A novel method of analyzing casting defects such as shrinkage cavities by utilizing high-energy x-ray computed tomography (CT) has been developed. The method was realized as the module of three-dimensional (3-D) bitmap CAD software StereoCooker for utilizing x-ray CT images. The cavity measurement method was based on the defocusing feature of an x-ray CT image. The authors assumed the defocusing to Gaussian, and therefore the diameter of the cavity could be calculated from the summation of the voxel value profile of the cavity and the circumference. The Gaussian defocusing hypothesis was confirmed by the CT reconstruction simulation with an accuracy higher than 10% for the conditions of the actual x-ray CT apparatus. The cavity measurement method was verified by applying it to cavity test pieces. The test pieces had cavity diameters of 0.5, 0.6, 0.7, 0.8 and 1.0mm. Using the rotate-only mode of the 6MeV x-ray CT, cavities of 0.6mm or greater in diameter could be detected. The accuracy of the cavity size is higher than 0.1mm for diameters of 0.7mm and greater. The verification of simulation by a comparison of the defects predicted by a simulation and those measured by this method has been proposed.

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