Thermal and cutting behaviour of Ti6Al4V in laser-assisted machining

Titanium alloy is highly valued in the aerospace and biomedical sectors. However, its poor machinability remains a critical challenge. The alloy's low thermal conductivity causes severe heat accumulation during cutting, which significantly limits both processing efficiency and surface quality. This study investigates the influence of laser-induced thermal effects on chip morphology evolution and surface integrity during laser-assisted machining (LAM) of Ti6Al4V. An integrated microhardness prediction framework, coupled with finite element (FE) simulations, is established based on a novel constitutive model that explicitly captures dynamic phase transformation (PT) mechanisms. The results reveal that laser heating enhances material flowability via the α→β transition, thereby reducing cutting forces and modifying surface hardening behaviour. Furthermore, an analytical model of the primary shear zone (PSZ) rooted in continuum mechanics demonstrates that elevated cutting depths, speeds, and initial temperatures accelerate thermoplastic instability, driving serrated chip formation and lowering the critical cutting speed. Experimental validation confirms that the physical competition between thermal softening and this localized instability strictly dictates both chip morphology and surface integrity. To quantitatively guide process optimization, this study introduces the laser preheating effect factor (f_LPE) as a macroscopic metric to accurately predict subsurface hardened layer thickness. Overall, these findings elucidate the intrinsic coupling between chip formation and surface modification, providing a mechanistic foundation for dynamic parameter regulation in the high-performance machining of complex-geometry titanium components.