Flutter Stability Of Longitudinal Torsional Composite Ultrasonic Vibration Milling Of Thin Plates

Thin-walled parts have the advantages of smaller size,lighter weight,and more functions.They are widely used in aerospace structures,but their structures are complex,their stiffness is too weak,their quality requirements are very strict,accuracy is difficult to achieve,and the processing process is easily destabilized,causing waste of resources..Traditional processing methods have low productivity and some parts cannot even be processed.Ultrasonic vibration milling,as a new processing method,has the advantages of small cutting force,rapid heat dissipation,high processing precision,small tool wear,and easy chip removal.In this paper,based on the self-developed longitudinal-torsional composite ultrasonic vibration milling system,the stiffening effect of the stiffness and the flutter stability of the machining process are studied.In order to study the stability improvement effect of longitudinal-torsional composite ultrasonic vibration milling on the processing process of weakly rigid sheet metal parts,a three-dimensional model of the tool tip trajectory was constructed based on the kinematics theory of the milling cutter to determine the trajectory shape.For the convenience of further research,a two-dimensional elliptical tool tip trajectory of ultrasonic vibration milling was constructed,and the influence law of the ultrasonic transducer's excitation frequency,ultrasonic amplitude and milling feed rate on the two-dimensional tool tip trajectory was analyzed.Through analysis,it was found that the reason why the longitudinal-torsional composite ultrasonic vibration milling can improve the stability of the machining process lies in its ultra-high-frequency "cut-separate" intermittent cutting method.In order to study the strain hardening stifness of the longitudinal torsional composite ultrasonic vibration milling of thin plate parts,based on the Fourier theory,the equivalent stiffness enhancement factor of the longitudinal torsional composite ultrasonic vibration milled thin plate part was obtained by deriving the milling dynamics equation.In order to study the variation of the equivalent stiffness of the thin plate during the milling process,the milling force model was established by the identification of the milling force coefficient.By the finite element simulation method,calculating of the strain hardening stifness.In order to study the chatter stability of thin-plate longitudinal-torsional composite ultrasonic vibration milling,a two-dimensional milling model with two flexible bodies was constructed.The stability vane diagram was drawn by the improved semi-discrete method.The influence of cutting-separation ratio,radial immersing ratio,sheet stiffness,ultrasonic amplitude and milling feed rate on the flutter stability was simulated and analyzed.In order to further improve the chatter stability of longitudinally torsional composite ultrasonic vibration milling of thin plate members,the spindle speed,feed per tooth,axial depth of cut,radial depth of cut,and ultrasonic transducer supply voltage were used as variables.The parameter optimization test aiming at the flutter-free stable cutting and machining surface quality in the machining process,the comparative test of longitudinal torsional composite ultrasonic vibration milling and traditional milling.A comparative test verifies the stiffness enhancement effect of the longitudinal torsional composite ultrasonic vibration milled sheet metal part and the stability of the machining process compared to the traditional milling.