English Author: Site Editor Publish Time: 2026-10-23 Origin: Site
In the field of modern precision manufacturing, four-axis machining centers have become the core equipment for processing scenarios such as aviation parts, precision molds, and irregular hardware, thanks to their core advantage of being able to complete the processing of multi-faceted complex contours in a single clamping. Compared with the conventional three-axis machining center, the newly added rotating axis structure in the four-axis system significantly increases the complexity of mechanical transmission, electrical control and software logic of the equipment, and also makes the causes of faults more concealed. Operation and maintenance data from many workshops show that faults related to the four axes account for over 60% of the total machine downtime faults. Once problems such as lockup and precision drift occur, it may lead to the scrapping of a batch of workpieces at the least, and irreversible damage to core transmission components at the worst, directly affecting the delivery rhythm of the entire production line.
Ⅰ. Core Classification and Typical Causes of Four-Axis System Failures
The faults of four-axis machining centers do not occur in isolation. According to the root causes of the faults, they can be clearly classified into four major categories: mechanical, electrical drive, hydraulic and pneumatic, and software and parameter. Faults of different categories will present differentiated abnormal manifestations.
mechanical faults
This is the most common type of failure in four-axis systems, mostly resulting from component wear, foreign object intrusion or lack of lubrication under long-term high-load operation. The most common ones include loss of rotational accuracy, which is manifested as obvious angular deviations in the indexing position of the workpiece after processing and regular vibration marks on the surface. The root causes are mostly long-term wear of the worm gear and worm pair leading to excessive backlash, or an increase in the clearance of the precision support bearing of the rotating shaft. Secondly, there are abnormal noises and jamming during operation. During rotation, friction and impact sounds are heard. When manually turning the turntable, there is obvious jamming. This is often due to chips and coolant invading the transmission box, causing rust on components, or insufficient lubrication resulting in dry friction. There is also the failure of the locking mechanism. During the processing, the four axes cannot maintain a fixed Angle, and a slight offset occurs during cutting, which directly affects the shape and position tolerance of the workpiece.
Electrical and drive faults
This type of malfunction occurs rapidly and is often accompanied by direct system alarms. The most common issue is that servo driver alarms frequently pop up signals such as overload, overcurrent, and abnormal encoder feedback. This is mostly due to the loosening of the motor power supply line and encoder signal line joints caused by long-term vibration, or the aging of internal components of the driver. The second issue is encoder failure. As the core of the position feedback for the four axes, once the encoder is damaged or the signal is interfered with, the positioning reference will be lost. In extreme cases, it may even cause the four axes to lose control and go out of control. In addition, power fluctuations and power supply overload can directly cause the four-axis movement to be interrupted, making it impossible to receive the rotation instructions from the system.
hydraulic and pneumatic faults
Most four-axis locking and releasing actions are driven by hydraulic or pneumatic systems. The typical manifestation of such faults is that the four axes cannot be unlocked or are not locked in place. Common causes include insufficient hydraulic oil level, clogged filter elements causing the system pressure to fail to reach the standard value, or wear of the hydraulic valve core and air leakage in the air pipe, which prevent the "release" signal from being normally transmitted to the actuator. In some workshops, the water content in the air source is too high. Long-term accumulation can cause rust and jamming of the pneumatic locking cylinder, and also lead to four-axis locking faults.
software and parameter faults
This type of malfunction is highly concealed and shows no obvious signs of hardware damage, making it the most difficult to troubleshoot. For instance, if parameters such as the transmission ratio of the four axes, the compensation value of backlash, and the soft limit are mistakenly modified or lost, it will directly lead to confusion in the rotation positioning logic. The PLC program logic of some devices has become disordered, resulting in a conflict where the "rotation command is output before the lock command is released", directly triggering the system protection mechanism. After long-term operation, the mechanical zero point position of the four axes is lost, which will also cause the reference of all rotational actions to be completely offset, and all processing coordinates will be incorrect.
Ⅱ. Hierarchical investigation Logic from phenomenon to root cause
In the face of four-axis faults, blindly disassembling the turntable not only fails to quickly locate the problem but may also damage the original mechanical accuracy. According to the hierarchical logic of "from easy to difficult and from outside to inside" for troubleshooting, the maintenance efficiency can be significantly improved.
The first step is to complete the collection and preliminary verification of fault information, fully record the alarm code that pops up by the system, confirm whether the fault is triggered at startup or suddenly occurs during the cutting process, and observe whether there are additional phenomena such as abnormal sounds, odors, and abnormal vibrations. Then, check whether the emergency stop button of the equipment has been fully released and whether the operation mode has been switched to the correct position. Confirm that the servo drive of the four axes has been powered on normally. First, eliminate the most easily overlooked operational errors.
The second step is to prioritize the inspection of non-invasive components on the periphery. First, check whether all related cable joints, air pipes and oil pipes have fallen off or been damaged. Confirm that the pressure of the hydraulic station and the air pressure of the air source are within the normal range marked in the equipment manual. Then, through the signal monitoring interface of the numerical control system, check whether the input and output signals such as locking, releasing and enabling of the four axes are triggered normally, and confirm that the signal transmission is not blocked by the program.
The third step is to complete the electrical and software verification. Use a multimeter to measure the supply voltage of the servo driver and the insulation resistance of the motor winding, and check for any short circuits or open circuits. Check the core system parameters of the four-axis system to confirm that there have been no recent mismodifications. Under the premise of having a complete backup, you can try to restore the parameter backup to rule out software logic abnormalities. After confirming that all electrical and software conditions are normal, cut off the power and release the four-axis brake. Manually rotate the turntable to feel the running resistance and determine if there is any mechanical jamming or damage to the transmission components.
Ⅲ. Practical Solutions for Targeted Faults
For the most commonly encountered typical four-axis faults in the workshop, based on the mature experience of on-site maintenance, the corresponding solutions can be directly referred to for quick handling:
If the four-axis turntable does not rotate smoothly: First, check the amount and condition of the lubricating oil in the bearings. If the oil has deteriorated or is insufficient, add the corresponding grade of special bearing oil in time. If there is still obvious jamming after supplementary lubrication, disassemble and check the condition of the bearings. If the wear is severe, replace the bearings directly with new ones to avoid minor faults causing chain damage to the transmission chain.
The working surface of the turntable is eccentric and laterally inclined: First, retighten all the lock bolts on the turntable surface one by one, adjust the levelness of the equipment support feet, and calibrate the base reference. If the fault has not been eliminated, use a dial indicator to calibrate the flatness of the working surface of the turntable and correct the deformation deviation caused by external impact and long-term eccentric loading.
Sudden four-axis lock and inability to operate: First, check the system alarm code. If it points to a hydraulic alarm, prioritize checking the hydraulic valve group and pressure reading. Replace the worn valve core directly to restore the oil passage to be unobstructed. If the four-axis function is blocked due to incorrect parameter Settings, check the corresponding system's axis function activation parameters. After correction, restart the device to unlock it. In an emergency, after the power is cut off, the four-axis electrical box can be opened. Press the manual unlock button and slowly rotate the turntable at the same time to get out of the stuck position. After completing the emergency unlock, the root cause of the fault must be thoroughly investigated to avoid the recurrence of the lock problem.
During processing, if there is significant vibration and precision drift, first check the operating status of the driver. If there is an unstable output, calibrate or replace the driver in a timely manner. Subsequently, disassemble the turntable to inspect the meshing clearance of the worm gear and worm, readjust the backlash and make compensation. Replace the transmission pairs that have exceeded the wear limit simultaneously. After the maintenance is completed, a full-stroke repeat positioning accuracy calibration must be carried out. Only after confirming that the accuracy meets the standards can production be resumed.
Ⅳ, proactive maintenance to reduce the probability of failure from the source
Industry operation and maintenance data shows that 70% of four-axis malfunctions result from the lack of daily maintenance. Establishing a standardized regular maintenance mechanism can reduce the downtime rate of four-axis malfunctions by more than 60%.
A 5-minute check before starting the machine on a daily basis cannot be omitted. Make sure the hydraulic oil level and air source pressure are within the normal range. Manually rotate the four axes slightly to confirm that there is no obvious jamming during operation, and then start the formal processing. Clean the protective cover of the four-axis turntable once a week, thoroughly remove the accumulated chips and residual coolant, and prevent foreign objects from entering the transmission box and causing wear. Change the hydraulic oil and clean the filter element once every quarter, and check the clearance and transmission clearance of the four-axis bearings once every six months to detect the trend of precision deterioration in advance. Back up the four-axis parameters of the numerical control system and the PLC program once a month to avoid the situation where parameters cannot be quickly restored after loss. During the processing, strictly control the cutting parameters to avoid long-term overloading operation and reduce the additional loss of the four-axis transmission system.
The fault handling of four-axis machining centers is never a passive remedial approach of "repairing after breaking down", but rather a full-process systematic work covering daily operation, regular maintenance and scientific investigation. Establishing a clear fault analysis logic and conducting proactive maintenance and upkeep can not only quickly resolve sudden faults and reduce downtime losses, but also maintain the accuracy and stability of the four axes for a long time, significantly extending the service life of the equipment.
