WO2024025596A1

WO2024025596A1 - Multiwall ceramic core and method of making a multiwall ceramic core using a non-sinterable ceramic fugitive

Info

Publication number: WO2024025596A1
Application number: PCT/US2022/074169
Authority: WO
Inventors: Ian T. DORAN; Gary B. Merrill; Louis Charles
Original assignee: Siemens Energy, Inc.
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2024-02-01

Abstract

A multiwall ceramic core (10) and method of making a multiwall ceramic core (10) using a non-sinterable ceramic fugitive, involving a main body portion (64) comprising a ceramic having a sintering temperature, and a non-sinterable ceramic fugitive arranged within and encapsulated by the main body portion (64), the non-sinterable ceramic fugitive having a sintering temperature above the sintering temperature of the ceramic, and the non-sinterable ceramic fugitive occupying a volume defining an internal geometry portion (66) of the multiwall ceramic core (10).

Description

MULTIWALL CERAMIC CORE AND METHOD OF MAKING A MULTIWALL CERAMIC CORE USING A NON- SINTERABLE CERAMIC FUGITIVE

BACKGROUND

1. Field

[0001] The present invention relates to a multiwall ceramic core and more specifically to a multiwall ceramic core with a non-sinterable ceramic fugitive designed and constructed for use in the manufacture of a multiwall gas turbine airfoil adapted for the power generation industry.

2. Description of the Related Art

[0002] Within the power generation industry, gas turbine engines are required to provide movement to produce electricity in a generator or to produce thrust. In gas turbine engines, compressed air discharged from a compressor section and fuel introduced from a source of fuel are mixed together and burned in a combustion section, creating combustion products defining a high temperature working gas. The working gas is directed through a hot gas path in a turbine section of the engine, where the working gas expands to provide rotation of a turbine rotor. The turbine rotor may be linked to an electric generator, wherein the rotation of the turbine rotor can be used to produce electricity in the generator, or to an exhaust to generate thrust.

[0003] In view of the high pressure ratios and high engine firing temperatures implemented in modern gas turbine engines, certain components, such as airfoils e.g., stationary vanes and rotating blades within the turbine section, must be cooled with cooling fluid, such as air discharged from a compressor in the compressor section, to prevent overheating of the components.

[0004] Effective cooling of the turbine airfoils requires delivering the relatively cool air to critical regions of the turbine airfoils, such as along internal passageways and the leading or trailing edge. For example, airfoils may include internal cooling channels which remove heat from the pressure sidewall and the suction sidewall in order to minimize thermal stresses. For another example, associated cooling apertures may extend between an upstream, relatively high pressure cavity within the airfoil and one of the exterior surfaces of the turbine blade. Thus, achieving a high cooling efficiency based on the rate of heat transfer is an airfoil design consideration in order to minimize the volume of coolant air diverted from the compressor for cooling.

[0005] Current methods of producing these modern airfoils utilize a master tooling to produce a mold from which a hollow ceramic core is made. The hollow ceramic core defines an open volume of shape that forms the shape of the airfoil when cast within an outer casting shell.

SUMMARY

[0006] One aspect or configuration involves a multiwall ceramic core comprising a main body portion comprising a ceramic having a sintering temperature; and a non- sinterable ceramic fugitive arranged within and encapsulated by the main body portion, the non-sinterable ceramic fugitive having a sintering temperature above the sintering temperature of the ceramic, and the non-sinterable ceramic fugitive occupying a volume defining an internal geometry portion of the multiwall ceramic core.

[0007] Another aspect or configuration involves a method of manufacturing a multiwall ceramic core using a non-sinterable ceramic fugitive comprising forming a mold from a master tooling assembly; introducing the non-sinterable ceramic fugitive into the mold; surrounding the non-sinterable ceramic fugitive with ceramic particles introduced into the mold to form a green body; and heating the green body to a temperature sufficiently high to sinter the ceramic particles but sufficient low so as to not sinter the non- sinterable ceramic fugitive and thereby form the multiwall ceramic core, wherein the sintered ceramic particles form a main body portion of the ceramic core and wherein the non-sinterable ceramic fugitive occupies a volume within the main body defining an internal geometry of the multiwall ceramic core. [0008] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.

[0010] FIG 1 is a logic flowchart illustrating steps to manufacture a multiwall ceramic core using a non-sinterable ceramic fugitive in accordance with an aspect of the subject matter;

[0011] FIG 2 is a perspective view of a portion of a hard master tooling assembly in accordance with an aspect of the subject matter;

[0012] FIG 3 is a perspective view of a portion of a flexible master tooling assembly in accordance with an aspect of the subject matter;

[0013] FIG 4 is a side view of a portion of the flexible master tooling assembly of Figure 3;

[0014] FIG 5 is a side view of a non-sinterable ceramic fugitive arranged within a mold made from the master tooling assembly;

[0015] FIG 6 is a side view of ceramic particles arranged within the mold and surrounding the non-sinterable ceramic fugitive to thereby form a green body multiwall ceramic core;

[0016] FIG 7 is a perspective view of an exemplary embodiment of a finished green body multi wall ceramic core of the subject matter castable into a multiwall airfoil of the subject matter; [0017] FIG 8 is a perspective view of another exemplary embodiment of a finished green body and multiwall ceramic core castable into a multiwall airfoil of the subject matter;

DETAILED DESCRIPTION

[0018] 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 spirit and scope of the subject matter or present invention.

[0019] For the purposes of this application, any reference to airfoils, gas turbines and the power industry may also be for other products, processes and industries that may require a core made from a casting or other manufacturing process. A turbine airfoil is used below as a contextual example of utilization of various master tooling assemblies and various ceramic cores from which a multiwall component may be made; however, the master tooling assemblies and ceramic cores may be used for any component requiring cast multiwall features. The exemplary multiwall gas turbine airfoil can be within the power generation industry. Also, while the core is often described in context of a ceramic material for casting purposes, the core may also be of any other material or purposes that functions in a similar fashion.

[0020] Broadly, a multiwall ceramic core 10 and a method of making a multiwall ceramic core 10 using a non-sinterable ceramic fugitive 6 is provided. The multiwall ceramic core 10 is designed and constructed for use in the manufacture of a multiwall gas turbine airfoil 12 and adapted for use in the power generation industry. As shown in the logic flowchart (Fig 1) the method of making a multiwall ceramic core 10 involves utilization of a master tooling assembly 2 (Fig 2) which may optionally include a flexible liner 40 (Figs 3 and 4) to generate a mold 4 in the desired form of the ceramic core 10. A non-sinterable ceramic fugitive 6 is then introduced into the mold 4 (Fig 5) followed by introduction of ceramic particles 8 into the mold 4 arranged to encapsulate the non- sinterable ceramic fugitive 6 (Fig 6) in order to form a green body 54 of the multiwall ceramic core 10. The green body 54 can then be treated e.g. heated (e.g. for binder 52 and carrier 62 removal), sintered (e.g. for ceramic particle 8 sintering and densification) and otherwise post-sinter processed (e.g. for loose-packed non-sinterable ceramic fugitive 6 removal) into a finished multiwall ceramic core 10, whereby the sintered ceramic particles 8 occupy a space or volume defining a main body 64 portion of the multiwall ceramic core 10 and the non-sinterable ceramic fugitive 6 occupies a space or volume defining an internal geometry 66 portion of the multiwall ceramic core 10 (Figs 7 and 8). The finished multiwall ceramic core 10 can then be cast to create a multiwall gas turbine airfoil 12 with the non-sinterable ceramic fugitive 6 removed to create a void to define internal geometry of the multiwall gas turbine airfoil 12.

[0021] A master tooling assembly 2 may be made and utilized in any of several ways, each of which having its own advantages and disadvantages. For example, a hard master tooling 14 may be used, or a flexible master tooling 16 may be used; both are described below. Additionally, aspects of one or more of the master tooling assemblies 2 may be combined or mixed and matched, as appropriate, such as using a flexible liner 40 of the flexible master tooling 16 with a hard master tooling 14.

[0022] As illustrated in Figure 2, one system to produce a master tooling assembly 2 for ceramic cores 10 includes a hard master tooling 14 that can be made via multi axis precision machining (typically from computer numerical control machines i.e. CNC) of a hard aluminum block to define the positive surface geometry of one side of a tooling block 18. Since intricate non-conformal master tooling features are quite difficult to machine, in areas where non-conformal features are required, an insert 20 can be applied to define the tooling block 18 surface geometry. The insert 20 is typically made from either photo foil, chemically etched copper foil, or other suitable material. The insert 20 is then bonded onto the tooling block 18 to form a three dimensional surface or electrical discharge machining (EDM) machined insert of the hard master tooling 14.

[0023] As illustrated in Figures 3 and 4, another way to produce a master tooling assembly 2 for ceramic cores 10 that allows for advanced and fine features and well as for rapid low cost master tooling assemblies 2 and multiple variants in the master tooling assembly 2 can start with a 3D computer model of a desired airfoil 12 to be created. The flexible master tooling 16 may be produced with a backing plate 22 and a plurality of lithographically derived inserts 24. With this flexible master tooling 16, there is no need for precision machined surfaces produced from CNC machines, which are replaced with the plurality of lithographically derived inserts 24 and backing plate 22 to form a flexible liner 40. An advantageously single step machined surface, the backing plate 22, may serve as a locator surface for the plurality of lithographically derived inserts 24 pieced together to define a tooling surface 32. Such features may include, but are not limited to, simple mechanical interlocking features and/or alignment locating features. Additionally, inserts may also be bonded with reversible bonding compounds. The backing plate 22 may be a single step machined surface. The backing plate 22 may include a top surface 30, side surfaces 28, and a bottom surface 26.

[0024] The plurality of lithographically derived inserts 24 may be produced by stereolithographic apparatus which converts liquid plastic into solid objects. Such technology may be used to create surface features not producible by traditional machining methods. Such technology may also be used to produce accurate surface tolerances as required for high definition applications.

[0025] Each of the plurality of lithographically derived inserts 24 may include a bottom surface 34, side surfaces 36, and a positive top surface 38, that may become the tooling surface 32. The positive top surface 38 may be non-conformal. The plurality of lithographically derived inserts 24 may expand across the entire top surface 30 of the backing plate 22. In certain embodiments, the plurality of lithographically derived inserts 24 may include various amounts of pieces. In certain embodiments, the plurality of lithographically derived inserts 24 includes three through eight inserts. The amount of plurality of lithographically derived inserts 24 may depend upon the complexity of the surface geometry and the degree of flexibility requested.

[0026] A method of manufacturing the flexible master tooling 16 may include providing the plurality of lithographically derived inserts 24. The backing plate 22 may be provided as a locating surface for the plurality of lithographically derived inserts 24. The plurality of lithographically derived inserts 24 may be pieced together and placed on the backing plate 22 to form a flexible liner 40. A non-conformal positive surface is generated from the plurality of lithographically derived inserts 24 pieced together. Examples of piecing together or combining a plurality of lithographically derived inserts 24 may involve, but is not limited to, 1) interlocking into the backing plate 22, 2) precision thin layer bonding, and 3) vacuum assisted surface contacting. The precision thin layer bonding may be with accomplished with a reversible thin layer bonding media. The backing plate 22 may include suction ports located in the top surface 30 of the backing plate 22. Once the plurality of lithographically derived inserts 24 is set in position along the backing plate 22, a portion of the flexible master tooling 16 forming a portion of the flexible liner 40 may be complete.

[0027] The first plurality of lithographically derived inserts 24 and the backing plate 22 may form a first half 42 of a flexible liner 40 of the flexible master tooling 16. A second half 44 of the flexible master tooling 16 may be formed by a second plurality of lithographically derived inserts 46 and a second backing plate 48 to form a second portion of the flexible liner 40. The second backing plate 48 may include a top surface 30, side surfaces 28, and a bottom surface 26. The second half 44 of the flexible master tooling 16 may be combined with the first half 42 of the flexible master tooling 16 to form a mold 4 cavity. The combining of the first half 42 and the second half 44 of the flexible master tooling 16 provides the assembled flexible master tooling 16 with flexible liner 40. Two negative flexible transfer molds may be created from the non-conformal positive surfaces of the plurality of lithographically derived inserts 24 and a second plurality of lithographically derived inserts 46 respectively. The negative flexible transfer molds may then be combined to produce a mold 4 having a flexible liner 40.

[0028] The illustrated second plurality of lithographically derived inserts 46 and the second backing plate 48 advantageously have the same or similar properties as the first plurality of lithographically derived inserts 24 and the backing plate 22 except for the second plurality of lithographically derived inserts 46 may have different non-conformal positive surfaces. Each of the second plurality of lithographically derived inserts 46 may include a bottom surface 34, side surfaces 36, and a positive top surface 38, that may become the tooling surface 26.

[0029] As mentioned above, the backing plate 22 may be a single step machined surface. Each of the first plurality of lithographically derived inserts 24 and second plurality of lithographically derived inserts 46 may be interchanged for other lithographically derived inserts 24, 46 for minor changes. In applications where rapid iterations and prototypes need to be made, this method with interchangeable first plurality of lithographically derived inserts 24 and second plurality of lithographically derived inserts 46 allows for quick adjustments. The flexible master tooling 16, being readily adjustable, allows for a reduction in manufacturing costs and reduces the time in between required changes.

[0030] Now referring back to the logic flowchart of Figure 1, the third logic box discloses a non-sinterable ceramic fugitive 6. The non-sinterable ceramic fugitive 6 is introduced into the mold 4 made from the master tooling assembly 2 such that the non- sinterable ceramic fugitive 6 occupies a space or geometric volume that will define an internal geometry 66 portion of the multiwall ceramic core 10, as discussed in more detail below.

[0031] As shown in Figure 5, the non-sinterable ceramic fugitive 6 may be made from any of a variety of materials that are non sinterable at the processing temperature of the ceramic core 4. Suitable materials include but are not limited to one or more of core packing media, saggar sand and inert ceramic particles. Exemplary core packing media includes those made with or form thermally treated kaolinite, halloysite and/or mullite. Exemplary saggar sand includes those made with or from alumina, silica and/or silicates. Exemplary inert ceramic particles include those ceramic particles disclosed is USPN 6,641,907 to Merrill et al. which is incorporated by reference herein.

[0032] Once the non-sinterable ceramic fugitive 6 material(s) is chosen for the particular core or airfoil application desired, the non-sinterable ceramic fugitive 6 can be advantageously adhered, tacked or otherwise bound with a binder 52 by any suitable technique, such as a three-dimensional printing technique that can include but is not limited to SLA, binder jet or fused deposition modelling, as well as injection molding techniques, and casting techniques. If used, suitable binders 52 include but are not limited to poly lactic acid, as well as photo sensitive polymers, high temperature waxes, and thermoset or optically cured polymers (printed or injected). In this configuration, the non-sinterable ceramic fugitive 6 notably lacks appreciable structural or strength capability to fully support as a core but does have appreciable dimensional stability as a particulate to occupy a space or volume to define an internal geometry 66 portion of the multiwall ceramic core 10. The non-sinterable ceramic fugitive 6 then may be introduced into the mold 4 by placing, adhering, pumping, injecting or otherwise arranging the non-sinterable ceramic fugitive 6 into the mold 4.

[0033] The specific location, size and geometry of the non-sinterable ceramic fugitive 6 within the mold 4 is typically an important core 10 and airfoil 12 design consideration. In context of the illustrated exemplarily cores 10 and airfoils 12, at least a first portion 56 of the internal geometry 66 occupied by the non-sinterable ceramic fugitive 6 extends contiguously along at least 25% of a length of the core 10, and depending on the particular application at least 50% of a length of the core 10, and in certain applications such as that shown in Figures 7 and 8, at least 75% of a length of the core 10. In other contexts, such as those also illustrated in Figures 7 and 8, a first portion 56 of the internal geometry occupied by the non-sinterable ceramic fugitive 6 extends contiguously along at least 25% of a first length of the core 10, a second portion 58 of the internal geometry occupied by the non-sinterable ceramic fugitive 6 extends contiguously along at least 25% of a second length of the core 10, and a third portion 60 of the internal geometry occupied by the non-sinterable ceramic fugitive 6 connects the first portion 56 and the second portion 58; although the at least 25% length of the first and/or second portions 56, 68 may be increased to at least 50% or even at least 75% as noted in the prior example. As also shown by Figures 7 and 8, the non-sinterable ceramic fugitive 6 may occupy a volume of between 5% and 25% of the total volume of the core 10, but depending on the particular application and airfoil 12, the non-sinterable ceramic fugitive 6 volume may instead be less than 5% or greater than 25%, with volumes of 2%-10% and 20%-50% and 60%-80% of the total volume of the core 10 suitable. There is no limitation of size, location or geometry of the non-sinterable ceramic fugitive 6, with the size, location and geometry being typically determined by design or other considerations. For example, the size, location and geometry occupied by the non-sinterable ceramic fugitive 6 space can be matched to the size, location and geometry of some or all of the ceramic core 10 and airfoil 12 internal cooling holes or a portion of or all of the leading or trailing edge portion of the airfoil 12.

[0034] Once the non-sinterable ceramic fugitive 6 is introduced into the mold 4, the mold 4 is ready for receipt of the ceramic particles 8 which are advantageously arranged to surround or encapsulate the non-sinterable ceramic fugitive 6. One way for the mold 4 to receive the ceramic particles 8 is to arrange the mold 4 onto a wax injection press and lock down the mold 4 thereon. The ceramic particles 8 then may be introduced in the mold 4 via any suitable means such as an injected pressurized wax/ceramic mixture discussed below

[0035] Now again referring back to the logic flowchart of Figure 1, the fourth logic box discloses ceramic particles 8. The ceramic particles 8 are introduced into the mold 4 made from the master tooling assembly 2 such that ceramic particles 8 surround or encapsulate the non-sinterable ceramic fugitive 6 while also occupying a space or volume defining a main body 64 portion of the multiwall ceramic core 10, as discussed in more detail below.

[0036] As shown in Figure 6, the ceramic particles 8 may be selected from any of a variety of ceramic material core mix compositions. Exemplary suitable ceramic particles 8 include compositions including one or more of silica, zircon, alumina and the like in order to provide for high temperature thermal stability and core teachability and also convert to a majority low volume phase (cristobalite) to allow for metal solidification without hot tear defects. Also, a binder could be optionally used with the ceramic particles 8, if used, suitable binders include but are not limited to waxes, ethyl silicates, liquid polymer or water based systems [0037] Once a ceramic particle 8 material composition is chosen for the particular application desired, it can be introduced into the mold 4 so as to surround or encapsulate the non-sinterable ceramic fugitive 6, in any of a variety of techniques. For example, the ceramic particles 8 can be placed within a carrier 62 such as liquid wax prepared to a desired consistency by any of a variety of mixing or combining techniques.

[0038] The mixture of ceramic particles 8 and carrier 62 may be introduced into the mold 4 by, for example, high pressure wax injection molding. This process may utilize a hydraulic wax press capable of injecting the ceramic/carrier mixture 8, 62 at pressure of 200 to 900 psi range and temperatures between 110 to 200 degrees F into the mold 4 to thereby surround or encapsulate the non-sinterable ceramic fugitive 6. The ceramic/carrier mixture 8, 62 may then be allowed to cool to between 110 to 80 degrees F prior to extraction from the mold 4. However, any of a variety of other suitable ceramic particle mold introduction techniques may be used including but are not limited to low pressure injection molding, vacuum injection, poured core under vibration etc. In this manner and construction, the introduced ceramic particles 8 form a main body 64 portion of the ceramic core 4. Thus, a green body 54 is thereby formed having a non-sinterable ceramic fugitive 6 forming an internal geometry 66 portion of the ceramic core 10 within and encapsulated by ceramic particles 8 forming a main body 64 portion of the ceramic core 10.

[0039] The green body 54 can then be further processed into a finished multiwall ceramic core 10, with the ceramic particles 8 forming a main body 64 portion of the multiwall ceramic core 10 and the non-sinterable ceramic fugitive 6 occupying a space or volume defining an internal geometry 66 portion of the multiwall ceramic core 10. In more detail, the green body 54 can then by treated e.g. heated to a temperature of 400 to 1400 degrees F in order to melt, burn off and otherwise remove binder 52 and carrier 62. Next, the green body 54 can be sintered at a temperature of 2190 to 2370 degrees F for sintering and densification of the ceramic particles 8, or other suitable temperatures based on the selected ceramic particles 8. The sintering advantageously occurs at a temperature sufficiently high to cause the ceramic particles 8 to densify and form into a ceramic but sufficiently low so as to not sinter the non-sinterable ceramic fugitive 6 and allow the non- sinterable ceramic fugitive 6 to remain stable and in its occupied space or volume within the ceramic core 10. Thus, during this sintering phase, the green body 54 is thereby transformed into a finished multiwall core 10 with the non-sinterable ceramic fugitive 6 not sintering and remaining dimensionally stable in its occupied space or volume as an unsupported particulate that does not provide appreciable structural integrity to the finished multiwall core 10. Optionally, the green body 54 may be further thermally treated to a temperature range of between 1800 to 2400 degrees F to a defined and closely controlled sintering cycle required to produce defect free partially sintered ceramic cores 10. Also optionally, the finished multiwall core 10 can be post-sinter processed e.g. to remove remaining loose-packed non-sinterable ceramic fugitive 6. By this method, the sintered ceramic particles 8 form a main body 64 portion of the ceramic core 10 while the non- sinterable ceramic fugitive 6 occupies a space or volume defining an internal geometry 66 portion of the multiwall ceramic core 10.

[0040] Referring again to Figure 7, an exemplary finished multiwall ceramic core 10 generated from a mold 4 made from a master tooling assembly 2 that optionally includes a flexible liner 40 is shown. The illustrated multiwall ceramic core 10 is designed and constructed such that the final casting geometry creates detailed, complex and otherwise unmanufacturable internal cooling geometries in the multiwall airfoil 12. The illustrated multiwall ceramic core 10 also enables advanced aerodynamic configurations for an advanced external casting geometry of the multiwall airfoil 12.

[0041] Referring again to Figure 8, another exemplary finished multiwall ceramic core 10 generated from a mold 4 from a master tooling assembly 2 that optionally does not include a flexible liner 40 is shown. The illustrated multiwall ceramic core 10 is designed and constructed such that the final casting geometry creates detailed, complex and otherwise unmanufacturable internal cooling geometries in the multiwall airfoil 12. The illustrated multiwall ceramic core 10 also enables advanced aerodynamic configurations for an advanced external casting geometry of the multi wall airfoil 12.

[0042] The finished multi wall ceramic core 10 can then be prepared and cast to create the multiwall airfoil 12 with the non-sinterable fugitive 6 being acid etched, burned off or otherwise removed to create a space or volume to define an internal geometry portion of the multi wall airfoil 12. The ceramic core 10 can be cast to form the multiwall airfoil 12 in any a variety of casting techniques, including using either an equiaxed or directionally solidified casting process using nickel-based alloys (precipitation hardened or crystallographically engineered for mechanical strength, with the core removeable via mechanical, chemical or other suitable means.

[0043] While an exemplary gas turbine airfoil for use in the power generation industry is illustrated for purposes of this application, as will be understood by those skilled in the art, reference to airfoils, gas turbines and the power industry may also be for other products, processes and industries that may require a core made from a casting process. The gas turbine airfoil illustrated above is a contextual example of utilization of various master tooling assemblies and various ceramic cores from which a multiwall component may be made; however, the master tooling assemblies and ceramic cores may be used for any component requiring cast multiwall features. Also, while the core is often described in context of a ceramic particle material and the fugitive in context of a non-sinterable ceramic material, for casting purposes, the core and fugitive may also be of any other materials that function in a similar fashion.

[0044] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the subject matter, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.

Claims

CLAIMS What is claimed is:

1. A multi wall ceramic core (10), comprising: a main body portion (64) comprising a ceramic (8) having a sintering temperature; and a non-sinterable ceramic fugitive (6) arranged within and encapsulated by the main body portion (64), the non-sinterable ceramic fugitive (6) having a sintering temperature above the sintering temperature of the ceramic (8), and the non-sinterable ceramic fugitive (6) occupying a volume defining an internal geometry portion (66) of the multiwall ceramic core (10).

2. The multiwall ceramic core (10) of claim 1, wherein a first portion (56) of the internal geometry portion (66) extends contiguously along at least 25% of a first length of the ceramic core (10).

3. The multiwall ceramic core (10) of claim 2, wherein the first portion (56) of the internal geometry portion (66) extends contiguously along at least 50% of the first length of the ceramic core (10), a second portion (58) of the internal geometry portion (66) extends contiguously along at least 50% of a second length of the ceramic core (10), and a third portion (60) of the internal geometry portion (66) connects the first portion (56) and the second portion (58).

4. The multi wall ceramic core (10) of claim 1, wherein the volume of the internal geometry portion (66) is between 5% and 25% of the total volume of the ceramic core (10).

5. The multiwall ceramic core (10) of claim 1, wherein at least a portion of the internal geometry portion (66) constitutes an internal cooling hole on a leading or trailing edge of a turbine airfoil (12).

6. The multi wall ceramic core (10) of claim 1, wherein the ceramic (8) comprises a composition selected from the group consisting of silica, zircon and alumina.

7. The multi wall ceramic core (10) of claim 1, wherein the non-sinterable ceramic fugitive (6) comprises a composition selected from the group consisting of core packing media, saggar sand and inert ceramic particles.

8. The multiwall ceramic core (10) of claim 1, wherein the non-sinterable ceramic fugitive (6) a comprises saggar sand selected from the group consisting of alumina, silica and silicates, mixed with a binder (52) selected from the group consisting of poly lactic acid, photo sensitive polymers, high temperature waxes, and thermoset or optically cured polymers.

9. The multi wall ceramic core (10) of claim 1, wherein the non-sinterable ceramic fugitive (6) comprises a core packing media selected from the group consisting of kaolinite, halloysite and mullite, mixed with a binder (52) selected from the group consisting of poly lactic acid, photo sensitive polymers, high temperature waxes, and thermoset or optically cured polymers.

10. A method of manufacturing a multiwall ceramic core (10) using a non- sinterable ceramic fugitive (6), comprising: forming a mold (4) from a master tooling assembly (2); introducing the non-sinterable ceramic fugitive (6) into the mold (4); surrounding the non-sinterable ceramic fugitive (6) with ceramic particles (8) introduced into the mold (4) to form a green body (54); and heating the green body (54) to a temperature sufficiently high to sinter the ceramic particles (8) but sufficient low so as to not sinter the non-sinterable ceramic fugitive (6) and thereby form the multiwall ceramic core (10), wherein the sintered ceramic particles (8) form a main body portion (64) of the ceramic core (10) and wherein the non-sinterable ceramic fugitive (6) occupies a volume within the main body portion (64) defining an internal geometry portion (66) of the multiwall ceramic core (10).

11. The method of claim 10, wherein the master tooling assembly (2) comprises: a multi axis precision machined aluminum block defining a positive surface geometry of one side of a tooling block (18); and an insert (20) made from either photo foil or chemically etched copper foil, the insert (20) bonded onto the master tooling assembly (2) to make a three dimensional surface or electrical discharge machining machined insert.

12. The method of claim 10, wherein the master tooling assembly (2) comprises: a plurality of lithographically derived inserts (24) and a second plurality of lithographically derived inserts (46) each comprising a bottom surface, side surfaces, and a positive top surface; a backing plate (22) and a second backing plate (48) each comprising a top surface, side surfaces, and a bottom surface, the backing plate (22) and the second backing plate (48) provided as a locator surface; a first non-conformal positive surface formed from the first plurality of lithographically derived inserts (24) and arranged on the first backing plate (22); a second non-conformal positive surface formed from the second plurality of lithographically derived inserts (46) and arranged on the second backing plate (48); a first negative flexible transfer mold formed from the non-conformal positive surface of the plurality of lithographically derived inserts (24); and a second negative flexible transfer mold from the non-conformal positive surface of the second plurality of lithographically derived inserts (46).

13. The method of claim 10, wherein the non-sinterable ceramic fugitive (6) comprises a saggar sand selected from the group consisting of alumina, silica and silicates tacked with a binder (52) selected from the group consisting of poly lactic acid, photo sensitive polymers, high temperature waxes, and thermoset or optically cured polymers.

14. The method of claim 13, wherein the ceramic particles (8) are mixed into a wax carrier (62) and the mixture is injected into the mold (4).

15. The method of claim 14, wherein the wax carrier (62) is injected into the mold (4) at a pressure of 200 to 900 psi and temperature of 110 to 200 degrees F.

16. The method of claim 10, wherein the sintering occurs at a temperature sufficiently high to cause the ceramic particles (8) to densify into a ceramic but sufficiently low for the non-sinterable ceramic fugitive (6) to remain dimensionally stable in its occupied volume as an unsupported particulate that does not provide appreciable structural integrity to the ceramic core (10).

17. The method of claim 16, wherein the sintering temperature is within the range of 2190 to 2370 degrees F.

18. The method of claim 10, wherein the multi wall ceramic core (10) is cast to form a multiwall airfoil (12).

19. The method of claim 18, wherein the multiwall airfoil (12) is a multiwall turbine blade.

20. The method of claim 19, wherein the multiwall turbine blade is used within the power generation industry.