What are the common mechanical failures of CNC machine tools?

1. Spindle component failure

Due to the use of speed regulating motors, the structure of the spindle box of CNC machine tools is relatively simple, and the parts that are prone to failure are the automatic tool clamping mechanism and automatic speed regulating device inside the spindle. In order to ensure that the tool clamp will not loosen by itself during work or power failure, the automatic tool clamping mechanism uses 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 of the tool loosening hydraulic cylinder and the travel switch device or adjusting the nut on the disc spring to reduce the spring compression amount. In addition, the problems of spindle heating and spindle box noise should not be ignored. At this time, the main considerations are cleaning the spindle box, adjusting the amount of lubricating oil, ensuring the cleanliness of the spindle box, replacing the spindle bearings, and repairing or replacing the spindle box gears.

2. Feed transmission chain failure

In the feed transmission system of CNC machine tools, ball screw pairs, hydrostatic screw nut pairs, rolling guides, hydrostatic guides and plastic guides are commonly used. Therefore, if there is a fault in the feed transmission chain, the main reflection is the decline in motion quality. For example: the mechanical parts do not move to the specified position, the operation is interrupted, the positioning accuracy is reduced, the reverse clearance is increased, creeping, the bearing noise becomes louder (after a collision), etc.

3. Automatic tool changing device failure

The main faults of automatic tool changer are: tool magazine movement failure, excessive positioning error, unstable tool holder gripping by the manipulator, large manipulator movement error, etc. If the fault is serious, the tool change action will be stuck and the machine tool will be forced to stop working.

1. Tool magazine movement failure

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

2. Tool changing robot failure

If the tool is not clamped tightly and falls off, adjust the clamping claw spring to increase its pressure, or replace the manipulator clamping pin. If the tool cannot be loosened after clamping, adjust the nut behind the loosening spring so that the maximum load does not exceed the rated value. If the tool falls off during tool exchange, it is caused by the spindle box not returning to the tool change point or the tool change point drifting during tool change. The spindle box should be re-operated to return to the tool change position and reset the tool change point.

4. Failure of the travel switch of each axis movement position

In order to ensure the reliability of automation work, a large number of travel switches for detecting motion positions are used on CNC machine tools. After long-term operation, the motion characteristics of moving parts change, and the reliability of the travel switch pressing device and the quality characteristics of the travel switch itself change, which has a great impact on the performance of the whole machine. Generally, it is necessary to check and replace the travel switch in time to eliminate the impact of such switch failure on the machine tool.

5. Failure of supporting auxiliary devices

1. Hydraulic system

The hydraulic pump should use a variable displacement pump to reduce the heating of the hydraulic system. The filter installed in the oil tank should be cleaned regularly with gasoline or ultrasonic vibration. Common faults are mainly pump body wear, cracks and mechanical damage. In this case, it is generally necessary to overhaul or replace parts.

2. Air pressure system

In the air pressure system used for tool or workpiece clamping, safety protection door switch and spindle taper hole chip blowing, the water separator should be drained and cleaned regularly to ensure the sensitivity of the moving parts in the pneumatic components. Failures such as valve core failure, air leakage, pneumatic component damage and failure are all caused by poor lubrication, so the oil mist device should be cleaned regularly. In addition, the sealing of the pneumatic system should be checked frequently.

3. Lubrication system

Including lubrication of machine tool guide rails, transmission gears, ball screws, spindle boxes, etc. The filter in the lubrication pump needs to be cleaned and replaced regularly, generally once a year.

4. Cooling system

It cools the tool and workpiece and flushes chips. 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 CNC 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.