The present disclosure generally relates to investment casting core-shell mold components and processes utilizing these components. The core-shell mold made in accordance with the present invention includes integrated ceramic indentations between the core and shell of the mold that can be utilized to form thin root components, i.e., angel wings, damper lugs and skirts in the turbine blade or stator vane made from these molds. The integrated core-shell molds provide useful properties in casting operations, such as in the casting of superalloys used to make turbine blades and vanes for jet aircraft engines or power generation turbine components.
Many modern engines and next generation turbine engines require components and parts having intricate and complex geometries, which require new types of materials and manufacturing techniques. Conventional techniques for manufacturing engine parts and components involve the laborious process of investment or lost-wax casting. One example of investment casting involves the manufacture of a typical rotor blade used in a gas turbine engine. A turbine blade typically includes hollow airfoils that have radial channels extending along the span of a blade having at least one or more inlets for receiving pressurized cooling air during operation in the engine. The various cooling passages in a blade typically include a serpentine channel disposed in the middle of the airfoil between the leading and trailing edges. The airfoil typically includes inlets extending through the blade for receiving pressurized cooling air, which include local features such as short turbulator ribs or pins for increasing the heat transfer between the heated sidewalls of the airfoil and the internal cooling air.
The manufacture of these turbine blades, typically from high strength, superalloy metal materials, involves numerous steps shown in
The cast turbine blade may then undergo additional post-casting modifications, such as but not limited to drilling of suitable rows of film cooling holes through the sidewalls of the airfoil as desired for providing outlets for the internally channeled cooling air which then forms a protective cooling air film or blanket over the external surface of the airfoil during operation in the gas turbine engine. After the turbine blade is removed from the ceramic mold, the ball chute 203 of the ceramic core 200 forms a passageway that is later brazed shut to provide the desired pathway of air through the internal voids of the cast turbine blade. However, these post-casting modifications are limited and given the ever increasing complexity of turbine engines and the recognized efficiencies of certain cooling circuits inside turbine blades, more complicated and intricate internal geometries are required. While investment casting is capable of manufacturing these parts, positional precision and intricate internal geometries become more complex to manufacture using these conventional manufacturing processes. Accordingly, it is desired to provide an improved casting method for three dimensional components having intricate internal voids.
U.S. Pat. No. 9,039,382, entitled “Blade Skirt” describes a turbine blade include details of the blade root. The blade 300 typically has an airfoil 302, a platform 304, a shank 306, and a multi-lobe dovetail 308 having a fir tree configuration. On the forward side of the blade 300, there is a forward angel wing 310. On the aft side of the blade 300, there is a distal aft angel wing 312 radially inward of that is a proximal aft angel wing 314 with a gap therebetween. Proximal of the aft proximal angel wing 314, there is a fillet 316 that blends into a blade skirt 318. A recess may be provided within the shank portion 306 between the forward and aft sides of the blade 300. Within that recess, there is a forward damper retention lug 324 and an aft damper retention lug 326, which are used in conjunction with one another to retain a damper (not shown). The dovetail section 308 is inserted in a rotor (not shown) such that the dovetail lobes 328 mate with the rotor to radially fix the blade in place.
During the investment casting process, the entire structure shown in
There remains a need to prepare ceramic core-shell molds produced using higher resolution methods that are capable of providing fine detail cast features in the end-product of the casting process.
In one embodiment, the invention relates to a method of making a ceramic mold for a turbine blade. The method having steps of (a) contacting a cured portion of a workpiece with a liquid ceramic photopolymer; (b) irradiating a portion of the liquid ceramic photopolymer adjacent to the cured portion through a window contacting the liquid ceramic photopolymer; (c) removing the workpiece from the uncured liquid ceramic photopolymer; and (d) repeating steps (a)-(c) until a ceramic mold is formed, the ceramic mold comprising a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of a turbine blade or vane upon casting and removal of the ceramic mold, and the cavity defining a turbine blade or vane root component having a minimum dimension of less than 0.64 mm. After step (d), the process may further include a step (e) of pouring a liquid metal into a casting mold and solidifying the liquid metal to form the cast component. After step (e), the process may further include a step (f) comprising removing the mold from the cast component, and this step preferably involves a combination of mechanical force and chemical leaching in an alkaline bath.
In another aspect, the invention relates to a method of preparing a turbine blade or vane. The method includes steps of pouring a liquid metal into a ceramic casting mold and solidifying the liquid metal to form the turbine blade or vane, the ceramic casting mold comprising a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of the turbine blade or vane upon casting and removal of the ceramic mold, and the cavity defining a turbine blade or vane root component having a minimum dimension of less than 0.64 mm.
In another aspect, the invention relates to a ceramic casting mold having a core portion and a shell portion with at least one cavity between the core portion and the shell portion, the cavity adapted to define the shape of the cast component upon casting and removal of the ceramic mold; and the cavity defining a turbine blade or vane root component having a minimum dimension of less than 0.64 mm. The ceramic may be a photopolymerized ceramic or a cured photopolymerized ceramic.
In yet another aspect, the invention relates to a single crystal metal turbine blade or vane having an inner cavity and an outer surface, a plurality of cooling holes providing fluid communication between the inner cavity and outer surface, and a turbine blade or vane root component having a minimum dimension of less than 0.64 mm. Preferably the single crystal metal is a superalloy.
In one aspect the turbine blade or vane root component has a minimum dimension in the range of 0.1 and 0.6 mm. In another aspect the turbine blade or vane root component has a minimum dimension in the range of 0.2 and 0.5 mm.
In one aspect the turbine blade or vane root component is an angel wing, skirt or damper lug.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. For example, the present invention provides a preferred method for making cast metal parts, and preferably those cast metal parts used in the manufacture of jet aircraft engines. Specifically, the production of single crystal, nickel-based superalloy cast parts such as turbine blades, stator vanes, and shroud components can be advantageously produced in accordance with this invention. However, other cast metal components may be prepared using the techniques and integrated ceramic molds of the present invention.
The present inventors recognized that prior processes known for making turbine blades and stator vanes i.e. investment casting, lacked the fine resolution capability necessary to produce turbine blades and vanes having thin blade root elements. In particular, the wax processing step in investment casting severely limits the ability to manufacture turbine blades where the blade or vane root elements may be made as thin or as fine as desired.
The present inventors have found that the integrated core-shell mold of the present invention can be manufactured using direct light processing (DLP). DLP differs from powder bed and SLA processes in that the light curing of the polymer occurs through a window at the bottom of a resin tank that projects light upon a build platform that is raised as the process is conducted. With DLP an entire layer of cured polymer is produced simultaneously, and the need to scan a pattern using a laser is eliminated. Further, the polymerization occurs between the underlying window and the last cured layer of the object being built. The underlying window provides support allowing thin filaments of material to be produced without the need for a separate support structure. In other words, producing a thin filament of material bridging two portions of the build object is difficult and was typically avoided in the prior art. For example, U.S. Pat. No. 8,851,151 assigned to Rolls-Royce Corporation describes a 3-D printing method of producing a ceramic core-shell mold that used vertical plate structures connected with short cylinders, the length of which was on the order of their diameter. Staggered vertical cavities are necessitated by the fact that the powder bed and SLA techniques disclosed in the '151 patent require vertically supported ceramic structures and the techniques are incapable of reliably producing thin indentations or recesses that correspond to thin turbine blade root components (i.e. angel wings, damper lugs, skirts) of the cast turbine blade. In addition, the available resolution within a powder bed is on the order of ⅛″ (3.2 mm) making the production of thin turbine blade root components impracticable. For example, these thin turbine blade root components generally have a minimum dimension of less 0.64 mm, preferably in the range of 0.1 to 0.6 mm, more preferably in the range of 0.2 to 0.5 mm. As used herein, the term “minimum dimension” means “smallest possible dimension”. Production of a turbine blade root component of such dimensions requires a resolution simply not available in a powder bed process. Similarly, stereolithography is limited in its ability to produce such thin indentations due lack of support and resolution problems associated with laser scattering. But the fact that DLP exposes the entire length of the indentation and supports it between the window and the build plate enables producing sufficiently thin indentations having the desired minimum dimensions . Although powder bed and SLA may be used to produce indentations, their ability to produce sufficiently fine indentations as discussed above is limited.
One suitable DLP process is disclosed in U.S. Pat. No. 9,079,357 assigned to Ivoclar Vivadent AG and Technische Universitat Wien, as well as WO 2010/045950 A1 and US 2011310370, each of which are hereby incorporated by reference and discussed below with reference to
Opposite the exposure unit 410, a production platform 412 is provided above the tank 404; it is supported by a lifting mechanism (not shown) so that it is held in a height-adjustable way over the tank bottom 406 in the region above the exposure unit 410. The production platform 412 may likewise be transparent or translucent in order that light can be shone in by a further exposure unit above the production platform in such a way that, at least when forming the first layer on the lower side of the production platform 412, it can also be exposed from above so that the layer cured first on the production platform adheres thereto with even greater reliability.
The tank 404 contains a filling of highly viscous photopolymerizable material 420. The material level of the filling is much higher than the thickness of the layers which are intended to be defined for position-selective exposure. In order to define a layer of photopolymerizable material, the following procedure is adopted. The production platform 412 is lowered by the lifting mechanism in a controlled way so that (before the first exposure step) its lower side is immersed in the filling of photopolymerizable material 420 and approaches the tank bottom 406 to such an extent that precisely the desired layer thickness Δ (see
These steps are subsequently repeated several times, the distance from the lower side of the layer 422 formed last to the tank bottom 406 respectively being set to the desired layer thickness Δ and the next layer thereupon being cured position-selectively in the desired way.
After the production platform 412 has been raised following an exposure step, there is a material deficit in the exposed region as indicated in
In order to replenish the exposure region with photopolymerizable material, an elongate mixing element 432 is moved through the filling of photopolymerizable material 420 in the tank. In the exemplary embodiment represented in
The movement of the elongate mixing element 432 relative to the tank may firstly, with a stationary tank 404, be carried out by a linear drive which moves the support arms 430 along the guide slots 434 in order to achieve the desired movement of the elongate mixing element 432 through the exposed region between the production platform 412 and the exposure unit 410. As shown in
Other alternative methods of DLP may be used to prepare the integrated core-shell molds of the present invention. For example, the tank may be positioned on a rotatable platform. When the workpiece is withdrawn from the viscous polymer between successive build steps, the tank may be rotated relative to the platform and light source to provide a fresh layer of viscous polymer in which to dip the build platform for building the successive layers.
The present invention may be used to make turbine blades and stator vanes having root feature minimum dimensions of less than 0.64 mm. As shown in
After printing the core-shell mold structures in accordance with the invention, the core-shell mold may be cured and/or fired depending upon the requirements of the ceramic core photopolymer material. Molten metal may be poured into the mold to form a cast object in the shape and having the features provided by the integrated core-shell mold. In the case of a turbine blade or stator vane, the molten metal is preferably a superalloy metal that formed into a single crystal superalloy turbine blade or stator vane using techniques known to be used with conventional investment casting molds.
In an aspect, the present invention relates to the core-shell mold structures of the present invention incorporated or combined with features of other core-shell molds produced in a similar manner. The following patent applications include disclosure of these various aspects and their use:
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE-SHELL STRUCTURE” with attorney docket number 037216.00036/284976, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE-SHELL STRUCTURE WITH FLOATING TIP PLENUM” with attorney docket number 037216.00037/284997, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “MULTI-PIECE INTEGRATED CORE-SHELL STRUCTURE FOR MAKING CAST COMPONENT” with attorney docket number 037216.00033/284909, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “MULTI-PIECE INTEGRATED CORE-SHELL STRUCTURE WITH STANDOFF AND/OR BUMPER FOR MAKING CAST COMPONENT” with attorney docket number 037216.00042/284909A, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE SHELL STRUCTURE WITH PRINTED TUBES FOR MAKING CAST COMPONENT” with attorney docket number 037216.00032/284917, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE-SHELL STRUCTURE AND FILTER FOR MAKING CAST COMPONENT” with attorney docket number 037216.00039/285021, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE SHELL STRUCTURE FOR MAKING CAST COMPONENT WITH NON-LINEAR HOLES” with attorney docket number 037216.00041/285064, and filed Dec. 13, 2016;
U.S. patent application Ser. No. ______, titled “INTEGRATED CASTING CORE SHELL STRUCTURE FOR MAKING CAST COMPONENT WITH COOLING HOLES IN INACCESSIBLE LOCATIONS” with attorney docket number 037216.00055/285064A, and filed Dec. 13, 2016.
The disclosures of each of these applications are incorporated herein in their entireties to the extent they disclose additional aspects of core-shell molds and methods of making that can be used in conjunction with the core-shell molds disclosed herein.
This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspect, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.