THERMOELASTIC INSTABILITY MONITORING FOR PREVENTING SPINDLE BEARING SEIZURE

Premature failure of machine tool spindle bearings is a major problem in production that results in enormous loss. One of the most common an d costly premature failure modes is bearing seizure caused by e,excess ive thermoelastic distortions. In this paper, a Stability Margin (SM) Chart is proposed to indicate bearing thermoelastic stability based on the expansions of the inner ring and rolling elements vs. the accommo dations of the outer ring and housing. This SM Chart is prepared numer ically based on a thermoelastic bearing model. The expansion vs. accom modation curve is obtained by a model-based monitor to estimate the te mperatures and corresponding expansions of different bearing parts usi ng online measurements of the spindle speed and the bearing outer ring / housing temperature. The experiments conducted on an instrumented sp indle bearing with grease-lubricated bearings showed that the proposed SM Chart can indicate the margin of bearing thermoelastic stability m ore consistently than bearing outer ring/housing temperature or the sp indle speed alone.