Structural Principle and Maintenance of Automatic Tool Changer in CNC Machining Center

The automatic tool changer is an important executive mechanism of the machining center. It has various forms, and the common ones are as follows.
1. Rotary tool holder for tool change
The rotary tool holder used by CNC machine tools is the simplest automatic tool change device. There are square tool holders and hexagonal tool holders, that is, four, six or more of knives.
The rotary tool holder must have good strength and rigidity to withstand the cutting force of rough machining: at the same time, it must ensure the repeat positioning accuracy of the rotary tool holder in each indexing.
Figure 1 is a hexagonal rotary tool holder for a CNC lathe, which is suitable for processing disc parts. When machining shaft parts, you can use the square rotary tool holder. Since the bottom installation dimensions of the two are the same, it is very convenient to replace the tool holder.

Figure 1 CNC lathe hexagonal rotary tool post

1-piston 2-tool holder body 3, 7-gear 4-ring gear 5-idle gear
6-piston 8-rack 9-fixed pin 10, 11-push rod 12-contact
The entire movement of the rotary tool post is controlled by the hydraulic system through the electromagnetic reversing valve and the sequence valve. Its action is divided into 4 steps:
(1) The tool post is lifted. When the CNC device issues a tool change command, The pressure oil enters the lower cavity of the compression hydraulic cylinder through hole a, the piston 1 rises, and the tool rest body 2 lifts, so that the movable pin 10 used for positioning is disengaged from the fixed pin 9 . At the same time, the end tooth clutch at the lower end of the piston rod is combined with the idler gear 5 .
(2) Tool holder indexing When the tool holder is lifted, the pressure oil enters the left chamber of the indexing hydraulic cylinder from the c hole, the piston 6 moves to the right, and drives the rack 8 to move through the connecting plate, so that the idler gear 5 Turn counterclockwise. The tool holder is turned by 60º through the end tooth clutch. The stroke of the piston should be equal to 1/6 of the circumference of the 5-point circle of the gear, and it should be controlled by the limit switch.
(3) Tool holder compression After the tool holder is indexed, the pressure oil enters the upper chamber of the compression hydraulic cylinder from the b hole, and the piston 1 drives the tool holder body 2 to descend. On the chassis of the gear 3, six cylindrical fixed pins 9 with wedges are precisely installed, and the movable pins 10 are used to eliminate positioning pins and holes.The gap between them realizes anti-relying positioning. When the tool rest body 2 descends, the positioning movable pin 10 is clamped with another fixed pin 9, and the gear 3 is in contact with the tapered surface of the ring gear 4 simultaneously, and the tool rest is positioned and clamped in a new position. At this time, the end tooth clutch is disengaged from the idler gear 5 .
(4) Indexing hydraulic cylinder reset After the tool post is pressed, pressure oil enters the right chamber of the indexing hydraulic cylinder from hole d, and the piston 6 drives the rack to reset. Since the end tooth clutch has been disengaged at this time, the rack The driving gear 3 idles on the shaft.
If the positioning and clamping actions are normal, the push rod 11 contacts the corresponding contact 12, and a signal is sent to indicate that the tool change process has ended, and the cutting process can be continued.
In addition to using hydraulic cylinder indexing and positioning pin positioning, the rotary tool holder can also use electric motors to drive clutch positioning, and other indexing and positioning mechanisms.
2. Spindle Head Replacement Tool Change
Spindle head replacement is a simple tool change in CNC machines with rotating tools. There are usually two types of spindle heads, horizontal and vertical, and the indexing of the turret is often used to replace the spindle head to realize automatic tool change. Rotary tools required for each process are pre-installed on each spindle head of the turret. When a tool change command is issued, each spindle head turns to the processing position in turn, and the spindle movement is turned on, so that the corresponding spindle drives the tool to rotate, while other spindles in the non-processing position are disengaged from the main movement.
Figure 8-18 is the horizontal eight-axis turret head. On the turret head, eight main shafts 7 with the same structure are radially distributed, and the rotary motion of the main shafts is input by a gear 12 . When the numerical control device issues a tool change instruction, firstly the moving gear 3 is disengaged from the gear 12 through the hydraulic shift fork, and pressure oil is passed through the upper cavity of the central hydraulic cylinder 14 at the same time. Since the piston rod and the piston 15 are fixed on the base, the central hydraulic cylinder 14 is lifted with the turret body 18 supported by the two thrust bearings 17 and 16, and the clutches 2 and 1 are disengaged. Then the pressure oil enters the indexing hydraulic cylinder, pushes the piston rack, and then passes through the intermediate gear to make the large gear 4 and the turret tool holder body 18 rotate 45° together, and turn the main shaft of the next process to the working position. After the indexing is completed, the pressure oil enters the lower cavity of the central hydraulic cylinder 14, which makes the turret head descend, and the clutches 2 and 1 are re-engaged, realizing precise positioning. Under the action of pressure oil, the turret head is compressed, and the indexing hydraulic cylinder returns to its original position. Finally, the gear 3 is moved by the hydraulic fork to mesh with the newly replaced main shaft gear 12 . In order to improve the assembling manufacturability of the main shaft structure, the whole main shaft part is contained in the sleeve 5, as long as the screw 10 is unloaded, the whole part can be drawn out. The main shaft front bearing 9 adopts double-row cylindrical roller bearings with tapered holes. When adjusting, first remove the end cover 6, and then tighten the nut 8 to make the inner ring move axially, so as to eliminate the radial clearance of the bearing.
In order to facilitate the unloading of the tool in the taper hole of the spindle, each spindle has a joystick 13, as long as the joystick is pressed, the rod 11 can be pushed through the inclined surface to eject the tool.
The indexing, positioning and pressing of the turret spindle headThe tightening method is very similar to the rattooth disc indexing table, but the structure is more complicated because there are many rotary spindle parts distributed on the turret.

1, 2-clutch 3, 4, 12-gear 5-sleeve 6-end cover 7-main shaft 8-nut
9, 16, 17-bearing 10-screw 1l-pushing rod 13-operating rod 14 A hydraulic cylinder 15 a piston 18 a turret tool holder body
Due to the limitation of space position, the structure of the main shaft parts cannot be designed to be very solid, thus affecting the rigidity of the main shaft system. In order to ensure the rigidity of the main shaft, the number of main shafts must be limited, otherwise the size of the structure will be greatly increased.
The main advantage of the turret spindle head tool change method is that it saves a series of complex operations such as automatic clamp release, tool unloading, tool loading, clamping and tool handling. Thus, the reliability of tool changing is improved, and the tool changing time is significantly shortened. However, due to the above-mentioned structural reasons, the turret spindle head is usually only used for machine tools with fewer processes and less high precision requirements, such as CNC drilling machines.
3. Automatic tool change system with tool magazine
The automatic tool change system with tool magazine is composed of tool magazine and tool exchange mechanism. Firstly, install all the tools that need to be used in the processing process on the standard tool handles, and after pre-adjusting the size outside the machine, put them into the tool magazine in a certain way. When changing the tool, the tool is first selected in the tool magazine, and the tool is taken out from the tool magazine and the spindle by the tool exchange device. After the tool is exchanged, the new tool is loaded into the spindle, and the old tool is put back into the tool magazine. The tool magazine for storing tools has a large capacity. It can be installed on the side or above the spindle box, or it can be installed outside the machine tool as a separate component, and the tool can be transported by the handling device.
Compared with the turret spindle head, since there is only one spindle in the CNC machine tool spindle box of the automatic tool changer with tool magazine, it is possible to fully enhance its rigidity by designing the spindle components, so that it can meet the requirements of precision machining. In addition, the tool magazine can store a large number of tools, so it can perform multi-process processing of complex parts, which obviously improves the adaptability and processing efficiency of the machine tool. Therefore, the automatic tool changer with tool magazine is especially suitable for CNCDrilling machines, CNC milling machines and CNC boring machines.
The tool magazine is the main part of the automatic tool changer, and its capacity, layout and specific structure have a great influence on the design of the CNC machine tool.

According to the required capacity of the tool magazine and the way of taking out the tool, the tool magazine can be designed in various forms. Figure 8-19 lists the most commonly used ones. Figure 8-19a~d is a single-disk tool magazine. In order to adapt to the layout of the machine tool spindle, the tool axis of the tool magazine can be configured in different directions (as shown in Figure 8-19a~c). The flipped disc tool magazine adopts this structure to simplify the tool picking action. The structure of the single-disk tool magazine is simple, and the capacity of the tool magazine is usually 15 to 30 pieces. It is more convenient to take out the knife, so it is the most widely used. Figure 8-19e is a drum magazine type (also known as a hedgehog type) tool magazine. Its structure is very compact. In the same space, its tool magazine has a larger capacity, but the actions of selecting and taking out knives are more complicated. Figure 8-19f is a chain-type tool magazine, its structure has greater flexibility, and the number of stored tools is also large, and the actions of selecting and taking out tools are very simple. When the chain is long, the number of supporting sprockets can be increased, so that the chain can be folded and rewinded, thereby improving the utilization rate of space. Figures 8-19g and 8-19h are the multi-disc type and grid type tool magazines respectively. Although they also have the characteristics of compact structure, the actions of tool selection and tool removal are complicated and their applications are seldom. The capacity of the tool magazine is generally 10~60, but with the development of processing technology, the capacity of the tool magazine seems to have a tendency to further increase. Figure 8-20 is an example of a chain tool magazine used in a gantry machining center, and Figure 8-21 is an example of a disc tool magazine in a vertical machining center.

8.4.3 Tool exchange device
The tool exchange method of CNC machine tools is usually divided into the tool magazine and the machine tool spindle.There are two types of relative motion to realize tool exchange and using manipulator to exchange tools. The way the tools are exchanged and their specific structure has a direct impact on the productivity and operational reliability of the machine tool.

The tool exchange device is realized by the relative movement between the tool magazine and the machine tool spindle. When changing the tool, the used tool must be sent back to the tool magazine, and then the new tool is taken out from the tool magazine. These two actions are impossible. Simultaneously, so the tool change time is long. The gantry machining center shown in Figure 8-20 is an example of this type of tool exchange method. Its tool selection movement is completed by the rotation of the chain tool magazine driven by the servo motor, and the tool change movement is completed by the spindle box moving along the Y and Z axes.
Using manipulators for tool exchange is the most widely used, because the manipulator tool change has great flexibility and can reduce tool change time. At present, most of the machining centers use the memory-type optional tool change method. This method can store the tool number and the position (address) of the tool holder in the tool magazine in the PC of the numerical control system correspondingly, no matter which tool holder the tool is placed in, it will always remember its trace. The tool magazine is equipped with a position detection device (generally installed together with the motor), which can detect the position of each tool holder, so that the tool can be taken out arbitrarily and sent back. There is also a mechanical origin on the tool magazine, so that each time a tool is selected, it is selected nearby. For example, for a disc tool magazine, each tool selection movement or forward rotation or reverse rotation will not exceed 180º.

Figure 8-22 is the structural diagram of the cam manipulator for tool change, and Figure 8-23 is an example of the cam manipulator tool change action.

The structure of the tool magazine and the tool changing manipulator is relatively complex, and they move frequently during work, so the failure rate is relatively high. At present, more than 50% of the failures on the machine tool are related to it. For example, the movement of the tool magazine is faulty, the positioning error is too large, the manipulator clamps the handle unstable, and the manipulator action error is too large. These failures eventually cause the tool change action to be stuck, and the whole machine stops working. Therefore, the maintenance of the tool magazine and the tool changing manipulator is very important.
1. Key points for maintenance of tool magazine and tool changing manipulator
1) It is strictly forbidden to put overweight and long tools into the tool magazine to prevent the tool from falling or colliding with the workpiece and fixture when the manipulator is changing the tool.
2) In the sequential tool selection method, attention must be paid to the order in which the tools are placed in the tool magazine. In other tool selection methods, attention should also be paid to whether the changed tool is consistent with the required tool, so as to prevent accidents caused by wrong tool replacement.occur.
3) When manually installing the tool on the tool magazine, make sure that it is in place and secure, and check whether the locking device on the tool holder is reliable.
4) Always check whether the zero return position of the tool magazine is correct, check whether the position of the machine tool spindle back to the tool change point is in place, and adjust it in time if any problem is found, otherwise the tool change action cannot be completed.
5) Pay attention to keep the knife handle and knife holder clean.
6) When starting up, the tool magazine and manipulator should be run dry first, and check whether all parts are working normally, especially whether the travel switch and solenoid valve can operate normally. Check whether the pressure of the hydraulic system of the manipulator is normal, and whether the tool is locked on the manipulator reliably. If it is found to be abnormal, it should be dealt with in time.
2. Faults of the tool magazine
The main faults of the tool magazine are: the tool magazine cannot rotate or the rotation is not in place; the tool holder cannot clamp the tool;
(1) The tool magazine cannot rotate or the rotation is not in place. The reasons why the tool magazine cannot rotate may be: ①The coupling connecting the motor shaft and the worm shaft is loose; ②The frequency converter is faulty, and the input and output voltage of the frequency converter should be checked Whether it is normal; ③plc has no control output, it may be that the relay in the interface board fails; ④The mechanical connection is too tight; ⑤The grid voltage is too low.
The reasons why the tool magazine does not turn in place may be: motor rotation failure, transmission mechanism error.
(2) The knife sleeve cannot clamp the tool. The reason may be that the adjustment screw on the knife sleeve is loose, or the spring is too loose, resulting in insufficient clamping force; or the tool is overweight.
(3) The upper and lower sides of the tool sleeve are not in place. The reason may be that the position of the shift fork is incorrect due to improper adjustment of the device or excessive processing error; the feedback signal error is caused by incorrect installation or adjustment of the limit switch.
3. Tool changing manipulator fault
(1) The tool is not clamped tightly and the tool is dropped. The reason may be that the spring pressure of the clamping claw is too small; or the nut behind the spring is loose; or the tool is overweight; or the clamping lock of the manipulator does not work wait.
(2) The tool cannot be released after being clamped. The reason may be that the spring of the loose lock is pressed too tightly, and the jaws cannot be retracted: the nut should be loosened so that the maximum load does not exceed the rated value.
(3) Tool drop during tool change If the spindle box does not return to the tool change point or the tool change point drifts when the tool is changed, the manipulator does not reach the position when grabbing the tool, and starts to pull the tool, which will cause the tool to drop during tool change. At this time, the spindle box should be moved again to make it return to the position of the tool change point, and the tool change point should be reset.
2. 10 maintenance cases of automatic tool changer failure
1. Maintenance of manipulator failure
Example 1. Fault phenomenon: A machining center uses a cam manipulator to change the tool. The structure of the manipulator and the tool change program are shown in Figure 2-22 and Figure 2-23. During the tool change process, the action is interrupted, and a 2035# alarm is issued, and the display content is:Manipulator out of order.
Analysis and processing: According to the content of the alarm, the machine tool is interrupted and an alarm is issued because the machine tool cannot perform the next step of “pulling out the tool from the spindle and tool magazine”.
The manipulator fails to stretch out to complete the action of pulling out the tool from the spindle and the tool magazine. The reasons for the failure may be:
(1) The “cutter release” sensor switch is out of order During the tool change process, the completion signals of each action are Sent by the induction switch, the next action can only be performed after the previous action is completed. The third step is “spindle tool loosening”. If the sensor switch does not send a signal, the manipulator will not act when “pulling the knife”. Check the two sensor switches, the signal is normal.
(2) “Loose knife” solenoid valve failure The “loose knife” of the spindle is completed by connecting the solenoid valve to the hydraulic cylinder. If the solenoid valve fails, the hydraulic cylinder will not be filled with oil, and the cutter will not be “loose”. Check that the “knife loose” solenoid valve of the spindle operates normally.
(3) The “loose knife” hydraulic cylinder does not move due to insufficient pressure of the hydraulic system or oil leakage, or the stroke is not in place. Check the tool magazine loose knife hydraulic cylinder, the action is normal, and the stroke is in place; open the headstock (Figure 8-2 ) rear cover, check the hydraulic cylinder of the spindle tool release, and found that it has reached the tool release position, the oil pressure is also normal, and the hydraulic cylinder has no oil leakage.
(4) There is a problem with the manipulator system, and the condition of “drawing the knife” cannot be established. The reason may be: there is a problem with the motor control circuit. Check the motor control circuit system is normal.
(5) There is a problem with the spindle system. The schematic diagram of the spindle structure is shown in Figure 8-2. The tool is tightened by the disc spring through the pull rod and the spring chuck to tighten the pull nail at the end of the tool handle; when the tool is released, the piston rod of the hydraulic cylinder presses the ejector rod, and the ejector rod pushes the pull rod through the hollow screw. On the one hand, the spring chuck Loosen the pull stud of the tool, and push the pull stud on the other hand, so that the cutter moves to the right and becomes “loose” in the taper hole of the spindle.
The reasons why the spindle system does not release the tool are estimated to be as follows: ①The length of the pull nail at the end of the tool is not enough, so that although the hydraulic cylinder has moved in place, the top of the tool has not been “loosen”; The stroke of the hydraulic cylinder cannot meet the requirement of “knife loosening”; ③There is a problem with the ejector rod, which has been deformed or worn; ④The spring chuck is faulty and cannot be opened; ⑤When the main shaft is assembled and adjusted, the tool movement is adjusted Too small, resulting in some comprehensive factors in the use process can not meet the “loose knife” condition.
Treatment method: Remove the “loose knife” hydraulic cylinder, check and find: this fault is due to the fact that the “extrusion” of the hollow screw is adjusted too small during manufacturing and assembly, so the stroke of the “loose knife” hydraulic cylinder is in place, and The tool does not “press out” enough in the spindle taper and the tool cannot be removed. Adjust the “extrusion” of the hollow screw to ensure that the extrusion of the tool handle in the taper hole of the spindle is 0.4~0.5mm after the hydraulic cylinder stroke of the spindle “loosen the knife” is in place. After the above adjustments, the fault is eliminated.
Example 2. Fault phenomenon: JCS-018A vertical machining center (produced by Beijing Precision Machine Tool Factory) manipulator fails; arm rotation speed is uneven, gas-liquid converter failsThe oil frequency is accelerated, the manipulator does not rotate properly, the arm does not move up and down, or the arm does not reset well. Adjusting the SC-15 throttle valve with manual adjustment can only maintain normal operation for a short period of time, and the exhaust sound gradually becomes muddy, not as clear as normal operation, and finally the tool cannot be changed.
Analysis and treatment process:
1) The arm rotates 75º to grab the tool on the spindle and the tool holder, and it must be firmly grasped in place before the tool can be lowered and removed. After the action is in place, rotate 180º, the tool change position rises to insert the knife respectively, the arm resets again, and the knife sleeve is put on. The arm rotates at 75º and 180º, and its power transmission is the compressed air source to push the gas-liquid converter to convert it into hydraulic oil, which is controlled by the electronic control program instructions, and its rotation speed is adjusted by the SC-15 throttle valve; the reversing is controlled by the 5ED-IONl8F solenoid valve . In general, the life of these components is very long, and problems with such components can be ruled out.

2) Since the upper and lower sides of the knife cover and the upper and lower sides of the arm are driven by independent air sources, and the exhaust is also an independent muffler exhaust port, it is not affected by the transmission of the arm’s rotational force; possible. According to this principle, it is necessary to focus on checking the actuators of the arm rotation system.

3) When the arm rotates at 75º and 180º or does not rotate, the expansion and contraction of the hydraulic cylinder corresponds to the ups and downs of the oil levels of the gas-liquid conversion. It is found that the left and right paired gas-liquid converters have the upper limit on the left and the lower limit on the right, and vice versa. However, a large amount of oil is discharged from the common exhaust port. Analyzing the gas-liquid converter and the nylon pipeline are all airtight installations, so the cause of this failure should be on the hydraulic cylinder of the actuator.

4) Disassemble the hydraulic cylinder of the manipulator and disassemble it for inspection. It is found that the O-ring of the piston support ring has linear wear and cannot be sealed. The inner wall of the hydraulic cylinder is rough, the annular knife pattern is obvious, and the precision is too poor. Replaced the 80 cylinder produced by Beijing Precision Machine Tool Factory, and the fault disappeared after reinstallation and adjustment. It has been in normal operation for 7 years, and the failure of manipulator tool change has not occurred again.

Example 3. Fault phenomenon: A BX-110P machining center equipped with FANUC 11 system, in JOG mode, the manipulator cannot retract its claws when picking up and delivering the tool. When the machine tool is processing the workpiece in the JOG state, the manipulator takes the tool out of the main tool magazine and puts it into the tool feeding box. It cannot retract the claws, but it does not alarm; if the mode is selected to be in the ATC state, the manual operation is normal.

Analysis and processing process: After checking the ladder diagram, it turned out that the limit switch LS916 was not pressed; after adjusting the position of the limit switch, the machine tool returned to normal. But after a period of time, the fault reappeared. It was checked that the LS916 was not loose, but it was not pressed, so it was suspected that the hydraulic cylinder tie rod of the manipulator was not in place. After investigation, it was found that the set screw of the lock nut at the top of the hydraulic cylinder tie rod was loose, which changed the telescopic stroke of the hydraulic cylinder; after adjusting the lock nut and tightening the set screw, the fault was eliminated.
Example 4. Fault maintenance of incomplete tool change
Fault phenomenon: The knife chain does not run properly during automatic tool change. When the automatic tool change program is performed, the tool magazine starts to run, but the tool to be changed is not driven in place, and the tool magazine stops running. After 3 minutes, the machine tool will automatically alarm.
Analysis and processing process: MPA-H100A machining center is produced by Hiroshima Koki Factory of Mitsubishi Corporation. According to the above fault checking and alarming, it is known that the tool change time is exceeded. At this time, in the MDI mode, no matter whether the clockwise rotation or counterclockwise rotation operation command of the tool magazine is manually input, the tool magazine will not act. Check the electrical control system, no abnormalities are found; the LED on the PLC output indicator lights up, indicating that the PLC has output, and the LED on the counterclockwise side of the solenoid valve for clockwise and counterclockwise transmission of the tool magazine lights up, indicating that the electromagnetic The valve is powered, and the tool magazine does not move at this time, then the problem should occur in the hydraulic system or other aspects. However, the pressure of the hydraulic system is normal, and all oil passages are unblocked without blockage; checking the hydraulic components of each hydraulic valve did not find any problems, and it is estimated that the fault may be on the hydraulic motor. For this reason, the protective cover was removed, the hydraulic motor was removed, and the parts that could be disassembled for inspection were inspected, and no problems were found; then the hydraulic motor was sent to Dalian Combined Machine Tool Research Institute for appraisal, and the test conclusion was that The hydraulic motor is intact. After careful analysis and research by the comrades present, it was believed that there could only be one problem, that is, a mechanical failure; however, there were no obvious signs of damage to all parts and components of the tool magazine, so mechanical damage could be ruled out; finally The problem comes down to one point, that is, the load of the tool magazine is too heavy, or there are blocked parts, so that the hydraulic motor cannot move.
In fact it is. When we process the 10t forklift box, due to the complex workpiece and many processing surfaces, we use more than 40 cutting tools, and the large cutting tools, long cutting tools (the longest cutting tool reaches 550mm), heavy cutting tools (the heaviest The amount of tool used is very large, and we ignore the distribution of tools on the tool magazine. The heavy and long tools are not evenly distributed on the tool magazine, but concentrated in one section, so that the chain belt of the tool magazine is caused. If the part is pulled too tightly, the deformation will be large, and there may be a block phenomenon, so the hydraulic motor of the machine tool cannot move. We ended up loosening the adjustable part of the tool changer chain belt a little bit and everything came back to normal, indicating that the problem was indeed mechanical.
Note: The chain belt of the tool magazine should not be adjusted too loosely, otherwise there will be a danger of “flying knives”. Once, when the manipulator was grabbing the tool on the side of the tool magazine, when the tool was pulled out, then raised, and then rotated 180°, the tool was suddenly thrown out, which almost caused a catastrophe. Analyzing the cause of this failure, it is because the chain belt of the tool magazine is too loose. The two claws of the manipulator of the machine tool are pushed outward by the outer diameter of the tool handle by the downward thrust, and then the tool is clamped by the tension of the spring. When the manipulator grabs the knife downward, because the chain belt is too loose, the chain belt also follows the machineThe hand arches downward due to the downward thrust. As a result, the jaws of the manipulator only grab more than half of the knife handle, and do not fully grasp and grasp it. When the manipulator rotates, due to the heavy weight of the knife, under the action of centrifugal force, The tool is thrown out along the tangential direction. After tightening the chain belt a little bit, it never happened again.
Maintenance experience: There are two types of drive systems for tool magazines, one is mechanical transmission and the other is hydraulic transmission. The MPA-H100A machining center is a product of the early 1980s. It adopts hydraulic transmission, that is, hydraulic motors, solenoid valves, flow control valves, etc. are used to drive the operation of the tool magazine. Compared with the tool magazine driven by frequency conversion speed regulating motor, its electrical control system is much simpler and more intuitive, and it is generally less prone to failure. But it will also change with the environment of the equipment, processing conditions, complexity of the workpiece, and the number of tools used, especially the length of the tool, the weight of the tool, and the distribution of the tool in the tool library. These are all faults. possible factors.
Maintenance of Rotary Turret Failure
Example 5. Fault phenomenon: SAG210/2NC CNC lathe tool post motor does not start, and the tool post cannot move.
Analysis and processing process: SAG210/2NC and CKD6140 and CNC lathe, the supporting tool post is LD4-I four-station electric tool post.
Analyzing the cause of the fault, it may be that the phase sequence of the motor is reversed or the power supply voltage is low, but the fault cannot be ruled out by adjusting the armature line of the motor and the power supply voltage. It indicates that the fault is caused by mechanical reasons. Remove the motor cover, rotate the fan blade of the motor, and find that the resistance is too large. After removing the motor for further inspection, it was found that the worm bearing was damaged, and the quality of the motor shaft and the worm clutch was poor, causing resistance to the motor.
After replacing the bearing and repairing the clutch, the fault is eliminated.
Example 6. Fault phenomenon: The upper tool body of the SAG210/2NC CNC lathe tool holder is lifted but the rotation is not in place.
Analysis and processing process: The supporting tool post of this lathe is the same as the above example. According to the analysis of the mechanical principle of the electric knife holder, if the upper knife body cannot rotate, it may be that the coarse positioning pin is stuck or broken in the taper hole. After disassembling the electric knife holder and replacing it with a new positioning pin, the upper knife body still cannot rotate in place. When re-disassembling, it was found that when assembling the upper cutter body, it should be aligned with the four sides of the lower cutter body, and the tooth disc must be engaged. After assembling according to the above requirements, the fault was eliminated.
Example 7. Fault phenomenon: The positioning of the tool post of the Hungarian EEN-400 CNC lathe is not accurate.
Analysis and processing process: EEN-400 CNC lathe is produced by SEIN Company in Hungary, and the matching tool holder is produced in Bulgaria, which can hold 6 knives. After investigation, the main reason for the inaccurate positioning is that the mechanical wear of the tool holder part is serious, which can no longer be solved by conventional adjustments, tool compensation gap compensation and other means, and the overall replacement needs to be considered. It is understood that the domestic CNC tool holder manufacturers have been able to produce horizontal 6-bit tool holders with the same performance, and they can be used after proper treatment.
Take Shaanxi ProvinceAfter replacing the original tool holder, the JYY horizontal CNC electric tool holder produced by the Machinery Research Institute has recovered its positioning accuracy. After more than a year of use, it has been normal.
Example 8. Fault maintenance of out-of-control processing dimensions
Fault phenomenon: The processing size of Nanjing JN series CNC system cannot be controlled.
Analysis and processing process: The machine tool is an economical CNC lathe transformed by adopting the JN series machine tool CNC system of Nanjing Jiangnan Machine Tool CNC Engineering Company, and its tool holder is LD4-I electric tool holder.
In the process of product processing, the processing size of this machine tool cannot be controlled. After the operator modifies the parameters in the system every time, the size displayed on the digital display is very different from the actual processed size. The change is irregular, even if the processing parameters of the system are not modified, the size of the processed product is constantly changing. Because the machine tool is mainly used for inner hole processing, the change of size is mainly reflected on the X axis. In order to determine the fault location, the replacement method is used to exchange the driving signal of the X-axis and the driving signal of the Z-axis, that is, the 2-axis control signal is used to drive the X-axis, and the X-axis control signal is used to drive the Z-axis. The fault still exists after the replacement, which means that the drive signal of the X-axis is not faulty, and it also shows that the source of the fault should be on the X-axis stepping motor and its transmission mechanism, ball screw and other hardware.
Check that the above-mentioned transmission mechanism, ball screw and other hardware are free of faults, and further check that the X-axis axial repeat positioning accuracy is also within its technical indicators. What is the reason that the X-axis processing size cannot be controlled? Thinking about the idea of ​​checking and analyzing the fault, it is found that an important part is ignored in the analysis and inspection-the electric tool holder.
Check the repetitive positioning accuracy of each tool number of the electric tool holder, and find that the positioning of the electric tool holder is not accurate. Analyze the reasons for the inaccurate positioning of the electric tool holder. If the mechanical positioning of the electric tool holder itself is inaccurate, the fault should be fixed and the processing size cannot be controlled. There must be other reasons for the failure. Check the rotation of the electric knife holder, and found that when the electric knife holder is lifted, there is an iron filing stuck in it. Iron filings make the positioning inaccurate, which is the source of the fault.

Disassemble the electric knife holder, blow off the iron filings on the positioning tooth plate of the electric knife holder with compressed air, and reassemble the electric knife holder, and the fault is eliminated.

Example. Troubleshooting when the tool magazine cannot rotate

Example 9. Fault phenomenon: The knife chain does not run properly during automatic tool change. When the automatic tool change program is performed, the tool magazine starts to run, but the tool to be changed is not driven in place, and the tool magazine stops running. After 3 minutes, the machine tool will automatically alarm.

Analysis and processing process: The chain tool magazine used by TH42160 gantry machining center is shown in Figure 8-20, and its supporting CNC system is SIEMENS 840D.
According to the above fault investigation and alarm, it is known that the tool change time is exceeded. At this time, in the MDI mode, no matter whether the clockwise rotation or counterclockwise rotation operation command of the tool magazine is manually input, the tool magazine will not act. Checked the electrical control system, found nothingAbnormal; the light-emitting diode on the PLC output indicator lights up, indicating that the PLC has output, then the problem should occur in the mechanical transmission. It is estimated that the fault may be on the reducer. For this reason, the protective cover was removed, the servo motor was removed, and the reducer was disassembled. It was found that the coupling key on a transmission shaft in the reducer fell off, causing the power transmission line to be interrupted, and the tool magazine could not rotate. After repairing the reducer, the fault was eliminated.
Example 10. Fault phenomenon: when the tool chain does not run properly during automatic tool change, the tool magazine stops running, and the machine tool automatically alarms.
Analysis and processing process: The chain tool magazine used by TH42160 gantry machining center is shown in Figure 8-20, and its supporting CNC system is SIEMENS 840D.
According to the above fault investigation and alarm, it is known that the servo motor of the tool magazine is overloaded. Check the electrical control system, no abnormality is found, the problem should occur in mechanical transmission or other aspects: ①There is a foreign object stuck in the tool magazine chain or reducer: ②The tool on the tool magazine chain is too heavy: ③Poor lubrication: After checking the above Three items are normal. After removing the servo motor, it was found that there was a lot of cutting fluid inside the servo motor, which caused a short circuit of the coil. The reason for the observation is that the sealing ring at the connection between the motor and the reducer is worn, which causes the cutting fluid to seep into the motor. After replacing the sealing ring and servo motor, the fault is eliminated.