Common faults and preventive measures of CNC machine tools
CNC machine tool is a typical technology-intensive automatic processing equipment integrating machinery, electronics, hydraulic pressure, optics and measurement technology. This paper discusses the common failures and preventive measures of CNC machine tools, and puts forward some opinions on how to use CNC machine tools reasonably to reduce their mechanical failures for your reference.
With the introduction and popularization of a large number of numerical control equipment, quite high requirements are put forward for the maintenance and repair of equipment. The key to the maintenance of CNC machine tools is the accurate diagnosis of faults, that is, the search for fault sources and the location of faults.
Common mechanical failures of CNC machine tools
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 holder will not loosen in vain 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 released after being clamped, consider adjusting the pressure of the tool release hydraulic cylinder and the travel switch device or adjusting the nut on the disc spring to reduce the amount of spring compression. In addition, the problems of spindle heating and spindle box noise cannot be ignored. At this time, the main considerations are 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.Feed drive chain failure
In the feed drive system of CNC machine tools, ball screw pairs, static pressure screw nut pairs, rolling guides, static pressure guides and plastic guides are commonly used. Therefore, there is a fault in the feed transmission chain, which mainly reflects the decline in motion quality. Such as: the mechanical parts do not move to the specified position, the operation is interrupted, the positioning accuracy decreases, the backlash increases, crawling, the bearing noise becomes larger (after a crash), etc.Such failures can be prevented by the following measures: (1) Improve transmission accuracy. Adjusting the pre-tightening force of each motion pair, adjusting the loose link, eliminating the transmission gap, shortening the transmission chain and setting the reduction gear in the transmission chain can also improve the transmission accuracy. (2) Improve transmission stiffness. Adjusting the pre-tightening force of the screw nut pair and supporting parts and choosing the size of the screw itself are effective measures to improve the transmission rigidity. Insufficient rigidity will also cause crawling and vibration of the workbench or pallet, and cause reverse dead zone, which will affect the transmission accuracy. (3) Improve movement precision. On the premise of satisfying the strength and rigidity of the components, the mass of the moving parts is reduced as much as possible, and the diameter and mass of the rotating parts are reduced to reduce the inertia of the moving parts and improve the motion accuracy. (4) guide rail. The rolling guide is sensitive to dirt, and good protective devices must be installed, and the preload of the rolling guide should be selected properly, and the traction force will increase significantly if it is too large. The hydrostatic guide rail should have a set of oil supply system with good filtering effect.
Automatic tool changer failure
The automatic tool changer failure 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. soWhen the failure is serious, the tool change action will be stuck, and the machine tool will be forced to stop working.(1) Motion failure of the tool magazine
If the coupling connecting the motor shaft and the worm shaft is loose or the mechanical connection is too tight due to mechanical reasons, the tool magazine cannot rotate, and the coupling must be tightened at this time screws.
If the rotation of the tool magazine is not in place, it is caused by motor rotation failure or transmission error. If the current tool holder cannot clamp the tool, it is necessary to adjust the adjusting screw on the tool holder, compress the spring, and tighten the clamping pin. When the up/down of the knife sleeve is not in place, check the dial position or the installation and adjustment of the limit switch.
(2) Fault of the tool changing manipulator
If the tool is not clamped tightly and the tool falls off, adjust the spring of the clamping claw to increase the pressure, or replace the clamping pin of the manipulator. If the tool cannot be loosened after being clamped, adjust the nut behind the loosening spring so that the maximum load does not exceed 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 to the tool change position and the tool change point should be reset.
Press-fit failure of travel position limit switches of each axis
On CNC machine tools, in order to ensure the reliability of automatic operation, a large number of travel position switches are used to detect the movement position. After a long-term operation of the machine tool, the movement characteristics of the moving parts change, the reliability of the travel switch pressing device and the quality characteristics of the travel switch itself change, which have a great impact on the performance of the whole machine. Generally, it is necessary to check and replace the limit switch in time to eliminate the influence of such a switch on the machine tool.Malfunction of auxiliary equipment
Hydraulic system. The hydraulic pump should adopt a variable displacement pump to reduce the heat generation of the hydraulic system. The filter installed in the fuel tank should be cleaned regularly with gasoline or ultrasonic vibration. Common failures are mainly pump body wear, cracks and mechanical damage. At this time, it is generally necessary to overhaul or replace parts.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 air filter should be regularly drained and cleaned regularly to ensure the sensitivity of the moving parts in the pneumatic components. Valve core action failure, air leakage, pneumatic component damage and action failure are all caused by poor lubrication, so the lubricator should be cleaned regularly. In addition, the airtightness of the pneumatic system should be checked frequently.
Lubrication system. Including the lubrication of machine tool guide rails, transmission gears, ball screws, spindle boxes, etc. The filter in the lubricating pump needs to be cleaned and replaced regularly, usually once a year.
Cooling system. It cools and flushes the cutting tool and workpiece. The coolant nozzles should be cleaned regularly.
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 heat generation 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.
Rationally use CNC machine tools
Selection of working sites for CNC machine tools
(1) Avoid sunlightDirect exposure and other heat radiation, avoid places with too much humidity or too much dust. Try to use it in an air-conditioned environment and keep the room temperature at about 20°C. Since our country is in a temperate climate, affected by the monsoon, and the temperature difference is large, the CNC machine tools with high precision and high price should be used in an air-conditioned room.(2) Avoid places with corrosive gases. The corrosive gas can easily deteriorate the electronic components, cause poor contact, or cause short circuit of the components, affecting the normal operation of the machine tool.
(3) Keep away from equipment with high vibration (such as punch presses, forging equipment, etc.). For high-precision machine tools, anti-vibration measures (such as anti-vibration grooves, etc.) should also be adopted.
(4) Keep away from strong electromagnetic interference sources to make the machine tool work stably.
