Influence of bearing configuration on spindle modal characteristics

Since bearing configuration has significant influence on the spindle modal characteristics which can reflect the dynamic performance of spindle system in machine tools, so it would be of extraordinary importance and necessity to analyze the spindle modal characteristics through simulation and experiment when it comes to designing spindle system. In this paper, the number and span of bearings, the spacer of bearing set and the overhang of spindle are considered as the main designing parameters of the spindle system. Firstly, a coupled spindle-bearing model is established considering the radial deformation of the bearing inner ring caused by interference fits of spindle assembly, as well as the centrifugal and thermal deformations. Based on the model, the modal characteristics of different bearing configurations are analyzed. Secondly, a spindle test bench is designed and constructed. Finally, modal characteristics of the spindle system are tested with different bearing configurations. From the simulation and experimental results, it's indicated that there is a correlation between the natural frequency and the number of bearings. The using of short spacer inside the bearing set can increase spindle natural frequency slightly. Besides, the first natural frequency of the spindle system rises with the bearing span, whereas the second one tends to decrease. And shortening the overhang of spindle can also increase its natural frequencies, which can be taken into account in spindle design.