Abstract

Nickel based superalloys are used in the aerospace industry for manufacturing gas turbines because of their ability to withstand large loads at high temperatures. But this property, however, makes it one of the most difficult materials to machine, necessitating frequent tool replacement due to wear and hence reduced productivity. Also, as the tool wears, the quality of the machined surface deteriorates correspondingly or may even become damaged. This thesis presents a study of how nickel-based superalloys respond to machining during a milling operation. Special consideration in this study has been given to experimental testing, accuracy and precision. Tool wear and surface roughness were investigated for Titanium Aluminum Nitride (TiAlN) coated and uncoated carbide tools under wet (coolant) and dry cutting conditions. Cutting tests were performed on a CNC milling machine to obtain tool wear and surface roughness. Average flank wear and maximum flank wear were determined by using a tool-wear measuring microscope. Surface roughness parameters were measured using a portable stylus type surface roughness tester (Mitutoyo). Based on tool wear, coated carbide tools performed better than uncoated tools and coolant further reduced tool wear and surface roughness during the cutting operation. Tool life equations were established from experimental results in order to determine tool life under wet (coolant) and dry cutting conditions. On the other hand, wear and surface roughness were also investigated for ceramic tools under different cutting conditions. Tests using ceramic tools (Whisker reinforced and Kyon 2100) were carried out under dry conditions and they performed well at high cutting speeds though the machined surface was found to deteriorate when the feed rate was high. The adhesion of workpiece material was confirmed through energy dispersive X-ray (EDX) analysis. Stability lobes were established in order to identify stable cutting conditions for nickel based superalloys. Wear mechanisms were determined under stable and unstable (chatter) conditions.