Vibration Assisted Machining (VAM) refers to a non-conventional machining process where high-frequency micro-scale vibrations are deliberately superimposed on the motion of the cutting tool during the machining process. The periodic separation of the tool and workpiece material, as a result of the added vibrations, leads to numerous advantages such as reduced machining forces, reduction of damages to the material, extended tool life, and enabling the machining of brittle materials. Vibration Assisted Drilling (VAD) is the application of VAM in drilling processes. The added vibrations in the VAD process are usually generated by incorporating piezoelectric transducers in the structure of the toolholder. In order to increase the benefits of the added vibrations on the machining quality, the structural dynamics of the VAD toolholder and its coupling with the dynamics of the piezoelectric transducer must be optimized to maximize the portion of the electrical energy that is converted to mechanical vibrations at the cutting edge of the drilling tool. The overall dynamic performance of the VAD system depends of the dynamics of its individual components including the drill bit, concentrator, piezoelectric transducer, and back mass. In this thesis, a substructure coupling analysis platform is developed to study the structural dynamics of the VAD system when adjustments are made to its individual components. In addition, the stiffness and damping in the joints between the components of the VAD toolholder are modelled and their parameters are identified experimentally. The developed substructure coupling analysis method is used for structural modification of the VAD system after it is manufactured. The proposed structural modification approach can be used to fine-tune the dynamics of the VAD system to maximize its dynamic performance under various operational conditions. The accuracy of the presented substructure coupling method in modeling the dynamics of the VAD system and the effectiveness of the proposed structural modification method are verified using numerical and experimental case studies. / Graduate

Vibration assisted drilling (VAD) is a type of machining process in which high-frequency vibrations with a small amplitude are induced in the cutting tool to improve the cutting process of hard and brittle materials. These vibrations create an unsteady repetitive processing effect which eventually reduce the cutting forces. It is also crucial to measure these forces in some way because their knowledge directly aids in determining the best machining parameters. Direct and indirect methods can be used to measure these forces, but due to serious limitations of direct measurement methods, an indirect measurement method is required which is capable of online monitoring of high-frequency cutting forces. In this thesis, an indirect method is proposed to estimate thrust force and torque from the voltage signal generated by piezoelectric sensor and torsional deflection signal measured through piezoelectric accelerometer. The estimation of two input signals requires a multi-input multi-output (MIMO) model of VAD system which is developed using Receptance Coupling and Substructure Analysis (RCSA) method. Experimental and numerical methods are used to validate the constituent single-input single-output (SISO) transfer functions of the MIMO model. As the estimated forces are distorted by the dynamics of VAD structure, a Kalman Filter is employed to compensate the dynamics. The accuracy and similarity of results is determined by comparing the estimated cutting force values with the force measured from a load cell in time and frequency domain. The reported experimental results confirm the possibility of using Kalman Filter in estimating high-frequency forces generated in VAD process. / Graduate