Simulation And Experimental Research On End Milling Chatter Considering Process Damping

Milling operation is widely utilized in key industries such as aviation,aerospace,automotive and mold.The chatter caused by the regeneration effect will strongly influence a workpiece surface’s machining quality and increase of tool wear during the milling process and decrease the efficiency of output.Furthermore,under the condition of stable machining,the study of the generative process and effect factors should be performed to achieve the optimum friction parameters.High efficiency and accuracy in the machining process are important.In particular,by simplifying the workpiece-tool milling system as a two-degree spring-damping system,a multi-factor coupled milling dynamics model that considers regenerative chatter,process damping,and modal coupling effects is established.Based on this model,the influence of milling cutter teeth,tooth pitch,helix angle,diameter and radial immersion ratio on milling force was explored.It is considered that appropriately changing the milling cutter geometry such as the tooth pitch and helix angle is beneficial to reduce the maximum value of the milling force,reduce the interruption of the milling process,and then facilitate the stable operation of the milling.The simulation results show that when the milling cutter helix angle satisfiesβ=arctan(πD/(a_pN)),it conforms to the"minimum cutting force principle".Based on the dynamic model,the dynamic differential equations are solved by the time and frequency domain analysis methods such as zeroth order approximation and full-discretization method and peak to peak method to obtain the chatter stability diagram to get the stable region of milling.And the above methods are used to simulate and explore the influence of key parameters that affect milling stability,such as modal parameters,milling force coefficients,milling cutter geometric parameters,and milling mode,on the lobe curve.The in-depth analysis of the process damping caused by the interference between the flank and the machined surface during the milling process,the results show that under the condition of a limited radial immersion ratio,the effect of the helix angle on machining stability is evident.The larger the radial immersion ratio,the lower the machining stability effect of the helix angle.When the spindle speed is small,the process damping will affect the machining stability for the greater stability region compared to the regeneration effect.The effect of process damping is steadily decreased with the increase in spindle speed.The region of stability obtained through process damping would correlate with the region of stability obtained through the effect of regeneration.Above all,a set of full-tooth milling experiments was designed to obtain the average force of a single cutter tooth per rotation,the milling force coefficients in the force model was calibrated,and the modal parameters of the spindle-tool system were obtained through modal hammering experiments.The milling force coefficients and modal parameters obtained from the experiment are brought into the above analysis process.The full-discretization method is used to obtain the stability lobe diagram.According to the curve of the lobe,23 sets of processing parameters are selected for milling verification experiments.The experimental results verified the prediction of the stability lobe diagram accuracy.