Dynamic Analysis And Structure Optimization Design Of Feed Drives In Five-axis Carving-milling Machine

With the rapid development of domestic machine tool industry and the requirement of high speed and high precision,the five-axis carving-milling machine arises in recent years.Its high motor power and high machining speed raise a higher demand to dynamic characteristics of the feed drives.In terms of the assembly structure which consists of X-axis,Z-axis and C-axis feed drives on a five-axis carving-milling machine,simply " XZC-axis feed drives" for short,the dynamics model was established,the dynamic characteristics was analyzed and the analysis results were validated by modal experiment.After that,some structural optimization works was carried out for the XZC-axis feed drives.Considering the defects of previous research on dynamic modeling and vibration prediction of feed drives on multi-axis NC machine tools,a modeling method was proposed.Based on the contact forces of the moving contact surfaces,the contact models were established.Based on the Hertz contact theory,A calculation formula of transient contact stiffness is deduced,and the contact rigidities were precisely calculated.A dynamic model of the XZC-axis feed drives was established with an improved meshing scheme in ANSYS.Based on the coupling nodes method,torsion spring units of the coupler and screw nut was established.The first-eight vibration modes and natural frequencies were acquired.The modal experiment was conducted using hammer impact excitation and the experimental vibration modes and natural frequencies were acquired.It was found that the simulated results corresponded closely with the experimental data and the maximal error of the natural frequency was within 10 percent.According to the analysis results,the structure optimization work was carried out for the XZC-axis feed drives.An electromagnetic brake was added to improve the torsional rigidity of C shaft,the span between both-ends bearing brackets was increased to improve the bending stiffness of C shaft.The dynamic characteristics under five different screw nut types was simulated and the more reasonable type was selected.The dynamic characteristics of optimized structure were simulated and analyzed.It was found the first three natural frequency were significantly improved.Based on the engineering examples of the dynamic analysis and structural optimization of XZC-axis feed drives in a five-axis carving-milling machine,a dynamic modeling method and analysis method was proposed.These works will contribute to the vibration analysis and structure optimization of feed drives on multi-axis NC machine tools.