Research On Influences Of Hydrostatic Bearing On Dynamic Characteristics Of Ultra-precision Diamond Lathe

Ultra-precision machining technology plays an important role in the modernnational defense system and high-tech field. Ultra-precision diamond lathe are keyequipments to achieve ultra-precision machining. Based on the viewpoint ofprocessing, the function of a machine tool is to accurately control the positionbetween the tool and workpiece. So an ultra-precision machine tool has to meet thefollowing requirements: high dynamic stiffness. However, due to the stiffnesses ofconnections between parts in the machine are limited, the vibration between tool tipand workpiece is inevitable in machining. Conection surfaces of an ultra-precisonmachine tool are the primary factors influencing dynamic performances of themachine. Contrast to general machine tools, the major feature of an ultra-precisionmachine tool is with hydrostatic supports. Performances of hydrostatic supports aredominating factors to affect the dynamic characteristics of an ultra-precisionmachine tool. This paper studies the performance of hydrostatic bearing and itsinfluence on ultra-precision diamond lathe dynamic characteristics.First, create the oil chamber flow formulas and film thickness expressions,consider hydrostatic guideway a support surface inclined, as a basis, establishfor theultra-precision diamond lathe hydrostatic guideway finite element model. Accordingto the model, developed a computer program calculated the stiffness and angularstiffness of five degrees of freedom direction of the slide, and its influencing factorswere studied. A finite element model of the spindle is established, on the basis ofanalysis similarities and differences of aerostatic spindle and hydrostatic guideway.An FEA program have been written to accurately calculate the stiffness and angularstiffness of the spindle in the direction of five degrees of freedom respectively, andits influencing factors were studied.One more accurate ultra-precision machine tool dynmics model has been found.Stiffnesses and dammpings of the hydrostatic rails and the aerostatic spindle areidentified by model experiments. Experimental results agrees well with thetheoretical calculation, proving the correctness of the finite element model. Acontrol system model has been built, which features the direct-driven linear motorand hydrostatic rails. Similarly, a control system, combing the brushless torquemotor and aeostatic bearings, is also established. Stiffnesses of control systems aresimulated respectively. Based on the results above, an ultra-precision diamond lathedynamic model has been achieved according to the Lagrange equation.Machine tool dynamic performace is featured by frequency response betweenthe tool nose and workpiece. Firstly, one mode analysis of the designed ultra- precision machine tool is done to obtain natural frequencies and mode shapes of themachine tool. Next, a response analysis is implemented to identify whichfrequency and mode shape have more impact on the machine accuracy. Influences ofthe stiffness， angular stiffness and damping of hydrostatic guideways on theultra-precision machine tool dynamic performance are investigated respectively.What’s more, the impacts of spindle stiffness, angular stiffness and damping on themachine tool dynamic characteristics are also investigated. All these work give clueson an ultra-precision machine tool design. At last, an mode experiment is done toverify the reliability of theoretical analysies. Slow tool servo technology and fasttool serveo technology are two common processes exploiting at an ultra-precisionmachine tool. So, in this paper, specialties of the slow slide servo maching areanalysed. Moreover, motion errors of hydrostatic guideway in the process of slowslide servo machining are reaserched. The reasons of motion errors and thoseinfluencing factors are studied respectively. A fast tool servo dynamics model hasbeen established. An analysis probes into the influence of high frequency vibrationon the machining accuracy in fast tool servo process, which uncovers the factorsdecrease the machining accuracy and provides a theoretical basis for the errorcompensation.Finally, the ultra-precision diamond lathe vibration signal are detected, andconducted face turning experimental study. Obtained the vibration frequencybetween the workpiece and tool tip through the vibration signal detection,comparing the theoretical calculated frequency and the theoretical analysis is correct.Power spectral density analysis of the experiment turning surface is conducted,obtained spatial frequency components of the surface topography, in contrast withthe machine vibration, reveal the relationship of vibration frequency of the machineand the spatial frequency of workpiece surface morphology. To extract thethree-dimensional surface topography of specific spatial frequency components onthe machining surface, make use of the method of combining power spectral densityand dimensional wavelet transform. calculated the degree of influence of thesespecific spatial frequency components for the original surface morphology,revealing the relationship between the machine vibration and the surfacemorphology.