Abstract:
A method of forming a component using electro-chemical machining includes the steps of providing a shield in a current distribution path between a workpiece and an electrode, with the shield concentrating current distribution upon an end of the workpiece.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/895,035, filed Oct. 24, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application relates to a method of using a non-contact machining method, such as electro-chemical machining (ECM) or electrolytic machining to form airfoil leading and trailing edges. 
         [0003]    Airfoils are utilized in any number of applications. As an example, a gas turbine engine commonly has airfoils associated with a number of rotating blades and a number of static vanes. A number of methods of manufacture are utilized to form the airfoils. 
         [0004]    Typically, an airfoil could be said to have a pressure side, a suction side, a leading edge and a trailing edge. Optimal edge shapes often include complex curves, such as spline, parabolas or ellipses. 
         [0005]    One popular method of manufacturing airfoils is electro-chemical machining (ECM). 
         [0006]    In a common ECM system, a conductive workpiece is machined to form the airfoil. A voltage is connected to the workpiece and to an electrode (cathode). The workpiece is in a chamber with an electrolytic fluid. Precision ECM systems use complex cathode shapes that are place in close proximity to the workpiece to create complex geometry. This technique is expensive and results in long lead time tooling. 
         [0007]    Metal is removed from the workpiece and complex shapes may be formed. However, as mentioned above, the leading and trailing edges, and in particular, very small sized edges, challenge traditional precision ECM methods. These methods have not been as effective in forming the desired edges. 
       SUMMARY OF THE INVENTION 
       [0008]    In a featured embodiment, a method of forming a component using electro-chemical machining includes the steps of providing a shield in a current distribution path between a workpiece and an electrode, with the shield concentrating current distribution upon an end of the workpiece. 
         [0009]    In another embodiment according to the previous embodiment, the workpiece is to form an airfoil, and the shield concentrating current distribution upon the end of the workpiece is to form at least one of a leading edge and a trailing edge of the airfoil. 
         [0010]    In another embodiment according to any of the previous embodiments, the shield is utilized to concentrate the current distribution on both the leading edge and the trailing edge. 
         [0011]    In another embodiment according to any of the previous embodiments, the shield includes two parallel shields that are spaced on sides of the workpiece. 
         [0012]    In another embodiment according to any of the previous embodiments, ends of the parallel shields deflect current at the one end of the workpiece. 
         [0013]    In another embodiment according to any of the previous embodiments, the shield sits between the end of the workpiece and the electrode and includes an aperture for concentrating the current distribution on the one end of the workpiece. 
         [0014]    In another embodiment according to any of the previous embodiments, the shield is formed of non-conductive material. 
         [0015]    In another embodiment according to any of the previous embodiments, the shield is formed of a plastic. 
         [0016]    In another embodiment according to any of the previous embodiments, electro-chemical machining is also utilized to form the workpiece to an intermediate shape prior to using the shield to form the one of the leading and trailing edges. 
         [0017]    In another embodiment according to any of the previous embodiments, the shield comprises a pair of parallel spaced shields on sides of the workpiece. 
         [0018]    In another embodiment according to any of the previous embodiments, ends of the parallel shields deflect current at the one end of the workpiece. 
         [0019]    In another embodiment according to any of the previous embodiments, the shields are formed of non-conductive material. 
         [0020]    In another embodiment according to any of the previous embodiments, the shields are formed of a plastic. 
         [0021]    In another embodiment according to any of the previous embodiments, the shields are formed of non-conductive material. 
         [0022]    In another embodiment according to any of the previous embodiments, the shields are formed of a plastic. 
         [0023]    In another embodiment according to any of the previous embodiments, the shield sits between the end of the workpiece. The electrode and the shield include an aperture for concentrating the current distribution on the one end of the workpiece. 
         [0024]    In another embodiment according to any of the previous embodiments, the shield is formed of non-conductive material. 
         [0025]    In another embodiment according to any of the previous embodiments, the shield is formed of a plastic. 
         [0026]    In another embodiment according to any of the previous embodiments, the shield is formed of non-conductive material. 
         [0027]    In another embodiment according to any of the previous embodiments, the shield is formed of a plastic. 
         [0028]    In another embodiment according to any of the previous embodiments, 
         [0029]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  schematically shows an airfoil. 
           [0031]      FIG. 2A  shows a first method step. 
           [0032]      FIG. 2B  shows a subsequent method step. 
           [0033]      FIG. 3  shows an alternative method. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    As shown, an airfoil  20 , which may be part of a blade, vane or other item within a gas turbine engine, has a curved shape along a central area  22  and extending between a trailing edge  24  and a leading edge  26 . 
         [0035]    More generally, components may include blades, vanes, tangential outboard injectors, integrally bladed rotors, and impellers. In fact, teachings of this application may even extend to components that do not include an airfoil, but which do require some complex shaping. As can be appreciated from  FIG. 1 , the trailing edge  24  and the leading edge  26  are curved. 
         [0036]      FIG. 2A  shows an electro-chemical machining process  126  schematically. As known, an electrolytic fluid  125  fills a chamber. This fluid may be driven through the chamber with forced or passive current streams. A preform or workpiece  120 , which is to form the airfoil  20 , is placed within the chamber. The workpiece  120  is formed of a conductive material, such as an appropriate metal. An end  122  is to form the leading edge while an end  124  is to form the trailing edge. An electrode  130  functions as a cathode. A voltage source  128  applies a charge between cathode  130  and the workpiece  120 , which functions as an anode. As known, material may be removed from the workpiece  120  by this process. 
         [0037]    Once a general or intermediate shape of the final airfoil is achieved by the method of  FIG. 2A , then a finish step, as shown in  FIG. 2B , is performed. On the other hand, the initial work, as shown in  FIG. 2A , to bring the workpiece  120  to the intermediate shape may be done by other processes beyond electro-chemical machining. 
         [0038]    As shown in  FIG. 2B , in the finish process, shields  132  and  134  are placed on each side of the workpiece  120 . The end  122 , which is to form the leading edge  26 , is spaced between the shields  132  and  134 . A current, which passes between the cathode  130  and the workpiece  120 , is deflected around ends  136  and  138  of the shields  132  and  123  and, thus, concentrated at the end  122  of the workpiece  120 . In this manner, a curve leading edge  26 , such as shown in  FIG. 1 , is formed. 
         [0039]    While the method is shown as two separate steps, in practice, automation techniques may be utilized to have the two happen serially, without any significant down time between the two steps. 
         [0040]    A worker of ordinary skill in this art would recognize that by controlling a distance W between the workpiece  120  and the shields  132  and  134  and a distance d between the end  122  and the cathode  130 , the extent and shape of the leading edge to be formed can be controlled. 
         [0041]      FIG. 3  shows an alternative shield  140 , which is not placed parallel to a second shield. Rather, it sits between the end of workpiece  120  and the electrode  130 . Shield  140  has a slot or aperture  142  aligned with the end  122  of the workpiece  120 , which is to form the leading edge. With this embodiment, the current will again be concentrated at the end  122  to form a leading edge  26 . 
         [0042]    Generically, the two embodiments could both be said to include the provision of a shield in a current distribution path to concentrate the current distribution on an end of a workpiece. 
         [0043]    The trailing edge is formed in a similar manner. 
         [0044]    The shields  132 ,  134  and  140  are all formed of an appropriate material which is generally non-conductive. As an example, an insulator, such as a plastic, may be utilized. 
         [0045]    In the  FIG. 2B  embodiment, the shields  132  and  134  may be parallel. 
         [0046]    Although an 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.