Fault Analysis of CNC Tool Holder

As an important configuration of the CNC lathe, the tool holder plays a vital role in the operation of the machine. Once the failure occurs, it is likely to cause the workpiece to be scrapped or even cause the chuck to collide with the tool holder. In the fault repair of CNC machine tools, the complex fault phenomenon of the electric control part is variable. Some fault phenomena are not obvious. The difficulty of finding is relatively large, and the mechanical part is similar to the ordinary machine tool. When looking for the cause of the fault, it is necessary to find both mechanical and electrical aspects at the same time.

First, CNC tool holder failure and handling

(1) The cause of the failure of the knife holder tool change or the tool holder cannot be locked and the treatment

1, the cause of the failure

The following is an example of a lathe equipped with a GSK980TD system (Guangzhou CNC system):

When the lathe is machining the outer circle of the workpiece, the outer knife suddenly appears to be “saw knife”. After the operator presses the “reset” button to return to the reference point, it is carefully checked: first check whether the tool is loose or damaged, and the tool is in good condition; secondly, check the workpiece blank amount. Whether it is too large to meet the requirements; because it is midway, it is certain that the machining program will not be problematic; therefore, the operator suspects that the "tool compensation value" may be incorrectly corrected after the tool is recalibrated. The same is true; the cause of the failure is difficult to detect.

The operator resets the machine system and reassembles another workpiece. The test results are normal. Just after several workpieces are continuously processed, the same fault suddenly appears again. After the above-mentioned series of inspections, the cause of the fault is still not detected. Finally, the professional maintenance personnel are communicated with the operator. The maintenance personnel first measure the input voltage and current of the machine tool system. The results are all normal and may be mechanical failure.

Therefore, the manual test drive moves the vertical and horizontal carriages, starts the spindle, and rotates the cutter holder. When the manual cutter is continuously rotated, the cutter holder is suddenly found to be loose. During the operation of the machine, the automatic locking is not determined. The tool holder system is faulty, but during the machining process. If the "alarm number" is not displayed after the fault occurs, it is definitely a mechanical failure of the tool post.

After the maintenance personnel disassembled the tool holder, it was found that one of the springs in the inner side was broken by the pin (the four sides of the CNC electric four-station square tool holder were equipped with four spring positioning anti-pins). When the workpiece was processed, the blank amount was slightly larger or When the hardness is too high, the tool holder rotates to a certain position and the spring is not broken. When the pin is pressed, the tool holder can automatically lock the tool. The turning is normal. When the tool holder rotates to a certain position, the spring positioning pin is too strong. The above-mentioned malfunction occurs when the tool holder cannot automatically lock the tool when turning.

2, troubleshooting

After the machine tool maintenance personnel comprehensively check, the tool control part of the tool post is normally a mechanical fault. After replacing the broken spring, the positioning of the pin is reversed, and the tool post is re-commissioned.

(2) The cause of the failure of the continuous operation of the tool holder or the non-stop of a certain position

The following is an example of a lathe equipped with a DTM system (Titma CNC system):

1, the cause of the failure

Occasionally, during the automatic operation of the lathe, the continuous operation of the tool holder or the non-stop of a certain position sometimes run continuously after 2 to 3 positions and then stop and lock. When continuous operation or a certain tool position does not stop, the “301” alarm appears on the display (tool holder failure). The machine automatically stops. When the continuous operation is 2~3 positions, the alarm number is not displayed and the machine automatically runs. normal.

Since the fault is random and random, it is not convenient to find the maintenance personnel to check that it belongs to the electrical control fault. After the output voltage measurement result of the tool holder control system is normal, the tool holder control system relay is also normal. Finally, the protective cover at the top of the tool holder was taken out and the input voltage of the Hall element signal line was measured one by one. It was found that the middle copper core of one signal line was broken temporarily by the wire protection rubber skin. When the tool holder was turned to a certain position, the wire protection rubber skin was affected. Forced tension copper core wire can not be normally connected to the program control system can not find the corresponding tool number, the "301" alarm will appear. When the machine tool is reset and the tool holder is rotated to a certain position by manual mode, the wire protection rubber skin is loosened. Both ends of the copper core wire are turned on. The tool holder rotates normally and no alarm number appears.

2, troubleshooting

After the maintenance personnel replace the Hall element connection signal line and replace the test drive, the machine is running normally.

Second, summary

Comprehensive analysis of the above two cases of fault finding and elimination process, we can be clear that CNC machine tool failures not only occur in the electrical part but also in the mechanical part. For the CNC lathe equipped with the above two systems, the semi-closed loop control system does not have the mechanical fault feedback function. In the operation and use, it is necessary to strengthen the daily maintenance and maintenance. If the "alarm number" is not displayed after the failure, it is likely to be a mechanical fault. Checking the mechanical part will make it more accurate and timely for the maintenance personnel to troubleshoot.