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|Title:||Modelling and simulation of nano-surface generation in ultra-precision grinding||Authors:||Chen, Shanshan||Degree:||Ph.D.||Issue Date:||2018||Abstract:||Ultra-precision grinding is widely applied to machine a wide range of precision components made of hard and brittle materials with remarkable surface integrity and surface quality. Surface quality is crucial to evaluate grinding performance, which results from the interaction of abrasive grains and machined material. However, grinding is a complex process, which is influenced by many factors, such as the workpiece material, wheel characteristics and grinding conditions. Atheoretical and experimental investigation is much needed to gain a better understanding of the process of surface generation in ultra-precision grinding. Hence, a theoretical model should be developed to predict the surface generation and better explain the interaction of the machine tool and the workpieces. Due to the random nature of the machine tool, it has been considered as a harder modelling than single point turning or multipoint milling. Although extensive research work has been carried out to model the surface generation in grinding, most of the modelling of the ground surface topography is based on either the abrasive kinematics (micro-level) or high-frequency vibration of the wheel (macro-level) to predict surface quality or grinding performance and considerable simplifications have been made for modelling work. Most of the previous research work is based on cylindrical surface grinding wheel for machining flat surface and neglected the wheel geometry. However, for the arc of the wheel, there is little work, especially for the lack of a comprehensive study of surface generation and a correlation model to relate the two levels together. In this thesis, a Taguchi method is employed to study the relative influence of machining parameters on the surface quality and an optimal combination of operation parameters in ultra-precision grinding of silicon carbide has been found. Hence, based on the optimal results of the Taguchi experiment, individual variable experiments were conducted to study the influence of every grinding parameter on the condition of the machined surface. Finally, the contribution of each factor affecting surface quality is evaluated. In this study, power spectrum analysis was employed to characterize the machined surface topography. It was found that the cumulative effect of the action of abrasive grains is essential to obtain a good surface. It was also found that the surface roughness pattern may be caused by the periodical micro-vibration of the grinding wheel. Based on the experimental result, a 2D surface generation model in ultra-precision grinding was developed by taking into account the micro-vibration of the grinding wheel so as to uncover the mechanism of spiral marks. It was found that a phase shift is inevitably introduced in the grinding due to the small speed errors of the wheel, which contributes to the accumulated effect of surface wave under a fine feed rate. It shows that micro-vibration with a medium phase can improve the machined surface quality resulting from dense spirals, which can suppress the amplitude of the surface topography.
Finally, a three-dimensional (3D)surface generation model for ultra-precision grinding was developed. It takes into account the grinding wheel geometry, random heights of abrasive grains, micro-vibration and phase shift. In this research work, wheel shape with two radii and wheel synchronous vibration were modelled first for the interference of the tool edge in 3D space so as to uncover the evolution mechanism of surface waviness under different phase shifts (0.0-1.0); then a multi-scale model was established to consider the diverse protrusion heights of the grits and incorporating the wheel shape and micro-vibration of the tool so as to elaborate the mechanism of grinding marks' generation on the ground surface. Four principal residual marks on the ground surface including spirals, tool feed marks, cumulative phase marks and abrasive grain scratches were found. For surface waviness resulting in the tool's imbalance, the amount of it is equal to the ratio of revolving speed of the grinding wheel and workpiece. The feed mark representing the tool locus and tool nose geometry is a spiral pattern from the edge area to the machined centre. Phase shift marks arecaused by the phase accumulation effect. The grit scratches are related to the wheel geometry, kinematics and its distribution of protrusion heights. With the successful development of the 2D and 3D surface generation models, multi-scale grinding marks including both the macro roughness patterns originating from wheel vibration and the micro scratches resulting from the wheel cutting profile and the abrasive actions can be predicted, which can further improve the accuracy of existing models separately considering the two levels.
|Subjects:||Hong Kong Polytechnic University -- Dissertations
Grinding and polishing
|Pages:||xxiii, 191 pages : color illustrations|
|Appears in Collections:||Thesis|
View full-text via https://theses.lib.polyu.edu.hk/handle/200/9686
Citations as of May 22, 2022
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