Experimental study and optimization of surface roughness and hardness in fiber laser cutting of carbon steel

Abstract

This study investigates the influence of laser cutting parameters on the surface quality of ST37 steel plates. Utilizing a high-power industrial laser system, the research evaluated the effects of laser power (6000–8500 W), cutting velocity (33–43 m/min), and assist gas pressure (0.8–1.2 bar) on two responses: roughness (Ra) and hardness (HR15N). A full factorial Design of Experiments (DOE) was implemented, resulting in 27 experimental runs that were statistically analyzed using Minitab software. The experimental results demonstrated that laser power is the most significant factor affecting both surface finish and material hardness. Increasing laser power from 6000 W to 8500 W led to a substantial reduction in surface roughness due to stabilized melt flow and lower melt viscosity, while simultaneously increasing hardness through higher peak temperatures and rapid self-quenching effects. Cutting velocity exhibited a non-linear relationship with roughness, identifying an optimal spot at 38 mm/min where heat input and material removal were balanced. Conversely, increased velocity resulted in lower average hardness due to reduced dwell time and a narrower heat-affected zone. Assist gas pressure showed a dual role, peaking in effectiveness at 1.0 bar before convective cooling effects slightly reduced thermal efficiency at higher pressures. Multi-objective optimization using the D-optimality desirability function identified the global optimal parameters as a laser power of 8500 W, a cutting velocity of 33 mm/min, and a gas pressure of 0.8 bar. This configuration achieved a composite desirability of 0.9793, effectively maximizing hardness while maintaining superior surface finish.