Abstract:
Provided are induction heating cells including pressure bladders used for supporting dies and methods of using these induction heating cells. A pressure bladder may be disposed between a die and a bolster of the cell. Even when the bolster is deformed during operation of the cell, the pressure bladder continues to provide uniform support to the die thereby preserving integrity of the die and prevents its cracking or braking. As such, the cell may be operated at a higher processing pressure inside the cavity formed by the die without further strengthening the bolster. The bolster is allowed to deform without compromising the integrity of the die. The deformation of the bolster is compensated by the shape change of the pressure bladder. The number and/or position of the bladders in the cell may depend on the shape of processed parts.

Description:
BACKGROUND 
       [0001]    Processing large parts and/or parts having complex shapes in pressurized tools can be very challenging. When a pressure is applied to a large surface of a tool, substantial forces may be generated and transferred to various supporting structures causing these structures to deform. Processing complex shapes may generate forces in many different complicating support functions. Furthermore, many materials used in these pressurized tools may not be able to support mechanical loads, such as tensile loads. For example, ceramic materials may be used in induction heating systems because many ceramic materials do not interact with electromagnetic radiation, which may be used for heating in these system. The ceramic materials allow electromagnetic waves to pass to other (e.g., internal) components of the tool to achieve, for example, localized heating. While ceramic materials can withstand high compressive loads, these materials are very brittle when subjected to tensile loads. Tensile loads may be generated when structures supporting ceramic components deform. 
       SUMMARY 
       [0002]    Provided are induction heating cells including pressure bladders used for supporting dies and methods of using these induction heating cells. A pressure bladder may be disposed between a die and a bolster of the cell. Even when the bolster is deformed during operation of the cell, the pressure bladder continues to provide uniform support to the die thereby preserving integrity of the die and prevents its cracking or breaking. As such, the cell may be operated at a higher processing pressure inside the cavity formed by the die without further strengthening the bolster. The bolster is allowed to deform without compromising the integrity of the die. The deformation of the bolster is compensated by the shape change of the pressure bladder. The number and/or position of the bladders in the cell may depend on the shape of processed parts. 
         [0003]    In some embodiments, a method for processing a part using an induction heating cell comprises positioning the part into a processing cavity formed by a first die and a second die and applying a processing pressure to the processing cavity while controlling a first pressure inside a first bladder and controlling a second pressure inside a second bladder. The first bladder may be disposed between the first die and a contact surface of a first bolster. The second bladder may be disposed between the second die and a contact surface of a second bolster. 
         [0004]    In some embodiments, the ratio of the first pressure inside the first bladder to the second pressure inside the second bladder is kept constant. Furthermore, the ratio the first pressure inside the first bladder to the processing pressure inside the processing cavity is kept constant for at least a period of time while changing the processing pressure inside the processing cavity. In some embodiments, controlling the first pressure inside the first bladder comprises controlling amount of gas inside the first bladder. The first bladder and the processing cavity may be connected to a gas source. Alternatively, controlling the first pressure inside the first bladder and controlling the second pressure inside the second bladder comprises changing position of the first die relative to the second die. In some embodiments, controlling the first pressure inside the first bladder comprises controlling a distance between the contact surface of the first bolster and the first dies. 
         [0005]    In some embodiments, the method further comprises controlling a third pressure inside a third bladder and controlling a fourth pressure inside a fourth bladder. The third bladder may be disposed between the first die and a contact surface of a third bolster. The fourth bladder may be disposed between the first die and a contact surface of a fourth bolster. The contact surface of the third bolster may be parallel to the contact surface of the fourth bolster. The contact surface of the first bolster may be perpendicular to the contact surface of the third bolster. In some embodiments, the third bladder is disposed between the second die and the contact surface of the third bolster. The fourth bladder may be also disposed between the second die and the contact surface of the fourth bolster. The third pressure inside the third bladder and the fourth pressure inside the fourth bladder may be independently controlled from the first pressure inside the first bladder and the second pressure inside the second bladder. In some embodiments, the ratio of the third pressure inside the third bladder to the fourth pressure inside the fourth bladder is kept constant. 
         [0006]    In some embodiments, the contact surface of the first bolster is parallel to the contact surface of the second bolster prior to applying the processing pressure to the processing cavity. More specifically, each of the contact surface of the first bolster and the contact surface of the second bolster is substantially planar prior to applying the processing pressure to the processing cavity. 
         [0007]    The contact surface of the first bolster may unevenly deform while applying the processing pressure to the cavity. The first bladder may fill all space between the contact surface of the first bolster and the first die above the cavity while the contact surface of the first bolster unevenly deforms away from the first die. The first bolster may be supported by at least one post relative to the second bolster. The first bolster may not apply a bending load onto the at least one post while the first bolster unevenly deforms away from the first die. The post has a cylindrical profile. The post protrudes through an opening in the first bolster. The opening has a cone profile. 
         [0008]    In some embodiments, the method further comprises monitoring deformation of the first bolster while applying the processing pressure to the cavity. The first pressure inside the first bladder may be controlled based on applied pressure inside the forming cavity. 
         [0009]    In some embodiments, the contact surface of the first bolster does not directly contact the first die while applying the processing pressure to the cavity. The contact surface of the second bolster may not directly contact the second die while applying the processing pressure to the cavity. 
         [0010]    In some embodiments, the method further comprising inductively heating a portion of the first die and the second die. The inductive heating may be performed while applying the processing pressure to the processing cavity. The inductive heating may commence prior to applying the processing pressure to the processing cavity. The first die and the second die may be permeable to electromagnetic waves of the inductive heating. For example, the first die and the second die may each comprise one of a ceramic or a composite material. The inductive heating may comprise providing an alternating current to a coil extending through the first die and the second die. The alternating current may have a frequency of between about 1-50 kHz. The part may be inductively heated to at least about 500 F. The processing pressure may be at least about 100 psi. 
         [0011]    In some embodiments, the part is a composite part. Applying the processing pressure to the processing cavity may be a part of curing the composite part. Alternatively, applying the processing pressure to the processing cavity is a part of superplastic forming. In some embodiments, the part is a non-planar part. 
         [0012]    Provided also is an induction heating cell comprising a first die, a second die, a first bolster, a second bolster, a first bladder, and a second bladder. The first die and the second die may form a cavity. The first bolster may comprises a contact surface facing the first die. The second bolster may comprise a contact surface facing the second die. The first dies and the second die may be disposed between the contact surface of the first bolster and the contact surface of the second bolster. The first bladder may be disposed between the first die and the contact surface of the first bolster. The second bladder may be disposed between the second die and the contact surface of the second bolster. 
         [0013]    In some embodiments, the induction heating cell further comprises a gas source connected to the first bladder for controlling a first pressure inside the first bladder and connected to the second bladder for controlling a second pressure inside the second bladder. The gas source may be coupled to the process cavity and used for controlling a processing pressure inside the processing cavity. 
         [0014]    The induction heating cell may comprise a system controller for determining a first pressure inside the first bladder and controlling a second pressure inside the second bladder. The system controller may be configured to apply a processing pressure inside the processing cavity. The system controller may be configured to determine deformation of at least one of the first bolster or the second bolster. 
         [0015]    In some embodiments, the induction heating cell also comprises a third bladder and a fourth bladder. The third bladder may be disposed between the first die and a contact surface of a third bolster, while the fourth bladder may be disposed between the first die and a contact surface of a fourth bolster. The contact surface of the third bolster may be parallel to the contact surface of the fourth bolster. The contact surface of the first bolster may be perpendicular to the contact surface of the third bolster. The third bladder may be also disposed between the second die and the contact surface of the third bolster. The fourth bladder may be also disposed between the second die and the contact surface of the fourth bolster. In some embodiments, the third pressure inside the third bladder and the fourth pressure inside the fourth bladder are independently controlled from a first pressure inside the first bladder and a second pressure inside the second bladder. 
         [0016]    In some embodiments, the contact surface of the first bolster is substantially parallel to the contact surface of the second bolster. The first bolster may be supported by at least one post relative to the second bolster. The post may have a cylindrical profile. The post may protrude through the opening in the first bolster. The opening may have a cone profile. 
         [0017]    In some embodiments, the induction heating cell also comprises an inductive coil disposed within the first die and the second die. The processing cavity may be non-planar. The first die and the second die may each be comprised of a ceramic or a composite material. 
         [0018]    These and other embodiments are described further below with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  is a schematic perspective view of an induction heating cell, in accordance with some embodiments. 
           [0020]      FIG. 1B  is a schematic cross-sectional view of an induction heating cell, in accordance with some embodiments. 
           [0021]      FIG. 1C  is a schematic cross-sectional view of another induction heating cell, in accordance with some embodiments. 
           [0022]      FIG. 1D  is a schematic cross-sectional view of yet another induction heating cell, in accordance with some embodiments. 
           [0023]      FIG. 1E  is a schematic view of an induction heating system including an induction heating cell and other components, in accordance with some embodiments. 
           [0024]      FIG. 2  is a process flowchart corresponding to a method for processing a part using an induction heating cell, in accordance with some embodiments. 
           [0025]      FIG. 3A  is a schematic cross-sectional view of a stack of a bolster, pressure bladder, and die prior to applying any pressure inside a processing cavity formed by the die, in accordance with some embodiments. 
           [0026]      FIG. 3B  is a schematic cross-sectional view of the stack of the bolster, pressure bladder, and die also shown  FIG. 3A  after to applying the pressure inside the processing cavity, in accordance with some embodiments. 
           [0027]      FIG. 3C  is a schematic cross-sectional view of a stack including a bolster and die after applying the pressure inside the processing cavity, in accordance with some embodiments. 
           [0028]      FIG. 4A  is a schematic cross-sectional view of a post and a bolster prior to deforming the bolster, in accordance with some embodiments. 
           [0029]      FIG. 4B  is a schematic cross-sectional view of the post and the bolster of  FIG. 4A  after deforming the bolster, in accordance with some embodiments. 
           [0030]      FIGS. 5A and 5B  are examples of pressure and temperature profiles applied to the part processed used an induction heating cell, in accordance with some embodiments. 
           [0031]      FIG. 6  illustrates the effect of the side bladders on the internal forces of the die showing that the brittle ceramic tool material can be kept in compression. 
           [0032]      FIG. 7  is a block diagram of aircraft production and service methodology that may utilize methods and systems for curing composite structures without collapsing cavity sections as described herein. 
           [0033]      FIG. 8  is a schematic illustration of an aircraft that may include composite structures described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the presented concepts. The presented concepts may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to not unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific embodiments, it will be understood that these embodiments are not intended to be limiting. 
       INTRODUCTION 
       [0035]    An induction heating cell may include two or more ceramic or composite dies forming a processing cavity for receiving parts processed using the cell. The induction heating cell may also include induction coils integrated into the dies. This cell can be used for consolidation and/or curing of thermoplastic and other composites. In some embodiments, the cell may be used for superplastic forming of titanium parts and/or other metal parts. One having ordinary skill in the art would understand that other applications of the induction heating cell are also within the scope of this disclosure. 
         [0036]    During operation of the cell, the induction coil generates an oscillating electromagnetic field, which can pass though the dies without much interference. The material of the die may be specifically selected to allow this unobstructed passage of the electromagnetic radiation. The induction heating cell and/or the processed part may include susceptors that absorb the electromagnetic energy of the field and converts this energy into the localized heat. As such, the processed part can be heated without heating most of the induction heating cell. This localized heating approach eliminates a substantial thermal mass from the overall cell and allows quick heating up and cooling down cycles. Not only processing throughput and efficiencies are substantially increased in comparison to convection or other types of heating, but this approach also results in substantial energy savings. 
         [0037]    During processing, the dies may be subjected to various loads generated, for example, by pressing the dies against each other and/or by pressurizing a processing cavity formed by the dies. As noted above, the material of the dies, such as ceramic or composite materials, are not susceptible to inductive heating. Furthermore, these materials may have small coefficients of thermal expansion and heat transfer and may be, resistant to a thermal shock. Finally, the materials may have high compression strength. However, these materials may easily crack when subjected to tensile loads. To address these issues, the dies may be reinforced with fiberglass rods and posts tensioned to apply compressive forces to the ceramic dies. While this approach works well for planar parts, it does not work well for curved parts. The tooling tolerances may be less than about 0.020 inches or even less than about 0.010 inches. 
         [0038]    When parts with complex geometries (e.g., highly convoluted parts) are being processed using an induction heating cell, tensile loads applied to the dies of the cell should be minimized. Achieving this goal can be challenging because even minor bending of supporting components, e.g., bolster, may cause large tensile loads. Overall, the loads applied to the induction heating cell and its component when processing large and/or convoluted parts can be non-uniform and may change as a result of bending. 
         [0039]    It has been found that positioning a pressure bladder between a die and its supporting structure (e.g., a bolster) provides uniform support to the die regardless of the deformation of the supporting structure. The pressure bladder may occupy the entire space between the die and supporting structure (at least corresponding to a projection of the processing cavity) even when the supporting structure deforms. Specifically, the pressure bladder changes its shape together with the deformation of the supporting structure and ensure continuous uniform support to the die. 
         [0040]    Any number of pressure bladders may be provided in the same induction heating cell. The pressure bladders may be sized and located based on the design of the processing cavity and, more specifically, based on evaluating the induction heating cell and determining the development of tensile loads acting on the ceramic dies during processing. 
         [0041]    In some embodiments, the method of using an induction heating cell may involve supplying a gas into a processing cavity to pressurize this cavity or, more specifically, to pressurize the part disposed within the cavity and being processed using the induction heating cell. The same or a different gas may be used for pressurizing bladders. In some embodiments, the amount of gas within the pressure bladders may change during operation of the induction heating cell and may depend, for example, on the processing pressure inside the cavity. This feature may be also used to advance dies with respect to each other and/or to balance the force generated while pressurizing the processing cavity. As such, the bladders may be pressurized in concert with pressurizing the processing cavity thereby ensuring that only compressive loads are being applied to the ceramic dies. 
         [0042]    Alternatively, the amount of gas in the bladders may remain constant and the pressure is controlled by changing the volume of the bladders. For example, supporting structures may be advanced in concert with pressurizing the processing cavity. 
         [0043]    Without being restricted to any particular theory, it is believed that pressure bladders disposed between dies and bolsters provide uniform support (e.g., exert evenly distributed force/pressure) to the dies while the bolsters are allowed to bend. To accommodate some bending, the openings in the bolsters that accept restraint posts may be conical in shape or at least some additional space for the posts to occupy as the bolsters are bending. This feature allows the bolsters to bend but without applying bending loads on the posts. 
       Examples of Systems and Methods of Using Such Systems 
       [0044]      FIG. 1A  is a schematic perspective view of induction heating cell  100 , in accordance with some embodiments. Induction heating cell  100  includes first die  112   a  and second die  112   b . Depending on the orientation of induction heating cell  100 , first die  112   a  may be also referred to as an upper die, while second die  112   b  may be referred to as a lower die. First die  112   a  and second die  112   b  in combination define processing cavity  114  as illustrated in  FIGS. 1B and 1C . Processing cavity  114  is shaped to correspond to a part being processed in processing cavity  114 . For example,  FIG. 1B  illustrates processing cavity  114  used for planar parts, while  FIGS. 1C and 1D  illustrate processing cavities  114  for non-planar parts. Because processing cavity  114  may be pressurized during processing, different forces will act on first die  112   a  shown in  FIG. 1B  in comparison to first die  112   a  shown in  FIG. 1C  or first die shown in  FIG. 1D . For example, first die  112   a  shown in  FIG. 1B  will experience forces primarily in the Z direction, at least prior to bending of first bolster  102   a . On the other hand, first die  112   a  shown in  FIG. 1C  will experience forces in both Z and X directions. One having ordinary skill in the art would understand the three dimensional aspects of the force distribution and examples when first die  112   a  will also experience forces in the Y direction. Furthermore, one having ordinary skill in the art would understand the forces applied to second die  112   a  and support need for this die  112   a . As such, other configurations of processing cavities  114 , corresponding first dies  112   a  and second dies  112   b , and support to these dies (further described below) are within the scope of this disclosure. 
         [0045]    First die  112   a  and second die  112   b  may be positioned between first bolster  102   a  and second bolster  102   b  as shown in  FIGS. 1A-1D . Depending on the orientation of induction heating cell  100 , first bolster  102   a  may be also referred to as an upper bolster or an upper strongback, while second bolster  102   b  may be referred to as a lower bolster  102   b  or a lower strongback. First bolster  102   a  and second bolster  102   b  may be formed of steel, aluminum, or any other material capable of handling the loads present during panel forming. In some embodiments, a non-magnetic material, such as aluminum or some steel alloys, may be used for bolsters  102   a  and  102   b  to avoid any distortion to the magnetic field produced by induction coils  142 , as described below. 
         [0046]    Induction coils  142  may be integrated into first die  112   a  and second die  112   b , for example, shown in  FIG. 1B . For simplicity and clarity of  FIGS. 1C and 1D , induction coils are not shown in these figures. Referring to  FIG. 1A , induction coils  142  may be a part of heating system  186  used for heating the part disposed within processing cavity  114 . Induction coils  142  may extend longitudinally through the length of first die  112   a  adjacent to processing cavity  114  and through the length of second die  112   b  adjacent to processing cavity  114 . As one example, induction coils  142  may be embedded within and extend through an interior of dies  112   a  and  112   b . In some embodiments, each of dies  112   a  and  112   b  holds straight tubing sections  153  of induction coils  142  in proper position in relationship to susceptor liners forming processing cavity  114 . Specifically, each induction coil  142  may be formed from straight tubing sections  153  that extend along the length of each of dies  112   a  and  112   b  and flexible coil connectors  155  that join straight tubing sections  153  in first die  112   a  to straight tubing sections  153  in second die  112   b.    
         [0047]    Induction coils  142  may be connected to an external power source (e.g., a coil driver) and, in some embodiments, to a source of coolant. Connectors  174  located at the ends of inductive coils  142  may be used for these purposes. As such, induction coils  142  may also remove thermal energy by serving as a conduit for a coolant fluid, such as water. As one example, four separate induction coils  142  may be used. However, other numbers of induction coils  142  may also be used without limitation. 
         [0048]    Referring to  FIGS. 1A and 1B , dies  112   a  and  112   b  may be reinforced with fiberglass rods  148 . Fiberglass rods  148  may extend both longitudinally and/or transversely in a grid through each of dies  112   a  and  112   b  to increase the strength of dies  112   a  and  112   b . As one example, fiberglass rods  148  extend both longitudinally and transversely each of dies  112   a  and  112   b . After casting the interior of dies  112   a  and  112   b , fiberglass rods  148  may be post-tensioned through the use of tensioning nuts  170 . Post-tensioning fiberglass rods  148  maintains a compressive load on dies  112   a  and  112   b  to prevent cracking or damage of dies  112   a  and  112   b  during operation of induction heating cell  100 . 
         [0049]    First bolster  102   a  and second bolster  102   b  may be supported with respect to each other using posts  104 . Posts  104  may be threaded. For example, jackscrews may be used as posts  104 . In some embodiments, first bolster  102   a  and second bolster  102   b  may be threadably coupled to each of posts  104  using threads on first bolster  102   a  and second bolster  102   b  or a set of nuts. With this threadable coupling, posts  104  may be used to change the distance between first bolster  102   a  and second bolster  102   b , e.g., by turning posts  104  using a bellows or other actuation mechanisms. Movement of first bolster  102   a  and second bolster  102   b  move respective first die  112   a  and second die  112   b  in relation to each other to form processing cavity  114 . Furthermore, movement of first bolster  102   a  and second bolster  102   b  may be used to control the pressure inside first bladder  116  and second bladder  116   a  as further described below. 
         [0050]    As shown in  FIG. 1B , first bolster  102   a  has first contact surface  103   a  facing first die  112   a , while second bolster  102   b  has second contact surface  103   b  facing second die  112   b . Conventionally, bolsters come in direct contact with dies and have to be rigid and be able to maintain their surfaces substantially flat (e.g., within the planar deviation of 0.003 inches per square foot or less) to prevent bending and/or cracking of the dies. This approach requires bulky bolsters, posts, and other components and is generally limited to small dies. Even small deformation of a bolster may create highly undesirable tensile loads within the dies. 
         [0051]    In order to maintain even support to first die  112   a  and second die  112   b  without requiring first bolster  102   a  and second bolster  102   b  to remain substantially flat, induction heating cell  100  may include pressure bladders  116   a  and  116   b . Specifically, first bladder  116   a  may be positioned between first bolster  102   a  and first die  112   a , while second bladder  116   b  may be positioned between second bolster  102   b  and second die  112   b . First bladder  116   a  may be in direct contact with one of first bolster  102   a  or first die  112   a  (e.g., at least first bolster  102   a ) or both first bolster  102   a  or first die  112   a . Likewise, second bladder  116   b  may in direct contact between the second bolster  102   b  or second die  112   b  (e.g., at least second bolster  102   b ) or both second bolster  102   b  or second die  112   b . Despite first bolster  102   a  and second bolster  102   b  not being substantially flat (e.g., the planar deviation of at least about 0.005 inches per square foot or even of at least about 0.010 inches per square foot), first die  112   a  and second die  112   b  experience uniform support. In some embodiments, the maximum planar deviation of first bolster  102   a  and second bolster  102   b  may be set by the maximum thickness of first bladder  116   a  and second bladder  116   b.    
         [0052]    Pressure bladders  116   a  and  116   b  may have the same size and construction or different sizes and/or construction. Referring to  FIG. 1B , pressure bladders  116   a  and  116   b  may be greater than the projection of processing cavity  114  in the Z direction. As such, pressure bladders  116   a  and  116   b  may provide support to dies  112   a  and  112   b  over the area larger than the area of processing cavity  114  (the areas being parallel to the X-Y plane). 
         [0053]    In some embodiments, pressure bladders  116  and  116   b  may be made from a thin metal (e.g., steel) or polymer. The selection of the material for pressure bladders  116   a  and  116   b  may depend on the operating temperatures and/or pressure. In some embodiments, even though the part may be heated to at least about 500 F, the temperature of pressure bladders  116   a  and  116   b  may be less than 200 F. In fact, the temperature variation of pressure bladders  116   a  and  116   b  during operation of induction heating cell  100  may be less than 100 F or even less than 50 F to ensure that this temperate variation does not cause undesirable pressure variations (e.g., when no gas is added or removed from pressure bladders  116   a  and  116   b ). 
         [0054]    In some embodiments, first die  112   a  and first bladder  116   a  may be attached to first bolster  102   a  such that when first bolster  102   a  moves away from second bolster  102   b , first bolster  102   a  is also able to lift first die  112   a  and first bladder  116   a  away from second die  112   b . Any suitable fastening devices, such as bolting or clamping, may be used for this purpose. It should be noted that this attachment may not transfer any substantial force when first die  112   a  is pressed against second die  112   b  and/or when a processing pressure is applied into processing cavity  114 . During such operations, substantially all support (e.g., more than 90%) is provided by first bladder  116   a . In other words, a suitable fastening device may allow for changes in the gap between first bolster  102   a  and first die  112   a  thereby allowing deformations of first bolster. The same or similar fastening device may be used to support second die  112   b  and second bladder  116   b  relative to second bolster  102   b.    
         [0055]    Referring to  FIG. 1E , induction heating system  150  or induction heating cell  100  may include gas source  154  coupled to first bladder  116   a  and second bladder  116   b . Gas source  154  may be used for controlling the pressure inside first bladder  116   a  and controlling the pressure inside second bladder  116   b  using, for example, valves  156   a  and  156   b , respectively. In some embodiments, system controller  152  may control valves  156   a  and  156   b . Gas source  154  may be also coupled to processing cavity  114  for controlling the pressure inside processing cavity  114  using, for example, valve  156   c  as shown in  FIG. 1E . In other words, the same gas may be used for pressurizing bladders  116   a  and  116   b  and cavity  114 . 
         [0056]    System controller  152  may be configured to apply the desired pressure inside first bladder  116   a  and use this information for controlling the pressure inside second bladder  116   b . In some embodiments, system controller  152  may be configured to apply the pressure inside second bladder  116   b  and use this information for controlling the pressure inside first bladder  116   a . Other factors used by system controller  152  to control the pressure inside first bladder  116   a  and/or to control the pressure inside second bladder  116   b  may include, but are not limited to the pressure inside processing cavity  114 , deformation of first bolster  102   a  and/or second bolster  102   b , temperature of various components of system  150 , and the like. 
         [0057]    Referring to  FIGS. 1C and 1D , induction heating cell  100  may comprise third bladder  116   c  and fourth bladder  116   d . Third bladder  116   c  may be disposed between the first die  112   a  and contact surface  103   c  of third bolster  102   c . Fourth bladder  116   d  may be disposed between first die  112   a  and contact surface  103   d  of fourth bolster  102   d . The number and position of additional pressure bladders may be determined by loads applied to dies  112   a  and  112   b . For example, die  112   a  shown in  FIG. 1C  may experience loads along both X and Z axis because of the shape of processing cavity  114 . It should be noted that while first die  112   a  may be supported by third bolster  102   c  and fourth bolster  102   d  in addition to first bolster  102   a , second die  112   b  may be supported by only second bolster  102   b.    
         [0058]    Contact surface  103   c  of third bolster  102   c  may be parallel to contact surface  103   d  of fourth bolster  102   d . This parallel orientation of contact surfaces  103   c  and  103   d  used for supporting die  112   a  may be used to minimize tensile load components. In some embodiments, contact surface  103   a  of first bolster  102   a  may be perpendicular to contact surface  103   c  of third bolster  102   c.    
         [0059]    Referring to  FIG. 1D , third bladder  116   c  may be also disposed between second die  112   b  and contact surface  103   c  of third bolster  102   c  while fourth bladder  116   d  may be also disposed between second die  112   b  and contact surface  103   d  of fourth bolster  102   d . In this case, bladders  116   c  and  116   d  may be used to support both dies  112   a  and  112   b . Contact surface  103   b  of second bolster  102   b  may be perpendicular to contact surface  103   c  of third bolster  102   c . In some embodiments, contact surface  103   a  of first bolster  102   a  is substantially parallel to contact surface  103   b  of second bolster  102   b  regardless of the presence of bladders  116   c  and  116   d.    
         [0060]    In some embodiments, the pressure inside third bladder  116   c  and the pressure inside fourth bladder  116   d  may be independently controlled from the pressure inside first bladder  116   a  and the pressure inside second bladder  116   b . The ratio of the pressure inside third bladder  116   c  to the pressure inside fourth bladder  116   d  may be kept constant. Furthermore, the pressure inside third bladder  116   c  and the pressure inside fourth bladder  116   d  may depend on the pressure inside first bladder  116   a , the pressure inside second bladder  116   b , and/or the processing pressure inside processing cavity  114 . 
         [0061]    In some embodiments, first bolster  102   a  is supported by at least one post  104  relative to second bolster  102   b . For example,  FIG. 1A  illustrates four posts  104  supporting first bolster  102   a  relative to second bolster  102   b , but one having ordinary skill in the art would understand that any number of posts  104  may be used. Post  104  may have a cylindrical profile and may protrudes through opening  106  in first bolster  102   a  as, for example, shown in  FIGS. 1C, 4A, and 4B . Opening  106  may have a cone profile thereby allowing first bolster  102   a  to deform without applying bending loads to post  104  as schematically shown in  FIGS. 4A and 4B . More generally, the cross-sectional profile of opening  106  may be larger than the cross-sectional profile of post  104  thereby allowing first bolster  102   a  to deform. The same feature may be used on second bolster  102   b  as well. 
         [0062]      FIG. 2  is a process flowchart corresponding to method  200  for processing a part using induction heating cell  100 , in accordance with some embodiments. Various examples of induction heating cell  100  and its components are described above. 
         [0063]    Method  200  may commence with positioning the part into processing cavity  114  (referring to block  210  in  FIG. 2 ). As described above, processing cavity  114  may be formed by first die  112   a  and second die  112   b . During this operation, first die  112   a  may be moved away from second die  112   b  (e.g., lifted by first bolster  102   a ) such that a sufficient space is available between first die  112   a  and second die  112   b  to advance the part towards portions of dies  112   a  and  112   b  forming processing cavity  114 . The part may be positioned into a portion of processing cavity  114  formed by either first die  112   a  or second die  112   b . The part may be a composite layup for consolidation and/or cure, a metal part to be formed and/or heat treated. Some examples of parts that may be processed using this method and system include, but not limited to, thermoplastic composite wing structures, air vehicle body panels (e.g., made via super-plastically formed titanium), thermoplastic composite fuselage sections, hot formed metallic engine nacelle components, and the like. At the end of operation  210 , first die  112   a  and second die  112   b  may be brought closer together such that processing cavity  114  is formed. In some embodiments, when two dies  112   a  and  112   b  are brought together to seal processing cavity  114 , the compression force applied to dies  112   a  and  112   b  may be negligible in comparison to the forces generated when the pressure is applied to processing cavity  114 . 
         [0064]    Method  200  may comprise heating the part while the part is inside processing cavity  114  of induction heating cell  100 . This heating may be performed prior to applying a processing pressure to processing cavity  114  (referring to block  212  in  FIG. 2 ), while applying the processing pressure to processing cavity (referring to block  220  in  FIG. 2 ), or in both instances as will now be described with reference to  FIGS. 5A and 5B . 
         [0065]    Specifically,  FIGS. 5A and 5B  illustrate two examples of temperature and pressure profiles  500 . Referring to  FIG. 5A , the processed part is heated by heating system  186  (e.g., induction coils  142 ) to its processing temperature T. Once heated to that temperature T, the pressure is applied to the part disposed inside processing cavity  114 . For example, when forming a metal part at an elevated temperature or consolidating and/or curing a thermoplastic composite, processing cavity  114  may be pressurized.  FIG. 5B  is another example of temperature and pressure profiles  500 . 
         [0066]    Heating the part may expedite the curing process and/or make the part more conformal when, for example, the processing pressure is later applied. Heating the part may involve passing the electrical current through the induction coils of induction heating cell  100 . More specifically, heating may be inductive heating. First die  112   a  and second die  112   b  may be permeable to electromagnetic waves of the inductive heating. Specifically, first die  112   a  and second die  112   b  may each be comprised of a ceramic or a composite material. The inductive heating may comprise providing an alternating current to induction coil  142  extending through first die  112   a  and second die  112   b . The alternating current may have a frequency of between about 1-50 kHz. The part may be inductively heated to at least about 500 F. 
         [0067]    Method  200  may proceed with applying a processing pressure to processing cavity  114 , referring to block  220  in  FIG. 2 . Specifically, processing cavity  114  may be connected to an external gas source. In some embodiments, the processing pressure is constrained to processing cavity  114 . In other words, the ambient pressure outside of first die  112   a  and second die  112   b  may be different (e.g., less) that the processing pressure inside processing cavity  114 . In some embodiments, the processing pressure is between about 50 psi and 500 psi or, more specifically, between about 100 psi and 400 psi, such as at least about 100 psi or even at least about 150 psi or at least about 200 psi. 
         [0068]    In some embodiments, applying the processing pressure to cavity  114  may be performed while controlling the first pressure inside first bladder  116   a  and controlling the second pressure inside second bladder  116   b  (referring to blocks  230  and  240  in  FIG. 2 ). As described above, first bladder  116   a  may be disposed between first die  112   a  and first bolster  102   a  or, more specifically, between first die  112   a  and contact surface  103   a  of first bolster  102   a . Second bladder  116   b  may be disposed between second die  112   b  and second bolster  102   b  or, more specifically, between second die  112   b  and contact surface  103   b  of second bolster  102   b . Specifically, the pressure inside both bladders  116   a  and  116   b  may be self-controlled by changing the average thickness of bladders  116   a  and  116   b . For example, the relative position of bolsters  102   a  and  102   b  may be adjusted. Alternatively, the pressure inside both bladders  116   a  and  116   b  may be controlled by adding or removing gas from bladders  116   a  and  116   b . In some embodiments, controlling the pressure inside bladders  116   a  and  116   b  is performed in such a way that the relative position of first die  112   a  and second die  112   b  remain the same as the processing pressure is applied into processing cavity  114  during operation  220 . 
         [0069]    In some embodiments, the ratio of the first pressure inside first bladder  116   a  to the second pressure inside second bladder  116   b  is kept constant during operation  220 . 
         [0070]    This ratio ensures the force balance within induction heating cell  110  such that a combination of first die  112   a  and second die  112   b  remains stationary relative to both bolsters  102   a  and  102   b . The ratio may depend on the size of each of first bladder  116   a  and second bladder  116   b  or, more specifically, on the area of first bladder  116   a  contacting first die  112   a  and on the area of second bladder  116   b  contacting second die  112   b . In some embodiments, the ratio of the first pressure to the second pressure is between 0.9 and 1.1 or, more specifically, between 0.95 and 1.05, such as about 1. In some embodiments, the ratio of the first pressure to the second pressure is kept constant for at least a period of time while changing the processing pressure inside processing cavity  114 . 
         [0071]    Contact surface  103   a  of first bolster  102   a  may be substantially parallel to contact surface  103   b  of second bolster  102   b . However, when the processing pressure is applied to processing cavity  114 , one or both of contact surfaces  103   a  and  103   b  may deform and become non-planar. 
         [0072]    In some embodiments, contact surface  103   a  of first bolster  102   a  unevenly deforms away from first die  112   a  while the processing pressure is applied to processing cavity  114 . First bladder  116   a  may fill all space between contact surface  103   a  of first bolster  102   a  and first die  112   a  above cavity  114  while contact surface  103   a  of first bolster  102   a  unevenly deforms away from first die  112   a  as schematically shown by  FIGS. 3A and 3B . 
         [0073]    In some embodiments, method  200  further comprises monitoring deformation of first bolster  102   a  while applying the processing pressure to processing cavity  114 . The first pressure inside the first bladder  116   a  may be selected based on the level of deformation of first bolster  102   a , e.g., a higher pressure may be used for higher levels of deformation. 
         [0074]    In some embodiments, contact surface  103   a  of first bolster  102   a  does not directly contact first die  112   a  while applying the processing pressure to processing cavity  114 . Likewise, contact surface  103   a  of second bolster  102   b  may not directly contact second die  112   b  while applying the processing pressure to processing cavity  114 . 
         [0075]    In some embodiments, controlling the first pressure inside first bladder  116   a  comprises controlling amount of gas inside first bladder  116   a . For example, gas may be added into first bladder  116   a  (e.g., from gas source  154 ) or removed from first bladder  116   a  to adjust the pressure. 
         [0076]    In the same or other embodiments, controlling the first pressure inside first bladder  116   a  comprises controlling a distance between contact surface  103   a  of first bolster  102   a  and first dies  112   a . In other words, the volume available for first bladder  116   a  may change thereby changing the pressure inside first bladder  116   a.    
         [0077]    In some embodiments, induction heating cell  100  may include additional bladders, such as third bladder  116   c  and fourth bladder  116   d  as shown in  FIG. 1C  and described above with reference to this figure. First bladder  112   a  and second bladder  112   b  may be oriented along a first axis, while third bladder  116   c  and fourth bladder  116   d  may be oriented along a second axis not parallel to the first axis. For example, as shown in  FIG. 1C , first bladder  112   a  and second bladder  112   b  may be oriented along the X axis, while third bladder  116   c  and fourth bladder  116   d  may be oriented along the Z axis, which is perpendicular to the X axis. 
         [0078]    Third bladder  116   c  may be disposed between first die  112   a  third bolster  102   c  or, more specifically, between first die  112   a  and contact surface  103   c  of third bolster  102   c . Fourth bladder  116   d  may be disposed between first die  112   a  and fourth bolster  102   d  or, more specifically, between first die  112   a  contact surface  103   d  of fourth bolster  102   d . In this example, both third bladder  116   c  and fourth bladder  116   d  support first die  112   a  and prevent first die  112   a  from expanding and cracking. The considerations for design, position, and controlling pressures inside third bladder  116   c  and fourth bladder  116   d  may be different from those for first bladder  116   a  and second bladder  116   b , which support different dies  112   a  and  112   b . In some embodiments, contact surface  103   c  of third bolster  102   c  may be parallel to contact surface  103   d  of fourth bolster  102   d . However, contact surface  103   a  of first bolster  102   a  may be perpendicular to the contact surface  103   c  of the third bolster  102   c.    
         [0079]    In some embodiments, third bladder  116   c  may be disposed between second die  112   b  and contact surface  103   c  of third bolster  102   c  in addition to being disposed between first die  112   a  and contact surface  103   c  of third bolster  102   c . Likewise, fourth bladder  116   d  may be also disposed between second die  112   b  and contact surface  103   d  of fourth bolster  102   d  in addition to being disposed between first dies  112   a  and contact surface  103   d  of fourth bolster  102   d.    
         [0080]    Method  200  may comprise controlling a third pressure inside third bladder  116   c  and controlling a fourth pressure inside fourth bladder  116   d . The third pressure and the fourth pressure may be independently controlled from the first pressure inside first bladder  116   a  and the second pressure inside second bladder  116   b . In some embodiments, the ratio of the third pressure to the fourth pressure may be kept constant. 
       Experimental Data/Modeling 
       [0081]      FIG. 6  is a plot of cross-sectional forces within a die, such as dies  102   a  and  102   b  described above, due to pressurization of processing cavity  114  and subsequent pressurization of bladders  116   c  and  116   d . It can be seen that pressurizing side  116   c  and  116   d  bladders decrease the tensile forces within dies  102   a  and  102   b  and at a high enough pressure actually causes dies  102   a  and  102   b  to undergo compression loading. If the pressure inside processing cavity  114  the pressure inside side bladders  116   c  and  116   d  are applied simultaneously, dies  102   a  and  102   b  may never experience any tensile forces during the processing, which is important for eliminating cracks in the ceramic materials used to form dies  102   a  and  102   b.    
       Examples of Aircraft and Methods of Fabricating and Operating Aircraft 
       [0082]    Examples of the present disclosure may be described in the context of aircraft manufacturing and service method  1100  as shown in  FIG. 7  and aircraft  1102  as shown in  FIG. 8 . During pre-production, illustrative method  1100  may include specification and design (block  1104 ) of aircraft  1102  and material procurement (block  1106 ). During production, component and subassembly manufacturing (block  1108 ) and inspection system integration (block  1110 ) of aircraft  1102  may take place. Induction heating cell  100  described above and corresponding methods of using induction heating cell  100  may be utilized during component and subassembly manufacturing (block  1108 ). 
         [0083]    Thereafter, aircraft  1102  may go through certification and delivery (block  1112 ) to be placed in service (block  1114 ). While in service, aircraft  1102  may be scheduled for routine maintenance and service (block  1116 ). Routine maintenance and service may include modification, reconfiguration, refurbishment, etc. of one or more inspection systems of aircraft  1102 . 
         [0084]    Each of the processes of illustrative method  1100  may be performed or carried out by an inspection system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, an inspection system integrator may include, without limitation, any number of aircraft manufacturers and major-inspection 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. 
         [0085]    As shown in  FIG. 8 , aircraft  1102  produced by illustrative method  1100  may include airframe  1118  with a plurality of high-level inspection systems  1120  and interior  1122 . Examples of high-level inspection systems  1120  include one or more of propulsion inspection system  1124 , electrical inspection system  1126 , hydraulic inspection system  1128 , and environmental inspection system  1130 . Any number of other inspection 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. Accordingly, in addition to aircraft  1102 , the principles disclosed herein may apply to other vehicles, e.g., land vehicles, marine vehicles, space vehicles, etc. 
         [0086]    Apparatus(es) and method(s) shown or described herein may be employed during any one or more of the stages of manufacturing and service method (illustrative method  1100 ). For example, components or subassemblies corresponding to component and subassembly manufacturing (block  1108 ) may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft  1102  is in service (block  1114 ). Also, one or more examples of the apparatus(es), method(s), or combination thereof may be utilized during production stages (block  1108 ) and (block  1110 ), for example, by substantially expediting assembly of or reducing the cost of aircraft  1102 . Similarly, one or more examples of the apparatus or method realizations, or a combination thereof, may be utilized, for example and without limitation, while aircraft  1102  is in service (block  1114 ) and/or during maintenance and service (block  1116 ). 
       CONCLUSION 
       [0087]    Different examples of the apparatus(es) and method(s) disclosed herein include a variety of components, features, and functionalities. It should be understood that the various examples of the apparatus(es) and method(s) disclosed herein may include any of the components, features, and functionalities of any of the other examples of the apparatus(es) and method(s) disclosed herein in any combination, and all of such possibilities are intended to be within the spirit and scope of the present disclosure. 
         [0088]    Many modifications of examples set forth herein will come to mind to one skilled in the art to which the present disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. 
         [0089]    Therefore, it is to be understood that the present disclosure is not to be limited to the specific examples illustrated and that modifications and other examples are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated drawings describe examples of the present disclosure in the context of certain illustrative combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative implementations without departing from the scope of the appended claims. Accordingly, parenthetical reference numerals in the appended claims are presented for illustrative purposes only and are not intended to limit the scope of the claimed subject matter to the specific examples provided in the present disclosure.