Abstract:
A method of forming a blade comprising the steps of forging a part comprising a suction side, a pressure side, and a dividing portion of material greater than a portion of material to be sacrificed between the suction side and the pressure side, splitting the part through the dividing portion of material to form a suction side inner surface and a pressure side inner surface, and joining the suction side inner surface and the pressure side inner surface to form the blade.

Description:
U.S. GOVERNMENT RIGHTS 
   The invention was made with U.S. Government support under contract F33657-98-C-2004 awarded by the U.S. Government. The U.S. Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present invention relates to a method for forging articles requiring a single forging such as hollow fan blades for gas turbine engines. 
   (2) Description of the Related Art 
   It is current practice to fabricate hollow fan blades, typically fabricated from titanium, for use in gas turbine engines. It is preferable that such fan blades be hollow. By fabricating hollow fan blades, the mass of the fan blades may be substantially reduced resulting in notable efficiencies. Typically the hollow fan blade halves are forged separately, one half corresponding to the pressure side with the other corresponding to the suction side. Once forged, each half is substantially machined to create the airfoil contour, the airfoil root block, datum features such as holes, hollow cavities, and diffusion bond surfaces. As noted this is done for both the pressure side and the suction side from each oversize “pancake” forging. The suction side and the pressure side are then subsequently diffusion bonded together to make a single hollow fan blade. 
   The use of diffusion bonding in turbine blade formation is well known. An example may be found in U.S. Pat. No. 5,711,068, the disclosures of which is incorporated by reference herein as if set forth at length. The &#39;068 patent discloses a specific situation in which two blade halves are cut from a single piece and are diffusion bonded with uncut surfaces facing each other. 
   Such a process requires extensive machining time to achieve both the airfoil contour and the root block. In addition, a significant amount of scrap titanium is generated. What is therefore needed is a method for forging hollow fan blades, particularly titanium fan blades, which requires less machining and results in a reduction in the amount of scrap titanium generated. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a method for forging articles requiring a single forging. 
   In accordance with the present invention, a method of forming a blade comprises the steps of forging a part comprising a suction side, a pressure side, and a dividing portion of material greater than a portion of material to be sacrificed between the suction side and the pressure side, splitting the part through the dividing portion of material to form a suction side inner surface and a pressure side inner surface, and joining the suction side inner surface and the pressure side inner surface to form the blade. 
   In further accordance with the present invention, a forged part comprises a suction side, a pressure side, and a dividing portion of material between the suction side and the pressure side the dividing portion of a width greater than or equal to a separation destruction width. 
   In further accordance with the present invention, a method for forming a part comprises the steps of providing a mold, forging a part in the mold the part having a suction side, a pressure side, and a dividing portion of material between the suction side and the pressure side the dividing portion of a width greater than or equal to a separation destruction width. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  An illustration of the part of the present invention post forging and both pre and post separation. 
       FIG. 2  An illustration of the part of the present invention and the cutting apparatus. 
       FIG. 3  An illustration of the cavities fabricated in the inner surfaces of the present invention. 
       FIG. 4  An illustration of the part of the present invention showing a non-planar dividing portion. 
       FIG. 5  An illustration of the six point trap of the present invention. 
       FIG. 6  An illustration of the mold of the present invention. 
   

   DETAILED DESCRIPTION 
   It is therefore a teaching of the present invention to provide a method for forging articles such as hollow fan blades, particularly titanium fan blades, requiring a minimum of post forging machining therefore significantly reducing the amount of scrap titanium generated. This is accomplished by forging a single part comprised of a pressure side and a suction side separated by a dividing portion of material. The dividing portion of material is only slightly larger than that which is needed to permit the suction side and the pressure side to be separated by a cutting operation. Once cut and separated, the suction side and the pressure side may be machined, particularly to include hollow cavities, then attached to one another through a process of diffusion bonding to produce a hollow part. 
   With reference to  FIG. 1 , there is illustrated the construction of the part  10 . Part  10 , preferably utilized to create a fan blade, is comprised of a suction side  21  and a pressure side  23  separated by a dividing portion of material  25 . 
   The forging process is performed such that the outer surfaces of suction side  21  and pressure side  23  are of a shape requiring little or no post forging processing to achieve a finished exterior surface. Typically, the amount of material removed during post forging processing ranges on average from 0.030 inches to 0.125 inches. In particular, the root block  29  and diffusion bond face feature  27  are forged in a substantially finished form suitable for machining so as to enable the bonding of the part  10  to a hub. The temperatures and pressures under which the forgings are performed vary depending on the desired mechanical properties of the finished part and are known in the art. Specifically, the temperatures and pressures for the forgings are selected to produce a finished part which exhibits desired tensile and compressive strengths as well as sufficient low and high cycle fatigue resistance. 
   Root block  29  is formed of an amount of manufacturing material intended to be sacrificed during post-diffusion bonding machining. Specifically, root block  29  is not forged into a finished form, but, rather, is intended to be machined. In a preferred embodiment, root block  29  is constructed to allow for the part  10  to be gripped and friction welded to a hub or other receiving fixture. After friction welding part  10  to the hub, the remaining portion of root block  29  is machined off so as to leave a clean airfoil extending smoothly along the expanses formed by each of suction side  21  and pressure side  23 . 
   As noted, located between pressure side  23  and suction side  21  is a dividing portion of material  25 . As illustrated, dividing portion of material  25  is of a width w. Width w is chosen depending upon the method by which pressure side  23  is to be separated from suction side  21 . Preferably, pressure side  23  is separated from suction side  21  by cutting through and along dividing portion of material  25  with a band saw  31  as illustrated in  FIG. 2 . Alternative methods include, but are not limited to, utilizing a water jet, or employing wire EDM. Each of the above-noted cutting methodologies results in a cut which destroys an approximately uniform width of material in the direction of the cut. As a result, the width, w, of the dividing portion of material  25  should be equal to, or preferably greater than, the separation destruction width of the cutting technology utilized. As used herein “separation destruction width” refers to the width of material which is sacrificed when employing a chosen methodology for cutting. In a preferred embodiment, the width, w, of dividing portion of material is approximately 10–20% wider than the separation destruction width. 
   In a preferred embodiment, the dividing portion of the material  25  forms a generally planar expanse. In such an instance, all of the above identified methods of cutting dividing portion of the material  25  may be utilized to achieve a generally planar cut. With reference to  FIG.4 , there is illustrated a part  10  of the present invention wherein the dividing portion of the material  25  does not form a generally planar expanse. Rather, dividing portion  25  generally follows the twisting contours of both suction side  21  and pressure side  23 . In such an instance, it is possible to program the operation of a wire EDM to alter its orientation as the cut along dividing portion  25  progresses so as to effectively remove dividing portion  25 . 
   Preferably, part  10  is fabricated from titanium. However, part  10  may be formed of any metallic material exhibiting desired tensile and compressive strength as well as sufficient low and high cycle fatigue resistance. Such metals include, but are not limited to, titanium based alloys, forgeable alloys, aluminum, and steels. 
   With continued reference to  FIG. 1 , there is illustrated both suction side  21  and pressure side  23  post forging and post separation utilizing a cutting technique as described above. Once cut and separated, both suction side  21  and pressure side  23  possess an inner surface  33 . Inner surface  33  is subsequently machined to contain at least one cavity  31  as illustrated with reference to  FIG. 3 . Preferably, each cavity formed into the inner surface  33  of suction side  21  has an associated, reciprocating cavity machined into the inner surface  33  of the opposing pressure side  23 . By reciprocating cavity, it is meant that when suction side  21  and pressure side  23  are aligned and joined through the process of diffusion bonding, a cavity  31  located on the inner surface of suction side  21  is aligned with a cavity  31  fabricated into the inner surface  33  of pressure side  23  such that one continuous cavity is formed inside the bonded part  10 . The fabrication of such cavities adds strength and resistance to deformation to the post-bonded part  10 . 
   While described with reference to reciprocating cavities  31 , the present invention is not so limited. Rather, the present invention encompasses any and all cavities, including cooling microcircuits, which may be fabricated into the inner surfaces of suction side  21  and pressure side  23 . 
   With continued reference to  FIG. 3 , at least two alignment holes  51  are drilled or otherwise machined through both suction side  21  and pressure side  23  post forging and separation. The alignment holes  51  are used to precisely align the inner surfaces  33  of the suction side  21  and pressure side  23  for diffusion bonding. It is therefore important that the alignment holes are drilled in precisely the desired location. 
   Referring now to  FIGS. 5 and 6 , it is therefore common practice to place the both the suction side  21  and the pressure side  23  in a six point trap  65  formed of at least six traps  61  and configured for use with either the suction side  21  or the pressure side  23 . Each of the traps  61  restricts the part from movement in one of the six degrees of motion (three translational and three rotational) . Because the part  10  is forged such that the exterior surfaces of both the suction side  21  and the pressure side  23  are in near finished condition (i.e. “near net”), they may each be placed in their respective six point traps  65  in a manner which precisely controls the orientation and placement of the sides  21 ,  23 . A drilling mechanism  63  may then be positioned to precisely drill holes in the side  21 ,  23 . As noted, these holes are then used to align the suction side  21  with the pressure side  23  for diffusion bonding to each other using a mold  62  as shown in  FIG. 6 . 
   It is apparent that there has been provided in accordance with the present invention a method for forging hollow blades requiring a single forging which fully satisfies the objects, means, and advantages set forth previously herein. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.