Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference (한국윤활학회:학술대회논문집)

Korean Tribology Society (한국트라이볼로지학회)
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A Study on Hydrodynamic Stiffness Characteristics of Air Bearing for High Speed Spindle

  • Lee, J.Y. (Department of Mechanical and Precision Engineering, Graduate School, Pusan National University) ;
  • Lee, D.W. (Department of Mechanical and Precision Engineering, Graduate School, Pusan National University) ;
  • Seong, S.H. (Department of Mechanical and Precision Engineering, Pusan National University) ;
  • Lee, Y.C. (Department of Precision Mechanics, Yonam College of Engineering)
  • Published : 2002.10.21
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Abstract

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

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