Nonlinear Dynamics Study And Stability Forecast Of The Time Varying Stiffness System

High speed milling(HSM),which is one of the advanced manufacturing technologies,has been become the important part of modern manufacture technology in 21st century and used in many different field,e.g.aeronautics,automobile,die and mould,energy,and rail transit.While the material removal rate(MRR),reflecting the machining efficiency,is often limited by the occurrence of an instability phenomenon called chatter in HSM processes.Practices and studies have been proven that chatter plays an important role in high speed milling.So the vibration of the thin wall integral structure is an urgent problem in the aviation machining industry.In this paper,the time-varying quality and stiffness of the thin wall integral structure is studied,the stability is obtained by theoretical analysis and experimental validation.The dynamics model of high-speed milling system with time-varying parameters is established.For the characteristics of time-varying quality and stiffness with the change of the remaining wall thickness,the multi-degree freedom model of the tool and the time-varying nonlinear dynamics model of the flexible workpiece are built;Based on the dynamic response of the output signal(output only),it is determined that the quality, stiffness and other parameters of time-varying system frequency response function. From the view of engineering application,the critical stiffness of workpiece corresponding to the critical mass is identified as the critical criterion.The critical mass is obtained according to the different structures of machine tools,tools and workpiece;Stability forecast analysis is carried out based on the dynamic model which is built in the rigid,the no time varying stiffness of the flexible and time varying stiffness of the flexible.For the time-varying properties of the quality and stiffness in time varying stiffness of the flexible,modal sensitivity analysis is used to analyze the sensitivity which is made by the quality and stiffness of workpiece.FRF is defmited based on dynamic response output signal(output only) with the parameters of quality and stiffness.The stability lobe diagram(SLD) of the whole milling process is drawn with the matlab simulation;Studying the influential discipline of stability from the influential elements such as clamping number,clamping position and the remaining wall thickness,and then the stability lobe of the thin walled workpiece is separately drawn.Analysing the stability influence from clamping number.clamping position and the remaining wall thickness can strengthen the system stability.The flow chart of clamping based on stability is raised and built;Experimentations of modal analysis,idling of spindle and high-speed milling are designed and carried out to investigate and validate the dynamics models,theory and method proposed and the dynamic characteristics.The experimental methods suitable for performance examination and evaluation of HSM system with respect to stability are researched and established.