Method, apparatus and device for preventing vacuum bag wrinkling

A substantially rigid batten is attached to an external face of a vacuum bag to reduce wrinkling of the bag during vacuum bag compaction of a composite laminate layup.

BACKGROUND INFORMATION

The present disclosure generally relates to vacuum bag processing of composite laminate, and deals more particularly with a method, apparatus and device for preventing wrinkling of vacuum bags during compaction of the laminate.

Vacuum bags are commonly employed to compact uncured composite laminate layups in order to eliminate air, volatiles and excess resin from the layup. As the bag is evacuated, atmospheric pressure is applied to the layup, causing compaction and shrinkage of the layup. During this compaction process, the bag may deform in some areas, causing wrinkles to form in the bag. The applied compaction force may press the bag wrinkles against the surface of the layup, resulting in indentations referred to as “mark-off”.

Mark-off may be undesired in several composite laminate applications, either for aesthetic reasons or because mark-off reduces the performance of the laminate. For example, the presence of mark-off in composite laminate stiffeners may have an undesirable effect on the structural qualities of the stiffener.

Accordingly, there is a need for a method and apparatus for reducing or eliminating wrinkling of vacuum bags during the compaction of composite laminates. There is also a need for a method and apparatus of the type mentioned above which reduces or eliminates mark-off on the surface of a laminate that is compacted using vacuum bag processing.

SUMMARY

The disclosed embodiments provide a method and apparatus that reduces or eliminate wrinkling of vacuum bags used to compact composite laminate structures. The apparatus is simple in construction, easy to install and may be used with existing tools with minor or no modifications. The disclosed embodiments may reduce the need for hard tooling in order to reduce mark-off on features of the laminate.

According to one disclosed embodiment, a method is provided of vacuum bag processing a composite laminate structure. A vacuum bag is placed over the composite laminate structure and a substantially rigid batten is attached to an outer face of the bag over a portion of the structure. The composite laminate structure is compacted by evacuating the vacuum bag. The batten may be attached by placing an adhesive layer between the batten and the outer face of the bag. The attachment may be carried out by placing a layer of double-sided adhesive tape between the batten and the outer face of the bag. The method may further comprise installing the batten on a tool, and the batten may be attached to the bag bringing the tool into contact with the outer face of the bag. Installing the batten on the tool includes indexing the batten on the tool to a location aligned with a feature of the composite laminate structure. The batten may be held against the tool using a suction force.

According to another disclosed embodiment, a method is provided of reducing wrinkling of a vacuum bag during vacuum bag compaction of a composite laminate structure. A generally rigid batten is attached to an external face of the vacuum bag at a location on the vacuum bag covering a feature of the composite laminate structure. Attachment of the bag may be performed by applying an adhesive layer between the external face of the vacuum bag and one side of the batten. The attachment process may include aligning the batten with a feature of the composite laminate structure. The batten may be installed on a tool, and the batten may be attached to the bag by bringing the tool into contact with the vacuum bag. The adhesive layer may be placed on the batten before the tool is brought into contact with the vacuum bag.

According to still further embodiment, a method is provided of fabricating a composite laminate structure. The method comprises assembling a composite laminate layup, and installing a vacuum bag over the composite laminate layup. A batten is attached on an external face of the bag covering a feature of the composite layup, and the bag is evacuated. The batten is used to substantially prevent wrinkling of the vacuum bag covering the feature. The composite layup is then cured. The batten may be attached by adhering it in face-to-face contact with the external face of the vacuum bag. The attachment process may include installing the batten on a tool, and bringing the tool into contact with the vacuum bag.

According to still another embodiment, apparatus is provided for curing a composite laminate structure. The apparatus includes at least one tool, a vacuum bag and at least one substantially rigid batten. The tool is capable of having a composite laminate layup placed thereagainst, and includes at least one pocket therein facing a feature of the composite laminate layup. The vacuum bag is sealed over the composite laminate layup. The substantially rigid batten is capable of being received within the pocket and engaging an external face of the vacuum bag. The tool includes an indexing device for indexing the batten in a preselected positioned within the pocket. The tool may also include a wall within the pocket against which the batten may be held, and a plurality of perforations in the wall adapted to be coupled with a vacuum for creating a suction force holding the batten against the wall. The batten may be a cured, multi-ply composite laminate having a face substantially matching the feature of the composite laminate layup.

According to a further disclosed embodiment, a device is provided for reducing wrinkling of a vacuum bag during vacuum bag compaction of a composite laminate. The device includes a substantially rigid batten having a geometry substantially matching a feature of the composite laminate, and an adhesive layer attaching the batten to the vacuum bag. The adhesive layer may include a layer of double-sided adhesive tape covering one side of the batten.

DETAILED DESCRIPTION

Referring first toFIG. 1-4, a device in the form of a substantially rigid batten20is externally attached on the outside face22aof a flexible vacuum bag used to vacuum bag compact a composite laminate structure24during curing, bonding or other operations requiring compaction of the composite laminate structure24. The batten20may be employed during autoclave or out-of-autoclave processing of composite laminate structure24. The batten20is attached to the vacuum bag22in an area of the vacuum bag22that overlies one or more features25of the composite laminate structure24. In the illustrated example, the batten20is substantially flat, however as will be discussed later in more detail, the batten20may have other geometries configured to substantially match the geometry of features25of the composite laminate structure24.

The batten20has a degree of rigidity suitable for the application, and may vary depending upon the geometry of the features25, compaction pressures, bag material and other variables that depend on the application. In one embodiment, the batten20may comprise a pre-cured multi-ply composite laminate such as a CRFP (carbon reinforced fiber plastic). In other embodiments, the batten20may be formed of other materials reinforced with wire or fiberglass mesh.

As shown inFIGS. 2, 3 and 4an adhesive layer34may be used to attach to the vacuum bag22. In one embodiment, the adhesive layer34is applied to the batten20which is then placed on and adhered to the vacuum bag22. However in other embodiments, it may be possible to apply the adhesive layer34to the vacuum bag22, and then place the batten20on the adhesive layer34. In one embodiment, the adhesive layer34may comprise a layer of double-sided adhesive tape. Generally, the adhesive layer34is coextensive with the inside face20aof the batten20such that the entire area of the inside batten face20ais adhered to the vacuum bag22.

FIG. 5broadly illustrates the overall steps of a method of vacuum bag compaction of a composite laminate structure24that reduces or eliminates localized wrinkling of the bag22during the compaction process. Beginning at26, a vacuum bag22is placed over the composite laminate structure24and is sealed to a tool (not shown) or other structure, forming a vacuum chamber around the structure24. At28, a generally rigid batten20is attached by adhering it to the outer face22aof the vacuum bag22over a portion of the structure containing one or more features25. At step30the composite laminate structure24is compacted by evacuating the vacuum bag22. At32, the applied compaction force causes the composite laminate structure24to compact and shrink in volume.

As the composite laminate structure24shrinks in volume, the vacuum bag22deforms, creating excess bag material that may wrinkle in some areas of the vacuum bag22. As the composite laminate structure24shrinks in volume, the batten20is drawn down along with the vacuum bag22, but the adherence of the vacuum bag22to and throughout the inside face20a(FIG. 2) of the batten prevents deformation and related wrinkling of the vacuum bag in the area covering the feature25, thereby preventing mark-off on the feature25.

The use of a generally rigid batten20applied to a vacuum bag22may be employed in a wide range of composite laminate manufacturing processes to prevent mark-off caused by bag wrinkling. For example, referring now toFIG. 6, the disclosed batten20may be employed in combination with a set of tools44to compact and cure a composite laminate structure24which in the illustrated example, comprises a blade type stringer48. The stringer48may comprise a preformed multi-ply prepreg charge that is located and held located between the tools44, and vacuum bagged for compaction and curing.

The stringer48comprises a pair of generally L-shaped members assembled together in the tools44. Each of the L-shaped members includes an outwardly turned flange portion54and a web portion56. The two L-shaped members form a stringer base50, and a web or blade52which are supported and located by the tools44. A caul plate58is placed over the stringer base50in order to apply a more even compaction pressure to the flanges54, and a vacuum bag assembly45is installed around the stringer48and the caul plate58. The vacuum bag assembly45comprises a release film40such as FEP overlying the charge, covered by a breather38and the vacuum bag22. The vacuum bag22is sealed to the tools by any suitable means such as sealant tape42. The tools44may have open interiors and include longitudinally extending recesses or pockets46therein which respectively face the stringer web52. Each of the pockets46is configured to receive and hold one of the battens20therein.

Attention is now directed toFIGS. 7-10which illustrate additional details of the tools44, and the battens20used in compacting and curing the stringer48shown inFIG. 6. The pockets46in the tools44may extend substantially the entire length of the stringer48and include an interior wall55against which the batten20is held while the tools44are being assembled around the stringer48. The interior wall55includes a plurality of perforations60therein which are adapted to be coupled with a vacuum source (not shown).

The vacuum source is adapted to draw air in through the perforations66, creating a suction or vacuum force on the interior wall55which holds the battens20within the pockets46. Each of the tools44may include one or more indexing pins62or similar indexing devices or features that locate the battens20in any desired preselected position on the tools44. Indexing of the battens20on the tools44in turn allows the battens20to be indexed relative to features on the composite laminate, such as the web portions56which form the web82of the stringer48(FIG. 6).

Referring toFIG. 9, generally, the depth “D” of the pockets46is equal to or slightly greater than the battens20so that the battens20are fully recessed within the pockets46, but yet may come into contact with the vacuum bag22when the stringer charge48and the tool44are assembled together. The assembly procedure of the battens20and the tools44may begin with applying the adhesive layer34, such as double-sided adhesive tape on the battens20, and then placing the battens20in the pockets46of the tools44indexed to the indexing pins62. Air is drawn through the perforations60in the interior wall55by the vacuum source, creating a vacuum suction force that holds the battens20on the tools44during the assembly process that follows.

The vacuum bag assembly45is assembled around the stringer charge48, and the bagged stringer charge48along with the vacuum bag assembly45are assembled with the tools44. During this assembly process, the vacuum applied to the battens20hold the battens20within the pockets46. After the tools44and the stringer charge48have been assembled, the vacuum holding the battens20in the pockets46is removed, thereby releasing the battens20from the tools44. Assembly of the tools44with the stringer charge48brings the adhesive layer34on the battens20into contact with the vacuum bag22, thereby adhering the battens20in flush, face-to-face contact with the vacuum bag22.

As the vacuum bag22is evacuated during the compaction and cure process, the volume of the stringer48shrinks, and the bag22is drawn away from the tools44as a result of the stringer shrinkage. The battens20remain adhered to the vacuum bag22and are drawn away from the pockets46along with the vacuum bag22as the vacuum bag moves inwardly away from the tool44(seeFIG. 10). As the vacuum bag22deforms, the adhesion between the battens20and the vacuum bag maintain and holds the vacuum bag22flush and flat against the battens20, thereby preventing bag wrinkling in the area of the stringer web52.

FIG. 11broadly illustrates the overall steps of a method of vacuum bag compaction of a composite laminate structure24that reduces or eliminates wrinkling of the bag during compaction of the structure24. At66, battens20suitable for the application are fabricated which match the geometry of one or more features of the composite laminate structure24where mark-off is to be avoided due to bag wrinkling. At68, an adhesive layer34such as double-sided adhesive tape is applied to one side of each of the battens20. At70, the battens20are indexed and installed in pockets46within tools44used to locate and hold the composite laminate structure24. At72, the battens20are held on the tools using a vacuum force. Next, at74, the composite laminate structure is vacuum bagged, following which, the vacuum bag structure24is assembled with the tools44. At78, the battens20are brought into contact with the vacuum bag22, thereby adhering the battens20to the outer face22aof the vacuum bag22.

At80, the vacuum force holding the battens20on the tools44is released, following which, at82, the vacuum bag22is evacuated, causing the bag to be drawn down onto the composite laminate structure24and apply a compaction force which compacts the composite laminate structure24. As the volume of the composite laminate structure24compacts and shrinks, the battens20move away from the tools44and are drawn down along with the vacuum bag22. As shown at86, the vacuum bag22remains flat against the battens20to prevent wrinkling of the bag as a composite laminate structure24is being compacted.

In the embodiments previously discussed, the batten20has a substantially planar face20a(FIG. 2) along its length. However, as already mentioned, the battens20may be configured to substantially match the geometry of features of a composite laminate structure where bag wrinkling and resulting mark-off are to be avoided. For example, referring toFIG. 12, the batten20may be curved along its length to substantially match, for example and without limitation, a contoured stringer web (not shown). Similarly, as shown inFIG. 13, the batten20may have one or more bends, steps or joggles90along its length to match corresponding features of the composite laminate structure24being vacuum compacted.

In some cases where the composite laminate structure is particularly long, the batten20may be assembled in a plurality of sections. For example referring toFIG. 14, a long stringer100includes a web or blade102. A plurality of batten sections20bare assembled end-to-end along the web102in order to prevent bag wrinkling in the area of the web102throughout its entire length.

The disclosed battens20for preventing vacuum bag wrinkling and attendant mark-off may be used in a variety of aircraft applications to fabricate various components and subassemblies. For example, referring toFIG. 15, the disclosed battens20may be employed in connection with the fabrication of integrally stiffened panels104comprising a composite skin106integrally stiffened by a plurality of stringers48. The stringers may extend in a longitudinal direction108of the integrally stiffened panel104, and may be longitudinally spaced apart in a transverse direction110. The stringers48may be co-cured with, or bonded to the composite skin106.

Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where the composite laminate structures, such as stringers, spars and beams to name only a few, may be used. Thus, referring now toFIGS. 16 and 17, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method140as shown inFIG. 16and an aircraft122as shown inFIG. 17. Aircraft applications of the disclosed embodiments may include, for example, without limitation, a composite laminate structures, compliments or parts used in the aircraft122, or the maintenance thereof. During pre-production, exemplary method120may include specification and design124of the aircraft122and material procurement126. During production, component and subassembly manufacturing128and system integration130of the aircraft122takes place. Thereafter, the aircraft122may go through certification and delivery132in order to be placed in service134. While in service by a customer, the aircraft122is scheduled for routine maintenance and service136, which may also include modification, reconfiguration, refurbishment, and so on.

As shown inFIG. 17, the aircraft122produced by exemplary method120may include an airframe138with a plurality of systems140and an interior142. Examples of high-level systems140include one or more of a propulsion system144, an electrical system146, a hydraulic system148and an environmental system150. Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries.

Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method120. For example, components or subassemblies corresponding to production process128may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft122is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages128and130, for example, by substantially expediting assembly of or reducing the cost of an aircraft122. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft122is in service, for example and without limitation, to maintenance and service136.