Machinability improvement of titanium alloy (Ti–6Al–4V) via LAM and hybrid machining

Titanium alloy (Ti–6Al–4V) is one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance, but it also presents problems wherein it is an extremely difficult material to machine. The cost associated with titanium machining is also high due to lower cutting speeds (<60 m/min) and shorter tool life. Laser-assisted machining (LAM) and consequently hybrid machining is utilized to improve the tool life and the material removal rate. The effectiveness of the two processes is studied by varying the tool material and material removal temperature while measuring the cutting forces, specific cutting energy, surface roughness, microstructure and tool wear. Laser-assisted machining improved the machinability of titanium from low (60 m/min) to medium-high (107 m/min) cutting speeds; while hybrid machining improved the machinability from low to high (150–200 m/min) cutting speeds. The optimum material removal temperature was established as 250 °C. Two to three fold tool life improvement over conventional machining is achieved for hybrid machining up to cutting speeds of 200 m/min with a TiAlN coated carbide cutting tool. Tool wear predictions based on 3-D FEM simulation show good agreement with experimental tool wear measurements. Post-machining microstructure and microhardness profiles showed no change from pre-machining conditions. An economic analysis, based on estimated tooling and labor costs, shows that LAM and the hybrid machining process with a TiAlN coated tool can yield an overall cost savings of ∼30% and ∼40%, respectively.