CNC machine tools are the key to modern manufacturing equipment, to a large extent, influence the development of equipment manufacturing industry. In practicaloperation, however, and there is a variety of common failure, where the problem has its roots, tracing back we always find the way out.
Method of fault analysis
Common fault and its classification
1. classified by fault location
⑴ host failure host usually refers to components of NC machine tool CNC machinery, lubrication, cooling and chip, hydraulic, pneumatic and protection, and so on.Host common faults are:
1) because of mechanical part installation, commissioning, operation mechanical transmission failures caused by improper
2) interference with moving parts such as Rails, spindle, friction causes failure
3) due to damage to the mechanical parts, poor connection causes of failure, and so on
Host failures mainly as a transmission noise, processing accuracy, run resistance movement without damage, mechanical parts, mechanical parts, and so on. Poor lubrication, hydraulic, piping of the pneumatic system blocked or bad seal, is a common reason for host fails. Regular maintenance of CNC machine tools. To control and eradicate "three missed" phenomena are important measures for reducing hostpart.
B electrical control system failure on the type of components used. According to the usual habits, electrical control systems, usually described as "weak" fault and "high voltage" failed two classes,
The "weak" part refers to the control system for electronic components, IC-oriented control sections. Weak part of the CNC machine tools including CNC, PLC, MDI/CRT and servo unit, transmission and output units, and so on.
"Weak" points of failures, hardware failures and software failures. Hardware failurerefers to the specific IC chips, discrete electronic components, connectors and external connection component failures that occurred. Software failure refers to hardware actions that occur under normal conditions of germanium, loss of data, failure,common. Process error, system procedures and parameters to be changed or missing computer errors, and so on.
The "strong" part refers to the main circuit in the control system or high-voltage, high-power circuits, relays, contactors, switches, fuses, power transformer, motors,solenoids, trip switches and other electrical components and the control circuit. This part of the fault repair, diagnosis is more convenient but because it is in a high-voltage, high-current working status, rates of failure than the "weak" part. Maintenance personnel must be of sufficient importance.
2. Classified according to the nature of the fault
⑴ certainty certainty fault fault control system of host hardware damage or as long as certain conditions are met, failure of NC machine will happen. This symptom is most common in CNC machine, but because it has certain rules, and therefore certainty brings convenience to repair faults with non-recovery of fault event, such asdo not repair process, the machine does not automatically return to normal. But as long as the root cause of trouble, machine can return to normal immediately after maintenance is complete. Correct use and careful maintenance is to prevent or avoid the failure of important measures.
B randomness fault randomness fault is refers to NC machine in work process in the accidentally occurred of fault this class fault of occurred reasons more hidden, hard find its regularity, so often called "soft fault", randomness fault of reasons analysis and fault diagnosis compared difficult, generally, fault of occurred often and parts of installation quality, and parameter of set, and components of quality, and software design not perfect, and work environment of effect, many factors about.
Random failure recoverability, failure occurs, through measures such as reboot, the machine can usually return to normal, but in the course of operation, the same fault may occur.
Strengthen numerical control system for maintenance checks, ensure the electricalbox sealing, reliable installation, connection, proper grounding and shielding is reduced, avoiding such an important measure of the failure.
3. Directed by the fault classification
⑴ with display fault display fault of NC machine tools can be divided into light displays and display shows two situations:
1) led display alarm led display and alarm by means of controlling the system status indicator on the unit (composed by LED light tubes or small led) display of thealarm. According to the CNC system status led, even when the monitor, can be analyzed to determine the location and nature of the failure, so. Maintenance, troubleshooting process should carefully work up the status led's status.
2) display shows alarm. Display shows alarm refers to CNC display shows the alarm, the alarm and alarm information. Because of the numerical control system generally have a strong sense of self diagnosis function, if the system diagnostic software, and display circuit is working correctly, the event of a system failure, can display that alarm and display text information. NC alarm system can display at least dozens of species, many thousands, it is important for troubleshooting information. The monitor display alarm, alarm and PLC can be divided into NC news and other categories. CNC manufacturers set the drop shows the former. It can control the system's "repair manual" to determine possible causes of the failure. The latter is setby the manufacturer of CNC machine tools PLC alarm message text belongs to thedrop in the machine shows. It can control machine tool manufacturers to provide"machine repair manual" about the content. Determine the cause of the fault.
B non-alarm display of fault fault occurs. Machine and system alarm display, usually of a larger analysis very difficult. Through careful, careful analysis is required to confirm. Especially for some of the earliest numerical control system, due to the diagnostic functions of the system itself is not strong, or no PLC alarm message text,gives non-alarm display is more.
For non-alarm display fault, usually concrete analysis of concrete conditions, changes according to the fault. Analyze, analysis method and PLC program analysis is the main method to solve non-alarm display.
4. Classified according to cause of failure
⑴ CNC machine tool's own fault that such failure is due to the caused by CNC machine tools, has nothing to do with the external environment conditions. Supermajority in the NC machine tool failure is such a failure.
B outside of CNC machine tools fault this fault is caused by external factors. Power supply voltage is too low, too high, excessive fluctuations: power phase sequence is incorrect or unbalanced three-phase input voltage; environment temperature is too high: harmful gases, moisture, dust given in: external vibration and interferenceare the cause of the failure.
In addition, the human factor is also one of the CNC machine tools failure caused by external causes, according to the statistics, used CNC machine tools for the first time or by unskilled workers to operate CNC machines, in the first year of use, improper operation caused by external fault accounted for more than one-third of total machine failure.
In addition to the above common fault classification method, there are a variety ofdifferent classification methods. Example: when there is no destructive failure occurred. Destructive faults and non destructive faults can be divided into two kinds. According to the function part of the failure and in need of repair. Can be divided into numerical control device fault, feeding servo system fault, spindle drive system,white wouldn't stayput long enough for system failures, and so on, this classification method used in repair.
Second, the basic method of malfunction analysis
Failure analysis is the first step for NC machine tool maintenance, fault analysis, on the one hand you can quickly identify troubleshooting the fault: can also play a role in prevention of failure and expanding. In General, the method of fault analysis of NC machine tool has the following types of
⑴ General analysis of NC machine tool for routine analysis is the mechanical, electrical, hydraulic and other parts of the routine inspection, in order to determine why the failure occurred. Conventional analysis in numerical control machine typicallyincludes the following:
1) check power supply specification (such as voltage, frequency, phase and volume) compliance
2) check the CNC servo drives, spindle drives, motors, input/output signal connections are correct, reliable
3) check the CNC servo drives and other devices within the printed circuit board isinstalled securely, connector parts loose
4) check the CNC servo drives, spindle drive, part of the set ends, setting, adjust the potentiometer is correct
5) check the hydraulic, pneumatic, lubricating parts of hydraulic and pneumatic meets machine requirements
6) check the electrical components, mechanical components for obvious damage,and so on
⑵ movement analysis motion analysis method is by observing, monitoring, machine tool actual action, judge bad parts and thus a way to trace fault causes.
In General, hydraulic and pneumatic control of CNC machine tool parts such as: automatic tool changer, exchange table device, fixture and transmitting devices are accessed via diagnosis to determine the cause of the failure.
C analysis method of State analysis is through the work of monitoring the implementation of components, determine failure causes a method this method is the mostwidely used in numerical control machine tool maintenance.
In modern numerical control system of servo feed system, the spindle drive system, power supply and other parts of the main parameters of dynamic and static testing, these include: input/output voltage, input/output current, given the speed, location, actual/actual load fine condition. In addition, numerical control system including internal input/output signal relays, timers and other State can also be examined by NC system diagnostic parameters through the State of analysis, in the absence of instruments and equipment based on the internal state of the system to quickly find the cause of the failure, most widely used in the NC machine tool maintenance, maintenance personnel must be familiar with.
D operation, program analysis method, program analysis is by some special operations or produce specialized test procedures section, confirmed the cause of thefailure is a way. Manually step through the automatic tool changer, automatic switching table actions, performs a single function of the action and function of the processing instructions, and so on. In this way, you can determine the causes of failurewith the part, check the correctness of the program.
⑸ system self-diagnosis self diagnosis method of CNC system is to use the internal self-diagnostics or specialized diagnostic software, within the system of key hardware self diagnosis, testing and software for system diagnosis. It includes power-on self diagnosis and online monitoring and test offline this one aspect (see below)
Third, CNC fault diagnosis
1. Post diagnosis
Index of so-called power-on self diagnosis is controlled when the system is powered on, the troubleshooting performed automatically by the system internal diagnostics, it is similar to the boot of the computer Diagnostics.
Post Diagnostics can key on the system hardware, such as CPU, memory, I/O units,CRT/MDI units, automatic check paper tape reader, floppy drives and other devices; specified at the installation, connection status and performance: some part of the system but also to the key chip, such as PAM, ROM, special-purpose LSI for diagnosis. Self diagnosis for numerical control system at boot time, only if all day afterit has been confirmed, to enter the normal operating state.
Time more than a dozen of the diagnosis of control system takes only a few seconds, however, it takes a few minutes. Post diagnosis according to the steps provided, FANUC FANUCII system for cases diagnosed during execution of the program, seven-segment display on the system board by 9 → 4 → 5 → 6 → 7 → 8 → 3 → 2 →1 changes in the order, appropriate checks says:
9, the CPU is reset, start Diagnostics command:
8, ROM test, said ROM check if an error occurs, the display becomes b;
7 – the RAM is cleared to zero, the system to clear the contents of the RAM, preparation for normal operation;
61 on the BAC (bus random control) chip is initialized. At this point, if the show becomes a, description of motherboard and CRT
Transmission goes wrong; c, says connection error: f, I/O Board or poor connection cable: h that represents the connection unit identification number is wrong; display lowercase letter c cable transmission error also appears j, PLC or poor interface converter circuit, and so on.
5 to examine the MDI unit
4, to initialize the CRT Unit
3 – display the initial screen of the CRT, such as the software version number, serial number, etc. If at this point, the l, indicate that PLC
Software problem: o, it means that the system failed to initialize, control softwareproblems:
2-completed system initialization;
1 to indicate that the system can function properly if display e indicates that the system motherboard or ROM Board, or CNC control software is faulty.
General CRT under clear conditions after the initialization is complete, fault condition exists if the other parts, CRT can display alarm messages.
2. Online monitoring
Online monitoring can be divided into CNC internal monitoring and external device monitoring form CNC internal monitoring through internal procedures, on the part of the State automatic diagnostic, inspection and surveillance methods. Onlinemonitoring range includes CNC itself connected to the CNC and servo units, servomotor, servo unit, spindle motor, external devices, and so on. Online monitoring system in the process of work force.
Numerical control system including monitoring interface signals, internal status and fault display three aspects.
⑴ interface signals that it can display the CNC and PLC, CNC, machine tool between the current status of all interface signals.
That do not pass digital input/output signals clear and help analyze failures. Maintenance must learn about CNC and PLC, CNC between the machine and the meaning of the signals, and undo should have the conditions to make the appropriate checks. Numerical control system provided by the manufacturer of the "functional specifications, '" connection instructions "as well as machine tool manufacturers to provide" machine tool electrical schematics "technical guidelines for these status checks are conducted.
B internal status shows generally use internal State will not function, you can display the contents of the following aspects:
1) cycle instructions (program) does not perform an external cause. Such as: CNCsystem is in "check": whether it is "tool lock" status: "waiting for speed" signal connected: waiting on each revolution of the spindle feed programming "position encoder" signals; when the thread cutting, whether it is waiting for ' spindle I turn signal"feeding speed ratio is set to 0%, and so on.
2) reset status displays indicate that the system is in "stop" or "external reset" signal the on State.
3) TH alarm status is displayed. It can show the police tape error when hole locations.
4) display memory contents and the magnetic bubble memory exception state.
5) position the follow error displays.
6) servo Locke moved part of the control information display
7) encoder, grating position measure components of the input pulse is shown, and so on
⑶ fault information is displayed in numerical control system of fault information to"alarm display" in the form of CRT displays. Alarm display the contents differ according to numerical control system. Most of the information in "alarm", and come in the form of text, content and solution in CNC system provided by the manufacturer "maintenance instructions" can be read.
Through an external device monitoring refers to the use of equipment such as computers, PLC programming, all parts of an NC machine tool to automatically diagnose, inspection and surveillance methods. For example: by computers, PLC programming of PLC program in ladder diagram, function in the form of dynamic testing, it can be used in machine tools PLC programs not provided by manufacturer, the PLC program of reading content such as dynamic waveform displays, usually also require online monitoring equipment necessary.
With the development of computer networks, as a kind of external equipment online monitoring and remote diagnosis through Internet connection technology was further popularized and perfected. Through the network, CNC system manufacturerdirectly for their products in the field of performance testing, monitoring and timely resolution of problems encountered in the system, providing guidance to field maintenance personnel and assistance.
3. Offline testing
Offline test, also known as "off-line diagnostics", it is reaching out to CNC and machine tools, CNC systems for testing and inspection. Offline test can further localization of the fault of the system, to minimize down. Such as by offline testing of printed circuit boards, you can navigate down some part of the printed circuit board or even a chip or device, this is I need to repair of printed circuit boards. Offline tests require specialized diagnostic software for CNC system or special testing devices, so it may only be the manufacturer of CNC or specialized maintenance department.
With the development of computer technology, modern CNC off-line diagnostic software is gradually and CNC control software integration system has "expert systems" introduction of fault diagnosis. Through the software, the operator just makesimple conversation on CRT/MDI operations can be diagnosed or CNC system ofmachine malfunction.
CNC common mechanical failure and preventive measures
, Spindle failure
Due to the use of speed-regulating motor, spindle box of NC machine tool structure is relatively simple, is prone to failure of the parts inside the spindle automatic clamping, automatic speed control device. In order to ensure the tool holder or power failure in the work itself loose, automatic tool clamping clamping by spring, and with limit switch clamp or relaxed signal issued. If the tool clamping cannot release, consider adjusting the song knife cylinder pressures and limit switch devices ornut on the adjusting disc springs, reduce spring pressure. In addition, heating andheadstock spindle noise problem, can not be ignored, mainly cleaning the spindlebox, adjust the amount of lubricant to ensure cleanliness and replacement the headstock spindle bearings, repair or replacement of the headstock gear and so on.
Second, the feed chain failures
In numerical control machine tool feed drive system, common ball screw and hydrostatic lead screw and nut, rolling guideway, hydrostatic guideway and the plasticGuide. So the feed chain is faulty, mainly reflects the movement quality. Such as: mechanical part is not moving to a defined location, outages, positioning accuracy,bigger backlash increases, crawling, bearing noise (after the crash).
For this type of problem can adopt the following preventive measures:
(1) increase the precision adjustment the movement under preload, adjust the loose link, elimination of transmission clearance and shorten the drive chain and gear set in the transmission chain, also improves driving precision.
(2) increase the stiffness. Adjusting screw-nut pairs, supporting part of pretightening force and reasonable choice of screw itself, are effective measures to increasethe stiffness. Rigidity will also cause the bench or carriage creeping and vibrationas well as causing the reverse die, affecting the transmission accuracy.
(3) to improve accuracy. Meet the part strength and stiffness of the premise, minimizing moving parts quality, reducing the diameter of the rotating parts and quality in order to reduce the inertia of the moving parts, improve the accuracy of movement.
(4) rail rolling Guide to the booty is more sensitive, it is necessary to have good guards, and rolling guide preload image to the right, which significantly increased traction. Hydrostatic guideway system should have a filtering effect is good for oil.
Third, automatic tool changer fault
Automatic tool changing device failure is mainly manifested in: cutter motor failure,error too large unstable, manipulator, a robotic arm clamp handle large movement errors. Fault severity will result in tool change stuck, the machine was forced to stop work.
1. the cutter motion fault
Connect the motor shaft and worm shaft coupling loose or mechanical causes such as mechanical connection too tight will cause cutter cannot turn, must tighten screw on the coupling. If the cutter rotation is not in place, belongs to the motor or transmission error causes. If the knife not clamped tool, you will need to adjust theadjustment screws on the knife, compression spring, pushing clamp/on pins whentool is not in place, the forks location should be checked or limit switch installationand adjustment.
2. tool change manipulator fault
If the holder is not tight, the knife, adjust the clamping claw spring, its pressure increases, or replace the mechanical clamping PIN if the tool clamping pine does notopen, loose lock nut after the spring should be adjusted so that maximum load does not exceed the rated value. If the tool switching off knife, belongs to the tool spindle box there is no back to the ATC or ATC drift caused should be reactivated in the headstock, to return to the tool change position, reset tool change.
Four, the axis position journey switch pressing fault
In numerical control machine tool, in order to ensure the reliability of the automation, using a large number of moving position limit switch machines. After a long run, changes in kinetic properties of the moving parts, switch compression fittings for reliability and a change in quality characteristics of the switch itself, have a greater impact on overall performance. General inspection and replacement switch at theright time, can eliminate the influence of such poor switch on the machine.
Five, auxiliary device failure
1. hydraulic system
Variable displacement pump hydraulic pump should be used to reduce heating fuel tanks installed in the hydraulic system filter should be regularly cleaned with petrol or ultrasonic vibrations. Common trouble key is pump body wear, cracks andmechanical damage must repair or replace parts.
2. pressure systems
Used in tool or workpiece clamping, safety door switches and pneumatic system of spindle taper hole blow crumbs, water air filter should be regularly with water, cleaning on a regular basis, to ensure that the pneumatic components of the sensitivity of moving parts. Heart valve failure, pneumatic components, air leakage damage action failures and faults are caused by poor lubrication, the Lubricator should be regularly cleaned. In addition, you should always check the tightness of the pneumatic system.
3. lubrication system
Includes Guide, gear, boxes, such as ball screws, spindle lubrication. Lubrication pumps filters need regular cleaning, replacement, should be replaced once a year.
4. cooling system
It is cooling and flushing effect on the tool and workpiece. Coolant nozzles should be cleaned on a regular basis.
5. chip removal device
Annex to the chip device is an independent function, mainly ensuring automatic cutsmoothly and reduce the fever of CNC machine tools. Chip removal device shall be automatic chip in time, and the installation location should be as close to the cutting area.
Six, conclusion
CNC machine tools are controlled by computer, mechanical and electrical integration of automated processing equipment, CNC machine tools is the use of a technology project. Correct and effective preventive maintenance is the basic guarantee for improving efficiency of CNC machine tools using. Common mechanical failures,despite not many opportunities, but should never lose sight of comprehensive analysis and troubleshooting, root cause, downtime as short as possible, to facilitate the performance of CNC machine tool and efficient play.
