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Digital Radiography (DR) and Computed Tomography (CT) imaging has historically has been
used to evaluate parts for indication of density variation The images were displayed on a
workstation and were evaluated for flaws and non-conforming indications. The next step was to
perform elementary measurements, statistic, graphical, etc. by operating on the digital data using the
computer. Finally, the complete 3D model was constructed from contiguous CT images to defines
the part in 3D. Since this is the 3D definition of the part, the next logical step is to extract geometry
definition similar to a CAD model.
GE has developed algorithms and methods to obtain geometry definition of parts using both Digital
Radiography and Computed Tomography x-ray inspection techniques (referred to as X-ray Metrology).
CT imaging yields a complete 3D model of the part with a sacrifice of time, whereas multiple DR
(2.5D) imaging is acquired must more rapidly with a sacrifice of volumetric information. Where the
characteristics can be defined with 2.5D, this method can be used in more nearly real time applications.
Originally, GE used X-ray Metrology information to reverse engineer the part where only partial CAD
data exits To completely reverse engineer a part, extensive manual labor is required if the geometry is
complex as for the turbine blade. As more parts are being designed using 3D solid modeling, there will
be less need for reverse engineering. But, X-ray Metrology can have a very important role in part
development and process control.
GE is successfully using X-ray Metrology to extract part geometry and perform sampling process
monitoring. X-ray Metrology provides geometry definition of the part both inside and outside with out
destroying the inspected part. The increased computer system performance has enable the rapid
generation of large x-ray data set from image processing. In some cases, commercially available
software has enabled manipulation of the x-ray data to assist in filtering the data into process control
formats.
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