Patent Application
20110094698
The present invention relates to manufacture of a ceramic core for use in casting a hollow metallic article, such as a hollow turbine components, and more particularly, to tooling and a method for making a ceramic core.
Most manufacturers of gas turbine engines are evaluating advanced multi-walled, thin-walled superalloy gas turbine airfoils (i.e. turbine blade or vane) which include intricate air cooling channels to improve efficiency of airfoil internal cooling to permit greater engine thrust and provide satisfactory airfoil service life. U.S. Pat. Nos. 5,295,530 and 5,545,003 describe advanced multi-walled, thin-walled turbine blade or vane designs which include intricate air cooling channels to this end.
In casting hollow gas turbine engine blades and vanes (airfoils) and also shrouds having internal cooling passageways, a fired ceramic core is positioned in a ceramic investment shell mold to form internal cooling passageways in the cast airfoil. The fired ceramic core used in investment casting of hollow airfoils typically has an airfoil-shaped region with a thin cross-section leading edge region and trailing edge region. Between the leading and trailing edge regions, the core may include elongated and other shaped openings so as to form multiple internal walls, pedestals, turbulators, ribs, chambers, plenums, and similar features separating and/or residing in cooling passageways in the cast airfoil or cast shroud.
The ceramic core typically is formed to desired core configuration by injection molding, transfer molding or pouring of an appropriate fluid ceramic core material that includes one or more ceramic powders, a binder, and optional additives into a suitably shaped core molding die. After the green molded core is removed from the die, it is subjected to firing at elevated (superambient) temperature in one or more steps to remove the fugitive binder and sinter and strengthen the core for use in casting metallic material, such as a nickel or cobalt base superalloy typically used to cast gas turbine engine blades and vanes (airfoils).
Conventional core tooling requires expensive EDM machining for hardened tool steel permanent tooling and sophisticated machining techniques for tooling dies and tooling inserts, ribs, inserts, and other cooling features to be imparted to the core formed using the tooling. Unfortunately, the ceramic core materials are abrasive to tooling and result in wear of the tooling over time. Such tooling wear produces undesirable changes and inconsistencies in core geometry and performance of castings made with the cores over time.
The fired ceramic core then is used in manufacture of the shell mold by the well known lost wax process wherein the ceramic core is placed in a pattern molding die and a fugitive pattern is formed about the core by injecting under pressure pattern material, such as wax, thermoplastic and the like, into the die in the space between the core the inner die walls. The pattern typically has an airfoil-shaped region with a thin cross-section trailing edge region corresponding in location to trailing edge features of the core. The pattern also can include other features such as including, but not limited to, one or more platforms, shrouds and the like.
The fugitive pattern with the ceramic core therein is subjected to repeated steps to build up the shell mold thereon. For example, the pattern/core assembly is repeatedly dipped in ceramic slurry, drained of excess slurry, stuccoed with coarse ceramic stucco or sand, and then air dried to build up multiple ceramic layers that form the shell mold on the assembly. The resulting invested pattern/core assembly then is subjected to a pattern removal operation, such as steam autoclaving, to selectively remove the fugitive pattern, leaving the shell mold with the ceramic core located therein. The shell mold then is fired at elevated temperature to develop adequate shell mold strength for metal casting.
Molten metallic material, such as a nickel or cobalt base superalloy, is cast into a preheated shell mold and solidified to produce an equiaxed grain, columnar grain or single crystal airfoil. The resulting cast airfoil includes the ceramic core therein so as to form internal cooling passageways upon removal of the core. The core can be removed by leaching or other conventional techniques, leaving a hollow cast metallic airfoil.
The present invention provides tooling for making a ceramic core wherein the core tooling employs one or more fugitive tooling liners and optional fugitive tooling inserts that are placed in a simple-geometry back-up or support body in a manner to form at least a portion of a core-shaped cavity and that eliminate the need for costly hardened/machined permanent steel tooling.
In an illustrative embodiment of the invention, each fugitive tooling liner includes an outer surface having a simple geometry to conform to that of an adjacent inner support surface of the back-up body and an inner surface that is configured to form desired core surface features when the tooling liners are placed in the back-up body with the tooling liners forming the core-shaped cavity. Optional fugitive inserts can be placed between the tooling liners to form ribs, holes, passages and other features on and/or in the ceramic core. The core-shaped cavity may have one or more airfoil-shaped surfaces in the production of a ceramic core for use in casting of a hollow airfoil, such as a hollow gas turbine blade or vane, or other hollow article.
A ceramic core is produced pursuant to a method embodiment of the invention by introducing a fluid ceramic core mixture typically under pressure into the core-shaped cavity formed at least in part by the fugitive tooling liners in the back-up body, removing the molded ceramic core from the cavity, and removing the fugitive tooling liners with the core or from the back-up die body (separately from the core) for discarding. The next ceramic core is produced using fresh (un-used) tooling liners and optional tooling inserts. Alternately, the fugitive tooling liners may be left in the back-up body and reused if the liners are in acceptable condition to this end. That is, the fugitive tooling liners and inserts are used in one or more production cycles (e.g. ceramic slurry injection cycles) to make a single ceramic core and then replaced with fresh (un-used) tooling liners and optional inserts.
Other advantages of the present invention will become more readily apparent from the following detailed description taken with following drawings.
The present invention provides tooling for making a ceramic core wherein the tooling employs one or more fugitive tooling liners and optional fugitive tooling inserts that are placed in a simple-geometry back-up or support body in a manner to form at least a portion of a core-shaped cavity and that eliminate the need for costly hardened/machined permanent steel tooling. Although the invention is described in detail below with respect to making a ceramic core having an airfoil shape for use in casting metallic airfoils, such as gas turbine engine blades and vanes, it is not so limited and can be used to make a ceramic core having any desired shape.
Referring to
The back-up body 10 comprises multiple parts (first and second parts 10a, 10b shown) positionable to form a tooling cavity TC to receive the tooling liners 20a, 20b. The multiple parts of the back-up body can be incorporated and positioned as an injection die of a conventional core injection machine.
Referring to
In
The core tooling includes one or more fugitive tooling liners 20. For purposes of illustration, the core tooling is shown including first and second fugitive tooling liners 20a 20b that are placed in the tooling cavity TC. Each first and second tooling liner includes an outer surface 20s having a simple flat and/or curved or other simple geometry to conform to or match that of an adjacent inner support surface 10s of an adjacent part of the back-up body 10 and an inner surface 10c that is configured to form desired core surface features when the tooling liners 20a, 20b are placed in the back-up body 10 in facing relation to form the core-shaped cavity C. Although the tooling liners are shown including flat and curved outer surfaces 20s that mate with an adjacent flat and curved surface 10s of the back-up body, other simple surfaces 20s can be used that match or mate with those of the adjacent parts of the back-up body 10. The tooling liners 20a, 20b can be designed to snap-fit into place in the parts 10a, 10b of the back-up body 10, or they can be held by releasable adhesive or releasable fasteners or clamps.
The inner surfaces 20c of the tooling liners form an air-foil core-shaped cavity C therebetween,
The fugitive tooling liners typically are injection molded to shape using a suitable polymer, although other fugitive liner materials can be used including, but not limited to, polylactone, polyvinyl, and starch-modified polymers.
The core tooling can include one or more optional fugitive inserts 30a-30h placed between the tooling liners 20a, 20b and/or on the inner surfaces 20c of the tooling liners 20a, 20b,
The fugitive inserts alternately can be provided as fugitive subassemblies where different inserts are provided in one subassembly to form through-passages and core surface features as shown for inserts 30a and 30b in
The fugitive inserts can include connection features to the liner surface 20c that may be normal (perpendicular) to the liner surface 20c as shown for insert 30d in
A ceramic core is produced pursuant to a method embodiment of the invention by introducing a fluid ceramic core material, such as a ceramic slurry, typically under pressure into the core-shaped cavity C formed by the fugitive tooling liners 20a, 20b in the back-up body 10. The fluid ceramic material is introduced via a passage CP (
The next ceramic core is produced using fresh (un-used) tooling liners 20a, 20b and optional fresh tooling inserts 30. That is, the fugitive tooling liners and inserts can be used in one production cycle (e.g. ceramic injection cycle) to make a single ceramic core and then replaced with fresh (un-used) tooling liners and optional inserts. Alternately, the fugitive tooling liners may be left in the back-up body 10 and reused if the tooling liners are in acceptable condition to this end. That is, the fugitive tooling liners and inserts can be used in multiple production cycles (e.g. ceramic slurry injection cycles) to make multiple ceramic cores and then replaced with fresh (un-used) tooling liners and optional inserts when the tooling liners are not longer in acceptable condition to this end. However, when back-locked core features are produced, the tooling liners are used only in one production cycle since they are destroyed to separate them from the core.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention described above without departing from the spirit and scope of the invention as set forth in the appended claims.
