Download or read book Modelling and Analysis of Material Removal Characteristics in Computer Controlled Ultra-precision Polishing written by Zhongchen Cao and published by . This book was released on 2016 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Secondly, a comprehensive computational fluid dynamic (CFD)-based erosion model was developed by a combination of CFD simulation, erosion model, and experimental research so as to predict the material removal characteristics and surface generation in fluid jet polishing. In the computational fluid dynamic simulations, an Eulerian-Eulerian-Lagrangian method is used which treats the water and air as an Eulerian phase and the particles as Lagrangian particles. The coupled discrete phase model (DPM) and the volume of fluid (VOF) model are used to describe the multiphases in the FJP process. This CFD model also presents the application of the k-w model, together with the level set method, to describe the slurry/air interface in the commercial finite element analysis package FLUENT. After solving the stream flow characteristics, the motion of individual particles is also calculated in order to obtain more accurate predictions of the trajectories of individual particles impacting on the surface. The predicted results are used to integrate with the developed erosion model for the prediction of the material removal characteristics. Hence, the polishing path planning is determined based on the desired surface integrity of the optical surface to be generated using the data of the material removal characteristics. Finally, a theoretical model is built for predicting and simulating the surface generation in FJP. A series of spot and pattern polishing tests as well as simulation experiments by the theoretical model were conducted. The results not only show that the theoretical model predicts well for the surface generation under different polishing conditions but also helps to gain a better understanding of the polishing process in FJP. In the third part, a multi-scale theoretical model was established for predicting and characterizing the material removal characteristics and surface generation in bonnet polishing based on contact mechanics, kinematics theory and abrasive wear mechanism. Specifically, the pressure and velocity distributions are determined based on the kinematics theory and contact mechanics at the macro scale, and the pad topography which affects the contact ratio and hence the material removal rate at the micro scale, while the micro- or nano-sized abrasive particles scratch the surface at the nano scale. The model developed in this study attempts to capture much of the basic physics of the polishing process including the tool radius, polishing depth, head speed, precess angle, pad topography, polishing time, particle shape, slurry concentration, and the mechanical properties of the pad and workpiece. Experimental results show that the theoretical model predicts well that the material removal amount which increases with increasing precess angle and tool offset, depends linearly on the head speed and slurry concentration. A pattern test was also conducted to validate the surface generation model. The originality and significance of this research lies in the provision of CFD-based modelling of the material removal characteristics and surface generation for fluid jet polishing and multi-scale modelling of the material removal characteristics and surface generation for bonnet polishing. The successful development of the theoretical model helps greatly to make the CCUP process more predictive, so as to further optimize the manufacturing process for different work materials without the need for costly trial and error polishing tests. Moreover, this is the first of its kind in which the deterministic model has been successfully built which acquires much of the basic physics of the polishing process. This contributes significantly to form the theoretical basis for the better understanding of the polishing process.