Abstract:
A method of forming a fan blade includes the step of applying an adhesive layer around a leading edge of a fan blade body. The adhesive layer includes an adhesive film supported by a scrim cloth, and the adhesive layer contacts a portion of an inner surface of the fan blade body and a portion of an outer surface of the fan blade body. A leading edge sheath is positioned relative to the fan blade body such that a first flank and a second flank of the leading edge sheath is positioned over the portion of the inner surface and the portion of an outer surface, respectively, of the fan blade body. Pressure is applied to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body and curing the adhesive film.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A gas turbine engine includes a fan section that drives air along a bypass flowpath while a compressor section drives air along a core flowpath for compression and communication into a combustor section then expansion through a turbine section. 
         [0002]    Fan blades are commonly made of titanium or carbon fiber. Titanium is strong, allowing a leading edge of the fan blade to protect the gas turbine engines from strikes from foreign objects. 
         [0003]    A fan blade could be made of other materials, and a leading edge sheath can be attached to a blade body of a fan blade with an adhesive to strengthen the fan blade. The leading edge sheath can be attached to the blade body with a mold. However, due to its size, employing a mold increases the thermal mass in the autoclave, which could increase cure time of the adhesive. 
       SUMMARY OF THE INVENTION 
       [0004]    A method of forming a fan blade according an exemplary aspect of the present disclosure includes, among other things, the steps of applying an adhesive layer around a leading edge of a fan blade body. The adhesive layer includes an adhesive film supported by a scrim cloth, and the adhesive layer contacts a portion of an inner surface of the fan blade body and a portion of an outer surface of the fan blade body. The method further includes the step of then positioning a leading edge sheath relative to the fan blade body such that a first flank of the leading edge sheath is positioned over the portion of the inner surface of the fan blade body and a second flank of the leading edge sheath is positioned over the portion of an outer surface of the fan blade body. The method further includes the steps of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body and curing the adhesive film. 
         [0005]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a fan blade body made of aluminum or an aluminum alloy. 
         [0006]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a leading edge sheath made of titanium or a titanium alloy. 
         [0007]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include an adhesive film that is an epoxy film. 
         [0008]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a scrim cloth that is mesh. 
         [0009]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a scrim cloth that is nylon. 
         [0010]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive film and the step of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body that occur simultaneously. 
         [0011]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the steps of placing the leading edge sheath and the blade body in a vacuum bag and applying a vacuum to the vacuum bag. 
         [0012]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive film, the step of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body, and the step of applying a vacuum that occur simultaneously. 
         [0013]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying pressure to the first flank and the second flank of the leading edge by an autoclave. 
         [0014]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying an additional piece of material over the adhesive layer. 
         [0015]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include an additional piece of material that is fiberglass. 
         [0016]    Another method of forming a fan blade according an exemplary aspect of the present disclosure includes, among other things, the step of applying an adhesive layer around a leading edge of a fan blade body. The adhesive layer includes an adhesive film supported by a scrim cloth, the adhesive layer contacts at least a portion of an inner surface of the fan blade body and at least a portion of an outer surface of the fan blade body, the fan blade body is made of aluminum or an aluminum alloy, and the adhesive film is an epoxy film. The method further includes the step of then positioning a leading edge sheath relative to the fan blade body such that a first flank of the leading edge sheath is positioned over the at least a portion of the inner surface of the fan blade body and a second flank of the leading edge sheath is positioned over at the least a portion of the outer surface of the fan blade body, where the leading edge sheath is made of titanium or a titanium alloy. The method further includes the steps of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body and curing the adhesive film. 
         [0017]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a scrim cloth that is nylon. 
         [0018]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive film and the step of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body that occur simultaneously. 
         [0019]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the steps of placing the leading edge sheath and the blade body in a vacuum bag and applying a vacuum to the vacuum bag. 
         [0020]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive film, the step of applying pressure to the first flank and the second flank of the leading edge sheath to secure the leading edge sheath to the blade body, and the step of applying a vacuum that occur simultaneously. 
         [0021]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying pressure to the first flank and the second flank of the leading edge by an autoclave. 
         [0022]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying an additional piece of material over the adhesive layer. 
         [0023]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include an additional piece of material that is fiberglass. 
         [0024]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  illustrates a schematic view of a gas turbine engine; 
           [0026]      FIG. 2  illustrates an exploded view of a fan blade; 
           [0027]      FIG. 3  illustrates a side view of a leading edge sheath attached to a blade body with a scrim cloth and adhesive therebetween; 
           [0028]      FIG. 4  illustrates a side view of the fan blade; 
           [0029]      FIG. 5  illustrates a method of attaching the leading edge sheath to the blade body; and 
           [0030]      FIG. 6  illustrates how an A angle of the fan blade is defined. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]      FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. 
         [0032]    Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool or geared turbofan architectures. 
         [0033]    The fan section  22  drives air along a bypass flowpath B while the compressor section  24  drives air along a core flowpath C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . 
         [0034]    The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
         [0035]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and a high pressure turbine  54 . 
         [0036]    A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . 
         [0037]    A mid-turbine frame  58  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  58  further supports bearing systems  38  in the turbine section  28 . 
         [0038]    The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with their longitudinal axes. 
         [0039]    The core airflow C is compressed by the low pressure compressor  44 , then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  58  includes airfoils  60  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
         [0040]    The engine  20  is in one example a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6:1) with an example embodiment being greater than ten (10:1). The geared architecture  48  is an epicyclic gear train (such as a planetary gear system or other gear system) with a gear reduction ratio of greater than about 2.3 (2.3:1). The low pressure turbine  46  has a pressure ratio that is greater than about five (5:1). The low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. 
         [0041]    In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), and the fan diameter is significantly larger than that of the low pressure compressor  44 . The low pressure turbine  46  has a pressure ratio that is greater than about five (5:1). The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.5 (2.5:1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0042]    A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 feet (10,668 meters), with the engine at its best fuel consumption, also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’),” is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. 
         [0043]    “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. 
         [0044]    “Low corrected fan tip speed” is the actual fan tip speed in feet per second divided by an industry standard temperature correction of [(Tambient deg R)/518.7) 05 ]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 feet per second (351 meters per second). 
         [0045]    The fan  42  includes a plurality of hybrid metallic fan blades  62 . As shown in  FIG. 2 , each fan blade  62  includes a blade body  64  having an inner surface  70  including a plurality of cavities  66 , such as grooves or openings, surrounded by ribs  68 . A plurality of strips or pieces of a low density filler  72  are each sized to fit in one of the plurality of cavities  66 . The fan blade  62  also includes a cover  74  and a leading edge sheath  76  attached to the blade body  64 . 
         [0046]    In one example, the blade body  64  is made of aluminum or an aluminum alloy. Employing aluminum or an aluminum alloy for the blade body  64  and the cover  74  provides a weight and cost savings. There is one strip or piece of the low density filler  72  for each of the plurality of cavities  66  of the blade body  64 . In one example, the low density filler  72  is foam. In one example, the foam is aluminum foam. The low density filler  72  is secured in the cavities  66  with an adhesive  78 , shown schematically as arrows. In one example, the adhesive  78  is urethane. In another example, the adhesive  78  is an epoxy film. 
         [0047]    The cover  74  is then secured to the blade body  64  with an adhesive  80 , shown schematically as arrows. In one example, the adhesive  80  is urethane. In one example, the cover  74  is made of aluminum or an aluminum alloy. The adhesive  80  then cured during a bonding cure cycle in a pressure vessel. 
         [0048]    The leading edge sheath  76  is then attached to the blade body  64  with an adhesive layer  82 . In one example, the adhesive layer  82  includes an adhesive film supported by a scrim cloth. In one example, the adhesive film is an epoxy film. In one example, the scrim cloth is nylon. In one example, the scrim cloth is mesh in structure. In one example, the leading edge sheath  76  is made of titanium or a titanium alloy. The adhesive film in the adhesive layer  82  is then cured during a sheath bonding cure cycle in an autoclave. 
         [0049]    The leading edge sheath  76  provides additional strength (for example, for bird-strike events) to the fan blade  62  (made of a lighter material) and is more resistant to erosion than the aluminum or aluminum alloy of the blade body  64 . As shown in  FIGS. 3 and 4 , the leading edge sheath  76  includes a first sheath flank  84  and a second sheath flank  85 . When the leading edge sheath  76  is applied to a leading edge  88  of the blade body  64 , the first sheath flank  84  is located over the inner surface  70  of the blade body  64 , and the second sheath flank  84  is located over an outer surface  89  of the blade body  64 . 
         [0050]    When attaching the leading edge sheath  76  to the blade body  64 , the adhesive layer  82  is applied to the blade body  64 . In one example, the adhesive layer  82  is folded over the leading edge  88  of the blade body  64  and covers the inner surface  70  and the outer surface  89  of the blade body  64  near the leading edge  88 . 
         [0051]    In one example, an additional piece of material (not shown) can be folded over the adhesive layer  82 . In one example, the additional piece of material is fiberglass. The additional piece of material can be woven or non-woven. 
         [0052]    The leading edge sheath  76  is then positioned such that the first sheath flank  84  is positioned over the inner surface  70  of the blade body  64 , and the second sheath flank  85  is positioned over the outer surface  89  of the blade body. The scrim cloth of the adhesive layer  82  retains the adhesive film between the leading edge sheath  76  and the blade body  64 . A gap  94  is defined between the leading edge sheath  76  and the blade body  64 , and the adhesive layer  82  fills in the gap  94  once the adhesive film is cured. In  FIG. 3 , the gap  94  is shown in an exaggerated manner for illustrative purposes only. 
         [0053]    As shown in  FIG. 5 , in step  96 , the leading edge sheath  76  is positioned on the blade body  64  with the adhesive layer  82  therebetween. In step  98 , the leading edge sheath  76  and the blade body  64  are sealed in a vacuum bag and connected to a vacuum source. In step  100 , the leading edge sheath  76  and the blade body  64  are then placed in an autoclave. In step  102 , a vacuum is applied to the vacuum bag by the vacuum source to evacuate the vacuum bag of air. 
         [0054]    In step  104 , pressure  108  (shown in  FIG. 3 ) and heat is then applied by the autoclave, and the adhesive film in the adhesive layer  82  cures simultaneously. In one example, the autoclave applies about 90 psi of pressure at a temperature of about 250° F. (121.1° C.) for at least about 2 hours. The increased pressure applied to the leading edge sheath  76  during bonding and exposure to the high pressure allows the leading edge sheath  76  to float and self-center, forcing the flanks  84  and  85  of the leading edge sheath  76  against the blade body  64 . The leading edge sheath  76  is then properly aligned with the blade body  64  without the use of external tooling. In step  106 , the attached leading edge sheath  76  and the blade body  64  are then removed from the vacuum bag and the autoclave. Once attached, the leading edge sheath  76  defines a leading edge  110  of the fan blade  62   
         [0055]    As shown in  FIG. 6 , it is important that the bonding of the leading edge sheath  76  with the blade body  64  is precise to ensure that the A angle, which is defined by the alignment of the leading edge sheath  76  on the blade body  64 , is within a tolerated range. A desired A angle is associated with each fan blade  62 . 
         [0056]    A location B is defined at a distance C from the leading edge  110  of the fan blade  62 , and a location D is defined at a distance E from the leading edge  110  of the fan blade  62 . In one example, the distance C is 0.430 inch (1.09 cm), and the distance D is 2.580 inch (6.55 cm). A line F passes through the location B and the location D. The line F intersects a plane G that is substantially vertical. The actual A angle is the angle defined at the intersection of the line F and the plane G. The desired A angle is compared to the actual A angle. If a difference between the desired A angle and the actual A angle are within a tolerance range, this means that the leading edge sheath  76  is properly aligned with the blade body  64 . In one example, the difference is about 1° or less. 
         [0057]    The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.