Patent Publication Number: US-2013233476-A1

Title: Out-of-autoclave and alternative oven curing using a self heating tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending U.S. patent application Ser. No. 12/870,556 filed on Aug. 27, 2010, entitled the same as above, is herein incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The United States Government may have certain rights to this application under contract No. FA9453-06-D0368-0003. 
    
    
     BACKGROUND 
     Composite structures formed from pre-impregnated (pre-preg) material are used in the formation of high strength-low weight structures such as, but not limited to, parts used to build aircraft and spacecraft. Pre-preg material is made of composite fibers such as carbon, glass, aramid and the like, that are bonded together with a resin that is activated with heat to cure. The pre-preg material is typically supplied in sheets or plies. The manufacturer then forms stacks of plies of pre-preg material on a forming surface of a tool having a desired shape. Once the pre-preg material is formed on the tool, the tool is placed in an autoclave or conventional oven to cure the resin. The aerospace industry&#39;s desire for increasingly larger structures has resulted in larger autoclaves and conventional ovens needed to cure the pre-preg material. The larger the autoclaves and conventional ovens, the more costs associated with building and operating them. 
     For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an effective and efficient method of forming composite structures without the use of an autoclave or conventional oven. 
     SUMMARY OF INVENTION 
     The above-mentioned problems of current systems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention include both apparatuses and methods. The following summary is made by way of example and not by way of limitation. It is merely provided to aid the reader in understanding some of the aspects of the invention. 
     In one embodiment, a method of curing composite material to form a composite structure is provided. The method including, laying up and forming pre-preg material on a forming surface of cured pre-preg material of a composite structure forming tool and passing current through nano tube impregnated resin within the forming tool to heat the tool internally to cure the pre-preg material. 
     In another embodiment, a curing tool is provided. The curing tool includes cured nano tube impregnated resin. At least two conductors are formed in the nano tube impregnated resin. The curing tool also includes a forming surface portion. The forming surface portion includes cured composite material of pre-preg material. The curing tool further includes at least a first insulation layer that separates the cured composite material from the nano tube impregnated resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more easily understood and further advantages and uses thereof will be more readily apparent, when considered in view of the detailed description and the following figures in which: 
         FIG. 1  is a tool formation flow diagram of one embodiment of the present invention; 
         FIG. 2  is a partial side perspective view illustration of the formation of a support base portion of a tool of one embodiment of the present invention; 
         FIGS. 3A-3I  are partial side perspective views illustrating the further formation of a heating tool of one embodiment of the present invention; 
         FIG. 3J  is a bottom perspective view of the tool with formed passages of one embodiment of the present invention; 
         FIG. 3K  is a cross-sectional end view of a heating tool of one embodiment of the present invention; 
         FIG. 3L  is a cross section end view of the heating tool of  FIG. 3H  coupled to a controller and power source of one embodiment of the present invention; 
         FIG. 3M  is a side perspective view of the forming of conductors in a heating tool of another embodiment of the present invention; 
         FIG. 4  is a composite structure forming flow diagram of one embodiment of the present invention; 
         FIG. 5A and 5B  are partial side perspective views in forming a composite structure on a self heated tool of one embodiment of the present invention; and 
         FIG. 6  is a side perspective view of a lay up of the heating tool of another embodiment; and 
         FIG. 7  is a tool formation flow diagram of the formation of the tool of  FIG. 6 . 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims and equivalents thereof. 
     Embodiments of the present invention provide methods and apparatuses for fabricating molds, forms, or mandrels (that can be generally referred to as a tool) that are self heating. Hence, in embodiments, a tool is provided that includes an internal heating source. Embodiments allow composite structures to be cured on the same tool as they were fabricated on without the need for an autoclave or an oven. Hence, large out-of-autoclave structures are cured while sitting on a production floor thereby eliminating size constraints on autoclaves and ovens. Also, embodiments of the self heating tools allow for the mass production of smaller composite parts. Rather than stacking hundreds of uncured parts into an autoclave in a time-consuming process, each part could have its own self heating tool. Each self heating tool can be heated on the production floor thereby providing an efficient part flow through the manufacturing plant. 
     In embodiments, a tool is formed with resin impregnated with nano tubes. The nano tubes in embodiments are electrically conductive. In one embodiment the nano tubes used to impregnate the resin are carbon nanofibers (nano tubes). Passing current through the resin results in heat being generated due to electrical resistance in the nano tube impregnated resin. In embodiments, by varying the electrical power, the amount of heat created by the tool is varied. Moreover, in embodiments, conductive strips, such as, but not limited to, copper strips are embedded in the cured nano tube impregnated resin. An electrical potential is created between adjacent conductive strips (conductive strips that are near each other) which cause a current to pass through the nano tube impregnated resin. In an embodiment, an alternating current (AC) is applied to the adjacent conductive strips to produce the current through the nano tube impregnated resin. 
     Referring to  FIG. 1 , a formation flow diagram  100  of one embodiment is illustrated. The formation flow diagram  100  is described below in concert with illustrations in  FIGS. 2 through 3I . In forming a tool, a first step is determining what resin is compatible with a heat range needed to cure pre-preg material (out of autoclave material) used to form a composite structure ( 102 ). Then it is determined what the nano tube percentage should be in relation to the resin ( 104 ). The percentage ratio is based on a desired outcome (desired heat to be generated by a tool). The nano tubes are then mixed with the resin to form carbon nano tube impregnated resin ( 106 ). A type of resin that can be used is K-factor resin provided by Boyce Components LLC. Example nano tubes used are carbon nano tubes provided by Polygraf Products which is a part of Applied Sciences Inc. 
     A foundation for the nano tube impregnated resin has to be provided to form the self heating tool. In one embodiment, plies of pre-preg material  204   a,    204   b,    204   c  are laid up and formed on a mandrel  202  ( 108 ). The plies of pre-preg material form a support base portion  204 . In one embodiment six to eight layers (plies) of carbon pre-preg material are used to form the support base portion  204  which is approximately 0.180 to 0.250 inches thick.  FIG. 2  illustrates ply layers  204   a,    204   b  and  204   c  being applied to the mandrel  202 . In one embodiment, the ply layers of pre-preg material  204   a,    204   b  and  204   c  include carbon fibers. The plies that make up the support base portion  204  are then cured ( 110 ). After the support base portion  204  is cured, a first insulation layer  300  is applied ( 112 ). This is illustrated in  FIG. 3A . In one embodiment, the first insulation layer  300  is a dry woven glass layer  300  that is laminated on the support base portion  204 . The insulation layer (dry woven glass layer  300 ) is then cured on the support base portion  204  ( 113 ). The thickness of the insulation layer  300  in one embodiment is in the range of 0.003 to 0.005 inches. 
     Once the first dry woven glass layer  300  has been cured, a first coat of carbon nanotube impregnated resin  302   a  is applied over the dry woven glass layer  300  ( 114 ). This is illustrated in  FIGS. 3B and 3C . In one embodiment, a sponge brush  304  is used to apply the first coat of carbon nano tube impregnated resin  302   a  to the first dry woven glass layer  300 . In one embodiment, the first coat of carbon nano tube impregnated resin  302   a  is applied with a uniform thickness of approximately 10 to 11 mils. The desired spacing of the conductive strips  306  to be used in the tool is then determined ( 116 ). In one embodiment, the conductive strips  306  (conductors) are made of a metal such as copper. The conductive strips  306  are then placed on a surface of the first coat carbon nano tube impregnated resin  302   a  ( 118 ) as illustrated in  FIG. 3D . A second coat of carbon nano tube impregnated resin  302   b  is then applied over the first coat of carbon nano tube impregnated resin  302   a  and the conductive strips  306  ( 120 ). The first and second coats of carbon nano tube impregnated resin  302   a  and  302   b  are then cured ( 122 ). The tool in this state is illustrated in  FIG. 3F . Although, the conductive strips  306  are illustrated above as being substantially straight in the embodiment illustrated in  FIGS. 3D and 3E , in other embodiments, the conductive strips  306   a  can take any shape as needed to distribute the heat in the tool  350  as desired. For example, in  FIG. 3M  the conductive strips  306   a  and  306   b  are patterned to achieve a desired heating distribution. 
     A second insulation layer  310  is laminated then laid up and laminated on the carbon nano tube impregnated resin  302   b  ( 124 ). This layer of the insulation  310  is then cured ( 125 ). In one embodiment, the second insulation layer  310  is a dry woven glass layer  310  having a thickness in the range of 0.003 to 0.005 inches. The addition of the second insulation layer  310  is illustrated in  FIG. 3G . Once the second insulation layer  310  has been formed, ply layers  312   a  and  312   b  of pre-preg material are laid up ( 126 ) and cured ( 126 ) to form a tool forming surface  312  of the tool  350 . The lying up of the ply layers  312   a  and  312   b  are illustrated in  FIG. 3H  and the formed tool forming surface  312  is illustrated in  FIG. 3I .  FIG. 3I  also illustrates the layers of a formed tool  350  in an embodiment. In one embodiment, the ply layers of pre-preg material  312   a  and  312   b  include carbon fibers. Moreover, the number of ply layers  312   a  and  312   b  used to form the tool forming surface portion  312  can vary depending on a desired outcome. In one embodiment, the thickness of the tool forming surface  312  is in a range of 0.035 to 0.040 inches. Although, the formed tool  350  illustrated in  FIG. 3I  is generally C-shaped, the tool can have any desired cross-sectional shape desired depending on the application. Moreover, the tool can be straight along its length, it can be curved along its length and its cross-sectional geometry can vary along its length. Hence, any shaped tool is contemplated and tool  350  of  FIG. 3I  is merely an example of one shape of a tool used to form a C-shaped composite structure. 
     In one embodiment, the tool  350  is removed from the base mold  124  once the tool is formed. Bores  330  are then selectively formed through the base support portion  204 , the first insulation layer  300  and the first cured carbon nano tube impregnated resin  302   a  to the conducting strips  306  ( 130 ). This is illustrated in  FIG. 3J  and  FIG. 3K . In one embodiment, a Dremel® power tool by the Robert Bosch Tool Corporation, or similar tool, is used to make the bores through the tool  350  to the respective conducting strips  306 . Conductive wires  340  are then coupled to the conductive strips  306  ( 132 ) as illustrated in  FIG. 3L .  FIG. 3L  further illustrates, a power source  342  coupled to the conductive wires  340  and a controller  344 . The controller  344  is designed to control the power source  342 . As stated above, in one embodiment, the power source  342  provides an alternating current (AC) to respective conductive strips  306  to heat up the tool  350 . As illustrated in  FIG. 3L , the first and second insulation layers  300  and  310  insulate the conductors  306  and nano tube impregnated resin  302   a  from the material that makes up the support base portion  204  and the tool forming surface portion  312 . This prevents the support base portion  204  and the tool forming surface portion  312  from passing current out of the tool  350 . This would be an issue in an embodiment where the support base portion  204  and the tool forming surface  312  include conductive material such as carbon fibers. The insulation layers  300  and  310  also help prevent the nano tube impregnated resin from spreading onto the composite material of the support base portion  204  and the tool forming surface portion  312  during formation of the tool. 
     Referring to  FIG. 4 , an illustration of a composite structure forming flow diagram  400  is illustrated. The flow diagram  400  is described in concert with  FIGS. 5A and 5B . The process starts by laying up and forming pre-preg material on the tool ( 402 ). In one embodiment, this is done by applying one or more layers of pre-preg material on the tool forming surface portion  312  of the tool  350  and pressing the one or more layers of pre-preg material onto the tool forming surface portion  312  of the tool  350  to form the pre-preg material into the shape of the tool forming surface portion  312 . An example of laying up a layer of ply material  500  on a tool  350  is illustrated in  FIG. 5A . Any method known in the art to lay up and form the pre-preg material  500  on the tool  350  can be used. An example method of laying up and forming pre-preg material on a tool is illustrated in commonly assigned U.S. Pat. No. 7,249,943 entitled “Apparatus for Forming Composite Stiffeners and Reinforced Structures” that issued on Jul. 31, 2007 and U.S. Pat. No. 7,513,769 entitled “Apparatus and Methods for Forming Composite Stiffeners and Reinforcing Structures” that issued on Apr. 7, 2009 both of which are incorporated herein by reference. Moreover, any other method of laying up and forming the pre-preg material on a tool can be used, such as hot drape forming and other methods known in the art. Once the pre-preg material is positioned on the tool, the power source  342  provides power to the conductive strips  306  in the tool  350  ( 404 ). An example, of the power source  342  coupled to heat a tool  350  is illustrated in  FIG. 5B . In  FIG. 5B  pre-preg material on the tool  350  is cured to form a composite structure  550 . In particular, the heat of the tool  350 , as a result of the power being supplied to conductors (conductive strips) in the tool  350 , cures the pre-preg material ( 404 ) to form the composite structure  550 . In one embodiment, a vacuum bag system known in the art is used to compact the pre-preg material during curing ( 403 ). Once the pre-preg material is cured, the formed composite structure  550  is removed from the tool  350  ( 406 ). 
     Referring to  FIG. 6 , a lay up (formation) of the tool  350  of another embodiment is illustrated. In this embodiment the tool is formed on a master  602  (mandrel) in an opposite manner as the embodiment discussed above. In this embodiment, the master  602  is generally in the shape of the part to be made on the heated tool  305 . Hence, the formation of the tool on a mandrel can be made in different ways. One advantage to the formation of the tool  350  as illustrated in  FIG. 6  is that the tool forming surface portion  312  will be relatively smooth and provide a good surface on which to form the composite structures. Conversely, a surface of the support base portion  102  will be rougher due to the use of one or more vacuum bags used to cure the tool  350 . 
       FIG. 7  illustrated a tool formation flow diagram  700  pursuant to the lay up illustrated in  FIG. 6 . The flow diagram  700  starts similar to the flow diagram  100  described above. The resin is selected ( 102 ). The nano tube percentage is selected ( 104 ). The nano tubes and resin are mixed to form the nano tube impregnated resin  302  ( 106 ). Plies of pre-preg material are layed up on the master ( 708 ). The plies are then cured ( 710 ) to form the tool forming surface portion  312  on a surface of the master  702 . A first insulation layer  300  is then laminated on a back side of the tool forming surface portion  312  ( 712 ). The first insulation layer  300  is then cured ( 713 ). A first coat of nano tube resin  302   a  is then applied to the cured first insulation layer  300  ( 714 ). It is then determined what the spacing should be for the conductive strips ( 716 ). The conductive strips  306  are then placed on the first coat of nano tube resin  302   a  ( 718 ). A second coat of nano tube resin  302   b  is then applied covering the conductive strips  306  ( 720 ). The nano tube resin  302   a  and  320   b  is then cured ( 722 ). A second layer of insulation  310  is then laminated over the nano tube resin  302   a  and  320   b  ( 724 ). The insulation layer  310  is then cured ( 725 ). Plies of pre-preg material are then layed up on the second layer of insulation  310  ( 726 ). The plies of pre-preg material are then cured to form the support base portion ( 128 ). Bores are then formed through the support base portion  204  to the conductive strips ( 130 ) as described above in regards to  FIG. 3J . Conductive wires are then coupled to the conductive strips ( 132 ). As understood in the art, curing of the various materials to make the tool  350  may include various forms of vacuum bagging techniques. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.