2D and 3D numerical models of metal cutting with damage effects

In this paper a two-dimensional and a three-dimensional finite element models of unsteady-state metal cutting are presented. These models take into account dynamic effects, thermo-mechanical coupling, constitutive damage law and contact with friction. The simulations concern the study of the unsteady-state process of chip formation. The yield stress is taken as a function of the strain, the strain rate and the temperature in order to reflect realistic behavior in metal cutting. Unsteady-state process simulation needs a material separation criterion (chip criterion) and thus, many models in the literature use an arbitrary criterion based on the effective plastic strain, the strain energy density or the distance between nodes of parts and tool edge. The damage constitutive law adopted in models presented here allows defining advanced simulations of tool's penetration in workpiece and chip formation. The originality introduced here is that this damage law has been defined from tensile and torsion tests, and we applied it for machining process. Stresses and temperature distributions, chip formation and tool forces are shown at different stages of the cutting process. Finally, we present a three-dimensional oblique model to simulate the unsteady-state process of chip formation. This model, using the damage law defined before, allows an advanced simulation close to the real cutting process. The final part shows a milling application. An arbitrary Lagrangian Eulerian formulation (ALE) is used for these simulations; this formalism combines both the advantages of Eulerian and Lagrangian representations in a single description, it is exploited to reduce finite element mesh distortions. (C) 2004 Elsevier B.V. All rights reserved.