Common Faults and Troubleshooting Methods for the Spindle of Machining CentersAbstract: This paper elaborates in detail on the eight common faults of the spindle of machining centers, including failure to meet the processing accuracy requirements, excessive cutting vibration, excessive noise in the spindle box, damage to gears and bearings, inability of the spindle to change speed, failure of the spindle to rotate, spindle overheating, and failure to push gears into place during hydraulic speed change. For each fault, the causes are analyzed in depth, and corresponding troubleshooting methods are provided. The aim is to help operators and maintenance personnel of machining centers quickly and accurately diagnose faults and take effective solutions to ensure the normal operation of machining centers and improve processing quality and production efficiency.
I. Introduction
As a high-precision and high-efficiency automated machine tool, the spindle component of a machining center plays a crucial role throughout the processing. The rotational accuracy, power, speed, and automated functions of the spindle directly affect the processing accuracy of workpieces, processing efficiency, and the overall performance of the machine tool. However, in actual use, the spindle may experience various faults, affecting the normal operation of the machining center. Therefore, understanding the common faults of the spindle and their troubleshooting methods is of great significance for the maintenance and use of machining centers.II. Common Faults and Troubleshooting Methods for the Spindle of Machining Centers(I) Failure to Meet the Processing Accuracy RequirementsCauses of Faults:
- During transportation, the machine tool may be subjected to impacts, which could damage the accuracy of the spindle components. For example, the axis of the spindle may shift, and the bearing housing may deform.
- The installation is not firm, the installation accuracy is low, or there are changes. An uneven installation foundation of the machine tool, loose foundation bolts, or changes in the installation accuracy due to foundation settlement and other reasons during long-term use can affect the relative position accuracy between the spindle and other components, resulting in a decline in processing accuracy.
Troubleshooting Methods:
- For machine tools impacted during transportation, a comprehensive accuracy inspection of the spindle components is required, including indicators such as radial runout, axial runout, and coaxiality of the spindle. Based on the inspection results, appropriate adjustment methods, such as adjusting the bearing clearance and correcting the bearing housing, are adopted to restore the accuracy of the spindle. If necessary, professional machine tool maintenance personnel can be invited for repairs.
- Regularly check the installation status of the machine tool and tighten the foundation bolts to ensure a firm installation. If any changes in installation accuracy are found, high-precision detection instruments should be used to readjust the levelness of the machine tool and the relative position accuracy between the spindle and components such as the worktable. Equipment like laser interferometers can be used for precise measurement and adjustment.
(II) Excessive Cutting VibrationCauses of Faults:
- The screws connecting the spindle box and the bed are loose, reducing the connection rigidity between the spindle box and the bed and making it prone to vibration under the action of cutting forces.
- The preload of the bearings is insufficient, and the clearance is too large, resulting in the bearings being unable to effectively support the spindle during operation, causing the spindle to wobble and thus inducing cutting vibration.
- The preload nut of the bearings is loose, causing the spindle to move axially and destroying the rotational accuracy of the spindle, which then leads to vibration.
- The bearings are scored or damaged, resulting in uneven friction between the rolling elements and the raceways of the bearings and generating abnormal vibration.
- The spindle and the box are out of tolerance. For example, if the cylindricity or coaxiality of the spindle does not meet the requirements, or the accuracy of the bearing mounting holes in the box is poor, it will affect the rotational stability of the spindle and lead to vibration.
- Other factors, such as uneven tool wear, unreasonable cutting parameters (such as excessive cutting speed, excessive feed rate, etc.), and loose workpiece clamping, may also cause cutting vibration.
- In the case of a lathe, the moving parts of the turret tool holder may be loose or the clamping pressure may be insufficient and not tightened properly. During cutting, the instability of the tool holder will be transmitted to the spindle system, causing vibration.
Troubleshooting Methods:
- Check the screws connecting the spindle box and the bed. If they are loose, tighten them in time to ensure a firm connection and improve the overall rigidity.
- Adjust the preload of the bearings. According to the type of bearings and the requirements of the machine tool, use appropriate preloading methods, such as adjusting through nuts or using spring preloading, to make the bearing clearance reach an appropriate range and ensure stable support for the spindle.
- Check and tighten the preload nut of the bearings to prevent the spindle from moving axially. If the nut is damaged, replace it in time.
- In the case of scored or damaged bearings, disassemble the spindle, replace the damaged bearings, and clean and inspect the relevant components to ensure that no impurities remain.
- Detect the accuracy of the spindle and the box. For the parts that are out of tolerance, methods such as grinding and scraping can be used for repair to ensure good cooperation between the spindle and the box.
- Check the tool wear situation and replace severely worn tools in a timely manner. Optimize cutting parameters by selecting appropriate cutting speeds, feed rates, and cutting depths based on factors such as workpiece material, tool material, and machine tool performance. Ensure that the workpiece is clamped firmly and reliably. For problems with the turret tool holder of a lathe, check the connection status of the moving parts and adjust the clamping pressure to enable it to clamp the tools stably.
(III) Excessive Noise in the Spindle BoxCauses of Faults:
- The dynamic balance of the spindle components is poor, generating unbalanced centrifugal forces during high-speed rotation, which causes vibration and noise. This may be due to uneven mass distribution of the parts installed on the spindle (such as tools, chucks, pulleys, etc.), or the dynamic balance of the spindle components being disrupted during the assembly process.
- The meshing clearance of the gears is uneven or seriously damaged. When the gears mesh, impact and noise will be generated. During long-term use, the meshing clearance of the gears may change due to wear, fatigue, and other reasons, or the tooth surfaces may have flaking, cracks, and other damages.
- The bearings are damaged or the drive shafts are bent. Damaged bearings will cause the spindle to operate unsteadily and generate noise. Bent drive shafts will lead to eccentricity during rotation, triggering vibration and noise.
- The lengths of the drive belts are inconsistent or they are too loose, causing the drive belts to vibrate and rub during operation, generating noise and also affecting the transmission efficiency and the stability of the spindle speed.
- The gear accuracy is poor. For example, if the tooth profile error, pitch error, etc. are large, it will result in poor gear meshing and generate noise.
- Poor lubrication. In the absence of sufficient lubricating oil or when the lubricating oil deteriorates, the friction of components such as gears and bearings in the spindle box increases, making it easy to generate noise and accelerating the wear of the components.
Troubleshooting Methods:
- Conduct dynamic balance detection and correction on the spindle components. A dynamic balance tester can be used to detect the spindle and related parts. For areas with large unbalanced masses, adjustments can be made by removing materials (such as drilling, milling, etc.) or adding counterweights to make the spindle components meet the dynamic balance requirements.
- Check the meshing situation of the gears. For gears with uneven meshing clearances, the problem can be solved by adjusting the center distance of the gears or replacing severely worn gears. For gears with damaged tooth surfaces, replace them in time to ensure good meshing of the gears.
- Check the bearings and drive shafts. If the bearings are damaged, replace them with new ones. For bent drive shafts, they can be straightened by using straightening methods. If the bending is severe, replace the drive shafts.
- Adjust or replace the drive belts to make their lengths consistent and the tension appropriate. The appropriate tension of the drive belts can be achieved by adjusting the belt tensioning devices, such as the position of the tensioning pulley.
- For the problem of poor gear accuracy, if they are newly installed gears and the accuracy does not meet the requirements, replace them with gears that meet the accuracy requirements. If the accuracy decreases due to wear during use, repair or replace them according to the actual situation.
- Check the lubrication system of the spindle box to ensure that the amount of lubricating oil is sufficient and the quality is good. Regularly replace the lubricating oil, clean the lubrication pipelines and filters to prevent impurities from blocking the oil passages and ensure good lubrication of all components.
(IV) Damage to Gears and BearingsCauses of Faults:
- The shifting pressure is too high, causing the gears to be damaged by impact. During the speed change operation of the machine tool, if the shifting pressure is too high, the gears will bear excessive impact forces at the moment of meshing, easily leading to damage to the tooth surfaces, fractures at the tooth roots, and other situations.
- The shifting mechanism is damaged or the fixing pins fall off, making the shifting process abnormal and disrupting the meshing relationship between the gears, thus causing damage to the gears. For example, deformation and wear of the shifting forks, fracture of the fixing pins, etc. will affect the accuracy and stability of the shifting.
- The preload of the bearings is too large or there is no lubrication. An excessive preload causes the bearings to bear excessive loads, accelerating the wear and fatigue of the bearings. Without lubrication, the bearings will work in a dry friction state, resulting in overheating, burning, and damage to the balls or raceways of the bearings.
Troubleshooting Methods:
- Check the shifting pressure system and adjust the shifting pressure to an appropriate range. This can be achieved by adjusting the pressure valves of the hydraulic system or the pressure adjustment devices of the pneumatic system. At the same time, check the shifting control circuits and solenoid valves and other components to ensure that the shifting signals are accurate and the actions are smooth, avoiding excessive gear impact due to abnormal shifting.
- Inspect and repair the shifting mechanism, repair or replace damaged shifting forks, fixing pins, and other components to ensure the normal operation of the shifting mechanism. During the assembly process, ensure the installation accuracy and firm connection of each component.
- Adjust the preload of the bearings. According to the technical requirements of the bearings and the working conditions of the machine tool, use appropriate preloading methods and appropriate preload magnitudes. At the same time, strengthen the lubrication management of the bearings, regularly check and add lubricating oil to ensure that the bearings are always in a good lubrication state. For bearings damaged due to poor lubrication, after replacing them with new bearings, thoroughly clean the lubrication system to prevent impurities from entering the bearings again.
(V) Inability of the Spindle to Change SpeedCauses of Faults:
- Whether the electrical shifting signal is output. If there is a fault in the electrical control system, it may not be able to send the correct shifting signal, resulting in the inability of the spindle to perform the speed change operation. For example, failures of relays in the control circuit, errors in the PLC program, and malfunctions of sensors may all affect the output of the shifting signal.
- Whether the pressure is sufficient. For hydraulic or pneumatic speed change systems, if the pressure is insufficient, it cannot provide enough power to drive the movement of the speed change mechanism, causing the spindle to be unable to change speed. Insufficient pressure may be caused by failures of hydraulic pumps or pneumatic pumps, pipeline leaks, improper adjustment of pressure valves, and other reasons.
- The shifting hydraulic cylinder is worn or stuck, making the hydraulic cylinder unable to work normally and unable to push the speed change gears or clutches and other components to perform the speed change action. This may be caused by damage to the internal seals of the hydraulic cylinder, severe wear between the piston and the cylinder barrel, and impurities entering the hydraulic cylinder.
- The shifting solenoid valve is stuck, preventing the solenoid valve from changing direction normally, resulting in the inability of the hydraulic oil or compressed air to flow along the predetermined path, thus affecting the action of the speed change mechanism. The solenoid valve being stuck may be caused by the valve core being stuck by impurities, damage to the solenoid valve coil, and other reasons.
- The shifting hydraulic cylinder fork falls off, causing the connection between the hydraulic cylinder and the speed change gears to fail and unable to transmit power for speed change. The fork falling off may be caused by loose fixing bolts of the fork, wear and fracture of the fork, and other reasons.
- The shifting hydraulic cylinder leaks oil or has internal leakage, reducing the working pressure of the hydraulic cylinder and unable to provide enough force to complete the speed change action. Oil leakage or internal leakage may be caused by aging of the seals of the hydraulic cylinder, excessive clearance between the piston and the cylinder barrel, and other reasons.
- The shifting compound switch malfunctions. The compound switch is used to detect signals such as whether the speed change is completed. If the switch malfunctions, it will cause the control system to be unable to correctly judge the speed change state, thus affecting subsequent speed change operations or the operation of the machine tool.
Troubleshooting Methods:
- Check the electrical control system. Use tools such as multimeters and oscilloscopes to detect the output lines of the shifting signal and related electrical components. If a relay failure is found, replace it. If there is an error in the PLC program, debug and modify it. If a sensor malfunctions, replace it with a new one to ensure that the shifting signal can be output normally.
- Check the pressure of the hydraulic or pneumatic system. For insufficient pressure, first check the working status of the hydraulic pump or pneumatic pump. If there is a failure, repair or replace it. Check whether there are leaks in the pipelines. If there are leaks, repair them in time. Adjust the pressure valves to make the system pressure reach the specified value.
- For the problem of the shifting hydraulic cylinder being worn or stuck, disassemble the hydraulic cylinder, check the wear conditions of the internal seals, piston, and cylinder barrel, replace the damaged seals, repair or replace the worn piston and cylinder barrel, clean the inside of the hydraulic cylinder, and remove impurities.
- Check the shifting solenoid valve. If the valve core is stuck by impurities, disassemble and clean the solenoid valve to remove the impurities. If the solenoid valve coil is damaged, replace it with a new coil to ensure that the solenoid valve can change direction normally.
- Check the shifting hydraulic cylinder fork. If the fork falls off, reinstall it and tighten the fixing bolts. If the fork is worn or fractured, replace it with a new fork to ensure a reliable connection between the fork and the speed change gears.
- Deal with the problem of oil leakage or internal leakage of the shifting hydraulic cylinder. Replace the aging seals, adjust the clearance between the piston and the cylinder barrel. Methods such as replacing the piston or cylinder barrel with appropriate sizes and increasing the number of seals can be used to improve the sealing performance of the hydraulic cylinder.
- Check the shifting compound switch. Use tools such as multimeters to detect the on-off status of the switch. If the switch malfunctions, replace it with a new switch to ensure that it can accurately detect the speed change state and feed back the correct signal to the control system.
(VI) Failure of the Spindle to RotateCauses of Faults:
- Whether the spindle rotation command is output. Similar to the inability of the spindle to change speed, a fault in the electrical control system may lead to the inability to output the spindle rotation command, making the spindle unable to start.
- The protection switch is not pressed or malfunctions. Machining centers usually have some protection switches, such as the spindle box door switch, the tool clamping detection switch, etc. If these switches are not pressed or malfunction, for safety reasons, the machine tool will prohibit the spindle from rotating.
- The chuck does not clamp the workpiece. In some lathes or machining centers with chucks, if the chuck does not clamp the workpiece, the machine tool control system will limit the rotation of the spindle to prevent the workpiece from flying out during the processing process and causing danger.
- The shifting compound switch is damaged. The malfunction of the shifting compound switch may affect the transmission of the spindle start signal or the detection of the spindle running state, resulting in the inability of the spindle to rotate normally.
- There is internal leakage in the shifting solenoid valve, which will make the pressure of the speed change system unstable or unable to establish normal pressure, thus affecting the rotation of the spindle. For example, in a hydraulic speed change system, the leakage of the solenoid valve may lead to the inability of the hydraulic oil to effectively push components such as clutches or gears, making the spindle unable to obtain power.
Troubleshooting Methods:
- Check the output lines of the spindle rotation command in the electrical control system and related components. If a fault is found, repair or replace them in time to ensure that the spindle rotation command can be output normally.
- Check the status of the protection switches to ensure that they are pressed normally. For malfunctioning protection switches, repair or replace them to ensure that the safety protection function of the machine tool is normal without affecting the normal start of the spindle.
- Check the clamping situation of the chuck to ensure that the workpiece is clamped firmly. If there is a fault with the chuck, such as insufficient clamping force or wear of the chuck jaws, repair or replace the chuck in time to make it work normally.
- Check the shifting compound switch. If it is damaged, replace it with a new one to ensure the normal transmission of the spindle start signal and the accurate detection of the running state.
- Check the leakage situation of the shifting solenoid valve. Methods such as pressure testing and observing whether there is oil leakage around the solenoid valve can be used for judgment. For solenoid valves with leakage, disassemble, clean, check the valve core and seals, replace the damaged seals or the entire solenoid valve to ensure good sealing performance and stable pressure of the speed change system.
(VII) Spindle OverheatingCauses of Faults:
- The preload of the spindle bearings is too large, increasing the internal friction of the bearings and generating excessive heat, resulting in spindle overheating. This may be due to improper operation during the assembly or adjustment of the bearing preload or the use of inappropriate preloading methods and preload magnitudes.
- The bearings are scored or damaged. During the working process, the bearings may be scored or damaged due to poor lubrication, overload, foreign matter entering, etc. At this time, the friction of the bearings will increase sharply, generating a large amount of heat and causing the spindle to overheat.
- The lubricating oil is dirty or contains impurities. Dirty lubricating oil will increase the friction coefficient between the bearings and other moving parts, reducing the lubrication effect.
Media Contact
Company Name: Qingdao Taizheng Precision Machinery Co., Ltd.
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Phone: 13605328581
Address:C-101, Building 31, Zhongnan High tech Jimo Technology Innovation Industrial Park, No. 76 Dazhong 1st Road, Jimo District
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Website: https://www.ncmillingmachine.com/