Abstract:
One embodiment of the present invention is a unique method for forming a cast porous article. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for forming cast porous articles. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application No. 61/232,453, filed Aug. 9, 2009, and is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to castings, and more particularly in one form to processing a porous cast article. 
       BACKGROUND 
       [0003]    Casting technology, including casting porous articles, remains an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0004]    One embodiment of the present invention is a unique method for forming a cast porous article. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for forming cast porous articles. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  is a system for freeform fabricating a casting mold in accordance with an aspect of the present invention. 
           [0007]      FIG. 2  illustrates a casting mold in accordance with an embodiment of the present invention. 
           [0008]      FIG. 3  is an enlarged partial cross section through an airfoil portion of the casting mold of  FIG. 2 . 
           [0009]      FIG. 4  schematically depicts a cross section of a blade casting produced in accordance with an embodiment of the present invention. 
           [0010]      FIG. 5  schematically depicts a cross section of the blade casting of the embodiment of  FIG. 4 . 
           [0011]      FIG. 6  schematically depicts a cross section of a blade casting produced in accordance with an embodiment of the present invention. 
           [0012]      FIG. 7  schematically depicts a cross section of the blade casting of the embodiment of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0014]    Referring to  FIG. 1 , there is schematically illustrated a non-limiting example of a freeform fabrication system  10  for freeform fabrication of a component, such as a ceramic gas turbine engine blade, in accordance with an embodiment of the present invention. Ceramic materials contemplated herein include, but are not limited to, alumina, zirconia, silica, yittria, magnesia, and mixtures thereof. In one form, system  10  is a selective laser activation (SLA) stereolithography system. Selective laser activation is based upon a stereolithography process that utilizes resins which solidify when exposed to an energy dose. In one form, the resin includes ceramic particles disposed within a photo-polymerizable monomer(s) and/or oligomer(s), and the energy dose is a polymerizing energy dose. The present application contemplates the use of an oligomer(s) resin alone or in combination with a monomer resin. Although the present application is described with respect to a component in the form of ceramic blade mold  12 , it will be understood that the present application is also applicable to other types of materials and to other types of components. While the present application will be generally described with respect to an SLA stereolithography system, it is equally applicable to other freeform fabrication systems, such as flash cure systems and other forms of scanned cure systems, as well as other freeform fabrication systems not mentioned herein. 
         [0015]    System  10  is used to create gas turbine engine blade mold  12  as a three dimensional ceramic component formed of a plurality of layers, some of which are labeled as layers  14 ,  16 ,  18  and  20 . In one form, stereolithography system  10  employs a ceramic loaded resin  22 , and includes a resin containment reservoir  24 , an elevation-changing member  26 , a laser source  28  and a scanning device  30  operative to scan a laser beam  32  across elevation changing member  26 . Resin containment reservoir  24  is filled with a quantity of ceramic loaded resin  22  from which component  12  is fabricated. In one form, ceramic loaded resin  22  contains a photoinitiator. In another form, ceramic loaded resin  22  contains a dispersant, in addition to the photoinitiator. Scanning device  30  scans a laser beam  32  from laser source  28  across ceramic loaded resin  22 , e.g., on a surface  34  ceramic loaded resin  22 , in the desired shape to form each layer of gas turbine engine blade mold  12 . The ceramic particles contained in ceramic loaded resin  22  ultimately form the completed mold  12 . 
         [0016]    A three dimensional coordinate system including a first axis, a second axis and a third axis is utilized as a spatial reference for the item being fabricated, e.g., ceramic mold  12 . In one form, the three-dimensional coordinate system is a Cartesian coordinate system having X, Y and Z axes corresponding to the axes of stereolithography system  10 . However, other three-dimensional coordinate systems are contemplated herein, including but not limited to polar, cylindrical and spherical. 
         [0017]    In one form, gas turbine engine blade mold  12  is built at a build orientation angle as measured from axis Z. The build orientation angle illustrated in  FIG. 1  is zero degrees. Other build orientation angles are fully contemplated herein. The three-dimensional coordinate system is aligned with the build orientation angle. In one form the three dimensional coordinate system of mold  12  and stereolithography system  10  coordinate system are coextensive. 
         [0018]    Blade mold  12  is freeform fabricated by system  10  in layer-by-layer fashion by applying an energy dose to cure a film of ceramic-laden photo-polymerizable resin into a polymerized layer, applying a new film of the resin, and applying an energy dose sufficient to both photo-polymerize the new film of resin into a new layer and to provide an overcure to bind the new layer to the previous layer. In one form, each new resin film is formed over the topmost polymerized layer by lowering elevation changing member  26  to submerge the topmost polymerized layer in the ceramic loaded resin  22  in reservoir  24 . In other embodiments, new layers of ceramic loaded resin  22  may be applied to the topmost polymerized layer using other means. The process is repeated to form a plurality of polymerized layers, i.e., layers of ceramic particles that are held together by a polymer binder, e.g., such as the illustrated layer  14 ,  16 ,  18  and  20 . The successively formed cured layers ultimately form the three-dimensional shape of gas turbine engine blade mold  12  having the desired three-dimensional features formed therein. As described herein, the three-dimensional features of blade mold  12  include a controlled porosity distribution in portions of the mold. 
         [0019]    In one form, each polymerized layer is on the order of 0.05 mm (0.002 inches) thick, e.g., as measured along the Z axis, which may be referred to as the build direction. Thinner or thicker layers may be employed in other embodiments. For example, the thickness of each layer may vary with the needs of the particular application, including the desired resolution of the finished mold  12 . In some embodiments, some layers may have a greater thickness than other layers within the same mold It should understand that there is no intention herein to limit the present application to any particular number of layers or thickness of layers. In addition, although only a single gas turbine engine blade mold  12  is illustrated, it will be understood that a plurality of gas turbine engine blade mold  12  may be formed as a batch in system  10 . 
         [0020]    In one form, the formation of the polymerized layers includes the use of a leveling technique to level each of the layers of the photo-polymerizable ceramic loaded resin prior to receiving the energy used to polymerize the resin. Examples of leveling techniques include ultrasonic processing; time delay; and/or a mechanically assisted sweep, such as the use of a wiper blade. The present application also contemplates embodiments that do not employ active leveling techniques. 
         [0021]    The energy dose used to polymerize and overcure each layer may be varied or otherwise controlled. In one form, the energy dose is controlled by fixing a laser  28  power and beam  32  diameter, and then controlling the laser scan speed (rate) across the resin surface. In another form, such as with a flash cure system, the laser scan speed and laser power are replaced with exposure time and lamp power. In yet another form, the parameters that control cure and overcure are lamp power and scan speed. In other embodiments, other energy sources maybe employed, e.g., UV sources. In various embodiments, other parameters may control cure and/or overcure. 
         [0022]    After the formation of blade mold  12  in stereolithography system  10 , blade mold  12  may be subjected to additional processing prior to use. In one form, blade mold  12  is subjected to burnout processing and sintering to yield an integral ceramic casting mold for creating a gas turbine engine blade casting. In other embodiments, blade mold  12  may not be subjected to burnout processing or may not be subjected to sintering. In other embodiments, one or more of various techniques may be employed to remove polymeric material from blade mold  12 , if desired, and/or to enhance the structural integrity of blade mold  12 , if desired, e.g., depending upon the particular application. 
         [0023]    Referring now to  FIGS. 2 and 3 , a non-limiting example of blade mold  12  in accordance with an embodiment of the present invention is depicted. In one form, blade mold  12  includes an airfoil portion  36 , a platform portion  38 , an attachment portion  40  and a cooling air passage core  42 . In other embodiments, blade mold  12  may include other portions not mentioned herein, and/or may not include all of portions  36 ,  38  and  40 . Cooling air passage core  42  extends in a spanwise direction  44  through attachment portion  40 . In one form, core  42  forms a single cooling air passage in the blade casting produced using blade mold  12 . In other embodiments, core  42  may form a plurality of passages of various orientations, which may or may not be interconnected. In one form, core  42  extends through attachment portion  40  and terminates adjacent to platform portion  38 . In another form, core  42  extends further toward airfoil portion  36 . In yet another form, core  42  extends through a substantial portion of airfoil portion in spanwise direction  44 . In other embodiments, core  42  may extend completely through airfoil portion  36 . In still other embodiments, blade mold  12  may not include core  42 . 
         [0024]    Airfoil portion  36 , platform portion  38  and attachment portion  40  are structured to yield an airfoil, platform and attachment in the gas turbine engine blade casting. Portions of blade mold  12  include a controlled porosity distribution  46 . In one form, controlled porosity distribution  46  is a distribution of interconnected nodules  48  spaced apart by a plurality of interconnected pores  50  that are formed layer by layer as part of blade mold  12 . In one form, interconnected nodules  48  and interconnected pores  50  are operable to form a metal foam or other porous form with an open cell structure in selected portions of the blade casting produced using blade mold  12 , e.g., in the airfoil. In other embodiments, a closed cell structure may be formed in the casting by controlled porosity distribution  46 . In one form, controlled porosity distribution  46  is generated by defining a desired form, such as the desired geometric shapes, sizes and distribution of interconnected nodules  48  and interconnected pores  50 . In one form, interconnected nodules  48  and interconnected pores  50  are defined electronically e.g., using commercially available stereolithography computer aided design (CAD) software to generate an STL (.stl) file. The electronic definition is then supplied to system  10 , whereby scanning device  30  selectively cures subsequent layers in order to yield the desired three-dimensional interconnected nodules  48  and interconnected pores  50  based on the STL file. 
         [0025]    In one form, blade attachment portion  40  operable to form a fully dense attachment in the blade casting, and hence, does not include a controlled porosity distribution. It will be understood that in other embodiments, controlled porosity distribution  46  may be incorporated into all or part of attachment portion  40 . In one form, blade platform portion  38  operable to form a fully dense platform in the blade casting, and hence, does not include a controlled porosity distribution. In another form, blade platform portion  38  includes a controlled porosity distribution  46 , e.g., to supply cooling air from the passage formed by core  42  to the airfoil. It will be understood that in other embodiments, controlled porosity distribution  46  may be incorporated into all or part of platform portion  38 . 
         [0026]    A blade casting is produced using mold  12  by supplying a molten alloy into mold  12 , including directing the molten alloy into the interconnected pores  50  of controlled porosity distribution  46 . In one form, the alloy is a nickel-based superalloy. In other embodiments, other alloys may be used, including aluminum alloys and titanium alloys. The molten alloy is then solidified, e.g., via cooling. In one form, the molten alloy is solidified in a controlled manner to yield a single crystal structure. In other embodiments, other crystalline structures may be obtained, including but not limited to directionally solidified and equiax crystal orientations. In some embodiments, the crystal structure may not be controlled. Once the alloy is solidified, mold  12  is removed to yield a cast metallic article in the form of a gas turbine engine blade casting. In one form, mold  12  is removed by leaching. In a particular form, interconnected nodules  48  are removed by leaching to yield a blade casting with an airfoil having a plurality of interconnected pores extending therethrough. 
         [0027]    Referring now to  FIGS. 4 and 5 , a non-limiting example of a blade casting  60  produced using casting mold  12  in accordance with an embodiment of the present invention is depicted. In one form, blade casting  60  is a turbine blade. In another form, blade casting  60  is a compressor blade. In yet another form, blade casting  60  is a fan blade. Blade casting  60  includes an airfoil  62 , a platform  64 , and an attachment  66  having a passage  68 . Platform  64  is disposed between airfoil  62  and attachment  66 . In one form, passage  68  is a cooling air passage that extends through attachment  66  in spanwise direction  44  toward airfoil  62 . In other embodiments, passage  68  may extend in other directions in addition to or in place of direction  44 . In still other embodiments, blade casting  60  may be devoid of passages such as passage  68 . In one form, airfoil  62 , platform  64  and attachment  66  are integrally formed together as a unitary blade casting without the use of bonds or joints using mold  12 . In one form, blade casting  60  has a density that varies with location in blade casting  60 . In a particular form, blade casting  60  has a metallographic structure that ranges from fully dense, e.g., in attachment  66 , to porous, e.g., in airfoil  62 . 
         [0028]    In one form, controlled porosity distribution  46  in mold  12  forms a plurality of interconnected pores in blade casting  60  to yield a metal foam  70  in blade casting  60 . In a particular form metal foam  70  is formed in airfoil  62  and a portion of platform  64 . In the depiction of  FIGS. 4 and 5 , metal foam  70  is depicted in the form of “bubbles” of varying size. In one form, metal foam  70  has a porosity in the range of 10 pores per inch to 100 pores per inch. In a particular form, the porosity ranges from 10 pores per inch to 60 pores per inch. In other embodiments, other porosities may be utilized, including distributions of pores of the same size. In one form, controlled porosity distribution  46  yields a pore size in the blade casting  60  that decreases with increasing proximity to an outer surface of the cast metallic article. For example, as depicted in  FIGS. 4 and 5 , pores  70 A in a central portion of airfoil  62  are of a larger size than pores  70 B that are adjacent to an outer surface  72  of airfoil  62 . In one form, the pore size in the metallic airfoil is largest in locations adjacent to the passage  68  and transitions to the smallest pore size adjacent to outer surface  72  of airfoil  62 . In one form, the plurality of interconnected pores forming metal foam  70  have an open cell structure and are operable to transmit cooling air from passage  68  to outer surface  72  on airfoil  62 . 
         [0029]    Referring now to  FIGS. 6 and 7 , a non-limiting example of a blade casting  80  produced using casting mold  12  in accordance with an embodiment of the present invention is depicted. In one form, blade casting  80  is a turbine blade. In another form, blade casting  80  is a compressor blade. In yet another form, blade casting  80  is a fan blade. Blade casting  80  includes an airfoil  82 , a platform  84 , and an attachment  86  having a plurality of passages  88 . Platform  84  is disposed between airfoil  82  and attachment  86 . In one form, passages  88  are cooling air passages that extend through attachment  86  in spanwise direction  44  and passes through the bulk of airfoil  82 . In other embodiments, passages  88  may extend in other directions in addition to or in place of direction  44 . In yet other embodiments, passages  88  may extend completely through airfoil  82 . In still other embodiments, blade casting  80  may be devoid of passages such as passage  88 . In one form, airfoil  82 , platform  84  and attachment  86  are integrally formed together as a unitary blade casting without the use of bonds or joints using mold  12 . In one form, blade casting  80  has a density that varies with location in blade casting  80 . In a particular form, blade casting  80  has a metallographic structure that ranges from fully dense, e.g., in attachment  86 , to porous, e.g., in airfoil  82 . 
         [0030]    In one form, controlled porosity distribution  46  in mold  12  forms a plurality of interconnected pores in blade casting  80  to yield a metal foam  90  in blade casting  80 . In a particular form, metal foam  90  is formed in airfoil  82 , whereas platform  84  and attachment  86  are fully dense. In other embodiments, platform  84  and/or attachment  86  may not be fully dense, but may have a controlled porosity, such as metal foam  90 . In the depiction of  FIGS. 6 and 7 , metal foam  90  is depicted in the form of “bubbles” of varying size. In one form, metal foam  90  has a porosity in the range of 10 pores per inch to 100 pores per inch. In a particular form, the porosity ranges from 10 pores per inch to 60 pores per inch. In other embodiments, other porosities may be utilized, including distributions of pores of the same size. In one form, controlled porosity distribution  46  yields a pore size in the blade casting  80  that decreases with increasing proximity to an outer surface of the cast metallic article. For example, as depicted in  FIGS. 6 and 7 , pores  90 A in a central portion of airfoil  82  are of a larger size than pores  90 B that are adjacent to an outer surface  92  of airfoil  82 . In one form, the pore size in the metallic airfoil is the largest in locations adjacent to the passages  88  and transitions to the smallest pore size adjacent to outer surface  92  of airfoil  82 . In one form, the plurality of interconnected pores forming metal foam  90  have an open cell structure and are operable to transmit cooling air from passages  88  to outer surface  92  in selected portions of airfoil  82 . In one form, airfoil  82  also includes a fully dense outer skin portion  94  that is devoid of pores. In a particular form, fully dense skin portion  94  has a thickness in the range of 0.005 inches to 0.030 inches. In other embodiments that have a fully dense skin portion, other skin thickness values may be employed. In one form, passages  88  are defined by ribs  96 , which in some embodiments may be used to stiffen a hollow airfoil  82  and/or direct the flow of cooling air. 
         [0031]    Because controlled porosity distribution  46  is explicitly defined and freeform fabricated to generate the defined porosity distribution, some embodiments of the present invention may have fully dense portions that seamlessly blend to a porous structure, such as a porous airfoil. Some embodiments of the present invention may provide a gradation of properties though the casting produced using mold  12 . In one form, controlled porosity distribution  46  is used to produce an open cell structure for use as cooling air passages, e.g., for transpiration cooling of the blade produced using mold  12 . In one form, cooling air can be bled into the passage(s) in the blade root (attachment) and discharged through the outer skin of the airfoil and/or other portions of the blade. This may include cooling the structure through convection, and discharging the air through the outer skin to shield the exterior surface of the blade from hot engine gases. In one form, the outer skin can have varying density to control cooling air flow and direction. In addition, by freeform fabricating the size and shape of the pores, the amount of cooling can be controlled. Further, the metal foam could be open in some portions of the blade, e.g., the pressure side of the airfoil, and closed in other portions of the blade, e.g., the suction side of the airfoil. 
         [0032]    Embodiments of the present invention include a method for forming a porous article, comprising: freeform fabricating a ceramic mold having a controlled porosity distribution; sintering the ceramic mold; supplying a molten alloy to the sintered mold; and removing the ceramic mold to yield a cast metallic article. 
         [0033]    In a refinement, the cast metallic article has a density that varies with location in the cast metallic article. 
         [0034]    In another refinement, the controlled porosity distribution in the ceramic mold forms a metal foam in a portion of the cast metallic article. 
         [0035]    In yet another refinement, the metal foam has a porosity in the range of 10 pores per inch to 100 pores per inch. 
         [0036]    In still another refinement, the controlled porosity distribution yields a pore size in the cast metallic article that decreases with increasing proximity to an outer surface of the cast metallic article. 
         [0037]    In yet still another refinement, the cast metallic article is a gas turbine engine blade; wherein the gas turbine engine blade includes an airfoil and an attachment structured to secure the airfoil to a gas turbine engine disc; wherein the attachment is fully dense; and wherein the airfoil has a controlled distribution of pores. 
         [0038]    In a further refinement, the gas turbine engine blade includes a platform disposed between the attachment and the airfoil. 
         [0039]    In a yet further refinement, the attachment includes a passage extending therethrough toward the airfoil. 
         [0040]    In a still further refinement, the passage extends at least partially through the airfoil in a spanwise direction. 
         [0041]    In a yet still further refinement, the ceramic mold is freeform fabricated to yield an open cell structure in at least one portion of the cast metallic article. 
         [0042]    Embodiments of the present invention also include a method for forming a gas turbine engine blade casting, comprising: defining a distribution of interconnected nodules spaced apart by a first plurality of interconnected pores; freeform fabricating a ceramic mold, the ceramic mold including an airfoil portion having the defined distribution of interconnected nodules spaced apart by the first plurality of interconnected pores; supplying a molten alloy to the ceramic mold; solidifying the molten alloy; and leaching the interconnected nodules to yield a metallic airfoil having a second plurality of interconnected pores extending therethrough. 
         [0043]    In a refinement, the supplying the molten alloy to the ceramic mold includes directing the molten alloy into the first plurality of interconnected pores of the ceramic mold. 
         [0044]    In another refinement, a pore size in the metallic airfoil is in the range of 10 pores per inch to 100 pores per inch. 
         [0045]    In yet another refinement, the embodiment further includes freeform fabricating the ceramic mold to include a blade platform portion that is operable to form a blade platform in the blade casting, wherein the blade platform is integrally formed with the metallic airfoil. 
         [0046]    In still another refinement, the embodiment further includes freeform fabricating the ceramic mold to include an attachment portion that is operable to form a fully dense attachment in the blade casting, wherein the attachment is integrally formed with the metallic airfoil. 
         [0047]    In yet still another refinement, the embodiment further includes freeform fabricating the ceramic mold to form a passage in blade casting that extends in a spanwise direction through the attachment toward the metallic airfoil. 
         [0048]    In a further refinement, a pore size in the metallic airfoil is a largest pore size in locations adjacent to the passage and transitions to a smallest pore size adjacent to an outer surface of the metallic airfoil. 
         [0049]    In a yet further refinement, the second plurality of interconnected pores are operable to transmit a fluid from the passage to an outer surface of the blade casting. 
         [0050]    In a still further refinement, the outer surface is an outer surface of the metallic airfoil. 
         [0051]    In a yet still further refinement, the embodiments further includes freeform fabricating the ceramic mold to form a passage in the blade casting that extends through the attachment and at least partially through the metallic airfoil in a spanwise direction; and wherein a pore size in the metallic airfoil is a largest size in locations adjacent to the passage and transitions to a smallest size in locations adjacent to an outer surface of the metallic airfoil. 
         [0052]    In an additional refinement, the metallic airfoil includes a central portion having a largest pore size; and wherein a pore size transitions to a smallest pore size adjacent an outer surface of the metallic airfoil. 
         [0053]    In another additional refinement, the metallic airfoil includes a fully dense outer skin portion. 
         [0054]    Embodiments of the present invention also include a method for forming a gas turbine engine blade casting, comprising: means for forming a mold having a plurality of interconnected nodules; supplying a molten alloy to the mold; and means for removing the plurality of interconnected nodules to yield a metallic airfoil having a plurality of interconnected pores extending therethrough. 
         [0055]    In a refinement, a density of the metallic airfoil varies with location in the metallic airfoil. 
         [0056]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.