Effects of minimum uncut chip thickness on tungsten nano-cutting mechanism

Tungsten is considered as the preferred material for plasma-oriented materials in fusion reactors, and its ultra -precision machining is a concern at present. However, the critical cutting depth for chip generation is an important parameter affecting the surface formation and removal behavior of materials in ultra-precision machining. Herein, the simulation analysis of nano-cutting tungsten using molecular dynamics (MD) was per-formed, and a new method to determine the minimum uncut chip thickness hmin by identifying the atomic trajectory and calculating the relative coordinate value was proposed. Then, the effects rarely reported of the chip formation on the removal mechanism of tungsten were studied. The research showed that when the cutting depth h was 0.253 times of the cutting edge radius r, the critical cutting depth without chip was reached, namely hmin. The increasing cutting temperature and stress led to the decrease of machined surface quality and the increase of subsurface damage with the rising in h/r. Meanwhile, the dislocation slip dominated by the direction of 1/2 < 111 > was the main plastic deformation mechanism during cutting without chip, but the dislocation slip dominated by direction of < 100 > was main plastic deformation mechanism during processing with chip. The plastic deformation dominated by dislocation slip was also accompanied by the amorphization. The dislocation reaction from 1/2 < 111 > dislocation to < 100 > dislocation occurred under both energy and geometry conditions. Moreover, the dislocations had more energy to expand and evolve as a result of thermal-activated effect induced by elevated cutting force and temperature, which increased the dislocation density, depth of subsurface damage layer, and the stress variation degree of the machined area with the enhancement of hmin during cutting. This research provides a reference method for determining the minimum uncut chip thickness during material removal and is of significance for mastering the microscopic removal mechanism of tungsten.