The fault curve conceptually represents the relationship between the failure rate of CNC machine tool processing and time. As this curve is bathtub-shaped, it is often referred to as the "bathtub curve." It divides the service life of CNC machine tools into three stages: the early failure period, the unexpected failure period, and the loss failure period. In the early stage of failure, the failure rate of machine tools follows a negative exponential curve function.
Initially, the failure rate was very high, but as the operating time increased, the failure rate rapidly decreased and entered a stage of constant failure rate. There were many reasons for the high failure rate in the early stages, such as design defects, manufacturing and installation errors, hardware component processing operations, and incorrect usage. After running and identifying the causes of the failures and eliminating them, the failure rate would gradually stabilize. This stage is referred to as the tuning period or磨合期.
Early failure periods occur not only in the initial stages of new machine tools being put into use but also during the repair or replacement of parts in CNC lathes and their subsequent reintegration into operation.
Incidental failure period, also known as effective failure period, has a very low failure rate and a constant failure rate. Under normal circumstances, this stage should not lead to major malfunctions and is an excellent working period for metal hardware components. However, improper use, operator errors, or other unforeseen reasons can also cause some failures. Additionally, if certain components have a smaller design stability coefficient, they may encounter load limits during use and could be damaged or fail due to overload. Therefore, it is crucial to pay special attention to proper use, enhance maintenance, avoid operator errors, and extend the machine tool's effective lifespan as much as possible during the unexpected failure phase.
After entering the wear-out period, the failure rate increases due to normal wear of machine tool parts, chemical corrosion, changes in physical and electrical properties, and material fatigue. For CNC machine tools, by employing various diagnostic techniques, understanding the wear patterns of parts, and taking corresponding maintenance or replacement measures before the parts enter the failure wear phase, the occurrence of wear-out failures can be controlled, thereby extending the actual lifespan of CNC machine tools.
