Abstract:
A method for manufacturing a wall of a thin-walled structure is described. The method includes receiving parameters for the wall and one or more stiffening features associated with the wall via a user interface, providing the parameters to a machine configured to fabricate the wall and incorporate the one or more stiffening features, the machine using a direct manufacturing process and operating the machine to integrally fabricate the wall and the one or more stiffening features.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to manufacturing of composite structures, and more specifically, to methods for stiffening thin wall direct manufactured structures. 
         [0002]    Certain composite structures, for example, aircraft structures or parts such as ductwork and air handling plenums, are typically fabricated from composite materials that can require tedious hand lay up procedures and complex tooling. In these composite structures, complex internal features, which are sometimes referred to as blind features, are typically avoided to maintain a capability for production. Maintaining an ease of production, however, limits the designs to shapes and features that are accessible for laying up the composite materials. 
         [0003]    In composite structure production, the parts are typically configured with thickened walls to maintain stiffness from buckling and collapse. Any additional stiffening features, for example, angled clips or ribs, are attached as a secondary operation. Secondary operations add costs and increase part counts. Secondary operations and thickened walls also typically increase the weight of the parts. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    A method for manufacturing a wall of a thin-walled structure is provided. The method includes receiving parameters for the wall and one or more stiffening features associated with the wall via a user interface, providing the parameters to a machine configured to fabricate the wall and incorporate the one or more stiffening features, the machine using a direct manufacturing process, and operating the machine to integrally fabricate the wall and the one or more stiffening features. 
         [0005]    In another aspect, an air handling aerospace structure is provided that comprises a plurality of walls defining a chamber and at least one stiffening feature. The stiffening features are formed integrally with at least one of the walls. The walls and the stiffening features fabricated utilizing a direct manufacturing process. 
         [0006]    In still another aspect, a method for direct manufacturing a structure having at least one substantially enclosed chamber defined by a plurality of walls is provided. The method includes defining, for input into the direct manufacturing process, the plurality of walls, a stiffening feature for at least one of the walls, and a remainder of the structure, and integrally forming the walls, any stiffening feature associated with each respective wall, and the remainder of the structure, with the direct manufacturing process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]      FIG. 1  is an illustration of a system utilized in the direct manufacture of composite structures. 
           [0008]      FIG. 2  is a cutaway view illustration of an air plenum fabricated utilizing the system of  FIG. 1 . 
           [0009]      FIG. 3  is a perspective view of the air plenum of  FIG. 2 . 
           [0010]      FIG. 4  is a cutaway view illustration of a baffled air plenum, portions of which are in a single opposing arch configuration. 
           [0011]      FIG. 5  is a cross-sectional view of a portion of a wall of the air plenum of  FIG. 4 , illustrating the single opposing arch configuration. 
           [0012]      FIG. 6  is a cutaway view illustration of another embodiment of air plenum, portions of which are in a double opposing arch configuration. 
           [0013]      FIG. 7  is a cross-sectional view of a portion of a wall of the air plenum of  FIG. 6  in a first direction. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Described herein are methods that fill the need for lightweight and inexpensive composite structures while also reducing the above described secondary operations. In practice, utilization of the described methods result in structures that possess relatively thin walls. These structures further include stiffening features, which may be formed integrally with the walls. Such a structure provides strengthened walls, which may be utilized instead of structures that include relatively thicker walls that are fabricated utilizing other composite fabrication methods. Such a structure also reduces secondary operations associated with current composite material structure production, such as inclusion of angled clips or ribs within the walls of the structure. 
         [0015]      FIG. 1  is an illustration of a system  10  utilized in the direct manufacture of structures  12  in accordance with the methods described herein. In one embodiment, system  10  includes a direct manufacturing assembly  14 , for example, a selective laser sintering assembly, to generate the desired structure (or structures)  12  in a single build run which is controlled utilizing a computer assembly  15 . At least in the selective laser sintering example, direct manufacturing assembly  14  incorporates a laser  16  to integrally fabricate solid structures within a build chamber  18  during the build run. 
         [0016]    Selective laser sintering (SLS) is a process for generating a material from a powdered sintering compound, and is one type of direct manufacturing process. In the SLS process, the powdered compound is distributed onto a surface within build chamber  18 , and laser  16 , is directed onto at least a portion of the powder, fusing those powder particles together to form a portion of a sintered material. Successive layers of the powder are distributed onto the surface, and the laser sintering process continues, fusing both the particles of the powdered material together into layers and the adjacent layers together, until the fused layers of laser sintered material are of a shape and thickness as appropriate for the intended use of the material. 
         [0017]    Through laser sintering of polymer materials, integral internal features may be incorporated into structures that heretofore have been impossible to attain, including, but not limited to complex shapes and integrated external features that replace the above described stiffening angled clips and ribs. Although laser sintering has been described, other layer build methodologies are contemplated. 
         [0018]      FIG. 2  is a cutaway view illustration of one embodiment of a structure, an air plenum  100 , that is fabricated utilizing the system  10  of  FIG. 1 . For reference, air plenum includes an air inlet  102 , an air outlet  104 , and a chamber  106  in between. Chamber  106  is substantially rectangular and is defined by four side walls  110 ,  112 ,  114 , and  116  (shown in  FIG. 3 ). Chamber  106  is further defined by a top wall  120  and a bottom wall  122 , which are described as “top” and “bottom” respectively for reference only. 
         [0019]      FIG. 3  is a perspective view of air plenum  100  that includes side wall  116 . As illustrated by  FIGS. 2 and 3 , side walls  110 ,  112 ,  114 , and  116  intersect top and bottom walls  120  and  122  to form the chamber  106  (shown in  FIG. 2 ). The six walls have a have a minimum thickness, in the illustrated embodiment, of about 0.030 inch, but are stiffened by integral raised ridges  130  or bosses in a shape and size (thickness and height) commensurate with a load the walls have to resist during use, for example, from an air pressure within the plenum  100 . Specifically in the illustrated embodiment, raised ridges  130  are incorporated in a honeycomb or hexagonal shape. The shape of raised ridges  130  also aid in resisting torque within the walls defining chamber  106  resulting in a stiff structure for air plenum  100 . 
         [0020]    With regard to SLS, fabrication of air plenum  100  is accomplished in successive layers being “sintered” together. Assuming the plenum  100  is fabricated from the bottom up, the sintering compound would be distributed in a circular pattern within build chamber  18  (shown in  FIG. 1 ). As the circular distribution of sintering compound and successive sintering continues air outlet  104  is formed. As air outlet  104  is completed, the sintering compound is distributed in the honeycomb pattern to begin fabrication of the raised ridges  130  adjacent bottom wall  122  and so on until the raised ridges  130  are complete and fabrication of the solid portion of bottom wall  122  begins. The process continues and successive layers are built up until fabrication of the plenum  100  is complete. It should be noted that air plenum  100  could be fabricated in any “direction” including from top to bottom, from front to back, or from back to front, depending on the dimensions of air plenum  100  and the dimensions of build chamber  18 . 
         [0021]      FIG. 4  is a cutaway view illustration of a baffled air plenum  150 . Air plenum  150  includes a top wall  152 , a bottom wall  154 , and a baffling wall  156  substantially centrally located within plenum  150 . Air plenum  150  is fabricated utilizing the same processes as air plenum  100  (shown in  FIGS. 2 and 3 ). Rather than incorporating the raised ridges  130  described with respect to air plenum  100 , the walls  152 ,  154 , and  156  of air plenum  150  have been fabricated to have a corrugated shape utilizing single opposing arches.  FIG. 5  is a cross-section of a portion of wall  152 , for example, illustrating the single opposing arches, for example, arches  158  and  159 . It is to be understood that the cross-section of  FIG. 5  is also illustrative of the cross sections of walls  154  and  156 . 
         [0022]    Referring back to  FIG. 4 , air plenum  150  includes an air inlet  162 , an air outlet  164 , and sides  166  and  168 . A front wall is not shown so that the detail of the chambers  170  and  172  can be illustrated. Similar to the walls of air plenum  100 , walls  152 ,  154 , and  156  have a minimum thickness of about 0.030 inch, but are stiffened by utilization of the single opposing arch configuration. The arches  158  and  159  are shaped and sized (width and height of each arch) commensurate with a load the walls  152 ,  154 , and  156  have to withstand during use, for example, from an air pressure within the plenum  150 . 
         [0023]    When fabricated utilizing the selective laser sintering process, individual layers of the sintering compound are serially subjected to the laser to “build up” the air plenum  150 . In one example, layers of sintering compound are built up to fabricate air outlet  164 , the arches of bottom wall  154 , a bottom portion  180  and  182  of respective sides  166  and  168 , the arches of baffling wall  156 , a top portion  184  and  186  of respective sides  166  and  168 , the arches of top wall  152 , and air inlet  162 . It should be noted that air plenum  150  could be fabricated in any “direction” including from top to bottom, from front to back, or from back to front, depending on the dimensions of air plenum  100  and the dimensions of build chamber  18 . 
         [0024]    It should also be noted that in the illustrated embodiment, air plenum  150  is overall slightly wedge-shaped, as best illustrated by the overall shape of side  168 . With respect to baffling wall  156 , the wedge shape may be obtained by either fabricating baffling wall  156  to be thicker from a front to a back (as illustrated) of air plenum  150 , or by fabricating baffling wall  156  as two gradually separating corrugated structures. 
         [0025]      FIG. 6  is a cutaway view illustration of an another embodiment of an air plenum  200 . Air plenum  200  includes an air inlet  202 , an air outlet  204 , and a chamber  206  in between. Chamber  206  is substantially rectangular and is defined by four side walls  210 ,  212 ,  214 , and a fourth side wall that is not shown due to the cutaway view. Chamber  206  is further defined by a top wall  220  and a bottom wall  222 , which are described as “top” and “bottom” respectively for reference only. Air plenum  200  is fabricated utilizing the same processes as air plenum  100  (shown in  FIGS. 2 and 3 ). Rather than incorporating the raised ridges  130  described with respect to air plenum  100 , the walls  210 ,  212 ,  214 , and the fourth wall of air plenum  200  have been fabricated to have a waffle-pattern shape utilizing double opposing arches.  FIG. 7  is a cross-sectional view of a portion of top wall  220 , for example, in a first direction as viewed from the direction of wall  214  illustrating single opposing arches. The cross-section is the same when viewed from the direction of wall  212 . It is to be understood that the cross-section of  FIG. 7  is also illustrative of the cross sections of walls  210 ,  212 ,  214 ,  222 , and the non-illustrated wall. 
         [0026]    Therefore, as utilized herein, double opposing arches refers to a configuration as a first set of singles opposing arches in a first direction and a second set of single opposing arches in a second direction substantially perpendicular to the first direction. Such double opposing arches tend to tend to create a quilted pattern as illustrated in  FIG. 6 . 
         [0027]    Referring back to  FIG. 6 , a front wall is not shown so that the detail of the chamber  206 , and specifically the walls that form the chamber can be better illustrated. Similar to the walls of air plenums  100  and  150 , walls  210 ,  212 , and  214 , top wall  220 , bottom wall  222 , and the non-illustrated wall have a minimum thickness of about 0.030 inch, but are stiffened by utilization of the double opposing arch configuration. The arches are shaped and sized in each direction (width and height of each arch) commensurate with a load the walls  210 ,  212 , and  214 , top wall  220 , bottom wall  222 , and the non-illustrated wall have to withstand during use, for example, from an air pressure within the plenum  200 . 
         [0028]    When fabricated utilizing the selective laser sintering process, individual layers of the sintering compound are serially subjected to the laser to “build up” the air plenum  200  as previously described with respect to air plenums  100  and  150  and the dimensions of build chamber  18 . 
         [0029]    The arch shape (both single opposing and double opposing) and the honeycomb shape have inherent compression properties. By taking advantage of these properties, wall thicknesses can be reduced in panels, without reducing strength properties. Such configuration also reduce overall weight of structures that incorporate such walls. Utilization of the herein described arch shapes and/or honeycomb configurations provide stiffening for the relatively thin wall panels. The thickness and height of the raised hexagonal ridge, or boss, in the honeycomb configuration is tailored to resist the pressure loads being applied within the structure. Similarly, the widths and heights of the opposing arches (single and double) are tailored to resist the pressure loads being applied within the structure. 
         [0030]    In addition, the description herein demonstrate how these shapes can be integrally fabricated into a structure, for example, an air handling plenum, to stiffen the thin wall structure from buckling and collapsing with integral torque stiffness. These shapes also aid in resisting torque within the box resulting in a stiff structure. 
         [0031]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.