Papers by Author: Seyed Vahid Hosseini

Abstract: Nowadays, the nano-machining process is used to produce high quality finished surfaces with precise form accuracy. To understand and analyze the chip formation mechanism of nano-machining process on an atomistic scale, since the experimentation is not an easy task, numerical simulation such as molecular dynamic (MD) simulation is a very useful method. In this paper, MD simulation of the nano-metric cutting of single-crystal copper was performed with a single crystal diamond tool. The model was solved with both pair wise Morse potential function and embedded atom method (EAM) potential to simulate the inter-atomic force between the work-piece and a rigid tool. The chip formation mechanism, dislocation generation, tool forces and generated temperature were investigated. Results show that the Morse potential cannot perform an appropriate defect formation and plastic deformation in nano-metric cutting of metals. Also, tool forces in Morse potential are more than the forces in EAM potential. Furthermore, the fluctuations of resultant forces in Morse potential are greater than that of EAM. In addition, using many-body interaction potentials like EAM can lead to substantial changes in surface energies, elastic-plastic properties and atomic displacement, compared with the pair-wise potentials like Morse. Finally, the atomic displacement investigation shows that in EAM potential study, only the atoms in a local region near the cutting process are displaced, but in Morse potential a large portion of atoms has affected during cutting process. Subsequently, the chip temperature in EAM potential is more than that of Morse potential.

Abstract: Today, there is a need to understand the micro mechanism of material removal to achieve a better roughness in ultra precision machining (UPM). The conventional finite element method becomes impossible to use because the target region and grids are very tiny. In addition, FEM cannot consider the micro property of the material such as atomic defect and dislocation. As an alternative, molecular dynamics (MD) simulation is significantly implemented in the field of nano-machining and nano-tribological problems to investigate deformation mechanism like work hardening, stick-slip phenomenon, frictional resistance and surface roughness [1]. One of the machining parameters than can affect nano-cutting deformation and the machined surface quality is tool nose radius [2]. In this paper molecular dynamics simulations of the nano-metric cutting on single-crystal copper were performed with the embedded atom method (EAM). To investigate the effect of tool nose radius, a comparison was done between a sharp tool with no edge radius and tools with a variety of edge radii. Tool forces, coefficient of friction, specific energy and nature of material removal with distribution of dislocations were simulated. Results show that in the nano-machining process, the tool nose radius cannot be ignored compared with the depth of cut and the edge of tool can change micro mechanism of chip formation. It appears that a large edge radius (relative to the depth of cut) of the tool used in nano-metric cutting, provides a high hydrostatic pressure. Thus, the trust force and frictional force of the tool is raised. In addition, increasing the tool edge radius and the density of generated dislocation in work-piece is scaled up that is comparable with TEM photographs [6].