Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies

Development of a machine-tooling-process integrated approach for abrasive flow machining (AFM) of difficult-to-machine materials with application to oil and gas exploration componenets

This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel UniversityAbrasive flow machining (AFM) is a non-traditional manufacturing technology used to expose a substrate to pressurised multiphase slurry, comprised of superabrasive grit suspended in a viscous, typically polymeric carrier. Extended exposure to the slurry causes material removal, where the quantity of removal is subject to complex interactions within over 40 variables. Flow is contained within boundary walls, complex in form, causing physical phenomena to alter the behaviour of the media. In setting factors and levels prior to this research, engineers had two options; embark upon a wasteful, inefficient and poor-capability trial and error process or they could attempt to relate the findings they achieve in simple geometry to complex geometry through a series of transformations, providing information that could be applied over and over. By condensing process variables into appropriate study groups, it becomes possible to quantify output while manipulating only a handful of variables. Those that remain un-manipulated are integral to the factors identified. Through factorial and response surface methodology experiment designs, data is obtained and interrogated, before feeding into a simulated replica of a simple system. Correlation with physical phenomena is sought, to identify flow conditions that drive material removal location and magnitude. This correlation is then applied to complex geometry with relative success. It is found that prediction of viscosity through computational fluid dynamics can be used to estimate as much as 94% of the edge-rounding effect on final complex geometry. Surface finish prediction is lower (~75%), but provides significant relationship to warrant further investigation. Original contributions made in this doctoral thesis include; 1) A method of utilising computational fluid dynamics (CFD) to derive a suitable process model for the productive and reproducible control of the AFM process, including identification of core physical phenomena responsible for driving erosion, 2) Comprehensive understanding of effects of B4C-loaded polydimethylsiloxane variants used to process Ti6Al4V in the AFM process, including prediction equations containing numerically-verified second order interactions (factors for grit size, grain fraction and modifier concentration), 3) Equivalent understanding of machine factors providing energy input, studying velocity, temperature and quantity. Verified predictions are made from data collected in Ti6Al4V substrate material using response surface methodology, 4) Holistic method to translating process data in control-geometry to an arbitrary geometry for industrial gain, extending to a framework for collecting new data and integrating into current knowledge, and 5) Application of methodology using research-derived CFD, applied to complex geometry proven by measured process output. As a result of this project, four publications have been made to-date – two peer-reviewed journal papers and two peer-reviewed international conference papers. Further publications will be made from June 2014 onwards.Engineering and Physical Sciences Research Council (EPSRC) and the Technology Strategy Board (TSB

PRECISION POLISHING DYNAMICS: THE INFLUENCE OF PROCESS VIBRATIONS ON POLISHING RESULTS

The optical pitch polishing process has been used over 300 years to obtain high quality optical surface finish with little subsurface damage. A pitch tool consists of a metal platen coated with a layer of polishing pitch whereby pitch is a highly viscoelastic material. In polishing the workpiece is rubbed against the tool while abrasive slurry is supplied in between them. During polishing the workpiece is subjected to process vibrations, whereby be these vibrations are generated by the machine itself due to moving parts, or that are transmitted from the shop floor through the machine to the workpiece. To date, little is available in the public domain regarding the role of process induced vibrations on polishing outcomes. This research investigates such vibrations, how they transfer through the pitch layer on the tool, and ultimately how they affect the material removal rates and surface finishes obtainable on fused silica workpieces. Fundamental understandings with respect to the process vibration will reduce the heuristic nature of pitch polishing and generate deterministic polishing outcomes. Key findings include the following. The pitch selection has little influence on the magnitude or range of process vibrations transmitted through the tool to the workpiece in the 1 Hz to 16 kHz range. Within the same frequency bandwidth the recorded process vibrations are in the range of 0.2 to 10 nm and the main factors found to affect their magnitude include; the polishing machine itself, process speeds, and the use of passive damping materials in the tool construction. Material removal rates and surface finishes obtained on fused silica workpieces were found to be sensitive to the extent of the process vibrations. Up to 30% changes in the material removal rates were observed with increasing vibrational magnitudes. The higher level vibrations were also found to have a negative impact on the finishes obtained in the lower spatial domains. Additional testing on a specifically made test-bed demonstrated a linear correlation between the material removal rates and the vibrational power input. This relationship was further explored by adding external vibrational sources to an existing machine, and as expected the increased vibrational power resulted in 80% higher material removal rates. The results from this experimental work facilitated Dr. Keanini’s development of a vibrational based material removal model. Additional polishing tests combined with surface topography analysis of both hard and soft pitch tools demonstrated the robustness of the proposed model to accommodate the influence of different pitch grades. The summary in general is that in pitch polishing the process vibrations are important to monitor and control for process optimization

PRECISION POLISHING DYNAMICS: THE INFLUENCE OF PROCESS VIBRATIONS ON POLISHING RESULTS

The optical pitch polishing process has been used over 300 years to obtain high quality optical surface finish with little subsurface damage. A pitch tool consists of a metal platen coated with a layer of polishing pitch whereby pitch is a highly viscoelastic material. In polishing the workpiece is rubbed against the tool while abrasive slurry is supplied in between them. During polishing the workpiece is subjected to process vibrations, whereby be these vibrations are generated by the machine itself due to moving parts, or that are transmitted from the shop floor through the machine to the workpiece. To date, little is available in the public domain regarding the role of process induced vibrations on polishing outcomes. This research investigates such vibrations, how they transfer through the pitch layer on the tool, and ultimately how they affect the material removal rates and surface finishes obtainable on fused silica workpieces. Fundamental understandings with respect to the process vibration will reduce the heuristic nature of pitch polishing and generate deterministic polishing outcomes. Key findings include the following. The pitch selection has little influence on the magnitude or range of process vibrations transmitted through the tool to the workpiece in the 1 Hz to 16 kHz range. Within the same frequency bandwidth the recorded process vibrations are in the range of 0.2 to 10 nm and the main factors found to affect their magnitude include; the polishing machine itself, process speeds, and the use of passive damping materials in the tool construction. Material removal rates and surface finishes obtained on fused silica workpieces were found to be sensitive to the extent of the process vibrations. Up to 30% changes in the material removal rates were observed with increasing vibrational magnitudes. The higher level vibrations were also found to have a negative impact on the finishes obtained in the lower spatial domains. Additional testing on a specifically made test-bed demonstrated a linear correlation between the material removal rates and the vibrational power input. This relationship was further explored by adding external vibrational sources to an existing machine, and as expected the increased vibrational power resulted in 80% higher material removal rates. The results from this experimental work facilitated Dr. Keanini’s development of a vibrational based material removal model. Additional polishing tests combined with surface topography analysis of both hard and soft pitch tools demonstrated the robustness of the proposed model to accommodate the influence of different pitch grades. The summary in general is that in pitch polishing the process vibrations are important to monitor and control for process optimization

A Micro-milling cutting force and chip formation modeling approach for optimal process parameters selection

Las últimas décadas evidencian una demanda creciente por componentes miniaturizados con dimensiones reducidas y tolerancias estrechas, lo cual ha conllevado al desarrollo de la micro y nanotecnología. El micro-fresado, dentro de los procesos de micro-mecanizado, tiene el potencial de ser uno de los procesos de remoción de material más costo-efectivos y eficientes debido a su facilidad de aplicación, variedad de materiales de trabajo y flexibilidad geométrica. Se enfrenta a unos retos complejos debido al efecto de tamaño, vibraciones y otros factores incontrolables. Este estudio analiza dicho proceso orientado hacia desarrollar una mejor comprensión de la mecánica del micro-corte para ser aplicada en la optimización de parámetros de proceso. Se propone un acercamiento al modelado híbrido en forma novedosa, que permite una evaluación numérica a priori para evaluación de fuerzas y esfuerzos, combinado con experimentación para evaluar parámetros relevantes a la industria (formación de rebabas, desgaste de herramientas, entre otros).DoctoradoDoctor en Ingeniería Mecánic

Shape memory polyurethanes. Application in smart fabrics

269 p.En los últimos años, los polímeros con memoria de forma (Shape Memory Polymers, SMPs) han sido foco de atención, tanto en investigaciones básicas, como en sectores tecnológicamente avanzados. En esta Tesis Doctoral se presenta un estudio sobre los poliuretanos con memoria de forma (SMPUs) para aplicaciones en tejidos inteligentes. En primer lugar, se describe la síntesis de SMPUs mediante el método del prepolímero. A continuación, se ha analizado el comportamiento térmico, las propiedades termomecánicas, la permeabilidad y el efecto de memoria de forma. Además, se han creado fibras y tejidos a partir de los SMPUs con el fin de aportar una comprensión más profunda sobre los poliuretanos en la industria textil. Finalmente, tras los resultados obtenidos, se puede concluir que los poliuretanos con memoria de forma sintetizados poseen aplicaciones prometedoras en la industria textil.CTCR: Centro Tecnológico del Calzado de la Rioja LABQUIMAC : Laboratorio de Química Macromolecular. Facultad de Ciencia y Tecnología Gobierno de la Rioj