reference to normal operational attitude and should not be considered otherwise limiting.

0071While the present invention has been described with reference to an illustrative embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention as defined by the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope of the invention as defined by the claims. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present invention, but that the present invention will include all embodiments falling within the scope of the claims.