Patent Publication Number: US-11047058-B2

Title: Method for manufacturing leading edge guard

Description:
BACKGROUND 
     Embodiments of the present invention relate generally to fan blade protective leading edges and in particular to methods for manufacturing such leading edges. 
     Fan blades used in jet engine applications are susceptible to foreign object impact damage such as bird ingestion events. Blades made of graphite fiber reinforced composite material are attractive due to their high overall specific strength and stiffness. However, graphite composites are particularly prone to brittle fracture and delamination during foreign object impacts due to their low ductility. Blade leading edges, trailing edges, and tips are particularly sensitive because of the generally lower thickness in these areas and the well-known susceptibility of laminated composites to free edge delamination. In addition blade geometry and high rotational speeds relative to aircraft speeds cause ingested objects to strike the blade near the leading edge. 
     Metallic guards bonded to the leading edges of composite fan blades are known to provide impact damage protection. However, newer fan blade designs require that such guards be both thin and made of high-density alloys. These requirements make manufacture of leading edge guards difficult with known methods such as conventional machining or hot creep forming. 
     It has been proposed to form metal leading edge guards using an electroforming process. However, the proposed methods require either that excess material remain after the electroforming process, or that a complex process be used with multiple sets of tooling. 
     Accordingly, there remains a need for an efficient method of producing fan blade metallic leading edge guards. 
     BRIEF DESCRIPTION 
     This need is addressed by embodiments of the present invention, which provide a method for manufacturing metal leading edge guards using a combination of electroforming and conventional machining. 
     According to one aspect of the invention, a method is provided for making a metallic leading edge guard of the type having a nose with first and second wings extending therefrom. The method includes: machining from a metallic blank a first half comprising a first portion of the nose and one of the wings, wherein the first portion of the nose includes an interface surface; and electroforming a second half comprising a second portion of the nose and the second wing, wherein the second half is joined to the first half at the interface surface. 
     According to another aspect of the invention, the leading edge guard includes an interior surface collectively defined by the nose and the wings, and a portion of the interior surface defined by the first half is machined to final dimensions before the electroforming step. 
     According to another aspect of the invention, the first half is mounted to an electrically-conductive mandrel for the electroforming step. 
     According to another aspect of the invention, the leading edge guard includes an exterior surface collectively defined by the nose and the wings, and wherein, during the electroforming step, a fixture is mounted over a portion of the exterior surface that is defined by the first half. 
     According to another aspect of the invention, the interface surface is disposed such that a maximum thickness of metal to be deposited in the electroforming step is less than an axial length of the nose. 
     According to another aspect of the invention, the interface surface is disposed such that the first and second portions of the nose are of substantially equal thickness. 
     According to another aspect of the invention, the interface surface is disposed such that second portion of the nose is significantly thinner than the first portion of the nose. 
     According to another aspect of the invention, the exterior surface is machined to final dimensions subsequent to the electroforming step. 
     According to another aspect of the invention, the first and second halves are made of a nickel-based alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a view of a gas turbine engine fan blade incorporating a leading edge strip constructed in accordance with an aspect of the present invention; 
         FIG. 2  is a cross-sectional view of a portion of the fan blade of  FIG. 1 ; 
         FIG. 3  is a block diagram showing the method steps according to an embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a first half of a leading edge guard being formed; 
         FIG. 5  is a cross-sectional view of an alternative first half configuration; 
         FIG. 6  is a cross-sectional view of a second half of a leading edge guard being formed; 
         FIG. 7  is a cross-sectional view of a leading edge guard; 
         FIG. 8  is a cross-sectional view of a second leading edge guard; and 
         FIG. 9  is a cross-sectional view of a leading edge guard during a final machining process. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts an exemplary fan blade  10  for a gas turbine engine. The fan blade  10  includes an airfoil  12 , shank  14 , and dovetail  16 . The airfoil  12  extends between a root  18  and a tip  20 , and has a leading edge  22  and a trailing edge  24 . Opposed convex and concave sides  26  and  28 , respectively, extend between the leading edge  22  and the trailing edge  24 . 
     The fan blade  10  may be made from a known nonmetallic material, such as a carbon fiber-epoxy composite system. 
     The fan blade has a metallic leading edge guard  30  attached to the leading edge  16 . The leading edge guard  30  helps provide the fan blade  10  with additional impact resistance, erosion resistance and improved resistance of the composite structure to delamination. 
     The leading edge guard  30  includes a nose  32  with a pair of wings  34  and  36  extending aft therefrom. The wings  34  and  36  taper in thickness as they extend away from the nose  32 . Exterior surfaces of the nose  32  and wings  34  and  36  collectively define an exterior surface  38  of the leading edge guard  30 . The shape and dimensions of the exterior surface  38  are selected to act as an aerodynamic extension of the airfoil  12 . The leading edge guard  30  may be attached to the airfoil  12  with a known type of adhesive. 
     Interior surfaces of the nose  32  and wings  34  and  36  collectively define an interior surface  40  of the leading edge guard  30 . The shape and dimensions of the interior surface  38  are selected to closely fit the exterior of the airfoil  12 . 
     The leading edge guard  30  has an overall length “L 1 ” measured in an axial direction. The nose  32  has an axial length designated “L 2 ,” and a thickness “T 1 ” measured perpendicular to the lengths. All of these dimensions will vary to suit a particular application; however in general, the length L 1  is about 3 to 6 times the length L 2 . The length “L 2 ” is typically significantly larger that can be achieved with known electroforming processes. For example it may be about 3.8 cm (1.5 in) to about 10.2 cm (2.0 in). 
     Embodiments of the present invention provide a method for making the leading edge guard  30 . The process is explained with reference to the block diagram shown in  FIG. 3 . The leading edge guard  30  is an integral or unitary component formed from two major parts, herein referred to as a “first half” and a “second half.” The term “half” is used merely for reference and does not necessarily imply that the two components are equal in terms of size, shape, volume, or mass. In a first step (block  100 ), the first half  42  is machined from a blank of material (shown schematically in dashed lines in  FIG. 4 ) using conventional machinery and processes, such as milling operations. The portion of the interior surface  40  defined by the first half  42  is machined to its final dimensions using one or more conventional processes. The portion of the exterior surface  38  defined by the first half  42  is rough machined, that is, close to the required net shape. 
     The first half  42  includes a planar interface surface  44  which extends in a generally axial direction through the nose  32 . The location of the interface surface  44  can be selected to provide the best balance of process and product characteristics. In the example shown in  FIG. 4 , the interface surface  44  approximately cuts the nose  32  in two equal parts, providing the largest area for the interface surface  44 . In the example shown in  FIG. 5 , the interface surface  44  is offset away from the center position. This reduces the amount of electroform buildup required, as described in more detail below. 
     In a second step (block  200  of  FIG. 3 ), the first half  42  is mounted onto a mandrel  46 . The mandrel  46  ( FIG. 6 ) is made from or coated with an electrically conductive material. It has a surface  48  that closely matches the interior surface  40  of the leading edge guard  30 . A fixture  50  with a surface  51  closely matching the portion of the exterior surface  38  defined by the first half  42  is placed against the first half  42 . This serves to physically locate the first half  42  and to mask it from electroforming buildup. 
     The fixtured first half  42  is placed in an electroforming apparatus  52  comprising a tank  54 , an electrolytic solution  56 , and a source electrode  58 . The source electrode  58  and the mandrel  46  are connected in an electric circuit with a suitable electric power supply, shown schematically at  60 . 
     The source electrode  58  is made from a metal alloy of the desired composition. A non-limiting example of an alloy suitable for construction of the electrode  58  (and also of the first half  42 ) is a nickel-based alloy commercially available as INCONEL 718 or IN718. 
     When the circuit is closed, material is transferred from the electrode  58  through the electrolytic solution  56  and deposited on the interface surface  44  of the first half  42  as well as the mandrel  46 , effectively building up a second half  62  in rough form, as depicted by the arrows in  FIG. 6 . Once a suitable thickness has formed, the circuit is opened and the mandrel  46  with leading edge guard  30  attached is removed from the electroforming apparatus  52 . 
     During the electroforming process, the maximum thickness of material to be built up occurs in the nose  32 . This is designated as “T 2 .” In an embodiment of the present invention, T 2  is much less than L 2 , which would otherwise represent the maximum required thickness buildup. For example, T 2  may be less than half of L 2 . In many cases, the dimension L 2  is greater than practically possible with known electroforming processes, and the present invention permits the use of electroforming where it would otherwise be unusable. As noted above, the position of the interface surface  44  may be selected so that T 2  is a desired dimension. 
     For example,  FIG. 7  illustrates a completed leading edge guard  30  with two halves  42  and  62  joined at an interface surface  44 . The distance T 2  divides the nose  32  approximately in half. In contrast,  FIG. 8  illustrates a completed leading edge guard  30 ′ with two halves  42 ′ and  62 ′ joined at an interface surface  44 ′. The distance T 2 ′ is significantly smaller than then distance T 2  shown in  FIG. 7 . 
     Referring to block  300  of  FIG. 3 , the exterior surface  38  of the leading edge guard  30  may be machined to its final dimensions using conventional machining processes and apparatus, such as the illustrated milling cutter ( FIG. 9 ). The mandrel  46  may be used as a fixture to hold the leading edge guard  30  during the final machining process. Alternatively, the mandrel  46  could be removed and a similar fixture used to hold the leading edge guard  30  during final machining. 
     The completed leading edge guard  30  can be attached to an airfoil  12  in a conventional manner. The process described herein may have several benefits over prior art methods. By preforming the first half  42 , the thickness that needs to build up with electroforming is reduced, making electroforming a viable process for the leading edge guard  30 . The same alloy is electroformed on both sides of the interface surface  44 , and material strength is not degraded at the interface surface  44 . Furthermore, there is no limitation or restriction on the internal corner radii of the interior surface  40 . 
     The foregoing has described a method for making a metallic leading edge guard. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments have been set forth in the foregoing description, together with details of the structure and functions of various embodiments, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings disclosed herein can be applied to other systems without departing from the scope and spirit of the application.