What are the common faults of CNC lathes?

What are the common faults of CNC lathes

Since we have been in CNC machining for a long time, we will encounter various mechanical failures, but if you say that a small factory, it is impossible to hire a professional master to stay in the factory for a long time, so this time is needed We deal with some faults that we can handle by ourselves. If the faults are too serious, we still need a professional master to deal with them.

Because the current CNC lathes can already be mechatronics equipment, it is necessary to comprehensively analyze the mechanical structure and electrical control of the CNC lathe in the event of a failure. Then go to deal with the fault.

One: The CNC lathe workbench stops suddenly

This phenomenon is generally caused by a mechanical failure, but it may also be caused by a failure of the control system. At this time, the worktable can be returned to the origin first, and the processing program can be restarted. If the worktable is always stopped when it runs to a certain position, it should be that a certain part of the transmission system is damaged, deformed or blocked by foreign objects. Turn off the power first, and then check whether the gap between the nut and the lead screw or the slide plate is too tight, whether there are foreign objects in the ball guide groove of the ball screw, whether the lead screw is bent or deformed, and whether the flexible gear in the stepper motor reducer is loose Or foreign matter is stuck, etc. If there is no abnormality in the manual cranking, it means that the control system is faulty and should be checked according to fault 1.

Two: CNC lathe motor jitter does not rotate

This phenomenon is generally caused by a phase failure of the stepper motor or its control system. It may be a failure of the stepper motor itself or a failure of its drive circuit. First check whether the connecting plug of the stepper motor is in good contact. If the contact is good, the motor without fault can be replaced to verify whether the motor is in good condition. If the motor still fails to work normally after changing the motor, it means that the control part is abnormal. You can focus on checking the high-power triode on the drive board and its protective component release diode.

3: The tool does not return to the zero point at the end of the program operation

Generally it is a control system failure. When the tool is in feed or in processing, the stepper motor runs at a low speed, and when the program returns to the zero point, it is required to return quickly. The stepping motor runs at high speed and uses high-voltage drive power to increase the output torque. There is a switching Transistor that controls the output of the high-voltage drive power supply. When the switching transistor is damaged, the high-voltage power supply cannot be turned on during the high-speed zero return, and the output torque of the stepping motor is not enough, so that the tool does not return to the zero point. It can be eliminated by replacing the switching transistor.

4: Stepper motor loses steps at high speed

It may be that the drive power supply voltage is reduced, which reduces the output torque of the stepper motor. The driving power supply part should be checked. When the high-voltage switch transistor is damaged, the high-voltage power supply is turned on, and the output torque of the stepping motor decreases at high speed and loses steps. There may also be a mechanical failure, so you should also check the lead screw, nut, slide, stepper motor reducer, etc. When parts are bent, deformed, or there are foreign objects, the running resistance will increase. The phenomenon is not obvious when running at low speed, but the running resistance cannot be completely overcome at high speed.

Five: Offside when the tool returns to the zero point

Generally it is caused by too much running resistance of the mechanical transmission system. When cutting feed, the tool post runs at low speed, is driven by low voltage, and the stepping motor has a small running torque, which is not enough to overcome resistance and cause lost steps. When returning to zero, the stepper motor is driven by high voltage, with high running speed, large torque, and no cutting resistance, so the stepper motor does not lose steps. In this way, losing steps when going and returning to normal will cause the phenomenon of non-return to zero. At this time, you can check whether there is any iron filings or foreign matter on the transmission gear in the stepper motor reducer or the transmission gear between the stepper motor and the lead screw, or whether the slide plate is too tight to increase the running resistance, etc.

Six: The size of the workpiece after processing has a large error

One possibility is that the screw or nut is loosely connected to the lathe. There is no tool resistance during idling, and the slide plate operates normally. Due to the increase in cutting resistance during processing, the connection between the lead screw or nut and the lathe becomes loose, causing the size of the workpiece to drift. The fault can be eliminated by tightening the connection part. Another possibility is caused by the electric tool post. If the tool post cannot be automatically locked after the tool is changed, the tool deviates from the machining point during cutting, which may also cause the above phenomenon. At this time, check the knife holder locking device and the knife holder control box.

Seven: The local size error of the workpiece is large

Mainly due to the excessive clearance between the nut and the lead screw. Because the screw nut and the lead screw run in a certain section for a long time, the gap between this section is increased. At the beginning of the program, the measured lead screw clearance is compensated into the program, but it cannot be compensated in the wear section, so that the partial size of the workpiece is out of tolerance. The solution is to repair or replace the lead screw.

Eight: The electric tool post cannot be positioned and rotated when changing the tool

This is because when the program asks for a certain tool, the electric tool post is transferring the tool. When the tool is rotated to the tool, there is no response signal, so that the tool post cannot stop rotating and cannot be positioned. The Hall element on the electric tool post should be checked. When the Hall element is damaged, the signal output will not be detected when the tool is in place, which will cause the above phenomenon. Just replace the Hall element of the knife.

Nine: CNC machining programs are often lost

If the machining program is lost after the control system is powered off, and the machining program is re-input after the CNC lathe is powered on, the CNC lathe can process normally, it may be that the backup battery voltage is reduced or disconnected, causing the machining program in the data memory to be powered off on the CNC lathe It cannot be kept and lost. Just replace the backup battery. If the processing program is often partly or completely lost during processing, it is most likely that the data memory is faulty. At this time, the off-chip data memory or the single-chip microcomputer itself can be replaced.

Ten: Return to monitoring state and work stop during program execution

It is usually caused by a failure of the monitoring program or strong magnetic interference. For strong magnetic interference, grounding or shielding can be used to solve the problem. If the program is not executed or the execution instruction is not followed when the program is started, it will immediately return to the monitoring state. Generally, the monitoring program or computer hardware fails, and the suspicious chip can be replaced, such as the off-chip program memory chip, the programmable interface chip or the single-chip microcomputer itself. Sometimes an off-chip data memory failure can also cause this phenomenon. Otherwise, we have to find the manufacturer to re-debug.