Traditional approaches about error modeling and analysis of machine tool few consider the probability characteristics of the geometric error and volumetric error systematically. However, the individual geometric error measured at different points is variational and stochastic, and therefore the resultant volumetric error is aslo stochastic and uncertain. In order to address the stochastic characteristic of the volumetric error for multiaxis machine tool, a new probability analysis mathematical model of volumetric error is proposed in this paper. According to multibody system theory, a mean value analysis model for volumetric error is established with consideration of geometric errors. The probability characteristics of geometric errors are obtained by statistical analysis to the measured sample data. Based on probability statistics and stochastic process theory, the variance analysis model of volumetric error is established in matrix, which can avoid the complex mathematics operations during the direct differential. A four-axis horizontal machining center is selected as an illustration example. The analysis results can reveal the stochastic characteristic of volumetric error and are also helpful to make full use of the best workspace to reduce the random uncertainty of the volumetric error and improve the machining accuracy.
Lots of key parts of rail vehicles are connected by screw thread fastening. Therefore, it is very important to evaluate the service performance of bolt correctly and efficiently. Through the evaluation of the service performance of bolts, a series of engineering application problems of bolt connection can be well solved. In this paper, model building, theory checking, simulation analysis and bench test verification are studied in a unified way, so as to get the theory and research method of engineering application. According to the bench fatigue test, the 10.9 grade bolt was fractured after loading about 3 million times, so the bolt could not meet the life cycle requirement under this working condition.
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