Research On Machining Precision Reliability Of CNC Machine

Machining accuracy is an important evaluation indicator for machine tool performance,besides,improving machining accuracy is the inevitable developing trend of modern machine tools.Therefore,in this dissertation,turning process and milling process were the research objects,and machining error were studied based on the mechanics phenomenon that the craft system produced vibration and deformation because of the influence of cutting force.The reliability and the reliability sensitivity of the precision were studied.The aim of this dissertation is to provide theoretical basis for the rational design of process parameters in machining process via studying machining error and reliability and reliability sensitivity of machining,which lays a foundation for improving the machining precision of machining tool.The specific work content is as follows:(1)The two-dimensional orthogonal cutting model was established,and the cutting force was calculated under steady cutting state via analyzing the chip formation mechanism and combining with the metal material constitutive equation and the cutting parameter.The oblique cutting was converted to the two-dimensional cutting model in equivalent shear plane by coordinate transformation,and oblique cutting force was calculated.The consequence indicated that the accuracy of theoretical calculation is high when comparing the oblique cutting force value calculated above with experiments in existed literature.The milling force calculation model is established via dividing milling into micro oblique cutting units.The milling force on every micro unit was calculated in numerical calculation based on the theory of oblique cutting and the superposition of all milling forces on the micro units was the milling force on the milling blade.(2)The frequency response of the lathe spindle system was analyzed by using finite element method,and the vibration displacement between cutting tool and the component was calculated in the working frequency range of lathe spindle.The dynamic response of slender shaft was analyzed based on the theory of rotating beam vibration.The component and milling cutter coupling model was set up based on the theory of thin plate deformation under loading and the cantilever beam deformation under loading in milling process.The machining error of the thin-walled component was calculated by using numerical iteration method.(3)The influence of random factors in machining process and affect of lathe spindle in manufacturing process was taken into consideration.The explicit function relation between machining error and parameters of cutting and process was achieved by using Latin hypercube sampling,normal sampling and BP neural network technology.The reliability and the reliability sensitivity of machining precision in a certain process were analyzed based on FOSM method of structure reliability calculation theory.