Patent Application
20100029189
This invention relates generally to manufacturing of composite structures, and more specifically, to methods for stiffening thin wall direct manufactured structures.
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.
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.
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.
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.
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.
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.
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.
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.
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
Referring back to
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.
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.
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
Referring back to
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.
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.
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.
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.
