Abstract:
A blade is repaired by utilizing a super abrasive machining quill and/or wheel to form the contour and restore the height of the blade. By utilizing super abrasive machining, the contour and height can be quickly returned to desired dimensions by removing unwanted added material.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to a method of repairing a compressor or turbine blade airfoil, wherein super abrasive machining (SAM) quills are utilized to form the contour on the airfoil. 
     Gas turbine engines are known, and typically include a plurality of sections mounted in series. Two of the sections are the turbine section and the compressor section. These sections each include a plurality of rotors, each mounting a plurality of circumferentially spaced blades. 
     Air enters a gas turbine engine via a fan. Some air is bypass air, while some air enters a compressor section, where it is compressed. The compressed air moves downstream where it is mixed with fuel and is combusted in a combustor section. The hot products of combustion then move downstream over the turbine blades, driving them to rotate. The turbine blades exist in a very harsh environment, and may also be subject to rubbing with spaced stationary surfaces. 
     The turbine blades as known have very complex structures. As an example, complex cooling channels are formed within the blades, and receive cooling air to assist the blades in resisting high temperatures. 
     Even with the design of the cooling channels, etc., turbine blades will often wear. This is particularly true at the tip of an airfoil on the blade. Since the blades are formed with the complex channels, they are expensive. Thus, rather than simply replace worn blades, it has become standard in the industry to repair the blades. 
     The compressor blades are not subject to the high temperatures that the turbine blades face, but have their own challenges. As an example, sand or other impurities can damage the blade. Compressor blades are also repaired. 
     When either type blade has worn at the outer tip of its airfoil, one common technique for repairing the blade is to apply a weld material at the tip to return the blade to its original height. This weld material must then be machined such that it approximates the desired airfoil shape and height. 
     In the prior art, hand blending techniques, and grinding wheels are utilized. Also, milling may be used for restoring the tip and upper wall areas. Typically, hand blending is performed after a milling operation to meet finish requirements. 
     The prior art techniques are relatively time-consuming. Moreover, for smaller blades having an airfoil that curves around a smaller radius of curvature, the prior art grinding and machining tools may be too large. 
     Super abrasive machining techniques have been known and have been utilized for originally forming portions of turbine blades. As an example, U.S. Pat. No. 7,101,263 discloses a super abrasive machine tool. However, super abrasive machining techniques have not been utilized for repairing the tips of blade airfoils. 
     SUMMARY OF THE INVENTION 
     In a disclosed embodiment of this invention, a blade has its airfoil tip repaired by applying a welding material to extend the tip back toward its original height. Excess material is then machined away by using a super abrasive machining (SAM) technique to return the contour of the airfoil to its desired shape. A quill having SAM materials is utilized to return the contour to its original shape. Another SAM tool, such as a grinding wheel, may then be utilized to return the airfoil to its desired height. By utilizing the smaller SAM quill, one can machine a relatively small radius of curvature on the airfoil. 
     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  shows a first step in the repair of a turbine blade. 
         FIG. 2  shows a second step. 
         FIG. 3A  shows a subsequent step. 
         FIG. 3B  shows a tool for performing the  FIG. 3A  step. 
         FIG. 4  shows another step. 
         FIG. 5A  schematically shows a first machining embodiment. 
         FIG. 5B  shows a second machining embodiment. 
         FIG. 5C  shows a third machining embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a worn turbine blade  20 . As known, an airfoil  22  extends toward a tip. The tip is shown to be worn at  24 . Such a turbine blade  20  will typically be taken out of service for repair. While the drawings show a turbine blade, it should be understood the invention extends to repair of compressor blades also. 
       FIG. 2  shows a first step in the repair of the blade  120 . As shown, the airfoil  22  now is returned beyond its original height by adding weld material  26  to extend the height from the worn shape  24  of  FIG. 1 . The weld material is deposited at the tip, but may extend too far, and also would typically not have the desired contour shape for the airfoil  22 . 
     Thus, as shown in  FIG. 3A , a super abrasive machine quill  30  is now used to machine the contour  32  of the airfoil  120 . As shown, there may be excess weld material  34  which is cut away by the SAM quill  30  to define the final shape  36 . 
       FIG. 3B  shows a known SAM quill  30 . As known, a tip  31  performs the actual machining, and has a smaller diameter than a base portion  33 . The base portion  33  has a larger diameter than a shaft  35  that is received in a spindle for driving the SAM quill  30  at relatively high speeds. As known, SAM quills have their abrasive material  37  formed from a group including diamonds, and cubic boron nitride. An example of a known quill is disclosed in U.S. Pat. No. 7,101,263, the description of which is incorporated herein by reference. 
     With use of the SAM machining, a relatively small diameter quill  30  is used to form the contour  32  as shown in  FIG. 3A . In this manner, a blade having a relatively small radius of curvature can be machined back to its desired shape. 
       FIG. 4  shows a subsequent step, wherein the weld material  26  is cut away by an SAM grinding wheel  40  to remove excess material  42 , and return the airfoil  22  to its desired height. 
       FIG. 5A  shows an embodiment wherein a tool  100  has a dual spindle  102  extending to each side. Grinding wheel  40  is mounted to one side, and SAM quill  30  is mounted to the opposed side. 
       FIG. 5B  shows another machining embodiment  104  wherein a single spindle  106  mounts grinding wheel  40  and quill  30 . 
       FIG. 5C  shows yet another embodiment where one machine  108  includes a spindle  110  driving grinding wheel  40 , while a second machine  112  includes a spindle  114  driving SAM quill  30 . 
     In each of  FIGS. 5A ,  5 B and  5 C, the size of the grinding wheels  40  are not shown to scale relative to the SAM quills  30 . 
     With this method, the blade can be quickly and accurately returned to its desired shape and height. 
     While a preferred embodiment of this invention 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.