Abstract:
A portable device for refurbishing an edge of an airfoil is provided that has an edge shaper and airfoil positioners that positively engage the airfoil. A method for refurbishing an edge of an airfoil is also provided that includes the steps of (a) providing the portable refurbishing device; (b) locating the edge shaper and the airfoil edge relative to one another with the positioners; and (c) moving one of the device or the airfoil relative to the other along the airfoil edge.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to gas turbine airfoils in general, and to methods and apparatus for refurbishing gas turbine airfoils in particular. 
     2. Background Information 
     Gas turbine engines, particularly those in aircraft applications, will occasionally ingest substances (e.g., water and sand) entrained within air drawn into the engine. The substances will wear rotorblades and stator vanes (“airfoils”) located within the engine. The leading edge of an airfoil is particularly susceptible to this type of damage. Left unchecked, deformation and erosion will negatively affect the performance of the airfoil and can eventually cause irreparable damage to an airfoil. To minimize performance loss and to ensure safe operation, airfoils are periodically inspected for deformation and wear both on-wing and during regularly scheduled overhaul and maintenance. In those instances where the wear is beyond acceptable standards, the rotor blade or stator vane must be refurbished or replaced. A person of skill in the art will recognize that airfoils within a gas turbine engine, particularly fan blades within modern high-bypass ratio fan blades, are very expensive to replace. Hence, there is considerable advantage in refurbishing gas turbine airfoils when possible. 
     If, for example, the leading edge of a fan blade is worn beyond acceptable standards, present refurbishment methods generally require that the aircraft be taken off-line, and the fan assembly subsequently removed from the engine and disassembled so the worn airfoil can be refurbished. If the wear is within predetermined limits, the leading edge is refurbished by machining the leading edge back to or near original specifications Although refurbishing a blade using presently known techniques is preferable to replacing the blade, there are nevertheless several undesirable aspects associated with such a process. First, the aircraft is typically taken out of service thereby eliminating its revenue producing potential. Second, there is considerable labor and cost involved in removing the blade from the engine particularly when the engine is mounted on-wing. In addition, when a rotor assembly is disassembled it is sometimes necessary to perform a “run-up” test before the engine can be allowed back in service. Testing of this nature, while prudent and necessary, nevertheless also increases the cost of the repair. Third, fan blade leading edges are typically refurbished using a manual process. The accuracy of the refurbishment is important because the leading edge profile is critical to the aerodynamic performance of the airfoil, and consequent performance of the engine. Accurately refurbishing the edge by hand requires considerable skill and time and is generally considered to be a long lead-time process. This is particularly true for ultra-high bypass fan blades that have significant twist and curve. 
     In instances where a foreign object more substantial than water or sand (e.g., rocks, birds, etc.) is ingested into the engine and impacts a rotor blade or stator vane, quite often a nick or dent occurs too large to be accommodated by refurbishment. If the damage is within allowable standards, a blending operation can be used to repair the damage. To our knowledge, blending operations do not restore the airfoil leading edge to its original profile. In fact some practices involve removing a curved portion out of the edge to eliminate the damage. The depth of the curved portion into the airfoil causes the repaired edge to be blunter than the original edge. A person of skill in the art will recognize that a blunter edge, even one that is only slightly different, will likely have appreciable impact on the aerodynamic performance of the airfoil. Another problem with some blending operations is that they involve forming tools that are not completely guided or have only limited guidance relative to the edge to be blended. Limited guidance cutting tools are often harder to control making it harder for the operator to produce the desired leading edge profile. In addition, if used improperly, a blending tool can gouge and irreparably damage an airfoil during the repair process. For these reasons, blending tools are not well suited for edge refurbishment. 
     What is needed, therefore, is a method and/or an apparatus for refurbishing gas turbine airfoils that can be used on airfoils mounted within a gas turbine engine, and one that does not require considerable skill to perform or use. 
     DISCLOSURE OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an apparatus and a method for refurbishing gas turbine airfoils that requires less skill than is necessary to perform some conventional refurbishment methods. 
     It is another object of the present invention to provide an apparatus and a method for furbishing gas turbine fan blades that can be used on engine mounted fan blades. 
     According to the present invention, a method for refurbishing an edge of an airfoil is provided that includes the steps of: (a) providing a portable refurbishing device having an edge shaper and airfoil positioners that positively engage the airfoil; (b) locating the edge shaper and the airfoil edge relative to one another with the positioners; and (c) moving one of the device or the airfoil relative to the other along the airfoil edge. 
     The present invention provides several significant advantages over the prior art of which we are aware. One of those advantages lies in the ability of the present invention to refurbish the edge of a fan blade while that fan blade is mounted within the engine. As a result, the amount of time an aircraft is out of service for fan blade refurbishment is significantly decreased. Performing the refurbishment on a mounted fan blade also eliminates the substantial cost of removing and reinstalling the engine, and the cost of testing the reassembled engine. 
     Another significant advantage of the present invention is that the refurbishment does not require a highly skilled operator. The positioners within the device ensure the airfoil edge is properly located relative to the edge shaper, thereby decreasing the opportunity for error, consequently facilitating the refurbishment process. The positive engagement of the positioners also helps to prevent inadvertent gouging that may occur with some prior art devices. 
     Another advantage of the present invention is that a method and device is provided that is designed to refurbish substantially all of the airfoil edge. Pushing the present device along the airfoil edge helps to create a continuous uniform machined surface. Hand-held blending devices are typically designed to machine small, localized areas and are not well-suited to provide a continuous machined surface. The continuous uniform surface possible with the present method and device can be shaped in agreement with the original specification geometry to ensure improved aerodynamic performance. 
     These and other objects, features and advantages of the present invention will become apparent in light of the detailed description of the best mode embodiment thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the refurbishing device. 
     FIG. 2 is an exploded view of the refurbishing device. 
     FIG. 3 is a sectional view of the refurbishing device shown in FIGS. 1 and 5, sectioned along plane  3 — 3  as shown in FIG.  5 . 
     FIG. 4 is a sectional view of the refurbishing device shown in FIG. 1 sectioned along plane  4 — 4 . 
     FIG. 5 is a top view of the refurbishing device. 
     FIG. 6 is a diagrammatic enlarged view of the edge shaper. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, an airfoil edge refurbishment device  10  includes a housing  12 , an edge shaper  14  (see FIG.  2 ), positioners  16  for positively positioning an airfoil  18  (see FIGS. 3 and 4) relative to the edge shaper  14 , and a drive  20 . The housing  12  includes a channel  22  within which the airfoil edge is received and an aperture  24  (see FIG. 3) for receiving the edge shaper  14 . The aperture  24  intersects the channel  22  and allows the edge shaper  14  to be mounted at a fixed position within the channel  22 . The housing  12  is sized so that it may be hand held by an operator. 
     Referring to FIGS.  1  and  3 - 5 , the positioners  16  include three airfoil locator sets  26 , 28  attached to the interior side surfaces  34  of the channel  22 , and a set of base pads  32  in the base  36  of the channel  22 . The locator sets include a center locator set  26  and a pair of end locator sets  28 . The center locator set  26  includes a pair of slides  38 , 40  positioned opposite one another, and one or more biasing pads  42  extending out from one or both slides  38 , 40  in a direction toward the opposite slide  40 , 38 . The end locator sets  28  each include a pair of slides  44 , 46  positioned opposite one another, and one or more biasing pads  48  extending out from one or both slides  44 , 46  in a direction toward the opposite slide  46 , 44 . The slides  38 , 40 , 44 , 46  of each locator set are angularly disposed relative to one another in the same set. The biasing pads  42 , 48  are spring-loaded or otherwise biased to cause the airfoil  18  to be positively engaged while received within the channel  22 . In the preferred embodiment, the slides  38 , 40 , 44 , 46  and biasing pads  42 , 48  of the center and end locator sets  26 , 28  are arcuately shaped to accommodate three-dimensional curved and twisted airfoils  18 . 
     Referring to FIG. 4, the base pads  32  extend lengthwise along the base  36  of the channel  22 . When an airfoil  18  is engaged within the channel  22 , the base pads  32  extend lengthwise along the edge of the airfoil  18 , substantially aligned with the airfoil edge. The base pads  32  are biased (e.g., by a spring) toward the top of the channel  22 , preferably extending above the edge shaper  14  to prevent inadvertent engagement of the edge shaper  14  with the airfoil edge. The base pads  32  can be depressed toward the base  36  of the channel  22  to a position where the airfoil contact surface  50  of each base pad  32  is aligned with or below the cutting surface  52  of the fixed position edge shaper  14 , thereby exposing the edge shaper  14  to the airfoil edge. The distance  53  between the airfoil contact surfaces  50  of the base pads  32  and the cutting surface  52  of the edge shaper  14  represents the airfoil edge depth of cut per pass. 
     Referring to FIG. 6, the edge shaper  14  includes a rotary wheel  54  mounted on a shaft  56 . The circumferential surface profile of the rotary wheel  54  permits the airfoil edge to be refurbished substantially within original manufacturing geometric tolerances for the airfoil edge. The profile is asymmetric and includes a pressure-side machining surface  58  and a suction-side machining surface  60  that arcuately meet one another. The length of the pressure-side machining surface  58  is shorter than that of the suction-side machining surface  60 . Preferably, the pressure-side machining surface  58  is approximately one-half the length of the suction-side machining surface  60 . In the preferred embodiment, a portion of the profile of the rotary wheel  54  has a contour that follows the original cross-sectional geometry of the fan blade at the leading edge and in some cases the profile also follows a portion of the blade aft of the leading edge as well. The method by which the shaping wheel  54  removes material from the airfoil edge can be selectively chosen to suit the airfoil material at hand; e.g., a milling or an abrasive type operation. 
     Referring to FIG. 2, the drive  20  for the edge shaper  14  can be electrical, hydraulic, or pneumatic. An example of an acceptable drive is a commercially available variable speed electrical drive having a flexible output shaft  62 . One end of the flexible shaft  62  is connected to an electric motor  64  and the other end is connectable to a chuck  66  for holding the shaft  56  of the edge shaper  14 . The chuck  66  is attachable to the housing  12  of the refurbishing device  10 . The electric motor  64  may be mountable in a harness or other operator supported device (not shown). Alternative drives may be mounted directly to the refurbishing device housing  12 , thereby avoiding the need for flex shaft and motor separate from the chuck. 
     During periodic maintenance airfoils within a gas turbine engine are inspected for wear and damage. Airfoil edge wear that is beyond acceptable operating standards but still within repairable limits can be refurbished back to within acceptable standards. Nicks, dents, and other types of localized damage are distinguishable from wear and are typically caused by foreign object impacts. Airfoil edge wear is more widespread, generally extending over more than 50% of the fan blade leading edge. The present refurbishment method is described below as an “onwing” refurbishment of a fan blade. The present method and device are not limited, however, to fan blade on-wing refurbishments. As will be shown below, the present method and device provide a means by which the leading edge of a fan blade or other airfoil can be refurbished to within or very near original specifications without complicated set-up or highly skilled labor. As a result, there is considerable utility in using the present method and device to refurbish disassembled airfoils as well. 
     For an on-wing refurbishment, the fan blade to be refurbished is first locked into position using wedges or other means to prevent the fan stage containing the fan blade assembly from rotating. The fan blade is cleaned with a solvent to remove contaminants that may impede, interfere, or negatively affect the refurbishment process. Because fan blade leading edge wear is typically more pronounced in the middle half to three-quarters of the airfoil span, the refurbishment device  10  is placed on the fan blade near the base or tip. The fan blade is inserted into the channel  22  of the device until the edge of the airfoil contacts the contact surfaces  50  of the spring loaded base pads  32  extending out from the base  36  of the channel  22 . In this position, the base pads  32  help prevent inadvertent contact between the airfoil edge and the edge shaper  14 . The center locating slides  38 , 40  and associated biasing pads  42  locate the airfoil edge relative to edge shaper  14 . The end locating slides  44 , 46  and associated biasing pads  48  cooperate with one another to guide the airfoil  18  into and out of the center locating slides  38 , 40 , and therefore the edge shaper  14 . The operator engages the refurbishing device  10  by pushing it toward and along the edge of the fan blade. Push the refurbishing device  10  toward the edge causes the base pads  32  to depress a distance  53  below the cutting surface  52  of the edge shaper  14 , thereby exposing the edge of the airfoil to the edge shaper  14 . The refurbishment device  10  is subsequently pushed along substantially the entire span of the fan blade, refurbishing the leading edge as it goes. In some embodiments, a first guide fixture is attached to the fan blade adjacent the tip of the fan blade. In other instances, a second guide fixture is attached adjacent the base of the fan blade. Surfaces attached to the guide fixtures help transition the refurbishment device  10  into or out of engagement with the airfoil edge. The depth of cut per pass is controlled by the distance between the airfoil edge contact surfaces  50  of the base pads  32  when fully depressed and the cutting surface  52  of the edge shaper  14 . The depth of cut per pass is, therefore, predetermined and fixed as a function of the positioners  16 . This process is repeated as many times as is necessary to contour the airfoil edge back within acceptable standards. After the airfoil edge refurbishment is complete, the edge is polished and cleaned using standard practices. 
     Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and the scope of the invention. For example, the present method has been described in terms of an on-wing refurbishment process. The method can be used for airfoils not assembled within an engine as well.