Research On The Oil Film Performance In Constant Surface Cutting Speed Of Multi-Pad Hydrostatic Turntable

As an indispensable function of the high-end CNC lathe,the constant surface cutting speed function can improve the processing efficiency and ensure the consistency of the machined surface quality,which has broad application prospects.In this mode,the spindle speed changes constantly with the workpiece diameter,and the oil film in the hydrostatic bearing gap is always in a process of transferring from one stable operating state to another,leading to fluctuated oil chamber cavity pressure and thereby affecting the operational accuracy.Therefore,special research was conducted on the oil film performance of the hydrostatic turntable under the constant surface speed state in this paper.In this paper,the lubrication characteristics of hydrostatic thrust bearing with double rectangular cavities under constant surface speed state were analyzed theoretically.The rotary speed equation of the working table under the constant surface speed was derived based on the features of the running state at constant surface speed.According to the theory of fluid dynamics,the Couette flow velocity field with acceleration boundary was solved,and the law of velocity field variations with time was obtained through analysis.According to the fluid lubrication theory,the unsteady gap flow equation,the instantaneous oil film temperature rise equation and the doublerectangular-cavity oil pad bearing capacity equation were derived.A prediction model for the lubrication performance of the oil film of the hydrostatic rotary table under constant surface speed state was established.A geometric model of the fluid lubricating oil film basin was established,and the oil film model was meshed with ICEM software.The numerical simulation method was adopted to obtain the law of variations of the temperature field and pressure field of lubricating oil film with time under different influencing factors,as well as the transient response of oil film performance as disturbed by velocity at different initial rotary speed and angular acceleration conditions.It is found that the cutting speed,feed rate and working load leave a significant impact on the law of variations of oil film performance with time,while the transient flow term has limited impact on the performance of lubricating oil film.The above laws were verified by experiments on the Q1-224 hydrostatic bearing experimental platform.The experiments tested the oil film temperature rise and oil cavity pressure variation laws of the rotary table that was operated under the constant surface speed state,with the data compared with the simulation results.The numerical simulation results agree well with the experimental data,which verify the correctness of the simulation results.The research conclusion has certain guiding significance for predicting the lubrication performance of the working table and ensuring the operational accuracy of the constant surface speed of the turntable.