Chatter vibration of workpiece deformation type in cutting thin-walled cylindrical workpiece (Generation mechanism of chatter vibration)

Abstract

In aerial industry, to improve the mileage, workpiece such as jet engine turbine case has been lightened and thinned. However, cutting workpiece with thin-walled structure causes vibration called "chatter vibration of workpiece deformation type". Chatter vibration affects not only processing accuracy but also wear of cutting tool. This paper describes chatter vibration generated in cutting thin-walled cylindrical workpiece. Firstly, by cutting various thickness workpieces, limit thickness and waveform of chatter vibration was investigated. In workpiece with axis length 200mm, 150mm and 100mm, vibration generation limit thickness is 16mm, 12mm and 4mm, respectively. Chatter vibration consists of sine mode vibration with node in tool position and cosine mode vibration with anti-node in tool position. Secondly, natural frequencies and natural vibration modes of the workpieces were measured. A thin-walled cylindrical workpiece has natural vibration similar to chatter vibration in frequency and vibration mode. When tool contacts workpiece, natural vibration is separate in 2 which are sine mode and cosine mode. Finally, coupling of two natural vibrations was investigated. Vibration system from thrust force to translational displacement (cosine mode) and vibration system from principal force to rotational displacement (sine mode) are coupled by two cross feedback in tool position. Cross feedback 1 is transfer characteristics from translational displacement to principal force, and cross feedback 2 is transfer characteristics from rotational displacement to thrust force. When the feedback system which consists of two natural vibration systems and two cross feedback becomes unstable, chatter vibration is generated.

Experimental Study on Application of Tuned Mass Dampers for Chatter in Turning of a Thin-Walled Cylinder

“…As listed in Table 3, the decreasing wall thickness generated a higher order mode of chatter owing to the reduced rigidity of the workpiece. More precisely, the occurrence tendency of higher order modes with respect to the decreasing wall thickness was consistent with the results reported earlier by Kurita et al [33]. For the wall thickness of 2.6 mm, the (4, 1) mode occurred while cutting in the vicinity of the workpiece tip, and the (3, 1) and (4, 1) modes occurred simultaneously while cutting 8.2 mm from the tip.…”

“…As the dimensional ratio of the inner diameter to the workpiece wall thickness and that of the outer diameter to the axial length of the workpiece increased, the natural frequencies of the radial vibration modes with circumferential nodes (shell modes) became lower than the natural frequencies of the cantilever beam modes of the workpiece. Moreover, the shell modes were dominant in the lower-order modes [32,33]. In the present study, carbon steel (C45) was used as the workpiece material for the machine structure considering its workability.…”