Research On Dynamic Characteristics Of The Aerostatic Bearing Spindle And Its Influence On Ultra-precision Milling

Ultra-precision raster milling(UPRM)is an advanced manufacturing technology,mainly used in the manufacture of non-symmetric freeform components with super mirror quality,without any subsequent polishing,especially suitable for the processing of optical crystal materials special.In UPRM,due to the advantages of high speed and high precision of the aerostatic bearing spindle,it is usually used as the only power source to drive the single-point diamond cutter,which is mounted on the rotor to rotate at high speed to remove excess material on the workpiece surface.Therefore,the performance of the spindle in ultra-precision machining is closely related to the quality of the surface machining.However,the influence of dynamic characteristics of the spindle on the machined surface is seldom taken seriously.In the actual process of cutting,the cutting force,unbalanced magnetic pulling force and uneven rotor mass distribution caused by eccentricity and so will cause rotor vibration,rotor vibration will directly reduce the quality of the machined surface;and in the ultra-precision machining,when using new tools,machining new materials or processing newly designed surfaces,trial and error is still used to experiment repeatedly.Finishing surfaces with high-precision quality is still largely dependent on the experience and skill of the machine operator.In order to study the dynamic characteristics of the spindle with different rotating speeds,a 5-DOF rotor dynamics milling model is established.The rotor eccentricity,imbalanced magnetic pull force and cutting force are considered in the model,and then analyzed and calculated the unbalanced magnetic pull force;After the model was established,the rotor dynamics equations were deduced based on the Newton-Euler equation,and the rotor dynamics equations were obtained by combining the state space model,the characteristic equation,the impedance method and the initial conditions of the system.The numerical simulation program was programmed by using MATLAB,The dynamic characteristics and the analytical solution of the rotor under empty cutting and intermittent cutting also further verify the correctness of the theoretical simulation.In order to study the influence of rotor vibration on the machined surface quality,a workpiece model was established by using Z-map method based on the point cloud.Considering the influence of the feed speed and step size on the surface quality,the surface of workpiece is meshed.In the process of simulation,the cutter contact point(CC point)is calculated according to the cutter location point(CL point)and the two-dimensional array which stores the topographical coordinates of the surface is updated in real time.After the simulation is finished,the surface topography simulation result can be obtained.Comparison of the cutting experiment with the rotor at different speeds shows that there is a good agreement between theoretical research and experiments,which also shows the feasibility and correctness of the simulation algorithm.This topic provides the basis for the influence of the rotor dynamic characteristics on the machined surface and avoids the repeated trial cutting process when using new tools or cutting new materials,which is of great significance for reducing the production cost,improving the processing efficiency and optimizing the cutting parameters.