Research On Analysis Of Multi-field Coupling Thermal Characteristics For CNC Machine Tool Spindle System

The thermal characteristics of CNC machine tool has become as one of the most important factors for the high speed machine tools performance. The spindle system is the core component of CNC machine tool, thus its thermal characteristics determine that the cutting speed and processing accuracy of the CNC machine tool can reach. How to obtain the thermal characteristics of spindle system quickly in multi-physical coupling condition accurately has been the research focus and challenge in the field of CNC machine tool thermal characteristics. The dissertation is supported by National Nature Science Foundation of China-’Thermal close theory and space coupling thermal error compensation basic technology research for multi-spindle of compound machine tool "(No.51175461) and the Science and Technology Project of China-(No.2012ZX04010-011&No.2009R50008), research on the thermal characteristics of the CNC machine tool and correlative technologies oriented to spindle system’s. The innovation is developed both in theories and methods based on the existing achievement in order to achieve the thermal characteristics analysis and test technology research, mainly include establishing multi-physical coupling model of thermal characteristics for spindle system, multi-physical field coupling FEM simulation, the fast calculation of thermal characteristics based on the heat source method and multi-parameter, multi-objective correction method of thermal model and the theory validation and experiments based on thermal equilibrium test method.In Chapter1, the background and significance of the research for the analysis and test technology of CNC machine tool’s thermal characteristics are introduced, and the research status and development trend in the spindle system’s are intensively analyzed. At last, the contents of the dissertation are proposed based on the analysis of the current disadvantages.In Chapter2, the heat conduction differential equation was established according to the theory of heat transfer, and the multi-physical coupling model of CNC machine tool was established too. This model mainly includes two parts, i.e. the fluid-temperature field coupling model and the temperature-structure field coupling. It analyzed the boundary conditions calculation of the coupling field, the thermal load classification and calculation of coupling field, the heat transfer coefficient calculation, the thermal stress and thermal deformation calculation and so on. It can be used for the finite element multi-physical coupling model subsequently.In Chapter3, upon the basis of the comprehensive analysis for boundary conditions of CNC machine tool’s spindle system, the3d multi-physical coupling model of thermal characteristics which concluded fluid-temperature-structure field’s steady state and transient state analysis model was established. The established model fully considered the boundary conditions of the spindle system, and the influence of the spindle system with cooling lubricant in non-circle-section curved channel to temperature field analysis was also considered. And then by employing FEM, the spindle models were simulated and optimized. It was shown that the thermal characteristics of spindle systems can be obtained by presented model effectively and accurately.In Chapter4, a multi-parameter and multi-objective correction method was presented, which is hybrid response surface model and multi-objective genetic algorithm (MOGA). Based on the thermal characteristic datum of spindle system from thermal equilibrium test, the central composite experiment design method and surface response method were combined to establish the second-order surface models of thermal characteristic for the multi-parameter finite element thermal model of spindle system. Then these surface models were optimized by employing the approximation loop technique of MOGA, and a distributed Pareto solution set was obtained. Finally, the accuracy of initial thermal model was improved. By the example analysis, the results show that the presented model correction method can use the test datum effectively, and obtain the optimal solution for corrected parameters by limited simulation, and then make the correction model analysis results more realistic.In Chapter5, in order to obtain the thermal characteristics of the spindle-bearing integrated system of the CNC machine tools effectively, a mathematical model is established by employing the heat source method (HSM). The mathematical model took the bearing heat source as a finite large cylindrical surface heat source which is instantaneous heating or continuous heating conditions. And this mathematical model can be used to calculate the temperature rise value of any point at the concerned part from conductor at any moment under specified heat quantity after a heating period of time. The thermal characteristics of spindle system were identified by using the derived mathematical formula, and the thermal characteristics (i.e. the temperature rise, the temperature field distribution, the temperature rise time history, etc.) of spindle were obtained. Validated by FEM and experiment method, the method possesses a series of advantages for thermal characteristics calculation and analysis:simple, accurate, clear physical concept, low computer configuration requirements, fast calculation, and less occupied resource, etc.In Chapter6, this paper proposed a thermal equilibrium test method for CNC machine tool. The method can be used to research on regular working condition experiment and idle running experiment which can obtained the thermal characteristics of spindle system, such as the temperature field, the thermal sensitive points, the datum of temperature field and thermal-displacement field and so on. And the calculation method of thermal equilibrium time was presented. In addition, through test method can verify theoretical simulation and analysis above, such as the multi-physical coupling model, the correction method of thermal model and the thermal characteristics model based on HSM and so on, and the error model can be established by test results. It also can help to realize the fast verification of thermal characteristics and compensation of thermal error for spindle system. Taking a precision curved surface linear rolling guide CNC forming grinding machine tool as an example, the multi-spindle system thermal equilibrium test was carried out in real working condition. Through the test, the lack of pure theoretical analysis and simulation were made up. The proposed method is obvious to improve machining precision and working efficiency.In Chapter7, the main achievement and innovation are concluded, and the further research is finally conceived.