Observed edge radius behavior during MD nanomachining of silicon at a high uncut chip thickness

Abstract

During ultraprecision turning of optical silicon, size effect determined by the ratio of undeformed chip thickness to tool cutting edge radius remains an important determinant of both compressive and shear stresses in the workpiece around the cutting edge (cutting zone). Plastic deformation which is a factor of both stresses is considered crucial to achieving appropriate and effective result. Invariably, since plastic deformation is required to ensure chip formation/removal in ductile mode, this ratio therefore does not only determine surface damage but also determine tool longevity. Although it has been established that nanoscale ductile mode cutting of optical silicon requires small undeformed chip thickness as compared cutting edge radius, it is however still important to study the characteristic behavior of workpiece and tool and the attained surface when turning is done at edge radius less than undeformed chip thickness. The high ratio resulting from high uncut chip thickness to edge radius as studied with molecular dynamics (MD) showed the superiority of low edge radius as compared the higher edge during nanometric silicon turning. Aside from both tool wear and kinetic friction which were evidently higher with the smaller edge radius, all other studied parameters appeared better with the smaller edge radius as compared the bigger edge when turning was done at uncut chip thickness higher and equal to the edge radius. Also, tool rake wear was observed to be prominent than flank wear in all the tested tools, even though it was highly pronounced with the 5 A edged radius tool.