Filtern
Dokumenttyp
- Zeitschriftenartikel (5) (entfernen)
Referierte Publikation
- ja (5)
Schlagworte
Organisationseinheit der BAM
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.
The interest in using computer simulations of dimensional x-ray computed tomography (dXCT) for various metrological purposes—such as measurement planning, performance prediction, performance optimisation and, finally, measurement uncertainty estimation—is increasing along with the ever-growing demand for more reliable measurements with dXCT. However, before a piece of simulation software can be used for tasks related to coordinate metrology, it has to be ensured that it is able to simulate physical laws, characteristic effects and basic CT system functionalities correctly and with sufficient accuracy. In short, the software must be qualified for dimensional metrology tasks. As one part of such a qualification process, a method is presented here for determining conformity intervals of 2D tests (projection-based tests) based on 3D tests (testing based on dimensional evaluations in a reconstructed volume) for the assessment of dXCT simulation software. The method consists of varying relevant parameter values in order to verify their influence on 3D measurement results. The results of the 3D tests with varied parameter values are then transferred to the quantities tested in the 2D tests and used as the basis for determining conformity intervals. Two approaches are applied for determining whether or not a variation of a parameter value is significant: (a) statistical and (b) heuristic. Two examples are presented, each based on simulated images, which show the application of the two different approaches for determining conformity intervals for the results of the 2D tests.