Abstract:
There are provided apparatuses and related methods for forming sheets. The formed sheets can be formed of a thermoplastic material, such as flat sheets of reinforced thermoplastic, which can be lightweight, strong, and perform well in flammability, smoke, and toxicity tests. The apparatus includes a heater for heating the sheet to a processing temperature and a structure for configuring the sheet to a desired shape using one or more rollers, shapers, longitudinal members, and/or support members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 10/435,843, filed May 12, 2003, which is a continuation-in-part of copending U.S. patent application Ser. No. 10/215,815, filed Aug. 9, 2002, each of which is hereby incorporated herein in its entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1) Field of the Invention  
         [0003]     The present invention relates to apparatuses and methods for forming thermoplastic materials and, more specifically, to apparatuses and methods for bending thermoplastic sheets to form ducts, channels, arcs, spirals, and the like.  
         [0004]     2) Description of Related Art  
         [0005]     Longitudinal passages such as ducts, channels, arcs, spirals, and the like are used to provide passageways for a wide variety of applications. For example, tubular ducts are widely used for air flow in aircraft environmental control systems. Similarly, ducts provide passageways for transporting gases for heating and ventilation in other vehicles and in buildings. Water distribution systems, hydraulic systems, and other fluid networks also often use ducts for fluid transport. In addition, solid materials, for example, in particulate form can be delivered through ducts and channels. A variety of longitudinal shapes can also be used as conduits in which electrical wires or other components are placed. Such longitudinal passages for the foregoing and other applications can be formed of metals, plastics, ceramics, composites, and other materials.  
         [0006]     One conventional aircraft environmental control system utilizes a network of ducts to provide air for heating, cooling, ventilation, filtering, humidity control, and/or pressure control of the cabin. In this conventional system, the ducts are formed of a composite material that includes a thermoset matrix that impregnates, and is reinforced by, a reinforcing material such as Kevlar®, registered trademark of E.I. du Pont de Nemours and Company. The thermoset matrix is typically formed of an epoxy or polyester resin, which hardens when it is subjected to heat and pressure. Ducts formed of this composite material are generally strong and lightweight, as required in many aircraft applications. However, the manufacturing process can be complicated, lengthy, and expensive, especially for ducts that include contours or features such as beads and bells. For example, in one conventional manufacturing process, ducts are formed by forming a disposable plaster mandrel, laying plies of fabric preimpregnated with the thermoset material on the mandrel, and consolidating and curing the plies to form the duct. The tools used to mold the plaster mandrel are specially sized and shaped for creating a duct of specific dimensions, so numerous such tools must be produced and maintained for manufacturing different ducts. The plaster mandrel is formed and destroyed during the manufacture of one duct, requiring time for curing and resulting in plaster that typically must be removed or destroyed as waste. Additionally, the preimpregnated plies change shape during curing and consolidation and, therefore, typically must be trimmed after curing to achieve the desired dimensions. The jigs required for trimming and for locating the proper positions for features such as holes and spuds are also typically used for only a duct of particular dimensions, so numerous jigs are required if different ducts are to be formed. Like the tools used for forming the mandrels, the jigs require time and expense for manufacture, storage, and maintenance. Additionally, ducts formed of conventional thermoset epoxies typically do not perform well in certain flammability, smoke, and toxicity tests, and the use of such materials can be unacceptable if performance requirements are strict. Further, features such as beads typically must be post-formed, or added after the formation of the duct, requiring additional manufacture time and labor.  
         [0007]     Alternatively, ducts can be formed of thermoplastic materials. A thermoplastic duct can be manufactured by cutting a sheet of thermoplastic material to a size and shape that corresponds to the desired dimensions of the duct, bending the sheet to the desired configuration, and joining longitudinal edges of the sheet to form a longitudinal joint or seam. For example, apparatuses and methods for forming thermoplastic ducts and consolidation joining of thermoplastic ducts are provided in U.S. application Ser. Nos. 10/216,110 and 10/215,833, titled “Thermoplastic Laminate Duct” and “Consolidation Joining of Thermoplastic Laminate Ducts,” both filed on Aug. 9, 2002 and assigned to the Assignee of the present invention. Such thermoplastic ducts can be formed by retaining the thermoplastic sheet in the bent configuration until the ends are joined, and then releasing the duct so that the resulting joint continues to restrain the duct in the bent configuration. However, stresses induced in the thermoplastic material during bending can cause the duct to deform or distort from the desired configuration after joining, e.g., when released from the joining apparatus.  
         [0008]     Thus, there exists a need for improved apparatuses and methods for forming a thermoplastic sheet to correspond generally to a desired configuration in a substantially unstressed condition. The method should not require the laying of individual plies on a disposable plaster mandrel. Preferably, the method should be compatible with thermoplastic ducts, including reinforced thermoplastic ducts formed from flat sheets, which provide high strength-to-weight ratios and meet strict flammability, smoke, and toxicity standards.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an apparatus and method for forming sheets to desired configurations. The sheets can be formed to the desired configuration of a finished shape such as an arc, channel, or spiral. Alternatively, each sheet can be formed as a preform that generally corresponds to the desired configuration of a finished shape such as a duct and is subsequently joined to form the finished shape. Joining can be accomplished by consolidation joining. The sheets can be formed from thermoplastic materials, such as flat sheets of reinforced thermoplastic laminate that are lightweight, strong, and perform well in flammability, smoke, and toxicity tests.  
         [0010]     According to one embodiment of the present invention, the apparatus includes a rotatable roller, an elastically flexible shaper, and a heater. The apparatus can be used to hold the sheet in a predetermined configuration while the heater is used to heat the sheet. The shaper receives the thermoplastic sheet on one side so that rotation of the roller advances the shaper around the roller to bend the thermoplastic sheet. An index feature can be provided on the shaper for engaging the thermoplastic sheet so that the adjustment of the index feature toward the roller advances the thermoplastic sheet around the roller. The apparatus can also include a second shaper that is disposed on the thermoplastic sheet so that the second shaper is bent between the sheet and the roller and advancement of the second shaper toward the roller urges the thermoplastic sheet radially outward from the roller. Longitudinal members can be configured to adjust radially toward the roller to bend the thermoplastic sheet to a predetermined configuration.  
         [0011]     According to another embodiment of the present invention, the apparatus includes at least two support members that extend, for example, in a longitudinal direction, to define at least one space therebetween. A shaper is configured to be disposed with one side against the support members so that the shaper extends across the at least one space. The shaper receives the thermoplastic sheet on a side opposite the support members and bends partially around the members, which can be adjustable. A heater is configured to heat the thermoplastic sheet to a processing temperature less than a glass transition temperature of the thermoplastic member and within about 70° F. of the glass transition temperature.  
         [0012]     The present invention also provides a method of forming a thermoplastic sheet. According to one embodiment of the present invention, the thermoplastic sheet is disposed on a first side of a shaper. A longitudinal roller connected to the shaper is then rotated, for example, by at least one revolution, to advance the shaper circumferentially around the roller so that the thermoplastic sheet is disposed between the roller and the shaper and bent to a predetermined shape. Longitudinal members can be radially adjusted toward the roller to bend the thermoplastic sheet to a predetermined configuration. The shaper can be advanced toward the roller so that the shaper adjusts radially outward from the roller to define a maximum size for the thermoplastic sheet, for example, so that an index feature of the shaper engages the sheet and adjusts the sheet radially outward from the roller. According to one aspect, a second shaper is disposed on the sheet so that the second shaper is advanced around the roller between the sheet and the roller. The second shaper can be adjusted radially outward from the roller to urge the thermoplastic sheet to a predetermined configuration. The thermoplastic sheet is heated to a processing temperature, for example, within about 70° F. of a glass transition temperature of the thermoplastic sheet. The thermoplastic sheet can be cooled in the apparatus to a temperature below about 70° F. less than the glass transition temperature before the sheet is removed.  
         [0013]     According to another embodiment of the present invention, at least two support members are provided with a space therebetween. A shaper is disposed on the support members so that the shaper extends across the space and bends partially around the support members to a predetermined shape. A thermoplastic sheet is disposed on the shaper and heated to a processing temperature. The thermoplastic sheet can be cooled to a temperature below about 70° F. less than the glass transition temperature of the thermoplastic sheet while the thermoplastic sheet and the shaper are disposed on the support members. The support members can be adjustable. According to one aspect, a second shaper can be disposed on the thermoplastic sheet opposite the first shaper and some of the support members can be adjusted in a direction toward the sheet so that the sheet is bent between the support members. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:  
         [0015]      FIG. 1  is a perspective view illustrating a forming apparatus according to one embodiment of the present invention;  
         [0016]      FIG. 2  is a perspective view illustrating a formed sheet according to one embodiment of the present invention;  
         [0017]      FIG. 2A  is a perspective view illustrating a formed sheet according to another embodiment of the present invention;  
         [0018]      FIG. 3  is a section view illustrating the forming apparatus of  FIG. 1 , shown with the shaper in a first position;  
         [0019]      FIG. 4  is a section view illustrating the forming apparatus of  FIG. 1 , shown with the shaper advanced to a second position;  
         [0020]      FIG. 5  is a section view illustrating a forming apparatus according to another embodiment of the present invention, shown with a second shaper disposed on the sheet and both shapers advanced to the second position;  
         [0021]      FIG. 6  is a section view illustrating a forming apparatus according to another embodiment of the present invention, shown with the shaper in a first position and with longitudinal members in a first position;  
         [0022]      FIG. 7  is a section view illustrating the forming apparatus of  FIG. 6 , shown with the shaper in a second position and with the longitudinal members in a second position;  
         [0023]      FIG. 8  is a perspective view illustrating a forming apparatus according to another embodiment of the present invention;  
         [0024]      FIG. 9  is a section view illustrating the forming apparatus of  FIG. 8 , shown with a thermoplastic sheet and a shaper disposed on the support members;  
         [0025]      FIG. 10  is a section view illustrating a forming apparatus with a second set of support members, according to another embodiment of the present invention; and  
         [0026]      FIG. 11  is a perspective view illustrating a forming apparatus according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.  
         [0028]     Referring now to  FIG. 1 , there is shown a forming apparatus  10  for forming a formed sheet  60 , such as the one shown in  FIG. 2 , from a thermoplastic member, such as a thermoplastic sheet  50 . Forming generally refers to bending the thermoplastic member to a bent or curved configuration and processing the member, for example, using heat, so that the member generally remains in a desired configuration when unrestrained. The formed sheet  60  can be a finished shape, such as an arc, spiral, channel, and the like. Alternatively, the formed sheet  60  can be used as a preform, i.e., a formed shape that is joined or otherwise processed to form a finished shape and remains in the desired configuration when unrestrained. For example, the flat sheet  50  can be bent and heated to form the cylindrical formed sheet  60 , shown in  FIG. 2 , which extends from a first end  62  to a second end  64  and defines a passage  66 . Longitudinal edges  68 ,  70  of the formed sheet  60  can define a gap therebetween, can be overlapped, or can be joined to form a seam or joint. If used as a preform, the longitudinal edges  68 ,  70  of the formed sheet  60  can be joined to form a duct which, when unrestrained, defines a partially closed cylindrical shape. The preform can be formed to have a diameter slightly larger or smaller than the desired diameter of the duct. Thereafter, the formed sheet  60  can be subjected to a compressive or expansion force for holding the formed sheet during subsequent processing, such as joining, to arrive at the desired configuration of the duct. The longitudinal edges  68 ,  70 , or other portions of the formed sheet  60 , can be joined using adhesives, heat, or other joining methods. For example, joining can be achieved by applying heat and pressure to the edges  68 ,  70  to form the seam. As the thermoplastic material of the formed sheet  60  is heated above its glass transition temperature, the material becomes plastic and the pressure consolidates and joins the interface. Joining can be performed by manual or automated methods, for example, as described in U.S. application Ser. No. 10/215,833, titled “Consolidation Joining of Thermoplastic Laminate Ducts,” the entirety of which is incorporated herein by reference. Thus, as used throughout this application, the term “formed sheet” refers generally to a sheet that has been formed to a curved or bent configuration, including sheets that are formed to a final desired configuration without joining, preforms that require joining or other processing to achieve the final configuration, and partially closed shapes that are formed by joining such preforms.  
         [0029]     The shape of the formed sheet  60  is determined by projecting the desired shape of the formed sheet  60  onto the flat sheet  50 . Although the ends  62 ,  64  and edges  68 ,  70  of the formed sheet  60  are shown to be straight and parallel in  FIG. 2 , the formed sheet  60  can alternatively be straight, curved, tapered, or otherwise contoured. For example, there is shown in  FIG. 2A  an alternative formed sheet  60 , which defines a non-uniform, or transitional, radius that tapers between the ends  62 ,  64 . The sheet  50  and, hence, the formed sheet  60  can also define a variety of features such as holes, for example, for connecting spuds, brackets, and the like to the formed sheet  60 . Methods and apparatuses for forming sheets and for determining geometric patterns that correspond to ducts are provided in U.S. application Ser. No. 10/216,110, titled “Thermoplastic Laminate Duct,” the entirety of which is incorporated herein by reference. It is also appreciated that marks can be provided on the formed sheet  60 , for example, to accurately identify the location of post-formed features such as beads, bells, and assembly details or to facilitate the manufacture or assembly of the formed sheet  60 , as also provided in the application entitled “Thermoplastic Laminate Duct.” 
         [0030]     Preferably, the formed sheet  60  is formed of a thermoplastic sheet or of a composite laminate that includes a thermoplastic matrix and a reinforcing material. Thermoplastic materials are characterized by a transition to a plastic state when heated above a glass transition temperature. For example, the formed sheet  60  can be formed of polyetherimide (PEI) or polyphenol sulfide (PPS), both of which can be thermoplastic. Thermoplastic PEI is available under the trade name Ultem®, a registered trademark of General Electric Company. According to one embodiment of the present invention, each formed sheet  60  is comprised of a composite material that includes a matrix of thermoplastic PEI that is reinforced with a reinforcing material such as carbon, glass, or an aramid fabric such as a Kevlar® aramid, or fibers of such a material. Alternatively, the formed sheet  60  can be formed of other thermoplastic materials, which can be reinforced by other reinforcing materials, or can include no reinforcing materials.  
         [0031]     The formed sheet  60  can be used in numerous applications including, but not limited to, environmental control systems of aerospace vehicles. For example, the formed sheet  60  can be used as a preform that is used to form a duct, as described above. The resulting duct can be used as a passage in a system though which air is delivered to provide heating, cooling, ventilation, and/or pressurization of an aircraft cabin. Alternatively, the formed sheet  60  can be used without further processing, for example, as a channel or conduit for wires or cables. The ends of the formed sheet  60  can be connected to other channels, ducts, tubes, formed sheets, or other devices such as ventilators, compressors, filters, and the like. Multiple formed sheets  60  can be connected so that a longitudinal axis of each formed sheet  60  is configured at an angle relative to the longitudinal axis of the adjoining formed sheet(s). Thus, the formed sheet  60  can be connected to form an intricate passage system (not shown) that includes numerous angled or curved passages for accommodating the various devices connected by the passage system and for meeting layout restrictions as required, for example, on an aircraft where space is limited. In addition, formed sheets according to the present invention can be used to form barriers or walls that are used to separate lighted areas from darker areas, people from secure areas, or cold from warm areas. Further, the formed sheets can provide visual barriers.  
         [0032]     The forming apparatus  10  shown in  FIG. 1  includes a roller  12  and a shaper  14 , both of which are provided on a frame  16 . The roller  12  extends longitudinally and is supported by the frame  16  such that the roller  12  is rotatable. The roller  12  can be at least partially surrounded by an insulative heat shroud  18 , which extends parallel to the roller  12  and facilitates the heating of a space  20  within the shroud  18  by a heater  22 . The heater  22  can be any of various types of heaters such as electric and gas heaters, and can be positioned on either end of the shroud  18  or along the longitudinal length of the shroud  18 . The heater  22  can be configured to heat the sheet  50  through the shroud  18  or by heating air that is blown into the space  20  within the shroud  18 . Alternatively, the apparatus  10  can be used without the shroud  18 , and the heater  22  can be configured to heat the space around the roller  12 . The roller  12  can also be heated directly by a heater, for example, by an electric heater disposed within the roller  12 .  
         [0033]     The shaper  14  is an elastically flexible laminar sheet, i.e., a sheet that can be bent from its initial configuration during forming without undergoing any appreciable plastic deformation so that the shaper  14  can return to its initial configuration after processing and can be re-used. The shaper  14  can be formed of a variety of materials, including, for example, a sheet of stainless steel which is about 0.015 inches thick. In the illustrated embodiment, the shaper  14  is configured so that a first edge  24  is parallel to the roller  12  and connected to the roller  12 , though in other embodiments, the first edge  24  can be oriented in other configurations and need not be connected to the roller  12 . The shaper  14  is slidably adjustable relative to the roller  12  so that a second edge  26  of the shaper  14  opposite the first edge  24  is adjustable between first and second positions. In the first position, the shaper  14  extends from the roller  12  as shown in  FIGS. 1 and 3 . In the second position, the second edge  26  of the shaper  14  is adjusted toward the roller  12  and the shaper  14  is at least partially bent around the roller  12 , as shown in  FIG. 4 . The shaper  14  can engage tracks  17  or other features provided on the frame  16 , which maintain the second edge in a parallel arrangement with the roller  12 . By the term “advanced” it is generally meant that a portion of the shaper  14  that is not bent around the roller  12  is adjusted toward the roller  12  to increase the portion of the shaper  14  that is bent around the roller  12 , for example, by increasing the diameter of the portion bent around the roller  12  or by further extending the shaper  14  circumferentially around the roller  12 . If the apparatus  10  is configured as shown in  FIGS. 3 and 4 , the shaper  14  can be advanced by adjusting the second edge  26  toward the roller  12 .  
         [0034]     Adjustment of the shaper  14  to the second position can be accomplished by rotating the roller  12  in a first direction, clockwise as shown in  FIGS. 3 and 4 , so that the first edge  24  of the shaper  14  rotates around at least part of the roller  12 , the shaper  14  bends, and the second edge  26  of the shaper  14  is advanced toward the roller  12 . As the roller  12  is rotated in a second direction, counterclockwise in  FIGS. 3 and 4 , the shaper  14  unrolls from the roller  12  and the second edge  26  is retracted from the roller  12 . The roller  12  can be actuated by an automated device such as an electric motor or the roller can be manually actuated, for example, by a crank  13  that is rotated by an operator. Alternatively, the roller  12  can be configured to rotate freely so that the shaper  14  can be advanced toward the roller  12 , either manually or by an actuator, thereby rotating the roller  12  and rolling the shaper  14  around the roller  12 . In another embodiment, the first edge  24  of the shaper  14  is not connected to the roller  12 , and the shaper  14  can be advanced into the shroud  18  so that the shaper  14  bends around the roller  12 , which can remain stationary. In either case, the second edge  26  of the shaper  14  can be adjusted relative to the roller  12  while the roller  12  is held in place so that a portion of the shaper  14  that is disposed around the roller  12  is adjusted radially outward from the roller  12  to a desired configuration, generally defining a maximum circumference of the sheet  50 , as described further below.  
         [0035]     The extent to which the shaper  14  is rolled around the roller  12  can be determined according to the desired shape of the formed sheet  60 . For example, the shaper  14  and thermoplastic sheet  50  can be advanced slightly more than one revolution around the roller  12  so that the resulting formed sheet  60  defines a generally cylindrical shape with overlapping longitudinal edges that can be joined to form a tubular duct. Alternatively, the sheet  50  can be rotated less than one revolution around the roller  12  to form an arc or, channel, or spiral, or the sheet  50  can be rotated more than one revolution to form a spiral shape.  
         [0036]     During operation, the thermoplastic sheet  50  is disposed on the shaper  14  as shown in  FIG. 1  so that the sheet  50  is rolled around the roller  12  between the shaper  14  and the roller  12 . While the sheet  50  is supported between the shaper  14  and the roller  12 , the heater  22  can be used to heat the sheet  50 , e.g., by connecting a power supply (not shown) to the heater  22  and energizing the heater  22 . Preferably, the sheet  50  is heated to a processing temperature that is less than the glass transition temperature of the thermoplastic material of the sheet  50 . For example, the processing temperature can be between about 5° F. and 70° F. less than the glass transition temperature. In the case of PEI, which has a glass transition temperature of about 417° F., the sheet  50  can be heated to a processing temperature of between about 347° F. and 412° F. The sheet  50  can be maintained at the processing temperature for a predetermined period, such as about 10 minutes, after which the heater  22  can be turned off and the formed sheet  60  is preferably at least partially cooled in the apparatus  10 . The formed sheet  60  can be removed from the apparatus  10  through openings  28 ,  30  at the longitudinal ends of the heat shroud  18 , or the heat shroud  18  can be configured to disassemble or otherwise open to facilitate the removal of the formed sheet  60 . Alternatively, the formed sheet  60  can be removed by reversing the load process, i.e., unwinding the formed sheet  60  from the heat shroud  18  in a direction opposite to the direction in which the sheet  50  is inserted so that the formed sheet  60  unwinds around the outside of the heat shroud  18 .  
         [0037]     The thermoplastic sheet  50  can be a precut sheet that corresponds to the desired dimensions of the formed sheet  60  so that the formed sheet  60  is trimmed only slightly or not at all after processing in the apparatus  10 . Alternatively, the thermoplastic sheet  50  can be part of a long continuous sheet, such as a roll of thermoplastic laminar material, and the sheet  50  can be cut during or after processing. In either case, the shaper  14  can include an index feature that engages a portion of the sheet  50  so that the adjustment of the sheet  50  into the apparatus  10  can be easily controlled and/or measured. For example, the shaper  14  can include a gate  32  at the second edge  26 , as shown in  FIGS. 1, 3 , and  4 . The sheet  50  can be disposed on the shaper  14  so that an edge of the sheet  50  rests against the gate  32 , and the gate  32  prevents the sheet  50  from slipping relative to the shaper  14  when the shaper  14  is advanced around the roller  12 .  
         [0038]     According to one embodiment of the present invention, the sheet  50  is disposed on the shaper  14 , and the roller  12  is rotated through a predetermined angle of rotation. The roller  12  can be rotated using the actuator or crank  13 , or the second edge  26  of the shaper  14  can be urged toward the roller  12  to rotate the roller  12 . The roller  12  is then held at the desired rotational position while the second edge  26  of the shaper  14  is adjusted toward or away from the roller  12  to increase or decrease the diameter of a generally cylindrical portion of the shaper  14  bent around the roller  12 . By keeping the second edge  26  parallel to the first edge  24 , a constant radius can be imparted to the formed sheet  60 . Alternatively, the second edge  26  can be positioned in a non-parallel, or skewed, relationship relative to the first edge  24  so that a non-uniform, or transitional radius, is imparted to the formed sheet  60 , i.e., the radius at one end  66  is different than the other end  64  of the formed sheet  60 .  
         [0039]     The shaper  14  also adjusts the sheet  50  to a desired configuration. For example, the sheet  50  can be engaged by the gate  32 , and the gate  32  can be adjusted toward the roller  12  so that substantially all of the sheet  50  is bent around the roller  12 . Thus, if the sheet  50  is long enough to extend substantially from the first edge  24  of the shaper  14  to the gate  32 , the sheet  50  will be disposed against the shaper  14  when the shaper  14  is bent around the roller  12 . The length of the sheet  50  can be selected according to the desired size of the finished shape, and the gate  32  can be adjustable on the shaper  14  so that the shaper  14  can be used for sheets  50  of different lengths, the length of each sheet  50  generally determining the circumferential size of the formed sheet  60 . If the sheet  50  is longer than the circumference of the formed sheet  60 , the formed sheet  60  can be trimmed after forming.  
         [0040]     A second shaper  34  similar to the first shaper  14  can also be disposed on the thermoplastic sheet  50  so that the second shaper  34  is rolled around the roller  12  between the sheet  50  and the roller  12 , as shown in  FIG. 5 . The second shaper  34  can be slidably adjustable toward the roller  12 , as described above in connection with the first shaper  14 . Thus, the first shaper  14  can be advanced a predetermined distance toward the roller  12  to define a maximum outer dimension of the formed sheet  60 , and the second shaper  34  can be advanced a predetermined distance toward the roller  12  to urge the sheet  50  radially outward toward the first shaper  14 . The shapers  14 ,  34  can be adjusted radially outward by advancing the rollers  14 ,  34  after the roller  12  has been rotated to a desired position and held in that position. Alternatively, the shapers  14 ,  34  can be adjusted radially outward by advancing the shapers  14 ,  34  while the roller  12  is being rotated, the shapers  14 ,  34  being advanced at a rate faster than the speed of a periphery of the roller  12 . The second shaper  34  can be connected to the roller  12  or the first shaper  14 , or the second shaper  34  can be connected to neither. In the illustrated embodiment, however, the second shaper  34  is also attached to the roller  12 , albeit at a location spaced circumferentially from the location at which the first shaper  14  is attached to the roller  12  so that the sheet  50  may be disposed therebetween. Additionally, the second shaper  34  can have a gate  35  or other index feature for engaging the sheet  50 . As shown, for example, the gate  35  of the second shaper  34  may extend toward the first shaper  14  such that the sheet  50  is retained therebetween.  
         [0041]     In another embodiment of the present invention, the apparatus  10  includes one or more radially adjustable members  40 , as shown in  FIGS. 6 and 7 . Each member  40  can be a longitudinal member such as a rod, a shoe, or the like that extends generally parallel to the roller  12 . The members  40  are configured to be adjusted relative to the roller  12  to provide support to the shaper  14  and the sheet  50 . The members  40  can be adjusted to a first position, shown in  FIG. 6 , so that the members  40  do not interfere with the entry and bending of the shaper  14  and sheet  50  around the roller  12 . The members  40  can then be adjusted toward the roller  12  to bias the shaper  14  and the sheet  50  to a particular configuration. For example, if the shaper  14  and sheet  50  do not maintain a cylindrical shape when bent around the roller  12 , the members  40  can be actuated radially inwards, as shown in  FIG. 7 , to engage the shaper  14  and urge the shaper  14  to the desired configuration. The members  40  can also be used to bend the shaper  14  to other shapes, including shapes with flattened portions or complex curves. Any number of members  40  can be provided in the apparatus  10 , and the members  40  need not be straight or extend the entire length of the apparatus  10 . Further, the members  40  can be positioned within the shaper  14 , i.e., between the sheet  50  and the roller  12 , so that the members  40  can be actuated outward toward the sheet  50  and shaper  14 .  
         [0042]      FIGS. 8 and 9  illustrate an alternative forming apparatus  110  in which a shaper  114 , similar to the shaper  14  described above, is supported on a plurality of support members  140  that are supported by a frame  116 . The support members  140  can be longitudinal members such as rods or other shapes that are arranged in a generally parallel configuration, as shown in  FIG. 8 , so that the members  140  define spaces  142  therebetween. In other embodiments, the support members  140  can be arranged in other configurations, in which the support members  140  need not be parallel. A heater  122  can be provided within each member  140  or elsewhere in the apparatus  110 , and the apparatus  110  can be partially or completely enclosed by an insulative shroud  118 . The thermoplastic sheet  50  is disposed on a first side of the shaper  114 , and a second side of the shaper  114  is disposed against the members  140  so that the shaper  114  extends across the spaces  142  between the members  140  and so that the sheet  50  can bend between the members  140 , as shown in  FIG. 9 . The shaper  114  and the sheet  50  can be bent by gravity, or opposing support members  144  can be provided, as shown in  FIG. 10 , for urging the sheet  50  to a desired configuration. A second shaper  134  can also be provided on the sheet  50  opposite the first shaper  114 , as shown in  FIG. 10 , i.e., between the sheet  50  and the members  144 .  
         [0043]     Each of the members  140 ,  144  can be adjustable in position, for example, in a direction transverse to the longitudinal direction of the members  140 ,  144 . Thus, as shown in  FIG. 10 , each of the members  140 ,  144  can be adjusted in any direction to determine the shape of the formed sheet  60 . The members  140 ,  144  can be mounted on tracks or other adjustable supporting devices, and each member  140 ,  144  can be adjusted manually, or actuators can be provided for such adjustment. For example,  FIG. 10  illustrates a plurality of actuators  146 , each of which is configured to extend or retract a respective one of the members  140 ,  144  toward or away from the sheet  50 .  
         [0044]     During one typical method of operation, the shaper  114  is disposed on the members  140 , the sheet  50  is disposed on the shaper  114 , the second shaper  134  is disposed on the sheet  50 , and the members  140 ,  144  are adjusted to a desired configuration. The heater  122  is used to heat the sheet  50 , preferably to a processing temperature that is less than the glass transition temperature of the thermoplastic material of the sheet  50 , as described above. The sheet  50  can be maintained at the processing temperature for a predetermined period, after which the heater  122  can be turned off. Preferably, the formed sheet  60  is at least partially cooled in the apparatus  110 . The formed sheet  60  is then removed from the apparatus  110 .  
         [0045]     The support members  140  can define different shapes than that shown in  FIGS. 8-10 . For example, as shown in  FIG. 11 , an apparatus  110   a  can include one or more rod- or tube-shaped support members  140   a  defining ends that extend from a frame  116   a  and upon which a shaper  114   a  can be disposed. The shaper  114   a  can extend perpendicular to the longitudinal direction of the support member  140   a , and the sheet  50  can be disposed on the shaper  114   a . Further, the shaper  114   a  and, hence, the sheet  50  can be elastically deformed to a compound contour, i.e., bent about more than one axis. For example, as shown in  FIG. 11 , the shaper  114   a  can define a partial spherical surface.  
         [0046]     As described above, the edges  68 ,  70  or other portions of the formed sheet  60  can be joined, for example, by consolidation joining. Further, the formed sheet  60  can be post-formed to provide additional contours or features, such as bells, beads, and the like. A discussion regarding the formation of features such as bells and beads through post-forming, i.e., after the forming and/or the consolidation joining of the sheet, is provided in U.S. application Ser. No. 10/215,780, titled “Post-Forming of Thermoplastic Ducts” filed Aug. 9, 2002, which is assigned to the Assignee of the present invention and the entirety of which is incorporated herein by reference. It is also appreciated that marks can be provided on the thermoplastic sheet, for example, to accurately identify the location of such post-formed features or to facilitate the manufacture or assembly of the formed sheets, as provided in the application entitled “Thermoplastic Laminate Duct.” 
         [0047]     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, it is appreciated that each of the components of the described apparatuses can be formed of a variety of materials such as aluminum, steel, and alloys thereof, and each of the working surfaces of the apparatuses can include a low friction layer or release layer, e.g., Teflon®, registered trademark of E.I. du Pont de Nemours and Company. The release layer can be a durable layer of material or a release agent that is wiped or sprayed periodically onto the working surfaces. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.