CNC machine tools common faults and troubleshooting methods - Database & Sql Blog Articles

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CNC system fault repair is usually carried out in three major steps: diagnosis and analysis of on-site faults, fault diagnosis and repair, and system commissioning.

1. CNC machine tool fault diagnosis

The following principles should be mastered in troubleshooting:

1.1 First external and internal

The reliability of modern CNC systems is getting higher and higher, the failure rate of CNC system itself is getting lower and lower, and most of the failures are caused by non-system itself. Since the CNC machine tool is a machine tool integrating mechanical, hydraulic and electrical, the occurrence of faults will be reflected by the three. Maintenance personnel should first conduct an investigation from the outside to the inside. Try to avoid unpacking and disassembly at will, otherwise it will expand the fault and make the machine lose precision and reduce performance. Faults outside the system are mainly caused by problems with the detection switches, hydraulic components, pneumatic components, electrical actuators, mechanical devices, and the like.

1.2 First mechanical and electrical

In general, mechanical faults are easier to detect, and the diagnosis of CNC systems and electrical faults is more difficult. Before troubleshooting, first take care to eliminate mechanical failures.

1.3 Dynamic after static

First, in the static state of the machine power failure, by understanding, observing, testing, and analyzing, it is confirmed that the power will not be expanded after the power is turned on, and the machine can be energized after an accident occurs. In the running state, perform dynamic observation, inspection and testing to find faults. If a destructive fault occurs after power-on, the danger must be removed before powering up.

1.4 First simple and complicated

When there are multiple faults intertwined, when there is no way to start, you should solve the easy problem first, and then solve the difficult problem. Often, after a simple problem is solved, a difficult problem may become easier.

2. Fault diagnosis technology for CNC machine tools

CNC systems are high-tech intensive products. Diagnostic techniques are needed to quickly and correctly identify the cause and determine the location of the fault. With the continuous development of microprocessors, diagnostic techniques have evolved from simple diagnostics to versatile advanced diagnostics or intelligence. The strength of diagnostic capabilities is also an important indicator for evaluating the performance of CNC systems. The diagnostic techniques of the various CNC systems currently in use can be broadly classified into the following categories:

2.1 Startup diagnosis

Starting diagnosis means that the CNC system automatically performs diagnostics every time the power is turned on from the system. The diagnostic content is the most critical hardware and system control software in the system, such as CPU, memory, I/O and other unit modules, as well as MDI/CRT units, tape readers, floppy disk units and other devices or external devices. Only when all the items are confirmed to be correct, can the entire system enter the normal preparation state. Otherwise, the fault message will be indicated on the CRT screen or LED with an alarm mode. At this point, the start-up diagnostic process cannot be completed and the system cannot be put into operation.

2.2 Online diagnosis

On-line diagnosis refers to the automatic diagnosis and inspection of the CNC system itself and the various servo units, servo motors, spindle servo units, spindle motors and external devices connected to the CNC system through the built-in program of the CNC system when the system is in normal operation. Online diagnostics will not stop as long as the system does not lose power.

Online diagnostics generally include thousands of status displays of the self-diagnostic function, often displaying their status in binary 0 and 1. For positive logic, 0 means the off state, 1 means the on state, and the status display can determine the location where the fault occurred. Commonly used interface status and internal status display, such as using I / O interface status display, combined with plc ladder diagram and strong electric control circuit diagram, using the inference method and exclusion method to determine the true location of the fault point. Most of the fault information appears in the form of an alarm number. Generally can be divided into the following categories: overheat alarm class; system alarm class; storage alarm class; programming / setting class; servo class; travel switch alarm class; connection fault between printed circuit boards.

2.3 Offline diagnosis

Offline diagnosis is the failure of the index control system, CNC system manufacturers or professional repair centers use dedicated diagnostic software and test equipment for downtime (or offline) inspection. Try to locate the fault to the smallest possible range, such as shrinking to a functional module, some part of the circuit, or even a chip or component, this fault location is more accurate.

2.4 Modern diagnostic technology

With the development of telecommunications technology, the cost performance of IC and microcomputer has increased. In recent years, some new concepts and methods have been successfully cited in the field of diagnosis.

(1) Communication diagnosis

Also known as remote diagnosis, that is, using a telephone communication line to test and diagnose the faulty CNC system and a dedicated communication diagnostic computer of a professional repair center through connection. If Siemens uses this diagnostic function in the diagnosis of the CNC system, the user connects the dedicated "communication interface" in the CNC system to the ordinary telephone line, and the "dataphone" of the dedicated communication diagnostic computer of the two subsidiary service centers. It is also connected to the telephone line, and then the computer sends a diagnostic program to the CNC system, and the test data is returned to the computer for analysis and conclusion, and then the diagnosis conclusion and processing method are notified to the user.

The communication diagnosis system can also make regular preventive diagnosis for the user. The maintenance personnel do not have to visit the site, and only need to perform a series of operation inspections on the machine tool according to the scheduled time. The diagnosis data can be analyzed in the maintenance center, and the hidden troubles can be found, so as to be early. Take measures. Of course, such CNC systems must have a remote diagnostic interface and networking capabilities.

(2) Self-repairing system

That is, a spare module is installed in the system, and a self-repair program is installed in the software of the CNC system. When a certain module is found to be faulty when the software is running, the system displays the fault information on the CRT on the one hand, and automatically searches for it. Whether there is a spare module, if there is a spare module, the system can automatically take the fault offline, and the standby module can be turned on to make the system enter the normal working state faster. This solution is suitable for unmanaged automated workplaces.

It should be noted that there are some faults in the actual use of the machine tool, and there is no alarm. The phenomenon is not very obvious. For this situation, it is not so simple to deal with. In addition, after the failure of this equipment, there is no alarm information, and there is a lack of information required for maintenance. The diagnosis and treatment of such faults must be carefully checked according to the specific circumstances, and analyzed from the tiny points of the phenomenon to find out the real cause. To find out the cause of such a fault, we must first find out the true fault phenomenon of various surface phenomena, and then find out the cause of the fault from the confirmed fault phenomenon. A comprehensive analysis of a fault phenomenon is an important factor in determining whether a fault is correct. Before looking for the cause of the fault, you must first understand the following situation: whether the fault occurred during normal work or just started; the number of times the mountain is the first time or has occurred many times; confirm the correctness of the machine tool processing program; other people.

3. Common troubleshooting methods for CNC machine tools

Because the CNC machine tool fault is more complicated, and the CNC system self-diagnosis ability can not test all the components of the system, it is often an alarm number indicating a large number of fault causes, making it difficult for people to start. The following describes the troubleshooting methods commonly used by maintenance personnel in production practice.

3.1 Visual inspection

The visual inspection method is to determine the fault range according to the observation of various abnormal phenomena such as light, sound and taste when the fault occurs, and the fault range can be reduced to a module or a circuit board, and then eliminated. Generally includes:

a. Inquiries: Ask the fault site personnel carefully the process of the fault, the fault image and the consequences of the fault;

b. Visual inspection: Overall check whether the working status of each part of the machine tool is in a normal state, whether there is any alarm indication for each electronic control device, partial inspection for burnout, component burnt, cracking, wire and cable falling off, and the position of each operating component is correct. Or not, etc.

c. Touch: Under the condition of power failure, you can touch the installation status of each main circuit board, the plugging status of each plug, the connection status of each power and signal wires, and touch and shake the components by hand, especially Large volume of resistive capacitance, semiconductor device with or without the sense of looseness, in order to detect some broken feet, virtual soldering, poor contact and other faults;

d. Power-on: Refers to the power-on analysis in order to check for smoke, fire, abnormal sound, odor, and presence or absence of overheating of the motor and components. If there is a catastrophic failure, it must be excluded before powering up.

Example: After a CNC machining center is running for a period of time, the CRT display suddenly shows no display failure, and the machine can continue to run. After the shutdown, it will be turned on again and everything will be normal. It has been observed that a fault can occur whenever vibration occurs during operation of the equipment. The initial judgment is that the components are in poor contact. When the display panel is inspected, the CRT display suddenly disappears. Check that two pins with one crystal are loose soldered. After re-welding, the fault is eliminated.

3.2 Initialization reset method

Under normal circumstances, due to system alarms caused by transient faults, hardware reset or switching system power can be used to clear faults. If the working memory area of ​​the system is confusing due to power failure, plug-in circuit board or battery undervoltage, the system must be initialized and cleared. Before copying, pay attention to making data copy records. If the fault cannot be eliminated after initialization, perform hardware. diagnosis.

Example: When a CNC lathe is pressed, the microcomputer refuses to execute the machining program, and does not display the fault self-test prompt. The display screen is in the reset state (only the menu is displayed). Sometimes the manual and editing functions are normal, the user program is checked, and various parameters are completely correct. Sometimes, due to memory battery failure, battery replacement, etc., the system displays oversize or oversize in all directions (display size exceeds the machine tool) The maximum size that can be processed by the jin or exceeds the maximum size that the system can recognize. Remedy: Use the initial reset method to reset the system to zero (usually use a special combination or password). 3.3 Self-diagnosis

The CNC system has a strong self-diagnosis function and can monitor the working status of the hardware and software of the CNC system at any time. The self-diagnosis function can display the status of the interface information between the system and the host, thereby judging whether the fault occurs in the mechanical part or the numerical control part, and displays the general part of the fault (fault code).

a. Hardware alarm indication: refers to various status and fault indicators on various electrical devices including numerical control system and servo system. Combined with the indicator status and corresponding function description, the indication content and the cause of the failure and the elimination method can be obtained. b. Software alarm indication: The faults in the system software, PLC program and machining program usually have alarm display. According to the displayed alarm number, the corresponding fault description and troubleshooting method can be obtained by comparing the corresponding diagnosis manual.
The function program test method is to program the G, M, S, T, F functions of the numerical control system into a functional test program by programming, and store them on the corresponding media, such as paper tape and tape. Run this program during troubleshooting to quickly determine the likely cause of the failure.

Functional program testing is often used in the following situations:

a. The machine tool processing causes waste and cannot be determined at the moment whether the programming operation is improper or the CNC system is faulty;

b. The numerical control system has a random failure. It is difficult to distinguish between external interference and system stability.

c. When the CNC machine tool with a long idle time is put into use or when the CNC machine tool is regularly inspected.

Example: A vertical milling machine of the FANUC9 system crawls when machining a curved part automatically, and the surface roughness is extremely poor. When running the test program, there is no crawling during linear and circular interpolation, thus determining the cause in programming. Careful inspection of the machining program revealed that the curve consisted of many small arcs, and the C61 command was used to check the correct positioning. The G61 in the program is canceled, and after the G64 is used, the crawling phenomenon is eliminated.

3.5 Spare Parts Replacement Method

Replace the bad circuit board with a good spare part. In the case of analyzing the general cause of the fault, the maintenance personnel can replace the suspected part with the spare printed circuit board, integrated circuit chip or component, thereby narrowing the fault range. To the printed circuit board or chip level. And do the corresponding initialization start, so that the machine tool is quickly put into normal operation.

For the maintenance of modern CNC, more and more cases use this method for diagnosis, and then replace the damaged module with spare parts to make the system work normally. Do as much as possible to reduce the downtime. Use this method to ensure that the operation must be carried out in the power outage state. Also check the version, model, various marks, and jumpers of the circuit board. If they are not the same, they cannot be replaced. Marks and records should be made when the line is removed.

Generally, do not easily replace the CPU board, memory board and electric ground. Otherwise, the program and machine parameters may be lost, and the fault may be expanded.

Example: A CNC machine tool using Siemens SINUMERIK SYSTEM 3 system, its PLC Chuanchuan S5-130w/B, when a fault occurs, the R parameter input through the NC system PC function does not work during processing, can not be changed plus The value of the R parameter in the program. Through the analysis of the working principle and fault phenomenon of the NC system, it is considered that there is a problem with the motherboard of the PLC, and after being replaced with the motherboard of another machine tool, the problem of the PLC motherboard is further determined. After repair by professional manufacturers, the fault was eliminated.

3.6 Crossover method

When a faulty board or a faulty board is found and there is no spare part, the same or compatible two boards in the system can be interchanged, for example, the exchange of two coordinate command boards or servo boards. Determine the fault board or fault location. This cross-transposition method should pay special attention to not only the correct exchange of hardware wiring, but also a series of corresponding parameters exchange, otherwise it will not only achieve the purpose, but will generate new faults and cause confusion, must be considered in advance. , design a good software and hardware exchange program, and then exchange and check accurately. #p#分页头#e#

Example: A CNC lathe has a normal X-direction feed, and the Z-direction feed has vibration, noise, and precision. This is also the case when using manual and manual pulse feed. Observing the brightness of the indicator light of each driver board and its change is basically normal. It is suspected that the Z-axis stepping motor and its lead open circuit or Z-axis mechanical failure.换 Change the Z-axis motor lead to the X-axis motor, the X-axis motor runs normally, indicating that the Z-axis motor lead is normal; and the X-axis motor lead is changed to the Z-axis motor, the fault remains; it can be concluded that the Z-axis motor is faulty or Z-axis mechanical failure. The motor leads were measured and an open phase was found. Repair stepper motor, troubleshooting.

3.7 Parameter check method

System parameters are the basis for determining system functions. If the parameters are set incorrectly, the system may be faulty or a function may be invalid. When a fault occurs, the system parameters should be checked in time. The parameters are usually stored in the bubble memory or stored in the CMOS RAM to be held by the battery. Once the battery is low or due to external interference, the individual parameters are lost or changed, and confusion occurs. Make the machine not working properly. At this point, the fault can be eliminated by checking and correcting the parameters.

Example: A CNC milling machine uses a measuring cycle system. This function requires a background memory. This function cannot be realized during debugging. The check found that the data bit existing in the background memory was not set, and the function was normal after being set.

Another example: a CNC lathe CNC tool holder has a sudden failure, the system can not automatically run, in the manual tool change, it will take a while to change the knife again.遂 Check the parameters such as the tool compensation, and find that the parameter P20 that is not described in the manual becomes 20, and the relevant data P20 is the tool change time parameter of the tool holder, which is cleared and the fault is eliminated.

Sometimes due to user program and parameter errors can also cause downtime, you can use the system's program self-diagnosis function to check and correct all errors to ensure its normal operation.

3.8 Measurement comparison method

When designing printed circuit boards, CNC system manufacturers designed some test terminals on the printed circuit board for adjustment and maintenance. The maintenance personnel can check whether the working state of the circuit is normal by measuring the voltage or waveform of these detection terminals. However, before using the test terminals for measurement, you should be familiar with the function of these test terminals and the circuit or logic relationship of the relevant parts.

3.9 tapping

When the system failure is manifested as sometimes normal and sometimes abnormal, it can be basically determined that the component is in poor contact or the solder joint is open. When using the tapping method, when the fault is touched to the faulty part or the contact failure, the fault will be appear.

3.10 Local heating method

After long-term operation of the CNC system, the components are aging and the performance is deteriorated. When they are not completely damaged, the failure will sometimes be absent. At this time, the suspected component is locally heated by a soldering iron or a hair dryer, which causes a rapid failure. When operating, pay attention to the temperature parameters of the components, etc., be careful not to damage the good components.

3.11 Principle analysis method According to the composition principle of the numerical control system, the logic level and characteristic parameters of each point, such as voltage value and waveform, can be logically analyzed, and the instrumentation is used for measurement, analysis and comparison to determine the fault location.

In addition to the above commonly used fault detection methods, the plug-in board method, the voltage pull-off method, the open-loop detection method, and the like can also be used. In short, according to different fault phenomena, several methods can be selected at the same time for flexible application and comprehensive analysis, in order to gradually narrow down the fault range and eliminate faults faster.

4. Commissioning after CNC machine tool repair

After the troubleshooting of the machine tool, the power test is usually carried out in two major steps:

4.1 Automatic state test

Lock the machine tool, use the programmed program to carry out the dry running test, verify the correctness of the program, then release the machine tool, and make various changes to the feedrate override switch, the fast overrun switch, and the spindle speed overshoot switch respectively. In the case of various changes of the above switches, the operation is fully performed, and then the overshoot switches are placed at 100% to fully operate the machine tool and observe whether the working condition of the whole machine is normal.

4.2 Normal processing test

The workpiece is clamped and processed according to the normal procedure. After processing, the machining accuracy of the workpiece is checked to meet the standard requirements.

5. Technical treatment after maintenance and commissioning

After the on-site repair is completed, the maintenance records should be carefully filled out, list the necessary spare parts, and create a user profile. For fault time, phenomena, analysis and diagnosis methods, and troubleshooting methods, if there are any remaining problems, it should be recorded in detail, so that not only can each fault be well documented, but also the maintenance experience can be accumulated.