Abstract:
A method for replacing a blade ( 12 ) of a rotor ( 2 ) having integral blades, wherein a new blade ( 22 ) is joined to a base ( 34 ) arranged on a separation surface ( 28 ) on the main rotor body, and to a rotor repaired or mended according to said method.

Description:
[0001]    The present invention relates to a method for replacing a blade of an integrally bladed rotor, and to a rotor having a blade replaced in this manner. 
       BACKGROUND 
       [0002]    Integrally bladed rotors have either a disk-shaped or a ring-shaped main body having blades integrally provided on the outer periphery thereof. A rotor having a disk-shaped main body is called “blink” (bladed disk), and a rotor having a ring-shaped main body is called “bling” (bladed ring). 
         [0003]    Methods for manufacturing integrally bladed rotors are described in Patent Application WO 2005/024185 of the Applicant. In one method, the rotors and their blades are milled from a solid piece of material. In another manufacturing method, the blades are manufactured separately from the main body of the rotor and subsequently attached to the rotor main body using a joining method. Examples of joining methods include linear friction welding, inductive pressure welding or diffusion welding. In the case of the latter manufacturing method, the blading is constituted by forged parts which are already adapted to the desired blade shape in such a manner that after attachment to the rotor main body, only fine machining needs to be performed. However, the blading may also be constituted by a plurality of blade blanks, which are severed from a pressed shape and machined to their desired shape only after they are attached to the rotor main body. 
         [0004]    International Patent Application WO 2008/046388 of the Applicant describes a method for manufacturing an integrally bladed rotor, in which at least portions of the rotor are manufactured using a generative method. WO 2008/046388 proposes, in particular, that the blading, or the entire rotor including the blading, be manufactured generatively. 
         [0005]    However, since the blades are integrally provided on the rotor main body, replacement of an old blade, such as a damaged blade or one that has reached its maximum life, requires a relatively large amount of effort compared to conventionally manufactured rotors, where the blades are inserted into the main rotor body. 
         [0006]    A known method for replacing a damaged blade of an integrally bladed rotor is disclosed in German Patent Application DE 10 2005 033 625 A1 of the Applicant. In this method, the damaged blade is cut off and replaced by a new one that is manufactured using a powder-metallurgical injection molding method. However, German Patent Application DE 10 2005 033 625 A1 does not provide information on whether the new blade is mounted directly on the outer periphery of the rotor main body or whether it is joined to a blade stub left on the rotor main body by the damaged blade that has been cut off. 
         [0007]    German Patent Application DE 39 09 733 A1 proposes a method for replacing a blade, in which the new blade is welded to a stub on the rotor main body. The damaged blade is cut off at a defined distance from the rotor main body, leaving a stub whose radial surface provides a blade connection surface for the new blade. In order to stabilize the stub during the joining of the new blade, the stub is stabilized at its circumference by a multi-part metallic collar which forms a metallurgical bond with the stub and the new blade. The height of the collar corresponds to the radial length of the stub, so that the stub and the collar provide the blade connection surface for the new blade. After the joining process, surplus material of, for example, the collar is removed and the stub-new blade connection is machined to its desired final size. 
         [0008]    European Patent EP 1 535 692 B1 also describes a method for replacing a blade, in which a blade stub left on the rotor main body by a damaged blade that has been cut off is stabilized during the joining of the new blade. A framing is created around the stub, into which a metal powder is filled. The new blade is attached by friction welding to a radial blade connection surface of the stub, during which process the metal powder forms a stabilizing coating for the stub. After the joining of the new blade, the stub-new blade connection is machined to its desired final size. 
         [0009]    However, from European Patent EP 0 376 874 131 it is also known that instead of stabilizing the stub on the rotor main body, the new blade can be provided with a collar in the region of its joining surface to allow for uniform heating and prevent deformation during the joining process. The separation of the damaged blade can be accomplished using the electrical discharge machining (EDM) method. After the joining of the new blade, the collar and surplus material are removed and the stub-new blade connection is machined to its desired final size. 
         [0010]    U.S. Pat. No. 6,095,402 presents a method for manufacturing or repairing an integrally bladed rotor, in which a new blade is also mounted on a blade stub left on the rotor main body by a damaged blade that has been cut off The subject-matter of this U.S. patent is directed to the particular geometric configuration of the blade connection surface of the stub, so that the new blade can be joined by linear friction welding even if the blade connection surface is not plane. 
         [0011]    The aforementioned known methods have in common that the radial blade connection surface of the stub is formed during the separation of the damaged blade. A separation surface formed during the separation of the damaged blade serves as a blade connection surface for a new blade. In order to prepare the joining process, the separation surface is merely suitably cleaned. This has the disadvantage that the damaged blade must be cut off at a defined distance from the outer periphery of the rotor main body and, in addition, that the cutting must be performed very accurately to allow for precise joining of the new blade. This requires the use of technically complex cutting methods. Another disadvantage is that either the stub must be stabilized in a complex manner during the joining process, or the new blade must have special design features because the finished shape of the stub is unable to withstand the loads occurring during the joining process. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide a method for replacing a blade of an integrally bladed rotor which method overcomes the aforementioned disadvantages and allows for simple and precise joining of a new blade, and to provide a rotor having a blade replaced in this manner. 
         [0013]    The present invention provides a method for replacing a blade of an integrally bladed rotor. 
         [0014]    In a first step, the old blade is cut off from the rotor main body. In the process, a separation surface is formed on the rotor main body, on which a base is formed in a subsequent step according to the present invention. Once the base has reached its desired radial length or height, the blade connection surface for a new blade is formed on its radial surface facing away from the rotor main body. Then, the new blade is joined to the blade connection surface. 
         [0015]    It is an advantage of the method of the present invention that, unlike in prior art methods, where the blade connection surface is identical to the separation surface formed on the rotor main body during the separation of the old blade, a new blade connection surface is formed. Therefore, the old blade can be removed from the rotor main body using technically simple cutting methods. It is also advantageous that the old blade can be cut off not too close to the outer periphery of the rotor main body, because the new blade is not joined directly to the remaining stub, but instead a base is formed whose radial length is freely selectable. Furthermore, the base does not need to be stabilized in a complex manner during the joining process, because its shape can be flexibly selected during its creation or formation. The shape of the base can be prepared such that the joining and final machining of the new blade corresponds to the mounting of a blade during new part manufacture. 
         [0016]    In one exemplary embodiment, the old blade is cut off from the rotor main body in such a way that the separation surface is formed on a stub on the rotor main body. 
         [0017]    In another exemplary embodiment, the old blade is removed from the rotor main body in such a way that the separation surface is flush with the outer periphery of the rotor main body. 
         [0018]    The base may be provided with oversized dimensions in both the circumferential and axial directions. 
         [0019]    Final machining to the desired size may be performed according to the oversize of the base, the joint itself, and the shape of the new blade. 
         [0020]    In one exemplary embodiment, the base is formed using a generative manufacturing method, such as laser deposition welding. 
         [0021]    In one exemplary embodiment, the joining of the new blade to the blade connection surface is accomplished using a welding method. Examples of such methods include electron beam welding, linear friction welding, inductive high-frequency pressure welding and diffusion welding. 
         [0022]    An integrally bladed rotor according to the present invention includes a rotor main body on which are mounted a plurality of blades, where at least one old blade has been replaced by a new blade. According to the present invention, the new blade is mounted on a blade connection surface of a base which is formed on a separation surface left on the rotor main body by the old blade that has been cut off. 
         [0023]    Other advantageous exemplary embodiments are the subject matter of further dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    A preferred exemplary embodiment of the present invention is described below in more detail with reference to highly simplified schematic drawings, in which: 
           [0025]      FIG. 1  is a cross-sectional view through an integrally bladed rotor being newly manufactured, the cross-sectional view showing the region of an attached blade; 
           [0026]      FIG. 2  is a view showing the cross section of  FIG. 1  after the final machining of the joint; 
           [0027]      FIG. 3  is a cross-sectional view through an integrally bladed rotor, showing the region of a removed old blade; 
           [0028]      FIG. 4  is a view showing the cross section of  FIG. 3  prior to joining a new blade; 
           [0029]      FIG. 5  is a view showing the cross section of  FIG. 4  after the joining of a new blade; and 
           [0030]      FIG. 6  is a view showing the cross section of  FIG. 5  after the final machining of the joint. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  shows, in simplified form, the new manufacture of an integrally bladed rotor  2  of a gas turbine, in particular of an aircraft engine. Rotor  2  has a disk-shaped main body  4  having a plurality of radial projections  6 ,  8 ,  10  to each of which a blade  12  of the integral blading is or will be directly joined. For the sake of clarity, only central projection  8  and blade  12  shown in  FIG. 1  will be discussed below as an example for all projections  6 ,  8 ,  10  and all blades  12 . 
         [0032]    Projection  8  has a radial blade connection surface  14  and is provided with oversized dimensions, as indicated by a broken line in  FIG. 2 . 
         [0033]    Blade  12  has a root portion  16  and a tip portion  18  which is remote from root portion  16  and is here provided with a shroud. Root portion  16  has a joining surface  20  facing rotor main body  4  and is provided with oversized dimensions which correspond to those of radial projection  8  and are indicated by a broken line in  FIG. 2 . Joining surface  20  is complementary to blade connection surface  14  of radial projection  8 . 
         [0034]    When joining blade  12  to rotor main body  4 , it is placed with its joining surface  20  on blade connection surface  14  of projection  8  and metallurgically bonded to projection  8  using a suitable method. Examples of suitable joining methods include electron beam welding (electric beam welding, EB welding), linear friction welding, inductive high-frequency pressure welding (IHFP) and diffusion welding. 
         [0035]    Referring to  FIG. 2 , after the joining process, projection  8  and root portion  16  of blade  12  are machined to their desired final dimensions. In the process, the oversized portions (indicated by broken lines) of projection  8  and of root portion  16 , as well as material accumulations formed during joining, are removed. Examples of methods for final machining include electrochemical machining (ECM) and milling. 
         [0036]    If blade  12  is damaged during operation, or when blade  12  has reached its maximum life, it must be replaced by a new blade  22 , which is shown in  FIG. 5 . The replacement of exiting or old blade  12  by new blade  22  in accordance with the present invention will be described in the following  FIGS. 3 through 6 . 
         [0037]      FIG. 3  shows a cross-sectional view through an integrally bladed rotor  2 . There is shown a rotor main body  4  having two undamaged blades  24 ,  26  between which was located an old blade  12 , which is shown in  FIG. 2 . The joining of blades  24 ,  26  and of old blade  12  (not shown in  FIG. 3 ) was carried out during new part manufacture as illustrated in preceding  FIGS. 1 and 2 . 
         [0038]    At the beginning of the replacement of old blade  12 , a parting plane  28  is defined in which old blade  12  is to be cut off from rotor main body  4 . In the exemplary embodiment shown in  FIG. 3 , parting plane  28  is selected such that a stub  30  of radial projection  8  (shown in  FIG. 1 ), on which old blade  12  was mounted, remains on the rotor main body. Old blade  12  was removed from rotor main body  4 , for example, by electrical discharge machining (EDM). 
         [0039]    Stub  30  has a separation surface  32  which is located in parting plane  28  and on which a radial base  34  is formed, as shown in  FIG. 4 , to receive new blade  22 . Stub  30  is smaller than original projection  6 . However, its height or radial length can be selected as desired. In order to improve the bond of base  34  to separation surface  32 , the separation surface is suitably cleaned prior to forming base  34 . The formation of base  34  is accomplished using a generative manufacturing method, such as laser-beam or laser deposition welding. During the formation process, base  34  forms a metallurgical bond with rotor main body  4 . 
         [0040]    Consequently, base  34  extends beyond parting plane  28  and provides a radial blade connection surface  14  for attachment of new blade  22 . The radial length or height h so  of the base is a function of the radial length or height h st  of stub  30  and of the shape of a root portion  16  (shown in  FIG. 5 ) of new blade  22 , since the sum of the heights h so  and h st  is equal to the radial distance a of blade connection surface  14  from outer periphery  36  of rotor main body  4 . Base  34  is formed with oversized dimensions, as indicated by a broken line in  FIG. 6 . These may extend in both the circumferential and axial directions of rotor main body  4 . If root portion  16  of new blade  22  has the same shape as old blade  12  during new part manufacture, the shape of base  34  including stub  30  and the oversized portions, and, in particular, distance a of blade connection surface  14  from outer periphery  36  of rotor main body  4 , correspond to radial projection  8  (shown in  FIG. 1 ) and its radial length  1 , as measured from the outer periphery  36  of rotor main body  4 . 
         [0041]    Referring to MG.  5 , once blade connection surface  14  is formed, new blade  22  is positioned with its root portion  16 ; i.e., its joining surface  20 , which is complementary to blade connection surface  14 , on base  34 ; i.e., on blade connection surface  14 , and is joined to rotor main body  4 . The joining is preferably accomplished using one of the direct joining methods mentioned in  FIG. 1 . 
         [0042]    Referring to  FIG. 6 , after new blade  22  is joined, base  34  and root portion  16  of new blade  22 , as well as the joint, are machined to final shape; i.e., the oversized portions indicated by broken lines and other material accumulations formed during joining are removed, just as in new part manufacture as shown in  FIG. 2 . 
         [0043]    Thus, after final machining of the joint, an integrally bladed rotor  2  is created that has a new blade  22  configured on a blade connection surface  14  of a base  34  which is formed on a separation surface  32  left on the rotor main body by a previously removed old blade  12  and which corresponds to a radial projection  8  of rotor main body  4 , to which projection old blade  12  was attached during new part manufacture when it was new. 
         [0044]    It should be noted that parting plane  28  may also be selected such that no stub  34  remains on rotor main body  4 , but that, instead, separation surface  32  merges into outer periphery  36  of rotor main body  4  in flush relationship therewith and base  34  is formed directly on outer periphery  36 . 
         [0045]    It should also be noted that the method of the present invention is not limited to disk-shaped rotors  2  having integral blading, but encompasses also ring-shaped rotors having integral blading as well as rotors for compressors. 
         [0046]    Furthermore, it should be noted that, in accordance with the present invention, the term “new blade” may also refer to an old blade that has been overhauled or repaired. 
         [0047]    Moreover, it is also conceivable to cut off all old blades  12  from rotor main body  4  when rotor main body  4  has reached its maximum life, to machine their joining surfaces  20  for use on a new rotor main body, and to attach the so-prepared old blades  12  to the new rotor main body. 
         [0048]    Rotor main body  4  may be milled from a solid piece of material or be manufactured, for example, using a generative manufacturing method. Similarly, the blades may also be manufactured generatively or be, for example, forged parts, milled parts or pressed shapes. 
         [0049]    Furthermore, it is conceivable for base  34  to be formed using a generative manufacturing method other than laser deposition welding. 
         [0050]    Disclosed are a method for replacing a blade of an integrally bladed rotor, in which a new blade is joined to a base formed on a separation surface on the rotor main body, and a rotor repaired or overhauled using this method.