The fault curve can conceptually show the relationship between failure rate and time in NC machining. Because the shape of the curve is bathtub shaped, it is often called “bathtub curve”. It divides the service life of CNC machine tools into three stages: early failure period, accidental failure period and loss failure period.
At the beginning, the failure rate is very high, but with the increase of operation time, the failure rate decreases quickly and enters the stage of constant failure rate. There are many reasons for the high early failure rate, such as design defects, manufacturing and installation errors, hardware parts processing and operation errors and so on. After running in, find out the cause of the fault and eliminate it, the failure rate will gradually tend to be stable. This stage is called the commissioning period or running in period.
The early failure period not only occurs in the initial stage of the new machine tool, but also occurs when the parts processed by the CNC machine tool are repaired or replaced and put into use again.
The accidental failure period is also called effective failure period, in which the failure rate is the lowest and the failure rate is constant. In general, this stage should not be the main fault. It is the best working period of hardware parts processing. However, due to improper use, misoperation or other unexpected reasons, some faults can also be caused. In addition, if the safety factor of some components is small and the upper limit of load is encountered in use, it may be damaged and fail due to overload. Therefore, we should pay special attention to rational use, strengthen maintenance, avoid operational errors, and extend the effective life of the machine tool as far as possible.
After entering the wear failure period, the failure rate rises again due to the normal wear, chemical corrosion, physical and electrical performance changes, and material fatigue and other aging processes. For CNC machine tools, if we can use all kinds of diagnostic techniques, master the wear law of parts, and take corresponding maintenance or replacement measures before the parts enter the failure and loss period, we can control the occurrence of loss faults, thus extending the actual life of CNC machine tools
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