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Fault Diagnosis And Repair of CNC Machining Center Tool Holder-6 Core Problems

The CNC tool post is the most common auxiliary device of the CNC machining center. It enables the CNC lathe to complete various or even all processing procedures in one clamping of the workpiece, to shorten the auxiliary time of processing and reduce the number of installations of the workpiece during the processing.

The errors caused thereby improve the machining efficiency and machining accuracy of the machine tool.

Learn more: How To Improve Accuracy And Precision In CNC Machining?

Yijin Solution repair engineers have many years of maintenance experience to share with you the fault diagnosis and maintenance of the tool holder.

Fault Diagnosis And Repair of CNC Machining Center Tool Holder

The Fault Diagnosis and Maintenance of the Tool Holder

1. The Tool Rest Will Not Start

The preload of the tool post is too large. When the end of the worm is inserted with a wrench to rotate, it is not easy to rotate, but it can be rotated when it is pressed, but the tool holder still cannot start after the next clamping.

When this phenomenon occurs, it can be determined that the reason why the tool post cannot be started is that the pre-tightening force is too large, which can be eliminated by adjusting the clamping current of the small tool post motor.

  • Mechanical Reasons

The internal mechanism of the rack is stuck. When the worm is rotated from the end of the worm, it cannot rotate in a clockwise direction. The reason is that the machine is stuck.

First of all, check whether the clamping device is in the groove of the ratchet against the positioning pin.

If it is, you need to rotate the ratchet and the screw connection pinhole by an angle to re-punch and connect; second, check if the spindle nut is locked, such as the nut is locked and should be re-adjusted again, due to poor lubrication, the rotating parts should be ground to death. At this time, it should be disassembled to observe the actual situation and be lubricated.

  • Electrical Reason

The power is not connected and the motor does not rotate. Check whether the fuse is intact, whether the power switch is well connected, whether the switch position is correct, and whether the voltage value is within the specified range when measuring the voltage with a multimeter.

It can be eliminated through corresponding measures such as replacing the fuse, adjusting the switch position, and making the connected part contact well. In addition to this, the reasons for the power failure can also be considered as the cable break between the tool post and the controller, the internal disconnection of the tool post, the change of the position of the brush-type Hall element, and the failure of normal on and off.

The forward input terminal and the reverse input terminal of the converter are disconnected.

The moving tool is normal, and the machine control does not change the tool. The lead wire of the grating machine and the tool holder controller, the computer I/O interface, and the tool holder-in-place response signal should be checked.

In the ladder diagram, the forward output signal Y0.0 and the reverse output signal Y0.1 are output at a low level when a signal is an input, which causes the corresponding relay to have no output.

  • A Certain Knife Mark of the Knife Rest Can Be Rotated

The hall element of this tool position is damaged. Confirm which tool position is causing the tool post to rotate continuously, input a command on the system to rotate the tool position, and use a multimeter to measure whether there is a voltage change between the signal contact of the tool position and the 24V contact.

If there is no change, it can be judged that the Hall element of the tool position is damaged, just replace the sending plate or the Hall element.

The tool position signal line is broken, causing the system to fail to detect the tool position signal. Check whether the connection between the tool position signal and the system is open, and connect it correctly.

There is a problem with the system’s tool position signal receiving circuit. Replace the main board when it is confirmed that the Hall element of the tool position is Okay and the connection between the tool position signal and the system is okay.

2. The Knife Holder Does Not Lock Properly

1) The position of the sending plate is not aligned. Disassemble the top cover of the knife holder, rotate and adjust the position of the sending plate, make the hall element of the knife holder align with the magnetic steel, and stop the knife position at an accurate position.

2) The system anti-lock time is not long enough. Just adjust the system anti-lock time parameter (the new tool post-anti-lock time t is 1.2s).

3) Failure of the mechanical locking mechanism. Disassemble the knife holder, adjust the machine, and check whether the positioning pin is broken.

The Tool Post Runs Continuously and Does Not Stop in Place

1) Since the CNC machining center’s tool post can run continuously, the possibility of mechanical failure is small, and the inspection is mainly from the electrical aspect.

2) Check whether the in-position signal is sent out. If there is no in-position signal, it is a failure of the sending board.

3) Check whether the elastic contact of the sending plate is worn out, whether the ground wire of the sending plate is open, poor contact, or missing. At this time, it is necessary to replace or re-repair the elastic contact.

According to the contact of the relay in the circuit, the contact of the switch in place, and the connection of the circuit, carry out the line fault elimination accordingly.

4. The Tool Post Is Overshooting or Not Turning in Position

1) The tool post overshoots offside. The mechanical cause of this failure is more likely, mainly because the backing device does not work.

  • First, check whether the back positioning pin is flexible and whether the spring is fatigued. At this time, the positioning pin should be repaired to make it flexible or replace the spring.
  • Secondly, check whether the connection between the rear ratchet and the worm is disconnected. If disconnected, the connection pin needs to be replaced.
  • If the overshoot still occurs, it may be due to the tool being too long and heavy. The positioning pin spring with a slightly larger elastic modulus should be replaced.

2) The fault is mainly caused by the dislocation of the contact between the sending plate and the elastic plate, that is, the fixed offset of the bakelite plate position of the tool position signal.

  • First, adjust the position of the sensing plate and the contact of the elastic plate and fix it firmly.
  • If the fault still cannot be eliminated, the clamping nut of the sending plate may be loose, causing the position to move.

5. The Tool Post Can Be Rotated By Inputting The Tool Number, and the Tool Post Cannot Be Rotated By Directly Pressing The Tool Change Key

1) The Hall element deviates from the magnetic block and is placed in front of the magnetic block. When the tool is changed by manual key, the tool post is detected as soon as the tool post rotates, and then the tool post is reversed immediately.

At this time, check whether the Hall element on the sending plate of the tool post deviates from the position, and adjust the position of the sending plate to make the Hall element align with the magnetic block.

2) The manual tool change key fails, and the manual tool change key can be directly replaced at this time.

6. The Cutter Number is Not the Same as That Shown in the Lathe System

  • This situation usually occurs after the tool post is repaired, and it is a new problem caused by the repair. One possibility is that the position of the magnetic block is incorrect; the other possibility is the connection problem of the circuit in the tool holder.
  • Part of the magnetic block of the knife holder is in the upper cover of the knife holder. At this time, the position of the upper cover cannot be installed arbitrarily after repair.
  • Generally, mark the subsequent installation before repairing. Of course, you can also change the position of the upper cover after repair to find its correct position.
  • Generally, the circuit problem of the tool holder cannot be solved by simply changing the position of the magnetic block. Now you can only change the position of the wiring head.

As a repairer, you must pay attention to the correct position of each wiring head in the tool holder before repairing it.

Some repairers think that they see instructions printed in the tool holder and figure out the marked wiring sequence of each line. That is to say, this is not enough. In addition to the sequence, pay attention to which wire pile the joint is connected to.

Generally, when the sequence of each thread is known, the corresponding two thread ends are marked with thread deduction and other means.

Based on the above cause analysis, inspection methods, and solutions, it is helpful CNC machining center to find the cause of the fault in a timely and effective manner, and quickly eliminate the fault.

Economical CNC lathes are commonly used machine tools. In the maintenance process, we must pay attention to not only good repairs but also fast repairs.

To do a good job in machine tool maintenance is not only to master the theory but more importantly, to continuously summarize and improve in practice to accumulate rich maintenance experience, so that the CNC lathe tool holder can be repaired efficiently.


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