The use of numerical control devices is becoming more and more widespread, and what follows is how to ensure the effective utilization of the device. When the device fails, it is necessary to restore the device to normal use as soon as possible. In order to solve this problem, maintenance personnel are required to have high quality first, and not only are they required to have rich professional knowledge, such as electromechanical integration technology, computer principle, numerical control technology, PLC technology, automatic control technology, dragging principle, hydraulic technology, etc. We must also master the general knowledge of machining and the simple programming of numerical control devices. In addition, we must have a certain level of English and be able to read English technical materials. Must have enough data, including machine, electricity, liquid drawing, machine parameter backup, system use and maintenance manual, PLC ladder diagram and so on. There must also be a certain amount of spare parts. In addition, maintenance personnel are required to have certain experience and master certain maintenance methods. The author engaged in numerical control equipment maintenance for many years, has accumulated certain experience, summed up a set of methods for maintenance of numerical control equipment, is introduced as follows for reference.

To find out the fault phenomenon

When the numerical control equipment fails, first of all to find out the fault phenomenon, to the operator to understand the first time the fault occurred, observe the process of the fault when possible, observe the fault is under what circumstances, how to happen , what caused the consequences. Only knowing the first-hand situation will help to eliminate the fault and clarify the fault process. The problem will be solved by half. Clearly understand the fault phenomenon, and then according to the working principle of the machine tool and numerical control system, you can quickly diagnose the problem and troubleshooting, so that the device back to normal use.

For example, when a CNC cylindrical grinder using the American Bryant company TEACHABLE III system is used for automatic machining, the grinding wheel wears off one piece of the dresser. In order to observe the phenomenon of failure and prevent accidental recurrence, the grinding wheel was removed to run the machine tool. At this time, the failure phenomenon was observed. It was found that during the automatic grinding process, there was no problem with grinding. After the grinding of the workpiece was completed, the grinding wheel was normal when dressing the grinding wheel. The feed, while the dresser rotates very quickly, quickly presses the upper limit switch. If the grinding wheel is not removed at this time, the grinding wheel must hit the dresser. According to the working principle of the machine tool, the wheel dresser is driven by the E-axis servo motor and the rotary encoder is used as a position feedback element. Normally, when the dresser trims the grinding wheel, the Z-axis slide moves the E-axis dresser to the dressing position, and the dresser makes a 30° to 120° swing to dress the grinding wheel. We observed the failure phenomenon several times and found that when the E axis is at the pressure upper limit switch, the coordinate value of the E axis on the screen is only about 60°, and the actual position is about 180°. Obviously, the position feedback has a problem, but the position is changed. Both the control board and the encoder did not solve the problem. After repeated observations and experiments, we found that: When the E-axis dresser is at the edge of the Z-axis, there is no problem with the reference point and rotary swing. Use the system's alarm information.

Now the self-diagnosis ability of the numerical control system is getting stronger and stronger. Most of the faulty numerical control systems of the equipment can be diagnosed and take corresponding measures, such as shutdown, etc., and generally can generate an alarm display. When the numerical control device fails, sometimes the alarm information is displayed on the display, and sometimes there are alarm indications on the numerical control device, the PLC device and the drive device. At this time according to the manual analysis of these alarm information, some according to the alarm information can directly confirm the cause of the fault, as long as the content of the alarm information, you can eliminate the numerical control equipment failures.

For example, a CNC channel grinder using the German SIEMENS 810 system will generate an alarm number “BATTERY ALARM POWER SUPPLY” after powering on. It clearly indicates that the power failure protection battery of the CNC system is dead and a new battery has been replaced (Note: Always replace the battery while the system is live. Reset the fault and return the machine to service. Another CNC grinding machine adopting SIEMENS 3 system is not displayed on the screen after power on. Check the numerical control device and find that a light emitting diode on the CPU board flickers. According to the instructions, analyze the flicker frequency and confirm that the power supply is low. After the battery is replaced, the battery voltage is low. , restart the system failure disappears.

For example, a numerical control lathe adopting Japan's FANUC 0TC system has alarm No. 2043 indicating “HYD. PRESSURE DOWN” indicating that the hydraulic system pressure is low. According to the alarm information, the hydraulic system was inspected and it was found that the hydraulic pressure was indeed very low. The hydraulic pressure was adjusted so that the machine tool returned to normal use.

Other fault alarm information does not reflect the root cause of the fault, but reflects the result of the fault or other problems arising therefrom. At this time, careful analysis and inspection are required to determine the cause of the fault. The following methods are applicable to such faults. The detection of some faults without alarm is effective.

To use the CNC status display function of the CNC system

Many CNC systems have PLC status display functions, such as PC STATUS under Siemens 3 system PC menu, PLC STATUS function under Siemens 810 system DIAGNOSIS menu, and PMC status display function of Fanuc 0T system DGNOS PARAM function, etc. The function can display the status and content of PLC input, output, timer, counter, etc. According to the working principle of the machine tool and the electrical schematic diagram provided by the machine tool manufacturer, some faults can be diagnosed by monitoring the corresponding state.

For example, a CNC lathe using FANUC 0TC in Japan fails once and the alarm 2041 appears when the power is turned on, indicating an X-axis overrange alarm, but the X-axis does not exceed the limit, and the X-axis limit switch is also No pressure is applied, but using the PMC status display function of the NC system, check that the XC limit switch's PMC input X0.0 is “1” and that the switch contact is actually connected, indicating that there is a problem with the switch. Replace it with a new one. After switching, the machine tool failure is eliminated.

For example, a CNC lathe using the Japan MITSUBINSHI MELDAS L3 system fails once and the turret does not rotate. According to the working principle of the turret, when the turret rotates, the turret is first floated by a hydraulic cylinder before it can rotate. Observe the phenomenon of failure, when manually pressing the turret rotation button, the turret did not respond, that is, the turret did not float, according to the electrical schematic, PLC output Y4.4 control relay K44 to control the solenoid valve, The solenoid valve controls the hydraulic cylinder to lift the turret, first through the PLC system status display function of the NC system to observe the status of Y4.4. When the manual turret rotation button is pressed, the status changes to “1”, and there is no problem. Continue The inspection found that the contacts of its controlled DC relay K44 were damaged and replaced with new ones. The turret resumed normal operation.

To use the PLC ladder diagram provided by the machine tool builder

Most of the failures of numerical control equipment are detected by the PLC device. The mechanism of PLC fault detection is to perform logic judgments based on various input and output states by running the PLC ladder diagram (program) for the specific machine tool. If a problem is found, an alarm is generated and an alarm message is generated on the display. Therefore, for some PLCs that generate alarms or some failures that do not have alarms, faults can be diagnosed by analyzing the ladder diagrams of the PLC. The ladder diagram display function of the NC system or the off-board programmer can be used to track the operation of ladder diagrams online. Diagnose the speed and accuracy of the fault.

For example, a CNC grinding machine adopting SIEMENS 810 system will fail once. After the machine is turned on, the machine tool does not return to the reference point and there is no fault display. Check the control panel to find that the indicator light of the indexing device is not bright. This machine tool is for safety reasons. The indexing device does not fall and the machine's feed axis cannot move. However, checking the indexing device has fallen without problems. According to the PLC ladder diagram provided by the machine tool manufacturer, the output of the PLC A7.3 falls on the indexing device on the control panel. Using the programmer to observe the operation of the ladder diagram online, it was found that F143.4 was not closed, resulting in the state of A7.3 being "0". F143.4 indicates that the workpiece indexing table is in the falling position. Continuing inspection showed that the status of F143.4 was "0" because input E13.2 was not closed. According to the electrical schematic diagram, the PLC input E13.2 is connected to the proximity switch 36PS13 which detects the falling of the workpiece indexing device. The indexing device is disassembled and the mechanical device is found to be problematic and the mechanical device driving the proximity switch cannot be driven. Therefore, E13. 2 can't be closed at all times. After the mechanical device is repaired, the machine tool resumes normal use.

A CNC milling machine adopting SIEMENS 3TT system. In the automatic cycle processing, the workpiece has been processed, the table is about to rotate, the spindle has not returned to the position. At this time, the second station spindle is stopped, the automatic cycle is interrupted, and an alarm is generated. F97 "SPINDLE1 SPEED NOT OK STATION2" and F98 "SPINDLE2 SPEED NOT OK STATION2" indicate that the two spindle speeds of the second station are not normal. However, no problem was found in the detection of the spindle system. In order to determine the cause of the fault, an external programmer is used to dynamically monitor the operation of the PLC ladder diagram and check according to the logical relationship. Finally, it is found that the workpiece clamping hydraulic pressure switch of the second station, E21.1 at the moment of its failure status The change takes place. The "1" signal momentarily changes to a "0" signal, which is followed by a "1" signal. E21.1 is connected to the pressure switch P21.1, and its state is changed to "0". The signal indicates the workpiece. No clamping, so the spindle stops and the automatic cycle stops. Since the clamping of the workpiece was performed by hydraulic pressure, the hydraulic system was inspected and the pressure was found to be somewhat unstable. The hydraulic system was adjusted to make it stable and the machine tool resumed normal work. This fault alarm message reflects the phenomenon of spindle stall caused by hydraulic instability, and does not reflect the root cause of hydraulic instability.

The above two methods are very effective for the detection of machine-side faults, because these faults are nothing more than detecting the damage of switches, relays, and solenoid valves or mechanical execution structure problems. These problems can basically be detected according to the PLC program by detecting their corresponding Status to confirm the point of failure. In the event of some system failures, sometimes the situation is more complex, and the following methods and detection principles can be used to quickly identify the failure point.

Using Exchange Method to Accurately Locate Faults

For some failures involving control systems, it is sometimes not easy to identify which part is problematic. To ensure that there is no further damage, replacing the suspected control board with a backup control board is an effective way to accurately locate the failure point. Sometimes interchange with the control board of the same type of control system on other machine tools will diagnose faults more quickly (in this case, ensure that good boards are not damaged).

For example, a CNC internal grinding machine using the US company BRYANT TEACHABLE III system has a failure. When the E axis moves, an alarm occurs: "E AXIS EXCESS FOLLOWING ERROR". The meaning of this alarm is that the following error of the E axis displacement is exceeded. Predetermined area. This alarm is generated on the E-axis and the E-axis cannot be referenced. Manually move the E-axis to observe the fault phenomenon. When the E-axis moves, the display shows the change of the E-axis displacement. When going from 0 to 14, the value on the screen suddenly jumps to 471. The same is true for the reverse movement. When it reaches -14, it also jumps to 471. At this time, the above alarm occurs and the feed stops. The analysis may be the problem of the E-axis position feedback system. This includes the E-axis encoder, connection cable, the position control board of the CNC system, and the CNC system CPU board. In order to find the problem as soon as possible, the principle of simple and complicated Replace the position control board and the fault is eliminated. This machine has another alarm on the X-axis. First replace the position control board. The fault has not been eliminated. Therefore, it is suspected that the possibility of damage to the encoder is relatively large. When the encoder is removed, the coupling is disconnected and replaced. Couplings, fault elimination.

It is necessary to check the faults based on the following principles: first, peripheral, internal, mechanical, electrical, first, complex, static, dynamic, first, public, and first, followed by software.

For more complex faults in numerical control equipment, especially when it comes to control systems, applying these principles simplifies the fault diagnosis process and avoids detours. Sometimes these principles should be used in combination so that the fault can be eliminated as soon as possible.

For example, a CNC grinding machine adopting SIEMENS 3 system can not find the reference point on the X-axis when returning to the reference point. Finally, an X-axis over-limit alarm appears. In the principle of first outside and inside, first check the zero point of the X-axis. Switch, normal no problem, observe the phenomenon of failure, after the X axis pressure limit switch, can also slow down; afterwards according to the principle of simple and complex first, check the position control board of the NC system, because the feedback hardware uses a grating ruler, so On the position control board, an EXE processing board is added to each of the X-axis and Y-axis. Firstly, the X-axis and Y-axis EXE boards are interchanged. At this time, the power-on test is performed, the X-axis is returned to the reference point, and the fault is transferred to the Y-axis. The reference point is not found on the Y-axis. The fault phenomenon is the same. This confirms that there is a problem with the EXE board and the replacement of the EXE board eliminates the fault.

For example, a CNC quenching machine adopting SIEMENS 810 system will fail once and start to return to the reference point. When the X axis is taken, alarm 1680 “SERVO ENABLE TRAV. AXIS X” will appear. This alarm will also appear on the manual X axis. The device was found to have an overload alarm indication. According to the Siemens instructions, the cause of this fault is excessive mechanical load, servo control power supply problems, servo motor failure, etc. In line with the principle of mechanical first and then electrical, firstly detect the X-axis sliding table and manually turn the X-axis sliding table. The discovery was very heavy, and it was definitely a mechanical problem. When the X-axis ball screw was dismantled and inspected, it was found that the ball screw had been rusted. The original seal of the slide was not good, the quenching liquid entered the ball screw, and the ball screw rusted. The replacement of the new ball screw was eliminated.

For example, a CNC grinder using SIEMENS 3 system, during a period of automatic processing, often stops the automatic cycle halfway, and alarm 114 "SERVO LOOP HARDWARE" appears, indicating a problem with the Y-axis servo system. According to the manual, it is the servo Measure feedback system problems. In order to further confirm the failure, in accordance with the principle of “quiet front and rearward”, after the machine tool returns to the reference point after starting the machine, the machine tool is not waiting for any operation. At this time, the machine tool does not display an alarm. Occasionally, this alarm occurs when automatic processing is performed. , And each time when the movement to about 190mm alarm occurs, because the X-axis and Y-axis position feedback of this machine uses a grating ruler, and the outgoing cable moves with the sliding table, so it is suspected that the cable often moves Some signal lines are broken and disconnected when the movement reaches a certain position. The inspection confirms this judgment. After the replacement of the new cable, the failure is eliminated. Another failure of this machine, this alarm appears when you stand still, so you suspect that there is a problem with the control board, swap the y-axis EXE board on the position control board with the X-axis, then start the test, the failure to On the X-axis, the original Y-axis EXE board is damaged, and the replacement of the new EXE board is eliminated.

The above describes several common methods for detecting faults in CNC equipment. There will be many other methods, but the most critical issue in solving numerical control equipment problems is to master the working principle of the CNC system and the working principle of the machine tool. When dealing with the problems that arise in numerical control equipment, it can be handy. Based on this, the faults are observed, thought, checked, analyzed, diagnosed, and finally eliminated. When the dresser moves to the center of the Z-axis slide, manual rotation fails. Judging from this phenomenon may be due to the fact that the encoder of the E-axis often moves back and forth along the Z-axis with the dresser and breaks some of the wires in the encoder cable, resulting in different positions of the cable with the dresser, at the edge of the Z-axis, The contact is good and there is no failure, but in the middle of the Z axis, some signal lines are disconnected and the feedback pulse is lost. Based on this judgment, we started the school line. At this time, it was found that there were indeed several bad wires. After finding the disconnected part, we welded the broken wire and took anti-folding measures. After restarting the test, the failure was eliminated and the machine tool resumed normal use. .

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