Sectional model involving two Weibull distributions for CNC lathe failure probability

To quantificationally analyze failure distribution law of CNC (computerized numerical control) lathes, and to provide the theoretical basis for improving their reliability level, the failure data from 14 CNC lathes over two years were collected, and the failure probability character of CNC lathes was analyzed. Probability and statistics method was introduced, and the sectional model involving two Weibull distributions was established. The analytical method of Weibull plotting paper was applied to estimate the parameters, hereby curve fitting was implemented for the observed values, and the results validated the sectional model. Laplace tendency test method was used to examine the model. The earlier failure period and the random failure period of CNC lathes can be distinguished based on the sectional model and the relevant failure rate curve. It can be calculated that earlier failure period is about 5 months, which is coincident with the consumer feedback that CNC lathe failure occurs frequently at about the first semiannual period with high failure probability. The occurrence of earlier failure period in this series of lathes shows that the early period faults are not totally excluded before leaving factory, so that the reliability level is degraded.