1. Classification according to the location of the fault

_The main machine of CNC machine tool with malfunction usually refers to the mechanical, lubricating, cooling, chip removal, hydraulic, pneumatic and protective parts of CNC machine tool. The main common faults of the main engine are:

1) Mechanical transmission failure caused by improper installation, commissioning and operation of mechanical components

2) Faults caused by interference and excessive friction of moving parts such as guideways and spindles

3) Faults caused by damage of mechanical parts, bad connection, etc.

The main faults of the main engine are large transmission noise, poor processing accuracy, large operating resistance, no movement of mechanical parts, mechanical parts damage and so on. Poor lubrication, pipeline blockage and poor sealing of hydraulic and pneumatic systems are common causes of main engine failure. Regular maintenance and control of CNC machine tools and elimination of "three leaks" are important measures to reduce part of the main engine failure.

(2) Faults in electrical control systems are classified into two categories: weak-current faults and strong-current faults, according to common habits.

The "weak current" part is the control part of the command and control system, which mainly consists of electronic components and integrated circuits. The weak current part of NC machine tool includes CNC, PLC, MDI/C RT, servo drive unit and output unit.

"Weak current" fault can be divided into hardware fault and software fault. Hardware fault refers to the faults of integrated circuit chips, discrete electronic components, connectors and external connection components of the above parts. Software failure of CNC machine tools refers to the failure of germanium and data loss caused by the normal operation of hardware. Common faults are: faults in processing program, changes or losses of system program and parameters, and errors in computer operation.

The "strong power" part is the main circuit or relays, contactors, switches, fuses, power transformers, motors, electromagnets, stroke switches and other electrical components in the command and control system and their control circuits. Although the maintenance and diagnosis of this part of the fault is more convenient, but because it is in the high voltage and high current working state, the probability of failure is higher than that of the "weak current" part. Maintenance personnel must pay enough attention to it.

2. Classification according to the nature of the fault

(1) The deterministic faults refer to the faults of CNC machine tools that are inevitable if the hardware of the host computer of the control system is damaged or if certain conditions are met. This kind of fault is the most common phenomenon in CNC machine tools, but because it has certain rules, it also brings convenience to maintenance.

Certain faults are irrecoverable. Once the faults occur, if they are not repaired, the machine tool will not automatically return to normal. But as long as the root cause of the faults is found, the machine tool can immediately return to normal after the repair is completed. Correct use and careful maintenance are important measures to eliminate or avoid failure.

(2) Random faults refer to the occasional faults occurring in the working process of CNC machine tools. The causes of such faults are hidden and it is difficult to find out their regularity. So they are often called "soft faults". It is difficult to analyze and diagnose the causes of random faults. Generally speaking, the occurrence of faults is often related to the installation quality of components, the setting of parameters and the products of components. There are many factors related to quality, imperfect software design and the influence of working environment.

Random faults can be restored. After the faults occur, the machine tool can normally restore to normal by restarting the machine, but in the process of operation, the same faults may occur.

Strengthening the maintenance and inspection of NC system, ensuring the sealing of electric box, reliable installation and connection, correct grounding and shielding are important measures to reduce and avoid such faults.

3. Classification according to fault indication form

(1) The failure display of CNC machine tools with tape display can be divided into two kinds: indicator display and display display.

1) Indicator display alarm indicator light display alarm refers to the alarm displayed by the state indicator light on each unit of the control system (usually composed of LED light-emitting tubes or small indicator lights). According to the state indicator light of the numerical control system, even when the display fails, the location and nature of the failure can be roughly analyzed and judged. Therefore, it should be recognized in the process of maintenance and troubleshooting. Verify the status of these status indicators.

2) Display alarm. Display alarm refers to the alarm that can display alarm number and alarm information through CNC display. Because CNC system generally has strong self-diagnosis function, if the system's diagnostic software and display circuit work normally, once the system fails, it can display fault information in the form of alarm number and text on the display. CNC system can display dozens of alarms and thousands of alarms, which is an important information of fault diagnosis.

In display alarm, it can be divided into NC alarm and PLC alarm. The former is an accident display set up by a CNC manufacturer. It can determine the possible cause of the failure by referring to the "maintenance manual" of the system. The latter is the text of PLC alarm information set by the manufacturer of NC machine tool, which belongs to the fault display of machine tool side. It can be compared with machine tool production.