Supporting Characteristics Analysis Of Liquid Hybrid Bearing On Ultra-high-speed Grinding

The ultra-high speed grinding is a high-new grinding technology developed since the1980s, and since emerging, the technology has received extensive concern of academia and manufacturing at home and abroad. Compared with conventional grinding, ultra-high speed grinding has great advantages in increasing productivity, reducing the thermal deformation, thermal stress of products in the grinding process, alleviating the grinding force, mitigating vibration of processing equipment and lapping tool during the processing, as well as processing the parts with high precision and high quality.The highest grinding speed limit which ultra-high speed grinder can achieve depends on the performance of the spindle unit, and the bearing performance is also crucial. Liquid hybrid bearing, which integrated characteristics of hydrostatic bearing and of hydrodynamic bearing, have many important advantages, such as little wear, large bearing capacity, long service life, wide speed range, good dynamic performance and rigidity, etc. Hydraulic Dynamic and Static bearings are widely used in ultra-high speed grinding machine. The study on Hydraulic Dynamic and Static Bearings has important significance. On the one hand, the bearing capacity and stiffness of the bearing have a direct impact on the accuracy and stability of the machining tool; On the other hand, with the rotational speed rising further, the calorific value of the bearing will increase, and the instability of the oil film will improve, which will easily lead to a few accidents, such as "axle suspension","scraping axle", etc. In view of this, liquid hybrid bearing and spindle system are studied in this paper, and the main research contents are as follows.(1) Computational fluid dynamics software FLUENT is used to analyze the dynamic characteristics of five-chamber hybrid bearing, and the internal pressure and temperature field of hybrid bearing are obtained. The carrying capacity, temperature, stiffness, damping and other dynamic parameters are further calculated, and the influence of eccentricity and speed on the dynamic parameters is further analyzed. In the condition of oil pressure and bearing eccentricity constant, with the rotate speed increasing, the oil temperature rises, and the carrying capacity and the attitude angle increase. In the condition of oil pressure and rotate speed constant, with the increasing of eccentricity ratio, the flow and the carrying capacity increases, and the attitude angle is essentially unchanged.(2) The carrying of Liquid hybrid bearing for ultra-high speed grinding is complex. The oil film temperature distributions in different input state were obtained through CFD analysis by FLUENT. On this basis, the temperature characteristics laws of the oil film with the input parameters change were obtained. Analysis shows that, the relationships of oil film temperature with spindle speed and eccentricity ratio are directly proportional and super linear, the relationship between oil film temperature and oil supply pressure is inverse, and the relationship with oil supply temperature is approximation directly proportional to the linear. Finally the significant of the various input parameters were analyzed through the orthogonal test. The results show that the effect of spindle speed is most significantly(3) The dynamic stiffness of the hydrodynamic bearing on high speed grinding spindle system was solved by FLUENT. The3D finite element model of the spindle system on the super-high speed grinder was established, and the natural frequencies and mode shapes were obtained by utilizing ANSYS. The results show that in high-speed rotation state, the centrifugal stiffening effect occurs due to the changes in structural stiffness of the system. With the rise of rotational speeds the differences become more significant. Finally, the results of dynamic modal analysis were obtained by setting different stiffness in different rotational speeds, and the critical speeds of the spindle system were obtained through graphical method.(4) Natural frequencies of the spindle system are obtained by using dynamic signal analyzer to test the vibration for spindle system of ultra-high speed grinder. Finite element analysis and CFD analysis are verified to be reliable and the results and dynamic parameters are verified to be accurate through comparing simulation results to experimental results. At last errors are analyzed.