Investigation On Dynamic Characteristics Of BTA Deep Hole Drilling Shaft System

In the deep-hole process,the dynamic characteristics of drilling shaft play an important role in the quality and efficiency of deep-hole machining.In order to improve the quality and efficiency of deep-hole machining,this paper will analyze the main factors that affect the dynamic characteristics of deep-hole drilling.Profound research will be carried out from auxiliary support,coolant flow rate,axial force and torque on the drilling bit and rotational speed of drilling shaft to explore the mechanism and improve the stability of deep-hole drilling shaft.Based on fluid-structure interaction and vibration mechanics,the nonlinear dynamic model of fluid-structure interaction in BTA deep-hole drilling shaft system is established to study the nonlinear dynamic characteristics of fluid-structure interaction in drilling shaft system.The influence law of various factors on the stability of drilling shaft is analyzed to seek the mutual offsetting mechanism between various factors.By studying the dynamic characteristics of deep-hole drilling system,the aim is to improve the stability of deep-hole processing system and,improve the quality and efficiency of deep-hole processing.The main contents of this paper are as follows:(1)The distribution characteristics of cutting hydrodynamic pressure in deep hole drilling system are studied.The governing equation of nonlinear fluid dynamics is established.The governing equation of fluid force is solved by the finite difference method.The influence of eccentricity,ratio of length to diameter,vorticity velocity and vibration velocity on the fluid force distribution is discussed.The eccentricity,vorticity velocity and vibration velocity have a great influence on the fluid force distribution,while the influence of ratio of length to diameter on the fluid force distribution is relatively small,especially for the larger ratio of length to diameter.(2)The investigation of modal simulation and experiment of drilling shaft is carried out.By comparing the frequency of simulation and experimental mode,the reliability of the analysisresult of simulation and experimental mode is validated mutually.Based on the above analysis,the influence of the parameters of drilling shaft system on the mode of drilling shaft is further analyzed by using the modal simulation model of drilling shaft.The wall thickness and inner diameter have little effect on the stiffness of the drilling shaft.By selecting a suitable wall thickness and inner diameter,the purpose of both smooth liquid supply and unobstructed chip can be achieved.However,the length and supporting position have a great influence on the natural frequency of the drilling shaft.The appropriate length and supporting position should be chosen according to the actual situation.(3)The dynamic characteristics of deep hole drilling system is investigated.By using the dynamics model of drilling shaft system,the dynamic response of the system can be numerically solved to obtain natural frequency of drilling shaft system.In the drilling state,the vibration acceleration data of drilling shaft system is collected to obtain natural frequency of drilling shaft system under the cutting condition.The relative error of natural frequency obtained from the simulation and experiment of drilling shaft system is within the allowable range,so it can be judged that the established dynamic model of drilling shaft system is effective.In addition,it is possible to intuitively understand the dynamic characteristics of drilling shaft system during deep-hole machining through waveform panoramic analysis and3 D spectral analysis.Based on time series analysis,the system identification of deep hole drilling shaft is studied.The time series analysis method is used to establish the vibration signal output model of the drilling shaft system.The results of system identification were in good agreement with the experimental analysis ones,which lays the foundation for the prediction and control of the vibration of deep-hole drilling shaft system.(4)The stability of deep hole drilling system is studied.The horizontal vibration dynamics model of drilling shaft system is established.The influences of cutting fluid flow velocity,rotational speed,axial force,torque and support constraint and their coupling effect on natural frequency and stability of drilling system are analyzed.The flow rate and axial force reduce natural frequency of drilling shaft system,while the support constraint and the rotational angular velocity can improve the stability of the system.However,torque and rotationalangular velocity have a relatively little effect on natural frequency of the drilling shaft,and even the effect of torque is negligible.(5)The fluid-structure interaction dynamics of deep-hole drilling shaft system is studied.The fluid-structure interaction dynamics model of drilling shaft system is established and the influence of pulsation frequency and support constraint on the fluid-structure interaction dynamics of drilling shaft system is discussed.The fluid-structure interaction nonlinear dynamic characteristics of the drilling shaft system are analyzed by means of the system bifurcation diagram,phase trajectory and Poincare map.When the system is without support constraints,the drilling shaft system always presents nonlinear characteristics.When single support constraints is applied to the drilling shaft,single support constraint can significantly improve the nonlinear characteristics of the system.Chaos and quasi-periodic motions rarely occur.More importantly,the stable movement of the drilling shaft system occurs repeatedly.Therefore,the stability of the drilling shaft system can be maintained by selecting the appropriate pulsation frequency.