Study On Dynamic Characteristics And Vibration Response Of Thin-walled Workpieces Milling With Variable Pitch End Mill

As a typical vibration-damping tool,the variable pitch end mill changes the dynamic characteristics of the system constantly in the process of machining thinwalled workpieces,and the cutting vibration response changes,which affects the cutting stability and the machining quality of the workpiece surface.In this paper,the dynamic characteristics and vibration response of the cutting process are studied based on the milling force and dynamics model of a variable pitch end mill milling thin-walled parts.The modal parameters of the workpiece and the change of the forced vibration output response under material removal are analyzed to clarify the influence of the interdental angle of the variable pitch end mill on the vibration amplitude and to obtain the optimum interdental angle and cutting parameters for milling thin-walled workpieces with variable pitch end mills.The research in this paper is of great significance to the vibration reduction performance of cutting tools and the selection of process parameters of key components in milling process.Firstly,according to the structural characteristics of variable pitch end mill,the expression of the cutting thickness of the tool-workpiece contact is analyzed and the transient micro-element milling force model of the end mill is established.At the same time,due to the relative rigidity of variable pitch end mill and thin-walled workpieces,a corresponding milling dynamics model is established to analyze the milling system transfer function and provide a theoretical basis for the analysis of the dynamic characteristics of thin-walled parts milled with variable pitch end mills.Secondly,the modal tests are carried out of variable pitch end mill and workpieces with different thicknesses respectively,to obtain the measured modal parameters of the tool and workpieces.Combining the finite element modal and harmonic response analysis of the variable pitch end mill with that of the equal tooth end mill,the modal vibration and response curves of the different tool structures are obtained,and it is clear that the variable pitch end mill is more stable than the equal tooth end mill.At the same time,carrying out the finite element simulation analysis of workpieces with different thicknesses to determine the relationship between the size structure and dynamic characteristics of the workpieces.As the material removal amount of the workpiece increases,its modal frequency decreases,and the milling vibration is more easily excited,resulting in greater vibration response.Then,the experiments of thin-walled workpiece milling with variable pitch end mill are carried out.The milling force coefficients are identified according to the measured milling forces to verify the validity of the milling force model.By collecting milling signals at different speeds,the frequency spectrum of milling force are analyzed to obtain the milling force frequency in the steady-state cutting process.Based on the theoretical model of milling force,the frequency spectrum characteristics of milling force of end mills with different interdental angles are studied to determine the influence of interdental angle on the amplitude of milling force,and to obtain the optimal vibration reduction effect of asymmetric interdental angle.At the same time,by considering the material removal effect of the workpiece,combining the time-domain vibration signals under different rotational speeds and number of tool movements,and comparing the frequency-domain amplitude diagram of the acceleration signal,it is obtained that the milling vibration more stable when the rotational speed is 6000 rpm.It is determined that the spectral amplitude of the thin-walled workpiece becomes larger as the amount of material removal increases.Finally,based on the theory of forced vibration,the frequency range of resonance occurrence of thin-walled workpieces milled with variable pitch end mills is determined.The dynamic simulation of free vibration and forced vibration are carried out respectively,to verify the reliability of vibration prediction by combining the actual milling vibration signal,and then the forced vibrations of different interdental angle end mills are simulated and compared to determine the vibration reduction effect of variable pitch end mills.Based on the milling force model,combining with the dynamic characteristics of thin-walled workpieces,to analyze and predict the resonance output of thin-walled workpieces milling with variable pitch end mill,and verify the vibration response prediction results by experiment.