Stiffness increase in main spindles by using tapered roller bearings for aluminum cutting tests

Abstract

Due to increasing demands regarding higher manufacturing accuracy and the machining of high-strength materials, the stiffness and load-carrying capacity of main spindles must be enhanced. One approach is to replace the conventionally used angular contact ball bearings, so called spindle bearings, with tapered roller bearings of the same size, which have a higher stiffness and load carrying capacity due to their larger rolling contact. In case the speed requirement is below a speed parameter $$n\cdot d_{m}=0.9\times 10^{6}$$ n · d m = 0.9 × 10 6 mm/min, the poorer speed parameter of tapered roller bearings can be compensated by a sufficiently high lubrication quantity. However, the stiffness increase by using this bearing type in main spindles has not yet been quantified in field tests. Therefore, the aim of this paper is to demonstrate the stiffness advantage of a spindle with an elastically arranged tapered roller bearing compared to a conventional spindle with angular contact ball bearings by machining tests. First, the radial load displacement characteristic of the newly developed tapered roller bearing spindle is tested in advance on an isolated test rig. In machine cutting tests, full slots are milled in an aluminum block. During the tests, the axial and radial displacements of the spindle shaft relative to the housing are measured and evaluated in radial and axial direction. These tests are repeated and compared with the conventional spindle. By varying the process parameters such as cutting depth, feed rate or rotational speed, the increased stiffness of the tapered roller bearing spindle compared to the conventional spindle is illustrated based on the measured displacements. Moreover, frequency response measurements at different speeds underpin the improved damping of the tapered roller bearing spindle. Assuming that the speed requirements are not too high and the tapered roller bearing is sufficiently lubricated, the use of this type of bearing can significantly increase the stiffness and thus the manufacturing precision in the long term for main spindles.