Avaliação do desempenho metrológico dos métodos de ajuste utilizados nas máquinas de medir por coordenadas

Abstract

In this work, was evaluated the metrological performance of fitting methods (least squares, minimum circumscribed, maximum inscribed and minimum zone) used in CMM software. For this, was developed, calibrated and applied an artefact, called Holes Plate for Evaluation of Fitting Methods. The artefact is a rectangular plate of stainless steel AISI 304, with twelve cylindrical holes manufactured with nominal diameters (10 mm, 15 mm, 25 mm and 35 mm) and degrees of tolerance standard (IT4, IT7 and IT9). The performance of fitting methods was evaluated in four machines (Zeiss, Hexagon, Mitutoyo BR and Mitutoyo QM). The artefact was placed at one position on the work volume of the machines. The diameter of the holes and the circularity deviation were obtained by the four fitting methods. To investigate whether there were significant differences between the average values supplied by each method, the variance analysis was applied. To make multiple comparisons between levels of the fitting method factor, the Tukey test was applied. The expanded measurement uncertainty was assessed according to the recommendations of the Guide to the Expression of Uncertainty in Measurement (GUM). The results indicated that the proposed methodology for evaluating the performance of fitting methods based on PLAFAMA was appropriate, and that it can be used by operators and manufacturers for this purpose. It was observed that there were significant differences between the diameter values obtained by different fitting methods. These differences were more significant for the minimum circumscribed and maximum inscribed methods. It was also noted that the least squares and minimum zone methods showed the best performance for the MMC Zeiss. In turn, for CMMs Hexagon and Mitutoyo BR, the minimum circumscribed method was superior. However, the maximum inscribed method was the most suitable for measurements in CMM Mitutoyo QM. The minimum zone method gave the minimum circularity deviation value for CMMs Zeiss, Mitutoyo BR and Mitutoyo QM. In turn, the minimum circumscribed method exhibited the maximum values.