Abstract:
Methods and apparatus for curing curved cylinder-like workpieces (e.g., in the shape of a half or full barrel) made of composite material, such as nacelle honeycomb core composite sandwich structures. These methods enable tailored curing of composite nacelle structures, to significantly reduce capital cost and fabrication cycle time. In lieu of an autoclave or oven, a pressurized ring-shaped cure volume is defined by a partitioned enclosure that mimics the cylinder-like shape of the composite nacelle structure with only limited clearance (e.g., a partitioned enclosure comprising inner and outer concentric cylinder-like walls). A tool (e.g., a mandrel) and at least one composite nacelle structure supported thereon are placed in the cure volume for curing. Integrally heated tooling, optionally in combination with other heating methods, such as infrared heaters, is utilized to provide the temperature profile necessary for cure.

Description:
BACKGROUND 
       [0001]    This disclosure generally relates to methods and apparatus for fabricating composite structures. In particular, this disclosure relates to methods and apparatus for curing composite structures, such as honeycomb sandwich composite structures. 
         [0002]    Airplane manufacturers are under increasing pressure to produce lightweight, strong, and durable aircraft at the lowest cost for manufacture and life-cycle maintenance. An airplane must have sufficient structural strength to withstand stresses during flight, while being as light as possible to maximize the performance of the airplane. To address these concerns, aircraft manufacturers have increasingly used fiber-reinforced resin matrix composites. 
         [0003]    These composites provide improved strength, fatigue resistance, stiffness, and strength-to-weight ratio by incorporating strong, stiff, carbon fibers into a softer, more ductile resin matrix. The resin matrix material transmits forces to the fibers and provides ductility and toughness, while the fibers carry most of the applied force. Unidirectional continuous fibers can produce anisotropic properties, while woven fabrics produce quasi-isotropic properties. Honeycomb core is often sandwiched between composite sheets to provide stiff panels having the highest specific strength. More specifically, honeycomb core sandwich panels or composite structures, which typically comprise composite laminate skins co-cured with adhesives to the honeycomb core, are widely used in aerospace applications, among others, because of their high stiffness-to-weight (i.e., “specific stiffness”) and strength-to-weight (i.e., “specific strength”) ratios. 
         [0004]    Honeycomb sandwich composite structures may be fabricated utilizing various composite forming methods. The most commonly employed technique involves the use of a vacuum bag molding assembly wherein an impervious membrane or “vacuum bag” is employed for consolidating the composite skins or layers and ensuring proper adhesion thereof to the centrally disposed honeycomb core. More specifically, the lower or base composite skin, the honeycomb core, and the upper or face composite skin are sequentially laid in a rigid mold member so that the honeycomb core is overlaid or covered by the upper and lower composite skins. The upper and lower composite skins are typically formed from uncured “prepreg” or “B-stage” laminates that comprises a fiber reinforcement such as graphite, aramid, or fiberglass fibers (e.g., linear, weaves, or both) disposed in a binding polymeric matrix such as epoxy, phenolic, or other similar organic resinous material. Film adhesive typically forms the bonds between the upper and lower composite skins and the honeycomb core. A vacuum bag is disposed over the rigid mold member and seals thereto, thereby forming a mold cavity that is occupied by the uncured/unbonded composite lay-up. The mold cavity is then evacuated to subatmospheric pressure within the mold, and superatmospheric pressure is applied to the exterior (in an autoclave), and the temperature of the composite lay-up is increased while in the autoclave to cure the lay-up. The combination of subatmospheric internal pressure and superatmospheric external pressure consolidate the composite skins, remove air and volatiles from the resin binder, and apply the necessary compaction pressure to ensure full and uniform adhesion of the lay-up. 
         [0005]    Because of the noise regulations governing commercial transport aircraft, high bypass engines incorporate acoustic panels within the nacelles. Conventionally, these elements are made with an inner perforated skin, a surrounding buried septum honeycomb core, and a non-perforated outer skin. 
         [0006]    Curing of complex composite nacelle structures traditionally requires an autoclave to provide the temperature and pressure necessary for cure. Due to the high capital cost, autoclaves are typically sized to cure multiple parts in a batch, and the cost of purchase and operation is high due to the volume. Other methods of manufacturing, such as resin infusion, have been successfully used to eliminate the need for an autoclave or oven. However, nacelle honeycomb core composite structures, including nacelle acoustic structures in their current architecture, cannot be readily manufactured using other methods. 
         [0007]    Improvements in methods for curing nacelle honeycomb core composite sandwich structures that reduce costs and increase production rates are wanted. 
       SUMMARY 
       [0008]    The subject matter disclosed herein is directed to methods and apparatus for curing curved cylinder-like workpieces (e.g., in the shape of a half or full barrel) made of composite material, such as nacelle honeycomb core composite sandwich structures. The methods disclosed herein enable tailored curing of curved cylinder-like workpieces, such as composite nacelle structures, to significantly reduce capital cost and fabrication cycle time. These methods take advantage of the cylinder-like (e.g., the diameter may vary in an axial direction) geometry associated with nacelle components. 
         [0009]    In lieu of an autoclave or oven, a pressurized ring-shaped cure volume is defined by a partitioned enclosure that mimics the cylinder-like shape of the uncured composite nacelle structure with only limited clearance (e.g., a partitioned enclosure comprising inner and outer concentric cylinder-like walls). In accordance with some embodiments, the top and bottom of the enclosure volume are defined by a fixed bottom plate and a movable top plate; the top plate is attached or connected to a pair of concentric cylinder-like walls; and a tool (e.g., a mandrel) and one or more composite nacelle structures supported thereon are disposed in the ring-shaped cure volume for curing. Integrally heated tooling, optionally in combination with other heating methods, such as infrared heaters, is utilized to provide the temperature profile necessary for curing the uncured composite nacelle structure. No changes in part configuration or materials are required, so the architecture of nacelle acoustic structures and weight efficiency of honeycomb core sandwich structure can be preserved. 
         [0010]    The methods and apparatus disclosed in detail hereinafter eliminate the need for a typical autoclave but retain the ability to use equivalent temperature and pressure for adequate cure, and significantly reduce the cure system cost. Furthermore, the mode(s) of heat transfer used in the methods disclosed in detail below enable more rapid and uniform heating. This reduces cure cycle time and energy consumption, and ensures superior part cure quality. Finally, the methods and apparatus disclosed herein provide an approach to composite part cure that is “right-sized” to the part and thus supports lean manufacturing objectives. 
         [0011]    One aspect of the subject matter disclosed in detail below is an apparatus for curing a composite structure, comprising: an enclosure comprising a top plate, a base, and an outer wall disposed between the top plate and the base, the outer wall having a closed contour; an inner wall disposed between the top plate and the base and surrounded by the outer wall, the inner wall having a closed contour, wherein surfaces of the inner and outer walls, the top plate, and the base define a ring-shaped cure volume; and a hollow tool comprising a surface having a closed contour and heating elements, wherein the hollow tool surrounds the inner wall, is surrounded by the outer wall, and is thermally coupled to the composite structure to allow heat transfer from the heating elements to the composite structure. In accordance with some embodiments, the heating elements transform electric current into heat. In accordance with other embodiments, the heating elements carry heated fluid. The apparatus may further comprise a heater attached to an outer surface of the inner wall and/or a heater attached to an inner surface of the outer wall. 
         [0012]    Another aspect of the subject matter disclosed herein is a method for curing a composite structure, comprising: (a) forming a tool-composite structure assembly by placing an uncured composite structure in contact with a surface of a tool having a closed contour and having integrated heating elements; (b) placing the tool-composite structure assembly on a base; (c) enclosing a ring-shaped cure volume having an outer boundary that surrounds the tool; (d) activating the integrated heating elements to heat the uncured composite structure during a cure cycle; and (e) producing a specified pressure inside the ring-shaped cure volume during the cure cycle. The method may further comprise: removing the tool-composite structure assembly from the ring-shaped cure volume; and demolding the composite structure from the tool. In accordance with some embodiments, the uncured composite structure has a closed contour, surrounds the tool and is surrounded by the outer boundary of the ring-shaped cure volume. The method further comprises coupling the heating elements integrated in the tool to a source of energy after step (b) and prior to step (d). 
         [0013]    A further aspect of the subject matter disclosed herein is an apparatus for curing a composite structure, comprising: an enclosure comprising a top plate, a base, and a wall disposed between the top plate and the base, the wall having a closed contour; a tool disposed between the top plate and the base and surrounded by the wall, the tool comprising a surface having a closed contour and heating elements, wherein the surface of the tool and respective surfaces of the wall and the top plate at least partly define a ring-shaped cure volume, and the tool is thermally coupled to the composite structure to allow heat transfer from the heating elements to the composite structure. In accordance with some embodiments, the cure volume is further partly defined by a surface of the base. This apparatus may further comprise means for coupling the heating elements in the tool to a source of energy and a heater attached to an inner surface of the wall. In accordance with some embodiments, the heating elements transform electric current into heat and the source of energy is a current generator electrically coupled to the heating elements. In accordance with other embodiments, the heating elements carry heated fluid and the source of energy is a source of heated fluid. 
         [0014]    Yet another aspect is a system comprising: an enclosure comprising a top plate, a base, and an outer wall disposed between the top plate and the base, the outer wall having a closed contour that forms an outer boundary of an internal volume of the enclosure; a means for partitioning the internal volume of the enclosure to form a ring-shaped cure volume disposed between the wall and the partitioning means; an uncured composite structure disposed within the cure volume; heating elements situated to heat the uncured composite structure during a cure cycle; and means for producing a specified pressure inside the cure volume during the cure cycle. In accordance with some embodiments, the means for partitioning comprises a tool comprising a surface having a closed contour, the heating elements being integrated in the tool, and the tool being surrounded by the outer wall and thermally coupled to the uncured composite structure to allow heat transfer from the heating elements to the uncured composite structure. In accordance with other embodiments, the means for partitioning comprises an inner wall, the apparatus further comprising a hollow tool comprising a surface having a closed contour, the heating elements being integrated in the hollow tool, wherein the hollow tool surrounds the inner wall, is surrounded by the outer wall, and is thermally coupled to the uncured composite structure to allow heat transfer from the heating elements to the uncured composite structure. 
         [0015]    Other aspects of methods and apparatus for curing composite nacelle structures are disclosed and claimed below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a diagram representing an isometric view showing the geometry of some components of an assembled apparatus for curing a composite nacelle structure in accordance with some embodiments. The assembled apparatus is shown with a top plate of an enclosure removed. 
           [0017]      FIG. 2  is a diagram representing a sectional view of some components of an assembled apparatus for curing a composite nacelle structure in accordance with one embodiment. 
           [0018]      FIG. 3A  is a diagram representing a sectional view of a portion of a sealed interface between an annular recess in a base and a bottom edge of a plug in accordance with one embodiment. 
           [0019]      FIG. 3B  is a diagram representing a sectional view of a portion of a sealed interface (indicated by a dashed circle in  FIG. 2 ) between a base and a bottom edge of a plug in accordance with another embodiment. 
           [0020]      FIG. 4  is a diagram representing a sectional view of a portion of an assembled part curing enclosure containing a tool-mounted part to be cured (the depicted portions being indicated by a dashed circle in  FIG. 2 ) in accordance with one embodiment. 
           [0021]      FIG. 5  is a diagram representing a sectional view of some components of an assembled apparatus for curing a composite nacelle structure in accordance with a plug-less embodiment. 
           [0022]      FIG. 6  is a block diagram showing some components and subsystems of a system for assembling the apparatus depicted in  FIG. 2  or  5 . 
           [0023]      FIG. 7  is a block diagram showing some subsystems of a system for curing a composite nacelle structure in accordance with various embodiments. 
           [0024]      FIG. 8  is a flow diagram of an aircraft production and service methodology. 
           [0025]      FIG. 9  is a block diagram showing systems of an aircraft. 
       
    
    
       [0026]    Reference will hereinafter be made to the drawings in which similar elements in different drawings bear the same reference numerals. 
       DETAILED DESCRIPTION 
       [0027]    Various embodiments of an apparatus having a ring-shaped cure volume for curing cylinder-like composite structures, such as composite nacelle structures, wrapped around the surface of a tool will now be described in detail for purposes of illustration only. The apparatus comprises an enclosure that defines a ring-shaped cure volume in which the uncured composite structure is disposed. In accordance with the embodiment shown in  FIGS. 1 ,  2  and  4  (described in detail below), the inner and outer boundaries of the ring-shaped cure volume are respectively formed by inner and outer walls (also referred to herein as “plug” and “sleeve” respectively) which extend from a top plate to a base. The uncured composite structure is supported by and in contact with a surface of a tool having a closed contour, which tool is disposed within the ring-shaped cure volume. In accordance with another embodiment, the tool that supports the uncured composite structure forms the inner boundary of the ring-shaped cure volume, as will be described in detail below with reference to  FIG. 5 . 
         [0028]    A first illustrative geometry of an apparatus for curing a composite structure  22  is schematically depicted in  FIGS. 1 and 2 .  FIG. 1  represents an overall isometric view of components of the apparatus with a top plate omitted, while  FIG. 2  represents a sectional view of an apparatus including a top plate  14 . In this example, an uncured cylinder-like composite structure  22  is completely wrapped around and supported by a tool  20 , which may take the form of a hollow mandrel made of metal or composite material. The resulting tool-composite structure assembly is disposed between a plug  18  and a sleeve  16 , which (as best seen in  FIG. 1 ) may comprise concentric circular cylindrical inner and outer walls respectively. 
         [0029]    Preferably, the profile of tool  20  is a closed contour. The tool  20  (or tools) can be a closed volume or may be segmented and still work. The external surface of tool  20  may be shaped to conform to the inner mold line of the composite structure  22 . If the inner mold line of the composite structure  22  is axially symmetric, then the external surface of tool  20  will approximate a surface of revolution. Examples of surfaces of revolution generated by a straight line are cylindrical and conical surfaces, depending on whether or not the line is parallel to the axis. Surfaces of revolution generated by a curved line have a radius that varies along the axis. If the inner mold line of the composite structure  22  is not axially symmetric, then the external surface of tool  20  will not approximate a surface of revolution. 
         [0030]    As shown in  FIG. 2 , the upper ends of plug  18  and sleeve  16  are attached or connected to the top plate  14 , while the lower ends of plug  18  and sleeve  16  are seated on a base  12 , which may comprise a circular plate. Respective surfaces of base  12 , top plate  14 , and sleeve  16  form an enclosure  10  having an internal volume which is partitioned to form a ring-shaped cure volume  8 . In this embodiment, the internal volume of the enclosure  10  is partitioned by plug  18 , which forms the radially inner boundary of the ring-shaped cure volume  8 , while sleeve  16  forms the radially outer boundary of the ring-shaped cure volume  8 . The assembly comprising tool  20  and composite structure  22  is disposed within the ring-shaped cure volume  8 . System interfaces for providing electrical power and for controlling the pressure inside the ring-shaped cure volume  8  may be incorporated in top plate  14  or base  12 . In addition, equipment for monitoring the temperature and pressure inside the ring-shaped cure volume  8  may be incorporated in top plate  14  or base  12 . 
         [0031]    Although not shown in  FIGS. 1 and 2 , the tool  20  has a multiplicity of heating elements integrated therein (see, e.g., heating elements  52  in  FIG. 7 ). These heating elements may be distributed around the entire circumference of tool  20  and are thermally coupled to the composite structure  22  via the tool surface (which is in contact with the composite structure  22 ) to allow conduction and/or radiation of heat from the heating elements into the composite structure  22 . In accordance with some embodiments, the heating elements are resistive heating elements, embedded in tool  20 , which transform electric current into heat. In accordance with other embodiments, the heating elements embedded in tool  20  are pipes, tubes or capillaries which carry heated fluid (e.g., superheated steam or hot oil). 
         [0032]    The apparatus further comprises means for coupling the heating elements in tool  20  to a source of energy (not shown in  FIG. 2 ). In the example shown in  FIG. 2 , the tool  20  is seated on a circular manifold  24 , which manifold  24  in turn is attached or connected to the base  12  and coupled to provide heating. The manifold  24  is disposed between sleeve  16  and plug  18 . In cases where resistive heating elements are used, the manifold  24  may comprise electrical conductors and switches for providing electrical current from a current generator to the resistive heating elements. In cases where the heating elements convey heated fluid, the manifold  24  may comprise pipes, tubes or channels incorporated in tool  20  for distributing heated fluid current from a source of heated fluid to the distribution network inside the manifold  24 . 
         [0033]    The apparatus shown in  FIGS. 1 and 2  is suitable for curing composite nacelle structures. Given the generally cylindrical shape of composite nacelle structures, it is assumed for the purpose of illustration only that tool  20  and composite structure  22  are surfaces of revolution. However, it should be appreciated that, in the alternative, tool  20  and composite structure  22  do not need to be surfaces of revolution. In addition, as explained in detail below, the composite structure need not have a closed contour. To simplify the discussion, it is also assumed herein that sleeve  16  and plug  18  are circular cylindrical. However, it should be appreciated that, in the alternative, sleeve  16  and plug  18  do not need to be circular or cylindrical. 
         [0034]    The composite structure  22  depicted in  FIGS. 1 and 2  may comprise any one of the following typical nacelle composite structures: 
         [0035]    (a) an inlet inner acoustic panel in one 360-degree structure or in a plurality of segments, depending on the design; 
         [0036]    (b) a fan cowl panel, typically in two segments of approximately 160 degrees each; 
         [0037]    (c) a thrust reverser outer acoustic panel, typically in two segments of approximately 160 degrees each; 
         [0038]    (d) a thrust reverser outer cowl panel, typically in two segments of approximately 160 degrees each; or (e) a thrust reverser inner wall panel (which, although not completely cylindrical, could conceivably be cured using the apparatus disclosed herein). 
         [0039]    Still referring to  FIGS. 1 and 2 , the tool  20  may take the form of a bond assembly jig that is used as the layup and cure mandrel for the composite structure. The tool  20  can be designed to be integrally heated using known methods (e.g., electrical heating elements, fluid heating, etc.). The tool  20  is preferably indexed to the base  12 , for example, using mechanical guides and pins in a well-known manner. The tool  20  may also be designed to allow de-molding of the composite structure  22  as required using existing tool design approaches. 
         [0040]    The base  12  depicted in  FIGS. 1 and 2  is the platform on which the tool  20  rests during a curing operation. As depicted in  FIG. 4 , the base  12  also have provisions  50  for connecting the manifold  24  to the energy source (e.g., electrical supply or heated fluid source). In addition, the sleeve  16  and plug  18  could be fitted with suitable heaters in a suitable pattern around their circumferences to provide uniform heating.  FIG. 4  shows one heater  30  attached to an outer surface of plug  18  and another heater  32  attached to an inner surface of sleeve  16 . Similar heaters can be placed around the respective circumferences of sleeve  16  and plug  18 . 
         [0041]    Referring again to  FIG. 2 , the sleeve  16  forms the outer boundary of ring-shaped cure volume  8 . Sleeve  16  is designed to withstand cure pressure and sized diametrically to minimize the cure volume. The top of sleeve  16  may be attached or connected to the top plate  14  so that the sleeve  16  is raised or lowered when the top plate  14  is raised or lowered. The bottom of sleeve  16  can be sealed against the base  12  by means of a typical high-temperature pressure seal. The sleeve  16  should be designed to minimize heat loss during the cure cycle and may be provided with additional heating elements. 
         [0042]    The plug  18  forms the inner boundary of the ring-shaped cure volume  8 . Plug  18  is also designed to withstand cure pressure and sized diametrically to minimize the cure volume. The top of plug  18  may be attached or connected to the top plate  14  so that the plug  18  is also raised or lowered when the top plate  14  is raised or lowered. The bottom of plug  18  can also be sealed against the base  12  by means of a typical high-temperature pressure seal. The plug  18  should also be designed to minimize heat loss during the cure cycle and may be provided with additional heating elements. The plug  18  would not be required if it is acceptable for the entire cylindrical volume to be the cure volume, based on impact to the equipment and cure cycle. 
         [0043]      FIGS. 3A and 3B  are detailed views taken from  FIG. 2  that show respective interfaces between base  12  and the bottom of plug  18  in accordance with respective implementations. 
         [0044]    In the implementation depicted in  FIG. 3B , the plug-base interface is a planar interface comprising a seal  28  (e.g., an O-ring with opposing seal grooves formed in the surface of base  12  and the end face of plug  18 ). The bottom of the sleeve  16  can be sealed to the base  12  in a similar manner. 
         [0045]    In the implementation depicted in  FIG. 3A , the interface is a recessed interface comprising a seal  28 . This recessed interface comprises a recess  26  formed in base  12  which receives the bottom of plug  18 , either with or without draft (e.g., beveling) on the base surface to facilitate insertion. This recessed interface could be designed to react cure pressure loads. The bottom of the sleeve  16  can be sealed to the base  12  in a similar manner. 
         [0046]      FIG. 5  is a diagram representing a sectional view of some components of an assembled apparatus for curing a cylinder-like composite nacelle structure in accordance with an alternative embodiment which does not use a plug. In accordance with this concept, a portion of a tool  34  forms the inner boundary of the ring-shaped cure volume  8  and the plug is eliminated. The tool  36  has heating elements (of the types previously described) integrated therein and should be designed to withstand the cure pressure. The tool  34  is thermally coupled to the composite nacelle structure  22  to allow conduction and/or radiation of heat from the heating elements to the composite nacelle structure  22 . 
         [0047]    In accordance with the implementation depicted in  FIG. 5 , the tool  36  comprises a cylinder-like wall  36 , an annular radial flange  38  connected to a bottom of the conical wall  36  and seated on the base  12 , and a horizontal member  40  disposed inside and connected to the cylinder-like wall  36  near the top of the latter. Respective surfaces of the top seal  14 , sleeve  16 , cylinder-like wall  36 , and annular radial flange  38  define a ring-shaped cure volume  8 . The top of the cylinder-like wall  36  abuts the top plate  14  with a pair of seals  28  therebetween. The bottom of sleeve  16  abuts the annular radial flange  38  of tool  34  with a seal  28  therebetween. An appropriate interface between the heating elements integrated in the tool  34  and the source of energy (e.g., heated fluid or electric current) can be provided in the base  12 , the interface elements being aligned by manipulation of tool  34  as it is lowered onto the base  12 . 
         [0048]    The horizontal member  40  may be designed to withstand the cure pressure in ring-shaped cure volume  8 . For example, horizontal member  40  may comprise a plate with supporting structure as required to react pressure loads. In accordance with an alternative implementation, the annular radial flange  38  and horizontal member of tool  34  could be eliminated if the cylinder-like wall  36  were designed to react pressure loads, with or without reaction of pressure loads by top plate  14  and base  12 . In this case the top and bottom of the cylinder-like wall  36  of tool  34  will be respectively sealed to top plate  14  and base  12 . 
         [0049]    The apparatus depicted in  FIG. 2  is assembled by first placing an uncured composite structure  22  in contact with a surface of a tool  20  having a closed contour and having integrated heating elements, the result being a tool-composite structure assembly. That tool-composite structure assembly is then placed on a base  12 .  FIG. 6  is a block diagram showing some components and subsystems of a system for assembling the apparatus depicted in  FIG. 2 . The tool  20  (with the uncured composite structure supported thereon) is manipulated (indicated by a downward arrow in  FIG. 6 ) into proper position (using indexing) onto the base  12  by tool handling equipment  44 . When the tool  20  is positioned correctly, the heating elements integrated in the tool  20  will be coupled to a source of energy via the manifold  24  seen in  FIG. 2 . After the heating elements have been successfully coupled, the top plate  12 , with sleeve  18  and plug  16  attached or connected thereto, is lowered (indicated by a downward arrow in  FIG. 6 ) into position using lifting equipment  42 . More specifically, the rigid structure formed by top plate  14 , sleeve  16  and plug  18  is lowered until the bottom edges of sleeve  16  and plug  18  abut and are sealed against the upper surface of base  12 , as seen in  FIG. 2 . Optionally, the bottom edges of sleeve  16  and plug  18  are inserted into recesses formed in base  12 , as depicted in  FIG. 3A . 
         [0050]    Upon completion of the assembly of the apparatus depicted in  FIG. 2 , an airtight ring-shaped cure volume  8  is formed. The temperature and pressure inside the cure volume are then controlled in accordance with the cure cycle specified for the particular uncured composite structure being cured. As depicted in  FIG. 7 , the heating elements  52  inside the cure volume  8  are activated by a temperature control system  46  while a specified pressure is produced inside the cure volume  8  by a pump  54  operated by a pressure control system  48 . The heating elements  52  includes at least a plurality of heating elements integrated in the tool, which heat the uncured composite structure by thermal conduction and/or radiation, and optionally also includes heaters  30  and  32  seen in  FIG. 4 , which heat the atmosphere inside the cure volume  8 . 
         [0051]    After the cure cycle has been completed, the heating elements  52  and pump  54  are turned off and the cured composite structure is allowed to cool. The top plate  14  and associated walls are raised by the lifting equipment  42  (see  FIG. 6 ); then the tool  20  (with the cured composite structure supported thereon) is raised and separated from the base  12  using the tool handling equipment  44 ; and then the cured composite structure is demolded from the tool  20 . 
         [0052]    The curing apparatus and methodology disclosed herein has the following technical advantages: 
         [0053]    (1) A typical cure vessel (autoclave) must be significantly larger than the part/tool, and is usually sized to accommodate curing of multiple parts (batch processing). Thus the energy and inerting required to achieve the necessary cure pressure profiles and inert environment is significant. The apparatus disclosed herein only involves pressurization and inerting of a volume that is only nominally larger than the part/tool. 
         [0054]    (2) The mode of heat transfer in an autoclave or oven to heat the tool/part is primarily convection, which is inefficient, and consistent air velocities which are essential for uniform curing are difficult to achieve, especially when multiple parts are cured simultaneously. The apparatus disclosed herein provides heat via thermal conduction and/or radiation using integrally heated tools, supplemented as required by other heating methods such as infrared heaters (radiation). This enables increased temperature and pressure ramp rates, and thus reduces energy consumption and fabrication cycle time. 
         [0055]    (3) Given their size and complexity, the cost and lead time to procure autoclaves is much higher than the smaller cure apparatus disclosed herein. 
         [0056]    (4) The methodology disclosed herein involves an approach to composite part cure that is “right-sized” to the part and supports lean manufacturing objectives. 
         [0057]    (5) With a typical autoclave, achieving current maximum cure temperature ramp rates (e.g., 5° F./minute) can be unachievable for larger or more complicated nacelle composite parts. The apparatus and methodology disclosed herein not only make that possible, but also enable far more rapid and uniform heating rates, thus significantly reducing cure cycle time without degradation of part quality. 
         [0058]    The apparatus and methodology disclosed herein have significant potential for reduced capital cost and lead time, reduced part fabrication cost and lead time, and reduced energy consumption. 
         [0059]    The apparatus and method disclosed above may be employed in an aircraft manufacturing and service method  200  as shown in  FIG. 8  for manufacturing and servicing an aircraft  202  as shown in  FIG. 9 . During pre-production, exemplary method  200  may include specification and design  204  of the aircraft  202  and material procurement  206 . During production, component and subassembly manufacturing  208  and system integration  210  of the aircraft  202  take place. Thereafter, the aircraft  202  may go through certification and delivery  212  in order to be placed in service  214 . While in service by a customer, the aircraft  202  is scheduled for routine maintenance and service  216  (which may also include modification, reconfiguration, refurbishment, and so on). 
         [0060]    Each of the processes of method  200  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
         [0061]    As shown in  FIG. 9 , the aircraft  202  produced by exemplary method  200  may include an airframe  218  with a plurality of systems  220  and an interior  222 . Examples of high-level systems  220  include one or more of the following: a propulsion system  224  (including engine nacelles of the type described above), an electrical system  226 , a hydraulic system  228 , and an environmental control system  230 . Any number of other systems may be included. Although an aerospace example is shown, the principles disclosed herein may be applied to other industries, such as the automotive industry. 
         [0062]    The apparatus and methods embodied herein may be employed during one of the stages of the production and service method  200 . For example, composite nacelle components or subassemblies fabricated or assembled during component and subassembly manufacturing  208  may be cured using the apparatus and methods disclosed herein, thereby reducing the manufacturing cost of an aircraft  202 . 
         [0063]    While apparatus and methods for have been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the teachings herein. In addition, many modifications may be made to adapt the concepts and reductions to practice disclosed herein to a particular situation. Accordingly, it is intended that the subject matter covered by the claims not be limited to the disclosed embodiments. 
         [0064]    The method claims set forth hereinafter should not be construed to require that the steps recited therein be performed in alphabetical order (any alphabetical ordering in the claims is used solely for the purpose of referencing previously recited steps) or in the order in which they are recited. Nor should they be construed to exclude respective portions of two or more steps being performed concurrently or alternatingly. 
         [0065]    The alternative structures corresponding to the “a means for partitioning” recited in the claims include at least the following: plug  18  depicted in  FIG. 1  and equivalents thereof; and tool  36  depicted in  FIG. 5  and equivalents thereof. The alternative structures corresponding to the “means for producing a specified pressure” recited in the claims include at least the following: pump  54  depicted in  FIG. 1  and equivalents thereof.