Design and analysis of aerostatic spindle with high load characteristics for large ultra-precision drum lathe

Aerostatic spindles offer low heat generation and high rotation accuracy, which make them an ideal choice for ultra-precision drum lathe, where extremely high motional accuracy and thermal stability are required. However, the limitations such as insufficient load capacity and stiffness have restricted their permissible application range and make them not suitable for large ultra-precision machine tools including drum lathe. In order to improve the load capacity and stiffness, this paper presents a high load capacity aerostatic spindle with pocketed orifice-type restrictors. Fluent is adopted and three-dimensional simulation models of aerostatic spindle with orifice and feeding pocket are set up to analyze the load characteristics. The simulation results show that this restrictor can enhance the throttling effect of orifice and suppress the pressure drop away from the orifice. Moreover, for aerostatic journal bearing, when eccentricity ratio is in the range of 0.2-0.3 and gas supply pressure is 0.6 MPa, carrying capacity and stiffness can reach up to 9499.4 N and 2813.1 N/μm. Finally, a group of loading experiments are carried out which prove that the novel three-dimensional simulation method is feasible and accurate to calculate the load characteristics of aerostatic spindles.