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1. main shaft component failure

due to the use of speed control motors, the structure of the cnc machine tool spindle box is relatively simple, and the parts that are prone to failure are the automatic tool clamping mechanism and automatic speed control device inside the spindle. in order to ensure that the tool holder will not loosen by itself 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 hydraulic cylinder pressure and travel switch device for loosening the tool or adjust the nut on the disc spring to reduce the amount of spring pressing. in addition, the heating of the spindle and the noise of the spindle box cannot be ignored. at this time, the main consideration is 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.

2. failure of the feed transmission chain

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, the failure of the feed transmission chain is mainly reflected in the decline in the quality of motion. such as: mechanical parts do not move to the specified position, operation is interrupted, positioning accuracy decreases, backlash increases, crawling, bearing noise increases (after a crash), etc.

such failures can be prevented by the following measures: (1) improve the transmission accuracy, adjust the preload of each motion pair, adjust the loose links, eliminate the transmission gap, shorten the transmission chain and set a reduction gear in the transmission chain, which can also improve the transmission accuracy. (2) improve transmission rigidity. adjusting the pre-tightening force of the screw nut pair and supporting parts and reasonably selecting the size of the screw itself are effective measures to improve the transmission rigidity. insufficient rigidity will also cause the table or carriage to crawl and vibrate and cause reverse dead zone, which affects the accuracy of transmission. (3) improve motion accuracy. on the premise of satisfying the strength and rigidity of the parts, the mass of the moving parts should be reduced as much as possible, and the diameter and mass of the rotating parts should be reduced to reduce the inertia of the moving parts and improve the motion accuracy. (4) the guide rail is more sensitive to stolen goods, so it is necessary to have a good protective device, and the pre-tightening force of the rolling guide rail should be selected properly. if it is too large, the traction force will be significantly increased. the hydrostatic guide rail should have a set of oil supply system with good filtering effect.

3. failure of automatic tool changer

the failure of the automatic tool changer is mainly manifested in: tool magazine movement failure, excessive positioning error, unstable gripping of the tool handle by the manipulator, and large movement error of the manipulator. when 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 be able to 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 holder cannot clamp the tool, adjust the adjusting screw on the tool holder, compress the spring, and tighten the clamping pin. when the tool holder is not up/down in place, check the position of the fork or the installation of the limit switch. with adjustment.

2. tool change manipulator failure

if the tool is not clamped tightly or the tool is dropped, adjust the clamping claw spring to increase the pressure, or replace the clamping pin of the manipulator. if the tool cannot be loosened after clamping, adjust the nut behind the locking spring so that the maximum load does not increase. exceeds the rated value. if the tool is dropped during the tool change, it is caused by the spindle box not returning to the tool change point or the tool change point drifting during the tool change. the spindle box should be re-operated to return it to the tool change position, and the tool change point should be reset.

4. press-fit fault of travel position switch of each axis

in cnc machine tools, in order to ensure the reliability of automation work, a large number of travel switch machine tools are used to detect the movement position. after long-term operation, the movement characteristics of the moving parts will change, the reliability of the travel switch pressing device and the quality characteristics of the travel switch itself will have a great impact on the performance of the whole machine. generally, it is necessary to check and replace the travel switch in a timely manner, which can eliminate the influence of such poor switches on the machine tool.

5. failure of supporting auxiliary devices

1. hydraulic system

the hydraulic pump should be a variable pump to reduce the filter installed in the heating oil tank of the hydraulic system, and 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 pneumatic system used for tool or workpiece clamping, safety door switch and chip blowing in the taper hole of the spindle, the water separator and air filter should be drained regularly and cleaned regularly to ensure the sensitivity of the moving parts in the pneumatic components. failure of valve core action, air leakage, damage to pneumatic components and failure of action are all caused by poor lubrication, so the lubricator should be cleaned regularly. in addition, the tightness of the pneumatic system should be checked frequently.

3. lubrication system

including the 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, usually once a year.

4. cooling system

it cools and flushes the tool and workpiece. coolant nozzles should be cleaned regularly.

5. chip removal device

the chip removal device is an accessory with independent functions, which mainly ensures automatic cutting plus smooth progress and reduces the heat 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 as possible to the cutting area of ​​the tool.

6. conclusion

cnc machine tools are automatic processing equipment controlled by computer and mechatronics. the use of cnc machine tools is a technical application project. correct prevention and effective maintenance are the basic guarantees to improve the efficiency of cnc machine tools. for common mechanical failures, although there are not many opportunities, it must not be ignored that the root cause of the failure should be comprehensively analyzed and judged, and the downtime of failures should be shortened as much as possible, so as to facilitate the effective performance of cnc machine tools.