This paper discusses the effects of ploughing and friction in microscale machining. The friction coefficient has previously been shown to be sensitive to the geometry of the abrasive particle and the depth of indentation. From a micromachining standpoint, the friction coefficient is modeled to be a function of the tool edge radius and the undeformed chip thickness, wherein the tool edge is modeled as a sliding cylinder on a flat workpiece. The contributions of ploughing force, which assumes significance in microscale machining, are better modeled using an integration approach over the edge of the tool. Two force models for the estimation of ploughing forces are compared, wherein one model uses a slip-line field analysis and the other uses a method of force balance on the deformation boundary. Basic microcutting (shaping) experimental data are presented and compared to the prediction results. The results show that a nonuniform friction coefficient improves the predictability of the force model.
This paper presents a physics-based analysis to quantitatively describe the effects of grain size, grain boundaries, and crystallographic orientation on the flow stress of the polycrystalline material and thereby on the cutting and thrust forces. The model has been experimentally validated, in terms of the force intensities and sensitivities to microstruc ture attributes such as the grain size and the misorientation by comparing the forces to measured data in micromachining of polycrystalline silicon carbide (p-SiC). Molecular dynamics (MD) simulations are performed to explore the effects of grain boundaries and misorientation and to validate the modeling analysis in the context of resulting force ratios.
This paper studies the effects of crystallography on the microscale machining characteristics of polycrystalline brittle materials on a quantitative basis. It is believed that during micromachining of brittle materials, plastic deformation can occur at the tool-workpiece interface due to the presence of high compressive stresses which leads to chip formation as opposed to crack propagation. The process parameters for such a machining process are comparable to the size of the grains, and hence crystallography assumes importance. The crystallographic effects include grain size, grain boundaries (GB), and crystallographic orientation (CO) for polycrystalline materials. The size of grains (crystals), whose distribution is analyzed as a log-normal curve, has an effect on the yield stress of a material as described by the Hall–Petch equation. The effects of grain boundary and orientation have been considered using the principles of dislocation theory. The microstructural anisotropy in a deformed polycrystalline material is influenced by geometrically necessary boundaries (GNB) and incidental dislocation boundaries (IDB). The dislocation theory takes both types of dislocations into account and relates the material flow stress to the dislocation density. The proposed analysis is compared with previously reported experimental data on polycrystalline germanium (p-Ge). This paper aims to provide a deeper physical insight into the microstructural aspects of polycrystalline brittle materials during precision microscale machining.
Surface contamination is one of the major causes of yield loss, with a unique set of challenges for large display glass sheets that support the industry. Here, we review the use of different cleaning approaches applied to display glasses during manufacturing, discussing the advantages of some choices over others.
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