First, when operating the positive and negative directions of the linear axis of a CNC machine tool, the linear axis moves in one direction.
In the maintenance of CNC machine tools, no matter what brand of CNC system the CNC machine tool uses, many maintenance personnel have encountered the following faults, that is, the linear axis of CNC machine tools moves in the direction of collision, whether positive or negative. Take the X axis of CNC lathe as an example to explain in detail. When the X-axis of the CNC lathe moves near the limit in the +X direction, the X-axis moves in the +X direction regardless of whether you press the +X direction or the -X direction.
When this kind of fault occurs, due to the inertia of the X axis of the machine tool, the position of the X axis is between the soft limit and the hard limit of the +X axis, and the general display unit does not give an alarm.
The solution to this kind of fault is to modify the positive and negative soft limit of X axis to a value greater than the hard limit (for example, the coordinates of the positive and negative hard limit of X axis are 100, -800, and the soft limit can be temporarily set to 1000,-1000), and manually open the X axis to deviate from the fault direction of X axis (as shown in the above example).
Two, grating ruler as the position detection element of the linear axis of CNC machine tools, several common faults.
1, the direct axis is at the reference point, and no zero pulse can be found. In the form of expression, the shaft runs to the limit of the shaft when it returns to the reference point.
The reason for this failure is generally that the reading head or grating ruler is dirty.
The solution of this kind of fault is: take off the reading head and wash it with anhydrous alcohol, and wash the marked part on the silk cloth with anhydrous alcohol.
2. The linear axis of the NC machine tool gives an alarm during operation.
In the operation of CNC machine tools, if a straight axis of Siemens 840D or German Rexroth CNC system is used, an alarm of "hardware encoder error" will appear; If the direct axis of Spanish FAGOR numerical control system is used, the alarm of "following error out of bounds" will appear. At this point, the grating ruler, which is generally used as the linear axis position detection element of the machine tool, fails.
In this case, due to vibration or other reasons, the distance between the reading head and the grating ruler is generally far when the machine tool is used, and the numerical control system mistakenly thinks that the grating ruler is broken. The method to deal with this fault is to adjust the distance between the reading head and the grating ruler according to the requirements of the specification of the grating ruler. The distance between the reading head and the grating ruler is about 1 ~ 1.5 mm, preferably no more than 2 mm. ..
Another reason for the above failure is that the grating ruler is not installed correctly. For example, if it is installed near the oil pool, the grating ruler will be polluted by oil and gas. At this time, the "fixed scale" and "moving scale" of the grating ruler should be cleaned separately, and then the grating ruler can be debugged after installation.
There is also a fault situation where the above alarm will occur, that is, the reading head is damaged due to improper installation of the reading head, and what's more, aluminum alloy debris appears in the length of the grating ruler, and the grating scribe line is damaged, resulting in the complete scrapping of the grating ruler length.
3. The linear axis of the NC machine tool runs off.
When the linear axis of a CNC machine tool is equipped with a grating ruler, if the linear axis deviates, the grating ruler, the position detection element of the linear axis, is generally polluted, and the grating or reading head of the grating ruler needs to be cleaned to eliminate the fault.
In the years of maintenance of CNC machine tools, we found that the grating ruler, as a position detection element of CNC system, can improve the positioning accuracy of the linear axis of the machine tool when the mechanical part of the machine tool is intact. In addition, the grating ruler can also detect hidden dangers or problems existing in the mechanical parts of the machine tool. The following is a further explanation of several maintenance cases.
4, HG30 18 American CAPCO grinder machine tool trembling
HG30 18 roller CNC grinding machine imported by CAPCO Company of the United States adopts German BOSCC220 CNC system, the X-axis is fully closed-loop control mode, and the displacement detection element adopts German Heidenham glass grating ruler. When the operator of the machine tool accidentally hits the shell of the grinding wheel frame of the machine tool with a wooden stick, people stand on the workbench and feel the machine tool vibrate violently.
Judging from this phenomenon, the fault must have some actions of the machine tool itself, and it is definitely not the result of a loose part of the machine tool and a person gently "smashing" the machine tool shell with a wooden stick. It has been verified that it is caused by the looseness of the back of the X-axis ball screw: when someone hits the shell of the grinding wheel frame of the machine tool with a piece of wood, the X-axis is driven by the ball screw, so it is very light, and the grinding wheel frame will move slightly because of the looseness of the back of the X-axis ball screw. At this time, the numerical control system detected that the X-axis has moved, and did not send out the X-axis movement signal, which is definitely illegal. At this time, the numerical control system will send a "given" signal opposite to the movement direction of the grinding wheel frame, so that the grinding wheel frame moves in the opposite direction. Because of the looseness of the ball screw, the X axis will go too far when moving in the opposite direction. At this point, under the command of the numerical control system, the grinding wheel frame moves in the opposite direction to the previous direction. . . . . This reciprocation causes the vibration of the grinding wheel frame.
In the long-term maintenance of CNC machine tools, we found that the grating ruler can not only be used as the detection element of the position ring, but also as the "supervision" element of the linear axis of the machine tool. When there are hidden dangers in machinery, if the axis is controlled by the grating ruler, the hidden dangers will be "amplified" by the grating ruler and displayed in the form of faults. When there are hidden mechanical faults in machine tools without grating ruler, it is often difficult to show them until the hidden mechanical faults expand into hard faults.
5. When C61200 CNC lathe processes the roller body, the X axis moves back and forth.
Our company purchased C6 1200 lathe from Wuzhong, and adopted Spanish FAGOR 8055TC CNC system after numerical control transformation. One day, when the machine was processing a roll, the roll body of the roll was eccentric. Under normal circumstances, the roller body of the roller should be cylindrical, but due to pouring, the diameter of each part of the roller body is different and oval. As a result, when the tool of the machine tool eats a place with a large roll size, the X axis moves away from the roll itself without the X axis movement instruction. When the cutter touches the thin part of the upper roller, the X axis moves itself, causing the X axis to move back and forth.
The reasons are as follows: First, we checked the numerical control system of the machine tool, and found that the AC servo motor of X axis added self-locking force when adding the "enable" signal. When the X-axis position detection element is shielded, it is changed to a semi-closed loop, and then the tool is processed. It was found that the phenomenon that the X axis moved back and forth before disappeared. After seeing this phenomenon, some people judged that there was something wrong with the grating ruler. I think it was the X-axis grating ruler that was in good condition that discovered the mechanical hidden trouble. By checking the X-axis ball screw, it was found that the back cover of the ball screw was loose. Because the back cover of the X-axis ball screw is loose, when the roller rotates, because the roller body is oval, and when the cutter touches the place where the size of the upper roller body is relatively large, because the roller body has a "jacking force away from the roller diameter direction" on the X-axis, the X-axis is "jacked" away from the roller diameter direction, and the movement of the X-axis at this time is not caused by the numerical control instruction of the machine tool. However, the grating ruler used to detect the position of the X-axis found that the X-axis moved in the direction of "+X" (away from the diameter of the roller) without the instruction of the numerical control system. The function of grating ruler is to detect whether the linear axis moves accurately under the action of numerical control instructions. If the linear axis does not move accurately, the linear axis will be positioned to an accurate position through the intervention of numerical control system. Therefore, when the cutter touches the place where the size of the upper roller is thin, there is a certain gap between the cutter and the roller. Under the action of the grating ruler, the X axis moves in the direction close to the roller diameter, and is positioned at the X axis coordinate position issued by the numerical control system. In this way, every time the roller rotates, the X axis moves alternately "away from the roller diameter direction" and "close to the roller diameter direction" without numerical control instructions. Therefore, when machining eccentric rollers, the X axis moves back and forth because the back cover of the ball screw is loose.
6. Jizhong RT 125 CNC lathe vibrates when it moves the Z axis.
One day, the RT 125 CNC lathe we bought from Zhong Qi vibrated while moving the Z axis. We thought it was the grating ruler. Later, after inspection, we found traces of iron filings on the upper surface of the guide rail of the lathe.
The way to verify whether the cause of the fault is correct is to change the control mode of the shaft into a semi-closed loop, that is, the shielded grating ruler, which can disappear or reduce the vibration a lot. At this point, some people will say, simply shield the grating ruler and let the machine work. This is only a temporary measure, and the machining accuracy of the rear shaft of the shielding grating ruler is definitely much lower than before.
In the maintenance of CNC machine tools for more than ten years, we have encountered numerous faults related to grating ruler, which are basically the problems of the machine itself. This shows that the grating ruler can also detect the potential mechanical problems of CNC machine tools and show them in the form of faults.
7. The phenomenon that the linear axis of CNC machine tool has a fault when using full closed loop, and it seems to be eliminated when using semi-closed loop.
When the linear axis of the NC machine tool is fully closed, the motor jitter and shaft vibration occur, and the position detection element is shielded, which disappears. Generally speaking, the methods to deal with this kind of fault are as follows:
Firstly, check whether the position detection elements such as grating ruler and reading head are clean, whether the installation position of reading head is reasonable, and eliminate the abnormal factors of position detection elements.
If the position detection element can be guaranteed to be in good condition, there is generally a problem with the mechanical transmission chain of the linear shaft. At this point, check whether the mechanical transmission chain of the linear shaft is loose, whether the mechanical parts are worn, and whether the related lubrication of the mechanical transmission chain is good.
Three, related to the servo motor encoder fault
As the speed feedback element of the servo motor, the encoder will make the linear shaft deviate, no matter whether there is a position detection element or not, as long as the encoder of the servo motor or its line has a virtual connection. Sometimes it is not easy to check the virtual connection of the encoder wire: whether the pin of the plug is short, whether the pin of the plug is skewed, and whether the signal wire welded by the plug is in poor contact with the power wire. Digital multimeter must be used for calibration. Let's give a concrete example to illustrate the difficulty and matters needing attention of calibration.
TS69 16 floor-mounted double-sided boring and milling machine is a product of Qier Machine Tool Works. Before June 5438+00, 2004, it was a machine tool with FAGOR digital display device, but the machinery of each linear axis was configured according to the needs of CNC machine tools. The motor of each linear shaft adopts FXM series AC servo motor of Spain FAGOR company, and the control device of linear shaft adopts AXD series drive device of FAGOR company. The spindle motor adopts Nanyang AC variable frequency motor, and the spindle control system adopts Siemens 6SE70 inverter. In June 2004, it was transformed into a CNC machine tool, and the Spanish FAGOR 8055M CNC system was added. Linear shaft and spindle still use the previous products.
During the period from May 2004 to June 2004, 5438+ 10, the same ram ran about a dozen times. At that time, I was not very familiar with FAGOR CNC system, and everyone thought it was caused by electromagnetic interference. At that time, it was said that the power cord of the spindle motor was ordinary cable, and there was no shielded wire, which affected the operation of the Z axis and occasionally interfered, resulting in the Z axis being out of control. This is just a guess, so at that time, in order to shield the interference signal, a copper wire mesh was pulled around the electrical cabinet. After this treatment, the number of failures did decrease (which proved to be coincidental), but the failure of the same phenomenon still happens once a month from time to time.
At that time, everyone thought that the power cord of spindle motor could be eliminated with shielded cable. In June 2004, at 5438+00, the power cord of the spindle motor was replaced with a shielded cable. The power cord and encoder cable of each servo shaft adopt foreign original high flexible cable. After half a year's transformation, there has not been a fault. Therefore, we believe that the phenomenon of ram flying away before NC transformation is the signal interference caused by the spindle motor not using shielded wire. In May 2005, the same fault occurred five times in a row, which broke people's previous understanding of the cause of the fault. People began to shake the previously formed ideas.
At that time, the control device of ram motor was sent to our electrical laboratory for testing, and it was found that runaway often occurred. Through the search of the line, we sent the drive device to Beijing FAGOR Company for repair, and found no problem with the line. After inspection and testing, there is nothing wrong with the driving device.
Taking the driver back to our electrical laboratory for testing will still lead to deviation from time to time. Re-check the wiring, but still no problem was found. Note: It was later confirmed that the angle of 12 of the encoder cable was a virtual connection. We are prone to make mistakes when checking both ends of the line. This time, I found that the line in the wiring plug leading to the driver's side was loose. At that time, I was holding the plug in my hand, ignoring that the solder joint of the plug itself was open, but there were other wires in the plug, so the 12 corner line would not completely leave the 12 corner.
Reinstall the original drive on the machine tool, check the cable of the test encoder, and no problems are found in the circuit. The machine tool starts to work normally after being electrified. The night after that, the ram ran away. Because of the explanation given to the night shift maintenance personnel, I quickly measured the Z-axis encoder line with a multimeter. At that time, a pointer table was used to measure the lines at all angles of the encoder. After going to work in the morning, I looked at the measurement and sent it to the machine for testing, and found that it was still off track. Quickly measure the line resistance of Z-axis encoder at all angles with a digital multimeter. It is found that all angles except 12 are 0.3 ohms, and it seems that the problem is 0.6 ohms. For the traditional electrical system measurement, generally, the switch is measured by pointer instrument and the numerical control system is measured by digital instrument. 0.6 ohm means that the numerical control system thinks the angle is open. At this point, the cause of the failure is basically clear.
Then why did it happen occasionally before, and then the motor bed returned to normal after the failure?
We know that the formula for calculating wire resistance is r = ρ * l/s.
In the formula, r is the resistance of a piece of wire.
ρ is the resistivity, and its value is related to the material of the wire. The material is unchanged, and the ρ value is unchanged. .
L is the length of the conductor.
S is the cross-sectional area of the conductor.
I analyze that during the operation of the machine tool, the cable of Z-axis encoder is laid in two groove chains, and the passing line is relatively long. In some cases, when the tank chain occasionally stretches the cable, the length of the cable changes little, but the diameter becomes smaller, and its resistance value becomes larger, resulting in the phenomenon that the ram is out of control. When the ram deviates sharply, the machine tool shakes violently and the cable is restored, which makes the machine tool return to normal after re-power.
Replace Z-axis encoder cable and troubleshoot.
Four, CNC lathe spindle box abnormal sound
The newly purchased CK84 140 roll lathe in Qinghai Heavy Machine Tool Factory has two gears in the headstock, and the machine operator responded that there was a sound of gear knocking in the headstock when using high gear. At that time, the mechanic wanted to remove the big cover of the spindle box, so I asked him to pause. In my opinion, if the spindle rotates only when it is in gear position, as the machine tool operator said, then the abnormal sound that hits the gear in the spindle box must be caused by mechanical reasons. I need to check whether the feedback from the machine operator is correct. The results show that in the low speed section of the two gears of the spindle, both the rotating spindle and the spindle box make gear knocking sound. The operator's reaction was incorrect, because the spindle was in the low-speed section of the low-speed gear at that time, and the speed range was very short, so the potentiometer was used to adjust the speed carelessly.
Because the spindle is in the low speed section of two gears, abnormal noise occurs in the spindle box when rotating the spindle. First, it is necessary to check whether the spindle motor rotates smoothly in this speed section. The spindle control system adopts Siemens 6SE70 frequency converter. On the display screen of the frequency converter, the read-only parameter r 19 is used to diagnose the speed of the spindle motor. It is found that the spindle speed is unstable in this speed range. After debugging the spindle speed control system and optimizing the load, the spindle speed is stable, and there will be no gear knocking sound caused by the unstable operation of the spindle motor, and the meshing gear cannot rotate at a uniform speed.
Five, CNC grinding machine grinding cone products abnormal
When CNC grinding machine needs X-axis and Z-axis linkage when grinding conical products or dressing conical grinding wheel, sometimes it will appear: Z-axis moves in one direction and eats more knives; When the Z axis moves in the other direction, the knife is small or intermittent. This phenomenon is that when grinding conical products, when the Z axis moves back and forth, the cutting direction is big, the grinding spark is big, the cutting direction is small and the grinding spark is very small. If the above phenomenon occurs when repairing the tapered grinding wheel, it can be judged from the "rustling" sound of the contact between the diamond pen and the grinding wheel.
In this case, it shows that although the grinding program of CNC grinder is compiled according to the designated cone surface of grinding wheel or product, the linkage speed of X axis and Z axis is not perfectly coordinated at the same time. Why is the NC machining program compiled according to the specified grinding path, but it can't reach the ideal state? This kind of failure without machine alarm is difficult to deal with, and the treatment method is as follows:
1, check whether the diamond pen holder for grinding wheel dressing on the tailstock of CNC grinder is firmly closed on the tailstock and whether the diamond pen holder is loose.
2. Generally speaking, the "proportional coefficient" parameter in the axis parameters of X axis and Z axis is adjusted to the same value, regardless of whether the CNC system adopted by CNC grinding machine is Siemens series, Fager series, bosch rexroth series and Fanuc series. At this time, in the above grinding, the Z axis is in reciprocating grinding. Because the response characteristics of the X axis and the Z axis are the same, the linkage effect of the two axes will be very good.
Six, CNC grinder grinding products appear vibration and spiral phenomenon.
When grinding a product with a CNC grinder, if there are vibration lines or spirals on the surface of the ground product, there may be many reasons, which can be found according to the following conditions:
1. Is the diamond pen loose?
If the diamond pen for correcting the grinding wheel is loose, the surface of the corrected grinding wheel will naturally be uneven, and the surface quality of the ground product is inevitable.
2, grinding wheel spindle and workpiece spindle speed stability.
Check whether the rotating speed of the grinding wheel spindle and the workpiece spindle is stable: when diagnosing the rotating speed of the spindle, let the spindle give a speed, and you can check whether it is changing and how much from the diagnostic parameters of the spindle controller. You can also use a tachometer to measure speed. If the spindle speed is unstable, the surface of the ground workpiece will appear dull.
3, grinding wheel spindle and workpiece spindle motor cooling fan whether there is vibration.
The vibration of the main motor cooling fan directly affects the surface quality of grinding products.
4, grinding head inspection
If the radial runout and axial movement of the grinding head exceed the standard, technical measures should be taken. If the radial runout of the grinding head exceeds the standard value, the viscosity of the grinding head spindle oil can be increased without replacing the grinding head to reduce the influence of the shortcomings of the grinding head on the grinding products.
5. Headbox claw and self-positioning plate
In the rotation of the ground workpiece, if there is relative displacement between the jaw of the spindle box and the ground workpiece; If the spindle box centering plate slides intermittently during the rotation of the workpiece, the surface quality of the ground workpiece will be greatly affected.
Seven, CNC machine hand pulse common faults
Hand-held unit is an indispensable manual operation part of NC machine tool, which can facilitate the tool alignment of machine tool operators. In the years of CNC machine tool maintenance, in order to facilitate the operators to use the machine tool, the common faults and precautions of the handheld unit are as follows:
1. Automatic movement of linear axis of NC machine tool
If the CNC machine tool of Siemens CNC system is used in the manual interface, the linear axis will move slowly without the instruction of the machine operator; If the CNC machine tool equipped with FAGOR CNC system is in the manual interface, the linear axis will move quickly without the instruction of the machine tool operator. At this time, when the handheld unit is in the X-axis activation state, the X-axis will move illegally, and if the Z-axis of the handheld unit is in the activation state, the Z-axis will move illegally. At this point, the root cause of the fault is the loose or virtual connection of the 0 volt line of the handheld unit.
2. When operating with handheld devices, there will be confusion in the selection of axes.
If the hand-held unit is selected to operate the machine tool manually, if the X axis is selected, the X axis will occasionally not run and other axes (such as Z axis) will run during the operation of the X axis. In general, there is no problem with the wire between the handheld unit and the handheld plug from the handheld unit to the operating station. The real fault source is the bare wire sheath on the related line of the handheld unit between the operating station and the electrical cabinet.
3. Several improvements to avoid product accidents or equipment accidents
In daily work, occasionally encounter CNC machine tool operators in the knife or hand-held unit movement, the knife or the knife touches the product quality accident, investigate its reason, generally due to the use of too fast or wrong operation, so in view of these situations, you can take the following error prevention and correction measures.
When moving quickly, use the operation on the numerical control panel. Handheld devices can be used for tool calibration or short-distance movement. At this time, the magnification of "X 100" on the handheld unit can be blocked. The method is to remove the "X 100" line on the handheld unit or modify the PLC program to make the amplification of "X 100" invalid.
Eight, CNC machine tools can't power on normally.
No matter which numerical control system is adopted, when the numerical control machine tool restarts and the display unit cannot run to the normal operation interface, an alarm prompt will appear. In this case, the operating system is usually lost or damaged. If you want to restore the normal operation of the machine tool, you must reinstall the CNC operating system. In view of this situation, as a machine tool maintainer, it is necessary to back up the hard disk when the machine tool is in good condition. If the numerical control system is economical or there is no hard disk, it is necessary to contact the manufacturer to master the handling methods when there is a failure.
Nine, the adjustment method of linear axis motor or drive model change of CNC machine tools.
When the servo motor or its control device of the linear axis of a CNC machine tool fails and needs to be replaced, if there are no ready-made spare parts of the same model, the following steps are generally taken to restore the machine tool to normal.
1. Copy the transmission ratio and pitch parameters of the original machine tool on the display unit before replacing the damaged motor or driving device.
2. Use the corresponding driving software to reconfigure the parameters according to the existing conditions, and set them according to the transmission ratio and pitch parameters.
3. Since the wires of the motor and the driving device are unchanged, after parameterized configuration, the current is limited in the software according to the wire diameters of the original motor and the driving device to prevent the newly replaced motor or the driving device from burning wires due to excessive starting or running current.
Ten, CNC machine tool linear axis positioning accuracy is not allowed.
After some machine tools run for a period of time, the positioning accuracy and repeated positioning accuracy of the linear axis may be accurate. This situation is generally caused by mechanical wear of machine tools after several years of use. In this case, the machine tool can be adjusted according to the following steps.
1. In the past, the transmission ratio on the linear shaft was only the factory value. After several years of use, due to the wear and tear of machinery and other parts, the transmission ratio should be modified according to the actual situation to correct the positioning accuracy of the linear shaft. Some measuring tools, such as standard rod, can be used to measure the positioning accuracy of linear axis. By comparing the command value of the numerical control system with the actual moving length value, the transmission ratio parameters can be fine-tuned in the previous numerical control parameters, especially near the common section, so that the actual moving value of the linear shaft is completely close to the command value.
2. On the basis of correct positioning accuracy, if the repeated positioning accuracy of the linear shaft is still poor, the reverse clearance can be tested in the ordinary section of the linear shaft, and the corresponding parameters can be used to compensate the reverse clearance through the shaft parameters of the numerical control system, so that the repeated positioning accuracy of the ordinary section can meet the requirements of the machine tool.
Eleven, numerical control system and some other cooling faults.
If the dust on the use site of CNC machine tools is large, the maintenance personnel do not check in place or other reasons, the following failures involving heat dissipation often occur.
1. If the numerical control system reports that the similar numerical control system or drive unit is overheated, the general fault reason is that the cooling fans of the numerical control system and drive device referred to in the alarm do not turn, resulting in poor internal cooling of the system. At this point, repair or replace the fan to make the CNC system cool well, that is, cancel the machine tool alarm.
2. If the numerical control system alarms that a system is grounded, it will be inspected and observed. If the appearance is good, mainly check whether the internal components of the system are loose and whether there are scattered screws or gaskets in the system. Under normal circumstances, careful inspection can be repaired.
3. Generally speaking, if the display part alarms overheating, it is caused by the display unit being closed too tightly.
4, CNC machine tool spindle motor overheating phenomenon, generally caused by the following circumstances:
The magnetic field winding of DC motor sends electricity, but the motor does not rotate, so the energy of the magnetic field winding can not be converted into mechanical energy, but can only be converted into heat energy and distributed to the motor.
Although the spindle motor of the CNC machine tool does not rotate, the machine operator does not press the "spindle stop" button, but turns the spindle magnification switch to 0. At this time, the current of the spindle motor is greater than the current during normal rotation and close to the rated current. Because the spindle motor does not rotate, the electromagnetic energy of the main motor can not be converted into mechanical energy, but can only be converted into heat energy, which is dispersed in the motor, which makes the temperature rise of the motor increase sharply and may cause damage to the motor for a long time.
12. Failure caused by poor optimization of drive unit or frequency converter and improper setting of numerical control protection parameters.
In the maintenance of CNC machine tools, we often encounter "seemingly" mechanical faults caused by poor or no optimization of frequency converter, DC speed regulation system and drive unit, which are actually electrical faults. When optimizing, it should follow the requirements and steps of its debugging manual, and if necessary, it should be optimized with load. If the inverter controlling the spindle rotation of CNC machine tools is not optimized, and the starting and braking time is too short, the spindle rotation may be unstable. When the linear axis runs at the start and stop, the setting of the proportional gain coefficient is too large, the setting of the integration time is too small, and the setting of the acceleration parameter of the driving unit is too large, which may cause vibration.
The linear axis of CNC machine tools sometimes has mechanical parts damaged. In addition to the misoperation and collision of machine tool operators, it is also necessary to check whether the numerical control protection parameters of the linear axis are set reasonably. Take FAGOR 8055 numerical control system as an example to illustrate. After the configuration of the drive debugging software, it is necessary to check the set value of the drive parameter CP20 (the limit value of current), which is generally not greater than the rated current value of the servo motor controlled by the drive unit. In addition, a protection parameter, P2 1 (following error in dynamic motion) of "axis parameter" is set. In general, the set value of this parameter is slightly larger than the following error value observed during the normal operation of the linear axis. For other types of CNC systems, you can refer to it.
The above parameter settings are unreasonable. Sometimes when machining a workpiece, especially when two axes are linked, the processed products will have problems or be scrapped. The reason is that the mechanical transmission chain is loose when the machine tool is processed, the numerical control protection parameter setting is unreasonable, and the machine tool does not give an alarm.
Thirteen, contour monitoring or following error cross-border fault
During the operation of CNC machine tools, if Siemens series CNC systems or some CNC systems produced in Europe give an alarm of "contour monitoring", Spain FAG CNC system gives an alarm of "following error out of bounds". In general, don't set the corresponding contour monitoring parameters too large at will, which will cover up the hidden dangers or faults of the machine tool and easily amplify the budding faults. It is to check whether the mechanical transmission chain of the linear shaft is loose, unreasonable assembly, poor lubrication and other problems. Only by solving these problems, when the linear shaft is running, it will not give an alarm under normal circumstances.
In another case, this kind of alarm will also appear, that is, the machine tool parameters are set reasonably, the mechanical transmission chain is good, the tool consumption exceeds the process requirements when machining the workpiece, the process route is unreasonable, there is a problem with the process formulation, or the machine tool stiffness is not enough to maintain the tool consumption at the current shaft running speed. The solution is to reduce the running speed of the shaft and reduce the cutting amount.
Fourteen, some seemingly CNC machine tool equipment failure cases
In the use of CNC machine tools, we often encounter the following situations of machine tool alarm or machine tool operator reporting for repair. Be considerate of the following situations.
1. If the words "XXX characters are impossible" appear, it means that some characters in the processing program do not conform to the specifications and belong to "illegal" instructions. If it is modified to conform to the legal instructions of CNC system, the machine tool alarm will be eliminated.
2, in the long-term maintenance of CNC machine tools, if the product is damaged or scrapped, at this time to judge whether there is a fault in the machine tool, the previous fault and operation information must be accurate. At this time, some people may not tell the truth for their own benefit. If there is a size error below 1mm, it may be caused by the accuracy of the machine tool; If there is an error of more than a few millimeters, it is generally caused by misoperation.
3. The products ground by CNC grinder have poor roundness, so it is necessary to check the tips of headstock and tailstock spindle, and check whether the back cone surface and end surface of the tip and the taper hole on the spindle are clean. If the rear cone and end face of the blade and the taper hole in the spindle are not wiped with clean cloth when replacing the blade, the roundness of the ground product will often exceed the tolerance.
4. When replacing the cutter head, the boring and milling machine should also wipe the inner cone hole of the spindle with a clean cloth. If it is not cleaned, it may cause the tool to jam and easily cause grinding damage to the spindle taper hole.
5. In some numerical control systems, such as FANUC 0TD numerical control system in Japan, when the machine tool operator presses a key less before executing the machining program, the second sentence of the machining program will be skipped and not executed, which will lead to product quality accidents.