Faults and maintenance cases of NC Machining Cente

2022-05-25
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NC machining center failure and maintenance case

in order to give full play to the due efficacy of NC machining center, the normal operation of NC machine tool is very key. In case of problems in NC equipment, it is particularly important to eliminate the faults in time. However, for the maintenance personnel who have little contact with the machining center, when the machine tool fails, they often don't know where to start, delaying the maintenance time. At this time, if we can make use of the self diagnosis function of the NC system itself, it will be of great help to our maintenance. At the same time, as maintenance personnel, when the CNC machine tool breaks down, they should first learn from the operator about the symptoms of the failure, the program and time of the failure, and whether the operation method is appropriate. Only the blood provided by illegal financial institutions can find the problems in time, so as to avoid excessive hidden dangers and losses. Secondly, check whether the button, fuse, wiring terminal and other components are tightened during wiring, whether the aviation plug and socket are tightened, whether the plug on the circuit board is tightened, whether each toggle switch and operation mode are correct, etc. Moreover, according to the characteristics that mechanical failure is easy to detect, when the machine tool overload and overheating alarm occurs, first check whether the insert of the sliding plate is too tight, and the friction between the sliding plate and the bed guide rail increases, so as to make the motor difficult to operate, and whether the ball screw and the bracket are concentric. For example, if the ball in the lead screw is worn, resulting in the lead screw being too tight, the motor can also be overloaded and overheated, resulting in electrical failure. Therefore, in the normal maintenance of CNC machine tools, we should do a good job in the above aspects and cooperate with each other. We can avoid detours, eliminate faults quickly, reduce the downtime of CNC machine tools, improve the utilization rate of CNC machine tools, and enable the company to carry out production smoothly and complete the production progress

next, combined with my own maintenance methods and experience in CNC machine tools, I will introduce several representative fault examples to you for reference

there are two JCS-018 vertical machining centers produced by Beijing Machine Tool Research Institute. The system adopts the full-function CNC machine tool of Japan fanvc-besk7m system. The 7m system is controlled by 16 bit microprocessor. The servo driving unit is a large inertia DC servo motor. The main motor is driven by three-phase full wave controllable silicon non circulating circuit, the resolver is used as the position detection element, and the tachogenerator forms speed feedback, During the operation of the machine tool, many abnormal alarms and abnormal phenomena have occurred. We quickly eliminate the faults according to the alarm answer number displayed by CRT to ensure the normal operation of the machine tool

example 1: fault phenomenon: CRT displays 05 # 07 alarm

fault inspection and analysis: check the maintenance manual of anvc-besk7m system of F hardness tester. 05 # is the emergency stop signal on, and 07 # is the speed control unit alarm. From the maintenance manual, 05 alarm is caused by emergency stop, so it is easier to eliminate the fault. For example, whether the emergency stop switch is pressed, whether the overtravel limit of X, y and Z axes is pressed, and the inspection is normal, press the clear key, 05 # disappears, 07 # alarm still exists, raise your hand and 05 # appears again. After analysis, it is considered that 07 alarm is the key. After it is abnormal, emergency shutdown is adopted to protect it, so that 05 and 07 alarms appear at the same time. For 07 alarm, it is pointed out in the maintenance manual that the speed control unit of any axis is in the alarm condition, or the contactor of the motor power line is open circuit. The following reasons can be considered for this alarm: ① motor overload. ② The speed controlled power transformer is overheated. ③ The power fuse of the speed control power transformer is broken. ④ The fuse of the speed control unit is broken. ⑤ On the power input bracket of the control part, the contact between zmgin and 2 points of the wiring base is open circuit. ⑥ On the power input bracket of the control part, the AC 100V fuse (F5) is disconnected. ⑦ The signal cable connecting the speed control unit and the control section is disconnected or detached from the plug. ⑧ Due to the alarm of some other servo mechanism, the contactor (MCC) on the motor power line is disconnected

analysis: check one by one, easy before difficult. Item a: check whether the thermal element element is abnormal with the meter, and the 05 # and 07 # alarms are generated due to the non movement of X axis, Y axis, Z axis and each axis of the tool magazine after NC is turned on, so item a is No. Item B: touch the transformer by hand without overheating. Check that oh1 and oh2 are normal with a multimeter, and check the insurance in C, D and f without breaking. Item e: check the contact between zmgin and 2 with a multimeter, and the result is normal. Therefore, the contradiction is concentrated on G and h. check with the resistance gear of the multimeter and find that the y-axis speed control unit board is abnormal. Because the motor has an overheat protection, each shaft is connected in series with each other in this electrical wiring, and there should be 24V voltage. The process is 24V → X-axis overheat protection normally closed → speed control unit → Y-axis overheat protection normally closed → speed control unit → z-axis overheat protection normally closed → z-axis speed control unit → tool holder overheat protection normally closed → magazine speed control unit → NC is normal. When it is checked that Y-axis overheat protection normally closed → y-axis speed control unit → z-axis overheat protection normally closed, there is no connection and open circuit, so check the y-axis speed control board and find it by line, It was found that a short-circuit bar was open circuit, which was caused by greasy and dirty. It was plugged in after cleaning and turned on normally

example 2. Fault phenomenon: the spindle cannot be oriented, and the load expression red zone 08 alarm

fault inspection and analysis: check the machine tool maintenance manual. The 08 alarm is the spindle positioning fault. According to the requirements of the manual, we open the machine tool power cabinet and find 7 light-emitting diodes (6 green and 1 red) on the AC spindle control circuit board, These seven indicator lights (from left to right) respectively indicate ① orientation command ② low speed gear ③ track peak detection ④ deceleration command ⑤ fine positioning ③ positioning completion ⑤ test method (① one ③ is green, ① red) when the machine tool is oriented, observe the conditions of these seven command lights as follows: 1 light is on, 3 and 5 lights are on, which indicates that the positioning command has been issued, the track peak has been detected, the positioning signal has been detected, but the system cannot complete positioning, The main shaft is still running at a low speed, so the 3 and 5 lights are constantly on. From the above analysis, we suspect that the amplifier on the main shaft box is the problem. Open the main shaft protective cover and check the magnification. At the same time, we found that the tool clamping oil cylinder hose on the main shaft is twisted and wound on the main shaft. Analyzing this abnormal phenomenon, we judge that the hose is coiled, resulting in the deviation of the positioning of the main shaft, The composite technology 8 alarm of D graphene based electrode material was caused, and the tube was unloaded

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