Research On Mass Matching Of Supports For Machine Tool Dynamics

Modern industry puts stringent requirements on the precision and efficiency of machine tool.Dynamic characteristics also have become more and more important as an important factor affecting the accuracy and efficiency of machine tool.The support member is an important part of the machine tool.According to the kinetic theory,its mass directly affects the pros and cons of the dynamic characteristics of the machine tool.However,in the traditional method,the designer mainly designs the support structure based on experience or foreign products,and then uses the theory of material mechanics and theoretical mechanics to check the strength and stiffness of the support.Although this design method ensures the designed support members meet the strength and rigidity requirement,the lack of research on the mapping relationship between the mass of the support and dynamic characteristics of the machine tool leads to unreasonable quality matching and excessive mass of the machine support.Eventually resulting in wasting material and deteriorating dynamic characteristics.Aiming at this problem,this paper proposes a method to optimize the dynamic characteristics of the whole machine by matching the mass of support of the machine tool.The main work contents are as follows:(1)Based on the Hertz contact theory,the joint stiffness model of the rolling guide,the ball screw and the rolling bearing was established.On this basis,the influence of preload,external load and adhesion on the contact stiffness is analyzed,which lays a foundation for the establishment of the machine tool finite element model.(2)Taking a horizontal machining center as an example,the method of establishing the finite element model of the machine tool is explained,and the finite element modal analysis results of the machine tool are compared with the experimental modal test results to verify the accuracy of the finite element model.Based on the finite element model of the machine tool,the harmonic response analysis of the whole machine is completed to match the mass of the support.(3)The Latin hypercube experimental design method is used to extract multiple sets of sample points,and the machine dynamics evaluation values corresponding to each set of sample points—first order natural frequency and three-way amplitude of X,Y and Z are calculated.In order to establish the approximation model with the highest fitting accuracy,the response surface model,the radial basis neural network model and the Kriging model of the first order natural frequency and three-way amplitude of X,Y and Z and the mass of each supportare established.After using the unified standard evaluation,the Kriging model with the highest fitting accuracy is selected.(4)Based on the Kriging model,the machine tool support mass matching model is established and solved by multi-objective genetic algorithm soon after.The results show that the first-order natural frequency of the machine tool is increased by 2.25% and the three-way amplitude of X,Y and Z are reduced by 6.55%,12.81% and 33.33% respectively under the condition that the sum of the masses of the supports is reduced by 7.93%.Accoroding to the mass of the support matching results,structural topology optimization and size optimization are combined to design the support structure under a given mass,so that the quality of the support is approximate equal to the matching design quality,thus providing the possibility of engineering application of the method proposed in this paper.