Research On High Efficiency&Precision Wheel Hybrid Bearing Spindle In NC Grinder

High efficiency&precision NC grinder is the equipment that can achive the high efficiency and precision grinding.As a core functional component of the machine,the static and dynamic characteristics of wheel spindle play a key role on the processing quality of the machine.Under the pressure of the external oil,a layer of liquid oil film is formed between the shaft shoulder and the hybrid journal bearing.The spindle is immersed into the oil film all the time from start to stop,so it has the characteristic of no wear,long life,low start-power,wide speed range,high carring capacity and high precision.Therefore the hybrid spindle has been widely used in high efficiency&precision grinder.This paper will do some research and finite element numerical simulation about the wheel spindle include the following aspects:Firstly,this paper introduces some basic equations used in designing and calculating the liquid hybrid(hydrostatic/hydrodynamic)bearings,including mass conservation equation,momentum equation,energy equation and the Reynolds equation.Then illustrates that the fluid flow condition in the bearing can be determined by calculating the Reynolds number,as well as the selection criterion of capillary restrictor’s structural parameters.And then,this article introduces the way to calculate the bearing capacity,oil film flow and temperature rise.Secondly,this paper analyzes how the seven parameters influence the hybrid bearing capacity,stiffness,oil film temperature and flow.These parameters include three operating parameter(oil pressure,spindle speed and lubricant viscosity)and four structural parameter(bearing wide-diameter ratio,axial length of oil seal edges,initial diameter gap and the depth of shallow cavity).A group of optimal parameters are selected to make the bearing stiffness reache the top on the basis of controlling oil film temperature under 20℃.Thirdly,we analyze and calcultate the static and dynamic characteristics of the liquid hybrid spindle system.Here we use numerical calculation to analyze the static property and the influence of the spindle’s structural parameter and bearing stiffness on the spindle’s stiffness.In terms of the spindle’s dynamic performance,we bring the finite element numerical simulation.This paper calculates the spindle system’s first eight modes and natural frequencies,analyzes the changes of spindle system’s critical speed and dynamic stiffness caused by the length of the grinding wheel overhanging,bearing support space,grinding wheel specification and bearing stiffness.Then,improvement measures to increase the static and dynamic characteristics of the spindle are put forward.Finally,the test of natural frequency of the hybrid spindle is carried out.By comparing the experimental data and the simulation data,we can conclude that simulating calculation is reliable.