Bearings having a small clearance during normal operation are selected. In some cases, bearings having a negative clearance when mounted are selected, to generate internal stress which enables achieving various effects. This so-called preload can be applied only to rolling bearings and not sliding ones. The performance of bearings is greatly affected by the applied preload. Application of a heavy preload to enhance the stiffness at the spindle undermines the high-speed rotation performance. In contrast, when a light preload is applied for high speed rotation, the stiffness is undermined. Therefore, a variable preload method is required. This study aims to develop a variable preload device using a linear actuator of the ball screw type, and to perform the performance evaluation of the developed device. Our studies verified that the proposed device worked satisfactorily.
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Micro hole drilling in precision production industries requires smaller holes, higher aspect ratios, and higher working speeds. However, the undesirable characteristics of micro drilling are small signal to noise ratios, wandering drill motion, high aspect ratio, and increasing cutting quality as cutting depth increases. In this study, two different types of experiments are performed on single crystal silicon to decrease crack formation. The first experiment compares the efficiency of various micro hole machining processes using ultrasonic impact grinding and micro drilling. The second experiment suggests optimum conditions for the micro drilling process. The experimental results show that micro drilling technology can be effectively used for drilling single crystal silicon.
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