Effect of sodium chloride addition on the jet stability in liquid-jet guided laser processing

Liquid-jet guided laser (LJGL) processing holds significant promise in precision manufacturing. Currently, pure water is generally employed as the jet medium because of its wide transmission window and cost saving. However, its jet stable length is insufficient because of its low viscosity, and expensive shielding gas is required. In this study, an aqueous sodium chloride (NaCl) solution was proposed as the jet medium to enhance the jet stable length in LJGL processing. A two-dimensional computational fluid dynamic model was developed to investigate the stable length of high-speed jet with high spatial resolution. The morphology and jet stable length with NaCl concentration from 0 to 20 wt. % were systematically investigated. A high-speed imaging technique was utilized to detect the jet evolution. The results show that increasing NaCl concentration significantly improves the jet stability, with the stable length extending from 173 mm with pure water to 190 mm with 10 wt. % NaCl solution under 1.5 MPa liquid pressure, achieving a 9.8% growth rate. This improvement is primarily due to the increased viscosity which suppresses interfacial disturbances. Simulation results agree well with the experiment, with only a 15.9% error. A predictive model correlating jet stability with Reynolds and Weber numbers was established, aligning well with simulation data. Notably, the addition of NaCl marginally increases laser attenuation by only 2.1% for a 10 wt. % solution, confirming compatibility with high-power near-infrared lasers at 1064 nm.