Influence of the Rake Angle on Nanocutting of Fe Single Crystals: A Molecular-Dynamics Study

Iyad Alabd Alhafez,Herbert M Urbassek

doi:10.3390/cryst10060516

Abstract

Using molecular dynamics simulation, we study the cutting of an Fe single crystal using tools with various rake angles α . We focus on the (110)[001] cut system, since here, the crystal plasticity is governed by a simple mechanism for not too strongly negative rake angles. In this case, the evolution of the chip is driven by the generation of edge dislocations with the Burgers vector b = 1 2 [ 111 ] , such that a fixed shear angle of ϕ = 54.7 ∘ is established. It is independent of the rake angle of the tool. The chip form is rectangular, and the chip thickness agrees with the theoretical result calculated for this shear angle from the law of mass conservation. We find that the force angle χ between the direction of the force and the cutting direction is independent of the rake angle; however, it does not obey the predictions of macroscopic cutting theories, nor the correlations observed in experiments of (polycrystalline) cutting of mild steel. Only for (strongly) negative rake angles, the mechanism of plasticity changes, leading to a complex chip shape or even suppressing the formation of a chip. In these cases, the force angle strongly increases while the friction angle tends to zero.

Highlights

While in applications, cutting processes are usually performed on poly-crystalline materials, from a materials-science point of view, it is interesting to study the cutting of single crystals.In micro- and nano-cutting [1], the cutting depth may be smaller than the grain size of the material, so that crystal plasticity effects need to be taken into account. from the point of view of machining mechanics, this topic is interesting
The dominant mechanism was the formation of edge dislocation with the Burgers vector b = 21 [111], which moved upward in the [111]
The motion could effectively be described as the shear of the material with the shear plane given by the glide plane of the dislocation system; this shear plane is conventionally denoted as the primary shear plane (PSZ)

Summary

Introduction

While in applications, cutting processes are usually performed on poly-crystalline materials, from a materials-science point of view, it is interesting to study the cutting of single crystals.In micro- and nano-cutting [1], the cutting depth may be smaller than the grain size of the material, so that crystal plasticity effects need to be taken into account. from the point of view of machining mechanics, this topic is interesting. It is known that this concept is an idealization (see for instance the critical review by Astakhov [4]), and several extensions of the basic framework have been formulated [5,6,7]. The application of these concepts to nanocutting has been recently reviewed by Fang and Xu [1]. In the cutting of single crystals, plasticity will as a rule be based on the dislocation slip. If the cut system—that is, the surface orientation and the cut direction—is carefully chosen, only a single slip system will be activated, and the shear plane is determined by crystallography

Methods

Results

Conclusion