Structure Optimization Design Of Small Vertical Precision Machine Tools Based On Stiffness Matching

With the rapid development of the machinery industry and the arrival of the intelligent era,the precision requirements for machining are becoming higher and higher,improving the machining accuracy and comprehensive performance of CNC machine tools is of great significance to the development of the machinery industry.In this paper,a vertical CNC machining center is taken as the research object,the stiffness matching between its components and the whole machine is analyzed,the stiffness matching evaluation criteria are defined,and the multi-objective topology optimization design for machine tool components that do not meet the standard is carried out..The details are as follows:(1)The CAD,CAE model and virtual prototype model of G-type vertical machining center were established.The modal test was carried out on the machine column to verify the correctness of the finite element model.(2)Change the stiffness of each part of the machine tool,and carry out static analysis,free modal analysis and kinematics simulation analysis of the whole machine,and obtain the influence of each component on the performance of the whole machine.A stiffness matching evaluation criterion is proposed for the evaluation criteria of the stiffness of the base parts and the stiffness of the whole machine for the vertical precision machine tool.The details are as follows:1)Static stiffness matching criterion: When the elastic modulus of a component changes to twice the original value,if the deformation of the tool tip deformation does not exceed 25% in the static analysis,it is considered that the component is static with other components in the machine tool.Stiffness matching2)Dynamic stiffness matching criterion: When the elastic modulus of a component changes to twice the original value,if the change of the first six natural frequencies of the whole machine does not exceed 15% in the modal analysis,the component and the machine tool are considered The dynamic stiffness of the whole machine is matched.3)Kinematic matching criterion: When the elastic modulus of a part changes to twice the original value,if the average value and the maximum rate of change of the total displacement deviation of the tool nose trajectory in the kinematics simulation analysis are not more than 30 %,that is,the part is considered to match the kinematics of the machine tool.If all the components of this type of machine meet the above three matching criteria,the stiffness of each part of the machine tool can be considered to match thestiffness of the machine.(3)Combining the compromise programming approach and the mean frequency method as the total function of multi-objective topology optimization.Multi-objective topology optimization for components that do not meet the machine tool stiffness matching criteria with the overall machine stiffness,tool nose static deformation and the natural frequencies of the first few stages of the machine.Finally,the structural modification of the machine column is carried out according to the optimization result.(4)The modified column is loaded into the machine tool to analyze whether the new column meets the stiffness matching criterion,and the static analysis,modal analysis and kinematics simulation analysis of the new machine are carried out.The results show that the new column meets the stiffness matching.According to the guidelines,the average value,maximum value and standard deviation of the tool nose trajectory of the new machine tool were reduced by 17.84%,17.74% and 19.48%,respectively,and the machine tool stiffness was improved.21.53%;the overall deformation of the tool tip is reduced by 13.69%;the natural frequencies of the first four orders are increased by 5.09%,7.66%,4.16%,and 5.45%,respectively,while the mode shape is basically unchanged.,with the machine tool quality increased by1.81%.The performance of the whole machine is significantly improved.