Troubleshooting and Emergency Handling for Common Faults in CNC Machining Centers: From Alarm Codes to Mechanical Failures, Rapidly Resume Production

As highly integrated equipment, CNC machining centers inevitably encounter faults during long-term operation — ranging from minor issues like system alarms and tool jamming to major problems such as spindle abnormal noise and guideway seizing. If not addressed promptly, these faults can lead to hours or even days of downtime, resulting in significant production losses. Many factories, when facing faults, often fall into the dilemma of "blind maintenance" due to a lack of systematic troubleshooting approaches. This article outlines 8 common types of faults in CNC machining centers, breaking down the full process of "fault phenomenon → troubleshooting steps → emergency handling" to help you quickly locate problems, resume production, and minimize secondary damage caused by incorrect operations.

I. System Alarm Faults: Start with Codes to Quickly Locate Software or Parameter Issues

1. Common Alarm 1: "Program Error" Alarms (e.g., FANUC Alarm 100, Siemens Alarm 1202)

• Fault Phenomenon: When calling a machining program, the system displays "program format error," "illegal character," or "duplicate program number," and machining cannot start.

• Troubleshooting Steps:

  1. Refer to the alarm code description (detailed code explanations are usually in the machine tool operation manual) to confirm the error type (e.g., format error, character error);

  2. Open the faulty program and check if it starts with "OXXXX" (program number) and ends with "M30" (program end code), ensuring the format complies with standards (e.g., G-codes and M-codes are in correct positions, coordinate values include decimal points);

  3. Check for special characters (e.g., Chinese punctuation, spaces) or duplicate program numbers (e.g., two programs numbered O0001 in the same machine tool) in the program.

  
  

• Emergency Handling:

  • If it is a format error, modify the program according to standard formatting (e.g., add the missing M30, delete illegal characters);

  • If there is a duplicate program number, rename one of the programs (e.g., change O0001 to O0002);

  • If on-site modification is not possible, call a backed-up correct program (regularly back up frequently used programs to a USB drive or computer) to prioritize resuming production, and troubleshoot the original program later.

  
  

2. Common Alarm 2: "Parameter Loss" Alarms (e.g., FANUC Alarm 300, Siemens Alarm 2000)

• Fault Phenomenon: After the machine tool is powered off and restarted, the system displays "parameter abnormality" or "parameter loss," and some functions become unavailable (e.g., axes cannot move, tool magazine fails to operate).

• Troubleshooting Steps:

  1. Confirm if there have been recent power outages, battery replacements, or system upgrades (parameter loss is often caused by dead backup batteries or unexpected power failures);

  2. Access the system parameter page and check if key parameters (e.g., axis travel parameters, tool compensation parameters) show "0" or abnormal values.

  
  

• Emergency Handling:

  • If a parameter backup exists, directly import the backup file (via USB drive or internal machine storage); parameters will be restored after restarting the system;

  • If no backup is available, contact the machine tool manufacturer or supplier, provide the machine model and system version to obtain the default parameter file. After import, re-calibrate key parameters such as axis travel and tool compensation (professional operation is recommended to avoid equipment collisions due to parameter errors);

  • Temporary Emergency: If only non-critical parameters (e.g., display parameters) are lost, temporarily ignore them and prioritize machining simple parts that rely less on parameters. Restore parameters before machining complex parts.

  
  

II. Tool-Related Faults: From Clamping to Tool Changing, Resolve "Unable to Cut, Inaccurate Cutting, Tool Jamming" Issues

1. Common Fault 1: Excessive Tool Runout During Clamping (Rough Machined Surfaces, Dimensional Deviations)

• Fault Phenomenon: After machining, the part surface shows obvious chatter marks, and dimensional deviations exceed tolerances (e.g., the outer diameter is 0.02mm smaller than the set value). No significant tool edge wear is observed upon inspection.

• Troubleshooting Steps:

  1. Install the tool on the spindle and use a dial indicator to measure the radial runout of the tool edge (place the dial indicator probe against the tool outer diameter and manually rotate the spindle);

  2. If the runout exceeds 0.01mm (for ordinary machining) or 0.005mm (for precision machining), sequentially check: whether the tool holder taper surface has scratches or oil stains (affecting fit with the spindle taper hole); whether the spindle taper hole contains chips or impurities; whether the tool is fully inserted into the holder (incomplete insertion causes runout).

  
  

• Emergency Handling:

  • Clean the tool holder taper surface and spindle taper hole (wipe with alcohol to remove oil and chips), re-clamp the tool, and ensure it is fully inserted and tightened;

  • If the tool holder taper surface has minor scratches, lightly polish with fine sandpaper (1000# or higher); replace the holder if damage is severe;

  • Temporary Emergency: If runout is small (0.01-0.02mm), temporarily adjust the tool radius compensation (e.g., if runout increases the actual cutting radius by 0.01mm, reduce the radius compensation value by 0.01mm) to meet machining requirements. Replace the tool holder later to fully resolve the issue.

  
  

2. Common Fault 2: Automatic Tool Change Failures (Tool Magazine Not Rotating, Tool Change Jamming, Tool Dropping)

• Fault Phenomenon 1: Tool Magazine Not Rotating: When a tool change command is issued, the tool magazine does not move, and the system displays a "tool magazine timeout" alarm.

  • Troubleshooting Steps: Check if the tool magazine power is connected (whether the tool magazine motor switch in the distribution box is closed); if the tool magazine limit switch is triggered (the tool magazine automatically stops when reaching the limit position — manually push the magazine away from the limit); if the tool magazine motor makes abnormal noise (a humming sound without rotation indicates motor failure or mechanical jamming).

  • Emergency Handling: If the issue is power or a limit switch, restore power and reset the limit switch to resume operation; if the motor fails, temporarily rotate the tool magazine manually (some machines have a manual crank), locate the required tool, and clamp it manually to prioritize production. Replace the motor later.

• Fault Phenomenon 2: Tool Change Jamming: The robot gripper gets stuck on the tool holder or tool pocket when grabbing the tool, failing to complete the tool change.

  • Troubleshooting Steps: Check if the tool is securely clamped in the tool pocket; if the robot gripper is worn (wear reduces gripping stability); if the tool change position is offset (misalignment between the robot, tool magazine, and spindle).

  • Emergency Handling: Press the emergency stop button, manually reset the robot via the machine’s "manual tool change" mode, and clean chips from the robot gripper; if the gripper is worn, temporarily pad it with a shim (or replace with a spare gripper) to ensure secure tool gripping; if position is offset, contact professionals to calibrate the tool change position, and manually clamp tools temporarily.

• Fault Phenomenon 3: Tool Dropping: The tool suddenly falls from the robot gripper while moving, hitting the worktable or part.

  • Troubleshooting Steps: Check the clamping force of the robot gripper (whether the spring is broken); if the positioning groove on the tool holder is worn (affecting gripper clamping); if the tool change speed is too fast (excessive speed increases centrifugal force).

  • Emergency Handling: Stop the machine immediately, check for damage to the part and worktable, and remove the dropped tool; replace the robot gripper spring (some machines have spare springs), reduce the tool change speed by 20%-30%, and temporarily reduce the number of tools in the magazine (to avoid overloading the robot). Fully inspect the tool change mechanism later.

III. Mechanical Motion Faults: From Axes to Spindle, Resolve "Unable to Move, Inaccurate Movement, Abnormal Noise" Issues

1. Common Fault 1: Axis Movement Jamming and Abnormal Noise (Axis cannot move normally or makes a "clunking" sound when moving)

• Fault Phenomenon: When moving the axis manually or automatically, it moves slowly with jitter, accompanied by metal friction noise. In severe cases, the axis cannot move, and the system displays an "axis overload" alarm.

• Troubleshooting Steps:

  1. Power off the machine tool, manually push the axis, and feel for obvious resistance or jamming points;

  2. Check if the guideway contains chips or foreign objects (chips stuck in guideway gaps cause jamming); if the guideway is adequately lubricated (insufficient lubrication causes dry friction and abnormal noise); if the ball screw nut is loose or worn (worn screws cause uneven movement).

  
  

• Emergency Handling:

  • Use compressed air (with an oil-water separator) to blow away chips from the guideway, wipe it clean with a cloth, manually add guideway-specific grease (per the machine manual), restart the machine, and test axis movement;

  • If jamming persists, check if the ball screw nut locking screws are loose, and retighten them to the specified torque (usually 20-30N·m) with a torque wrench;

  • Temporary Emergency: If jamming is mild, reduce the axis movement speed by 50%, temporarily machine parts with short travel to avoid 加剧 wear from long-term high-speed movement, and contact professionals to repair the screw and guideway later.

  
  

2. Common Fault 2: Spindle Abnormal Noise and Overheating (Spindle makes a sharp noise when rotating or exceeds 40℃ in temperature)

• Fault Phenomenon: After the spindle starts, it emits a "squealing" or "buzzing" noise, with obvious vibration during machining. Touching the spindle housing by hand reveals excessive heat (10℃ above normal operating temperature).

• Troubleshooting Steps:

  1. Check the spindle cooling system (whether the chiller is working, if the coolant level is normal, and if the pipeline is blocked);

  2. Check the spindle lubrication system (whether lubricating oil is sufficient and if the lubrication pump is supplying oil normally);

  3. Power off the machine and manually rotate the spindle to feel for jitter or uneven resistance (if present, spindle bearing wear is likely).

  
  

• Emergency Handling:

  • If the issue is with the cooling system, clean the cooling pipeline (remove blocked impurities), replenish coolant, and ensure the chiller operates normally (set temperature to 20-25℃);

  • If the issue is with lubrication, check the oil level and add or replace lubricating oil (per the machine manual);

  • If spindle bearing wear is suspected, stop using the spindle immediately to avoid further damage. Temporarily switch to a backup machine (or manual machining), and have professionals replace the spindle bearings later (strict calibration is required to avoid precision loss).

  
  

IV. Hydraulic/Pneumatic System Faults: Resolve "Insufficient Pressure, Air/Oil Leakage, Malfunctioning Actuation" Issues

1. Common Fault 1: Insufficient Pneumatic System Pressure (Fixture Clamping Failure, Weak Spindle Tool Release)

• Fault Phenomenon: When activating the pneumatic fixture, clamping force is insufficient (parts loosen during machining); when releasing the spindle tool, the tool holder cannot pop out smoothly, and the system displays a "tool release timeout" alarm.

• Troubleshooting Steps:

  1. Check the pneumatic system pressure gauge to confirm pressure is within the specified range (usually 0.5-0.8MPa);

  2. Verify if the air compressor is working normally (whether pressure meets standards); if pneumatic pipelines have leaks (apply soapy water to pipe joints and check for bubbles); if the filter is blocked (impurities in compressed air clog the filter, reducing pressure).

  
  

• Emergency Handling:

  • If the air compressor pressure is insufficient, adjust it to 0.6-0.8MPa;

  • If pipelines leak, replace leaking joints or hoses (temporarily seal with tape and replace with new parts later);

  • If the filter is blocked, disassemble and clean or replace the filter element;

  • Temporary Emergency: If fixture clamping force is insufficient, temporarily extend the clamping time (prolong the solenoid valve energization time) or manually assist clamping to ensure parts are securely fixed.

  
  

2. Common Fault 2: Hydraulic System Oil Leakage (Oil Seepage at Hydraulic Pipe Joints, Falling Oil Level in Tank)

• Fault Phenomenon: Oil stains appear at hydraulic pipe joints, the oil level in the tank drops significantly in a short time, and hydraulically driven components (e.g., tool magazine lifting mechanism) move slowly or weakly.

• Troubleshooting Steps:

  1. Check if hydraulic pipe joints are loose (gently tighten with a wrench and observe if leakage persists);

  2. Inspect if seals are aged (aged seals in pipe joints or hydraulic cylinders cause leakage);

  3. Check if the hydraulic pump has leaks (poor pump body sealing causes oil leakage).

  
  

• Emergency Handling:

  • If joints are loose, retighten to the specified torque (avoid over-tightening to prevent thread damage);

  • If seals are aged, replace with spare seals (stock common seal sizes such as O-rings in advance);

  • Replenish hydraulic oil to the specified level (use oil of the type specified in the machine manual; avoid mixing different types of hydraulic oil);

  • Temporary Emergency: If leakage is mild, temporarily seal joints with Teflon tape (for emergency use only), increase inspection frequency, and replenish oil promptly. Fully replace sealing components during production breaks.

  
  

V. 3 General Principles for Troubleshooting: Avoid Secondary Damage and Improve Efficiency

1. Safety First: Regardless of the fault type, first press the emergency stop button, cut off power and air supply (relieve pressure if the hydraulic system is involved), and ensure the equipment is in a safe state before troubleshooting. Never disassemble components or touch moving parts (e.g., spindle, guideways) while the machine is running.

2. Software Before Hardware: Prioritize troubleshooting software and parameter issues (e.g., program errors, parameter loss, alarm codes) before checking mechanical and hardware problems (e.g., axis jamming, tool wear). Software issues are usually easier to resolve and do not cause secondary equipment damage.

3. Simplicity Before Complexity: Start with the simplest, easiest-to-check causes (e.g., power, air supply, chip blockages) before investigating complex causes (e.g., motor failures, bearing wear, system malfunctions). For example, if an axis cannot move, first check the power and limit switches before inspecting the ball screw and guideway — avoid disassembling complex components immediately, which wastes time.

Conclusion: The Core of Fault Handling is "Rapid Localization + Minimal Loss"