Abstract
As a fundamental study to develop the most suitable design of threaded joints used in ultrasonic vibration system, the effects of tightening conditions on vibrational characteristics of the joints are investigated by using the model in which the bar having threaded joints is replaced by a single degree-of-freedom system with viscous damper. The obtained results are as follows : (1) Damped natural frequency of the bar is affected by finishing and form accuracy of contact surface, and also by lubrication condition of joint. (2) Logarithmic decrement of the bar is affected by finishing and form accuracy of contact surface, tightening force, lubrication condition and interaction between form accuracy and tightening force. (3) Stiffness and damping characteristics of threaded joints are conducted as equivalent viscous damping coefficient C and equivalent spring constant k from the equivalent model proposed for the bar. Therefore the tightening state can be evaluated by the use of C and k. It is recognized that good tightening state, that is, C is small and k is large, is obtained under the conditions of high form accuracy, finishing by grinding and large tightening force. Silicone grease has an effect on improving the tightening state in case of low form accuracy of contact surface.
