Outside turning of commercially pure titanium alloys by minimum quantity lubrication

M.Ing. (Mechanical Engineering)Abstract: Machining is a widely used class of industrial manufacturing operation, wherein cutting fluids play a vital role in terms of machining accurate dimensional quality objects due to their cooling, lubricant and chip removal abilities. Although certain advanced cutting fluids have changed the manufacturing industry for the better, there are some environmental concerns associated with some of these fluids. The use and disposal of cutting fluids may be costly and subjected to stringent government laws. Hence, the ever-growing research conducted on environmentally friendly cutting fluids that may lead to enhanced sustainable manufacturing. The aim of this investigation is therefore to investigate the viability of Minimum Quantity Lubrication (MQL) during machining of titanium alloys with specific focus on the commercially pure grades (Grade 2 & 4). This implies minimizing the consumption of harmful cutting fluids by exploring the use of environmentally friendly lubricants and sustainable lubrication techniques. In addition, minimizing the overall manufacturing cost by increasing the tool life, enhancing the work surface integrity, eliminating the need of post finishing operations and minimizing the energy consumption and cutting forces. An extensive literature review was conducted with the focus of machining titanium, effect of machining parameters on tool wear, surface roughness, cutting forces, cutting temperatures and power consumption. A related review was also conducted on the effect of MQL during the turning of titanium alloys. This was followed by the development of an experimental program, which comprised of the design of experiment, experimental setup, measurement and compilation of data. The experimental work was subdivided into; pilot experiments, main experiments and a comparative study. The aim of the pilot experiment was to determine the experimental protocol that was ultimately used in the main experiments. This included: exploring and solving all practical issues or challenges that may occur during the experimentation and optimizing the settings of MQL parameters in order to fix them during the main experiments. During the pilot experiment, the machining tests were conducted according to a 3-level and 3-factor 9 orthogonal array, at 3 different levels of MQL flow rate, nozzle distance and air pressure. The machining parameters; cutting speed, feed rate and depth of cut were kept constant at 125m/min, 0.2mm/rev and 1mm respectively. The Taguchi method and Grey relational optimisation was used to obtain the optimized parameters settings for Grade 4. The optimization showed that flow rate was the most significant parameter, followed by nozzle distance. Air pressure was the least significant. The analysis showed that the optimum MQL parameters for Grade 4 were: flow rate of 70ml/hr, nozzle distance of 30 mm and air pressure of 4 bar. A similar scheme was used to optimize the MQL parameters for Grade 2. The relative significance of the MQL parameters were similar to Grade 4. The analysis showed that the optimum MQL parameters for Grade 2 were: flow rate of 50ml/hr, nozzle distance of 30 mm and air pressure of 5 bar..