Analysis of error motions of ultra-high-speed (UHS) micromachining spindles

This paper presents an experimental approach to analyze radial and axial error motions of miniature ultra-high-speed (UHS) spindles. The present work focuses on identifying the sources of error motions and quantifying them, specifically for the UHS spindles with hybrid ceramic bearings. Since effective application of micromachining processes, which commonly utilize miniature UHS spindles, require a high level of dimensional accuracy, form accuracy, and surface finish, the (unwanted) motions of the UHS spindles (and the associated tool-tip runout) must be well-understood. In this work, a laser Doppler vibrometer (LDV)-based measurement technique is used to measure radial and axial motions of the spindle from a sphere-on-stem precision artifact. The influence of temperature fluctuations, dynamically-induced effects, contact-bearing defects, and tool-attachment errors are analyzed. The spindle speeds are varied from 40 krpm to 160 krpm, and the over-hang lengths of 15 mm and 7.5 mm are considered. The variations arising from tool attachment to the collet are also studied. It is seen that (1) the thermal state of the spindle exhibits a cyclic behavior that results in significant changes to the spindle motions, (2) spindle speed and over-hang length significantly affect the spindle motions, and (3) the variations arising from the tool attachment to the collet can be described using a normal distribution, and may cause more than ±50% amplitude variations to the spindle motions.

► Experimental approach analyzing radial and axial error motions of UHS spindles.
► Identifying the sources of error motions of UHS spindles with ceramic bearings.
► Quantifying the effect of various sources on radial and axial spindle motions.
► Quantifying the uncertainties associated with the measurement approach.