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Brief Analysis of Common Faults and Treatment of NC Lathe


Simple NC lathe, also known as economical NC lathe, is developed on the basis of ordinary lathe. Its automatic control system is mainly composed of single-chip computer. Through the control program, the longitudinal and horizontal feeding device and tool changing device of the machine tool are controlled to automatically complete the processing of parts. Therefore, the simple NC lathe is still a mechatronics equipment, so in the event of failure, it should be analyzed comprehensively from the mechanical structure and electrical control of the machine tool. 1. After the program runs, the jitter of the stepper motor does not turn. This phenomenon is usually caused by the phase breaking of the stepper motor or its control system. It may be the fault of the stepping motor itself or the fault of its driving circuit. Firstly, check whether the connection plug of stepper motor is in good contact. If it is in good contact, the motor without fault can be replaced to verify whether the motor is in good condition. If the motor can't work properly after switching, it shows that the control part of the motor is abnormal. The high-power triode on the drive board and the release diode of its protective element can be checked. Generally, the sudden stop of the workbench in the operation of the two elements 2 and the program is usually caused by mechanical failure, but it may also be caused by the failure of the control system. At this time, the workbench can be returned to the origin and the processing program can be restarted. If the workbench always stops at a certain position, it should be damaged, deformed or stuck by foreign bodies in a certain part of the transmission system. First power off, then check whether the gap between the screw mother and the screw or the slide insert is too tight, whether there is foreign body in the ball guide groove of the ball screw, whether the screw has bending deformation, whether the flexible gear in the stepping motor reducer is loose or the foreign body is stuck, etc. If there is no abnormality in manual turning, it is the fault of control system, which should be checked according to fault 1. 3. The step loss of stepper motor at high speed may be due to the decrease of driving power supply voltage, which reduces the output torque of stepper motor. The driving power supply should be inspected. When the high-voltage switch transistor is damaged, the high-voltage power supply is connected by the sky method, and the output torque of the stepper motor decreases and the step is lost at high speed. It may also be a mechanical failure, so we should also check the screw, screw mother, slide, stepping motor reducer and so on. When parts are bent, deformed or foreign bodies, the operating resistance will increase. The phenomenon is not obvious at low speed, but it can not be completely overcome at high speed. 4. When the program runs out, the tool does not return to zero, which is usually the fault of the control system. When the tool is feeding or processing, the stepping motor runs at a low speed, while when the program returns to zero, it requires a quick return. Stepper motor runs at high speed and uses high voltage driving power supply to increase the output torque. There is a switch triode which controls the output of the high-voltage driving power supply. When the switch triode is damaged, the high-voltage power supply can not be opened when the high-speed return to zero, and the output torque of the stepping motor is not enough, so that the tool does not return to zero. The switch triode can be replaced to eliminate it. 5. When the cutter returns to zero, offside is usually caused by too much resistance of the mechanical transmission system. When cutting feed, the tool holder runs at low speed, drives at low voltage, and the stepping motor runs at low torque, which is insufficient to overcome the resistance and cause step loss. When returning to zero, the stepper motor is driven by high voltage, with high speed, high torque, no cutting resistance and no step loss. In this way, when you lose your step and return to normal, you will not return to zero. At this time, it can be checked whether there are iron scraps on the transmission gears between the stepper motor and the screw, or whether the slider inserts are too tight to increase the running resistance, etc. 6. The dimension error of the workpiece after processing is very large. One possibility is that the connection between the screw or screw mother and the lathe is loose. There is no knife resistance during empty running, and the sliding plate runs normally. Because of the increase of cutting resistance, the connection between the screw or screw mother and the lathe is loosened, resulting in the size drift of the workpiece. Tighten the connection, and the fault can be eliminated. Another possibility is the electric tool holder. If the tool holder can not be locked automatically, the tool will deviate from the processing point during cutting, which will also cause the above phenomenon. At this time, the tool holder locking device and the tool holder control box should be checked. 7. The large part size error of the workpiece is mainly caused by the excessive gap between the screw nut and the lead screw. Because the screw mother and the screw run in a certain section for a long time, the gap of the section increases. At the beginning of the program, the measured clearance of the lead screw is compensated to the program, but it can not be compensated in the wear section, so that the part size of the workpiece is out of tolerance. The solution is to repair or replace the lead screw. 8. Electric tool holder can't locate and rotate when changing tool. This is not only because when the program wants a certain tool, the electric tool holder is turning the tool. When turning to the tool, there is no response signal, so that the tool holder rotates continuously and can't locate. Hall elements on the electric tool holder should be inspected. When Hall element is damaged, the signal output will not be detected when the tool is in place, thus causing the above phenomenon. The Hall element of the knife can be replaced. 9. When the program returns to the monitoring state during execution and stops working, it is usually caused by the malfunction 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 started according to the execution instructions, it will return to the monitoring status immediately. Generally, when the monitoring program or computer hardware fails, suspicious chips can be replaced, such as the off-chip program memory chip, the programmable interface chip or the single chip computer itself. Sometimes the failure of off-chip data memory can also cause this phenomenon. Otherwise, we have to find the manufacturer to re-adjust. 10. Processing programs are often lost if the control system loses processing programs after power failure, and when the machine tool is powered up and re-input processing programs, the machine tool can process normally. It may be that the backup battery voltage is reduced or disconnected, resulting in the loss of processing programs in data memory after power failure of the machine tool. Replace the spare battery. If the processing program is often partially or totally lost in the process of processing, it is very likely that the data memory will fail. At this time, the off-chip data memory or the microcontroller itself can be replaced. In a word, the simple NC lathe is composed of mechanical and electrical parts. After failure, it should be analyzed from mechanical and electrical aspects to determine whether it is mechanical or electrical fault, and then find out the fault point through in-depth analysis.