Bearing condition monitoring for preventive maintenance in a production environment

Premature failure of machine tool spindle bearings is a major problem in production that can result in an enormous loss in production and spindle rehabilitation cost. The bearing internal contact force tends to change when the spindle is subjected to abnormal operating conditions. In this paper, the complicated variations in the condition of a grinding spindle in a three-shift production line were studied with a focus on examining the drift of bearing operating conditions over a long period of time. The results show that a stable operating condition was achieved and this condition gradually shifts due to factors such as the start-stop of the spindle between shifts, wear, contamination, and temperature. It is shown in this paper that the bearing condition can be explicitly expressed on-line in a chart, denoted as a stability margin (SM) chart, where the nominal operating condition can be specified. As a result, predictive maintenance can be achieved by examining the bearing condition in comparison with the nominal operating condition specified in the chart.