Abstract:
Methods for manufacturing a composite fan inlet housing are disclosed. The methods include inserting a first piece of composite material and a second piece of composite material into a molding tool, inserting an inflatable bladder between the first piece and the second piece, and pressurizing the inflatable bladder to a curing pressure for a length of time sufficient to allow the first piece and second piece to cure.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to turbine engines, and more particularly to methods for manufacturing composite inlet housings used with turbine engines. 
       BACKGROUND 
       [0002]    Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air, which is mixed with fuel and channeled to the combustor. The mixture is then ignited and generates hot combustion gases. The combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator. In the instance of an aircraft engine, the useful work may take the form of a jet exhaust stream. Alternatively, the turbine may power a propeller or a fan. 
         [0003]    Though highly unlikely, it is postulated that a fan blade in the turbine engine may become damaged and tear loose from the rotor during operation. It is further postulated that this unlikely event would cause the damaged fan blade to pierce the surrounding engine housing, which may result in cracks along the exterior surface of the engine housing. To alleviate concerns associated with a postulated fan blade separation event, at least some known engines are assembled with an inlet housing shell that increases the radial and axial stiffness of the engine and that reduces stresses near the engine housing penetration. 
         [0004]    Known fan inlet housing assemblies include a double-walled structure. The primary and secondary walls are typically separated by a distance of one or more inches, depending on the size of the engine, in order to provide structural redundancy. Some existing fan inlet housings include either an aluminum alloy or a graphite epoxy composite material for the primary wall, a graphite epoxy composite material for the secondary wall, and a low density honeycomb or foam core material to effect load transfer between the walls. In these housings, the core is typically arranged between the walls in a “sandwich” configuration. 
         [0005]      FIGS. 1   a  and  1   b  depict an example double-walled assembly  100  ( FIG. 1   a  is provided in axial cross-section with respect to the engine housing, and  FIG. 1   b  is provided in radial cross-section). The primary wall  110  extends axially to a length L 1 . The length L 1  is dependent on the size of the engine, and can readily be selected by a person of ordinary skill in the art. In some implementations, the length L 1  can range from approximately 8 inches to approximately 36 inches, although smaller and larger lengths are possible. The primary wall  110  includes two flanges  111   a , 111   b  located at each axial end thereof. The flanges  111   a , 111   b  are oriented generally perpendicularly with respect to the axial length of the wall  110 . Adjoined to the primary wall  110  is the secondary wall  120 . The secondary wall  120  extends axially along the length of the primary wall  110  at a length L 2 , which is less than L 1 , and can range from approximately 4 inches to approximately 18 inches, although smaller and larger lengths are possible. The secondary wall  120  can be a generally trapezoidal shape, having flanges  121   a , 121   b  oriented parallel to primary wall  110  for adhesively adjoining the secondary wall  120  thereto. The secondary wall has a width W 1 , which can typically range from approximately 1 to 3 or more inches, depending on the strength characteristics desired. Positioned (“sandwiched”) between the primary wall  110  and the secondary wall  120  is a honeycomb or foam material core layer  130 . 
         [0006]    To fabricate the assembly  100 , in the past, the graphite epoxy composite wall structures  110 , 120  were molded under high pressure (for example, approximately 50-100 psi was a typical molding pressure) to achieve the desired properties (strength, load transfer, etc.). In practice, it was observed that high molding pressure caused the low density core  130  to collapse, so the individual walls  110 , 120  were molded separately, and then assembled to the core  130  using an adhesive. The process was labor-intensive and had an undesirably high fabrication cost. 
         [0007]    With reference to  FIGS. 2   a  and  2   b , the current state of the art typically employs a three-step process (illustrated as process flow chart  200   a  in  FIG. 2   a  and as schematic flow diagram  200   b  in  FIG. 2   b ). First, at step  201   a , 201   b,  the primary wall  110  is fabricated as a separate detail by high pressure molding, using mold  140 , if a composite material is used or by machining if a metal material is used. Second, at step  202   a , 202   b,  an adhesive  125  is applied to bond the low-density core  130  to the primary wall  110 . Third, at step  203   a , 203   b,  in-situ fabrication techniques are employed to shape the secondary wall  120  directly to the core  130  and primary wall  110  using low pressure molding (arrows  122 ). For example, approximately 10-15 psi is a typical molding pressure, to avoid collapse of the low density core. This approach results in less than optimal properties in the secondary wall (as compared to past techniques where both were high-pressure molded, then adhered to the core), but somewhat reduces fabrication complexity and therefore cost. As such, there is currently a trade-off between material properties and fabrication cost. 
         [0008]    In an alternative process, a high-density core material could be used, thereby allowing for high-pressure molding to achieve the desired wall characteristics. However, in many applications, high-density core materials add an unacceptable amount of weight to the housing, and are therefore impractical. 
         [0009]    Therefore, what is needed in the art is an improved method for manufacturing a composite fan inlet housing that achieves optimal material properties, including high strength and low weight, while maintaining a low cost of fabrication. 
       BRIEF SUMMARY 
       [0010]    Methods are provided for manufacturing a composite inlet housing. In accordance with one embodiment, a method includes inserting a first piece of composite material and a second piece of composite material into a molding tool, inserting an inflatable bladder between the first piece and the second piece, pressurizing the inflatable bladder to a curing pressure for a length of time sufficient to allow the first piece and second piece to cure, optionally removing the inflatable bladder from the molding tool, and injecting foam between the cured first piece and second piece. The composite material may be configured in a redundant structure to minimize damage caused by the impact of a fan blade separated from a rotating turbine shaft. 
         [0011]    In accordance with a further embodiment, a method includes inserting a first piece of composite material and a second piece of composite material into a molding tool, inserting a multi-segment, connected inflatable bladder between the first piece and the second piece, inserting additional composite material between the segments of the multi-segment, connected inflatable bladder; and pressurizing the inflatable bladder to a curing pressure for a length of time sufficient to allow the first piece, the second piece, and the additional composite material to cure. 
         [0012]    In accordance with yet another embodiment, a method includes inserting a first piece of composite material and a second piece of composite material into a molding tool, inserting an inflatable bladder between the first piece and the second piece, and pressurizing the inflatable bladder to a curing pressure for a length of time sufficient to allow the first piece and second piece to cure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0014]      FIG. 1   a  (prior art) depicts a double-walled fan inlet housing in axial cross-section; 
           [0015]      FIG. 1   b  (prior art) depicts the double-walled fan inlet housing of  FIG. 1   a  in radial cross-section; 
           [0016]      FIG. 2   a  (prior art) depicts a process flow chart for manufacturing a double-walled fan inlet housing; 
           [0017]      FIG. 2   b  (prior art) depicts a process diagram in accordance with the flow chart of  FIG. 2   a;    
           [0018]      FIG. 3  depicts an apparatus for manufacturing a double-walled fan inlet housing in accordance with one embodiment of the invention; 
           [0019]      FIG. 4   a  depicts a process flow chart for manufacturing a double-walled fan inlet housing using the apparatus of  FIG. 3 ; 
           [0020]      FIG. 4   b  depicts a process diagram in accordance with the flow chart of  FIG. 4   a;    
           [0021]      FIG. 5  depicts an apparatus for manufacturing a double-walled fan inlet housing in accordance with another embodiment of the invention; 
           [0022]      FIG. 6   a  depicts a process flow chart for manufacturing a double-walled fan inlet housing using the apparatus of  FIG. 5 ; and 
           [0023]      FIG. 6   b  depicts a process diagram in accordance with the flow chart of  FIG. 6   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
         [0025]    This disclosure, described with reference to the embodiments detailed hereafter, includes methods for high-pressure molding both walls of a double-walled composite fan inlet housing as a single structure in one process step. A fully enclosed space or cavity is reserved for the insertion of a low-density core material. The low density core material is installed in the cavity in a separate step after completion of the molding process. In variations of the described methods, the composite material that forms the double-walled structure can also be used to form in situ shear webs, in which case the low density core material can be omitted. 
         [0026]      FIG. 3  depicts an example apparatus for use in one embodiment of a method for forming a double-walled fan inlet housing. The apparatus includes a molding tool  300  having an upper piece  300   a  and a lower piece  300   b.  The pieces  300   a , 300   b  are brought into abutting contact along lines  310   a , 310   b,  and form a cavity in the general shape of the double-walled housing structure. An inflatable, flexible bladder  320  is inserted within the cavity, the bladder having a fill tube portion  325  that extends through a channel  315  in the lower piece  300   b.  The bladder  320  can be inflated with a fluid, for example, air. In between the bladder  320  and the molding tool  300 , a graphite epoxy composite material is provided in two pieces to form the primary wall  110  and the secondary wall  120 , as shown in  FIG. 3 . While the graphite epoxy composite material is mentioned herein as a suitable material for forming the walls  110 , 120 , the present invention is not limited to any particular composite material, and it is expected that those having ordinary skill in the art will be able to select a suitable composite material for use in particular applications. A gap  313 , also referred to as a bladder fill port, remains in the primary wall  110  coterminous with the channel  315  to allow the bladder fill tube  325  to pass therethrough. 
         [0027]      FIGS. 4   a  and  4   b  depict an example process flow chart  400   a  and process diagram  400   b,  respectively, for use with the apparatus described above in  FIG. 3 . At step  401   a , 401   b,  with the molding tool  300  in the closed position (upper piece  300   a  and lower piece  300   b  brought into abutting contact, as shown), the bladder  320  is inserted between the primary wall  110  composite material piece and the secondary wall  120  composite material piece to form a cavity between the two pieces. Alternatively, the bladder  320  may be positioned with the composite material piece prior to closure of the tool. The bladder  320  is pressurized (arrows  322 ) to force the walls  110 , 120  to conform to the molding  300  tool shape, i.e., the desired shape of the double-walled fan inlet housing. The bladder  320  can be pressurized to a relatively high pressure for curing (as compared to pressures previously used to protect low-density foams from collapsing), for example, approximately 50-100 psi, to ensure the desired characteristics, without fear of collapsing the low-density core, as the low-density core has not yet been put in place. It is also noted that the curing process involves the use of elevated temperatures, for example, approximately 200-300 degrees Fahrenheit. Curing is generally accomplished in about one, two, or more hours at the elevated temperature and pressure. 
         [0028]    At step  402   a , 402   b,  the bladder  320  is depressurized and optionally removed after curing is complete, and a low-density foam material  130  is injected or pumped into the empty cavity through the bladder fill port  313 . Where the bladder  320  is removed, it is selected from a material or treated such that it will release from the molded composite material. Where the bladder  320  is not removed, the bladder remains in place and become a functional element of the structure, and is selected from a material or treated such that it will adhere to the molded composite material. The foam material  130  can be provided in liquid form from a foam container  450  and through a foam-filling tube  451  connected to the container  450 . In one example, the foam is a polypropylene (PP) or a polyurethane (PU) foam. The invention is not limited to any particular type of foam; rather, it is expected that those having ordinary skill in the art will easily be able to select a suitable foam material having the desired density properties for the particular application. The foam is then allowed to set. 
         [0029]    At step  403   a , 403   b,  the foam-filling tube  451  has been removed, and the bladder fill port  313  is optionally plugged using a plug  460  that can be made of a fill material, for example, the same graphite epoxy composite material as the walls  110 , 120 . Adhesive may be required to ensure secure placement of the plug  460 . 
         [0030]      FIG. 5  depicts an example apparatus for use in another embodiment of a method for forming a double-walled fan inlet housing. In this embodiment, the molding tool configuration is generally the same as discussed above with regard to  FIG. 3 . However, a multi-segment, connected bladder is provided having bladder segments  520  (three are shown in this example, however two, three, four, or more segments may be provided in variations of this embodiment) that are fluidly and hermetically connected to one another with connection portions  522 . The segments  520  can be arranged either circumferentially or axial to suit the desired web geometry. The bladder fill tube  325  allows fluid (e.g., air) to enter into a first bladder segment  520 , and the fluid can flow into the additional connected segments  520  through the connection portions  522 . The multi-segment, connected bladder can be pressurized to the same relatively high pressure to allow for high-pressure molding operations. Furthermore, the individual segments  520  are surrounded with additional graphite epoxy composite material  521 , or other suitable composite material. The additional composite material  521 , when cured, forms walls within the cavity for providing the same load transfer between walls  110 , 120  as the foam did in the previous embodiment. In this embodiment, the bladder segments  520  remain in-place as the composite material  521  cures, thereby also forming part of the cavity walls. 
         [0031]      FIGS. 6   a  and  6   b  depict an example process flow chart  600   a  and process diagram  600   b,  respectively, for use with the apparatus described above in  FIG. 5 . At step  601   a , 601   b,  with the molding tool  300  in the closed position, the connected bladder segments  520  are inserted in the desired arrangement between the primary wall  110  and the secondary wall  120  composite material pieces. Alternatively, the bladder segments  520  may be positioned with the composite material piece prior to closure of the tool. The connected bladder segments  520  are pressurized to force the walls  110 , 120  to conform to the molding tool  300  shape, i.e., the desired shape of the double-walled fan inlet housing, and form the cavity. Further, in this embodiment, the additional composite material  521  between the segments is forced into a generally perpendicular (with respect to walls  110 , 120 ) shear web within the cavity. Elevated temperatures and pressures are used in the curing process as described above. 
         [0032]    At step  602   a , 602   b,  the cured inlet housing structure (including primary and secondary walls  110 , 120 , and the perpendicular load transfer webs made of the bladder segments  520  that remain in place and the additional composite material  521 ) is removed from the molding tool  300 . No foam is added. The components  520 , 521  within the cavity form a molded-in-place (in situ) shear web that is designed to afford the double-walled structure similar strength and load transfer characteristic as if foam had been used, but without the need to add foam in an additional step. Also, the bladder fill port  313  can optionally be plugged using the plug  460 , as above. 
         [0033]    The embodiments presented in this disclosure allow a double-walled fan inlet housing to be manufactured using high-pressure molding in a simple process that avoids the cumbersome and costly fabrications processes used previously. Furthermore, embodiments of the present disclosure allow for various combinations of relatively light-weight materials (graphite/epoxy walls, low density foams, etc.) to be used to suit the particular needs of the implementation while maintaining the desired material properties. 
         [0034]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.