Structural Optimization Design Of Lathe Bed Based On The Stiffness Of The Whole Machine

Structural design of machine tool’s components is an important part of machine tool design. With the modern machine tool becoming more and more efficient, high-precision and faster, traditional structural design of machine tool based on experience couldn’t meet the design requirements any more. Topology optimization design method of machine tool structure combined of finite element method and topology optimization is valued highly by structural engineers in recent years due to its scientificity and high efficiency. Static, dynamic and thermal analysis of conceptual structure can be made with finite element method which offers support for topological design.This research subject is funded by the National Major Science and Technology Project ’High-grade CNC machine tools digital design Gordian technique and its and application on model product’. In this thesis, researches on the structural characteristic of lathe bed and the static performance of the whole machine of CNC machine tool is done. The relationship between the static performance of the whole machine tool in different working positions and the weight coefficient of multiple working positions in structural topology optimization was analyzed. Topology optimization and size optimization of lathe bed were implemented. The improved structure design was discussed based on the material distribution of the lathe bed. The work in this thesis are as follow:(1) Make an introduction to Finite Element Method and structural optimization which includes three levels:size, shape and topology optimization. The main solution procedures of FEM and the general process of structural optimization design are given.(2) The structural form of CNC machine tool was analyzed and the solution formula of cutting force was given. The equivalent method of sliding guide based on FEM contact theory was studied.The contact stiffness of bearing and ballscrew based on Hertz contact theory were deduced and the integrated axial stiffness and radial stiffness of bearing-ballscrew system was obtained with the help of MATLAB.(3) The finite element model of the whole machine tool was built and the static performance of different working positions within the lathe’s working space were analyzed. The stiffness curve was plotted based the data exported from the result of the static analysis and the weight coefficient of different working positions in structural topology optimization was given based on the stiffness curve. (4) The mechanical model of lathe bed was build and the loads under normal working conditions were acquired. Topology optimization model based on multi-position and multi-objective considering static and dynamic performances was build and the topology optimization analysis was executed using software OptiStruct which helps to get the optimal material distribution of the lathe bed. A conceptual structure of the lathe bed was put forward based on the topology optimization and size optimization of it was carried out. The comparison of the new structure and the original one shows that the new structure’s stiffness of direction X increases by an average of66.23Nμm under9working positions along Z axis while the mass changes little.