Abstract:
A method of repairing an aperture and adjacent defect in a part which is started by removing one or more defects adjacent an aperture in a base material. The material is removed to create a weld seam that extends past an area of high stress concentration on the aperture. An insert of material containing a profile that corresponds to the profile of the base material removed adjacent the aperture and a combination top and runoff plate that encompasses the insert of material are provided. A backing plate is inserted underneath the combination top and runoff plate and insert such that there remains an air space between the backing plate and the combination plate which prevents the combination plate from becoming fused to the backing plate during a welding process. The insert is welded to the base material, and the backing plate is removed. Excess material is removed from the insert to obtain an aperture containing a profile essentially the same as the profile of the aperture prior to initiating the repair.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority as a divisional application under 35 U.S.C. §121 of earlier filed application Ser. No. 11/588,786, entitled “INSERT WELD REPAIR” and filed on Oct. 27, 2006, which is hereby incorporated by reference. Further, U.S. patent application Ser. No. 12/901,608, by Philip R. Bellanger, entitled “INSERT WELD REPAIR”, filed on even date with this application, is also a divisional application of U.S. patent application Ser. No. 11/588,786. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the repair of turbine engine components, and in particular to the repair of small diameter holes located on the flange of a part such as the forward inner nozzle support. 
     During operation of a turbine engine, the forward inner nozzle support can be damaged. Repairs must be done to the nicks and surface imperfections caused during normal operation. One common repair is cracks that emanate from the small diameter holes on the front flange of the forward inner nozzle support. 
     There are many techniques known in the art for repairing larger diameter holes, such as bolt holes about 0.30″ or greater in diameter. As shown in  FIG. 1 , in one such prior art repair, an area on a line about 45° on either side of the radial center line RC of hole  11  is removed. This material is then replaced with wedge  13  constructed of a similar material as the base material of the part being repaired. Wedge  13  contains at least two sides  17 ,  19  that are at approximately 90 degrees to one another. The remaining geometry of the wedge is not critical to the repair, and the remaining side(s)  21 , can be of varying shapes and angles. This approximately perpendicular corner is inserted into the area of removed base material, the corner mating with edges  23 ,  25  of the base material left on the part. Wedge  13  is surrounded by three runoff plates  27 ,  29 , and  31 . Additionally, a backing plate may be used in the repair. Thus, five separate pieces are required to initiate the repair. Wedge  13  and run off plates  27 ,  29 , and  31  are attached by tack welds  33  prior to initiating the repair. The multiple run off plates  37 ,  29 , and  31  are small and difficult to assemble about wedge  13 . 
     In the prior art repair, wedge  13  is welded into place with welds that are approximately 45 degrees from the original base material. In this configuration, the welds move the weld material (the weld zone with depleted material properties) outboard of the highest stressed areas at the hole location. This allows the raw material of the replacement wedge (with base materials properties) to remain in the highest stressed areas. The highest stressed areas surrounding the hole are located approximately 90 degrees from one another. This repair works well for holes down to about 0.30 inches in diameter, but on smaller holes the wedge becomes so small that the weld used to retain the wedge extends into the highest stressed areas of the flange. Prior to this invention, repairs to smaller diameter holes (i.e., holes having a diameter of about 0.30″ or less) on flanges were viewed as being unrepairable. Thus, a repair for smaller holes was needed. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, the invention is a method of repairing an aperture and adjacent defect in a part which is started by removing one or more defects adjacent an aperture in a base material. The material is removed to create a weld seam that extends past an area of high stress concentration on the aperture. An insert of material containing a profile that corresponds to the profile of the base material removed adjacent the aperture and a combination top and runoff plate that encompasses the insert of material are provided. A backing plate is inserted underneath the combination top and runoff plate and insert such that there remains an air space between the backing plate and the combination plate which prevents the combination plate from becoming fused to the backing plate during a welding process. The insert is welded to the base material, and the backing plate is removed. Excess material is removed from the insert to obtain an aperture containing a profile essentially the same as the profile of the aperture prior to initiating the repair. 
     In another embodiment, the invention is an apparatus for use in repairing a defect adjacent an aperture in a first flange. The first flange is parallel to a second flange. The apparatus has an insert of material that corresponds to a profile of material removed proximate the aperture in the first flange and a combination top and runoff plate that encompasses the insert material. The insert of material is fabricated from the original piece of material that comprises the combination top and runoff plate. The apparatus also has a backing plate for placement between the second flange and the combination plate and insert. The backing plate is of a thickness that is less that the thickness between the first and second flanges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a prior art repair for a hole utilizing a wedge and multiple run off plates. 
         FIG. 2  is a perspective view of a forward inner nozzle support of a dual annular combustor configuration of a high pressure turbine. 
         FIG. 2A  is a magnification of an area of the perspective view of the nozzle support illustrating a crack at one of the flange bolt holes. 
         FIG. 3  is a plan view illustrating a defect adjacent an aperture on a flange. 
         FIG. 4  is a plan view illustrating a portion of the flange to be removed. 
         FIG. 5  is a plan view illustrating the portion of the flange removed and a parallel flange. 
         FIG. 6  is a plan view illustrating a combination runoff and top plate tacked to the flange. 
         FIG. 7  is a plan view illustrating a biscuit insert tacked to the combination plate. 
         FIG. 8  is a plan view illustrating a backing plate placed below the combination plate and insert. 
         FIG. 9  is a cross-sectional elevation view of the bolt hole repair apparatus for refabrication of the flange of the nozzle support illustrated in  FIG. 7 . 
         FIG. 10  is a plan view illustrating a completed weld between the insert, combination plate, and flange with the backing plate still in place. 
         FIG. 11  is a plan view illustrating the completed weld with the backing plate removed. 
         FIG. 12  is a plan view illustrating the completed weld with a portion of the combination plate and insert removed. 
         FIG. 13  is a plan view illustrating the combination plate and insert removed to produce the original flange profile. 
         FIG. 14  is a plan view illustrating the complete repair with a new aperture in the flange. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a perspective view of a forward inner nozzle support  10  of a dual annular combustor (DAC) of a higher pressure turbine. The nozzle support  10  contains a series of small diameter holes  12  circumferentially spaced about an outer diameter flange  14 . Holes  12  are apertures used to receive small diameter pins or bolts for additional parts that are mounted to the flange.  FIG. 2A  is a closeup view of the nozzle support  10  illustrating a crack  16  at one small diameter hole  12  on flange  14 . Cracks  16  typically emanate from the holes  12  in an outward radial direction. In the past, cracks  16  in small diameter holes  12  of nozzle support  10  were unrepairable. 
       FIG. 3  is a plan view illustrating defect  16  adjacent hole  12  on flange  14 . Hole  12  is an aperture through flange  14  which is capable of receiving a pin or bolt to fasten another object to the nozzle support  10 . In the embodiment illustrated, hole  12  is circular, although other aperture profiles are envisioned. Hole  12  is a small diameter aperture, less than about 0.30 inches in diameter, which was previously unrepairable when a defect was detected adjacent the aperture. 
     Flange  14  is constructed from a heat resistant base material. The base material is a super alloy, such as a nickel base or cobalt based superalloy, or other alloys common in the gas turbine industry. Examples of alloys include Inconel7 718 (IN718), IN617, IN625, Ti 6Al 4V and other titanium alloys, Al 6061 and 4043, Waspaloy, Astroloy, Udimet7 500, and HA230. Crack  16  is the result of thermal stress that often emanates from hole  12  to the outer surface of flange  14 . 
       FIG. 4  is a plan view illustrating a portion  18  of flange  14  to be removed. Portion  18  of flange  14  is extracted by common techniques known to those of skill in the art for material removal, such as laser cutting or machining. Portion  18  is to be removed in a parabola centered about an axis that runs through the diameter of hole  12 , without completely removing the hole  12 . The material is removed by cutting perpendicular to the top surface of flange  14 . Removing material in the shape of a parabola or similar shape removes the defect and provides an attachment surface outside the high stress zones which are adjacent hole  12 . Typically, the position of a hole located nearest the outer edge of the flange, or perpendicular to the outer edge, as well as areas offset 90 degrees, 180 degrees, and 270 degrees therefrom, contain the highest stresses (See A, B, C, and D, respectively,  FIG. 2A ). Creating a repair where the weld seams fall between these areas (at approximately 45 degrees, 135 degrees, 225 degrees, and 315 degrees) moves the welds out of high stress zones surrounding the hole  12  (See E, F, G, and H, of  FIG. 2A ). Moving the weld out of the high stress zones surrounding the hole  12  is similar to what occurs when large holes are repaired as described above. This assures good fatigue life for the repaired part. 
       FIG. 5  is a plan view illustrating portion  18  of flange  14  removed, which reveals lower flange  20 . With portion  18  removed, only a small arc  22  of the hole  12  is left. The remaining arc  22  acts as a guide and locator for finishing the repair to assure that the repaired hole is nominally placed in the same position on flange  14  as the original hole  12 . Lower flange  20  is a parallel structure to flange  14 , and a slot  15  exists between the two flanges  14  and  20 , which run circumferentially around the base of the forward inner nozzle support (See  FIGS. 2 and 2A ). 
       FIG. 6  is a plan view illustrating a combination plate  24  (i.e., combination runoff and top plate) attached to flange  14 . Combination plate  24  is attached to flange  14  by placing tack welds  26 ,  28  where the edges of combination plate  24  meet the outer edge of flange  14 . Tack welds  26 ,  28  hold combination plate  24  temporarily in place. Also, tack welds can be easily removed later, without damaging flange  14 , to remove combination plate  24 . Combination plate  24  may be fabricated from the same material as the base material of flange  14 , or a material that has consistent metallurgical properties. In embodiments, combination plate  24  has a central portion removed that reveals lower flange  20 , and covers arc  22 . In alternate embodiments (not illustrated), combination plate  24  does not cover arc  22 . 
       FIG. 7  is a plan view illustrating insert  34  attached to the combination plate  24  via tack welds  30 ,  32 , which hold the insert  34  in place until the final welding process occurs. Insert  34  is a plug of material that is preferably the same material as, or contains the same metallurgical properties as, that of the base material of flange  14 . Insert  34  is sized to be positioned against the edge of portion  18  of flange  14  previously removed (see  FIG. 4 ), as well as mate with the profile of the aperture in combination plate  24 . In the embodiment illustrated, insert  34  is circular. Although illustrated as circular, insert  34  may be elliptical, biscuit shaped, or have an arced portion that matches the profile of the removed material  18  of flange  14 . When the weld is complete, tack welds  30 ,  32  will be incorporated into the final repair weld. 
     In embodiments, combination plate  24  is larger than the diameter of the hole  12  being repaired. In embodiments, combination plate  24  has a length (measurements of the sides generally parallel to the outer edge of flange  14 ) of at least two times the diameter of the original hole  12  ( FIG. 2 ), and has a width (measurements of the sides generally perpendicular to the outer edge of flange  14 ) of at least two times the diameter of hole  12 . The aforementioned dimensions of combination plate  24  assure good support for insert  34 , and allow for locating tack welds  26 ,  28  an adequate distance from the repair weld(s) around insert  34 . 
       FIG. 8  is a plan view illustrating backing plate  36  placed below combination plate  24  and insert  34 . Backing plate  36  may be fabricated from a similar metal that is used to construct combination plate  24  and insert  34 . In alternate embodiments, backing plate  36  is constructed from a different metal, or a heat resistant material such as ceramic. In  FIG. 8 , backing plate  36  is illustrated as containing larger dimensions than combination plate  24 , but backing plate  36  may be smaller in size than combination plate  24  so long as the backing plate  36  covers the area underneath where the repair weld is to be made. When backing plate  36  is larger than combination plate  24 , backing plate  36  protects adjacent areas from weld run off or spatter, as well as protects lower flange  20  from penetration of the electron beam or similar welding source. 
       FIG. 9  is a cross-sectional elevation view of the bolt hole repair apparatus for refabrication of flange  14  illustrated in  FIG. 8 . In this view, the remaining portion of the base material of flange  14  is visible. Also illustrated are insert  34 , combination plate  24 , and backing plate  36 . Insert  34  is a thickness that is approximately equivalent to the thickness of the rear edge  38  of combination plate  24 , which is also approximately equivalent to the thickness of the front end  40  of combination plate  24  added to thickness of the remnant of hole  12  left on flange  14 . Small clearance gaps  42 ,  44  exist between insert  34  and plate  24 . The clearance allows for the easy insertion of insert  34  into the aperture contained in combination plate  24 . Clearance gaps  42 ,  44  will cease to exist as the material from insert  34  and combination plate  24  fuse together during the repair weld. 
     Front end  40  of combination plate  24  is contoured to mate with remaining surface  46  of flange  14  and hole  12 . Although flange  14  is illustrated in this view as containing a radius, other geometries of the contour are envisioned including bevels, chamfers, rabbets, dados, or stepped notches, the geometry of the contour depending on the geometry of the base material left on flange  14 . Insert  34  and combination plate  24  contain more material than the thickness of the material removed from flange  14  so that insert  34  can be machined to the appropriate size after the weld repair has been completed. 
     The part illustrated in  FIG. 9  is a section of nozzle support  10  of  FIG. 2 . Nozzle support  10  contains two flanges, flange  14  which is to be repaired, and a lower flange  20 . Lower flange  20  and flange  14  are spaced close together, and a typical spacing is less than about 0.25 inches. Backing plate  36  is placed between flange  14  and lower flange  20 , and protects the lower flange  20  from any slag, spatter, or similar byproduct resulting from the welding process. 
     In a typical prior art welding repair utilizing a backing plate, the weld must penetrate through the repair portions to assure a good weld. In such repairs, the backing plate is placed directly behind the weld to adsorb the residual energy from the weld, which allows the backing plate to fuse to the repair. Then, after the repair, the backing plate must be removed. The relatively small distance between flange  14  and lower flange  20  makes such a removal difficult. 
     Thus, in this invention, an air gap  48  is left between the top surface of backing plate  36  and the bottom surfaces of insert  34 , combination plate  24 , and the remaining portion of flange  14 . In embodiments, air gap  48  is about 0.10 inches or less, which assures that the excess energy from the weld beam is adsorbed, but is far enough from the bottom edge of the repair pieces (insert  34 , combination plate  24 , and flange  14 ) to assure that backing plate  36  does not become fused to the repair pieces. Utilizing combination plate  24  to provide a good weld, while separating the repair pieces from the backing plate  36  via air gap  48 , assures that a good, structurally sound weld repair can be obtained. Backing plate  36  should be large enough to cover the clearance gaps  42 ,  44  between the combination plate  24  and the edges of the insert all the way around the edge of insert  34 . The thickness of backing plate  36  is less than the distance between flange  14  and lower flange  20  so that air gap  48  exists as shown. 
       FIG. 10  is a plan view illustrating a completed weld  50  between insert  34  and combination plate  24 . Insert  34  is welded into place by a process such as electronic beam welding. Electronic beam welding (EBW) uses a narrow beam of high velocity, high energy electrons to generate the heat necessary to create a weld in a metal work piece. Special equipment is used to focus the electron beam in a vacuum chamber, and the kinetic energy of the electrons is converted to heat energy as it strikes the metal. The welds created by EBW are characteristically deep and narrow with a very small heat affected zone and low distortion. The current repair moves the weld seams out of the high stress areas surrounding the hole  12 . The weld seams are left in the low stress areas of the flange  14 . 
     EBW is typically autogenous, that is, does not require a filler material. Thus, a tight fit of insert  34  with the remaining base material and combination plate  24  will occur as the pieces fuse together during the welding process without the addition of a filler material. Weld  50  is a butt weld joining insert  34 , base material of flange  14 , and combination plate  24  together. While weld  50  is done from the top of insert  34 , the weld extends around the entire perimeter of insert  34  and throughout the entire thickness of insert  34 . 
     EBW can leave depressions in the parts welded. Thus, ensuring that insert  34  and combination plate  24  are thicker than the original thickness of flange  14  allows for the melting and fusing of material from the respective top sides of insert  34  and combination plate  24  to flow down and fill in the weld against the base material of flange  14 . Thus, when material is removed to finish the repair, none of the base material that has been left will be machined, only the newly welded materials will be removed. 
     EBW is considered a high energy density welding process and is used extensively in the aerospace industry to join difficult to weld alloys where high quality, low distortion welds are required, such as in the instant case. Those of skill in the art are familiar with the process of electron beam welding, and can perform this repair with an electron beam with a voltage above about 100 kV and a current above about 25 mA. Higher voltage and/or currents are utilized to prevent fusion defects caused when the weld only partially penetrates through the thickness of the repaired part, which can result in reducing the cyclical fatigue life of the joint in the repaired part. The above parameters, as well as other common parameters including travel speed, oscillation, frequency, and focus, can be modified according to principles known to those of skill in the art. 
     By utilizing a combination run off and top plate (i.e., combination plate  24 ) in the current repair process, the need for three separate plates utilized by the prior art are eliminated. Common problems associated with the assembly of the three plates are also eliminated. Combination plate  24  and insert  34  can be constructed by fabricating insert  34  out of plate  24  from a single piece of material. That is, a blank is formed which will mate with the outer surfaced of flange  14 . From this blank, a central portion is removed that becomes the insert  34 , and the remainder will become combination plate  24 . Similarly, combination plate  24  and insert  34  are quicker to assemble, and can be pre-assembled together. This saves time in repairing hole  12 . 
       FIG. 11  is a plan view illustrating completed weld  50  with backing plate  36  removed. Since backing plate  36  does not become fused to the repair pieces (insert  34 , combination plate  24 , and flange  14 ), after weld  50  has been completed, backing plate  36  may simply be pulled out from the repaired part. There is no need to use material removal equipment, such as grinders or similar machines to remove backing plate  36 . Backing plate  36  may be reused as there will be minimal damage to the top surface as it will not contain removal scars associated with plates that become fused during the welding process. 
       FIG. 12  is a plan view illustrating completed weld  50  with portions of combination plate  24  and insert  34  removed. Combination plate  24  and insert  34  are cut along a path that substantially follows the outer profile of flange  14 . A mill, laser, or similar material removal machine is used to cut combination plate  24  and insert  34 . A nominal amount of material of combination plate  24  and insert  34  may remain after an initial cut to ensure that the cutting process does not affect the integrity of the original flange profile. 
       FIG. 13  is a plan view illustrating combination plate  24  removed to produce the original profile of flange  14 . To remove combination plate  24 , first tack welds  26 ,  28  are detached from flange  14 . Next, a mechanized process such as machining is utilized to remove combination plate  24  and excess material from insert  34  until the original profile of the top surface of flange  14  is obtained. After combination plate  24  is removed, arc  22  of the original aperture in flange  14  is again visible. Weld  50  will also be machined on the top and bottom surfaces to obtain nominally the same surfaces of flange  14  as those prior to the repair. Finally, the outer edge of flange  24  is machined to obtain substantially the same profile and outer diameter as the profile prior to the repair. 
       FIG. 14  is a plan view illustrating the complete repair with a new hole  52  in flange  14 . After the flange profile has been nominally obtained, an aperture is machined in the flange to create nominally the same hole  12  that existed prior to the repair. Arc  22  is used as a guide to machine hole  52  to assure the location is nominally the same as prior to the repair. In an alternate embodiment, the hole in lower flange  20  (See  FIGS. 2A and 9 ) is used as a guide to create hole  52  in flange  14 . 
     To repair small holes of the forward inner nozzle support, a part is first removed and received for inspection. The part is cleaned to assure all facets can be inspected. Various repairs are done, including the electron beam welding of inserts for the cracked pinholes as described above. 
     After the part has been welded, the part is then machined to assure the flange is within tolerances. The machining process (or other material removal process) removes excess material from the completed weld and creates a new hole  12  and restores the outer perimeter of flange  14 . It is the material from insert  34  that is used to create the repaired flange  14 . Combination plate  24  is removed by cutting and extracting the tack welds holding combination plate  24 . The portion of plate  24  not needed to create a smooth outer profile for flange  24  is removed. Finally, the remaining material from insert  34  is machined down to create a new, refurbished flange  14 , and hole  12  is refabricated. 
     After material removal is complete, a further inspection is done. Known nondestructive inspection (NDI) techniques, such as visual inspection, flourescent penetrant inspection (FPI), eddy current inspection, ultrasonic inspection and x ray inspection, etc. can be used. The inspection assures the part is back to near identical dimensions that the part had prior to the repair. It is important that the minimum edge distance from the flange outer diameter to the aperture is maintained after the repair as the fatigue life of the part will be greatly reduced if the dimensions are varied from the original specifications. Upon passing a final inspection, the part may be replaced within the turbine. 
     On a part that contains holes next to a flange, such as the forward inner nozzle support illustrated in  FIG. 2 , defects often appear after extended use. Typically, the defect is a crack that initiates from one of the apertures in the flange and propagates towards the outer diameter of the flange. The crack is likely created by a thermal cycle hoop stress and the load on the pin through the flange on the attached vane. The stress around the hole is highest adjacent the outer diameter of the flange. Utilizing an insert (i.e., a biscuit or generally circular shape or other suitable shape) to create the repair results in a weld that is similar to that achieved with the known wedge repair for larger holes. The resultant weld is approximately at 45° on either side of the radial centerline of the hole. This moves the weld out of the highest stress areas surrounding the hole to the lower stress areas of the base material, which results in improved fatigue life for the repaired hole. At the same time, the weld is accomplished with a continuous movement of the part in an arced path under the electron beam rather than requiring separate line welds such as associated with the prior art wedge repair processes. With such a small area in the current repair, an abrupt change in the weld path would result in an uneven weld where the weld beam must pause to change direction. 
     The current repair will not degrade the fatigue life of the part, and thus the life of the part is renewed with the section replacement of the defect near the aperture. The fatigue life of the repaired part is substantially restored to that of the original part. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.