Analysis And Experimental Study On The Static And Dynamic Performance Of Ultra High-speed Aerostatic Spindle

With microminiaturization of electronic components and complexity of electrical products, integration rate in PCB circuit board becomes higher and micro holes in it become more concentrated. To raise drilling efficiency for dense holes and improve machining quality for micro holes, the frequently used equipment is ultra high-speed aerostatic spindle in PCB holes drilling process. The ultra high-speed aerostatic spindle has to rely on aerostatic bearings as supporting, which not only can still keep rotating precision higher under ultra high-speed rotation, but also is no pollution, no wear and long-life. However, the deadly disadvantages with low loading capacity, low stiffness as well as the common occurrence of self-excited vibration and unstable whirling motion, conclusively affect stability and reliable operation of ultra high-speed aerostatic spindle.It is desirable to master design approach of dynamic-static performance for ultra high-speed aerostatic spindle by studying loading capacity and static stability of aerostatic bearings, dynamic-static characteristic of ultra high-speed aerostatic spindle and their influencing factors. The main research of this article includes as in the following:1,Through in-depth analyses of gas lubrication theories, based on Reynolds equations of general form, combining the actual state of aerostatic bearings, it is important to set up mathematical model of pressure distribution for gas film in aerostatic bearings in order to devise loading capacity of aerostatic radial and thrust bearings. On this basis, it is able to calculate static characteristics of aerostatic radial and thrust bearing with combination of different structural parameters and air supplying pressure, analyze the influence of these factors on loading capacity and self-excited vibration of aerostatic thrust bearing. For parameters optimization, many factors should be considered, such as loading capacity, stiffness, gas consumption, static stability and practical situation.2,CFD module of soft ANSYS is used to study the change law of loading performance of aerostatic bearings under ultra high-speed rotation. The studies show that loading performance of aerostatic radial bearings increase obviously. As for value added of stiffness, there are certain differences between the different rotation speed intervals. However, loading performance of aerostatic thrust bearings remains relatively stable and it is influenced much less by high-speed rotation.3,From the perspective of spindle whirling occurring, firstly by researching on the relationship between damping coefficient and eccentricity, whirling speed and spindle rotation speed. Research suggests raising damping area, monishing average thickness of gas film, properly increasing eccentricity and enhancing whirling speed can improve damping of gas film and dynamic stability of spindle. Then numerical calculation study of terminal velocity is researched about ultra high-speed aerostatic spindle.4,Based on practical structure parameters of gas film and spindle, building integral model of them, gas-solid coupled method is used to study static loading capacity of ultra high-speed aerostatic spindle. Also, it is able to discover equivalent material feature of gas film. On this base, it is feasible to study dynamic performance of ultra high-speed aerostatic spindle, including modal characteristics and harmonic response analysis. According to the study, as the applied radial load increases, radial stiffness of spindle nearly keeps constant and increases quite slowly. However, as the applied axial load increases, axial stiffness of spindle increases more sharply. In addition, at the resonant frequency, the level of vibration on spindle tip become much higher and dynamic radial stiffness of spindle falls more sharply than at other working frequency. In machining process, rotation speed of spindle must keep away from the resonant frequency.5,To demonstrate the correctness of simulation result, it is not difficult to perform tests of static stiffness and dynamic operation experiment on ultra high-speed aerostatic spindle. Also, it is prepared to compare the date of experiment test with the result of simulation analysis. At last, the reasons for causing the error is analyzed in depth.