Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 43-45). Also available in electronic version.

The work reported in this thesis is concerned with both a fundamental assessment and the provision of a comprehensive MDI system for milling machines. The conceptual design has led to the realisation of a prototype work station which represents advances beyond the current state of the art for systems containing an APT-like processor and employs a powerful and flexible conversationally-based system with graphics support. The work station has been interfaced in STR mode to a numerically controlled milling machine and the effectiveness of the programming system has been demonstrated by the production of four workpieces.

One of the major limitations on productivity in metal cutting is chatter. Chatter is a form of unstable self-excited vibration which causes poor surface finish, as well as cutter and machine tool damage. The investigation of chatter suppression in milling using continuously variable spindle speed is presented in this thesis. The fundamental mechanism in regenerative chatter is due to favorable phasing between the inner and outer modulations on the chip thickness. In this thesis, the spindle speed is sinusoidally varied to prevent the dynamic cutting process from locking on to a constant phase shift and causing unstable cutting, or chatter. Because of the nonlin-earities and complexities of the process, time domain simulation of the dynamic cutting process has been modelled. The influence of various parameters, such as axial depth of cut, process damping from flank interference, and amplitude and frequency of speed variation have been investigated using the simulation model. The trends predicted by simulation results have been experimentally verified using cutting tests on a milling machine. It has been concluded from simulation and milling tests that a variable spindle speed can partially increase the chatter limit, but can never totally prevent chatter. The variable spindle speed strategy is incorporated into a proposed in-process chatter detection and avoidance algorithm. The milling process is monitored using the sound pressure signal measured by a microphone. When the amplitude of the sound spectrum near the natural frequency exceeds a threshold value, chatter has been detected and the spindle speed is oscillated until stability is regained. The proposed algorithm is implemented on line and experimental results are presented. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The fungal disease Fusarium head blight affects cereal grains and can produce mycotoxins, like the water-soluble deoxynivalenol (DON). Wheat wet milling process begins with ground endosperm obtained by dry milling and ends with the separation of starch from gluten. Research was conducted on hard red spring wheat and durum wheat samples naturally contaminated with DON. The fate of DON in wheat dry milled fractionations (farina/semolina, shorts, and bran) during wet milling was investigated. Three wet milling processes were evaluated. DON levels were assessed by GC-ECD. Results showed that DON was present in all dry milled fractions. DON concentration in farina and semolina exceeded the safety threshold for human consumption. After wet milling farina and semolina, nearly all the DON was found in the water-soluble fraction, regardless the wet milling process. A negligible level of DON was found in the gluten extracted from HRSW with Martin wet milling process.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Materials which are both lighter and stronger have faced an increased demand over the past decades to fulfil the requirements across a range of industrial applications. More specifically, demands for titanium alloys have increased significantly due to its high strength to weight ratio which is particularly attractive for increasing fuel efficiency in aircrafts and cars and is also used in biomedical implants. Despite the increasing demand for titanium made products, machining titanium alloys remains a significant challenge. High material strength and hardness lead to excessive heat generation at the cutting zone which accumulates and results in high cutting temperatures due to the poor thermal conductivity. The high cutting temperatures together with inherent material properties of titanium are responsible for short tool life and poor surface finish. Despite the environmental and health drawbacks, a generous amount of cutting fluids is commonly used to control the cutting temperature in machining titanium alloys. However, conventional cutting fluids evaporate at high cutting temperatures which isolate the cutting zone by forming a vapour cushion resulting in further increases in cutting temperatures. This research investigates the effects of cryogenic cooling on machinability of Ti-6Al-4V alloy in CNC milling as compared to conventional dry and wet machining environments. Two literature reviews were conducted and a methodology has been developed and implemented consisting of three experimental stages of i) design and manufacture of a cryogenic cooling system, ii) comparative study of cryogenic cooling with dry and wet machining and iii) optimisation of cutting parameters for cryogenic machining. The major contribution of this research can be summarised as design, realisation and assessment of a novel cryogenic cooling system for CNC milling, termed cryogenic shower, which is retrofitable to an existing CNC machining centre. In addition, the research provides a thorough study on the effects of cryogenic cooling on machinability of Ti-6Al-4V alloy in comparison with dry and wet machining. The studies range from power consumption and tool wear through to surface topography and surface integrity. Furthermore, the optimum cutting parameters for cryogenic machining are identified. The research demonstrates that using the cryogenic shower has significantly improved machinability of Ti-6Al-4V through realisation of higher material removal rates, reduced tool wear and improved surface finish, surface topography and surface integrity.

Thesis (M.S.)--Ohio University, June, 1996. / Title from PDF t.p.

Pearl millet is a staple food in Namibia. It is milled into flour by traditional and industrial dry milling processes. This research was conducted to help determine how to improve the nutritional value and acceptability of pearl millet. The traditional milling process involves a lactic acid fermentation step which lowers the pH of kernels. The effects of the traditional Namibian and industrial “dry milling” processes on the physical and nutritional composition of pearl millet grain were compared. Additionally, the effect of steeping three different Namibian pearl millet varieties (Kangara, Kantana and Okashana 2) in lactic acid and water on the colour and the phenolic content of the flour were determined. Regarding comparing the milling processes, variety Kangara was conditioned and decorticated traditionally with a pestle and mortar and industrially with an abrasive decorticator. The traditional decorticated grain was steeped and sun dried for 24 h before hammer milling, whereas the industrially decorticated grain was roller milled. Tristimulus colorimetry and proximate analyses were conducted on the samples. Concerning acid steeping, kernels were steeped in a pH 3.5 solution and in water as a control. Colour, total polyphenol and c-glycosyl flavone contents were determined. The determination of cglycosylflavone content was particularly important because these compounds are considered goitrogenic. The traditionally milled flour was lighter in colour than industrial milled flour. However, it was significantly lower in protein, ash and c-glycosyl flavone contents in comparison to industrial milled flour. This was due to the removal of more pericarp and germ in the traditional process. The industrial dry milling process therefore produces flour with a higher nutrient content in terms of protein, fat and minerals. However, the traditional Namibian milling process makes the colour of the pearl millet flour lighter, which is probably the reason that it is more acceptable to consumers. Kernels steeped in a lactic acid solution were lighter in colour than those steeped in water. Irrespective of the steeping media, the total polyphenol content was significantly lower in steeped kernels compared to those unsteeped. A similar trend was observed for the cglycosyl flavone content. This indicates that some of these compounds may have leached out during steeping. For all varieties, kernels steeped in lactic acid had a significantly higher total polyphenol content than those in water, probably due to the dissociation of metal-polyphenol complexes in the acidic medium whereby these polyphenols became free and available for measurement. Thus, steeping in a lactic acid solution can lead to better colour improvement of kernels compared to steeping in water. Thus, lactic acid steeping can improve the sensory quality of pearl millet products. An industrial process can thus be designed to include tempering the grain with food grade lactic acid to produce sour taste and leach out the colour pigments, particularly the cglycosyl flavones hence lightening the colour of the industrial milled flour. This produces a product with high nutritional content, lighter in colour and has the sour taste that consumers find appealing. Copyright 2007, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Barrion, SC 2007, Pearl millet milling : comparison between traditional Namibian fermentation - semi-wet milling and dry milling, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-01282009-132241 / > E1209/gm / Dissertation (MSc(Agric))--University of Pretoria, 2009. / Food Science / unrestricted

This thesis provides a brief introduction to the technology milling and analysis of various parts of milling machines. In addition, this thesis focuses on the design of a dedicated milling machine for machining functional areas of aluminum cast.