An Improved Method of Cutting Forces Prediction for the Primary Cutting Edges of Twist Drills

This thesis originally proposes an improved theoretical method to predict thrust and torque of twist drills in high speed drilling. The three existing models and methods are thoroughly studied and evaluated. It has been observed that each method has its own advantages as well as drawbacks and some errors. A fundamental geometrical analysis is carried out on the primary cutting edge of a twist drill to understand the correlation between the geometrical features of the drill and the distribution of cutting forces. The improved method is based on the representation of the cutting forces along the cutting edge as a series of oblique cutting elements. The elemental forces are then integrated to determine the overall thrust force and drilling torque in terms of the basic geometrical features of the drill, the cutting conditions and the properties of the machined material. The improved method presents the proper definitions of the dynamic rake angle and the uncut chip thickness, proves the negligibility of the feed angle and gives accurate representation of the elemental forces acting along the primary cutting edge, as well as the total thrust force and the torque. A good agreement between the predicted and the experimentally measured forces and torques was found for low carbon steels.

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