METHOD FOR FORMING CASTING MOLDS TECHNICALFIELD
This disclosure generally relates to casting, and, more specifically, to manufacturing molds used in casting operations.
BACKGROUND
Casting processes are widely employed for the formation of articles. In general, casting processes can be described as any process wherein a flowable material is introduced into a mold, allowed to solidify therein, and then removed in solid form. Exemplary casting processes include investment casting, slip casting, gel casting, sand casting, plaster casting, die-casting, injection molding, slurry injection, powder forming (compaction), reaction forming, colloidal forming, cold isostatic pressing, hot isostatic pressing, and so forth. However, investment casting in particular is extensively utilized as the investment core allows for the formation of east articles häving greater detail than is achievable in other casting processes and allows for the efficient production of the casting mold.
The investment casting process begins with fabricating a sacrificial wax pattern that comprises a similar geometrical shape as the desired cast part Patterns are normally made of investment casting wax that is injected into a metal mold via a wax injection molding process. Once a wax pattern is produced, U is assembled to other wax components to form a gate and runner system through which the casting material will flow. The entire wax assembly is then dipped in a ceramic slurry, covered with a sand stucco, and allowed to dry. The dipping and stuccoing process is repeated until a desired shell thickness is obtained (e.g., about 6-10 mm (0.25-0.675 in)). Once the ceramic has dried, the entire assembly is placed in a steam autoclave to remove a majority of the wax. After autoclaving, if additional wax remains in the shell, it is burned out in a furnace (e.g., about 400°C). At this point, the impressum of the wax pattern and me gate and runner system remains in the ceramic mold. The mold is then preheated to a specific temperature and filled with molten metal, which solidifies therein, creating the metal casting. Once the casting has cooled sufficiently, the mold
shell is chipped away from the casting. Next, the gates and runners are cut from the casting and the casting is optionally subjected to final post processing operations (e.g., sandblasting, machining, and so forth).
In alternative processes, the ceramic mold can be formed in sections, such as mold halves, or even more sections, which can be assembled together to form the finished mold. This is advantageous as the mold can be disassembled to remove east parts therefrom, enabling the mold to be utilized multiple times.
Although investment casting can provide improved detail and allow for casting molds to be formed using the dipping process, investment casting processes as well as other ceramic mold forming processes remain deficient in replicating fine surface features. For example, investment cores häving surface features and/or textures such as pattems, protrusions and/or figuring that comprises intricate details and/or relatively small details (e.g., patterns comprising lines häving a height that is less than or equal to about 0.010 inches) are generally poorly replicated (e.g., non-uniformly replicated and/or distorted) after the mold is heat treated.
As a result, there is a need for methods for forming casting molds häving detailed surface features.
BRIEF SUMMARY
Disclosed herein are methods for forming casting molds and methods for casting articles.
In one embodiment, a method for forming a mold comprises casting a mold häving a cavity surface, forming surface features on the cavity surface, wherein the surface features comprise a mixture, and heat treating the mixture. In another embodiment an article is disclosed.
In another embodiment, a method for forming a mold comprises forming a die, casting a mold within the die using a ceramic composition and a casting process selected from the group consisting of investment casting, slip casting, gel casting, sand casting, plaster casting, die-casting, injection molding, slurry injection, powder
forming (compaction), reaction forming, colloidal forming, cold isostatic pressing, hot isostatic pressing, and combinations comprising at least one of the foregoing, heating the mold, extruding a mixture onto a cavity surface of the mold to form surface features thereon, wherein the mixture is extruded through the nozzle of an apparatus, and heat treating the mixture.
In other embodiments, articles are formed from the methods fonning molds disclosed.
The above described and other features are exemplified by the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Refer now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike.
Figure l is an exemplary illustration of a first die half. Figure 2 is an exemplary illustration of a second die half.
Figure 3 is an exemplary illustration of a first die half filled with a ceramic composition.
Figure 4 is an exemplary illustration of the second die half filled with a ceramic composition.
Figure 5 is an exemplary illustration of a second mold half being removed from the first die half.
Figure 6 is an exemplary illustration of the first mold half being removed from the second die half.
Figure 7 is an exemplary illustration of Ae first mold half and the second mold half assembled.
Figure 8 is an exemplary illustration of a pen depositing a mixture onto the cavity surface of the second die forming protrusions thereon.
Figure 9 is an exemplary illustration of a molten alloy being poured into the sprue of the assembled die to form a turbine blade.
Figure 10 is an exemplary illustration of a east turbine blade comprising an exemplary pattern of dimples.
DETAILED DESCRIPTION
Disclosed herein is a method for forming surface features on casting molds comprising, after a mold has been formed, depositing metal and/or ceramic materials onto the surface of the casting mold to form the desired surface features thereon. Thereafter, the material can be heat treated to harden and bond it to the casting mold. The mold can then be employed to east an article, wherein the surface features formed in the casting mold form the negative geometry in the east part.
The method of forming surface features on a ceramic casting mold begins with the construction of the mold. The mold can be formed via ceramic forming methods such as investment casting, slip casting, gel casting, sand casting, plaster casting, die-casting, injection molding, slurry injection, powder forming (compaction), reaction forming, colloidal forming, isostatic pressing (e.g., hot isostatic pressing or cold isostatic pressing), and so forth, as well as combinations comprising at least one of these methods. The mold is constructed such that the internal surfaces of the mold are accessible to allow surface features to be formed thereon in a later process. Hence, the mold can be formed in sections (e.g., mold halves), which can be assembled together to form the finished mold and disassembled to remove east parts.
The materials employed for the mold can comprise materials that are capable of withstanding the temperatures endured during casting of desired east articles, such as metallic parts, in particular heat resistant superalloys. Exemplary materials comprise alumina, silica, and so forth.
One exemplary method employed for forming a casting mold employs a casting process wherein metal dies are constructed to form the casting mold halves. The dies are formed with internal geometries that replicate the desired outer surfaces of the part
to be east and comprise the basic form of the mold. For example, refer now to Figures l and 2 wherein and exemplary first die half 2 and second die half 4 are illustrated. The geometry of the first die half 2 and the second die half 4 will be employed to form a ceramic mold that will be utilized to east a turbine blade. The dies can be formed from metals, such as tool steels (e.g., P-20 mold steel häving 0.28-0.40 wt.% carbon, O.60-1.00 wt.% manganese, 0.20-0.80 wt.% silicon, 1.40-2.00 wt.% chromium, 0.30-0.55 wt.% molybdenum, 0.25 wt.% copper, 0.03 wt.% phosphorus, and 0.03 wt.% sulfur, per the American Iron and Steel Institute (AISI)) shock-resistant steels (e.g., S2 mold steel häving 0.40-0.55 wt.% carbon, 0.30-0.50 wt.% manganese, 0.90-1.20 wt.% silicon, 0.30 wt. % nickel, 0.30-0.50 wt.% molybdenum, 0.50 wt.% vanadium, 0.25 wt% copper, 0.03 wt.% phosphorus, and 0.03 wt.% sulfur, per AISI), and so forth. To be even more specific, any metals can be employed that will endure (i.e., not melt or deform) at the temperatures at which the material employed to form the casting mold will be processed; e.g., generally a temperature of about 700°C. The dies can be formed using metal working processes, (such as electrical discharge machining, milling, and grinding), rapid manufacturing methods (such as selective laser sintering, and layer deposition technologies), and so forth, as well as combinations comprising at least one of the foregoing processes.
Once the die formation process is complete, the dies are filled with a ceramic composition 6, as illustrated in Figures 3 and 4. Optionally, the ceramic composition 6 can be compressed within the dies, using, for example, mechanical pressure (e.g., a punch), isostatic pressure techniques, and so forth. In one example, a set of dies (e.g., first die half 2 and second die half 4) is filled with a ceramic composition and then subjected to an isostatic pressing process wherein the ceramic composition 6 is subjected to about 15,000 pounds per square inch (psi) of pressure in a pressurized air chamber.
The ceramic composition 6 can employ ceramic powders such as alumina, silica, zirconia, zirconium silkate (zircon), aluminum silicate (mullite), yttria, yttrium silicate, yttrium aluminate (garnet), yttrium aluminate (Perovskite), rare-earth oxides, rare earth silicates, rare earth aluminates, and so forth, as well as combinations comprising at least one of the foregoing. The specific ceramic powder(s) chosen will
be based on the desired properties of the molds, such as thermal conductivity, wear resistance, and so forth. The average partide size of the powders employed are also dependent upon the particular properties desired, such as surface roughness. The average partide size, is generally less than or equal to about 100 micrometers (), and, more specifically, less than or equal to about 70 μm, and, even more specifically, less than or equal to about 30 (im. The partide size influences the size of the specific surface features that can be replicated and the resulting surface finish of the mold. For example, in particular embodiments the powder employed can comprise an average partide size of about 0.001 jtm to about 10 urn.
In addition to the various powder(s), the ceramic composition 6 can also comprise a lquid media (such as alcohol(s), water, and/or (oil(s)), to form a slurry. A slurry can be advantageous if it is capable of flowing into complex mold geometries (e.g., undercuts, channels, and so forth). Additives can also be added to the ceramic composition 6. Exemplary additives are reinfbrcing fibers (e.g., silica fibers), processing aids (such as mold release material(s), e.g., paraffin wax), binders (e.g., polyoxymethylene, starch, celluloses, and so forth), as well as combinations comprising at least one of the foregoing. It is to be apparent that the materials employed (e.g., ceramics) for the mold, the mold's geometry (e.g., thickness), and other variables will influence the durability, eost, and performance of the mold. For example, in one specific cmbodiment, an alcohol can be added to a silica powder to form a slurry that is capable of flowing into a die at a desired rate. A silica fiber is also added to the ceramic composition 6 to increase the strength of the mold, and the thickness of the mold (e.g., the walls of the mold, not shown) is configured such that the casting material cools at a desired rate to provide a desired microstructure in the east article. Exemplary materials can also be found in U.S. PaL No. 4,989,664 (Roth), which is incorporated herein by reference.
Once filled, the die halves/mold halves (e.g., the die hälve comprise the mold halves in the form of the ceramic composition 6 therein) are heated. This allows binders within the ceramic composition 6 to bind together to form a weakly bound east mold. The die halves/mold halves can be heated in an oven for an amount of time mat is sufficient to bind the ceramic composition 6. In order to enable alteration of the

mold, the temperature is below a sintering temperature at this point in the process. In some circumstances, depending upon the additive(s) and/or liquid media employed, the die halves/mold halves can be heated for an additional amoimt of time to drive off any moisture or volatile liquids. In such situations, the oven employed can be equipped with a desiccant apparatus capable of drying the air within the oven during the process.
During the heating process the ceramic composition 6 can shrink to some degree (e.g., a volumetric). If the shrinkage is predictable, the dies can be oversized so that the molds produced will shrink to the desired specifications. The predictability of the ceramic composition's shrinkage can be increased by controlling the composition (e.g., partide size, purity, and so forth), and the ceramic mold's properties (e.g., density). For example, consistency in the partide size of the ceramic, the purity of the ceramic, the loading of additives, and other variables, can improve shrinkage predictability. In one embodiment, a hot isostatic pressing process can be employed to compress the ceramic composition 6 as it is heated. Employing such a process can also increase the density of the ceramic powders, which can reduce shrinkage when the molds are sintered.
After the dies have been heated for the desired amount of time (e.g., about four hours at 700°C for a non-slurry ceramic composition 6) the first mold half 8 and second mold half 10 are cooled (actively and/or passively), and are then removed from the die halves, as illustrated in Figure 5.
The first mold half 8 and second mold half 10 (also referred to as mold halves and molds) are prone to damage when they are removed from the die halves as die binders provide weak bonding of the ceramic powder. However, if handled carefully, the molds can be inspected and/or optionally modified when in the nqn-sintered state. For example, referring now to Figure 7, me first mold half 8 and the second mold half 10 are assembled so that they can be evaluated for fit, especially in areas of the parting Une 14 and the cavity 16. If modifications to the molds are desired, they can be achieved by machining and/or utüizing other modification methods. For example, vent(s) and sprue(s) can be machined into the mold halves to facilitate the flow of the
casting material into the cavity 16 using a drilling or milling operation. In addition, any flash around the parting line 14 can be removed utilizing a grinding operation and then the mold halves can be fitted with locatcrs and/or guides so that the molds will be mated properly during a casting process.
After inspection and optionally alteration, the molds can be sintered at a temperature sufficient to cause the ceramic powder(s) to adhere to one another. Exemplary temperatures generally employed are about 1,000°C to about 2,200°C. The time of the sintering process can vary based on the ceramic composition 6, the mass and geometry of the molds, as well as other variables; however, generally it is about 8 hours to about 30 hours. The sintering process can comprise various stages (e.g., temperature hoid stages, temperature rämps, gradual cooling stages, and so forth), which can provide a mold comprising the desired microstructure, reduce warpage, reduce shrinkage, and so forth.
Once the mold halves have been sintered, they are allowed to cool and subjected to any optional secondary operations. Exemplary operations comprise inspection, coating processes (e.g., coatings to reduce surface roughness, wear resistant coatings, and so forth), machining processes (e.g., addition of vents, addition of sprues, removal of flash, and so forth), labeling processes, fixturing processes (e.g., within a carrier mold base), modification processes (e.g., addition of guides, and the addition of elements to attach the molds to one another), and so forth. For example, in one embodiment the cavity 16 (Figure 7) can be polished.
Polishing the cavity 16 can be achieved either by polishing the actual interior surface of the cavity 16, such as using an ultrasonic polishing apparatus with diamond paste, and/or by coating the desired surface with a coating, polishing the coating, heat treating the coating, and re-polishing. These processes can be repeated as many times as desired to yield an acceptable finish. For example, in one embodiment, a slurry comprising a ceramic powder häving an average diameter of less than or equal to about 100 urn can be applied to the surfaces of the cavity 16. Thereafter, the slurry can be worked into the surface of the cavity (e.g., polished) and the cavity surface can
be sintered. Next, the surface can be further polished and/or additional coats can be applied and the process can be repeated.
To be inore specific, the interior surface of the cavity 16 can be finished with either ground or polished finishcs, Surface finishes which are ground (e.g., formed from grinding processes) generally comprise average surface roughness (Ra) values that are less than or equal to about 50 microinches, uin (1.27 /zm). Exemplary ground finishes can be represented by the Society for the Plastic Industry's surface finish characterization system, such as an SPI #6 surface finish, which is representative of surfaces produced using 320-grit paper exhibiting an Ra of about 38 to about 42 uin (0.97 nm to 1,07 jim), or an SPI #4 surface finish, which is representative of surfaces produced using 600-grit paper exhibiting an Ra of about 2 to about 3 uin (0.051 fnm to 0.075 (im). Exemplary polished finishes (i.e., glossy or high gloss finishes) generally comprise Ra values that are less than or equal to about 5 uin (0.127 /im), such as an SPI #3 surface finish, which is representative of surfaces produced via polishing with a grade #15 diamond buff exhibiting an Ra of about 2 to about 3 uin (0.051 fimto 0.075 ^m), or an SPI #1 surface finish, which is representative of surfaces produced via polishing with a grade #3 diamond buff exhibiting an Ra of about l uin (0.025 /«n).
Either prior to sintering or thereafter, the molds can be modified with surface features using an applicable deposition process. Exemplary deposition processes include chemical vapor deposition, ion plasma deposition, electron beam physical vapor deposition, and electroplating. The specific deposition process can dispose a ceramic material onto the surface of the mold with the desiied fidelity. One exemplary deposition process is the "Direct Write" (DW) process, which also referred to as a "pen-type" or "nozzle" deposition process. Exemplary Direct Write techniques (e.g., pen, nozzle, laser, thermal spray, and so forth) are described in commonly owned U.S. Patent Application Serial No. 11/170579 (Hardwicke, et ai), and in U.S. Published Application No. 2005-0013926 (Rutkowski et ai), which are incorporated herein by reference.
Refer now to Figure 8, wherein a pen 20 deposits a mixture 26 onto the cavity surface 24 of the second mold half 10 forming protrusions 22 thereon. The mixture 26 flows through the pen 20 under pressure and exits at a nozzle 28. The pressure employed is dependent upon rhe desired flow rate as well as other variables such as the inner diameter of the nozzle 28, the viscosity of mixture 26, and so forth. The size of the nozzle 28 is generally about 0.010 mm to about 1.0 mm, and is selected to provide a desired extrudate diameter.
The pen 20 is displaced relative to the cavity surface 24 and capable of translating along the cavity surface 24 to form surface features thereon. Beneficially, surface features (e.g., layers) may be deposited rapidly and precisely on a complex-shaped cavity surface 24 in an automated manner. The motion of the pen 20 coupled with control of the mixtures flow through the pen. allow for layers, drops, smears, and combinations thereof to be formed by the pen 20. In addition, multiple passes of the pen 20 over an area can build layers of the mixture 26 and/or multiple pens can be employed to increased the speed of the deposition process or to modify multiple mold surface simultaneously. Therefore, the pen 20 can form a large number of surface features, wherein the term surface features is to be interpreted as any form created by disposing mixture 26 onto a surface, such as patterns (e.g., crosshatching, or weave patterns), drops, smears, layers, Unes, shapes (e.g., circles, wavy lines, fish-scales, tessellations, or polygons), and so forth.
Controller 30 is connected in operational communication with the pen 20. The controller 30 is capable of controüing the motion of the pen 20, the flow rate at which the mixture 26 is extruded from the pen 20, and other processes and/or operations of the apparatus during operation. For example, the cavity surface 24 and a desired surface feature (protrusions 22) can be generated and stored in a computer as a CAD/CAM file that can be accessed by the controller 30 and executed to form the desired surface features on the cavity surface 24. Therefore, these methods can be embodied in the form of computer or controller implemented processes and apparatuses for practicing those processes. These methods can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-
readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the method. The methods may also be embodied in the form of computer program code or signal, for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber opücs, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the method. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.
The mixture 26 employed by the pen 20 can comprise a slurry häving a loading of about 50 to about 98 wt.% solids and a liquid. The solids can be a metal (e.g., copper, gold, platinum, nickel, cobalt, titanium, or iron), a ceramic (e.g., alumina, zirconia, zirconium silicate (zircon), aluminum silicate (mullile), yttria, yttrium silicate, yttrium aluminale (garnet), yttrium aluminale (Perovskite), rare-earth oxides, rare earth silicates, rare earth aluminates, silica, silicon carbide, and so forth), and combinations comprising at least one of the foregoing, e.g., cobalt-based superalloys, nickel-lilanium alloy, and so forth. The specific powder employed will be chosen based on compalibility wilb the cavily surface 24 (e.g., ability to bond therelo) as well as other variables, such as the mixture's resulting properties (e.g., wear resistance or Ihermal transfer).
The liquid employed in llie slurry can be any liquid that can be blended with the solids and allows the solids to fiow into the mold, such as water, oils, alcohols, ethers, and so forth.
The mixture 26 can comprise additives, such as surfactants, binders (e.g., ethyl silicate and colloidal süica), processing aids (e.g., paraffin wax), viscosity modifiers, pore formers, and so forth. In one embodiment, a mixture comprises about 82 wt.% alumina, about 8 wt% starch, and about 10 wt% isopropyl alcohol.
The mixture 26 can be formulated in batches. For example, a 100 pound batch can be produced by first adding a silica ceramic powder häving an average partide size of about 10 microns or less into a tumble drum. A starch binder and an alcohol carrier is added to the drum. The mixture 26 is then mixed using a rotating canister, high-speed blender, ribbon blender, or shear mixer (e.g., roll miil).
Once protrusions 22 have been disposed on the cavity surface 24, the second mold half 10 is heated. During the heating process, the protrusions 22 (e.g., bumps, lines, and so forth) harden and fuse to the cavity surface 24. In addition, any liquids, as well as any volatüe additives, are evaporated. The time and temperature employed to sinter the composition, will be dependent upon the composition of the mixture 26, the size of the protrusions 22, and the heat source employed, among other variables. Exemplary heat treatments indude focused energy sources (e.g., that employ a plasma, a microwave, a laser beam, an electron beam, and/or another local heat source). Alteraatively, or in addition, the heat treatment may comprise heating the second mold half 10 in a furnace, provided the sintering temperature of the mixture 26 is less than the temperature at which the second mold half 10 can incur damage.
Opüonally, a masking process can be employed prior to the deposition process to mask portions of the cavity surface 24 that will not comprise surface features. The specific masking employed can be a material that can adhere to the cavity surface 24 and will be easy to remove therefrom. In one exemplary embodiment, an adhesively backed polymer sheet can be employed.
After the surface features (e.g., protrusions 22) have been sintered, they are cooled (actively and/or passively). Optionally, the mold can thereafter be post processed using various operations such as those described above. In other words, surface features can be formed on the surface(s) of the mold half(ves) before and/or after the optional processing of the mold (e.g., the polishing, coating, and/or other processes described above).
Once the molds have been sintered, they can be assembled and employed for casting. Materials that can be east therein can comprise any article material(s) that raelt at a
temperature below tbat which would cause damage to the mold. In addition, the material will desirably flow at a rate so that the die cavity 16 can be filled prior to solidification, or the mold can be preheated to retard solidification. In one exemplary embodiment shown in Figure 9, a casting material 34 (e.g., nickel-based super alloy) has been heated above its melting point and is poured into the sprue 32 of the assembled die to form a turbine blade (e.g., in cavity 16). The protrusions 22 formed by the deposition process are within the cavity 16, and will therefore form indentations on the east turbine blade. An exemplary east turbine blade 40 is shown in Figure 10. The turbine blade 40 comprises surface details 42 (e.g, dimples), that were formed during casting by the protrusions 22 on the second mold half 10.
Once the article material(s) solidify, the mold is disassembled and the casting is removed therefrom. At mis point, any additional post processing or secondary operations (e.g., machining, polishing, coating, assembly, and so forth) can be employed.
In another embodiment, after the molds have been sintered they can be subjected to secondary operations. Exemplary operations comprise inspection, coating processes (e.g., coatings to reduce surface roughness and wear resistant coatings), machintng processes (e.g., addiüon of vents, addition of sprues, and removal of flash), labeling processes. fixturing processes (e.g., within a carrier mold base), modification processes (e.g., addition of guides and addition of elemente to attach the molds to one another), and so forth. For example, in one embodiment a thermal barrier coating can be applied to the cavity to cover the cavity surface 24 and the protrusions 22 disposed thereon to provide a surface häving a uniform surface finish.
Surface features can be formed on any ceramic and/or metal dies and/or molds employed for casting as well as east articles. In one embodiment, a ceramic tool for polymer injection molding can be produced, wherein an investment core of the desired part can be employed in an investment casting process to form the ceramic mold. The mold can then be subjected to a deposition process to form detailed patterns on the surface of the mold that will serve as a decoration on the injection molded articles formed therein. These surface features can have a size of less than or
equal to about 2,000 fim. or, more specifically less than about l.OOOjtm, or, even more specifically, about 5 /mi to about SOOjim.
The processes disclosed herein are particularly useful for forming surface features on the surfaces of molds that will be employed to form turbine engine components. While the formation of a turbine blade has been discussed herein, due to the high operating temperature of turbines, many components used therein are formed via casting processes that can employ the methods disclosed herein. For example, parts employed in the high-pressure stage of a turbine engine, such as stationary airfoils (e.g., nozzles or vanes) and rotating airfoils (e.g., buckets or blades). Other components used in areas of the turbine engine outside the high-pressure stage indude shroud clearance control areas, which include flanges, casings, and rings, as weil as combustor liners, and combustor domes. In addiüon, the methods herein are also useful in missile and rocket components such as booster cones, fins, and so forth. However, it is to be apparent that the methods disclosed herein are not limited to such appiications. Other appiications include automotive appiications (e.g., fuel injectors, turbocharger turbines and impellors, fuel reformers, and so forth), industrial appiications (e.g., east machine components), computer appiications (e.g., storage device drive or cooling components), and so forth, as well as appiications that form plastic articles.
The methods for forming surface features on casting molds described herein addresses an unmet need in the art. The process allows for the formation of surface featured on a cavity surface of a casting mold, wherein the surface features can comprise intricate shapes, patterns, and so forth. This method of producing east articles with surface features is particularly useful in prototyping east articles. To be more specific, this allows manufacturers of east articles to start with the manufacture of a standard die which is used to form as many sets of standard casting molds (e.g., molds without surface features). The standard casting molds can then be modified with the material deposition method disclosed herein to form differing surface features thereon. Once the surface features are sintered, the molds can be employed to then east articles häving the surface details formed by the surface featurec in the mold. For example, a series of turbine blades can be east häving varying surface features from molds all
created from one die. Thus enabling for expedited research and development of the effects of various surfaces at a reduced eost and within a shorter amount of time.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this inventkm belongs. The terms "first", "second", and the iike, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item, and the terms "front", "back", "bottom", and/or "top", unless otherwise noted, are merely used for convenience of description, and are not lünited to any one position or spatial orientation. If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and Jndependently combinable (e.g., ranges of "up to about 25 wt,%, or, more specifically, about 5 wt.% to about 20 wt.%," is inclusive of the endpoints and all intermediate values of the ranges of "about 5 v/t% to about 25 wt.%," ete.). The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., indudes the degree of error associated with measurement of the particular quantity). The suffk "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the colorant(s) indudes one or more colorants). Furthermore, as used herein, "combination" is inclusive of blends, mixtures, alloys, reaction products, and the Iike. Lastly, when "e.g.," is used, Üte values or terms thereafter are exemplary and non-limiting.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be subsütuted for elements thereof without departing from the scope of the invention. In addition, many modif ications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out
this inventioa, but that the invention will include all embodiments falling within the scope of the appended claims.

What is claimed is: CLAMS
1. A method for forming a mold comprising:
casting a mold (8,10) häving a cavity surface (24);
forming surface features on the cavity surface (24), wherein the surface features comprise a mixture (26);
heat treating me mixture (26).
2. The method of Claim l, further comprising extruding the mixture (26) through the
nozzle (28) of an apparatus.
3. The method of Claim 2, further comprising, controlling the motion of the nozzle
(28) and a flow rate at which the mixture (26) is extruded through the nozzle (28).
4. The method of Claim l, wherein the surface features are selected from the group
consisting of patterns, drops, smears, layers, lines, shapes, and combinations
comprising at least one of the foregoing.
5. A method for formiiig a mold comprising:
forming a die (2,4);
casting a mold (8, 10) within the die (2,4) using a ceramic composition and a casting process selected from the group consisting of slip casting, gel casting, sand casting, plaster casting, die-casting, injection molding, slurry injection, powder forming (compaction), reaction forming, colloidal forming, cold isostatic pressing, hot isostatic pressing, and combinations comprising at least one of the foregoing;
heating the mold (8,10);
extruding a mixture (26) onto a cavity surface (24) of the mold (8, 10) to form surface features thereon, wherein the mixture (26) is extruded through the nozzle (28) of an apparatus; and,
heat treating the mixture (26).
6. The method of Claim 5, further comprising, controlling the motion of the nozzle
(28) and a flow rate at which the mixture (26) is extruded through the nozzle (28).
7. The method of Claim 5, wherein me surface features are selected from the group
consisting of pattems, drops, smears, layers, lines, shapes, and combinations
comprising at least one of the foregoing.
8. The method of Claim 5, wherein the mixture is selected from the group consisting
of metals, ceramics, and combinations comprising at least one of the foregoing.
9. An article formed by the method of Claim 1.
10. An article formed by the method of Claim 5.