Elastic strain induced shear bands in the microcutting process

Abstract

Machining of copper-based alloys tends to produce irregularly spaced chip serration. However, turning cold-rolled material could sometimes produce regularly spaced chip serration. The regularly spaced chip serration is indeed layers of shear bands that grow and agglomerate to become chip serration. In this paper, an investigation into the formation of shear bands in the microcutting process of single point diamond turning is presented. The experimental results reveal how shear bands are initiated at the free edge of the chip and then propagated towards the tool tip. A new finite element model is developed to simulate the initiation and formation of these shear bands and to provide evidence for how these shear bands are induced by the elastic strain concentration. In contrast to the popular assumption that materials behave as rigid plastic during machining, the results reveal that elastic strain is one of the dominant factors leading to the formation of shear bands. Finally, an analytical model is proposed to reveal the influence of shear bands on the cutting force and on the formation of serrated chips.