Abstract:
A reusable vacuum bag for processing parts is made by encapsulating a generally rigid frame within a flexible diaphragm.

Description:
BACKGROUND INFORMATION 
     1. Field 
     The present disclosure generally relates to equipment used to fabricate composite parts, and deal more particularly with a vacuum bag used to compress composite part layups. 
     2. Background 
     Flexible vacuum bags may be used to process parts in a wide variety of applications. In the composites industry, vacuum bags are used to consolidate, laminate, mold or bond composite parts using a vacuum drawn within the bag to apply atmospheric pressure to the parts. The bag comprises a flexible membrane or diaphragm that may be an extruded polymer film such as nylon. 
     Polymer film type vacuum bags are typically not re-usable and must be discarded after each use, thus representing a recurring production cost. Reusable type vacuum bags are known which employ a rubber coated fabric or film, however these types of bags, which typically employ stiffening structures, are relatively complex, heavy and relatively expensive to fabricate. For example, reusable elastomeric type vacuum bags are fabricated using metallic stiffening frames. Separate bonding operations are required to attach the bag diaphragm, seal and frame to each other. Each component is fabricated separately, and the tooling used to produce the bags must be oversized in order to allow for shrinkage of the bag diaphragm during fabrication. 
     Accordingly, there is a need for an improved, reusable, integrally stiffened vacuum bag that reduces the number of steps required for its fabrication, while reducing weight and complexity of the bag. 
     SUMMARY 
     The disclosed embodiments provide an integrally stiffened, reusable vacuum bag, and related method of making the same, which reduce the number of fabrication steps and parts, thereby reducing costs. The bag is integrally stiffened with a rigid, peripheral frame that is encapsulated in the bag diaphragm, thereby eliminating the need for a separate operation to join the stiffener to the bag diaphragm. A peripheral bag seal may be integrally formed with the bag diaphragm, thereby eliminating the need for a separate bonding operation to attach the seal to the bag assembly. In one embodiment, the reusable vacuum bag may be fabricated on the layup tool that is used to layup and/or cure a composite part, thus eliminating the need for a separate tool to fabricate the vacuum bag. Relatively large, lightweight reusable vacuum bags may be fabricated that avoid the need for heavy outer support frames. 
     According to one disclosed embodiment, a vacuum bag for processing parts is provided comprising a flexible diaphragm and a generally rigid frame. The diaphragm is adapted to be placed over a part, and the frame is encapsulated within the diaphragm. The bag may comprise an elastomeric material such as a room curable RTV silicone. The frame may comprise a composite that extends around the periphery of the diaphragm and has its sides covered by the diaphragm. The vacuum bag may further comprise a seal for sealing the diaphragm against a surface during processing of the part. The seal may be formed integral with the diaphragm or alternatively, may be bonded to the frame. 
     According to another disclosed embodiment, an integrally stiffened, reusable vacuum bag for processing parts comprises a flexible diaphragm having an integral stiffener around its periphery. The bag may further comprise a seal integral with and extending around the periphery of the diaphragm for sealing the diaphragm against the surface during processing of the part. The stiffener may include a generally rigid frame encapsulated in the diaphragm which may comprise a vulcanized elastomer. 
     According to a further embodiment, a method is provided of making a vacuum bag for processing parts. The method comprises forming a flexible diaphragm, and encapsulating a generally rigid frame within the diaphragm. Forming the diaphragm may include coating a tool surface with an elastomer, and encapsulating the frame includes placing the frame on the elastomer coating and applying additional elastomer over the frame. The method may further comprise forming a seal integrally with the diaphragm. Forming the seal may include placing a seal element on a tool surface, and forming the diaphragm may include spraying a coating of elastomer over the tool surface covering the seal. The method may further comprise co-curing the seal and the elastomer coating. 
     According to still another embodiment, a method is provided of making an integrally stiffened, reusable vacuum bag for processing parts. The method comprises fabricating a generally rigid frame, and forming a diaphragm by spraying a first coating of an elastomer over a tool surface. The method also comprises placing the frame on the diaphragm, and encapsulating the frame with elastomer by spraying a second coating of the elastomer over the frame and onto the diaphragm. The method also includes co-curing the first and second elastomer coatings. The method may further comprises placing a seal on the tool surface, wherein spraying the first coating includes spraying the elastomer over the seal, and co-curing the first and second coatings and the seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the advantageous embodiments are set forth in the appended claims. The advantageous embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an advantageous embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an illustration of a perspective view of an integrally stiffened, reusable vacuum bag according to the disclosed embodiments. 
         FIG. 2  is an illustration of a sectional view of an edge of a composite layup assembly, showing the bag installed over a composite part layup on a tool. 
         FIG. 3  is an illustration of a perspective view of a tool used to make the vacuum bag shown in  FIGS. 1 and 2 . 
         FIG. 4  is an illustration of a flow diagram showing the steps of a method of making a reusable vacuum bag having an integrated seal. 
         FIG. 5  is an illustration of a perspective view of a stiffening frame prior to being assembled with the bag. 
         FIGS. 6-11  are illustrations of cross sectional views diagrammatically showing the sequential steps of the method of  FIG. 5 . 
         FIG. 12  is an illustration of a flow diagram showing the steps of an alternate method of making a reusable bag having a bonded seal. 
         FIGS. 13-17  are illustrations of cross sectional views diagrammatically showing the sequential steps of the method of  FIG. 12 . 
         FIG. 18  is an illustration of a flow diagram of aircraft production and service methodology. 
         FIG. 19  is an illustration of a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIGS. 1 and 2 , the disclosed embodiments relate to an integrally stiffened, reusable vacuum bag  20  that may be used, for example and without limitation, to consolidate and/or compress a composite part  34  on a tool  30 . The bag  20  includes a generally planar, elastic bag diaphragm  22  having dimensions that are suited to the particular application, covering the part  34 . The bag  20  also includes an outer frame  24  and a peripheral seal  26  beneath the frame  24  which seals the bag diaphragm  22  against a tool surface  28 . The frame  24  may be manufactured of any suitable rigid or semi-rigid material, such as a composite or a lightweight metal, and may be provided with attachments such as handles  27  to aid in handling or manipulating the bag  20 . In the illustrated embodiment, the frame  24  is generally rectangular, however it may have other shapes that are suited to the geometry of the composite part  34  being processed. The frame  24  has a generally rectangular cross section, as shown in  FIG. 2 , however other cross sectional shapes are possible. 
     The diaphragm  22  extends outwardly across the bottom  67  of the frame  24 , and encapsulates  32  the sides  68 ,  72  and top  70  of the frame  24 . Encapsulation  32  of the frame  24  within the diaphragm  22  essentially provides the elastic diaphragm  22  with integral stiffening that allows the bag  20  to be easily handled and manipulated. The seal  26  extends around the entire periphery of the composite part  34  and creates an air tight seal between the bag diaphragm  22  and the upper surface  28  of the tool  30 , allowing a vacuum to be drawn within the bag  22 . As will be discussed below, in one embodiment, the seal  26  is formed integral with the bag  22 , while in another embodiment, the seal  26  is bonded to the frame  24  in a separate fabrication operation. 
     Referring to  FIG. 3 , in one method embodiment, the vacuum bag  20  is fabricated using a tool  36  having a generally flat tool surface  38  and a peripheral groove  40 . In other embodiments, the vacuum bag  20  may be fabricated using the same tool  30  that is used to process the composite part  34 . 
     Attention is now directed to  FIG. 4 , along with  FIGS. 5-11  which sequentially illustrate the steps of one method of fabricating the vacuum bag  20  shown in  FIGS. 1 and 2 . Beginning at step  42 , the frame  24  is fabricated ( FIG. 5 ) using any of various fabrication techniques, including laminating and curing prepreg fiber. Where the frame  24  is formed of the composite, it may be laid up on either tool  30  ( FIG. 2 ) or tool  36  ( FIG. 3 ). Next, at step  44 , a peripheral seal  26  is fabricated using a suitable elastic material such as an elastomer that is molded or extruded into the desired cross section. As used herein, “elastomer” and “elastomeric” refer to natural and synthetic polymers that exhibit elastic properties, similar to natural rubber. For example, and without limitation, the elastomer may comprise a thermoset or a thermoplastic that can stretch and return substantially to its original shape without material deformation. At step  44  the seal  26  may be placed in a groove  40  ( FIG. 6 ) of tool  36  such that the seal  26  is generally coplanar with the upper surface  38  of the tool  36 . The groove  40  assists in holding and stabilizing the seal  26  during subsequent processing steps. Alternatively, as shown in  FIG. 7 , where the vacuum bag is fabricated directly on the layup tool  30  used to fabricate the composite part  34  ( FIG. 2 ), shims  58  may be placed on the tool surface  28  surrounding the seal  26  in order to stabilize and hold the seal  26  during subsequent processing operations. 
     Referring now again to  FIG. 4 , the diaphragm  22  ( FIG. 8 ) is formed by applying a first elastomeric coating  64  over the surface  38  of tool  36 . The application of the first coating  64  may be performed by spraying  60  an elastomer from a spray head  62  over tool surface  38 . The first coating  64  extends over the seal  26 . In one embodiment, the first elastomeric coating  64  may comprise a sprayable, RTV catalyzed silicone, which may be a one or two part system that cures relatively quickly at room temperature, without the need for oven or autoclave processing, and exhibits little or no shrinkage following curing. Other forms of elastomers are possible, some of which may require curing at elevated temperatures using an oven or other suitable heating devices. In one embodiment, the seal  26  is formed from an elastomer that is substantially identical to the elastomer used in the first elastomeric coating  64  forming the diaphragm  22 . Other techniques for applying the first coating  64  may be used, including but not limited to extrusion. 
     At step  50  ( FIG. 4 ), the frame  24  is placed on the diaphragm  22 , as shown in  FIG. 9 , with the frame bottom  67  generally overlying and registered with the peripheral position of the seal  26 . Next, at step  52  in  FIG. 4 , the frame  24  is encapsulated  32  ( FIG. 10 ) with an elastomer, by applying, as by spraying  60  a second elastomeric coating  66  over the exposed sides  68 ,  72  and top  70  of the frame  24 . The second coating  66  extends over onto the first coating  64  previously applied. Thus, in this embodiment, the diaphragm  22  along with the seal  26  and the encapsulation  32  on the frame  24  are formed of substantially the same material, which at this point in the fabrication process, are uncured. At step  54 , optionally, suitable hardware or handling attachments, such as handles  27  shown in  FIG. 1 , may be attached to the frame  24 . Finally, at step  56  shown in  FIG. 4 , the diaphragm  22 , frame encapsulation  32  and the seal  26  are cocured or vulcanized through the application of heat  74 . As previously discussed, where a suitable RTV silicone elastomer is used, the heat  74  may comprise room temperature heat. Cocuring integrates the diaphragm  22 , the encapsulation  32  around the frame  24  and the seal  26  into a continuous, unitary viscoelastic structure. 
     Attention is now directed to  FIG. 12  which, along with  FIGS. 13-17 , illustrates the steps of another method of fabricating the vacuum bag  20 . At  76 , a suitable frame  24  is fabricated following which at  78  a diaphragm  22  ( FIG. 13 ) is formed by applying an elastomeric coating  64  over the tool surface  38 , either by spraying  60 , extruding or other application techniques. Next, at step  80 , the frame  24  ( FIG. 14 ) is placed on the outer periphery of the diaphragm  22 , in contact with the first elastomeric coating  64 . At step  82 , the frame  24  is encapsulated  32  by applying a second elastomeric coating  66  over the sides  68 ,  72  and top  70  of the frame  24 , as shown in  FIG. 15 . The second coating  66  may be applied as by spraying  60 , from a spray head  62  or by using other techniques including but not limited to extrusion. The second coating  66  both covers the sides  68 ,  72  and top  70  of the frame  24 , and joins with and overlies the first coating  64 , forming a substantially, one-piece, unitary structure following curing. 
     At step  84  shown in  FIG. 12 , the diaphragm  22  along with the encapsulation  32  surrounding the frame  24  are cured ( FIG. 16 ) by applying heat  74  to the elastomer coatings  64 ,  66 . As previously mentioned as in connection with the embodiments shown in  FIGS. 4-11 , the elastomer may comprise an RTV silicone that cures at room temperature. At step  86  suitable hardware or attachments may be installed on the frame  24  as previously described. At step  88  shown in  FIG. 12 , a seal  26  ( FIG. 17 ) is bonded to the lower surface  24   a  of the diaphragm  26 , beneath the frame  24 , using any suitable techniques, such as using a bonding adhesive. The seal  26  may or may not be formed of a material that is the same as that of the diaphragm  26 . 
     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 automated layup equipment may be used. Thus, referring now to  FIGS. 18 and 19 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  90  as shown in  FIG. 18  and an aircraft  92  as shown in  FIG. 19 . Aircraft applications of the disclosed embodiments may include, for example, without limitation, layup of stiffener members such as, without limitation frames, stiffeners, hatches, spars and stringers, to name only a few. During pre-production, exemplary method  90  may include specification and design  94  of the aircraft  92  and material procurement  96 . During production, component and subassembly manufacturing  98  and system integration  100  of the aircraft  92  takes place. Thereafter, the aircraft  92  may go through certification and delivery  102  in order to be placed in service  104 . While in service by a customer, the aircraft  92  is scheduled for routine maintenance and service  106 , which may also include modification, reconfiguration, refurbishment, and so on. 
     Each of the processes of method  90  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 19 , the aircraft  92  produced by exemplary method  90  may include an airframe  108  with a plurality of systems  110  and an interior  112 . Examples of high-level systems  110  include one or more of a propulsion system  114 , an electrical system  116 , a hydraulic system  118 , and an environmental system  120 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries. 
     Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method  90 . For example, components or subassemblies corresponding to production process  98  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  92  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  98  and  100 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  92 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  92  is in service, for example and without limitation, to maintenance and service  106 . 
     The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.