Patent Application
20130280093
This disclosure relates to a core for manufacturing an airfoil used in a gas turbine engine. The disclosure also relates to a method of manufacturing the airfoil using the core.
Typically, turbine airfoils are cast using an investment casting process, or lost wax process. A ceramic core is coated and then arranged in a mold and enveloped in wax, which provides a desired airfoil shape. The wax airfoil is subsequently coated in a ceramic slurry that is hardened into a shell. The wax is melted out of the shell, which is then filled with metal to provide the airfoil. The core provides the shape of internal cooling passages within the airfoil. The core may be removed chemically, for example.
In one common manufacturing process, the ceramic core exits the wax airfoil at its trailing edge. The area around this ceramic/wax airfoil interface is typically rough and requires post operations to grind down the excess material. The post operations are typically done by hand and, due to the curved contours of the surfaces of the airfoil, inspection of the final finished surface is difficult to quantify and qualify. As a result, the finally finished metal airfoil often includes undesired positive raised alloy material resulting in local discontinuities on the local external airfoil surface geometry. In this particular instance the positive material is coincident with the aerodynamic throat or gage area at the trailing edge slot location. Typically this area of raised material has been referred to as a “ski jump.” A “ski jump” is a step or a discontinuity in the desired surface contour of the airfoil exterior surface. In order to remove the positive material that results, hand finishing operations are required. If the hand finishing is severe or overly aggressive and deep into the local wall adjacent to the trailing edge coolant ejection location, a thin wall can be formed that will adversely impact the local thermal cooling performance and structural capability of the part. Locally thin walls at the trailing edge slot ejection locations can present subsequent manufacturing challenges associated with collapsing or significantly deforming the locally thin walls due to coating processing requirements. Local positive features or steps can cause disturbances within the boundary layer flow across the external surface of the airfoil, resulting in flow separation increasing aerodynamic losses. Additionally the local positive features or steps can cause local body film and trailing edge slot film cooling to eject into the gas path without properly attaching to the airfoil adversely impacting the local thermal cooling performance.
In one exemplary embodiment, a core has a body that includes a cooling passage portion with a film cooling passage portion extending there from to a cooling hole portion. An exterior airfoil portion is connected to the cooling hole portion and is spaced apart from the cooling passage portion to provide a space surrounding the film cooling hole portion that corresponds to an exterior airfoil wall.
In a further embodiment of any of the above, the cooling passage portion, the film cooling passage portion, the cooling hole portion and the exterior airfoil portion provide a unitary body having uniform material properties.
In a further embodiment of any of the above, the unitary body includes a refractory metal.
In a further embodiment of any of the above, the cooling passage portion includes an inner surface, and the exterior airfoil portion includes an outer surface and an exterior core surface spaced apart from one another. The inner and outer surfaces face one another to provide the space.
In a further embodiment of any of the above, the film cooling passage portion includes first and second passage portions joined to one another by a bend.
In a further embodiment of any of the above, the film cooling passage portion includes a diffusion exit.
In a further embodiment of any of the above, the cooling hole portion includes a trough.
In a further embodiment of any of the above, the exterior airfoil portion wraps about an entire perimeter of the core to provide an exterior airfoil surface.
In a further embodiment of any of the above, the exterior airfoil portion includes contoured features that are configured to provide correspondingly-shaped contoured features on an airfoil exterior surface.
In another exemplary embodiment, a method of manufacturing an airfoil comprising the step of providing a core that has a body including a cooling passage portion with a film cooling passage portion extending there from to a film cooling hole portion. An exterior airfoil portion is connected to the cooling hole portion and is spaced apart from the cooling passage portion to provide a space surrounding the film cooling hole portion that corresponds to an exterior airfoil wall.
In a further embodiment of any of the above, the method includes depositing multiple layers of powdered metal onto one another, and joining the layers to one another with reference to CAD data relating to a particular cross-section of the core.
In a further embodiment of any of the above, the method includes coating the core with a metallic coating.
In a further embodiment of any of the above, the method includes enveloping the coated core in wax to provide a wax airfoil with the exterior airfoil portion proud of the wax airfoil.
In a further embodiment of any of the above, the method includes coating the wax airfoil in a ceramic slurry to provide a ceramic airfoil mold, and the ceramic airfoil mold is bonded to the exterior airfoil portion.
In a further embodiment of any of the above, the method includes melting the wax and filling the ceramic airfoil mold to produce an airfoil including leading and trailing edges joined by spaced apart pressure and suction sides that provide an exterior airfoil surface.
In a further embodiment of any of the above, the method includes processing the airfoil to provide desired structural characteristics.
In one exemplary embodiment, a core has a body that includes a cooling passage portion with a film cooling passage portion extending there from to a cooling hole portion. An exterior airfoil portion is connected to the film cooling hole portion and is spaced apart from the cooling passage portion to provide a space surrounding the cooling hole portion that corresponds to an exterior airfoil wall. The cooling passage portion includes an inner surface, and the exterior airfoil portion includes an outer surface and an exterior core surface spaced apart from one another. The inner and outer surfaces face one another to provide the space. The outer surface configured to provide a desired an exterior airfoil surface contour.
In a further embodiment of any of the above, the exterior airfoil portion wraps about an entire perimeter of the core to provide an exterior airfoil surface.
The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
The turbine section 11 includes alternating rows of blades 20 and static airfoils or vanes 19. It should be understood that
An example blade 20 is shown in
Referring to
Referring to
The film cooling passage portion 46 corresponds to the film cooling passage 68 that feeds cooling fluid from the internal cooling passage 70 to the film cooling hole 66. Film cooling holes provided in this manner may be arranged in close proximity to one another near the trailing edge, for example, or any other desired location. For example, the film cooling holes 66 may be arranged in chord-wise and/or radial rows. Contour features, such as dimples and trenches, may also be provided on the exterior airfoil surface 38 by providing correspondingly shaped features on the outer surface 54 of the exterior airfoil portion 50.
An exterior airfoil portion 50 is integrally connected to the film cooling hole portion 48 and is spaced apart from the cooling passage portion 44 to provide a space surrounding the film cooling hole portion 48 that corresponds to an exterior airfoil wall 64. The cooling passage portion 44 includes an inner surface 52, and the exterior airfoil portion 50 includes an outer surface 54 and an exterior core surface 62 spaced apart from one another. The inner and outer surfaces 52, 54 face one another to provide the space corresponding to the cast wall 64. Fillets and chamfers may be provided where desired.
The cooling passage portion 44, the film cooling passage portion 46, the film cooling hole portion 48 and the exterior airfoil portion 50 provide a unitary body having uniform material properties. The unitary body includes a refractory metal, such as molybdenum, for example. Although the exterior airfoil portion 50 is illustrated as truncated, the exterior airfoil portion could wrap about the entire perimeter of the core thereby defining the entire airfoil exterior surface, as shown in
The exterior airfoil portion 50 may be used to provide surface contours or features on the airfoil 26, as shown in
Another example core 140 and resulting airfoil 26 are shown in
The film cooling configuration in
The airfoil geometries disclosed in
To form the core, powdered metal 82 suitable for refractory metal core applications, such as molybdenum or tungsten, is fed to a machine 84, which may provide a vacuum, for example. The machine 84 deposits multiple layers of powdered metal onto one another. The layers are joined to one another with reference to CAD data 86, which relates to a particular cross-section of the core 40. In one example, the powdered metal 82 may be melted using a direct metal laser sintering process or an electron-beam melting process. With the layers built upon one another and joined to one another cross-section by cross-section, a core with the above-described geometries may be produced, as indicated at 88. A single piece core including both the first and second cores 40, 42 can be produced that requires no assembly and can be directly placed into the wax mold after being coated.
The coating 90 may be applied to the exterior surface of the core 40, which enables the core 40 to be more easily removed subsequently. The core 40 is coated with a metallic coating 77, shown in
The core 40 is enveloped in wax to provide a wax airfoil and core assembly with the exterior airfoil portion 50 proud of the wax airfoil 60, for example. The wax airfoil 60 is coated in a ceramic slurry to provide a ceramic airfoil mold 78, as shown in
Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.
