Modelling of segmentation-driven vibration in machining

Abstract

Excessive vibration, such as chatter, is a common problem in machining processes. Meanwhile, numerous hard, brittle metals have been shown to form segmented chips, also known as sawtooth chips, during machining. In the literature, a cyclic cutting force has been demonstrated where segmented chips are formed, with the force cycle corresponding to the formation of segments. Segmented chip formation has been shown to be linked to high vibration levels in turning and milling processes. Additionally, it has been proposed that the amplitude of chatter vibrations can be limited by interference between the tool flank and wavy workpiece surface, a phenomenon known as tool-flank process damping. In this contribution, a model is proposed to predict the amplitude of forced vibration arising due to the formation of segmented chips during turning. The amplitude of vibration was calculated as a function of cutting parameters. It was demonstrated that the model can be extended to account for the effect of tool-flank process damping. For validation, titanium Ti6Al4V alloy was turned using a flexible toolholder, with surface speed ranging from 10 to 160 m/min, feed rate from 0.1 to 0.7 mm/rev and width of cut from 0.35 to 4 mm. In the experimental validation, 25 of 68 test cuts exhibited high-amplitude vibration. In 16 of these cases, the main cause was concluded to be chip segmentation, which can be predicted by the model. The model is thus considered of practical value to machinists.