Design And Characteristics Research On Damping Boring Bar With Variable Stiffness And Constrained Damping

During the cutting process, the vibration is often caused by the system rigidity, which makes unstable system and the reduction of processing quality. Long overhanging of boring process leads to reduction of dynamic stiffness and static stiffness. The stiffness of the boring bar will be much smaller, when the length diameter of the boring bar is relatively large particularly.It causes the unexpected violent vibration, reduction of processing quality and production efficiency in processing. How to adjust the dynamic stiffness and restrain the vibration in the deep hole processing becomes a new focus. This thesis analyzed the domestic and foreign researches on passive control types of damping boring bar and active control of vibration damping boring bar. The design of vibration absorption boring bar with variable stiffness and constrained damping is presented.The dynamic model of variable stiffness damping boring bar is established, and the structure design, simulation and stiffness control is carried on based on model.The main research contents are as follows:According to the structural characteristics and vibration reduction characteristics of the vibration absorption boring bar with variable stiffness and constrained damping,a simplified mathematical model of the constrained damping dynamic vibration absorption boring bar system is established. Analysis of the optimum damping ratio and optimum frequency ratio, the optimum mass ratio and stiffness ratio is conducted. And the optimal matching region of the constrained damping layer loss factor and the system is also analyzed, which provide theoretical basis for the next step of the design and simulation.According to the theoretical model of variable stiffness damping vibration damper, thevibration absorption and constrained damping boring bar with adjustable stiffness system was designed. The amplitude frequency characteristics of the common boring bar, the dynamic damping boring bar and the boring bar with variable stiffness and constrained damping were analyzed.The influence of damping block, rubber ring, damping oil and external wall thickness on the vibration reduction performance of the boring bar was analyzed.Thus, the boring bar with variable stiffness and damping constrainedwas designed and manufactured, and the optimal processing parameters were obtained through analysis of the simulation.According to the need of stiffness adjustment of boring bar with variable stiffness and damping constrained, least square method was adopted to real time on-line identification. The high precision control of servo motor was implemented based on the fuzzy PID controller. The feasibility of the control program was realized through the ASMEsim platform. The simulation results showed that the changes of support stiffnesscan change with the tip vibration to a stable time.In order to verify the effectiveness of the vibration absorption boring bar with variable stiffness and constrained damping, the experimental modal analysis was analyzed.Three kinds of boring contrast experiments are carried out. The influence of cutting parameters(cutting speed, feed rate, depth of cut etc.) and stiffnessvariation on boring bar vibration reduction performance were studied. The accuracy of the model in the second chapterwas verified by the experiment. The experimental results showed that the vibration characteristics of the damping boring bar can be adjusted by adjusting the stiffness of the vibration absorber k2. Finally, the purpose of reducing the vibration amplitude of the vibration damping boring bar was realized.A damping vibration reduction method with variable stiffness was proposed and the variable stiffness control theory was studied by means of design and dynamic characteristics analysis of boring bar with variable stiffness and constrained damping.The proposed method laid the foundation for the development of the special vibration damping boring bar for deep hole processing.A new analytical method is thus provided for the study of dynamic vibration absorption technology.