Research On Reliability Of Machining Accuracy Of Three Axis Vertical CNC Machine Tool

With the progress of science and technology,machinery manufacturing industry is developing towards the direction of flexibility,integration and intelligence.Machine tools is the core industry of machinery manufacturing industry,is the production of machines,also known as the "mother machine",the precision of the machine tool itself determines the processing accuracy of the product.The machining accuracy of the product is caused by the deviation from the ideal position between the cutting tools and the workpiece in cutting motion.Machine tools,fixture,tools and workpiece constitute a complete process system.Various errors in the process system are the root cause of parts processing errors,so they are called original errors.The original errors of the process system can be divided into two categories: the first type is the original errors related to the initial state of the process system,which can be called "static errors",including geometric errors,original errors,positioning errors,etc.The second type is the original error related to the process,which can be called "dynamic error",which mainly includes stress and heat deformation,tool wear and so on.The geometric errors of machine tools directly lead to the reduction of machining accuracy and reliability of CNC machine tools.Therefore,it is of great significance to study geometric errors of CNC machine tools to improve the reliability of machining accuracy.In this paper,the three-coordinate vertical machining center is taken as the research object.Based on the geometric error modeling of the three-coordinate CNC machine tools,the influence degree of the geometric error on the spatial position error of the three-coordinate CNC machine tools is analyzed.The improved first-order second-moment method and Monte Carlo method are used to analyze the reliability of the machining accuracy of the three-coordinate CNC machine tools.Based on RBF neural network,the reliability prediction model of machining accuracy of three-coordinate CNC machine tools is established and the optimization design of machining accuracy reliability is carried out.To sum up,the following research work has been carried out.(1)In the establishment of three-dimensional CNC machine tools geometric accuracy model.With the multi-body system kinematics as the core theory and the homogeneous coordinate transformation as the mathematical tool,the mathematical modeling of the geometric error of the three-coordinate CNC machine tools is carried out.(2)In the geometric error sensitivity analysis of three-axis CNC machine tools.Different from the traditional Sobol method,this paper proposed to use EFAST global sensitivity analysis method in Simlab software to analyze the geometric error sensitivity of the three-axis CNC machine tools,explored the influence of geometric error on the spatial position error of the machine tools,and based on the analysis results,established a simplified geometric error model of the three-axis CNC machine tools.And compared with the geometric error model of three-axis CNC machine tools.The analysis results show that this method can provide an important theoretical basis for improving the machining accuracy and geometric error compensation of three-coordinate CNC machine tools reasonably and economically.(3)In the reliability analysis of the machining accuracy of three coordinate CNC machine tools.The improved first order second moment method and Monte Carlo method are used to calculate the reliability and reliability sensitivity of the three coordinate numerical control machine tools,obtain the reliability values of the three coordinate numerical control machine tools at different positions,and explore the influence of 21 geometric errors on the reliability of the processing accuracy of the three coordinate numerical control machine tools.(4)In the establishment of three-axis CNC machine tools machining accuracy reliability prediction model.Based on the 21 geometric errors identified and the reliability analysis results of the three-coordinate CNC machine tools,the reliability prediction model of the machining accuracy of the three-coordinate CNC machine tools was established by using RBF neural network.The results show that the reliability model of machining precision of three-axis CNC machine tools established by using RBF neural network successfully predicts the reliability value and trend of machining precision of three-axis CNC machine tools,and provides theoretical support for improving machining precision of three-axis CNC machine tools.(5)In the aspect of reliability optimization of machining accuracy of CNC machine tools.Taking the reliability analysis results as the judgment standard of geometric accuracy performance,an optimization model of geometric accuracy allocation is established with the lowest manufacturing cost as the optimization goal and the satisfaction of accuracy requirements as the constraint,and the geometric accuracy allocation optimization that affects the machining accuracy of 3D CNC machine tools is carried out.