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.
Highlights
Applying injection molds has become one of the main production methods in the modern manufacturing industry
The outcome of the study was a spatial model of the gap between the surfaces, and the model dimensions were verified experimentally using a measuring microscope and a confocal microscope for freeform samples made of aluminum alloy
The dimensions of the CAD model of the gap and these of the actual gap between the surfaces vary by an average of 10%, which sufficiently verifies the method proposed in this article and makes it a useful tool in analyzing and improving the accuracy of injection molds production
Summary
Applying injection molds has become one of the main production methods in the modern manufacturing industry. They, too, applied Moran’s I statistics and B-spline modeling to remove the random component from the data obtained from machine tool measurements in which they used a ball tip of 6 mm in diameter This resulted in mechanical filtration of much information on the surface irregularities. Paper [8] proposes the use of the CAD model machining pattern determined on the data obtained on a CMM, and spatial statistics for the correction of free surface milling errors. The present paper proposes a new method of simulation tests of the accuracy of fitting two freeform surfaces For this purpose, the CAD models of both actual surfaces should be determined on the basis of the coordinate measurement data obtained in measurements along a regular grid of points in the UV space. The outcome of the study was a spatial model of the gap between the surfaces, and the model dimensions were verified experimentally using a measuring microscope and a confocal microscope for freeform samples made of aluminum alloy
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