Brief analysis of common faults and treatment of CNC lathes

Simple CNC lathes are also called economical CNC lathes. They are developed on the basis of ordinary lathes. Its automatic control system is mainly composed of single-chip microcomputers. Through the control program, the longitudinal and transverse feed devices and tool change devices of the machine tool are controlled automatically. Processing of parts. Therefore, simple CNC lathes are still mechatronics equipment, so when a failure occurs, a comprehensive analysis must be made from the mechanical structure and electrical control of the machine tool.

　　 1. The stepper motor jitters and does not rotate after the program runs

　　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, you can replace the motor with no fault to verify whether the motor is in good condition. If the motor still does not work normally after changing the motor, it means that the control part is abnormal. You can focus on checking the high-power transistor on the drive board and the release diode of its protection component. In general, these two components

　　2, the workbench stops suddenly while the program is running

　　 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, you can first return the worktable to the origin and restart the processing program. If the worktable always stops 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 screw nut and the screw or the slide plate is too tight, whether there are foreign objects in the ball guide groove of the ball screw, whether the 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.

　　3, stepper motor loses steps at high speed

　　 It may be that the driving power supply voltage is reduced, which reduces the output torque of the stepping 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.

　　4, the tool does not return to zero at the end of program operation

　　 is generally a control system failure. When the tool is feeding or processing, the running speed of the stepper motor is low, and when the program returns to the zero point, a quick return is required. The stepping motor runs at high speed and adopts 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.

　　 5. Offside when the tool returns to the zero point

　　 is generally caused by too much resistance in the mechanical transmission system. When cutting feed, the tool post runs at low speed, is driven by low voltage, and the stepper 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 not returning 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.

　　 6. 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 runs 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 processed 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, and the tool deviates from the machining point during cutting, the above phenomenon will also be caused. At this time, check the knife holder locking device and the knife holder control box.

　　7, the local size error of the workpiece is large

　　 is mainly caused by the excessive clearance between the nut and the 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 screw clearance is compensated into the program, but it cannot be compensated in the wear section, resulting in the partial size of the workpiece exceeding the tolerance. The solution is to repair or replace the lead screw.

　　 8. The electric tool post cannot be positioned and rotated when changing tools

　　 This is because when the program requires a certain number of tools, the electric tool post is transferring the tools. When the tool is rotated to this number, 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, causing the above phenomenon. Just replace the Hall element of the knife.

　　9. During program execution, return to monitoring state and work stop

　　 is generally caused by a failure of the monitoring program or strong magnetic interference. The strong magnetic interference can be solved by grounding or shielding. 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.

　　10. Processing programs 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 process normally, it may be that the backup battery voltage is reduced or disconnected, causing the machining program in the data memory to not be maintained after the machine is powered off 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 microcontroller itself can be replaced.

　　 In short, a simple CNC lathe is composed of mechanical and electrical parts. After a fault occurs, it must be analyzed from both mechanical and electrical aspects to determine whether it is a mechanical or electrical fault, and then in-depth analysis to find the fault point.