Investigation of laser milling process characteristics for micro tooling applications

Laser milling is a new application that is challenging for the power contained in the laser light. Due to its small unit of material removal, accuracy and repeatability, laser milling has found an application area in micro manufacturing, especially the manufacturing of microtools. There is a number of micro manufacturing and replication processes on the market at present. Their needs raise the requirements that have to be met by the microtool manufacturing process. Initially, the requirements of micro manufacturing processes, such as micro-injection moulding and hot-embossing, are identified and compared to what the laser milling process can achieve. An investigation is carried out to identify the capabilities of the laser milling process and match them to these requirements. The investigated process characteristics are surface finish, aspect ratio, accuracy and minimum feature size. Furthermore, as surface finish is identified to be a considerable constraint, an investigation is undertaken to improve the resulting surface finish obtained from the laser milling process. A two-dimensional theoretical model is developed to investigate the crater formation on a metal target by a microsecond laser pulse. The model takes into account the absorption of the laser light by the target, and simulates the heating and vaporisation of the material, including an adjustment to compensate for the change of state. A simple numerical technique is employed to describe the major physical processes taking part in the laser milling process. Experimental validation of the proposed model is provided for two common tooling materials. To investigate the formation of the material surface after laser milling, a complex 3D surface model is presented based on the single crater profiles of the 2D theoretical model together with a consideration for the overlapping of the craters. Additional factors, that are influential in the formation of the final material surface, are also considered and their effect on the surface roughness estimated. Finally, a number of techniques for reducing surface roughness are presented. Laser cleaning is a technique that utilises the de-focused laser beam to "smooth out" the material surface irregularities. The other three techniques are applied after laser milling, and are ultrasonic cleaning bath, chemical pickling and electro-chemical polishing.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A genealogical critique of Beauchamp and Childress' for principles approach to medical ethics

<bold>Part Three</bold> examines the development of Beauchamp and Childress 'four principles' approach to medical ethics from the 1<super> st</super> to the 6<super>th</super> Editions of <italic>Principles of Biomedical Ethics,</italic> arguing that it has, thanks to changes in the authors' conception of philosophical moral theory, been able to productively incorporate the views of many of its critics over this time; that it is also able to incorporate features of different ethical approaches such as virtue ethics, narrative ethics and ethics of care; and that, properly understood, it continues to provide a good framework both for moral reflection in medicine and the provision of concrete action-guides. The thesis concludes by considering this view of the four principles in the light of the earlier sections' approach, and attempting to demonstrate further demonstrate their value through two case-studies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Isotopic content of rainfall as climatic indicators, Comptes Rendus Acad. Scie. Paris, Geosciences, 334, 7, 519-520

ECLOGAE GEOL. HELV

Carbon isotope exchange rate of DIC in karst groundwater, Chemical Geology

WATER RESSOURCE