Simulation of Sinuous Flow in Metal Cutting

Sinuous flow is a recently discovered mode of unsteady plastic flow in the cutting of metal involving large plastic strains, extensive material folding, and consequences ranging from paradoxically large cutting forces to poor surface finish. Here we use full-scale simulations to show how sinuous flow, and the concomitant redundant plastic deformation in cutting, are caused by microstructure-related inhomogeneity. The computations are carried out in a Lagrangian continuum mechanics framework using a simple, but effective, pseudograin model to represent metal as a polycrystalline aggregate. Our simulations successfully capture all experimentally observed aspects of sinuous flow in metals, including highly undulating, non-laminar streaklines of flow in the chip, folds, and mushroom-like features, and severely deformed high aspect ratio grains. The simulations also shed light on the mechanism of sinuous flow, and the effect of deformation geometry, explaining why it is suppressed at high rake angles. We find that folding and sinuous flow can occur even at low friction, for grain sizes as small as 25–50 microns, and at very low-cutting speeds. Our study clearly points at the critical importance of incorporating microstructure in cutting simulations of pure metals.