Research On Dynamics And Vibration Characteristics Of CNC Machine Tool Under Cutting Excitation

Dynamic characteristics of machine tool have a significant impact on machining performance and efficiency.Study on machine tool dynamics has an important guidance for machine structure design and optimization of machining parameters.The widely used method of experimental modal analysis is limited within static state of machine tool.However,dynamics of machine tool under static and working state have difference.In consideration of operating conditions,operational modal analysis can better characterize machine dynamics under working state.Vibration characteristics of machine tool in cutting process are affected by structure dynamic characteristics and excitation.Therefore,combining with the method of self-excitation,this paper studies prediction method of cutting force and machine vibration characteristics.Besides,modal parameters identification of machine tool under cutting excitation is proposed.Firstly,a prediction method of cutting force in milling process based on machine tool vibration response signal is put forward.In the scheme,experimental modal analysis is used to extract machine dynamic parameters.Then,the transfer function model and state space of the spindle system are established.In order to expand the bandwidth of the testing system by compensating for the spindle dynamics,a Kalman filter scheme is constructed.The cutting force is estimated from the vibration response signal.The frequency characteristics of the system after compensation are analyzed.Secondly,the research of modal parameters identification under machining operation is carried out.In order to eliminate the interference of the harmonics excited in the cutting process on modal parameters identification.By combining measured cutting force signal and response signal,the operational frequency response function is calculated for parameters identification.In the experimental verification,the difference of machine dynamic characteristics under static and operational state is studied.Furthermore,the influence of cutting parameters on modal parameters is expounded.Lastly,this paper puts forward a method for modal vibration signals estimation and dominant mode identification.Principal vibration characteristics of machine tool structure in machining state are studied.Operational deflection shape analysis is used for dominant modes identification in the cutting process.In addition,a dominant mode analysis method based on system state space model and modal decoupling principle is proposed.Modal vibration signals are estimated for principal vibration analysis under cutting excitation.In general,this paper mainly studies cutting force signal prediction and modal parameter identification under cutting excitation.The research result can be applied to machine tool dynamics analysis and vibration characteristics research.