CT may be performed on an object when it is in the as-cast, intermediate, or final machined condition. A CT examination can be used as a design tool to improve wax forms and moldings, establish process parameters, randomly check process control, perform final quality control (QC) examination for the acceptance or rejection of parts, and analyze failures and extend component lifetimes.
The most common applications of CT for castings are for the following: locating and characterizing discontinuities, such as porosity, inclusions, cracks, and shrink; measuring as-cast part dimensions for comparison with design dimensions; and extracting dimensional measurements for reverse engineering.
The extent to which a CT image reproduces an object or a feature within an object is dictated largely by the competing influences of spatial resolution, contrast discrimination, and artifacts of the imaging system. Operating parameters strike an overall balance between image quality, examination time, and cost.
Artifacts are often the limiting factor in CT image quality. (See Practice E 1570
1.1 This practice covers a uniform procedure for the examination of castings by the computed tomography (CT) technique. The requirements expressed in this practice are intended to control the quality of the nondestructive examination by CT and are not intended for controlling the acceptability or quality of the castings. This practice implicitly suggests the use of penetrating radiation, specifically X rays and gamma rays.
1.2 This practice provides a uniform procedure for a CT examination of castings for one or more of the following purposes:
1.2.1 Examining for discontinuities, such as porosity, inclusions, cracks, and shrink;
1.2.2 Performing metrological measurements and determining dimensional conformance; and
1.2.3 Determining reverse engineering data, that is, creating computer-aided design (CAD) data files.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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