Patent Publication Number: US-2010116938-A1

Title: Method and apparatus for joining composite structural members and structural members made thereby

Description:
TECHNICAL FIELD 
     This disclosure generally relates to composite structures, and deals more particularly with a method and apparatus for joining composite sections together using bonded splices, as well as composite structural members made thereby. 
     BACKGROUND 
     In order to produce relatively long composite structural members, composite sections are sometimes joined together using a splice joint. For example, in the aircraft industry, relatively long wing stringers, spars, frames, and other complex composite geometries may be formed by joining two or more long composite sections together using a metal splice member and fasteners. However, metal splice members may be undesirable for a number of assembly reasons. 
     It may be possible to join composite structural member using composite splice members. However, it may not be practical to form composite splice joints between long composite sections because commercial autoclaves may not be large enough to accommodate the length of relatively long parts, such as wing stringers, spars, and frames. 
     Accordingly, there is a need for a method and apparatus for joining structural members such as stringer, spar, and frame sections that allow the use of composite splice members. There is also a need for composite structural members formed from composite sections joined together by composite splice members. 
     SUMMARY 
     The disclosed embodiments provide a method and apparatus for structural bonding of relatively large composite structural members in a localized area that obviates the need for curing the bond in an autoclave. The ability to apply localized heat and pressure to the bond joint allows the use of a composite splice member and may eliminate the need for fasteners. 
     According to one disclosed embodiment, a composite structural member comprises a first composite section and a second composite section. A composite splice member at least partially overlaps and splices together the first and second sections. The splice member forms a joint between the first and second composite sections having a V-shaped cross section. The composite sections may have complex geometries, including but not limited to a C shape, Z shape, J shape, T shape, an I shape and a hat shape cross section. 
     According to a disclosed method embodiment, producing a composite structural member comprises forming a first and a second composite section. A composite splice member is formed and to form a splice joint between the first and second composite sections. The splice member is bonded to the first and second composite sections. Bonding the splice member may include using a press to locally apply heat and pressure to the joint. The bonding may be performed using an inflatable pressure bladder to apply pressure to the joint within a press while heat is being applied to the joint. 
     According to another embodiment, apparatus for curing composite parts comprises a first platform and a second platform relatively moveable between an open, part loading position and a closed, part curing position; a tool against which a part may be pressed. The tool is supported by the first platform. At least a first bladder adapted to be pressurized and supported by the second platform for pressing the part against the tool. Means are provided for heating the tool. The first and second platforms may be independently portable. 
     According to a further disclosed embodiment, apparatus is provided for joining composite sections of a composite structural member. The apparatus includes a bonding machine for bonding a composite splice member onto a joint between adjacent ends of two elongated, composite sections and, jigs on opposite sides of the bonding machine for supporting the composite sections in end-to-end relationship. 
     According to a further method embodiment, joining two elongated composite sections comprises: supporting the composite sections in aligned, end-to-end relationship. Adjoining ends of the composite sections are placed within a press. A joint is formed between the composite sections by placing an uncured splice member over the adjoining ends of the composite sections. The press is closed and the splice member is bonded to the ends of the composite sections by using the press to apply heat and pressure to the joint. 
     According to another embodiment, a heated tool assembly for forming a part comprises a first tool and a second tool between which a part may be formed. Means are provided for heating the first tool, including a heater for heating a medium, a blower for blowing the heated medium, a plurality of nozzles for directing the heated medium over the first tool, and a plenum coupled between the blower and the nozzles. 
     The disclosed embodiments satisfy the need for a method and apparatus for forming a structural bond between two composite sections which eliminates the need for metal splice plates and does not require the bonded joint to be cured within an autoclave. 
    
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         FIG. 1  is a broad block diagram of apparatus for joining composite sections to form a continuous structural member. 
         FIG. 2  is an elevational view of the splice joint between two composite sections shown in  FIG. 1 . 
         FIG. 3  is a sectional view taken along the line  3 - 3  in  FIG. 2 . 
         FIG. 4  is a sectional view taken along the line  4 - 4  in  FIG. 2 . 
         FIGS. 5-9  are cross sectional views illustrating the shapes of other types of structural members. 
         FIG. 10  is a sectional view in the area designated as “B” in  FIG. 3 . 
         FIG. 11  is a simplified flow diagram illustrating a method for structural bonding of composite sections. 
         FIG. 12  is a block diagram illustrating a control system used in apparatus for structural bonding of composite sections. 
         FIG. 13  is a functional block diagram of apparatus for structural bonding of composite sections. 
         FIG. 14  is a block diagram of a bonding machine in an open position. 
         FIG. 15  is a perspective view of the bonding machines shown in  FIG. 14 . 
         FIG. 16  is another block diagram of the bonding machine, shown in a closed position. 
         FIG. 17  is a block diagram of a pressure bladder. 
         FIG. 18  is a block diagram illustrating the installation of a vacuum bag and a splice member on the bonding machine. 
         FIG. 19  is a block diagram showing a pair of hold down plates used to hold the composite sections during the curing process. 
         FIG. 20  is a block and diagrammatic view illustrating heating systems used to heat the mandrel and bladder. 
         FIG. 21  is a block diagram illustrating components of control systems forming part of the bonding machine. 
         FIG. 22  is a diagrammatic illustration of an alternate form of the tool tower, and showing a modular heating/cooling system. 
         FIG. 23  is a block diagram illustrating additional components of the modular heating and cooling system shown in  FIG. 22 . 
         FIG. 24  is a block diagram illustrating connections between a mandrel assembly and the modular heating and cooling system. 
         FIG. 25  is a block diagram of a diverter valve forming part of the modular heating and cooling system, wherein the valve has been switched to a heating mode. 
         FIG. 26  is a block diagram similar to  FIG. 25 , but showing the valve having been switched to a cooling mode. 
         FIG. 27  is a block diagram illustrating components of the mandrel assembly. 
         FIG. 28  is another block diagram illustrating additional components of the mandrel assembly. 
         FIG. 29  is a block diagram illustrating details of the mandrel useful in indexing the spar sections. 
         FIG. 30  is a block diagram of the mandrel carrier. 
         FIG. 31  is a block diagram illustrating the relationship between components of the mandrel assembly and mandrel base. 
         FIG. 32  is a block diagram of a bladder and shroud assembly. 
         FIG. 33  is a block diagram showing a removable bladder and frame. 
         FIG. 34  is a block diagram of a dual pressure bladder. 
         FIG. 35  is a block diagram illustrating the pressure bladder for applying pressure to composite sections. 
         FIG. 36  is a block diagram illustrating an alternate form of a frame useful in holding composite sections in place during cure. 
         FIG. 37  is a block diagram illustrating a portable pressure shroud cart in relation to the tool platform. 
         FIG. 38  is a block diagram illustrating the tool platform in a retracted position. 
         FIG. 39  is a view similar to  FIG. 38  but showing the tool platform having been moved to a forward position and the mandrel assembly having been disconnected from the heating/cooling system in preparation for removal of the mandrel carrier. 
         FIG. 40  is a flow diagram of aircraft production and service methodology. 
         FIG. 41  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a typical production cell  208  that may be used to join elongate composite sections, such as composite sections  104   a ,  104   b ,  104   c , to form a continuous structural member  104 , such as without limitation, a stringer, a spar, or a frame. At least a first composite section  104 ( a ) and a second composite section  104 ( b ) are joined in end-to-end relationship using a structural bond that form a splice joint  110 . The composite sections  104 - 104   c  may be supported by a plurality of aligned bond assembly jigs  184 . The bond assembly jigs  184  support the composite sections  104   a - 104   c  in aligned relationship while allowing the latter to be pulled along their longitudinal axes  265  into bonding machines  186  respectively located at bonding stations  210 ,  212 . The bonding stations  210 ,  212  are located along the length of the structural member  104  where the splice joints  110  are to be bonded. 
     Referring to  FIGS. 2-4 , in accordance with the disclosed embodiments, the structural member  104  may be formed by joining a number of composite sections such as composite sections  104   a ,  104   b  and  104   c , in end-to-end relationship using splice joints  110 .  FIG. 3  illustrates a top view of one specific structural member  104 , in which first and second composite sections  104   a ,  104   b  respectively, are joined together at a splice joint  110  forming a “kink” or angle designated as “A”. Each of the composite sections  104   a - 104   c  may comprise a cured composite laminate having any of various cross sectional geometries, however as will be described below, the composite sections  104   a - 104   c  chosen to illustrate the embodiments have a C-shape cross section as shown in  FIG. 4 . 
     It should be noted here that while a particular structural member  104  has been illustrated in the Figures, the disclosed embodiments may be employed to form any of a wide variety of elongate, structural members by bonding composite sections together using composite splice joints  110 . For example, and without limitation, the disclosed embodiments may be used to splice composite sections, especially elongate sections to form composite floor beams, frames, stringers, to name only a few. Moreover, the structural members may have any of a wide variety of cross sectional shapes, including, without limitation, a Z-shape shown in  FIG. 5 , a T shape shown in  FIG. 6 , a J shape shown in  FIG. 7 , a hat shape shown in  FIG. 8  or an I shape shown in  FIG. 9 . 
     Referring now to  FIGS. 2 and 3 , first and second adjacent composite sections  104   a ,  104   b  may be bonded together using a composite splice member  112  which, as best shown in  FIG. 4 , has a generally C-shape cross section corresponding to that of the composite sections  104   a ,  104   b . The splice member  112  includes top and bottom flanges  112   a ,  112   b  connected by a web  112   c . Although the splice member is shown as being of a one-piece construction in the illustrated example, the splice member  112  may comprise two or more sections or pieces in some applications. Since the composite sections  104   a ,  104   b  form a slight angle “A” ( FIG. 3 ), the splice member  112  includes two adjacent sections  114  as shown in  FIG. 2  which form an angle that is substantially equal to the angle “A”. As best seen in  FIG. 9 , the splice member  112  forms an overlapping, scarf type joint  110  with the adjoining composite sections  104   a ,  104   b . It should be noted here however, that while a scarf joint has been illustrated, other types of joints may be employed to form the splice joint  112 , including but not limited to lap joints, step lap joints, tabled splice joints, etc. 
     Referring now to  FIG. 10 , the composite sections  104   a ,  104   b  each may comprise multiple laminated plies (not shown) of a fiber reinforced polymer resin, such as carbon fiber epoxy, in which the outer edges  117  include ply drop-offs (not shown) forming tapered or ramp geometry. Similarly, the splice member  112  may be formed from multiple plies (not shown) of a fiber reinforced polymer resin which may be respectively aligned with the plies of the composite section  104   a ,  104   b . The splice member  112  has a substantially V-shape cross section defining inclined or ramped surfaces  116  which overlap and are bonded to corresponding tapered edges  117  on the outer, adjoining ends of the composite sections  104   a ,  104   b  to form the splice joint  110 . As previously noted, although a splice joint  110  has been illustrated, other splice configurations may be possible, depending on the application. 
     Attention is now directed to  FIG. 11  which broadly illustrates the steps of a method for structural bonding of the composite sections  104   a - 104   c . Beginning at step  126 , the composite sections  104   a - 104   c  are laid up on a suitable tool (not shown) and are then individually cured at step  128 , using heat and pressure, typically within an autoclave (not shown). Next, at  130 , a bonding machine  186  ( FIG. 1 ) is opened in preparation for receiving the ends of two adjacent composite sections, such as first and second composite sections  104   a ,  104   b.    
     At  132 , the first and second composite sections  104   a ,  104   b  are loaded into bond assembly jigs  184  (BAJ) (see  FIG. 1 ) and aligned with each other. Next, at  134 , the ends of the composite sections  104   a ,  104   b  are pulled into the bonding machine  186 . After the splice member  112  has been laid up and formed over a tool (not shown) at step  124 , the splice member  112  is aligned and installed on the composite sections  104   a ,  104   b  at the splice joint  110 , as shown at step  138 . 
     At  140 , a vacuum bag is installed over the splice area which includes the splice member  112 , following which, at  142 , the bonding machine  186  may be closed. The green (uncured) splice member  112  is then bonded to the ends of the composite sections  104   a ,  104   b  by a series of steps shown at  144 . Beginning at  146 , a vacuum is drawn in the vacuum bag in order to partially consolidate the plies of the splice member  112  layup. Next, at  148 , a bag-like pressure bladder (discussed later) is pressurized which presses the splice member  112  and composite sections  104   a ,  104   b  against a mandrel  194  ( FIG. 13 ) thereby further consolidating the plies of the splice member  112  layup. 
     At this point, a heating cycle is commenced at  150  in which the composite sections  104   a ,  104   b  and the splice member  112  are locally heated in order to cure the green splice member  112  and thereby bond it to the composite sections  104   a ,  104   b  to form a splice joint  110 . Finally, at  152 , the splice member  112  is cooled, following which the bonding machine  186  may be opened at  154 . At  156 , the vacuum bag is removed following which the splice member  112  is trimmed, as may be required, as shown at step  158 . The resulting bonded splice joint  110  may be nondestructively inspected (NDI) at step  160 , following which the structural member  104  may be removed from the bond assembly jigs  184 . Depending upon the application, the completed structural member  104  may be painted and sealed at step  164 . It should be noted here that steps  158 - 164  may be carried out in any desired order. 
     In the method embodiment described above in connection with  FIG. 11 , the composite sections  104 ( a ),  104 ( b ) are cured before the uncured splice member  112  is applied to the splice joint  110 . In other embodiments however, it is possible that only portions of the composite sections  104 ( a ),  104 ( b ) are cured before the uncured splice member  112  is applied to the splice joint  110 . For example, as shown in  FIG. 2 , portions  115  of the composite sections  104 ( a ),  104 ( b ) spanning the splice member  112  may be in an uncured or partially cured (“staged”) state at the time the splice member  212  is applied to the joint  110 , while remaining areas of the composite sections  104 ( a ),  104 ( b ) are in a cured state. In this alternative embodiment, the uncured portions  115  of the composite sections  104 ( a ),  104 ( b ) may be cocured with the uncured splice member  112 . 
       FIG. 12  broadly illustrates components of a control system for the bonding machine  186 . A controller  166 , which may comprise a programmable logic controller (PLC) or a personal computer (PC), may use various software programs  178  to automatically carry out control functions in a preprogrammed manner. Operator controls and displays  180  allow operator access to the software programs  178  and form an interface with the controller  166  to allow adjustment of settings and display of process information. In some cases, controller  166  may be coupled with the bond assembly jigs  184  ( FIG. 1 ) to sense or control the position of the long composite sections  104   a ,  104   b  relative to each other. 
     The controller  166  may control various components and systems on the bonding machine  186 , including heating/cooling systems  192 ,  196 , bladder pressurization  174  and a bag vacuum  176 . The bonding machine  186  may include a variety of later discussed sensors  182  that provide signals to the controller  166 , such as temperatures and pressures. 
       FIG. 13  is a functional block diagram of the bonding machine  186 , which broadly comprises a first, tool platform  188  and a second, pressure platform  190 . Platforms  188 ,  190  may be mounted for sliding or rolling movement by guides  204  on a common base  202  for linear horizontal movement toward and away from each other. As will be discussed below, the platforms  188 ,  190  may be moved from an open position shown in  FIG. 13  to a closed position ( FIGS. 16 and 21 ) in which heat and pressure are locally applied to the splice area comprising the splice member  112  and the ends of the assembled composite sections  104   a ,  104   b  while being supported by the bond assembly jigs  184 . This locally applied heat and pressure structurally bond the splice member  112  to the composite sections  104   a ,  104   b  to create the bonded splice joint  110 . The platforms  188 ,  190  may be drawn and locked into their closed position using draw downs and locks  206 . The tool platform  188  may include sensors  182 , a heating/cooling system  192  and a mandrel  194 . Similarly, the pressure platform  190  may include sensors  182 , a heating/cooling system  196 , a pressure bladder  198  and pumps  200  used to draw a bag vacuum and pressurize the bladder  198 . 
     Attention is now directed to  FIGS. 13-15  which illustrate further details of the bonding machine  186 . The bonding machine  186  broadly includes a tool tower  235  and a pressure tower  245  between which the assembled splice member  112  and composite sections  104   a ,  104   b  may be structurally bonded to form a bonded splice joint  110 . The tool tower  235  includes a tool platform  188  mounted for linear horizontal movement on a base  202  by any suitable means. In the illustrated example, platform  188  includes feet  204  that are guided by tracks  220 . A tool, which may comprise a mandrel  194 , is mounted on a mandrel base  215  which in turn is secured to a platen plate  214 . The platen plate  214  is supported on the tool platform  188 . The mandrel base  215  is releasable from the platen plate  214  by means of a series of locking levers  225  to allow the mandrel  194  to be easily removed and/or replaced. 
     The pressure tower  245  includes a pressure platform  190  which also has feet  204  engaging the tracks  220 . An inflatable pressure bladder  198  is held in a frame  199  that is secured to a shroud  224 . The shroud  224  in turn, is secured to a platen plate  222  mounted on the pressure platform  190 . Heating/cooling systems  192 ,  196  are respectively mounted on the traveling platforms  188 ,  190  for heating and cooling the mandrel  194 , and the area surrounding the pressure bladder  198 . Outer covers  226 ,  228  may be employed to protectively surround components on the tool and pressure towers  235 ,  245  respectively. An electric or other form of motor (not shown) may be used to power the platforms  188 ,  190  to travel along the track  220  between an open, part-loading/unloading position as shown in  FIGS. 13 and 14 , to a closed, part curing position as shown in  FIG. 16 . A draw bar  221  ( FIG. 14 ) may be connected between the towers  235 ,  245  and employed to draw the platforms  188 ,  190  into a final closed position. Locking arms  218  may be used to lock the platforms  188 ,  190  together in their closed position. 
     Referring particularly to  FIG. 17 , the pressure bladder  198  may have a cross section that is substantially a C-shape, similar to the shape of the mandrel  194 . The bladder  198  may be formed of any suitable material capable of withstanding temperatures and pressures for the particular application, including for example and without limitation, silicone rubber. A fluid fitting  232  allows pressurized fluid, which may be a gas or a liquid to enter and exit the bladder  198 . 
     Attention is now directed to  FIG. 17  which illustrate steps for readying and closing the bonding machine  186  in preparation for a bonding operation. The splice member  112  is first applied over the joint  110  between the composite sections  104   a ,  104   b  which are held in an engineering defined space by the previously discussed bond assembly jigs  184 . Next, with the bonding machine  186  still open, a vacuum bag  234  may be applied over the splice member  112 . Both the splice member  112  and the vacuum bag  234  extend the full thickness of the composite sections  104   a ,  104   b  which may include ply build-ups (not shown) on each side of the joint  110 . With the splice member  112  and vacuum bag  234  having been installed, the bonding machine  186  is closed by moving the platforms  188 ,  190  toward each other. As previously mentioned, a draw bar  221  ( FIG. 14 ) may be employed if necessary to pull the platforms  188 ,  190  together until locking arms  218  ( FIG. 15 ) can be rotated to lock the position of the mandrel  194  relative to the pressure bladder shroud  224 . 
     Referring now to  FIG. 19 , during the curing process in which the composite sections  104   a ,  104   b  are locally heated, the composite sections  104   a ,  104   b  may experience movement along their longitudinal axes  265 . In order to achieve final assembly requirements, this movement may be substantially reduced by holding the composite sections  104   a ,  104   b  using a pair of hold down plates  236  which span the splice joint  110  and clamp the adjacent ends of the composite sections  104   a ,  104   b  together. The hold down plates  236  may be fixed to abrasive, excess edge sections (not shown) on the top and bottom of the composite sections  104   a ,  104   b  overlying the splice joint  110  and rigidly connecting the composite sections  104   a ,  104   b.    
     Attention is now directed to  FIG. 20  which illustrates further details of the heating/cooling systems  192 ,  196  ( FIG. 14 ) that are used to heat the area of the splice joint  110  to a temperature sufficient to result in the curing of the slice member  112 , and then cool the splice member  112  after curing. On the side of the tool tower  235 , a heating element  216  heats a medium that is delivered through a supply duct  238  to a manifold  240  which routes the heated medium to distribution ducts  242 . The distribution ducts  242  supply the heated medium to nozzles  244  which direct heated medium onto the inside surface of the mandrel  194  which is hollow on one side thereof. As used herein, “medium” and “heated medium” are intended to include a variety of flowable mediums, including without limitation, air and other gases, as well as fluids, including oil. Other forms of heating such as without limitation, induction heating may also be possible. 
     On the side of the pressure tower  245 , the heating element  230  heats a medium that is delivered through a supply duct  246  to a manifold  248  which routes the hot medium to distribution ducts  250 . The distribution ducts  250  deliver the hot medium to nozzles  252  which direct the medium to the area surrounding the pressure the bladder  198  and the outside mold line (OML) of the splice member  112 . 
       FIG. 21  illustrates additional components of the heating/cooling systems  192 ,  196  as well as other systems such as a vacuum bag control  274  and bladder pressure control  282 . An ambient medium is drawn through the heating element  216  and distributed by the manifold  240  to the nozzles  244  in order to heat the mandrel  194 . The heating element  216  is controlled by a heat control  272 , based in part on data received from a vacuum bag pressure sensor  295 , a mandrel heater medium temperature sensor  277 , a mandrel lag temperature sensor  262  and a mandrel control temperature  264 . Vacuum within the vacuum bag  234  ( FIG. 18 ) is controlled by a vacuum bag control  274 . 
     On the side of the pressure tower  245 , an ambient medium is drawn through the heat element  230  to the hot medium manifold  248  which distributes the hot medium to the nozzles  244 . Pressure applied to the pressure bladder  198  is controlled by a pressure control  282  which includes a pressure sensor  297  that provides pressure data to the heat control  276 . The medium flowing through the heater  230  may further be controlled by the control  276  based on data generated by a pressure control temperature sensor  266  and a pressure heater temperature sensor  301 . 
     Attention is now directed to  FIG. 22  which illustrates an alternate embodiment of the tool tower  235 . In this example, a self-contained, modular heating/cooling system  284  is supported by rails (not shown) on a traveling platform  288 . The platform  288  is linearly displaceable on a portable base  290 . The mandrel  194  is secured to a mandrel base  342  which is removably supported on a mandrel carrier  286 . The mandrel carrier  286  is removably mounted on supports  357  positioned on the top of the platform  288 . Thus, the mandrel carrier  286  may be easily removed from the platform  288 , and the mandrel  194  along with the mandrel base  342  may be removed from the mandrel carrier  286 . The heating/cooling system  284  includes later discussed medium supply and return ducts (not shown in  FIG. 22 ) that are releasably coupled with the mandrel  194  by releasable connections  327 . 
     Additional details of the heating/cooling system  284  are shown in  FIGS. 22-25 . Blower drive motor  325  drives a blower  294  which moves the medium through a heating element  216 , and then through a duct  296  to a pair of hot medium supply ducts  314 ,  316 . The hot medium supply ducts  314 ,  316  are respectively coupled with inlet connections  326 ,  328  ( FIG. 25 ) passing through the back of the mandrel base  342 . The hot medium supplied through inlet connections  326 ,  328  may be delivered to a nozzle plenum assembly  300  ( FIG. 24 ) that will be discussed later in more detail below. Medium returning from the nozzle plenum assembly passes through a return medium inlet connection  330  and is delivered via a return duct  318  to a diverter valve  322 . 
       FIG. 24  illustrates further details of the nozzle plenum assembly  300 . The nozzle plenum assembly  300  is secured to the back of the mandrel  194 . A plenum frame  334  to which box-shaped, perforated nozzles  338  are attached. The perforated nozzles  338  extend into compartments or zones  339  in the mandrel  194  that are defined by partial partition walls  194   a . Each of the nozzles  338  is secured with fasteners (not shown) to the plenum frame  334 . Medium inlet connections  326 ,  328  are secured to a plate  331  which is fixed to the plenum frame  334 . The return medium connection  330  is mounted on a plate  336  that may include openings (nor shown) through which the connections  326 ,  328  extend. Incoming medium to inlet connections  326 ,  328  pass through the nozzles  338  which deliver the medium substantially evenly over the interior surface of the mandrel  94 . Return medium passes through the connection  330  and  327  back to the diverter valve  322  ( FIG. 23 ). 
     Referring to  FIGS. 25-26 , the diverter valve  322  includes a pair of hinged valve members  378 ,  380  respectively controlled by arms  374  and  376 . A cool medium inlet  372  may be selectively opened to allow cool medium to flow into the valve  322 . In the condition shown in  FIG. 26 , valve  380  is closed, and valve  378  is open to allow return medium received through the inlet  324  and to exit through the through the outlet  370  and thereby re-circulate during a heating cycle. The valve member  380  closes off the cool medium inlet  372  during the heating cycle. 
       FIG. 26  illustrates the condition of the diverter valve  322  when cool medium is delivered to the mandrel  194  during a cooling cycle. Valve  378  is moved to a second closed position which diverts the return medium received through inlet  324  out through a medium vent  375 . Valve member  380  has also been moved to its open position, allowing cool medium to enter through the inlet  372  and pass through the outlet  370  for delivery to the mandrel  194 . 
     Attention is now directed to  FIGS. 26-30  which better illustrate details of the mandrel  194  and mounting of the mandrel base  342  on the mandrel carrier  286 . Pins ( FIG. 30 ) on the mandrel carrier  286  are received within the sockets  348  ( FIGS. 27 and 28 ) secured to brackets  346  fixed to the mandrel base  342 . A position limiting pin  363  on the back side of the mandrel base  342  provides a third contact point between the mandrel base  342  and the mandrel carrier  286 . The positioning pin  363  engages a stop  367  ( FIG. 30 ) on the mandrel carrier  286 . Ball joint connections formed between the sockets  348  and the pins  351  allow the mandrel  194  and the mandrel base  342  to expand along Y and Z axes shown in  FIG. 30 , while the limiting pin  363  restrains such movement along the X axis. The mandrel base  342  is designed to minimize deflection and react the force of the pressure system through the mandrel  194 . As shown in  FIG. 29 , the mandrel  194  may include end brackets  352  each provided with a retaining pin  350 . The retaining pins  350  are received within openings (not shown) in the composite sections  104   a ,  104   b  in order to maintain the composite sections  104   a ,  104   b  in aligned registration during the bonding process. 
     Referring to  FIG. 31 , the mandrel  194  is secured to the mandrel base  342  using fasteners (not shown). A sheet of insulation  358  along with spaced apart thermal barriers  364  are sandwiched between the mandrel  194  and the mandrel base  342  in order to insulate the mandrel  194  from the mandrel base  342 . 
       FIG. 31  illustrates the use of insulation  366  surrounding the bladder  198  which functions to assist in retaining heat in the area of the splice joint  110  ( FIG. 10 ) during the curing process. In this embodiment, heat required for curing of the splice member  112  ( FIG. 10 ) may be provided only from the tool side (tool tower  235  in  FIG. 15 ) using the heating system  284  previously described in connection with  FIG. 23 . In some applications, it may be necessary or desirable to place an optional heater element (not shown) between the bladder  198  and the surrounding insulation  366 . 
     Referring now to  FIG. 33 , a removable bladder assembly  382  includes an inflatable bladder  198 . The edges of the bladder  198  may be secured to a semi-rigid frame  199  which may be formed of a semi-flexible material. The bladder frame  199  is releasably held in the bladder shroud  224  by a series of retainers  386  which hold the frame  199  in snap fit relationship, allowing the bladder assembly  382  to be easily removed and/or replaced. 
     The bladder  198  may be a single bladder, or may comprise a redundant, double bladder of the type shown in  FIGS. 33 and 34 . The bladder frame retainers  386  are secured to the bladder shroud  224  and may have a substantially circular cross section. The bladder frame  199  may be formed of a semi-rigid material such as reinforced silicone and may include a circular groove (not shown) along its periphery which receives the retainer  386  in a snap fit relationship. A second inflatable inner bladder  398  may be positioned inside the first, outer bladder  198  for redundancy in the event that the first bladder  198  develops a leak.  FIG. 35  illustrate the use of the insulation  366  to retain the heat that is generated through the mandrel  194  where heating is provided only on the tool side of the bonding machine  186 . 
     Attention is now directed to  FIG. 36  which illustrates an alternate embodiment of a bladder frame  199  that may eliminate the need for use of the hold down plates  236  previously described in connection with  FIG. 19 . A pressure bladder  198  is attached to a bladder frame  199  supported on the shroud  224  along with the insulation  366 . Bladder  198  bears against a composite section  104   a  which is captured between the bladder  198  and the mandrel  194 . The frame  199  has a rigid flange  355  which includes a portion  394  overlying and bearing against the composite section  104   a . The flange  355  may assist in bagging and may apply sufficient force against the composite section  104   a  to hold down composite section  104   a  against movement, thereby eliminating the need for the hold down plates  236 . 
     Attention is now directed to  FIG. 37  which illustrates the use of a shroud cart  388  to position the shroud  224  relative to the mandrel  194 . The shroud cart  388  is manually positioned in the work area. After being raised to a working height, it is moved toward the mandrel  194 . The cart  388  includes a portable base  390  mounted on rollers (not shown) and a lifting mechanism  388  powered by an actuator piston  391 . The lifting mechanism  388  may be used to lift the shroud  224  to the desired height, while the portable base  390  may be used to move the shroud  224  into the position shown in  FIG. 37  in readiness for a bonding operation. The lifting mechanism  388  may be compliant to allow subtle adjustments to the shroud position without imparting load onto the composite sections  104   a ,  104   b  or the mandrel  194 . Locating devices  392   a ,  392   b  on the shroud  224  and the platform  288  to assure that the shroud  224  and the mandrel  194  may be in aligned relationship to each other when the shroud has been moved into its closed position. 
       FIGS. 38 and 39  illustrate the modular nature of the mandrel assembly and the heating system  284 . As shown in  FIG. 38 , the platform  288  is in a retracted position, and the mandrel  194  is coupled with the heating system  284 . In order to remove and/or replace the mandrel  194 , the platform  288  is moved to its forward position on the base  290  as shown in  FIG. 39 . Then, the heating system  284  maybe disconnected from the mandrel  194 , using the releasable connections  327 . 
     Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine and automotive applications. Thus, referring now to  FIGS. 40 and 41 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  400  as shown in  FIG. 40  and an aircraft  402  as shown in  FIG. 41 . During pre-production, exemplary method  400  may include specification and design  404  of the aircraft  402  and material procurement  406 . During production, component and subassembly manufacturing  408  and system integration  410  of the aircraft  402  takes place. Thereafter, the aircraft  402  may go through certification and delivery  412  in order to be placed in service  414 . While in service by a customer, the aircraft  212  is scheduled for routine maintenance and service  416  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  400  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 vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 41 , the aircraft  402  produced by exemplary method  400  may include an airframe  418  with a plurality of systems  420  and an interior  422 . Examples of high-level systems  420  include one or more of a propulsion system  424 , an electrical system  426 , a hydraulic system  428 , and an environmental system  430 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries. 
     Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method  400 . For example, components or subassemblies corresponding to production process  408  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  402  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  408  and  410 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  402 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  402  is in service, for example and without limitation, to maintenance and service  416 . 
     Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.