Patent Description:
Impingement cooling is often used to cool gas turbine engine components that are exposed to hot combustion gas, for example ring segment shrouds and airfoil leading and trailing edges. The backside of a component surface that is heated by the combustion gas is cooled by one or more jets of cooling fluid directed against the backside surface from holes formed in an impingement structure which is spaced apart from the backside surface. The impingement structure is typically a perforated plate that is manufactured separately and is later attached mechanically or brazed into position after the component is cast. However, problems can arise due to this complex and time consuming assembly process. <CIT> issued to the assignee of the present invention describes a self-locking impingement device which simplifies the installation of an impingement structure into a cast engine component.

Cooling fluid is provided in a gas turbine engine at the cost of efficiency. In order to increase engine efficiency, combustion firing temperatures are periodically increased as material technology and component cooling schemes continue to improve. In order to improve cooling and to minimize the amount of cooling fluid consumed, some modern component designs include the use of engineered cooling features formed on the backside cooled surface to more efficiently transfer heat from the metal surface to the jet of impinging coolant fluid. Further improvements in heat transfer efficiency and reductions in manufacturing and assembly costs are desired. In <CIT> a composite core for forming a passage in an investment casting mold is disclosed including a core element. A generally hollow structural element is positioned about an exterior of the core element. The structural element is configured to deform when a force is applied to the structural element. A rigid shell element is integrally formed about the structural element. Further, in <CIT> an integral ceramic casting core is disclosed which includes a base portion with a plurality of rods extending therefrom and a plurality of apertures formed therein. The base portion defines a passageway for the passage of a cooling media within a cast component. In <CIT> methods for rapid prototype casting metal components are disclosed wherein the metal components are cast in a secondary ceramic mold. The secondary ceramic mold is cast in a primary mold, and the primary mold is formed by rapid prototyping or rapid manufacturing. Furthermore, in <CIT> a gas turbine engine blade is disclosed, which is cooled by the circulation of cooling fluid in its internal cavity. The leading edge of the blade consists of a cell which is produced by a lost wax moulding method. In <CIT> the production of a gas turbine component is disclosed, wherein a one-part disposable core and shell mold of a gas turbine component is provided.

The present inventors have recognized that the heat transfer efficiency of engineered impingement cooling features is heavily dependent upon the impinging jet of cooling fluid impacting the cooling feature at the intended impingement target location. The inventors have also recognized that manufacturing and assembly tolerances existing with prior art processes can result in functionally significant misalignment of the impingement structure relative to the associated cooling feature. Accordingly, the inventors disclose herein an investment casting core and related processes which produce the impingement structure in the same casting operation as the cooling feature. This is accomplished by utilizing a casting core incorporating a pre-positioned alignment guide which establishes alignment of a coolant outlet opening in the impingement structure with an associated target impingement area of the cooling feature.

The invention is explained in the following description in view of the drawings that show:.

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention.

<FIG> is a cross-sectional view of an investment casting core <NUM> in accordance with an embodiment of the invention. The core <NUM> is used when casting a metal component such as the gas turbine engine component <NUM> of <FIG> in an investment casting process described more fully below with reference to <FIG>. The core <NUM> includes a body <NUM> having an impingement plate side <NUM> and an impingement surface side <NUM> opposed the impingement plate side <NUM>. The impingement plate side <NUM> will define a surface of the impingement structure <NUM> in the later-cast metal component <NUM>, and the impingement surface side <NUM> will define an impingement-cooled surface <NUM> in the later-cast component <NUM>.

In order to increase the efficiency of the impingement cooling scheme of the later-cast component <NUM>, a geometrically engineered cooling feature <NUM> may be formed on the impingement-cooled surface <NUM> of the component <NUM>. The shape <NUM> of the impingement cooling feature <NUM> is formed on the impingement surface side <NUM> of core <NUM>. The impingement cooling feature shape <NUM> is illustrated in <FIG> as two recesses <NUM> separated by an impingement target area <NUM>. It will be recognized by one skilled in the art that the shape <NUM> in the core <NUM> is the same as, but a negative of, the shape of the corresponding cooling feature <NUM> to be formed in the later-cast metal component <NUM>; i.e. the recesses <NUM> in the core <NUM> will result in two corresponding protuberances in the later-cast component <NUM>.

The core <NUM> also includes an alignment guide <NUM> extending through the body <NUM> from the impingement target area <NUM> to the impingement plate side <NUM>. The alignment guide <NUM> defines a coolant flow path <NUM> to be formed in the later-cast metal component <NUM>. A portion <NUM> of the alignment guide <NUM> extending away from the body <NUM> beyond the impingement plate side <NUM> results in a coolant outlet opening <NUM> being formed in the impingement structure <NUM> of the later-cast component <NUM>. The opposed end of the alignment guide <NUM> is positioned in the impingement target area <NUM> and ensures a precise alignment of the coolant jet and the impingement target area <NUM> of the later-cast component <NUM>. A portion <NUM> of the alignment guide <NUM> may extend away from the body <NUM> beyond the impingement surface side <NUM> in order to facilitate manufacture of the core <NUM>, as will be discussed further with respect to <FIG> below, although this portion <NUM> may be removed prior to using the core <NUM> in a metal casting process.

The impingement plate side <NUM> of the core <NUM> is illustrated in <FIG> as including a plurality of peaks <NUM> and valleys <NUM> relative to the impingement surface side <NUM>. Such a sinusoidal shape in three dimensions may define an auxetic surface shape <NUM> which exhibits a negative Poisson's ratio, i.e. a structure that will expand both along and transverse to a direction of an applied load. The present inventors have recognized that an impingement structure exhibiting a negative Poisson's ratio may be advantageous in order to control loads for embodiments such as a gas turbine engine component. Moreover, by locating the alignment guide <NUM> at the apex of a valley <NUM>, the length of the resulting cooling fluid flow path <NUM> in the later-cast metal component <NUM> is minimized, thereby maximizing cooling effectiveness. Other embodiments of the invention may utilize a core having a planar, non-sinusoidal, and/or non-auxetic impingement plate side to form an impingement structure having the traditional positive Poisson's ratio.

<FIG> illustrates a core casting mold <NUM> and a method which may be used to form the core <NUM> of <FIG>. The mold may be a flexible mold formed of two or more parts <NUM>, <NUM> for easy separation and removal of the core <NUM> after being cast in the mold <NUM>. A first mold part <NUM> has an interior surface <NUM> defining the impingement plate side <NUM> of the core <NUM>, and the second mold part <NUM> has an interior surface <NUM> defining the impingement surface side <NUM> of the core <NUM>, including the impingement cooling feature shape <NUM> and impingement target area <NUM>. The second mold part <NUM> includes a first recess <NUM> corresponding to the location of the impingement target area <NUM> for receiving a first end <NUM> of the alignment guide <NUM>. The second mold part <NUM> includes a second recess <NUM> for receiving a second end <NUM> of the alignment guide <NUM>. In the embodiment shown, the second recess <NUM> is a through hole ending at the apex <NUM> corresponding to a valley <NUM> of the core <NUM>. When the two mold parts <NUM>, <NUM> are joined together, the alignment guide <NUM> assures that the second recess <NUM> is perfectly aligned with the first recess <NUM>, which ensures alignment of the coolant jet <NUM> and impingement target area <NUM> in the later-cast metal component <NUM>, as will be discussed more fully below.

Core material is introduced into the mold <NUM>, such as in the form of a ceramic slurry, and is allowed to solidify around the alignment guide <NUM> to form the core <NUM>. The material of the alignment guide <NUM> is selected to be compatible with the core material, and may be a high density silica material, for example. The alignment guide <NUM> may have a circular cross section, such as a <NUM> diameter silica rod, or have any other cross-sectional shape desired for the resulting cooling fluid channel <NUM> in the later-cast metal component <NUM>. After drying/solidifying, the core <NUM> is removed from the mold <NUM>, sintered and trimmed as necessary, and is available for use in a subsequent metal casting process, as described further below with reference to <FIG>.

<FIG> illustrates the core <NUM> after its removal from the mold <NUM> of <FIG>. A layer of wax such as wax sheet <NUM> is applied to the impingement plate side <NUM> of the core <NUM>. The wax sheet <NUM> will function in a subsequent lost wax process to define a volume of the impingement structure <NUM> of the later-cast metal component <NUM>. The wax sheet <NUM> may be separately formed in a flexible mold (not shown) including openings for receiving the portion <NUM> of the alignment guides <NUM> extending beyond the impingement plate side <NUM>. The exposed alignment guide portions <NUM> can be used as an effective anchor for a subsequent shell dip operation described with reference to <FIG> below. The portion <NUM> of the alignment guide <NUM> extending beyond the impingement surface side <NUM> in <FIG> may be removed (as illustrated in <FIG>) if desired. To ensure a good seal between the wax sheet <NUM> and the protruding alignment guides <NUM>, a thin spray coating of wax <NUM> may optionally be applied over the wax sheet <NUM> at least in regions surrounding the alignment guides <NUM>.

<FIG> illustrates the core <NUM> and layer of wax <NUM> of <FIG> being attached to a wax base <NUM> to form a wax pattern <NUM>.

The wax pattern <NUM> is processed in a standard shelling operation to be encased by a ceramic shell <NUM>, as illustrated in <FIG>, and the resulting assembly <NUM> is dried, dewaxed and sintered to form a casting mold <NUM>, as illustrated in <FIG>. The casting mold <NUM> includes the core body <NUM> and alignment guides <NUM> within the ceramic shell <NUM> and it defines voids <NUM> therein having the shape of a desired metal component <NUM>.

The casting mold <NUM> is then utilized in a metal casting process wherein molten metal is introduced into the voids <NUM> and allowed to cool and to solidify to form a cast metal component <NUM>. <FIG> illustrates the cast metal component <NUM> after removal of the ceramic casting mold <NUM>. The cast metal component <NUM> is illustrated as embodiment is a gas turbine engine ring segment having a wall <NUM> with a surface <NUM> that will be exposed to a hot combustion gas during operation of the component <NUM> in a gas turbine engine. The wall <NUM> includes a backside impingement surface <NUM> having engineered cooling features <NUM> with respective impingement target areas <NUM>. The component <NUM> also includes an impingement structure <NUM> spaced apart from the impingement surface <NUM> and including a plurality of coolant outlet openings <NUM> through which coolant will flow during operation of the component <NUM> in a gas turbine engine. The presence of the alignment guides <NUM> in the casting mold <NUM> defines an impingement jet flow path <NUM> precisely aligned between each of the outlet openings <NUM> and a respective impingement target area <NUM>.

Demolding of component <NUM> from the casting mold <NUM> can be accomplished by standard mechanical and/or leaching processes. In one embodiment, the ceramic shell <NUM> is removed by mechanical means, the alignment rods <NUM> are at least partially drilled out to clear the openings <NUM> in the impingement structure <NUM>, and then chemical leachate is introduced through the openings <NUM> for removing the core body <NUM>. Inspection of interior portions of the demolded component <NUM>, including inspection of the cooling features <NUM> and impingement target areas <NUM> for proper geometry and complete cleaning, may be accomplished via access through the openings <NUM> with a borescope or fiber optic inspection tool.

The present invention allows an impingement structure <NUM> to be cast together with the impingement cooling features <NUM> on a impingement cooled wall <NUM> of a component <NUM>, thereby ensuring perfect alignment there between, eliminating the need for separate fabrication and attachment of the impingement structure <NUM>. In this manner, cooling efficiency is optimized and the duration and cost of production can be reduced when compared to prior art methods.

Claim 1:
A core (<NUM>) for use in an investment casting process for casting a gas turbine engine component (<NUM>) comprising an impingement structure (<NUM>), an impingement-cooled surface (<NUM>) and an impingement cooling feature (<NUM>) on the impingement-cooled surface (<NUM>),
the core (<NUM>) comprising:
a body (<NUM>) comprising an impingement plate side (<NUM>) defining a surface of the impingement structure (<NUM>) in the gas turbine engine component (<NUM>) to be cast and an impingement surface side (<NUM>) opposed the impingement plate side defining the impingement-cooled surface (<NUM>) in the gas turbine engine component (<NUM>) to be cast;
a shape (<NUM>) formed on the impingement surface side (<NUM>), wherein the shape (<NUM>) is a negative of, a shape of the corresponding impingement cooling feature (<NUM>) on the impingement-cooled surface (<NUM>) of the gas turbine engine component (<NUM>) to be cast, the impingement cooling feature shape (<NUM>) defining an impingement target area (<NUM>); and
an alignment guide (<NUM>) extending through the body (<NUM>) from the impingement target area (<NUM>) to the impingement plate side (<NUM>) to define an impingement jet flow path (<NUM>) to be formed in the turbine engine component (<NUM>) to be cast, and a portion (<NUM>) of the alignment guide (<NUM>) extending away from the body (<NUM>) beyond the impingement plate side (<NUM>) resulting in an outlet opening (<NUM>) being formed in the impingement structure (<NUM>) of the turbine engine component (<NUM>) to be cast,
wherein the alignment guide (<NUM>) establishes alignment of the outlet opening (<NUM>) in the impingement structure (<NUM>) with an associated target impingement area (<NUM>) of the cooling feature (<NUM>) on the impingement-cooled surface (<NUM>) of the gas turbine engine component (<NUM>) to be cast.