Method and system for forming a composite stringer assembly

Abstract

To provide a method and a system for manufacturing a composite stringer assembly.SOLUTION: A system comprises a bladder 110 having a bladder core 120 and a bladder skin 130. The bladder core is a foam. The bladder skin is formed from an elastic material and encloses the bladder core. When a composite stringer assembly is manufactured, the bladder is positioned over a charge base 182. The charge base becomes a constituent of a stringer base, such as a fuselage or a wing skin plate. A charge hat 180 is then positioned over the bladder and is conformed to the bladder. A combination of the bladder skin and the bladder core functions as a support structure while the stringer assembly is cured during this manufacturing operation. In some examples, the bladder core is collapsible for removal of the bladder from a cavity of the stringer assembly.SELECTED DRAWING: Figure 13C-13D

Description

[Technical field]

[0001] The present disclosure relates to methods and systems for forming composite stringer assemblies. [Background technology]

[0002] Composite materials have gained increasing attention in various applications, including but not limited to, aircraft manufacturing. In particular, composite materials have an excellent strength-to-weight ratio, making them well suited for applications requiring light weight. For example, aircraft fuselages and wings may be constructed using composite sheets. The composite sheets are reinforced with composite stringers to further stiffen the overall assembly.

[0003] In many cases, the composite stringers, fuselage sections, and wing skins are fabricated as separate components. These separately fabricated components are then attached, for example, using fasteners or adhesives. In some cases, some of the component fabrication steps overlap. For example, the stringers, fuselage sections, and / or wing skins are co-cured together. Such a co-curing process is also used for the attachment of these components.

[0004] In either case, the fabrication of composite structures requires sophisticated and complex equipment. Furthermore, many aircraft components are large, which also complicates the fabrication process and equipment. For example, a support structure (e.g., a mandrel) is required to mold a composite stringer on a composite sheet. This support structure defines the final shape of the composite stringer. It must first be placed between the composite stringer and the composite sheet, and the sheet must conform closely to the shapes of both components. Furthermore, the support structure must later be removed from the cavity formed between the composite stringer and the composite sheet. This removal process is also difficult with conventional support structures, especially for long stringers. Summary of the Invention

[0005] Methods and systems for fabricating composite stringer assemblies are disclosed, and more particularly, methods and systems for shaping composite charges in fabricating such stringer assemblies. The system includes a bladder having a bladder core and a bladder membrane. The bladder core is constructed from a foam. The bladder membrane is constructed from an elastic material and surrounds the bladder core. During fabrication of a composite stringer assembly, the bladder is placed on a charge base. The charge base becomes part of the stringer base, e.g., a fuselage or wing skin. A charge hat is then placed on and conforms to the bladder. The combination of the bladder membrane and the bladder core serves as a support structure during curing of the stringer assembly in the fabrication process. In some embodiments, the bladder core is collapsible to remove the bladder from the stringer assembly cavity.

[0006] According to some embodiments, a bladder for shaping a composite charge in fabricating a composite stringer assembly includes a bladder core and a bladder membrane. The bladder core is constructed from a foam and includes a base surface and a hat molding surface. The bladder membrane is constructed from a resilient material. The bladder membrane surrounds the bladder core. At least a portion of the bladder membrane contacts, conforms to, and compresses each of the base surface and the hat molding surface.

[0007] According to some embodiments, a method of assembling a bladder using a bladder assembly tool having a bladder assembly cavity includes placing a bladder membrane having an inner membrane surface into the bladder assembly cavity having a cavity surface. The method further includes sealing the bladder membrane to the cavity surface at each end of the bladder assembly tool, reducing a first pressure between the cavity surface and the bladder membrane relative to a second pressure at the inner membrane surface, thereby stretching the bladder membrane and conforming the bladder membrane to the cavity surface. The method further includes inserting a bladder core into the bladder membrane with the bladder membrane conforming to the cavity surface, and equalizing the first pressure and the second pressure, thereby contracting the bladder membrane and conforming at least a portion of the bladder membrane to the bladder core.

[0008] According to some embodiments, a method of producing a composite stringer assembly from a composite charge using a stringer forming tool including a bladder includes placing the bladder on a charge base portion disposed on a tool base of the stringer forming tool, placing a charge hat portion on the bladder including a bladder core and a bladder membrane, placing a flexible cover of the stringer forming tool over the charge hat portion, and sealing the flexible cover to the tool base. The method further includes providing a first molding pressure between the flexible cover and the tool base that is less than a second molding pressure at a cover outer surface and a third molding pressure inside the bladder, thereby forcing the charge hat portion against the bladder by the flexible cover. The method further includes curing the charge base and charge hat with the charge hat pressed against the bladder to form a stringer base and stringer hat that comprise the composite stringer assembly, and removing the bladder from the stringer cavity. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 1 is a schematic diagram illustrating a composite charge including a charge base portion and a charge hat portion used to create a composite stringer assembly, according to some embodiments. [Figure 1B] FIG. 1B is a schematic diagram illustrating a composite stringer assembly made from the composite charge shown in FIG. 1A and including a stringer base section and a stringer hat section, in accordance with some embodiments. [Figure 2A-2C] 1 is a schematic cross-sectional view illustrating a bladder for forming a composite charge, according to some embodiments. [Diagram 3] 10 is a flowchart illustrating a process for assembling a bladder using a bladder assembly tool, according to some embodiments. [Figure 4A-4C] 1 is a schematic cross-sectional view of a bladder assembly tool during placement of a bladder membrane within a bladder assembly cavity of the bladder assembly tool, according to some embodiments. [Diagram 5] 1 is a schematic cross-sectional view of a bladder assembly tool during sealing of a bladder membrane to a cavity surface of the bladder assembly tool, according to some embodiments. [Figures 6A-6F] 1 is a schematic cross-sectional view illustrating a bladder assembly tool stretching a bladder membrane to conform to a cavity surface, according to some embodiments. [Figure 7A-7C] 1 is a schematic cross-sectional view of a bladder assembly tool during insertion of a bladder core into a bladder membrane along a cavity surface, according to some embodiments. [Figure 8A-8B] 1 is a schematic cross-sectional view illustrating a bladder assembly tool during shaping of a bladder membrane to a bladder core, according to some embodiments. [Figure 9A-9B] 1 is a schematic cross-sectional view illustrating removal of a bladder from a bladder assembly tool, according to some embodiments. [Figure 10A-10C] 11 is a schematic cross-sectional view illustrating sealing an end member to an extension of a pouch according to some embodiments. [Figure 11A-11B]1A-1C are schematic cross-sectional views illustrating two examples of different end members attached to a pouch, according to some embodiments. [Figure 12] 1 is a flowchart illustrating a process for producing a composite stringer assembly from a composite charge using a stringer forming tool, in accordance with some embodiments. [Figure 13A-13D] 1A-1D are schematic diagrams illustrating several stages in the fabrication of a composite stringer, according to some embodiments. [Figure 14] 1 is a flowchart illustrating a process for an aircraft production and service method in accordance with some embodiments. [Figure 15] 1 is a block diagram illustrating an example of an aircraft in accordance with some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following description, numerous specific details are presented to provide a thorough understanding of the concepts of the present disclosure. However, in some embodiments, the concepts of the present disclosure are practiced without some or all of these specific details. In other embodiments, details of known processes are omitted so as to avoid unnecessarily obscuring the concepts of the present disclosure. In addition, although some concepts are described in connection with specific embodiments, it will be understood that these embodiments are not intended to limit the present disclosure. <Introduction>

[0011] As discussed above, the fabrication of composite stringers and assemblies including such composite stringers is difficult and requires complex tooling, particularly when the hat stringer and stringer base are formed simultaneously, and more particularly when co-cured. The complexity and difficulty are explained below with reference to FIGS. 1A and 1B. FIG. 1A is a schematic diagram of a composite charge 180 that is used to fabricate a composite stringer assembly 190, as shown in FIG. 1B. The composite charge 180 includes a charge base portion 182 and a charge hat portion 181. FIG. 1A shows the composite charge 180 in an as-formed state, although one skilled in the art will appreciate that the initial shape of the charge base portion 182 and / or charge hat portion 181 may differ from that shown. In some embodiments, the charge hat portion 181 is provided as a flat structure, for example as shown in dotted lines in FIG. 1A. In some embodiments, the charge base portion 182 and / or the charge hat portion 181 are formed using a stringer forming tool, described below. For simplicity, the bladder is not shown in Figures 1A and 1B.

[0012] FIG. 1B is a schematic diagram of a composite stringer assembly 190, which includes a stringer base portion 192 and a stringer hat portion 191. The stringer hat portion 191 is also referred to as a stringer. The composite stringer assembly 190, in some embodiments, is made from the composite charge 180 shown in FIG. 1A. As will be appreciated by those skilled in the art, the stringer base portion 192 is often part of another component, such as a fuselage section or a wing skin. The stringer base portion 192 is formed from the charge base portion 182 of the composite charge 180. The stringer hat portion 191 is formed from the charge hat portion 181 of the composite charge 180. The stringer base portion 192 and the stringer hat portion 191 are bonded together, for example by co-curing, when these components are formed.

[0013] As shown in FIG. 1B, the stringer base portion 192 and the stringer hat portion 191 define a stringer cavity 193. When forming the composite stringer assembly 190, the stringer base portion 192 and the stringer hat portion 191, and more specifically, the charge base portion 182 and the charge hat portion 181, need to be supported from the inside (from within the stringer cavity 193). This support is achieved by placing a bladder inside the stringer cavity 193. The bladder conforms to the shape of the stringer base portion 192 and the stringer hat portion 191, respectively. However, the bladder needs to be removed from the stringer cavity 193 after the composite stringer assembly 190 is formed. This combination of support, conformability, and removal properties makes the design and construction of the bladder difficult. For example, conventional bladders are difficult to remove because they remain in the same shape throughout all processing steps.

[0014] The methods and systems described herein use a bladder configured to address these challenges. Specifically, the bladder includes a bladder core and a bladder membrane. The bladder core is constructed of a foam that allows for fluid distribution in the bladder (e.g., by collapsing the bladder upon removal), and the bladder membrane is constructed of an elastic material. The bladder membrane surrounds the bladder core and separates it from the charge hat 181 and charge base 182. At least a portion of the bladder membrane contacts, conforms to, and compresses a surface of the bladder core. In other words, the portion of the bladder membrane is stretched along the bladder core. This stretching ensures a shape-fit of the bladder membrane. Additionally, the elasticity of the bladder membrane allows for assembly of the bladder. Specifically, the bladder membrane is stretched when the bladder core is inserted into the bladder membrane. The bladder membrane is also referred to as a smaller elastomeric sleeve, and the bladder core is also referred to as a foam mandrel. <Example of bag-shaped body>

[0015] The features and embodiments of the bladder are further described with reference to Figures 2A, 2B, and 2C. Specifically, Figure 2A is a cross-sectional view of the bladder 110 taken along a plane perpendicular to the longitudinal direction of the bladder 110 (YZ plane). For the convenience of this disclosure, the longitudinal direction of the bladder 110 is taken to extend along the X-axis. Figure 2B is a cross-sectional view of the bladder 110 taken along a plane including the longitudinal direction of the bladder 110 (XZ plane). Figure 2B is another cross-sectional view of the bladder 110 in the XZ plane, showing another example of an end fitting of the bladder 110.

[0016] 2A, the bladder 110 includes a bladder core 120 and a bladder membrane 130 surrounding the bladder core 120. The cross section of FIG. 2A corresponds to the cross section of the composite charge 180 shown in FIG. 1A and to the cross section of the composite stringer assembly 190 shown in FIG. 1B. More specifically, the contour of the bladder membrane 130 (e.g., the contour of the membrane outer surface 138 of the bladder membrane 130) is the same as the contour of the stringer cavity 193. When the bladder 110 is used to mold the composite charge 180, the bladder membrane 130, more specifically the membrane outer surface 138, contacts the composite charge 180. The bladder core 120 helps maintain the shape of the bladder membrane 130 and thus functions to define the shape of the composite charge 180.

[0017] In some embodiments, the bladder core 120 comprises an open or closed cell foam 121. In some embodiments, the foam 121 provides fluid communication within the bladder 110, for example, when the interior of the bladder 110 is depressurized. Gas can be injected into and removed from the bladder 110, allowing the bladder 110 to be compacted when removed from the composite stringer assembly 190. This feature is described in more detail below with reference to FIG. 13D. Examples of foams suitable for the bladder core 120 include, but are not limited to, polyethylene terephthalate (PET) foams, such as Divinycell P foam available from Diab Group, Helsingborg, Sweden. In some embodiments, the foam 121 is selected such that the bladder core 120 will withstand a full atmosphere of pressure at room temperature, but will collapse under vacuum pressure at elevated cure temperatures.

[0018] The bladder core 120 has a base surface 122 and a hat forming surface 124. The base surface 122 defines the shape of the stringer base portion 192, and the hat forming surface 124 defines the shape of the stringer hat portion 191. In some embodiments, the base surface 122 is substantially planar. In such embodiments or other embodiments, the hat forming surface 124 is curved. One of ordinary skill in the art will appreciate that the shape of the stringer hat portion 191, when formed using the bladder 110, is defined by the shape of the hat forming surface 124. Thus, hat forming surfaces 124 of various shapes are within the scope of the present disclosure. In some embodiments, the contours of the base surface 122 and the hat forming surface 124 plus the thickness of the bladder membrane 130 are the same as the contour of the stringer cavity 193.

[0019] The bladder membrane 130 is made of an elastic material 131. Examples of the elastic material 131 include, but are not limited to, silicone, viton, and butyl rubber. In some embodiments, the bladder membrane 130 has a thickness between 1 millimeter and 5 millimeters, more specifically between 2 millimeters and 4 millimeters, such as about 2.5 millimeters. At least a portion of the bladder membrane 130 contacts, conforms to, and compresses each of the base surface 122 and the hat molding surface 124 of the bladder core 120. In some embodiments, the bladder membrane 130 is stretched at least about 1%, at least about 2%, at least about 5%, and at least about 10%, and in some cases, about 20%, along the bladder core 120. Stretching the bladder membrane 130 allows the bladder membrane 130 to conform to the bladder core 120 without wrinkles or other defects. However, such stretching places the bladder core 120 in a compressed state, and too much compression can affect the shape of the bladder core 120. Therefore, excessive stretching (e.g., more than 50%) is desirably avoided.

[0020] 2B and 2C, in some embodiments, the bladder membrane 130 has one or two extensions, for example, extension 133 and second extension 134. The extensions of the bladder membrane 130 extend beyond the bladder core 120 and do not contact the bladder core 120. Other portions of the bladder membrane 130 contact the bladder core 120, for example, along the bladder core 120 and compress the bladder core. In some embodiments, the extensions are used to ensure a fluid connection to the bladder 110, more specifically, a fluid connection to the interior of the bladder 110 and to the bladder core 120. In certain embodiments, the extensions include extension 133 shown in FIGS. 2B and 2C and second extension 134 shown in FIG. 2C. In such or other embodiments, an extension may be used to seal an end of the bag 110, such as second extension 134 shown in FIG. 2B.

[0021] 2B and 2C, in some embodiments, the bladder 110 further includes an end member 140 sealed to the extension 133 of the bladder membrane 130. In some embodiments, the end member 140 has a pass-through 145 that is in fluid communication with the bladder core 120. The pass-through 145 is used to inject gas into the interior of the bladder 110 or to evacuate gas from the interior. For example, evacuating gas from the interior can cause the bladder membrane 130 to contract in size and collapse the bladder core 120, as described below with reference to FIG. 13D. In some embodiments, the pass-through 145 can be selectively connected to an external atmosphere or a vacuum source 109.

[0022] 2C and 2C, in some embodiments, the end member 140 includes a first component 141 and a second component 142. The second component 142 is removably connected to the first component 141, for example, by means of a screw 144. In some particular embodiments, the second component 142 forms a channel 143 between the first component 141 and the second component 142. The extension 133 of the bladder membrane 130 surrounds, conforms to, and compresses the first component 141, and extends partially into the channel 143. More specifically, the extension 133 is sandwiched and compressed between the first component 141 and the second component 142 in the channel 143, thereby ensuring that the bladder membrane 130 is sealed to the end member 140. This will be described in more detail below with reference to FIGS. 10A, 10B, and 10C.

[0023] 2B and 2C, in some embodiments, the first component 141 and the second component 142 are removably connected using a screw 144. This removably connected configuration allows the extension 133 to be placed over the first component 141 before connecting the second component 142, facilitating assembly of the bag 110. In a more specific embodiment, the through hole 145 passes through the screw 144. This feature allows the through hole 145 to be provided or removed by replacing the screw 144, e.g., by replacing a screw with a through hole 145 with a screw without the through hole 145.

[0024] 2B and 2C, in some embodiments, the bladder membrane 130 has a second extension 134 extending beyond the bladder core 120 so as to be spaced apart from the extension 133. That is, the bladder core 120 is located between the extension 133 and the second extension 134. The second extension 134 can form a fluid connection at the one end of the bladder 110 or seal the bladder 110. For example, in the configuration shown in FIG. 2B, the second extension 134 is sealed and impermeable to gas. More specifically, the bladder 110 in this embodiment includes a second end member 150 sealed to the second extension 134 of the bladder membrane 130, blocking fluid communication from at least the end on the second extension 134 side to the bladder core 120.

[0025] 2C, in some embodiments, second end member 150 has a second end member throughhole 155 fluidly connected to bladder core 120. For example, second end member throughhole 155 passes through second screw 154. By replacing second screw 154, the configuration of bladder 110 shown in FIG. 2B can be switched to the configuration of bladder 110 shown in FIG. 2C.

[0026] In some embodiments, the design of the second end member 150 is the same as the design of the end member 140. For example, the second end member 150 is composed of two components, one of which is sealed to the second extension portion 134. Furthermore, these two components are detachably connected to each other. Furthermore, when these two components are connected, a portion of the second extension portion 134 is sandwiched between these two components and is in a compressed state. <Example of a method for assembling a bag-shaped body>

[0027] FIG. 3 is a flow chart illustrating a process of a method 200 for assembling a bladder 110, according to some embodiments. In the above description, various embodiments of the bladder 110 have been described with reference to FIGS. 2A-2C. The various operations of the method 200 are performed using a bladder assembly tool 300. Key features of the bladder assembly tool 300 are described with reference to specific operations. Additionally, various stages of the method 200 are illustrated in FIGS. 4A-11, as described below.

[0028] In some embodiments, the method 200 begins by placing the bladder membrane 130 into the bladder assembly cavity 312 of the bladder assembly tool 300 (block 210). This process is shown, for example, in FIGS. 4A, 4B, and 4C. At this stage, the bladder membrane 130 does not conform to the shape of the bladder assembly cavity 312, which allows for easy insertion of the bladder membrane 130. Specifically, the bladder membrane 130 has an inner membrane surface 137 and an outer membrane surface 138. At this stage, the bladder membrane 130 is not stretched along or covering the bladder core 120. The bladder assembly cavity 312 has a cavity surface 313. The outer membrane surface 138 of the bladder membrane 130 does not conform to the shape of the cavity surface 313, which allows for this process. Referring to a cross-section of bladder membrane 130 and bladder assembly tool 300 , the circumference of membrane outer surface 138 is less than the circumference of cavity surface 313 .

[0029] In some embodiments, the method 200 then proceeds to sealing the bladder membrane 130 to the cavity surface 313 (block 220). Note that the bladder membrane 130 is sealed at each end 301 of the bladder assembly tool 300. Various sealing processes are within the scope of this disclosure. For example, FIG. 5 shows a wedge 320 inserted into the bladder membrane 130. The sealing process of this embodiment includes inserting the wedge 320 into the bladder membrane 130, thereby pressing the bladder membrane 130 against the cavity surface 313 (block 222). The wedge 320 stretches a portion of the bladder membrane 130. Note that the wedge 320 has a wedge through hole 322. The minimum cross-section of the wedge through hole 322 is larger than the cross-sectional shape of the bladder core 120. Thus, the bladder core 120 can be inserted into the interior of the bladder membrane 130 through the wedge through-hole 322 .

[0030] In some embodiments, the method 200 then proceeds to reduce the first pressure between the cavity surface 313 and the bladder membrane 130 relative to the second pressure at the membrane inner surface 137 (block 230). This pressure differential (the difference between the first pressure and the second pressure) stretches the bladder membrane 130, forcing the bladder membrane 130 against the cavity surface 313, as shown in Figures 6A-6B. More specifically, the bladder membrane 130 conforms to the cavity surface 313. This stretching of the bladder membrane 130 allows the bladder core 120 to be inserted without contacting the bladder membrane 130. At this stage, the cross-section of the membrane inner surface 137 is larger than the cross-section of the bladder core 120 (shown in dotted lines). Note that the first pressure can be reduced by sealing the bladder membrane 130 to the cavity surface 313. In some embodiments, reducing the first pressure includes connecting the bladder assembly tool 300 to a vacuum source. In other words, the first pressure is less than atmospheric pressure. The second pressure is, for example, at atmospheric pressure with the interior space of the bladder membrane 130 open to the atmosphere.

[0031] 6C and 6D, in some embodiments, the bladder assembly tool 300 includes an inward projection 314 that projects from the cavity surface 313 into the bladder assembly cavity 312. The inward projection 314 allows fluid passages 315 to be maintained between the cavity surface 313 and the bladder membrane 130 as the bladder membrane 130 is brought into contact with the cavity surface 313. These fluid passages 315 are formed around the inward projection 314 as shown in FIG. 6D, for example, when the bladder membrane 130 is brought into contact with the cavity surface 313. These fluid passages 315 allow the entire bladder membrane 130 (along the bladder's length, i.e., along the X-axis) to be pressurized to a second pressure and the entire membrane can be brought into contact with the cavity surface 313 by the pressure differential. 6E and 6F, in some embodiments, the bladder assembly tool 300 includes a fluid passageway 315 recessed from the cavity surface 313, for example.

[0032] In some embodiments, the method 200 then proceeds to insert the bladder core 120 into the bladder membrane 130 (block 240), for example, as shown in Figures 7A-7C. This is performed while the bladder membrane 130 is conformed to the cavity surface 313 (e.g., by maintaining a pressure differential on either side of the bladder membrane 130, which pressure differential presses the bladder membrane 130 against the cavity surface 313). Figure 7B shows that the cross-section of the membrane inner surface 137 is larger than the cross-section of the bladder core 120, allowing for contact-free insertion.

[0033] In some embodiments, the process of inserting the bladder core 120 into the bladder membrane 130 includes pushing the bladder core 120 through the wedge through-hole 322 (block 242), as shown, for example, in FIG. 7C. As described above, the wedge 320 is used to seal the bladder membrane 130 to the cavity surface 313. This seal is maintained during insertion of the bladder core 120 into the bladder membrane 130. Furthermore, as described above, the minimum cross-section of the wedge through-hole 322 is larger than the cross-sectional shape of the bladder core 120, so that the bladder core 120 can be inserted into the bladder membrane 130 through the wedge through-hole 322.

[0034] In some embodiments, the method 200 then proceeds to equalize the first pressure and the second pressure (block 250), for example, by bringing both the first pressure and the second pressure to atmospheric pressure levels. This equalization of pressures may cause the bladder membrane 130 to contract and may cause a portion of the bladder membrane 130 to conform to the bladder core 120, for example, as shown in FIGS. 8A and 8B. More specifically, this equalization of pressures eliminates the pressure differential that previously stretched the bladder membrane 130. Thus, the bladder membrane 130 contracts and returns to its original shape. However, in some embodiments, a portion of the bladder membrane 130 remains stretched while the bladder membrane 130 conforms to the bladder core 120, and at least that portion of the bladder membrane 130 contacts the bladder core 120. In some embodiments, the degree of stretch is at least about 1%, at least about 2%, at least about 5%, and at least about 10% along the bladder core 120. After this process, the cross-sectional shape of the cavity surface 313 conforms to the cross-sectional shape of the bladder core 120. Moreover, at this point, the combination of the bladder membrane 130 and the bladder core 120 can be removed from the bladder assembly tool 300.

[0035] In some embodiments, the method 200 further includes removing the bladder 110 from the bladder assembly tool 300 (block 258), for example as shown in Figures 9A and 9B. This is performed while a portion of the bladder membrane 130 is aligned with the bladder core 120 and the bladder membrane 130 is not aligned with the cavity surface 313. Thus, the bladder membrane 130 and the cavity surface 313 are not in contact at any point and the bladder 110 can be removed from the bladder assembly cavity 312. Figure 9B shows the bladder 110 after this removal process has been performed. For example, the bladder membrane 130 has an extension portion 133 and a second extension portion 134 that extend beyond the bladder core 120.

[0036] In some embodiments, the method 200 further includes sealing the end member 140 to the extension 133 of the bladder membrane 130 (block 260), for example, as shown in Figures 10A-10C. Specifically, the extension 133 extends beyond the bladder core 120 such that the bladder core 120 does not contact the end member 140. For example, the extension 133 covers the end member 140 and conforms to the shape of the end member.

[0037] In some embodiments, the end member 140 includes a first component 141 and a second component 142. In such embodiments, sealing the end member 140 to the extension 133 includes inserting the first component 141 into the extension 133 of the bag membrane 130 (block 262) and attaching the second component 142 to the first component 141 (block 264). In some embodiments, these operations shown in blocks 262 and 264 of FIG. 3 are performed such that a portion of the extension 133 of the bag membrane 130 enters the channel 143 between the first component 141 and the second component 142. More specifically, the portion of the extension 133 is sandwiched and compressed between the first component 141 and the second component 142 in the channel 143, as shown, for example, in FIG. 10C. 3, the second component 142 is attached to the first component 141 using a screw 144. More specifically, a through hole 145 also extends through the screw 144.

[0038] In some embodiments, the method 200 further includes sealing the second extension portion 134 of the bladder membrane 130 (block 270), for example as shown in FIG. 11A. The second extension portion 134 extends beyond the bladder core 120 in a direction away from the extension portion 133 such that the bladder core 120 is located between the extension portion 133 and the second extension portion 134.

[0039] In some embodiments, the method 200 further includes sealing the second end member 150 to the second extension 134 of the bladder membrane 130 (block 280), for example as shown in FIG. 11B. The second end member 150 has a second end member through hole 155 fluidly connected to the bladder core 120. Additionally, the end member 140 has a through hole 145 fluidly connected to the bladder core 120. <Example of a method for forming a composite stringer>

[0040] FIGURE 12 is a flow chart illustrating a process 600 for making a composite stringer assembly 190, according to some embodiments. The composite stringer assembly 190 is made from a composite charge 180 using a stringer forming tool 100. In the above description, various embodiments of the composite charge 180 and the composite stringer assembly 190 were described with reference to Figures 1A and 1B. In some embodiments, the stringer forming tool 100 includes the various embodiments of the bladder 110 described with reference to Figures 2A-11B.

[0041] In some embodiments, the method 600 includes placing the bladder 110 on a charge base 182 (block 610), for example as shown in FIG. 13A . The charge base 182 is part of the composite charge 180 and is placed on the tool base 102 of the stringer forming tool 100. In some embodiments, the charge base 182 is substantially planar. The bladder 110 is formed according to a design of the composite stringer assembly 190. As described above, the bladder 110 includes a bladder core 120 and a bladder membrane 130. The bladder core 120 defines a shape, and the bladder membrane 130 surrounds the bladder core 120 and contacts the charge base 182.

[0042] In some embodiments, the method 600 includes placing the charge hat 181 over the bladder 110 (block 620), for example, as shown in FIG. 13B. For example, in this process, the charge hat 181 is at least partially conformed to the bladder 110. In some embodiments, the charge hat 181 is initially provided as a planar component and then conformed around the bladder 110, such that the bladder 110 maintains its shape.

[0043] In some embodiments, the method 600 then proceeds to place the flexible cover 104 of the stringer forming tool 100 over the charge hat 181 and seal the flexible cover 104 to the tool base 102 (block 630), for example as shown in FIG. 13C. This sealing allows the pressure between the flexible cover 104 and the tool base 102 to be reduced, for example by applying external pressure (from atmospheric pressure) to force the charge hat 181 into conformity with the bladder 110. In some embodiments, the charge hat 181 has a hat end 183 that directly contacts the charge base 182.

[0044] In some embodiments, the method 600 then proceeds to reduce the first molding pressure (block 640) between the flexible cover 104 and the tool base 102, as shown in, for example, FIG. 13C. The first molding pressure is made lower than the second molding pressure at the cover outer surface 105. This pressure differential presses the flexible cover 104 and charge hat 181 against the bladder 110, thereby causing the charge hat 181 to conform to the bladder 110.

[0045] Further, in some embodiments, the first molding pressure is reduced to a pressure lower than a third molding pressure inside the bag 110, as shown in Figure 13C for example. This third pressure maintains the shape of the bag 110 even when the charge hat 181 is pressed against the bag 110. In some embodiments, the second molding pressure and the third molding pressure are at atmospheric pressure levels, with the associated structures open to the atmosphere.

[0046] In some embodiments, the method 600 then proceeds to cure (block 650) the charge base 182 and charge hat 181. For example, the entire assembly shown in FIG. 13C is placed in an autoclave, oven, or other similar tool. The cure is performed while the charge hat 181 is pressed against the bladder 110. Furthermore, the shape of the bladder 110 is maintained during the cure. The cure forms the stringer base 192 and stringer hat 191 that comprise the composite stringer assembly 190. The stringer base 192 and stringer hat 191 are rigid structures that no longer require support from the bladder 110. Thus, after cure, the bladder 110 is removed from the stringer cavity 193.

[0047] In some embodiments, the method 600 then proceeds to remove the bladder 110 from the stringer cavity 193 (block 660). More specifically, removing the bladder 110 from the stringer cavity 193 includes reducing a first removal pressure within the bladder 110 (block 662). The first removal pressure is reduced to a pressure lower than a second removal pressure within the stringer cavity 193. This pressure differential compresses the bladder 110 and separates the bladder 110 from the stringer base portion 192 and the stringer hat portion 191, as shown, for example, in FIG. 13D. In some embodiments, the second removal pressure is atmospheric pressure.

[0048] In some embodiments, the method 600 then proceeds to replace (block 670) the bladder core 120 of the bladder 110. For example, the bladder core 120 was crushed when the bladder 110 was removed from the stringer cavity 193 and no longer has the desired shape. This process of replacing the bladder core 120 may be performed similarly to the assembly process of the bladder 110 described above with reference to Figures 3-11B. <Aircraft example>

[0049] In some embodiments, the methods and systems described above may be used with aircraft, and more generally in the aircraft industry, and in particular in aircraft manufacturing, and aircraft service and maintenance methods.

[0050] Thus, the above described apparatus and methods are applicable to aircraft manufacturing and service method 900 shown in Figure 14 and aircraft 902 shown in Figure 15. Before production begins, method 900 includes specification and design 904 of the aircraft 902 and material procurement 906. During production, parts / subassembly manufacturing 908 and systems integration 910 of the aircraft 902 occur. The aircraft 902 then proceeds through certification and delivery 912 and into service 914. During its life in customer service, the aircraft 902 undergoes routine maintenance and service 916, including modifications, reconfigurations, refurbishments, etc.

[0051] In some embodiments, the steps of method 900 may be performed or implemented by an operator, such as a system integrator, a third party, and / or a customer. For purposes of illustration, a system integrator may include, but is not limited to, any number of aircraft manufacturers and major system subcontractors. A third party may include, but is not limited to, any number of vendors, subcontractors, and suppliers. An operator may be an airline, a leasing company, a military entity, a service organization, etc.

[0052] 15, the aircraft 902 produced by the method 900 includes an airframe 918 having a number of systems 920 and an interior 922. The airframe 918 includes the wings of the aircraft 902. Examples of the number of systems 920 include one or more of a propulsion system 924, an electrical system 926, a hydraulic system 928, and an environmental system 930, as well as any number of other systems.

[0053] Apparatus and methods provided herein may be employed during any one or more stages of method 900. For example, parts and subassemblies corresponding to manufacturing process 908 may be fabricated or manufactured similarly to parts and subassemblies manufactured during the in-service stage of aircraft 902. Also, one or more of the apparatus embodiments, method embodiments, or a combination thereof may be employed, for example, during manufacturing process 908 and system integration 910, to significantly improve, for example, the speed and cost of assembly of aircraft 902. Similarly, one or more of the apparatus embodiments, method embodiments, or a combination thereof may be employed during the in-service stage of aircraft 902, for example, but not limited to, during maintenance and service 916. <Other Examples>

[0054] The present disclosure further includes examples according to the following appendices.

[0055] Appendix 1. 1. A bag for shaping a composite charge in the fabrication of a composite stringer assembly, comprising: a bag-shaped core made of a foam and including a base surface and a hat molding surface; and a bladder membrane constructed of an elastic material, the bladder membrane surrounding the bladder core, with at least a portion of the bladder membrane contacting, conforming to, and compressing each of the base surface and the hat molding surface.

[0056] Clause 2. The pouch of clause 1, wherein the pouch membrane has an extension that extends beyond the pouch core.

[0057] Appendix 3. The pouch of Appendix 2, further comprising an end member sealed to the extension of the pouch membrane, the end member having a through hole fluidly connected to the pouch core.

[0058] Clause 4. The bag of clause 3, wherein the through-hole is selectively connectable to atmospheric or vacuum sources.

[0059] Addendum 5. The end member includes a first component and a second component that is detachably connected to the first component and forms a channel between the first component and a second component; 4. The bag of claim 3, wherein the extension of the bag membrane surrounds, conforms to, and compresses the first component, and a portion of the extension extends into the channel and is compressed between the first component and the second component.

[0060] Appendix 6. The bag-shaped body of Appendix 5, wherein the first component and the second component are detachably connected using a screw, and the through hole passes through the screw.

[0061] Addendum 7. A bag-shaped body described in any one of Addendums 2 to 6, wherein the bag-shaped body membrane includes a second extension portion extending beyond the bag-shaped body core so as to be spaced away from the extension portion, and the bag-shaped body core is located between the extension portion and the second extension portion.

[0062] Appendix 8. The bag-shaped body according to Appendix 7, wherein the second extension portion is sealed and impermeable to gas.

[0063] Appendix 9. The bag of Appendix 7, further comprising a second end member sealed to the second extension portion of the bag membrane, the second end member having a second end member through hole fluidly connected to the bag core.

[0064] Clause 10. The pouch of clause 1, wherein the foam constituting the pouch core comprises polyethylene terephthalate foam.

[0065] Appendix 11. The bag described in any one of appendices 1 to 10, wherein the elastic material constituting the bag membrane includes one or more materials selected from the group consisting of silicone, Viton, and butyl rubber.

[0066] Appendix 12. The pouch of any one of appendices 1-11, wherein the pouch membrane is stretched at least about 5% along the pouch core.

[0067] Clause 13. A method of assembling a bladder using a bladder assembly tool, the bladder assembly tool having a bladder assembly cavity, the method comprising: placing a bladder membrane having an inner membrane surface within the bladder assembly cavity having a cavity surface; sealing the bladder membrane to the cavity surface at each end of the bladder assembly tool; reducing a first pressure between the cavity surface and the bladder membrane relative to a second pressure at the membrane inner surface, thereby stretching the bladder membrane and conforming the bladder membrane to the cavity surface; inserting a bladder core into the bladder membrane while aligning the bladder membrane with the cavity surface; and equalizing the first pressure and the second pressure, thereby contracting the bladder membrane and conforming at least a portion of the bladder membrane to the bladder core.

[0068] Clause 14. The method of clause 13, wherein the second pressure is maintained at atmospheric pressure level.

[0069] Appendix 15. The method according to any one of appendices 13 to 14, wherein a cross-sectional shape of the cavity surface matches a cross-sectional shape of the sac-shaped core.

[0070] Addendum 16. Sealing the bladder membrane to the cavity surface includes inserting a wedge into the bladder membrane to press the bladder membrane against the cavity surface; The wedge has a wedge through hole; 16. The method of any one of claims 13 to 15, wherein inserting the bag core into the bag membrane comprises pushing the bag core through the wedge through-hole.

[0071] Addendum 17. The method further includes sealing an end member to the extension of the bag-shaped body membrane, the end member has a through hole fluidly connected to the bladder core; 17. The method of any one of claims 13 to 16, wherein the extension portion extends beyond the pouch core.

[0072] Addendum 18. The end member includes a first component and a second component; Sealing the end member to the extension portion includes: inserting the first component into the extension of the bladder membrane; 18. The method of claim 17, comprising attaching the second component to the first component, wherein a portion of the extension of the bladder membrane extends into a channel formed between the first and second components such that the portion is compressed within the channel between the first and second components.

[0073] Addendum 19. The method of Addendum 18, wherein the second component is attached to the first component using a screw, with the through hole passing through the screw.

[0074] Addendum 20. Further comprising sealing a second extension portion to the bag-shaped body membrane; 18. The method of claim 17, wherein the second extension portion extends beyond the sack core away from the extension portion, and the sack core is located between the extension portion and the second extension portion.

[0075] Addendum 21. Further comprising sealing a second end member to the second extension of the bag-shaped body membrane; the second end member has a second end member through hole fluidly connected to the bladder core; 18. The method of claim 17, wherein the end member has a through hole fluidly connected to the bladder core.

[0076] Addendum 22. The method of any one of Addendums 13 to 21, wherein the bag assembly tool has an inward protrusion that protrudes from the cavity surface into the bag assembly cavity.

[0077] Addendum 23. The method of any one of Addendums 13-22, further comprising removing the bladder from the bladder assembly tool after aligning the portion of the bladder membrane with the bladder core.

[0078] Addendum 24. The method of any one of Addendums 13-23, wherein the sac membrane stretches by at least 5% while reducing the first pressure.

[0079] Clause 25. A method of making a composite stringer assembly from a composite charge using a stringer forming tool including a bladder, comprising: placing the bag on a charge base portion disposed on a tool base of the stringer forming tool; placing a charge hat over the bladder including a bladder core and a bladder membrane; placing a flexible cover of the stringer forming tool over the charge hat and sealing the flexible cover to the tool base; A first molding pressure between the flexible cover and the tool base is lower than a second molding pressure on the outer surface of the cover and a third molding pressure inside the bag-like body, thereby pressing the charge hat part against the bag-like body by the flexible cover; hardening the charge base and the charge hat with the charge hat pressed against the bag-shaped body, thereby forming a stringer base and a stringer hat of the composite stringer assembly, the stringer base and the stringer hat constituting a stringer cavity; and removing the bladder from the stringer cavity.

[0080] Clause 26. The method of clause 25, wherein removing the bladder from the stringer cavity includes reducing a first removal pressure within the bladder relative to a second removal pressure within the stringer cavity, thereby compressing the bladder and separating the bladder from the stringer base portion and the stringer hat portion.

[0081] Clause 27. The method of clause 26, wherein the second removal pressure is atmospheric pressure.

[0082] Clause 28. The method of clause 26, further comprising replacing the bladder core of the bladder.

[0083] Addendum 29. The method according to any one of Addendums 25 to 28, wherein each of the second molding pressure and the third molding pressure is atmospheric pressure.

[0084] Addendum 30. The method of any one of Addendums 25 to 29, wherein the charge hat portion has a hat end that directly contacts the charge base portion. <Conclusion>

[0085] Although the above concepts have been described in detail to facilitate clarity of understanding, it will be apparent that certain modifications and variations are possible within the scope of the appended claims. The described processes, systems, and apparatus can also be implemented in many alternative ways. Thus, the presented examples should be construed as illustrative only and not limiting.

Claims

1. 1. A bag for shaping a composite charge in the fabrication of a composite stringer assembly, comprising: a bag-shaped core made of a foam and including a base surface and a hat molding surface; and a bladder membrane constructed of an elastic material, the bladder membrane surrounding the bladder core, with at least a portion of the bladder membrane contacting, conforming to, and compressing each of the base surface and the hat molding surface.

2. The bladder of claim 1 , wherein the bladder membrane has an extension that extends beyond the bladder core.

3. The bladder of claim 2 , further comprising an end member sealed to the extension of the bladder membrane, the end member having a through hole fluidly connected to the bladder core.

4. The pouch of claim 3 , wherein the through-hole is selectively connectable to an atmosphere or a vacuum source.

5. the end member includes a first component and a second component removably connected to the first component and forming a channel between the first component and a second component; 4. The bag of claim 3, wherein the extension of the bag membrane surrounds, lines, and compresses the first component, with a portion of the extension extending into the channel and compressed between the first and second components.

6. The bladder of claim 5 , wherein the first component and the second component are removably connected using a screw, and the through hole passes through the screw.

7. The bag-shaped body of any one of claims 2 to 6, wherein the bag-shaped body membrane includes a second extension portion extending beyond the bag-shaped body core so as to be spaced away from the extension portion, and the bag-shaped body core is located between the extension portion and the second extension portion.

8. The pouch of claim 7 , wherein the second extension is sealed and impermeable to gas.

9. 8. The bag of claim 7, further comprising a second end member sealed to the second extension of the bag membrane, the second end member having a second end member through hole fluidly connected to the bag core.

10. The pouch of any one of claims 1 to 9, wherein the foam constituting the pouch core comprises polyethylene terephthalate foam.

11. The bag of any one of claims 1 to 10, wherein the elastic material constituting the bag membrane comprises one or more materials selected from the group consisting of silicone, Viton, and butyl rubber.

12. The bladder of any one of claims 1 to 11, wherein the bladder membrane is stretched at least about 5% along the bladder core.

13. 1. A method of assembling a bladder using a bladder assembly tool, the bladder assembly tool having a bladder assembly cavity, the method comprising: placing a bladder membrane having an inner membrane surface within the bladder assembly cavity having a cavity surface; sealing the bladder membrane to the cavity surface at each end of the bladder assembly tool; reducing a first pressure between the cavity surface and the bladder membrane relative to a second pressure at the membrane inner surface, thereby stretching the bladder membrane and conforming the bladder membrane to the cavity surface; inserting a bladder core into the bladder membrane while aligning the bladder membrane with the cavity surface; and equalizing the first pressure and the second pressure, thereby contracting the bladder membrane and conforming at least a portion of the bladder membrane to the bladder core.

14. The method of claim 13 , wherein the second pressure is maintained at atmospheric pressure level.

15. 15. The method of claim 13 or 14, wherein the cross-sectional shape of the cavity surface matches the cross-sectional shape of the bladder core.

16. sealing the bladder membrane to the cavity surface includes inserting a wedge into the bladder membrane to press the bladder membrane against the cavity surface; The wedge has a wedge through hole; The method of any one of claims 13 to 15, wherein inserting the bladder core into the bladder membrane comprises pushing the bladder core through the wedge through-hole.

17. Further, the method includes sealing an end member to the extension of the bag-shaped body membrane, the end member has a through hole fluidly connected to the bladder core; The method of any one of claims 13 to 16, wherein the extension extends beyond the bladder core.

18. the end member includes a first component and a second component; Sealing the end member to the extension portion includes: inserting the first component into the extension of the bladder membrane; 18. The method of claim 17, comprising attaching the second component to the first component, such that a portion of the extension of the bladder membrane extends into a channel formed between the first and second components and is compressed within the channel between the first and second components.

19. The method further includes sealing a second extension portion to the bag-shaped body membrane, 19. The method of claim 17 or 18, wherein the second extension portion extends beyond the sack core so as to be spaced apart from the extension portion, and the sack core is located between the extension portion and the second extension portion.

20. The method of any one of claims 13 to 19, wherein the bladder assembly tool has an internal projection that projects from the cavity surface inwardly into the bladder assembly cavity.

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