Abstract:
An example method of repairing an airfoil includes securing a cap to an end portion of a worn airfoil and securing additional material to the cap. The method includes altering some of the cap to form a desired airfoil contour.

Description:
BACKGROUND OF THE INVENTION 
     The application relates to a method of repairing a blade airfoil, wherein additional material secures to a cap secured to the blade. 
     Gas turbine engines are known and typically include multiple sections, such as a fan, a compression section, a combustor section, a turbine section, and an exhaust nozzle. Blades are mounted within the compressor and turbine sections. The blades have airfoils extending from a platform toward a blade tip. 
     Rotating blades compress air in the compression section. The compressed air mixes with fuel and is combusted in the combustor section. Products of combustion expand to rotatably drive blades in the turbine section. As the blades are often exposed to extreme temperatures, some blades, especially the turbine blades, include internal channels for routing cooling air. 
     Some blades rub against other portions of the engine when rotating. The engine dimensions are controlled to prevent too much rubbing, which can fracture the blade or bind the engine. Rubbing wears and stresses the blades, particularly near the blade tip. Replacing an entire worn blade is often expensive due to material and machining costs. 
     To prevent replacing the entire blade, the worn area is often removed and replaced with a build-up of weld material that is then machined to an appropriate airfoil shape. But other areas of the blade, such as braze material from the OEM production process, can contaminate the build-up, and as known, contaminants weaken welds. 
     Therefore, what is needed is a method of repairing an airfoil that lessens contaminants in the repairing weld, especially repairing welds near the tip of the airfoil. 
     SUMMARY OF THE INVENTION 
     An example method of repairing an airfoil includes securing a new cap to an end portion of a worn airfoil and securing additional material to the cap. The method includes altering some of the cap to form a desired airfoil contour. In another example, the method includes capping a worn airfoil with a cap, and then securing additional material to the cap. An example repaired blade includes a blade having an airfoil profile extending toward a blade tip and a cap securing the blade tip to the airfoil of the blade. The airfoil profile is created in the cap by consuming a portion of the cap. In one example, welding consumes a portion of the cap. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an example gas turbine engine. 
         FIG. 2  shows a worn blade of the  FIG. 1  engine. 
         FIG. 3  shows the flow of an example method for repairing the  FIG. 2  blade. 
         FIG. 4  shows the  FIG. 2  blade during repair. 
         FIG. 5  shows an end view of the  FIG. 4  blade. 
         FIG. 6  shows the repaired  FIG. 2  blade. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  schematically illustrates an example gas turbine engine  10  including (in serial flow communication) a fan section  14 , a low pressure compressor  18 , a high pressure compressor  22 , a combustor  26 , a high pressure turbine  30  and a low pressure turbine  34 . The gas turbine engine  10  is circumferentially disposed about an engine centerline X. During operation, air is pulled into the gas turbine engine  10  by the fan section  14 , pressurized by the compressors  18 ,  22 , mixed with fuel, and burned in the combustor  26 . The high and low pressure turbines  30 ,  34 , extract energy from the hot combustion gases flowing from the combustor  26 . 
     In a two-spool design, the high pressure turbine  30  utilizes the extracted energy from the hot combustion gases to power the high pressure compressor  22  through a high speed shaft  38 , and a low pressure turbine  34  utilizes the energy extracted from the hot combustion gases to power the low pressure compressor  18  and the fan section  14  through a low speed shaft  42 . However, the invention is not limited to the two-spool gas turbine architecture described and may be used with other architectures such as a single-spool axial design, a three-spool axial design and other architectures. That is, there are various types of gas turbine engines, many of which could benefit from the examples disclosed herein, which are not limited to the design shown. 
     Referring now to  FIG. 2 , a worn turbine blade  60  within the high pressure turbine  30  of  FIG. 1  includes an airfoil profile  64  extending toward a tip portion  68 . The blade  60  includes a worn area  70  at the tip portion  68 . A blade core  72  with one or more strengthening ribs  74  extends through the interior of the blade  60 . As known, air moves through the blade core  72  to cool the blade  60 . Also as known, stresses from rubbing the blade  60  within the engine  10  wear the tip portion  68 . Although shown as a turbine blade  60 , it should be understood that other examples may include a compressor blade. 
     As shown in  FIG. 3 , an example method  100  for repairing the blade  60  of  FIG. 2  includes removing the worn area  70  at step  104 , which exposes the blade core  72  and the ribs  74 . The method  100  next caps the blade  60  and exposed blade core  72  at step  108 . The tip portion  82  is then welded to the capped blade at step  112 . 
     Referring now to the  FIGS. 4 and 5 , a cap  86  is welded to the blade  60 . Prior to welding, the cap  86  extends past the airfoil  64  about 0.01-0.06 inches (0.25-1.27 millimeters), and, in one example, the cap  86  extends about 0.03-0.04 inches (0.76-1.02 millimeters) proud of the airfoil  64 . The cap  86  is initially secured to the blade  60 , with plug welds  94 , for example. The blade core  72  is accessible through at least one aperture  90  within the cap  86 . The aperture  90  facilitates weldably securing the cap  86  to the blade  60 . 
     After initially securing the cap  86  using the plug welds  94 , additional welding, such as fusion welding, fills the aperture  90  with weld material  96  and seals the blade core  72 . The plug welds  94  maintain the position of the cap  86  relative to the blade  60  when sealing the blade core  72 . In this example, sealing the blade core  72  limits movement of residual braze from the blade core  72  past the cap  86 , which lessens the chance of contaminating further welds near the cap  86  with the residual braze from the blade core  72 . Thus, capping and sealing inhibits movement of contaminants from the blade core  72  to higher stress areas of the blade  60 . 
       FIG. 6  shows the repaired blade  60  with a weld  98  securing a tip portion  82  to the cap  86 , which is consumed as filler in the weld  98 . In this example, the tip portion  82  is a cast or machined virgin nickel super alloy material, such as Rene&#39;  80 , and not entirely weld build-up. The blade  60  and the cap  86  are also Rene&#39;  80  in this example. 
     Gas tungsten arc welding or fusion welding secure the tip portion  82  to the cap  86 . Some of the cap  86  is consumed as weld filler in the weld  98 , which reduces the amount of the cap  86  extending past the airfoil  64 . Consuming the cap  86  as weld filler in the weld  98  introduces a finite amount of weld filler to the weld  98  when welding. Because the cap  86  extends approximately evenly past the perimeter of the airfoil  64 , the amount of potential weld filler is generally evenly distributed about the airfoil  64 . As known, limiting weld filler lessens weld drop through into the blade core  72 . 
     Welding may not reduce all of the cap  86  extending past the airfoil  64 . Grinding or buffing the airfoil  64  may remove remaining extending portions to align the perimeters of the cap  86  and the weld  98  with the airfoil  64  and return the repaired airfoil to desired dimensions. 
     While a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.