Abstract:
A method for repairing a turbine blade for a gas turbine engine is provided. The method includes securing the blade into a clamping fixture, obtaining a zero reference from a gauging surface on the clamping fixture, coupling the clamping fixture to a grinding machine, and grinding the blade based on the zero reference.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to gas turbine engines, and more specifically to turbine blades used in gas turbine engines. 
         [0002]    In at least some gas turbine engines, turbine blades used within the engine are cast to an approximate final shape. Portions of the turbine blades, including, but not limited to, a root portion, are then shaped to a final desired form by a shaping technique, such as grinding. The finished turbine blades are assembled into a turbine disk or rotor, such that a “dovetail” formed on each turbine blade engages a complimentarily shaped slot on the turbine disk. 
         [0003]    Generally, turbine blades are constructed from a high-temperature, high-strength alloy that is adapted to withstand the temperatures and stresses imposed on the parts of a turbine assembly. Because of the high cost of materials, casting operations, and finishing operations, some turbine blades, after being in service, are refurbished to restore the original aerodynamic contours of portions of the blades. At least some known turbine blade repairs require building up the surface being repaired with a weld bead, and then grinding the surface back to its original contour. 
         [0004]    Occasionally, while refurbishing a turbine blade, because the dovetail section has been housed in the rotor disk slot and out of the gas stream. It may be the only datum available for referencing for the grinding operation. However, because the dovetail serrations may be small, in many applications, the clamping mechanisms may inhibit operation of the grinding machines. In contrast, other clamping arrangements use long locating pins to clamp the component such that grinding equipment operations are not inhibited. However, because such fixtures must generally be very large to generate a sufficient clamping force, such fixtures are generally much more expensive and far less portable than other clamping mechanisms. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In one aspect, a method for repairing a turbine blade for a gas turbine engine is provided. The method includes securing the blade into a clamping fixture, obtaining a zero reference from a gauging surface on the clamping fixture, coupling the clamping fixture to a grinding machine, and grinding the blade based on the zero reference. 
         [0006]    In another aspect, an apparatus for aligning a gas turbine engine blade including a dovetail is provided. The apparatus includes at least one locator pin configured to engage a serration formed on the blade dovetail, a locator block supporting the locator pin, wherein the locator block comprises at least one groove sized to receive the locator pin therein, and a slide block assembly for engaging a dovetail surface opposite the serration. The slide block assembly is configured to position the blade dovetail against the locator pin. 
         [0007]    In another aspect, a tool for securing a turbine blade including a dovetail is provided. The tool includes a pair of locator pins configured to engage adjacent serrations defined in the turbine blade. Each locator pin includes a first end, a second end, and a clamping section extending therebetween. The clamping section has a length that is substantially equal to a length of the blade dovetail. A locator block supports the locator pins. The locator block includes a plurality of grooves to receive each locator pin therein. A slide block assembly is configured to engage the blade dovetail opposite the locator pins such that the blade dovetail is secured in the tool by the locator pins. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of an exemplary turbine blade for use in a gas turbine engine; 
           [0009]      FIG. 2  is a schematic view of an exemplary fixture used to secure a turbine blade; 
           [0010]      FIG. 3  is a perspective view of the fixture shown in  FIG. 2 ; and 
           [0011]      FIG. 4  is an exploded view of the fixture shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a perspective view of an exemplary turbine blade  10  that may be used with a gas turbine engine (not shown). Blade  10  includes an airfoil  12  that extends radially outward from a blade root  14  to an airfoil tip  15 . Airfoil  12  includes a first contoured sidewall  16  and a second sidewall  18 . Sidewalls  16  and  18  are joined at a leading edge  20  and at an axially-spaced trailing edge  22 . 
         [0013]    Blade  10  also includes an integral dovetail  24  that is used for mounting blade  10  in a rotor or disk that has a complimentarily dovetail-shaped slot (not shown) for receiving dovetail  24 . Dovetail  24  is tapered from a platform  26  proximate blade root  14  to a radially inner surface  28 , and includes a plurality of serrations  30  defined therein. Serrations  30  extend from a leading edge side  32  of dovetail  24  to a trailing edge side  34 . Serrations  30  create a wavelike cross-sectional profile for dovetail  24  which has a series of alternating peaks  36  and valleys  38 . 
         [0014]      FIG. 2  is a schematic view of an exemplary fixture  50  used for securing a component, such as blade  10 .  FIG. 3  is a perspective view of fixture  50 .  FIG. 4  is an exploded view of fixture  50 . 
         [0015]    As used herein, the terms “repair” and “repairing”, may include any repair/inspection process. For example, repair processes may include various known repair techniques including welding, grinding, and/or machining. The above examples are intended as exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the terms “repair” and repairing”. In addition, as used herein the term “component” may include any object to which a repair process is applied. Furthermore, although the invention is described herein in association with a gas turbine engine, and more specifically for use with a turbine blade for a gas turbine engine, it should be understood that the present invention may be applicable to any component and/or any repair process. Accordingly, practice of the present invention is not limited to the repair of turbine blades or other components of gas turbine engines. 
         [0016]    Fixture  50  includes a base member  52 , a locator assembly  54 , a slide block assembly  56 , and a drive cylinder  58 . Base member  52  includes a substantially planar platform  60  that supports locator block assembly  54  and slide block assembly  56 . Platform  60  includes a slotted opening  62  defined therein. A reinforcing support rail  63  extends below platform  60 . Base member  52  includes an end plate  64  that extends outward from platform  60 . In the exemplary embodiment, end plate  64  is substantially perpendicular to platform  60 . End plate  64  includes a plurality of attachment holes  66  which enable drive cylinder  58  to couple to slide block assembly  56 . 
         [0017]    Locator assembly  54  includes a locator block  68  having a clamping end  70  that includes a pair of recessed grooves  72  defined therein. Grooves  72  are sized to partially receive upper and lower cylindrically shaped locator pins  74  and  76  respectively, therein. Locator pins  74  and  76  are spaced a distance d 1  which enables pins  74  and  76  to be partially inserted into a pair of adjacent dovetail serrations  30  when blade  10  is received in fixture  50 . In the exemplary embodiment, locator pins  74  and  76  are identical and are substantially cylindrical roll pins. Locator pins  74  and  76  each includes a shouldered end  88  and a clamping portion  91  that extends between ends  81  and  88  and has a length L 1  that is substantially equal to a length L 2  (shown in  FIG. 1 ) of dovetail section  24 . 
         [0018]    A locator pin bushing plate  78  is coupled to locator block  68  and includes a pair of apertures  80  that each receive a respective end  81  of locator pins  74  and  76  within bushings  82  installed in apertures  80 . A retainer plate  84 , and a locator pin lock plate  86  are coupled to opposite sides of locator block  68  and bushing plate  78  to retain pins  74  and  76 . Locator pin shouldered ends  88  are received in apertures  90  defined in lock plate  86 . 
         [0019]    Locator block  68  includes a pair of pins  92  that are received in apertures  94  defined in lock plate  86  for positioning lock plate  86  with respect to locator block  68 . A gauge plate  96  is coupled to an upper surface  98  of locator block  68  and a gauge set block  100  is coupled against gauge plate  96  at a side edge  102  of locator block  68 . 
         [0020]    Slide block assembly  56  includes a slide block body  110  and a push block  112  that is coupled to an external surface  114  of slide block body  110  by a fastener  116 . Push block  112  includes a contoured edge  118  that engages with blade dovetail  24 . 
         [0021]    Drive cylinder  58  is coupled against an outer surface  130  of end plate  64 . Bushings  120  within slide block body  58  are sized to receive shafts  122  extending from drive cylinder  58 . More specifically, bushings  120  facilitate controlling movement of slide block body  110  across platform  60 . In the exemplary embodiment, a threaded rod  132  and lock pin  134  are used to secure slide block assembly  56  to drive cylinder  58 . It is to be understood, however, that other methods of coupling slide block assembly  56  to drive cylinder  58  may be used. In an exemplary embodiment, drive cylinder  58  is a pneumatic cylinder. 
         [0022]    During operation, a component to be repaired, such as a turbine blade, first undergoes a process to build up the blade material in the area of the repair. This buildup may be accomplished by welding wherein one or more weld beads of blade material are applied to the blade surface. 
         [0023]    Slide block assembly  56  is slidable across platform  60  in a first direction toward locator assembly  54 , as indicated by arrow A, to clamp against turbine blade  10  such that turbine blade  10  is secured in position relative to fixture  50 . Slide block assembly  56  is also retractable in a second direction, away from locator assembly  54 , as indicated by arrow B, to release blade  10  from fixture  50 . Movement of slide block assembly  56  is controlled by drive cylinder  58 . In the exemplary embodiment, cylinder  58  is actuated by air pressure. An amount of travel can be limited by varying the position of slide block  56  relative to platform  60  using threaded rod  132 . Moreover, a distance d 2  from fastener  116  to push block  112  is adjusted such that interference between push block  112  and end plate  64  limits travel of slide block assembly  56  in second direction B. In an exemplary embodiment, slide block assembly  56  has a range of travel from the clamped position to the retracted position of about 0.030 inches. 
         [0024]    Fixture  50  clamps on turbine blade/dovetail  24 . For blades that have been in service, dovetail  24  provides a datum reference for restoring turbine blade  10  to original dimensions. In fixture  50 , dovetail  24  is clamped between locator pins  74  and  76  on one side, and push block  112  on the opposite side. Locator pins  74  and  76  are sized to substantially mate against dovetail  24  such that pins  74  and  76  engage adjacent dovetail serrations  30 . Push block  112  substantially facilitates centering a respective dovetail peak  36  between locator pins  74  and  76 . More specifically, locator pins  74  and  76  are received in grooves  72  such that locator block  68  facilitates providing structural support for the clamping load induced to locator pins  74  and  76 . 
         [0025]    When inserting blade  10  into fixture  50 , push block  112  is initially retracted to allow insertion of blade dovetail  24 . The push block travel length is adjusted such that dovetail  24  is retained in fixture  50  so that an operator does not have to physically hold blade  10  while clamping blade  10 . More specifically, when inserted, blade  10  contacts locator pin bushing plate  78 , which acts as a positioning stop. When air pressure is supplied to cylinder  58  blade  10  is clamped within fixture  50 . After clamping blade  10  into fixture  50 , gauge plate  96  and gauge set block  100  are used to establish a zero datum reference such that blade  10  can be measured to determine how much material should be removed during grinding to restore blade  10  to its dimensional specifications. 
         [0026]    After clamping blade  10  into fixture  50 , fixture  50  can be coupled to a grinding machine (not shown). The grinding machine may gain access to blade  10  via platform slot  62 . 
         [0027]    The above-described turbine blade root clamping fixture provides a cost effective and highly reliable apparatus that may be safely used for clamping turbine blades for grinding operations. The fixture provides a compact package that is capable of generating a sufficient clamping force to securely retain the blade for grinding while also providing access to the blade by the grinding equipment. The fixture also retains the turbine blade when the blade is released such that an operator can remove his hands from the fixture when clamping the blade. 
         [0028]    Exemplary embodiments of a turbine blade root clamping apparatus are described above in detail. The clamping and locating assemblies are not limited to the specific embodiments described herein, but rather each component may be utilized independently and separately from other components described herein. Each component can also be used in combination with other turbine blade clamping and locating components. 
         [0029]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.