Abstract:
An example method of attaching an airfoil for an integrally bladed rotor includes placing a support collar in an installed position around at least a leading edge and trailing edge of an airfoil stub to be repaired in an integrally bladed rotor. The support collar and the airfoil stub together have a midline that is positioned between opposing, laterally outer surfaces of the airfoil stub when the support collar is in the installed position. The method performs linear friction welding to add a replacement airfoil to the airfoil stub.

Description:
[0001]    This invention was made with government support under Contract No. F33657-03-D-0016-0010 awarded by the United States Air Force. The Government has certain rights in this invention. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates generally to turbomachine airfoils and, more particularly, to repairing or replacing airfoils using linear friction welding techniques. 
         [0003]    As known, gas turbine engines, and other turbomachines, include multiple sections, such as a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The compressor section and the turbine section include airfoil arrays mounted for rotation about an engine axis. The airfoil arrays include multiple individual airfoils (i.e., blades) that extend radially from a mounting platform to an airfoil tip. The blade arrays and mounting platform may form a one piece, integrally bladed rotor or bladed disk/blisk. 
         [0004]    Air moves into the engine through the fan section. Rotating the airfoil arrays in the compressor section compresses the air. The compressed air is then mixed with fuel and combusted in the combustor section. The products of combustion are expanded to rotatably drive airfoil arrays in the turbine section. Rotating the airfoil arrays in the turbine section drives rotation of the fan and compressor sections. Airfoils in the gas turbine engine may become damaged. Replacing the damaged airfoils in a conventionally bladed rotor is relatively simple. Replacing the damaged airfoils in an integrally bladed rotor is often significantly more difficult (sometimes not feasible) and expensive. 
       SUMMARY 
       [0005]    An example method of attaching an airfoil for an integrally bladed rotor includes placing a support collar in an installed position around at least a leading edge and trailing edge of an airfoil stub to be repaired in an integrally bladed rotor. The support collar and the airfoil stub together have a midline that is positioned between opposing, laterally outer surfaces of the airfoil stub when the support collar is in the installed position. The method performs linear friction welding to add an airfoil to the airfoil stub. 
         [0006]    Another example method of attaching an airfoil for an integrally bladed rotor includes placing a support collar in an installed position around at least a leading edge and a trailing edge of an airfoil stub to be repaired in an integrally bladed rotor. The support collar and the airfoil stub together have a midline that does not extend laterally past a laterally outer surface of the blade stub. The method includes performing linear friction welding to add an airfoil to the airfoil stub. 
         [0007]    An example integrally bladed rotor includes a rotor hub and a plurality of blades extending radially outwardly of the rotor hub. At least one of the blades is attached by a linear friction welding operation. The blade includes an airfoil stub portion that was associated with the rotor hub prior to the attachment and an airfoil portion that has been linear friction welded to the airfoil stub as part of the attachment. A collar supported the airfoil stub during the linear friction welding and is then machined away. The collar includes a consumable portion that is consumed during the linear friction welding. The consumable portion and the blade stub have a midline that is bounded by opposing laterally outer surfaces of the blade stub during the linear friction welding. 
         [0008]    These and other features of the disclosed examples can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]      FIG. 1  shows a schematic view of an example gas turbine engine. 
           [0010]      FIG. 2  shows an integrally bladed rotor in a repair tooling fixture from the  FIG. 1  engine. 
           [0011]      FIG. 3  schematically shows a top view of an airfoil stub ready for a linear friction welding operation. 
           [0012]      FIG. 4  shows a perspective view of the  FIG. 3  airfoil stub. 
           [0013]      FIG. 5  shows a close up view of a trailing edge of an airfoil stub in the  FIG. 3  linear friction welding operation. 
           [0014]      FIG. 6  shows a section view at line  6  of  FIG. 5  with an airfoil. 
           [0015]      FIG. 7  shows the  FIG. 6  section view after partially linear friction welding the airfoil to an airfoil stub. 
           [0016]      FIG. 8  shows the  FIG. 6  section view after linear friction welding the airfoil to an airfoil stub. 
           [0017]      FIG. 9  shows the  FIG. 6  section view after machining away excess material. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  schematically illustrates an example gas turbine engine  10  including (in serial flow communication) a fan  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 axis X. The gas turbine engine is an example turbomachine. 
         [0019]    During operation, air is pulled into the gas turbine engine  10  by the fan  14 , pressurized by the compressors  18  and  22 , mixed with fuel, and burned in the combustor  26 . The turbines  30  and  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 . The low pressure turbine  34  utilizes the extracted energy from the hot combustion gases to power the low pressure compressor  18  and the fan  14  through a low speed shaft  42 . 
         [0020]    The examples described in this disclosure are not limited to the two-spool engine architecture described and may be used in other architectures, such as a single spool axial design, a three-spool axial design, and still other architectures. That is, there are various types of engines, and other turbomachines, that can benefit from the examples disclosed herein. 
         [0021]    Referring to  FIGS. 2-5  with continuing reference to  FIG. 1 , an example integrally bladed rotor  50  includes a plurality of airfoils  52  extending radially away from a rotor hub. The example integrally bladed rotor  50  includes a damaged airfoil stub  56 . During operation, the integrally bladed rotor  50  typically forms part of the low pressure compressor  18  and/or high pressure compressor  22  of the gas turbine engine  10 . The integrally bladed rotor  50  is made of a titanium alloy, in this example, but may be made of nickel alloy or other materials. 
         [0022]    The damaged airfoil stub  56  is to be repaired. During repair, the integrally bladed rotor  50  is mounted within a linear friction welding machine incorporating a fixture  54 . The airfoil stub  56  is supported by a collar assembly  100 . In this example, the collar  100  includes a sub-collar  64  associated with a leading edge  40  of the airfoil stub  56  and a sub-collar  68  associated with a trailing edge  41  of the airfoil stub  56 . The sub-collars  64  and  68  each include a base portion  90  and a consumable portion  86 . The consumable portion  86  is consumed during the linear friction welding. Although the example describes replacing a damaged airfoil stub, another example may include attaching an airfoil during initial assembly of the rotor  50 . 
         [0023]    The example airfoil stub  56  includes a convex (or suction) side  74  and a concave (or pressure) side  78 . The consumable portion  86  is defined by a surface  75  that is typically aligned with the convex side  74 , and a surface  79  that is typically aligned with the concave side  78 . The consumable portion  86  of the sub-collar  68  thus has a lateral profile that matches the geometry of an airfoil stub  56 . 
         [0024]    A midline  82  of the consumable portion  86  and the portion of the airfoil stub  56  within the sub-collar  68  is centered between the surface  75  and the surface  79 . That is, at a given chord position X, the distance D 1  between the surface of the surface  75  and the midline  82  is the same as the distance D 2  between the surface of the concave side surface  79  and the midline  82 . In this example, the midline  82  is positioned between (or bounded by) the surface  74  and the surface  78 . 
         [0025]    During the linear friction welding process, the consumable portion  86  is consumed while the base portion  90  remains. A person having skill in the art of linear friction welding, and the benefit of this disclosure, would understand how material is consumed during the linear friction welding. 
         [0026]    The sub-collars  64  and  68  are the same material as the airfoil stub  56  and the replacement airfoil  94  in this example. In another example, one or both of the sub-collars  64  and  68  is a different material than the airfoil stub  56 , the replacement airfoil  94 , or both. 
         [0027]    Referring now to  FIGS. 6-9  with continuing reference to  FIG. 5 , a replacement airfoil  94  is positioned against the airfoil stub  56  and the consumable portion  86  of the sub-collar  64  at an interface  96 . During the linear welding process, the replacement airfoil  94  oscillates back and forth in a weld direction D that is generally parallel to a chord of the airfoil stub  56 . 
         [0028]    By moving the replacement airfoil  94  and the airfoil stub  56  rapidly relative to each other, heat is built up, and will weld the two together. The linear friction welding technique is known. 
         [0029]    In this example, the consumable portion  86  and a portion of the airfoil stub  56  are consumed during the linear friction welding. Again, the consumable portion  86  is sized such that the midline  82  is positioned between the surface  74  and the surface  78 . This arrangement causes material in the consumable portion  86  to flow away from, rather than toward, the airfoil stub  56  as the material in the consumable portion  86  is consumed. As can be appreciated, the midline is radially extending relative to the engine axis X, in this example. 
         [0030]    In this example, the midline  82  represents the circumferential center of the section of the consumable portion  86  and the blade stub  56 . That is, the midline is centered between the surface  74  and the surface  78 , and the distance D 1  is about the same as the distance D 2 . The consumable portion  86  includes substantially the same amount of material (within 5%, for example) on either side of the midline. 
         [0031]    In other examples, the midline  82  is not centered between the surface  74  and the surface  78 . However, in such examples, the midline still does not extend laterally past the surface  74  or the surface  78 . Thus, it is possible that the distance D 1  is not the same as the distance D 2  After securing the airfoil  94  to the airfoil stub  56  and the consumable portion  86 , the consumable portion  86  is machined away along with a portion of the replacement airfoil  94  and some of the airfoil stub  56 . 
         [0032]    Features of the disclosed examples include laterally balancing the amount of consumable material during a linear friction weld to avoid polluting desired welds with the material that would otherwise be expelled from the resultant linear friction weld joint. In the prior art, the consumable portion may contain more material on the concave side than on the convex side, or vice versa. Significantly more material on one of the sides could cause material intended for expulsion from the consumable portion to flow back toward the airfoil stub during the linear friction welding, which can pollute or otherwise foul the weld bond. 
         [0033]    The surface of the consumable portion of the collar in contact with the airfoil matches with the profile of the airfoil to provide intimate structural support during welding. The size of the airfoil is used to determine the size of the convex side of the collar and the size of the concave side of the collar resulting the flow of material away from the airfoil during the linear friction welding. 
         [0034]    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 disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.