Research On Nonlinear Turning Chatter With Flexible Feed System And Workpiece

During the turning process of the machine tool,chatter will lead to the reduction of machining accuracy,the deterioration of workpiece surface finish and the decrease of productivity.For this reason,turning chatter has become one of the hot topics in the field of machining.However,the current research generally assumes that the workpiece is a rigid body and the tool feed system is a linear elastic body,which is not consistent with the actual working conditions.To solve this problem,a two degree of freedom nonlinear turning chatter model composed of nonlinear flexible tool feed system and linear elastic workpiece is proposed in this paper.The nonlinear dynamic characteristics and chatter stability of the system in the turning process are studied.The main research contents of the thesis are as follows:(1)The axial nonlinear static stiffness model of CNC lathe feed system composed of screw-nut assembly-support bearing is established.Based on Hertz contact theory,the load deformation relationship of three parts is derived,and the nonlinear restoring force function of axial vibration displacement of feed system is obtained.The influence of preload is considered in both double nut assembly and angular contact ball bearing.The force and deformation of the nonlinear feed system are simulated and analyzed,and the static experiment is designed to verify the model.(2)A two degree of freedom model is established,in which the feed system and the workpiece are both flexible bodies,and its dynamics and stability are analyzed.The relevant parameters of the tool and workpiece are measured by modal test.The time domain,phase diagram,three-dimensional phase diagram and FFT of the tool and workpiece are obtained by numerical simulation.The nonlinear dynamic characteristics and stability of the system under different cutting conditions are analyzed.The stability lobes of the nonlinear two degree of freedom system are plotted and compared with the linear system.(3)The turning chatter experiment is designed to observe the vibration of the workpiece in the actual turning process and verify the accuracy of stability prediction.The influence of chatter on the acceleration of tool in three directions is studied by using the control variable method.The acceleration response of tool tip and the vibration response of workpiece in stable and chatter turning process are collected by using three-phase acceleration sensor and laser displacement sensor,respectively.The collected signals are compared with the simulation results,and the influence of different cutting conditions on the stability of turning process is investigated.(4)The influence factors of dynamics and stability of turning system are analyzed.The influence of main structural parameters of ball screw feed system on dynamic response is explored.The effects of dynamic parameters of tool and workpiece,different cutting conditions and nonlinear restoring force coefficient on chatter stability of nonlinear two degree of freedom turning system are further studied.In this paper,theoretical derivation and experimental verification are combined.The experimental results show that the proposed two degree of freedom nonlinear turning chatter model composed of flexible tool feed system and linear elastic workpiece and its solution method are reasonable,which provides theoretical and method support for suppressing turning chatter and improving dynamic machining accuracy of CNC lathe.