Detection and maintenance of common faults in CNC lathe rotary tool holder - News - Global IC Trade Starts Here Free Join

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As an important configuration of CNC lathes, rotary tool holder plays a vital role in the operation of machine tools. Once a fault occurs, it is likely to cause the workpiece to be scrapped or even cause an accident of collision between the chuck and the tool holder. In the fault repair of CNC machine tools, the circuit of the electric control part is complicated, the fault phenomenon is changeable, some fault phenomena are not obvious, the search difficulty is relatively large, and the mechanical part is similar to the ordinary machine tool, and the fault is relatively easy to eliminate.
CNC tool holder: CNC tool holder is the most common auxiliary device for CNC lathe. It can make CNC lathe complete a variety of or even all processing steps in the workpiece one-time clamping, in order to shorten the auxiliary time of processing and reduce the processing time. The error caused by the installation of the workpiece multiple times, thereby improving the machining efficiency and machining accuracy of the machine tool. Divided into row of tool holders, rotary tool holders and automatic tool changers with tool magazines! Also divided into a universal knife holder and a special knife holder! Working principle: When the tool change is needed, the control system issues the tool post indexing signal, the three-phase asynchronous motor rotates in the forward direction, and the screw rotates forward through the worm pair. The upper body of the screw is gradually lifted up, the upper body and the lower part The face tooth between the cutter bodies is slowly disengaged; at the same time, the upper cover disc also rotates with the forward direction of the screw (the upper cover disc 1 is coupled with the screw through the cylindrical pin), when rotated about 270°, The other end of the straight groove of the cover disc is turned directly above the cylindrical pin. Due to the action of the spring, the cylindrical pin falls into the straight groove, so that the upper cover disc passes the cylindrical pin to rotate the upper cutter body (the end face tooth has already been Completely disengaged).
During the rotation of the upper cover disc, the cylindrical pin and the upper cutter body, the opposite pin can slide out from the left side slope of the cross recess in the opposite disc, without affecting the forward rotation of the upper cutter body when searching for the cutter position.
When the upper cutter body drives the magnet to the required tool position, the corresponding Hall element on the transmitting plate outputs a low level signal, and immediately after the control system receives the control, the tool holder motor is reversed, and the upper cover disk is driven by the cylindrical pin. The upper body begins to reverse, and the opposite pin will fall into the cross groove against the disc, and the coarse positioning is completed. At this point, the opposite pin can't climb up from the cross groove against the disc, so the upper body stops rotating and begins to descend, while the upper cover disc continues to reverse, and the left side slope of the straight groove will be the head of the cylindrical pin. The portion is pressed into the pin hole of the upper cutter body, and then the lower surface of the upper cover disc starts to slide with the head of the cylindrical pin. During this period, the face teeth of the upper and lower cutter bodies are gradually meshed to achieve fine positioning. After the set delay time, the tool holder motor stops, and the entire tool change process ends.
Since the worm pair has a self-locking function, the tool holder can work stably. Function: The tool holder on the CNC machine tool is an important part of the tool placement. Many tool holders also directly participate in the cutting work, such as the square tool holder on the horizontal lathe, the turret tool holder on the turret lathe, and the return-turn turret lathe. The returning knife holder, the turret of the automatic lathe and the balance tool holder. These tool holders are placed in the tool and are directly involved in cutting and subjected to great cutting forces, so it is often a weak link in the process system. With the development of automation technology, there are many changes in the tool holder of the machine tool, especially the automatic tool holder that uses electric (liquid) transposition on the CNC lathe, and some also use two rotary cutters. The machining center further uses the tool magazine and the tool changer to determine the function of the large-capacity storage tool and the automatic exchange tool. The number of tools placed in the tool magazine ranges from tens to hundreds, and the time for automatic tool exchange is changed from Decrease in a dozen seconds to a few seconds or even a fraction of a second. Therefore, the performance and structure of the tool holder often directly affect the cutting performance, cutting efficiency of the machine tool and reflect the design and manufacturing technology level of the machine tool.

In the process of using the CNC lathe, various failures will inevitably occur, so the repair of the fault becomes the most critical factor for the users of the CNC lathe. Among the many failures, the tool holder failure accounts for a large proportion. Since the after-sales service of the machine tool sales company cannot be guaranteed in time, it is understood that some maintenance techniques can quickly determine the fault location, shorten the repair time, and enable the machine tool to operate as soon as possible. Here, it is necessary to analyze the faults encountered in the daily work of the tool holder and the corresponding solutions.

Preliminary judgment method for a tool post failure condition

1 Listen. 1) When receiving the maintenance request, you should listen carefully to the phenomenon reflected by the operator. If there is any doubt, you should ask clearly to eliminate the problems caused by human factors. 2) Listen to the operation sound of the tool holder in order to observe whether there is abnormal noise.
2 Look. 1) See if the tool holder is running normally. 2) Observe the accuracy of the machined part and the chip marks on the part surface to judge whether the tool holder is locked and whether the repeating positioning is good.
3 turns. For some faulty tool holders, do not rush to disassemble, you can manually rotate the knife holder. For the four-station tool holder, the worm end has a 6mm hexagon socket. First remove the sealing screw at the section, then use the hex wrench or the screw driver to rotate the worm to make the tool holder index and lock. .

Causes and troubleshooting methods for common faults of two tool holders

1 Motor failure 1) The phase sequence of the three-phase power line is reversed. Remedy: Turn off the power immediately and adjust the phase sequence of the three-phase power supply. 2) The voltage is too low. Remedy: After the power supply voltage is normal, use or increase a stable voltage to provide a regulated power supply. 3) The motor is damaged. Remedy: Replace the motor.

2 The tool holder does not rotate or is stuck 1) The spring breaks. Remedy: Replace the spring, pay attention to the two pairs of pins do not mix. 2) The guide pin of the clutch is broken. Remedy: Replace the guide pin and pay attention to the position of the pin hole connecting the clutch to the screw. 3) The main shaft is bent or broken. Remedy: Replace the spindle. The replacement method should be based on the spindle description of the corresponding tool holder model. Do not change the spindle size at will, otherwise the service life of the tool holder will be seriously affected. 4) The guide pin at the outer end tooth plate is broken. Remedy: Replace the guide pin, pay attention to the positional relationship between the outer end tooth plate, nut and upper body. 5) The tool holder is indexed, but the tool holder is rotated over multiple positions and cannot be fixed at any position. Remedy: Detect the static parameters and dynamic parameters of the Hall element. If the parameters are not normal, replace the components. Replace the CPU board and position board.

3 The knife holder lock is not tight 1) The position of the transmission tray is not aligned. Remedy: Disassemble the top cover of the tool holder, turn and adjust the position of the transmission plate, so that the Hall element of the tool holder is aligned with the magnetic steel, so that the position is stopped at the exact position. 2) The system lock time is not long enough. Remedy: Adjust the system anti-lock time parameter (new tool post lock time t = 1.2s). 3) The mechanical locking mechanism is faulty. Remedy: Remove the tool holder, adjust the machine, and check if the positioning pin is broken.

4 Tool holder accuracy is not allowed 1) The tool holder lock is not tight. Remedy: Extend the tool holder locking time. 2) There is garbage at the broken teeth. Remedy: Disassemble the knife holder, remove the garbage, clean the parts, add the cleaning butter to the rotating part, and add the clean machine oil to the end teeth. 3) The pressure of the upper cutter body is deformed by the pressure to make the gear teeth poor. Remedy: Replace the upper body. 4) The tool holder does not stop continuously or the tool holder does not stop at a certain position. Remedy: Check the transmitter wiring for short circuit or open circuit. 5) Hall element and magnet steel height position is not allowed. Remedy: Adjust the relative position of the Hall element to the magnet.

Analysis of three tool post failure examples

The general process of changing the tool of the CNC car is: after the tool change motor receives the tool change signal, the tool holder rotates by the worm gear speed reduction, and the tool position signal is sent by the Hall element, and the numerical control system uses this signal to compare with the target value to judge. Whether the tool is in place. After the knife is changed into position, the motor reverses and tightens the tool holder.
Fault 1: A six-knife CNC lathe, all the tool positions can not be found when the tool is changed, the tool holder rotates after several weeks, and the CNC system displays the tool change alarm: the tool change timeout or no signal input.
Fault analysis: For this fault, mechanical faults can still be ruled out due to electrical faults. The electrical causes for this fault are as follows: 1 the magnetic component is off; 2 the six Hall components are all damaged at the same time; 3 the power supply of the Hall component and the open signal line result in no voltage signal output. Among them, the third reason is the most likely. Therefore, the circuit diagram is found, and the power supply line of the electric circuit of the Hall element is inspected by the multimeter. It was found that the 24V supply voltage on the terminal block of the tool post detection line was 0V, and the other lines were normal. Looking along the line with this line as a clue, it was found that the 24V wire lead drawn from the electrical cabinet fell off and remained unresponsive after the connection. Therefore, it should be judged that the line is broken and caused a malfunction.
Solution: After replacing the broken wire with the same specification wire, the fault is eliminated.
Fault 2: A four-blade CNC lathe, the failure of the No. 1 tool position can be found, and other tool positions can be changed normally.
Fault analysis: Since only the No. 1 knife can not find the tool position, the problem of mechanical transmission can be ruled out and it is determined that it is an electrical fault. It may be that there is a problem with the Hall element of the tool location and its surrounding lines, so that the tool position signal cannot be sent to the plc. After checking the multimeter with the multimeter, it is found that the 24V power supply of the No. 1 tool position Hall element is normal, the GND line is normal, and the T1 signal line is normal. Therefore, it can be concluded that the Hall element is damaged and the position signal cannot be emitted.
Solution: After replacing the new Hall element, the fault is solved and the first knife is found normally.
Fault 3: A six-position lathe equipped with the FANUC-0imate system Dalian Machine Tool Plant, the knife selection is normal but cannot be properly locked after the selected tool position is in place. System alarm: Tool change timed out.
Fault analysis: The tool holder is normal, and it is normal, that is, it cannot be locked in reverse. It shows that the worm gear transmission is normal, and it is initially determined to be an electrical circuit problem. On the electrical schematic diagram of the machine tool holder control, it is found that the reverse locking signal of the tool is controlled by a position switch. Is there a problem with the switch? In order to confirm the cause of the failure, open the top cover and side cover of the tool holder, check the circuit with the multimeter with reference to the circuit diagram, and find that there is no open circuit or short circuit on the line. By pressing the tool holder to lock the position switch by hand, observe the ladder diagram. Signal input, thus eliminating electrical wiring problems. It is inferred that the movement of the stopper is not in place and the position micro switch does not operate. So I changed the knife again to observe it, and found that: the block did not move in place. Then tighten the stopper bolts and try to change the knife once. After changing the knife again, the original fault appeared again, and the sleeve of the worm end was found to slip and climb. Is it that the stop of the position switch is not in place when the motor is reversely locked, so the sleeve is axially positioned and the top cover of the tool holder is mounted. As a result, the tool holder is locked properly.
Solution: The axial positioning of the bushing is solved.

Four conclusions

Generally, for any fault, firstly, according to the phenomenon, the fault point is judged according to the principle, and each possibility is analyzed, such as a switch, a wire joint, and a screw will be the cause of the fault, referring to the previous operation and maintenance history. Analysis can help narrow down the search range and help improve the efficiency of maintenance.