Abstract:
A system and a method for making a composite containment casing are provided. The method includes providing a mandrel, applying at least one ply of a material about the mandrel to form a first annular facesheet, applying a plurality of core segments surrounding the first facesheet, forming a casing surrounding the core segments. and curing the facesheet, core segments, and casing together forming a unitary composite containment casing. Alternatively, the facesheet and the core segments can be formed and cured first, and then form and cure the outer casing to complete the manufacture of a unitary composite containment casing,

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The field of the invention relates generally to a system and methods for making composite containment casings, and more specifically, to methods for making composite fan casings having greater stiffness, and having fewer manufacturing steps. 
         [0002]    In gas turbine engines, such as aircraft engines, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel in a combustor. The mixture is then burned and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas expands through the turbine which in turn spins the shaft and provides power to the compressor. The hot exhaust gases are further expanded through nozzles at the back of the engine, generating powerful thrust, which drives the aircraft forward. 
         [0003]    At least some known fan containment case assemblies include segmented composite sandwich panels made separately from each other and the case assembly and then bonded on to the containment case inner surface. These segmented composite sandwich panels provide an air flowpath and sometimes other functions such as acoustic treatment to reduce engine noise. Similar concepts and manufacturing processes are used on both metallic and composite fan cases, and used by most manufacturers. Such a process of assembly is costly in terms of labor and time to produce the final casing. Moreover, such a process produces a less stiff casing due to many pieces being bonded together to form the final casing. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one embodiment, a method for making a composite containment casing includes providing a mandrel, applying at least one ply of a material about the mandrel to form a first annular facesheet, applying a plurality of core segments surrounding the first facesheet, forming a casing surrounding the core segments using an automated fiber placement (AFP) process, and curing the facesheet, core segments, and casing together forming a unitary composite containment casing. 
         [0005]    In another embodiment, a method of forming a composite containment casing assembly includes forming a first annular radially inner facesheet using an automated fiber placement (AFP) process, installing a core surrounding the facesheet forming a core assembly, forming a radially outer casing surrounding the core using the AFP process, curing the casing assembly. 
         [0006]    In yet another embodiment, a composite containment casing system includes a first radially inner annular facesheet layer configured to surround a gas turbine engine duct, a core assembly surrounding said facesheet layer, and a casing structure wound around the core assembly, said facesheet layer, core assembly, and said casing structure cured together to form a unitary containment casing system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIGS. 1-5  show exemplary embodiments of the methods and system described herein. 
           [0008]      FIG. 1  is a schematic representation of one embodiment of a conventional gas turbine engine that generally includes a fan assembly and a core engine. 
           [0009]      FIG. 2  is a side cross-sectional view of a portion of composite fan containment casing in accordance with an exemplary embodiment of the present invention. 
           [0010]      FIG. 3  is a flow chart of a method of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. 
           [0011]      FIG. 4  is a flow chart of a method of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. 
           [0012]      FIG. 5  is a flow chart of a method of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to forming of composite structures in industrial, commercial, and residential applications. 
         [0014]    As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
         [0015]    With a composite fan containment case, it is now feasible to integrate the sandwich panels as part of the fan containment case design, and to fabricate them together with the fan containment case. In various embodiments, of the present disclosure automated fiber placement (AFP) is used to automatically place multiple individual tows formed of, for example, a pre-impregnated composite material onto a mandrel at high speed, using a numerically controlled, articulating robotic placement head to dispense, clamp, cut and restart as many as 32 tows simultaneously. Advantages of fiber placement include processing speed, reduced material scrap and labor costs, parts consolidation and improved part-to-part uniformity. However, the general design and manufacturing concepts described here are applicable to other manufacturing processes such as hand layup process. 
         [0016]    In one embodiment, the sandwich panels are fabricated as a full 360° casing structure. The sandwich structure is inspected and cured separately from the casing or the casing is formed with the sandwich structure and the entire assembly is cured together forming a unitary sandwich panel/casing structure. The casing and other portions of the structure are formed of a pre-impregnated composite material laid using an automated fiber placement or any other appropriate method. 
         [0017]      FIG. 1  is a schematic representation of one embodiment of a conventional gas turbine engine  10  that generally includes a fan assembly  12  and a core engine  14 . Fan assembly  12  may include a composite fan casing  16  having a body  17 , and an array of fan blades  18  extending radially outwardly from a rotor disc  20 . Core engine  14  may include a high-pressure compressor  22 , a combustor  24 , a high-pressure turbine  26  and a low-pressure turbine  28 . Engine  10  has an intake end  30  and an exhaust end  32 . 
         [0018]      FIG. 2  is a side cross-sectional view of a portion  300  of composite fan containment casing  16  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, a layer of abradable material  202  is coupled to casing  16  and is configured to extend axial length  204  outboard of fan blade  18 . Casing  16  includes first layer  206  formed by wrapping layers of tow around a mandrel (not shown) shaped complementary to a desired casing inside surface using for example, an automated fiber placement (AFP) process. Layer  206  may also be formed of a variable thickness over the axial extent of layer  206 . Moreover, layer  206  may extend the entire axial length  208  or may only extend over a partial distance of length  208 . 
         [0019]    Layer  206  may be cured separately from other casing components or may be cured after other casing components have been coupled to layer  206 . A layer of non-composite filler material  210  is applied to a radially outer surface of layer  206 . Layer  210  may be applied in a manual process and may be coupled to layer  206  using adhesives or mechanical means. Layer  210  usually comprises circumferential segments of material positioned around layer  206  of casing  16 . Each segment of layer  210  may extend along the entirety of length  208  or may extend only partially along length  208 . Moreover, layer  210  may be formed of various smaller “tiles” of material positioned in an overlapping and/or abutting configuration. 
         [0020]    Casing  16  may also include a second facesheet layer  212 . Layer  212  is also applied using an AFP process around layer  210 . In various embodiments, layers  206 ,  210 , and  212  are cured together forming a single annular body comprising a composite shell surrounding the filler material. 
         [0021]    The assembly process is monitored by inspections of the components of casing  16  at intermediate steps during the process. For example, when layer  206  is fabricated from segments, each segment may be inspected after curing and any not meeting manufacturing tolerances may be discarded or reworked. Generally, after each curing step, the solid component is inspected for defects. Such inspections can reduce the wastage of defects in the process, but also may increase manufacturing costs and structural strength of the final casing  16 . Generally, when more components are cured together into a unitary piece, the stronger the piece is. When more components are formed separately and subsequently bonded together, the less stiff and/or strong the final casing structure will be. 
         [0022]    Casing  16  also includes a radially outer casing layer  214  formed of composite material using the AFP process. The casing is built up to desired outer dimensions and the entire casing assembly is cured to form a unitary annular structure suitable for housing a gas turbine engine. 
         [0023]      FIG. 3  is a flow chart of a method  400  of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method  400  includes forming  402  a facesheet extending 360° about a mandrel. In one embodiment, the facesheet is formed by manually positioning a plurality of layers of tow pre-impregnated with a resin, such as an epoxy, around the mandrel. In various embodiments, the facesheet is formed using an automated process, such as, an automated fiber placement (AFP) process. Method  400  also includes installing  404  a layer of core material surrounding the facesheet layer. The core material is generally a honeycomb or foam material, but may also include open structures, such as a truss structure. The layer of core material may be installing manually surrounding the facesheet and may be adhered to the facesheet by adhesives or other bonding process. A containment casing is formed  406  about the layer of core material using the AFP process to build up a layer of composite material, for example, tows pre-impregnated with resin. The build up process may apply an axially variable thickness of composite material to form an outer surface of the casing matching predetermined specifications. Method  400  includes curing  408  the entire casing structure together to form a unitary casing structure. The cured casing structure is then inspected  410  to ensure quality of the casing forming process. 
         [0024]      FIG. 4  is a flow chart of a method  500  of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method  500  includes forming  502  a facesheet extending 360° about a mandrel. In one embodiment, the facesheet is formed by manually positioning a plurality of layers of tow pre-impregnated with resin around the mandrel. In various embodiments, the facesheet is formed using an automated process, such as, an automated fiber placement (AFP) process. Method  500  also includes installing  504  a layer of core material surrounding the facesheet layer. The core material is generally a honeycomb or foam material, but may also include open structures, such as a truss structure. The layer of core material may be installing manually surrounding the facesheet and may be adhered to the facesheet by adhesives or other bonding process. A second facesheet may be applied to the outer surface of the layer of core material for stability of the layers and the facesheets and core material are then cured  506  together to form a unitary interior casing portion. After the assembly is inspected  508 , a containment casing is formed  510  about the assembly using the AFP process to build up a layer of composite material, for example, tows pre-impregnated with resin. The build up process may apply an axially variable thickness of composite material to form an outer surface of the casing matching predetermined specifications. Method  500  includes curing  512  the entire casing structure together to form a unitary casing structure. The cured casing structure is then inspected  514  to ensure quality of the casing forming process. 
         [0025]      FIG. 5  is a flow chart of a method  600  of forming a composite containment casing in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method  600  includes forming  602  a segmented facesheet that extends less than 360° circumferentially. Each segmented facesheet may be formed individually and cured  604  separately from others of the plurality of facesheets needed to circumscribe the fan duct when the engine is fully assembled. In one embodiment, the facesheet is formed by manually positioning a plurality of layers of tow pre-impregnated with resin. In various embodiments, the segmented facesheet portions are formed using an automated process, such as, an automated fiber placement (AFP) process. Method  600  also includes inspecting  606  the cured facesheets and installing  608  a layer of core material to the facesheet layers found to meet quality requirements. The core material is generally a honeycomb or foam material, but may also include open structures, such as a truss structure. The layer of core material is installed manually to the facesheet and may be adhered to the facesheet by adhesives or other bonding process. The facesheet and core material are then cured  610  together to form a panel. A containment casing is formed  614  about the mandrel using the AFP process to build up a layer of composite material, for example, tows pre-impregnated with resin. The build up process may apply an axially variable thickness of composite material to form an outer surface of the casing matching predetermined specifications. Method  600  further includes curing  616  the outer casing structure separately from the panels to form a cured casing structure. The cured casing structure is then inspected  618  to ensure quality of the casing forming process. Method  600  includes bonding  620  the cured panels to a radially inner surface of the cured casing structure and inspecting the entire casing  16 . 
         [0026]    Method  400  creates a potentially lower cost casing structure than methods  500  or  600  in that the major components are formed in sequence without a curing or inspection step until the end of the process where the entire structure is cured together and then inspected. This permits savings in fabrication on the order of approximately 20% over other methods. However, the drawback is if the final structure does not meet inspection standards the entire assembly must be rejected or reworked, potentially causing great loss of time and financial resources. Method  600  includes curing and inspection steps at many points in the fabrication process allowing for rejection of nonconforming components early in the fabrication process, which may increase costs and manufacturing time. Moreover, the processes described in methods  400  and  500  also provide for a stiffer and stronger casing than method  600 . 
         [0027]    The above-described embodiments of a methods and system of forming a composite containment casing assembly provides a cost-effective and reliable means for providing additional stiffness, strength and containment capability to engine casings over current segmented panel designs. More specifically, the methods and system described herein facilitate reducing man-hour assembly requirements. In addition, the above-described methods and system facilitate forming a stiffer and stronger casing structure. As a result, the methods and system described herein facilitate forming lighter and stronger casings for rotatable machines in a cost-effective and reliable manner. 
         [0028]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.