Common Faults and Analysis of CNC Lathes

The simple CNC lathe is a more complex machine-electric integration equipment. Therefore, in the event of a failure, it needs to be comprehensively analyzed from the mechanical structure and electrical control of the machine tool.

The following analysis of its common failures.
1. After the start of the program, the stepper motor does not rotate. This phenomenon is usually caused by the phase failure of the stepper motor or its control system. There may be a failure of the stepper motor itself or a failure of its drive circuit.
First check the contact plug of the stepper motor for good contact. If the connector plug is in good contact, replace the one-phase motor with no fault. If the motor is operating normally after the motor is replaced, the original stepper motor is faulty. If the motor still fails to work after the motor is exchanged, the control part is not normal, and the high-power transistor on the driver board can be inspected with extreme protection element release diode. Under normal circumstances, the chances of these two components breaking are relatively large.
2.During the running of the machining program, the worktable suddenly stops running and the stepper motor does not turn. This phenomenon is generally caused by a mechanical failure, but it may also be due to a failure of the control system. At this time, the workbench can be returned to the original point and the machining program can be restarted. If the workbench is always stopped when it is running to a certain position, it should be caused by damage, deformation or jamming of foreign matter in a certain part of the transmission system. . First, power off the control system, and then turn the screw by hand. If the sensor feels excessive resistance at a certain point or even does not move at all, it proves that this position is faulty. Check whether the gap between the screw nut and the screw or the slide plate is too tight, whether there is foreign matter in the ball guide groove of the ball screw, whether the screw is bent or not, whether the flexible gear in the stepping motor speed reducer is loose or there is no foreign matter, stuck and so on. If there is no abnormality in the manual car, the control system is faulty. Check the following steps.
3.When the stepper motor runs normally at low speeds, the stepper motor loses its steps at high speed. This phenomenon may be caused by a decrease in the drive power supply voltage and a decrease in the output torque of the stepper motor. Therefore, it is important to check the drive power section. When the high-voltage first transistor is damaged, the high-voltage power supply cannot be turned on, so that the output torque of the stepping motor decreases at a high speed, resulting in lost steps. It may also be caused by a mechanical failure. Therefore, in the case of checking the unsuccessfulness of the above components, it is also necessary to inspect parts such as a screw, a nut, a slide plate, and a stepping motor speed reducer. When a component is bent, deformed, or there is a foreign matter stuck, the running resistance will increase. When running at low speed, the phenomenon is not obvious, but when running at high speed, it cannot completely overcome the running resistance and cause lost motion.
4.The end of the program operation, the tool returns less than zero, this phenomenon is generally caused by the control system failure. The tool requires low-speed operation during feed or during processing. At this time, the stepper motor runs at a low speed and is powered by a low-voltage power supply. When the program returns to zero, it is required to quickly retract. At this time, the stepper motor is required to run at a high speed and high-voltage drive power is used. Increase the output torque to ensure normal zero return. There is a switch transistor that controls the output of the high voltage drive power supply. When the switch transistor is damaged, the high voltage power supply will not turn on when the high speed return to zero, and the output torque of the stepping motor is not enough, causing a zero return loss, resulting in the tool not returning to the original point. This fault can be eliminated by replacing the switching transistor.
5.The end of the program operation, the offside of the tool when it returns to the origin, this phenomenon is generally caused by the mechanical resistance of the drive system is too large. In cutting feed, the tool carrier runs at a low speed, drives with a low voltage, and the stepper motor has a small operating torque, which is not enough to overcome the resistance and cause lost motion. When the zero stepping motor is driven by high voltage, the operation speed is high, the torque is large, and there is no strenuous resistance. The stepping motor runs normally without losing steps. This will cause the above phenomenon when it is lost and the return is normal. At this time, check whether there are any foreign matters on the transmission gear between the stepping motor reducer or the drive gear between the stepper motor and the lead screw, or whether the slide bar is too tight and the running resistance is increased.
6.It is all normal when the empty knife passes, but the dimensional error when processing the workpiece is very large. This phenomenon may be caused by the loose connection of the screw or the nut and the lathe. There is no knife resistance during the empty run, the slide is running normally, the resistance of the knife increases when machining the workpiece, the connection of the screw or the nut and the lathe is loose, causing the size of the workpiece to drift. Robust connection failure can be eliminated. Another possibility is caused by the electric knife holder. If the tool post cannot be automatically locked after tool change, the tool will deviate from the machining point when eating the knife, which will also cause the above phenomenon. At this time, check the tool holder locking device and the tool holder control box.
7.There is a large error in the local size of the workpiece. This phenomenon is mainly caused by the gap between the screw nut and the screw. Since the screw nut and the screw run for a long period of time, the gap in the section is increased. At the beginning of the program, the measured screw clearance is compensated to the program, but when the wear section cannot be compensated, the local size of the workpiece is exceeded . The solution is to repair or replace the screw.
8.The electric tool rest rotates when changing the tool and cannot be positioned. This is because when the program wants a certain number of tools, the electric tool holder rotates forward to select the tool. When it is rotated to the number tool, there is no response signal, and the tool holder rotates. Not only cannot be positioned. At this time, the Hall element on the electric knife holder should be inspected. When the Hall element is damaged, there is no detection signal output when the desired tool is in place, resulting in the above phenomenon. In this case, replace the Hall element of the number knife.
9.During the execution of the program, the computer returns to the monitoring state and all work cannot be performed. This phenomenon is generally caused by the failure of the monitoring program, and may also be caused by strong magnetic interference. For strong magnetic interference, grounding or shielding can be used. If the program is not executed or the program is started, it will not return to the monitoring state immediately after the instruction is executed. Normally, the monitoring program or the computer hardware is faulty. The suspect chip can be replaced, such as an off-chip program memory chip, a programmable interface chip or the microcontroller itself. Sometimes the off-chip data memory failure may also cause this phenomenon. If it cannot be solved, you can find the manufacturer to re-debug.
10. The processing program is often lost, causing the control system to not work properly in severe cases. If the control system loses power and the machining program is lost, and the machine tool is re-entered after the power is turned on, the machine tool can be processed normally. It may be that the backup battery voltage is reduced or disconnected, causing the processing program in the data memory to be turned off after the machine is powered off. Can't keep it lost. At this time, replace the spare battery. If the processing program is often partially or completely lost during processing, it is most likely caused by a data memory failure. At this time, the off-chip data memory or the microcontroller itself can be replaced. In short, a simple CNC lathe is composed of mechanical and electrical components. After a fault occurs, both mechanical and electrical aspects must be analyzed to determine whether it is a mechanical fault or an electrical fault. In-depth analysis is then performed to identify the fault point and handle the fault accurately and quickly. , improve machine tool maintenance efficiency.
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