On the chip formation mechanism when cutting Ti6Al4V with localised supply of liquid nitrogen

In cryogenic machining, employing internal supply cooling through the tool not only diminishes tool wear and enhances workpiece machining quality but also offers the benefits of reduced liquid nitrogen consumption and more precise cooling. These advantages are particularly noteworthy for efficiently machining challenging materials. However, prevailing research on internal supply cooling through tools predominantly concentrates on aspects such as tool wear and surface integrity, with a relatively limited exploration of material removal mechanisms. The material removal process stands as a crucial factor influencing cutting stability and surface smoothness. Thus, this study focuses on the Ti-6Al-4 V alloy, utilizing numerical modeling to investigate the impact of liquid nitrogen cooling methods on the cutting deformation zone. In addition to its benefits for difficult-to-machine materials, internal supply cooling through the tool presents a promising avenue to enhance machining efficiency. Consequently, this study strategically selected the Ti-6Al-4 V alloy as the research subject, employing numerical modeling to delve into the influence of liquid-nitrogen cooling methods on the cutting deformation zone. Furthermore, employing a combination of cutting experiments and simulations, we analyzed the evolution of temperature fields and microstructures within the deformation zone to elucidate the chip formation mechanism under liquid nitrogen cooling conditions. The outcomes of this investigation reveal that in comparison to liquid nitrogen external supply cooling, internal supply cooling through the tool effectively restrains chip serration, thereby contributing to an enhancement in machining quality. The analysis demonstrates that, under conditions of internal supply cooling through the tool, chip formation is predominantly influenced by the adiabatic shear effect induced by low temperatures. In contrast, under external supply cooling conditions, susceptible to the low-temperature embrittlement effect, the chip's free surface tends to undergo brittle cracking. This shift in the chip formation mechanism toward the co-dominance of adiabatic shear and brittle cracking results in a more pronounced serration of the chips. This study establishes a theoretical foundation and guides the industrial application of cryogenic machining.