Patent Document

BACKGROUND OF THE INVENTION 
     This application relates to a method of repairing a worn blade airfoil by securing additional material to the blade. 
     At least some known gas turbine engines 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. 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 expensive due to material and machining costs. Accordingly blades are often repaired instead of replaced. The repairs generally involve removing the worn blade tip and then building up weld filler or similar material on the blade. The material build-up is then machined to an appropriate airfoil shape to form a restored blade tip. Automated weld build-up on the blade can be difficult, especially since the blade has a curved airfoil profile and new material is only desired near the tip end of the blade. Vision systems are sometimes used to control a robotic arm that deposits weld material on the worn area of the blade. Applications using the robotic arm involve complex controls and vision systems, especially if the robotic arm tracks the curved airfoil profile of the blade. Manual weld processes are also used to deposit weld material on the worn area of the blade. Manual weld processes are often more inconsistent than automated processes. 
     Known cold metal transfer techniques are utilized for welding in various applications. However, cold metal transfer techniques have not been utilized to repair worn blades. 
     SUMMARY 
     An example method of repairing an airfoil includes the steps of securing additional material to a worn airfoil and limiting movement of the additional material with a guide. 
     An example method of repairing a blade for a gas turbine engine includes removing a worn tip area from a blade and utilizing cold metal transfer techniques to deposit additional welding material on the blade to form a different tip area for the blade. 
     An example intermediately repaired blade includes a blade having an airfoil profile, which includes a repaired section. Additional material is deposited on a worn portion of the blade to fabricate the repaired section using cold metal transfer welding techniques. 
     An example method of forming a portion of an airfoil includes securing additional material to the airfoil, limiting movement of the additional material with a guide, and altering some of the additional material to form a desired airfoil contour. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the example disclosure can be best understood from the following specification and drawings, the following of which is a brief description: 
         FIG. 1  schematically shows an example gas turbine engine; 
         FIG. 2  shows a worn blade of the  FIG. 1  gas turbine engine; 
         FIG. 3  shows the flow of an example method for repairing the  FIG. 2  blade; 
         FIG. 4  shows an example guide for repairing the  FIG. 2  blade; 
         FIG. 5  shows an example fixture for repairing the  FIG. 2  blade; 
         FIG. 6  shows an example of the  FIG. 2  blade after material is deposited; 
         FIG. 6A  shows a top view of the  FIG. 6  blade; and 
         FIG. 7  shows a partial view of the  FIG. 2  blade after repair. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The disclosed examples facilitate depositing additional material on worn blade tips. 
       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 is circumferentially disposed about an engine centerline X. During operation, the fan section  14  intakes air, the compressors  18 ,  22  pressurize the air. The combustor  26  burns fuel mixed with the pressurized air. The high and low pressure turbines  30 ,  34  extract energy from the 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 . The example method is not limited to the two-spool gas turbine architecture described above 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  66  extending from a base  65  toward a tip portion  68 , which is generally the portion of the airfoil profile  66  furthest from the base  65 . In this example, a dashed line  62   a  is shown within the tip portion  68  of the airfoil profile. The blade  60  includes a worn area  70  near the tip portion  68 . As known, stress from the blade  60  rubbing within the gas turbine engine  10  removes material from the tip portion  68  causing the worn area  70 . For example, the blade  60  may rub against a surrounding engine portion such as an outer air seal. Although shown as a turbine blade  60 , it should be understood that disclosed examples may be applied to a blade in the compressor  18  or low pressure turbine  34 . 
     As shown in  FIG. 3 , an example method  100  for repairing the blade  60  of  FIG. 2  includes a step  104  of removing the worn area to smooth the blade tip portion  68 . In this example, approximately 25 mm of the worn area  70  is removed to smooth a tip end of the blade  60  prior to further repairs. Machine grinders or similar tools may remove the worn area. 
     After removing the worn area  70 , the end of the blade  60  corresponds generally to the blade surface  62 , as illustrated by the dashed line  62   a  in  FIG. 2 . Other examples may remove more or less material depending on the desired location of the blade surface  62  and how severely the blade  60  is worn. The method  100  next includes inserting the tip portion  68  into a guide at step  108  to secure the blade  60 . Material is added to the tip portion at step  112 . At step  116  the guide is removed, and at step  120  a different tip is shaped from the material added at step  112 . In another example, the step of inserting the tip portion  68  into the guide at step  108  is eliminated. In such an example, additional material is added to the tip portion at step  112  without using the guide. 
       FIGS. 4-7  are used to describe an example implementation of the method  100 . Referring to  FIG. 4 , an example guide  72   a  includes an aperture  76   a  for receiving the tip portion  68  of the blade  60  ( FIG. 2 ). The profile of the aperture  76   a  aligns with the airfoil profile  66  of the tip portion  68 . In this example, two milled guide halves are joined with tack welds  77  to fabricate the aperture  76   a  within the guide  72   a . Slots  78  or seams are created where the halves join. The example guide  72   a  is a plate, but other guides  72   a  could be used and fall within the scope of this disclosure. 
       FIG. 5  shows another example guide  72   b  without slots  78 . An Electrical Discharge Machining (EDM) cutter forms the aperture  76   b  within the guide  72   b , for example. A fixture assembly  80  secures the guide  72   b  relative to the blade  60  when adding additional material  84  using a welder  88 . Other examples include utilizing manual welding processes to add the additional material  84 , such as, adding the additional material  84  with a handheld welder for example. Securing the guide  72   b  and the blade  60  within the fixture  80  represents step  108  of the  FIG. 3  method. The worn area  70  of the blade  60  ( FIG. 1 ) is typically removed prior to securing the blade  60  within the fixture  80 . 
     In this example, the additional material  84  is added to the blade surface  62  using a modified Metal Inert Gas (MIG) welding process, such as the cold metal transfer welding process developed by Fronius Inc. As known, cold metal transfer and similar processes facilitate weld droplet formation. Cold metal transfer and similar processes also utilize less heat than other welding processes to facilitate reducing burn through or warp. Both automated and manual cold metal transfer welding processes may be used to add the additional material  84  to the blade surface  62 . 
     In this example, the fixture  80  secures the guide  72   b  relative to the blade  60  such that the blade surface  62  is substantially flush with a surface  73  of the guide  72   b . Together, the blade surface  62  and the surface  73  of the guide  72   b  provide a relatively flat rectangular area larger than the blade surface  62 . Although application of the additional material  84  is desired on the blade surface  62 , moving the welder  88  in multiple directions to apply additional material  84  to the blade surface  62  is undesirable in some examples. That is, an operator of the welder  88  may desire to apply the additional material  84  by moving the welder  88  in a single direction rather than multiple directions. Adding the guide  72   b  to provide the relatively rectangular area facilitates supporting additional material  84  in areas other than the blade surface  62 . Thus, the welder  88  may move in a single direction to apply the additional material  84  without the additional material  84  dripping down the blade  60  or otherwise moving away from the blade surface  62 . 
     In other examples, the worn area  70  of the blade  60  is secured within the aperture  76   b , but slightly above or recessed from the surface  73  of the guide  72   b . Other examples include applying the additional material  84  on the blade surface  62  without using the guide  72   b  or the fixture  80 , such as when manually applying the additional material  84 . 
     Referring again to the example utilizing the guide  72   b  and the fixture  80 , when the blade surface  62  is positioned within the aperture  76   b , the guide  72   b  limits movement of the additional material  84  away from the blade surface  62  toward the base  65  of the blade  60 . The additional material  84  instead remains near the blade surface  62 , the surface  73  of the guide  72   b  or both. Without the guide  72   b , additional material  84  would spill down the sides of the blade  60  toward the base  65 . Thus the guide  72   b  acts like a platform to hold the additional material, here weld filler, near the blade surface  62 , which facilitate concentrated application of the additional material  84  to the blade surface  62 . 
       FIGS. 6 and 6A  illustrate the intermediately repaired blade  60  removed from the fixture  80  and having additional material  84  secured to the blade surface  62  and the guide  72   a . As shown, particularly in the top view of  FIG. 6A , the example welder  88  adds the additional material  84  in a single pass represented by the illustrated directional arrows. Previously, adding additional material  84  to the airfoil profile of the worn area  70  required complex multi-directional control of the welder  88 . Using the guide  72   b  enables the welder  88  to apply more additional material  84  during the single pass without the additional material moving away from the blade surface  62 , such as down the sides of the blade  60  toward the base  65 . The added additional material  84  forms a repaired section of the blade  60 . As known, the width of the additional material  84 , here a weld bead, can be controlled by adjusting welding parameters. 
     After removing the blade  60  and guide  72   b  from the fixture  80 , the guide  72   b  is separated from the additional material  84  and the blade  60 , which may require cutting the guide  72   b  from the blade  60 . After removing the guide  72   b  from the blade  60 , the additional material  84  is shaped to form a different blade tip  90  and repaired blade  60 , as shown in  FIG. 7 . Grinders or similar machining tools are often used to shape the additional material  84  into the desired airfoil profile. 
     Although a preferred embodiment has been disclosed, a worker of ordinary skill in this 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.

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