Abstract:
A process is provided for repairing an airfoil structure adapted for use in a gas turbine engine comprising: providing an airfoil structure having a section with a defect; removing airfoil structure material comprising the section with the defect such that a through hole is created; providing a replacement element; providing interlocking structure; positioning the replacement element relative to the through hole; and securing the replacement element to the airfoil structure via the interlocking structure such that the through hole is covered.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to a process for repairing a damaged section of a gas turbine engine airfoil structure by mechanically coupling a replacement element to the airfoil structure. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are a series of rows of stationary vanes and rotating blades in a turbine section of a gas turbine engine. The blades are coupled to a rotor disc assembly. Hot working gases travel to the rows of blades. As the working gases expand through the turbine, the working gases cause the blades and, hence, the rotor disc assembly to rotate. 
         [0003]    An airfoil structure may comprise a stationary vane or a rotatable blade. The stationary vane may comprise an airfoil, a platform coupled to each end of the airfoil and rails extending from the platforms. The blade may comprise an airfoil, a platform coupled to a lower end of the airfoil and a root extending from the platform. During engine operation, a vane or a blade may become worn or damaged. Known techniques for repairing a worn or damaged vane or blade comprise welding, brazing or transient liquid phase bonding. For example, filler material may be welded to a damaged section. 
         [0004]    Thereafter, the repaired section may be heat treated. However, because vanes and blades are typically made from superalloys, repair welding often produces liquation cracking and post weld heat treatment often produces strain age cracking. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with a first aspect of the present disclosure, a process is provided for repairing an airfoil structure adapted for use in a gas turbine engine comprising: providing an airfoil structure having a section with a defect; removing airfoil structure material comprising the section with the defect such that a through hole is created; providing a replacement element; providing interlocking structure; positioned the replacement element relative to the through hole; and securing the replacement element to the airfoil structure via the interlocking structure such that the through hole is covered. 
         [0006]    Removing may comprise forming a through hole comprising a first outer section and a second inner section. The first section may have a diameter greater than that of the second section. 
         [0007]    The replacement element may comprise a first outer portion and a second inner portion. The first portion may have a diameter slightly less than the diameter of the through hole first section and the second portion may have a diameter slightly less than the diameter of the through hole second section. The first outer portion may be received in the through hole first section and the second inner portion may be received in the through hole second section. 
         [0008]    The interlocking structure may comprise threads on the replacement element and a section of the airfoil structure adjacent the through hole. 
         [0009]    The process may further comprise sealing the replacement element to the airfoil structure. 
         [0010]    The interlocking structure may comprise a pin positioned through the replacement element and a section of the airfoil structure adjacent the through hole. 
         [0011]    The process may further comprise sealing the replacement element and the pin to the airfoil structure. 
         [0012]    The pin may be threaded. 
         [0013]    The pin may be positioned at a non-orthogonal angle to an outer surface of the replacement element. 
         [0014]    The airfoil structure may comprise a vane or a blade. 
         [0015]    The replacement element may comprise a main body portion and the interlocking structure may comprise at least one tongue extending from the main body portion. The process may further comprise forming at least one groove in a section of the airfoil structure adjacent the through hole. The tongue is adapted to be received in the groove. 
         [0016]    The interlocking structure may comprise first, second, third and fourth tongues extending out from the main body portion. The process may comprise forming first, second, third and fourth grooves in the airfoil structure section adjacent the through hole. 
         [0017]    The first, second, third and fourth tongues may have curved shapes and the first, second, third and fourth grooves may have curved shapes. 
         [0018]    Positioning may comprise positioning the replacement element upside down relative to an outer surface of the airfoil structure and securing may comprise rotating the replacement element 180 degrees such that the first and second tongues move through the third and fourth grooves and then into the first and second grooves and the third and fourth tongues move into the third and fourth grooves when the first and second tongues move into the first and second grooves. 
         [0019]    In accordance with a second aspect of the present disclosure, a repaired airfoil structure is provided comprising: an airfoil structure having a through hole formed therein so as to remove a section with a defect; a replacement element positioned in the through hole; and interlocking structure to mechanically couple the replacement element to the airfoil structure. 
         [0020]    The interlocking structure may comprise a pin positioned through the replacement element and a section adjacent the through hole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
           [0022]      FIG. 1  illustrates a vane having an airfoil with a defect; 
           [0023]      FIG. 2  illustrates the vane in  FIG. 1  including a through hole formed when a section of the airfoil including the defect is removed; 
           [0024]      FIG. 3  is a side view of a replacement element of a first embodiment of the present disclosure; 
           [0025]      FIG. 4  is a top view of the replacement element illustrated in  FIG. 3 ; 
           [0026]      FIG. 5  is a cross sectional view illustrating the replacement element fitted into a through hole in the vane; 
           [0027]      FIG. 6  is front view of a curved portion of an airfoil of a vane; 
           [0028]      FIG. 7  is a view taken along view line  7 - 7  in  FIG. 6 ; 
           [0029]      FIG. 8  is a top view of a replacement element of a further embodiment of the present disclosure; 
           [0030]      FIG. 9  is a side view of the replacement element illustrated in  FIG. 8 ; 
           [0031]      FIG. 10  is an end view of the replacement element illustrated in  FIGS. 8 and 9 ; 
           [0032]      FIG. 11  is a view of a through hole in an airfoil formed in accordance with a further embodiment of the present disclosure; and 
           [0033]      FIGS. 12A-12D  illustrate steps for assembling the replacement element of  FIG. 8  to the airfoil illustrated in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
         [0035]    An airfoil structure may comprise a stationary vane or a rotatable blade for use in a gas turbine engine. An example stationary vane  10  is illustrated in  FIGS. 1 and 2 . The vane  10  comprises an airfoil  12 , first and second platforms  14 A and  14 B coupled to opposing ends of the airfoil  12  and rails  16  extending outward from the platforms  14 A and  14 B. A blade (not shown) may comprise an airfoil, a platform coupled to a lower end of the airfoil and a root extending from the platform. 
         [0036]    There are a series of rows of stationary vanes and rotating blades in a turbine section of a gas turbine engine. The blades are coupled to a rotor disc assembly. Hot working gases travel to the rows of blades. As the working gases expand through the turbine, the working gases cause the blades and, hence, the rotor disc assembly to rotate. 
         [0037]    During gas turbine engine operation, one or more of the vanes and blades may become worn or damaged. In accordance with the present disclosure, a process is provided for repairing an airfoil structure adapted for use in a gas turbine engine. While the process of the present disclosure will be discussed herein in the context of repairing a vane, the process of the present disclosure may also be used to repair a defect in an airfoil structure comprising a blade. 
         [0038]    In  FIG. 1 , a section  12 A of the vane airfoil  12  is shown having a defect D. The defect D may comprise worn away (missing) material, burned (oxidized or melted) material, corroded material, cracked material, or damage from foreign object impact. 
         [0039]    The defect D is repaired in accordance with a first embodiment of this disclosure as follows. Material including the defect D is removed, i.e., the section  12 A with the defect D is removed, using a conventional cutting process, such that a through hole  120  is created in the airfoil  12 , see  FIGS. 2 and 5 . The cutting process may comprise machining by grinding, turning, milling, routing, drilling, water jet cutting, laser cutting or electro-discharge machining. In the illustrated embodiment, the through hole  120  comprises a first outer section  120 A and a second inner section  120 B, see  FIGS. 2 and 5 . The first outer section  120 A has a first diameter D 1  and the second inner section  120 B has a second diameter D 2 . In the illustrated embodiment, the first diameter D 1  is greater than the second diameter D 2 . 
         [0040]    Next, a replacement element  30  is provided to fill and seal the through hole  120 , see  FIGS. 3-5 . Also provided is interlocking structure, which, in the illustrated embodiment, comprises a pin  40 , see  FIG. 5 . The replacement element  30  comprises a first outer portion  30 A and a second inner portion  30 B. The first portion  30 A has a third diameter D 3  slightly less than the first diameter D 1  of the through hole first section  120 A and the second inner portion  30 B has a fourth diameter D 4  slightly less than the second diameter D 2  of the through hole second section  120 B, see  FIGS. 3 and 5 . The pin  40  has a cylindrical shape in the illustrated embodiment. 
         [0041]    The replacement element  30  is fitted into the through hole  120  such that the first outer portion  30 A is received in the through hole first section  120 A and the second inner portion  30 B is received in the through hole second section  120 B. 
         [0042]    In the illustrated embodiment, a first bore  30 C is formed in the replacement element first outer portion  30 A, see  FIGS. 4 and 5 . The bore  30 C does not extend through the replacement element second inner portion  30 B, see  FIG. 4 . A second bore  12 B is formed in a section  12 C of the airfoil  12  adjacent the through hole  120 , see  FIG. 5 . In the illustrated embodiment, the first and second bores  30 C and  12 B are aligned with one another. So as to secure the replacement element  30  to the airfoil  12 , the pin  40  is press fitted into the bores  30 C and  12 B such that a friction fit is created between the pin  40  and each of the replacement element  30  and the airfoil  12 . 
         [0043]    In the illustrated embodiment, the pin  40  is positioned relative to the replacement element  30  such that its longitudinal axis is generally orthogonal to an outer surface  30 D of the replacement element  30 . However, it is also contemplated that the first and second bores  30 C and  12 B may be formed in the replacement element  30  and the airfoil  12  such that the pin  40  extends at a non-orthogonal angle, e.g., 45 degrees, to the outer surface  30 D of the replacement element  30 . It is further contemplated that threads (not shown) may be provided on the pin  40  and the structure of the replacement element  30  defining the bore  30 C and the structure of the airfoil  12  defining the bore  12 B. Hence, instead of using a friction or press fit to secure the pin  40  to the replacement element  30  and the airfoil  12 , a threaded connection may be used. 
         [0044]    Instead of using a pin  40  to secure the replacement element  30  to the airfoil  12 , it is further contemplated that threads may be provided on the replacement element  30  and the structure defining the through hole  120  such that the replacement element  30  may be threadedly coupled to the airfoil  12 . The threads on the replacement element  30  and the structure defining the through hole  120  define interlocking structure in this embodiment. 
         [0045]    After the replacement element  30  has been assembled and secured to the airfoil  12 , the replacement element  30  and the pin  40  are further secured to the airfoil  12  via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may be effecting during the process of assembling the replacement element  30  and the pin  40  to the airfoil  12 . In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element  30  and/or the pin  40 . 
         [0046]    The process of the present invention may also be used to repair a damaged section on a curved portion  12 D, e.g., a leading or trailing edge, of the airfoil  12 , see  FIGS. 6 and 7 . The airfoil  12  has a wall  320 . A section of the wall  320  having a defect is removed to create a through hole  220 . A section  320 A of the airfoil wall  320  surrounding the through hole  220  is notched so as to have a first thickness T 1 , which is less than a second thickness T 2  of sections  320 B of the airfoil wall  320  that are not notched. A replacement element  230  is then fitted over the through hole  220  and a pin  240  is press fit into bores  230 A and  320 C provided in the replacement element  230  and the airfoil wall section  320 A so as to secure the replacement element  230  to the airfoil  12 , see  FIG. 7 . 
         [0047]    After the assembly process of the replacement element  230  and the pin  240  to the airfoil  12 , the replacement element  230  and pin  240  are further secured to the airfoil  12  via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may be effecting during the process of assembling the replacement element  230  and the pin  240  to the airfoil  12 . In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element  230  and/or the pin  240 . 
         [0048]    In accordance with a further embodiment of the present disclosure, a defect in an airfoil  412  is repaired as follows. Material is removed, i.e., a section with a defect is removed, using a conventional cutting process, such that a through hole  420  is created in the airfoil  12 , see  FIG. 11 . Curved end walls  412 A and  412 B and generally planar side walls  412 C and  412 D of the airfoil  412  define the through hole  420 . First, second, third and fourth curved engagement grooves  414 A- 414 D are formed in airfoil structure adjacent the through hole  420  such that the grooves  414 A- 414 D extend inwardly from the airfoil side walls  412 C and  412 D. The grooves  414 A- 414 D may be formed via conventional milling cutters or electro-discharge machining. Further, the grooves  414 A- 414 D may have a cross sectional shape of a square, semi-circle or dove-tail. 
         [0049]    Next, a replacement element  430  is provided to fill and seal the through hole  420 , see  FIGS. 8-10  and  12 A- 12 D. The replacement element  430  may comprise a main body portion  430 A having generally curved end walls  430 B and  430 C, generally planar side walls  430 D and  430 E and generally planar upper and lower surfaces  430 F and  430 G, see  FIGS. 8-10 . The curvature of the main body portion curved end walls  430 A and  430 B is generally the same as the curvature of the curved end walls  412 A and  412 B of the airfoil structure defining the through hole  420 . 
         [0050]    The interlocking structure comprises first, second, third and fourth curved tongues  440 A- 440 D extending from the main body portion  430 A of the replacement element  430 , see  FIGS. 8-10 . The curvature of the tongues  440 A- 440 D is generally the same as the curvature of the curved engagement grooves  414 A- 414 D, see  FIGS. 8-11  and  12 A- 12 D. Further, the tongues  440 A- 440 D may have a cross sectional shape matching the cross sectional shape of the grooves  414 A- 414 D. 
         [0051]    To assemble and secure the replacement element  430  to the airfoil  412 , the replacement element  430  is initially positioned upside down relative to an outer surface  413  of the airfoil structure  412 , see  FIG. 12A . The replacement element  430  is then rotated 180 degrees. In  FIG. 12B , the replacement element  430  is shown rotated about 30 degrees from its position shown in  FIG. 12A  such that the first and second tongues  440 A and  440 B are located respectively in the third and fourth curved engagement grooves  414 C and  414 D. In  FIG. 12C , the replacement element  430  is shown rotated about 90 degrees from its position shown in  FIG. 12A  such that the first and second tongues  440 A and  440 B have moved out of the third and fourth curved engagement grooves  414 C and  414 D. In  FIG. 12D , the replacement element  430  is shown rotated about 170 degrees from its position shown in  FIG. 12A  such that the first and second tongues  440 A and  440 B have moved respectively into the first and second curved engagement grooves  414 A and  414 B and the third and fourth tongues  440 C and  440 D have moved into the third and fourth curved engagement grooves  414 C and  414 D. When the replacement element  430  has rotated 180 degrees from its position shown in  FIG. 12A , the first, second, third and fourth tongues  440 A- 440 D are respectfully fully engaged with and positioned within the curved engagement grooves  414 A- 414 D such that the upper surface  430 F of the replacement element  430  is generally coplanar with the outer surface  413  of the airfoil. Hence, the replacement element  430  is assembled and secured to the airfoil  412 . 
         [0052]    After the assembly process of the replacement element  430  to the airfoil  412 , the replacement element  430  is further secured to the airfoil  412  via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may also be effecting during the process of assembling the replacement element  430  to the airfoil  412 . In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element  430 . 
         [0053]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.