The phenomenon that the CNC machine tool completely or partially loses the specified function is called the fault of the CNC machine tool.

CNC machine tool is the product of mechatronics, advanced technology, complex structure. The faults of CNC machine tools are also various and different, and the causes of the faults are generally more complex, which brings a lot of difficulties to the fault diagnosis and maintenance of CNC machine tools. In order to facilitate the fault analysis and diagnosis of the machine tool, this section roughly divides the fault of the CNC machine tool 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 fault nature of CNC machine tools classified

(1) Systemic failure

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

For example, one uses the SINUMERIK810

The CNC machine tool of the system in the process of processing, the system sometimes automatically power off and shut down, after restarting, it can still work normally. According to the working principle of the system and the fault phenomenon suspected that the cause of the fault is the system power supply voltage fluctuations, measuring the 24V input power supply on the system power module, found to be about 22.3V, when the machine tool processing, this voltage also fluctuates downward, especially when the cutting amount is large, the voltage drop is large, sometimes close to 21V, then the system automatically power off and shut down, in order to solve this problem, Replacing the large capacity 24V power transformer will completely eliminate this problem.

(2) Random faults

This type of failure refers to the failure that only occasionally occurs once or twice under the same conditions. It is not easy to artificially reproduce the same failure, and sometimes it is difficult to encounter it again for a long time. It is difficult to analyze and diagnose this kind of fault. Under normal circumstances, 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 CNC system, and the reliability of the electrical components of the machine tool.

For example, a CNC groove grinder occasionally has problems in the processing process, and the position of the grinding groove changes, resulting in waste products. Analyzing the working principle of this machine tool, the measuring arm first swings down to the clamping position of the workpiece during grinding, and then the workpiece begins to move. When the reference end face of the workpiece touches the measuring head, the numerical control device records the position data at this time, and then the measuring arm is lifted and the machining program continues to run. According to the position data of the end face, the CNC device grinds the groove at a certain distance from the end face, so the groove position is not allowed to have a very big relationship with the accuracy of the measurement. Because it does not happen often, it is difficult to observe the fault phenomenon. Therefore, according to the working principle of the machine tool, the measuring head was checked and no problem was found; When checking the rotation of the measuring arm, it was found that the rotation axis was a little tight, and the measuring arm may not be accurately in place sometimes, resulting in measurement errors. The rotating shaft was disassembled and found to be seriously worn. A new spare part was made, and this fault did not occur after replacement.

1. The use environment of CNC machine tools

For CNC machine tools, it is best to place them in a constant temperature environment and away from equipment with large vibrations (such as punches) and equipment with electromagnetic interference.

2. Power requirements

3. CNC machine tools should have operating procedures

Carry out regular maintenance, maintenance, failure to pay attention to record the protection site, etc.

4. CNC machine tools should not be stored for a long time

5. Pay attention to the training and staffing of operators, maintenance personnel and programming personnel

Maintenance of numerical control system

1. Strictly follow the operating procedures and daily maintenance system

2. Prevent dust from entering the CNC device

Floating dust and metal powder may cause the insulation resistance between components to decrease, resulting in failure or even damage to components.

3. Regularly clean the heat dissipation and ventilation system of the CNC cabinet

4. Often monitor the power grid voltage of the CNC system

The grid voltage ranges from 85% to 110% of the rated value.

5. Replace memory batteries regularly

6. Maintenance of CNC system when it is not used for a long time

Often power on the numerical control system or make the numerical control machine run the temperature program.

Seven. Maintenance of spare circuit boards Maintenance of mechanical components

Maintenance of mechanical parts

1. Maintenance of tool store and tool changing manipulator

① When installing knives to the knife store manually, ensure that they are installed in place and check whether the lock on the knife holder is reliable;

(2) It is strictly prohibited to put overweight and ultra-long tools into the tool library to prevent the manipulator from losing the tool or colliding with the workpiece and fixture when changing the tool;

③ The sequential knife selection method must pay attention to whether the order of the tool placed on the knife library is correct. Other tool selection methods should also pay attention to whether the changed tool number is consistent with the required tool to prevent the wrong tool from causing accidents;

④ Pay attention to keep the tool handle and sleeve clean; ⑤ Often check whether the zero position of the tool library is correct, check whether the position of the tool point of the machine spindle is in place, and adjust it in time, otherwise the tool change action can not be completed;

When starting up, the tool store and the manipulator should first run empty, and check whether all parts work normally, especially whether the stroke switch and solenoid valve can operate normally.

2. Maintenance of ball screw pairs

① Regularly check and adjust the axial clearance of the screw nut pair to ensure the reverse transmission accuracy and axial stiffness;

② Regularly check whether the connection between the lead screw support and the bed is loose and whether the support bearing is damaged. If there are the above problems, it is necessary to tighten the loose part in time and replace the support bearing;

③ The ball screw with grease is used to clean the old oil on the screw every six months and replace the new oil. Ball screw lubricated with lubricating oil, refueling once a day before machine work;

④ Pay attention to avoid hard dust or chips into the lead screw protective cover and touch the protective cover during the work process, and the protective device should be replaced in time when there is damage.

3. Maintenance of the main drive chain

① Regularly adjust the tightness of the spindle drive belt;

② Prevent all kinds of impurities from entering the tank. Replace the lubricating oil once a year;

③ Keep the connecting parts of the spindle and the tool handle clean. It is necessary to adjust the displacement of hydraulic cylinder and piston in time;

④ Adjust the counterweight in time.

4. Hydraulic system maintenance

① Filter or replace the oil regularly;

② Control the temperature of the oil in the hydraulic system;

③ Prevent leakage of hydraulic system;

④ Check and clean the fuel tank and pipeline regularly;

⑤ Implement daily point inspection system.

5. Pneumatic system maintenance

① Remove impurities and moisture from compressed air;

② Check the oil supply of the oil mist in the system;

③ Maintain the tightness of the system;

④ Pay attention to adjust the working pressure;

⑤ Clean or replace pneumatic components and filter elements;