Excessive vibrations continue to be a major hurdle in improving machining efficiency and achieving stable high speed cutting. To overcome detrimental vibrations, an enhanced understanding of the underlying nonlinear dynamics is required. Cutting instability is commonly studied through modeling and analysis which incorporates linearization that obscures the true nonlinear characteristics of the system which are prominent at high speeds. Thus to enhance cutting dynamics knowledge, a comprehensive nonlinear turning model that includes tool-workpiece interaction is experimentally validated using a commercial laser vibrometer to capture tool and workpiece vibrations. A procedure is developed to use instantaneous frequency for experimental time-frequency analysis and is shown to thoroughly characterize the underlying dynamics and identify chatter. For the tests performed, chatter is associated with changing spectral components and bifurcations which provides a view of the underlying dynamics not experimentally observed before. Validation of the turning model revealed that the underlying dynamics observed experimentally are accurately captured, and the coupled tool-workpiece chatter vibrations are simulated. The stability diagram shows an increase in the chatter-free limit as the spindle speed increases until 1500rpm where it begins to level out. At high speeds the workpiece dominates the dynamics, and excessive workpiece vibrations create another stability limit to consider. Thus, workpiece dynamics should not be neglected in analyses for the design of machine tools and robust control laws. The chip formation mechanisms and high speeds make micro-milling highly non-linear and capable of producing broadband frequencies that negatively affect the tool. A nonlinear dynamic micro-milling model is developed to study the effect of parameters on tool performance through spectral analysis using instantaneous frequency. A lumped mass-spring-damper system is assumed for modeling the tool, and a slip-line force mechanism is adopted. The effective rake angle, helical angle, and instantaneous chip thickness are accounted for. The model produced the high frequency force components seen experimentally in literature. It is found that increasing the helical angle decreased the forces, and an increase in system stiffness improved the dynamic response. Also, dynamic instability had the largest effect on tool performance with the spindle speed being the most critical parameter.

La selección de centros de mecanizado de alta velocidad es un proceso complejo que requiere de mucha experiencia, puesto que en él intervienen un gran número de variables, tanto tecnológicas como económicas. Existen metodologías orientadas a seleccionar el centro de mecanizado óptimo, considerando únicamente una de estas dos tipologías de variables, sin embargo, esta tesis propone una metodología que contempla ambos tipos. Para ello se identifican las variables que tienen mayor influencia sobre los resultados del proceso de mecanizado, tanto desde un punto de vista de calidad de las piezas fabricadas como de la economía de la fabricación, y se propone un modelo de selección basado en los resultados de un trabajo experimental realizado sobre piezas de aluminio. Dicho modelo se implementa mediante redes neurales, cuyo entrenamiento se realiza en base a los resultados del trabajo experimental mencionado.

Condition monitoring of critical machine tool components and machining processes is a key factor to increase the availability of the machine tool and achieving a more robust machining process. Failures in the machining process and machine tool components may also have negative effects on the final produced part. Instabilities in machining processes also shortens the life time of the cutting edges and machine tool. The condition monitoring system may utilise information from several sources to facilitate the detection of instabilities in the machining process. To avoid additional complexity to the machining system the use of internal sensors is considered. The focus in this thesis has been to investigate if information related to the machining process can be extracted directly from the internal sensors of the machine tool. The main contibutions of this work is a further understanding of the direct response from both linear and angular position encoders due the variations in the machining process. The analysis of the response from unbalance testing of turn tables and two types of milling processes, i.e. disc-milling and slot-milling, is presented. It is shown that operational frequencies, such as cutter frequency and tooth-passing frequency, can be extracted from both active and inactive machine axes, but the response from an active machine axis involves a more complex analysis. Various methods for the analysis of the responses in time domain, frequency domain and phase space are presented. / QC 20100518

[Truncated abstract] Many researchers have proposed the use of silicate rock fertilizers (SRFs) as alternatives to chemical fertilizers. However, the application of SRFs in modern agricultural practices is limited due mainly to the slow release of plant-nutrient elements from SRFs and consequently many tonnes/ha of SRFs may need to be applied. Simple and inexpensive methods of modifying the physicochemical properties of SRFs are needed to improve the agronomic effectiveness of SRFs. This thesis is focused on the evaluation of high-energy milling to produce superfine particles to improve the effectiveness of mafic (basalt and dolerite) and felsic (gneiss and K-feldspar) rocks for use as fertilizers. The ground mafic rocks are for use as Ca and Mg fertilizers and the ground felsic rocks as K fertilizers. Laboratory and glasshouse experiments were conducted with several potential SRFs. In laboratory experiments, initially milled rocks (Ø< 250 μm for basalt, dolerite, and gneiss; Ø < 150 μm for K-feldspar) were further milled with a ball mill (Spex-8000) for 10, 30, 60, 90, and 120 min under dry and wet (rock/water ratio = 1/3) conditions. To investigate possible reaction between constituents, other subsamples of initially milled basalt, dolerite, and gneiss were added to reagent grade NaCl or KCl (4.5 g rock + 0.5 g NaCl or KCl) and milled for 120 min under dry and wet conditions. Basalt and dolerite were also mixed with K-feldspar at a ratio of 1 : 1 and milled for 120 min under dry and wet conditions. For use in the glasshouse experiment, the initially milled rocks were further milled with a vertical stirred ball mill for 1 h in a dry condition. The elemental and mineralogical compositions of the SRFs were determined using XRF and XRD. Effects of milling on major physicochemical properties of milled rocks were determined, including particle size (Malvern Mastersizer), surface area (BET-N2), quantities of amorphous constituents (XRD, oxalic acid-oxalate extraction, TEM), extractable cations (1M CH3COONH4 pH 7), pHH2O, and electric conductivity. Dissolution kinetics in 0.01M acetic-citric acids (for 56 days) and soil (for 10 months) were determined. Based on the results of these laboratory experiments, a glasshouse experiment was carried out for 12 months to evaluate the effects of SRF application on growth and nutrient uptake of ryegrass grown on several soils. Milling reduced particle size, enhanced amorphism, and increased the release of structural cations from the rocks, with the effects due to dry milling being greater than for wet milling. The optimum milling times which produced maximum amounts of exchangeable cations (Na, K, Ca, and Mg) were 30 - 90 min, depending on rock type. The use of NaCl and KCl as milling additives did not enhance the properties of the SRF

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Thesis (M.S.)--Ohio University, June, 2004. / Title from PDF t.p. Includes bibliographical references (leaves 96-99).

Thesis (Ph.D.(Electronic Engineering))--University of Pretoria, 2009. / Summaries in Afrikaans and English. Includes bibliographical references.

Thesis (B.S.) Magna Cum Laude--Butler University, 2007. / Includes bibliographical references (leaves 26-27).

The As- and Mo- bearing secondary mineral phases formed during the neutralization of uranium mill wastes were studied for a variety of ore blends including current and future ore sources at the Key Lake milling operation, northern Saskatchewan, Canada. A lab-scale plant model was employed to characterize secondary precipitates obtained during the mill waste neutralization process. Three scenarios of ore blends were processed through the lab-scale plant to produce mill waste solutions for neutralization before combination into final tailings. Slurry samples (n = 12) were collected from the secondary precipitates formed during the neutralization of mill wastes (raffinate) by precipitation with Ca(OH)2 (slaked lime) from pH 1.5 to 10.5. Synchrotron based X-ray absorption spectroscopy of mill and lab-scale plant precipitates showed arsenate adsorbed to ferrihydrite was the dominant As mineral phase regardless of pH or sample blend (53-77%), with fractional contributions from ferric arsenates, and adsorption to aluminum phases (AlOHSO4, As(OH)3 and hydrotalcite). Molybdate adsorbed to ferrihydrite was the dominant Mo mineral phase, regardless of pH or sample blend, with fractional contribution decreasing with increasing pH, and minor contributions from calcium molybdate, ferric molybdate and nickel molybdate. These results were used in geochemical modelling to predict the source terms for these mineral phases in tailings facilities. Sequestration of As and Mo in the model showed solubility was controlled by adsorption to both Fe and Al oxide surfaces as well as by direct precipitation with other dissolved constituents (Ni, Ca and SO4).The models developed pH profiles of mineral phase precipitation to explain the solubility of As, Mo, Fe, Al, Mg and Ni during sequestration from pH 1.5 to 10.5 that were consistent regardless of ore blend used in simulations. Since adsorption of anions to the surface of ferrihydrite has been shown to slow conversion to crystalline forms of Fe oxides (goethite and hematite) and sequestration of arsenate effectively controls As solubility at high pH (pH >10), As-bearing mineral phases are expected to be stable for thousands of years. With adsorption as well as direct precipitation considered, Mo phases though effectively sequestering below pH 8, became unstable and released Mo back into the tailings porewater (pH >10), as predicted by the thermodynamic model. Historical data obtained from as-discharged tailings as well as previously published U mill tailings studies agree with these findings.

Thesis (MScEng (Industrial Engineering))--Stellenbosch University, 2008. / There is a growing global demand for titanium. The aircraft industry is the driving force behind the demand for titanium. The reason for this is that titanium has attractive properties that justify its use both economically and environmentally. Titanium alloys have superior strength-to-weight ratios. This implies that by substituting components manufactured from other metals in the aircraft with titanium components, a substantial reduction in structural weight can be achieved. From an economical point of view a lower mass implies lower fuel consumption. From an environmental point of view lower fuel consumption implies less harmful greenhouse emissions. Ti6Al4V components are the most widely used titanium alloy products in aircraft components. Ti6Al4V is known as a difficult-to-machine material. This is due to its low thermal conductivity and small contact area between the tool and the chips causing higher temperatures to be generated closer to the cutting edge of the insert. This will subsequently increase the rate at which the cutting tool wears. For this reason relatively low cutting speeds and feed rates are employed for the machining of Ti6Al4V compared to the machining of steels. Ti6Al4V is an exceptionally high cost material. The low cutting speeds and feed rates used in Ti6Al4V machining raises the machining cost of parts and contributes to an increase in the price of Ti6Al4V parts. By employing higher cutting speeds and feed rates machining times on Ti6Al4V products could be decreased, subsequently lowering the price for Ti6Al4V components. An increase in cutting speeds and feed rates will subsequently cause an increase in generated cutting temperatures, resulting in an increase in tool wear. This stresses the importance of controlling the cutting temperature during machining of Ti6Al4V in order to prolong tool life. The focus of this work was to investigate different lubrication strategies for polycrystalline diamond (PCD) and tungsten carbide inserts for Ti6Al4V milling operations in the quest to develop improved feasible cutting parameters. The results of this study showed that flood lubrication should be utilized for PCD inserts, while a “softer” 60 bar high pressure through spindle lubrication worked best for the tungsten carbide inserts. By utilizing these lubrication strategies, cutting speeds of 100 m/min and feeds per tooth of 0.05 mm/rev for both the PCD and tungsten carbide grades could be attained with satisfactory tool life.