Common CNC lathe common faults and countermeasures

The simple CNC lathe is also called economical CNC lathe. It is developed on the basis of ordinary lathe. The automatic control system is mainly composed of single-chip microcomputer. It controls the vertical and horizontal feeding device and tool change device of the machine tool through the control program. Processing of parts. Therefore, the simple CNC lathe is still a mechatronics device, so it should be comprehensively analyzed from the mechanical structure and electrical control of the machine tool in case of failure.

1. The stepper motor does not turn after the program runs.

This phenomenon is generally caused by the phase failure of the stepper motor or its control system. It is possible that the stepper motor itself may be malfunctioning or its drive circuit may be faulty. First check if the connection plug of the stepping motor is in good contact. If the contact is good, replace the motor with no fault to verify that the motor is good. If the motor still does not work normally after changing the motor, the control part is not normal. You can focus on checking the high-power transistor on the driver board and its protection component release diode.

2. The workbench suddenly stops during the running of the program.

This phenomenon is generally caused by mechanical failure, but it may also be caused by a failure of the control system. At this time, the workbench can be returned to the origin first, and the machining program can be restarted. If the workbench always stops when it is running to a certain position, it should be damaged or deformed by a certain part of the transmission system or stuck by foreign matter. First, power off, then check if the nut and screw gap or the slide strip is too tight, whether there is any foreign matter in the ball guide groove of the ball screw, whether the screw is bent or not, and whether the flexible gear in the stepper motor reducer is loose. Or foreign matter stuck. If there is no abnormality in the manual drive, it is a control system failure and should be checked according to fault 1.

3. Stepping motor lost at high speed

It may be that the drive power supply voltage is lowered, so that the stepper motor output torque is reduced. The drive power supply should be inspected. When the high-voltage switch transistor is damaged, the high-voltage power supply is turned on, and the stepper motor output torque is reduced and lost at high speed. It is also possible to have a mechanical failure somewhere, so check the screw, the nut, the slide, the stepper motor reducer, etc. When there are parts bent, deformed, or have foreign matter, the running resistance will increase, and the phenomenon will not be obvious when running at low speed, but the running resistance cannot be completely overcome at high speed.

4. The program does not return to zero when the program runs.

It is generally a control system failure. When the tool is being fed or machining, the stepper motor runs at a lower speed, and when the program returns to zero, it needs to be quickly retracted. The stepping motor runs at high speed and uses a high voltage drive power source to increase the output torque. A switch triode that controls the output of the high-voltage drive power supply, when the switch triode is damaged, the high-voltage power supply cannot be turned on when the high-speed return to the zero point, and the output torque of the stepping motor is not enough, so that the tool does not return to the zero point. Replace the switch transistor to eliminate it.

5. Offside when the tool returns to zero

Generally, the mechanical transmission system has too much resistance to running. When the cutting feed is in progress, the tool holder runs at a low speed, and the low voltage is driven. The stepping motor has a small running torque, which is insufficient to overcome the resistance and cause lost steps. When the zero is returned, the stepping motor is driven by high voltage, the running speed is high, the torque is large, and there is no cutting resistance, and the stepping motor does not lose steps. If you go back and lose when you go back, it will cause no return to zero. At this time, it can be checked whether there is any iron scrap foreign matter on the transmission gear between the stepping motor gearbox or the stepping motor and the lead screw, or whether the slide plate is too tight to increase the running resistance.

6. The workpiece size error after processing is very large

One possibility is that the screw or the nut is loosely connected to the lathe. When there is no knife resistance during idling, the slide is running normally. Due to the increased cutting resistance during processing, the screw or the connection between the screw and the lathe is loose, causing the workpiece to drift in size. When the connection is tightened, the fault can be eliminated. Another possibility is caused by the electric knife holder. If the tool holder cannot be automatically locked after the tool change, the tool will deviate from the machining point during cutting, which will also cause the above phenomenon. In this case, check the tool holder locking device and the tool holder control box.

7. The workpiece has a large dimensional error

Mainly due to excessive gap between the mother and the screw. Since the nut and the screw are operated in a certain section for a long time, the gap of the section is increased. At the beginning of the program, the measured 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.

8. The electric knife holder can't be positioned and rotated when changing the knife.

This is because when the program requires a certain knife, the electric tool holder is transferring the tool. When the tool is rotated to the tool, there is no response signal, so that the tool holder rotates and cannot be positioned. The Hall element on the motorized tool holder should be inspected. When the Hall element is damaged, the required tool will not be inspected when it is in place. ? The signal is output, which causes the above phenomenon. Replace the Hall element of the knife.

9. Return to monitoring status and stop working during program execution

Usually the monitoring program is faulty or caused by strong magnetic interference. For strong magnetic interference, grounding or shielding can be used. If you do not follow the program or start the program without pressing the execution command, immediately return to the monitoring state, generally the monitoring program or computer hardware failure, you can replace the suspect chip, such as off-chip program memory chip, programmable interface chip or microcontroller itself. Sometimes an off-chip data memory failure can also cause this phenomenon. Otherwise, I have to find a manufacturer to re-commission.

10. Processing procedures are often lost

If the machining program is lost after the control system is powered off, and the machining program is re-entered after the machine is powered on, the machine can be processed normally, the backup battery voltage may be reduced or disconnected, and the machining program in the data memory cannot be maintained after the machine is powered off. And lost. Replace the spare battery. If the machining program is often partially or completely lost during the machining process, it is most likely a data memory failure, in which case the off-chip data memory or the microcontroller itself can be replaced.

In short, the simple CNC lathe consists of two parts, mechanical and electrical. After the failure, it should be analyzed from both mechanical and electrical aspects to determine whether it is a mechanical fault or an electrical fault, and then analyze and find out the fault point.