Abstract:
A method of repair of a turbine blade involves inspecting a turbine blade having an internal cavity and a cap. The cap is removed and replaced with a replacement cap. The replacement cap has an opening. The opening provides access to the internal cavity of the internal blade so that the replacement cap may be attached to the turbine blade through the opening.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to a method of repairing a turbine blade of a turbine engine. 
         [0002]    A turbine blade of a turbine engine has a blade body and an integrally formed blade tip. A tip cap is a piece that is inserted into a recess formed in the blade tip to cover the internal cavity of the blade body. The area near the tip of the turbine blade is subject to significant stress and wear. Accordingly, the turbine blade may require repair or replacement because of wear proximate the tip. Because of the high expense of the turbine blade, it is preferable to attempt to repair the turbine blade rather than replace it. However, this process may be both labor intensive and time consuming. 
         [0003]    Techniques do exist for removing and replacing the blade tip from the blade body of the turbine blade. A challenge faced in the replacement of a blade tip is to create a strong connection between the tip and the blade body. Generally, the edge of the tip is welded to the exterior walls of the blade body. This connection may not be as secure, however, as the connection between the original blade tip and the original blade body. 
         [0004]    A need therefore exists for a more secure connection between blade tip and blade body in the repair of the turbine blade. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention involves a technique for repairing a turbine blade. The turbine blade has an internal cavity with a cap that covers the cavity. The old cap is removed and replaced with a replacement cap. The replacement cap is then connected to the turbine blade through an opening in the replacement cap that provides access to the internal cavity of the turbine blade. 
         [0006]    The turbine blade may have a structural support disposed in the internal cavity. The opening provides access to the structural support for attaching the replacement cap. The opening may be further aligned with the structural support and allow direct attachment of the replacement cap to the structural support. The replacement cap may be welded to the structural support through the opening. 
         [0007]    The replacement cap has a perimeter for attachment to the turbine blade. Disposed within the perimeter of the cap is an opening sized to permit attachment of the cap to the internal structural supports of the turbine blade through the opening. The opening is further arranged within the perimeter to allow its direct alignment with the internal structure of the turbine blade. The opening may be subsequently filled following attachment of the cap to the turbine blade. 
         [0008]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  illustrates a view of a turbine engine known in the art. 
           [0010]      FIG. 2  illustrates a cross-sectional view of a turbine blade of the turbine engine of  FIG. 1 . 
           [0011]      FIG. 3  illustrates an example of a worn turbine blade. 
           [0012]      FIG. 4  illustrates an aspect of the inventive technique of repairing a turbine blade. 
           [0013]      FIG. 5  illustrates another aspect of the inventive technique, highlighting replacement cap with openings permitting access to an internal cavity of the turbine blade. 
           [0014]      FIG. 6  illustrates a side cross-sectional view of the turbine blade with replacement cap. 
           [0015]      FIG. 7  illustrates a perspective view of the turbine blade with replacement cap. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  illustrates an example of a gas turbine engine  10 , here a turbofan engine, that would benefit from the inventive repair technique. As other types of gas turbine engines will likewise benefit from the inventive technique, the term gas turbine engine is not limited to the disclosed embodiment. As shown, gas turbine engine  10  has fan  14  which propels ambient air into gas turbine engine  10 . Multi-stage high and low pressure compressors  18  compress the air. The compressed air is then mixed with fuel and ignited in a combustor  22 , where the gas expands. Expanded gas then passes through high pressure turbine section  20  and low pressure turbine section  32  as known and passes out of gas turbine engine  10 . 
         [0017]      FIG. 2  illustrates a turbine blade  30  as known in the art. Here, turbine blade  30  is shown in cross-section with dashed lines showing the perimeter of turbine blade  30 . As shown, turbine blade  30  has blade body  34  and blade tip  38 . In addition, blade tip  38  has cap  42  that covers internal cavity  54 . Squealer  50 , a rail, extends around the perimeter  62 . Within blade body  34  is internal cavity  54 , which has structural supports  66  extending throughout to support turbine blade  30  as known. Between structural supports  66  are cooling passages  67 ,  69 . These cooling passages  67 ,  69  permit air to cool blade body  34  as known. Cap  42  has internal cavities  71  that permit air to come close to surface  73  of cap  42  for air to cool so as to relieve heat buildup within blade body  34 . 
         [0018]    Due to stress and wear, turbine blade  30  may develop areas of wear  70  and cracks  74 , as shown in  FIG. 3 . Indeed, areas of wear may be large enough to expose internal cavity  54  as shown. Because of the high expense of replacing turbine blade  30 , it may be desirable to repair it.  FIGS. 3-7  illustrate the inventive repair technique. 
         [0019]    As shown in  FIG. 3 , the inventive repair technique involves grinding down squealer  50  of the worn turbine blade  30  shown in  FIG. 3  to the level of cap  42  as shown in  FIG. 4 . Following this step, areas of wear  70  and cracks  74  are built-up by welding with weld wire to the level of cap  42 . When this step is complete, cap  42  is removed by electrical discharge machining, leaving blade body  34  with exposed internal cavity  54  as shown in  FIG. 5 . 
         [0020]    Following removal of cap  42 , replacement cap  46  is disposed over blade body  34 . Replacement cap  46  is similar to cap  42  in shape and structure. However, replacement cap  46  has openings  58  that permit access to internal cavity  54  when replacement cap  46  is placed into blade body  34 . Replacement cap  46  has perimeter  62  that serves to interface with wall  36  of blade body  34  so that replacement cap  46  may nest flush with wall  36  as shown in  FIG. 7 . 
         [0021]    As shown in  FIG. 5 , openings  58  are aligned with structural supports  66  disposed within internal cavity  54  so that when replacement cap  46  is seated in blade body  34  within wall  36 , openings  58  will provide direct access to structural supports  66  as shown in  FIG. 6  in cross-section. Openings  58  are aligned along arrows A and B as shown in  FIG. 5 . Furthermore, perimeter  62  is sized and shaped so that when replacement cap  46  is disposed in blade body  34  alignment of openings  58  occurs just by seating replacement cap  46  in blade body  34 . In addition, internal cavities  75  are positioned within replacement cap  46  to mimic internal cavities  71  of original cap  42 . 
         [0022]    As shown in  FIG. 6 , openings  58  are sized sufficiently large enough to permit welding of replacement cap  46  to structural supports  66  at points C and D by weld source  80  projecting beam  84 . Beam  84  may be a laser or other known welding technique. In this way, replacement cap  46  may be directly welded to structural supports  66  located within internal cavity  54 . Following this welding operation, openings  58  are then filled with welding wire of the same material as replacement cap  46 . 
         [0023]    With reference to  FIG. 7 , perimeter  62  of replacement cap  46  is also welded along wall  36 . Then, with weld wire, squealer  88  is built to the original shape of squealer  50  but to a height higher than the original height of squealer  50  so that squealer  88  may be ground down to the correct height. Following this operation, the outside of turbine blade  30  is ground to remove weld beads. Electrical discharge machining may be used to remove weld beads around perimeter  62  of replacement cap  46 . 
         [0024]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.