Assessment of machining quality by determining the law of accuracy distribution

The article proposes a methodology for assessing the quality of machined parts by determining the distribution law of the accuracy of the actual dimensions of parts. Knowledge of the law of distribution of random variables of scattering of actual dimensions of parts after machining is important, as it makes it possible to control quality by small samples. It is proposed to use Pearson curves to determine the distribution law. The hypothesis that the distribution laws correspond to certain accuracy qualifications has been tested on mass experiments. It is proposed to use Pearson's curves to determine the law of distribution of actual dimensions after machining. The formulas and methods for determining the coefficients of skewness and kurtosis from empirical values are presented. The analysis carried out using mass experiments confirmed the study in that with rough machining methods, the law of distribution of the actual dimensions of parts is close to normal, and with precision machining methods - to Simpson's law and equal probability. For the equal probability distribution, the skewness square is 0 and the kurtosis is 1.8. For the Simpson distribution, the skewness square is 0 and the kurtosis is 2.4.