Mechanical Micromachining-Effect of Crystallographic Anisotropy on Machining Forces

With increased application of mechanical micromachining for creating small features with complex geometries on a broad range of materials, the need for understanding the mechanics of machining at the micro-scale has been recognized. During mechanical micromachining of metals, the tool-workpiece interaction occurs entirely within either a single crystal or a few crystals of the workpiece material. Consequently, the crystallographic properties (e.g., anisotropy) of individual crystals strongly affect the machining response, including micromachining forces and resulting surface finish. Hence, the crystallographic effects that are generally neglected (due to the perceived isotropic nature of the workpiece) in macro-scale machining need to be studied both experimentally and theoretically for gaining a better understanding of the micromachining process. This thesis aims to understand the effects of crystallographic anisotropy on machining response of face centered cubic metals through physics-based modeling and experimental analysis. The thesis begins with an introduction to micromachining and the associated crystallographic effects on the micromachining response. Subsequently, a literature review is presented and the shortcomings of the available research are identified. In particular, (a) the lack of physically realistic machining force models incorporating the effects of anisotropy, and (b) a necessity for experimental data analyzing the effect of anisotropy over a broad range of machining conditions, are addressed. The work is performed in three stages, with the first two addressing the former, and the last one addressing the latter shortcoming. First, a simplified machining force model incorporating the effects of anisotropy is developed by combining a plasticity theory and the Merchant’s machining model. Since the deformation geometry is unknown a-priori in machining operations, a shear angle determination scheme is necessary before predicting the forces. For a given crystallographic orientation, the model considers the minimization of the total power, including the shearing (plastic) and rake-face friction power, to determine the shear angle and predict the machining forces. The calculation of shearing power is performed using the Bishop and Hill’s plasticity theory, thus incorporating the effects of anisotropy. The model is calibrated and validated using the available (but limited) machining force data from the literature. An analysis of the model is also performed to observe the effects of orientation, friction angle and rake angle. The simplified model neglected the effects of hardening and lattice rotation observed during large strain deformation (such as that experienced in machining). Second, a more physically realistic rate sensitive plasticity-based machining (RSPM) force model is developed to enhance the simplified model by incorporating the hardening and lattice rotation