Do you know the definition of numerical control machine tool failure and the counting principle of failures?

I. Definition of Failures
As a key equipment in modern manufacturing industry, the stable performance of numerical control machine tools is of crucial importance. The following are the detailed definitions of various failures of numerical control machine tools:

1. Failure
   When a numerical control machine tool loses its specified function or its performance index exceeds the specified limit, a failure has occurred. This means that the machine tool cannot normally perform the scheduled processing tasks, or there are situations such as decreased precision and abnormal speed during the processing, which affect the quality and production efficiency of products. For example, when processing precision parts, if the positioning accuracy of the numerical control machine tool suddenly decreases, resulting in the part size exceeding the tolerance range, it can be determined that the machine tool has a failure.
2. Associated Failure
   A failure caused by a quality defect of the machine tool itself when the numerical control machine tool is used under specified conditions is called an associated failure. This is usually due to problems in the design, manufacturing or assembly process of the machine tool, resulting in failures during normal use. For example, if the design of the transmission parts of the machine tool is unreasonable and excessive wear occurs after long-term operation, thus affecting the precision and stability of the machine tool, this belongs to an associated failure.
3. Unassociated Failure
   A failure caused by misuse, improper maintenance or other external factors other than associated failures is called an unassociated failure. Misuse may include operators not operating according to operating procedures, such as overloading the machine tool and setting incorrect processing parameters. Improper maintenance may be the use of inappropriate accessories or methods during the maintenance process, resulting in new failures of the machine tool. External factors may include power fluctuations, excessively high or low environmental temperatures, vibrations, etc. For example, during thunderstorm weather, if the control system of the machine tool is damaged due to lightning strike, this belongs to an unassociated failure.
4. Intermittent Failure
   A failure of a numerical control machine tool that can restore its function or performance index within a limited time without repair is called an intermittent failure. This kind of failure is uncertain and may occur frequently within a period of time or may not occur for a long time. The occurrence of intermittent failures is usually related to factors such as unstable performance of electronic components and poor contact. For example, if the machine tool suddenly freezes during operation but can work normally after restarting, this situation may be an intermittent failure.
5. Fatal Failure
   A failure that seriously endangers personal safety or causes significant economic losses is called a fatal failure. Once this kind of failure occurs, the consequences are often very serious. For example, if the machine tool suddenly explodes or catches fire during operation, or if the failure of the machine tool causes all the processed products to be scrapped, causing huge economic losses, these all belong to fatal failures.

1. Classification and counting of associated and unassociated failures
   Each failure of a numerical control machine tool should be classified as an associated failure or an unassociated failure. If it is an associated failure, each failure is counted as one failure; unassociated failures should not be counted. This is because associated failures reflect the quality problems of the machine tool itself, while unassociated failures are caused by external factors and cannot reflect the reliability level of the machine tool. For example, if the machine tool collides due to the misoperation of the operator, this is an unassociated failure and should not be included in the total number of failures; if the machine tool cannot operate normally due to a hardware failure of the control system, this is an associated failure and should be counted as one failure.
2. Counting of failures with multiple functions lost
   If several functions of the machine tool are lost or the performance index exceeds the specified limit, and it cannot be proved that they are caused by the same reason, then each item is judged as a failure of the machine tool. If it is caused by the same reason, it is judged that the machine tool only generates one failure. For example, if the spindle of the machine tool cannot rotate and the feed system also fails. After inspection, it is found that it is caused by a power failure. Then these two failures should be judged as one failure; if after inspection, it is found that the spindle failure is caused by the damage of the spindle motor, and the feed system failure is caused by the wear of the transmission parts. Then these two failures should be judged as two failures of the machine tool respectively.
3. Counting of failures with multiple causes
   If a function of the machine tool is lost or the performance index exceeds the specified limit, and they are caused by two or more independent failure causes, then the number of independent failure causes is judged as the number of failures of the machine tool. For example, if the machining accuracy of the machine tool decreases. After inspection, it is found that it is caused by two independent reasons: tool wear and deformation of the machine tool guide rail. Then this should be judged as two failures of the machine tool.
4. Counting of intermittent failures
   If the same intermittent failure mode occurs multiple times in the same part of the machine tool, it is only judged as one failure of the machine tool. This is because the occurrence of intermittent failures is uncertain and may be caused by the same underlying problem. For example, if the display screen of the machine tool often flickers, but after inspection, no obvious hardware failure is found. In this case, if the same flickering phenomenon occurs multiple times within a period of time, it should only be judged as one failure.
5. Counting of failures of accessories and wearing parts
   The replacement of accessories and wearing parts that reach the specified service life and the damage due to overuse are not counted as failures. This is because accessories and wearing parts will gradually wear out over time during use. Their replacement is a normal maintenance behavior and should not be included in the total number of failures. For example, if the tool of the machine tool needs to be replaced after being used for a period of time due to wear, this does not belong to a failure; but if the tool suddenly breaks within the normal service life, this belongs to a failure.
6. Handling of fatal failures
   When a fatal failure occurs in a machine tool and it is an associated failure, it shall be immediately judged as unqualified in reliability. The occurrence of a fatal failure indicates that there are serious safety hazards or quality problems in the machine tool. It needs to be stopped immediately and a comprehensive inspection and maintenance should be carried out. In reliability evaluation, fatal failures are usually regarded as serious unqualified items and have a significant impact on the reliability evaluation of the machine tool.
   In conclusion, accurately understanding and following the definition and counting principles of failures of numerical control machine tools is of great significance for improving the reliability of machine tools, ensuring production safety and improving production efficiency. Through accurate statistics and analysis of failures, problems existing in machine tools can be found in time, and effective improvement measures can be taken to improve the performance and quality of machine tools.