How to solve the vibration problem of CNC lathe

Shenyang First machine Tool Factory CNC lathe vibration in the process of processing, will cause the workpiece surface chatter, rework rate, reject rate is high, accompanied by shock knife phenomenon.
1, CNC lathe vibration is generally divided into three kinds: free vibration, forced vibration and self-excited vibration.
Free vibration
Free vibration is a vibration caused by an initial excitation, usually a pulse. This vibration depends on the initial excitation, one-time vibration energy, the process is limited, generally will not cause damage to the CNC lathe. Therefore, the influence of free vibration on CNC lathes is generally not considered.
Forced vibration
The object is in the vibration that produces below the external force action of lasting cycle change, call force vibration, be like the vibration that unbalanced, wrong place causes.
Self-excited vibration
Self-excited vibration is the vibration caused by the excitation caused by the system itself without external force. Self-excited vibration is a kind of dangerous vibration. Once the self-excited vibration occurs, the operation of equipment will lose stability.

2, numerical control lathe forced vibration causes and solutions
The main reason
(1) centrifugal force generated by the eccentric mass of rotating parts;
(2) Transmission error of parts in the process of motion transmission;
(3) Clearance characteristics in the cutting process.
The solution
(1) Reduce the excitation force. In order to improve assembly accuracy, the motor rotor, belt pulley and chuck should be tested for static balance.
(2) Improve the stiffness and damping of the process system. Lathe system stiffness and system damping increase, can improve the resistance to vibration, also can reduce vibration.
(3) Adjust the natural frequency of the system to avoid the generation of resonance. In the selection of speed, as far as possible to make the rotating workpiece frequency away from the machine tool related to the original natural frequency, to avoid the resonance zone.
(4) Use shock absorbers or dampers. When the above methods do not work, consider using dampers or shock absorbers.

3. Causes and solutions of self-excited vibration of CNC lathe
The reasons causing
In the process of machining, the self-excited vibration is caused by the vibration process itself a periodic change in the cutting force, and by the periodic change of the cutting force, in turn to strengthen and maintain the vibration, is the vibration system to supplement the energy consumed by the damping effect. When the vibrating motion stops, the alternating force disappears. This self - excited vibration in metal cutting is generally called cutting chatter.
In particular, the occurrence rate of self-excited vibration is much higher than that of forced vibration. The cutting relative vibration will reduce the surface quality of the machined workpiece and affect the service life of the tool and even the machine tool. In particular, now the use of a large number of high-precision CNC lathes, CNC lathes to ensure the accuracy of the workpiece and other indicators, will become meaningless when the flutter occurs.
The solution
(1) Select the right center height when installing the tool. When turning the inner hole groove, the tip point is theoretically required to be consistent with the center line of the hole, but in fact, when the tool is installed, the tip point is often on the center line 0.1mm or so, which is mainly the tool in the cutting, the tip point is often offset due to the reaction, so to give it a compensation amount.
(2) as far as possible to shorten the extension of the tool bar to improve the rigidity of the tool. When the cutter rod is stressed, it will bend and cause vibration, and the longer the suspension length, the vibration will be intensified. In general, the length of the tool should not exceed 2-3 times the length of the tool bar, which can greatly improve the bending strength of the slender tool bar.
(3) Reasonable selection of tool geometric parameters. The geometric parameters of the tool are: the tool Angle, the main Angle, the Angle and so on. The forward Angle has a great influence on vibration, and the vibration amplitude decreases with the increase of forward Angle. However, at higher cutting speed, the influence of rake Angle on vibration will be weakened. Therefore, when high speed cutting, even the use of negative rake tool, will not produce strong vibration. If the main deflection Angle increases, the cutting force will be reduced, and the cutting width will also be reduced. With the increase of the main deflection Angle, the vibration amplitude decreases gradually, but when the Angle is greater than 90°, the vibration amplitude increases. For the selection of rear Angle, it can be reduced to 2°~3°, and the vibration is obviously weakened. You can also grind out a negative inverted edge Angle on the main back corner of the tool, which can play a good role in eliminating energy.
(4) Improve the vibration resistance of the workpiece system. Improving the vibration resistance of process system is one of the important measures to control and prevent self-excited vibration. In the process system, the workpiece system is often prone to vibration weak link, so it is very necessary to improve the vibration resistance of the workpiece system.


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