Abstract:
A method of forming a fan blade includes the step of positioning a piece of low density filler in a cavity of an inner exposed surface of a fan blade body. An upper surface of the piece of low density filler is located above the inner exposed surface of the fan blade body, and the low density filler has a density lower than a density of a material of the fan blade body. The method further includes the steps of positioning the fan blade body in a lower die of a press and applying pressure to the inner exposed surface of the fan blade body with an upper die of the press to compress the low density filler such that the upper surface of the piece of low density filler is approximately flush with the inner exposed surface of the fan blade body.

Description:
BACKGROUND OF THE INVENTION 
     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. 
     One example fan blade includes a cover attached to a blade body. An inner surface of the blade body of the fan blade includes cavities. A piece of low density filler is placed into a corresponding cavity in the blade body. An exposed surface of the low density filler must conform closely to a surface of the blade body to enable a robust bond joint to a mating surface of the cover. Due to variation in the manufacturing processes, currently an operator manually applies pressure to any high spots in the low density filler, and then taps the high spots of the low density filler with an instrument so that an upper surface of the low density filler is approximately flush with the inner surface of the blade body to create a smooth surface. A drawback to this method is that it is labor intensive for an operator to manually tap each piece of low density filler. 
     SUMMARY OF THE INVENTION 
     A method of forming a fan blade according an exemplary aspect of the present disclosure includes, among other things, the step of positioning a piece of low density filler in a cavity of an inner exposed surface of a fan blade body. An upper surface of the piece of low density filler is located above the inner exposed surface of the fan blade body, and the low density filler has a density lower than a density of a material of the fan blade body. The method further includes the steps of positioning the fan blade body in a lower die of a press and applying pressure to the inner exposed surface of the fan blade body with an upper die of the press to compress the low density filler such that the upper surface of the piece of low density filler is approximately flush with the inner exposed surface of the fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include the step of applying an adhesive in a cavity. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include the step of placing a low density filler in a cavity after the step of applying an adhesive in the cavity. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include partially curing an adhesive during the step of applying pressure to an inner exposed surface of a fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include an adhesive that is urethane. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a press having a lower die having a contour that matches a contour of an outer surface of a fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler of foam. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler of aluminum foam. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a fan blade body made of aluminum or an aluminum alloy. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler that is compressed and partially bonded to a fan blade body concurrently. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include the step of applying pressure to an inner exposed surface of a fan blade body including compressing an upper surface of a piece of low density foam below the inner exposed surface of the fan blade body and then allowing the piece of low density foam to spring back such that the upper surface of the piece of low density foam is substantially flush with the inner exposed surface of the fan blade body. 
     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 in each of a plurality of cavities of an inner exposed surface of a fan blade body and positioning one of a plurality of pieces of low density filler in each of the plurality of cavities after the step of applying the adhesive in each of the plurality of cavities. An upper surface of the plurality of pieces of low density filler is located above the inner exposed surface of the fan blade body, and the plurality of pieces of low density filler have a density lower than a density of a material of the fan blade body. The method further includes the step of positioning the fan blade body in a lower die of a press, and the lower die of the press has a contour that matches a contour of an outer surface of the fan blade body. The method further includes the step of applying pressure to the inner exposed surface of the fan blade body with an upper die of the press to compress the plurality of pieces of low density filler such that the upper surface of the plurality of pieces of low density filler is approximately flush with the inner exposed surface of the fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include partially curing an adhesive during the step of applying pressure to an inner exposed surface of a fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include an adhesive that is urethane. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a press having a lower die having a contour that matches a contour of an outer surface of a fan blade body. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler of foam. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler of aluminum foam. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a fan blade body made of aluminum or an aluminum alloy. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include a low density filler that is compressed and partially bonded to a fan blade body concurrently. 
     In a further non-limited embodiment of any of the forgoing method embodiments, the method may include the step of applying pressure to an inner exposed surface of a fan blade body including compressing an upper surface of a plurality of pieces of low density foam below the inner exposed surface of the fan blade body and then allowing the plurality of pieces of low density foam to spring back such that the upper surface of the plurality of pieces of low density foam is substantially flush with the inner exposed surface of the fan blade body. 
     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 
         FIG. 1  illustrates a schematic view of a gas turbine engine; 
         FIG. 2  illustrates an exploded view of a fan blade; 
         FIG. 3  illustrates a press including an upper die and a lower die; 
         FIG. 4  illustrates the lower die of the press; 
         FIG. 5  illustrates the lower die of the press receiving the blade body; 
         FIG. 6  illustrates low density filler inserted into the cavities in the blade body prior to pressure being applied by the press; and 
         FIG. 7  illustrates the low density filler inserted in the cavities in the blade body after pressure is applied by the press. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       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. 
     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. 
     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 . 
     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. 
     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 . 
     A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . 
     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 . 
     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. 
     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. 
     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. 
     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. 
     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. 
     “Low fan pressure ratio” is the pressure ratio across the fan blade alone. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. 
     “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). 
     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 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 . 
     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 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. 
     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. 
     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. 
     The density of the low density filler  72  less than the density of the material of the blade body  64 . In one example, the density of the low density filler  72  is about 8% to 10% of the density of the material of the blade body  64 . Employing the low density filler  72  reduces the weight of the blade body  64 , but allows for the surface area of the inner surface  70  of the blade body  64  to be smooth to provide sufficient surface area for bonding with the cover  74 . 
       FIG. 3  illustrates a press  88  including a lower die  90  and an upper die  92 . An inner surface  96  of the upper die  92  of the press  88  matches a contour of an outer surface of the cover  74  that will be eventually secured to the blade body  64 . 
       FIG. 4  illustrates the lower die  90  of the press  88 . The lower die  90  includes a cavity  91  sunk about 0.3 inch (0.726 mm) to prevent sliding of the blade body  64  in the lower die  90  and to accommodate for the bow/twist shape in an outer surface  86  of the blade body  64  when the blade body  64  is nested in the lower die  90  of the press  88 , as shown in  FIG. 5 . The cavity  91  is defined by walls  94 . 
     Returning to  FIG. 2 , adhesive  78  is applied in the cavities  66  of the blade body  64 . The pre-cut low density filler  72  is then placed in each of the cavities  66 . In one example, the low density filler  72  is manually placed in each of the cavities  66 . In one example, the low density filler  72  is robotically placed in each of the cavities  66 . Each piece of pre-cut low density filler  72  is cut to size to fit in a specific cavity  66 . 
     As shown in  FIG. 6 , when the low density filler  72  is placed in each of the plurality of cavities  66 , an upper surface  98  of the low density filler  72  extends above the inner surface  70  of the blade body  64  (this is shown in an exaggerated manner in  FIG. 6 ). 
     Once the blade body  64  is positioned in the cavity  91  in the lower die  90  of the press  88 , a sheet of plastic can be placed on the inner surface  70  of the blade body  64  to provide a barrier between the upper die  92  and the blade body  86 . The upper die  92  of the press  88  is lowered and pressed against the inner surface  70  of the blade body  64 . The pressure applied by the upper die  92  of the press  88  compresses the low density filler  72 . 
     The upper surface  98  of the low density filler  72  could be pressed slightly below the inner surface  70  of the blade body  64  during pressing to accommodate for any spring back of the low density filler  72  once the upper die  92  is lifted. In one example, the upper surface  98  of the low density filler  72  is compressed so that the height of the low density filler  72  is reduced by about 10%. 
     As shown in  FIG. 7 , once the low density filler  72  springs back, the upper surface  98  of the low density filler  98  is approximately flush with the inner surface  70  of the blade body  86  once pressing is complete. This creates a smooth, flush and continuous surface that can form a strong bond with the cover  74 . Any spaces that do exist between the upper surface  98  of the low density filler  98  and the cover  74  can be filled in with the adhesive  80 . This also eliminates any tolerance stack issues between the blade body  64 , the low density filler  72 , and the cover  74 . 
     In one example, the press  88  containing the blade body  64  remains closed for approximately 30 to 45 minutes. During this time, the adhesive  78  can begin to partially cure such that the blade body  64  can be removed from the lower die  90  of the press  88  with the low density filler  72  sufficiently bonded in the cavities  66  of the blade body  64 . In one example, a pressure of about at least 400 psi is applied. The pressing process combines two steps: compressing the low density filler  72  and assisting in bonding the low density filler  72  to the blade body  64  concurrently. 
     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.