| The optimization of machine tool structure and light-weight design is an important way to improve the performance of CNC machining and processing efficiency. Structure analysis and optimization method based on finite element is being gradually applied to the process of machine design, providing a theoretical basis for the structure design of machine tool. The combination of structural optimization theory and machine tool production process significantly improves the efficiency of structure design of machine tools.This project is funded by the national major science and technology project’high-grade CNC machine tools and basic manufacturing equipments’and national technology support project. The project names are "digital design&software of machine tool oriented its static-dynamic-thermal characteristics"(NO.2009ZX04014-034) and“concept-unit’Techno-logy and Application in light-weight design of machine tools’(NO.2011BAF11B03). In this paper, the typical joint surfaces in machine tools have been discussed and structure optimization of the saddle bed with elastic constraints based on the joint surface parameters is carried out. After that, the structure design of the saddle bed is implemented by the way of using combinations of the structure units. The concrete research works are focused on the following aspects:(1) The process of bearing structure design of machine tools is summarized and formed by combining the machine production process and the theory of structural optimization which plays as a base. Four main steps of the process are put forward which consists the analysis of initial conditions, the construction of physical model, the design of conceptual model and finally the detailed structure design. The element parameters involved during finite element modeling process which could influence the calculation accuracy are also studied in this part and the method of parameter selection is also put forward according to the practical engineering conditions.(2) The working conditions of the turning center are analyzed. By studying typical joint surfaces of the turning center, equivalent load distribution and constraint forms containing the surface parameters have been proposed and they help to establish the mechanical model of the saddle bed and to obtain the equivalent loads and constraints which consist of the boundary condition of the saddle bed. (3) The topology optimization of the saddle bed based on the variable density method was carried out using the ’Hyper Works’ platform in this part. Optimizations are implemented based on two finite element models which share the same volume fraction and the same optimization objective but with different constraint forms—namely, one model is impose elastic constraint and the other rigid constraint. The results showed that the model with elastic constraints obtained clearer material distribution form compared to the model with rigid constraints which indicates that the equivalence of the joint surface has a significant impact on the acquiring of clear material distribution during topology optimization.(4) In this part, the research of the common forms of load-bearing structure in machine tools has been conducted and the design method of structure units in structure design of has been proposed. By this method, the structure design of the saddle bed has been carried out and several design plans have been put forward. One of the design plans is considered to be the best after comparing the static and dynamic performances of them to the original saddle bed. The comparison showed that the selected new design plan reduces the weight by13.2%while the performances keep unchanged, explaining that the structure of new design plan tends to be more reasonable and in return, it proves the validity of the optimization model. Through the basic works in this paper, the concept of modular structure design of machine tools has been preliminarily formed. |
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