Inhomogeneity of Strain in Metal Particulates Produced by Modulation-Assisted Machining

Modulation-Assisted Machining (MAM) is an emerging method of metal particulate production where the tool feed rate in a metal cutting process is modulated to form chip particles directly from a solid workpiece. During the cutting process, a periodic disengagement occurs between the tool and the workpiece forming discrete corresponding particles of uniform shape and size. As a result of the large plastic strains that occur during metal cutting, the final particle morphology (size and shape) produced by MAM is determined by the deformation conditions. Average strains in MAM are in the range of ~2–4 depending on the modulation and cutting conditions. Numerical simulation and finite element analysis have shown that the strain imparted in MAM can vary significantly even during the formation of an individual chip. The variation of deformation is a result of the transient nature of cutting and commonly observed in periodic deformation processes. In the present paper, the particle shape, strain and hardness were studied using Al6061-T6 as a model material. Particles of short fiber-like morphology were produced. The cross-sectional shape of the fibers was dictated by the amount and distribution of strain during the cutting process. Hardness measured by nano-indentation at different points on the fiber cross-section varied between 1.7–2 GPa consistent with the variations in strain reported in individual MAM particles. Consequently, the cross-sectional shape of fibers differs from the one simulated using only process kinematics and assuming steady-state conditions.