Calculation On Thermal Characteristics Ofmachining Center Spindle Oriented At Reliability Virtual Analysis

Due to the complexity of structure and control on machining center, its reliability is usually difficult to ensure. Traditional reliability test has shortcomings, like high cost, low efficiency. The reliability test by building virtual prototype and using computing power of computer can obtain results with low cost and high efficiency. Therefore, the new test has become an inevitable choice. In this dissertation, taking NBP1100 machining center spindle for example, the reliability virtual prototype modeling theory was studied. The reliability virtual prototype model was built and the effects of thermal characteristics on reliability were analyzed.Firstly, according to the structure and characteristics of NBP1100 vertical machining center and its spindle, FFS(Function-Fault-Structure) tree structured analytic method was studied. The method followed the principle of functional decomposition. The network structure model was built from three dimensions of function, fault and structure. Based on these analyses, the reliability evaluation model of spindle was established.Secondly, based on the FFS tree and its logic relation between layers, the requirements of reliability virtual prototype modeling were raised, and the 3-D models of spindle element structure were built by Pro/Engineer. According to the reliability analysis, the element structure models were turned into elementary cell models by variant design, and the spindle reliability virtual prototype model was accomplished by virtual assembly.Then, the thermal analysis of spindle was done by virtual prototype model and finite element method. The temperature field finite element model of spindle was established. The thermal load and boundary conditions of spindle were analyzed. Bearing heat intensity, cutting heat power and convective heat transfer were calculated. On the basis, the temperature field and thermal deformation analysis of idle run and cutting were done. The finite element model was validated by actual test.Lastly, the spindle thermal reliability was analyzed by reliability simulation system in ANSYS. The distribution type and characteristic parameters of input variables were identified. The distributions of random sample variables were analyzed. The cumulative distribution function and failure probability of output variables were obtained. According to the sensitivity map, the main variables influencing spindle thermal characteristics were obtained. Methods and suggestions of improving spindle thermal reliability were also presented with the scatter diagrams.