Numerical study of microstructural effects on chip formation in high speed cutting of ductile iron with discrete element method

Microstructural deformation and fracture process is important for chip formation and finished surface quality during metal cutting. In this paper, discrete element method (DEM) is introduced to establish a heterogeneous material model for cutting simulation to understand the microstructural deformation and fracture behaviors. A typical heterogeneous engineering material, ISO 450-10 ductile iron, was selected for modeling and experiments. Graphite nodules and ferrite grains were modeled respectively for studying their deformation behaviors. Cutting force and chip morphology obtained by simulation were compared with the experimental results. It shows that lamellar structure and unequal segments form at the chip free surface, which was also observed by optical microscope (OM) and scanning electron microscopy (SEM). The deformed degree of graphite nodules is much higher than that of ferrite grains. In addition, cracks are prone to produce and the chip size becomes smaller as the cutting speed increases. The velocity field and stress distribution of material near the rake face were investigated and the relationship between stress and cutting speed was further discussed. The velocity fluctuation of discrete particles in heterogeneous model is more obvious due to the microstructures compared with that in homogeneous model. Furthermore, the stress of material changes significantly with the increase of cutting speed since velocity vortexes may occur, resulting in the occurrence of the fracture. The results demonstrate that the influences of microstructure on crack initiation and chip formation are more significant at high cutting speeds.