Reasons For Self-excited Vibration Of Precision Cnc Lathe

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Cause:

In the machining process, the self-excited vibration is caused by the periodic variation of a certain cutting force caused by the vibration process itself, and by this periodically changing cutting force, which in turn strengthens and maintains the vibration, the vibration system supplements the consumption by the damping action. energy of. When the vibration motion stops, the alternating force disappears. This self-excited vibration during metal cutting is generally referred to as cutting chatter.

In particular, the probability of self-excited vibration is much higher than forced vibration. Cutting relative vibrations reduce the surface quality of the workpiece and affect the life of the tool and even the machine. Especially in the current use of high-precision CNC lathes, the high precision of the workpieces guaranteed by CNC lathes will become meaningless when flutter occurs.

Solution:

(1) Select the appropriate center height when installing the tool. When turning the inner hole groove, the tool tip point theoretically needs to be consistent with the center line of the hole, but in fact, when the tool is installed, the tooltip point tends to be about 0.1 mm above the center line, which is mainly when the tool is cutting. Since it is often reversed due to reaction, it is necessary to give it a compensation amount.

(2) Minimize the overhang of the shank to increase the rigidity of the tool. When the arbor is stressed, it will bend and cause vibration, and the longer the overhang, the more the vibration will be. Under normal circumstances, the length of the tool extension should not exceed 2-3 times the length of the arbor, which can greatly improve the bending strength of the elongated shank.

(3) Reasonably select the geometric parameters of the tool. The geometric parameters of the tool mainly include the rake angle of the tool, the main declination, the back angle and so on. The rake angle has a great influence on the vibration, and as the rake angle increases, the vibration amplitude also decreases. However, when the cutting speed is high, the influence of the rake angle on the vibration will be weakened. Therefore, when cutting at high speed, that is, using a tool with a negative rake angle, it does not cause strong vibration. If the lead angle is increased, the cutting force will be reduced and the cutting width will be reduced. As the lead angle increases, the amplitude of the vibration gradually decreases, but when the angle is greater than 90°, the amplitude of the vibration increases. For the selection of the relief angle, it can be reduced to 2°~3°, and the vibration is obviously weakened. It is also possible to grind a negative chamfering angle on the main corner of the tool to achieve a good vibration damping effect.

(4) Improve the vibration resistance of the workpiece system. Improving the vibration resistance of the processing system is one of the important measures to control and prevent self-excited vibration. In the processing system, the workpiece system is often a weak link that is prone to vibration, so it is necessary to improve the vibration resistance of the workpiece system.

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