What Are the Common Mechanical Faults of CNC Machine Tools

Due to the use of speed regulating motor, the spindle box structure of NC machine tool is relatively simple, and the parts prone to failure are the tool automatic clamping mechanism and automatic speed regulating device inside the spindle. In order to ensure that the tool holder will not loosen automatically during work or power failure, the automatic tool clamping mechanism adopts spring clamping and is equipped with a travel switch to send a clamping or loosening signal. If the tool cannot be loosened after clamping, consider adjusting the pressure and travel switch device of the tool loosening hydraulic cylinder or adjusting the nut on the Belleville spring to reduce the spring compression. In addition, the problems of spindle heating and spindle box noise can not be ignored. At this time, it is mainly considered to clean the spindle box, adjust the amount of lubricating oil, ensure the cleanliness of the spindle box, replace the spindle bearing, repair or replace the spindle box gear, etc.

In the feed transmission system of NC machine tools, ball screw pair, hydrostatic screw nut pair, rolling guide rail, hydrostatic guide rail and plastic guide rail are widely used. Therefore, the failure of feed transmission chain mainly reflects the decline of motion quality. For example, the mechanical parts do not move to the specified position, the operation is interrupted, the positioning accuracy decreases, the reverse clearance increases, crawling, and the bearing noise increases (after collision).

The faults of automatic tool change device are mainly manifested in: motion fault of tool magazine, excessive positioning error, unstable tool handle held by manipulator, large motion error of manipulator, etc. When the fault is serious, the tool change action will be stuck and the machine tool will be forced to stop working.

1. Magazine motion fault

If the coupling connecting the motor shaft and worm shaft is loose or the mechanical connection is too tight, the tool magazine will not rotate. At this time, the screws on the coupling must be tightened. If the tool magazine does not rotate in place, it is caused by motor rotation fault or transmission error. If the tool sleeve cannot clamp the tool, adjust the adjusting screw on the tool sleeve, compress the spring and tighten the clamping pin. When the tool sleeve is not in place up / down, check the position of the shift fork or the installation and adjustment of the limit switch.

2. Tool change manipulator failure

If the tool cannot be clamped tightly and the tool falls off, adjust the clamping jaw spring to increase its pressure, or replace the clamping pin of the manipulator. If the tool cannot be loosened after clamping, adjust the nut after loosening the locking spring so that the maximum load does not exceed the rated value. If the tool falls during tool exchange, it is caused by the failure of the spindle box to return to the tool change point or the drift of the tool change point during tool change. Operate the spindle box again to return to the tool change position and reset the tool change point.

4 Pressing failure of travel switch of each axis movement position

In order to ensure the reliability of automation, a large number of travel switch machines are used to detect the moving position on NC machine tools. After long-term operation, the motion characteristics of moving parts change, the reliability of travel switch pressing device and the quality characteristics of travel switch itself change, which has a great impact on the performance of the whole machine. Generally, the travel switch shall be checked and replaced in time to eliminate the impact of such poor switches on the machine tool.

1. Hydraulic system

The variable displacement pump shall be adopted for the hydraulic pump to reduce the heating of the hydraulic system. The filter installed in the oil tank shall be cleaned regularly with gasoline or ultrasonic vibration. Common faults mainly include wear, crack and mechanical damage of the pump body. At this time, it is generally necessary to overhaul or replace parts.

2. Pneumatic system

In the air pressure system used for tool or workpiece clamping, safety door switch and chip blowing in the taper hole of the main shaft, the water distribution air filter shall be drained and cleaned regularly to ensure the sensitivity of moving parts in the pneumatic components. Valve core action failure, air leakage, pneumatic element damage and action failure are all caused by poor lubrication, so the oil mist should be cleaned regularly. In addition, the tightness of the pneumatic system shall be checked frequently.

3. Lubrication system

Including lubrication of machine tool guide rail, transmission gear, ball screw, spindle box, etc. The filter in the lubrication pump needs to be cleaned and replaced regularly, generally once a year.

4. Cooling system

It plays the role of cooling and chip punching for cutting tools and workpieces. The coolant nozzle should be cleaned regularly.

5. Chip removal device

The chip removal device is an accessory with independent functions, which mainly ensures the smooth progress of automatic cutting and reduces the heating of NC machine tools. Therefore, the chip removal device should be able to automatically remove chips in time, and its installation position should generally be as close to the tool cutting area as possible.