The Study Of Cast Iron Machine Bed Inner Cavity Sand Seal Structure Characteristics

Machine tool is the mother tool of modern manufacturing technology. In a sense,The machine tool design and manufacturing of a country decides. the manufacturing level of the whole country. In fact, with the improvement of the manufacture precision, the requirement of the machine tool's dynamic characteristic is raising. The machine bed is an important foundation parts for machine. The dynamic performance of machine bed affects the manufacture precision directly. So it is necessary to study the dynamic performance of machine bed.The paper'author takes the production PTW-40 CNC lathe bed (inner cavity sand seal structure) of Yunnan Machine Tool Group as study objects. The dynamic characteristics of the bed and the effect on dynamic characteristics of the sand in the bed cavity are mainly researched.According to requirements of the subject, First of all through the experimental modal analysis to extract the modal parameters of PTW-40 CNC lathe bed and analyzed its dynamic performance. Then through the method of comparative analysis, the effects of the sand in the cavity on the bed dynamic performance is analyzed. Finally, after the simplify replacement of the sand free rule state with a uniform loose sand. We discussed the effect on the dynamic performance of the machine bed..The specific work as follows:1 The general viscous damping system mode model and the basic theory of frequency response function estimation is described.classification and identification of modal parameters, modal parameter modeling guidelines, the typical modal parameter identification method and model validation theory was introduced. Lay the foundation of the dynamic characteristics for the subsequent chapters.2 The PTW-40 CNC lathe bed which the sealed sand is hollowed by the casting riser ("referred to cavity bed") and the PTW-40 CNC lathe bed filled with artificial sanders after being hollowed through the casting riser (referred to "loose sand filling bed") are experimented through modal analysis. Then apply the frequency domain modal parameter identification method extracted modal frequencies, modal damping ratios and mode vibration type and other parameters.3 With the application of model validation to test the accuracy and reliability of the three model bed.4 By modal parameter analysis of "sand closure machine bed", obtained the inherent dynamic characteristic parameter of the bed. And found out inherent frequency is the weak link of the bed. provide guidance for the further dynamic performance improvement of the machine bed.5. the dynamic characteristics comparison of the "sand closures machine bed" and "empty cavity machine bed" study indicates that the sand in the bed increased damping, but has little effect on modal natural frequency and modal stiffness.6 through the comparative analysis of "sand bed closures" and "loose fill sand bed," shows the dynamic characteristics of the two bed except for the fifth natural frequency and modal stiffness, there is no significant difference overall. In addition, the difference of damping ratio is 0.0016, which provides some reference value for the building of finite element model to simplify the no uniform rules sand sealed in the cavity with uniform sand.7 According to the measured parameters of experimental modal analysis.three machine bed damping identification are carried out. The study shows:The damping ratio of "Sand closures machine bed" and "sand filled machine bed" is twice of the "empty cavity machine bed".