Error Modeling And Precision Design Of Mass Three-Axis Vertical Machining Centers

With the support of Chinese National Science and Technology Major Projects,this research has established the error model and done the precision design on a mass of three-axis machine tools VMC850 B manufactured by Shenyang Machine Tool Group(SYMG).Firstly,the volumetric error model of the machine tools and the error model of the related single-axis assemblies have been built.Next,the precision analysis has been done based on the error models of the machine tools and their axes.It has validated the models established before.Then the precision allocation has been abstracted to an optimization problem and been solved based on the result of precision analysis above.The main contents of this thesis are as followed:(1)This thesis established the volumetric error model of the type of the vertical machining center based on the homogeneous transition matrix(HTM),considering the position-dependent geometric errors(PDGEs)and the position-independent geometric errors(PIGEs).Considering the actual initial position,the axis is thought to have 12 error parameters,including 6 PDGEs and 6 PIGEs.The corresponding volumetric error model was accomplished after the identification of the error chains,the foundation of HTMs and the solution of these matrices.Then the volumetric error model,including 36 error parameters was adjusted and agreed with the leading theory that a three-axis has 21 error parameters.In this volumetric error model,the perpendicularity errors were introduced as PIGEs according to the setting-up process.(2)The thesis accomplished the error modeling of the single-axis assembly systematically based on the theory of small displacement torsor(SDT).The tolerance requirements of main parts in the single-axis assembly were determined by analyzing the setting-up process.The error modeling related to the guides and the ball screw,was finished based on the tolerance representation of SDTs and the error propagation of HTMs.The terminal error parameters of the single-axis assembly were obtained by the synthesis of errors related to the two setting-up paths,which is controlled by the related tolerance requirements.(3)The thesis did the precision analysis of the three-axis vertical machining centers based on the Monte Carlo simulation.Without a mass of measurement error data,the research got 1000 groups of error data by the simulation according to the actual precision level of the main parts in VMC850 B.And the precision analysis was done from parts to assemblies and from assemblies to the whole machine tool.Firstly,from parts to assemblies,the analyzed results in single-axis assemblies were compared with the related standards and the measurement data of 11 machine tools.The comparison validated the error model of the single-axis assembly.Then from assemblies to the whole machine tools,the analyzed results related to the volumetric errors of the whole machine tool were presented as the error ellipsoids and statistical charts based on the precision analysis from assemblies to the whole machine tool.According to the final results of the precision analysis,the research analyzed the value of the volumetric errors in the machine tools.(4)The thesis did the precision allocation of the three-axis vertical machining centers based on the constrained minimization.Based on the contribution analysis,the precision allocation was abstracted to an optimization problem with the confirmation of the designed variables,the objective function and the constraint conditions.Then aimed at two allocation tasks,the research was done to meet the constraint conditions.Based on the results,the importance of positioning errors on the volumetric errors was discovered.Afterwards,considering both the allocation results above and the influence of the part errors on single-axis assemblies,the research adjusted the precision levels of main parts in VMC850 B and did the precision analysis again to validate the precision allocation method.In all,the thesis established the error models of the vertical machining center VMC850 B and its axes,and then did the precision design of a mass of VMC850 B,including analysis and allocation,based the error models above.The thesis finally adjusted the precision levels of main parts in VMC850 B to achieve both the optimal machining accuracy and the optimal cost.