Repair of several non alarm faults in the hottest

2022-08-21
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Repair of several non alarm faults in CNC machine tools

the control system of CNC machine tools has the function of fault self diagnosis. Generally, there is an alarm message when a fault occurs. According to the control system used by the machine tool, the alarm content is different, but according to the fault handling method in the manual, most of the faults can be solved. In the actual use of machine tools, there are also some faults that have no alarm and the phenomenon is not very obvious. In this case, it is not as simple as it is documented. In addition, after the failure of some equipment, there is not only no alarm information, but also the lack of information required for maintenance. If some machine tools fail in use, if they do not pay attention to it a little, it will also cause the workpiece to be rejected in batches, so it is more difficult to deal with it. For this kind of fault treatment, when the repair personnel lack certain work experience, they often make wrong judgments, causing unnecessary economic losses or extending the repair time. In addition, sometimes, due to the low frequency of faults, we will encounter great trouble when we ask the special maintenance service department to deal with them. For this kind of fault, we believe that we must carefully check it according to the specific situation, analyze the tiny parts of the phenomenon, and find out the real cause

to find out the cause of this kind of fault, we must first find out its real phenomenon from the crisscross of various surface phenomena (this "phenomenon" is the real situation of the fault), and then find out the cause from the confirmed fault phenomenon. A comprehensive analysis of a fault phenomenon is an important factor to determine whether the judgment is correct. Before finding out the cause of the fault, you must first understand the following:

① whether the fault occurs in normal work or just after startup

② the number of occurrences, whether it is the first time or has occurred many times

③ confirm that the machining program of the machine tool is correct

④ whether other personnel have repaired or adjusted the machine tool

⑤ is there any difference between the fault phenomenon when requesting repair and the situation on site

the following are the handling and analysis methods of some non alarm faults we encounter in maintenance

fault - Zoje thy5640 vertical machining center found that there was abnormal sound at the spindle and gearbox when the spindle speed was below 500r/min during operation. By observing the power meter of the motor, it was found that the output power of the motor was unstable and the pointer oscillated greatly. However, the abnormal sound disappears when using more than 1201r/min. After starting up, the power meter of the motor will swing automatically without rotation command, and the motor will drift and rotate automatically. After normal operation, the braking time is too long, and the machine tool has no alarm

according to the observed phenomenon, the cause of the fault may be the loss of control of the spindle controller, and the cause of the mechanical transmission or motor cannot be eliminated. Due to the heavy workload of dismantling the mechanical part for inspection, the spindle controller of the electrical part shall be inspected first, and the controller is Siemens 6sc-6502. First check the preset parameters in the controller, and then check the control board. There is no abnormality. After checking that the circuit board is dirty, clean the circuit board as required, but the boot fault is still the same after installation. Therefore, the cause of the fault in the controller can be temporarily eliminated. In order to determine whether the fault is in the motor or the mechanical transmission part, the motor must be separated from the machine. After separation, the startup and commissioning found that the continuous abnormal sound began to appear when the motor speed command was close to 450r/min, but the abnormal sound disappeared when the 1201r/min command was given. Therefore, we analyzed the main shaft part. The original 450r/min command given at low speed and the 4500r/min command given at high speed are the same for the motor at the highest speed, but the speed is reduced by gears at low speed, so the fault can be basically determined in the motor part. After analysis, the abnormal sound may be caused by poor bearing. The motor was disassembled for inspection, and it was found that the bearing was indeed damaged. At high speed, the bearing was stuck, causing the load to increase, causing the power meter to swing and deflect. After stopping, the motor drifted and braking was too slow. After inspection, the encoder disc was scratched. After replacing the bearing and encoder, all faults were eliminated. This fault is mainly caused by abnormal sound when the main shaft rotates, so the sound source should be checked before troubleshooting. Abnormal sound is usually caused by mechanical friction, jamming and bearing damage

fault 2: the spindle orientation of the machining center is inaccurate or misplaced

the spindle orientation of machining center usually adopts three ways, magnetic sensor, encoder and mechanical orientation. When using magnetic sensors and encoders, in addition to adjusting the position of components, you can also adjust machine parameters. There is no alarm when orientation error occurs, and it can only be found when there is an interruption in the process of tool change. Once, there was a fault of inaccurate orientation on a modified machining center. At the beginning, the machine tool was often interrupted in the work, but the number of times was not very many. It could work again after restarting, and the fault occurred repeatedly. After careful observation of the machine tool after the fault occurred, it was found that the real cause of the fault was the position shift of the spindle after orientation. It was strange that if the spindle was touched by hand after orientation (similar to the situation when the tool was inserted into the spindle during tool change in work), the spindle would drift in the opposite direction. Check that there was no alarm in the electrical part, and the mechanical part was very simple. The orientation of the machine tool uses encoder, so from the phenomenon of fault and possible parts, the possibility of electrical part is relatively small, and the most important mechanical part is connection. Therefore, it was decided to check the mechanical connection part. When checking the connection of the encoder, it was found that the set screw of the coupling sleeve on the encoder was loose, which made the coupling sleeve retreat, resulting in excessive clearance with the connecting part of the main shaft, which would lead to asynchronous rotation. After fixing the set screw as required, the fault is eliminated. In case of spindle orientation failure, analyze and deal with it according to the specific structure of the machine tool. Check the electrical part first, and then consider the mechanical part if it is confirmed to be normal

fault 3: the manual movement of the CNC lathe is normal in use. When it automatically returns to zero, it moves for a certain distance and then does not move. When it is restarted, the manual movement is normal again

the lathe uses economic numerical control and stepping motor. When moving manually, it moves normally due to a slightly slow speed. When returning to zero automatically, it moves quickly with a long distance, resulting in mechanical jamming. According to the analysis of the fault, it was mainly due to mechanical reasons. After inquiry, it was learned that the machine tool disassembled the motor on another machine tool for use due to the inaccurate size during processing. After careful inspection, it was caused by the too small gear clearance in the gearbox, which was normal after readjustment. This is a fault caused by human factors, which often occurs in the repair without paying attention. Therefore, attention should be paid in the work to avoid this phenomenon

no display on the machine screen after fault 4 is started

the first step to eliminate this kind of fault is to make the screen work normally. Sometimes it's just the reason for showing part. But in many cases, there may be many kinds of faults

a Japanese h500/50 horizontal machining center, the screen is black when starting up, the NC power switch on the operation panel has been pressed, and the red and green lights are on. Check that the switch and main parts in the electric cabinet are normal. Restart after shutdown, and the fault is the same. After investigation, the fault was caused by multiple damages. After replacing the display and displaying the control panel, the screen appeared, enabling the machine tool to enter other fault maintenance

Tena DM4800 vertical machining center, no display on the screen after startup

the machining center uses the three edge M300 system, and there are many reasons for the lack of display on the screen. After checking the fault, it is confirmed that it is caused by the main board fault, so it was replaced. Because the parameters of the main board need to be reset after replacement, according to the system parameter setting steps, the machine tool is normal after setting and adjusting according to the parameter table attached to the machine tool

there are many causes of faults that are not displayed on the screen. First of all, we must find out the causes and eliminate them. If there are other faults, we should deal with them according to the alarm and other fault information of the machine tool

fault V in CNC equipment, the most common non alarm faults are machine tool error, oil tank leakage, rapid fire or inaccurate size

there are many error faults, which have different performances on various devices. For example, there are many phenomena of large and small in the diameter direction of CNC lathe. There are many errors in the vertical axis of the machining center. It is common that the size gradually increases downward, but there is also the phenomenon of the size increasing upward. On the horizontal axis, there are often some faults with small errors, some of which often change, sometimes good or bad, making the size of parts difficult to control

there are mainly several situations that cause error fault but no alarm in the CNC machine tool: ① the CNC system of the machine tool is relatively simple, and there is no set detection for the error in the system, so there can be no alarm display when the machine tool fails. ② The error in the machine tool is not within the range predicted at the time of design, so it cannot be detected when there is an error. Because most CNC machine tools use a semi closed-loop system, the actual position of the machine tool cannot be detected. ③ The coupling structure of lead screw and motor has different frequency and possibility of failure, and the phenomenon after failure is not the same. Japan is committed to developing new polymer materials to realize automobile lightweight. Similarly, some sizes will only increase in the negative direction, but some possibilities of positive and negative changes will occur. According to various situations in repair, we come to the conclusion that the elastic coupling in the middle of the coupling basically increases more in the negative direction, Two kinds of faults with key connection in the middle will occur. ④ The zero return mode in the electrical system of the machine tool is not set properly. It is not as good as finding looseness to ensure consistency. The error of this kind of fault is generally small. In addition to general faults caused by poor deceleration switch, too short deceleration distance when returning to zero will also cause zero deviation. In some systems, there is an item of "deletion" in the monitoring page, which can be recorded and checked frequently to find problems in time

the non alarm faults in CNC machine tools are mostly difficult to deal with. Among these faults, mechanical causes are more common, followed by some comprehensive factors. It is generally difficult to repair these faults, especially to judge the fault phenomenon. In the repair of CNC machine tools, the judgment experience of this aspect of failure can only be explored in practice, summarized and improved continuously, so as to meet the needs of modern industrial new equipment maintenance. (end)

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