With the enhancement of the function and technology of modern CNC system, the fault-free working time of CNC system has been greatly improved, but occasionally some faults still occur in CNC system. Common faults in CNC system can be divided into software faults and hardware faults. Software failures are caused by errors in processing procedures, problems in machine tool data, or problems in setting some parameters. This kind of fault can be checked and analyzed by alerting the alarm information, and the fault can be eliminated by modifying the corresponding program after finding the problem.
Hardware failure, as the name implies, is that CNC machine tools can not operate normally because of the damage of the hardware module of the CNC system. The hardware module of NC system includes CPU module, memory module, display module, measurement module and PLC.
Interface module, power module, display, etc.
Aiming at the hardware fault of CNC machine tools, only after finding the module in question and repairing or replacing it, the fault can be eliminated.
2. Servo System Failure and Maintenance Skills
Servo system is a kind of feedback control system. By comparing the input given value with the output measured value, the system can be adjusted automatically to eliminate the deviation. Servo system is the key executive mechanism of NC machine tools. Therefore, the fault of servo system is an important part of the whole CNC machine tool fault.
Following are some typical faults of servo system, and the common faults and diagnosis methods of servo system are discussed.
(1) Back Reference Point Fault: The common faults of machine tool back reference point can generally be divided into two kinds: unable to find reference point and inaccurate reference point. The former fault is mainly caused by the failure of the signal of the reference point deceleration switch or the zero mark pulse signal (including the signal not produced and lost in transmission). When eliminating such faults, we should first understand the way of machine tool returning to reference point, and then analyze the phenomenon of faults. The latter kind of faults is often caused by improper setting of switch block position of reference point, so long as the position of block is adjusted again, the faults can be eliminated.
(2) Servo motor does not turn: because the CNC system to the feed drive unit in addition to speed signals, there are enabling control signals. Therefore, the reasons for the servo motor not turning are: CNC system fault, inaccessible enable signal, feed drive unit fault, servo motor fault. Solution: Check whether the CNC system has signal output, whether the signal is connected to the motor and the servo motor itself.
(3) Position error: When the motion of servo axis exceeds the allowable range of position error, CNC system will produce alarm of excessive position error, including following error, contour error and positioning error. The main reasons are: the allowable range of system setting is too small, the gain of servo system is not set properly, the position detection device is polluted or damaged, and the accumulated error of feed transmission chain is too large.
3. Faults of Hydraulic System and Maintenance Skills
Hydraulic system, as an important part of Electromechanical-hydraulic integration system, has an important impact on the performance and reliability of CNC machine tools. Hydraulic system works in a closed environment, its common fault types are: large vibration and abnormal noise: it is a comprehensive manifestation of system failure. The analysis is based on fault data bits, focusing on the main fault points such as the change of hydraulic oil characteristics, the process of oil suction of hydraulic pumps, and the blockage of hydraulic pumps. The main causes of this failure are serious pollution of hydraulic oil, poor sealing of pipelines and joints, etc.
Insufficient or fluctuating pressure: The main manifestation of the fault is load immovable or time-varying stop. The analysis mainly starts from hydraulic pump, leakage of hydraulic circuit and series cylinder of hydraulic actuator. The main causes of this fault are hydraulic oil pollution, poor sealing of pipes and joints, improper assembly and sealing of hydraulic cylinders, etc. Flow instability: The main performance of the fault is that the execution speed is fast and slow.
The starting point and cause of the fault analysis are similar to the previous one. Component failure: The main failure is the failure of hydraulic pumps, control valves, hydraulic cylinders and other components under normal conditions. It can be analyzed from the mechanical structure and working mode of components. The main causes of this fault are hydraulic oil pollution, poor assembly of components, improper maintenance of users, etc.
4. Grinding Machine Auxiliary Device Faults and Maintenance Skills
CNC grinding machine has many special auxiliary devices, such as grinding wheel spindle, grinding wheel automatic balancer, grinding wheel dresser, etc. Its common faults are: grinding wheel spindle faults: grinding wheel spindle faults can generally be divided into mechanical faults, control part faults.
Frequency converter faults and motorized spindle faults. The common faults are that the spindle speed is not feedback, the wheel speed is abnormal, the spindle is overloaded, and the spindle stops running before it reaches the working speed. Grinding wheel automatic balancer failure: Grinding wheel balancer start balancing role, automatic balancing of grinding wheel. When the balance of the grinding wheel does not meet the requirements, the machine tool will alarm and stop the rotation of the grinding wheel. Its failure often occurs when the grinding wheel spindle stops running and the spindle does not start.
5. Concluding remarks
The structure of CNC machine tools is complex and diverse, which leads to the ever-changing faults. Faults play an important role in reliability analysis and improvement of NC machine tools. As we all know, high reliability CNC machine tools can reduce the production cost of users and the after-sale cost of manufacturers, and have obvious economic benefits. At the same time, it can also promote the development of national industry. Therefore, in the actual production, manufacturing and maintenance process, enterprises should pay attention to the collection of fault data, and ensure the integrity and comprehensiveness of data in the collection process.