Creating Data Packages For Aircraft Resupply
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Mat. Res. Soc. Symp. Proc. Vol. 503 01998 Materials Research Society
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any part of any material composition; no need for special set-ups, programming, or fixturing; and, the acquisition of very well-behaved, dense point data. Film
Radiography
~X-ray
Sorce
Computed Tomography Detector Array X-ray Source CT Image
Figure 1. Comparison between Conventional Radiography and Computed Tomography. CT-Assisted Reverse Engineering CT-assisted reverse engineering is the process of going from CT data to a CAD file. Since CAD is required to access all new-generation manufacturing techniques such as numerically-controlled (NC) machining and rapid prototyping, it is becoming essential to have CAD descriptions of manufactured parts. There are many cases where 3-D CAD files are not available for both older and newer parts. An example of a part that has been successfully reverse engineered using CT is shown in Figure 2. Figure 2 a) shows a photograph of the original part. The part is a sand casting with an internal passageway which cannot be seen from the outside. The casting is a military component which needed to be reproduced where an adequate set of technical data did not exist. Due to the complex internal geometry, CT was the only nondestructive digitizing technique that could be used. A full set of CT images was acquired using a 9-MeV CT system. Figure 2 b) shows the point cloud generated from the CT data. The point cloud is a dense, well-behaved set of points in space which represents the internal and external geometry of the part. Figure 2 c) shows the CAD model of the part which was produced by fitting surfaces to the point cloud. Figure 2 d) shows the CAD model of the internal core. The point cloud can be used as a template for various operations including generating a CAD model, generating an STL or SLC file for input to rapid prototyping equipment, or generating NC toolpaths. There are now many software packages available that process 3-D point clouds and generate the required files. Figure 3 shows an added advantage of using CT for enhancing or creating geometric descriptions of components. Figure 3 a) shows a single CT image of a fully assembled automobile engine. The gray parts of the image represent aluminum components and the brighter parts of the image represent steel components. The steel exhaust manifold is circled on the CT image and the solid STL model of the exhaust manifold, created from several contiguous CT slice images, is shown in Figure 3 b). Since there is a significant density contrast between the steel and aluminum components, a thresholding algorithm can easily separate the steel from the aluminum. Currently, this can be carried out in a matter of minutes once the proper threshold is defined. This highlights the ability of CT to generate geometric models of ind
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