This work addresses the advanced probabilistic modeling of the stochastic nature of microgrinding in the machining of high-aspect ratio, ceramic micro-features. The heightened sensitivity of such high-fidelity workpieces to excessive grit cutting force drives a need for improved stochastic modeling. Statistical propagation is used to generate a comprehensive analytic probabilistic model for static wheel topography. Numerical simulation and measurement of microgrinding wheels show the model accurately predicts the stochastic nature of the topography when exact wheel specifications are known. Investigation into the statistical scale affects associated microgrinding wheels shows that the decreasing number of abrasives in the wheel increases the relative statistical variability in the wheel topography although variability in the wheel concentration number dominates the source of variance. An in situ microgrinding wheel measurement technique is developed to aid in the calibration of the process model to improve on the inaccuracy caused by wheel specification error. A probabilistic model is generated for straight traverse and infeed microgrinding dynamic wheel topography. Infeed microgrinding was shown to provide a method of measuring individual grit cutting forces with constant undeformed chip thickness within the grind zone. Measurements of the dynamic wheel topography in infeed microgrinding verified the accuracy of the probabilistic model.

Student number : 0318567G School of Chemical and Metallurgical Engineering Faculty of Engineering / Comminution is an important process in mineral processing, power plants, cement production and pharmaceutical industries. It is costly and an inefficient process in terms of energy requirements and steel consumption related to grinding media and liners. Spherical grinding media are predominantly used in final stages of ore grinding. The spherical balls change shape through breakage and wear. Though this is universal in milling, its contribution and effect on milling kinetics, load behaviour and mill power is not fully established. One area that is usually ignored is the relationship between media shape and mill power. The objective of this dissertation was to investigate how media shape affects grinding. Ball size distribution inside an industrial mill was analysed in terms of shapes and sizes. Load behaviour, mill power and breakage as affected by media shapes were studied in a pilot laboratory mill. An inductive proximity probe, light emitting diode, phototransistor and video photographs were used to determine the load orientation in terms of toe and shoulder positions. A load beam was used to measure the torque exerted by the charge. The variation in load orientation and mill power with speed among different media shapes was observed. Higher shoulder positions were noted with cylpebs than with worn and spherical balls. The power increased to a maximum with increasing mill speed for all media shapes reaching its peak at different mill speeds for the three shapes studied. Variations of breakage rates with media shapes were found; higher breakage rates were noted with spherical media but the differences narrows with decreasing feed size and increasing material fractional filling U. Considering that worn balls in an industrial mill charge constitute about 15 to 40 percent and that the highest difference in breakage rate observed being nine percent for purely one shape charge; it is very doubtful whether it is worthwhile in attempting to develop techniques for removing worn balls from the mill.

IsaMill is a stirred type mill used in mineral industry for fine and ultra-fine grinding. The difficulty in obtaining the internal flow information in the mill by experimental techniques has prevented the development of the fundamental understanding of the flow and generating general methods for reliable scale-up and optimized design and control parameters. This difficulty can be effectively overcome by numerical simulation based on discrete element method (DEM). In this work a DEM model was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern and power draw with those measured from a same scale lab mill. Spatial distributions of microdynamic variables related to flow and force structure such as local porosity, particle interaction forces, collision velocity and collision frequency have been analyzed. Among the materials properties of particles, it is shown that by decreasing particle/particle sliding friction coefficient, the particle flow becomes more vigorous which is useful to grinding performance. Restitution coefficient does not affect the particle flow significantly. A too low or too high particle density could decrease grinding efficiency. Although grinding medium size affects the flow, its selection may depend on the particle size of the products. Among the operational variables considered, the results show that fill volume and mill speed proved to be important factors in IsaMil process. Increase of fill volume or mill speed increases the interaction between particles and agitating discs which results in a more vigorous motion of the particles. Among the mill properties, particle/stirrer sliding friction plays a major role in energy transfer from stirrer to particles. Although there exists a minimum collision energy as particle/stirrer sliding friction increases, large particle/stirrer sliding friction may improve grinding performance as it has both large collision frequency and collision energy. However, that improvement is only up to a critical particle/disc sliding friction beyond which only input energy increases with little improvement on collision frequency and collision energy. Reducing the distance between stirrers or increasing the size of disc holes improves high energy transfer from discs to particles, leading to high collision frequency and collision energy. Among the different stirrer types, the energy transfer is more effective when disc holes are present. Pin stirrer shows increased collision energy and collision frequency which also result in a high power draw. Using the DEM results, a wear model has been developed to predict the wear pattern of the discs. This model can be used to predict the evolution of the disc wear with the time. It is shown that energy transfer from discs to particles are increased when discs are worn out. An attempt has also been made to analyze the microdynamic properties of the mill for different sizes. It is shown that specific power consumption and impact energy are correlated regardless of the mill size and mill speed.

The ceramic ball bearing has been used to exact machine for its good properties such as heat-resistant, corrosion-resisting, and wear-resisting. The old grinding methods of ball bearing spend much time and power. Although the magnetic fluid grinding method economizes time, but cost much money. This study research the effects of spindle speed, grit size, load, and the material of float-ring and fixed-ring on the grinding characteristics by using a new ultra-precision ball grinding machine which developed by our lab. Search the optimum operating conditions of this machine for the requirement of industrial circles. Experimental results show that the converge rate of the saturated value for the sphericity, surface roughness (Ra), and the removal rate are increased with increasing spindle speed, grit size, or load. The sphericity and surface roughness (Ra) are increased when spindle speed, grit size, or load is increased. The sphericity and surface roughness (Ra) are increased with increasing removal rate in using the same grit size and load. Under a certain operating parameter of grinding process, the mean diameter and removal rate are decreased with increasing grinding time. The sphericity and surface roughness (Ra) are better when using the plastic than the float-ring and fixed ring of aluminum, but its removal rate is lower than aluminum¡¦s. First, let the average sphericity achieve saturated value by using diamond grind disk to grinding the Al2O3 ceramic ball. Then, the optimum sphericity can achieve 0.7£gm and the surface roughness (Ra) can achieve 0.1£gm by using the B4C grits of 0.5£gm to grinding.

Mechanical grinding processes is the most popular way to fabricate the endface of optical fibers, although there are some other methods like chemical etching and leaser machining. Mechanical grinding has its uniqueness in cases of grinding Conical-Wedge-Shaped Fiber Endface¡]CWSFE¡^, polygon-cone-shape fiber endface and fiber endface with double-variable curvatures. Despite Mechanism Design Lab of National Sun Yat-sen university has successfully developed Unsymmetrical Fiber Endface Grinding Mechanism and Torque-Control Fiber Endface Grinding Mechanism in NSC 94-2212-E-230-005 and NSC 95-2221-E-230-020, it still face difficulties when fabricating the fiber endface with double-variable curvatures due to the mechanism constraints. In this study, the focus are concentrated on both the designing and implementing of a mechanism for grinding optical-fiber endface with double-variable curvatures, which controls Material Removal Rate by simultaneously and periodically adjusting the relative positions, as well as the normal pressure between the fiber endface and the grinding film. This study is composed of first, the reviewing the anterior references, both the papers and the patents, and then a series of engineering design methods, which involve the design requirements and constraints, conceptual design, evaluating alternatives, detail design, assembly and calibration. The mechanism, the research result, and those needed to be ameliorated will be demonstrated in the conclusion and discussion part, so as to offer the investigating direction in the future. It¡¦s believed that the grinding machine system developed in this study can be successfully applied to fabricating optical fiber lenses as well as different types of micro probes , micro electrodes, and micro spectroscopefors for other applications, with little adjustment of the jig and ferrule of this machine .

Grinding is an abrasive machining process used for the final shaping of components that require very smooth surfaces and a high dimensional accuracy. In recent years, the costs of industrial grinding operations have increased with a greater demand for high-strength, low-weight superalloy components. Titanium and nickel-based alloys are desirable for their high creep-rupture strength and corrosion and oxidation resistance in high-temperature environments. However, they are very difficult to grinding due to a combination of poor thermal properties, rapid work-hardening, and a high level of chemical reactivity. In this thesis, two methods are investigated to improve process performance in plunge centerless grinding of Inconel 718 and Ti-6Al-4V superalloy fasteners: (i) economic optimization of grinding process parameters and (ii) reduced quantity lubrication using a graphite nanoplatelet-enhanced grinding fluid. In the first part, a systematic methodology is presented for finding the optimum parameters in two stages: (i) modeling of process and part quality constraints, and (ii) determination of optimum grinding conditions in the feasible operating region. In the second part, the performance of a graphite nanoplatelet-enhanced grinding fluid in reduced quantity lubrication centerless grinding is evaluated to assess its potential as a cost-effective alternative to the traditional flood cooling method. The results of the study indicate that an appreciable reduction in the cost of the superalloy grinding operation can be achieved by operating at the optimum parameters. In addition, it is shown that the application of a graphite-enhanced fluid at a reduced flow rate is more effective than high-volume flood cooling in reducing specific grinding energy levels and wheel wear rates, thus offering the potential to increase process productivity.

No description available.

IsaMill is a stirred type mill used in mineral industry for fine and ultra-fine grinding. The difficulty in obtaining the internal flow information in the mill by experimental techniques has prevented the development of the fundamental understanding of the flow and generating general methods for reliable scale-up and optimized design and control parameters. This difficulty can be effectively overcome by numerical simulation based on discrete element method (DEM). In this work a DEM model was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern and power draw with those measured from a same scale lab mill. Spatial distributions of microdynamic variables related to flow and force structure such as local porosity, particle interaction forces, collision velocity and collision frequency have been analyzed. Among the materials properties of particles, it is shown that by decreasing particle/particle sliding friction coefficient, the particle flow becomes more vigorous which is useful to grinding performance. Restitution coefficient does not affect the particle flow significantly. A too low or too high particle density could decrease grinding efficiency. Although grinding medium size affects the flow, its selection may depend on the particle size of the products. Among the operational variables considered, the results show that fill volume and mill speed proved to be important factors in IsaMil process. Increase of fill volume or mill speed increases the interaction between particles and agitating discs which results in a more vigorous motion of the particles. Among the mill properties, particle/stirrer sliding friction plays a major role in energy transfer from stirrer to particles. Although there exists a minimum collision energy as particle/stirrer sliding friction increases, large particle/stirrer sliding friction may improve grinding performance as it has both large collision frequency and collision energy. However, that improvement is only up to a critical particle/disc sliding friction beyond which only input energy increases with little improvement on collision frequency and collision energy. Reducing the distance between stirrers or increasing the size of disc holes improves high energy transfer from discs to particles, leading to high collision frequency and collision energy. Among the different stirrer types, the energy transfer is more effective when disc holes are present. Pin stirrer shows increased collision energy and collision frequency which also result in a high power draw. Using the DEM results, a wear model has been developed to predict the wear pattern of the discs. This model can be used to predict the evolution of the disc wear with the time. It is shown that energy transfer from discs to particles are increased when discs are worn out. An attempt has also been made to analyze the microdynamic properties of the mill for different sizes. It is shown that specific power consumption and impact energy are correlated regardless of the mill size and mill speed.

Thesis (M.Eng.)--University of Wollongong. / Typescript. Includes bibliographical references: leaf 131-135.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillments of the requirements for The Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 104-110.