Common Fault Diagnosis Methods and Troubleshooting Skills of CNC Lathe Tool Holder
As an important configuration of the CNC lathe, the tool post plays a vital role in the operation of the machine tool. Once a failure occurs, the workpiece may be scrapped, and even an accident of collision between the chuck and the tool post may occur. In the fault maintenance of CNC machine tools, the circuit of the electrical control part is complex, and the fault phenomena are changeable. Some fault phenomena are not obvious, and it is difficult to find them. However, the mechanical part is similar to ordinary machine tools, and the faults are relatively easy to eliminate.
It is inevitable that there will be various failures during the use of CNC lathes, so the maintenance of failures has become the most critical factor for users of CNC lathes. Among the many failures, tool holder failures account for a large proportion. Since the after-sales service of the machine tool sales company cannot be guaranteed in time, knowing some maintenance techniques can quickly determine the location of the fault, shorten the maintenance time, and allow the machine tool to start operating again as soon as possible. Here, it is necessary for us to analyze the failures encountered in the daily work of the tool post and the corresponding solutions.
Preliminary Judgment Method for Tool Post Failure
1. Listen. 1) When receiving a maintenance request, listen carefully to the phenomenon reflected by the operator, and ask clearly about the place where there is any doubt, so as to eliminate the problem caused by human factors. 2) Listen to the running sound of the tool holder on site to observe whether there is any abnormal noise.1. Look. 1) Check whether the tool holder is running normally. 2) Observe the precision of the processed parts and the chip marks on the surface of the parts, so as to judge whether the tool holder is locked and whether the repeated positioning is good.
1. Turn. For some faulty tool holders, do not rush to disassemble them, and turn the tool holders manually. For the four-station tool holder, there is a 6mm inner hexagonal hole at the end of the worm, first remove a sealing screw at the section, and then use a hexagonal wrench or screwdriver to turn the worm, so that the tool holder can be indexed and locked .
Causes and troubleshooting of common tool post failures
Motor failure1) The phase sequence of the three-phase power line is reversed. Remedy: cut off the power immediately, and adjust the phase sequence of the three-phase power supply. 2) The voltage is too low. Troubleshooting method: use it after the power supply voltage is normal or add a stabilized voltage supply to provide a stabilized power supply. 3) The motor is damaged. Remedy: replace the motor.
The tool holder does not rotate or is stuck
1) The spring is broken. Remedy: replace the spring, pay attention not to confuse the two pairs of pins. 2) The guide pin of the clutch is broken. Remedy: Replace the guide pin, pay attention to the position of the pin hole where the clutch is connected to the screw. 3) The main shaft is bent or broken. Remedy: Replace the spindle. The replacement method should be determined by referring to the spindle description of the corresponding tool holder model. Do not change the size of the spindle at will, otherwise it will seriously affect the service life of the tool holder. 4) The guide pin at the outer chainring is broken. Troubleshooting method: replace the guide pin, pay attention to the positional relationship of the outer tooth plate, nut and upper cutter body. 5) The tool post is turned, but the tool post has rotated through multiple tool positions and cannot be fixed at any tool position. Remedy: Detect the static state of the Hall elementState parameters and dynamic parameters, if the parameters are not normal, replace the component. Replace the CPU board and position doubler board.
The knife holder is not locked tightly
1) The position of the sending plate is not aligned. Troubleshooting method: remove the top cover of the knife holder, turn and adjust the position of the sending plate, make the Hall element of the knife holder align with the magnetic steel, and make the knife position stop at an accurate position. 2) The system anti-lock time is not long enough. Troubleshooting method: Just adjust the system anti-lock time parameters (new tool post anti-lock time t=1.2s is enough). 3) The mechanical locking mechanism is faulty. Remedy: Disassemble the knife holder, adjust the machine, and check whether the positioning pin is broken.
The accuracy of the knife holder is not accurate
1) The knife holder is not locked tightly. Remedy: Prolong the locking time of the tool post. 2) There is garbage at the broken teeth. Remedy: Disassemble the knife holder, remove the garbage, clean the parts, add clean butter to the rotating part, and clean engine oil to the end teeth. 3) The pressure mold part of the upper cutter body is deformed under pressure, which makes the gear mesh bad. Remedy: Replace the upper cutter body. 4) The tool holder does not stop continuously or the tool holder does not stop at a certain tool position. Troubleshooting method: Check whether there is a short circuit or an open circuit in the wiring of the sending board. 5) The height position of the Hall element and the magnetic steel is not accurate. Remedy: adjust the relative position of the Hall element and the magnetic steel.
Example analysis of tool post failure
The general process of tool change in CNC lathe is: after the tool change motor receives the tool change signal, it drives the tool post to rotate through the deceleration of the worm gear, and the Hall element sends out the tool position signal. The system then uses this signal to compare with the target value to determine whether the tool is in place. After the knife is in place, the motor reverses to tighten the knife holder.Fault 1: A six-tool CNC lathe, all the tool positions cannot be found when changing the tool, the tool post stops after several weeks of rotation, and the CNC system displays a tool change alarm: tool change timeout or no signal input.
Fault analysis: For this fault, the mechanical fault can still be ruled out, and it is attributed to the electrical fault. The electrical reasons for this fault are as follows: ① The magnetic element falls off; ② All six Hall elements are damaged at the same time; ③ The power supply and signal lines of the Hall element are open, resulting in no voltage signal output. Among them, the third reason is the most likely. Therefore, I found the circuit diagram and used a multimeter to check the power supply circuit of the electrical circuit of the Hall element. It was found that: the 24V power supply voltage on the terminal block of the tool post detection line is 0V, and other lines are normal. Using this line as a clue to search along the line, it was found that the 24V lead from the electrical cabinet fell off, and there was still no response after connecting it. Judging from this, it should be the fault caused by the disconnection of the line.
Solution: Use the wire of the same specification to replace the broken wire, and the fault is eliminated.
Fault 2: In a CNC lathe with four tool positions, the first tool position cannot be found, and other tool positions can be changed normally.
Fault analysis: Since only the No. 1 tool cannot find the tool position, the problem of mechanical transmission can be ruled out, and it is determined to be an electrical fault. It may be that there is a problem with the Hall element of the tool position and its surrounding circuits, causing the tool toBit signals cannot be sent to the plc. After checking with a multimeter against the circuit diagram, it was found that the 24V power supply of the Hall element of tool position 1 is normal, the GND line is normal, and the T1 signal line is normal. Therefore, it can be concluded that the tool position signal cannot be sent out due to the damage of the Hall element.
Solution: After replacing the Hall element with a new one, the fault is eliminated, and the No. 1 knife can be found normally.
Fault 3: A six-tool lathe equipped with FANUC-0imate system Dalian Machine Tool Factory, the tool selection is normal but cannot be locked normally after the selected tool position is in place. System alarm: tool change timeout.
Fault analysis: The tool holder selects the tool normally, and the forward rotation is normal, but it cannot be locked in the reverse direction. 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 post control, it is found that the signal of the tool reverse locking in place is controlled by a position switch. (Source of information: http://www.diangon.com) Is this switch or the surrounding circuit existing? What’s the problem? In order to confirm the cause of this failure, open the top cover and side cover of the tool holder, check the circuit with a multimeter and refer to the circuit diagram, and find that there is no open circuit or short circuit in the circuit, press the reverse locking position switch of the tool holder by hand, and observe the ladder diagram. Signal input, so far eliminate electrical circuit problems. It may be inferred that the block movement is not in place, and the position micro switch has not acted. So I changed the tool again to observe it, and found that: Sure enough, the stopper did not move in place. Then tighten the block bolts and try to change the tool once to be normal. Change the knife again, the original fault reappeared, and at the same time, it was found that the bushing at the end of the worm slipped and climbed. Could it be that the stopper of the position switch was not in place when the motor reversed and locked, so the shaft sleeve was axially positioned, and the top cover of the tool holder was installed. As a result, the knife holder is locked normally.
Solution: Axially locate the shaft sleeve to solve the fault.
Generally, for any fault, first judge the fault point according to the phenomenon and principle, and analyze every possibility, such as a switch, a wire connector, and a screw, all of which will be the cause of the fault. Refer to the previous operation, Analysis of the maintenance history can help narrow the scope of search and improve the efficiency of maintenance.