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The Effects of Bolt Preload on Vibration Amplitude of Gantry CNC Router

The joint properties significant affect on the dynamic performance and spindle vibration of gantry CNC router structure. This paper presents the relationship between the vibration amplitude of the spindle nose of a gantry CNC router and a bolt pre-tightening force. The dynamic model from machine structures with bolt joints was developed to consider the impact of a bolt pre-tightening force to spindle vibration of CNC router structures and dynamic behavior. Based on the dynamic model, harmonic analysis is conducted to specify the spindle nose’s displacement corresponding to the different bolt pre-tightening force. The FE analysis results indicate that bolt pretightening forces have great influence on the spindle nose vibration amplitude and when the pre-tightening force of bolt joints was increased, the dynamic stiffness of the spindle also increases while the vibration amplitude decreases. The accuracy and effectiveness of the model have also been confirmed by experimental results. The achieved result will enhance the rigidity, improve the vibration resistance of the machine structure to improve the reliability as well as machining precision, and attain the best surface quality.