How to Repair CNC Machine Tools?

How to Repair CNC Machine Tools? 1

As we all know, CNC machine tools are modern high-tech products that can’t be interchanged from the 1970s to the 1990s, and the fault phenomenon is also strange and different, especially large and heavy CNC machine tools, which are expensive, about several million dollars each, and the installation and adjustment time is long (from a few months to more than a year).

There are thousands of components in large-scale CNC machine tools.

If one of them fails, it will cause abnormal phenomena of the machine tools, as well as the connection of wires and pipes.

A little negligence will cause problems.

In addition, large-scale and heavy-duty CNC machine tools are huge in volume, and they are used without constant temperature workshop, so the impact of the environment is easy to cause failures.

Therefore, the problem of “difficult maintenance” of CNC machine tools is put in front of us.

With so many CNC machine tools imported and manufactured in China, how can we quickly find out the faults and hidden dangers and eliminate them in time?

How can we repair these expensive equipment?

I think first of all, we should have a high sense of responsibility and the spirit of not afraid of difficulties;

Second, we should strive to master numerical control technology and summarize my practice of repairing numerical control machine tools for more than ten years.

I think we should see more, ask more, remember more, think more and practice more, and gradually improve our technical level and maintenance ability, so as to adapt to various complex situations, solve difficult problems and repair numerical control machine tools.

1. See more

To see more, we should:

  • Understand the characteristics and functions of various CNC systems and PLC programmable controllers;
  • To understand the alarm and troubleshooting methods of CNC system;
  • Understand the meaning of NC and PLC machine tool parameter setting;
  • Understand the programming language of PLC;
  • To understand the method of NC programming;
  • Understand the operation of the control panel and the contents of each menu;
  • To understand the performance of the spindle and the cutter motor and the characteristics of the driver, etc;

1. Read more NC data

But often there are a lot of numerical control data, how should we choose?

I think the main thing is to highlight the key points and clarify the context.

The key point is to understand the basic composition and structure of the CNC system and master the block diagram.

The rest can be “toured” and read through, but each part of the content should be understood and mastered with emphasis.

Because the internal circuit diagram of the CNC system is quite complex, and the manufacturer does not provide it, there is no need to make it clear in detail.

How to Repair CNC Machine Tools? 2

For example, NX-154 four axis five link blade processing machine adopts A-B10 system.

We should focus on understanding the function of each part, the function of each board, the destination of the interface, the meaning of LED lights, etc.

Now there are many types of CNC systems, which are updated quickly.

Different manufacturers and models often differ greatly.

We should understand their commonness and individuality (particularity).

Generally, people who are familiar with the maintenance of Siemens CNC system may not be proficient in troubleshooting A-B system.

Therefore, we should see more and constantly learn and update knowledge.

2. Read and understand the electrical diagram

How to Repair CNC Machine Tools? 3

For each electrical component, such as contactor, relay, time relay, etc., as well as the input and output of PLC, it should be indicated on the electrical diagram one by one.

For a simple example, for example, 1A1 is the contactor that starts the hydraulic pump motor 1m.

Generally, the whereabouts of its normally open and normally closed contacts are indicated in the figure.

Therefore, the normally open or normally closed contact 1A1 on its corresponding page can be marked with the hydraulic pump motor on.

For large-scale CNC machine tools, the electrical diagram has dozens of pages, or even hundreds of pages.

To understand, it means that the function of each component takes a long time.

Sometimes, you may not understand the function of this element after reading it once or twice.

You should read it more and write it later.

Therefore, the starting hydraulic pump motor 1M mentioned just now should also clearly indicate which external output of PLC drives the action of contactor 1A1, and the context should be clear.

For some block diagrams in the electrical circuit diagram, such as the driver of each axis, it is only a block diagram.

As long as you know a certain control condition (on-off condition), you can wait for time to study and consider the detailed things.

The electrical symbols of various countries are different.

How to Repair CNC Machine Tools? 4

First of all, we should clearly understand them.

For the thick PLC statement tables prepared by the manufacturer, you should also read them more, master their programming language, and annotate and translate them in Chinese on the basis of understanding.

This can greatly save the time of troubleshooting in the future.

If you get familiar with the electrical diagram and PLC statement table after a fault occurs, it will inevitably take a lot of time and often lead to wrong judgment.

3. Read more hydraulic and pneumatic diagrams and have an in-depth understanding

How to Repair CNC Machine Tools? 5

For the mechanical, hydraulic and pneumatic diagrams of CNC machine tools, we should make clear their functions and context.

It should be noted on the drawing that, for example, the installation action of accessories and tools of German COBURG CNC gantry milling is relatively complex.

Its diagram should be broken down, such as which solenoid valve acts to lock the tool?

What are the corresponding PLC outputs and inputs?

It is indicated in the figure that the electrical and mechanical actions are clear at a glance.

At the same time, we should pay special attention to the parts with close relationship between machine and electricity.

For example, the Italian INNSE CNC milling machine adopts the electro-hydraulic proportional valve technology, and we should focus on understanding its function, especially its adjustment method and adjustment data.

How to Repair CNC Machine Tools? 6

In static and dynamic situations, the proportional valve current and the corresponding balance pump pressure, both electricity and machine, and electromechanical integration.

Master a variety of skills, so that the ability to solve problems is great.

4. Improve your professional foreign language reading ability

How to Repair CNC Machine Tools? 7

If you don’t know foreign languages, especially English, you can’t understand a large number of foreign technical materials.

Just relying on translation is often not ideal.

It’s difficult to read the technical materials in foreign languages at the beginning.

There are many new words.

After reading and remembering more, it looks smooth, because there are only so many commonly used professional words.

A competent maintenance personnel should basically master language tools.

2. Ask more questions

1. Ask more foreign experts

How to Repair CNC Machine Tools? 8

If you have the opportunity to go abroad for training or foreign experts come to your factory to install and debug machine tools, you’d better have the opportunity to participate.

This is the best learning opportunity, because you can get a lot of first-hand information and machine tool debugging methods and skills.

For example, after laser measurement of the accuracy of each axis, how to correct the electrical method, etc.

Ask more questions, and make it clear if you don’t understand.

Through this period of time, you will gain a lot, and you can get a lot of internal information and manuals (which are confidential to users).

When the machine tool is put into formal production, it should also keep close contact with relevant foreign experts.

Through fax and e-mall, it is very useful to ask for the methods and relevant data to solve the difficult faults of machine tools, and to get special and special spare parts.

At the same time, we should also maintain a good relationship with the agents of the CNC system, such as Siemens, FANUC and other companies, ask more questions, and get further information and relevant spare parts of the CNC system in time.

How to Repair CNC Machine Tools? 9

We can also have the opportunity to participate in special courses on the CNC system.

2. The whole process of asking for faults

After a fault occurs, you should ask the operator about the whole process of the fault.

In this way, you often can’t get the correct field data, which will lead to wrong judgment and complicate the problem.

Therefore, you should ask more and ask in detail to understand the whole process of the fault (start, middle, end), what alarm number was generated, what components were operated at that time, what was touched, and what was changed, How about the external environment?

On the basis of fully investigating the scene and mastering the first-hand materials, we should correctly list the fault problems, do well in half of these problems that have been solved, and then analyze and solve the remaining problems.

For experienced and skilled operators, they are familiar with the operation of machine tools, processing procedures and common problems of machine tools.

Close cooperation with them is very beneficial to the rapid troubleshooting.

How to Repair CNC Machine Tools? 10

3. Ask other maintenance personnel more

When other maintenance personnel are repairing the machine tool and you don’t go, when they come back, you should also ask more about what happened just now? How did he rule it out? Ask him to introduce his troubleshooting methods.

This is also a good learning opportunity. Learn the correct troubleshooting skills and methods of others, especially from experienced old maintenance personnel, and learn their skills to improve their knowledge and level.

How to Repair CNC Machine Tools? 11

3. Remember more

1. Relevant parameters shall be recorded

Focus on recording various relevant parameters after the machine tool is adjusted, such as NC machine tool parameters, PLC machine tool parameters, PLC program (the above can be stored in the disk), as well as the current, voltage, speed and other data of the spindle and each tool feeding motor.

Also note the status (on or off) of relays, contactors, etc. in the electrical cabinet during power on and formal processing, as well as the status (light, dark, flashing) of all PLC inputs and output LED, or record whether the PLC status IB (input bit) and QB (output bit) on the screen are 0 or 1, such as IB1=:00000001, that is, I1.0=1, I1.1-1.7=0.

This record is of great benefit to the future analysis and judgment of faults.

For example, the Z-axis motor current relay action occurred in the German Schiess CNC vertical lathe.

How to Repair CNC Machine Tools? 12

We quickly found the cause of the fault by checking the PLC state (0, 1) of the Z-axis motor when it was working normally and comparing it with the abnormal condition.

The reason is that one of the comparison relays was in the wrong state.

Through adjustment, the fault was eliminated immediately.

2. Record the hydraulic and pneumatic status

Similarly, record the pressure of various pressure gauges and barometers and the suction and disconnection state of solenoid valves when hydraulic and pneumatic are formally processed or not, which is also very helpful for adjustment and judgment.

For example, the static pressure of the American Ingersoll openside masterhead CNC milling machine adopts the double film technology, and there are more than 100 pressure measurement points.

The level of its pressure directly affects the normal operation of the machine tool function.

It is very important to record the static and dynamic pressure.

3. Take a notebook with you

How to Repair CNC Machine Tools? 13

Record the faults that occur every day and the process of how to eliminate them one by one. People’s minds are easy to forget for a long time. “A good memory is better than a bad pen”.

Recording it is of great benefit.

We found that some faults of CNC machine tools often occur repeatedly, and they are always these faults.

As long as we check how they were solved at that time, the faults can be eliminated in a few minutes, which is fast and good.

Our company has a “numerical control machine tool operation diary” and a “numerical control machine tool troubleshooting record book”.

These two materials should be recorded well.

This is a complete historical file of a numerical control machine tool.

4. Think more

How to Repair CNC Machine Tools? 14

1. Think more and broaden your horizons

Sometimes the repair is not calm enough, and there is no good analysis to get to the point.

I remember that once the Y-axis of Coburg gantry milling stopped suddenly during processing, and the 1361Y-axis grating dirty alarm occurred many times on the screen.

At that time, we cleaned the grating ruler and the grating head as it was, and the result was still shutdown.

It took several days to solve it, and finally the real reason was found.

The reason was that there was a problem with the wire between the y-axis grating head and the EXE amplifier.

Because the serpentine tube was bent for a long time when the y-axis moved, one of the position feedback lines was bad, and it broke at a certain position, causing the machine tool to stop.

At that time, we only paid attention to the static state and ignored the dynamic state.

There was an open circuit alarm of 1321 control circuit, but it did not attract our sufficient attention.

Therefore, we should list all the alarms and faults that have occurred, and conduct comprehensive judgment and screening by eliminating the false and preserving the true from the outside to the inside, so as to predict the maximum possibility of faults, and then eliminate them.

“At the end of the mountain and the river, there is no doubt, and there is another village with bright flowers in the dark”, think more, and point out the direction for you.

2. Think more and know why

Often when we are troubleshooting, sometimes we fail to find the real cause of the fault, and then the fault continues to occur.

I remember that the main shaft SL of Ingersoll rotor blade root slot milling machine had the fault of “automatic shutdown” after running for 2 hours.

At that time, the foreign expert changed a sequence board, and the problem seemed to be solved, but after more than a month, the old problem was committed again.

It was better to change the standby board of a sequence board, but the damage reason was not clear.

After careful inspection, we found that the reverse peak voltage of the optocoupler corresponding to the “start” command was particularly high with the help of the oscilloscope. After adding a ground wire alone, the reverse peak voltage of the optocoupler was greatly reduced.

Since then, there has been no “automatic shutdown” fault, because the reverse peak voltage was too high and the optocoupler gradually failed after a long time.

3. Think more and consider taking the lead

Spare parts shall be carefully prepared according to the frequency, repeatability and service life of machinery and electrical appliances.

This is an important work to ensure the continuous and normal operation of the machine tool, which must be done well.

At the same time, for some devices, with the delay and elimination of time, they have been unavailable or very expensive in the market. What should we do?

It should be considered in advance.

For example, there is a photoelectric reader used for CNC machine tools in the early 1980s, which reads the processing program in the loop mode, and selects the original belt (machine tool setting data) in the spool mode.

In case it cannot be sent in, the whole machine tool will become a “dead” machine, and the consequences are very serious.

Because we took a step ahead and cooperated with relevant units, after many tests, we adopted a floppy disk processor to solve this problem.

This ensures that this machine tool can be used up to now.

Think more, think in advance, give reasonable suggestions to leaders, strive to improve the external environment of CNC machine tools, think of ways from the aspects of temperature, dust, humidity, etc., and take measures such as installing power regulators, installing electric cabinets, air-conditioning small houses, etc., so as to greatly reduce the failure of machine tools.

5. Practice more

How to Repair CNC Machine Tools? 15

1. Practice more, dare to do it, and be good at it

For maintenance personnel, they should be bold and careful, and dare to do it. They can’t repair CNC machine tools well if they only talk and don’t do it.

But don’t do it blindly until you are familiar with the situation, otherwise it will expand the fault and cause an accident, and the consequences will be unimaginable.

At the same time, we should also be good at hands-on.

First of all, we should be familiar with the operation panel of the machine tool and the contents of each menu, and operate freely, because the operation of various models and systems are the same.

At the same time, we should also make full use of the self diagnosis technology of CNC machine tools to quickly deal with and solve the faults.

Now, with the development of numerical control technology, the self diagnosis ability is becoming stronger and stronger.

For example, A-B10 system has special diagnosis software, which can be connected to the network for diagnosis, etc.

2. Practice more, cultivate your hands-on ability and master experimental skills

Sometimes some faults look vague, and it is difficult to distinguish between electrical faults and mechanical faults.

For example, Coburg gantry milling has experienced such faults, that is, whether the z-axis is raised or lowered, the z-axis ram always moves downward and alarms.

How to Repair CNC Machine Tools? 16

We adopted the “separation method”, which completely separated the control of the electrical part from the original circuit, removed the line on the wiring terminal of the z-axis DC motor, and connected the DC power (which can be given by the AC 220V power supply through the voltage regulator through four diode rectification) to the two ends of the motor.

It was found that the electric function changed the direction of rotation according to the conversion energy of the polarity of the DC power, eliminating the electrical fault.

The re inspection found that it was caused by the mechanical friction plate slipping and the ram sagging.

There are many other methods, such as “isolation method”, “replacement method”, “comparison method”, “percussion method” and other methods can be used as an effective means to help us find and eliminate faults.

3. Practice more and learn to use relevant instruments

For example, oscillograph, multimeter, online circuit detector, short circuit detector, computer, programmer, etc. can help us judge and check specific circuits, especially PLC programmer and computer.

How to Repair CNC Machine Tools? 17

They should be proficient in using, and can freely input and output machine parameters, online test relevant States, system initialization, etc.

This is of great help to analyze faults, especially complex faults, and solve problems.

4. Practice more and carry out “minor changes”

When a component is damaged in normal operation (such as selector switch, button, relay, etc.) and there are no spare parts for the time being, do it yourself and try to repair it by sticking it or using temporary special methods, so that the machine tool can work normally until the spare parts come.

For example, there are five miniature pressure switches for clamping in the second knife back of the German VDF CNC cart, two of which were accidentally damaged without spare parts.

How to Repair CNC Machine Tools? 18

We adopted the “short-circuit method” to make the contact of the pressure switch meet the input conditions of PLC, so that the machine tool can work normally without alarm.

Sometimes, after the machine has been used for a long time, the positioning accuracy is poor, resulting in a positioning alarm.

When the machine cannot be readjusted, the machine parameters can be temporarily modified, and the “tolerance” zone can be increased to make it work normally.

In short, there are still many such methods.

After more than ten years of maintenance practice, we also feel that the CNC machine tools designed by foreigners, especially large CNC machine tools, are not perfect, and there are also many problems and defects.

Through our study and deepening of CNC machine tools, we found out the problems, boldly improved some problems, and achieved good results.

For example, the German VDF CNC cart originally designed two static pressure brackets to work as soon as they are powered on, and the static pressure pump operates continuously, which consumes electricity and shortens the service life of the imported pump.

We modified the PLC by adding two switches, which cost only dozens of yuan, so that the two static pressure brackets can be opened or stopped at will according to needs, thus extending the service life of the imported pump and saving more than 20000 degrees of electricity throughout the year.

In addition, in the original design of Ingersoll impeller slot milling, the main head and auxiliary head only have reverse milling, and there is no same direction milling.

When machining the 20th stage impeller of high and intermediate pressure rotor, because the distance between the impellers is small, reverse milling cannot be used, so only one head can be used for machining.

After our research, the two-way limit wiring was cleverly changed and the PLC program was added.

As a result, there was almost no money and the same direction milling was realized.

Now two heads can be processed at the same time, double the work efficiency, and the task of processing rotors can be completed 3-4 days in advance.

Therefore, we should further tap the potential of CNC machine tools and give better play to its power to serve production.

5. Practice more and repair the board by yourself

Generally speaking, the reliability of the circuit board of the CNC machine tool is good, and the failure rate is extremely low. Generally, when checking the CNC machine tool, don’t doubt the problem of the board first.

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For example, in Siemens 850 system, sometimes there will be 41nc-cpu alarm or 43plc-cpu alarm. In fact, it is not the fault of the board.

It can be generally eliminated by repeated tests through the removal method, NC initialization, cold and hot start PLC and other methods.

If it turns out to be a circuit board problem, repair it.

These boards (generally without drawings) are expensive, which usually cost thousands of yuan or tens of thousands of yuan.

For every enterprise, “spare parts are difficult”, and the price is too expensive to afford to prepare.

Therefore, the quality of the circuit board of the CNC machine tool is extremely important.

Once the circuit board is damaged without spare parts and cannot be repaired for a while, it is bound to shut down and seriously affect production.

Sometimes, the circuit board is only a tiny fault.

As long as we carefully check it, it is not difficult to find the problem.

We have found several faults such as capacitor leakage, board soldering, short circuit and so on. Some circuit board faults are more complex, but as long as it takes time, it can still be repaired by checking with instruments;

However, some circuit boards are in serious condition, especially large-scale integrated circuits, which are difficult to maintain.

In addition, the original devices have no spare parts, so we can only buy spare boards in advance or send them out for repair.

Repairing boards by yourself has great benefits.

On the one hand, it can save costs for enterprises and solve urgent problems.

On the other hand, it can “dissect sparrows” to be familiar with electronic circuits, and it is very beneficial to cultivate their own analytical judgment and practical ability.


Although the faults of CNC machine tools are complex and ever-changing, as long as we take them seriously, cultivate a high-quality electromechanical integration maintenance team, through watching more, asking more, thinking more, practicing more, accumulating experience, and mastering all kinds of skills, we will be able to mainly rely on our own strength to repair, use, and manage CNC machine tools well.

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