Variable preload technology is used to achieve appropriate preload applied on spindle bearing based on machining conditions. However, the bearing temperature rise will be directly affected by bearing preload as well as bearing rotation accuracy. So, the main objective of this paper is to propose a method to determine the rotation accuracy of the spindle affected by the thermal expensive due to heat generation under variable preloads. Five degrees of freedom (5-DOF) quasi-static model of angular contact ball bearing was established to investigate the internal load distribution of the contact areas between the race way and balls. Then local contact heat generation of the bearing is calculated based on hertz contact theory. Finally, an experimental platform equipped with hydraulic system is designed and fabricated, which is preloaded by a hydraulic chamber. Studies have shown that the rotation accuracy presents drastically with the spindle rotational speed. Moreover, the influence of the bearing preload has a secondary importance. Comparative analysis about the rotation accuracy between starting running state and stable running state after a few hours under the same preload has been investigated. Results show that the accuracy of rotation spindle present no obviously difference when the uneven thermal deformation of parts occurs in the spindle system.

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