Quantification of the capability of micro-CT to detect defects in castings using a new test piece and a voxel-based comparison method

We present a modified aluminium casting which is especially suited as test piece for measuring casting defects and the geometry by means of cone-beam micro-focus X-ray systems, and which may become a reference standard for dimensional measurements and defect detection.To obtain a test piece with inner geometries measured by tactile means, we divided a small aluminium cylinder head into four pieces in such a way that most inner surfaces can be reached with a tactile probe. Reference geometries (spheres and cylinders) were applied to define a coordinate system for aligning the measurements in the disassembled and re-assembled state. The four pieces were re-assembled after the tactile measurement.The test piece also contains casting defects. In order to be able to use the assembled cylinder head as reference sample for defect detection, measurements with higher spatial resolution and better signal-to-noise ratio were performed on the single parts. For improving the reliability of the reference measurements, CT measurements of each part were carried out in three different orientations, and the individual defect detections were combined to obtain a reference data set with a high probability of defect detection and a low rate of erroneous detections.A new method for comparing the defect detection in a CT measurement to a reference data set is demonstrated, which provides individual information on every detected flaw.We discuss the results of measurements in the assembled state with respect to the reference data for flaw detection.