Three CNC machine tool failure analysis and repair of various departments
3.1 CNC machine tool spindle servo system failure inspection and repair
The rapid development of the electronics industry, so that a variety of high integration, advanced performance of the speed drive endless, to the renewal of CNC machine tools to provide favorable conditions, but for the current large and medium-sized enterprises have not been able to transform all the old CNC machine tools. In reality, the repair of the old drive system is still a difficult task on the maintenance front. In the maintenance of the main circuit using a staggered selective contact loop-free reversible speed control drive system of the CNC lathe encountered in some of the faults and methods of treatment.
1. Trouble phenomenon: 1.8m horizontal car in the point of action, the disk swing back and forth.
Check: Measurement of the drive control system in the ± 20V DC regulated power supply ripple of 4V peak-to-peak value, greatly exceeding the specified range.
Analysis: In the amplifier circuit of the control system, the high and low-pass filters can filter out, such as: speedometer feedback, current feedback, voltage feedback in the various harmonics of the interference signal, but can not filter out the harmonic component of the DC power supply circuit of the system itself, because it exists in the whole system, these harmonics into the amplifier will make the amplifier blocked, so that the system produces a variety of abnormal phenomena. In the pointing state, because of the low speed of the motor, these harmonics have exceeded the voltage value at pointing, causing the system to oscillate, making the spindle disc swing back and forth, and once the harmonic signals are removed, the fault disappears immediately.
Processing: the voltage board in the 100MF and 1000MF filter capacitors replaced welded on the new capacitors, and measure the ripple is only a few millivolts will be installed after the power supply board, power on the test run, the fault is eliminated.
2. Trouble phenomenon: 5m vertical car in the operation of the processing of clunk sound, burn insurance.
Check: found 5FC5FG, 5RG5RQ positive and negative group all no pulse output (line see Figure 2), the measurement results, IC7 inverter is damaged, and found that the 1FG1FC output waveform than the other waveform amplitude is much lower.
Analysis: 5m riser main drive DC motor drive voltage provided by the thyristor full-control bridge anti-parallel rectifier circuit. 12-way trigger pulse, two disappeared, the other trigger pulse amplitude than the other normal trigger pulse to be shorter than one-third of the normal trigger pulse, when there is a clunking sound of gears, mistakenly thought that the hydraulic motor coupling joints at the problem, but a little while later the two-way fuse blown, the two-way fuse. In fact, some time before this failure has been burned twice the insurance, at that time only thought it was caused by the occasional grid instability, because after replacing the fuse, the fault is eliminated. Due to the low rotational speed of 5m vertical lathe machining operation, although the SCR rectifier circuit is a bridge rectifier, but when the trigger pulse in the line is lost and the amplitude is small at the same time, it will also cause the current to be discontinuous, and the output voltage will be unstable, thus making the speed of the motor unstable. The clunking sound at the beginning is actually a sign of unstable speed. Burning fuse failure due to discontinuous current can occur at any moment after running stop and normal operation.
Treatment: the amplifier T1 (another set of trigger circuit amplifier, function as T7 in Figure 2) and inverter IC7 replacement, the fault is eliminated.
3.2 Diagnosis of initial machine tool PLC failure
Diagnosis of initial machine tool PLC failure in order to protect the machine tool and maintenance convenience, PLC has the ability to display and detect machine tool failure. Once the fault occurs, the maintenance personnel will be able to determine the fault category according to the fault display number of the machine, to be eliminated. However, in the actual machining process, we found that sometimes the PLC at the same time to display several faults, they are caused by a fault caused by a chain of faults, eliminating the initial trigger faults, other faults alarms will disappear. However, from the machine tool PLC shows all the alarm faults, maintenance personnel do not know which fault is the initial trigger fault, maintenance personnel can only be fault by fault to check, which increases the difficulty of maintenance. Machine tool PLC initial fault diagnosis function, through the PLC program, accurately determine the initial fault alarm number. Maintenance, the first to rule out the initial fault, other triggered by the disappearance of the fault itself, which greatly facilitates the maintenance of the machine tool, improve the rapidity and accuracy of machine tool maintenance. 2 initial fault diagnosis principle design of the PLC program is not only to detect and display the various faults, but also the most critical initial fault automatically determine.
Initial fault diagnosis principle: 3 faults as an example, which set up three fault detection bits, respectively, R500.0, R510.0, R520.0; three initial fault detection bits for R500.2, R510.2, R520.2; F149.1 for the system reset signal. In the initial state, there is no alarm, the fault detection bits are all "0", the initial fault detection bits are all "0", and the reset signal F149.1 is "0". It is assumed that the second of the three faults occurs first. During the first cycle of the program scan, its corresponding fault detection bit R510.0 becomes "1", R500.2, R520.2, and F149.1 are initially "0", and the initial fault detection bit R510.2 becomes "1". The initial fault detection bit R510.2 becomes "1" and is held as "1" by self-locking until the fault is removed and the system reset signal is issued before the "1" state is released. During the second cycle of the program scan, R510.2 is held as "1", realizing the blocking of R500.1 and R520.1, so that even if another fault detection bit is "1" at this time, it cannot lead to the initial fault detection bit becoming "1". "1". By controlling this PLC program, the initial fault can be accurately determined from the many faults occurring at the same time. In the JCS018 CNC machine tool, a problem was encountered in which multiple faults occurred simultaneously, such as a tool change alarm and a hydraulic alarm at the same time. When repairing the machine, we first checked the hydraulic control part, and then we could confirm that the fault was in the tool change process. After checking, we realized that the tool change is powered by the hydraulic drive, and the PLC control program was designed to disconnect the hydraulic control at the same time as the alarm in order to prevent greater accidents when a tool change fault occurs, so that two alarms appeared at the time of the tool change fault. In order to follow the original machine design ideas, but can accurately send alarm messages, to the JCS018 CNC machine tool to add the initial fault check function. According to the previous program analysis, the tool change and hydraulic fault detection bits are R500.0 and R510.0 respectively, and the initial faults can be read out from the initial fault detection bits R500.2 and R510.2. When similar faults occur again on this machine, the initial fault can be quickly determined.
3.3 CNC equipment detection element failure and maintenance
The detection element is an important part of the servo system of the CNC machine tool, it plays a role in detecting the displacement and speed of the control axes, which feeds back the detected signals to form a closed-loop system. Measurement can be divided into direct measurement and indirect measurement: direct measurement is the linear displacement of the machine tool using linear detection element measurement, direct measurement of commonly used detection elements generally include: linear induction synchronizer, metering grating, magnetic scale laser interferometer. Indirect measurement is the linear displacement of the machine tool using rotary detection element measurement, indirect measurement of commonly used detection elements generally include: pulse encoder, resolver, circular induction synchronizer, angle grating and angle grating.
When the machine appears the following failure phenomenon, should consider whether it is caused by the failure of the detection element:
1. Mechanical oscillation (acceleration/deceleration):
(1) pulse encoder failure, this time to check the speed unit on the feedback line terminal voltage at certain points in the voltage drop, such as a drop in the pulse encoder is bad, replace the encoder.
(2) pulse encoder cross coupling may be damaged, resulting in shaft speed and the detected speed is not synchronized, replace the coupling.
(3) The speed generator is faulty, repair and replace the speed generator.
2. Mechanical storm (flying car):
In the case of checking the position control unit and speed control unit, you should check:
(1) whether the pulse encoder wiring is incorrect, check whether the encoder wiring is positive feedback, A phase and B phase is connected to the opposite.
(2) Whether the pulse encoder coupling is damaged, replace the coupling.
(3) Check whether the speed generator terminals are connected inversely and whether the excitation signal line is connected incorrectly.
3. spindle can not directional or directional not in place:
In checking the directional control circuit settings and adjustments, check the directional board, the spindle control printed circuit board adjustments at the same time, you should check whether the position detector (encoder) is bad, at this time, measure the encoder output waveform.
4. Coordinate axis vibration feed:
In checking the motor coil is short-circuited, mechanical feed screw and motor connection is good, check whether the entire servo system is stable, check whether the pulse encoding is good, coupling coupling is smooth and reliable, speed machine is reliable.
The detection element is an extremely precise and easy to damage the device, must pay attention to the following aspects, the correct use and maintenance.
1. Can not be subjected to strong vibration and friction to avoid damage to the code board, can not be contaminated by dust and oil, so as not to affect the normal signal output.
2. The temperature around the working environment can not be exceeded, the rated supply voltage must be satisfied in order to facilitate the normal operation of the integrated circuit piece.
3. To ensure that the feedback line resistance, capacitance is normal, to ensure normal signal transmission.
4. To prevent external power supply, noise interference, to ensure that the shielding is good, so as not to affect the feedback signal.
5. Installation should be correct, such as the encoder coupling shaft to be concentric to the right, to prevent the shaft exceeds the allowable load capacity to ensure that its performance is normal.
In short, in the failure of CNC equipment, the detection of component failure ratio is relatively high, as long as the correct use and strengthen the maintenance, in-depth analysis of the problems that arise, it will be able to reduce the failure rate, and can quickly solve the problem, to ensure the normal operation of the equipment.
3.4 CNC machine tool processing accuracy abnormal faults and maintenance
Production often encountered CNC machine tool processing accuracy abnormal faults. This kind of failure is hidden and difficult to diagnose. Causes of such failures are mainly five aspects: (1) the machine tool feed unit is altered or changed. (2) machine tool axis of the zero offset (NULL OFFSET) abnormal. (3) Axial backlash (BACKLASH) abnormal. (4) Abnormal motor operation status, i.e., electrical and control part failure. (5) Mechanical failure, such as screws, bearings, shaft couplings and other components. In addition, the preparation of the machining program, tool selection and human factors, may also lead to abnormal machining accuracy.
1. System parameters changed or altered
System parameters mainly include machine feed unit, zero offset, backlash and so on. For example, SIEMENS, FANUC numerical control system, its feed unit has metric and imperial two kinds. Machine tool repair process, often affecting the zero offset and gap changes, troubleshooting should be adjusted and modified in due course; on the other hand, due to severe mechanical wear and tear or loose connection may also cause changes in the measured value of the parameters, the need to do the corresponding modification of the parameters in order to meet the requirements of machine tool machining accuracy.
2. Mechanical failure caused by abnormal machining accuracy
A THM6350 horizontal machining center, using FANUC 0i-MA CNC system. Once in the process of milling turbine blades, suddenly found that the Z-axis feed abnormality, resulting in at least 1mm of cutting error amount (Z direction overcut). During the investigation, it was learned that the fault occurred suddenly. Machine tool in the point of action, MDI mode of operation under the normal operation of the axes, and back to the reference point is normal; without any alarm prompts, the possibility of hard failure of the electrical control part of the exclusion. Analysis that the main should be the following aspects of each check.
(1) check the machine tool accuracy is abnormal when running the machining program, especially the tool length compensation, machining coordinate system (G54 ~ G59) calibration and calculation.
(2) The Z-axis was repeatedly moved in the pointing mode, and after diagnosing its motion status by sight, touch, and sound, it was found that the sound of the Z-direction motion was abnormal, and the noise was more obvious especially in the fast pointing motion. From this judgment, there may be hidden problems in the mechanical aspect.
(3) Check the precision of the Z-axis of the machine tool. Move the Z-axis with a hand pulse generator, (the hand pulse multiplier is set at 1 × 100 stops, i.e., every step of change, the motor feed 0.1mm), with the percentage table to observe the movement of the Z-axis. In the unidirectional movement accuracy to maintain normal as the starting point of the forward movement, hand pulse every change in one step, the machine tool Z-axis movement of the actual distance d = d1 = d2 = d3 ... = 0.1mm, indicating that the motor is running well, positioning accuracy is good. And return to the machine tool on the change of the actual movement displacement, can be divided into four stages: ① machine tool movement distance d1> d=0.1mm (slope greater than 1); ② shown as d=0.1mm> d2> d3 (slope less than 1); ③ machine tool mechanism is not actually moving, showing the most standard backlash; ④ machine tool movement distance is equal to the value given by the hand pulse (slope is equal to 1), back to the machine tool's normal motion.
No matter how to compensate for the backlash (parameter 1851), its performance is characterized by: in addition to the ③ stage can be compensated for, the other segments of the change still exists, especially the ① stage of the serious impact on the machining accuracy of the machine tool. In the compensation, it was found that the larger the gap compensation, the larger the moving distance of the ① stage.
Analysis of the above checks that there are several possible causes: First, the motor has an abnormality; Second, there is a mechanical failure; Third, there is a certain gap. In order to further diagnose the fault, the motor and screw completely disengaged, respectively, the motor and mechanical parts of the inspection. Motor operation is normal; in the mechanical part of the diagnosis found that the hand disk screw, the return movement of the initial very obvious sense of vacancy. Under normal circumstances, the bearing should be able to feel the orderly and smooth movement. After dismantling and inspection found that its bearings have indeed been damaged, and there is a ball off. Replace the machine back to normal.
3. The machine's electrical parameters are not optimized for abnormal motor operation
A CNC vertical milling machine, configured with FANUC 0-MJ CNC system. In the process of machining, found that the X-axis accuracy is abnormal. Inspection found that the X-axis there is a certain gap, and the motor start-up phenomenon of instability. When touching the X-axis motor by hand, I feel that the motor jitter is more serious, and it is less obvious when starting and stopping, and more obvious in the JOG mode.
Analysis suggests that the cause of the failure of two points, one is the mechanical backlash is large; the second is the X-axis motor work abnormally. Utilizing the parameter function of the FANUC system, the motor is debugged. First of all, the existence of the gap is compensated; adjust the servo gain parameters and N pulse suppression function parameters, X-axis motor jitter elimination, machine tool machining accuracy back to normal.
4. machine position loop abnormal or improper control logic
A TH61140 boring and milling machine machining center, CNC system for FANUC 18i, full closed-loop control mode. In the process of machining, found that the machine tool Y-axis accuracy is abnormal, accuracy error minimum in about 0.006mm, the maximum error can reach 1.400mm. check, the machine tool has been set up in accordance with the requirements of the G54 workpiece coordinate system. In the MDI mode, the G54 coordinate system to run a section of the program that is "G90 G54 Y80 F100; M30;", to be the end of the machine tool operation after the display shows the value of the mechanical coordinates of "-1046.605", record the value. Then in the manual mode, the machine tool Y-axis point to any other position, again in the MDI mode to perform the above statements, to be stopped after the machine tool, found that the machine tool mechanical coordinates of the digital value of "-1046.992", with the first time after the implementation of the number of display value of the difference between the number compared to the value of 0.387mm. according to the same approach According to the same method, the Y-axis is moved to a different position, and the statement is executed repeatedly, and the digital display value is not stable. The Y-axis is detected with a percentage meter, and it is found that the actual error of the mechanical position is basically the same as the error shown on the digital display, which is considered to be the cause of the fault for the Y-axis repetitive positioning error is too large. Y-axis backlash and positioning accuracy for careful inspection, re-compensation, are no effect. Therefore, suspect that the scale and system parameters and other problems, but why produce such a large error, but there is no corresponding alarm information? Further inspection found that the axis for the vertical direction of the axis, when the Y-axis is released, the spindle box downward drop, resulting in overdifference.
The machine's PLC logic control program has been modified, that is, when the Y-axis is loosened, the first Y-axis enables the loading, and then the Y-axis is loosened; and in the clamping, the first axis clamping, and then the Y-axis enables the deletion. Adjustment of the machine tool failure can be solved.
Four CNC machine tool maintenance
CNC system is the core component of the CNC machine tool, therefore, CNC machine tool maintenance is mainly the maintenance of the CNC system. CNC system after a long period of time, the performance of electronic components to aging and even damage, some mechanical parts are more so, in order to maximize the life of components and parts of the wear cycle, to prevent a variety of failures, especially the occurrence of malicious accidents, it is necessary to carry out routine maintenance of the CNC system. To summarize, pay attention to the following aspects.
(1) the development of routine maintenance of the CNC system regulations
According to the characteristics of the various components, to determine the respective maintenance regulations. Such as the explicit provisions of what needs to be cleaned up every day (such as CNC system input / output unit - photoelectric reader clean, check whether the mechanical structure of the part is well lubricated, etc.), which parts to be regularly inspected or replaced (such as DC servomotor brushes and commutator should be inspected once a month).
(2) should be as little as possible to open the door of the CNC cabinet and strong electrical cabinet
Because the air in the machine shop generally contains oil mist, dust and even metal powder. Once they fall in the CNC system within the printed circuit or electrical parts, easy to cause a decrease in insulation resistance between components, and even lead to components and printed circuit damage. Some users in the summer in order to make the CNC system overload long-term work, open the door of the CNC cabinet to heat, which is a kind of never desirable method, and ultimately will lead to accelerated damage to the CNC system. The correct method is to reduce the external ambient temperature of the CNC system. Therefore, there should be a strict regulation, unless the necessary adjustments and maintenance, not allowed to open the cabinet door, not to mention the use of open cabinet door.
(3) regular cleaning of the CNC cabinet cooling and ventilation system
Should be checked every day on the CNC system cabinet on the various cooling fans work properly, should be depending on the working environment conditions, every six months or every quarter to check the duct filter whether there is a clogging phenomenon. If too much dust accumulates on the filter, it needs to be cleaned up in time, otherwise it will cause high temperature inside the CNC system cabinet (generally not allowed to exceed 55 ℃), resulting in overheating alarms or unreliable work of the CNC system.
(4) often monitor the network voltage used by the CNC system
FANUC produced by the CNC system, allowing the network voltage in the rated value of 85% to 110% of the range of fluctuations. If this range is exceeded, the system will not work properly and may even cause damage to the internal electronic components of the CNC.
(5) Regular replacement of batteries for memory
There are two types of memories within the CNCs manufactured by FANUC:
(a) Magnetic bubble memory that does not require batteries for retention.
(b) CMOS RAM devices that require battery retention, in order to maintain the stored content during the period when the CNC is not powered on, there is an internal rechargeable battery maintenance circuit, when the CNC is powered on, the +5V power supply is supplied to the CMOS RAM through a diode and the rechargeable battery is charged; when the CNC cuts off the power supply, it is changed to a battery to maintain the information in the CMOS RAM. CMOS RAM information, in general, even if the battery has not yet failed, the battery should be replaced once a year in order to ensure that the system can work properly. In addition, it must be noted that the battery replacement should be carried out in the state of power supply of the CNC system.
6. CNC system maintenance when not in use for a long time
In order to improve the utilization rate of the CNC system and reduce the failure of the CNC system, CNC machine tools should be used at full capacity, rather than long-term inactivity, due to some reason, resulting in long-term inactivity of the CNC system, in order to avoid damage to the CNC system, the need to pay attention to the following two points:
(1) to often give the CNC system Energized, especially in the rainy season with high ambient humidity should be more so, in the case of the machine tool is locked motionless (i.e., servo motor does not rotate), so that the CNC system is running empty. Use the heat of the electrical components themselves to dissipate the moisture in the CNC system to ensure stable and reliable performance of electronic devices, practice has proved that in areas with high air humidity, often energized is an effective measure to reduce the failure rate.
(2) CNC machine tools using DC feed servo drive and DC spindle servo drive, the brush should be removed from the DC motor, so as not to corrode the surface of the commutator due to chemical corrosion, resulting in deterioration of commutation performance, or even damage to the entire motor.
References
1 Zhang Chaoying, Xie Fuchun, eds. CNC Programming Technology. Beijing: Chemical Industry Press, 2004
2 Zhang Chaoying, Luo Keji ed. Comprehensive practical training of CNC machining technology. Beijing: machinery industry press, 2003
3 CNC technology training series tutorial. Century star CNC system programming \ operation manual. Huazhong CNC. 2001
4 National CNC training network Tianjin sub-center ed. CNC Programming. Beijing: Machinery Industry Press, 1997
Acknowledgements
Four years of study in this season will soon draw a period, but in my life is just a comma, I will face the beginning of another journey. Four, with the strong support of friends and family, go hard but also harvest full bag, in the paper is about to go to press, thinking a thousand thoughts, the mood can not be calm for a long time. Great men, celebrities for my worship, but I'm more eager to dedicate my respect and praise to an ordinary people, my mentor. I am not your most outstanding students, but you are my most respected teacher. You are rigorous, knowledgeable, deep thinking, broad vision, for me to create a good spiritual atmosphere. Teach a man to fish is not as good as teach a man to fish, to be in the middle of it, influence, implicitly, so that I not only accepted a new concept of thought, set up a grand academic goals, and comprehend the basic way of thinking, from the selection of thesis topics to the guidance of the thesis writing, through your careful instruction, and then after thinking about the comprehension, often let me have a "mountain after mountain of doubt, and then a village in the dark, and then a village in the dark, and then a village in the dark. I'm not sure if I'm going to be able to do this, but I'm sure I'll be able to do it again.
Thanks to my mom and dad, how can I deceive the grass, said the back of the tree, the grace of parenting, no return, you will always be healthy and happy is my biggest wish. In the dissertation is about to be completed, my mood can not be calm, from the beginning of the subject to the successful completion of the dissertation, how many honorable teachers, classmates, friends gave me wordless help, here please accept my sincere thanks!
At the same time, I would like to thank the college for providing me with a good environment to do my graduation design.
Last but not least, I would like to thank all my teachers, friends and classmates who have helped me in my graduation design, as well as the authors of the books that I have cited or referred to in my design.