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Fault diagnosis and repair of CNC lathes
  • First, the tool changer failure

CNC lathe tool change process in general: After receiving ATC ATC motor signals, driven by the worm gear rotating turret, tool signal emitted by the Hall element, CNC system and then use this signal to be compared with the target value judgment The tool is in place. After changing the knife in place, tighten the turret motor reversal. Maintenance NC I encountered during the following symptoms.

Fault 1: a six-cutter CNC lathes, tool change all pockets are found, a few weeks after the cessation of the rotating turret, and numerical control system displays the tool change warning: ATC timeout or no signal input.
Finding fault analysis: For this fault, you can still rule out mechanical failure, caused by an electrical fault to blame. The failure of the electrical generating the following reasons: a magnetic element off; two of the six Hall elements while all the damage; 3 power and signal lines of the Hall element of open results in no output voltage signal.... The third reason which most likely. Therefore recruited circuit, use a multimeter to the supply line of the Hall element electrical lines to be checked. The results showed that: turret detection circuit terminal block 24V supply voltage is 0V, the other lines were normal. Along the line as a clue to find, find leads from 24V electrical cabinet thread off, still no response after connecting. Judging should be the line break caused by a fault.
Solution: replace the broken wire using the same specifications, troubleshooting.

Failure II: a four-cutter lathe, cutter One occurrence is not found, a normal symptom of other potential energy knife tool change.
Failure Analysis: Since there is only One could not find a knife cutter, you can eliminate the problem of mechanical transmission aspects that determine the electrical aspects of the fault. The cutter may be a Hall element and its surrounding line problems, causing the cutter signal can not be sent to the PLC. After use a multimeter to check the control circuit diagram found: 24V power supply on the 1st normal cutter Hall element, GND line is normal, T1 signal line is normal. Therefore it can be concluded that the Hall element is damaged causing the tool signal can not be issued.
Workaround: After the replacement of the Hall element troubleshooting, One knife normally found.

Failure3: one with FANUC-0imate system Dalian Machine Tool Plant six cutter lathe, tool selection normal but when selected cutter not normally locked in place. Alarm systems: ATC timeout.
Finding fault analysis: normal turret tool selection, forward normal, that is not the reverse lock. Description normal worm gear, for an initial electrical wiring problems. Turret on the machine control electrical schematics, found the reverse lock the tool in place by a position switch signal is sent to the control, this switch is not a problem that is around the line? In order to confirm the cause of the failure, open top turret cover and side cover, use a multimeter to check the line referring to the circuit diagram, found no open and short circuit, reverse turret by manually pressing the lock position switch, observe the ladder display signal input, so far ruled out electrical wiring problems. Inference may be a stopper movement is not in place, position micro switch is not action. Then re-tool change time to look, and found: not really stop the movement in place. So the stopper bolt tightening, try a normal tool change. Pulls a knife, the original fault has emerged, also found that the worm end of the sleeve to slip and climb phenomenon. Is it caused by a locked position when the motor reversing switch stopper is not in place? So the axial positioning of the sleeve has been processed, the turret roof installed. The results turret lock normal.
Workaround: sleeve axial positioning troubleshooting.
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  • Second, the power supply failure


The machine when the machine is running lights suddenly does not shine, the machine operator panel lights do not light, the system power supply is normal, while the emergency stop alarm system, and the spindle is no signal to the police. Re-power the fault persists after the shutdown.
Failure analysis of inspection: The operator then asked, no illegal operations, excluding man-made causes, you can rule out mechanical reasons, it should be caused by an electrical fault. The machine's electrical schematics show that these areas are and 24V power loss related to, and the machine has two power supply, one I / O interface power and the other for the system power. Loss of power regions and I / O interface related, then open the electrical cabinet observed I / O interface power supply indicator fails to light up, indicating that the power supply is not working or damaged. From the power supply works know a current regulated power supply circuit and overload protection function, when the power short circuit or overload the power supply output is automatically shut off to protect the power supply circuit is not damaged. So try to remove the power supply output to the load line, and found again after the power supply indicator light. This shows that the power supply itself is not damaged. By analyzing the power that the I / O interface power, the load is not, it will not overload phenomenon, it should be the output circuit short-circuit fault. Were found to have a 24V + output cable connector is exposed from the insulating tape and exposed to the machine bed along the output line number. The reason is obvious: As the line-to-ground short circuit occurs with the machine, causing the power supply is in a state of self-protection, making the operation panel and some I / O interface relay power to stop, leading to more failures. As for 24V inverter alarm signal may not be in place alarm.
Solution: Use insulating tape to wrap the joints again, turn on the power again all troubleshooting, alarm reset lights are bright.

  • Third, the system program lock failure


A CNC lathe with FANUC-0i-mate system, you can not enter a value for knives and other parameters, you can not edit the program, accompanied by the police.
Failure analysis of inspection: this phenomenon first thought of procedural protection switch, found by comparing the normal system: the system is locked phenomena. It is believed the system lock switch is broken, but after a short, still can not solve the problem. By observing system failure X56 input ladder found no signal input, the input circuit breaker to illustrate this article. Along this line number use a multimeter to check and found the back of the operation panel selected axis joints thread off switch, causing the line can not input signal to PLC logic is incorrect, only the failure to occur.
The solution: use a soldering iron to solder well off the thread again, alarm reset, parameter input is normal, the fault disappears.

  • Fourth.Conclusion


Maintenance above case can be ruled out as a reference for similar failures. In general, for any failure, the first is based on the phenomenon, according to the principle to determine the point of failure, analyze every possibility, such as a switch, a cable connector, a screw will be the cause of the fault will be the reference to the previous operation, maintenance
history analysis, can help to narrow the Look, help to improve the efficiency of maintenance

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