The Key Technical Research In Five-Axis NC Machining Based On Fillet-End Milling Cutter

At present,five-axis CNC machine tools have found wide range of applications in such fields like national defense industry,aerospace,automobile manufacturing,medical instruments and other industries.Five-axis CNC machine tools play an irreplaceable role in machining complex free surfaces,since the machine tools have two additional degrees of freedom of rotation,enabling the position and orientation of tools to alter as machined surfaces changes.As a typical tools for five-axis NC machining fillet-end milling cutter combines the characteristics of both ball-end milling cutter and straight milling cutter,featuring high machining quality and high machining efficiency;the cutter has attracted increasing attention in the NC machining of complex surfaces,and has a promising future of applications.Research on the applications of the fillet-end milling cutter in five-axis NC machining seems,however,inadequate,due to the complexity of five-axis NC machining of complex free-form surfaces,some of the key technical problems remain unsolved.The present dissertation intends to conduct the key technical researches concerning five-axis NC machining with fillet-end milling cutter,including cutter path planning,stability analysis,chatter suppression technology,process and machining parameter optimization and prediction.Principal research activities are as follows:1.Firstly,the geometric model of fillet-end milling cutter is established.Based on this,the expressions of arbitrary points,tool location points and tool axis vector on fillet-end milling cutter are established.Based on the analysis of tool path planning process,tool contact algorithm and bow height error checking,an improved tool contact point algorithm with constant bow height and variable step length was established.Based on the principle that the outer surface of filletend milling cutter forms an envelope surface,an improved tool path planning method with equal residual height is proposed.The residual height point and actual residual height were calculated respectively.Taking the error between the actual residual height and the allowable residual height as the optimization condition,the machining path planning of fillet-end milling cutter based on the improved equal residual height method was realized.Compared with the traditional equal residual height method and UG software automatic path planning,the feasibility and efficiency of the improved equal residual height method for tool path planning are verified.2.The stability of five-axis NC machining of fillet-end milling cutter is analyzed under specific conditions,and a method of solving the stability of fillet-end milling cutter by using 3/8 Simpson formula is presented.The stability of the single-degree of freedom model and the two-degree of freedom model are calculated respectively,and compared with the stability lobe plot drawn by the traditional first-order semi-discrete method and the second-order fully discrete method,the effectiveness and correctness of the proposed method are shown.3.The stability test scheme for groove milling aluminum alloy workpiece with solid carbide fillet-end milling cutter was designed.The milling force signal was collected by dynamometer,the time domain waveform was obtained by fast Fourier transform,and the cutting force amplitude and the corresponding frequency spectrum were analyzed.The stability test of milling process shows that the stable lobe plot based on 3/8 Simpson formula method is effective4.A chatter suppression passive control device with nonlinear cubic stiffness-Nonlinear Energy Sink(NES)is designed,which can be directly attached to the five-axis NC machining tool system of fillet-end milling cutter.The dynamic model of fillet-end milling cutter-NES system is established,and the dynamic equation of fillet-end milling cutter-NES system is established by generalized Hamiltonian principle.5.The dynamic equation of the fillet-end milling cutter and the NES system is solved by harmonic balance method,and the transient and steady-state responses of the system are obtained.The numerical simulation results show that:With the addition of the nonlinear dynamic vibration suppressing device NES,the peak amplitude decreases with the increase of the damping and stiffness of NES,and the vibration suppressing effect can be presented in a wide frequency range,which verifies the effectiveness of the device on the chatter suppression effect of five-axis CNC machining system with fillet-end milling cutter.6.The optimization and prediction model experiments of milling process parameters for fillet-end milling cutter are studied.The orthogonal experiment scheme of three factors(namely milling speed,feed and depth),four levels are designed,The machining surface roughness comparison test between the ballend milling cutter and fillet-end milling cutter are conducted,the influence law of cutting parameters on workpiece surface roughness,using range analysis method,verified that under the same machining condition fillet-end cutter surface roughness is better than that of ball-end milling cutter.The orthogonal test scheme of three-way cutting force of fillet-end milling cutter was designed,which was five factors and three levels: spindle speed,feed rate of each tooth,cutting depth,axial position Angle and radial position Angle.The influence law of five cutting parameters on three-way cutting force was obtained by range analysis method.7.Based on BP neural network,RBF neural network and PSO-LSSVM,the prediction models of workpiece surface roughness and three-way cutting force in fillet-end milling cutter are established.By comparing with the experimental results,the accuracy of the three prediction models is evaluated by the average error.The results show that among the three prediction models,the PSO-LSSVM prediction model has the most accurate prediction accuracy for surface roughness,the RBF neural network model has the most accurate prediction accuracy for radial cutting forces,the BP neural network model has the most accurate prediction accuracy for tangential cutting forces,and the PSO-LSSVM prediction model has the most accurate prediction accuracy for axial cutting forces.