Edinburgh Napier University

  The cutting of titanium alloys is usually associated with low productivity, poor surface quality, short tool life and high machining costs. This is due to the excessive generation of heat in the cutting zone and difficulties in heat dissipation due to the relatively low heat conductivity of this metal. Cooling applications in machining processes are crucial, since many operations cannot be performed efficiently without cooling. Improving machinability, increasing productivity, and enhancing surface integrity and part accuracy are the main advantages of the use of cutting fluids (CFs). Conventional cutting fluids such as mineral oil-based, synthetic and semi-synthetic fluids are the most common types used in the machining industry. Although these cutting fluids can be beneficial, they pose a great threat to human health and to ecosystems. Vegetable oils (VOs) are being investigated as a potential source of environmentally favourable lubricants, due to a combination of biodegradability, good lubrication properties, low toxicity, high flash points, low volatility, high viscosity indices and thermal stability. The fatty acids of vegetable oils are known to provide thick, strong, and durable lubricant films. These strong lubricating films give the vegetable oil base stock a greater capability to absorb pressure and a high load carrying capacity. This paper details the main experimental results from an investigation of the impact of various vegetable oil-based cutting fluids, cutting tool materials and working conditions when turning Ti-6Al-4V. A full factorial experimental design was employed involving 24 trials to evaluate the influence of process variables on average surface roughness (Ra), tool wear and chip formation. In general, values of Ra varied between 0.5 ?m and 1.56 ?m and the Vasco1000 cutting fluid exhibited a level of performance comparable to other fluids in terms of surface roughness, while the uncoated coarse grain WC carbide tool achieved lower flank wear at all cutting speeds. On the other hand, all tools tips were subject to uniform flank wear during the cutting trials. Additionally, formed chip thickness (tc) ranged between 0.1 mm and 0.14 mm with a noticeable decrease in chip size when higher cutting speeds were used.