Geometry and mechanics of spade drilling operations

The purpose of this work is to present an investigation of the spade drill-bit and drilling process. It will be based on rigorous geometric and drilling force models that uniquely describe the topology of the drill and its behavior. The objectives fall into four domains: experimental assessment of the performance and of the limitations of commercial spade drill bits, establishment of mathematical models for the bit's point geometry, establishment of mechanistic force models and force-model calibration procedures, and the development and experimental performance assessment of a new generation of spade drill bits.; In order to build an ideal drill-bit prototype and determinate the influence of the drill-bit's geometric features on their performance, an experimental comparison of different commercial drill bits has been done. It was found that the limitations of existing designs were identified and targets for improved performance measures were set.; To fundamentally understand the spade drill bit's behavior a complete mathematical model of its principal topological elements has been established. In conjunction with this model the corresponding analytical formulation of the geometry and kinematics of the appropriate manufacturing procedures has also been formulated.; In regard to the mechanistic force models, a chip removal model and an elemental mechanistic model were introduced first, followed by a complete model capable of predicting the resultant force system acting on the spade bit during all phases of its penetration into the workpiece. To complete the model a simplified and efficient model calibration method for the determination of the mechanistic force model coefficients has also been proposed.; Finally, the established analytical basis consisting of the comprehensive geometric model and the mechanistic force model was instrumental in the development of a new generation of spade bits with unique topological features. It has been shown, both analytically and through a systematic experimental study, that the performance of the newly developed topologies exceeds that of the commercially available designs. The new generation bits result in lower thrust and torque over the whole range of pragmatic operating conditions.