Design guidelines for high speed CNC machine tool spindle bearings

Abstract

 The manufacturing industries are facing challenges of designing high speed CNC machine tools to meet the demands of machining modern materials for different applications with wide range of higher spindle speeds. The spindle and bearing elements in headstock unit are subjected to structural loads which include cutting force, tool clamping force and bearing preload, thus producing reaction forces on the bearings during machining process. At higher speeds, large amount of heat is generated due to applied torque because of cutting load on bearings and viscous friction in the spindle bearing zone. This causes structural deformations in the bearing with the effect of thermal loads. The structural and thermal loads are calculated using appropriate theories for applying inputs during analysis. In the present study, an integrated thermo-structural couple field for super precision angular contact ball bearings, B7009ETP4S & HCB7009ETP4S in tandem arrangement is modelled, and design of experiments is simulated with varying boundary conditions in ANSYS Workbench to determine deformation, stresses and temperature variation induced in bearing elements. The temperature variation is also validated in numerical simulation using finite difference method, resistance network and experimental setup. The simulation results are in good agreement with experimental outputs and are within 10% variation, for reliable bearing performance. This approach has provided guidelines for system design to establish accurate prediction of bearing heat transfer and selection method.