Automatic registration of cast parts considering permitted component variations

Despite all process-securing measures, a manufactured component will never correspond exactly to its underlying CAD model. Especially in casting processes significant deviations may occur because the thermal and mechanical procedure stresses the model which possibly cause significant dimensional and shape changes. Up to a certain limit that depends on the application and the required degree of accuracy such shape changes are permissible.

On the other hand, during the manufacturing process may occur protrusions (burrs) which have to be removed after casting, or defects such as dents and scratches which disqualify the corresponding parts for further processing.

In order to automate this process, it is therefore necessary to take into account both the permissible deviations in the component's shape and additional artefacts that are not present in the CAD model but are allowed in a measurement. This means that an inspection of a component should not be based on its CAD model (target geometry) but on the actual, possibly shape-changed, geometry (actual geometry). However, within this registration process the CAD model must remain as identification basis and shape changes in the actual geometry must prove to be admissible to its target geometry and separated from unwanted protrusions or defects which have to be identified too. This flexibility in the registration process can only be achieved by fitting the existing CAD model to the observation by a non-rigid motion.

In summary, the aim of the proposed project is to be able to map a CAD model onto a measured, slightly different, object surface in such a way that globally permitted deviations are recorded without any loss of local defects.

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