A Computer-Experimental Approach to Modeling the Machine Tool Dynamics Including the Effect of Spindle Bearing Preload

Abstract

Machining performance of a milling machine is greatly affected by the frequency response function of the spindle tool. Investigation of the preload effect of the spindle bearing on the dynamic performance is of importance for design improvement of the milling machine. This study was therefore aimed to assess the dynamic characteristics of a milling machine by experimental and finite element approaches. To this end, the finite element model of a milling system was created for dynamic analysis. The milling system was composed of a vertical column structure, spindle tool module, and feeding mechanism of the spindle head stock, in which the rolling interfaces in linear components such as bearing and rolling guide were simulated by using surface to surface contact element at the raceways. To ensure the prediction accuracy, the spindle model was experimentally validated by conducting vibration tests on a physical spindle unit and then the frequency responses of milling system with different spindle bearing preload were predicted by harmonic analysis. Current results clearly show that the bearing preload directly affects the tool end frequency response functions to different extent. Compared with the low or high preloaded spindles, the spindle tool with medium preload enables the cutter to have a higher critical cutting depth, about an increment of 7-14%. This implies the machining stability can be improved by adjusting the spindle bearing preload at appropriate amount.