Faults and fault classification of CNC machine tools

CNC lathe is the product of mechatronics, advanced technology and complex structure. The faults of CNC machine tools are various, each of which is different. The causes of faults are generally complex, 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, according to the nature of the fault, the cause of the fault and the location of the fault and other factors, the number of faults of CNC machine tools is divided into the following categories.

According to the nature of CNC machine failure classification

（1）Systematic failure

This kind of fault means that as long as certain conditions are met, the machine tool or numerical control system will inevitably appear. For example, if the grid voltage is too high or too low, the system will produce an alarm of too high or too low voltage; if the cutting amount is too large, it will produce an overload alarm.

For example, in the process of machining, the CNC machine tool of the system sometimes cuts off the power automatically and can work normally after restart. According to the working principle and fault phenomenon of the system, it is suspected that the fault is caused by the fluctuation of the system supply voltage,The 24 V input power supply on the system power supply module is measured, and it is found that it is about 22.3 v. when the machine tool processes, the voltage still fluctuates downward, especially when the cutting amount is large, the voltage drops greatly, sometimes close to 21 v. at this time, the system automatically turns off. In order to solve this problem, the 24 V power transformer with large capacity is replaced to eliminate the fault.

（2）Random failure

This kind of fault refers to the fault that only happens once or twice occasionally under the same conditions,it is not easy to copy the same fault artificially. Sometimes it takes a long time and it is very accurate to encounter it again. It is difficult to analyze and diagnose this kind of fault. Usually, this kind of fault is related to the looseness and dislocation of the mechanical structure, the drift of the working characteristics of some components in the CNC system and the decline of the reliability of the electrical components of the machine tool.

For example, a CNC groove grinder, in the process of occasional problems, the grinding groove position changes, resulting in waste, this paper analyzes the working principle of the machine. In the grinding process, the measuring arm first 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 raised, and the machining program continues to run. 

The CNC equipment grinds the groove at a certain distance from the end face, and the position of the groove is not accurate, which has a great relationship with the measurement.Because it does not occur frequently, it is difficult to observe the fault. Therefore, according to the working principle of the machine tool, no problem is found in the inspection of the measuring head. When checking the rotation of the measuring arm, it is found that the rotating shaft is a little tight. Sometimes, the measuring arm may not be placed in place accurately, resulting in measurement error. After dismantling the rotating shaft, it is found that it has been seriously worn. A new spare part was made, and the failure did not occur after replacement.