CNC machine tools are high-efficiency and complex automated machine tools with high technological content, such as machines, electricity, and instruments. In the running process of machine tools, components will inevitably have different degrees of failure and different types of failures. Therefore, familiar with the machinery The characteristics of faults, and the common methods and means of mastering the mechanical fault diagnosis of CNC machine tools, play a significant role in determining the causes and elimination of faults.
First, the principle and basic requirements of the fault diagnosis of CNC machine tools <br> The failure (or failure) of the so-called CNC machine tool system is the loss of the prescribed function of the index-controlled machine tool system. Faults can be divided into many types based on the form, nature, and cause. Regardless of the type of failure, some principles and diagnostic techniques can be followed when making a diagnosis.
1.1 troubleshooting principles.
Mainly include the following aspects: 1) Fully investigate the phenomenon of failure, the first investigation of the operator, the detailed inquiry of the entire process of failure, some of what happened, what measures were taken. Then make a detailed survey of the site; 2) When looking for the cause of the failure, the idea must be broad. Whether it is integrated electrical equipment or mechanical and hydraulic pressure, as long as it may cause the cause of the failure, it should be listed as comprehensively as possible. Then make comprehensive judgments and optimization choices to determine the most likely cause of failure; 3) first mechanical and electrical, first static and dynamic principles. Before troubleshooting, first of all you should take care to eliminate mechanical failures. In the running state, dynamic observation, inspection and testing are performed to find faults. However, if a destructive fault occurs after power is applied, the danger must be eliminated before power is applied.
1.2 Fault diagnosis requirements.
In addition to rich professional knowledge, the personnel who perform numerical control fault diagnosis operations need to have a certain hands-on ability and practical operation experience, require the staff to combine practical experience, be good at analysis and thinking, and analyze the causes of faults through the actual operation of the faulty machine tool. No change should be made to achieve the same effect. Complete maintenance tools and diagnostic instruments are indispensable. Commonly used tools include screwdrivers, pliers, wrenches, and soldering irons. Commonly used detection instruments include multimeters, oscilloscopes, and signal generators. In addition to this, the staff also needs to prepare the necessary technical information, such as the electrical machinery principle drawing of the numerical control machine tool, the structure layout drawing, the numerical control system parameter manual, the maintenance manual, the installation, the operation, the use instruction and so on.
Second, the idea of troubleshooting <br> Different NC system design ideas vary, but no matter what kind of system, their basic principles and composition are very similar. Therefore, when the machine tool fails, the maintenance personnel must have a clear idea of troubleshooting: investigate the fault site, confirm the fault phenomenon, the nature of the fault, should fully grasp the fault information, so that "more brains, careful hands" to avoid the expansion of the fault . According to the mastered fault information, the complexity of the fault is clarified, and all the doubt points of the fault location are listed. Preparation of necessary technical information, such as machine tool manuals, electrical control schematics, etc., based on which to analyze the causes of failures, formulate troubleshooting plans, require open-minded thinking, and should not limit the faults to a certain part of the machine tool. After determining the troubleshooting plan, use a multimeter, oscilloscope, and other measurement tools to verify and detect faults with test methods, locate the fault location step by step, and confirm whether the fault belongs to an electrical fault or a mechanical fault. Is it systematic or random? Is it self-failure or external failure and so on. Troubleshooting. Usually the problem is solved immediately after finding the cause of the problem.
Third, the troubleshooting method <br> CNC machine tool CNC system is the core of CNC machine tools, its reliable operation, is directly related to the entire equipment operation is normal or not. The following summary summarizes some methods for determining and troubleshooting CNC machine tools.
3.1 Make full use of the numerical control system hardware and software alarm function.
Numerous hardware alarm indication devices are provided in modern numerical control systems. Setting hardware alarm indication devices is beneficial to improving the maintainability of the numerical control system. The CNC systems of CNC machine tools all have self-diagnostic functions. During the work of the CNC system, the system can be quickly diagnosed using the self-diagnostic program. Once a fault is detected, the fault is immediately displayed on the CRT as an alarm or an alarm indicator on the panel is illuminated. And this self-diagnostic function can also classify fault alarms.
3.2 CNC machine tool simple fault alarm processing method.
Generally, CNC machine tools have strong self-alert function and can monitor the system hardware and software working status at any time. Most of the faults of CNC machine tools can display alarm prompts. According to the fault prompts, the fault of the machine tool can be determined, and the faults can be processed and eliminated in time. Machine tool availability and efficiency.
3.3 direct observation method.
The direct observation method is a method of using the human sensory organs to observe various external phenomena at the time of failure (or after occurrence of a failure) and to determine possible locations of the failure. This is the first point of entry for dealing with faults in numerical control systems. It is often the most direct and effective method. Under such circumstances, “simple” faults can solve problems through this direct observation.
3.4 Usage Status Display Diagnosis Function How to determine the fault.
The modern numerical control system not only can display the fault diagnosis information, but also can provide various states of diagnosis in the form of diagnosis address and diagnosis data.
3.5 Failure occurred in a timely manner Checking the CNC system parameters to determine the fault.
The change of the parameters of the numerical control system of CNC machine tools will directly affect the performance of CNC machine tools, causing the failure of CNC machine tools, and even the whole machine can not work normally. Therefore, during the process of analyzing and diagnosing failures, although some measures cannot be taken to solve the problems or troubleshoot them, or if the source of the failures is not clear enough, we should change our thinking and start from what people call “soft” failures. Checking whether the parameters of the numerical control system are verified is due to the failure caused by changes in the parameters of the numerical control system. This is often an anomaly, which is the crux of the problem.
Fourth, fault example 4.1 NC machine chip remover failure analysis and improvement.
After the field operator removed the motor and tested it, the result showed that the operation was normal, so the cause of the motor failure could be eliminated. At the same time, it was observed that the key on the motor shaft was not on the keyway, so the direct cause of the failure could be diagnosed initially. For the motor shaft and chip removal spiral rod disengagement, further analysis, because the transmission key is subject to the load of instantaneous changing force, if the transmission key is divided at this time, then each part of the split can be seen as a beam, so you can It performs vibration analysis.
After analysis of the force conditions, the transmission key has the conditions for fretting wear. Therefore, the drive key wear is fretting wear, and the search found that the key has been dropped into the spiral rod hole, you can conclude that the key is intact and only slightly wear, so The reasons for the key crushing and key wear can be eliminated, and finally, the direct cause of the failure can be concluded that the key falls off, causing the spiral chip removing rod to disengage from the motor shaft and losing the transmission force. After installing the key and reassembling the motor, troubleshooting is working properly.
4.2 CNC machine tool vibration crawling process.
The oscillation phenomenon of numerical control system has become a common problem of NC closed-loop system. When the system oscillates, it will cause the machine to crash and vibrate. The oscillation of the machine usually occurs in the mechanical part and the feed servo system. There are many reasons for the oscillation, and Chen has mechanical factors such as transmission gap, elastic deformation, and frictional resistance that cannot be eliminated. The influence of the parameters of the servo system is also an important aspect. Sometimes the numerical control system will produce high-frequency harmonics in the feedback signal due to some oscillations in the expansion machinery. This will make the output torque unresolved and thus generate vibration. For such high-frequency oscillations, a first-order low-pass filter can be added to the speed loop, which is a torque filter.
The speed command and the speed feedback signal are converted into torque signals by the speed controller. The torque signal cuts off the high frequency components through the first-order filter link, thereby obtaining an effective torque control signal. By adjusting the parameters, the mechanically generated frequency above 100 Hz can be cut off, so that the effect of eliminating the high-frequency oscillation can be achieved.
V. Troubleshooting Confirmation and Aftermath Work <br> After troubleshooting, the maintenance work cannot be completed yet. It is still necessary to analyze the underlying causes of the fault from both technical and managerial aspects, and take appropriate measures to avoid the recurrence of the fault. If necessary, mature equipment can be used to retrofit and improve the equipment according to site conditions. Confirmation of troubleshooting, troubleshooting is completed. After finishing the lines, all the movements of the machine tool are tested and run again, and they can be delivered normally. At the same time, the operator can continue to observe the operation. After a while, ask about the operating conditions of the operator's machine tool, and conduct a thorough inspection of the fault point again. Finally, make a maintenance record, and record the entire process of maintenance in detail, including maintenance time, model specifications of replacement parts, and failure analysis. From the process of troubleshooting, discover what you lack, develop a learning plan, and ultimately enrich yourself.
