Dry machining parameter optimization for γ-TiAl with a rhombic insert

The application of high temperature materials is the key to technological advancement in engineering, particularly in the aerospace and automotive industries, where materials are expected to satisfy stringent operating requirements. New heat-resistant, light-weight materials, such as intermetallic gamma titanium aluminides (γ-TiAl) based alloys are attracting attention, and showing a great potential to meet severe operational demands due to their superior properties such as low density, high melting temperature, high specific yield strength, high specific stiffness, and excellent creep resistance. Consequently, γ-TiAl alloys have a great potential for high temperature applications in the aerospace and automotive industries. On the other hand, they are also well known as hard-to-machine materials due to poor ductility at low to intermediate temperatures that result in low fracture toughness and a fast fatigue-crack growth rate. In addition, there is no evidence in the open literature of these materials being subjected to production machining. These disadvantages have hindered their widespread application in industry. In this work, a rhombic turning tool is investigated to explore the machinability of γ-TiAl and to develop a cost-effective environmentally benign machining process. A set of central composite design (CCD) experiments are carried out for optimization of the machining process. The cutting parameters varied are cutting speed, feed rate, and depth of cut. Responses measured included thrust force, feed force, cutting force, specific cutting energy, surface roughness, chip morphology, and surface integrity. From the analysis of experimental data, quadratic models are developed, and 2-D contour and 3-D surface plots are drawn. Results obtained are of significant importance in terms of machinability of γ-TiAl and its application in the manufacturing of diesel engine valves and other tribological engine components subjected to operating temperatures range of 400 ºC to 800 ºC.