Patent Publication Number: US-8993923-B2

Title: System and method for manufacturing an airfoil

Description:
FIELD OF THE INVENTION 
     The present invention generally involves a system and method for manufacturing an airfoil. 
     BACKGROUND OF THE INVENTION 
     Turbines are widely used in industrial and commercial operations. A typical commercial steam or gas turbine used to generate electrical power includes alternating stages of stationary and rotating airfoils. For example, stationary vanes may be attached to a stationary component such as a casing that surrounds the turbine, and rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as but not limited to steam, combustion gases, or air, flows through the turbine, and the stationary vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work. 
     The efficiency of the turbine generally increases with increased temperatures of the compressed working fluid. However, excessive temperatures within the turbine may reduce the longevity of the airfoils in the turbine and thus increase repairs, maintenance, and outages associated with the turbine. As a result, various designs and methods have been developed to provide cooling to the airfoils. For example, a cooling media may be supplied to a cavity inside the airfoil to convectively and/or conductively remove heat from the airfoil. In particular embodiments, the cooling media may flow out of the cavity through cooling passages in the airfoil to provide film cooling over the outer surface of the airfoil. 
     As temperatures and/or performance standards continue to increase, the materials used for the airfoil become increasingly thin, making reliable manufacture of the airfoil increasingly difficult. Specifically, the airfoil is typically cast from a high alloy metal, and a thermal barrier coating may be applied to the outer surface of the airfoil to enhance thermal protection. The cooling passages are often drilled or machined into the high alloy metal at precise locations and in precise geometries after casting to optimize the cooling media flow over the airfoil. For example, a water jet may be used to drill the cooling passages through the high alloy metal at particular locations and angles to enhance the cooling media flow over the outer surface of the airfoil. Although effective at accurately drilling small diameter holes through the high metal alloy, the water jet may also damage the thermal barrier coating and/or introduce grit byproducts inside the airfoil that may be difficult to completely remove. Alternately or in addition, the water jet may inadvertently strike the interior of the airfoil on the opposite side of the cavity causing damage inside the airfoil. The grit byproducts inside the airfoil and/or damage to the interior of the airfoil may be difficult to detect during the finishing steps of the airfoil. As a result, a system and method for manufacturing an airfoil that reduces or prevents the damage to the thermal barrier coating, introduction of grit byproducts into the airfoil, and/or inadvertent damages to the interior of the airfoil would be useful. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     One embodiment of the present invention is a system for manufacturing an airfoil. The system includes a laser beam and a first fluid column surrounding the laser beam to create a confined laser beam directed at the airfoil. A liquid flowing inside the airfoil disrupts the first fluid column inside the airfoil. 
     Another embodiment of the present invention is a method for manufacturing an airfoil that includes confining a laser beam inside a first fluid column to create a confined laser beam and directing the confined laser beam at a surface of the airfoil. The method further includes creating a hole through the surface of the airfoil with the confined laser beam, flowing a liquid inside the airfoil, and disrupting the first fluid column with the liquid flowing inside the airfoil. 
     In yet another embodiment of the present invention, a method for manufacturing an airfoil includes directing a laser beam at a surface of the airfoil and confining the laser beam inside a first fluid column outside of the airfoil to create a confined laser beam outside of the airfoil. The method further includes creating a hole through the surface of the airfoil with the confined laser beam and disrupting the first fluid column with a liquid inside the airfoil. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  is a simplified cross-section view of an exemplary turbine that may incorporate various embodiments of the present invention; 
         FIG. 2  is a perspective view of an exemplary airfoil according to an embodiment of the present invention; and 
         FIG. 3  is a plan view of a core that may be used to cast the airfoil shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of a system for manufacturing the airfoil shown in  FIG. 2 ; and 
         FIG. 5  is a perspective view of the system shown in  FIG. 4  after the confined laser beam has penetrated through the airfoil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. In addition, the terms “upstream” and “downstream” refer to the relative location of components in a fluid pathway. For example, component A is upstream from component B if a fluid flows from component A to component B. Conversely, component B is downstream from component A if component B receives a fluid flow from component A. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Various embodiments of the present invention include a system and method for manufacturing an airfoil. The system generally includes an unfocused laser beam confined by a fluid column, and the confined laser beam may be used to create precise holes at particular angles through an airfoil surface. As the confined laser beam penetrates the airfoil surface, a liquid flowing inside the airfoil disrupts the fluid column inside the airfoil to prevent the confined laser beam from damaging the inside of the airfoil. Although exemplary embodiments of the present invention will be described generally in the context of an airfoil incorporated into a turbine, one of ordinary skill in the art will readily appreciate from the teachings herein that embodiments of the present invention are not limited to a turbine unless specifically recited in the claims. 
     Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures,  FIG. 1  provides a simplified side cross-section view of an exemplary turbine  10  according to various embodiments of the present invention. As shown in  FIG. 1 , the turbine  10  generally includes a rotor  12  and a casing  14  that at least partially define a gas path  16  through the turbine  10 . The rotor  12  is generally aligned with an axial centerline  18  of the turbine  10  and may be connected to a generator, a compressor, or another machine to produce work. The rotor  12  may include alternating sections of rotor wheels  20  and rotor spacers  22  connected together by a bolt  24  to rotate in unison. The casing  14  circumferentially surrounds at least a portion of the rotor  12  to contain a compressed working fluid  26  flowing through the gas path  16 . The compressed working fluid  26  may include, for example, combustion gases, compressed air, saturated steam, unsaturated steam, or a combination thereof. 
     As shown in  FIG. 1 , the turbine  10  further includes alternating stages of rotating blades  30  and stationary vanes  32  that extend radially between the rotor  12  and the casing  14 . The rotating blades  30  are circumferentially arranged around the rotor  12  and may be connected to the rotor wheels  20  using various means. In contrast, the stationary vanes  32  may be peripherally arranged around the inside of the casing  14  opposite from the rotor spacers  22 . The rotating blades  30  and stationary vanes  32  generally have an airfoil shape, with a concave pressure side, a convex suction side, and leading and trailing edges, as is known in the art. The compressed working fluid  26  flows along the gas path  16  through the turbine  10  from left to right as shown in  FIG. 1 . As the compressed working fluid  26  passes over the first stage of rotating blades  30 , the compressed working fluid expands, causing the rotating blades  30 , rotor wheels  20 , rotor spacers  22 , bolt  24 , and rotor  12  to rotate. The compressed working fluid  26  then flows across the next stage of stationary vanes  32  which accelerate and redirect the compressed working fluid  26  to the next stage of rotating blades  30 , and the process repeats for the following stages. In the exemplary embodiment shown in  FIG. 1 , the turbine  10  has two stages of stationary vanes  32  between three stages of rotating blades  30 ; however, one of ordinary skill in the art will readily appreciate that the number of stages of rotating blades  30  and stationary vanes  32  is not a limitation of the present invention unless specifically recited in the claims. 
       FIG. 2  provides a perspective view of an exemplary airfoil  40 , such as may be incorporated into the rotating blades  30  or stationary vanes  32 , according to an embodiment of the present invention. As shown in  FIG. 2 , the airfoil  40  generally includes a pressure side  42  having a concave curvature and a suction side  44  having a convex curvature and opposed to the pressure side  42 . The pressure and suction sides  42 ,  44  are separated from one another to define a cavity  46  inside the airfoil  40  between the pressure and suction sides  42 ,  44 . The cavity  46  may provide a serpentine or tortuous path for a cooling media to flow inside the airfoil  40  to conductively and/or convectively remove heat from the airfoil  40 . In addition, the pressure and suction sides  42 ,  44  further join to form a leading edge  48  at an upstream portion of the airfoil  40  and a trailing edge  50  downstream from the cavity  46  at a downstream portion of the airfoil  40 . A plurality of cooling passages  52  in the pressure side  42 , suction side  44 , leading edge  48 , and/or trailing edge  50  may provide fluid communication from the cavity  46  through the airfoil  40  to supply the cooling media over the outer surface of the airfoil  40 . As shown in  FIG. 2 , for example, the cooling passages  52  may be located at the leading and trailing edges  48 ,  50  and/or along either or both of the pressure and suction sides  42 ,  44 . One of ordinary skill in the art will readily appreciate from the teachings herein that the number and/or location of the cooling passages  52  may vary according to particular embodiments, and the present invention is not limited to any particular number or location of cooling passages  52  unless specifically recited in the claims. 
     The exemplary airfoil  40  shown in  FIG. 2  may be manufactured using any process known in the art. For example,  FIG. 3  provides a plan view of a core  60  that may be used to manufacture the airfoil  40  shown in  FIG. 2  by investment casting. As shown in  FIG. 3 , the core  60  may include a serpentine portion  62  with a number of long, thin branches or projections  64  that extend from the serpentine portion  62 . The serpentine portion  62  generally corresponds to the size and location for the cavity  46  in the airfoil  40 , and the projections  64  generally correspond to the size and location of the larger cooling passages  52  through the trailing edge  50  of the airfoil  40 . The core  60  may be manufactured from any material having sufficient strength to withstand the high temperatures associated with the casting material (e.g., a high alloy metal) while maintaining tight positioning required for the core  60  during casting. For example, the core  60  may be cast from ceramic material, ceramic composite material, or other suitable materials. Once cast or otherwise manufactured, a laser, electron discharge machine, drill, water jet, or other suitable device may be used to refine or form the serpentine portion  62  and/or projections  64  shown in  FIG. 3 . 
     The core  60  may then be utilized in a lost wax process or other casting process as is known in the art. For example, the core  60  may be coated with a wax or other suitable material readily shaped to the desired thickness and curvature for the airfoil  40 . The wax-covered core  60  may then be repeatedly dipped into a liquid ceramic solution to create a ceramic shell over the wax surface. The wax may then be heated to remove the wax from between the core  60  and the ceramic shell, creating a void between the core  60  and the ceramic shell that serves as a mold for the airfoil  40 . 
     A molten high alloy metal may then be poured into the mold to form the airfoil  40 . The high alloy metal may include, for example, nickel, cobalt, and/or iron super alloys such as GTD-111, GED-222, Rene 80, Rene 41, Rene 125, Rene 77, Rene N5, Rene N6, PWA 1484, PWA 1480, 4th generation single crystal super alloy, MX-4, Hastelloy X, cobalt-based HS-188, and similar alloys. After the high alloy metal cools and solidifies, the ceramic shell may be broken and removed, exposing the high alloy metal that has taken the shape of the void created by the removal of the wax. The core  60  may be removed from inside the airfoil  40  using methods known in the art. For example, the core  60  may be dissolved through a leaching process to remove the core  60 , leaving the cavity  46  and cooling passages  52  in the airfoil  40 . 
       FIG. 4  provides a perspective view of a system  70  for creating additional cooling passages  52  through the airfoil  40 . As shown in  FIG. 4 , the system  70  may include a laser  72  capable of generating an unfocused laser beam  74 . The unfocused laser beam  72  may have a wavelength of approximately 532 nm, a pulse frequency of approximately 10 kHz, and an average power of approximately 40-50 W. In the particular embodiment shown in  FIG. 4 , the laser  72  directs the unfocused laser beam  74  at the airfoil  40 , and a fluid column  76  surrounds the unfocused laser beam  74 . The fluid column  76  may be any gas or liquid capable of focusing the unfocused laser beam  74  and may have a pressure in the range of approximately 700-1,500 pounds per square inch, although the present invention is not limited to any particular pressure for the fluid column  76  unless specifically recited in the claims. The fluid column  76  acts as a light guide for the unfocused laser beam  74  to create a focused or confined laser beam  78  directed at the airfoil  40 . The confined laser beam  78  oblates the surface of the airfoil  40 , eventually creating the desired cooling passage  52  through the airfoil  40 . 
       FIG. 5  provides a perspective view of the system  70  shown in  FIG. 4  after the confined laser beam  78  has penetrated through the airfoil  40 . As shown in  FIGS. 4 and 5 , the system  70  further includes a liquid  80  flowing inside the airfoil  40 . The liquid  80  may be water, oil, steam, and/or any other liquid that may form a liquid column  82  inside the airfoil  40 . The liquid  80  flowing inside the airfoil  40  may have a pressure roughly commensurate with the pressure of the gas or liquid in the fluid column  76  and sufficient to disrupt the fluid column  76  inside the airfoil  40 . For example, the liquid  80  flowing inside the airfoil  40  may have a pressure greater than approximately 25 pounds per square inch, although the present invention is not limited to any particular pressure for the liquid  80  unless specifically recited in the claims. 
     As shown most clearly in  FIG. 5 , the liquid  80  may be aligned to intersect with the fluid column  76  and/or confined laser beam  78  inside the airfoil  40 . In particular embodiments, the liquid  80  may be aligned substantially perpendicular to the fluid column  76 , while in other particular embodiments, the liquid  80  may be aligned at an oblique or acute angle with respect to the fluid column  76  and/or confined laser beam  78 . As the liquid  80  intersects with the fluid column  76  inside the airfoil  40 , the liquid  80  disrupts the fluid column  76  and/or scatters the confined laser beam  78  inside the airfoil  40 . In this manner, the liquid  80  prevents the confined laser beam  78  from striking an inside surface of the airfoil  40  across from the newly formed cooling passage  52 . 
     One of ordinary skill in the art will readily appreciate from the teachings herein that the system  70  described and illustrated with respect to  FIGS. 4 and 5  may provide a method for manufacturing the airfoil  40 . For example, the method may include directing the unfocused laser beam  74  at the surface of the airfoil  40  and confining the unfocused laser beam  74  inside the fluid column  76  outside of the airfoil  40  to create the confined laser beam  78  outside of the airfoil  40 , as shown in  FIGS. 4 and 5 . The method may further include creating the hole or cooling passage  52  through the surface of the airfoil  40  with the confined laser beam  78  and disrupting the fluid column  76  and/or confined laser beam  78  inside the airfoil  40  with the liquid  80  inside the airfoil  40 , as shown in  FIG. 5 . In this manner, the method may scatter the confined laser beam  78  inside the airfoil  40  to prevent the confined laser beam  78  from striking the inside surface of the airfoil  40  across from the cooling passage  52 . 
     This written description uses examples to disclose the invention, including the best mode, 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 include 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.