Optimal design of thrust bearing for high-speed composite air spindles
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Optimal design of thrust bearing for high-speed composite air spindles KYUNG GEUN BANG 1, HUI YUN HWANG2, and DAI GIL LEE 2,* 1 Information Device B.U. 2 Team, Samsung Electro-Mechanics Co. Ltd. 314 Meatan 3-dong, Paldal-gu, Suwon-shi, Kyonggi-do 442743, Republic of Korea; 2 Mechanical Design Laboratory with Advanced Materials, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, ME3221, 373-1 Guseong-dong, Yuseong-gu, Daejeon-shi 305-701, Republic of Korea *Author for correspondence (E-mail:[email protected]; Phone:+82-42-869-3221; Fax:+82-42-869-3210)
Received 19 February 2003; accepted in revised form 13 May 2004 Abstract. High-speed air spindles are appropriate for high-speed and high-precision machining such as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors. The axial load capability and stiffness of the air spindles for drilling operation are dependent on the thrust bearings. The thrust bearings are composed of an air supply part in the housing and a rotating part. Since stresses induced in the rotating part of thrust bearing by centrifugal force are very high at high-rotational speed, the axial stiffness and load capability of an air spindle should be designed considering stresses due to centrifugal force as well as the natural frequency of the rotating shaft to avoid the resonant whip vibration of the spindle. In this work, the air supply part and the rotating part of a thin thrust bearing were designed for a high-speed carbon fibre composite air spindle using the stiffness map to maximize the stiffness of the thrust bearing under axial and centrifugal forces. Key words: centrifugal force, fatigue life, high-speed composite air spindle, load capability, natural frequency, stiffness map, thrust bearing
1. Introduction High precision products have been widely required with job shop type and small batch productions in the fields of manufacturing and machining (Weck and Koch, 1993). For this end, high speed and high precision air spindles are widely used as the high precision equipments such as computer hard disk drives, and dental drills. Also the polygon mirrors for laser scanners machined with high speed air spindles are increasingly employed with the development of high technology electrical products, medical and optical equipments. The journal and thrust bearings for the conventional air spindles are usually designed based on the stiffness and load capability supported by air pressure with the rigid body assumption. However, when the thrust bearing is operated at very high rotational speed up to 100,000 rpm, the root section of thrust bearings mounted on spindle shafts would fail due to excessive stresses induced by centrifugal force. Therefore, the thrust bearing for very high-speed air spindles should be designed considering stresses induced by centrifugal forces. Many researchers investigated the performance characteristics of thrust bearings, from which research results related with the current concern were listed: Cui e
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