Understanding fiber-coupled diode laser superheating in laser-assisted machining of silicon nitride (Si(3)N(4))

The use of advanced ceramics like silicon nitride (Si 3N4) can be found in many high-tech engineering applications ranging from NASA's Space Shuttle program to more recent areas such as ballistic protection (ceramic armor). In order for advanced ceramics to become more prevalent in industry, it is necessary to develop the adequate manufacturing equipment for processing at a much cheaper price and faster manufacturing time than conventional grinding does. Laser-assisted machining (LAM) of ceramics is one tool that can enable this growth while maintaining reasonable costs for making advanced ceramic parts in small quantities. Mostly CO2 and YAG lasers have been used for processing but now with the development of diode lasers a new tool has been introduced. The diode laser offers more flexibility over others and cheaper equipment costs, smaller footprint and highest wall plug efficiencies.;In LAM, the laser does not remove the material but helps the tool in removing the material with much greater ease, thus providing many advantages over conventional machining methods like grinding. In LAM of Si3N 4 it is required to melt the glassy phase present (at the grain boundaries) in the workpiece material around 1000 °C rather than evaporating the bulk of the material which happens above 1600 °C. The current thesis work obtains the temperatures achieved by a Si3N4 rod (1 x 6 inch) during laser-assisted turning at different sets of parameters: rpm, laser spot size, laser power, laser preheat time, and bulk preheat temperature (temperature of preheating the whole workpiece externally without laser). The temperatures obtained are analyzed with the help of a previously carried out numerical modeling in LAM and a mathematical study is done relating these temperatures with the corresponding laser energies absorbed.;In the process of the research conducted, the calibration of all the equipment/processes involved in the accurate estimations of temperatures, power outputs, and other parameters -- which plays a major role in this study -- has been done. The whole thesis work helps develop a complete understanding of various laser and machining parameters in LAM of ceramics, and makes some important conclusions that help in continuing the research for a fully developed LAM of ceramics system.