Research On Shaft-Bearing System Dynamic Characteristics Of High-Speed Motorized Spindle

High speed machining (HSM) technology can considerably accelerate the production efficiency, promote the manufacturing qualities of products and reduce the cost of productions. Especially in the area of mold manufacturing, the HSM technology can significantly shorten the period of mold manufacturing and create the favorable conditions for the products made by mold to occupy the market swiftly. The conventional machining technology dose not has these advantages in HSM. For developing and applying HSM technology, it is essential to own high-speed NC machine tools with excellent processing performance. The processing precision of high-speed NC machine tools is greatly decided by the dynamic characteristics of high speed spindle. Thus, the most crucial and fundamental research work is to establish the dynamic characteristics model of high speed motorized spindle. Based on the accurate dynamic model, the structure design of motorized spindle can be assessed and optimized, and the working abilities can be predicted as well.According to practical production of PUSH Ning Jiang Machine Tool Ltd. of Sichuan Province, this thesis, that combined numerical calculation with experimental modal analysis, established a reliable dynamic characteristics model about the shaft-bearing system of high-speed motorized spindle. Based on the model, the frequency respond characteristics of the system in free status and constrained status were predicted respectively and the effects of some design parameters on the dynamic characteristics of the system were studied. The main achievements in the thesis are summarized as follows:The theoretical models of the shaft-bearing system were established by used in the transfer matrix method (TMM) and the finite element method (FEM), respectively. The calculation results of the theoretical models show that the shaft-bearing system design is reasonable and available. However, the FEM is regarded as a more accurate theoretical method in the thesis through comparing with experimental modal analysis (EMA).A free modal experiment based on impact method was used in the shaft-bearing system, and the accuracy and reliability of the experiment results were verified by Modal Assurance Criterion (MAC). According to the experiments data, the initial FEM was modified through coupling DOF among spring-damper units and readjusting unit-stiffness. The difference between the results from modified FEM calculation and from EMA is quit little, among which the nature frequency deviation corresponding to the first and second deformed mode shape is 4.14% and 6.97%, respectively. The FRF (Frequency Respond Function) curves from modified FEM calculation and from EMA are similar in a certain frequency region. Utilizing modified FEM, the dynamic characteristics of shaft-bearing system where boundary constrained were predicted. And through the impact modal experiments, the results predicted were certified, among which the nature frequency deviation corresponding to the first and second deformed mode shape is 0.57% and 0.84%, respectively.Through researching, in modified FEM, the effects of some design parameters (DP) on the dynamic characteristics of shaft-bearing system, the thesis finds that the first mode frequency of the system can be theoretically promoted by adjusting these DP.Based on the modified FEM, the effect of the elasticity modulus of shaft material on the dynamic characteristics of shaft-bearing system was studied as well. The results show that the effect of the elasticity modulus of shaft material has almost nothing which compare with structure stiffness of the system.