Maintenance of the mechanical parts and auxiliary devices of CNC machine tools

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The mechanical parts and auxiliary devices are important components of CNC machine tools. Among them, the mechanical components mainly include: the machine tool spindle assembly, the lead screw and nut pair, and the guide rails. The auxiliary devices of Teguc include mainly: a CNC indexing head, an automatic tool changer, a hydraulic and pneumatic system, and cooling and lubrication systems. Therefore, daily maintenance is one of the components of the overall maintenance work for CNC machine tools. I. Maintenance of the mechanical components The maintenance of the mechanical components of CNC machines includes the upkeep of the machine’s spindle unit, feed drive mechanism, guide rails, and other related components. 1. Maintenance of the spindle assembly The spindle assembly is an important component of the mechanical part of CNC machines; it consists of the main spindle, bearings, spindle positioning device, as well as automatic clamping and chip removal mechanisms. Lubrication, cooling, and sealing of the spindle components in CNC machine tools are several important issues to consider during their use and maintenance. Firstly, good lubrication can reduce the operating temperature of bearings and extend their service life ； To this end, it should be noted during operation that at low speeds, circulating lubrication with grease or oil should be used ； At high speeds, oil mist and oil-gas lubrication are used. However, when using grease for lubrication, the amount of grease filled into the spindle bearing is usually 10% of the bearing’s internal volume; it is important not to fill it to capacity, as too much grease can increase the heating of the spindle. For oil circulation lubrication, it is necessary to check the lubrication thermostat tank of the spindle on a daily basis during operation to ensure that there is sufficient oil; if the oil level is low, lubricant should be added promptly ； At the same time, check whether the lubricant temperature range is appropriate. To ensure proper lubrication of the spindle, reduce frictional heat generation, and at the same time remove heat from the spindle assembly, a circulating lubrication system is typically used, with a hydraulic pump providing pressure to supply lubricant, and an oil temperature controller used to regulate the temperature of the oil in the tank. The spindle bearings of high-end CNC machine tools are lubricated using advanced grease sealing, and each application of grease can last for 7–10 years. The new lubrication and cooling method is intended not only to reduce the temperature rise of the bearings but also to minimize the temperature difference between the inner and outer rings of the bearings, thereby ensuring minimal thermal deformation of the spindle. There are two common methods for lubricating the spindle. The oil-gas lubrication method is similar to the oil mist lubrication method, but while oil mist lubrication involves a continuous supply of oil mist, oil-gas lubrication delivers oil mist into the bearing gap at regular intervals and in controlled amounts. This approach enables oil mist lubrication while preventing excessive oil mist from contaminating the surrounding air. The injection lubrication method involves injecting a large volume of constant-temperature fluid into the main shaft bearings in order to achieve lubrication and cooling. Here, the oil injected at a higher flow rate must be forced out by an oil discharge pump, rather than returning naturally. At the same time, dedicated large-capacity, high-precision constant-temperature oil tanks must be used, with oil temperature variations kept within 5°C. Secondly, the cooling of the main spindle components is primarily aimed at reducing bearing heating and effectively controlling heat sources. Third, the sealing of the spindle unit is intended not only to prevent dust, debris, and cutting fluid from entering the spindle unit, but also to prevent the leakage of lubricating oil. There are contact and non-contact seals for the main shaft components. For contact seals that use felt rings and oil-resistant rubber seals, it is important to check for aging and damage ； For contactless sealing, to prevent leaks, it is important to ensure that the return oil can be drained as quickly as possible, and that the return oil holes remain unobstructed. 2. Maintenance of the feed drive mechanism The main electromechanical components of the feed drive mechanism include: servo motors and sensing elements, reduction gears, ball screw nut assemblies, screw bearings, and moving parts (worktable, spindle head, columns, etc.). (1) Adjustment of the axial clearance in the ball screw nut assembly. In addition to requiring precision in feed movement in a single direction, ball screw nuts also have strict requirements regarding axial clearance, in order to ensure precision in reverse motion. Therefore, during operation, it is necessary to pay attention to the axial clearance caused by wear of the lead screw-nut pair and to eliminate it using adjustment methods. Dual-nut gasket type backlash elimination, dual-nut threaded type backlash elimination, tooth difference type backlash elimination. (2) Daily inspection of the sealing and lubrication of the ball screw nut pair. The daily inspection of the sealing and lubrication of the ball screw nut pair is something we need to pay attention to during operation. Regarding the sealing of the screw nut, it is important to check the sealing rings and protective covers to prevent dust and contaminants from entering the ball screw nut assembly. For the lubrication of the screw nut, if grease is used, it should be lubricated regularly ； If lubricant is used, be sure to apply it regularly through the oil filling hole. 3. Maintenance of machine tool guides The maintenance of machine tool guides primarily involves lubricating the guides and protecting them. (1) Lubrication of guides The purpose of lubricating the guides is to reduce frictional resistance and frictional wear, in order to avoid low-speed crawling and minimize temperature rise at high temperatures. Therefore, lubricating the guide rails is very important. For sliding guides, lubricating oil is used for lubrication ； For rolling guides, either lubricating oil or grease can be used. Check the oil level in the lubrication tank of the guide rails; if the level is insufficient, lubricant should be added promptly ； It is also necessary to check whether the lubricating oil pump can start and stop on a scheduled basis, as well as to ensure that it can supply lubricating oil when it starts automatically. (2) Protection of the guide rails: During operation, care must be taken to prevent chips, abrasive particles, or cutting fluid from falling on the surface of the guide rails, as this can lead to increased wear, scratches, and rust on those rails. To this end, it is necessary to pay attention to the regular inspection of the guide rail protection devices in order to ensure the protection of the guide rails. 4. Maintenance of the rotary worktable: The maintenance of the auxiliary devices in CNC machines includes the maintenance of CNC indexing heads, automatic tool changers, and hydraulic systems. 1. Maintenance of CNC indexing heads: CNC indexing heads are common accessories used in CNC milling machines and machining centers. Their function is to perform rotational indexing or continuous rotational feeding movements in accordance with the instructions from the CNC system, thereby enabling CNC machines to achieve the required processing precision. Therefore, it is important to follow the instructions in the user manual and the operating procedures carefully when using these heads. 2. Maintenance of the automatic tool changer The automatic tool changer is a distinctive feature of machining centers that sets them apart from other CNC machines. It has the capability to automatically replace the required cutting tools according to the requirements of the manufacturing process, thereby helping CNC machines save auxiliary time and meeting the need to complete multiple processes and operations in a single setup. Therefore, during operation, it is necessary to regularly check whether the mechanical structures of all components of the automatic tool changer are functioning properly and whether there are any abnormal phenomena ； Check whether the lubrication is adequate, etc., and pay attention to the reliability and safety checks of tool changes. 3. Maintenance of the hydraulic system (1) Regularly inspect, filter, and replace the oil in the reservoir ； (2) Check the operating performance of the cooler and heater, and control the oil temperature ； (3) Regularly inspect and replace seals to prevent leaks in the hydraulic system ； (4) Regularly inspect, clean, or replace hydraulic components and filters; regularly inspect and clean the reservoirs and pipelines of deep hole drilling machines ； (5) Strictly implement the daily inspection system to check whether the system’s leakage, noise, vibration, pressure, temperature, etc. are within normal ranges. 4. Maintenance of air pressure systems (1) Select appropriate filters to remove impurities and moisture from compressed air ； (2) Check the oil supply volume of the oil mister in the system to ensure an appropriate amount of lubricating oil is present in the air, so as to lubricate the pneumatic components and prevent rust and wear that could lead to air leaks and malfunctioning of the components ； (3) Maintain the sealing integrity of the pneumatic system, and regularly inspect and replace seals ； (4) Pay attention to adjusting work pressure ； (5) Regularly inspect, clean, or replace pneumatic components and filter elements.