DESIGN AND EVALUATION OF AN ULTRAHIGH SPEED MICRO-MACHINING SPINDLE

A new ultrahigh speed micro-spindle has been developed for micro-milling that can be used at rotational speeds approaching 500,000rpm. Since conventional ball bearings or fluid lubricated journal bearings cannot be used at such speeds, the new micro-spindle uses a set of journal and thrust foil bearings. Prior to fabrication of the micro-spindle, rotordynamic analysis of the rotor with an attached cutting tool confirmed that the rotor would be stable at the desired speeds. The cutting tool was then attached to the rotor using a shrink-fit approach. The micro-spindle was integrated with a 3-axis micro-milling machine. Cutting experiments were performed on an aluminum alloy at speeds greater than 300,000rpm using 125 and 300m end-mills. Vibration spectra for free rotation and during cutting confirmed the dynamic stability of the micro-spindle. The vibration spectrum was dominated by the rotational frequency and was free of deleterious vibrations. The increase in rotational speed to 450,000rpm in micro-milling of aluminum alloy allowed an increase in feed rate to nearly 750mm/min, thus increasing the material removal rate by more than two orders of magnitude. The dimensional accuracy of several straight cuts made at different feed rates was measured.