Machining Center Spindle System Work To Identify The Mode

In order to adapt to the modern development of the machine tool industry, a machine tool is required not only to be light weighted, low costing, operation convenient and well technologic, but also to have good machining capacity and efficiency. For decades, more and more high speed and high accuracy machine centers come forth constantly. Meanwhile, the problem of vibration and noise is increasingly outstanding, which leads to the higher requirement for the machine tool's dynamic characteristics.In the dissertation, TH6350 bed machining center produced by the limited Corporation of Xi'an Transportation University and Kunming Machine Tool is the research object. Our study focuses on the dynamic characteristics of spindle system at idle and the operational modal parameters extraction using time domain identification method. The works have been done include:1. During the spindle is rotating at different speeds at idle, we distribute 89 points on the spindle system in X, Y and Z directions and test responses. The data acquisition and signal analysis system we adopt is DASP2003 (professional version) produced by COINV ( China Orient Institute of Noise and Vibration) and the number of experimental speeds is 11 in all (from 600rpm to 4500rpm).2. By analyzing the time domain response waves on spindle system, the positions where vibration is intense are located. Moreover, by using DASP, the auto-power spectrum and the maximal entropy analysis results on each point are obtained. And then, the dominant vibrating frequencies at different speeds are indicated after removing those frequencies inspired by spindle, motor and meshing gears.3. When the operational response data are available only, stochastic subspace identification method applied to cross-correlation functions is employed to extract modal parameters directly from operating data of spindle system. The identification program is realized in MATLAB.Some conclusions can be derived from works above-mentioned: 1. After analyzing and comparing response wave peaks at five different speeds, we can find three positions on which vibrations are more intense: front nose of spindle, guideway surface of spindle box and joint of spindle box and coupling. These vibrations likely effect performance of machine center.2. From the auto-power spectrum and the maximal entropy spectrum diagram in DASP, by observing the peaks distribution along frequency axis, the dominant vibrating frequencies can be determined after removing those frequencies inspired by spindle, motor and meshing gears.3. Under the circumstance that operating data at idle are the only ones available, stochastic subspace identification method can extract modal parameters of spindle system. But it's difficult to select correct order for the model. When the method of determining the order by comparing singular values' change is invalid, the auto-power spectrum and the maximal entropy spectrum figures and experiences are useful to solve the problem to some extent.4. During the period that spindle speeds up from 600rpm to 4500rpm, although vibrations become lager when speed reaches 2100rpm once, vibrations decrease a little and then keep steady if speed continues increasing until 4500rpm. So the first critical speed of spindle system should be higher than 4500rpm.