Static And Dynamic Analysis Of VDF-850 Vertical Machining Center And Prediction Of Milling Stability

It is essential to use finite element method for machine tools’ analysis and optimization in machine design.In the design for high-grade CNC machine tools,accurate prediction for statics,dynamics and cutting stability have been emphasized on.In this paper,based on the finite element method,the experimental modal method and the cutting dynamics theory,the static and dynamic mechanism and the milling stability of the VDF-850 vertical machining center are researched and analyzed.The main contents are included as follows.(1)Studing on static and dynamic characteristics of Vertical Machining Center.On the basis of considering the dynamic characteristics of each interface,the static and dynamic analysis of VDF-850 vertical machining center is carried out by using the finite element software ANSYS Workbench.In addition,the influence of spindle natural frequency and bearing preload on spindle dynamic characteristics is analyzed.The results show that,1)all the strength and rigidity of the vertical machining center meet the design requirements,but the vibration is easy to be motivated at the first and the third natural frequencies.2)when the pretightening force varied from 0 to 500 N,the natural frequency of the spindle increases and is positively correlated with the pretightening force.3)The main axis is easy to cause resonance at the first natural frequency.(2)The test of vertical machining center is studied.Firstly,the relevant theory,test equipment,test steps and matters of attention for modal test are introduced in detail.Secondly,by hammering the tip point,the modal test for vertical machining center is carried out,and the frequency response function of the tip point is obtained.Finally,the measured data are compared with the calculated data from the finite element simulation on the vertical machining center.The results show that the test results of the tip point are very close to the simulation results,and the natural frequencies of each order are almost consistent and the maximum error is 10.21%,which verifies the accuracy of the finite element model.(3)The stability of milling system is analyzed.Based on the regenerative flutter theory,a dynamic cutting force simulation model reflecting the interaction between cutting tool and workpiece is built by MATLAB software.The stable blade diagram is obtained by using frequency domain method,and the logical relationship between cutting depth and rotational speed is determined.In order to accurately predict the stability of milling system,the influence of modal parameters on the stability region in the stable leaflet diagram was analyzed by single factor method.The results show that,1)when the cutting depth is less than 1.34 mm,the machine tool is in absolute stability.2)the stability of the milling system is proportional to the damping ratio,the radial milling coefficient and the natural frequencyof the machining center system,and is inversely proportional to the milling cutter and the tangent milling coefficients.