Practical Guide for Emergency Handling of Common Faults

During the long-term operation of the gantry milling machine, I have also accumulated a lot of practical experience in on-site troubleshooting under the guidance of my master. Many small problems can be quickly solved without waiting for maintenance personnel to arrive. Following the standard steps can not only reduce downtime but also prevent minor faults from developing into major damages.

The most frequently encountered issue is the problem of the ‌ worktable having no unidirectional feed ‌. I once came across a situation where the worktable only had forward feed and no backward movement at all. There's no need to rush to disassemble the complex components. First, check along the control loop: First, locate the travel limit switches at the front and back of the workbench. Use a multimeter to measure the continuity of the circuit. In most cases, the limit switch on the rear side has poor contact due to long-term chip intake. After cleaning the contacts and rewiring, it can return to normal. If the limit circuit is completely normal, then follow the circuit to the forward control terminal of the frequency converter, short-circuit the FWD and COM terminals to test the operating status of the frequency converter. In this way, it can be quickly determined whether it is a control circuit disconnection or a fault of the frequency converter itself, without blindly disassembling the transmission structure.

Another high-frequency fault is the shaking of the ‌ X-axis during operation and the appearance of vibration marks on the processed surface ‌. I encountered it once when I first started, and the surface roughness of the processed workpiece was completely substandard. It took me a long time to find out the cause: First, check the lifting pressure of the hydrostatic guide rail of the worktable to ensure that the pressure value is within the standard range. Then, use a feeler gauge to measure the gap between the worktable pressure plate and the guide rail. The normal gap should be controlled within 0.05mm. If the gap is too small, it will cause insufficient lifting and lead to vibration. If the clearance of the pressure plate is normal, disengage the servo motor and switch to the semi-closed loop mode for a test run. After eliminating the motor's own faults, focus on checking the meshing clearance between the hydrostatic worm and the worm mother bar. The normal clearance should be maintained at around 0.06mm. A too small clearance will damage the stability of the hydrostatic oil film. By adjusting the thickness of the gasket at the bottom of the worm box, the clearance can be brought back to the standard range. The jitter problem can be completely solved.

The ‌ Z-axis overload alarm ‌ of heavy-duty gantry milling machines is also a common and difficult problem. Previously, the TH42250 machine tool in the workshop had an alarm No. 300608, indicating that the Z-axis speed control output was restricted, accompanied by abnormal sounds from the hydraulic station and the oil tank temperature exceeding 58℃. When encountering such alarms, do not directly restart the system. First, check the accumulator control valve group of the spindle box balance circuit. In most cases, the pressure of the safety valve in the balance circuit deviates from the standard value. Under normal working conditions, the balance circuit should be adjusted to 5.5MPa, and the inflation pressure of the accumulator should be maintained at 4MPa. Abnormal pressure will cause a sudden increase in load when the Z-axis ram drops. After recalibrating the pressure of the relief valve, This can solve the problem of overload and jamming when the Z-axis moves, and prevent the servo motor from being burned out due to long-term overload.

In addition to the aforementioned types of high-frequency faults, there are also many unexpected problems in specific scenarios encountered in daily production. These are all practical solutions I have figured out on-site with my master, which can quickly resume production without extensive disassembly.

The crossbeam lifting jamming and inability to move synchronously ‌ are common problems for many long-used gantry milling machines. Previously, an X2010 type milling machine that had been in service for many years in the workshop once had a situation where the crossbeam could not be lifted. First, check the hydraulic clamping device: Most faults are due to insufficient pressure in the clamping oil circuit or metal chips blocking the pipeline filter screen. After removing the filter screen to clean the impurities and readjusting the oil pressure to fully release the clamping device, the crossbeam can resume normal lifting and lowering. If the lifting on both sides is not synchronized, adjust the clearance of the synchronous gears on the two transmission shafts respectively to ensure that the transmission ratios on both sides are exactly the same. Then, the problems of jamming and offset can be solved.

Insufficient flow in the cooling system, abnormal temperature rise in the processing area ‌. Many beginners will directly add coolant when encountering this problem. In fact, the core troubleshooting logic is very clear: First, open the bottom drain valve of the coolant tank to discharge the accumulated metal powder and oil sludge. These impurities are the main cause of pipeline blockage. Then, remove the filter screen at the inlet of the cooling pump, clean the adhering chips and residues, and finally check the Angle of the cooling nozzle. Adjust the nozzle position to ensure that the coolant is completely aligned with the cutting point of the milling cutter. This way, the cooling effect can be quickly restored and the rapid wear of the tool due to overheating can be avoided.

The automatic tool changing system gets stuck and the tool changing action is interrupted ‌. I encountered this once when I was working on a rush order before. The mechanical hand stopped in mid-air halfway through the tool changing. Do not forcibly cut off the power or break the components first: the first step is to bring up the status of the tool changing PLC in the system and manually output a signal to return the mechanical hand to the original position. The second step is to check whether the positioning pins of the mechanical hand are stuck by chips. After cleaning the pin holes, apply a small amount of grease. Finally, check the installation position of the tool recognition sensor, adjust the distance between the sensor and the tool holder to ensure that the signal can be accurately triggered, and the tool changing process can resume normal operation.

clutch slippage in the feed system and weak feed action ‌. Such faults occur frequently in old equipment. First, remove the side cover of the feed box, find the adjustment nut of the safety clutch, and appropriately tighten the nut to increase the spring preload. This can solve most minor slippage problems. If slippage still occurs after adjustment, remove the clutch plate for inspection. If there are obvious scratches on the surface of the friction disc, use a surface grinding machine to smooth out the scratches or directly replace the new friction plate. The feed power transmission can then return to normal.

The ‌ system frequently freezes and the processing program cannot be loaded normally ‌. When encountering such electrical faults, do not directly reinstall the system first: check the power supply voltage of the machine tool, measure the input terminal voltage with a multimeter, and confirm that the voltage fluctuation range does not exceed ±10% of the rated value. Many freeze problems are caused by unstable voltage. Clear the cache memory of the numerical control system again, delete the redundant processing programs that have existed for a long time, and finally update the software version of the system. In this way, 90% of the problems of program loading failure and random system crashes can be solved.