Measurement-based updating of turbine blade CAD models: a case study

Abstract

Manufacturing industries, especially the aerospace and the automotive, require updating of CAD models so that the manufactured geometry is accurately represented. Often, additional constraints such as continuity are imposed on the model. The updated model may be employed to provide a more realistic analysis of the part's in-service performance. The necessary tools for realizing this task included dimensional measurement and geometric modelling. This paper discussed how this was achieved in the case of an aeroengine gas turbine blade. Measurement was performed using a coordinate measuring machine equipped with a touch trigger probe. Measurement path plan is based on the pre-processed CAD model. The accuracy was improved using our method for probe radius compensation. The re-modelling steps include preparation of the base surface, registration and least squares surface fitting. The surface preparation is needed in order to maintain prescribed continuity. Also, special attention was paid to cure ill-conditioning, which occurs when fitting trimmed surfaces. The adopted novel solution involves regularization and introduces two additional terms in the fitting functional. Two weighting coefficients are introduced to improve flexibility of the solution and they represent the user's confidence in the measurements and quality of the initial model.