Abstract:
A method of forming a fan blade includes the steps of applying an adhesive to an inner surface of a cover and moving a toothed instrument along the inner surface of the cover to spread the adhesive over the inner surface of the cover to form a plurality of rows of adhesive on the inner surface of the cover. The method further includes the steps of applying the inner surface of the cover to a fan blade body and curing the adhesive to secure the cover to the fan blade body.

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. Sheet adhesive films, for example epoxy films, can be used to secure parts of the fan blade together as they are strong, durable, easy to apply, and have a consistent weight and thickness. Urethane based adhesives can provide more damping ability than conventional epoxy based adhesives. However, urethane is not available as a film, but as a liquid. When a liquid adhesive is applied to a surface and spread over a surface, unevenness and inconsistencies in the thickness of the adhesive can result. 
       SUMMARY OF THE INVENTION 
       [0003]    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 to an inner surface of a cover and moving a toothed instrument along the inner surface of the cover to spread the adhesive over the inner surface of the cover to form a plurality of rows of adhesive on the inner surface of the cover. The method further includes the steps of applying the inner surface of the cover to a fan blade body and curing the adhesive to secure the cover to the fan blade body. 
         [0004]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a cover made of aluminum or an aluminum alloy. 
         [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 adhesive that is urethane. 
         [0007]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a fan blade body having an inner surface including a plurality of cavities, and a low density filler is received in each of the plurality of cavities. 
         [0008]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a low density filler that is aluminum foam. 
         [0009]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying an adhesive to an inner surface of a cover near a first edge of the cover. 
         [0010]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of moving a toothed instrument along an inner surface of a cover from a first edge of the inner surface of the cover to an opposing second edge of the inner surface of the cover. 
         [0011]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying an inner surface of a cover to a fan blade body to spread rows of adhesive to form a layer of adhesive having a thickness. 
         [0012]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a layer of adhesive having a thickness of about 0.005 inch (0.0127 cm) to about 0.015 inch (0.0381 cm). 
         [0013]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of dampening vibrations with a layer of adhesive. 
         [0014]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive by employing a vacuum. 
         [0015]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive by employing pressure. 
         [0016]    Another method of forming a fan blade according an exemplary aspect of the present disclosure includes, among other things, the step of applying a urethane adhesive near a first edge of an inner surface of a cover made of aluminum or an aluminum alloy. The method further includes the step of moving a toothed instrument along the inner surface of the cover from a first edge of the inner surface of the cover to an opposing second edge of the inner surface of the cover to spread the adhesive over the inner surface of the cover to create a plurality of rows of adhesive on the inner surface of the cover. The method further includes the steps of applying the inner surface of the cover to a fan blade body made of aluminum or aluminum alloy and curing the adhesive to secure the cover to the fan blade body. 
         [0017]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a fan blade body having an inner surface including a plurality of cavities, and a low density filler is received in each of the plurality of cavities. 
         [0018]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a low density filler that is aluminum foam. 
         [0019]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of applying an inner surface of a cover to a fan blade body to spread the rows of adhesive to form a layer of adhesive having a thickness. 
         [0020]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include a layer of adhesive having a thickness of about 0.005 inch (0.0127 cm) to about 0.015 inch (0.0381 cm). 
         [0021]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of dampening vibrations with a layer of adhesive. 
         [0022]    In a further non-limiting embodiment of any of the forgoing method embodiments, the method may include the step of curing an adhesive by employing a vacuum and pressure. 
         [0023]    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 
         [0024]      FIG. 1  illustrates a schematic view of a gas turbine engine; 
           [0025]      FIG. 2  illustrates an exploded view of a fan blade; 
           [0026]      FIG. 3  illustrates an inner surface of a cover of a fan blade with an adhesive applied near an edge; 
           [0027]      FIG. 4  illustrates the inner surface of the cover of the fan blade once the adhesive has been spread over the inner surface of the cover with a toothed instrument; 
           [0028]      FIG. 5  illustrates a toothed trowel used to spread the adhesive over the inner surface of the cover; 
           [0029]      FIG. 6  illustrates a layer of adhesive after the application of the cover to a blade body; and 
           [0030]      FIG. 7  illustrates a flowchart showing a method of attaching the cover to a blade body. 
       
    
    
     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) 0.5 ]. 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 cost and weight 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 a 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]    To attach the cover  74  to the blade body  64 , the adhesive  80  is applied near a first edge  84  of an inner surface  86  of the cover  74 . The adhesive  80  is contained in a body  88  and is dispensed through a nozzle  90 . The adhesive  80  can be applied manually or robotically, shown schematically as a box  92 . 
         [0050]    As shown in  FIG. 4 , once the adhesive  80  is applied, a toothed instrument  94  is positioned on the inner surface  86  of the cover  74  and moved along the length L of the cover  74  from the first edge  84  to an opposing second edge  96 . After the toothed instrument  94  is along the length L of the inner surface  86  of the cover  74 , a plurality of rows  98  of adhesive  80  are defined. 
         [0051]    As shown in  FIG. 5 , in one example, the toothed instrument  94  is a toothed trowel that includes a plurality of teeth  100  that are separated by a space  102 . In one example, the height of the space  102  between each tooth  100  is ⅛ of an inch (0.3175 cm). In one example, the teeth  100  are spaced apart by a distance of ⅛″ (0.1375 cm). The depth, shape and spacing of the teeth  100  determine a final cured bondline thickness of the adhesive  80  by controlling an amount of the adhesive  80  on the inner surface  86  of the cover  74 . In one example, the toothed instrument  94  is made of plastic. In one example, the tooth instrument  94  is a roller including a plurality of teeth. As the roller is moved over the inner surface  86  of the cover  74 , the plurality of teeth create the plurality of rows  98  of adhesive  80 . 
         [0052]    The toothed instrument  94  controls the amount and distribution of the adhesive  80  spread over the inner surface  86  of the cover  74  to provide consistency and to remove any excess adhesive  80 . This also allows for consistency for different fan blades  62 , reducing weight variations in different fan blades  62 . The toothed instrument  94  makes application of the adhesive  80  on the inner surface  86  of the cover  74  less sensitive to variation as it removes excess adhesive  80  and leaves a consistent amount of adhesive  80  on the cover  74 . This also allows for the adhesive  80  to be applied manually without the use of a machine or robot. 
         [0053]    As shown in  FIG. 7 , after the rows  98  of adhesive  80  are formed on the inner surface  86  of the cover  74  in step  103 , the cover  74  is then placed over the inner surface  70  of the blade body  64  in step  104  (after the attachment of the low density filler  72  in the cavities  66  of the blade body  64 ). As shown in  FIG. 6 , once the cover  74  is applied on the inner surface  70  of the blade body  64  (the blade body  64  is not shown in  FIG. 6 ), the rows  98  of adhesive  80  spread to form a layer  116  of adhesive  80  of uniform thickness that covers the inner surface  86  of the cover  74 . 
         [0054]    In step  106 , the cover  74  and the blade body  64  are sealed in a vacuum bag and connected to a vacuum source to evacuate the vacuum bag of air. The vacuum bag is removed from the vacuum source, and inn step  108 , the cover  74  and the blade body  64  are then placed in a pressure vessel. The vacuum bag is then reattached to another vacuum source once the vacuum bag is located inside the pressure vessel. In step  110 , a vacuum is applied to the vacuum bag by the another vacuum source to continue to evacuate the vacuum bag of air. 
         [0055]    In step  112 , pressure is then applied by the pressure vessel, curing the layer  116  of adhesive  80 . In one example, the pressure vessel applies about 90 psi of pressure for at least 90 minutes. In one another example, the pressure vessel applies about 45 psi of pressure for at least 90 minutes. In step  114 , the attached cover  74  and the blade body  64  are then removed from the vacuum bag and the pressure vessel. In one example, if the adhesive  80  is urethane, the layer  116  of adhesive  80  has a hardness over about 80 durometer Shore A after a secondary elevated cure at about 250° F. 
         [0056]    Once cured, the layer  116  of adhesive  80  has a thickness of about 0.005 inch (0.0127 cm) to about 0.015 inch (0.0381 cm). The layer  116  of adhesive  80  not only secures the cover  74  to the blade body  64 , but also provides a dampening function. As the fan blade  62  vibrates, the layer  116  of adhesive  80  absorbs vibrations to provide a dampening effect. 
         [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.