Investigation on size effect of specific cutting energy in mechanical micro-cutting

Mechanical micro-cutting is one of advanced processes to manufacture the miniature parts. The uncut chip thickness is one of the two important parameters in mechanical cutting. The uncut chip thickness and the cutting edge radius are at the same length scale, and the cutting tool extrudes and shears the workpiece with the round cutting edge during micro-cutting process. Size effect of specific cutting energy in micro-cutting is significant in comparison with that in macro cutting. A slip-field model is proposed in this paper to analyze the deformation process of workpiece material in micro-cutting. Johnson-Cook constitutive model, which includes shear strain hardening, shear strain rate hardening, shear temperature softening, and plasticity strain gradient (PSG) effects, is applied to the calculation of the shear flow stress at the primary shear zone (PSZ). Predicted cutting force using the shear flow stress is validated by the micro-orthogonal cutting experiments. The specific cutting energy is also calculated. It shows that the size effect on specific cutting energy in micro-cutting is influenced greatly by the shear strain hardening, shear strain rate hardening, shear temperature softening, and relative cutting length due to the ratio of uncut chip thickness to cutting edge radius. The plasticity strain gradient has effect on the specific cutting energy when the uncut chip thickness is smaller than 25 mu m for micro-orthogonal cutting AISI 1045 steel.