A Comprehensive Maintenance Guide for CNC Machining Centres: A Must-Read for Factory Operators

CNC machining centres are key pieces of equipment in modern manufacturing; their correct operation and maintenance are crucial to ensuring the stable operation of the machines and extending their service life. Operators are responsible for the use of the equipment, as well as its day-to-day maintenance and basic servicing, whilst maintenance staff are responsible for specialist repairs and in-depth servicing. Workshop managers must exercise comprehensive oversight of operational procedures throughout the workshop and monitor the condition of the equipment.

When operating CNC equipment, it is essential to adhere to a series of basic requirements. These include ensuring the equipment is situated in a suitable working environment, away from dampness, dust and corrosive gases, whilst also keeping it at a distance from sources of heat radiation and vibration. The operating temperature of the equipment must be maintained between 15 and 35 degrees; for precision machinery, the machining temperature should be stabilised at around 20 degrees to strictly control temperature fluctuations. Furthermore, to ensure the quality of the power supply and minimise electrical interference, CNC equipment is generally connected to a dedicated power line and fitted with a voltage stabiliser.

During routine machining operations, a series of operating procedures must be followed to maintain machining accuracy. These include warming up the machine after start-up, checking that the oil lines are clear, and positioning the worktable and saddle at the centre of the machine before shutdown. At the same time, it is absolutely essential to keep the machine tool dry and clean.

Daily maintenance tasks are equally important; these include carrying out a thorough cleaning of the machine tool to ensure it is kept clean, checking the condition of the lubricating oil and coolant, and verifying that the air pressure and the air blow-through function for the spindle taper bore are operating normally. In addition, the cleaning and inspection of the tool magazine, tool arms and cutting tools are indispensable steps. Finally, a thorough check must be carried out to ensure that all signal lights and fault warning lights are functioning correctly. Through these daily maintenance tasks, it is possible to ensure that the CNC machining centre remains in a state of long-term, stable operation and to extend its service life.

Carefully check the hydraulic unit pipes for any signs of leakage;

At the end of each working day, ensure that the machine tool is thoroughly cleaned and swept;

Keep the area around the machine clean to prevent debris and dust from affecting the machine tool.

▌ Key points for weekly maintenance

Clean the air filter associated with the heat exchanger; at the same time, check the condition of the filter located at the cooling pump, and also check the condition of the filter in the lubricating oil pump.

Check carefully whether the blade retaining pins are loose, and ensure that the blade holder is clean;

Check whether the mechanical zero points of the three axes have shifted, thereby affecting machining accuracy;

Check that the tool magazine’s tool-changing arm moves smoothly and that the tool magazine turret rotates properly;

If an oil-cooled unit is fitted, check the oil level to ensure it is not below the mark;

Remove impurities and moisture from the compressed air, whilst checking the oil level in the oil-mist separator and inspecting the seals on all solenoid valves and the pneumatic system.

Prevent dust and debris from entering the interior of the CNC unit, and maintain the cleanliness and integrity of the circuit boards and electronic components within the CNC system.

▌ Key points for monthly maintenance

Check the lubrication of the shaft guideways to ensure that the guideway surfaces are adequately lubricated;

Check and clean the limit switches and stop blocks to ensure they are working properly;

Check the oil level in the cutting cylinder oil reservoir and top up if necessary;

Check that the instructions and warning labels on the machine are legible and present.

▌ Key points for the six-monthly service

Remove the spindle chip guard, clean the spindle oil pipe fittings, clean the ball screw, clean the limit switches on all three axes, and check that the spindle oil pipe fittings are functioning correctly, that the ball screw is functioning correctly, and that the limit switches on all three axes are functioning correctly. and whilst you are at it, check the effectiveness of the scraper blades on the hard rails of each axis.

Check the operating status of the servo motors on each axis and the print head, and check for any unusual noises or vibrations;

Change the oil in the hydraulic unit and the oil in the tool magazine reduction gear to ensure the machine tool is properly lubricated;

Test the clearance between each shaft and adjust the compensation as required;

Clean any dust from inside the electrical cabinet, ensuring that the machine tool is switched off whilst doing so;

Carry out a thorough inspection of the operational status of all terminals, connectors, sockets and switches;

Check that all buttons are responsive and functioning correctly;

Adjust the machine’s alignment to ensure its stability and machining accuracy;

Clean the coolant tank and replace the coolant to ensure effective cooling and lubrication during the machining process.

▌ Key points for annual professional maintenance or repairs (to be carried out by a qualified engineer)

Ensure the integrity and continuity of the earthing protection system to safeguard personal safety;

Inspections must be carried out at the prescribed intervals on circuit breakers, contactors and components such as single-phase or three-phase arc suppressors. These inspections should cover issues such as loose connections and excessive noise, and the underlying causes must be investigated in order to ultimately eliminate any potential hazards.

Please ensure that the cooling fans inside the electrical cabinet are in good working order to prevent damage to the components;

If a fuse blows or a circuit breaker trips frequently, the cause should be identified immediately and appropriate action taken.

A thorough inspection of the perpendicularity of each axis is carried out, followed by adjustments to the machine tool’s geometric accuracy, with the aim of ensuring that it meets or restores the specified standards. Geometric accuracy is key to the overall performance of a machine tool. Why is this so? If, for example, the perpendicularity between the XZ and YZ axes is poor, this will affect the workpiece’s concentricity and symmetry; whilst any issues with the perpendicularity of the spindle relative to the worktable will affect the workpiece’s parallelism. Therefore, restoring geometric accuracy is an extremely important and crucial aspect of maintenance work—it is of the utmost importance.

Carefully inspect the wear and play in the motors and lead screws on each axis, whilst also checking that the support bearings at both ends of each axis are in good condition. Should any damage to the couplings or bearings be detected, they must be replaced promptly; otherwise, this will lead to increased operating noise in the machine tool, affect transmission accuracy, and may even result in damage to the lead screw cooling seals, causing coolant leakage, which in turn will seriously compromise the service life of the lead screw and the spindle.

The protective covers on each axis must be inspected at the specified intervals and replaced where necessary. Should the protective covers become damaged, the rate of wear on the guideways will accelerate; furthermore, if the protective covers become significantly deformed, this will not only increase the load on the machine tool but also cause extremely serious damage to the guideways.

The straightening of lead screws is of paramount importance. Deformation of the lead screw caused by machine tool collisions or inadequate clearance between the lead screw and the thrust block will directly affect the machine tool’s machining accuracy. After loosening the lead screw to allow it to return to its natural state, it should be installed in accordance with maintenance procedures to ensure that tangential forces during movement are minimised, thereby maintaining the natural state of the machining process.

The belt drive system of a machine tool spindle requires regular inspection and adjustment. The tension of the V-belt must be adjusted appropriately to prevent slippage or loss of revolutions during machining; the spindle V-belt must also be replaced in a timely manner. At the same time, the oil level in the cylinder of the tensioner pulley—which controls the high-to-low speed changeover for the 1000 r/min spindle—must be checked to ensure that oil can be topped up promptly when necessary. This prevents faults during the low-speed changeover from affecting the surface roughness of the milled workpiece and the cutting torque.

Cleaning the tool magazine must not be neglected, nor should the adjustment procedure be overlooked. To ensure the tool magazine rotates and remains parallel to the worktable, the retaining rings must be replaced if necessary. At the same time, the angle of the spindle orientation bridge and the rotation coefficient of the tool magazine must be adjusted, and grease must be applied to all moving parts.

To prevent the system from overheating, it is essential to check carefully that all the cooling fans on top of the CNC cabinet are operating correctly. At the same time, you should also check whether the air duct filters are blocked; if an excessive amount of dust has accumulated on the filter mesh, it should be removed promptly to maintain the correct temperature inside the CNC cabinet.

The input and output devices of the CNC system also require regular maintenance. Check whether the machine tool’s signal cables are damaged, whether the screws and nuts on the interfaces and connectors are loose or missing, and whether the network cables are securely plugged in. In addition, cleaning and maintenance work must be carried out on the router to ensure it functions correctly.

The regular inspection and replacement of brushes in DC motors is of the utmost importance. This is because excessive wear on the brushes can directly affect the motor’s performance and may even lead to damage to the motor. It is therefore recommended that the brushes in DC motors fitted to equipment such as CNC lathes, CNC milling machines and machining centres be subjected to a comprehensive inspection at least once a year, and replaced in a timely manner as required.

Regular inspection of the battery used for storage is just as important as replacing it. The CMOS RAM memory in CNC systems is usually equipped with a rechargeable battery maintenance circuit, the purpose of which is to ensure that stored data is retained in the event of a power failure; the battery can continue to be used even before it fails. However, to ensure the stable operation of the system, it is recommended that the battery be replaced at least once a year. It should be noted that power to the CNC system must be maintained during the battery replacement process to prevent the loss of data in the RAM.

The cleaning and maintenance of electrical components within the control cabinet are equally crucial. The electrical components inside the control cabinet must be cleaned regularly, inspected, and the condition of the terminal blocks checked and tightened. At the same time, cleaning and maintenance operations must be carried out on the CNC system’s control modules, circuit boards, fans, air filters, and heat dissipation devices; and ensure that the internal components, circuit boards and fans of the operator panel are in good working order, and that the connectors are securely fastened and reliable.