Design Optimization And Dynamic Characteristic Analysis Of Hydrostatic Turntable For CNC Machine Tools

Heavy CNC machine tool is the key equipment in the national key manufacturing field,which is widely used in the production of aerospace,ship,energy and other largescale core parts.Hydrostatic bearing system is the key support and lubrication equipment of heavy machine tool,which has the advantages of high load,low wear and strong damping.Hydrostatic bearing system transmits pressure oil to the oil pad through the oil supply pump,and separates the two bearing surfaces to realize the load-bearing and lubrication functions.Because the static pressure turntable is inevitably affected by the overturning moment.In addition,the turntable will inevitably have various defects in the process of manufacturing,assembly and use.Its processing error,especially flatness error,cannot be effectively controlled,resulting in obvious tilt of the turntable,affecting the machining accuracy of the machine tool and reducing the anti tilt ability of the machine tool.The structure size of the hydrostatic support system of heavy machine tools is usually several meters,and the load is tons.In the process of workpiece clamping,the center of gravity of the processed workpiece can't coincide with the center of the turntable accurately,and some parts need eccentric clamping because of the complex shape and special processing technology.In addition,the cutting force on the workpiece hardly acts on the center point of the turntable,which will impose a overturning moment on the turntable to cause the tilt of the turntable.Therefore,the stability of turntable is an important factor to be considered in the design and manufacture of hydrostatic turntable.Hydrostatic oil pad is an important part of the heavy-duty hydrostatic turntable.The structure and arrangement of the oil pad are directly related to the anti tilt ability of the turntable.Therefore,in order to improve the anti tilt ability of hydrostatic turntable and optimize the layout parameters of oil pads,this paper studies the number of oil pads,oil pad installation position,oil pad flatness error and oil pad layout.The optimal solution of the oil pad layout planning parameters is given when the basic parameters of the turntable are known.Secondly,if the tilt is inevitable or through theoretical design,the turntable layout parameters have reached the optimal solution.In order to improve the efficiency of turntable,a method to determine the maximum reasonable rotation speed of hydrostatic turntable under the condition of known tilt angle of turntable is proposed,and the oil film is not damaged.The main contents of this paper are as follows:(1)Based on the numerical solution of partial differential equation and ordinary differential equation,the Reynolds equation is derived based on the force equilibrium state of fluid micro element,and the second-order partial differential equation describing the pressure distribution in the oil pad is obtained;the numerical distribution of decompression strength is obtained by using the finite difference method and successive over relaxation iteration,and the dimensionless bearing capacity,flow rate,damping and other dimensionless bearing capacity of the oil pad are calculated through its integration in different sections It provides a tool set of numerical solution for the calculation of bearing capacity of oil pad.(2)The basic assumption of oil film in hydrostatic system is listed and the theoretical model of hydrostatic oil pad is established.Combined with Navier Stokes equation and continuous equation,the Reynolds equation of rectangular and cylindrical coordinates is derived,and the mathematical models of hydrostatic rectangular,circular and annular oil pads are established.Through the finite difference method and successive overrelaxation method to solve the Reynolds equation,the pressure of each point in the domain grid is calculated.(3)The influences of the number of oil pads,the installation position of oil pads,the flatness error of oil pads and the layout of oil pads on the stability of hydrostatic turntable are analyzed.The calculation method of the inclination and oil film thickness of the hydrostatic turntable is given.The load-bearing characteristics of the single circle and double circle arrangement of the oil pad of the hydrostatic table are compared.Given the basic parameters of the turntable,the optimal solution of the oil pad layout planning parameters is given.(4)This paper analyzes the change rule of oil film bearing capacity of tilting static pressure turntable in rotation.Considering the influence of tilt and rotation speed on the stability of the oil pad,the change rule of the impact force on the oil film under different rotation speed is analyzed.The dynamic response of oil film under step load and positive load is analyzed to provide theoretical support for the study of oil film stability.(5)Experimental verification and simulation analysis are carried out for the above research contents.In the experimental verification,by applying different loading methods to the turntable,the displacement sensor and pressure sensor are used to collect the experimental data,and the sensor is connected to the data acquisition system,and the data is compared with the theoretical analysis.In the simulation part,the shape variable and the deflection curve in the diameter direction of the turntable are analyzed.In addition,the force displacement curve of the equivalent nonlinear spring of the oil pad is obtained.