Thermo-mechanical aspects of cutting forces and tool wear in the laser-assisted turning of Ti-6Al-4V titanium alloy using AlTiN coated cutting tools

Machining of hard-to-cut materials with conventional processes is still considered as a challenge, as the special properties of these materials often lead to rapid tool wear and reduced surface integrity. For that reason, it is preferable to combine conventional machining processes with other technologies in order to overcome the problems of machining these materials. In the present work, laser-assisted turning experiments on a Ti-6Al-4V workpiece were conducted using AlTiN coated cutting tools in order to investigate the effect of laser heating on cutting forces, cutting temperature, tool wear and microstructure alterations. Two series of experiments were performed under varying cutting speed, laser spot diameter and workpiece diameter values; the first series involved only laser heating of the workpiece and the second both laser heating and cutting. The findings revealed the effect of process parameters on cutting forces and temperature determining the importance of workpiece diameter size, indicated the formation of martensite phase at the top of the heat-affected zone of the workpiece and also showed that high temperatures can lead to intensive tool wear, instead of having a beneficial effect for the cutting tool. Finally, finite element (FE) simulations were carried out in order to study the time evolution of the temperature field and calculate the heating and cooling rates during the process. From the FE results, relatively high heating and cooling rates were observed for smaller workpiece diameters and lower cutting speed, whereas the high magnitude of these rates justified the creation of the martensite phase through a diffusionless transformation.