Structure Characteristic Analysis And Optimal Design Of Critical Component Of Direct Drive A/C Bi-rotary Milling Head

High-grade CNC machine tool as widely represented by the five-axis machine tools, is a symbol of industrial development level for a country, and also is focus and emphasis of current machine tools industry. As a core component of five-axis CNC machine, bi-rotary milling head has been the focus of competition in the five-axis CNC machine tools market. Moreover the bi-rotary milling head determines the accuracy of the whole machine tools to a large extent. Therefore it's necessary to analyze the structural characteristic of bi-rotary milling head and to optimize its critical component in the design stage.Firstly, a description has been proposed for the overall layout, the drive system structure, the drive control scheme, and the lubrication cooling system of the direct drive A/C bi-rotary milling head in this paper. And according to the structure layout of the bi-rotary milling head, a geometric motion errors model has been established using multi-body kinematics theory, and the influence on the machining accuracy result from the geometric motion errors can be evaluated.Secondly, based on its mechanical structure, according to the simplification principle of large complex structures and the equivalence principle of the connecting bearing using link element, finite element models about different A-axis rotate angle of the bi-rotary milling head have been built. Analyzed the influence on structure's static characteristic, which is because of the rotation of A-axis of the bi-rotary milling head. Result shows that, under the action of the cutting force, the displacement on the end of the high frequency spindle fluctuate result from the rotation of A-axis.Additionally, in order to evaluate the effect to the bi-rotary milling head, which is generated by the alternating milling force load and the thermal load, dynamic characteristic analysis and thermal analysis are conducted. Following the guidance of the basic theory of FEM modal analysis and harmonic analysis, analyzed the dynamic characteristic of the bi-rotary milling head and then obtained its inherent characteristic and the steady-state response under the action of the alternating cutting force. Found that natural frequencies of each order except zero frequency fluctuate with the rotation of A-axis of the bi-rotary milling head and that the overall dynamic performance of the whole structure is determined by the C-axis combination bearing, which is the weakness of the whole structure. Thus, improve the stiffness of C-axis bearing benefits the dynamic characteristic of the whole machine. Furthermore, explained the dealing method to the thermal boundary condition, the steps of the thermal and the thermal-structural coupling analysis following the guidance of the basic theory of the FEM thermal analysis and the thermo-elasticity mechanics analysis. Conducted the thermal and thermal-structural coupling analysis, and obtained the steady-state temperature distribution and thermal deformation of the bi-rotary milling head.Finally, the applicability and the selection principle of the structural optimization method were illustrated. And for the gimbal mount, which is also critical component of the bi-rotary milling head, selected topology optimization method to reduce its weight according to its structural feature. Described the principle and procedure of the topology optimization method and optimized the gimbal mount using topology optimization module in ANSYS software. The result is satisfactory and beneficial to the improvement of the characteristic of the whole machine since the mass of the gimbal mount decreased by 21% after being optimized and modified, while its stiffness and strength still meet the design requirements.