Research On Joint Characteristics Of MV-1690 Vertical Machining Center And Structural Optimization Of Key Components

Machine tools are assembled with many parts whose various contact surfaces make the dynamics of machine tools more complex.As researches showed that more than a 90% damping of a machine tool,a 60%-80% total stiffness and a 80%-90% total deformation of the machine come from joint part of the machine tool.Therefore,it is the key for dynamics analysis and optimization design to build a reasonable model and identify its parameters of joint surfacesThe MV-1690 vertical machining center is as a research object in this thesis.Based on the fractal theory and Hertzian contact theory,the mathematical model of the joint dynamics is established.Introducing the virtual material and establishing the dynamic model of fixed joint and slid joint,and then dynamic parameters are obtained at different surface pressures.Finally,a finite model of the center including the joint influence is set up,and the key components such as the column and the headstock are optimized.The main research work is as follows:(1)Based on the W-M fractal function,a three-dimensional micro-rough surface joint model is established using Ansys,and the contact behavior of the joint is simulated under different pressure loads.Through APDL parametric design language,the contact pressure and contact rate is extracted at each load step,and their mathematical model is obtained by fitting method.(2)According to the Hertz contact theory,fractal theory,and contact stiffness theory,the mathematical models of the elastic modulus,Poisson's ratio,density and thickness of the equivalent virtual material of the joint are established.The elastic modulus and Poisson's ratio are functions of the fractal parameters and the contact rate.(3)The equivalent virtual material model is utilized to a dumbbell joints and the results are compared with the experimental modal after modal analysis.It shows that the first six modal modes are consistent,the absolute relative error of frequencies is less than 12%.Meanwhile,it indicates that the equivalent virtual material model and its parameters are feasible,It can accurately characterize the dynamic performance of the vibration mode and natural frequency of the joint,which is significant for building joint's models and modal analysis in the following work.(4)The equivalent virtual material dynamic modeling of the joint is applied to the dynamic modeling of the MV-1690,and the dynamic parameters of the fixed joint and the sliding joint are identified,and then static analysis,modal analysis and harmonic response analysis are carried out.Based on the response surface size optimization design the column and headstock are optimized.The results show that the total deformation is reduced by 7.83% under the premise of little change in mass of the whole machine.The first six natural frequencies increased in different degree,and the first natural frequency increase is the most obvious,and it was 7.615%.After harmonic response analysis,it was found that the dynamic performance in the Z direction changed greatly.Its maximum resonance amplitude reduced by 28.83%.In a word,The maximum static deformation of the whole machine is obviously reduced,and the maximum resonance amplitude is greatly reduced,and the low order natural frequency and the specific stiffness in the X,Y and Z directions are improved to different degrees.