The causes of medium vibration in actual production are complex and varied. According to the vibration phenomenon in the machining industry and two different types of vibration manifestations (forced vibration and self-excited vibration), the cause analysis is roughly as follows:
1. Forced vibration
(1) The periodically changing centrifugal force caused by the imbalance of rotating parts on the machine tool. For example, it is caused by unbalanced rotation of motor, chuck and belt.
(2) The transmission force of periodic changes caused by the defects of machine tool transmission parts. Such as the periodic vibration caused by the loosening of machine tool parts such as tool rest, spindle bearing, carriage plug iron or the manufacturing error of transmission parts such as gears and bearings.
(3) The periodically changing cutting force caused by the non-uniformity of the cutting process itself. Such as turning polygonal or uneven surface workpiece and machining rough workpiece with irregular shape on lathe.
(4) Inertial impact produced when the moving direction of reciprocating parts changes. For example, the direction of the surface grinding process changes or changes the rotation direction of the machine tool instantaneously.
(5) Interference force transmitted by other external vibration sources. Around the casting workshop, the vibration of air hammer causes forced vibration and even resonance of other machine tools.
2. Self excited vibration
(1) The change of friction between chip and tool, tool and workpiece during cutting.
(2) The hardness inside the metal of the cutting layer is uneven. The uneven hardness of the excircle or end face after turning and repair welding often causes tool collapse and lathe self vibration.
(3) The installation rigidity of the tool is poor. If the size of the tool bar is too small or the extension is too long, the tool bar will tremble.
(4) Poor rigidity of workpiece. If machining workpieces with poor rigidity such as slender shafts, ripple or taper will appear on the surface of the workpieces.
(5) The chip buildup occurs and disappears from time to time, and the rake angle of the tool and the cross-sectional area of the cutting layer change from time to time during the cutting process.
(6) The vibration caused by different cutting quantities is easy to vibrate when cutting wide and thin.