By considering the effects of drill grinding errors and drill deflections, dynamic cutting chip thickness models were developed which in combination with workpiece surface inclination effects allowed the formulation of expressions for the dynamic cutting chip cross-sectional area. By using the dynamic chip thickness and dynamic cutting chip area to replace their static counterparts, static drilling force models were extended to facilitate the prediction of dynamic cutting forces in micro-drilling processes. The geometric characteristics of micro-drills were considered in these mechanistic force models. Separate thrust, torque and radial force models for the major cutting edges, secondary cutting edge and for the indentation zone were developed. The effects of drill installation errors on the radial cutting forces acting on the chisel edge and the major cutting edges were also included.

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