Dynamic Stability of High Speed Micromilling Based on Modal Analysis for Determining the Tool-tip Dynamics

Micromilling process is used for fabrication and manufacturing of miniaturized components. Very high spindle rotational speeds are required in micromilling to reduce the chip load and to counter the low flexural rigidity of the micro-tool while machining hard materials. Apart from the high rotational speed (>100,000 rpm) which can excite dynamic instability, the dynamic force variation in micromachining can also occur due to micro-machine tool system limitations (limited tool stiffness and misalignments), micro scale cutting mechanics (critical chip thickness and size effect) and material inhomogeneity. The dynamic instability can induce surface/form errors and can result in catastrophic tool failure. This paper is focused on developing a two-degree of freedom model of the micromilling process for predicting chatter via stability lobe diagram.The dynamics of the cutting tool has been predicted by finite element analysis. After prediction of tool tip dynamics, the cutting coefficient has been determined experimentally. Finally, the dynamic stability has been predicted after considering the regenerative effect. Experimental verification of predicted stability shows the good agreement between analytical and experimental chatter free depth of cut and cutting speed. Hence, modal analysis by FEM can efficiently be used for determination of the tool tip dynamics. The predicted stability lobe diagram can be used for selection of chatter free combination of depth of cut and cutting speed prior to machining of Ti6Al4V.