The Effect of SpeedVarying MicroCutting Tool Dynamics on Stability During HighSpeed Micromilling of Ti6Al4V

Abstract

Chatterfree machining is necessary in micromilling to avoid the catastrophic failure of microend mill. The accuracy of the prediction of chatterfree machining conditions in highspeed micromilling has been improved in this work by including speedvarying microend mill dynamics. An optimum design of exponential window has been devised to remove the unwanted spindle dynamics from the displacement signal to construct the speeddependent frequency response function (FRF) of microend mill. The stiffness of the microend mill has been found to be increasing with increase in spindle speed and the natural frequency of the microend mill has been found to be changing with change in spindle speeds. The cutting velocitychip loaddependent cutting coefficients have been included to predict the stability using Nyquist criterion. The predicted stability lobe with speedvarying microend mill dynamics has increased chatterfree depth of cut significantly compared to the chatterfree depth of cut predicted with static microend mill dynamics. The increase in depth of cut with speedvarying dynamics has been found to be 28% at 20,000 rpm, 150% at 52,000 rpm, and 250% at 70,000 rpm. A critical value of acceleration of the workpiece has been identified for chatter onset detection and it has been validated with machined surface image analysis. The magnitude of acceleration in both feed and normal to feed direction has been characterized to analyze the effect of spindle speed and depth of cut on the vibration of workpiece.