Modeling and simulation of micro-drilling dynamics

To improve efficiency and hole quality in micro-drilling processes, a better understanding of its dynamics and stability needs to be developed. With this objective in mind, this research work emphasizes two areas of investigation.; The first area, relating to dynamic drilling force modeling, introduces two new concepts, the dynamic cutting chip thickness and dynamic cutting chip area. To define these quantities, the effects of the drill's dislocation errors, drill grinding and installation errors and workpiece inclination are taken into consideration. By using the dynamic chip thickness and area instead of their static counterparts, existing static drilling force models are improved and extended to predict dynamic drilling forces. Separate force component models for the major cutting edges and the chisel edge are developed.; The second area deals with the development of a dynamic drill motion model. This model is established based on Hamilton's principle and includes the effects of transverse shear, rotary inertia and gyroscopic moments. The finite element method is used to solve the resulting equations. Utilizing the drill's deflections and drill installation errors, models for drill skidding, wandering, and for the hole's location are developed. Combining the drill's deflection and the spindle's rotation, a model for the hole's profile is also developed.; Subsequently, models for the prediction of the dynamic characteristics of micro-drills, such as critical speeds and buckling loads are built. Computer programs are developed to simulate the drill's dynamic characteristics. The influences of the helix angle, drill diameter, flute length, boundary restraints, rotation speed and cross sectional area are evaluated.; Based on the drilling force and drill motion models, software is developed to simulate the complete micro-drilling process dynamics. Micro-drilling processes in the presence of drill grinding errors, installation errors, workpiece inclination and random factors are simulated by the program and compared to the case of idealized drilling.; Conventional size drills with similar aspect ratios and characteristics to those applied in micro-drilling are used to experimentally investigate the effects of drilling process parameters, drill geometrical parameters and workpiece inclination on the dynamic drilling process. The experimental results are in close agreement with the simulations performed under the same drilling conditions.