A finite element spindle dynamic model is validated experimentally to characterized thermo-mechanical-dynamic behaviors of a motorized machine tool spindle. Several systematic tests are also developed to make the measurement of system natural frequencies feasible while the spindle is rotating at very high speeds. Based on the experimental and theoretical results, we can conclude that: 1. The system stiffness increases with the initial front bearing preload (Fig. 6). 2. When the high speed spindle is under appropriate cooling and lubrication conditions as the spindle studied in this paper, the system is softened by the high speed mechanical effects of the spindle shaft, such as centrifugal forces and gyroscopic moments, while it is stiffened with increasing bearing preload (Fig. 7). 3. The overall spindle stiffness is determined by the relative effects between the bearing preload and the speed effects (Fig. 8). The above results can be applied to the high speed machine tool dynamic analysis, such as chatter in metal cutting, where the centrifugal and gyroscopic effects have to be included in the estimation of system's transfer function. The proposed model can also provide a guideline for machine tool designer to estimate correct bearing stiffness and system dynamics for different operation conditions, which is important in the control issue of the machine tool as well. These issues will be addressed in our future work.
展开▼
