Multiple Degree of Freedom Rotordynamics based Stability Modeling in High-speed Micromilling of Ti-6Al-4V

Abstract

The micromilling process has great potential in fabrication of complex 3D miniaturized components in biomedical, defence, electronics and aerospace industries. Despite the potential, the lower flexural stiffness of the micro-tool makes micromilling process challenging for hard-to-cut materials due to catastrophic tool failure. The limited flexural stiffness can be overcome by using high rotational speeds but high spindle speeds in conjunction with low tool-stiffness can render the process unstable. The misalignments and runouts can be amplified at high rotational speeds resulting in dynamic variation in the cutting forces which can lead to chatter. Most of the chatter models are based on a single degree or two degrees of translation motion which do not capture the rotational degrees of freedom which can introduce gyroscopic couples. The gyroscopic effects due to rotational degrees of freedom will affect the stability limits which can be more pronounced in high-speed micromilling. In this study, a Jeffcott rotor analysis has been done assuming that the micro-tool acts as a rotor with compliant supports at two ends. The stability lobe diagrams has been generated using frequency domain solution and compared with single and two degrees of freedom chatter model and the experimental chatter onset. It has been observed that chatter limits increases if rotational degrees of freedoms are incorporated in the stability model.