Patent Description:
Many modern engines and next generation turbine engines require components and parts having intricate and complex geometries, which require new types of materials and manufacturing techniques. Conventional techniques for manufacturing engine parts and components involve the laborious process of investment or lost-wax casting. One example of investment casting involves the manufacture of a typical rotor blade used in a gas turbine engine. A turbine blade typically includes hollow airfoils that have radial channels extending along the span of a blade having at least one or more inlets for receiving pressurized cooling air during operation in the engine. The various cooling passages in a blade typically include a serpentine channel disposed in the middle of the airfoil between the leading and trailing edges. The airfoil typically includes inlets extending through the blade for receiving pressurized cooling air, which include local features such as short turbulator ribs or pins for increasing the heat transfer between the heated sidewalls of the airfoil and the internal cooling air.

The manufacture of these turbine blades, typically from high strength, superalloy metal materials, involves numerous steps shown in <FIG>. First, a precision ceramic core is manufactured to conform to the intricate cooling passages desired inside the turbine blade. A precision die or mold is also created which defines the precise <NUM>-D external surface of the turbine blade including its airfoil, platform, and integral dovetail. A schematic view of such a mold structure is shown in <FIG>. The ceramic core <NUM> is assembled inside two die halves which form a space or void therebetween that defines the resulting metal portions of the blade. Wax is injected into the assembled dies to fill the void and surround the ceramic core encapsulated therein. The two die halves are split apart and removed from the molded wax. The molded wax has the precise configuration of the desired blade and is then coated with a ceramic material to form a surrounding ceramic shell <NUM>. Then, the wax is melted and removed from the shell <NUM> leaving a corresponding void or space <NUM> between the ceramic shell <NUM> and the internal ceramic core <NUM> and tip plenum <NUM>. Molten superalloy metal is then poured into the shell to fill the void therein and again encapsulate the ceramic core <NUM> and tip plenum <NUM> contained in the shell <NUM>. The molten metal is cooled and solidifies, and then the external shell <NUM> and internal core <NUM> and tip plenum <NUM> are suitably removed leaving behind the desired metallic turbine blade in which the internal cooling passages are found. In order to provide a pathway for removing ceramic core material via a leaching process, a ball chute <NUM> and tip pins <NUM> are provided, which upon leaching form a ball chute and tip holes within the turbine blade that must subsequently brazed shut.

The cast turbine blade may then undergo additional post-casting modifications, such as but not limited to drilling of suitable rows of film cooling holes through the sidewalls of the airfoil as desired for providing outlets for the internally channeled cooling air which then forms a protective cooling air film or blanket over the external surface of the airfoil during operation in the gas turbine engine. After the turbine blade is removed from the ceramic mold, the ball chute <NUM> of the ceramic core <NUM> forms a passageway that is later brazed shut to provide the desired pathway of air through the internal voids of the cast turbine blade. However, these post-casting modifications are limited and given the ever increasing complexity of turbine engines and the recognized efficiencies of certain cooling circuits inside turbine blades, more complicated and intricate internal geometries are required. While investment casting is capable of manufacturing these parts, positional precision and intricate internal geometries become more complex to manufacture using these conventional manufacturing processes. Accordingly, it is desired to provide an improved casting method for three dimensional components having intricate internal voids.

Methods for using <NUM>-D printing to produce a ceramic core-shell mold are described in <CIT> assigned to Rolls-Royce Corporation. The methods for making the molds include powder bed ceramic processes such as disclosed <CIT> assigned to Massachusetts Institute of Technology, and selective laser activation (SLA) such as disclosed in <CIT> assigned to 3D Systems, Inc. The ceramic core-shell molds according to the '<NUM> patent are limited by the printing resolution capabilities of these processes. As shown in <FIG>, the core portion <NUM> and shell portion <NUM> of the integrated core-shell mold is held together via a series of tie structures <NUM> provided at the bottom edge of the mold. Cooling passages are proposed in the '<NUM> patent that include staggered vertical cavities joined by short cylinders, the length of which is nearly the same as its diameter. A superalloy turbine blade is then formed in the core-shell mold using known techniques disclosed in the '<NUM> patent. After a turbine blade is cast in one of these core-shell molds, the mold is removed to reveal a cast superalloy turbine blade. From the document <CIT> a system for fabricating three-dimensional objects is known, including an optical imaging system providing a light source and a photosensitive medium adapted to change states upon exposure to a portion of the light source from the optical imaging system. The document <CIT> teaches a cooling system for a turbine airfoil of a turbine engine having at least one diffusion film cooling hole positioned in an outer wall defining the turbine airfoil.

There remains a need to prepare ceramic core-shell molds produced using higher resolution methods that are capable of providing fine detail cast features in the end-product of the casting process.

In one embodiment, the invention relates to a method of making a ceramic mold. The method includes steps of (a) contacting a cured portion of a workpiece with a liquid ceramic photopolymer; (b) irradiating a portion of the liquid ceramic photopolymer adjacent to the cured portion through a window contacting the liquid ceramic photopolymer; (c) removing the workpiece from the uncured liquid ceramic photopolymer. Steps (a) - (c) are repeated until a ceramic mold is formed. The ceramic mold has a (<NUM>) a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of a cast component upon casting and removal of the ceramic mold, and (<NUM>) a plurality of filaments joining the core portion and the shell portion where each filament spans between the core and shell and defines a hole in the cast component upon removal of the mold, wherein at least one filament includes at least a portion having a non-linear geometry and a cross sectional area ranging from <NUM> to <NUM><NUM>. The process includes a step of pouring a liquid metal into a casting mold and solidifying the liquid metal to form the cast component, and then removing the mold from the cast component, this step preferably involves a combination of mechanical force and chemical leaching in an alkaline bath.

In one embodiment, the invention relates to a method of preparing a cast component. The method includes steps of pouring a liquid metal into a ceramic casting mold and solidifying the liquid metal to form the cast component, the ceramic casting mold comprising a (<NUM>) a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of a cast component upon casting and removal of the ceramic mold, and (<NUM>) a plurality of filaments joining the core portion and the shell portion where each filament spans between the core and shell and defines a hole in the cast component upon removal of the mold, wherein at least one filament includes at least a portion having a non-linear geometry and a cross sectional area ranging from <NUM> to <NUM><NUM>; and removing the ceramic casting mold from the cast component by leaching at least a portion of the ceramic core through the holes in the cast component provided by the filaments.

In one aspect, the cast component is a turbine blade or stator vane. Preferably the turbine blade or stator vane is used in a gas turbine engine in, for example, an aircraft engine or power generation. The turbine blade or stator vane is preferably a single crystal cast turbine blade or stator vane having a cooling hole pattern defined by the ceramic filaments mentioned above. Preferably, the filaments join the core portion and shell portion where each filament spans between the core and shell, the filaments having a cross sectional area ranging from <NUM> to <NUM><NUM>.

The large number of filaments used to form a cooling hole pattern may provide sufficient strength to support the tip core. If the tip filaments are made to support tip plenum core, they may be made larger, i.e., ><NUM> cross section area, and a much lower number of filaments, or a single filament, could be used. Although two to four of these larger filaments is a desirable number. After casting, any holes or notches remaining in the tip plenum sidewalls as a result of the filaments may be brazed shut or incorporated into the turbine blade stator vane design, or the filaments may be placed outside the finish machined shape of the component to prevent the need for this.

In one aspect, the invention relates to a ceramic casting mold including a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of a cast component upon casting and removal of the ceramic mold, and a plurality of filaments joining the core portion and the shell portion where each filament spans between the core and shell and defines a hole in the cast component defined by the core portion and an outer surface of the cast component upon removal of the mold, wherein at least one filament includes at least a portion having a non-linear geometry and a cross sectional area ranging from <NUM> to <NUM><NUM>. Preferably, the cast component is a turbine blade or stator vane and the plurality of filaments joining the core portion and shell portion define a plurality of cooling holes in the turbine blade or stator vane upon removal of the mold. The plurality of filaments joining the core portion and shell portion have a cross sectional area ranging from <NUM> to <NUM><NUM>. The ceramic may be a photopolymerized ceramic or a cured photopolymerized ceramic.

Preferably, the cast component is a turbine blade or stator vane and the plurality of filaments joining the core portion and shell portion define a plurality of cooling holes in the turbine blade or stator vane upon removal of the mold. The plurality of filaments joining the core portion and shell portion have a cross sectional area ranging from <NUM> to <NUM><NUM>. The ceramic may be a photopolymerized ceramic or a cured photopolymerized ceramic.

In one aspect, the invention relates to a single crystal metal turbine blade or stator vane having an inner cavity and an outer surface, a plurality of cooling holes providing fluid communication between the inner cavity and outer surface, the plurality of cooling holes having at least a portion having a non-linear geometry and a cross sectional area ranging from <NUM> to <NUM><NUM>.

Preferably the non-linear geometry reflects a non-linear geometry that forms an "S" shaped hole upon removal of the mold. In one aspect, the hole exits the surface at an angle of less than <NUM>°. In another aspect, the hole exits the surface at an angle in the range of <NUM>° to <NUM>°.

For example, the present invention provides a preferred method for making cast metal parts, and preferably those cast metal parts used in the manufacture of jet aircraft engines. Specifically, the production of single crystal, nickel-based superalloy cast parts such as turbine blades, vanes, and shroud components can be advantageously produced in accordance with this invention. However, other cast metal components may be prepared using the techniques and integrated ceramic molds of the present invention.

The present inventors recognized that prior processes known for making integrated core-shell molds lacked the fine resolution capability necessary to print filaments extending between the core and shell portion of the mold of sufficiently small size and quantity to result in effusion cooling holes in the finished turbine blade. In the case of earlier powder bed processes, such as disclosed in <CIT> assigned to Massachusetts Institute of Technology, the action of the powder bed recoater arm precludes formation of sufficiently fine filaments extending between the core and shell to provide an effusion cooling hole pattern in the cast part. Other known techniques such as selective laser activation (SLA) such as disclosed in <CIT> assigned to 3D Systems, Inc. that employ a top-down irradiation technique may be utilized in producing an integrated core-shell mold in accordance with the present invention. However, the available printing resolution of these systems significantly limit the ability to make filaments of sufficiently small size to serve as effective cooling holes in the cast final product.

The present inventors have found that the integrated core-shell mold of the present invention can be manufactured using direct light processing (DLP). DLP differs from the above discussed powder bed and SLA processes in that the light curing of the polymer occurs through a window at the bottom of a resin tank that projects light upon a build platform that is raised as the process is conducted. With DLP an entire layer of cured polymer is produced simultaneously, and the need to scan a pattern using a laser is eliminated. Further, the polymerization occurs between the underlying window and the last cured layer of the object being built. The underlying window provides support allowing thin filaments of material to be produced without the need for a separate support structure. In other words, producing a thin filament of material bridging two portions of the build object is difficult and was typically avoided in the prior art. For example, the '<NUM> patent discussed above in the background section of this application used vertical plate structures connected with short cylinders, the length of which was on the order of their diameter. Staggered vertical cavities are necessitated by the fact that the powder bed and SLA techniques disclosed in the '<NUM> patent require vertically supported ceramic structures and the techniques are incapable of reliably producing filaments. In addition, the available resolution within a powder bed is on the order of <NUM>/<NUM>" resulting in a minimum feature cross sectional dimension on the order of <NUM><NUM>, making the production of traditional cooling holes impracticable. For example, round cooling holes generally have a diameter of less than <NUM> corresponding to a cooling hole area below <NUM> mm2. Production of a hole of such dimensions requires a resolution far below the size of the actual hole given the need to produce the hole from several voxels. This resolution is simply not available in a powder bed process. Similarly, stereolithography is limited in its ability to produce such filaments due to lack of support and resolution problems associated laser scattering. But the fact that DLP exposes the entire length of the filament and supports it between the window and the build plate enables producing sufficiently thin filaments spanning the entire length between the core and shell to form a ceramic object having the desired cooling hole pattern. Although powder bed and SLA may be used to produce filaments, their ability to produce sufficiently fine filaments as discussed above is limited.

One suitable DLP process is disclosed in <CIT> assigned to Ivoclar Vivadent AG and Technische Universitat Wien, as well as <CIT> and <CIT>, each of which are discussed below with reference to <FIG>. The apparatus includes a tank <NUM> having at least one translucent bottom portion <NUM> covering at least a portion of the exposure unit <NUM>. The exposure unit <NUM> comprises a light source and modulator with which the intensity can be adjusted position-selectively under the control of a control unit, in order to produce an exposure field on the tank bottom <NUM> with the geometry desired for the layer currently to be formed. As an alternative, a laser may be used in the exposure unit, the light beam of which successively scans the exposure field with the desired intensity pattern by means of a mobile mirror, which is controlled by a control unit.

Opposite the exposure unit <NUM>, a production platform <NUM> is provided above the tank <NUM>; it is supported by a lifting mechanism (not shown) so that it is held in a height-adjustable way over the tank bottom <NUM> in the region above the exposure unit <NUM>. The production platform <NUM> may likewise be transparent or translucent in order that light can be shone in by a further exposure unit above the production platform in such a way that, at least when forming the first layer on the lower side of the production platform <NUM>, it can also be exposed from above so that the layer cured first on the production platform adheres thereto with even greater reliability.

The tank <NUM> contains a filling of highly viscous photopolymerizable material <NUM>. The material level of the filling is much higher than the thickness of the layers which are intended to be defined for position-selective exposure. In order to define a layer of photopolymerizable material, the following procedure is adopted. The production platform <NUM> is lowered by the lifting mechanism in a controlled way so that (before the first exposure step) its lower side is immersed in the filling of photopolymerizable material <NUM> and approaches the tank bottom <NUM> to such an extent that precisely the desired layer thickness Δ (see <FIG>) remains between the lower side of the production platform <NUM> and the tank bottom <NUM>. During this immersion process, photopolymerizable material is displaced from the gap between the lower side of the production platform <NUM> and the tank bottom <NUM>. After the layer thickness Δ has been set, the desired position-selective layer exposure is carried out for this layer, in order to cure it in the desired shape. Particularly when forming the first layer, exposure from above may also take place through the transparent or translucent production platform <NUM>, so that reliable and complete curing takes place particularly in the contact region between the lower side of the production platform <NUM> and the photopolymerizable material, and therefore good adhesion of the first layer to the production platform <NUM> is ensured. After the layer has been formed, the production platform is raised again by means of the lifting mechanism.

These steps are subsequently repeated several times, the distance from the lower side of the layer <NUM> formed last to the tank bottom <NUM> respectively being set to the desired layer thickness Δ and the next layer thereupon being cured position-selectively in the desired way.

After the production platform <NUM> has been raised following an exposure step, there is a material deficit in the exposed region as indicated in <FIG>. This is because after curing the layer set with the thickness Δ, the material of this layer is cured and raised with the production platform and the part of the shaped body already formed thereon. The photopolymerizable material therefore missing between the lower side of the already formed shaped body part and the tank bottom <NUM> must be filled from the filling of photopolymerizable material <NUM> from the region surrounding the exposed region. Owing to the high viscosity of the material, however, it does not flow by itself back into the exposed region between the lower side of the shaped body part and the tank bottom, so that material depressions or "holes" can remain here.

In order to replenish the exposure region with photopolymerizable material, an elongate mixing element <NUM> is moved through the filling of photopolymerizable material <NUM> in the tank. In the exemplary embodiment represented in <FIG>, the mixing element <NUM> comprises an elongate wire which is tensioned between two support arms <NUM> mounted movably on the side walls of the tank <NUM>. The support arms <NUM> may be mounted movably in guide slots <NUM> in the side walls of the tank <NUM>, so that the wire <NUM> tensioned between the support arms <NUM> can be moved relative to the tank <NUM>, parallel to the tank bottom <NUM>, by moving the support arms <NUM> in the guide slots <NUM>. The elongate mixing element <NUM> has dimensions, and its movement is guided relative to the tank bottom, such that the upper edge of the elongate mixing element <NUM> remains below the material level of the filling of photopolymerizable material <NUM> in the tank outside the exposed region. As can be seen in the sectional view of <FIG>, the mixing element <NUM> is below the material level in the tank over the entire length of the wire, and only the support arms <NUM> protrude beyond the material level in the tank. The effect of arranging the elongate mixing element below the material level in the tank <NUM> is not that the elongate mixing element <NUM> substantially moves material in front of it during its movement relative to the tank through the exposed region, but rather this material flows over the mixing element <NUM> while executing a slight upward movement. The movement of the mixing element <NUM> from the position shown in <FIG>, to, for example, a new position in the direction indicated by the arrow A, is shown in <FIG>. It has been found that by this type of action on the photopolymerizable material in the tank, the material is effectively stimulated to flow back into the material-depleted exposed region between the production platform <NUM> and the exposure unit <NUM>.

The movement of the elongate mixing element <NUM> relative to the tank may firstly, with a stationary tank <NUM>, be carried out by a linear drive which moves the support arms <NUM> along the guide slots <NUM> in order to achieve the desired movement of the elongate mixing element <NUM> through the exposed region between the production platform <NUM> and the exposure unit <NUM>. As shown in <FIG>, the tank bottom <NUM> has recesses <NUM>' on both sides. The support arms <NUM> project with their lower ends into these recesses <NUM>'. This makes it possible for the elongate mixing element <NUM> to be held at the height of the tank bottom <NUM>, without interfering with the movement of the lower ends of the support arms <NUM> through the tank bottom <NUM>.

Other alternative methods of DLP may be used to prepare the integrated core-shell molds of the present invention. For example, the tank may be positioned on a rotatable platform. When the workpiece is withdrawn from the viscous polymer between successive build steps, the tank may be rotated relative to the platform and light source to provide a fresh layer of viscous polymer in which to dip the build platform for building the successive layers.

<FIG> shows a schematic side view of an integrated core-shell mold with filaments <NUM> connecting the core <NUM> and shell portions <NUM>. By printing the ceramic mold using the above DLP printing process, the mold can be made in a way that allows the point of connections between the core and shell to be provided through filaments <NUM>. Once the core-shell mold is printed, it may be subject to a post-heat treatment step to cure the printed ceramic polymer material. The cured ceramic mold may then be used similar to the traditional casting process used in the production of superalloy turbine blades. Notably because the filaments <NUM> are provided in a large quantity consistent with formation of a pattern of effusion cooling holes in the surface of a turbine blade, the need for a ball chute structure as shown in <FIG> may be eliminated. In this embodiment, the tip pins <NUM> connecting the tip plenum core <NUM> to the core <NUM> are retained. After removal of the ceramic mold, tip holes exist between the core <NUM> and tip plenum core <NUM> that may be subsequently brazed shut. However, the tip pins <NUM> may be eliminated, avoiding the need to braze shut tip holes connecting the core cavity with the tip plenum.

The filaments <NUM> are preferably cylindrical or oval shape but may be curved or non-linear. Their exact dimensions may be varied according to a desired film cooling scheme for a particular cast metal part. For example cooling holes may have a cross sectional area ranging from <NUM> to <NUM><NUM>. In a turbine blade, the cross sectional area may range from <NUM> to <NUM><NUM>, more preferably from <NUM> to <NUM><NUM>, and most preferably about <NUM><NUM>. In the case of a vane, the cooling holes may have a cross sectional area ranging from <NUM> to <NUM><NUM>, more preferably <NUM> to <NUM><NUM>, and most preferably about <NUM><NUM>. The spacing of the cooling holes is typically a multiple of the diameter of the cooling holes ranging from <NUM>× to <NUM>× the diameter of the cooling holes, most preferably about <NUM>-<NUM>× the diameter of the holes.

The length of the filament <NUM> is dictated by the thickness of the cast component, e.g., turbine blade or stator vane wall thickness, and the angle at which the cooling hole is disposed relative to the surface of the cast component. The typical lengths range from <NUM> to <NUM>, more preferably between <NUM> to <NUM>, and most preferably about <NUM>. The angle at which a cooling hole is disposed is approximately <NUM> to <NUM>° relative to the surface, more preferably between <NUM> to <NUM>°, and most preferably approximately <NUM>°. It should be appreciated that the methods of casting according to the present invention allow for formation of cooling holes having a lower angle relative to the surface of the cast component than currently available using conventional machining techniques.

The specific shape of a cooling hole made in accordance with the present invention is determined by the shape of the filament connecting the core to the shell portion of the mold. Because the process for making filaments allows complete control over the dimensions of the filament, the present invention can be used to make any shape cooling hole. Moreover, a single cast object may be provided with several kinds of cooling hole designs. The following describes several non-limiting examples for cooling hole designs that may be used in accordance with the present invention. One key characteristic of the cooling holes of the present invention is that they may be provided with a non-line-of-sight shape. In practice, cooling holes drilled through a completed turbine blade using electro discharge machining (EDM) were limited to cooling holes that were generally shaped to have a line of sight through the cast metal object. This is because the EDM apparatus has a generally linear shape and operates by drilling through outer surface of the cast object to reach the core cavity. It is generally not possible to drill from the core cavity side of the cast object because the core cavity is inaccessible.

<FIG> shows a schematic side view of an integrated core-shell mold with non-linear filaments <NUM> in accordance with the present invention connecting the core <NUM> and shell portions <NUM>. By printing the ceramic mold using the above DLP printing process, the mold can be made in a way that allows the point of connections between the core and shell to be provided through non-linear filaments <NUM>. Once the core-shell mold is printed, it may be subject to a post-heat treatment step to cure the printed ceramic polymer material. The cured ceramic mold may then be used similar to the traditional casting process used in the production of superalloy turbine blades. Notably because the non-linear filaments <NUM> are provided in a large quantity consistent with formation of a pattern of effusion cooling holes in the surface of a turbine blade, the need for a ball chute structure as shown in <FIG> may be eliminated. In this embodiment, the tip pins <NUM> connecting the tip plenum core <NUM> to the core <NUM> are retained. After removal of the ceramic mold, tip holes exist between the core <NUM> and tip plenum core <NUM> that may be subsequently brazed shut. However, the tip pins <NUM> may be eliminated, avoiding the need to braze shut tip holes connecting the core cavity with the tip plenum.

The non-linear filaments <NUM> are preferably cylindrical or oval shape. Their exact dimensions may be varied according to a desired film cooling scheme for a particular cast metal part. For example cooling holes may have a cross sectional area ranging from <NUM> to <NUM><NUM>. In a turbine blade, the cross sectional area may range from <NUM> to <NUM><NUM>, more preferably from <NUM> to <NUM><NUM>, and most preferably about <NUM><NUM>. In the case of a vane, the cooling holes may have a cross sectional area ranging from <NUM> to <NUM><NUM>, more preferably <NUM> to <NUM><NUM>, and most preferably about <NUM><NUM>. The spacing of the cooling holes is typically a multiple of the diameter of the cooling holes ranging from <NUM>× to <NUM>× the diameter of the cooling holes, most preferably about <NUM>-<NUM>× the diameter of the holes.

The length of the filament <NUM> is dictated by the thickness of the cast component, e.g., turbine blade wall thickness, and the angle at which the cooling hole is disposed relative to the surface of the cast component. The typical lengths range from <NUM> to <NUM>, more preferably between <NUM> to <NUM>, and most preferably about <NUM>. The angle at which a cooling hole is disposed is approximately <NUM> to <NUM>° relative to the surface, more preferably between <NUM> to <NUM>°, and most preferably approximately <NUM>°. It should be appreciated that the methods of casting according to the present invention allow for formation of cooling holes having a lower angle relative to the surface of the cast component that currently available using conventional machining techniques.

The present invention relates also to methods of making cast metal objects, in particular single crystal turbine blades and stators used in jet aircraft engines that have non-linear cooling holes such as the exemplary design shown in <FIG>. The method begins with the production of the ceramic mold using DLP. The DLP process involves a repetition of steps of (a) contacting a cured portion of a workpiece with a liquid ceramic photopolymer; (b) irradiating a portion of the liquid ceramic photopolymer adjacent to the cured portion through a window contacting the liquid ceramic photopolymer; and (c) removing the workpiece from the uncured liquid ceramic photopolymer. The steps (a) - (c) are repeated until the ceramic mold shown in <FIG> is formed. After the mold is formed, liquid metal is poured into the casting mold and solidified to form the cast component. The ceramic mold is then removed from the cast component using, for example, combination of mechanical removal of the outer shell and leaching of the inner ceramic core.

The specific geometry of the non-linear cooling hole filaments shown in <FIG> may be varied based on the needs for specific effusion cooling hole pattern to be placed in the turbine blade or stator. For example, the direction of the hole may be opposite that shown in <FIG> with holes aligned toward the top of the turbine blade. The filament may have a curvature that forms an "S" shaped hold upon removal of the mold. Alternatively, the holes may be aligned horizontally along the turbine blade such that they project inward or alternatively outward of the page. Given the flexibility possible for DLP processing, there are no limitations on the shape of the cooling hole. A few alternative exemplary cooling hole geometries are shown in <FIG> and <FIG>.

<FIG> shows a side view of a non-linear cooling hole that can be made in a cast object in accordance with one aspect of the invention. In this example, the effusion cooling hole <NUM> extends from the inner surface <NUM> of the cast component <NUM> to the outer surface <NUM> of the cast component <NUM>. The cooling hole <NUM> has an upstream portion <NUM> with an inlet <NUM>, an intermediate portion <NUM>, and a downstream portion <NUM> with an outlet <NUM>. The cooling hole <NUM> has a non-linear line of sight, meaning that no virtual, single straight line segment may be extended between the inlet <NUM> and outlet <NUM>, given the areas of the inlet <NUM> and outlet <NUM>, and the diameters, shapes, and angles of the respective portions <NUM>, <NUM>. The exemplary cooling hole geometry may be implemented by printing a filament in the reverse pattern of the cooling hole within a core-shell assembly such as shown in <FIG>.

<FIG> shows an effusion cooling hole <NUM> in accordance with an embodiment of the invention. The cooling hole <NUM> extends from the inner surface <NUM> of the cast component <NUM>, through the cast component <NUM>, to an outer surface <NUM> of the cast component <NUM>. The cooling hole <NUM> extends from an upstream portion <NUM> with an inlet <NUM>, through a chamber <NUM>, to a downstream portion <NUM> with an outlet <NUM> to the outer surface of the cast object. The cooling hole <NUM> of the present invention may have a chamber <NUM> that is defined by having at least one height or width dimension that is greater than the minimum diameter of the inlet <NUM>. The cooling hole may have a ramp structure <NUM> adjacent to the inlet <NUM>.

The chamber <NUM> is designed to provide additional heat transfer capability to the cooling holes while serving as a trap for dust and particulate matter that makes its way into the supply of cooling air. This can be particularly advantageous when operating a jet aircraft in dusty or sandy environments. Preventing dust or sand from entering the flowpath can add useful life to downstream engine parts that may be damaged over time by dust or sand contamination. For example, turbine blades and stators in the low pressure turbine region of the jet aircraft engine may benefit from reduced contamination. In addition the ramp structure <NUM> can optionally be included in the design to further reduce contamination by sand or dust.

After leaching, the resulting holes in the turbine blade from the core print filaments may be brazed shut if desired. Otherwise the holes left by the core print filaments may be incorporated into the design of the internal cooling passages. Alternatively, cooling hole filaments may be provided to connect the tip plenum core to the shell in a sufficient quantity to hold the tip plenum core in place during the metal casting step.

After printing the core-shell mold structures in accordance with the invention, the core-shell mold may be cured and/or fired depending upon the requirements of the ceramic core photopolymer material. Molten metal is poured into the mold to form a cast object in the shape and having the features provided by the integrated core-shell mold. In the case of a turbine blade, the molten metal is preferably a superalloy metal that formed into a single crystal superalloy turbine blade using techniques known to be used with conventional investment casting molds.

In an aspect, the present invention relates to the core-shell mold structures of the present invention incorporated or combined with features of other core-shell molds produced in a similar manner.

Claim 1:
A method of preparing a cast component comprising:
(a) pouring a liquid metal into a ceramic casting mold and solidifying the liquid metal to form the cast component, the ceramic casting mold comprising:
(<NUM>) a core portion (<NUM>) and a shell portion (<NUM>) with at least one cavity between the core portion (<NUM>) and the shell portion (<NUM>), the cavity adapted to define a shape of the cast component upon casting and removal of the ceramic casting mold, and
(<NUM>) a plurality of filaments (<NUM>) joining the core portion (<NUM>) and the shell portion (<NUM>) wherein each filament spans between the core portion (<NUM>) and the shell portion (<NUM>) and defines a hole in the cast component, wherein at least one filament (<NUM>) includes at least a portion having a non-linear geometry and a cross sectional area ranging from <NUM> to <NUM><NUM>;
and
(b) removing the ceramic casting mold from the cast component by leaching at least a portion of the core portion through the holes in the cast component.