Dynamic Responses And Vibration Suppression For Thin-Walled Workpiece Milling

With the development of modern industry,thin-walled workpiece is widely used in aerospace,automotive,energy and many other fields and the requirement of its machining quality and processing efficiency is increasing.However,due to its low stiffness,serious forced vibration or even chatter phenomenon always occurs during the machining process,which greatly affects the finished surface quality and limits the material removal rate.Therefore,this paper concentrates on the dynamic model of thin-walled workpiece milling system.Based on theoretical analysis and experiments,this paper predicts the forced vibration of thin-walled workpiece,analyzes its dynamic characteristics and milling stability,and proposes vibration suppression method.Firstly,a method used to predict the dynamic response of thin-walled plate subjected to moving load is proposed.Based on Ritz method and Lagrange equation,this method establishes the dynamic model of thin-walled plate subjected to moving load,treats the complex boundary conditions by Courant penalty method and sovle the governing equation by differential quadrature method.Then,the forced vibration of thin-walled workpiece during milling is studied.Considering the effect of material removal,the forced vibration of thin-walled workpiece with variable thickness during milling is investigated,where the milling force is seen as moving load and the influence of material removal on system's dynamic characteristics is expressed by its negative kinetic energy and strain energy.After that,the time-space discretization method is proposed to predict the position-dependent milling stability of thin-walled workpiece.Based on continuum dynamics,the position-dependent dynamic characteristic of thin-walled workpiece is studied and the time-space discretization method is proposed to predict the thin-walled workpiece's position-dependent milling stability.In order to obtain system's energy expression and derive its frequency response function,instead of damping ratio,the loss factor is used to represent the influence of damping on system's dynamic characteristics.After obtaining the system's frequency response function,the influence of boundary condition,mode shape and cutter's position on system's modal parameters and stability are analyzed.Meanwhile,the influence of multimode on thin-walled workpiece's stability is analyzed and the stability prediction method is also proposed.Finally,a machining vibration suppression method based on constraining layer damping is proposed.In order to suppress the vibration of components with low stiffness during machining,the constraining layer damping structure is applied for boring bar with large ratio of overhanging length to diameter and thin-walled workpiece.Based on the establishment of dynamic model of boring bar and thin-walled workpiece with constraining layer damping structure,the experiments are conducted to verify the accuracy of the established model and test its damping performance.Meanwhile,the influence of dimensional parameters of constraining layer damping structure on damping performance is analyzed.