The investigation of dynamic machining efficiency in femtosecond laser machining of tungsten carbide

Fabrication of microstructures on flank/rake faces of cutting tools can improve wear resistance via modifying the states of tool/chip and tool/workpiece abrasion. With the advances in laser technology, femtosecond laser machining has emerged as a promising method in high-efficiency and high-precision fabrication of structures in micro/nano scale on the ultrahard tool surfaces. Currently, most studies focus on surface finish, whereas the investigation of machining efficiency is limited. In this study, the underlying mechanisms of how laser-induced periodic surface structure (LIPSS), plasma shielding, and heat accumulation influence the machining efficiency in femtosecond laser ablation (FLA) of tungsten carbide (WC) is comprehensively analyzed, which is overlooked in previous studies. The relationship between laser fluences at different laser parameters and the evolution of LIPSS, thermal-activated defects, and states of plasma shielding are investigated, and the new principles by which these three factors affect dynamic MRR are revealed. Intact LIPSS is the key factor contributing to higher MRR, and the destruction of LIPSS at higher fluences due to the thermal cracks and craters reduce MRR. With the increase of groove depth, the effect of plasma shielding becomes significant, eventually preventing the absorption of laser energy, resulting in the decrease of MRR. Defects including cracks, pits, and recast layers caused by the accumulation of pulse energy appear at higher laser fluences. Findings in this study provide theoretical support for the optimization of processing parameters in the machining of ultrahard materials with high efficiency.