Maintenance skills of CNC spindle fault, and the diagnosis methods of spindle fault generally adopt intuitive method and vibration method. The mechanical structure should be carefully analyzed before diagnosis, and all factors should be considered comprehensively. Attention should be paid to the following points in maintenance skills:
1. Pay attention to the disassembly sequence of parts
The spindle box must be opened and the spindle parts must be disassembled for spindle maintenance. Because the spindle structure of CNC is complex and there are many parts, the removed parts should be numbered in sequence, and then cleaned, tested and replaced one by one. Spindle selection, quality assurance, installation and restoration should follow the reverse order of disassembly.
2. Special pin puller for disassembly
A pin puller should be used to disassemble the top cover of the spindle box. There are two locating pins on the top cover. The upper end of the locating pin has M5 threaded hole for pin pulling. Generally, users don't have a special pin puller, so they can make a special tool to drill three holes in the steel plate, with a 6mm smooth hole in the middle and an M6 threaded hole on each side. When the pin is pulled out, the 6mm smooth hole is aligned with the M5 threaded hole on the locating pin, and an M5 screw is screwed to make the screw press the steel plate. Then screw M6 screws in the threaded holes on both sides of the steel plate respectively, and screw down evenly to lift the steel plate, and the steel plate drives M5 screws, thus pulling out the locating pin.
3, wave spring assembly
When the spindle parts are assembled, the wave spring must be restored to the compressed state before disassembly. At this time, it may be difficult to compress with Lamar, and special tools can be made to complete the compression.
4. Common faults and troubleshooting methods of CNC spindle components
The rotary accuracy of CNC spindle directly affects the machining accuracy of workpiece. The main failure forms of spindle components are spindle heating, noise during spindle operation, large spindle vibration or tool clamping. The main reasons for the above faults are the wear of the spindle after long-term work, the excessive cutting load of the spindle, and the poor maintenance and lubrication of the spindle.
Maintenance and treatment measures for common faults of mechanical spindle:
1. Problems of spindle heating and decreasing rotation accuracy
Phenomenon of faults: the machined workpiece hole has low accuracy, poor cylindricity, rapid heating of spindle and great processing noise.
failure cause analysis: after long-term observation of the machine tool spindle, it can be determined that the centering cone hole of the machine tool spindle was damaged during tool changing for many times. The main damage reason is that the cone surface of the spindle centering hole was damaged due to the wrong pulling and inserting of the tool changing during use. After careful analysis, it is found that there are four reasons for the failure of the spindle components:
(1) the grease of the spindle bearing is not up to requirements and mixed with dust impurities. These impurities mainly come from the compressed air used in the machining center without rectification and drying. During pneumatic chip removal, dust and water vapor enter the grease of the spindle bearing, resulting in poor lubrication of the spindle bearing and a lot of Jehol noise.
(2) There is damage on the locating surface of the conical hole used to locate the cutter in the spindle, which leads to the imperfect fit between the conical surface of the spindle and the conical surface of the tool holder, and the machined hole is slightly eccentric;
(3) The pre-tightening force of the front bearing of the spindle decreases, which leads to a larger clearance of the bearing;
(4) The spring of the automatic clamping device inside the spindle is fatigued, and the cutter cannot be completely tightened, which deviates from the original position.
For the above reasons, troubleshooting measures:
(1) Replace the front bearing of the spindle, use qualified grease, and adjust the bearing clearance;
(2) Grinding the locating surface of the tapered hole in the spindle to be qualified, and testing with the coloring method to ensure that the contact surface with the tool handle is not less than 9%;
(3) Replace the spring of the clamping device and adjust the preload of the bearing.
In addition, during the operation, it is necessary to check the cleanliness and cooperation of the shaft hole and the handle of the spindle frequently, to add air fine filtration and drying devices, to arrange the processing technology reasonably, and not to overload the machine.
2. Damage of the drawbar steel ball of the spindle part of the machining center
Phenomenon of failure: The drawbar steel ball of the automatic clamping mechanism of the tool in the spindle is often damaged, and the taper surface at the end of the tool handle is also often damaged.
Cause analysis: It was found through research that the spindle loosening action was not in harmony with the manipulator pulling out action. The specific reason was that the limit switch was installed at the tail of the booster cylinder, and the piston of the booster cylinder could not be put in place in time when the piston of the cylinder was in place, which led to the violent pulling out of the knife before the manipulator of the clamping structure was completely loosened, seriously damaging the steel ball of the pull rod and the tightening screw.
troubleshooting measures: clean the oil cylinder and the air cylinder, replace the sealing ring, adjust the pressure, and make them act in harmony. At the same time, check the gas-liquid booster cylinder regularly to eliminate potential safety hazards in time.
3. The positioning key of the spindle component is damaged.
The phenomenon of failure: the tool changing sound is loud, and the positioning key rotated by the tool handle at the front end of the spindle is partially deformed.
Cause analysis: Through research, it is found that the loud noise in the tool changing process occurs in the tool inserting stage of the manipulator, which is caused by the error in the quasi-stop position of the spindle and the drift of the reference point of the spindle tool changing. Hall element is usually used in machining center for orientation detection. After long-term use, the fixing screw of Hall element is loose, which leads to the keyway of the tool handle not aligned with the positioning key on the spindle when the manipulator inserts the tool, so the positioning key will be damaged. The mechanical spindle should be maintained accurately, and the reference point of spindle tool changing may be caused by poor contact of the circuit board of CNC system, change of electrical parameters, loose fixation of proximity switch, etc. When the tool holder is inserted into the spindle taper hole, the cone surface directly impacts the centering taper hole, resulting in abnormal sound.
troubleshooting measures: adjust the installation position of Hall element and fasten it with locking glue. At the same time, adjust the tool changing reference point and replace the locating key at the front end of the spindle. In addition, in the process of using the machining center, it is necessary to regularly check the position change of the spindle quasi-stop position and the reference point of spindle tool change, and timely check if there is any abnormality.
Maintenance of mechanical spindle:
Lubricating oil is often used to reduce the working temperature of bearings. There are two kinds of lubrication methods: oil-gas lubrication and oil circulation lubrication. When using these two methods, we should pay attention to the following points:
1. When using oil circulation lubrication, we should ensure that the oil quantity in the spindle constant temperature oil tank is sufficient.
2. Oil-gas lubrication is just the opposite of oil circulation lubrication, which only needs to fill 1% of the bearing space capacity.
the advantage of circulating lubrication is that it can reduce friction heating and absorb part of the heat of the spindle assembly under the condition of satisfying lubrication.
There are also two ways to lubricate the spindle: oil mist lubrication and jet lubrication. The cooling of spindle components is mainly to reduce the bearing heating and effectively control the heat source.
The sealing of spindle parts should not only prevent dust, chips and cutting fluid from entering the spindle parts, but also prevent the leakage of lubricating oil. There are contact and non-contact seals for spindle parts. For the contact seal with linoleum ring and oil-resistant rubber sealing ring, attention should be paid to check its aging and damage; For non-contact seals, in order to prevent leakage, it is important to ensure that the oil return can be discharged as soon as possible and that the oil return hole is unobstructed. Good lubrication effect can reduce the working temperature and prolong the service life of bearings; Therefore, it should be noted in operation that at low speed, grease and oil are used for circulating lubrication; Oil mist and oil-gas lubrication are used at high speed. However, when grease lubrication is used, the sealing capacity of the spindle bearing is usually 1% of the bearing space volume, so it is forbidden to fill it at will, because too much grease will aggravate the spindle heating. For oil circulation lubrication, check the spindle lubrication constant temperature oil tank every day to see if the oil quantity is sufficient. If the oil quantity is not enough, add lubricating oil in time. At the same time, pay attention to check whether the temperature range of lubricating oil is appropriate.
Accuracy of mechanical spindle:
Motion accuracy and structural rigidity of spindle components are important factors that determine machining quality and cutting efficiency. The main indexes to measure the performance of spindle components are rotation accuracy, stiffness and speed adaptability.
① rotational accuracy: radial and axial runout (see form and position tolerance) in the direction that affects machining accuracy when the spindle rotates mainly depends on the manufacturing and assembly quality of the spindle and bearing.
② Dynamic and static stiffness: mainly determined by the bending stiffness of the spindle, the stiffness and damping of the bearing.
③ speed adaptability: the allowable maximum speed and speed range mainly depend on the bearing structure, lubrication and heat dissipation conditions.
the mechanical spindle is characterized by three highs and one low (i.e. high speed, high precision, high efficiency and low noise).
1. High speed: CNC engraving and milling machine for mechanical spindle adopts precise and high-speed mating bearing and elastic/rigid pre-tightening structure, which can achieve higher rotation speed and make the cutter achieve the best cutting effect.
2. High speed: 7: 24 Tapered hole can ensure less than .5mm for installation and even radial runout. Because high-precision and high-precision parts manufacturing can be ensured.
3. high efficiency: continuous slight height can be used to change the speed, so that the cutting speed can be controlled at any time during the machining process, and thus high machining efficiency can be achieved.
4. low noise: the balance test shows that the spindle with G1/G.4(ISO194-1) has the characteristics of low noise when running at high speed.
Development situation of mechanical spindle:
Before 193s, the spindle of most machine tools used sliding bearing with single oil wedge. With the improvement of rolling bearing manufacturing technology, a variety of high-precision and high-rigidity rolling bearings for spindle appeared later. This kind of bearing has the advantages of convenient supply, low price, small friction coefficient and convenient lubrication, and can adapt to the working conditions with large changes in speed and load, so it is widely used. However, sliding bearings have the advantages of stable operation and good vibration resistance, especially various multi-wedge hydrodynamic bearings, which are widely used in some finishing machines such as grinders. Hydrostatic bearing, which appeared after 195s, has high precision, high rigidity, small friction coefficient, good vibration resistance and stability, but it needs a complex oil supply equipment, so it is only used in high-precision machine tools and heavy machine tools. Gas bearing has good high-speed performance, but because of its small bearing capacity and complicated gas supply equipment, it is mainly used in high-speed internal grinder and a few ultra-precision machining machines. Electromagnetic bearings, which appeared in the early 197s, have the advantages of good high-speed performance and large bearing capacity, and can make the spindle move slightly during the cutting process by adjusting the magnetic field, so as to improve the dimensional accuracy of machining, but the cost is high, and they can be used in ultra-precision machining machines.