Simulation Tests of the Accuracy of Fitting Two Freeform Surfaces

Abstract

The presented method is introduced to simulate and predict the accuracy of fitting two freeform surfaces. For this purpose, the CAD models of both actual surfaces should be determined on the basis of coordinate measurement data obtained in measurements along regular grids of points in the UV space. The NURBS regression surfaces are modeled on the measurement data. Adequate regression models are sought with the iterative procedure. In the following steps of the procedure, the number of control points and/or the degree of the surface is/are changed, and the autocorrelation of residuals from the models is tested using the spatial statistics methods. The designated models are optimal CAD representations of the actual surfaces. Tests of the accuracy of fitting the surfaces are carried out virtually by fitting together both models in the CAD software. The outcome of the study is a spatial model of the gap between the studied surfaces. The obtained model was verified experimentally by measuring the dimensions of the actual gap between the surfaces, applying a measuring microscope. The proposed method is a useful tool in analyzing and improving the accuracy of injection molds machining.