A DoE Approach to Hole Quality Evaluation in Drilling of an Electron Beam Melted Titanium Aluminide

Gamma titanium aluminides are heat-resistant intermetallic structural alloys with many attractive properties such as low weight, high stiffness, high refractoriness and high temperature strength. These alloys are excellent candidates to be used as alternative to Nickel-based superalloys for thermally and mechanically stressed components in aerospace and automotive engines. The material properties, however, lead to γ-TiAl difficult machinability, resulting in poor surface quality. In this paper, the geometrical accuracy of holes drilled on a Ti-48Al-2Cr-2Nb γ-TiAl component, produced via Electron Beam Melting (EBM), is analyzed. Particularly, the Design of Experiments (DoE) technique was selected because of its usefulness in determining simultaneously the individual and interactive effects of many variables, that could affect the output results. Experiments were conducted with uncoated carbide drills, varying the cutting parameters. Machined holes were measured by means of a coordinate measuring machine. Hole quality was assessed focusing on the dimensional and geometrical errors, in terms of both cylindricity and roundness, and taking into account the tool wear and the hole depth.