Development of a dynamic model for vibration during turning operation and numerical studies

Turning operation is a very popular process in producing round parts. Vibration and chatter noise are major issues during turning operation and also for other machining processes. Some of the effects of vibration and chatter are short tool life span, tool damage, inaccurate dimension, poor surface finish and unacceptable noise. The basic dynamic model of turning operation should include a rotating work piece excited by a force that moves in the longitudinal direction. Dynamic interaction between a rotating work piece and moving cutting forces can excite vibration and chatter noise under certain conditions. This is a very complicated dynamic problem. Vibration and chatter in machining is one example of moving load problems as the cutter travels along the rotating work-piece. These moving cutting forces depend on a number of factors and regenerative chatter is the widely accepted mechanism and model of cutting forces which then introduce time delays in a dynamic model. In this investigation, the work piece is modelled as a rotating Rayleigh beam and the cutting force as a moving load with time delay based on the regenerative mechanism. The mathematical model developed considers work piece and cutting tools both as a flexible. Without doubt, this dynamic model of vibration of work piece in turning operation is more realistic than previous ones as the dynamic model has multiple-degrees-of-freedom and considers the vibration of the cutter with regenerative chatter. It is found that the cutting force model of regenerative chatter which introduces time delay in a dynamic model leads to interesting dynamic behaviour in the vibration of rotating beams and a sufficient number of modes must be included to sufficiently represent the dynamic behaviour. The effects of depth of cut, cutting speed and rotational speed on the vibration and chatter occurrence are obtained and examined. Simulated numerical examples are presented. These three different parameters are vital and definitely influence the dynamic response of deflection in the y and z directions. The depth of cut is seen to be the most influential on the magnitude of the deflection. In addition, higher cutting speed combined with high depth of cut promotes chatter and produces a beating phenomenon whereas rotational speeds have a moderate influence on the dynamic response. Furthermore, several turning experiments are conducted that demonstrate vibration and chatter in the machining operations. There is fairly good qualitative agreement between the numerical results and the experimental ones