In drilling, the primary cutting lips and the secondary cutting lips of the drill shear the material while the central portion of the chisel edge indents the workpiece, making the cutting process complex to understand. As we go for micro-drilling, it exhibits an added complexity to the cutting mechanism when the edge radius gets comparable to chip thickness at low feeds. The presented work models the forces by the primary cutting lip of a micro-drill analytically using slip-line field that includes the changes in the effective rake angle and dead metal cap during cutting for cases of shearing as well as ploughing. To study the variation of forces experimentally, the primary cutting lip and chisel edge forces are separated out by drilling through pilot holes of diameter slightly above the drill-web thickness. Finally, the analytical and experimental results have been compared and the model has been calibrated.

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