First, the spindle component failure

Due to the use of the speed-regulating motor, the spindle box structure of the CNC machine tool is relatively simple, and the part that is prone to failure is the automatic clamping mechanism of the tool inside the spindle, and the automatic speed control device. In order to ensure that the tool holder will not loosen itself during work or power failure, the automatic clamping mechanism of the tool is spring-clamped and equipped with a travel switch to signal the clamping or relaxation. If the tool cannot be loosened after clamping, consider adjusting the loose cylinder pressure and the stroke switch device or adjusting the nut on the disc spring to reduce the amount of spring compression. In addition, the problem of spindle heating and headstock 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 and replace the spindle bearing, repair or replace the spindle box gear.

Second, the feed drive chain failure

In the CNC machine feed drive system, the ball screw pair, the static screw nut pair, the rolling guide, the static pressure guide and the plastic guide rail are generally used. Therefore, the feed transmission chain is faulty, mainly reflecting the deterioration of the motion quality. For example, the mechanical parts do not move to the specified position, the operation is interrupted, the positioning accuracy is decreased, the backlash is increased, the creeping, the bearing noise is increased (after the collision), and the like.

For such faults, the following measures can be taken to prevent: (1) Improve the transmission precision, adjust the pre-tightening force of each motion pair, adjust the looseness link, eliminate the transmission gap, shorten the transmission chain and set the reduction gear in the transmission chain, and also improve the transmission precision. (2) Improve the transmission stiffness. Adjusting the screw nut pair, the pre-tightening force of the support member and the reasonable selection of the size of the screw itself are effective measures to improve the transmission rigidity. Insufficient stiffness can also cause crawling and vibration of the workbench or pallet and cause reverse dead zones, affecting transmission accuracy. (3) Improve the accuracy of motion. Under the premise of satisfying the strength and rigidity of the component, the mass of the moving component is reduced as much as possible, and the diameter and mass of the rotating component are reduced to reduce the inertia of the moving component and improve the motion precision. (4) The guide rails are sensitive to the objects, and must have good protection devices, and the pre-tightening force of the rolling guides should be properly selected, and the traction force is significantly increased. The hydrostatic guide should have a well-filtered oil supply system.

Third, the automatic tool change device failure

The failure of the automatic tool changer is mainly manifested in: the movement of the tool magazine, the positioning error is too large, the manipulator grip is unstable, and the manipulator motion error is large. When the fault is serious, the tool change will be stuck and the machine will be forced to stop working.

1. Tool magazine motion failure

If the coupling of the motor shaft and the worm shaft is loose or the mechanical coupling is too tight, the tool magazine cannot be rotated. In this case, the screws on the coupling must be tightened. If the tool magazine is not rotated, it is caused by motor rotation failure or transmission error. If the tool holder cannot clamp the tool, adjust the adjusting screw on the knife sleeve, press the spring, and tighten the clamping pin. When the upper/lower position of the knife sleeve is not in place, check the position of the fork or the installation of the limit switch. And adjust the situation.

2. Tool changer failure

If the tool clamp is not tight and the tool is dropped, adjust the clamping claw spring to increase the pressure, or replace the mechanical clamping pin. If the tool is not loose after clamping, adjust the nut behind the loose spring so that the maximum load is not Exceeding the rating. If the tool is lost when the tool is exchanged, the spindle box does not return to the tool change point or the tool change point drifts when the tool change occurs. The spindle box should be re-operated to return to the tool change position and reset the tool change point.

Fourth, the movement position of each axis travel switch failure

On the CNC machine tools, in order to ensure the reliability of the automation work, a large number of stroke switch machine tools for detecting the movement position are used. After long-term operation, the moving characteristics of the moving parts change, the reliability of the stroke switch pressing device and the change of the quality characteristics of the stroke switch itself have a great influence on the performance of the whole machine. Generally, it is necessary to check and replace the travel switch in time to eliminate the influence of the poor switch on the machine tool.

V. Failure of supporting auxiliary equipment

Hydraulic system

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

2. Air pressure system

In the air pressure system for tool or workpiece clamping, safety guard door switch and spindle cone blower, the water separator should be regularly drained and cleaned regularly to ensure the sensitivity of moving parts in pneumatic components. Failures such as valve heart failure, air leakage, damage to pneumatic components, and malfunctions are caused by poor lubrication, so the oil mist eliminator should be cleaned regularly. In addition, the tightness of the pneumatic system should always be checked.

3. Lubrication system

Includes lubrication of machine guides, drive gears, ball screws, headstocks, etc. The filter in the lubrication pump needs to be cleaned and replaced regularly, and it should be replaced once a year.

4. Cooling system

It cools and smashes the tool and workpiece. The coolant nozzle should be cleaned regularly.

5. Chip removal device

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

Conclusion

CNC machine tools are computer-controlled, mechatronics automated processing equipment, the use of CNC machine tools is a technical application project. Proper prevention and effective maintenance are the basic guarantees for improving the efficiency of CNC machine tools. For common mechanical failures, although there are not many opportunities, it should not be overlooked that the root cause of the fault should be comprehensively analyzed and judged, and the downtime should be shortened as much as possible to facilitate the efficient performance of CNC machine tools.

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Label: Common mechanical failures and preventive measures for CNC machine tools

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