Machining Forces: Some Effects of Tool Vibration

Abstract

When tool vibration occurs during machining both the undeformed chip thickness and the cutting forces have oscillating components. An examination of previous work reveals that both the relative phases and amplitudes of the oscillating forces and the oscillating undeformed chip thickness can be affected appreciably by changes in frequency. The explanations for this behaviour which have been put forward are not entirely consistent with previous experimental evidence. In the present work an analysis of the thrust forces occurring during tool vibration is proposed. The analysis is based on the assumption that there are two components to the oscillating thrust force: (1) a component proportional to, and in phase with, the oscillations in undeformed chip thickness and (2) a component, caused by contact between a small area of the tool flank and the freshly cut work surface, which leads the oscillation in undeformed chip thickness by 90°. Experimental results are presented which validate the assumptions made in the analysis. On applying the analysis to present and past experimental results, there is good agreement between theory and experiment when cutting at sufficient speed to prevent the formation of a substantial built-up edge: when cutting within the built-up edge speed range the theoretical predictions are less satisfactory, though still qualitatively correct. The results also show that changes in undeformed chip thickness have a smaller effect on the tool forces under vibratory conditions than under steady conditions.