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Fault and Fault Classification of CNC Machine Tools

CNC machine tool all or part of the loss of the prescribed function of the phenomenon called the failure of CNC machine tools.

CNC machine tool is the product of mechanical and electrical integration, advanced technology, complex structure. The faults of CNC machine tools are also diverse and different. The causes of the faults are generally more complicated, which brings many difficulties to the fault diagnosis and maintenance of CNC machine tools. In order to facilitate the fault analysis and diagnosis of machine tools, this section roughly divides the faults of CNC machine tools into the following categories according to the nature of the fault, the cause of the fault and the location of the fault.

1, according to the nature of the failure of CNC machine tools classification

(1) Systematic failure

This kind of fault refers to the inevitable failure of the machine tool or numerical control system as long as certain conditions are met. For example, the grid voltage is too high or too low, the system will produce a voltage too high alarm or too low alarm; when the amount of cutting is too large, it will produce an overload alarm.

For example, a SINUMERIK810

The system of CNC machine tools in the processing process, the system sometimes automatically power off shutdown, restart, can also work normally. According to the working principle of the system and the fault phenomenon, it is suspected that the cause of the fault is the fluctuation of the power supply voltage of the system. The 24V power input on the power supply module of the system is measured and found to be about 22.3V V. When the machine tool is processed, the voltage still fluctuates downward, especially when the cutting volume is large, the voltage drop is large, sometimes close to 21V. At this time, the system is automatically powered off.

(2) Random failure

This kind of fault refers to the same conditions, only occasionally once or twice the fault. It is not easy to artificially reproduce the same fault, and sometimes it is difficult to encounter it again for a long time. This kind of fault analysis and diagnosis is difficult. In general, this kind of failure is often related to the loosening and dislocation of the mechanical structure, the drift of the working characteristics of some components in the numerical control system, and the decrease of the reliability of the electrical components of the machine tool.

For example, a CNC groove grinding machine, in the process of occasional problems, grinding groove position changes, resulting in waste. Analyze the working principle of this machine tool. During grinding, the measuring arm swings down to the clamping position of the workpiece, and then the workpiece starts to move. When the reference end face of the workpiece contacts the measuring head, the numerical control device records the position data at this time, then the measuring arm is lifted and the processing program continues to run. The numerical control device grinds the groove at a certain distance from the end face according to the position data of the end face, so the groove position is not allowed to have a very large relationship with the accuracy of the measurement. Because it does not occur frequently, it is difficult to observe the failure phenomenon. Therefore, according to the working principle of the machine tool, no problem was found in the inspection of the measuring head. When checking the rotation of the measuring arm, it is found that the rotating shaft is somewhat tight, and the measuring arm may sometimes not be accurately in place, resulting in measurement errors. The rotating shaft was disassembled and checked and found to have been severely worn. New spare parts were made. After replacement, this failure never occurred again.

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