Modal analysis of a spindle assembly on bearing supports with anisotropic elastic characteristics

The article deals with issues related to the influence of options for the design of the spindle assembly (SA), the anisotropy of the radial rigidity of the bearing supports, as well as the spindle speed on the dynamic quality of the machine. The problem statement is formulated as follows: it is necessary to determine the degree of influence of each of the above parameters on the eigen frequencies and vibration modes of the SA. To identify patterns, numerical finite element modeling was carried out in the ANSYS Workbench environment. Variants of the spindle assembly were considered on the example of four models of the CNC lathe model 16B16T1, which differ in the number of structural elements and their location along the length of the spindle. When modeling, the spindle bearings were represented as solid rings with certain elastic properties, varying which the anisotropy of the stiffness of the bearings was realized. During the numerical experiment, the spindle speed was taken into account in the range from 0 to 20,000 rpm. When analyzing the results, the values of six natural frequencies and modes of vibration were considered for each of the models with a change in the rigidity of the front support; Campbell diagrams were obtained, illustrating the dependence of the dynamic characteristics of the spindle on the rotational speed in the specified range. As a result of the research, it was found that design factors have a significant impact on the vibration modes and natural frequencies of the spindle assembly. The simulation showed that when machining in the centers, the fourth natural frequency and modes of vibration will affect the accuracy, and when using a chuck, the first one. Taking into account the fact that the difference between them is more than 2.5 times, then machining in the centers can be carried out at significantly higher cutting speeds. Changing the stiffness of the front support results in a range of natural frequencies for each waveform, which can be up to 200 Hz. Within the specified range, natural frequencies change depending on the spindle speed.